Sulfuric acid (sulphuric acid in British English) is a strong mineral acid with the molecular formula H2SO4. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion. Principal uses include lead-acid batteries for cars and other vehicles, ore processing, fertilizer manufacturing, oil refining, wastewater processing, and chemical synthesis.

History

John Dalton's 1808 sulfuric acid molecule shows a central sulfur atom bonded to three oxygen atoms.

The study of vitriol in ancient times. Sumerians had a list of types of vitriol that they classified according to substance's color. Some of the earliest discussions on the origin and properties of vitriol are in the works of the greek physician Dioscorides (first century AD) and the roman naturalist Pliny the Elder (23-79 AD). Galen also discussed its medical use. Metallurgical uses for vitriolic substances were recorded in the hellenistic alchemical works of Zosimos of Panopolis, in the treatise Phisica et Mystica, and the "Leyden Papyrus x".[8]

Iranian alchemists like Geber, Rhazes, Muhammad ibn Ibrahim al-Watwat, who included vitriol in their mineral classification lists. Avicenna focused on its medical uses. Several indian alchemical works also mention the different varieties of vitriol.[8]

Sulfuric acid was discovered by medieval European alchemists. They called it "oil of vitriol". There are mentions to it in the works of Vincent of Beauvais and in the Compositum de Compositis ascribed to Albertus Magnus. A passage from Pseudo-Geber´s Summa Perfectionis was long considered to be the first recipe for sulphuric acid, but this was a misinterpretation.[8]

In the 17th century, the German-Dutch chemist Johann Glauber prepared sulfuric acid by burning sulfur together with saltpeter (potassium nitrate, KNO3), in the presence of steam. As saltpeter decomposes, it oxidizes the sulfur to SO3, which combines with water to produce sulfuric acid. In 1736, Joshua Ward, a London pharmacist, used this method to begin the first large-scale production of sulfuric acid.

In 1746 in Birmingham, John Roebuck adapted this method to produce sulfuric acid in lead-lined chambers, which were stronger, less expensive, and could be made larger than the previously used glass containers. This lead chamber process allowed the effective industrialization of sulfuric acid production. After several refinements, this method remained the standard for sulfuric acid production for almost two centuries.

Sulfuric acid created by John Roebuck's process only approached a 35–40% concentration.[citation needed] Later refinements to the lead-chamber process by French chemist Joseph-Louis Gay-Lussac and British chemist John Glover improved the yield to 78%.[citation needed] However, the manufacture of some dyes and other chemical processes require a more concentrated product.[citation needed] Throughout the 18th century, this could only be made by dry distilling minerals in a technique similar to the original alchemical processes. Pyrite (iron disulfide, FeS2) was heated in air to yield iron (II) sulfate, FeSO4, which was oxidized by further heating in air to form iron(III) sulfate, Fe2(SO4)3, which, when heated to 480 °C, decomposed to iron(III) oxide and sulfur trioxide, which could be passed through water to yield sulfuric acid in any concentration. However, the expense of this process prevented the large-scale use of concentrated sulfuric acid.

In 1831, British vinegar merchant Peregrine Phillips patented the contact process, which was a far more economical process for producing sulfur trioxide and concentrated sulfuric acid. Today, nearly all of the world's sulfuric acid is produced using this method.

Chemical properties

Reaction with water

The hydration reaction of sulfuric acid is highly exothermic. One should always add the acid to the water rather than the water to the acid. Because the reaction is in an equilibrium that favors the rapid protonation of water, addition of acid to the water ensures that the acid is the limiting reagent. This reaction is best thought of as the formation of hydronium ions:

H 2 SO 4 (l) + H 2 O(l) -----> HSO 4 - (aq) + H 3 O + (aq)

HSO 4 - (aq) + H 2 O(l) SO 4 2- (aq) + H 3 O + (aq)

Because the hydration of sulfuric acid is thermodynamically favorable, sulfuric acid is an excellent dehydrating agent, and is used to prepare many dried fruits. The affinity of sulfuric acid for water is sufficiently strong that it will remove hydrogen and oxygen atoms from other compounds; for example, mixing starch (C6H12O6)n and concentrated sulfuric acid will give elemental carbon and water which is absorbed by the sulfuric acid (which becomes slightly diluted):

(C6H12O6)n → 6n C + 6n H2O

The effect of this can be seen when concentrated sulfuric acid is spilled on paper; the cellulose reacts to give a burnt appearance, the carbon appears much as soot would in a fire. A more dramatic reaction occurs when sulfuric acid is added to a tablespoon of white sugar in a beaker; a rigid column of black, porous carbon will quickly emerge. The carbon will smell strongly of caramel. Although less dramatic, the action

of the acid on cotton, even in diluted form, will destroy the fabric. Clothes like jeans and labcoats that accidentally come in contact with the acid will look perfect until they are received, in a barely recognizable state, from laundry.[citation needed]

Other reactions

As an acid, sulfuric acid reacts with most bases to give the corresponding sulfate. For example, the blue copper salt copper(II) sulfate, commonly used for electroplating and as a fungicide, is prepared by the reaction of copper(II) oxide with sulfuric acid:

CuO (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l)

Sulfuric acid can also be used to displace weaker acids from their salts. Reaction with sodium acetate, for example, displaces acetic acid, CH3COOH, and forms sodium bisulfate:

H2SO4 + CH3COONa → NaHSO4 + CH3COOH

Similarly, reacting sulfuric acid with potassium nitrate can be used to produce nitric acid and a precipitate of potassium bisulfate. When combined with nitric acid, sulfuric acid acts both as an acid and a dehydrating agent, forming the nitronium ion NO+2, which is important in nitration reactions involving electrophilic aromatic substitution. This type of reaction, where protonation occurs on an oxygen atom, is important in many organic chemistry reactions, such as Fischer esterification and dehydration of alcohols.

Sulfuric acid reacts with most metals via a single displacement reaction to produce hydrogen gas and the metal sulfate. Dilute H2SO4 attacks iron, aluminium, zinc, manganese, magnesium and nickel, but reactions with tin and copper require the acid to be hot and concentrated. Lead and tungsten, however, are resistant to sulfuric acid. The reaction with iron shown below is typical for most of these metals, but the reaction with tin produces sulfur dioxide rather than hydrogen.

Fe (s) + H2SO4 (aq) → H2 (g) + FeSO4 (aq)

Sn (s) + 2 H2SO4 (aq) → SnSO4 (aq) + 2 H2O (l) + SO2 (g)

These reactions may be taken as typical: the hot concentrated acid generally acts as an oxidizing agent whereas the dilute acid acts a typical acid. Hence hot concentrated acid reacts with tin, zinc and copper to produce the salt, water and sulfur dioxide, whereas the dilute acid reacts with metals high in the reactivity series (such as Zn) to produce a salt and hydrogen. This is explained more fully in 'A New Certificate Chemistry' by Holderness and Lambert.

Sulfuric acid undergoes electrophilic aromatic substitution with aromatic compounds to give the corresponding sulfonic acids:[6]

Physical properties

Grades of sulfuric acid

Although nearly 100% sulfuric acid can be made, this loses SO3 at the boiling point to produce 98.3% acid. The 98% grade is more stable in storage, and is the usual form of what is described as "concentrated sulfuric acid." Other concentrations are used for different purposes. Some common concentrations are:

Mass fractionH2SO4

Density(kg/L)

Concentration(mol/L)

Common name

10% 1.07 ~1 dilute sulfuric acid

29-32% 1.25–1.28 4.2–5battery acid(used in lead–acid batteries)

62–70% 1.52–1.60 9.6–11.5chamber acidfertilizer acid

78–80% 1.70–1.73 13.5–14tower acidGlover acid

95–98% 1.83 ~18 concentrated sulfuric acid

"Chamber acid" and "tower acid" were the two concentrations of sulfuric acid produced by the lead chamber process, chamber acid being the acid produced in lead chamber itself (<70% to avoid contamination with nitrosylsulfuric acid) and tower acid being the acid recovered from the bottom of the Glover tower.[3][4] They are now obsolete as commercial concentrations of sulfuric acid, although they may be prepared in the laboratory from concentrated sulfuric acid if needed. In particular, "10M" sulfuric acid (the modern equivalent of chamber acid, used in many titrations) is prepared by slowly adding 98% sulfuric acid to an equal volume of water, with good stirring: the temperature of the mixture can rise to 80 °C (176 °F) or higher.[4]

When high concentrations of SO3 gas are added to sulfuric acid, H2S2O7, called pyrosulfuric acid, fuming sulfuric acid or oleum or, less commonly, Nordhausen acid, is formed. Concentrations of oleum are either

expressed in terms of % SO3 (called % oleum) or as % H2SO4 (the amount made if H2O were added); common concentrations are 40% oleum (109% H2SO4) and 65% oleum (114.6% H2SO4). Pure H2S2O7 is a solid with melting point 36°C.

Pure sulfuric acid is a viscous clear liquid, like oil, and this explains the old name of the acid ('oil of vitriol').

Commercial sulfuric acid is sold in several different purity grades. Technical grade H2SO4 is impure and often colored, but is suitable for making fertilizer. Pure grades such as United States Pharmacopoeia (USP) grade are used for making pharmaceuticals and dyestuffs. Analytical grades are also available.

Polarity and conductivity

Anhydrous H2SO4 is a very polar liquid, having a dielectric constant of around 100. It has a high electrical conductivity, caused by dissociation through protonating itself, a process known as autoprotolysis.[5]

2 H2SO4 H3SO+4 + HSO−4

The equilibrium constant for the autoprotolysis is[5]

Kap(25°C)= [H3SO+4][HSO−4] = 2.7×10−4.

The comparable equilibrium constant for water, Kw is 10−14, a factor of 1010 (10 billion) smaller.

In spite of the viscosity of the acid, the effective conductivities of the H3SO+4 and HSO−4 ions are high due to an intra-molecular proton-switch mechanism (analogous to the Grotthuss mechanism in water), making sulfuric acid a good conductor. It is also an excellent solvent for many reactions.The equilibrium is actually more complex than shown above; 100% H2SO4 contains the following species at equilibrium (figures shown as millimoles per kilogram of solvent): HSO−4 (15.0), H3SO+4 (11.3), H3O+ (8.0), HS2O−7 (4.4), H2S2O7 (3.6), H2O (0.1).[5]

Uses

Sulfuric acid production in 2000

Sulfuric acid is a very important commodity chemical, and indeed, a nation's sulfuric acid production is a good indicator of its industrial strength.[7] The major use (60% of total production worldwide) for sulfuric acid is in the "wet method" for the production of phosphoric acid, used for manufacture of phosphate fertilizers as well as trisodium phosphate for detergents. In this method, phosphate rock is used, and more than 100 million tonnes are processed annually. This raw material is shown below as fluorapatite, though the exact composition may vary. This is treated with 93% sulfuric acid to produce calcium sulfate, hydrogen fluoride (HF) and phosphoric acid. The HF is removed as hydrofluoric acid. The overall process can be represented as:

Ca5F(PO4)3 + 5 H2SO4 + 10 H2O → 5 CaSO4·2 H2O + HF + 3 H3PO4

Sulfuric acid is used in large quantities by the iron and steelmaking industry to remove oxidation, rust and scale from rolled sheet and billets prior to sale to the automobile and white goods (appliances) industry. Used acid is often recycled using a Spent Acid Regeneration (SAR) plant. These plants combust spent acid with natural gas, refinery gas, fuel oil or other fuel sources. This combustion process produces gaseous sulfur dioxide (SO2) and sulfur trioxide (SO3) which are then used to manufacture "new" sulfuric acid. SAR plants are common additions to metal smelting plants, oil refineries, and other industries where sulfuric acid is consumed in bulk, as operating a SAR plant is much cheaper than the recurring costs of spent acid disposal and new acid purchases.

Ammonium sulfate, an important nitrogen fertilizer, is most commonly produced as a byproduct from coking plants supplying the iron and steel making plants. Reacting the ammonia produced in the thermal decomposition of coal with waste sulfuric acid allows the ammonia to be crystallized out as a salt (often brown because of iron contamination) and sold into the agro-chemicals industry.

Another important use for sulfuric acid is for the manufacture of aluminum sulfate, also known as paper maker's alum. This can react with small amounts of soap on paper pulp fibers to give gelatinous aluminum carboxylates, which help to coagulate the pulp fibers into a hard paper surface. It is also used for making aluminum hydroxide, which is used at water treatment plants to filter out impurities, as well as to improve the taste of the water. Aluminum sulfate is made by reacting bauxite with sulfuric acid:

Al2O3 + 3 H2SO4 → Al2(SO4)3 + 3 H2O

Sulfuric acid is used for a variety of other purposes in the chemical industry. For example, it is the usual acid catalyst for the conversion of cyclohexanone oxime to caprolactam, used for making nylon. It is used for making hydrochloric acid from salt via the Mannheim process. Much H2SO4 is used in petroleum refining, for example as a catalyst for the reaction of isobutane with isobutylene to give isooctane, a compound that raises the octane rating of gasoline (petrol). Sulfuric acid is also important in the manufacture of dyestuffs solutions and is the "acid" in lead-acid (car) batteries.

Sulfuric acid is also used as a general dehydrating agent in its concentrated form. See Reaction with water.

Sulfur-iodine cycle

The sulfur-iodine cycle is a series of thermo-chemical processes used to obtain hydrogen. It consists of three chemical reactions whose net reactant is water and whose net products are hydrogen and oxygen.

2 H2SO4 → 2 SO2 + 2 H2O + O2 (830 °C)

I2 + SO2 + 2 H2O → 2 HI + H2SO4 (120 °C)

2 HI → I2 + H2 (320 °C)

The sulfur and iodine compounds are recovered and reused, hence the consideration of the process as a cycle. This process is endothermic and must occur at high temperatures, so energy in the form of heat has to be supplied.

The sulfur-iodine cycle has been proposed as a way to supply hydrogen for a hydrogen-based economy. It does not require hydrocarbons like current methods of steam reforming.

The sulfur-iodine cycle is currently being researched as a feasible method of obtaining hydrogen, but the concentrated, corrosive acid at high temperatures poses currently insurmountable safety hazards if the process were built on a large scale.

Manufacture of Sulfuric Acid (H 2 SO 4 )

Most of the sulfuric acid manufactured is produced using the Contact Process .

Combustion Chamber (combustion of

sulfur) -->

Converter (conversion of sulfur

dioxide) -->

Absorption Tower (sulfur trioxide

absorbed into the sulfuric acid

mist

-->

Hydration of

Oleum to produce sulfuric

acid

The Contact Process is a process involving the catalytic oxidation of sulfur dioxide, SO 2 , to sulfur trioxide, SO 3 .

I. Solid sulfur, S(s), is burned in air to form sulfur dioxide gas, SO 2

S(s) + O 2 (g) -----> SO 2 (g)

II. The gases are mixed with more air then cleaned by electrostatic precipitation to remove any particulate matter

III. The mixture of sulfur dioxide and air is heated to 450 o C and subjected to a pressure of 101.3 - 202.6 kPa (1 -2 atmospheres) in the presence of a vanadium catalyst (vanadium (V) oxide) to produce sulfur trioxide, SO 3 (g), with a yield of 98%.

2SO 2 (g) + O 2 (g) -----> 2SO 3 (g)

IV. Any unreacted gases from the above reaction are recylced back into the above reaction

V. Sulfur trioxide, SO 3 (g) is dissolved in 98% (18M) sulfuric acid, H 2 SO 4 , to produce disulfuric acid or pyrosulfuric acid, also known as fuming sulfuric acid or oleum, H 2 S 2 O 7 .

SO 3 (g) + H 2 SO 4 ------> H 2 S 2 O 7

This is done because when water is added directly to sulfur trioxide to produce sulfuric acid

SO 3 (g) + H 2 O(l) -----> H 2 SO 4 (l)

the reaction is slow and tends to form a mist in which the particles refuse to coalesce.

VI. Water is added to the disulfuric acid, H 2 S 2 O 7 , to produce sulfuric acid, H 2 SO 4

H 2 S 2 O 7 (l) + H 2 O(l) -----> 2H 2 SO 4 (l)

The oxidation of sulfur dioxide to sulfur trioxide in step III above is an exothermic reaction (energy is released), so by Le Chatelier's Principle , higher temperatures will force the equilibrium position to shift to the left hand side of the equation favouring the production of sulfur dioxide. Lower temperatures would favour the production of the product sulfur trioxide and result in a higher yield. However, the rate of reaching equilibrium at the lower temperatures is extremely low. A higher temperature means equilibrium is established more rapidly but the yield of sulfur trioxide is lower. A temperature of 450 o C is a compromise whereby a faster reaction rate results in a slightly lower yield.

Similarly, at higher pressures, the equilibrium position shifts to the side of the equation in which there are the least numbers of gaseous molecules.

2SO 2 (g) + O 2 (g) -----> 2SO 3

On the left hand side of the reaction there are 3 moles of gaseous reactants, and the right hand side there are 2 moles of gaseous products, so higher pressure favours the right hand side, by Le Chatelier's Principle . Higher pressure results in a higher yield of sulfur trioxide.

A vanadium catalyst (vanadium (V) oxide) is also used in this reaction in order to speed up the rate of the reaction.

Other methods

Another method is the less well-known metabisulfite method, in which metabisulfite in placed at the bottom of a beaker, and 12.6 molar concentration hydrochloric acid is added. The resulting gas is bubbled through nitric acid, which will release brown/red vapors. The completion of the reaction is indicated by the ceasing of the fumes. This method does not produce an inseparable mist, which is quite convenient.

Sulfuric acid can be produced in the laboratory by burning sulfur in air and dissolving the gas produced in a hydrogen peroxide solution.

SO2 + H2O2 → H2SO4

Another method is to react hydrochloric acid with copper II sulfate:

2 HCl + CuSO4 → H2SO4 + CuCl2[citation needed]

Prior to 1900, most sulfuric acid was manufactured by the chamber process.[2] As late as 1940, up to 50% of sulfuric acid manufactured in the United States was produced by chamber process plants.

Industrial hazards

Although sulfuric acid is non-flammable, contact with metals in the event of a spillage can lead to the liberation of hydrogen gas. The dispersal of acid aerosols and gaseous sulfur dioxide is an additional hazard of fires involving sulfuric acid.

Sulfuric acid is not considered toxic besides its obvious corrosive hazard, and the main occupational risks are skin contact leading to burns (see above) and the inhalation of aerosols. Exposure to aerosols at high concentrations leads to immediate and severe irritation of the eyes, respiratory tract and mucous membranes: this ceases rapidly after exposure, although there is a risk of subsequent pulmonary edema if tissue damage has been more severe. At lower concentrations, the most commonly reported symptom of chronic exposure to sulfuric acid aerosols is erosion of the teeth, found in virtually all studies: indications of possible chronic damage to the respiratory tract are inconclusive as of 1997. In the United States, the permissible exposure limit (PEL) for sulfuric acid is fixed at 1 mg/m³: limits in other countries are similar. Interestingly there have been reports of sulfuric acid ingestion leading to vitamin B12 deficiency with subacute combined degeneration. The spinal cord is most often affected in such cases, but the optic nerves may show demyelination, loss of axons and gliosis.

Legal restrictions

International commerce of sulfuric acid is controlled under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances, 1988, which lists sulfuric acid under Table II of the convention as a chemical frequently used in the illicit manufacture of narcotic drugs or psychotropic substances.[9]

In the US sulfuric acid is included in List II of the list of essential or precursor chemicals established pursuant to the Chemical Diversion and Trafficking Act. Accordingly, transactions of sulfuric acid—such as sales, transfers, exports from and imports to the United States—are subject to regulation and monitoring by the Drug Enforcement Administration.[10][11][12]

Sulphur dioxide and environmental pollution

Sources:

The main sources of sulphur dioxide is

Coal power plants

Volcanic eruptions

Coal power plants:

Coal power plants produces large amount of sulphur dioxide as impurities. Sulphur dioxide is

produced during burning of coal. This gets emitted in the air using chimneys get mixed with

atmospheric air causes environmental pollution.

Volcanic eruptions:

During the volcanic eruptions various gases like carbon dioxide, nitrogen dioxide and sulphur

dioxide get evolved at heights. Where sulphur dioxide gets converted into sulphuric acid in the

atmosphere causes environmental pollution.

Environmental effects:

Sulphur dioxide is converted into sulphuric acid, sulphur trioxide and sulphates whenever a

contact with the atmosphere causes environmental pollution. Sulphur dioxide dissolves in water

form sulfurous acid. The main impact of sulphur dioxide is acid rain.

Acid rain:

Sulphur dioxide in the atmosphere gets contact with rain produces acid rain.

It corrodes monuments, statues and buildings.

In humans it causes cancer and leads to other diseases.

In affects the soil fertility and affects plants growth.

It turns out the water sources to acidic.

Smog:

Smog is produced as a result of reactions of sulphur dioxide with the environment.

Smog is caused due to the emissions of sulphur dioxide, carbon dioxide and nitrogen

dioxide by vehicles causes environmental pollution.

Smog affects human health causing respiratory and heart disorders in childrens and

peoples.

Global warming:

It is the greenhouse gases that increase the temperature of the earth by absorbing

sunlight as it is present in large amount in the atmosphere.

Effects on humans:

Sulphur dioxide is poisonous and hence irritates eyes, nose and lungs.

It induces respiratory disorders, breathing problems and cardiovascular diseases.

This also affects plants and animals.

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Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous. In 2006, worldwide production was estimated at 146.5 million tonnes.[4] It is used in commercial cleaning products.

Ammonia, as used commercially, is often called anhydrous ammonia. This term emphasizes the absence of water in the material. Because NH3 boils at −33.34 °C, (-28.012 °F) the liquid must be stored under high pressure or at low temperature. Its heat of vapourization is, however, sufficiently high so that NH3 can be

readily handled in ordinary beakers, in a fume hood (i.e., if it is already a liquid it will not boil readily). "Household ammonia" or "ammonium hydroxide" is a solution of NH3 in water. The strength of such solutions is measured in units of baume (density), with 26 degrees baume (about 30 weight percent ammonia at 15.5 °C) being the typical high concentration commercial product.[5] Household ammonia ranges in concentration from 5 to 10 weight percent ammonia

Structure and basic chemical properties

The ammonia molecule has a trigonal pyramidal shape with a bond angle of 107.8° as shown above, as predicted by the valence shell electron pair repulsion theory (VSEPR). The central nitrogen atom has five outer electrons with an additional electron from each hydrogen atom. This gives a total of eight electrons, or four electron pairs which are arranged tetrahedrally. Three of these electron pairs are used as bond pairs, which leaves one lone pair of electrons. The lone pair of electrons repel more strongly than bond pairs, therefore the bond angle is not 109.5° as expected for a regular tetrahedral arrangement, but is measured at 107.8°. The nitrogen atom in the molecule has a lone electron pair, which makes ammonia a base, a proton acceptor. This shape gives the molecule a dipole moment and makes it polar. The molecule's polarity and, especially, its ability to form hydrogen bonds, makes ammonia highly miscible with water. Ammonia is moderately basic, a 1.0 M aqueous solution has a pH of 11.6 and if a strong acid is added to such a solution until the solution is neutral (pH = 7), 99.4% of the ammonia molecules are protonated. Temperature and salinity also affect the proportion of NH4

+. The latter has the shape of a regular tetrahedron and is isoelectronic with methane. It is known to have the highest specific heat capacity of any substance.

History

The Romans called the ammonium chloride deposits they collected from near the Temple of Jupiter Amun (Greek Ἄμμων Ammon) in ancient Libya 'sal ammoniacus' (salt of Amun) because of proximity to the nearby temple.[7] Salts of ammonia have been known from very early times; thus the term Hammoniacus sal appears in the writings of Pliny, although it is not known whether the term is identical with the more modern sal-ammoniac.[8]

In the form of sal-ammoniac (nushadir), ammonia was important to the Muslim alchemists as early as the 8th century, first mentioned by the Islamic chemist Jābir ibn Hayyān,[9] and to the European alchemists since the 13th century, being mentioned by Albertus Magnus. It was also used by dyers in the Middle Ages in the form of fermented urine to alter the colour of vegetable dyes. In the 15th century, Basilius Valentinus showed that ammonia could be obtained by the action of alkalis on sal-ammoniac. At a later period, when sal-ammoniac was obtained by distilling the hooves and horns of oxen and neutralizing the resulting carbonate with hydrochloric acid, the name "spirit of hartshorn" was applied to ammonia.[10]

Gaseous ammonia was first isolated by Joseph Priestley in 1774 and was termed by him alkaline air.[11] Eleven years later in 1785, Claude Louis Berthollet ascertained its composition.

The Haber-Bosch process to produce ammonia from the nitrogen in the air was developed by Fritz Haber and Carl Bosch in 1909 and patented in 1910. It was first used on an industrial scale by the Germans during World War I,[4] following the allied blockade that cut off the supply of nitrates from Chile. The ammonia was used to produce explosives to sustain their war effort.[12]

Prior to the advent of cheap natural gas, hydrogen as a precursor to ammonia production was produced via the electrolysis of water or using the chloralkali process. The Vemork 60 MW hydroelectric plant in Norway, constructed in 1911, was used purely for plants using the Birkeland-Eyde process

Properties

Ammonia is a colourless gas with a characteristic pungent smell. It is lighter than air, its density being 0.589 times that of air. It is easily liquefied due to the strong hydrogen bonding between molecules; the liquid boils at −33.3 °C, and solidifies at −77.7 °C to white crystals. The crystal symmetry is cubic, Pearson symbol cP16, space group P213 No.198, lattice constant 0.5125 nm.[17] Liquid ammonia possesses strong ionising powers reflecting its high ε of 22. Liquid ammonia has a very high standard enthalpy change of vapourization (23.35 kJ/mol, cf. water 40.65 kJ/mol, methane 8.19 kJ/mol, phosphine 14.6 kJ/mol) and can therefore be used in laboratories in non-insulated vessels without additional refrigeration.

It is miscible with water. Ammonia in an aqueous solution can be expelled by boiling. The aqueous solution of ammonia is basic. The maximum concentration of ammonia in water (a saturated solution) has a density of 0.880 g/cm3 and is often known as '.880 Ammonia'. Ammonia does not burn readily or sustain combustion, except under narrow fuel-to-air mixtures of 15–25% air. When mixed with oxygen, it burns with a pale yellowish-green flame. At high temperature and in the presence of a suitable catalyst, ammonia is decomposed into its constituent elements. Ignition occurs when chlorine is passed into ammonia, forming nitrogen and hydrogen chloride; if chlorine is present in excess, then the highly explosive nitrogen trichloride (NCl3) is also formed.

The ammonia molecule readily undergoes nitrogen inversion at room temperature; a useful analogy is an umbrella turning itself inside out in a strong wind. The energy barrier to this inversion is 24.7 kJ/mol, and the resonance frequency is 23.79 GHz, corresponding to microwave radiation of a wavelength of 1.260 cm. The absorption at this frequency was the first microwave spectrum to be observed.[18]

Ammonia may be conveniently deodorized by reacting it with either sodium bicarbonate or acetic acid. Both of these reactions form an odourless ammonium salt.

Basicity

One of the most characteristic properties of ammonia is its basicity. It combines with acids to form salts; thus with hydrochloric acid it forms ammonium chloride (sal-ammoniac); with nitric acid, ammonium nitrate, etc. However, perfectly dry ammonia will not combine with perfectly dry hydrogen chloride: moisture is necessary to bring about the reaction.[19]

NH3 + HCl → NH4Cl

The salts produced by the action of ammonia on acids are known as the ammonium salts and all contain the ammonium ion (NH4

+). Anhydrous ammonia is often used for the production of methamphetamine. Dilute aqueous ammonia can be applied on the skin to lessen the effects of acidic animal poisons, such as from insects and jellyfish.

Acidity

Although ammonia is well known as a strong base, it can also act as an extremely weak acid. It is a protic substance and is capable of formation of amides (which contain the NH2

− ion). For example, lithium and ammonia react to give a solution of lithium amide:

2 Li + 2 NH3 → 2 LiNH2 + H2

Self-dissociation

Like water, ammonia undergoes molecular autoionisation to form its acid and base conjugates:

2 NH3 (l) NH+4 (aq) + NH−2 (aq)

At standard pressure and temperature, [NH+4][NH−2] = 10−30 M2.

Combustion

The combustion of ammonia to nitrogen and water is exothermic:

4 NH3 + 3 O2 → 2 N2 + 6 H2O (g) (Δ H º r = –1267.20 kJ/mol)

The standard enthalpy change of combustion, ΔHºc, expressed per mole of ammonia and with condensation of the water formed, is –382.81 kJ/mol. Dinitrogen is the thermodynamic product of combustion: all nitrogen oxides are unstable with respect to nitrogen and oxygen, which is the principle behind the catalytic converter. However, nitrogen oxides can be formed as kinetic products in the presence of appropriate catalysts, a reaction of great industrial importance in the production of nitric acid:

4 NH3 + 5 O2 → 4 NO + 6 H2O

A subsequent reaction leads to water and N2O

The combustion of ammonia in air is very difficult in the absence of a catalyst (such as platinum gauze), as the temperature of the flame is usually lower than the ignition temperature of the ammonia-air mixture. The flammable range of ammonia in air is 16–25%.[20]

Formation of other compounds

In organic chemistry, ammonia can act as a nucleophile in substitution reactions. Amines can be formed by the reaction of ammonia with alkyl halides, although the resulting –NH2 group is also nucleophilic and secondary and tertiary amines are often formed as by-products. An excess of ammonia helps minimise multiple substitution, and neutralises the hydrogen halide formed. Methylamine is prepared commercially by the reaction of ammonia with chloromethane, and the reaction of ammonia with 2-bromopropanoic acid has been used to prepare racemic alanine in 70% yield. Ethanolamine is prepared by a ring-opening reaction with ethylene oxide: the reaction is sometimes allowed to go further to produce diethanolamine and triethanolamine.

Amides can be prepared by the reaction of ammonia with a number of carboxylic acid derivatives. Acyl chlorides are the most reactive, but the ammonia must be present in at least a twofold excess to neutralise the hydrogen chloride formed. Esters and anhydrides also react with ammonia to form amides. Ammonium salts of carboxylic acids can be dehydrated to amides so long as there are no thermally sensitive groups present: temperatures of 150–200 °C are required.

The hydrogen in ammonia is capable of replacement by metals, thus magnesium burns in the gas with the formation of magnesium nitride Mg3N2, and when the gas is passed over heated sodium or potassium, sodamide, NaNH2, and potassamide, KNH2, are formed. Where necessary in substitutive nomenclature, IUPAC recommendations prefer the name azane to ammonia: hence chloramine would be named chloroazane in substitutive nomenclature, not chloroammonia.

Pentavalent ammonia is known as λ5-amine, or more commonly, ammonium hydride. This crystalline solid is only stable under high pressure, and decomposes back into trivalent ammonia and hydrogen gas at normal conditions. This substance is was once investigated as a possible solid rocket fuel in 1966.[21]

Ammonia as a ligand

Ball-and-stick model of the tetraamminediaquacopper(II) cation, [Cu(NH3)4(H2O)2]2+

Ball-and-stick model of the diamminesilver(I) cation, [Ag(NH3)2]+

Ammonia can act as a ligand in transition metal complexes. It is a pure σ-donor, in the middle of the spectrochemical series, and shows intermediate hard-soft behaviour. For historical reasons, ammonia is named ammine in the nomenclature of coordination compounds. Some notable ammine complexes include:

Tetraamminediaquacopper(II), [Cu(NH3)4(H2O)2]2+, a characteristic dark blue complex formed by adding ammonia to solution of copper(II) salts. Known as Schweizer's reagent.

Diamminesilver(I), [Ag(NH3)2]+, the active species in Tollens' reagent. Formation of this complex can also help to distinguish between precipitates of the different silver halides: silver chloride (AgCl) is soluble in dilute (2M) ammonia solution, silver bromide (AgBr) is only soluble in concentrated ammonia solution while silver iodide (AgI) is insoluble in aqueous solution of ammonia.

Ammine complexes of chromium(III) were known in the late 19th century, and formed the basis of Alfred Werner's theory of coordination compounds. Werner noted that only two isomers (fac- and mer-) of the complex [CrCl3(NH3)3] could be formed, and concluded that the ligands must be arranged around the metal ion at the vertices of an octahedron. This proposal has since been confirmed by X-ray crystallography.

An ammine ligand bound to a metal ion is markedly more acidic than a free ammonia molecule, although deprotonation in aqueous solution is still rare. One example is the Calomel reaction, where the resulting amidomercury(II) compound is highly insoluble.

Hg2Cl2 + 2 NH3 → Hg + HgCl(NH2) + NH4+ + Cl−

Uses

Fertilizer

Approximately 83% (as of 2004) of ammonia is used as fertilizers either as its salts or as solutions. Consuming more than 1% of all man-made power, the production of ammonia is a significant component of the world energy budget.[4]

Precursor to nitrogenous compounds

Ammonia is directly or indirectly the precursor to most nitrogen-containing compounds. Virtually all synthetic nitrogen compounds are derived from ammonia. An important derivative is nitric acid. This key material is generated via the Ostwald process by oxidation of ammonia with air over a platinum catalyst at 700–850 °C, ~9 atm. Nitric oxide is an intermediate in this conversion:[33]

NH3 + 2 O2 → HNO3 + H2O

Nitric acid is used for the production of fertilizers, explosives, and many organonitrogen compounds.

Cleaner

Household ammonia is a solution of NH3 in water (i.e., ammonium hydroxide) used as a general purpose cleaner for many surfaces. Because ammonia results in a relatively streak-free shine, one of its most common uses is to clean glass, porcelain and stainless steel. It is also frequently used for cleaning ovens and soaking items to loosen baked-on grime. Household ammonia ranges in concentration from 5 to 10 weight percent ammonia.

Minor and emerging uses

Refrigeration – R717

Because of its favourable vaporization properties, ammonia is an attractive refrigerant.[4] It was commonly used prior to the popularisation of chlorofluorocarbons (Freons). Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its high energy efficiency and low cost. The Kalina cycle, which is of growing importance to geothermal power plants, depends on the wide boiling range of the ammonia-water mixture. Ammonia is used less frequently in commercial applications, such as in grocery store freezer cases and refrigerated displays due to its toxicity.

For remediation of gaseous emissions

Ammonia is used to scrub SO2 from the burning of fossil fuels, and the resulting product is converted to ammonium sulfate for use as fertilizer. Ammonia neutralizes the nitrogen oxides (NOx) pollutants emitted by diesel engines. This technology, called SCR (selective catalytic reduction), relies on a vanadia-based catalyst.[34]

As a fuel

Ammonia was used during World War II to power buses in Belgium, and in engine and solar energy applications prior to 1900. Liquid ammonia was used as the fuel of the rocket airplane, the X-15. Although not as powerful as other fuels, it left no soot in the reusable rocket engine and its density approximately matches the density of the oxidizer, liquid oxygen, which simplified the aircraft's design.

Ammonia has been proposed as a practical alternative to fossil fuel for internal combustion engines.[35] The calorific value of ammonia is 22.5 MJ/kg (9690 BTU/lb) which is about half that of diesel. In a normal engine, in which the water vapour is not condensed, the calorific value of ammonia will be about 21% less than this figure. It can be used in existing engines with only minor modifications to carburettors/injectors.

To meet these demands, significant capital would be required to increase present production levels. Although the second most produced chemical, the scale of ammonia production is a small fraction of world petroleum usage. It could be manufactured from renewable energy sources, as well as coal or nuclear power. It is however significantly less efficient than batteries. The 60 MW Rjukan dam in Telemark, Norway produced ammonia via electrolysis of water for many years from 1913 producing fertilizer for much of Europe. If produced from coal, the CO2 can be readily sequestered [35][36] (the combustion products are nitrogen and water). In 1981 a Canadian company converted a 1981 Chevrolet Impala to operate using ammonia as fuel.[37][38]

Ammonia engines or ammonia motors, using ammonia as a working fluid, have been proposed and occasionally used [39]. The principle is similar to that used in a fireless locomotive, but with ammonia as the working fluid, instead of steam or compressed air. Ammonia engines were used experimentally in the 19th century by Goldsworthy Gurney in the UK and in streetcars in New Orleans in the USA.

Antimicrobial agent for food products

As early as in 1895 it was known that ammonia was "strongly antiseptic .. it requires 1.4 grams per litre to preserve beef tea."[40] Anhydrous ammonia has been shown effective as an antimicrobial agent for animal feed [41] and is currently used commercially to reduce or eliminate microbial contamination of beef.[42][43][44] The New York Times reported in October, 2009 on an American company, Beef Products Inc., which turns fatty beef trimmings, averaging between 50 and 70 percent fat, into seven million pounds per week of lean finely textured beef by removing the fat using heat and centrifugation, then disinfecting the lean product with ammonia; the process was rated by the US Department of Agriculture as effective and safe on the basis of a study (financed by Beef Products) which found that the treatment reduces E. coli to undetectable levels.[45] Further investigation by The New York Times published in December, 2009 revealed safety concerns about the process as well as consumer complaints about the taste and smell of beef treated at optimal levels of ammonia.[46]

As a stimulant in sports

Ammonia has found significant use in various sports – particularly the strength sports of powerlifting and Olympic weightlifting as a respiratory stimulant.[citation needed]

Textile

Liquid ammonia is used for treatment of cotton materials, give a properties like mercerisation using alkalies. In particular, it is used for pre-washing of wool.[47]

Lifting gas

At standard temperature and pressure ammonia is lighter than air, and has approximately 60% of the lifting power of hydrogen or helium. Ammonia has sometimes been used to fill weather balloons as a lifting gas. Because of its relatively high boiling point (compared to helium and hydrogen), ammonia could potentially be refrigerated and liquefied aboard an airship to reduce lift and add ballast (and returned to a gas to add lift and reduce ballast).

Woodworking

Ammonia was historically used to darken quartersawn white oak in Arts & Crafts and Mission style furniture. Ammonia fumes react with the natural tannins in the wood and cause it to change colours.[48]

Liquid ammonia as a solvent

Liquid ammonia is the best-known and most widely studied non-aqueous ionising solvent. Its most conspicuous property is its ability to dissolve alkali metals to form highly coloured, electrically conducting solutions containing solvated electrons. Apart from these remarkable solutions, much of the chemistry in liquid ammonia can be classified by analogy with related reactions in aqueous solutions. Comparison of the physical properties of NH3 with those of water shows that NH3 has the lower melting point, boiling point, density, viscosity, dielectric constant and electrical conductivity; this is due at least in part to the weaker H bonding in NH3 and the fact that such bonding cannot form cross-linked networks since each NH3 molecule has only 1 lone-pair of electrons compared with 2 for each H2O molecule. The ionic self-dissociation constant of liquid NH3 at −50 °C is about 10−33 mol2·L−2.

Solubility of salts

Solubility (g of salt per 100 g liquid NH3)

Ammonium acetate 253.2

Ammonium nitrate 389.6

Lithium nitrate 243.7

Sodium nitrate 97.6

Potassium nitrate 10.4

Sodium fluoride 0.35

Sodium chloride 3.0

Sodium bromide 138.0

Sodium iodide 161.9

Sodium thiocyanate 205.5

Liquid ammonia is an ionising solvent, although less so than water, and dissolves a range of ionic compounds including many nitrates, nitrites, cyanides and thiocyanates. Most ammonium salts are soluble, and these salts act as acids in liquid ammonia solutions. The solubility of halide salts increases from fluoride to iodide. A saturated solution of ammonium nitrate contains 0.83 mol solute per mole of ammonia, and has a vapour pressure of less than 1 bar even at 25 °C (77 °F).

Solutions of metals

Liquid ammonia will dissolve the alkali metals and other electropositive metals such as calcium, strontium, barium, europium and ytterbium. At low concentrations (<0.06 mol/L), deep blue solutions are formed: these contain metal cations and solvated electrons, free electrons which are surrounded by a cage of ammonia molecules.

These solutions are very useful as strong reducing agents. At higher concentrations, the solutions are metallic in appearance and in electrical conductivity. At low temperatures, the two types of solution can coexist as immiscible phases.

Redox properties of liquid ammonia

E ° (V, ammonia) E ° (V, water)

Li+ + e− ⇌ Li −2.24 −3.04

K+ + e− ⇌ K −1.98 −2.93

Na+ + e− ⇌ Na −1.85 −2.71

Zn2+ + 2e− ⇌ Zn −0.53 −0.76

NH4+ + e− ⇌ ½ H2 + NH3 0.00 —

Cu2+ + 2e− ⇌ Cu +0.43 +0.34

Ag+ + e− ⇌ Ag +0.83 +0.80

The range of thermodynamic stability of liquid ammonia solutions is very narrow, as the potential for oxidation to dinitrogen, E ° (N2 + 6NH4

+ + 6e− ⇌ 8NH3), is only +0.04 V. In practice, both oxidation to dinitrogen and reduction to dihydrogen are slow. This is particularly true of reducing solutions: the solutions of the alkali metals mentioned above are stable for several days, slowly decomposing to the metal amide and dihydrogen. Most studies involving liquid ammonia solutions are done in reducing conditions: although oxidation of liquid ammonia is usually slow, there is still a risk of explosion, particularly if transition metal ions are present as possible catalysts.

Synthesis and production

Production trend of ammonia between 1947 and 2007

Because of its many uses, ammonia is one of the most highly produced inorganic chemicals. Dozens of chemical plants worldwide produce ammonia. The worldwide ammonia production in 2004 was 109 million metric tonnes.[13] The People's Republic of China produced 28.4% of the worldwide production (increasingly from coal as part of urea synthesis)[14] followed by India with 8.6%, Russia with 8.4%, and the United States with 8.2%.[13] About 80% or more of the ammonia produced is used for fertilizing agricultural crops.[13]

Before the start of World War I, most ammonia was obtained by the dry distillation [15] of nitrogenous vegetable and animal waste products, including camel dung, where it was distilled by the reduction of nitrous acid and nitrites with hydrogen; in addition, it was produced by the distillation of coal, and also by the decomposition of ammonium salts by alkaline hydroxides[16] such as quicklime, the salt most generally used being the chloride (sal-ammoniac) thus:

2 NH4Cl + 2 CaO → CaCl2 + Ca(OH)2 + 2 NH3

Today, the typical modern ammonia-producing plant first converts natural gas (i.e., methane) or liquefied petroleum gas (such gases are propane and butane) or petroleum naphtha into gaseous hydrogen. The process used in producing the hydrogen begins with removal of sulfur compounds from the natural gas (because sulfur deactivates the catalysts used in subsequent steps). Catalytic hydrogenation converts organosulfur compounds into gaseous hydrogen sulfide:

H2 + RSH → RH + H2S (g)

The hydrogen sulfide is then removed by passing the gas through beds of zinc oxide where it is adsorbed and converted to solid zinc sulfide:

H2S + ZnO → ZnS + H2O

Catalytic steam reforming of the sulfur-free feedstock is then used to form hydrogen plus carbon monoxide:

CH4 + H2O → CO + 3 H2

In the next step, the water gas shift reaction is used to convert the carbon monoxide into carbon dioxide and more hydrogen:

CO + H2O → CO2 + H2

The carbon dioxide is then removed either by absorption in aqueous ethanolamine solutions or by adsorption in pressure swing adsorbers (PSA) using proprietary solid adsorption media.

The final step in producing the hydrogen is to use catalytic methanation to remove any small residual amounts of carbon monoxide or carbon dioxide from the hydrogen:

CO + 3 H2 → CH4 + H2O

CO2 + 4 H2 → CH4 + 2 H2O

To produce the desired end-product ammonia, the hydrogen is then catalytically reacted with nitrogen (derived from process air) to form anhydrous liquid ammonia. This step is known as the ammonia synthesis loop (also referred to as the Haber-Bosch process):

3 H2 + N2 → 2 NH3

Hydrogen required for ammonia synthesis could also be produced economically using other sources like coal or coke gasification, less economically from the electrolysis of water into oxygen + hydrogen and other alternatives which are presently impractical for large scale. At one time, most of Europe's ammonia was produced from the Hydro plant at Vemork, via the electrolysis route. Various renewable energy electricity sources are also potentially applicable.

Biosynthesis

In certain organisms, ammonia is produced from atmospheric nitrogen by enzymes called nitrogenases. The overall process is called nitrogen fixation. Although it is unlikely that biomimetic methods will be developed that are competitive with the Haber process, intense effort has been directed toward understanding the mechanism of biological nitrogen fixation. The scientific interest in this problem is motivated by the unusual structure of the active site of the enzyme, which consists of an Fe7MoS9 ensemble.

Ammonia is also a metabolic product of amino acid deamination. Ammonia excretion is common in aquatic animals. In humans, it is quickly converted to urea, which is much less toxic. This urea is a major component of the dry weight of urine. Most reptiles, birds, as well as insects and snails solely excrete uric acid as nitrogenous waste.

Ammonia's role in biological systems and human disease

Ammonia is an important source of nitrogen for living systems. Although atmospheric nitrogen abounds, few living creatures are capable of using this nitrogen. Nitrogen is required for the synthesis of amino acids, which are the building blocks of protein. Some plants rely on ammonia and other nitrogenous wastes incorporated into the soil by decaying matter. Others, such as nitrogen-fixing legumes, benefit from symbiotic relationships with rhizobia which create ammonia from atmospheric nitrogen.[50]

Ammonia also plays a role in both normal and abnormal animal physiology. Ammonia is biosynthesised through normal amino acid metabolism and is toxic in high concentrations.[51] The liver converts ammonia to urea through a series of reactions known as the urea cycle. Liver dysfunction, such as that seen in cirrhosis, may lead to elevated amounts of ammonia in the blood (hyperammonemia). Likewise, defects in the enzymes responsible for the urea cycle, such as ornithine transcarbamylase, lead to hyperammonemia. Hyperammonemia contributes to the confusion and coma of hepatic encephalopathy as well as the neurologic disease common in people with urea cycle defects and organic acidurias.[52]

Ammonia is important for normal animal acid/base balance. After formation of ammonium from glutamine, α-ketoglutarate may be degraded to produce two molecules of bicarbonate, which are then available as buffers for dietary acids. Ammonium is excreted in the urine, resulting in net acid loss. Ammonia may itself diffuse across the renal tubules, combine with a hydrogen ion, and thus allow for further acid excretion

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Alloy

Steel is a metal alloy whose major component is iron, with carbon content between 0.02% and 2.14% by mass.

An alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal (heat treatment) history. Alloys usually have different properties from those of the component elements.

Alloys' constituents are usually measured by mass.

History

This section requires expansion with:History of early intentional alloy use, History of science of modern metallurgical alloys.

The use of alloys by humans started with the use of meteoric iron, a naturally occurring alloy of nickel and iron. As no metallurgic processes were used to separate iron from nickel, the alloy was used as it was.[4] Meteoric iron could be forged from a red heat to make objects such as tools, weapons, and nails. In many cultures it was shaped by cold hammering into knives and arrowheads. They were often used as anvils. Meteoric iron was very rare and valuable, and difficult for ancient people to work.[5]

Iron is usually found as iron ore on Earth, except for one deposit of native iron in Greenland, which was used by the Inuit people. Native copper, however, was found worldwide, along with silver, gold and platinum, which were also used to make tools, jewelry, and other objects since Neolithic times. Copper was the hardest of these metals, and the most widely distributed. It became one of the most important metals to the ancients. Eventually, humans learned to smelt metals such as copper and tin from ore, and, around 2500 B.C, began alloying the two metals to form bronze, which is much harder than its ingredients. Tin was rare, however, being found mostly in Great Britain. In the Middle East, people began alloying copper with zinc to form brass.[6] Ancient civilizations made use of the information contained in modern alloy constitution

diagrams, taking into account the mixture and the various properties it produced, such as hardness, toughness and melting point, under various conditions of temperature and work hardening.[7]

The first known smelting of iron began in Anatolia, around 1800 B.C. Called the bloomery process, it produced very soft but ductile wrought iron and, by 800 B.C., the technology had spread to Europe. Pig iron, a very hard but brittle alloy of iron and carbon, was being produced in China as early as 1200 B.C., but did not arrive in Europe until the Middle Ages. These metals found little practical use until the introduction of crucible steel around 300 B.C. These steels were of poor quality, and the introduction of pattern welding, around the first century A.D., sought to balance the extreme properties of the alloys by laminating them, to create a tougher metal.[8]

Mercury had been smelted from cinnabar for thousands of years. Mercury dissolves many metals, such as gold, silver, and tin, to form amalgams, (an alloy in a soft, paste, or liquid form at ambient temperature). Amalgams have been used since 200 B.C. in China for plating objects with precious metals, called gilding, such as armor and mirrors. The ancient Romans often used mercury-tin amalgams for gilding their armor. The amalgam was applied as a paste and then heated until the mercury vaporized, leaving the gold, silver, or tin behind.[9] Mercury was often used in mining, to extract precious metals like gold and silver from their ores.[10]

Many ancient civilizations alloyed metals for purely aesthetic purposes. In ancient Egypt and Mycenae, gold was often alloyed with copper to produce red-gold, or iron to produce a bright burgundy-gold. Silver was often found alloyed with gold. These metals were also used to strengthen each other, for more practical purposes. Quite often, precious metals were alloyed with less valuable substances as a means to deceive buyers.[11] Around 250 B.C., Archimedes was commissioned by the king to find a way to check the purity of the gold in a crown, leading to the famous bath-house shouting of "Eureka!" upon the discovery of Archimedes principle.[12]

Investigating the Internal Structure of Metals

IntroductionDid you know that metals account for about two thirds of all the elements and about 24% of the massof the planet? They are all around us in such forms as steel structures, copper wires, aluminum foil, andgold jewelry. Metals are widely used because of their favorable properties such as strength, ductility, highmelting point, thermal and electrical conductivity, and toughness. These properties also offer clues as tothe structure of metals. As with all elements, metals are composed of atoms. The strength of metalssuggests that these atoms are held together by strong bonds. These bonds must also allow atoms to move;otherwise how could metals be hammered into sheets or drawn into wires?

A reasonable model would be one in which atoms are held together by strong, but delocalized, bonds.Such bonds could be formed between metal atoms that have low electronegativities and do not attract

their valence electrons strongly. This would allow the outermost electrons to be shared by all thesurrounding atoms, resulting in positive ions (cations) surrounded by a sea of electrons, or an “electroncloud.”

Strength and workability

Malleability and ductility

Metals are described as malleable (can be beaten into sheets) and ductile (can be pulled out into wires). This is because of the ability of the atoms to roll over each other into new positions without breaking the metallic bond.

If a small stress is put onto the metal, the layers of atoms will start to roll over each other. If the stress is

released again, they will fall back to their original positions. Under these circumstances, the metal is said to be elastic.

Because these valence electrons are shared by all the atoms, they are not considered to be associatedwith any one atom. This is very different from ionic or covalent bonds, where electrons are held by one ortwo atoms. The metallic bond is therefore strong and uniform. Above their melting point, metals areliquids, and their atoms are randomly arranged and relatively free to move. However, when cooled belowtheir melting point, metals rearrange to form ordered, crystalline structures.

If a larger stress is put on, the atoms roll over each other into a new position, and the metal is permanently changed.

The hardness of metals

This rolling of layers of atoms over each other is hindered by grain boundaries because the rows of atoms

don't line up properly. It follows that the more grain boundaries there are (the smaller the individual crystal grains), the harder the metal becomes.

Offsetting this, because the grain boundaries are areas where the atoms aren't in such good contact with

each other, metals tend to fracture at grain boundaries. Increasing the number of grain boundaries not only makes the metal harder, but also makes it more brittle.

Controlling the size of the crystal grains

If you have a pure piece of metal, you can control the size of the grains by heat treatment or by working the metal.

Heating a metal tends to shake the atoms into a more regular arrangement - decreasing the number of grain

boundaries, and so making the metal softer. Banging the metal around when it is cold tends to produce lots

of small grains. Cold working therefore makes a metal harder. To restore its workability, you would need to reheat it.

You can also break up the regular arrangement of the atoms by inserting atoms of a slightly different size into the structure. Alloys such as brass (a mixture of copper and zinc) are harder than the original metals because the irregularity in the structure helps to stop rows of atoms from slipping over each other.

Purpose of Making Alloys

Pure metals possess few important physical and metallic properties, such as melting point, boiling point, density, specific gravity, high malleability, ductility, and heat and electrical conductivity. These properties can be modified and enhanced by alloying it with some other metal or nonmetal, according to the need.

Alloys are made to:

Enhance the hardness of a metal: An alloy is harder than its components. Pure metals are generally soft. The hardness of a metal can be enhanced by alloying it with another metal or nonmetal.

Lower the melting point: Pure metals have a high melting point. The melting point lowers when pure metals are alloyed with other metals or nonmetals. This makes the metals easily fusible. This property is utilized to make useful alloys called solders.

Enhance tensile strength: Alloy formation increases the tensile strength of the parent metal.Enhance corrosion resistance: Alloys are more resistant to corrosion than pure metals. Metals in pure form

are chemically reactive and can be easily corroded by the surrounding atmospheric gases and moisture. Alloying a metal increases the inertness of the metal, which, in turn, increases corrosion resistance.

Modify color: The color of pure metal can be modified by alloying it with other metals or nonmetals containing suitable color pigments.

Provide better castability: One of the most essential requirements of getting good castings is the expansion of the metal on solidification. Pure molten metals undergo contraction on solidification. Metals need to be alloyed to obtain good castings because alloys expand...

Industrial Application of Alloys

Alloys have been used in industries for a long time. Few widely used applications are:

Stainless Steel is used in wire and ribbon forms for applications, such as screening, staple, belt, cable, weld, metalizing, catheter, and suture wire.

Alloys of Gold and Silver are used in the preparation of jewelry. White Gold, which is an alloy of Gold, Silver, Palladium, and Nickel is used as cheap alternative of Platinum. A wide selection of alloys is used in welding applications by numerous industries.

Some alloys function as corrosion-resistant materials and are used in moisture rich-environments.High temperature alloys have been used for many aerospace and petrochemical applications. In addition,

they have been used for welding wire, where elevated temperatures and harsh environments are routinely encountered. These alloys have been used in applications where corrosion resistance and high strength must be maintained at elevated temperatures.

Magnetic alloys are used for magnetic cores and dry reed switches. Quality control measures include magnetic testing to maintain consistently high standards of uniformity and performance.

Alloys are also used to produce internal and external leads.Nickel-Chromium, Nickel-Chromium-Iron, and Iron-Chromium-Aluminum alloys have been used for high-

temperature heating elements.Some alloys are used as resistance elements to control or measure electric current. Applications have

included wire-wound resistors, rheostats, potentiometers, and shunts.Thermocouple alloys have found a wide-range of use in temperature sensing and control.Alloys are also used as thermostat metals, radio and electronic devices, precision devises in aircraft controls,

telecommunications, automotive applications, and...

Examples of alloys

Bronze

Composition

有许多不同的青铜青铜合金，但通常是 88％ 和 12％ 。 阿尔法铜牌由阿尔法的铜锡研究。 There are many different bronze alloys but bronze is typically 88% copper and 12% tin . [ 6 ] Alpha bronze consists of the alpha solid solution of tin in copper. 阿尔法 4-5％的锡青铜合金，用来制造 ， ， 和 。 Alpha bronze alloys of 4–5% tin are used to make coins , springs , turbines and blades .

商业青铜 （铜 90％和 10％锌）及建筑青铜 （铜 57％，3％的铅，锌 40％）实际上是合金，因为它们含有为主要合金成分。 Commercial bronze (90% copper and 10% zinc) and Architectural bronze (57% Copper, 3% Lead, 40% Zinc) are actually brass alloys because they contain zinc as the main alloying ingredient. 它们通常用于建筑应用。 They are commonly used in architectural applications. [ 7 ] [ 8 ]

铅是青铜合金的零件 5的组成部分 52铜，镍 30件，12件锌，铋和 1份。 Bismuth bronze is a bronze alloy with a composition of 52 parts copper, 30 parts nickel, 12 parts zinc, 5 parts lead, and 1 part bismuth. 它能够保持一个良好的抛光，所以有时也用在光镜和反射。 It is able to hold a good polish and so is sometimes used in light reflectors and mirrors. [ 9 ]

其他铜合金包括 ， ，锰青铜， ， 和 。 Other bronze alloys include aluminum bronze , phosphor bronze , manganese bronze, bell metal , speculum metal and cymbal alloys .

Properties

什锦古代青青铜是相当少的比 Bronze is considerably less brittle than iron. 通常只青铜表面氧化，一旦一氧化铜（最终成为碳酸铜）层组成，基本金属进一步腐蚀保护。 Typically bronze only oxidizes superficially; once a copper oxide (eventually becoming copper carbonate) layer is formed, the underlying metal is protected from

further corrosion. 但是，如果铜的氯化物形成，一个腐蚀模式称为“青铜病”，最终彻底摧毁它。 铜基具有较低的比钢或铁，更容易从他们生产的金属成分。 However, if copper chlorides are formed, a corrosion-mode called "bronze disease" will eventually completely destroy it. [ 10 ] Copper-based alloys have lower melting points

than steel or iron, and are more readily produced from their constituent metals. 他们普遍重量超过百分之十左右钢，合金虽然使用或可能略低于致密。 They are generally about 10 percent heavier than steel, although alloys

using aluminum or silicon may be slightly less dense. 铜器和青铜更软低于钢 ，例如，不那么僵硬（以及存储相同的批量较少的能源）的。 Bronzes are softer and weaker than steel—bronze springs , for example, are less stiff

(and so store less energy) for the same bulk. 青铜抗 （尤其是 ）和钢多了，也是最钢材更好导体比热和电。

Bronze resists corrosion (especially seawater corrosion ) and metal fatigue more than steel and is also a better

conductor of heat and electricity than most steels. 该合金成本铜基一般高于钢认为，但低于基合金。 The cost of copper-base alloys is generally higher than that of steels but lower than that of nickel -base alloys.

铜及其合金有一个，和巨大的各种用途，反映他们的多才多艺的物理，机械 。 Copper and its alloys

have a huge variety of uses that reflect their versatile physical, mechanical, and chemical properties . 一些常见的例子是高纯铜，精良的的素质黄铜，青铜轴承摩擦性能低，青铜钟的共振素质，抗腐蚀的几个青铜合金。 Some common examples are the high electrical conductivity of pure copper, the excellent deep drawing qualities of cartridge case brass, the low-friction properties of bearing bronze, the resonant qualities of bell bronze, and the resistance to corrosion by sea water of several bronze alloys.

在青铜的熔点取决于该合金成分的实际比例，大约是 950摄氏度 The melting point of Bronze varies depending on the actual ratio of the alloy components and is about 950 °C.

Uses

Bronze was especially suitable for use in boat and ship fittings prior to the wide employment of stainless steel owing to its combination of toughness and resistance to salt water corrosion. Bronze is still commonly used in ship propellers and submerged bearings.

In the twentieth century, silicon was introduced as the primary alloying element, creating an alloy with wide application in industry and the major form used in contemporary statuary. Aluminum is also used for the structural metal aluminum bronze.

It is also widely used for cast bronze sculpture. Many common bronze alloys have the unusual and very desirable property of expanding slightly just before they set, thus filling in the finest details of a mold. Bronze parts are tough and typically used for bearings, clips, electrical connectors and springs.

Spring bronze weatherstripping comes in rolls of thin sheets and is nailed or stapled to wood windows and doors. There are two types, flat and v-strip. It has been used for hundreds of years because it has low friction, seals well and is long lasting. It is used in building restoration and custom construction.

Bronze also has very little metal-on-metal friction, which made it invaluable for the building of cannon where iron cannonballs would otherwise stick in the barrel.[citation needed] It is still widely used today for springs, bearings, bushings, automobile transmission pilot bearings, and similar fittings, and is particularly common in the bearings of small electric motors. Phosphor bronze is particularly suited to precision-grade bearings and springs. It is also used in guitar and piano strings.

Unlike steel, bronze struck against a hard surface will not generate sparks, so it (along with beryllium copper) is used to make hammers, mallets, wrenches and other durable tools to be used in explosive atmospheres or in the presence of flammable vapors.

Brass

Composition

Brass is any alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.[1] In comparison, bronze is principally an alloy of copper and tin.[2] Despite this distinction some types of brasses are called bronzes and vice-versa.[3] Brass is a substitutional alloy. It is used for decoration for its bright gold-like appearance; for applications where low friction is required such as locks, gears, bearings, doorknobs, ammunition, and valves; for plumbing and electrical applications; and extensively in musical instruments such as horns and bells for its acoustic properties. It is also used in zippers. Because it is softer than most other metals in general use, brass is often used in situations where it is important that sparks not be struck, as in fittings and tools around explosive gases.[4]

Properties

Microstructure of rolled and annealed brass (400X magnification)

The malleability and acoustic properties of brass have made it the metal of choice for brass musical instruments such as the trombone, tuba, trumpet, cornet, euphonium, tenor horn, and the French horn. Even though the saxophone is classified as a woodwind instrument and the harmonica is a free reed aerophone, both are also often made from brass. In organ pipes of the reed family, brass strips (called tongues) are used as the reeds, which beat against the shallot (or beat "through" the shallot in the case of a "free" reed).

Brass has higher malleability than copper or zinc. The relatively low melting point of brass (900 to 940°C, depending on composition) and its flow characteristics make it a relatively easy material to cast. By

varying the proportions of copper and zinc, the properties of the brass can be changed, allowing hard and soft brasses. The density of brass is approximately 8400 to 8730 kilograms per cubic metre[11] (equivalent to 8.4 to 8.73 grams per cubic centimetre).

Today almost 90% of all brass alloys are recycled.[12] Because brass is not ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a powerful magnet. Brass scrap is collected and transported to the foundry where it is melted and recast into billets. Billets are heated and extruded into the desired form and size.

Aluminium makes brass stronger and more corrosion resistant. Aluminium also causes a highly beneficial hard layer of aluminium oxide (Al2O3) to be formed on the surface that is thin, transparent and self healing. Tin has a similar effect and finds its use especially in sea water applications (naval brasses). Combinations of iron, aluminium, silicon and manganese make brass wear and tear resistant.

Applications

Harsh environments: The so called dezincification resistant (DZR) brasses are used where there is a large corrosion risk and where normal brasses do not meet the standards. Applications with high water temperatures, chlorides present or deviating water qualities (soft water) play a role. DZR-brass is excellent in water boiler systems. This brass alloy must be produced with great care, with special attention placed on a balanced composition and proper production temperatures and parameters to avoid long-term failures.

Germicidal properties: The copper in brass makes brass germicidal, via the oligodynamic effect. For example, brass doorknobs disinfect themselves of many bacteria within eight hours.[20] This effect is important in hospitals, and useful in many contexts.

Brass door hardware: Brass hardware is generally lacquered when new, which prevents tarnishing of the metal. Freshly polished brass is similar to gold in appearance, but becomes more reddish within days of exposure to the elements. A traditional polish is Brasso.

Other: Brass was used to make fan blades, fan cages and motor bearings in many antique fans that date before the 1930s. Brass can also be used for fixings for use in cryogenic systems.[21] Brass has also been used to make lower end Paiste cymbals.

Stainless steel

Composition

In metallurgy stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5[1] or 11% chromium content by mass.[2] Stainless steel does not stain, corrode, or rust as easily as ordinary steel, but it is not stain-proof.[3] It is also called corrosion-resistant steel or CRES when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment to which the material will be subjected in its lifetime. Stainless steel is used where both the properties of steel and resistance to corrosion are required.

Stainless steel differs from carbon steel by the amount of chromium present. Carbon steel rusts when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion and blocks corrosion from spreading into the metal's internal structure.

Properties

High oxidation-resistance in air at ambient temperature is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments.[9] The chromium forms a passivation layer of chromium(III) oxide (Cr2O3) when exposed to oxygen. The layer is too thin to be visible, and the metal remains lustrous. The layer is impervious to water and air, protecting the metal beneath. Also, this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, such as aluminium and titanium. Corrosion-resistance can be adversely affected if the component is used in a non-oxygenated environment, a typical example being underwater keel bolts buried in timber.

When stainless steel parts such as nuts and bolts are forced together, the oxide layer can be scraped off, causing the parts to weld together. When disassembled, the welded material may be torn and pitted, an effect known as galling. This destructive galling can be best avoided by the use of dissimilar materials for the parts forced together, e.g. bronze and stainless steel, or even different types of stainless steels (martensitic against austenitic, etc.), when metal-to-metal wear is a concern. Nitronic alloys (trademark of Armco, Inc.) reduce the tendency to gall through selective alloying with manganese and nitrogen. Threaded joints may also be lubricated to prevent galling.

Applications

Stainless steel’s resistance to corrosion and staining, low maintenance, relatively low cost, and familiar luster make it an ideal base material for a host of commercial applications. There are over 150 grades of stainless steel, of which fifteen are most commonly used. The alloy is milled into coils, sheets, plates, bars, wire, and tubing to be used in cookware, cutlery, hardware, surgical instruments, major appliances, industrial equipment e.g. in sugar refineries, and as an automotive and aerospace structural alloy and construction material in large buildings. Storage tanks and tankers used to transport orange juice and other food are often made of stainless steel, due to its corrosion resistance and antibacterial properties. This also influences its use in commercial kitchens and food processing plants, as it can be steam-cleaned, sterilized, and does not need painting or application of other surface finishes.

Stainless steel is used for jewellery and watches. 316L is the stainless steel commonly used for such purpose. It can be re-finished by any jeweller and will not oxidize or turn black.

Some firearms incorporate stainless steel components as an alternative to blued or parkerized steel. Some handgun models, such as the Smith & Wesson Model 60 and the Colt M1911 pistol, can be made entirely from stainless steel. This gives a high-luster finish similar in appearance to nickel plating; but, unlike plating, the finish is not subject to flaking, peeling, wear-off due to rubbing (as when repeatedly removed from a holster over the course of time), or rust when scratched.

Some automotive manufacturers use stainless steel as decorative highlights in their vehicles.

Uses in sculpture, building facades and building structures

Stainless steel was in vogue during the art deco period. The most famous example of this is the upper portion of the Chrysler Building (pictured). Some diners and fast-food restaurants use large ornamental panels, stainless fixtures and furniture. Owing to the durability of the material, many of these buildings retain their original appearance.

The forging of stainless steel has given rise to a fresh approach to architectural blacksmithing in recent years.

The Unisphere (pictured), constructed as the theme symbol of the 1964-4 World's Fair in New York City, is the world's largest global structure.

The Gateway Arch (pictured) is clad entirely in stainless steel: 886 tons (804 metric tonnes) of 0.25 in (6.4 mm) plate, #3 finish, type 304 stainless steel.[11]

Type 316 stainless is used on the exterior of both the Petronas Twin Towers and the Jin Mao Building, two of the world's tallest skyscrapers.[12]

The Parliament House of Australia in Canberra has a stainless steel flagpole weighing over 220 tons. The aeration building in the Edmonton Composting Facility, the size of 14 hockey rinks, is the largest

stainless steel building in North America. The United States Air Force Memorial has an austenitic stainless steel structural skin. The Atomium in Brussels, Belgium was renovated with stainless-steel cladding in a renovation completed in

2006; previously the spheres and tubes of the structure were clad in aluminium. The Cloud Gate sculpture by Anish Kapoor, in Chicago US. The Sibelius monument in Helsinki, Finland, is made solely of stainless steel tubes.

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Polymer

A polymer is a large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties.

Because of the extraordinary range of properties of polymeric materials,[2] they play an essential and ubiquitous role in everyday life[3], ranging from familiar synthetic plastics and elastomers to natural biopolymers such as DNA and proteins that are essential for life. A simple example is polyethylene, whose repeating unit is based on ethylene (IUPAC name ethene) monomer. Most commonly, as in this example, the continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. However, other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being silly putty and waterproof plumbing sealant. The backbone of DNA is in fact based on a phosphodiester bond, and repeating units of polysaccharides (e.g. cellulose) are joined together by glycosidic bonds via oxygen atoms.

Natural polymeric materials such as shellac, amber, and natural rubber have been used for centuries. Biopolymers such as proteins and nucleic acids play crucial roles in biological processes. A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper.

The list of synthetic polymers includes synthetic rubber, Bakelite, neoprene, nylon, PVC, polystyrene, polyethylene, polypropylene, polyacrylonitrile, PVB, silicone, and many more.

Polymers are studied in the fields of polymer chemistry, polymer physics, and polymer science.

Historical development

Starting in 1811, Henri Braconnot did pioneering work in derivative cellulose compounds, perhaps the earliest important work in polymer science. The development of vulcanization later in the nineteenth century improved the durability of the natural polymer rubber, signifying the first popularized semi-synthetic polymer. In 1907, Leo Baekeland created the first completely synthetic polymer, Bakelite, by reacting phenol and formaldehyde at precisely controlled temperature and pressure. Bakelite was then publicly introduced in 1909.

Despite significant advances in synthesis and characterization of polymers, a correct understanding of polymer molecular structure did not emerge until the 1920s. Before then, scientists believed that polymers were clusters of small molecules (called colloids), without definite molecular weights, held together by an unknown force, a concept known as association theory. In 1922, Hermann Staudinger proposed that polymers consisted of long chains of atoms held together by covalent bonds, an idea which did not gain wide acceptance for over a decade and for which Staudinger was ultimately awarded the Nobel Prize. Work by Wallace Carothers in the 1920s also demonstrated that polymers could be synthesized rationally from their constituent monomers. An important contribution to synthetic polymer science was made by the Italian chemist Giulio Natta and the German chemist Karl Ziegler, who won the Nobel Prize in Chemistry in 1963 for the development of the Ziegler-Natta catalyst. Further recognition of the importance of polymers came with the award of the Nobel Prize in Chemistry in 1974 to Paul Flory, whose extensive work on polymers included the kinetics of step-growth polymerization and of addition polymerization, chain transfer, excluded volume, the Flory-Huggins solution theory, and the Flory convention.

Synthetic polymer materials such as nylon, polyethylene, Teflon, and silicone have formed the basis for a burgeoning polymer industry. These years have also shown significant developments in rational polymer synthesis. Most commercially important polymers today are entirely synthetic and produced in high volume on appropriately scaled organic synthetic techniques. Synthetic polymers today find application in nearly every industry and area of life. Polymers are widely used as adhesives and lubricants, as well as structural components for products ranging from children's toys to aircraft. They have been employed in a variety of biomedical applications ranging from implantable devices to controlled drug delivery. Polymers such as poly(methyl methacrylate) find application as photoresist materials used in semiconductor manufacturing and low-k dielectrics for use in high-performance microprocessors. Recently, polymers have also been employed as flexible substrates in the development of organic light-emitting diodes for electronic display.

Polymer properties

Polymer properties are broadly divided into several classes based on the scale at which the property is defined as well as upon its physical basis[7]. The most basic property of a polymer is the identity of its constituent monomers. A second set of properties, known as microstructure, essentially describe the arrangement of these monomers within the polymer at the scale of a single chain. These basic structural properties play a major role in determining bulk physical properties of the polymer, which describe how the polymer behaves as a continuous macroscopic material. Chemical properties, at the nano-scale, describe how the chains interact through various physical forces. At the macro-scale, they describe how the bulk polymer interacts with other chemicals and solvents.

Microstructure

The microstructure of a polymer (sometimes called configuration) relates to the physical arrangement of monomer residues along the backbone of the chain[8]. These are the elements of polymer structure that require the breaking of a covalent bond in order to change. Structure has a strong influence on the other properties of a polymer. For example, two samples of natural rubber may exhibit different durability, even though their molecules comprise the same monomers.

Polymer architecture

Branch point in a polymer

An important microstructural feature determining polymer properties is the polymer architecture.[9] The simplest polymer architecture is a linear chain: a single backbone with no branches. A related unbranching architecture is a ring polymer. A branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Special types of branched polymers include star polymers, comb polymers, brush polymers, dendronized polymers, ladders, and dendrimers [9] .

Branching of polymer chains affects the ability of chains to slide past one another by altering intermolecular forces, in turn affecting bulk physical polymer properties. Long chain branches may increase polymer strength, toughness, and the glass transition temperature (Tg) due to an increase in the number of entanglements per chain. The effect of such long-chain branches on the size of the polymer in solution is characterized by the branching index. Random length and atactic short chains, on the other hand, may reduce polymer strength due to disruption of organization and may likewise reduce the crystallinity of the polymer.

A good example of this effect is related to the range of physical attributes of polyethylene. High-density polyethylene (HDPE) has a very low degree of branching, is quite stiff, and is used in applications such as milk jugs. Low-density polyethylene (LDPE), on the other hand, has significant numbers of both long and short branches, is quite flexible, and is used in applications such as plastic films.

Dendrimer and dendron

Dendrimers are a special case of polymer where every monomer unit is branched. This tends to reduce intermolecular chain entanglement and crystallization. Alternatively, dendritic polymers are not perfectly branched but share similar properties to dendrimers due to their high degree of branching.

The architecture of the polymer is often physically determined by the functionality of the monomers from which it is formed[10]. This property of a monomer is defined as the number of reaction sites at which may form chemical covalent bonds. The basic functionality required for forming even a linear chain is two bonding sites. Higher functionality yields branched or even crosslinked or networked polymer chains.

An effect related to branching is chemical crosslinking - the formation of covalent bonds between chains. Crosslinking tends to increase Tg and increase strength and toughness. Among other applications, this process is used to strengthen rubbers in a process known as vulcanization, which is based on crosslinking by sulfur. Car tires, for example, are highly crosslinked in order to reduce the leaking of air out of the tire and to toughen their durability. Eraser rubber, on the other hand, is not crosslinked to allow flaking of the rubber and prevent damage to the paper.

A cross-link suggests a branch point from which four or more distinct chains emanate. A polymer molecule with a high degree of crosslinking is referred to as a polymer network.[11] Sufficiently high crosslink concentrations may lead to the formation of an infinite network, also known as a gel, in which networks of chains are of unlimited extent—essentially all chains have linked into one molecule.[12]\\

Polymer synthesis

Main article: Polymerization

The repeating unit of the polymer polypropylene

Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain. During the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester. The monomers are terephthalic acid (HOOC-C6H4-COOH) and ethylene glycol (HO-CH2-CH2-OH) but the repeating unit is -OC-C6H4-COO-CH2-CH2-O-, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue.

Laboratory synthesis

Laboratory synthetic methods are generally divided into two categories, step-growth polymerization and chain-growth polymerization [4] . The essential difference between the two is that in chain growth polymerization, monomers are added to the chain one at a time only[5], whereas in step-growth polymerization chains of monomers may combine with one another directly[6]. However, some newer methods such as plasma polymerization do not fit neatly into either category. Synthetic polymerization reactions may be carried out with or without a catalyst. Laboratory synthesis of biopolymers, especially of proteins, is an area of intensive research.

Biological synthesisMain article: Biopolymer

There are three main classes of biopolymers: polysaccharides, polypeptides, and polynucleotides. In living cells, they may be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by DNA polymerase. The synthesis of proteins involves multiple enzyme-mediated processes to transcribe genetic information from the DNA to RNA and subsequently translate that information to synthesize the specified protein from amino acids. The protein may be modified further following translation in order to provide appropriate structure and functioning.

Modification of natural polymers

Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulfur.

Synthetic polymer and their uses

Polypropylene

Polypropylene (PP), also known as polypropene, is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles (e.g. ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.

In 2007, the global market for polypropylene had a volume of 45.1 million tons, which led to a turnover of about 65 billion US-dollars (47.4 billion Euro).[1]

Applications

Since polypropylene is resistant to fatigue, most plastic living hinges, such as those on flip-top bottles, are made from this material. However, it is important to ensure that chain molecules are oriented across the hinge to maximize strength.

Very thin sheets of polypropylene are used as a dielectric within certain high-performance pulse and low-loss RF capacitors.

High-purity piping systems are built using polypropylene. Stronger, more rigid piping systems, intended for use in potable plumbing, hydronic heating and cooling, and reclaimed water applications, are also manufactured using polypropylene.[10] This material is often chosen for its resistance to corrosion and chemical leaching, its resilience against most forms of physical damage, including impact and freezing, its environmental benefits, and its ability to be joined by heat fusion rather than gluing.[11][12][13]

Many plastic items for medical or laboratory use can be made from polypropylene because it can withstand the heat in an autoclave. Its heat resistance also enables it to be used as the manufacturing material of consumer-grade kettles. Food containers made from it will not melt in the dishwasher, and do not melt during industrial hot filling processes. For this reason, most plastic tubs for dairy products are polypropylene sealed with aluminum foil (both heat-resistant materials). After the product has cooled, the tubs are often given lids made of a less heat-resistant material, such as LDPE or polystyrene. Such containers provide a good hands-on example of the difference in modulus, since the rubbery (softer, more flexible) feeling of LDPE with respect to polypropylene of the same thickness is readily apparent. Rugged, translucent, reusable plastic containers made in a wide variety of shapes and sizes for consumers from various companies such as Rubbermaid and Sterilite are commonly made of polypropylene, although the lids are often made of somewhat more flexible LDPE so they can snap on to the container to close it. Polypropylene can also be made into disposable bottles to contain liquid, powdered, or similar consumer products, although HDPE and polyethylene terephthalate are commonly also used to make bottles. Plastic pails, car batteries, wastebaskets, cooler containers, dishes and pitchers are often made of polypropylene or HDPE, both of which commonly have rather similar appearance, feel, and properties at ambient temperature.

A common application for polypropylene is as biaxially oriented polypropylene (BOPP). These BOPP sheets are used to make a wide variety of materials including clear bags. When polypropylene is biaxially oriented, it becomes crystal clear and serves as an excellent packaging material for artistic and retail products.

Polypropylene, highly colorfast, is widely used in manufacturing carpets, rugs and mats to be used at home.[14]

Polypropylene is widely used in ropes, distinctive because they are light enough to float in water.[15] For equal mass and construction, polypropylene rope is similar in strength to polyester rope. Polypropylene costs less than most other synthetic fibers.

Polypropylene is also used as an alternative to polyvinyl chloride (PVC) as insulation for electrical cables for LSZH cable in low-ventilation environments, primarily tunnels. This is because it emits less smoke and no toxic halogens, which may lead to production of acid in high-temperature conditions.

Polypropylene is also used in particular roofing membranes as the waterproofing top layer of single-ply systems as opposed to modified-bit systems.

Polypropylene is most commonly used for plastic moldings, wherein it is injected into a mold while molten, forming complex shapes at relatively low cost and high volume; examples include bottle tops, bottles, and fittings.

Recently[when?], it has been produced in sheet form, which has been widely used for the production of stationery folders, packaging, and storage boxes. The wide color range, durability, and resistance to dirt make it ideal as a protective cover for papers and other materials. It is used in Rubik's cube stickers because of these characteristics.

The availability of sheet polypropylene has provided an opportunity for the use of the material by designers. The light-weight, durable, and colorful plastic makes an ideal medium for the creation of light shades, and a number of designs have been developed using interlocking sections to create elaborate designs.

Polypropylene sheets are a popular choice for trading card collectors; these come with pockets (nine for standard-size cards) for the cards to be inserted and are used to protect their condition and are meant to be stored in a binder.

Expanded polypropylene (EPP) is a foam form of polypropylene. EPP has very good impact characteristics due to its low stiffness; this allows EPP to resume its shape after impacts. EPP is extensively used in model aircraft and other radio controlled vehicles by hobbyists. This is mainly due to its ability to absorb impacts, making this an ideal material for RC aircraft for beginners and amateurs.

Polypropylene is used in the manufacture of loudspeaker drive units. Its use was pioneered by engineers at the BBC and the patent rights subsequently purchased by Mission Electronics for use in their Mission Freedom Loudspeaker and Mission 737 Renaissance loudspeaker.

Polypropylene fibres are used as a concrete additive to increase strength and reduce cracking and spalling.[16]

[edit] Clothes

Polypropylene is a major polymer used in nonwovens, with over 50% used[citation needed] for diapers or sanitary products where it is treated to absorb water (hydrophilic) rather than naturally repelling water (hydrophobic). Other interesting non-woven uses include filters for air, gas, and liquids in which the fibers can be formed into sheets or webs that can be pleated to form cartridges or layers that filter in various efficiencies in the 0.5 to 30 micrometre range. Such applications could be seen in the house as water filters or air-conditioning-type filters. The high surface area and naturally oleophilic polypropylene nonwovens are ideal absorbers of oil spills with the familiar floating barriers near oil spills on rivers.

In New Zealand, in the US military, and elsewhere, polypropylene, or 'polypro' (New Zealand 'polyprops'), has been used for the fabrication of cold-weather base layers, such as long-sleeve shirts or long underwear (More recently, polyester has replaced polypropylene in these applications in the U.S. military, such as in the ECWCS [17]). Polypropylene is also used in warm-weather gear such as some Under Armour clothing, which can easily transport sweat away from the skin. Although polypropylene clothes are not easily flammable, they can melt, which may result in severe burns if the service member is involved in an explosion or fire of any kind.[18]. Polypropylene undergarments are known for retaining body odors which are then difficult to remove. The current generation of polyester does not have this disadvantage.[19]

The material has recently been introduced into the fashion industry through the work of designers such as Anoush Waddington, who have developed specialized techniques to create jewelry and wearable items from polypropylene.

[edit] Medical

Its most common medical use is in the synthetic, nonabsorbable suture Prolene, manufactured by Ethicon Inc.

Polypropylene has been used in hernia and pelvic organ prolapse repair operations to protect the body from new hernias in the same location. A small patch of the material is placed over the spot of the hernia, below the skin, and is painless and is rarely, if ever, rejected by the body. However, a polypropylene mesh will erode over the uncertain period from days to years. Therefore, the FDA has issued several warnings on the use of polypropylene mesh medical kits for certain applications in pelvic organ prolapse, specifically when introduced in close proximity to the vaginal wall due to a continued increase in number of mesh erosions reported by patients over the past few years.[20]

[edit] Model Aircraft

Since 2001, expanded polypropylene (EPP) foams are gaining in popularity and in application as a structural material in hobbyist radio control model aircraft. Unlike expanded polystyrene foam (EPS) which is friable and breaks easily on impact, EPP foam is able to absorb kinetic impacts very well without breaking, retains its original shape, and exhibits memory form characteristics which allow it to return to its original shape in a short amount of time. In consequence, a radio-control model whose wings and fuselage are constructed from EPP foam is extremely resilient, and able to absorb impacts that would result in complete destruction of models made from lighter traditional materials, such as balsa or even EPS foams. EPP models, when covered with inexpensive fibreglass impregnated self adhesive tapes, and decorated with coloured self adhesive tapes, often exhibit much increased mechanical strength, in conjunction with a lightness and surface finish that rival those of models of the aforementioned types. EPP is also chemically highly inert, permitting the use of a wide variety of different adhesives. EPP can be heat molded, and surfaces can be easily finished with the use of cutting tools and abrasive papers. The principle areas of model making in which EPP has found great acceptance are the fields of:

Wind-driven Slope Soarers Indoor electric powered profile electric models Hand launched gliders for small children

In the field of slope soaring, EPP has found greatest favour and use, as it permits the construction of radio-controlled model gliders of great strength and maneuverability. In consequence, the disciplines of slope combat (the active process of friendly competitors attempting to knock each other's planes out of the air by direct contact) and slope pylon racing have become commonplace, in direct consequence of the strength characteristics of the material EPP.

Nylon

Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935 by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station. Nylon is one of the most commonly used polymers.

Uses

Nylon is a thermoplastic silky material, first used commercially in a nylon-bristled toothbrush (1938), followed more famously by women's stockings ("nylons"; 1940). It is made of repeating units linked by peptide bonds (or amide bonds) and is frequently referred to as polyamide (PA). Nylon was the first commercially successful synthetic polymer. There are two common methods of making nylon for fiber applications. In one approach, molecules with an acid (COOH) group on each end are reacted with molecules containing amine (NH2) groups on each end. The resulting nylon is named on the basis of the number of carbon atoms separating the two acid groups and the two amines. These are formed into monomers of intermediate molecular weight, which are then reacted to form long polymer chains.

Nylon was intended to be a synthetic replacement for silk and substituted for it in many different products after silk became scarce during World War II. It replaced silk in military applications such as parachutes and flak vests, and was used in many types of vehicle tires.

Nylon fibres are used in many applications, including fabrics, bridal veils, carpets, musical strings, and rope.

Solid nylon is used for mechanical parts such as machine screws, gears and other low- to medium-stress components previously cast in metal. Engineering-grade nylon is processed by extrusion, casting, and injection molding. Solid nylon is used in hair combs. Type 6,6 Nylon 101 is the most common commercial grade of nylon, and Nylon 6 is the most common commercial grade of molded nylon. Nylon is available in glass-filled variants which increase structural and impact strength and rigidity, and molybdenum sulfide-filled variants which increase lubricity.

Aramids are another type of polyamide with quite different chain structures which include aromatic groups in the main chain. Such polymers make excellent ballistic fibres.

Historical uses

Bill Pittendreigh, DuPont, and other individuals and corporations worked diligently during the first few months of World War II to find a way to replace Asian silk and hemp with nylon in parachutes. It was also used to make tires, tents, ropes, ponchos, and other military supplies. It was even used in the production of a high-grade paper for U.S. currency. At the outset of the war, cotton accounted for more than 80% of all fibers used and manufactured, and wool fibers accounted for the remaining 20%. By August 1945, manufactured fibers had taken a market share of 25% and cotton had dropped.

Some of the terpolymers based upon nylon are used every day in packaging. Nylon has been used for meat wrappings and sausage sheaths.

Polyethylene

Polyethylene or polythene (IUPAC name polyethene or poly(methylene)) is the most widely used plastic, with an annual production of approximately 80 million metric tons.[1] Its primary use is within packaging (notably the plastic shopping bag).

Uses

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SYNTHETIC POLYMERS NATURALLY OCCURRING POLYMERS

This group consists of naturally occurring polymers and chemical modifications of these

polymers. Cellulose, starch, lignin, chitin, and various polysaccharides are included in this group.

These materials and their derivatives offer a wide range of properties and applications. Natural

polymers tend to be readily biodegradable, although the rate of degradation is generally inversely

proportional to the extent of chemical modification.

– Naturally occuring polymers exist in plants or animals – Natural polymers are made up of carbon, hydrogen, nitrogen and oxygen – Examples of naturally occuring polymers are

(a)Protein : in muscles, skin, silk, hair, wool and fur

(b)Carbohydrates : in starch and cellulose

(c)Natural rubber : in latex– Proteins is formed by the polymerisation or monomers known as amino acids polymerisation amino acids protein (monomers) (polymer) – Carbohydrates such as starch and cellulose consist of monomers known as glucose joined together chemically. polymerisation glucose carbohydrates (monomers) (polymer) – Natural rubber found in latex consists of monomers known as isoprene ( 2 – methylbuta – 1, 3 – diene ) joined together chemically. – Natural rubber comprises the molecules of the monomer 2-methyl-1,3-butadiene, also called isopropene, joined together to form a long chain. SYNTHETIC POLYMERS •

Synthetic polymer is a polymer that is manufactured in industry from chemical

substances through the polymerisation process. Through research, scientists are now able

to copy the structure of natural polymers to produce synthetic polymers.•

Plastics, synthetic fibres and elastomers are examples of synthetic polymers. •

The raw materials for the manufacture of synthetic polymers are distillates ofpetroleum. •

However, most of them can be classified in at least three main categories: thermoplastics, fibres and elastomers. Thermoplastics

– is a polymer which, when subjected to heat, becomes soft so they can be moulded into various shapes. – the properties of plastics are : light, strong, inert to chemicalssuch as acids and alkali and are insulators of electricity and heat. – examples of plastics are polyethylene (PE), polyvinylchloride (PVC), polypropylene (PP), polystyrene, Perspex and Bakelite. Synthetic fibres

– are long chained polymers that withstand stretching.

– examples of synthetic fibres are nylon and Terylene.

–Nylon is used to make ropes, fishing lines, stocking, clothing and parachutes.

–Terylene is used to make clothing, sleeping bags and fishing nets. Clothes made fromTerylene do not crease easily. Elastomer

– is a polymer that can regain its original shape after being stretched or pressed.

– both natural rubber and synthetic rubber are examples ofelastom er.

– examples of synthetic rubbers are neoprene and styrene – butadiene rubber ( SBR )

– SBR is used to make car tyres.•

The two types of polymerisation are: – polymerisation by addition . – polymerisation by condensation . •

Polymerisation by addition involves monomers with >C = C< bonding, where the

monomers join together to make a long chain without losing any simple molecules from

it. Examples of polymers produced through this process are polythene, PVC perspex and

other plastics.

•

SYNTHETIC POLYMER & THEIR USES IN DAILY LIFE Synthetic Polymer Uses Neoprene Shoe soles, hoses, radiator hoses, wetsuits Polyvinyl chloride or PVC (polychloroethene) Raincoat, pipes, to insulate electric wires Polyamide (nylon) Parachutes, carpet, ropes, form-fitting skiwear,

hosiery Polypropene Plastics, bottles, plastic tables and chairs Teflon (polytetrafluoroethene or PTFE) To make non-stick pots and pans Polyester Filters, conveyor belts, sleeping bag insulation Polyethylene terephthalate (PET, PETE) Soft drink bottles, peanut butter jars, salad dressing bottles Polythene (polyethylene) Plastic bags, containers and cups Perspex (polymethyl2-methyl propene) Aeroplane window panes, lenses, car lamp covers Polystyrene Styrofoam® cups, , grocery store meat trays

– Synthetic polymers have been used widely to replace natural materials such as metals, wood, cotton, animal skin and natural rubber because of the following advantages : •

Strong and light •

Cheap •

Able to resist corrosion •

Inert to chemical reactions •

Easily moulded or shaped and becoloured

•

Can be made to have special properties

THE EFFECT OF THE USES OF SYNTHESIS POLYMERS TO OUR ENVIRONMENT The use of synthetic polymers, however results in environmental problems

Most polymers are not biodegradable. Polymers cannot be decomposed biologically or

naturally by bacteria or fungi as in the case of other garbage. Thus, the disposal of polymers

has resulted in environmental pollution because they remain in the environment forever.

Discarded plastic items may cause blockage of drainage systems and rivers thus causing

flash floods.

Plastic containers and bottles strewn around become good breeding places for mosquitoes

which cause dengue fever, or malaria.

Small plastic items that are thrown into the rivers, lakes and seas are somethings swallowed

by aquatic animals. These animals may die fromchoking.

The open burning of plastics gives rise to poisonous and acidic gases like carbon

monoxide, hydrogen chloride and hydrogen cyanide. These are harmful to the environment

as they cause acid rain.

Burning of plastics can also produce carbon dioxide, too much of this gas in the atmosphere

leads to the `green house effect'.

The main source of raw materials for the making of synthetic polymers isp etro leu m.

Petroleum is a non – renewable resource.This problem can be overcome by the following ways:

Recycling polymers: Plastics can be decomposed by heating them without oxygen at

700°C. This process is called pyrolysis. The products of this process are then recycled

into new products.

Inventing biodegradable polymers: Such polymers should be mixed with substances that

can be decomposed by bacteria (to become biodegradable) or light (to become

photodegradable) .

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Glass and ceramics

Uses of Glass and Ceramics

The raw materials used in the making of glass and ceramic materials are obtained from the earth's crust. Silica

or silicon(IV) dioxide, SiO2, form the most important component of glass and ceramics.

In the SiO2 molecule, each silicon atom is held in a tetrahedral structure by four oxygen atoms.

Each oxygen atom is held by two silicon atoms. This is repeated until a giant three-dimensional molecule results

Properties of glass and ceramic:

Both have the following properties:

1. Hard and brittle

2. Do not conduct heat electricity

3. Inactive towards chemical reactions

4. Weak when pressure is applied

5. Can be cleaned easily

Glass

It is a mixture of two or more types of metallic silicates but the main component is silicon(IV) dioxide.

Glass has the following properties:

1. Transparent and not porous

2. Inactive chemically

3. Can be cleaned easily

4. Good insulators of heat and electricity

5. Hard but brittle

6. Can withstand compression but not pressure

Due to the above reasons and the low cost involved to produce glass, it is used in industry to make bottles,

cooking utensils, plates and bowls, laboratory apparatus (such as conical flask, beakers and test tubes), window

panes, bulbs and others.

Different types of glass can be obtained depending on the composition of substances in it.

Soda lime glass:

This is obtained when limestone (CaCO3) and sodium carbonate (Na2CO3) are mixed with molten silica and cooled

down.

It is also known as soft glass as it has a low melting point.

Most glass produced is soda lime glass. But it breaks easily, thus it is mainly used to make kitchen utensils.

Lead glass:

This is formed when a mixture of lead(II) oxide, sodium oxide and silica is heated together.

Lead glass of better quality contains a higher percentage of PbO.

Its refractive index and density being high, it has a glittering and attractive surface, thus it is also called crystal

glass.

Borosilicate glass:

Boron oxide (B2O3) and sodium carbonate is added to molten silica to obtain borosilicate glass or pyrex..

The presence of B2O3 makes the glass able to withstand high temperatures and chemical reaction. It does not

break easily, thus it is used to make laboratory apparatus and cooking utensils.

Fused silicate glass:

Sand (silica) is heated until it melts at 1700°C, and the viscous liquid is cooled immediately. This produces a

transparent solid with an uneven arrangement of atoms, called fused silicate glass.

This glass cannot expand or contract easily when there are temperature changes. But it cannot become

misshapen because of its high melting point.

It is known as quartz glass.

Summary

Glass Composition Properties Uses

Soda lime,glass

SiO2 – 70%Na20 – 15%CaO – 10%Others – 4%

• Low melting point (700°C)

• Mouldable into shapes

• Cheap

• Breakable

• Can withstand high heat

Glass containers, Glass panes, Mirrors, Lamps and bulbs, Plates and bowls Bottles

Lead glass (crystal) SiO2 – 70% • High density and refractive Containers for drinks and fruit

Na20 – 20%PbO – 10%

index• Glittering surface

• Soft

• Low melting point (600°C)

Decorative glass and lamps

Crystal glassware Lenses for spectacles

Borosilicate glass (Pyrex)

SiO2 – 80%

B203 – 13%

Na2O – 4%

Al203 – 2%

• Resistant to high heat and chemical reaction

• Does not break easily

• Allows infra-red rays but not

ultra-violet rays

Glass apparatus in laboratories

Cooking utensils

Fused silicate glassSiO2 – 99%

6203 - 1%

• High melting point (1700°C)

• Expensive

• Allows ultraviolet light to pass

through

• Difficult to melt or mould into

shape

Scientific apparatus like lenses on

spectrometer

Optical lenses

Laboratory apparatus

Ceramics

Ceramic is a substance that is made from clay and hardened by heat in a furnace maintained at a high

temperature.

Clay is composed of aluminosilicate with sand and iron(III) oxide as impurities. Iron(III) oxide, Fe203, gives a

reddish colour to the clay.

Kaolin, or clay in its pure form, is white in colour. It consists of crystals of hydrated aluminosilicate with the

formula Al2Si2O7.2H2O or Al2O3.2SiO2.2H2O.

The different classes of ceramic include:Group Composition

Quartz – SiO2

Calcite – CaCO3

Mixture of CaSiO3 and aluminium silicate

Aluminium oxide – Al2O3

Silicon dioxide – SiO2

Magnesium oxide – MgO

Silicon nitride – Si3N4

Silicon carbide – SiC

Boron nitride – BN

Boron carbide – B4C3

The preparation of ceramic objects involves 3 stages:

1. A layer of water exists between the aluminosilicate crystals. This gives it a plastic-like property when wet.

Thus the clay is first wet to make it soft before it is shaped.

2. The shaped object is then dried. At this stage, the product can still be reshaped by adding more water.

3. The dried object is heated to a temperature of 1000°C in a furnace. The product of this stage cannot be

softened with water or reshaped.

The surface of ceramic object is usually coated with a layer of mineral or metallic silicate and baked again in the

furnace to produce a shining and impervious ceramic object.

The properties of ceramics include the following:

1. Hard

2. Strong but brittle

3. Chemically inactive

4. Poor conductor of heat and electricity

5. High melting point – heat resistant

6. Cannot be compressed easily

The differences between the properties of ceramics, metals and non-metals are given below.

Property Metals Non-metals Ceramic

Hardness Hard but malleable and ductile Soft and brittle Hard but brittle

Density High Low Average

Melting point High Low Very high

Resistance to heat High Low Very high

Heat and Electrical conductivity Good conductor Good insulator Good insulator

Chemical reactions Corrodes Corrodes Stable, does not corrode

New Uses of Glass and Ceramics

The latest use of glass is to make photochromic glass and conducting glass while ceramics is used to produce

superconductors and car engine blocks.

Photochromic glass

Photochromic glass is very sensitive to light. It darkens in the presence of bright light and lightens when the

amount of sunlight lessens.

The glass is produced by adding silver chloride (or silver bromide) and some copper(II) chloride to normal glass.

Silver halides decompose to silver and its halogen when exposed to ultraviolet rays. Thus we have:

It is the silver which makes the glass become dark.

When there is a decrease in light, silver chloride is formed again:

Therefore the glass lightens.

Conducting glass

Conducting glass is a type of glass which can conduct electricity. It is obtained by coating a thin layer of a

conducting material around the glass, usually indium tin(IV) oxide or ITO.

Conducting glass can also be obtained by embedding thin gold strips into a piece of glass. This is used to make

the front windows of aeroplanes which tend to mist at very high heights. By passing an electric current through

this glass (containing gold as conductors), the water of condensation will dry up.

Superconductors are electrical conductors which have almost zero (0) electrical resistance. Therefore, this

conductor minimises the loss of electrical energy through heat.

Perovsite is a type of ceramic superconductor composed of itrium oxide, copper oxide and barium oxide.

Superconductors are also used to make magnets which are light but thousands of times stronger than the

normal magnet.

Car Engine Block--When clay is heated with magnesium oxide, the ceramic that is produced has a high

resistance to heat. This material is used to build the engine blocks in cars as they can withstand high

temperatures.

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Composite MaterialHistory

Plywood is a commonly encountered composite material

Wood is a natural composite of Cellulose fibers in a matrix of lignin.[1][2] The earliest man-made composite materials

were straw and mudcombined to form bricks for building construction. The ancient brick-making process can still be

seen on Egyptian tomb paintings in theMetropolitan Museum of Art. The most advanced examples perform routinely

on spacecraft in demanding environments. The most visible applications pave our roadways in the form of

either steel and aggregate reinforced Portland cement or asphalt concrete. Those composites closest to our personal

hygiene form our shower stalls and bathtubs made of fibreglass. Imitation granite and cultured marble sinks and

countertops are widely used.

Composites are made up of individual materials referred to as constituent materials. There are two categories of

constituent materials: matrix and reinforcement. At least one portion of each type is required. The matrix material

surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements

impart their special mechanical and physical properties to enhance the matrix properties. A synergism produces

material properties unavailable from the individual constituent materials, while the wide variety of matrix and

strengthening materials allows the designer of the product or structure to choose an optimum combination.

Engineered composite materials must be formed to shape. The matrix material can be introduced to the

reinforcement before or after the reinforcement material is placed into the mould cavity or onto the mould surface.

The matrix material experiences a melding event, after which the part shape is essentially set. Depending upon the

nature of the matrix material, this melding event can occur in various ways such as chemical polymerization or

solidification from the melted state.

A variety of moulding methods can be used according to the end-item design requirements. The principal factors

impacting the methodology are the natures of the chosen matrix and reinforcement materials. Another important

factor is the gross quantity of material to be produced. Large quantities can be used to justify high capital

expenditures for rapid and automated manufacturing technology. Small production quantities are accommodated

with lower capital expenditures but higher labour and tooling costs at a correspondingly slower rate.

Most commercially produced composites use a polymer matrix material often called a resin solution. There are many

different polymers available depending upon the starting raw ingredients. There are several broad categories, each

with numerous variations. The most common are known as polyester, vinyl

ester, epoxy, phenolic, polyimide, polyamide,polypropylene, PEEK, and others. The reinforcement materials are

often fibres but also commonly ground minerals. The various methods described below have been developed to

reduce the resin content of the final product, or the fibre content is increased. As a rule of thumb, lay up results in a

product containing 60% resin and 40% fibre, whereas vacuum infusion gives a final product with 40% resin and 60%

fibre content. The strength of the product is greatly dependent on this ratio.

What Are Composite Materials?

Composite materials take advantage of the different strengths and abilities of different materials. In the case of mud and straw bricks, for example, mud is an excellent binding material, but it cannot stand up to compression and force well. Straw, on the other hand, is well able to withstand compression without crumbling or breaking, and so it serves to reinforce the binding action of the mud. Humans have been creating composite materials to build stronger and lighter objects for thousands of years.

The majority of composite materials use two constituents: a binder or matrix and a reinforcement. The reinforcement is stronger and stiffer, forming a sort of backbone, while the matrix keeps the reinforcement in a set place. The binder also protects the reinforcement, which may be brittle or breakable, as in the case of the long glass fibers used in conjunction with plastics to make fiberglass. Generally, composite materials have excellent compressibility combined with good tensile strength, making them versatile in a wide range of situations.

Engineers building anything, from a patio to an airplane, look at the unique stresses that their construction will undergo. Extreme changes in temperature, external forces, and water or chemical erosion are all accounted for in an assessment of needs. When building an aircraft, for example, engineers need lightweight, strong material that can insulate and protect passengers while surfacing the aircraft. An aircraft made of pure metal could fail catastrophically if a small crack appeared in the skin of the airplane. On the other hand, aircraft integrating reinforced composite materials such as fiberglass, graphite, and other hybrids will be stronger and less likely to break up at stress points in situations involving turbulence.

Advanced Material And The Future

Advanced Composite Materials, a quarterly publication of the Japan Society for Composite Materials and the Korean Society for Composite Materials, provides an international forum for researchers, manufacturers and designers who are working in the field of composite materials and their structures. Issues contain articles on all aspects of current scientific and technological progress in this interdisciplinary field. The topics of interest are physical, chemical, mechanical and other properties of advanced composites as well as their constituent materials; experimental and theoretical studies relating microscopic to macroscopic behavior; testing and evaluation with emphasis on environmental effects and reliability; novel techniques of fabricating various types of composites and of forming structural components utilizing these materials; design and analysis for specific applications. Advanced Composite Materials publishes refereed original research papers, review papers, technical papers and short notes as well as some translated papers originally published in the Journal of the Japan Society for Composite Materials.

Type of Composite Materials

The fiberglass materials are especially used in the pipe and tank industry as the fiberglass pipe have better physical properties as compared to the traditional pipes which were used earlier. These pipes are light in weight which makes it easy to transport them and install them. They are highly durable also as compared to the iron or steel pipes and tanks. It is easy to maintain fiber glass reinforced plastic (FRP) pipes over the metallic pipes as the former is noncorrosive and therefore it does not leads to leaks.

These composite materials are popularly used in different industries like aerospace, construction, Tank industry and therefore have a good prospect. This is why many companies are expanding into this sector and find it to be a profitable venture. However, it is essential to learn more about the industry and prepare your market entry strategy before you can get into this industry.

PropertiesMechanics

The physical properties of composite materials are generally not isotropic (independent of direction of applied force)

in nature, but rather are typically orthotropic (different depending on the direction of the applied force or load). For

instance, the stiffness of a composite panel will often depend upon the orientation of the applied forces and/or

moments. Panel stiffness is also dependent on the design of the panel. For instance, the fibre reinforcement and

matrix used, the method of panel build, thermoset versus thermoplastic, type of weave, and orientation of fibre axis

to the primary force.

In contrast, isotropic materials (for example, aluminium or steel), in standard wrought forms, typically have the same

stiffness regardless of the directional orientation of the applied forces and/or moments.

The relationship between forces/moments and strains/curvatures for an isotropic material can be described with the

following material properties: Young's Modulus, the shear Modulusand the Poisson's ratio, in relatively simple

mathematical relationships. For the anisotropic material, it requires the mathematics of a second order tensor and up

to 21 material property constants. For the special case of orthogonal isotropy, there are three different material

property constants for each of Young's Modulus, Shear Modulus and Poisson's ratio—a total of 9 constants to

describe the relationship between forces/moments and strains/curvatures.

Techniques that take advantage of the anisotropic properties of the materials include mortise and tenon joints (in

natural composites such as wood) and Pi Joints in synthetic composites.

Resins

Typically, most common composite materials, including fiberglass, carbon fiber, and Kevlar, include at least two

parts, the substrate and the resin.

Polyester resin tends to have yellowish tint, and is suitable for most backyard projects. Its weaknesses are that it is

UV sensitive and can tend to degrade over time, and thus generally is also coated to help preserve it. It is often used

in the making of surfboards and for marine applications. Its hardener is a MEKP, and is mixed at 14 drops per oz.

MEKP is composed of methyl ethyl ketone peroxide, a catalyst. When MEKP is mixed with the resin, the resulting

chemical reaction causes heat to build up and cure or harden the resin.

Vinylester resin tends to have a purplish to bluish to greenish tint. This resin has lower viscosity than polyester resin,

and is more transparent. This resin is often billed as being fuel resistant, but will melt in contact with gasoline. This

resin tends to be more resistant over time to degradation than polyester resin, and is more flexible. It uses the same

hardener as polyester resin (at the same mix ratio) and the cost is approximately the same.

Epoxy resin is almost totally transparent when cured. In the aerospace industry, epoxy is used as a structural matrix

material or as a structural glue.

Shape memory polymer (SMP) resins have varying visual characteristics depending on their formulation. These

resins may be epoxy-based, which can be used for auto body and outdoor equipment repairs; cyanate-ester-based,

which are used in space applications; and acrylate-based, which can be used in very cold temperature applications,

such as for sensors that indicate whether perishable goods have warmed above a certain maximum temperature.

[5] These resins are unique in that their shape can be repeatedly changed by heating above their glass

transition temperature. When heated, they become flexible and elastic, allowing for easy configuration. Once they

are cooled, they will maintain their new shape. The resins will return to their original shapes when they are reheated

above their.[6] The advantage of shape memory polymer resins is that they can be shaped and reshaped repeatedly

without losing their material properties, and these resins can be used in fabricating shape memory composites.

Products

Composite materials have gained popularity (despite their generally high cost) in high-performance products that

need to be lightweight, yet strong enough to take harsh loading conditions such as aerospace components

(tails, wings, fuselages, propellers), boat and scull hulls, bicycle frames and racing car bodies.[12] Other uses

include fishing rods, storage tanks, and baseball bats. The new Boeing 787 structure including the wings and

fuselage is composed largely of composites. Composite materials are also becoming more common in the realm

of orthopedic surgery.

Carbon composite is a key material in today's launch vehicles and spacecraft. It is widely used in solar panel

substrates, antenna reflectors and yokes of spacecraft. It is also used in payload adapters, inter-stage structures and

heat shields of launch vehicles.

In 2007, an all-composite military High Mobility Multi-purpose Wheeled Vehicle (HMMWV or Hummvee) was

introduced by TPI Composites Inc and Armor Holdings Inc, the first all-composite military vehicle. By using

composites the vehicle is lighter, allowing higher payloads. In 2008, carbon fiber and DuPont Kevlar (five times

stronger than steel) were combined with enhanced thermoset resins to make military transit cases by ECS

Composites creating 30-percent lighter cases with high strength.

Recently, composite materials are designed such that the material will have more than one specific function

therefore multi function structures emerge as a new technology.

Many composite layup designs also include a co-curing or post-curing of the prepreg with various other mediums,

such as honeycomb or foam. This is commonly called a sandwich structure. This is a more common layup process

for the manufacture of radomes, doors, cowlings, or non-structural parts.[13]

The finishing of the composite parts is also critical in the final design. Many of these finishes will include rain-erosion

coatings or polyurethane coatings.