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Diamond & Graphite

Mr. Rahul Dev M.Sc [Polymer

Science]

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Diamond• Introduction• In mineralogy Diamond is a metastable

allotrope of carbon.• Diamond is less stable than graphite, but

the conversion rate from diamond to graphite is negligible at standard conditions. 

• Most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers (87 to 118 mi) in the Earth's mantle.

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Natural history• The formation of natural diamond

requires very specific conditions exposure of carbon-bearing materials to high pressure, ranging approximately between 45 and 60 kilobars(4.5 and 6 GPa), but at a comparatively low temperature range between approximately 900 and 1,300 °C (1,650 and 2,370 °F). These conditions are met in two places on Earth; in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike.

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Structure Of Diamond• In diamond, the

carbon atoms are arranged tetrahedrally (sp3 hybridisation of C): each C atom is linked to its neighbours by four single covalent bonds. This leads to a three-dimensional network of covalent bonds.

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Material PropertiesFormula Mass: 12.01 gmol-1

Density: 3.5-3.53 g/m3

Colours: Typically Yellow, Brown or Gray to colourless. Less often blue, green, black, translucent white, pink, violet, orange, purple and red.

Crystal Structure: Octahedral

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Properties• Mechanical Hardness ~98 Gpa• Compressive Strength > 110 Gpa• Highest Bulk Modulus- 1.2*1012 N/M2

• Lowest Compressibility- 8.3*10-13 M2/N• Highest Thermal Conductivity- 2*103 W/M/K• Optically Transparent From Deep UV To Far IR• Good Electrical Insulator- R~1016 Ω• Highest Melting Point- 3820K• Resistant To Corrosion By Acid Or Base• Negative Electron Affinity

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Properties• Extreme Hardness• High Thermal Conductivity• Wide Bandgap And High Optical Dispersion• Resistant To Scratching• Excellent Electrical Insulators• Diamond Are Naturaly Liophilic And

Hydrophobic• Diamonds Are Chemically Stable

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Colour• Diamond has a wide bandgap of 5.5 eV

corresponding to the deep ultraviolet wavelength of 225 nanometers. This means pure diamond should transmit visible light and appear as a clear colourless crystal. Colours in diamond originate from lattice defects and impurities. The diamond crystal lattice is exceptionally strong and only atoms of nitrogen, boron and hydrogen can be introduced into diamond during the growth at significant concentrations

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Colour• Nitrogen is by far the most common

impurity found in gem diamonds and is responsible for the yellow and brown color in diamonds. Boron is responsible for the blue color.

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Hope Diamond, 45.52 carats (9.104 g), dark grayish-blue

 Indian Kohinoor 105.602 carats (21.1204 g) Finest White

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Synthetic Diamonds• Synthetic diamonds are diamonds manufactured

in a laboratory, as opposed to diamonds mined from the Earth

• The majority of commercially available synthetic diamonds are yellow and are produced by so-called High Pressure High Temperature (HPHT) processes

• Another popular method of growing synthetic diamond is chemical vapour deposition (CVD). The growth occurs under low pressure (below atmospheric pressure).

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Application• Optical Application• Glass Cutter• Jewelleries• Diamond guide• Speaker Domes• Windows • Antidote for Poison/Disease• Heat Sinks • Engraving • Diamond Microdermabrasion

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Applications• Diamond Microdermabrasion offers intensive

skin exfoliating. This treatment is non-invasive and uses a diamond encrusted tip to polish the skins surface without harsh chemicals or messy crystals.

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• It is used in protective windows for space probes as it can keep out harmful radiations.

• Because of its extra-ordinary sensitivity to heat rays, it is used in high precision thermometers.

• Sharp-edged diamonds are used by eye surgeons remove cataract from eyes high precision.

• It is used in dies for the manufacture of tungsten filaments for electric light bulbs.

• It is used for making tools for cutting grinding other hard material and also in oil-well drills for drilling holes through the earth’s rocky layers.

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Alternatives to Diamond

• Boron Nitrideo It’s hardness of 9.8 on the Mohs scale makes it

very useful for cutting tools and abrasiveso BN is isoelectronic with diamond, so it shares

many of its properties• Tungsten Carbide

o Can substitute for diamond in many placeso Actually used in HPHT synthesis

• But diamond is still the best

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Graphite• Introduction• The mineral graphite is an allotrope of carbon.• It was named by Abraham Gottlob Werner in 1789

from the Ancient Greek "to draw/write", for its use in pencils, where it is commonly called lead (not to be confused with the metallic element lead).

• Graphite is the most stable form of carbon under standard conditions. Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds.

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History• Graphite was used by the 4th millennium B.C.

Marita culture to create a ceramic paint to decorate pottery during the Neolithic Age in southeastern Europe.

• Historically, graphite was called black lead or plumbago

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Identification• Chemical Formula : C• Colour: Silver Grey To Black• Streak: Black• Crystal Structure: Hexagonal 3D Crystal Atlas• Crystal Forms and Aggregates : Crystals consist of thin hexagonal plates or

distorted clusters of flaky plates on a matrix. Large thick hexagonal crystals are rare. Most often occurs as veins and in massive form, and can be very large in size. Small, rounded ball-like aggregates and radiating spheres also occur.

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Identification• Transparency: Opaque• Luster : Metallic• Tenacity : Brittle; thin flakes are flexible• Other ID Marks : 1) Has a greasy feel.

2) Smudges the hands when touched.3) Is a good conductor of electricity (although it is a poor conductor of heat).

• In Group : Native Elements; Non-Metallic Elements• Striking Features : Low weight, greasy feel, smudge, and

low hardness.• Environment : Most often in metamorphic rock caused

from the metamorphism of carbonates.

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Occurence• Graphite occurs in metamorphic rocks as a result of the

reduction of sedimentary carbon compounds during metamorphism.

• It also occurs in igneous rocks and in meteorites.

• Minerals associated with graphite include quartz, calcite,micas and tourmaline. In meteorites it occurs with troilite and silicate minerals.

• Small graphitic crystals in meteoritic iron are called clifonite.

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Structure Properties• Structure- Graphite has a layered, planar

structure. In each layer, the carbon atoms are arranged in a honeycomb lattice with separation of 0.142 nm, and the distance between planes is 0.335 nm.

• The two known forms of graphite, alpha (hexagonal) and beta (rhombohedral) have very similar physical properties, except that the graphene layers stack slightly differently. The hexagonal graphite may be either flat or buckled Graphite's unit cell

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1. Ball and stick model of graphite (two graphene layers)

2. Side view of layer stacking

3. Plane view of layer stacking

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Properties• High Thermal Conductivity.• High Thermal Shock Resistance.• High Melting Temperature.• Low Density (28% Of Steel).• Low Hardness.• Low Friction And Self Lubrication.• Electrical Conductivity Highest Of Non-metallic

Materials.• Low Coefficient Of Thermal Expansion.• High Strength (Particularly Compressive Strength),

Which Increases With The Temperature Rise.• High Stiffness (Modulus Of Elasticity).

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• High Thermal Resistance. Graphite Is Capable To Work In The Temperature Range From Absolute Zero To 6330°F (3500°C) In Inert Atmosphere.

• High Chemical And Corrosion Resistance;• Good Oxidation Resistance. Graphite Starts To Be

Oxidized In Oxidizing Atmosphere At 932°F (500°C).• Low Absorption Coefficient For X-rays.• High Resistance To Neutron Radiation. Graphite

Slows Down Fast Neutrons And Scatters Thermal Neutrons.

• High Radiation Emissivity;• Ability To Absorb Radio Waves;• Low Wettability By Liquid Metals;• Good Machinability;• Ability To Absorb Gases.

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Application• Graphite is mostly used in pencils, steelmaking,

expanded graphite, brake linings,batteries,foundry facings and lubricants.

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Application• As a lubricant at higher temperatures.• As a refractory material of making crucibles and

electrodes for high temperature work.• In electrotyping and in the manufacture of

gramophone records: Graphite is used for making the non-conducting (generally wax) surface, so that electroplating can be done.

• For manufacturing lead pencils and stove paints.• It is a component of printers’ ink.

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Differences Diamond GraphiteDiamond Is Transparent Graphite Is Black And Opaque

Diamond Is A Poor Conductor Of Electricity, But Is A Good Conductor Of Heat.

Graphite On The Other Hand Is A Good Conductor Of Heat And Electricity.

Diamond Is Hardest Substance Known In Nature

Graphite Is Soft And Slippery To Touch

Density Of Diamond Is More Density Of Graphite Is Comparatively Less

It Is Insoluble In All Solvents It Is Insoluble In All Ordinary Solvents

Diamond Is The Ultimate Abrasive Graphite Is A Very Good Lubricant

Diamond Crystallizes In The Isometric System

Graphite Crystallizes In The Hexagonal System

It Occurs As Octahedral Crystals It Occurs As Hexagonal Crystals

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Reference• Properties and Growth Of Diamond By G. Davies

(1994). •  Applications of Diamond Films and Related

Materials. Elsevier. A . Feldman and L.H. Robins (1991).

• Optical Properties of Diamond: A Data Handbook. Springer. A.M. Zaitsev (2001). 

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ThanK YoU