Copper and its Alloys

Haseeb Ullah Khan JatoiDepartment of Chemical Engineering

UET Lahore

Non Ferrous Metals and Alloys•Usually metals and alloys are divided into two categories.1. Ferrous2. Non- Ferrous (All metallic elements other than iron

are referred to as non ferrous). •Iron occupy special position among alloys owing to its availability, comparatively low cost and useful range of alloys.

However, they have some distinct limitations, chiefly: (1) a relatively high density, (2) a comparatively low electrical conductivity, and (3) an inherent susceptibility to corrosion in some common environments. So there is the need of non- ferrous alloys.

Of all the non ferrous alloys only eight are produced in relatively large quantities, Al, Cu, Pb, Mg, Ni, Sn, Ti, and Zn

Copper and Its Alloys•Oldest metal known to man.•In early civilization Cu along with bronze used for decorative and utilitarian purposes.•Extremely useful, but due to high cost, Cu and its alloys are replaced with other cheap materials, such as plastic, aluminum in many applications.Occurrence:•High affinity for sulphur, so occurs in forms of oxides and sulphides. Copper Iron Sulphide, Copper Oxide, and copper silicates.

Native copper Copper mine in new Mexico

Properties•High electrical conductivity•High thermal conductivity•High corrosion resistance (unaffected by an oxidation environment)• Good ductility and malleability.• Reasonable tensile strength•Ease of joining (by adding other metals, soldering, brazing, welding) •Machinabilty and recyclability.•Greater affinity for sulphur

Physical properties of copper andcopper alloys

Crystal structure FCCAtomic number 29Atomic weight 63.546Density (g.cm-3) 8.933Melting point (oC) 1084.62Tensile Strength(MPa) 220Corrosion Resistance Very Good

Application of copper in automotivesCopper: working behind the scenes in automotive applicationsIncreasing use of electronic parts in cars raise the amount of copper used per vehicle.

Mineral Ores of Copper•Bornite (Cu5FeS4 ) ,

•Chalco pyrite (CuFeS2), •Covellite (CuS), •Chalco cite ( sulphide ores), •Malachite (Cu2CO3(OH)2) ,Azurite (Cu3(CO3)2(OH)2,

Cuprite (oxide form)•Native Cu (100% cu, red in color)

Chalcocite (Cu2S), Chalcopyrite (CuFeS2),

Cuprite (Cu2O), Bornite

Extraction of CopperOres of copper are generally complex mixtures of copper and iron sulphides.

Extraction ProcessMining. By mining, ores containing 1% cu is obtained.Ore is crushed, ground and separated, as a result of which the material becomes concentrated containing 40- 60% cu. Grinding is usually done to increase surface area.

Reverberatory furnaceA Reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with fuel but not from contact with combustion gases

Roasting (Concentration)

In the roaster, the copper concentrate is partially oxidized to produce iron oxide, copper sulfide and sulfur dioxide gas. The stoichiometry of the reaction which occurs is:

2 CuFeS2 + 3 O2 → 2 FeO + 2 CuS + 2 SO2

Reverberatory Furnace

The calcine is then mixed with silica and coke and smelted in an exothermic reaction at 1200 °C (above the melting point of copper, but below that of the iron and silica) to form a liquid called "copper matte". The high temperature allows reactions to proceed rapidly, and allow the matte and slag to melt.Iron oxides and sulfides are converted to slag, a less dense molten mass that is floated off the matte.

The reactions for slag formation isFeO(s) + SiO2(s) → FeSiO3 (l)

In a parallel reaction the iron sulfide is converted to slag:

2 FeS(l) + 3 O2 + 2 SiO2 (l) →2 FeSiO3(l) + 2 SO2(g)

The slag is discarded or reprocessed to recover any remaining copper.

Copper Convertor

The matte, which is produced in the smelter, contains around 70% copper primarily as copper sulfide as well as iron sulfide. The sulfur is removed at high temperature as sulfur dioxide by blowing air through molten matte:

2 CuS + 3 O2 → 2 CuO + 2 SO2

CuS + O2 → Cu + SO2

In a parallel reaction the iron sulfide is converted to slag:2 FeS + 3 O2 → 2 FeO + 2 SO2

2 FeO + 2 SiO2 → 2 FeSiO3

The purity of this product is 98%, it is known as blister because of the broken surface created by the escape of sulfur dioxide gas.

Refining FurnaceFire refining of blister copper is an interesting process. The bath of oxidized copper is then subjected to reducing conditions to reduce the oxygen content.The resulting product being termed as Tough Pitch Copper with a residual oxygen content of about 0.03 %. Necessary reducing conditions were obtained by poling the liquid bath.

Tough pitch copper is unsuitable for welding owing to the oxygen contents of the material. Unsuitable for applications requiring high electrical conductivity.

Arsenical CopperSome grades of copper contain up to 0.5% of arsenic. Arsenical copper which has improved tensile properties and an improved resistance to oxidation at high temperatures, is made by adding up to 0.5 % of arsenic to tough pitch.

The copper is refined by electrolysis. The anodes cast from processed blister copper are placed into an aqueous solution of 3–4% copper sulfate and 10–16% sulfuric acid. Cathodes are thin rolled sheets of highly pure copper. A potential of only 0.2–0.4 volts is required for the process to commence. At the anode, copper and less noble metals dissolve. More noble metals such as silver and gold as well as selenium and tellurium settle to the bottom of the cell as anode slime, which forms a saleable byproduct.

Electrolytic Refining

Copper(II) ions migrate through the electrolyte to the cathode. At the cathode, copper metal deposit but less noble constituents such as arsenic and zinc remain in solution. The reactions are:At the anode: Cu(s) → Cu2+

(aq) + 2e–

At the cathode: Cu2+(aq) + 2e– → Cu(s)

Cu produced in this way is termed as cathode copper(99.9%)

Alloys of CopperCopper may be alloyed with a number of elements to provide a range of useful alloys.1. Copper-Nickel (Cupronickels)Ni is soluble in solid copper. This alloy is strong and ductile and excellent resistance to corrosion. It is used for manufacturing condenser tubing and heat exchanger.2. Nickel –Silver Alloy (German silver)Addition of zn to cu and Ni produces this alloy. They are ductile. Nickel silver is used for silver-plated cutlery, better-quality keys, costume jewellery, for making musical instruments (e.g.,cymbals), production of coins. Its industrial and technical uses include plumbing fixtures for its corrosion resistance.

3. Beryllium – Copper AlloyIt contains up to 2.7% of Be, having the highest strength among all copper alloys available. These alloys may be strengthened by solution heat treatment and by this process tensile strength up to 1400 MN/m2 can be obtained. Normally Be- Cu contains 2% of Be.Applications. Manufacturing of spring pressure diaphragm and non-sparking tools.4. Cadmium – Copper alloysThe addition of 1% Cd to copper gives an alloy with a tensile strength approximately 50% higher than that of high conductivity copper but it decreases its electrical conductivity.

Application. Major applications are telephone wires, electrodes, electrodes holders for electrical resistance welding equipments. 5. Chromium- Copper AlloyIt contains 0.5% cr, and resultant will be formed having high strength coupled with high electrical and thermal conductivities.6. Tellurium- Copper AlloyThis alloy contains 0.3- 0.7% Te and it is alloy of high electrical conductivity. It is a free machining alloy. Te is virtually insoluble in cu and appears in the microstructure as small particles of copper telluride. These will act as internal chip breakers.

Major Alloys of Copper

Brass (peetal)It is a binary alloy of Cu and Zn. It has low density, low melting point. Zn can be added from 5-40%. On adding Zn, it becomes cheaper, it can be used in manufacturing of pressure vessels. Cu has good thermal, electrical and corrosion resistance properties but on adding Zn up to 36% , its mechanical properties get improved at the cost of reduction of thermal, electrical and corrosion resistance properties.Some of the common uses for brass alloys include costume jewelry, cartridge casings, automotive radiators, musical instruments, electronic packaging, and coins.

Bronze (kaansi)Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive, but Al, Si and Ni can also be used. It is hard and brittle. Bronze is typically 88% copper and 12% tin. It are used to make coins, springs, turbines, medal and blades.

Applications of Copper• About 37% of cu is used in building, construction, wiring, plumbing, heating, commercial refrigeration, hard ware and architectural materials.• 26% of cu is used in electrical and electronic devices.

• 15% of cu is used in industrial machinery and equipments.• 11% of cu is used in transportation equipment like marines, vehicles, buses and trucks.• Remaining 11% is used in cutlery, coins and ornaments