Wednesday, July 7, 2010

Copper, Cu

This the earlier metal used and, with aluminium, the most important non ferrous metal today. It is irreplaceable in electrical engineering and machine building.

Occurrence and Extraction
Copper generally occurs in ores. The important ore are; chalcocite (Cu2S) and copper pyrites (CuFeS2). The copper companion sulfur is removed in a roasting furnace. It combines with oxygen to form sulfur dioxide (SO2). The oxygen also oxidise the copper to copper oxide (CuO).

Cu2S + 2 O2 → SO2 + 2 CuO

Raw copper is extracted by reduction in a shaft furnace. Pure copper is produced by refining or by electrolyses.

Physical and Chemical Properties:
Density of copper is 8.9 kg/dm3, copper melt in temperature of 1084oC, the thermal conductivity is about 8 times of the steel, with electrical conductivity about 7 times of the steel.

Tensile strength up to 250 N/mm2, elongation of medium wires 30 to 50%. The hardness only 25% that of steel. Copper can be forged, rolled, hammered, stretched cut, and welded.

Note:
During cold working, e.g. white bending the crystal lattice is deformed, as a result of which hardness and strength increase, whereas malleability and breaking elongation are reduced. The hardness so produced can be reduced by intermediate annealing at around 600oC.

Copper readily absorbs gasses (oxygen, carbon dioxide) when it is molten. This makes cast copper ingots porous. A large rake angle is employed to advantage in machining copper. This result in long, curling chips.

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