Copper And Its Production

Copper is marked by a host of good engineering properties. The foremost is its good electrical conductivity and bulk of copper is used as electrical conductor. It also has a high thermal conductivity and coupled with its resistance to corrosion it is largely used as heat exchanger tubes particularly under circumstances when corrosive atmosphere exists. Its medium tensile strength and ease of fabrication are added advantages in its industrial application.

Copper is extracted from its sulfide ore. Such ores also contain sulfides of iron. Low grade ore is converted into sulfide concentrate which is smelted in reverberatory furnace to produce a mixture of sulfides of iron and copper, called mate. The slag is separated from matte. The copper sulfides is then chemically converted into impure or blister copper of 98% purity, by blowing air through the matte. The iron sulfides is oxidized and converted in slag. The blister copper is then transferred to refining furnace where most of impurities are converted into slag and removed. This fire refined cooper is called tough pitch copper and is further refined electrolytically to produce 99.95% pure copper called electrolytic tough pitch (ETP) copper.

ETP copper is used for production of wire, rod plate and strip. These products serve several industrial purposes. But ETP copper contains 0.04% oxygen which forms interdendritic Cu₂O when copper is cast. If copper is heated to a temperature of 400^oC in the atmosphere of hydrogen, then hydrogen reacts with densritic Cu₂O and produces steam. These H₂O molecules being large in size do not diffuse readily and cluster around grain boundaries thus causing internal holes. This phenomenon is called hydrogen embrittlement. The methods of avoiding hydrogen embrittlement are adding phosphorous in the alloy copper and thus allowing P₂O₅ to form. The other method is to cast ETP copper under a controlled reducing atmosphere to produce copper which is oxygen free high conductivity (OFHC) copper