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Copper of all non-ferrous metals was most widely applied in the earliest times. Copper alloys are called bronzes and are known to the mankind since prehistoric times, as they were the only metal to make weapons and instruments of labour (the Bronze Age). Copper is easy to distinguish from other metals in appearance, as it has a specific reddish-pink colour.
Copper is chemically low active. It dissolves in diluted hydrochloric and sulphuric acids only with an oxidizer (for example, oxygen). It dissolves easily in nitric acid. It is highly corrosion resistent in the atmosphere and in the water vapours. Its relative density is 8.95. Its melting point is 1083C.
Copper is highly thermal conductive. It occupies the first place among other technical metals in electrical conductivity. Only silver has an insignificantly higher parameter, but silver is considerably more expensive than copper. The purer the copper is, the higher is its electrical conductivity.
Copper is a malleable metal with a low lasting quality. Its mechanical qualities depend greatly from a delivery condition. Hammer-hardened copper (hardened through cold plastic yield) has a lower electrical conductivity. The hammering hardening can only be removed through recrystallization annealing. Copper crystallizes in a face-centred cubic lattice with a 3,6 А parameter. It undergoes no allotropic changes.
Ready crude converter copper is cast in metal forms (casting moulds) and poured out to billets. This copper cannot be used for technical purposes; it should undergo fire refining or electrolytic purification. At fire refining air is blown through crude copper in flame reverberatory furnaces under the pressure, and oxygen flames out impurities. This method is used to obtain copper of low purity and if copper ores, which were used to get crude copper, possess little or no precious metals. In this case they are not extracted, but stay in the resulting volcanic copper.
Nowadays electrolytic purification is used in most of the cases, as it provides for a better cleaning of copper from impurities. Successive combining of a cheaper fire refining with electrolytic purification is also used.
Electrolytic cathode copper to be re-melted into wire, sheets and other products is re-melted in melting furnaces and poured out into billets of various form easy to roll. If copper is meant to make copper alloys, cathode sheets are cut in parts and re-melted with necessary addition of alloy elements. There exist the following copper impurities: bismuth, antimony, arsenic, iron, phosphor and silver. Various impurities influence copper qualities differently, that is why contracts give not only their accumulated value, but also quote maximum allowed amounts of each impurity type.
Most harmful for copper are bismuth and lead. They form easily fusible eutectics, located at the grain junction line. At heating under pressure eutectics dissolve and make the substances brittle and not able to take up plastic deformation («short-red brittle»).
Due to this cause bismuth and lead impurities are allowed only up to thousandths and ten thousandths percent.
Technically pure copper is delivered as cathode sheets or semi-finished materials - billets to be deformed further through rolling. Also ready copper products are delivered through casting (castings of various forms and for various purposes) and through chipless shaping - wire, sheets, strands, coils and etc.
Copper alloys of two types are most widely spread: brass and bronze. back |
