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COPPER AND ITS ALLOYS

Copper is a valuable metal. Its wide application in many fields of engineering is due to its exceptionally high electrical and thermal conductivity, low oxidisability, good ductility and to the fact that it is the basis of the important industrial alloys, brass and bronze.

The raw materials for the production of copper are sulphide or oxide copper ores. Most of the copper is smelted from sulphide ores (about 80 per cent) while oxide ores account for only 15 to 20 per cent. Sulphide ores are more wide-spread in nature due to the higher affinity of copper for sulphur than for oxygen.

The most abundant copper sulphide ore is copper pyrite containing the mineral chalcopyrite. In some cases, the so-called copper glance is used; it contains the mineral chalcocite. All copper ores are very lean as they contain only from 1 to 5% Cu. Therefore, before smelting they must be concentrated by flotation. Flotation converts lean Copper sulphide ores into a con­centrate containing from 15 to 20% Cu. Before smelting, the copper concentrate and rich copper sulphide ores are subjected to an oxidising roasting process at 600-900° С thereby part of the sulphur is removed in the form of a gas. This gas is trapped and utilised in the production of sulphuric acid.

Various grades of copper are used for engineering purposes. It must be noted that even a minute amount of impurities sharply alters the properties of pure copper.

The mechanical strength of pure copper is not high and depends upon the degree of deformation (reduction in working). Pure copper is used chiefly for electrical engi­neering products such as cables, busbars and wire.

The copper alloys are more widely employed. The alloying of copper with other elements increases the strength of the metal in some cases and improves the anticorrosive and antifriction properties in others. Copper alloys comprise two main groups – brasses and bronzes. Alloys of copper and zinc are called brasses. The addition of appreciable, amount of tin, nickel, manganese, alumin­ium and other elements to copper-zinc alloys imparts higher hardness, strength and other desirable qualities. Complex copper-zinc alloys comprising three, four or more components are special brasses.

The copper alloys are more widely employed. The alloying of copper with other elements increases the strength of the metal in some cases and improves the anticorrosive and antifriction properties in others. Copper alloys comprise two main groups – brasses and bronzes. Alloys of copper and zink are called brasses. The addition of appreciable amount of tin, nickel, manganese, aluminium and other elements to copper-zink alloys imparts higher hardness, strength and other desirable qualities.

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Smelting, alloying, properties, ductility, sulphide.

1. The … of copper with other elements increases improves the anticorrosive and antifriction properties in some cases.

2. Before …, rich copper sulphide ores are subjected to an oxidising roasting process at 600-900° С.

3. Copper has an exceptionally high electrical and thermal conductivity, low oxidisability and good ...

4. … ore is more wide-spread in nature due to the higher affinity of copper for sulphur than for oxygen.

5. A minute amount of impurities sharply alters the … of pure copper.