Copper and its importance

An atomic number of the element is 29 and an atomic weight is 63.546. Natural copper consists of two stable isotopes 63 Cu (69.l%) and 65Cu (30.9%). The total content of copper in the earth's crust is 0.0047%.

In the nature copper is generally found as sulphide ore, but sometimes it may be found in a free state. Mineral formations which contain copper art called copper ores. Approximately 170 minerals which contain copper are known in the nature, but only 17 out of 170 have the industrial importance. They are: native copper, cuprite (contains copper up to 88.8%), Cu₂S (up to 79.9%), covellite (up to 66.5 percent), azurite (up to 55.3 percent), bornite (up to 655), and malacolite (up to 71.9% of CuO). Copper ores contain cobalt, nickel, gold, silver, zinc, lead, bismuth, etc. as admixtures.

Copper is a metal of a red colour, density of which is 8960 kg by m³. The temperature of fusion is 1084.5 degrees centigrade and the temperature of boiling is 2541 degrees centigrade. This metal is extremely plastic and it conducts electricity and heat better than other metals.

Copper forms many alloys with different metals, the most important of them are bronze and brass. The chemical activity of copper is not very high. When heating, copper reacts with oxygen, sulphur, halogens, etc. It dissolves in acid-oxidants, forming copper salts. For instance, they get the so called blue vitriol affecting the copper with concentrated sulphuric acid under heating.

There are two oxides of copper-viz. red or cuprous oxide (Cu₂0) and black or cupric oxide (CuO). Cuprous oxide is readily fusible at furnace temperature, and at a red heat is easily reduced by hydrogen, carbon monoxide, charcoal or other carbonaceous matters, and by iron, zinc, and metals having a strong affinity for oxygen. When heated with iron sulphide or cuprous sulphide it is reduced to metallic copper. Cupric oxide is as easily reduced as cuprous oxide and by the same reducing agents, but it is not fusible.

All copper compounds are poisonous. They are used for manufacturing of catalysts, preparations for pest and fungi control, etc. Copper with purity of 95-97% is got by smelting from sulphide ores. In order to get a very pure copper, it has to be yielded to electrochemical affinage. Affinage means purification from the admixtures of gold, platinum from the admixtures of gold, platinum, silver, etc. to high purity. The sulphide solution CuSO4 is used for this process as an electrolyte.

Copper is used in electrotechical industry and metallurgy. Comparatively a little quantity of copper is used for making pigments which are used for paint manufacturing, and catalysts, micro fertilizers, preparations for pest control and against plants ill nesses.

In human organism copper is in liver, bones, in blood and spinal fluid. Lack of copper in organism causes anemia. Overdose of copper is poisonous.

PROPERTIES OF COPPER

Malleability and Ductility. - It can be rolled into very thin sheets beaten out into leaves and drawn into fine wire, and thus possesses the properties of malleability and ductility in a high degree. By cold rolling or other mechanical treatment it becomes hard, but its malleability is regained by annealing. It is immaterial whether the copper be quenched in water or cooled slowly after the annealing process.

Tenacity. - Its tenacity when cast is 8 to 10 tons psi; when rolled or drawn 16 to 23 tons or even more, according to the amount of mechanical treatment it has received.

Specific Gravity.- The specific gravity of pure Cu, rolled, forged, or drawn, and afterwards annealed, may be taken as 8.89 at 20°C, but that of ordinary commercial copper usually ranges from 8.2 to 8.6.

Action of Heat. - The melting point of Cu lies somewhat about 1,083° C. When molten it is rapidly oxidised with the formation of cuprous oxide (Cu20), which dissolves in the metal. It also absorbs hydrogen, carbon, monoxide, and sulphur dioxide, which are given off during solidification, part, however, remains in the metal producing more or less porosity. Hence arises the difficulty of obtaining sound casting of copper.

The metal is not volatilised at the temperature of ordinary furnaces, but readily in the electric furnace, its boiling point being about 2.100°C. When heated to near its melting point it becomes so brittle that it may be easily powdered.

Electrical Conductivity. As a conductor of electricity copper is only surpassed by silver, and hence is largely used for electric wires and cables. Its electrical conductivity is 976 if silver be taken as 1000. This is greatly reduced by the presence of impurities, especially by cuprous oxide, phosphorus, arsenic, antimony, and silicon.

Conductivity for Heat. Copper is an excellent conductor of heat, and in this property is about two and a half times more efficient than iron.

Chemical Properties. Copper undergoes no change in dry air at ordinary temperatures, but in moist air a green coating of basic carbonate is formed. When heated to redness with access of air, as in annealing sheets, etc., a dark coloured scale is formed, which consists almost wholly of cuprous oxide. It may be removed by plunging the copper when red-hot into cold water; in practice the water used contains sulphuric acid. Copper is slowly dissolved by weak acids in the presence of air. It is soluble in nitric acid, “aqua regia”, and in hot concentrated sulphuric acid.

Дата добавления: 2015-07-20