化学化工专业英语(杨定乔 )15 Aluminium.doc

15 Aluminium 15.1 Introduction This is probably the most abundant metal on the earth, as the oxide ,alumina Al2O3,makes up the chief part all clays and many other rocks. The metal was first isolated as a powder by Wohler. It was not until about 1854 that it was obtained on a manufacturing scale. Aluminum is a very light metal. Weighing only about 2.7 times that of water. And it is therefore only about one-third the weight of iron. It is good conductor of electricity ,and although inferior to copper for the long distance transmission of electric power owing to its lightness and lower cost.It forms a valuable alloy with copper, known as aluminum bronze. To obtain the bronze a mixture of corundum(alumina), charcoal and granulated copper is heated in an electric furnace. The carbon takes up the oxygen of the alumina, while the copper unites with the aluminum to form a golden-colored alloy which has great strength and elasticity. The development of the motor and aircraft industries led to the introduction of a number of aluminum alloys of great value owing to their lightness and strength. The most important of these are ‘magnalium’,containing magnesium, and ‘duralumin ’,which is aluminum with about 4percent of copper and a litter magnesium. Other alloys with copper, nickel and zinc are used in the construction of motor-car and aeroplane parts. Alloys of aluminum and silicon, with small amounts of other substances, are used in shipbuilding ,as after heat treatment they are very strong and resist the corrosive action of sea water. Aluminum has been made for many years by the electrolysis of alumina (prepared bauxite, Al2O3●2H2O)dissolved in fused cryolite (sodium aluminum fluoride the cathode. The current is brought in by thick carbon rods forming the anode which while carbon monoxide gas escapes. As the metal is removed the supply of alumina is kept up by adding more bauxite to the molten mixture. In the production of aluminum,as in so many other processes, t