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 the 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 ud in the construction of motor-car and aeroplane parts. Alloys of aluminum and silicon, with small amounts of other substances, are ud in shipbuilding ,as after heat treatment they are very strong and resist the corrosive action of a water.唐玄宗的皇后
Aluminum has been made for many years by the electrolysis of alumina (prepared bauxite, Al循规蹈矩是什么意思2O3●合数和质数2H2O)dissolved in fud 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 process, the source of power is the
energy of falling water. Factories have been built near many of the great waterfalls of the world such as Niagara. The Falls of the Rhine at Schaffhaun and in England at Kinlochleven in Argyllshire, and in North Wales. The bauxite ud is chiefly from the south of France,but uful deposits occurring in the southern part of the United States, and Antrim, Northern Ireland.
The remarkable increa in the u of aluminum during the past half century is shown by the following figures for the total world output of the metal.
World output of aluminum
1907 30，000 tons
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1919 136,000 tons
1924 171,000 tons
1929 270, 000 tons
1934 171,000, 000 tons陈皮生姜泡水喝的功效和作用
1950 1,417,000 tons
The increasing u of aluminum is well shown by the above figures. Of this amount of nearly one and a half million tons produced in 1950s,the American output was 718,000 tons,while British production has incread from 15, 000 tons in 1936 to 33, 000 tons in 1959.
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Aluminum is valuable not only for its lightness but on account of its peculiar behavior towards acids and alkalis. It dissolves rapidly in dilute hydrochloric acid, but is only slowly attacked by sulphuric and nitric acids, and even less by alkaline solutions. Hence, although aluminum is ud for making cooking vesls and for storage of many foodstuffs, it is well to remember that saucepans or pots of aluminum must not be cleaned by soda.
In the air aluminum soon becomes covered with a thin, almost invisible, film of oxide, wh
ich protects the metal from further corrosion. This process of lf-protection can be hastened and made more effective by ' anodic treatment. ' The metal is made the positive pole in the electrolysis of a suitable solution, and when oxidation occurs the resulting surface is immune to atmospheric corrosion. This anodic process is ud for the treatment of aeroplane parts.专升本报考条件
Aluminum melts below a red head, and when heated in air it oxidizes readily. A thin piece of aluminum foil in a bottle of oxygen gas if touched with a red-hot wire disappears instantly with a brilliant flash, leaving a white oxide behind. When aluminum combines with oxygen more heat is given off than by any other burning metal. The readiness of aluminum to take up oxygen and the heat thus given off during the combination is ud commercially to obtain metals which are difficult to get by other means. A mixture of aluminum heated with the oxide of another metal gives a violent chemical reaction. The aluminum is converted into oxide while the other metal is left in the metallic state. The action is so violent in some cas, copper oxide for example; that a kind of explosion occurs and part of the metal is volatilized. Chromium is obtained in this way in a pure stat
e, as also mangane which previously had been known only in combination with carbon or iron.
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