Aluminium

“ The metal aluminium has come into general use with surprising rapidity, and during the last twenty-five or thirty years the amount of this metal produced annually has increased from two or three tons to many thousands of tons. Aluminium occurs naturally in large quantities, in the form of alumina, or oxide of aluminium, but for a long time experimenters despaired of ever obtaining the pure metal cheaply on a commercial scale. The oxides of most metals can be reduced, that is deprived of their oxygen, by heating them with carbon ”

“ Aluminium is frequently employed as a powerful reducing agent, many metallic oxides which resist reduction by carbon being readily reduced by it. The aluminium in the form of a fine powder is mixed with the metallic oxide, together with some substance such as fluorspar to act as a flux. The mixture is ignited, and the aluminium unites with the [Pg 331] oxygen of the metallic oxide, liberating the metal. ”

“ Aluminium takes a sketch as perfectly as does the stone, with the inestimable advantages that the metal may be readily curved for a cylinder press, that it is compact and light in storage, while without the brittleness which has made stone so costly a servant to both artists and printers. To produce a deep color from stone it may be necessary to print one impression over another again and again; from aluminium a single impression is enough, as severe pressure may be safely applied. ”

“ There is a special difficulty in the metallurgy of aluminium, arising from the fact of the qualities of the metal being much deteriorated by the presence of a very small amount of foreign matters such as iron, silicon, &c., at the same time that no process has been found for purifying the product from these substances. ”

“ Aluminium has so great an affinity for oxygen as to play a conspicuous part in the metallurgy of other metals. In the casting of iron, steel or brass, the addition to each ton of two to five pounds of aluminium greatly improves the product; the aluminium by combining with the occluded gases reduces the blowholes and renders the molten metal more fluid and therefore more homogeneous. ”

“ The use of the metal is spreading rapidly—the year 1942 has been “ear-marked” as the beginning of the age of aluminium, when thirty billion kilowatt hours, or a third of all the power generated on earth will be electrical, and a great proportion of it will be used for producing aluminium. For most purposes it will probably be alloyed with some other metal—an eight per cent addition of copper gives a standard casting alloy. ”

“ The chief objection to aluminium is its low tensile strength, which, for the cast metal is only 10,000 to 16,000 pounds per square inch. An improvement is effected by adding as an alloy a small quantity of some other metal, such as nickel or copper. When one part of aluminium is joined with nine parts of copper we have aluminium bronze, the strongest and handsomest of copper alloys, much resembling gold in its lustre. ”

“ While it is impossible to tell when this industrial revolution will be consummated, there can be no doubt that the future belongs to aluminium, and that in times to come it will be the chief means of increasing human performance. It has in this respect capacities greater by far than those of any other metal. I should estimate its civilizing potency at fully one hundred times that of iron. This estimate, though it may astonish, is not at all exaggerated. First of all, we must remember that there is thirty times as much aluminium as iron in bulk, available for the uses of man. ”

“ Mechanically, aluminium is somewhat inferior to copper, as its coefficient of expansion with temperature is 50% greater; and its elastic limit is very low, the metal tending to take a permanent set under comparatively light tension, and being seriously affected at less than half its ultimate tensile strength. Joints in aluminium wire are difficult to make, since the present methods of soldering are little better than cementing the metal with the flux; in practice the joints are purely mechanical, being usually made by means of tight-fitting sleeves forced into Contact with the wire. ”

“ The largest expense in the process, apart from the cost of electrical energy, is the preparation of aluminium oxide free from other oxides, for most of the oxide found in nature is too impure to serve without refining. Bauxite is the principal ore used as a source of the aluminium because it is converted into pure oxide without great difficulty. Since common clay is a silicate of aluminium and is everywhere abundant, it might be expected that this would be utilized in the preparation of aluminium. ”

“ A very intense action occurs: the chlorine, quitting the aluminium, seizes on the sodium, and their combination is attended by an enormous increase of temperature. The fused aluminium is run off from the furnace together with the slags which are produced by the operation. In this way, with a furnace having a hearth 16 ft. square, about 16 lbs. of aluminium can be obtained in one operation.
Rose, the eminent German metallurgist, prefers to obtain aluminium from cryolite, which is a compound of sodium, aluminium, and fluorine, found in large quantities in Greenland. ”

“ Later in that year they patented a process for the reduction of aluminium by carbon, and in 1886 an electric furnace with sliding carbon rods passed through the end walls to the centre of a rectangular furnace. The impossibility of working with just sufficient carbon to reduce the alumina, without using any excess which would be free to 234 form at least so much carbide as would suffice, when diffused through the metal, to render it brittle, practically restricts the Aluminium alloys. ”

“ Aluminium is not reduced to the metallic state from its compounds by the ordinary smelting processes. The principal method of producing it consists in passing a powerful electric current through melted cryolite in which aluminium oxide is dissolved. ”

“ If we go right down the line, aluminium will impress us as a very wonderful substance. It does all sorts of things according to the temperature and other conditions. The metal, when it approaches its temperature of fusion, is very brittle and can be easily reduced to powder. This powder mixed with a varnish-like vehicle constitutes aluminum bronze paint. It can also be beaten out until it is almost as thin as gold leaf. And now we come to a mechanical operation based on its affinity for oxygen. ”

“ Solutions containing alumina free from the other metals are diluted to a convenient bulk and heated nearly to boiling. Add chloride of ammonium, and then ammonia in slight excess; boil, allow to settle, filter, and wash with hot water. Dry the precipitate, and ignite in a platinum or porcelain crucible at the strongest heat. Cool, and weigh. The substance [Pg 316] is alumina, Al2O3, which contains 52.94 per cent. of aluminium. It is only in special cases, such as the analysis of metals and alloys, that it is reported as aluminium. The percentage of alumina is generally given. ”

“ Electrolytic Processes.—The application of electrolysis for the production of metals from a fused electrolyte is most important in the case of aluminium. This metal cannot be produced by direct electrolysis in aqueous solution, but is deposited electrolytically from a fused bath of cryolite, containing alumina in solution. As the metallic aluminium is extracted from the molten bath, further quantities of purified oxide are added. The anodes consist of carbon blocks suspended in the molten bath, and the cathode consists of the carbon lining of the furnace. ”

“ Aluminum has already played a part in the manufacture of steel. The metal from the open hearth or Bessemer converter is liable to contain oxides or oxygen gas. By adding aluminium to the melted metal, it takes up most or all of the oxygen forming iluminium oxide which goes off with the slag. ”

“ Assuming the materials to be of equal tensile strength per unit of area—hard-drawn copper is stronger, but has a lower conductivity—the adoption of aluminium thus leads to a reduction of 52% in the weight, a gain of 60% in the strength, and an increase of 26% in the diameter of the conductor. Bare aluminium strip has recently been tried for winding-coils in electrical machines, the oxide of the metal acting as insulators between the layers. When the price of aluminium is less than double the price of copper aluminium is cheaper than copper per unit of electric current conveyed ”

“ THE metal aluminium, which has the better termination, although the word aluminum is very common, ranks as the third commonest element on the surface of the earth. Any number of rocks contain it with various other constituents. It forms the basis of clay, so that every one of our dinner plates or tea cups represents the compound of this metal with oxygen and sometimes with another element or elements in small proportion. The commonest pottery, such as a flower pot, is based upon the use of clay, which is the use of aluminium oxide. ”

“ Many metals, of which copper, silver and nickel are types, can be readily won or purified by the electrolysis of aqueous solutions, and theoretically it may be feasible to treat aluminium in an identical, manner. In practice, however, it cannot be thrown down electrolytically with a dissimilar anode so as to win the metal, and certain difficulties are still met with in the analogous operation of plating by means of a similar anode. ”

“ Copper being 31/3 times as heavy as aluminium, whenever the latter costs less than 31/3 times as much as copper it is actually cheaper. It must be remembered, too, that electrolytic aluminium only became known during the last decade of the 19th century. Samples dating from the old sodium days are still in existence, and when they exhibit unpleasant properties the defect is often ascribed to the metal instead of to the process by which it was won. ”

“ My attention was first attracted to the matter by an article in the Archives des Sciences physiques et naturelles de Genève, 1894, by M. Margot. It appears that clean aluminium used as a pencil will leave a mark on clean damp glass. If, instead of a pencil, a small wheel of aluminium — say as big as a halfpenny and three times as thick — is rotated on the lathe, and a piece of glass pressed against it, the aluminium will form an adherent, though not very continuous coating on the glass. ”

“ Titanium is alloyed in small quantities with aluminium for use in naval architecture. Aluminium, when alloyed with a few per cent of magnesium, gains greatly in rigidity while remaining very light; this alloy, under the name of magnalium, is coming into use for small articles in which lightness and rigidity have to be combined. One of the most interesting amongst recent alloys is Conrad Heusler's alloy of copper, aluminium and manganese, which possesses magnetic properties far in excess of those of the constituent metals. ”

“ Aluminium oxide is then added, and under the influence of the electric current it decomposes into aluminium and oxygen. The temperature is maintained above the melting point of aluminium, and the liquid metal, being heavier than cryolite, sinks to the bottom of the vessel, from which it is tapped off from time to time through the tap hole C. The oxygen in part escapes as gas, and in part combines with the carbon of the anode, the combustion being very brilliant. ”

“ Experiments on a large scale have proved that metallic aluminium, although possessed of great lightness, strength, and durability, is not so generally suitable for technical purposes as was at first thought. ”

“ Exposure to air and rain also causes slight corrosion, but to nothing like the same extent as occurs with iron, copper or brass. Commercial electrolytic aluminium of the best quality contains as the average of a large number of tests, 0·48% of silicon and 0·46% of iron, the residue being essentially aluminium itself. The metal in mass is not affected by hot or cold water, the foil is very slowly oxidized, while the amalgam decomposes rapidly. ”

“ Incidentally it may be mentioned that aluminium is not altogether a new metal, neither is its use confined to civilized countries, where metallurgists have proved its advantages; for the natives of the Philippines, Borneo, and other islands in the Pacific have long used it as an independent metal, and also for the purposes of ornamenting other materials. Many of the copper and brass curios brought into this country, the products of native smiths, working far from civilized lands, are partly made of aluminium, alloyed chiefly with native copper. ”

“ From Indian handicrafts, developed by aboriginal skill, patience and good taste to remarkable triumphs, let us turn to an achievement of a modern chemist who, calling electricity to his aid, bestowed a new metal upon industry, making possible new economies in a wide sisterhood of arts. Aluminium was discovered in 1828 by Wohler, a German chemist, who noted its lightness, toughness, and ductility. ”

“ Aluminium is so light that it is a matter requiring some ingenuity to select a convenient solvent through which it shall sink quickly, for if it does not sink, it short-circuits the electrolyte. The molten metal has a specific gravity of 2·54, that of molten cryolite saturated with alumina is 2·35, and that of the fluoride Al2F6 2NaF saturated with alumina 1·97. ”