Popular Science Monthly/Volume 44/January 1894/The Past and Future of Aluminum
|THE PAST AND FUTURE OF ALUMINUM.|
AT the Universal Exposition of 1855 appeared for the first time an ingot of that silver-white metal from clay, as Sir Henry Roscoe called it. Aluminum does not seem to have attracted much attention from the public at that time. When it was exhibited again at London in 1862 and at Paris in 1867, in the shape of utensils of every sort, and jewelry, it had at first a success of curiosity, provoked by its extraordinary lightness of weight. But the difficulty of its manufacture and the consequent high price at which it was held, the delicacy of its color so easily soiled, caused it to be gradually abandoned in some of the arts, for which it was at first thought a new resource had been discovered. Its alloy with copper, aluminum bronze, notwithstanding its remarkable qualities of resistance and its beautiful golden color, hardly kept its place in industrial practice. Perhaps aluminum would have passed out of mention, except in laboratories, where its place is always marked, if its early history had not been associated with that of the progress of electricity, and if, by the aid of this new agent, its manufacture had not become so easy and so economical as to permit a considerable extension of its applications, and to provoke a revival of the hopes which had welcomed its beginning. These hopes are reasonable and are founded on the solid basis of the most serious scientific considerations. We have a right to expect much from this metal, an extensive use of it, and its substitution in many cases for others now at our service, provided it can be furnished at a price corresponding with that of other materials known in the arts.
Whether it presents itself in the earth of colors varying from yellow to brown, of which our fields are composed; or showing itself pure white, as in kaolin, clay is nothing else than a combination of alumina, silica, water, and other foreign bodies in varying proportions. Of this abundant earth, which forms approximately about half of the crust of the globe, the mass is about equally divided between silica the substance of rock crystal, and alumina; and this, in turn with its earthy appearance, is oxide of aluminum. This metal, therefore, constitutes nearly a sixth part of the soil on which we spend our lives. The most abundant of all the metals, it is at the same time the one that is nearest to us. Thus alumina, and consequently aluminum, is literally under our feet—clay, of which it is the principal component, being found nearly everywhere. Rarely, and scattered in the masses of the rocks, precious gems may be found—emeralds, amethysts, sapphires, rubies, and topazes—which are only alumina, nearly pure in corundum, but alloyed with a little magnesia or lime in spinel.
It was not till modern chemistry was born that it became possible to separate aluminum from its earth. Carbon, which had been the chief agent for isolating the known metals from oxygen, was not effective in separating the elements of alumina; and even the electrical process with which Sir Humphry Davy produced sodium and potassium failed here. A roundabout process was devised. Oersted converted the intractable oxides of aluminum and magnesium, also not yet conquered, into chlorides, and Woehler decomposed them with potassium, taking advantage of the superior affinity of that metal for chlorine. Applying potassium to chloride of aluminum in the crucible, he obtained metallic aluminum and chloride of potassium. It appeared as a grayish dust, with a few globules, the largest of which was not bigger than a pinhead. From this small quantity only an incomplete determination of the properties of the element could be made. A more exact description was reserved for Henri Sainte-Claire Deville, who repeated Woehler's experiment in 1854. For the rare, expensive, difficult, and somewhat dangerous potassium he substituted sodium, which he found a simple method of extracting from sea salt; and instead of clay, the use of which required a preliminary separation of the silica and the alumina, he employed hydrated alumina, known as bauxite, of which considerable beds were worked in France for the manufacture of alum. Under the direct action of chlorine, a mixture of bauxite and sea salt became a double chloride of sodium and aluminum. The addition to this mixture, at the melting point, of the proper quantity of sodium, caused a separation of the aluminum, which collected in the bottom of the crucible. By remelting, the metal was cleared of most of its impurities and greater cohesion was given to its molecules, so that it could be cast into ingots. All this involved great expense, and the investigation could not have been effectively continued had not Napoleon III come to the chemist's aid with some of the unlimited funds of which he had the control. The next year, June 18, 1855, Jean Baptiste Dumas presented to the Academy of Sciences the first ingot of aluminum made in an industrial shop.
Under more extensive manufacture the metal has been studied at ease, and its physical and chemical properties have been exactly determined. It is silver-white, but little changed by the air, which gives it a slightly bluish tinge—except when it contains iron. Its most striking quality, and one which makes it most suitable for a large number of industrial applications, is its lightness of weight. Its density varies from 2·56, when it is in a molten condition, to 2·71, when its particles have been consolidated by hammering, and its mean density may be put at about 2·60—that is, it weighs about two and a half times as much as water, while steel is nearly three times as heavy, and copper three and a half times, silver four times, and gold nearly eight times; so that four times as many articles can be made from a given weight of aluminum as from the same weight of silver. In many cases one metal may be substituted for the other without inconvenience. While not so hard as gold or silver, aluminum is equally malleable and ductile: it can be beaten into thin pellicles that a breath will blow away, with which objects can be aluminum-coated as they are gilded. It can be drawn into wires finer than a hair, and yet so firm and supple that they can be woven with silk. It is less fusible than zinc and more so than silver, and is easy, therefore, to cast and mold. Although very sonorous, it has not yet been successfully cast into bells, because the repeated strokes of the hammer make it hard and brittle; but the tuning forks made from it are satisfactory to musical artists. The sulphurets, which blacken silver so quickly, are without action on aluminum. Similarly insensible to organic secretions, it lends itself to the making of certain surgical apparatus. Ingenious tubes have been made from it which permit patients who have been operated upon for tracheotomy to breathe, and American dentists have utilized it in the construction of their modern apparatus. It is equally fitted for making into plate and kitchen utensils, for which its specific lightness makes its use convenient. Its conductibility for both heat and electricity authorizes us to predict a fine future for it. It is, it is true, an inferior conductor to gold and silver, about as good as copper, and twice as good as iron; hence an aluminum wire will carry twice as great a quantity of electricity in a given time as an iron wire; or, to carry an equal quantity the aluminum wire need be only half as large; and aluminum being only one third as heavy as iron, it will have to be only one sixth as heavy. These properties should, were the cost equalized, make aluminum vastly more available for telegraphic and other electric wires than iron. Furthermore, aluminum not being acted upon by the air, galvanization, which is necessary for the preservation of iron wire, could be dispensed with.
Aluminum is, however, inferior to iron and steel in tenacity. the quality of resisting the forces of pulling, bending, and twisting, which tend to break the metal or separate its molecules. Equal volumes of aluminum and cast iron have about the same power of resistance to these actions. That of copper is not quite double, but that of wrought iron is more than three times, and that of steel about five times as great. For purposes, therefore, where this quality is demanded, aluminum offers no advantages; but there are numerous other uses in which the question of a greater or less resistance is of no interest; and the other qualities of aluminum—its ductility, conductibility, and lightness—may be dominant reasons for employing it. Its use has hitherto been limited by the consideration of cost.
This difficulty is fast passing away as improved processes are applied, and the use of aluminum has been greatly extended and diversified since Sainte-Claire Deville exhibited the first manufactured specimen. In 1856 it cost one hundred and eighty dollars a kilogramme; the next year Deville was able to prepare it at La Glacière under more favorable conditions, and the price fell to sixty dollars. A year afterward the factory was removed to Salindres, where fuel and bauxite were within convenient reach. The price gradually fell; cryolite, a new aluminum mineral, discovered in Greenland, was introduced, and the metal cost only eighteen dollars a kilogramme in 1883. The manufacture was undertaken at several places in England, with improved processes based on the method of Sainte-Claire Deville. Mr. Castner devised a method of producing sodium by which the cost of that metal was largely reduced, and the price of aluminum suffered another fall. Then Mr. C. Netto devised a direct process for producing sodium by exposing pulverized caustic soda to the action of incandescent charcoal, and the cost of aluminum fell to seven dollars a kilogramme.
The brightest promises for the future of aluminum are offered through the electrical processes. When the flame of the voltaic arc is turned upon a mixture of pulverized mineral and charcoal a fusion takes place, and the metal, relieved by dissociation, flows out fluid, limpid, and brilliant. So fine a result, however, can be obtained only under the most favorable conditions, to secure which, not always with certainty, great pains are required. An easier process is to turn the voltaic arc, not upon the pulverized mixture, but upon a bath of mineral substances which have been previously brought to a condition of igneous fusion, as is done in the Cowles electrical process. Complex phenomena are then produced, both calorific and chemical. Important factories have been established for obtaining by this process both pure aluminum and its alloys with other metals, particularly with iron and copper. By it the company at Pittsburg obtained almost chemically pure aluminum from the crude bauxites and corundums of which considerable quantities have been discovered in the northern United States. The factory at Neuhausen utilizes a part of the falls of the Rhine at Schaffhausen for the propulsion of powerful turbines which directly work the dynamos whence electricity is obtained for the production of aluminum and its alloys. Important manufacturing centers have also been established in England and Germany, and there-are some in France.
By these new methods, which are still susceptible of improvement, a considerable saving over the old purely chemical processes is gained in the treatment of the minerals. In either case the chief effective agent is heat, and it is utilized far more completely in the electrical furnaces than in the older furnaces, which were subject to many cooling influences. Not more than four hundred grammes of coal burned in the furnace of a steam engine driving a dynamo will produce electrical energy sufficient to isolate in a molten electrolyte one kilogramme of aluminum. More than twenty times as much would have been required in the old chemical process. By virtue of this better utilization of heat, with greater profection in the equipment and management of the shops, the price of aluminum has continued to decline, till it is now very near the point when the metal can be profitably applied to the fabrication of many articles.
The alloys of aluminum now occupy a high position in practical industry. Aluminum bronzes and platings, lighter and more tenacious and more resisting than copper, and conducting heat and electricity better, will take its place. The new shops are also working for the production of cast and malleable iron, and they are in request by smiths for refining cast iron and steel.
The metallurgy of iron is now an exact science as well as an industry. Informed by analysis of the exact composition of the elements that enter into the fusion-bed, and of the character of the products at each moment of the operation, the metallurgist can determine with accuracy what be must eliminate and what add to give his product the quality required for the use to which it is to be put. A few hundredths of alloy will decide what it shall be. A little chromium will render artillery projectiles proof against breaking; nickel increases the resisting power of sheathings. Introduced at the right time into the Bessemer converter or the Martin furnace, a small proportion of the alloy of iron and aluminum communicates to the melted metal a fluidity which facilitates the disengagement of the gases that would otherwise remain imprisoned in the metallic bath, producing blow-holes, and destroying homogeneity and resistance in large pieces.
New uses are constantly found for the pure metal; less employed in jewelry, it is more used in the modest ranks of plated ware and kitchen vessels. In Germany it has been introduced experimentally into the equipment of soldiers. Its alloy with the rare metal titanium, while still light, is very hard and tough. Could not picks, bayonets, sabers, and mess plates, imposing lighter loads on foot-soldiers, be made of it? The Russian army tried horseshoes of aluminum, and the horses of the Finnish dragoons, on which the experiment was made, are said to have gained perceptibly in speed by it. It has been introduced into machines, to reduce the dead weight a gain of special value for aërial navigation and for cyclers. A canoe entirely of aluminum, hull and machinery, has been launched on the lake of Geneva, and suggests a new resource for the bold explorers of rivers with numerous rapids in Africa and elsewhere. Its application to aërostats is talked of.
The supposition is consistent with past experiences that new wants will arise as the means of satisfying them increase, and that the new metal, without infringing upon the domains of its predecessors, will in some way create the uses for which it will be employed. A salient fact in the history of the aluminum industry is the rigorously scientific character of the progressive steps in the discovery and production of the metal. Nothing has come about by chance, but all is the work of human intelligence.—Translated for The Popular Science Monthly from the Revue des Deux Mondes.