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ALUMINIUM (symbol Al; atomic weight 2...
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See also:ALUMINIUM (See also:symbol Al; atomic See also:weight 27.0) , a metallic chemical See also:element. Although never met with in the See also:free See also:state, aluminium is very widely distributed in See also:combination, principally as silicates. The word is derived from the See also:Lat. alumen (see See also:ALUM), and is probably akin to the Gr. Ors (the See also:root of See also:salt, halogen, &c.). In 1722 F. See also:Hoffmann announced the See also:base of alum to be an individual substance; L.B. Guyton de Morveau suggested that this base should be called alumine, after Sel alumineux, the See also:French name for alum; and about 182o the word was changed into alumina. In 176o the French chemist, T. See also:Baron de Henouville, unsuccessfully attempted " to reduce the base of alum " to a See also:metal, and shortly afterwards various other investigators essayed the problem in vain. In 18o8 See also:Sir See also:Humphry See also:Davy, fresh from the electrolytic See also:isolation of See also:potassium and See also:sodium, attempted to decompose alumina by See also:heating it with potash in a See also:platinum crucible and submitting the mixture to a current of See also:electricity; in 1809, with a more powerful See also:battery, he raised See also:iron See also:wire to a red See also:heat in contact with alumina, and obtained distinct See also:evidence of the See also:production of an iron-aluminium alloy. Naming the new metal in anticipation of its actual See also:birth, he called it alumium; but for the See also:sake of See also:analogy he was soon persuaded to See also:change the word to aluminum, in which See also:form, alternately with aluminium, it occurs in chemical literature for some See also:thirty years. In the See also:year 1824,endeavouring to prepare it by chemical means, H. C. Oersted heated its chloride with potassium See also:amalgam, and failed in his See also:object simply by See also:reason of the See also:mercury, so that when F. See also:Wohler repeated the experiment at t onpar°. See also:Gottingen in 1827, employing potassium alone as the reducing See also:agent, he obtained it in the metallic state for the first See also:time. Contaminated as it was with potassium and with platinum from the crucible, the metal formed a See also:grey See also:powder and was far from pure; but in 1845 he improved his See also:process and succeeded in producing metallic globules wherewith he examined its See also:chief Ammonium Alum. See also:Caesium Alum. Potash Alum. See also:Rubidium Alum. t°C. too parts See also:water t°C too parts water t°C. too parts water t°C See also:loo parts water dissolve. dissolve. dissolve. dissolve. 0 2.62 0 0.19 0 3.9 0 0.71 to 4'5 to 0.29 to 9.52 to I•09 50 15.9 50 1.235 5o 44•II 50 4.98 8o 35'2 8o 5.29 8o 134'47 8o 21.6o too 70'83 too 357.48 _ Poggiale C. Setterberg Poggiale C. Setterberg See also:Ann. Chico. phys. Ann. 1882, 211, p. 104. [3] 8, p• 467. properties, and prepared several compounds hitherto unknown. See also:Early in 1854, H. St Claire Deville, accidentally and in See also:ignorance of WShler's later results, imitated the 1845 experiment. At once observing the reduction of the chloride, he realized the importance of his See also:discovery and immediately began to study the commercial production of the metal. His See also:attention was at first divided between two processes—the chemical method of reducing the chloride with potassium, and an electrolytic method of decomposing it with a See also:carbon anode and a platinum See also:cathode, which was simultaneously imagined by himself and R. See also:Bunsen. Both schemes appeared practically impossible; potassium cost about X17 per lb, gave a very small yield and was dangerous to manipulate, while on the other See also:hand, the only source of electric current then available was the See also:primary battery, and See also:zinc as a See also:store of See also:industrial See also:energy was utterly out of the question. Deville accordingly returned to pure See also:chemistry and invented a practicable method of preparing sodium which, having a See also:lower atomic weight than potassium, reduced a larger proportion. He next devised a See also:plan for manufacturing pure alumina from the natural ores, and finally elaborated a process and plant which held the See also: M. See also: See also:Bauxite is a hydrated oxide of aluminium of the ideal See also:composition, Al203.2H20. It is a somewhat widely distributed mineral, being met with in See also:Styria, See also:Austria, See also:Hesse, French See also:Guiana, India and See also:Italy; but the most important beds are in the See also:south of See also:France, the See also:north of See also:Ireland, and in See also:Alabama, See also:Georgia and See also:Arkansas in North See also:America. The chief Irish deposits are in the neighbourhood of Glenravel, Co. See also:Antrim, and have the See also:advantage of being near the coast, so that the alumina can be transported by water-See also:carriage. After being dried at 1o0° C., Antrim bauxite contains from 33 to 6o % of alumina, from 2 to 30% of ferric oxide, and from 7 to 24% of silica, the See also:balance being titanic See also:acid and water of combination. The See also:American bauxites contain from 38 to 67 % of alumina, from 1 to 23 % of ferric oxide, and from i to 32 % of silica. The French bauxites are of fairly See also:constant composition, containing usually from 58 to 70 % of alumina, 3 to 15 % of See also:foreign See also:matter, and 27 % madeup of silica, iron oxide and water in proportions that vary with the See also:colour and the situation of the beds.
Before the application of electricity, only two compounds were found. suitable for reduction to the metallic state. Alumina itself is so refractory that it cannot be melted See also:save by the oxyhydrogen See also:blowpipe or the electric arc, and except in the molten state it is not susceptible of decomposition by any chemical reagent. Deville first selected the chloride as his raw material, but observing it to be volatile and extremely deliquescent, he soon substituted in its See also:place a double chloride of aluminium and sodium. Early in 1855 See also: See also:Rose also carried out experiments on the decomposition of cryolite, and expressed an See also:opinion that it was the See also:beet of all compounds for reduction; but, finding the yield of metal to be See also:low, receiving a See also:report of the difficulties experienced in See also:mining the ore, and fearing to cripple his new industry by basing it upon the employment of a mineral of such uncertain See also:supply, Deville decided to keep to his chlorides. With the See also:advent of the dynamo, the position of affairs was wholly changed. The first successful See also:idea of using electricity depended on the enormous heating See also:powers of the arc. The infusibility of alumina was no longer prohibitive, for the molten oxide is easily reduced by carbon. Nevertheless, it was found impracticable to See also:smelt alumina electrically except in presence of See also:copper, so that the Cowles See also:furnace yielded, not the pure metal, but an alloy. So See also:long as the metal was principally regarded as a necessary ingredient of aluminium-See also:bronze, the Cowles process was popular, but when the advantages of aluminium itself became more apparent, there arose a fresh demand for some chief method of obtaining it unalloyed. It was soon discovered that the See also:faculty of inducing See also:dissociation possessed by the current might now be utilized with some See also:hope of pecuniary success, but as electrolytic currents are of lower voltage than those required in electric furnaces, molten alumina again became impossible. Many metals, of which copper, See also:silver and See also: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. Of the See also:simple compounds, only the fluoride is amenable to electrolysis in the fused state, since the chloride begins to volatilize below its melting-point, and the latter is only 5° below its boiling-point. Cryolite is not. a safe body to electrolyse, because the minimum voltage needed to break up the aluminium fluoride is 4.0, whereas the sodium fluoride requires only 4.7 volts; if, therefore; the current rises in tension, the See also:alkali is reduced, and the final product consists of an alloy with sodium. The corresponding double chloride is a far better material; first, because it melts at about i8o° C., and does not volatilize below a red heat, and second, because the voltage of aluminium chloride is 2.3 and that of sodium chloride 4-3, so that there is a. much wider margin of safety to See also:cover irregularities in the electric pressure. It has been found, however, that molten cryolite and the analogous double fluoride represented by the See also:formula Al2Fs.2NaF are very efficient solvents of alumina, and that these solutions can be easily electrolysed at about 800° C. by means of a current that completely decomposes the oxide but leaves the haloid salts unaffected. Molten cryolite dissolves roughly 30 % of its weight of pure alumina, so that when ready for treatment the See also:solution contains about the same proportion of what may be termed " available " aluminium as does the fused double chloride of aluminium and sodium. The advantages See also:lie with the oxide because of its easier preparation. Alumina dissolves readily enough in aqueous hydrochloric acid to yield a solution of the chloride, but neither this solution, nor that containing sodium chloride, can be evaporated • to dryness without decomposition: To obtain the anhydrous single or double chloride, alumina must be ignited with carbon in a current of See also:chlorine, and to exclude iron from the finished metal, either the alumina must be pure or the chloride be submitted to purification. This preparation of, a chlorine compound suited for electrolysis becomes more costly and more troublesome than that of the oxide, and in addition four times as much raw material must be handled. At different times propositions have been made.to win the metal from its sulphide. This compound possesses a heat of formation so much lower that electrically it needs but a voltage of o•9 to decompose it, and it is easily soluble in the fused sulphides of the alkali metals. It can also be reduced metallurgically by the See also:action of molten iron. Various considerations, however, tend to show that there cannot be so much advantage in employing it as would appear at first sight. As it is easier to reduce than any other compound, so it is more difficult to produce. Therefore while less energy is absorbed in its final reduction, more is needed in its initial preparation, and it is questionable whether the See also:economy possible in the second See also:stage would not be neutralized by the greater cost of the first stage in the whole operation of winning the metal from bauxite with the sulphide as the intermediary. The Deville process as gradually elaborated between 1855 and 1859 exhibited three distinct phases:—Production of metallic Chemical sodium, formation of the pure double chloride of sodium reduction. and aluminium,and preparation of the metal by the inter- action of the two former substances. To produce the alkali metal, a calcined mixture of sodium carbonate, See also:coal and See also:chalk was strongly ignited in See also:flat retorts made of See also:boiler-See also:plate; the sodium distilled over into condensers and was. preserved under heavy See also:petroleum. In See also:order to prepare pure alumina, bauxite and sodium carbonate were heated in a furnace until the reaction was See also:complete; the product was then extracted with water to dissolve the sodium aluminate, the solution treated with carbon dioxide, and the precipitate removed and dried. This purified oxide, mixed with sodium chloride and coal See also:tar, was carbonized at a red heat, and ignited in a current of dry chlorine as long as vapours of the double chloride were given off, these being condensed in suitable See also:chambers. For the production of the final aluminium, Too parts of the chloride and 45 parts of cryolite to serve as a See also:flux were powdered together and mixed with 35 parts of sodium cut into small pieces. The whole was thrown in several portions on to the See also:hearth of a furnace previously heated to low redness and was stirred at intervals for three See also:hours. At length when the furnace was tapped a See also: Tissier, formerly his assistants, who had devised an improved sodium furnace and had acquired a thorough knowledge of their See also:leader's experiments, also See also:left, and erected a factory at Amfreville, near See also:Rouen, to See also:work the cryolite process. It consisted simply in reducing cryolite with metallic sodium exactly as in Deville's chloride method, and it was claimed to possess various mythical advantages over its See also:rival. Two See also:grave disadvantages were soon obvious—the limited supply of ore, and, what was even more serious, the large proportion of silicon in the reduced metal. The Amfreville works existed some eight or ten years, but achieved no permanent prosperity. In 1858 or 1859 a small factory, the first in See also:England, was built by F. W. See also:Gerhard at See also:Battersea, who also employed cryolite, made his own sodium, and was able to sell the product at 3S. gd. per oz. This enterprise 1. asonly lasted about four years. Between 186o and 1874 Messrs See also:Bell Brothers manufactured the metal at See also:Washington, near See also:Newcastle, under Deville's supervision, producing nearly 2 cwt. per year. They took See also:part in the See also:International Exhibition of 1862, quoting a See also:price of 40S. per lb See also:troy. In 1881 J. See also:Webster patented an improved process for making alumina, and the following year he organized the Aluminium See also:Crown Metal Co. of Hollywood to exploit it in See also:conjunction with Deville's method of reduction. Potash-alum and See also:pitch were calcined together, and the See also:mass was treated with hydrochloric acid; See also:charcoal and water to form a See also:paste were next added, and the whole was dried and ignited in a current of See also:air and See also:steam. The See also:residue, consisting of alumina and potassium sulphate, was leached with water to See also:separate the insoluble matter which was dried as usual. All the by-products, potassium sulphate, See also:sulphur and aluminate of iron, were capable of recovery, and were claimed to reduce the cost of the oxide materially. From this alumina the double chloride was prepared in essentially the same manner as practised at Salindres, but sundry economies accrued in the process, owing to the larger scale of working and to the See also:adoption of W. See also:Weldon's method of regenerating the spent chlorine liquors. In 1886 H. Y. Castner's sodium See also:patents appeared, and The Aluminium Co. of See also:Oldbury was promoted to combine the advantages of Webster's alumina and Castner's sodium. Castner had long been interested in aluminium, and was desirous of lowering its price. Seeing that sodium was the only possible reducing agent, he set himself to cheapen its cost, and deliberately rejecting sodium carbonate for the more ex-pensive sodium hydroxide (See also:caustic soda), and replacing carbon by a mixture of iron and carbon—the so-called See also:carbide of iron—he invented the highly scientific method of winning the alkali metal which has remained in existence almost to the present See also:day. In 187 2 sodium prepared by Deville's process cost about 4S: per lb, the greater part of the expense being due to the constant failure of the retorts; in 1887 Castner's sodium cost less than Is. per lb, for his cast-iron pots survived 125 distillations. In the same year L. Grabau patented a method of reducing the simple fluoride of aluminium with sodium, and his process was operated at Trotha in See also:Germany. It was distinguished by the unusual purity of the metal obtained, some of his samples containing 99.5 to 99.8 %. In 1888 the See also:Alliance Aluminium Co., organized to work certain patents for winning the metal from cryolite by means of sodium, erected plant in See also:London, See also:Hebburn and See also:Wall--send, and by 1889 were selling the metal at IIs. to 15s. per lb. The Aluminium See also:Company's price in 1888 was 2os. per lb and the output about 250 lb per day. In 1889 the price was lbs., but by 1891 the electricians commenced to offer metal at 4s. per lb, and aluminium reduced with sodium became a thing of the past. About 1879 dynamos began to be introduced into metallurgical practice, and from that date onwards numerous schemes for utilizing this cheaper source of energy were brought eeatdca before the public. The first See also:electrical method worthy reduction. of See also:notice is that patented by E. H. and A. H. Cowles in 1885, which was worked both at See also:Lockport, New See also:York, U.S.A., and at See also:Milton, See also:Staffordshire. The furnace consisted of a flat, rectangular, See also:firebrick See also:box, packed with a layer of finely-powdered charcoal 2 in. thick. Through stuffing-boxes at the ends passed the two electrodes, made after the See also:fashion of arc-See also:light carbons, and capable of being approached together according to the requirements of the operation. The central space of the furnace was filled with a mixture of See also:corundum, coarsely-powdered charcoal and copper; and an iron lid lined with firebrick was luted in its place to exclude air. The See also:charge was reduced by means of a 50-volt current from a 3oo-kilowatt dynamo, which was passed through the furnace for1 hours till decomposition was complete. About loo lb of bronze, containing from 15 to 20 lb of aluminium, were obtained from each run, the yield of the alloy being reported at about lb per 18 e.h.p.-hours. The composition of the See also:alloys thus produced could not be pre-determined with exactitude; each batch was therefore analysed, a number of them were bulked together or mixed with copper in TI the necessary proportion, and melted in crucibles to give merchantable bronzes containing between r; and ro % of aluminium; Although the copper took no part in the reaction, its employment was found indispensable, as otherwise the aluminium partly volatilized, and partly combined with the carbon to form a carbide. It was also necessary to give the See also:fine charcoal a thin coating of calcium oxide by soaking it in See also:lime-water, for the temperature was so high that unless it was thus protected it was gradually converted into See also:graphite, losing its insulating See also:power and diffusing the current through the lining and walls of the furnace. That this process did not depend upon electrolysis, but was simply an instance of electrical smelting or the decomposition of an oxide by means of carbon at the temperature of the electric arc, is shown by the fact that the Cowles furnace would work with an alternating current. In 1883 R. Cratzel patented a useless electrolytic process with fused cryolite or the double chloride as the raw material, and in 1886 Dr E. Kleiner propounded a cryolite method which was worked for a time by the Aluminium See also:Syndicate at See also:Tyldesley near See also:Manchester, but was abandoned in 1890. In 1887 A. Minet took out patents for electrolysing a mixture of sodium chloride with aluminium fluoride, or with natural or artificial cryolite. The operation was continuous, the metal being regularly run off from the bottom of the bath, while fresh alumina and flouride were added as required. The process exhibited several disadvantages, the electrolyte had to be kept constant in composition lest either See also:fluorine vapours should be evolved or sodium throwh down, and the raw materials had accordingly to be prepared in a pure state. After prolonged experiments in a factory owned by Messrs See also:Bernard Freres at St See also:Michel in See also:Savoy, Minet's process was given up, and at the See also:close of the 19th See also:century the Heroult-Hall method was alone being employed in the manufacture. of aluminium throughout the world. The See also:original Deville process for obtaining pure alumina from bauxite was greatly simplified in 1889 by K. T. Bayer, whose improved process is exploited at Larne in Ireland and at Gardanne in France. New works on the same process have recently been erected near See also:Marseilles. Crude bauxite is ground, lightly calcined to destroy organic matter, and agitated under a pressure of 70 or 8o lb per sq. in. with a solution of sodium hydroxide having the specific gravity 1.45. After two or three hours the liquid is .diluted till its See also:density falls to 1.23, when it is passed through See also:filter-presses to remove the insoluble ferric oxide and silica. The solution of sodium aluminate, containing aluminium oxide and sodium oxide in the molecular proportion of '6 to 1, is next agitated for thirty-six hours with a small quantity of hydrated alumina previously obtained, which causes the liquor to decompose, and some 70 % of the aluminium hydroxide to be thrown down. The filtrate, now containing roughly two molecules of alumina to one of soda, is concentrated to the Original gravity of 1.45, and employed instead of fresh caustic for the attack of more bauxite; the precipitate is then collected, washed till free from soda, dried and ignited at about r000° C. to convert it into a crystalline oxide which is less hygroscopic than the former amorphous variety. The process of manufacture which now remains to be described was patented during 1886 and 1887 in the name of C: M. Hall in America, in that of P. T. L. Heroult in England and France. It would be idle to discuss to whom the See also:credit of first imagining the method rightfully belongs, for probably this is only one of the many occasions when new ideas have been See also:born in several brains at the same time. By r888 Hall was at work on a commercial scale at See also:Pittsburg, reducing See also:German alumina; in 1891 the plant was removed to New See also:Kensington for economy in See also:fuel, and was gradually enlarged to 1500 h.p.; in 1894 a factory driven by water was erected at See also:Niagara Falls, and subsequently works were established at Shawenegan in See also:Canada and at See also:Massena in the United States. In 1890 also the Hall process operated by steam power was installed at Patricroft, See also:Lancashire, where the plant had a capacity of 300 lb per day, but by 1894 the turbines of the Swiss ' and French works ruined the enterprise.' About 1897 the Bernard factory at St Michel passed into the hands of Messrs Pechiney, the machinery soon being increased, and there, under the See also:control of a See also:firm that has been concerned in the industry almost from its inception, aluminium is being manufactured by the Hall process on a large scale. In See also:July 1888 the SocieteMetallurgique Suisse erected plant driven by a 500 h.p. See also:turbine to carry out Heroult's alloy process, and at the end of that year the Allgemeine Elektricitats Gesellschaft united with the Swiss firm in organizing the Aluminium Industrie Actien Gesellschaft of Neuhasen, which has factories in See also:Switzerland, Germany and Austria.. The Societe Elecirometallurgique Francaise, started under the direction of Heroult in 1888 for the production of aluminium . in France, began operations on a small scale at Froges in See also:Isere; but soon after large works were erected in Savoy at La Praz, near Modane, and in 1905. another large factory was started in Savoy at St Michel. In 1895 the See also:British Aluminium Company was founded to mine bauxite and manufacture alumina in Ireland, to prepare the necessary electrodes at See also:Greenock, to reduce the aluminium by the aid of water-power at the Falls of Foyers, and to refine and work up the metal into marketable shapes at the old Milton factory of the Cowles Syndicate, re-modelled to suit See also:modern requirements. In 1905 this company began works for the utilization of another water-power at See also:Loch See also:Lever}. In .1907 a new company, The Aluminium See also:Corporation, was started in England to carry out' the production of the metal by the Heroult process, and new factories were constructed near See also:Conway' in North See also:Wales and at See also:Wallsend-on-See also:Tyne, quite close to where, twenty. years before, the Alliance Aluminium Co. had their works. The Heroult See also:cell consists of a square iron or See also:steel box lined with carbon rammed and baked into a solid mass; at the bottom is a' cast-iron plate connected with the negative See also:pole of the dynamo, but the actual working cathode is undoubtedly the layer of already reduced and molten metal that lies in the bath. The anode is formed of a bundle of carbon rods suspended from overhead so as to be capable of See also:vertical See also:adjustment. The cell is filled up with cryolite, and the current is turned on till this is melted; then the pure powdered alumina is fed in continuously as long as the operation proceeds. The current is supplied at a tension of 3 to 5 volts per cell, passing through ro or 12 in See also:series; and it performs two distinct functions:—(1) it overcomes the chemical See also:affinity of the aluminium oxide, (2) it overcomes the resistance of the electrolyte, heating the liquid at the same time. As a part of the voltage is consumed in the latter See also:duty, only the residue can be converted into chemical work, and as the theoretical voltage of the aluminium fluoride in the cryolite is 4.0, provided the bath is kept properly supplied with alumina, the fluorides are not attacked. It follows, therefore, except for See also:mechanical losses, that one charge of cryolite lasts indefinitely, that the sodium and other impurities in it are not liable to contaminate the product, and that only the alumina itself need be carefully purified. 'The operation is essentially a dissociation of alumina into aluminium, which collects at the cathode, and into See also:oxygen, which combines with the anodes to form carbon monoxide, the latter escaping and being burnt to carbon dioxide outside. Theoretically 36 parts by weight of carbon are oxidized in the production of 54 parts of aluminium; practically the anodes See also:waste at the same See also:rate at which metal is deposited. The current density is about 700 amperes per sq. ft. of cathode See also:surface, and the number of rods in the anode is such that each delivers 6 or 7 amperes per sq. in. of See also:cross-sectional See also:area. The working temperature lies between 750 and 85n° C., and the actual yield is r lb of metal per 12 e.h.p. hours. The bath is heated internally with the current rather than by means of See also:external fuel; because this arrangement permits the See also:vessel itself to be kept comparatively cool; if it were fired from without, it would be hotter than the electrolyte, and no material suitable for the construction of the cell is competent to withstand the attack of nascent aluminium at high temperatures. 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 See also: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. The latter therefore appears the better material, and was originally preferred by Hall; cryolite, however, dissolves more alumina, and has been finally adopted by both inventors. Aluminium is a white metal with a characteristic tint which most nearly resembles that of See also:tin; when impure, or after See also:pro- longed exposure to air, it has a slight See also:violet shade. Its Properties. atomic weight is 27 (2 6.77, 77, 11=1, according to J. See also:Thomsen). It is trivalent. The specific gravity of cast metal is 2.583, and of rolled 2.688 at 4° C. It melts at 626° C. (freezing-point 6 54.5°, Heycock and See also:Neville). It is the third most malleable and See also:sixth most ductile metal, yielding sheets 0.000025 in. in thickness, and wires 0.004 in. in See also:diameter. When quite pure it is somewhat harder than tin, and its hardness is considerably increased by See also:rolling. It is not magnetic. It stands near the See also:positive end of the See also:list of elements arranged in electromotive series, being exceeded only by the alkalis and metals of the alkaline earths; it therefore combines eagerly, under suitable conditions, with o::ygen and chlorine. Its coefficient of linear expansion by heat is o•0000222 (See also:Richards) or 0.0000231 (See also:Roberts-See also:Austen) per 1° C. Its mean specific heat between o° and too° is 0.227, and its latent heat of See also:fusion soo calories (Richards). Only silver, copper and See also:gold surpass it as conductors of heat, its value being 31.33 (Ag= too, Roberts-Austen). Its electrical conductivity, determined on 99.6 % metal, is 60.5 % that of copper for equal volumes, or double that of copper for equal weights, and when chemically pure it exhibits a somewhat higher relative efficiency. The See also:average strength of 98 % metal is approximately shown by the following table: 1 Elastic Limit, Ultimate Reduction tons tons per sq. in. per sqstrength, of Area % sq. in. Cast . 3 7 15 See also:Sheet . 52 11 35 Bars 6i 12 40 Wire '. 7-13 13-29 60 Weight for weight, therefore, aluminium is only exceeded in tensile strength by the best cast steel, and its own alloy, aluminium bronze. An absolutely clean surface becomes tarnished in See also:damp air, an almost invisible coating of oxide being produced, just as happens with zinc; but this film is very permanent and prevents further attack. Exposure to air and See also:rain also causes slight corrosion, but to nothing like the same extent as occurs with iron, copper or See also: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 See also:cold water, the See also:foil is very, slowly oxidized, while the amalgam decomposes rapidly. Sulphuretted See also:hydrogen having no action upon it, articles made of it are not blackened in foggy See also:weather or in rooms where crude coal See also:gas is burnt. To inorganic acids, except hydrochloric, it is highly resistant, ranking well with tin in this respect; but alkalis dissolve it quickly. Organic acids such as See also:vinegar, common salt, the natural ingredients of See also:food, and the various extraneous substances used as food preservatives, alone or mixed together, dissolve traces of it if boiled for any length of time in a chemically; clean vessel; but when aluminium utensils are submitted to the See also:ordinary routine of the See also:kitchen, being used to heat or See also:cook See also:milk, See also:coffee, vegetables, See also:meat and even See also:fruit, and are also cleaned frequently in the usual fashion, no appreciable quantity of metal passes into the food. Moreover, did it do so, the action upon the human See also:system would be infinitely less harmful than similar doses of copper or of See also:lead. The highly electro-positive See also:character of aluminium is most important. At elevated temperatures the metal decomposes nearly all other metallic oxides, wherefore it is most serviceable as a metallurgical reagent. In the casting of iron, steel and brass, the addition of a trifling proportion (0.005 %) removes oxide and renders the molten metal more fluid, causing thefinished products to be more homogeneous, free from See also:blow-holes and solid all through. On the other hand, its electro-positive nature necessitates some care in its utilization. If it be exposed to damp, to See also:sea-water or to corrosive influences of any See also:kind in contact with another metal, or if it be mixed with another metal so as to form an alloy which is not a true chemical compound, the other metal being highly negative to it, powerful galvanic action will be set up and the structure will quickly deteriorate. This explains the failure of boats built of commercially pure aluminium which have been put together with iron or copper rivets, and the decay of other boats built of a light alloy, in which the alloying metal (copper) has been injudiciously chosen. It also explains why aluminium is so difficult to join with low-temperature solders, for these mostly contain a large proportion of lead. This disadvantage, however, is often overestimated since in most cases other means of uniting two pieces are available. The metal produces an enormous number of useful alloys, some of which, containing only r or 2 % of other metals, combine the lightness of aluminium itself with far greater hardness Alloys. and strength. Some with 90 to 99 % of other metals exhibit the See also:general properties of those metals conspicuously improved. Among the heavy alloys, the aluminium bronzes (Cu, 90-97.5 %; Al, 10-2.5 %) occupy the most important position, showing mean tensile strengths increasing from 20 to 41 tons per sq. in. as the percentage of aluminium rises, and all strongly resisting corrosion in air or sea-water. The light copper alloys, in which the proportions just given are practically reversed, are of considerably less utility, for although they are fairly strong, they lack power to resist galvanic action. This subject is far from being exhausted, and it is not improbable that the alloy-producing capacity of aluminium may eventually prove its most valuable characteristic. In the meantime, ternary light alloys appear the most satisfactory, and See also:tungsten and copper, or tungsten and nickel, seem to be the best substances to add. The uses of aluminium are too numerous to mention. Probably the widest field is still in the purification of iron and steel. To the general public it appeals most strongly as a material for constructing cooking utensils. It is not brittle Uses.
like See also:porcelain and cast iron, not poisonous like lead-glazed earthenware and untinned copper, needs no See also:enamel to chip off, does not See also:rust and See also:wear out like cheap tin-plate, and weighs but a fraction of other substances. It is largely replacing brass and copper in all departments of industry—especially where dead weight has to be moved about, and lightness is synonymous with economy—for instance, in See also:bed-plates for See also:torpedo-See also:boat engines, See also:internal fittings for See also:ships instead of See also:wood, complete boats for See also:portage, motor-See also:car parts and boiling-pans for See also:cone fectionery and in chemical works. The British See also:Admiralty employ it to save weight in the See also:Navy, and the See also:war-offices of the See also:European powers equip their soldiers with it wherever possible. As a substitute for Solenhofen See also: It is the weight of a mass of metal which governs its See also:financial value; its industrial value, in the vast See also:majority of cases, depends on the See also:volume of that mass. Provided it be rigid, the bed-plate of an See also:engine is no better for weighing 30 cwt. than for weighing 10 cwt. A saucepan is required to have a certain diameter and a certain See also:depth in order that it may hold a certain bulk of liquid: its weight is merely an encumbrance. Copper being 31 times as heavy as aluminium, whenever the latter See also:costs less than 31 times as much as copper it is actually cheaper. It must be remembered, too, that electrolytic aluminium only became known during the last See also: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. Much has yet to be learr}t about the See also:practical qualities of the electrolytic product, avid although every day's experience serves to place the metal in a firmer industrial position, a final See also:verdict can only be passed after the See also:lapse of time. The individual and collective See also:influence of the several impurities which occur in the product of the Heroult cell is still to seek, and the importance of this inquiry will be seen when we consider that if cast iron, wrought iron and steel, the three totally distinct metals included in the generic name of " iron "—which are only distinguished one from another chemically by See also:minute See also:differences in the proportion of certain non-metallic ingredients—had only been in use for a comparatively few years, attempts might occasionally be made to forge cast iron, or to employ wrought iron in the manufacture of edge-tools. (E. J. K J) Compounds of Aluminium. Aluminium oxide or alumina, AI203, occurs in nature as the mineral corundum (q.v.), notable for its hardness and abrasive power (see See also:EMERY), and in well-crystallized forms it constitutes, when coloured by various metallic oxides, the See also:gem-stones, See also:sapphire, See also:oriental See also:topaz, oriental See also:amethyst and oriental See also:emerald. Alumina is obtained as a white amorphous powder by heating aluminium hydroxide. This powder, provided that it has not been too strongly ignited, is soluble in strong acids; by ignition it becomes denser and nearly as hard as corundum; it fuses in the oxyhydrogen See also:flame or electric arc, and on cooling it assumes a crystalline form closely resembling the mineral See also:species. Crystallized alumina is also obtained by heating the fluoride with See also:boron trioxide; by fusing aluminium phosphate with sodium sulphate; by heating alumina to a dull redness in hydrochloric acid gas under pressure; and by heating alumina with lead oxide to a See also:bright red heat. These reactions are of See also:special See also:interest, for they culminate in the production of artificial See also:ruby and sapphire (see GEMS, ARTIFICIAL).
Aluminium Hydrates.—Several hydrated forms of aluminium oxide are known. Of these hydrargillite or gibbsite, Al(OH)3, See also:diaspore, A1O(OH), and bauxite, Al2O(OH)4, occur in the mineral See also:kingdom. Aluminium See also:hydrate, Al(OH)3, is obtained as a gelatinous white precipitate, soluble in potassium or sodium hydrate, but insoluble in ammonium chloride, by adding See also:ammonia to a cold solution of an aluminium salt; from boiling solutions the precipitate is opaque. By drying at ordinary temperatures, the hydrate AI(OH)3•H20 is obtained; at 300° this yields AlO(OH), which on ignition gives alumina, Al203: Precipitated aluminium hydrate finds considerable application in See also:dyeing. Soluble modifications were obtained by See also:Walter Crum (Journ. Chem. See also:Soc., 1854, vi. 216), and See also: Trans., 1861, p. 163); the first named decomposing aluminium acetate (from lead acetate and aluminium sulphate) with boiling water, the latter dialysing a solution of the basic chloride (obtained by dissolving the hydroxide in a solution of the normal chloride) Both these soluble hydrates are readily coagulated by traces of a salt, acid or alkali; Crum's hydrate does not combine with dye-stuffs, neither is it soluble in excess of acid, while Graham's compound readily forms lakes, and readily dissolves when coagulated in acids. In addition to behaving as a basic oxide, aluminium oxide (or hydrate) behaves as an acid oxide towards the strong bases with the formation of aluminates. Potassium aluminate, K2Al204, is obtained in solution by dissolving aluminium hydrate in caustic potash; it is also obtained, as crystals containing three molecules of water, by fusing alumina with potash, exhausting with water, and crystallizing the solution in vacuo. Sodium aluminate is obtained in the manufacture of alumina; it is used as a See also:mordant in dyeing, and has other commercial applications. Other aluminates (in particular, of iron and magnesium), are of frequent occurrence in the mineral kingdom, e.g. See also:spinel, gahnite, &c. Salts of Aluminium.—Aluminium forms one series of salts, derived from the trioxide, Al203. These exhibit, in certain cases, marked crystallographical and other analogies with the corresponding salts of See also:chromium and ferric iron. Aluminium fluoride, AlF3, obtained by dissolving the metal in hydrofluoric acid, and subliming the residue in a current of hydrogen, forms transparent,. very obtuse rhombohedra, which are insoluble in water. It forms a series of double fluorides, the most important of which is cryolite (q.v.); this mineral has been applied to the commercial preparation. of the metal (see above). Aluminium chloride, AiCla, was first prepared by Oersted, who heated a mixture of carbon and alumina in a current of chlorine, a method subsequently improved by Wohler, Bunsen, Deville and others. A purer product is obtained by heating aluminium turnings in a current of dry chlorine, when the chloride distils over. So obtained, it is a white crystalline solid, which slowly sublimes just below its melting point (r94°). Its vapour density at temperatures above 750° corresponds to the formula AICI3; below this point the molecules are associated. It is very hygroscopic, absorbing water with the See also:evolution of hydrochloric acid. It combines with ammonia to form AlC13.3NH3; and forms double compounds with See also:phosphorus peutachloride, phosphorus oxychloride, See also:selenium and See also:tellurium chlorides, as well as with many metallic chlorides; sodium aluminium chloride, AlC13•NaCl, is used in the production of the metal. As a synthetical agent in organic chemistry, aluminium chloride has rendered possible more reactions than any other substance; here we can only mention the classic syntheses of See also:benzene homologues. Aluminium bromide, AIBr3, is prepared in the same manner as the chloride. It. forms colourless crystals, melting at 90°, and boiling at 265°-270°. Aluminium iodide, A113, results from the interaction of See also:iodine and aluminium. It forms colourless crystals, melting at 185°, and boiling at 36o°. Aluminium sulphide, Al2S3, results from the See also:direct See also:union of the metal with sulphur, or when carbon disulphide vapour is passed over strongly heated alumina. It forms a yellow fusible mass, which is decomposed by water into alumina and sulphuretted hydrogen. Aluminium sulphate Al(SO4)3, occurs in the mineral kingdom as keramohalite, Al2(SO4)3.18H20, found near volcanoes and in alum-shale; aluminite or websterite is a basic salt, Al2(SO4)(OH)4.7H2O. Aluminium sulphate, known commercially as " concentrated alum" or " sulphate of alumina," is manufactured from kaolin or china clay, which, after roasting (in order to oxidize any iron present), is heated with sulphuric acid, the clear solution run off, and evaporated. Alum cake " is an impure product. Aluminium sulphate crystallizes as Al2(SO4)3.18H20 in tablets belonging to the See also:monoclinic system. It has a sweet astringent See also:taste, very soluble in water, but scarcely soluble in See also:alcohol. On heating, the crystals lose water, swell up, and give the anhydrous sulphate, which, on further heating, gives alumina. It forms double salts with the sulphates of the metals of the alkalis, known as the alums (see ALUM). Aluminium nitride (See also:AIN) is obtained as small yellow crystals when aluminium is strongly heated in See also:nitrogen. The nitrate, Al(NO3)3, is obtained as deliquescent crystals (with 8H20) by evaporating a solution of the hydroxide in nitric acid. Aluminium See also:phosphates may be prepared by precipitating a soluble aluminium salt with sodium phosphate. See also:Wavellite Als(PO4)3(OH),5.oH2O, is a naturally occurring basic phosphate, while the gem-stone See also:turquoise (q.v.) is Al (PO4) (OH)3•H2O, coloured by traces of copper. Aluminium silicates are widely diffused in the mineral kingdom, being present in the commonest See also:rock-forming minerals (felspars, &c.), and in the gem-stones, topaz, See also:beryl, See also:garnet, &c. It also constitutes with sodium silicate the mineral lapis-lazuli and the pigment See also:ultramarine (q.v.). Forming the basis of all clays, aluminium silicates See also:play a prominent part in the manufacture of pottery and porcelain. Additional information and CommentsThere are no comments yet for this article.
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