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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, See also: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
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See also:Bunsen
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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
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Deville accordingly returned to pure See also:chemistry and invented a practicable method of preparing sodium which, having a See also:lower atomic See also:weight than potassium, reduced a larger proportion
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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
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See also:
See also:Bauxite is a hydrated oxide of aluminium of the ideal See also:composition, Al203.2H20
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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
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The chief Irish deposits are in the neighbourhood of Glenravel, Co
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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
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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
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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
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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
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Before the application of electricity, only two compounds were found. suitable for reduction to the metallic state
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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
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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
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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
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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
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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
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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
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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
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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: |