Alumina Sentence Examples
Marggraf demonstrated that alumina was another constituent.
Aluminium, when pure and kept out of contact with siliceous matter, is only oxidized at a white heat, and then very slowly, into alumina, Al 2 O 3.
The term clay is often used by chemists to denote hydrated silicate of alumina (Al 2 O 3 2SiO 2.2H 2 O), of which kaolin or china clay is a fairly pure form.
The reduction is not due to electrolysis, but to the action of carbon on alumina, a part of the carbon in the charge being consumed and evolved as carbon monoxide gas, which burns at the orifice in the cover so long as reduction is taking place.
Filtration in the chemical laboratory is commonly effected by the aid of a special kind of unsized paper, which in the more expensive varieties is practically pure cellulose, impurities like feric oxide, alumina, lime, magnesia and silica having been removed by treatment with hydrochloric and hydrofluoric acids.Advertisement
Many of the oceanic islets are composed of coral limestone, which in this way becomes phosphatized; others are igneous, consisting of trachyte or basalt, and these rocks are also phosphatized on their surfaces but are not so valuable, inasmuch as the presence of iron or alumina in any quantity renders them unsuited for the preppration of artificial manures.
Verneuil succeeded in imparting a sapphire-blue colour to artificial alumina by addition of i 5% of magnetic oxide of iron and o.
Chromium sesquioxide is a basic oxide, although like alumina it acts as an acid-forming oxide towards strong bases, forming salts called chromites.
In the later years of his life he applied himself to the problem of obtaining alumina in the crystalline form, and succeeded in making rubies identical with the natural gem not merely in chemical composition but also in physical properties.
Besides a large number of animal and vegetable substances, many precipitates formed in the course of inorganic chemical reactions are non-crystalline and appear in the colloidal state, instances are the sulphides of antimony and arsenic and the hydroxides of iron and alumina.Advertisement
The matter was carefully investigated, and it was found that the sulphate of magnesia in the sea-water has a decomposing action on Portland cements, especially those which contain a large proportion of lime or even of alumina.
But to ensure the permanence of structures in sea-water the great object is to choose a cement containing as little lime and alumina as possible, and free from sulphates such as gypsum; and more important still to proportion the sand and stones in the concrete in such a way that the structure is practically non-porous.
Guyton de Morveau suggested that this base should be called alumine, after Sel alumineux, the French name for alum; and about 1820 the word was changed into alumina.
In 1808 Sir Humphry Davy, fresh from the electrolytic isolation of potassium and sodium, attempted to decompose alumina by heating it with potash in a platinum crucible and submitting the mixture to a current of electricity; in 1809, with a more powerful battery, he raised iron wire to a red heat in contact with alumina, and obtained distinct evidence of the production of an iron-aluminium alloy.
He next devised a plan for manufacturing pure alumina from the natural ores, and finally elaborated a process and plant which held the field for almost thirty years.Advertisement
Kaolin thus seems to be the best ore, and it would undoubtedly be used were it not for the fatal objection that no satisfactory process has yet been discovered for preparing pure alumina from any mineral silicate.
If, according to the present method of winning the metal, a bath containing silica as well as alumina is submitted to electrolysis, both oxides are dissociated, and as silicon is a very undesirable impurity, an alumina contaminated with silica is not suited for reduction.
Antrim, and have the advantage of being near the coast, so that the alumina can be transported by water-carriage.
The American bauxites contain from 38 to 67% of alumina, from 1 to 23% of ferric oxide, and from 1 to 32% of silica.
The French bauxites are of fairly constant composition, containing usually from 58 to 70% of alumina, 3 to 15% of foreign matter, and 27% made up of silica, iron oxide and water in proportions that vary with the colour and the situation of the beds.Advertisement
Alumina itself is so refractory that it cannot be melted save by the oxyhydrogen blowpipe or the electric arc, and except in the molten state it is not susceptible of decomposition by any chemical reagent.
The first successful idea of using electricity depended on the enormous heating 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 smelt alumina electrically except in presence of copper, so that the Cowles furnace yielded, not the pure metal, but an alloy.
It was soon discovered that the faculty of inducing dissociation possessed by the current might now be utilized with some hope of pecuniary success, but as electrolytic currents are of lower voltage than those required in electric furnaces, molten alumina again became impossible.
Molten cryolite dissolves roughly 30% of its weight of pure alumina, so that when ready for treatment the solution contains about the same proportion of what may be termed "available" aluminium as does the fused double chloride of aluminium and sodium.Advertisement
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 chlorine, and to exclude iron from the finished metal, either the alumina must be pure or the chloride be submitted to purification.
In order to prepare pure alumina, bauxite and sodium carbonate were heated in a furnace until the reaction was 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.
The residue, consisting of alumina and potassium sulphate, was leached with water to separate the insoluble matter which was dried as usual.
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 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 looo C. to convert it into a crystalline oxide which is less hygroscopic than the former amorphous variety.
By 1888 Hall was at work on a commercial scale at Pittsburg, reducing German alumina; in 1891 the plant was removed to New Kensington for economy in fuel, and was gradually enlarged to 150o h.p.; in 1894 a factory driven by water was erected at Niagara Falls, and subsequently works were established at Shawenegan in Canada and at Massena in the United States.
In 1895 the British Aluminium Company was founded to mine bauxite and manufacture alumina in Ireland, to prepare the necessary electrodes at 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, remodelled to suit modern requirements.
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.
As a part of the voltage is consumed in the latter 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.
The operation is essentially a dissociation of alumina into aluminium, which collects at the cathode, and into oxygen, which combines with the anodes to form carbon monoxide, the latter escaping and being burnt to carbon dioxide outside.
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.
Alumina is obtained as a white amorphous powder by heating aluminium hydroxide.
Crystallized alumina is also obtained by heating the fluoride with 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 bright red heat.
Potassium aluminate, K 2 Al 2 0 4, 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 mordant in dyeing, and has other commercial applications.
Aluminium chloride, AlC1 3, 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.
Aluminium sulphide, Al2S3, results from the direct 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, 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.
On heating, the crystals lose water, swell up, and give the anhydrous sulphate, which, on further heating, gives alumina.
Of these the silica and alumina are chiefly those which the gangue of the ore and the ash of the fuel introduce, whereas the lime is that added intentionally to form with these others a slag of the needed physical properties.
This silt consists largely o alumina (about 48%) and calcium carbonate (18%) with smalle quantities of silica, oxide of iron and carbon.
Cements of the Portland type differ in kind from those of the pozzuolanic class; they are not mechanical mixtures of lime and active silica ready to unite under suitable conditions, but consist of definite chemical compounds of lime and silica and lime and alumina, which, when mixed with water, combine therewith, forming crystalline substances of great mechanical strength, and capable of adhering firmly to clean inert material, such as stone and sand.
The commonest of such substances in England are chalk and clay, but where local conditions demand it, limestone, marl, shale, slag or any similar material may be used, provided that the correct proportions of lime, silica and alumina are maintained.
Thus the silica may range from 19 to 27%, the alumina and ferric oxide jointly from 7 to 14%, the lime from 60 to 67%.
All such variations are permissible provided that the quantity of silica and alumina is sufficient to saturate the whole of the lime and to leave none of it in a "free" condition, likely to cause the cement to expand after setting.
The function of the ferric oxide present in ordinary cement is little more than that of a flux to aid the union of silica, alumina and lime in the clinker; its role in the setting of the cement is altogether secondary.
It contains but little alumina and oxide of iron, which are the constituents generally necessary to bring about the union of silica and lime to form a cement, but in spite of this the silica is so finely divided and so well distributed that it unites readily with the lime when the limestone is burned at a sufficiently high temperature.
English hydraulic limes are of a different class; they contain a good deal of alumina and ferric oxide, and in composition resemble somewhat irregular Portland cement.
The high percentage of alumina causes the cement to be quick-setting, and it becomes hard in about five minutes.
Alumina is treated at works near Foyers in the shire of Inverness, where abundant water power enables electricity to be generated cheaply.
The metals, which by combination with oxygen became oxides, were antimony, silver, arsenic, bismuth, cobalt, copper, tin, iron, manganese, mercury, molybdenum, nickel, gold, platinum, lead, tungsten and zinc; and the "simple earthy salifiable substances" were lime, baryta, magnesia, alumina and silica.
The operation is finished when all the sodium sulphide has been converted into normal sodium carbonate, partly also into acid sodium carbonate (bicarbonate) NaHCO 3; at the same time a precipitate is formed, consisting of ferrous sulphide, alumina and silica, which is removed by another settling tank, and the clear liquor is now ready either for boiling down in a " fishing-pan " for the manufacture of white soda-ash, or for the process of causticizing.
In another research dealing with the nature of alum he showed that one of the constituents of that substance, alumina, is contained in common clay, and further that the salt cannot be prepared by the action of sulphuric acid on alumina alone, the addition of an alkali being necessary.
It is certain, however, that the finer-grained rocks are richest in alumina, and in combined water; hence the inference is clear that kaolin or some other hydrous aluminium silicate is the dominating constituent.
Alumina is high in the finer clays (18 to 30%), and they are the most aluminous of all sediments, except bauxite.
Some clays, however, such as fireclays, contain very little potash or soda, while they are rich in alumina; and it is a fair inference that hydrated aluminous silicates, such as kaolin, are well represented in these rocks.
There are, in fact, a few clays which contain about 45% of alumina, that is to say, more than in pure kaolin.
Among such substances are fireclay and firebricks, certain sandstones, silica in the form of ganister, and Dinas stone and bricks, ferric oxide and alumina, carbon (as coke and graphite), magnesia, lime and chromium oxide - their relative importance being indicated by their order, the last two or three indeed being only of limited use.
Alumina as a refractory material is chiefly used in the form of bauxite, but its applications are somewhat special.
In the Paris Exhibition of 1878 bricks very hard and dense in character, said to be of pure alumina, were exhibited by Muller & Co.
The latter, especially when brought to the burning point at a high temperature, produces a heat that can be resisted by the most refractory substances only, such as silica, alumina and magnesia.
Made from clay, ceramics or refractory concrete consisting of pumice or kiln burnt aggregate bonded with high alumina cement.
This is known to be the optimum conditions for the doped alumina.
The white storage elements consist of a highly heat resistant material based on special fused alumina which has very high heat capacity and conductivity.
Two patents have been granted on the manufacture of low dielectric loss alumina.
Alumina substrates can also be used to produce chemically stable, strongly hydrophobic surfaces.
The high signal to noise ratio in alumina fluorescence spectra is not achieved in the true Raman spectra developed by other types of ceramic.
For cables, one approach is to incorporate a high proportion of fire retardant filler such as alumina trihydrate.
For example, at first he represented ferrous and ferric oxides by the formulae Fe02, Fe03, and by the analogy of zinc and other basic oxides he regarded these substances as constituted similarly to Fe02, and the acidic oxides alumina and chromium oxide as similar to FeO 3.
It follows, therefore, except for 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.
Aluminium oxide or alumina, Al 2 0 3, occurs in nature as the mineral corundum, notable for its hardness and abrasive power (see Emery), and in well-crystallized forms it constitutes, when coloured by various metallic oxides, the gem-stones, sapphire, oriental topaz, oriental amethyst and oriental emerald.
The sandstones commonly contain grains of felspar - a complex silicate of alumina and an alkaline base.
The oxide is a black or brown powder according as it is prepared from the exalate or sulphate, and when pure it is non-fluorescent, but mixed with gadolinia or alumina it possesses this property.
The precipitated alumina is filtered off, the filtrate evaporated and the ammonium salt of the acid purified by recrystallization.
The precipitate, after having been collected and washed, is digested with a warm concentrated solution of ammonium carbonate, which dissolves the uranium as a yellow solution of ammonium uranate, while the hydrated oxide of iron, the alumina, &c., remain.
Alumina and lime, for example, which cannot be reduced at ordinary furnace temperatures, readily give up their oxygen to carbon in the electric furnace, and then combine with an excess of carbon to form metallic carbides.
The impossibility of working with just sufficient carbon to reduce the alumina, without using any excess which would be free to, ix.
A sheet iron case is then placed within the furnace, and the space between it and the walls rammed with limed charcoal; the interior is filled with fragments of the iron or copper to be alloyed, mixed with alumina and coarse charcoal, broken pieces of carbon being placed in position to connect the electrodes.
Webster patented an improved process for making alumina, and the following year he organized the Aluminium Crown Metal Co.