Silicon

“ Silicon, in the form of silicic acid and its compounds, is a fundamental constituent of all varieties of glass, and in this form is in no sense a colouring substance; on the other hand, there is no doubt that under some conditions silicon may be reduced to the metallic state at temperatures which normally occur in glass-furnaces, and it is practically certain, that if present in glass in this condition, silicon would colour the glass. ”

“ Silicon hydride, SiH4, is obtained in an impure condition, as a spontaneously inflammable gas, by decomposing magnesium silicide with hydrochloric acid, or by the direct union of silicon and hydrogen in the electric arc. ”

“ If the vapor of silicon follows the general rule—that the density of gases is in proportion to their atomic weights—then it was but a fraction heavier than oxygen, and therefore not far below it in the atmospheric strata. The unceasing commotion of the elements would soon have brought this first cloud-mist of silicon into contact with oxygen, to which it has a strong affinity under high heat. Oxidized, and in molten drops of silica, or crystals of quartz, this new-formed material commenced its descent toward the centre of gravity—the first creation from the primordial elements. ”

“ The simple oxidation of silicon develops an enormous quantity of heat, very much more than the combustion of carbon; a heat which is sufficient to refine the metal in the retorts of iron and steel works without the addition of carbon. Silicon, which in nature has passed wholly into the state of silicic acid, or been burned, must, at the moment of its combination with oxygen, have been the cause of an intense heating both in our own globe and in the other stars, which are also composed of silicates. ”

“ In a free state silicon is also a non-volatile, slightly energetic non-metal, like carbon. Therefore the form and nature of the compounds of carbon and silicon are very similar. In addition to this resemblance, silicon presents one exceedingly important distinction from carbon: namely, the nature of the higher degree of oxidation. That is, silica, silicon dioxide, or silicic anhydride, SiO2 is a solid, non-volatile, and exceedingly infusible substance, very unlike carbonic anhydride, CO2, which is a gas. This expresses the essential peculiarity of silicon. ”

“ These facts seem to indicate that nitrogen plays a part in the transportation of the silicon, as this is only prevented by the same means made use of in order to prevent the passage of nitrogen.
3. The volatility of free silicon at a high temperature is too slight to account for the alteration of the platinum at a distance. This can be shown by placing several decigrammes of crystallized silicon on the bottom of a small crucible of retort carbon, covering the silicon with a small flat disk of retort carbon upon which is placed the slip of platinum. ”

“ Amorphous silicon is produced, like aluminium, by decomposing the double fluoride of sodium and silicon (sodium silicofluoride) by means of sodium: Na2SiF6 + 4Na = 6NaF + Si. By treating the mass thus obtained with water the sodium fluoride may be extracted and the residue will consist of brown, powdery silicon. In order to free it from any silica which might be formed, it is treated with hydrofluoric acid. This silicon powder is not lustrous; when heated it easily ignites, but does not completely burn. It fuses when very strongly heated, and [102] has then the appearance of carbon. ”

“ It is a non-conductor of electricity, is unaffected by nitric or sulphuric acid, but dissolves readily in hydrofluoric acid, and in a warm solution of caustic potash. It burns with great brilliancy when heated in air or oxygen, and becomes converted into silica, which, owing to the great heat of combustion, fuses, and thus forms a superficial crust over the unburnt silicon. A crystalline variety of silicon may also be procured by heating the brown amorphous silicon, already described, intensely in a platinum crucible, with exclusion of air. ”

“ Silicon and its oxide, silica, find important applications in the manufacture of iron and steel. Silicon, like manganese, is an important constituent of many steels, the alloy ferrosilicon being added to deoxidize and purify the metal and thus to increase its tensile strength. Like titanium, it is added chiefly for its curative effect rather than as a useful ingredient. On an average 4 pounds of 50 to 55 per cent ferrosilicon are used in the United States for each ton of steel produced. ”

“ Or, if it were conceded that silicon ever formed the surface of the earth, then all other materials of what is now the crust must have been gases above it; and, as nine-tenths of the elements in vapor are heavier than oxygen—many of them more than ten times as heavy—this gas could never have even touched this imaginary sea of silicon. The oxidation, then, was only possible in the regions of the atmosphere where oxygen existed and abounded. There only among the free-moving gases could the incalculable amount of heat evolved in the combination be carried off. ”

“ Silicon and rate of cooling are the two most powerful influences but presence of certain elements other than silicon also influences to some extent the degree of hardness. However, while silicon has a strong softening effect, manganese and sulphur have an opposite or hardening tendency. ”

“ When the experiment is performed in the fluorspar tube, the gaseous fluoride may be collected over mercury. The gas fumes strongly in the air, and is instantly decomposed by water.
Silicon.—The reaction between fluorine and silicon is one of the most beautiful of all these extraordinary manifestations of chemical activity. The cold crystals become immediately white-hot, and the silicon burns with a very hot flame, scattering showers of star-like, white-hot particles in all directions. If the action is stopped before all the silicon is consumed, the residue is found to be fused. ”

“ When required, the analysis is best made on the ignited residue, and separately reported as "analysis of the insoluble portion."
Silicon only occurs in nature in the oxidised state; but the oxide generally known as silica (SiO2) is common, being represented by the abundant minerals—quartz, flint, &c. Silica, combined with alumina, lime, oxide of iron, magnesia and the alkalies, forms a large number of rock-forming minerals. Most rock masses, other than limestones, contain over 50 per cent. of silica. The following are analyses of some of the commoner silicates ”

“ It is very remarkable that silicon decomposes carbonic anhydride at a white heat, forming a white mass which, after being treated with potassium hydroxide and hydrofluoric acid, leaves a very stable yellow substance of the formula SiCO, which is formed according to the equation, 3Si + 2CO2 = SiO2 + 2SiCO. It is also slowly formed when silicon is heated with carbonic oxide. It is not oxidised when heated in oxygen. A mixture of silicon and carbon when heated in nitrogen gives the compound Si2C2N, which is also very stable. ”

“ Carbon, which gives the compounds CH4, and CO2, belongs to the fourth group of elements. The nearest element to carbon is silicon, which forms the compounds SiH4 and SiO2; its relation to carbon is like that of aluminium to boron or phosphorus to nitrogen. As carbon composes the principal and most essential part of animal and vegetable substances, so is silicon almost an invariable component part of the rocky formations of the earth's crust. Silicon hydride, SiH4, like CH4, has no acid properties, but silica, SiO2, shows feeble acid properties like carbonic anhydride. ”

“ The compound which is in excess in all granite rocks is silica, the oxide of the element silicon. The varieties are formed chiefly by small percentages, more or less, of the oxides, alumina, and magnesia. This silica, or quartz, as well as the other components of the igneous rocks, is what has been termed "burnt material." It is the product of a most complete and tremendous conflagration; for the oxidation of silicon is as much and as powerful a combustion as the oxidation or burning of coal. ”

“ Silicon, especially when crystalline, like graphite and charcoal, does not in any way act on the above-mentioned acids. It forms black, very brilliant, regular octahedra having a specific gravity of 2·49; it is a bad conductor of electricity, and does not burn even in pure oxygen (but it burns in gaseous fluorine) . The only acid which acts on it is a mixture of hydrofluoric and nitric acids; but caustic alkalis dissolve in it like aluminium, with evolution of hydrogen, thus showing its acid character. In general silicon strongly resists the action of reagents, as do also boron and carbon. ”

“ As the iron oxide is stirred into the molten metal laboriously by the workman or “puddler” with his hook or “rabble,” it oxidizes the silicon to silica and the phosphorus to phosphoric acid, and unites with both these products, forming with them a basic iron silicate rich in phosphorus, called “puddling” or “tap cinder.” It oxidizes the carbon also, which escapes in purple jets of burning carbonic oxide. ”

“ The iron and the silicon revert to their oxides while the hydrogen of the water is set free. The French "silikol" method consists in treating silicon with a 40 per cent. solution of soda.
Another source of hydrogen originating with the electric furnace is "hydrolith," which consists of calcium hydride. Metallic calcium is prepared from lime in the electric furnace. Then pieces of the calcium are spread out in an oven heated by electricity and a current of dry hydrogen passed through. The gas is absorbed by the metal, forming the hydride (CaH2) . ”

“ If we continue this sub-division further, the molecule of sand separates itself into its chemical constituents, consisting of silicon on the one side, and oxygen on the other. Thus we arrive at last at the smallest body which can call itself silicon, and the smallest which can call itself oxygen, and we have no reason to suppose that either of these is capable of sub-division into something else, since we regard oxygen and silicon as elementary or simple bodies. ”

“ Silicon is always considered as a non-essential element, although it occurs in such large proportions in some plants as to indicate that it cannot be wholly useless. It accumulates in the stems of plants, chiefly in the cell-wall, and has sometimes been supposed to aid in giving stiffness to the stems. ”

“ The result of the application has been, that phosphorus has been converted from an enemy into a friend, and aids in producing and maintaining the temperature that is needed. Silicon is also useful as a combustible, and in preventing the metal from becoming honeycombed by escaping gases while solidifying. This it does by combining with oxygen and preventing the latter substance from combining with carbon and forming a gaseous product. ”

“ The white powdery precipitate is silica (SiO2) , and its weight, multiplied by 100, and divided by the weight of ore taken, gives the percentage of silica in the sample. Where the percentage of silicon is wanted, which is very rarely the case, it is got by multiplying this result by 0.4667. It is always necessary to examine the purity of the body weighed as silica. ”

“ Silicon, so far as we know, behaves to metals pretty much like carbon, but our knowledge of facts is limited. What is known as cast iron is essentially an alloy of iron proper with 2 to 6% of carbon and more or less of silicon (see Iron) . Alloys of copper and silicon were prepared by Deville in 1863. The alloy with 12% of silicon is white, hard and brittle. ”

“ In many respects it resembles silicon; it does not fuse when heated, and even oxidises with difficulty, but liberates hydrogen when fused with potash. When fused with silica it liberates silicon. With carbon in the electrical furnace it forms ZrC2, with hydrogen it gives ZrH2 (like CaH2, Winkler, Vol. I., p. 621) ; hydrochloric and nitric acids act feebly on it, but aqua regia [148] easily dissolves it. It is distinguished from silicon by the fact that hydrofluoric acid acts on it with great facility, even in the cold and when diluted, whilst this acid does not act on silicon at all. ”

“ The anhydrous acid is not known, since on evaporating the aqueous solution it gradually decomposes into silicon fluoride and hydrofluoric acid.
Silicon chloride, SiCl4, was prepared by J. J. Berzelius (Jahresb., 1825, 4, p. 91) by the action of chlorine on silicon, and is also obtained when an intimate mixture of silica and carbon is heated in a stream of chlorine and the products of reaction fractionated. It is a very stable colourless liquid which boils at 58° C. Oxygen only attacks it at very high temperatures. ”

“ The part of the aluminium remaining in the metallic state dissolves the silicon, and the latter separates from the solution on cooling in a crystalline form. The excess of aluminium after the fusion is removed by means of hydrochloric and hydrofluoric acid. The best silicon crystals are obtained from molten zinc; 15 parts of sodium silicofluoride are mixed with 20 parts of zinc and 4 parts of sodium, and the mixture is thrown into a strongly heated crucible, a layer of common salt being used to cover it ”

“ Silicon seems to be the most kindly element to use, and it is claimed that a content of silicon as high as 20 is not injurious; some people claim that it is beneficial. That it does help materially in the production of sound steel there can be no doubt, and if such steel meets all of the requirements of the engineer and of practice it would seem to be wise not to place the upper limit for silicon so low as to prevent its sufficient use in securing soundness. ”