. Nature . rced to conclude that the silicon must have crystallisedwith the carbide. It has long been known that on dissolving grey ferro-silicon containing even 6 per cent, silicon the silicagelatinises, whereas when the silicon approaches 10 percent, much of the silica remains in a dense form. It isalmost certain that during the solidification of the greypart of Mr. Hoggs pig iron a rich silicon cementite musthave primarily formed, for the high carbon would notallow the formation of any primary silico-austenite ; whenthis cementite decomposed the silicide part of it wouldbecome diluted with
. Nature . rced to conclude that the silicon must have crystallisedwith the carbide. It has long been known that on dissolving grey ferro-silicon containing even 6 per cent, silicon the silicagelatinises, whereas when the silicon approaches 10 percent, much of the silica remains in a dense form. It isalmost certain that during the solidification of the greypart of Mr. Hoggs pig iron a rich silicon cementite musthave primarily formed, for the high carbon would notallow the formation of any primary silico-austenite ; whenthis cementite decomposed the silicide part of it wouldbecome diluted with the iron of the decomposed was, no doubt, this diluted solid solution in the coldgrey metal which yielded the gelatinous silica. That silicon does diffuse into iron, even at relativelylow temperature, was proved by Lebeau. He found thatfree silicon and iron, when heated together in vacuo at960° C, chemically combine, a fact I have fullv con-iirmrd, although it is impossibleto get silicon to com-. FiG. 7.—An Iron^Carbon-Silicon Alloy, free from Phosphorus, made more stable by Sulphur. Groken-up £,tructure in the centre=the euteclic of two cementites, silico-cariiide and carbide. Half-tone=lhe carbide cementile. Dark area=decomposed eutectic. Light portion at right lower corner= crystallite of silico-pearlite. bine with iron on heating them together in a cementationfurnace where oxidising gases have access to the silicon. To determine whether silicide of iron would diffuse intoand precipitate the graphite in white iron, a sample ofcrushed white iron free from impurities, containing 35per cent, of carbon, was with 10 per cent, byweight of a silicon alloy containing 20 per cent, of silicon( = Fe,Sij, also in powder. The mixture, after compressionin a short piece of iron tube, was heated for two hoursat 1000° C. in an atmosphere of hydrogen gas, and wasthen removed and cooled in air. For comparison, a portion of the crushed white ironwas treated in the same wa
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