Silica refractories are those materials consisting of >93 percent silica, SiO_2, in one form or another. In its crystalline form it possesses quite unique hot strength properties leading to its use in furnace crowns and superstructures. The amorphous form, commonly called fused silica, has excellent thermal shock properties leading to it being used in a variety of hot insertion applications. Raw materials The most common raw material for this type of silica is quartzite rock, normally consisting of an irregular mosaic of quartz crystals cemented together by a deposit of colloidal silica. There are deposits throughout the world having varying properties with some more suited than others for silica brick manufacture. Generally, it is the proportion and dispersion of the impurities which determines the suitability of the rock for subsequent use as a raw material. The typical impurities are alumina and ferric oxide.
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