A process for the preparation of a air setting refractory material on the basis of silica

摘要

Refractories having a basis of silica are prepared by mixing a silica rock which has a substantially constant coefficient of thermal expansion between 900-1300 DEG C. e.g. silcrete or quartzite, with burnt magnesia and/or millscale (Fe3O4), phosphoric acid of specific gravity not less than 1,60 and water, 2,8% of magnesia and/or millscale based on the weight of silica and 2-15% of phosphoric acid is used based on the combined weight of silica, and magnesium and/or millscale the total liquid added being from 2-20%. The proportion of acid to magnesia and/or millscale is such that there is no substantial excess of acid over that required to form monobasic phosphates. The silica, magnesia and/or millscale is preferably graded, the magnesia having a particle size of 5-150m and the millscale a particle size of 2-150m . Up to 30% of the total silica content may be calcined silica which is added to give a very small firing expansion. When the composition is to be used in contact with metals e.g. iron or steel, the acid-metal reaction is reduced by the incorporation of inhibitors e.g. sulphonated coal tar products or mixtures of tertiary amines derived from coal tar bases. The composition may be used as a ramming mix i.e. the silica and magnesia and/or millscale are mixed and gauged on site with the aqueous phosphoric acid and rammed into place, or it may be used as a castable composition when the damp mixture is cast into moulds and naturally or artificially air dried.