GB474038A - Improvements in or relating to refractory materials - Google Patents

Abstract

Refractory articles are made by firing a mixture of coarse granules (not less than ,3 mm. in diameter) of material rich in magnesium orthosilicate and fine material (not more than ,2 mm. in diameter) consisting of at least 75 per cent of another refractory or mixtures of refractories; the fine material should preferably be free from magnesium orthosilicate or from substances which form magnesium orthosilicate on firing. The proportion of coarse granular material may be 10-80 per cent; when using the larger proportions of coarsely granular material a porous product is obtained and it is preferable to use low moulding pressures. The coarse granules, which are preferably angular and graded and have diameters of 1-10 mm. may consist of synthetic magnesium orthosilicate or minerals such as olivine; the raw materials, especially those containing considerable proportions of magnesium hydrosilicate such as serpentine, are preferably precalcined. Subordinate amounts of other coarse granular material, e.g. chromite or sintered or dead burnt magnesite may be incorporated in the mix. The fine material is preferably one which possesses good resistance against chemical attack and may be magnesium oxide preferably the crystalline varieties, sintered or dead burnt magnesite, caustic magnesite, chromite, chromium sesquioxide, zirconium oxide, zirconium silicate e.g. zircon, talc, soapstone, steatite, asbestos or natural or synthetic chromium spinel; certain mixtures of these fine materials are specified for special purposes. Alternatively, there may be used mixtures of substances which form by mutual reaction on firing the fine materials specified above, e.g. mixtures of chromium sesquioxide and magnesium oxide which on heating form chromium spinel. Small proportions of other materials may be incorporated in the mix, e.g. ceramic binders such as binding clay, bentonite, caustic magnesia, lime, borates; moistening liquids such as water, aqueous solutions of alkali silicates or magnesium chloride, or waste cellulose liquor; mineralizers such as fluorides of sodium, calcium or magnesium; pulverized hard substances such as silicon carbide; and materials such as gum or dextrin. Specification 441,516 is referred to.