GB579098A - Refractories - Google Patents

Abstract

In a refractory composition, synthetic crystalline magnesium orthosilicate is formed in the interstices between the grains of an acid, basic, or neutral refractory material, e.g. silica, magnesia, or chrome ore, by the interaction of finely-divided magnesia and silica. The magnesia in the magnesia-silica mixture may be slightly in excess of the amount required for correct synthesis of the magnesium orthosilicate in order to correct impurities in the other materials. The basic refractory material is ground to less than 4.0 mm. size, and dust below 0.1 mm., and preferably below 1.0 mm. is removed. The magnesium orthosilicate components should either or both be of amorphous nature and of particle-sizes of 0.01-0.005 mm. for the magnesia and 0.002-0.0005 mm. for the silica. The magnesia is preferably that collected by electrostatic precipitation from the flue gases from the production of dead-burned magnesite, while the silica may be that obtained from the exhaust gases produced in the production of ferro-silicon by the reduction of quartz by carbon in the presence of steel scrap, or by the reoxidation of silicon vapour obtained in the reduction of silica by carbon at high temperatures. The mixture of the components of the composition is pressed to shape, air-dried and heated to remove moisture and, if necessary, to dehydrate any hydrated magnesium silicates in the material, and then heated to the temperature of reaction of the magnesia and silica but below the point of fusion of the components. According to examples: (a) 60-85 parts of dead-burned magnesia are mixed with 40-15 parts of the magnesia-silica mixture containing 4 parts of magnesia to 3 of silica, and 1-4 per cent of a temporary binder such as a solution of magnesium sulphate or chloride is added, the mixture being used as a ramming-mixture or being pressed to shape under 1000 or, preferably 5000-10,000 lbs. per square inch and burnt at 1400-1600 DEG C.; (b) 60-80 parts of olivine rock may be used in place of the magnesia, an excess of magnesia being used with the silica to convert any iron oxide to p magnesium ferrite; (c) 70-85 parts of chrome ore are used and 4 per cent of kaolin is added to increase crushing strength. The Specification as open to inspection under Sect. 91 states also that in certain cases an excess of silica may be used in the magnesia-silica mixture. This statement does not appear in the Specification as accepted.