GB710562A - Improvements in or relating to the production of ceramic compositions - Google Patents

Abstract

A process for the production of a ceramic material comprises forming a mixture of alumina and chromic oxide, adding thereto a quantity of carbon sufficient to react with part or all of the chromic oxide to reduce it to chromium metal, and subjecting the mixture to heat treatment, which may be effected at sub-atmospheric pressure, at a temperature at which the carbon and chromic oxide react to reduce all or part of the chromic oxide to chromium metal. The mixture of alumina and chromic oxide and carbon may be prepared by mixing and grinding the ingredients or by co-precipitating the hydroxides of aluminium and chromium, heating the hydroxides to convert them to the corresponding oxides and mixing the oxides with carbon or by forming a solid solution of the oxides and pulverizing and mixing it with carbon. The proportions in the mixture are adjusted to yield a fired material which consists of a solid solution of alumina with up to 5 per cent. of its weight of chromic oxide and a proportion of metallic chromium which is 10 to 70 per cent. and preferably 10 to 50 per cent. by weight of the product. The mixture may also contain up to 5 per cent. of one or more of the oxides of silica, iron, magnesium, calcium or zirconium. Specification 676,441 is referred to.