Improvements in and relating to ceramic electric insulating materials

Abstract

Abstract Electric insulating-material is made by firing a mixture of 80-95 per cent of a magnesium compound or compounds other than asbestos, and 5-20 per cent of bentonite or a mixture of clay and bentonite, with an alumina content not exceeding 7 per cent. The magnesium compound or compounds may be partly replaced by another mineral or minerals but with the exclusion of felspar, e.g. quartz, zirconium oxide, zirconium earth, titanium oxide, rutile, cerium oxide, corundum, sillimanite, beryl, zinc oxide, baryta, limestone, bone ash and apatite. Magnesium minerals specified are magnesite, talcum, forsterite, periclase and magnesium hydroxide. It is stated that if the articles made will be subjected to considerable changes of temperature it is of advantage to prefire part of the mixture and then add it to the remainder in the form of coarse meal. The Provisional Specification also refers to the use of brucite and nemalite as suitable magnesium compounds.

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