GB446106A - Electrical insulator and method of making the same - Google Patents

Abstract

A composition suitable for sparking-plug insulation consists of a sintered mass containing at least 30 per cent of alumina, not more than 60 per cent of magnesia, with or without silica up to 25 per cent, the amount of magnesia being at least sufficient to form forsterite with all the silica present, and spinel with any alumina in excess of 40 per cent. Specified compositions are 12,5 per cent of silica, 36,4 per cent of magnesia, and 51,1 per cent of alumina, corresponding to 30 per cent of forsterite, and 70 per cent of spinel, and 7,5 per cent of silica, 40 per cent of magnesia, and 52,5 per cent of alumina, corresponding to 17,5 per cent of forsterite, 73,1 per cent of spinel, and 9,4 per cent of periclase. The second of these examples has a higher coefficient of expansion and retains its electrical insulating quality at a higher temperature, but has less mechanical strength than the first. As raw materials, magnesium carbonate, oxide, hydrate, brucite, talc, serpentine, spinel, rumpfite, iron-free chlorites, and bauxite, diaspore, corundum, fused alumina, silimanite, clay, may be employed. These may be ground and used raw, or fined or fused, for the body batch. This is ground, moulded, and sintered.