Abstract: A high-toughness ceramic tool material consisting essentially of 50-95% by volume of a main sialon base phase wherein at least 10% by volume of the sialon base phase consists of alpha-sialon, and 5-50% by volume of a SiC whisker phase. This ceramic material is produced by sintering a composition comprising:50-95% by volume of a sialon forming component such that at least 10% by volume, calculated on the entire sialon, of alpha-sialon is formed, and5-50% volume of SiC whiskers;said sialon forming component consisting essentially of 50-95% by weight of Si.sub.3 N.sub.4 and 50-50% by weight of constituents of sialon-consistituting elements other than Si.sub.3 N.sub.4,said constituents consisting of a mixture of AlN and Al.sub.2 O.sub.3, and at least one oxide selected from the group consisting of oxides of yttrium and rare earth elements, said mixture of AlN and Al.sub.2 O.sub.

Abstract: A precombustion chamber provided with an arrangement for thermally insulating a cylinder head of an internal combustion engine from a combustion gas in the precombustion chamber comprising: (a) a hollow ceramic body which provides a precombustion chamber and is disposed within the hollow space for the precombustion chamber; (b) a hollow fitting member disposed surrounding the hollow ceramic body within the hollow space for mitigating and absorbing the stress produced between the cylinder head and the hollow ceramic body; and (c) seal means for sealing a space between the hollow ceramic body and the fitting member to provide a closed space therebetween, wherein said hollow fitting member is tightly secured to the hollow ceramic body through the seal means.