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Ceramic powder material mainly consists of silicon nitride wherein the content of oxygen combined with generally unavoidable impurities as measured by activation analysis accounts for less than 2% by weight. The above-mentioned ceramic powder material can also be prepared preferably by the method wh

Ceramic powder material mainly consists of silicon nitride wherein the content of oxygen combined with generally unavoidable impurities as measured by activation analysis accounts for less than 2% by weight. The above-mentioned ceramic powder material can also be prepared preferably by the method which comprises the step of heating raw ceramic powder material mainly consisting of silicon nitride to 1,400°C. to 1,900°C. in the presence of a separately prepared nonsintered molding of ceramic material or sintered molding of ceramic material having a porosity of at least 10%.

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A ceramic powder material consisting essentially of silicon nitride powder consisting essentially of from 0.05 to 2.5% by weight of aluminium and from 0.4 to 8.0% by weight of yttrium, in which all or a part of the yttrium contained in the silicon nitride powder is present in the form of a crystalli

A ceramic powder material consisting essentially of silicon nitride powder consisting essentially of from 0.05 to 2.5% by weight of aluminium and from 0.4 to 8.0% by weight of yttrium, in which all or a part of the yttrium contained in the silicon nitride powder is present in the form of a crystalline compound of silicon nitride and yttrium oxide and in which the total oxygen content WO (% by weight) as measured by activation analysis falls within the range expressed by the following formula denoting the relationship between the content of aluminium WAl (% by weight) and the content of yttrium WY (% by weight): [Figure] [Figure]