METHOD OF FORMING CERAMIC MATERIALS AND CERAMIC PRODUCTS, AND CERAMIC MATERIALS AND CERAMIC PRODUCTS FORMED THEREBY

摘要

A method of producing a dense ceramic product comprises the steps of mixing a ceramic powder containing a major proportion of an alpha-phase substituted silicon nitride obeying the formula Mx(Si,Al)12 (O,N)16, where x is not greater than 2 and M is a modifying cation (e.g. yttrium, calcium, lithium, magnesium, cerium) with at least one nitride of silicon and/or alumina wherein the alumina represents not more than 10% by weight of the mixture; and sintering the mixture in a non-oxidizing atmosphere at a temperature of 1700 DEG C. to 1900 DEG C. so as to produce (1) a dense ceramic product consisting essentially of beta-phase substituted silicon nitride having the general formula Si6-zAlzN8-zOz, where z is greater than zero and not greater than 1.5, and 0.05% wt to 20% wt of a further phase containing said modifying cation M, or (2) a dense ceramic product consisting essentially of said beta-phase substituted silicon nitride a 0.05% wt to 90% wt of an alpha-phase substituted silicon nitride obeying said formula Mx(Si,Al)12(O,N)16 and a minor amount of a further phase containing said modifying cation M.