C - Chemistry – Metallurgy – 04 – B
Patent
C - Chemistry, Metallurgy
04
B
261/1
C04B 35/58 (2006.01) C04B 35/597 (2006.01)
Patent
CA 1200257
A B S T R A C T METHODS OF FORMING CERAMIC MATERIALS AND CERAMIC PRODUCTS, AND CERAMIC MATERIALS AND CERAMIC PRODUCTS FORMED THEREBY. 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,A1)12 (0.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-oxidising atmosphere at a temperature of 1700°C to 1900°C so as to produce (1) a dense ceramic product consisting essentially of beta-phase substituted silicon nitride having the general formula Si6-zA1zN8-z0z, 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,A1)12(0.N)16 and a minor amount of a further phase containing said modifying cation M. The ceramic powder is preferably produced by effecting a first stage nitriding by heating a powder mixture comprising silicon, aluminium alumina and an oxide or nitride of a modifying cation in a nitriding atmosphere at a temperature below the melting point of aluminium until said first stage nitriding is substantially complete; effecting a second stage nitriding by heating the first stage nitrided mixture at a temperature below the melting point of silicon whilst maintaining a nitriding atmosphere until the second stage nitriding is substantially complete whereby a friable material is produced; and subsequently sintering the comminuted friable product at a temperature between 1650°C and 1900°C whilst maintaining a non-oxidising atmosphere to obtain a friable ceramic material including more than 50% by weight of an alpha-phase substituted silicon nitride obeying the formula Mx(Si,A1)12(0.N)l6, where x is not greater than 1 and M is the modifying cation, or a friable ceramic material including greater than 50% by weight of a mixture of said alpha-phase substituted silicon nitride and a beta phase substituted silicon nitride of the formula Si6-zA1zN8-z0z, where z is greater than zero and not greater than 1.5.
422470
Butler Edwin G.
Szweda Andrew
Lucas Industries Public Limited Company
Marks & Clerk
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