Abstract: An oxide barrier coating for reinforcing fiber is provided with a preselected microstructure and thickness through control of the concentration of metal salt in heat decomposable form as a precursor of metal oxide. In one form, the salt is a metal oxyhalide salt such as zirconium oxyhalide or halfnium oxyhalide. Fibers, such as ones of alumina, aluminasilicate or silicon carbide, having the coating of the invention are especially useful as reinforcing fibers for reinforced ceramic matrix composites.

Abstract: 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 M.sub.x (Si,Al).sub.12 (O,N).sub.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.degree. C. to 1900.degree. C. so as to produce (1) a dense ceramic product consisting essentially of beta-phase substituted silicon nitride having the general formula Si.sub.6-z Al.sub.z N.sub.8-z O.sub.z, 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.