Abstract: A method for making essentially crack free large cross section ceramic articles by injection molding techniques comprises the use of from about 0.1 v/o to about 10 v/o fibers with the ceramic injection molding formulation followed by the injection molding, binder removal and densification steps to form an essentially crack free densified large cross section ceramic article. The fibers are softened prior to the onset of densification and incorporated into the ceramic intergranular phase. This process eliminates the component distortion during densification which would have occurred if the fibers remained in the component.

Abstract: A method of producing crack free ceramic parts having large cross-sections is disclosed. An initial mixture of ceramic powder containing a binder and from 0.1 v/o to 10 v/o of whiskers or fibers which are made of carbon, graphite or high temperature melting or decomposition point organic polymers. The mixture is either injection molded or slip cast to form a shaped article. The shaped article is heated in a nitrogen atmosphere to a temperature of 450.degree. C. and then in an atmosphere of air at a temperature of 450.degree. C. to 600.degree. C. to completely remove the binder. The resulting binderless shaped article is then heated at 800.degree. C. for a period of time sufficient to completely remove the whiskers or fibers from the shaped articles. The article is then encapsulated in glass and hot isostatically pressed at a pressure of 30,000 psi to densify the article to approximately 99% of theoretical. The resulting article has a complex geometry and a large cross-section but without detrimental cracks.

Abstract: A process for making a homogeneous yttria-alumina doped silicon nitride article is described. A uniform coating of yttria and alumina is applied to the surface of silicon nitride particles by a chemical application of the hydroxides of yttrium and aluminum followed by drying and a subsequent conversion of the hydroxides to the corresponding oxides. The resulting powder is formed into an article and pressureless sintered to a density greater than 99% of theoretical.