Accession Number : ADA116581

Title :   The Role of Additives in the Densification of Nitrogen Ceramics.

Descriptive Note : Annual rept. no. 2 (Final),


Personal Author(s) : Jack,K H

PDF Url : ADA116581

Report Date : Oct 1979

Pagination or Media Count : 97

Abstract : Densification of silicon nitride by either hot-pressing or pressureless sintering requires an additive which reacts with the surface silica and some of the nitride to give an oxynitride liquid that promotes shrinkage and, at the same time, the phase transformation from alpha to beta. Silicon nitride is densified by hot-pressing with scandia additive but theoretical density is not achieved by pressureless sintering. The kinetics of densification are interpreted in terms of a Kingery model with a slope of one-third for the solution-precipitation stage indicating that solution of alpha or precipitation of beta is rate-controlling. Sintering with equal weights of scandia and alumina gives improved densities. An important advantage over beta yttrium sialon is that the quaternary scandium oxynitride and glassy grain boundary phases do not undergo catastrophic oxidation at 1000 C.

Descriptors :   *Ceramic materials, *Nitrogen, *Density, *Additives, Silicon nitrides, Aluminum oxides, Yttrium oxides, Mechanical properties, Physicochemical properties, Hot pressing, Sintering, Crystal structure, Phase transformations, Precipitation, Catastrophic conditions, Oxynitrides, Silicon dioxide, Shrinkage

Subject Categories : Ceramics, Refractories and Glass

Distribution Statement : APPROVED FOR PUBLIC RELEASE