The role of additives in the densification of nitrogen ceramics. Annual report no. 2 (final)
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.
- Research Organization:
- Newcastle upon Tyne Univ. (UK)
- OSTI ID:
- 6527745
- Report Number(s):
- AD-A-116581/0
- Country of Publication:
- United States
- Language:
- English
Similar Records
{beta}-SiAlON-silicon nitride multilayered composites
Process for preparing a densified beta-phase silicon nitride material having at least one densification aid, and the material resulting therefrom
Related Subjects
360201* -- Ceramics
Cermets
& Refractories-- Preparation & Fabrication
ADDITIVES
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CERAMICS
CHALCOGENIDES
CHEMICAL PROPERTIES
CRYSTAL STRUCTURE
DENSITY
FABRICATION
HOT PRESSING
MATERIALS WORKING
MECHANICAL PROPERTIES
NITRIDES
NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PNICTIDES
PRECIPITATION
PRESSING
SEPARATION PROCESSES
SHRINKAGE
SILICON COMPOUNDS
SILICON NITRIDES
SILICON OXIDES
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
YTTRIUM OXIDES