Basic Research on Technology Development for Sintered Ceramics
Abstract
Pure silicon nitride powder is prepared by calcination of the reaction product obtained from SiH4 and anhydrous NH3 at 600 C and above. It is amorphous up to 1480 degrees and converts to alpha-Si3N4 above this temperature. Hot-pressing at 5 GPa at 1500 C and above yields dense specimens of near theoretical density and up to 3000 kg/sq m Knoop microhardness (200 g load). Annealing at 1750 C does not induce grain growth. Hot-pressing under nominal conditions up to 1800 C does not bring about appreciable densification. Exposure of compacts to various atmospheres at 1400-1800 C causes specific surface area reduction and weight loss but no densification. The weight loss is related to specific surface area. Both weight loss and coarsening is related to thermal decomposition of Si3N4. Selected non-oxide additions, on the 1-2% level, permit the attainment of nearly theoretical density in Si3N4 by hot-pressing at 1750- 1800 C and sintering at 1800-2000 C. Sintering was done under 8 MPa nitrogen pressure. The dense specimens are composed of beta-Si3N4 grains having a larger aspect ratio as the sintering temperature is increased.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1976
- Accession Number
- ADA038071
Entities
People
- Charles D. Greskovich
- Joseph H. Rosolowski
- Svante Prochazka
Organizations
- General Electric