Sinterable Powders from Laser Driven Reactions
Annual rept. no. 3, 1 Jul 1979-30 Jun 1980
MASSACHUSETTS INST OF TECH CAMBRIDGE ENERGY LAB
Pagination or Media Count:
Extremely fine, uniform ceramic powders have been synthesized from SiH4, NH3 and C2H4 gas phase reactants that are heated by absorbing optical energy emitted from a CO2 laser. Resulting Si, Si3N4 and SiC powders have been characterized in terms of parameters which are important for densification processes. They are virtually ideal. The spherical particles typically have mean diameters from 120 to 1000 A. The standard deviation is typically 25-45 and the diameter of the largest observed particle is typically less than twice that of the smallest particle. Purities are extremely high. The laser heated process has been modeled in terms of fluid flow and heat transfer criteria. Many fundamental property measurements were made to provide data for these calculations. The process is extremely efficient, approximately 95 of the SiH4 is reacted in a single pass through the laser beam and approximately 2 kwhr. of energy are required per kilo of Si3N4. The resulting powders have been processed into dense pieces using several shaping techniques. The Si powders were densified to precisely controlled levels designed to yield high density reaction bonded silicon nitride RBSN. Nitriding kinetics were rapid at low temperatures because of the small particle sizes. Characteristic dimensions of RBSN microstructures approximated the initial particle dimensions. Sintering experiments with pure Si3N4 powder gave indications that densification occurred on a local scale.
- Lasers and Masers
- Ceramics, Refractories and Glass