Electrostatic separation of CVD ultra-fine particles at high temperature

The feasibility of electrostatic precipitation above 500 degrees C was demonstrated for separation of ultrafine particles synthesized by thermally activated CVD (chemical vapor deposition) directly from the reaction gas stream. Silicon-nitride particles were prepared from a (SiCl/sub 4/+NH/sub 3/)/N/sub 2/ gas system at 1200 degrees C. This process produces NH/sub 4/Cl as solid particles at normal temperature, as a by-product. The high-temperature electrostatic precipitation method should collect only the Si/sub 3/N/sub 4/ particles directly from the reaction gas stream because the sublimation temperature of NH/sub 4/Cl is about 340 degrees C. An electrode system for corona discharge that can generate a stable corona discharge even in the reaction gas atmosphere at high temperature was developed. X-ray diffraction analysis shows that no NH/sub 4/Cl particles were collected at 500 degrees C.<>