Electrostatic separation of CVD ultra-fine particles at high temperature

The feasibility of electrostatic precipitation above 500°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 (SiCl₄+NH₃)/N₂ gas system at 1200°C. This process produces NH₄Cl as solid particles at normal temperature, as a by-product. The high-temperature electrostatic precipitation method should collect only the Si₃N₄ particles directly from the reaction gas stream because the sublimation temperature of NH₄Cl is about 340°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 NH₄Cl particles were collected at 500°C