Highly efficient and stable radio-frequency — thermal plasma system for the production of ultrafine and ultrapure β-SiC powder

Abstract

A new radio-frequency (r.f.) thermal plasma system has been developed that overcomes both the low power efficiency and the unstable plasma commonly used. The key features of this system are the application of all solid type r.f. power supply units and the superposition of a small r.f. — plasma on a main r.f. — plasma. A high power efficiency of 75% was obtained with the all solid type r.f. power supply units of 30 kW–3 MHz set. The main plasma used for preparing ultra fine β-SiC powder was operated stably by the superposition of a small plasma, which worked as the ignitor and the stabilizer of a main plasma. This new system, that is, the dual r.f. — torch system, has been used to produce ultrafine and ultrapure β-SiC powder. Pure phase of β-SiC powder in the range of 10 to 50 nm was prepared from the stoichiometric reactant composition of CH₄ and SiH₄. The reaction mechanism was also discussed based on the plasma diagnostics.