Microwave plasma characteristics of a circulating fluidized bed-plasma reactor for coating of powders

Coating of powders by Plasma-CVD is an adequate way to protect particles from environmental attack or to provide a large catalytic surface on carrier particles. The μ-SLAN® microwave plasma source is placed into the riser of a circulating fluidized bed, and its performance as a particle-coating reactor is evaluated for silicon oxide deposition on glass beads. Fluctuations of the particle concentration reduce the efficiency of MW coupling. The minimum MW input power for stable plasma generation is 4 times higher in the presence of particles and increases with oxygen partial pressure. The temperature of the entrained particles can be adjusted to very low values, but higher temperatures are achieved near the MW-coupling slots. The conversion ratio of HMDSO only depends on the specific power (P/F). It is slightly lower with particles and 5 W/sccm are required for 80% conversion.