Modeling of CVD Coating Inside Agglomerate of Fine Particles.

The coating of ultra-fine particles inside their agglomerates was performed by chemical vapor deposition. Mathematical models are adopted to describe the internal deposition process by chemical reaction and interparticle diffusion, and the porous structural change with the deposition progress. The effects of kinetic, diffusional and agglomerate-geometrical and structural parameters are analyzed for the radial distribution of the deposit. The experimental deposition profiles for the coating of Si3N4 ultra-fine particles with AlN are quantitatively compared with simulated ones for different reaction temperatures and agglomerate sizes. As a result, uniform deposition of AlN is proven to be obtained at comparatively low temperature with small loosely packed agglomerates.