The effect of the reaction conditions on the morphology of coating layers of alumina hydrate on silicon carbide whiskers

Abstract

Alumina hydrate-coated silicon carbide whiskers were prepared by a raw material injection method, which has already prepared several kinds of composite particles in an aqueous media by a similar manner with the fluidized bed coating method. This method injects the raw material for the coating layers into a precipitant solution in which the core particles are already dispersed to obtain the objective composite particles. In this study, the effect of the reaction conditions on the morphology of the coating layers was investigated. From the results, the surfaces were smoother under the following reaction conditions: higher silicon carbide whisker concentration, lower aluminum nitrate concentration, lower aluminum nitrate solution injection rate, higher partial pressure of carbon dioxide and lower reaction temperature. The coating process was considered to include a homogeneous nucleation and coalescence process, which had a significant effect on the surface morphology of the coating layer. From these conditions, a lower probability of collision between the particles grown from the homogeneous nuclei and a higher probability of collision between the particle from the homogeneous nuclei and the whiskers were considered to produce a smoother coating layer on the whiskers.