Diffusion of SiC Composites Fabricated by Si-Vapor Reactive Infiltration Process

摘要

Although the thermal stability of graphite facilitates its widespread use in crucibles and molds for high temperatures processes, graphite has weak molecular forces in its c axis, and its carbon atoms are easily detached from its pores and outer surfaces. These detached carbon atoms are a source of dust during fabrication, eventually lowering the effective product yield. We employ Si vapor infiltration to fabricate SiC composites in order to reduce the problems related to dust scattering. The Si and C atomic percentages of the fabricated SiC composites are carefully measured, and the diffusion law is used to estimate the diffusion coefficient of Si vapor in order to understand the diffusion process of the Si vapor infiltration. The least squares method is then used to obtain a quadratic equation form the results of the experiment, and the diffusion coefficient of the Si vapor is estimated using this quadratic equation. An Si concentration at 20 mu m over the diffusion depth from the graphite surface fits the quadratic equation well. These results show that the diffusion length obtained using the Si vapor infiltration method is about 11.5 times longer than that obtained using liquid Si. This longer diffusion length clearly indicates that Si vapor infiltrates porous graphite deeper than Si liquid, thus drastically reducing the problems related to carbon dust.