REACTIVITY OF THERMALLY OXIDIZED AND UNOXIDIZED SIC PARTICULATES WITH ALUMINUM SILICON ALLOYS

The reactivity of unoxidized and thermally oxidized SiC particulates with Al-Si alloys was investigated. The composites were fabricated by means of pressure infiltration, and had a particle volume fraction of around 0.58. The silicon content was varied in the range 0-8 wt.%. The particulates were characterized by means of thermal programmed desorption, thermal programmed reactions, scanning electron microscopy and IR absorption, and their oxidation was followed by means of weight gain techniques, adsorption isotherms and X-ray diffraction. The extent of the reaction was determined by means of optical microscopy and differential thermal analysis. The results for unoxidized SiC agree with those of previous studies in the sense that increasing the silicon content of the alloy retards the reaction between aluminium and SiC. However, those for oxidized SiC indicate that once aluminium has reacted with the oxide to produce aluminia, the direct reaction between aluminium and silicon carbide proceeds at a pace similar to that found for unoxidized SiC. However, optical microscopy shows that the morphologies and spatial distributions of the aluminium carbide produced in the reaction are different in the two cases.