SYNTHESIS OF SILICON CARBIDE FROM MONTMORILLONITE-POLYACRYLONITRILE INTERCALATION COMPOUNDS BY CARBOTHERMAL REDUCTION.

To apply intercalation compounds as precursors for carbide production by carbothermal reduction, n-CH//3(CH//2)//nNH//3** plus -montmorillonite polyacrylonitrile (PAN) intercalation compounds (n equals 5, 11) were converted into SiC. For the comparison, montmorillonite-carbon mixtures were also applied to the conversion. They were heated at 1100-1600 degree C for 1 h in Ar. From the intercalation compound with n equals 5, both alpha - and beta -SiC were detected. beta -SiC formed by the treatments above 1200 degree C, while alpha -SiC was obtained on heating above 1300 degree C. As oxides, only the Mg-Al-O compound crystallized, and no Si-containing oxides formed. The same products were obtained from the intercalation compound with n equals 11. However, it showed the lower reactivity in spite of its larger carbon content. On the other hand, only beta -SiC formed as carbide by heating the montmorillonite-carbon mixtures above 1200 degree C. Silicates of mullite and cordierite were obtained in addition to spinel, the Mg-Al-O compound, and alpha -Al//2O//3. These observations suggest that the presence of PAN in the interlayer space strongly affected the carbothermal reduction process.