SYNTHESIS OF SIMON CERAMICS FROM VARIOUS CLAYS AND DIFFERENT SOURCES OF CARBON

The preparation of beta-SiMONs by the thermal treatment (1373-1773 K) under nitrogen of various mixtures of clays and organic molecules (acrylonitrile) or carbon (charcoal) or graphitic oxide, was investigated. Cation (Na+, Y3+, C6-amine+) exchanged smectites (montmorillonite or hectorite) and kaolinite were used. With charcoal mixtures, a threshold of carbon content was found for each clay in the formation of beta-SiMONs: 23% for montmorillonite, 14% for hectorite and 21% for kaolinite. This threshold was not reached in the case of polyacrylonitrile or graphitic oxide smectite precursors and carboreduction under nitrogen of these precursors did not yield beta-SiMONs. The thermal evolution of the carbon phases at low temperature, before contact with clays, influenced the formation of beta-SiMONs which appears at 1673 K if the carbon content is greater than the threshold, but always with other minor phases.