Volatile products formed by carboreduction and nitridation of clay mixtures with silica and elemental silicon

Abstract

Simultaneous carboreduction and nitridation (CRN) of clays provides a useful route for the preparation of low-cost β-sialon powders. During the course of the CRN reaction at 1400–1450 °C, mass losses of ca. 10% in excess of the theoretical amounts are typically found. This discrepancy is mainly due to transport of gaseous SiO from the reactants into the N₂–CO gas stream, followed by condensation in the cooler parts of the furnace system. In this work, the condensed material lost from the reacting system was collected under controlled conditions, and its constitution studied by ²⁷Al and ²⁹Si magic-angle spinning nuclear magnetic resonance (MAS NMR) and complementary X-ray powder diffraction (XRD). Predictions from thermodynamic calculations of the various possible gas-phase reactions are compared with the observed results.