INFLUENCE OF METHANE ON THE NITRIDING GAS REDUCTION OF KAOLINITE

A new synthesis of beta'-SiAlON via the reduction and nitridation of a luminosilicates in the presence of a carbon source by a hydrogen-nitro gen gas mixture is presented. The formation of beta'-SiAlON on surface s (SiC, alumina) devoid of carbon was found to be impossible. Thermogr avimetric analysis and mass spectrometry showed that, in a carbon cruc ible, methane was formed from the reaction of hydrogen with carbon. Be ta'-SiAlON was obtained in the absence of free carbon by adding a smal l amount of methane to the hydrogen-nitrogen gaseous mixture. The form ation of beta'-SiAlON is thus the consequence of reduction by methane rather than by hydrogen. Parasitic reactions of hydrogen lead to silic on elimination as SiO in the gas phase, and to a Si/Al ratio lower tha n in the starting kaolinite.