Influence of methane on the nitriding gas reduction of kaolinite

Abstract

A new synthesis of β′-SiAION via the reduction and nitridation of aluminosilicates in the presence of a carbon source by a hydrogen–nitrogen gas mixture is presented.

The formation of β′-SiAION on surfaces (SiC, alumina) devoid of carbon was found to be impossible. Thermogravimetric analysis and mass spectrometry showed that, in a carbon crucible, methane was formed from the reaction of hydrogen with carbon. β′-SiAION was obtained in the absence of free carbon by adding a small amount of methane to the hydrogen-nitrogen gaseous mixture. The formation of β′-SiAION is thus the consequence of reduction by methane rather than by hydrogen. Parasitic reactions of hydrogen lead to silicon elimination as SiO in the gas phase, and to a Si/Al ratio lower than in the starting kaolinite.