PHASE EVOLUTION OF ANDALUSITE (AL2O3-SIO2)-AL SYSTEM IN NITROGEN ATMOSPHERE

Phases of the Si-Al-O-N system are very important in the ceramic field . The reduction and simultaneous nitriding of aluminosilicate compound s permits the formation of alumina and sialons phases. Products of the se reactions depend on several variables such as temperature, reaction time, metallic Al content, etc. In this work, reactions of Al with an dalusite (Al2O3 . SiO2) in N-2 atmosphere were studied up to 1923 K. T he crystalline phases formed were followed as a Function of temperatur e, Al content and reaction time. Nitride phases were measured quantita tively using X-ray diffraction. Mullite and X-phase were formed during the reaction but the final products were mainly beta'-sialon and alph a-Al2O3. The aluminium acts as a reducing agent and silicon appears at low temperatures. The reaction mechanism was established by taking th e consideration of intermediate compounds, such as mullite and X-phase . Volatilization of SiO(g) took place during the reaction and was dete rmined by weight loss and electron probe microanalysis.