STUDY OF THE REACTION CLAY-SI3N4-N-2 TO OBTAIN COMPOUNDS IN THE SI-AL-O-N SYSTEM

The study of the phases formed in the Si-Al-O-N system (Sialons) is ve ry important in the scientific and technological field. B' and O'-sial ons have interesting applications in ceramic due to their good propert ies at high temperatures. The main method to obtain these phases is th e reaction of mixtures of Si3N4, Al2O3, AlN and others Al and Si oxyni trides, at high temperature. There is an alternative method to obtain these compounds: the reaction of aluminosilicate and Si3N4. In this wo rk the reactions between clay and Si3N4 are studied. Two silicon nitri des were used in this work (commercial alpha-Si3N4 and a Si3N4 generat ed ''in situ''). The clay-Si3N4 reactions were studied using different clay/Si3N4 ratios, at temperatures in the range of 1400 to 1650 degre es C, using N-2 atmosphere. The reaction products were in the silicon- rich part of the Si-Al-O-N system. The principal crystalline phases ob tained were silicon-rich: O'- and B'-sialons. Mullite and silicon were detected in the samples treated at low temperatures and after reactio n times. During reaction a SiO2 loss was observed through SiO(g) volat ilization. This loss was monitored by weight measurements.