PROCESS FOR THE PREPARATION OF POWDER FOR OPTICALLY TRANSPARENT CERAMIC MADE OF GAMMA-ALUMINIUM OXYNITRIDE AND THE POWDER OBTAINED THEREOF

摘要

The process consists in reacting aluminium nitride with alpha -alumina and with an alumina with a high specific surface or a precursor which generates an alumina with a high specific surface. More precisely, the process consists in mixing the aluminium nitride, the alpha -alumina and the alumina with a high specific surface or the precursor of such an alumina, in drying the said mixture, in heating the said mixture at a temperature sufficient to obtain a gamma -aluminium oxynitride powder and then in grinding the powder thus obtained. The agglomerated gamma -aluminium oxynitride powder is characterised in that the porosity of the agglomerate is greater than 75%. The ground gamma -aluminium oxynitride powder is characterised in that 100% of the particles have a size of less than 10 mu m and in that it has a transmittance of at least 8% measured at 2500 cm-1 on a KBr disc with a thickness of 0.9 mm containing 3.33% of gamma -aluminium oxynitride.