THE FORMATION AND REACTIVITY OF ALUMINUM NITRIDE AND RELATED MATERIALS

Abstract

The preparation and properties of aluminium nitride are reviewed with special reference to the newer production methods and fabrication techniques. Information so far available on the sintering of materials is summarised. For nitrides the sintering is influenced by additives or impurities such as oxides formed by partial hydrolysis and oxidation. Resistance to oxidation is increased by sintering and hot-pressing the refractories. The kinetics and products of oxidation of nitrides so far studied depend mainly on the intrinsic reactivity of the material and available surface at which oxidation can occur. In the present research conditions are investigated for preparing aluminium nitride from ammonium hexafluoroaluminate, The x-ray characteristics and the thermal stability of a new compound, ^-AlP^ are established. Attempts to study the kinetics of the commercial methods of aluminium nitride formation are summarised. The reactivity of aluminium nitride is examined by correlating changes in phase composition, surface area, crystallite and aggregates sizes with hydrolysis and oxidation time and temperature. The kinetics and rates of reaction are influenced by the crystallite and aggregate sizes of the aluminium nitride , by differences in type of crystal structure, by the molecular volume of the oxide products, and by fluoride additives. Ageing and sintering of the aluminas are additional factors. The activation energy of the oxidation of aluminium nitride in air is determined as 53 k.cals/mole.