Investigation of the displacement reaction in mixed AIN + TiO₂ powders

Abstract

Following previous work (reported in Part I) on the reactions within compacts of mixed AIN + TiO, particles, the effects of changing the effective nitrogen pressure imposed to the system are investigated. Either increasing it (to 102–103 atm) or decreasing it (to 10⁻²10⁻³ atm) is shown to somewhat simplify the overall chemical scheme while also having an influence upon the development of microstructures. At high PNz AIN is passively oxidized and TiO₂ is reduced to Ti₄O₇ or Ti₃O₅ with limited Al₂O₃ dissolution into them before they get nitrided into TiN. At low PNz AIN is actively oxidized with copious AI transport toward Ti oxides via the gas phase. Simultaneously, TiO₂ is reduced to Ti₂O₃ which can be nitrided therefrom. In all cases TiN is also formed on AIN particles, following gas-phase transport of molecular TiO. The kinetics of the overall process is not limited by AIN oxidation except at high applied N₂ pressures. Varying the initial relative AIN-TiO₂ composition from the basic 2:1.5 molar ratio brings about no novelty in the nature of solid phases being formed or in the general course of events in the temperature range investigated here, i.e. T< 1800 K.