The influence of temperature and time on the AlN powder hydrolysis reaction products

The influence of hydration temperature and ageing time on the formation of crystalline phases found after the AlN powder hydrolysis was investigated. The AlN hydrolysis behavior was observed by measuring the pH of the suspension, whereas for the characterization of the reaction products XRD, SEM and TEM analyses were employed. The starting temperature, from RT up to 90 °C and the ageing time, from 10 min to 24 h, have an impact on the reaction products and their morphology. After prolonged time of the AlN reaction with water, the only crystalline product is bayerite at RT. At elevated temperatures the very first solid reaction product is pseudoboehmite, transforming to crystalline boehmite and part of it dissolving and recrystallizing to bayerite with ageing time. At temperatures above 80 °C, boehmite is the predominant crystalline phase, nevertheless, after long time of ageing in the mother liquor, even at these temperatures the boehmite → bayerite conversion was observed.