Calcination and associated structural modifications in boehmite and their influence on high temperature densification of alumina

A systematic study is reported on the calcination of boehmite and its associated structural changes, and their effect on densification features. Boehmite precursor gels have been calcined in the temperature range 250–1200 °C. The associated structural changes are identified by FTIR and XRD. The specific surface area measurements indicated a relatively high value of 169 m2/g for boehmite calcined at 400 °C; this value reduced to 4 m2/g on calcination at 1200 °C. In the temperature range 400–1000 °C, the coordination of aluminium changes from a quasioctahedral to a tetrahedral nature, which reverts to octahedral at 1200 °C. The precursor containing γ-alumina gives a 92.1% theoretical density, on sintering at 1500 °C due to the highly unstable quasioctahedral coordination. Boehmite precursors calcined at 400 °C and 1000 °C produced a density of 88.2% and 96.9%, respectively, in the sintered compact at 1500 °C. Boehmite calcined to α-alumina (1200 °C) possesses an octahedral structure having a density of 97.6% at 1500 °C.