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

Abstract

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 degrees C. The associated structural changes are identified by FTIR and XRD. The specific surface area measurements indicated a relatively high value of 169 m(2)/g for bochmite calcined at 400 degrees C; this value reduced to 4 m(2)/g on calcination at 1200 degrees C. In the temperature range 400-1000 degrees C, the coordination of aluminium changes from a quasioctahedral to a tetrahedral nature, which reverts to octahedral at 1200 degrees C. The precursor containing gamma-alumina gives a 92.1% theoretical density, on sintering at 1500 degrees C due to the highly unstable quasioctahedral coordination. Boehmite precursors calcined at 400 degrees C and 1000 degrees C produced a density of 88.2% and 96.9%, respectively, in the sintered compact at 1500 degrees C. Boehmite calcined to a-alumina (1200 degrees C) possesses an octahedral structure having a density of 97.6% at 1500 degrees C.