Thermal decomposition characteristics of boehmite gels under microwave heating and associated microstructural features

High temperature densification and associated microstructural features of alumina derived through sintering of microwave dehydroxylated boehmite are presented. alpha-alumina has been obtained through a series of transitional alumina phases within 60 min of exposure of boehmite eel to microwaves of 2.45 GHz and 600 W power. The phase formation has been identified by XRD. The surface al ea measurements on various gel samples exposed to microwaves at intermediate time intervals are also reported. The densification characteristics of microwave dehydroxylated gel precursors when sintered by conventional route resulted 95% of theoretical density at 1400 degrees C and an average grain size of 2 mu m. On the other hand, part of the same gel precursor conventionally dehydroxylated and sintered at 1400 degrees C resulted < 90% of density. The boehmite gel heated directly under microwaves reached > 97% theoretical density with very fine microstructure. Thus, the present study indicates the possibility of using low power microwaves for dehydroxylation of boehmite precursor gels to active phases which further can be sintered under conventional heating to dense, fine grained alumina. (C) 1998 Elsevier Science B.V.