STRUCTURAL-CHANGES INDUCED BY ULTRASOUND DURING AGING OF THE BOEHMITEPHASE

Structural changes induced by ultrasound during the aging of the alumi num monohydroxide (boehmite) were studied by means of X-ray diffractio n (XRD) and nitrogen adsorption. The BET surface area and the pore vol ume of the ultrasound stimulated hydroxide (HU) are about 40% less tha n those of the non-stimulated one (HS). The mean pore size practically does not change, while the mean crystallite size (L) is about 25% gre ater in the HU system. The increase of L alone is not enough to accoun t for the surface area diminution, suggesting that the sonication also induces compaction by elimination of some porosity. The sonication of the precursor hydroxide does not seem to play an apparent role in the structural properties of the resulting calcinated gamma-alumina. (C) 1997 Elsevier Science B.V.