Structural evolution of alumina membrane prepared on an alumina support using a sol-gel method

We prepared supported and unsupported alumina membranes using a sol-gel met hod. The supported membrane system consisted of an alumina support, two int ermediate alpha-Al2O3 layers, and a top alumina membrane. The theta- to alp ha-Al2O3 transformation in supported and unsupported alumina membranes was investigated using X-ray diffraction (XRD) and scanning electron microscopy . XRD patterns showed that the supported membrane had a 100 degrees C highe r theta- to alpha-Al2O3 transformation temperature than the unsupported one . A similar effect was observed for microstructures of the membranes. We ex plained their transformation-temperature difference with a stress generated in the supported top membrane using a theoretical approach. (C) 1999 Elsev ier Science S.A. All rights reserved.