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 method. The supported membrane system consisted of an alumina support, two intermediate alpha-Al2O3 layers, and a top alumina membrane. The theta- to alpha-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 higher theta- to alpha-Al2O3 transformation temperature than the unsupported one. A similar effect was observed for microstructures of the membranes. We explained their transformation-temperature difference with a stress generated in the supported top membrane using a theoretical approach. (C) 1999 Elsevier Science S.A. All rights reserved.