Nanoporous α-Alumina Membrane Prepared by Anodizing and Heat Treatment

We investigated the optimum conditions for the fabrication of an a-alumina membrane by the anodizing and subsequent heat treatment of an anodic film after detachment from an aluminum substrate and through-hole treatment. We evaluated the nanoporous structure of anodic alumina including pore diameter, the regularity of pore array and the surface morphology with respect to the thermal deformation of the membrane during heat treatment under loading with ceramic plates. Because the regularity of the pore arrangement of the film formed by two-step anodizing was greatly improved compared with that of the film formed by one-step anodizing, the deformation caused by heat treatment was suppressed. To detach the anodic film from the substrate, an advanced anodic polarization method was better than the conventional cathodic polarization method with a stepwise decrease in anodizing voltage, because the through-hole treatment was accomplished in a shorter time. As a result, the combination of two-step anodizing and the detachment by anodic polarization process was suggested to be optimum. Thermogravimetry and differential thermal analysis indicated a weight loss of approximately 1% originating from dehydration during the temperature change from room temperature to 400 degrees C. Moreover, the desorption of oxalate anions from the alumina film occurred at 900 degrees C, associated with a weight loss of approximately 5% and the anodic alumina simultaneously crystallized from amorphous to gamma-alumina. Finally, the crystal structure transformed to a-alumina at 1250 degrees C. It was found that a crack-free alumina membrane that maintained straight channels similar to those of amorphous anodic alumina was successfully obtained. (C) The Electrochemical Society of Japan, All rights reserved.