Fabrication and characterization of novel anodic alumina membranes

The objective of this work was to develop a novel approach to fabricate model membranes of well-defined and well-characterized morphology. The focus of the project was an electrochemical process involving anodic oxidation of high purity aluminum sheets to form porous aluminum oxide films.; Alumina films were prepared by anodizing high purity (99.0% and 99.999%) aluminum sheets using sulfuric acid and phosphoric acid solutions. Current density, temperature, and electrolyte concentration were selected depending on the nature of each electrolyte. From scanning electron micrographs of film cross-sections, the rate of growth of alumina films was observed to be higher when sulfuric acid was used as the anodizing electrolyte than when phosphoric acid was used.; The growth kinetics of porous anodic alumina films formed in phosphoric acid under galvanostatic conditions were studied. Scanning electron microscopy, Faraday's law and oxide film mass measurements were used to analyze the growth kinetics and to obtain film growth rates, pore density, and porosity.; Relationships between anodization conditions and morphological parameters were developed. The effect of current density and solution temperature on the oxide film growth rate and morphology was examined. The rate of growth of the alumina film was found to increase with an increase in current density and decrease with an increase in temperature. The pore density was found to decrease with an increase in current density and with a decrease in temperature. The porosity and the average cross-sectional pore area of the films were found to increase with anodization time and decrease with an increase of current density and temperature. By assuming a conical pore geometry, other morphological parameters such as the average pore size and the surface area of pores can be determined.; Porous films were formed under controlled conditions of concentration and temperature. Single layer films with straight non-intersecting pores of uniform pore size and multi-layer films of different pore size and pore density in each layer were prepared by changing electrolyte type or current density during anodization. These films were separated as membranes from the oxide barrier layer and the unoxidized aluminum using a voltage reduction scheme that did not affect the integrity of the porous structure. Membranes with pre-determined morphology were fabricated.; Diffusion measurements and water flow measurements were used to characterize the fabricated membranes. These techniques were used to compare the measured diffusive and hydraulic permeabilities of the membrane to that predicted using the morphological parameters which were obtained using the quantitative relationships developed from the analysis of the electrochemical process. Close agreement between experimental and predicted permeabilities was observed.