Compositional and structural characterization of alumina coatings deposited electrochemically on stainless steel

Alumina is widely employed as support of noble-metal automotive exhaust catalysts.With a view to practical use in catalytic converters, an electrochemical method for deposition of Al2O3 coatings on thin foils of stainless steel was developed. The coatings were deposited from AlCl3 diluted in alcohol solutions. The deposition experiments were performed under voltostatic regime at different voltages ranging from 1 to 45 V. Varying the forming voltage, the optimal deposition regime for obtaining uniform alumina coatings with a good adhesion to the stainless steel substrate was established. As-deposited coatings and coatings annealed in air to different temperatures were studied by SEM and XPS. The coatings deposited at 1–10 V were found to be homogeneous with a microstructure characterized by small (75–150 nm) compacted spherical microaggregates. The best alumina coatings obtained have a thickness of up to 6 mm and a specific surface area of 25– 30 m2/g. At higher voltages (U > 10 V), the deposited layers became discontinuous and formed an extensive network of interconnected surface cracks. # 2004 Elsevier B.V. All rights reserved