Table of Contents
ISRN Corrosion
Volume 2013 (2013), Article ID 424805, 8 pages
http://dx.doi.org/10.1155/2013/424805
Research Article

One-Step Anodization/Sol-Gel Deposition of -Doped Silica-Zirconia Self-Healing Coating on Aluminum

International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad, Andhra Pradesh 500005, India

Received 5 September 2013; Accepted 8 October 2013

Academic Editors: M. Aparicio, G. Bereket, and M. Sakairi

Copyright © 2013 N. Kumar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

A novel process was used for the preparation of dense, thick, and stable silica-zirconia coatings on aluminum by an in situ anodization along with sol-gel deposition. Anodic electrophoretic deposition was carried on aluminum using a SiO2-ZrO2 sol that was synthesized from an epoxy modified silane and zirconium n-propoxide along with a cerium salt (Ce(NO3)3·6H2O). Current density and time were varied during the deposition. The optimal parameters that yielded uniform coatings were determined. Coatings were characterized for their crystallinity, scratch hardness, and microstructure. The barrier properties of the coatings were tested using potentiodynamic polarization studies, electrochemical impedance spectroscopy, and neutral salt spray tests. Grazing angle incidence X-ray diffraction studies revealed that the coating comprised crystalline Al2SiO5 along with an amorphous phase. The novelty of the process was that the crystalline aluminosilicate phase was formed even at room temperature and could be deposited on aluminum by a simultaneous anodization of aluminum and sol-gel deposition. The coated substrates withstood more than 400 hours of salt spray tests. Polarization measurements reveal that the composite layer of aluminosilicate along with the Ce3+-doped silica-zirconia sol enhances the corrosion properties by forming a passive layer, which acts as a good barrier against corrosion.