%0 Journal Article
%T One-Step Anodization/Sol-Gel Deposition of -Doped Silica-Zirconia Self-Healing Coating on Aluminum
%A N. Kumar
%A A. Jyothirmayi
%A K. R. C. Soma Raju
%A V. Uma
%A R. Subasri
%J ISRN Corrosion
%D 2013
%R 10.1155/2013/424805
%X 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. 1. Introduction Aluminum, that is widely used as a structural material due to its high strength to weight ratio and low cost, is highly susceptible to corrosion attack in chloride containing environment [1, 2]. Chromate conversion coatings have been the most widely used self-healing, anticorrosion treatments for aluminum and its alloys. Due to the increasing demand for the development of an environmentally-friendly, effective, inexpensive, and technologically simple method for corrosion protection, anodization of aluminum, and conversion coatings based on vanadates, permanganates, tungstates, and rare-earth salts have recently attracted a lot of attention as a method for corrosion protection [3]. Anodization is an electrochemical oxidation process employed to increase the thickness of the native oxide layer on metals like Al, Mg, Ti, and so forth [4¨C15]. The anodized layer is porous and, hence, there are reports in which a sol-gel coating is deposited on top of the anodized layer to render good barrier properties [16, 17]. There are also reports where, initially, a purely inorganic sol-gel coating is deposited on the aluminum substrate, followed by heat treatment at high
%U http://www.hindawi.com/journals/isrn.corrosion/2013/424805/