Effect of Anodized Oxide Layer Aging on Wettability of Alkyl Silane Coating Developed on Aerospace Aluminum Alloy
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ALUMINUM alloys received wide applications from power transmission lines to aircraft structure.[1] Especially high strength aluminum alloys (or) aluminum alloy-coated materials are becoming popular in variety of applications such as ceilings, floors, escalator, and commercial buildings. The moisture with small impurities present in the environment can affect these metals to failure due to the presence of noble alloying elements.[2] Hence, in order to mitigate the corrosion, these alloys have been surface modified by different techniques such as phosphating, chemical conversion coating, anodic oxidation coating, organic finishing, and electroplating.[3] In the present scenario, among the different coating techniques, anodization is a preferably used technique for various applications such as electronic devices (micro chips, frames of mobiles and computers), roofs, curtain walls, ceilings, floors, escalator, staircases, commercial buildings, etc.,[4,5] because of its high durability, good electrical and thermal resistance, and environmentally safe.[6–9] Since anodic coatings have porous structure, the incorporation of organic/ inorganic inhibitors (or) surface modification with suitable technique is a mandate to improve its performance.[10] Generation of hydrophobic/superhydrophobic surface is one of the plausible ways to solve the above problems. G. YOGANANDAN, Senior Research Fellow, T. BHARATHIDASAN, Project Assistant, M. SOUMYA SRI, Project Student, D. VASUMATHY, Project Student, J.N. BALARAJU, Project Students, and BHARATHIBAIJ. BASU, Ex-Chief Scientist, are with the Surface Engineering Division, CSIR National Aerospace Laboratories, Post Bag No. 1779 Bangalore 560017 Karnataka, India. Contact e-mail: [email protected] Manuscript submitted September 26, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
Several techniques are available to generate the superhydrophobic surfaces.[11–19] In recent times, superhydrophobic (SH) surfaces have considerable attention for many industrial applications because of their unique self-cleaning property.[20–23] The development of superhydrophobic surface with a minor modification on the surface of anodized aluminum can rectify the short circuiting problem (EBs malfunction problem) in the case of electronic applications.[24] Such highly water-repellent surfaces are inspired by natural surfaces such as lotus leaf, on which water drops remain almost spherical which can easily roll off and removes the dirt particles from their path.[25] By mimicking this effect, artificial self-cleaning coatings can be prepared by using different methods. Even though several methods are already reported for the fabrication of such water repellent and self-cleaning coatings, many of them involve multi-steps or expensive reagents or special equipments, and may not be suitable for industrial applications. It is well known that the superhydrophobicity is governed by both the chemical composition and the geometrical structure of the solid surface.[26–30] Thus, it is possible to fabricate SH surfaces on various
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