Abstract
A hybrid sol synthesized from an acid-catalyzed hydrolysis and condensation reaction of 3-glycidoxypropyltrimethoxysilane (GPTMS) and zirconium n-propoxide was used as a matrix nanocomposite sol. To this sol, 0.01 M Ce3+ was added as an inhibitor to provide a self-healing coating system. The effect of an atmospheric air plasma surface pretreatment of aluminum alloy substrates prior to coating deposition of Ce3+-doped/undoped GPTMS-ZrO2 sol was studied with respect to corrosion protection. Coatings were generated by a dip coating technique employing a withdrawal speed of 5 mm/s and thermally cured at 130° C for 1 h. The coated Al surfaces were characterized using potentiodynamic polarization studies and electrochemical impedance spectroscopy. They were also subjected to accelerated corrosion testing using neutral salt spray test with 5% NaCl solution after creating an artificial scratch for more than 200 hours to assess the self-healing ability of coatings. It was observed that cerium (III) doping was effective for corrosion protection during long-term exposure to the electrolyte solution, and a plasma surface pretreatment of substrates prior to coating deposition of Ce3+-doped coatings improved the adhesion of coatings that provides enhanced corrosion protection along with self-healing ability exhibited in case of damages/scratches caused in the coating.
Highlights
Aluminum and Al alloys are widely used in structural applications mainly in aircraft and automobile industries due to their light weight and high strength properties [1]
There are several surface engineering treatments available to prevent corrosion on Al/Al alloys, surface treatments that require low temperatures for post-treatment processing are recommended to prevent a deterioration of mechanical strength that occurs by dissolution of intermetallic particles during high temperature post-treatment [2]
The effect of direct doping of Ce3+ in the silica-zirconia hybrid sol-gel matrix and effect of plasma pretreatment prior to sol-gel coating deposition was studied in terms of corrosion inhibition and self-healing ability under conditions of external damages caused to the coating
Summary
Aluminum and Al alloys are widely used in structural applications mainly in aircraft and automobile industries due to their light weight and high strength properties [1]. Since hexavalent chromium has been proved to be carcinogenic [5, 6], the rare earth element cerium is being studied extensively [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24] as a substitute to chromium since it provides a good inhibition effect in addition to being environmentally friendly and having a self-healing ability It blocks the pores and prevents corrosion even on scratched areas during longterm exposure. Cerium-doped hybrid sol-gel coatings have attracted a lot of attention in the recent past [7,8,9, 11, 12, 17, 20, 23, 24]
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