The effect of chloride concentration and pH on pitting corrosion of AA7075 aluminum alloy coated with phenyltrimethoxysilane |
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Authors: | A A Younis M M B El-Sabbah Rudolf Holze |
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Institution: | 1.AG Elektrochemie, Institut für Chemie,Technische Universit?t Chemnitz,Chemnitz,Germany;2.Department of Chemistry, Faculty of Science,Al-Azhar University,Cairo,Egypt |
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Abstract: | The effect of chloride ion concentration and pH of solution on the corrosion behavior of aluminum alloy AA7075 coated with
phenyltrimethoxysilane (PTMS) immersed in aqueous solutions of NaCl is reported. Potentiodynamic polarization, linear polarization,
open circuit potential, and weight loss measurements were performed. The surface of samples was examined using SEM and optical
microscopy. Elemental characterization of the coating by secondary ion mass spectrometry indicates an intermediate layer between
coating and aluminum alloy surface. The corrosion behavior of the aluminum alloy AA7075 depends on chloride concentration
and pH of solution. In acidic or neutral solutions, general and pitting corrosion occur simultaneously. On the contrary, exposure
to alkaline solutions results in general corrosion only. Results further reveal that aluminum alloy AA7075 is susceptible
to pitting corrosion in all chloride solutions with concentrations between 0.05 M and 2 M NaCl; an increase in the chloride
concentration slightly shifted both the pitting and corrosion potentials to more active values. Linear polarization resistance
measurements show a substantially improved corrosion resistance value in case of samples coated with PTMS as compared to uncoated
samples in both neutral (pH = 7), acidic (pH = 0.85 and 3), and alkaline chloride solutions (pH = 10 and 12.85). The higher
corrosion resistance of the aluminum alloy coated with PTMS can be attributed to the hydrophobic coating which acts as a barrier
and prevents chloride ion penetration and subsequent reaction with the aluminum alloy. |
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