Abstract
Plant extracts are intensively studied as green corrosion inhibitors of aluminum. Because these extracts are complex systems, the influence of their individual constituents on the corrosion of aluminum should be determined. In this work, gallic acid was tested for the first time as a corrosion inhibitor of aluminum in orthophosphoric acid aqueous solution. So far, its potential inhibiting properties in acidic solutions were only suggested based on promising results obtained for various plant extracts. Evaluation of the potential inhibiting properties of gallic acid was performed using electrochemical methods. The corrosion potential, polarization curves, and impedance spectra of aluminum in 0.5 M orthophosphoric acid, at T = 303 K, were determined. The corrosion potential, corrosion current density, and corrosion rate of aluminum in orthophosphoric acid were equal to −1.151 V vs. Ag|AgCl (3M KCl) reference electrode, 36 μA∙cm−2 and 0.39 mm∙year−1, respectively. These values did not change with the addition of gallic acid. The results obtained show that gallic acid does not inhibit aluminum corrosion. UV-Vis absorption spectra of gallic acid solutions and quantum mechanical calculations show that this organic compound did not adsorb onto the aluminum surface under the studied conditions.
Highlights
Accepted: 26 January 2022Aluminum alloys, due to their high strength-to-weight ratio, are commonly applied, especially in the aircraft industry [1]
When aluminum is exposed to an acidic or alkaline solution, an efficient corrosion inhibitor should be used. This problem is especially important in industrial processes, for instance, during electrochemical etching and acid pickling of components made of aluminum alloys or when the anodic coating must be stripped off the substrate without dissolution of the latter
M H3PO4 aqueous solutions containing gallic acid decreases immed of the aluminum corrosion potential. This was performed using the open circuit potential when aluminum is exposed to an acidic solution because this solution rapidly disso measurements
Summary
Due to their high strength-to-weight ratio, are commonly applied, especially in the aircraft industry [1]. Their applications usually require good corrosion resistance. This is based on the natural ability of aluminum to form a compact layer of Al2 O3. This protective layer becomes chemically unstable in acidic and alkaline solutions and these environments are corrosive for aluminum and its alloys [2]. When aluminum is exposed to an acidic or alkaline solution, an efficient corrosion inhibitor should be used. This problem is especially important in industrial processes, for instance, during electrochemical etching and acid pickling of components made of aluminum alloys or when the anodic coating must be stripped off the substrate without dissolution of the latter
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