Adsorption of oleylsarcosine sodium salt on aluminum alloy D16 in aqueous solution

• A.M. Semiletov, N.P. Andreeva, Yu.I. Kuznetsov and V.E. Kasatkin

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, bldg. 4, 119071 Moscow, Russian Federation

Abstract: The adsorption of oleylsarcosine sodium salt (OSS) from a neutral borate buffer solution on a pre-oxidized surface of aluminum alloy D16 at potential E=–0.3 V was studied by ellipsometry and electrochemical impedance spectroscopy (EIS). Adsorption isotherms of OSS have been obtained and can be adequately described by the full Temkin isotherm equation. The standard free energy of adsorption (–ΔG⁰_ads) was calculated by using this equation. According to ellipsometric data, the value of 53.3 kJ/mol suggests the formation of a chemisorption OSS monolayer. Adsorption measurements by the EIS method turned out to be significantly less sensitive and adsorption was detected at higher OSS concentrations C_in≥0.1 mmol·L^–1. It is not surprising that the value of ⁠–⁠ΔG⁰_ads in this case does not exceed 30.3 kJ/mol. This value is 23 kJ/mol less than –ΔG⁰_ads obtained by ellipsometric measurements and does not suggest that the EIS method detects OSS chemisorption. Probably, in this case, the formation of a polymolecular OSS film is determined, since the insufficiently sensitive the EIS method can register it only with thicker layers of physically adsorbed inhibitor on an electrode surface.

Keywords: adsorption, aluminum, oleylsarcosinate, corrosion inhibitors, ellipsometry, EIS

Int. J. Corros. Scale Inhib., 2024, 13, no. 3, 1724-1740
doi: 10.17675/2305-6894-2024-13-3-22

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