Adsorption and passivation of a copper alloy by teraphthal in neutral chloride solution

• O.Yu. Grafov, Yu.I. Kuznetsov, N.P. Andreeva and M.O. Agafonkina

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

Abstract: The adsorption and protective properties of teraphthal, the sodium salt of 4,5-octacarboxyphthalocyanine, on oxidized surface of copper–nickel alloy MNZh5-1 in a borate buffer solution have been studied. Teraphthal suppressed the active anodic dissolution of MNZh5-1 alloy in a neutral borate buffer with addition of 10 mmol/L NaCl. The protective effect is ΔE=0.35 V at С_inh=25 µmol/L. The adsorption isotherm of teraphthal on the oxidized surface of MNZh5-1 alloy was calculated using the full Temkin isotherm. The value of the standard free energy of adsorption –ΔG_a⁰=78.8 kJ/mol suggests the chemisorption interaction of these organic anions with the oxidized surface of the alloy. XPS studies of the surface layers of the alloy after soaking in a teraphthal solution showed that it is strongly adsorbed on the oxidized electrode surface mainly coated with Cu₂O. Binding of teraphthal to the alloy surface occurs due to oxygen atoms of carboxyl groups. The thicknesses of the adsorbed layer determined by ellipsometry and XPS coincide and amount to ~0.3 nm. This thickness indicates a flat arrangement of the teraphtal anion on the surface.

Keywords: copper alloy, sodium salt of 4,5-octacarboxyphthalocyanine, adsorption, neutral chloride solution, ellipsometry, Temkin isotherm, XPS, monolayer thickness

Int. J. Corros. Scale Inhib., 2022, 11, no. 4, 1787-1801
doi: 10.17675/2305-6894-2022-11-4-24

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