Inhibition of anodic dissolution of Mg90 alloy by adsorption layers of higher carboxylic acids

• V.A. Ogorodnikova, Yu.I. Kuznetsov, A.A. Chirkunov and A.M. Semiletov

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

Abstract: The passivating ability of thin adsorption films of oleic acid and its sodium salt previously formed on the surface of technical magnesium from ethanolic solutions was studied in borate buffer (pH 9.2) containing aggressive sodium chloride. Analysis of the anodic polarization curves showed that the adsorption protective films formed in an ethanolic solution of oleic acid are more stable than the films of stearic and tridecanoic acids or sodium oleate, which exhibits much more efficient passivating properties upon adsorption from aqueous solutions. Measurements of the wetting contact angle (Θ_c) on magnesium samples pre-oxidized and treated with ethanolic solutions of carboxylic acids showed that short-term treatment of Mg in oleic acid solution, even with C_in = 16 mM, does not hydrophobize its surface, although it increases the value of the Θ_c angle in time. However, after immersing the electrode in this solution for 15 hours and then washing it with pure ethanol, the value of Θ_c is 93 ± 1°, although this value is lower than Θ_c = 115° measured on the coating formed by the more hydrophobic stearic acid in a much shorter period (10 min). Oleic acid is inferior in the hydrophobizing effect not only to stearic acid but also to the less hydrophobic tridecanoic acid. However, it is possible to enhance the hydrophobization of magnesium surface by formulations of oleic acid with other higher carboxylic acids by means of relatively long treatment in an ethanolic solution.

Keywords: magnesium, corrosion inhibitors, carboxylic acids

Int. J. Corros. Scale Inhib., 2018, 7, no. 2, 260-270 PDF (464 K)
doi: 10.17675/2305-6894-2018-7-2-11

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