ISSN 2305-6894

Using data of weight tests and impedance spectroscopy to evaluate the protective effectiveness of zinc-rich oil coatings in corrosion of carbon steel

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1 All-Russian Scientific Research Institute of Use of Machinery and Oil Products, Novo-Rubezhnyi per., 28, Tambov, 392022, Russian Federation
2 Tambov State Technical University, ul. Sovetskaya, 106, Tambov, 392000, Russian Federation
3 Derzhavin State University, ul. Internatsyonalnaya, 33, Tambov, 392000, Russian Federation
4 Angara GmbH, In der Steele 2, D-40599, Düsseldorf, Germany

Abstract: Studies have been carried out in a 3% aqueous solution of NaCl, acidified in some cases to pH 3 or 4. The protective efficacy of zinc-rich coatings based on waste motor oil has also been studied in a thermal moisture chamber and natural conditions. Partial rates of oxidation of zinc from the coating and iron are estimated on the base of chemical analysis of saline solution for Zn2+ and Fe2+ + Fe3+ ions. The protective effect of zinc as a function of its concentration in the coating, which varies with time as a result of its anodic dissolution, is estimated. The effect of oil-zinc-containing (40, 50 and 60 wt.% Zn) coatings on the charge transfer resistance in partial electrode reactions occurring during steel corrosion has been investigated by impedance spectroscopy. It is shown that the protective effect (Z, %) of the oil compositions reaches 88, 86 and 90% for corrosion tests in the chloride salt solution, thermal moisture chamber and under natural conditions, respectively. However, in 3% NaCl solution it sharply decreases after a zinc concentration decrease in the oil film to 16–20%. The charge transfer resistance in the cathodic reaction (Rc) of unprotected steel is 45 Оhm·cm2 immediately after immersion in a solution with pH 6.5 and decreases to 33 Оhm·cm2 after 24 h exposure. When the pH of the corrosive medium drops to 3.0, the picture is analogous. At the initial stage, Rc equals 40 Ohm·cm2 and decreases to 24 Ohm·cm2 after 24 hours (in situ). The magnitude of the charge transfer resistance in the anodic reaction is 20–470 times greater than Rc under the indicated conditions. The presence of 60% zinc in the surface oil coating has a relatively weak effect on the Rc value and increases Ra 45–50 fold under comparable conditions (pH = 3.0, 24 h exposure). Corrosion of steel begins on the tenth day after immersion in a solution. At that the initial concentration of Zn (Cinitial = 60 wt.%) decreases twofold and steel corrosion rate increases with a further decrease in the zinc concentration in the oil coating.

Keywords: steel, corrosion, saline solution, thermal moisture chamber, natural conditions, charge transfer resistance, anode process, cathodic reaction, protective effect

Int. J. Corros. Scale Inhib., , 2, 212-224 PDF (864 K)
doi: 10.17675/2305-6894-2019-8-2-4

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