Inhibition of the Corrosion of Aluminum Alloy in Aqueous Solution of Ethylene Glycol by the Rhamnolipid Biocomplex
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INHIBITION OF THE CORROSION OF ALUMINUM ALLOY IN AQUEOUS SOLUTION OF ETHYLENE GLYCOL BY THE RHAMNOLIPID BIOCOMPLEX І. М. Zin’,1, 2 V. І. Pokhmurs’kyi,1 О. P. Khlopyk,1 О. V. Karpenko,3 Т. Ya. Pokyn’broda,3 S. А. Kornii,1 and М. B. Tymus’1 We study the efficiency of inhibition of corrosion processes in the aluminum alloy placed in an aqueous solution of ethylene glycol by an ecologically friendly rhamnolipid biocomplex obtained as the product of biosynthesis of the Pseudomonas sp. PS-17 strain. It is shown that the biogenic inhibitor added to an aqueous solution of ethylene glycol decreases the rates of both the anodic and cathodic reactions and makes the charge-transfer resistance of aluminum alloy 2.6 times higher, which indicates the possibility of formation of durable protective films on the metal as a result of the adsorption of inhibitor molecules and the formation of complex compounds with aluminum cations. It is shown that the rhamnolipid biocomplex is an efficient corrosion inhibitor on freshly formed surfaces of the aluminum alloy, as indicated by an increase in the rate of its repassivation. Keywords: aluminum alloy, aqueous ethylene-glycol solution, rhamnolipid biocomplex, polarization current, charge-transfer resistance.
Introduction In the systems of liquid cooling of internal-combustion engines, radioelectronic equipment, industrial heat exchangers, and other units, it is customary to use low-freezing cooling liquids, i.e., antifreezes, obtained as mixtures of diatomic alcohol (ethylene glycol) with water [1]. The antifreezes based on ethylene glycol are characterized by an elevated aggressiveness to the metals of liquid cooling systems and, therefore, it is necessary to add corrosion inhibitors to their composition [2, 3]. It is also necessary to take into account the possibility of cavitation, which breaks the continuity of protective films on the metal and intensifies its corrosion [2, 4]. As known corrosion inhibitors for cooling liquids, we can mention chromates, silicates, borates, phosphates, nitrates, triazoles, and their compositions [5, 6]. Hexavalent chromium is used in cooling liquids due to its high solubility in water, ability to passivate the metal surface, low cost, and simplicity of application [7, 8]. However, chromates are extremely toxic compounds and, hence, their subsequent utilization is problematic. In the course of operation, silicates cover the inner surface of the cooling system with a silicate layer, which worsens the conditions of heat exchange and, hence, decreases the efficiency of cooling of the engine. The application of borates in the compositions of antifreezes for the purposes of protection of ferrous metals leads to the corrosion of aluminum and its alloys. At the same time, liquids containing phosphates may form an insoluble deposits, which gradually accumulate 1 2 3
Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine. Corresponding author; e-mail: [email protected].
Department of Physicochemistry of Fossil Fuels, Lytvynenko
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