Corrosion of Aluminum in Contact with Oxidized Titanium and Zirconium
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CORROSION OF ALUMINUM IN CONTACT WITH OXIDIZED TITANIUM AND ZIRCONIUM V. V. Shtefan,1 B. I. Bairachnyi,1 G. V. Lisachuk,1 O. Yu. Smyrnova,1,2 V. A. Zuyok,3 R. O. Rud’,3 and O. V. Voronina1 We study the corrosion of alloys based on titanium, aluminum, zirconium, and iron in solutions of sodium chloride. The corrosion rate of aluminum significantly increases in contact with zirconium, titanium, and stainless steel. It is shown that the kinetics of aluminum corrosion is controlled by the cathodic reaction of reduction of molecular oxygen. It is also demonstrated that the corrosion rate of aluminum outside the contact zone is equal to the rate observed in contact with oxidized zirconium or titanium. The protective properties of oxide coatings on titanium and zirconium obtained by the method of microarc oxidation and high-temperature oxidation are investigated by the method of impedance spectroscopy. Keywords: contact corrosion, aluminum, zirconium, titanium, steel.
The water-storage reservoirs on nuclear power plants are, in fact, many-electrode systems. The main structural materials for these reservoir are aluminum alloys, e.g., SAV-1 [1]. The parts of reservoirs are joined by fastening elements made of the alloys of iron, titanium, and zirconium. The analysis of the available literature sources [2] shows that the probability of appearance of the electrochemical corrosion of aluminum and its alloys operating in contact with stainless steel and alloys of titanium and zirconium is very high. The main factors affecting the corrosion behavior of aluminum alloys operating in contact with the indicated materials are as follows: the chemical composition of the cooling liquid, the difference between the stationary potentials, and the ratio of the geometric surfaces of contacting alloys. As shown in [3], the process of contact corrosion may lead to a significant deterioration of the corrosion state of aluminum alloy and to the hydrogenation of titanium and zirconium alloys. Corrosion can be weakened by preventing the contact of alloys with the help of dielectric pads placed in all places, where this is possible. The results of investigations of contact corrosion in reservoirs aimed at cooling the spent nuclear fuel are described in [2, 3]. Corrosion was observed under the conditions of contact of aluminum with stainless steel in the course of regulation of water regime. After seven years of operation, the inspection revealed no corrosion pits in the materials due to the application of insulators and oxidized aluminum workpieces. Therefore, the oxide coatings on metallic materials can be regarded as one of possible means of protection against the contact corrosion. The method of microarc oxidation (MAO) makes it possible to produce oxide coatings with high corrosion resistance and stability in the process of heating in air at temperatures of up to 500°C. These coatings ensure the combined corrosion protection of the doped titanium and zirconium alloys [4–8]. The high-temperature reac1 2 3
“Kharkiv Polytechnic Institute” Nationa
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