О. М. Lavrynenko1,2, B. G. Shabalin2
1 Frantsevych Institute for Problems of Materials Science,
NAS of Ukraine, 3, Krzhyzhanovskyi st., Kyiv, 03680, Ukraine
2 SI “Institute of Environmental Geochemistry of NAS
of Ukraine”, 34a, Palladin ave, Kyiv, 03142, Ukraine
The experimental modeling of the corrosive phase formation processes was performed under conditions approaching the initial and transitional stages of evolution of the deep geological repository (the hydrogen index of the medium lied in the range of 9–12 and a temperature was 50–70 °C). The specificity of the system of rotating disk electrode made it possible to determine the phase composition of corrosion products formed under oxidative conditions (the near surface layer, NSL) and, conditionally, reductive — on the steel surface (SL) covered by NSL, that significantly complicated the access of oxygen into the reaction area. It was determined that phase composition of the corrosion products at the pH0 values 9–11 was identical and it is regulated by the compensative action of cathodic half-reaction of oxygen reducing on the steel surface. Green Rust and magnetite or non-stoichiometric spinel ferrite characterized by coagulative type of the structure and spherical particle shape were determined as the main phases of SL. Iron oxyhydroxides — goethite and lepidocrocite were presented as the phases of NSL. Increase in the pH0 to 12 changes the chemical mechanism of the corrosion process and it leads to the formation of weak crystallized iron oxyhydroxide phases. It was proved the main phase formed under corrosion of steel at 50–70 °C was spinel ferrite. Its morphology is presented as the cubic shaped particles that evidences about condensingcrystallizing mechanism of their formation. Generally, the presence of Co2+ and Mn2+ cations does not influence on the phase formation process and the phase composition as well, whereas the iron oxyhydroxides with admixture of Mn2+ and Mn3+ oxygen compounds are dominant in the sediment compositions when they are formed in the presence of Mn7+.
Keywords: corrosion of the steel, water-air medium, evolution of the deep geological repository, spinel ferrite, iron oxyhydroxides, coagulative and condensing-crystallizing type of the structures.
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