Shabalin, B.Zlobenko, O. Lavrynenko, S. Buhera

Abstract

The article presents the preliminary results of the experimental study of the corrosion and mineral formation processes on carbon and stainless steel plates contacting with a clay barrier material (bentonite) as well as the steel corrosion products interaction with the clay under simulated aerobic conditions of the geological repository. After the interaction, the clay and steel samples were studied by X-ray fluorescence analysis, infrared spectroscopy and electron microscopy. The corrosion processes at the steel-bentonite interface have been discovered to be less intensive than in a simulated natural water. The carbon steel samples have undergone the most significant corrosive changes, with the corrosion processes in the aqueous medium being most intensive. In the water-saturated bentonite medium, not only the carbon steel is corroded but the mechanical and chemical properties of the bentonite in the adjacent zones also change due to the corrosion products migration into it.

The transformed bentonite demonstrates changes in the colour, alteration of shrinkage, cracking, and swelling properties, and change of ion exchange capacity values and character. The mobile Fe corrosion products penetrate into bentonite and deposit in its interlayer space in the form of thin iron oxide or iron hydroxide deposits on the walls of microcracks and the outer surface of clay crystals, reducing the hydrophilicity of the bentonites. At the same time, under the given experimental conditions, transformation of montmorillonite into nontronite, saponite or chlorite (which crystalline lattice holds a significant number of Fe⁺³ ions) was not revealed by the available analytical methods. In the course of the experiment, no corrosion signs were found on the stainless steel plate surface. The bentonite, which was in direct contact with the plate, also did not undergo any changes. Any traces of transition of stainless steel elements into bentonite have not been found.

Key words: geological repository, metal canisters, bentonite, corrosion.

Article

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