Process for producing corrosion-inhibiting oxide layers

摘要

The invention relates to a process for producing corrosion-inhibiting oxide layers on surfaces of structural elements consisting of steels or nickel-based alloys by hot-water oxidation of the structural elements for several hours in an aqueous medium, in particular for suppression of the radioactive contamination of the inside surfaces of primary circuits of water-cooled nuclear reactors. The object according to the invention is achieved in such a way that at least hydrated oxides, known per se, of metals of subgroup IV of the periodic table of the elements are released in the aqueous solution and the concentration of the metal compounds, which lead to the formation of these hydrated oxides, does not exceed the order of magnitude of 1 mu mol/l. It has been found that the hydrated oxides of extremely low solubility of some metals, above all of titanium and zirconium, in a particle size of less than 10 nm act as crystallisation nuclei during the formation of the protective layer. They are also capable of penetrating into pores, which may already be present, having diameters of from 10 to 100 nm. The protection becomes effective in a total quantity, specific to unit area, of foreign metals in the order of magnitude from 0.1 g/m<2>, i.e. at only about 1/100 of the quantity hitherto used.