Oxidation of Steels and HgO Growth after 5000 Hours Exposure in Mercury at 573 K

Corrosion tests on martensitic steels, F82H and MANET-II, were conducted in static Hg at 573 K in two batches: 1) the Hg covered with air for 5000 h, and 2) the Hg covered with Ar for 2000 h. Different techniques (EPMA, SEM, RHEED, XRD, SIMS) have been applied for surface analysis. The main results show that the surfaces of the samples are oxidized and covered with large amounts of red HgO single crystals (1 mu m to 1 mm) under air atmosphere. The surface layers formed in the presence of air consist of oxides of types (Fe, Cr) sub 2 O sub 3 , Fe sub 3 O sub 4 , FeCr sub 2 O sub 4 and have a thickness up to 680 nm for F82H and 310 nm for MANET-II. Replacing air with Ar in the containers reduces drastically the oxidation of the steels. In this case the maximum thickness of oxide film is of 10 nm and no HgO crystals form.