Soo-Haeng Cho

High temperature corrosion behavior of Ni-based alloys

The high temperature corrosion behavior of N07263, N06600, and N06625 in LiCl-Li2O molten salt was investigated at temperatures ranging from 650 to 850 °C in a glove box. The high temperature corrosion behavior was observed using measurements of the oxide morphology and thickness, the extent of internal corrosion, and the compositional changes in the scale and in the substrate. Corrosion tests were performed, and these demonstrated that the main corrosion products were Fe(Ni,Co)3, FeNi3, and LiCrO2. The internal corrosion of N07263 was localized, while that of N06600 maintained intergranular corrosion throughout the test temperature range. N06625 exhibited uniform intergranular corrosion behaviors at low and high temperatures. N07263 exhibited superior corrosion resistance, as evidenced by its corrosion layer which was more continuous, dense, and adherent when compared with those of N06600 and N06625.

Cyclic Corrosion Behavior of Ni-Based Superalloys in Hot Lithium Molten Salt

In this study, the cyclic corrosion behavior of N06230, N07263, and N06625 in a LiCl–Li2O molten salt was investigated at 650xa0°C in argon atmosphere. The cyclic corrosion behavior was observed through measurements of the oxide morphology and thickness, the extent of internal corrosion, and compositional changes in the oxide scale and the substrate. The corrosion products in the surface corrosion layers of N07263 were (Ni,Co)O, (Ni,Co)Cr2O4, Cr2O3, and TiO2 and those in the surface corrosion layers of N06230 were NiO, NiCr2O4, and Cr2O3, while NiO, NiCr2O4, CrNbO4, and Cr2O3 were identified as the corrosion products of N06625. The internal corrosion behavior of N07263 was localized, while N06230 and N06625 showed uniform corrosion. N07263 exhibited superior corrosion resistance as its corrosion layer was more continuous, dense, and adherent as compared to those of N06230 and N06625.

High-temperature corrosion characteristics of yttria-stabilized zirconia material in molten salts of LiCl-Li2O and LiCl-Li2O-Li

ABSTRACT The isothermal and cyclic corrosion behavior of yttria (Y2O3)-stabilized zirconia (ZrO2) in a LiCl-Li2O molten salt were investigated at 650 °C in an argon atmosphere. During isothermal and cyclic corrosion tests in the molten salt of LiCl-Li2O for 168 h and 7 thermal cycles, the corrosion rate was very low, whereas under the molten salt of LiCl-Li2O-Li for 168 h, the corrosion rate was almost 10 times higher than that in the molten salt of LiCl-Li2O. No corrosion product was detected until 168 h for the isothermal corrosion test, however, after 7 thermal cycles, a very-low-intensity Li2ZrO3 peak was detected at the beginning stage of the chemical reaction between ZrO2 and Li2O. Additionally, in the molten salt of LiCl-Li2O-Li for 168 h, a large amount of Li2ZrO3 was formed, with evidence of marked cracks, pores, and spallations on the corroded surface. The introduction of Y2O3-stabilized ZrO2 was beneficial in increasing the hot corrosion resistance of the structural materials used to handle molten salts containing Li2O at elevated temperature without forming a lithium at the cathode during the electrolytic reduction process.

Corrosion behavior of ceramic structural materials in an electrolytic reduction process

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical alloying structural materials. Therefore, the choice of the optimum material for the processing equipment that handles molten salt is critical. We investigated the corrosion behaviors of CaO-stabilized ZrO2 (CSZ) and mullite (Al6Si2O13) at 650°C for 168 h in molten (1, 3) wt% Li2O–LiCl. The as-received and tested specimens were examined by scanning electron microscopy/X-ray energy dispersive spectrometry and X-ray diffraction. CSZ showed a much better hot-corrosion resistance in the presence of Li2O–LiCl molten salt than mullite. The surface corrosion layers of mullite consisted of LiAlSiO4 in 1 wt% Li2O–LiCl, and a LiAlO2 phase appeared as the Li2O concentration increased to 3 wt%. Furthermore, Li2SiO3 was the only corrosion product observed at 3 wt% Li2O–LiCl. The surface corrosion layers of CSZ were composed mainly of tetragonal-ZrO2 with partial monoclinic-ZrO2 in 1 wt% Li2O–LiCl, and a Li2ZrO3 phase appeared at 3 wt% Li2O–LiCl. There was no corrosion product detached from the surface for those specimens. CSZ was beneficial for increasing the hot-corrosion resistance of the structural materials that handle high-temperature molten salts containing Li2O.