Study On Corrosion Behaviors Of Fe-based And Ti-based Alloy In Molten LiCl-Li₂O

A lithium reduction technique has been developed as an effective method for reducing the volume and radiation of the spent nuclear fuel, which can benefit to the disposal and management of the spent nuclear fuel. In this process, structural materials used in the technique undertake serious corrosion in molten LiCl-Li₂O, which delayed the application of the new technique. To date, there have been few studies on the corrosion behavior of materials in molten LiCl-Li₂O. In this paper, immersion experiments are used to simulate service environment of structural material in the lithium reduction process. X-ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electron Microscopy with coupled with X-ray Microanalysis (SEM/EDAX), and Electron Probe Microanalysis (EPMA) are used to investigate the corrosion behaviors of pure Fe, 40Cr, 316L, 1Cr17, Ti₃Al, TiAl-5Nb, pure Ti and nitrided Ti in molten LiCl-Li₂O. It primarily discusses the corrosion mechanism and provides useful results and testing data for selecting materials and protective coatings under these conditions.The corrosion products of pure Fe and 40Cr steel at 750℃ in molten LiCl-10wt%Li₂O both are LiFeO₂. The weight losses of the two materials both increase with the increasing of time, and the weight loss of 40Cr steel is slight lower than that of pure Fe. Under these experimental conditions, the corrosion resistance of austenite is better than that of ferrite, and the process of the corrosion in the melt is dominated by chemical corrosion.The two stainless steels are all corroded severely. The products of 316L are iron oxides (LiFeO₂ and LiFe₅O₈) and chromium oxides (Cr₂O₃ and LiCrO₂). The products of 1Cr17 form three layers: LiFeO₂ (out layer), LiFeO₂ and LiCrO₂ (middle layer), Cr₂O₃ (inner layer). The weight loss of 1Cr17 is higher than that of 316L because of the difference of composition and structure between the two stainless steels. The corrosion resistance of austenitic is better than ferrite; Ni and Mo can improve the resistance of corrosion.The products of Ti₃Al show a bilayered structure: the thicker outer layer is composed of aluminum oxides (LiAlO₂, Al₂O₃), whereas the thinner inner layer is a compact titanium oxides (Li₂TiO₃, TiO₂) layer. The products of TiAl-5Nb also show a bilayered structure: the thicker outer layer is composed of grains of LiAlO₂, whereas the thinner inner layer is a compact titanium oxide-rich (Li₂TiO₃, TiO₂) layer. The fast corrosion at the beginning of corrosion is due to the fast growth of LiAlO₂, and the slower corrosion rate at the latter stageof corrosion is owing to the formation of protective inner layer of titanium oxides. Nb can improve the resistance of corrosion.Ti corrodes in the melt, forming layer of TiCh, which converted to I^TiCh. Because Li2TiC>3 is dense and continuous, which sets back the diffusion of O2" to the substrate, the corrosion rate becomes slow later. The bond strength of corrosion product and substrate being lower than that of product itself, the products separate from the substrate when the sample is carried out of the melt. The gas nitriding process has been used to treat pure titanium at a nitriding temperature of 900 °C for lOh. A dense and continuous nitrided layer 30⁷0/xm is obtained on pure titanium. Corrosion behavior of the nitrided layer has been investigated in molten LiCl-3%Li2O at 650°C under air. The nitrided layer effectively blocks the diffusion of O2', which improves the corrosion resistance of pure titanium in molten...