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The hot corrosion behaviors of Inconel alloys with different Cr contents (Inconel 600, 601, and 690), which are used widely in nuclear plants, were investigated in molten LiCl–Li2O salts. The hot corrosion behaviors were studied by measuring the mass and attack depth changes, surface and cross-sectional morphologies and elemental distributions, and compositional changes at the subscale and substrate scale as well as the spalled oxide scale. At 288 h, the weight losses of Inconel 601 and Inconel 690 were approximately four and twelve times higher, respectively, than that of Inconel 600. The corrosion products of all tested alloys were Cr2O3, NiO, and FeCr2O4. Inconel 600, which exhibited a dense and continuous external corrosion layer and an internal corrosion layer with localized corrosion behavior, exhibited superior corrosion resistance compared with those of Inconel 601 and 690, which showed a spalled external corrosion layer and an internal corrosion layer with uniform corrosion behavior. Thus, the corrosion resistance of the Inconel alloys tested in the hot lithium molten salts in an oxidizing atmosphere is closely related to the contents of the primary alloying elements in the alloys. Of the various alloys analyzed in this study, Inconel 600 exhibited the highest corrosion resistance. Thus, a Cr content of 16.30 wt% or less, Ni content of at least 73.66 wt%, and Fe content considerably lower than 8.15 wt% can result in excellent corrosion resistance. [ABSTRACT FROM AUTHOR]

The electroreduction of indium tin oxide (ITO) using a solid oxide membrane anode was investigated in a molten salt of CaF 2 –NaF–CaO at 1150 °C under an inert atmosphere. In the CaF 2 –NaF blank salt, the first reduction peak did not change from −0.25 V (vs. W pseudo reference electrode (R. E.)) for the addition of up to 2 wt% CaO, but the second reduction peak was observed at −0.55 V (vs. W pseudo R. E.) in 1 wt% CaO, and −0.4 V (vs. W pseudo R. E.) in 2 wt% CaO. Cyclic voltammetry analysis was carried out using ITO as the cathode, and a reduction peak was observed at +0.31 V (vs. W pseudo R. E.). This is a positive value about 0.24 V greater than the theoretical value, probably arising because of the increase in the oxygen ion activity of CaO. The optimum ITO particle size was determined to be 600–1000 μm considering the maximum reduction efficiency dependent on the sedimentation rate, specific melt droplet growth, and reduced InSn film formation. The formation of an InSn alloy with almost the same mass ratio as the initial ITO was confirmed by combining the results of X-ray diffraction and energy dispersive X-ray spectroscopy analysis. [ABSTRACT FROM AUTHOR]

Highlights • Corrosion mechanism of Ni-Co-based alloys in LiCl-Li 2 O molten salt is proposed. • Weight loss of alloys with low cobalt was less compared to those with high. • High content of Cr caused intergranular corrosion in the corrosion layer. • Excess Cr has a deleterious effect on kinetics during the hot corrosion process. Abstract In this study, hot corrosion behaviours of Haynes 282 (H282), Nimonic 90 (N90), and Haynes HR160 (HR160) in LiCl-Li 2 O molten salt were investigated at 650 °C under argon atmosphere. The corrosion rate was in the order of H282 < N90 < HR160, depending on the morphology and structure of the scale. H282 showed a localised corrosion behaviour, while N90 showed a uniform corrosion behaviour. For HR-160, intergranular corrosion was observed. The high Cr content caused intergranular corrosion in the corrosion layer. Thus, excess Cr has a deleterious effect on the corrosion kinetics during hot corrosion in LiCl-Li 2 O molten salt. [ABSTRACT FROM AUTHOR]

Abstract This study investigated the high-temperature stability of CSZ, YSZ, and MSZ specimens in a CaCl 2 -CaF 2 -CaO molten salt at 1200 °C for the application of the materials as oxygen-ion-conducting solid-oxide membrane anodes in the electroreduction process of metal oxides. YSZ exhibited the lowest degradation among the tested specimens in a high-temperature stability test, whereas CSZ showed the highest degradation. The weight loss was not severe with concentrations of CaO up to 10 wt%. CSZ showed peaks for m-ZrO 2 , YSZ showed peaks for t-ZrO 2 and CaZrO 3 , and MSZ showed peaks for t-ZrO 2 and m-ZrO 2 in 0 wt% CaO. In the case of 5 wt% CaO, all specimens exhibited m-ZrO 2 and CaZrO 3 peaks, In the cases of 10 wt% and 20 wt% CaO, CSZ and MSZ showed peaks for CaZrO 3 , and YSZ showed peaks for m-ZrO 2 and CaZrO 3. While CSZ and MSZ became significantly looser as the CaO concentration was increased to 10 wt%, YSZ became significantly denser due to the formation of a protective layer and attack dependent on the solubility of CaO in the molten CaCl 2. In terms of long-term operation, YSZ was demonstrated to possess superior high-temperature stability compared to CSZ and MSZ, and CaO concentrations from 5 wt% to 10 wt% were found to be significantly more stable than other concentrations. Highlights • The degradation mechanism of CSZ, YSZ, and MSZ in CaCl 2 -CaF 2 -CaO molten salt is proposed. • The formation of CaZrO 3 acts as a protective layer. • YSZ shows high degradation resistance to CaCl 2 -CaF 2 molten salt that contains up to 10 wt% of CaO. • In view of long-term operation, YSZ is demonstrated to possess superior high-temperature stability compared to CSZ and MSZ. [ABSTRACT FROM AUTHOR]

Abstract: The high‐temperature stability of YSZ and MSZ specimens was investigated in CaF2–MgF2–MgO molten salt at 1200°C. YSZ was mostly composed of m‐ZrO2 and a small part of YF3 in the early stages. The formation of YF3 was attributed to the chemical reaction between Y2O3 and MgF2, which can lead to the leaching of Y2O3 from YSZ. With an increase in exposure time, the degraded surface was coarser, and considerable amount of cracks, pores, and spallations were formed. Furthermore, no Y2O3 was found up to 120 μm of the YSZ bulk in the early stages. MSZ was composed of t‐ZrO2 after 24 hours. However, the volume fraction of m‐ZrO2 was 72% after 72 hours, and CaZrO3 was formed by the chemical reaction between CaO and ZrO2 after 168 hours. In addition, the volume fraction of m‐ZrO2 was 60% in 2.5 wt% MgO and 49% in 10 wt% MgO. In 5 wt% MgO, CaZrO3 was formed. We demonstrate that the high‐temperature stability of MSZ was better than that of YSZ, and that 10 wt% MgO was much more stable than the other concentrations of MgO. [ABSTRACT FROM AUTHOR]

The isothermal and cyclic corrosion behaviors of magnesia-stabilized zirconia in a LiCl-Li 2 O molten salt were investigated at 650 °C in an argon atmosphere. The weights of as-received and corroded specimens were measured and the microstructures, morphologies, and chemical compositions were analyzed by scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffraction. For processes where Li is formed at the cathode during electrolysis, the corrosion rate was about five times higher than those of isothermal and thermal cycling processes. During isothermal tests, the corrosion product Li 2 ZrO 3 was formed after 216 h. During thermal cycling, Li 2 ZrO 3 was not detected until after the completion of 14 cycles. There was no evidence of cracks, pores, or spallation on the corroded surfaces, except when Li was formed. We demonstrate that magnesia-stabilized zirconia is beneficial for increasing the hot corrosion resistance of structural materials subjected to high temperature molten salts containing Li 2 O. [ABSTRACT FROM AUTHOR]

The harsh atmosphere of the sulfur–iodine process used for producing hydrogen requires better corrosion resistance and mechanical properties than are possible to obtain with pure tantalum. Ta–W alloy is superior to pure tantalum but is difficult to alloy due to its high melting temperature. In this study, substrate samples were coated with Ta–W (Ta–7W, Ta–4W and Ta–1W) using the Multi-Anode Reactive alloy Coating (MARC) process in molten salt (LiF–NaF–K 2 TaF 7 ), with varying distances between cathode and anode. In the case of Ta–4W, a corrosion rate of less than 0.011 mm/year was attained in hydriodic acid at 160 °C, and thickness uniformity was 80.3 ± 2.15 μm. Also, the resulting coated films had hardnesses up to 12.9% stronger than pure tantalum coated film. The alloy coating films also contributed to significant enhancement of corrosion resistance. [ABSTRACT FROM AUTHOR]

Spent nuclear fuel is electro-reduced in a chemically aggressive atmosphere wherein oxygen is generated at the anode in the presence of lithium molten salt containing a strong basic oxide, Li 2 O. Herein, the effect of the Li 2 O concentration on the hot corrosion behaviour of Haynes 263 and Inconel X-750 was investigated by immersion in molten LiCl–Li 2 O salt (1, 3, and 5 wt% Li 2 O) for 72–288 h at 650 ℃ under oxidizing atmosphere. For Li 2 O concentrations of approximately 3%, the weight loss and the products formed by the basic fluxing mechanism differed due to the dependence on the O2− concentration. • Effect of Li2O concentration on corrosion of Ni-based alloys was investigated. • Corrosion occurred by basic fluxing with O2 − ; products varied with ≥ 3 wt% Li2O. • Dense and continuous Cr-rich oxide layer prevented the inward diffusion of oxygen. • Ni-rich layer hindered outward diffusion of the alloying elements in the base metal. • Excess Fe appeared to be deleterious to the overall corrosion resistance. [ABSTRACT FROM AUTHOR]

Abstract: Hot corrosion studies were performed on superalloy specimens. The IN713LC superalloy were sprayed with an aluminized NiCrAlY-bond coat and then with an yttria–zirconia top coat. The bare superalloy reveals an obvious weight loss due to spalling of the scales by the rapid scale growth and thermal stress. The top coatings showed a much better hot corrosion resistance in the presence of LiCl–3 wt.% Li2O molten salt when compared with those of the bare superalloy and the aluminized bond coatings. These coatings have been found to be beneficial for increasing hot corrosion resistance of structural materials for lithium molten salts. [Copyright &y& Elsevier]

The electrochemical behavior of Nd fluoride complexes for Nd electrowinning has been investigated according to the electrolyte composition in the LiF-NdF 3 system. The electrochemical characteristics of the LiF-NdF 3 electrolyte at low oxygen potential under acidic conditions and the LiF-NdF 3 -Nd 2 O 3 electrolyte at high oxygen potential under basic conditions were also studied. The Nd fluoride complex behavior in the electrolyte was investigated by cyclic voltammetry for a concentration change of NdF 3 with LiF at 1100 °C from 10 wt% to 64.6 wt%. The experimental results indicated that NdF 3 is reduced to Nd(0) via a multi-step process. NdF 2 could be produced by the comproportionation reaction between NdF 3 and Nd metal. Additionally, the rate equation for NdF 2 generation was derived through a reactivity test between the metal and the Nd 2 O 3 -free electrolyte. However, NdF 2 production was suppressed in LiF-NdF 3 -Nd 2 O 3 electrolyte. [ABSTRACT FROM AUTHOR]

• The corrosion resistance of YSZ was investigated in CaCl 2 -CaF 2 -CaO molten salt. • The reactivity between YSZ and molten salt was dependent on grain size. • Chemical attack occurred preferentially at the grain boundaries over YSZ grains. • With increasing grain size, grain boundary area decreased, reducing the attack path. • Larger grain sizes resulted in reduced reaction between YSZ and the molten salt. The hot corrosion behaviour of YSZ specimens sintered at 1500 °C (6 and 11 h) and 1600 °C (11 h) was evaluated in CaCl 2 -CaF 2 -CaO molten salt at 1150 °C. YSZ sintered at 1600 °C for 11 h exhibited the lowest corrosion, whereas YSZ sintered at 1500 °C for 6 h showed the most corrosion, with a grain size dependency. XRD analysis showed that all YSZ contained mainly CaZrO 3 with a small t-ZrO 2 peak. To use SOM anodes for the electrowinning of various metals, the corrosion resistance of YSZ can be improved by adjusting the grain size instead of adding stabilizers. [ABSTRACT FROM AUTHOR]

Among metal waste generated during the dismantling of a nuclear power plant, the steam generator, which is the main component of nickel alloy contaminated by Co-60, is classified as large-scale waste. Therefore, for the decontamination of cobalt in a contaminated nickel alloy, the separation behavior of nickel and cobalt in a LiCl-KCl molten salt containing NiCl 2 was investigated at 550 °C. Cyclic voltammetry (CV) measurements were recorded for determining the electrochemical properties of Ni and Co in molten salt. As CoCl 2 was added into the salt, the reduction peak of cobalt was observed. However, the oxidation peak of cobalt could not be observed owing to the dissolution of the cobalt resulting from the chemical reaction with NiCl 2. The highest separation factor of Co to Ni was calculated to be 1394 when the Ni2+/Co2+ ratio was 4, which indicated that Ni and Co can be separated. Therefore, the possibility of its application in the radioactive waste of Ni alloys from a steam generator via electrorefining using molten salt technology was confirmed. • The possibility of separating nickel and cobalt in molten salt was investigated. • CV was measured for the electrochemical properties of Ni and Co in the molten salt. • Chronopotentiometry measurements were taken for determining separation factor. • The higher is the Ni2+/Co2+ ratio, the higher is the separation factor. • The lowest concentration of Co and highest separation factor were 691 ppm and 1394. [ABSTRACT FROM AUTHOR]