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In order to investigate the corrosion behavior of Inconel 625 deposited metal in molten KCl and MgCl2, the corrosion behavior of deposited metal immersed in molten salt for 60 h at 700 °C and 900 °C was studied by static corrosion immersion method. X-ray diffraction (XRD) and Geminisem300 were used to systematically study the phase composition, cor...
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The single ion activity coefficients of Cl-,γCl-, in aqueous NaCl and MgCl2 solutions have been estimated at 25 °C potentiometrically by use of galvanic cells with ionic liquid salt bridge consisting of tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide. With increasing the ionic strength, Im, the γCl- decreases monotonously up...
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... KCl-MgCl 2 molten salts should also have good compatibility with heat storage containers, pipelines, and valves to realize their application as heat transfer and storage medium [3,9]. In order to explore the interaction between molten KCl-MgCl 2 salts and alloys, the corrosion behavior and mechanism have been investigated in the literature [10][11][12]. Similar to the NaCl-KCl-MgCl 2 [13][14][15], NaCl-MgCl 2 [16][17][18], NaCl-KCl-CaCl 2 [19], NaCl-KCl-ZnCl 2 [20], and nitrate salts [21,22], the corrosion control of the alloys in molten KCl-MgCl 2 salts is a challenging task. ...
... The dense MgO film formed on the alloy surface can slow down the alloy corrosion, and the molten salt temperature has a great influence on the stability of the MgO protective layer. High temperature damages the MgO protective layer, which will accelerate the corrosion [11]. For CSP equipment, a high working temperature can realize the more efficient conversion of thermal energy to electrical energy and faster corrosion [4,28]. ...
The corrosion resistance of 316 stainless steel (316SS) in molten KCl-MgCl2 salts was studied through static immersion corrosion at high temperatures. Below 600 °C, the corrosion rate of 316SS increased slowly with increasing temperature. When the salt temperature rises to 700 °C, the corrosion rate of 316SS increases dramatically. The corrosion of 316SS is mainly due to the selective dissolution of Cr and Fe at high temperatures. The impurities in molten KCl-MgCl2 salts could accelerate the dissolution of Cr and Fe atoms in the grain boundary of 316SS, and purification treatment can reduce the corrosivity of KCl-MgCl2 salts. Under the experimental conditions, the diffusion rate of Cr/Fe in 316SS changed more with temperature than the reaction rate of salt impurities with Cr/Fe.
... It can be seen from Figure 10c that, after high-temperature corrosion, a large corrosion channel formed in the Inconel 625 weld cladding. According to the EMPA element distribution, there are a large number of oxides in the corrosion channel, which reduces its corrosion resistance [21]. In addition to the influence of oxides on corrosion resistance, As shown in Figure 9b, layered Cr 2 O 3 formed on the surface of nitrogen-containing low-nickel weld cladding. ...
... It can be seen from Figure 10c that, after high-temperature corrosion, a large corrosion channel formed in the Inconel 625 weld cladding. According to the EMPA element distribution, there are a large number of oxides in the corrosion channel, which reduces its corrosion resistance [21]. In addition to the influence of oxides on corrosion resistance, the diffusion precipitation of Cr is also an important factor. ...
In this paper, the element nitrogen (N) is used to partially replace the element nickel (Ni) in flux-cored wire. A 44%Ni-24%Cr-0.18N nitrogen-containing low-nickel flux-cored wire with excellent corrosion resistance is prepared. The corrosion behavior of nitrogen-containing low-nickel weld cladding and Inconel 625 weld cladding in 40 KCl + 60 MgCl2 (wt%) molten salt at 900 °C is studied. The results show that the selective dissolution of Cr occurs in both weld claddings. The corrosion resistance of the 44%Ni-24%Cr-0.18N nitrogen-containing low-nickel weld cladding is better than that of the Inconel 625 weld cladding. The reason is that added N can react with H+ in molten salt to generate NH4+, remove corrosive impurities of MgOH+ in molten salt and change the corrosion environment. N preferentially combines with Cr to form Cr2N, reduces the diffusion precipitation of Cr and improves the corrosion resistance.
... Current regulations with the nuclear power section of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code are for traditional water-cooled reactors and cannot translate to MCFR structural materials. Many commercial structural alloys have been considered for construction of MCFRs, including alloys from the Inconel (Olson et al., 2009;Salinas-Solano et al., 2014;Grégoire et al., 2020;Yang et al., 2020;Lei et al., 2021;Pragnya et al., 2021) and Hastelloy series (Yang et al., 2016;Ye et al., 2016;Ding et al., 2018;Ezell et al., 2020;Knosalla et al., 2020). Informed qualification of structural materials for the construction of MCFRs in the future can only be ensured by expanding the fundamental knowledgebase pertaining to material performance under environmental stressors relevant to operation of the reactor, including corrosion susceptibility. ...
... Elucidating molten salt corrosion susceptibility requires delving further into the corrosion mechanism of MCFR structural materials, expanding on the relationship between alloy composition and microstructure on the kinetics and thermodynamics of the corrosion process. To assess changes in alloy composition and microstructure at a length scale indicative for elucidating the corrosion mechanism, a suite of advanced characterization techniques is needed (Indacochea et al., 2001;Shankar et al., 2013;Salinas-Solano et al., 2014;Vignarooban et al., 2014;Gomez-Vidal and Tirawat, 2016;Liu et al., 2017;Wang et al., 2017;Sun et al., 2018a;Ding et al., 2018;Ding et al., 2019;Jalbuena et al., 2019;Yu et al., 2019;Grégoire et al., 2020;JagadeeswaraRao and Ningshen, 2020;Knosalla et al., 2020;Yang et al., 2020;Bawane et al., 2021;Caldwell et al., 2021;Gill et al., 2021;Patel et al., 2021;Pragnya et al., 2021). More importantly, these characterization techniques need to be employed in a corroborative manner through a multi-modal approach to develop a comprehensive assessment of the corrosion mechanism. ...
... Together the two complimentary techniques captured key elements at different stages of the corrosion process to generate a comprehensive assessment. Assessing corrosion mechanisms in commercial alloys presents a more complex endeavor compared to that in model alloy systems (Indacochea et al., 2001;Shankar et al., 2013;Salinas-Solano et al., 2014;Gomez-Vidal and Tirawat, 2016;Zhu et al., 2016;Keny et al., 2019;Yu et al., 2019;Grégoire et al., 2020;Yang et al., 2020;Lei et al., 2021;Pragnya et al., 2021). An excellent example is Xi, et al. analysis of microstructural changes in Hastelloy N in FLiNaK molten salt through a complementary application of x-ray diffraction (XRD), electron probe micro-analyzer, synchrotron scanning transmission x-ray microscopy (TXM), SEM, S/TEM, and XAS (Ye et al., 2016). ...
The United States Department of Energy (DOE) has committed to expanding the domestic clean energy portfolio in response to the rising challenges of energy security in the wake of climate change. Accordingly, the construction of a series of Generation IV reactor technologies are being demonstrated, including sodium-cooled, small modular, and molten chloride fast reactors (MCFRs). To date, there are no fully qualified structural materials for constructing MCFRs. A number of commercial structural alloys have been considered for the construction of MCFRs, including alloys from the Inconel and Hastelloy series. Informed qualification of structural materials for the construction of MCFRs in the future can only be ensured by expanding the current fundamental knowledgebase of information pertaining to material performance under environmental stressors relevant to operation of the reactor, including corrosion susceptibility. The purpose of this investigation is to illustrate how a correlative multi-modal electron microscopy characterization approach, including the novel application of focused-ion beam 3D reconstruction capabilities, can elucidate the corrosion mechanism of a candidate structural material Inconel 617 for MCFR in NaCl-MgCl2 eutectic salt at 700°C for 1,000 h. Evidence of intergranular corrosion, Ni and Fe dealloying, and Cr-O enrichment along the grain boundary, which most likely corresponds to Cr2O3, is a phenomenon that has been documented in other Ni-based superalloys exposed to chloride molten salt systems. Additional corrosion products, including the formation of insoluble MgAl2O4, within the porous network produced by the salt attack is a novel observation. In addition, Mo3Si5 and τ2 precipitates are detected in the alloy bulk and are dissolved by the salt. Furthermore, the lack of detection of design γ′ precipitates in Inconel 617 after 1,000 h could indicate that the molten salt corrosion mechanism has indirectly induced a phase transformation of Al2TiNi (τ2) and Ni3(Al,Ti) (γ’) phase. This investigation provides a comprehensive understanding of molten salt corrosion mechanisms in a complex material system such as a commercial structural alloy for applications in MCFRs.
The corrosion behavior of GH3535 alloys in KCl–MgCl 2 eutectic salts with or without magnesium (Mg) was investigated using the static immersion tests. The effect of purification treatment on the corrosion of GH3535 specimens was also evaluated by the different analysis. The KCl–MgCl 2 salts purified with Mg and reducing service temperature can slow down the corrosion rate of GH3535 specimens. Infrared spectra results showed that purification treatment reduced the content of crystal water in the KCl–MgCl 2 salts. The difference of hydrate content in KCl–MgCl 2 salts and the diffusion rate of Cr in alloy are the main reasons for the change of GH3535 specimens corrosion rate.
In this paper, in order to improve the corrosion resistance of 316SS in molten chloride salt, an in-situ grown Al2O3 diffusion barrier is prepared through firstly electro-depositing an inner Ni-Al/NiO composite transition layer and an outer Ni layer through double-pulse composite electroplating technique, following by annealing at 800 oC for 12 h under Ar. The obtained Al2O3/Ni composite coating is dense and shows good adherence to the substrate. Then the corrosion resistance of Al2O3/Ni composite coating in molten 52MgCl2-48NaCl (wt.%) is measured through electrochemical technique and immersion tests and the corrosion mechanism is also discussed. The results show that the 316SS is effectively protected by the Al2O3/Ni composite coating from the corrosion of molten chloride salt.
There is currently an ever-increasing demand for higher process efficiencies in next generation (Gen3) concentrating solar power (CSP). Higher process efficiencies may be procured by increasing the operating temperature, and simultaneously, minimizing the degradation of materials used for construction of CSP plants (e.g., piping, thermal storage tanks, solar receivers and heat exchangers). Thus, understanding materials corrosion in the presence of molten salt mixtures used as thermal energy storage media and heat transfer fluids is indispensable for CSP development. The present paper provides insights into the effects of salt purification on the corrosion of a nickel-based alloy (Haynes 230) isothermally exposed to a stagnant chloride-based salt mixture at 800 °C. The MgCl2-based salt mixture was thermally dehydrated and chemically treated with (0.1 and 0.5 wt %) elemental magnesium. Results reveal the electrochemical nature of the corrosion process, and the formation of corrosion products such as oxides (MgO, MgCr2O4, and MgAl2O4) and nitrides (CrN) on the alloy surface and in sub-surface regions. Magnesium additions enhanced the ability to resist corrosion by reducing the concentration of impurities (H2O, MgOH⁺, OH⁻ species) and polarizing the alloy surface. The formation of nitrides in all cases studied indicates the impact of using nitrogen as a protective gas in the system. Results also reveal that a single step treatment of the salt using metallic Mg could be considered as a measure to control the salt's impurity level, e.g., if required for system control.
NaCl–KCl–CaCl2 eutectic salt was developed using the thermodynamic calculation and experimental validation for the ultra-high-temperature thermal storage. Substitutional solution model (SSM) was used to describe the liquid phase and solid solution phase, and stoichiometric compound was applied to depict the intermediate phase. The predicted eutectic temperature (481.3 °C) of NaCl–KCl–CaCl2 eutectic salt agrees well with experimental value (496.3 °C). The actual eutectic point of NaCl–KCl–CaCl2 system is placed at T = 496.3 °C, XNaCl = 0.408 mol, XKCl = 0.075 mol and XCaCl2 = 0.517 mol. The fusion enthalpy is 171.5 J/g. The weight loss is only 1.7 wt% even at 900.0 °C and 939.0 °C is determined to be the upper limit of working temperature. The average liquid specific heat capacity is 0.80 ± 0.15 (J/g⋅oC). The cost of NaCl–KCl–CaCl2 eutectic salt is only 51.6% of solar salt and 54.3% of NaCl–KCl–MgCl2 salt. SSM of thermodynamic calculation can be used as a reasonable model to optimize the chlorides salts in future. The developed NaCl–KCl–CaCl2 eutectic salts have relatively better thermo-physical properties particularly excellent ultra-high-temperature thermal stability and lower cost, and can be considered as the ultra-high-temperature thermal energy storage materials.
