The demand for hydrogen as a clean energy carrier has increased greatly. The Cu-Cl cycle is a promising thermochemical cycle that is currently being developed to be the large-scale method of hydrogen production. The lifetime of materials for the pipes transporting molten CuCl is an important parameter for an economic design of a commercial thermochemical Cu-Cl hydrogen plant. This research is an examination of candidate materials following an immersion test in molten CuCl at 500 °C for 100 h. Two alloys, Ni based super-alloy (Inconel 625) and super austenitic stainless steel (AL6XN) were selected as the base metal. There were two types of coating applied to improve the corrosion resistance of the base metals during molten CuCl exposure. A metallic of Diamalloy 4006 and two ceramic of yttria stabilized zirconia and alumina coatings were applied to the base metal using thermal spray methods. An immersion apparatus was designed and constructed to perform an immersion test that has a condition similar to those in a hydrogen plant. After the immersion test, the materials were evaluated using an electrochemical method in combination with ex-situ surface analysis. The surface condition including elemental composition, film structure and resistivity of the materials were examined and compared. The majority of the coatings were damaged and fell off. Cracks were found in the original coated specimens indicating the sample geometry may have affected the integrity of the sprayed coating. When the coating cracked, it provided a pathway for the molten CuCl to go under the coating and react with the surface underneath the coating. Copper deposits and iron chloride that were found on the sample surfaces suggest that there were corrosion reactions that involved the metal dissolution and reduction of copper during immersion test. The results also suggest that Inconel 625 performed better than stainless steel AL6XN. Both Diamalloy 4006 and YSZ (ZrO2 18TiO2 10Y2O3) coatings seemed to provide better protection to the underlying base metal than alumina (Al2O3 3TiO2) coating. / UOIT

Report (M. Eng.)--Virginia Polytechnic Institute and State University, 1991. / Includes bibliographical references (leaves 27-28). Also available via the Internet.

Since 1955 research has been conducted at North Texas State College on diffusion in molten salts. The object of this work was a continuation of the diffusion studies, specifically the diffusion of Pb210 and Cl36 in molten PbCl2-NaCl mixtures.

This work is an extension of Yin's work studying the diffusion of Na ion in the PbCl2-NaCl system, but at more dilute compositions of NaCl.

The molten salt reactor (MSR) is one of the advanced nuclear reactors expected to be alternatives to the conventional water-cooled nuclear reactor systems. Despite many advantages of MSRs, properties of molten salts have not been sufficiently measured in previous studies. In addition, the corrosion of structural alloys by molten salt is the biggest challenge for the operation of MSRs. This study focuses on measurements of thermophysical and thermodynamic properties of fluoride salt fuels, salt purification, and the degradation of structural materials in static and flowing molten-salt fuels. For the measurements of properties, phase transition, specific heat capacity, vapor pressure, contact angle on nuclear-grade graphite, and density were measured. The methodologies for the property measurements used in this study were validated by measuring the properties of metals or salts that have been well studied. For the flow-induced corrosion tests, the salt flow with different velocities was simulated by rotating the stainless steel 316H (SS316H) specimens in molten NaF-KF-UF4 (FUNaK) contained in glassy carbon crucibles at 1073 K. Salt samples were intermittently collected to monitor concentration changes of corrosion products in the salt, and surfaces and cross-sections of post-test SS316H specimens were analyzed to study their corrosion behaviors. Different batches of FUNaK were synthesized using different methods of purification, such as thermal purification, U-metal purification, and hydrofluorination with electrochemical purification (chemical purification) to study impacts of salt purification on the corrosion of SS316H. The corrosion test of SS316H by thermally purified FUNaK showed that the Fe concentration increased at the beginning and then decreased while the Cr concentration continued increasing while the rate decreased. In addition, (Cr, Fe)7C3 layers, Cr-metal particles, and dendritic structures concentrated with Cr and Fe were observed on the glassy carbon crucible after the 2 m/s test. The U-metal purification and hydrofluorination with electrochemical purification reduced concentrations of oxygen and hydrogen in FUNaK and mitigated the corrosion of SS316H significantly. The infiltration of the fluoride fuel salts into graphite and the fluorination of graphite by the salts at different pressures and temperatures were also studied. The salt infiltration into graphite at pressures above its threshold pressure was observed, and the formation of carbon fluorides on the surface of post-test graphite specimens was identified. / Doctor of Philosophy / As conventional water-cooled nuclear power systems showed safety issues, the Generation IV International Forum was established to expedite the development of next-generation nuclear reactor systems. Among the six advanced nuclear reactors, the molten salt reactor (MSR) stands out for its remarkable technical advantages, including low operating pressures and increased efficiency resulting from higher operating temperatures compared to water-cooled nuclear systems. Despite their advantages, further studies need to be conducted to develop and operate MSRs, as properties of molten salts have not been comprehensively measured in previous studies, and the corrosion of structural materials by molten salt is a significant challenge to their operation. The corrosion of alloys by molten salt can be attributed to many different factors, and the level of impurities in salt is an important factor directly linked to corrosion. Thus, the purification of salt is imperative to mitigate the corrosion of MSRs and needs to be well studied. In this study, methodologies for measuring thermophysical and thermodynamic properties of fluoride fuel salts were developed and validated using reference data. In addition, the corrosion of stainless steel 316H (SS316H) in a flowing fuel salt was also studied. Although various corrosion tests with static molten salts have been conducted, studies on corrosion of alloys in flowing molten salt fuels containing uranium fluorides are still limited. This study addresses this gap by developing a test apparatus equipped with a rotating disk to simulate the flow of molten salt on the surface of alloy specimens. Different batches of fuel salts with varying impurity levels, especially oxygen and hydrogen, were prepared using different purification methods. These salts were then used for corrosion tests under the same conditions, such as temperature and time duration, to explore the impacts of the non-metallic impurities on the corrosion of SS316H. The findings revealed that the salts with lower levels of oxygen and hydrogen caused less corrosion of SS316H, underscoring that the purification of salt is indispensable to the mitigation of corrosion in MSRs. This study also explored interactions of molten-salt fuels with graphite which is a promising candidate for a moderator or reflector of MSRs for enhancing neutron economy for thermal nuclear reactors. A high-pressure graphite-infiltration test apparatus was developed to investigate infiltration of fluoride fuel salts into graphite and the fluorination of graphite.

Room temperature molten liquids are proposed to be good alternates for volatile and harmful organic compounds. They are useful in varied areas of applications ranging from synthesis, catalysis to energy storage molten electrolytes have certain unique characteristics such as low vapour pressure, reasonably high ionic conductivity, high thermal stability and wide electrochemical window. These molten liquids can be classified in to two types depending on the nature of the species present in the liquids. One, those liquids consists only of ions (e.g) conventional imidazolium based ionic liquids and other that consists of ions and solvents (e g) acetamide eutectics. Acetamide and its eutectics from room temperature molten solvents that is unique with interesting physicochemical properties. The solvent properties of molten acetamide are similar to water, with high dielectric consist of 60 at 353 k. its acid – base properties are also similar to water, and it can solublise variety of organic and inorganic compounds as well. in the present studies room temperature molten liquids consisting of acetamide as one of the components have been prepared and used for various applications. Room temperature molten electrolytes consisting of magnesium perchlorate/magnesium triflate as one of the constituents have been used for rechargeable magnesium batteries where as those consisting of zinc perchlorate /zinc triflate have been used for zinc based rechargeable batteries. Full utilization of cathode material (y-mno2) is achieved using amide-based molten liquid as electrolyte in rechargeable zinc based batteries. Ammonium nitrate/ lithium nitrate containing electrolytes have been used for electrochemical super capacitors. They have been used as solvent cum stabilizers for metallic nanochains that can be used as substrate in surface enchanced Raman scattering studies.

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The stability of Haynes 230 and Hastelloy C-276 nickel alloys exposed to high temperature molten salt with trace contaminants (i.e., water and oxygen) is found to be acceptable for using these metals to house anaerobic MgCl2-KCl and NaCl-KCl-ZnCl2 molten salts at 800oC. The corrosion rate determined by gravimetric tests range from -98 µm/year to 20. 13 µm/year at 800˚C. The corrosion rate is estimated to be 16.14 µm/year for Haynes 230 and 10.03 µm/year for Hastelloy C-276 based on the weight loss and surface area of the coupons when the coupons of Haynes 230 and Hastelloy C-276 alloys are immersed in molten MgCl2-KCl salt in sealed quartz containers and left in an oven at a temperature of 800˚C up to 16 days. The corrosion rate is estimated to be -20.46 µm/year for Haynes 230 and -7.36 µm/year for Hastelloy C-276 based on the weight loss and surface area of the coupons when the alloys are immersed in molten NaCl-KCl-ZnCl2 salt in sealed quartz containers and left in an oven at 800˚C up to 56 days. The corrosion rate of the alloys are well below the DOE requirement of 50 µm/year for the alloys in molten chloride salts to be considered acceptably stable. Ultimate tensile strength (UTS) after immersion of Haynes 230 and Hastelloy C-276 in molten salt ranged from 634 MPa to 860 MPa. The UTS of Haynes 230 is estimated to be 642 MPa after exposure to NaCl-KCl-ZnCl2 for 4 weeks at 800˚c and 841 MPa after exposure to MgCl2-KCl for 4 weeks at 800˚c compared to an untreated sample which achieved a UTS of 851 MPa. Likewise, the UTS of Hastelloy C-276 is estimated to be 692 MPa after exposure to NaCl-KCl-ZnCl2 for 4 weeks at 800˚c and 842 MPa after exposure to MgCl2-KCl for 4 weeks at 800˚c compared to an untreated sample which achieved a UTS of 830 MPa. Molten chloride salts, such as NaCl-KCl-ZnCl2 and KCl-MgCl2, are pretreated by heating and bubbling dry Argon gas in the salt in order to remove oxygen and water and thereby reduce the corrosion of metal containers of molten salt. Monitoring the relative humidity and percent oxygen of the exhaust gas during the sparging of dry Argon at 240 sccm into 150 g of molten chloride salt at 500˚C for NaCl-KCl-ZnCl2 and 700˚C for KCl-MgCl2 allows an estimation time to reach a low level of oxygen and water in the salt and to estimate the amount of oxygen and water removed. Results show water is more difficult to remove than oxygen from the salt. Ten minutes of sparging with dry argon brings oxygen content of exhuast gas to<0.1% O2. Approximately fifty minutes of sparging leaves the exhaust gas only containing<0.7% RH. The total moles of oxygen removed from the salts are estimated to be 0.0043 moles for molten NaCl-KCl-ZnCl2 and 0.0076 moles for KCl-MgCl2. The total moles of water removed from the NaCl-KCl-ZnCl2 salt is estimated to be 0.016108379 moles and 0.002321214 moles from molten KCl-MgCl2.