Materials and Chemistry for Molten Salt Systems: Poster Session
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Stephen Raiman, University Of Michigan; Kumar Sridharan, University of Wisconsin-Madison; Nathaniel Hoyt, Argonne National Laboratory; Jinsuo Zhang, Virginia Polytechnic Institute and State University; Michael Short, Massachusetts Institute of Technology; Raluca Scarlat, University of California, Berkeley

Tuesday 5:30 PM
March 16, 2021
Room: RM 49
Location: TMS2021 Virtual

Session Chair: Stephen Raiman, Texas A&M University


A High-temperature Thermodynamic Reference Electrode Enclosed in an Alumina Tube: Mingyang Zhang1; Jinsuo Zhang1; 1Virginia Tech
    In electrochemical measurements, reference electrode (RE) is used to provide a standard for the potential on working electrode. Reference electrode should have three major capabilities: reversibility, reproducibility and stability. In the molten salt field, a thermodynamic RE is widely accepted to be an accurate standard. Since the great thermal properties and great ion conductivity of alumina; and low vapor pressure of NiCl2, the alumina tube enclosed NiCl2/Ni RE is designed for high temperature long-term usage in chloride salt. RE impedance measurement to check RE quality, CV measurement to check RE reversibility, and CP measurement to check RE potential stability were conducted at three temperatures (600 oC, 700 oC, and 800 oC) in a 10 days period. The SEM image scan provided information of the ion conduct path in alumina. The results will encourage the high-temperature electrochemical society.

An Update on the Round Robin for Molten Salt Chemical and Thermal Properties Characterization: Raluca Scarlat1; Theodore Bessman2; Jake McMurray3; 1University of California, Berkeley; 2University of South Carolina; 3Oak Ridge National Laboratory
    Under the informal umbrella of the Molten Salt Thermal Properties Working Group (MSTPWG), Oak Ridge National Laboratory (ORNL), UC Berkeley, and the University of South Carolina plan to organize a Round Robin on Chemical and Thermal Property Characterization of Molten Salts. Properties of two salt mixtures (FLiNaK and NaCl-KCl) will be measured by different groups using a diversity of methods and instruments. The results for each property will be inter-compared to understand the ability to reproduce measurements, the appropriateness and limitations of each technique, and the possible sources of error. The goals of this round robin exercise are: (1) development of standard procedures, (2) generation of calibration standards, (3) generation of verified properties (for FLiNaK and NaCl-KCl), and (4) sharing of best practices in the performance of these measurements. Molten Salt Round Robin 1.0 will run Aug 2020-Jul 2020, and this talk will provide a mid-point progress update.

Cost-effective, Reliable Containment of High-temperature Molten Chlorides for Heat Transfer and Thermal Energy Storage: Liangjuan Gao1; Elizabeth Laskowksi1; Kenneth McGowan1; Robert Cullen1; Mario Caccia1; Kenneth Sandhage1; 1Purdue University
    The drive for lower-cost dispatchable electricity from concentrating solar power plants has led to consideration of earth-abundant molten chlorides, such as MgCl2-KCl-NaCl salts, as media for high-temperature heat transfer and thermal energy storage. Large-scale, reliable containment of these molten chlorides requires cost-effective tanks and pipes with walls that are resistant to molten salt corrosion and penetration, and that provide the required resistance to heat transport. Unfortunately, upon exposure to such molten chlorides at 550-750°C, low-cost metal alloys have exhibited appreciable corrosion, whereas low-cost porous ceramics have exhibited appreciable molten chloride penetration. While such corrosion and penetration may addressed by using certain nickel-based superalloys or high-density (closed porosity) ceramics, these materials would be prohibitively expensive for long pipe lengths and large storage tanks. In this talk, cost-effective materials and processes for generating pipe and tank liners that are resistant to corrosion and penetration by molten chlorides at >750oC will be discussed.

Development and Demonstration of a Novel Spectroelectrochemical Cell for Molten Salts: Dimitris Killinger1; Supathorn Phongikaroon1; 1Virginia Commonwealth University
    A modular spectroelectrochemical cell (SEC) has been designed and fabricated for the elemental and speciation characterization of molten salts. The performance of stand-alone and combined electro- and spectro- analytical techniques of the SEC (e.g., alternating cyclic voltammetry and laser induced fluorescence spectroscopy, simultaneous chronopotentiometry and absorption spectroscopy) will be compared against the literature. This work will be based on alkali-alkali/alkali-alkaline chloride based eutectic salt systems with several analytes (e.g. U, Mg, Ce, Nd, Cs, Fe) in their chloride forms to simulate molten salt compositions often found in pyroprocessing and molten salt reactors to simulate fissionable material (including surrogate materials), neutron poisons, fission products, and corrosion products. Non-traditional spectroelectrochemistry techniques (e.g. normal pulse voltammetry with time resolved laser induced fluorescence spectroscopy) will be explored with the SEC. Unique and novel apparati associated with the SEC, along with lessons learned, will be discussed.

Electron Energy Loss Spectroscopy Characterization of Molten Salt Corrosion Damage in Pure Ni and Model Ni-20Cr Binary Alloy: Kaustubh Bawane1; Panayotis Manganaris1; Yachun Wang1; Jagadeesh Sure2; Arthur Ronne3; Xiaoyang Liu3; Phillip Halstenberg4; Simerjeet Gill2; Kotaro Sasaki2; Yu-chen Karen Chen-Wiegart3; Shannon Mahurin4; Simon Pimblott1; James Wishart2; Lingfeng He1; 1Idaho National Laboratory; 2Brookhaven National Laboratory; 3Stony Brook University; 4Oak Ridge National Laboratory
    Characterization of corrosion damage is integral to understanding fundamental mechanisms of interaction between structural alloys and highly corrosive molten salts. Pure Ni and Ni-20Cr model alloys were corroded in molten ZnCl2 and KCl-MgCl2 under argon atmosphere at various temperatures. Dual energy range electron energy loss spectroscopy (EELS) technique was utilized to understand elemental dissolution behavior and oxidation states of dissolved elements in molten salt. Here, we demonstrate Python-based data analysis techniques based on principal component analysis (PCA) and multiple linear least square (MLLS) to monitor changes in the shapes of L2,3 white lines in EELS spectra. The results showed the presence of Cr3+ and Ni2+ in the molten salt, indicating metal dissolution in the form of CrCl3 and NiCl2, respectively. This work was supported as part of the Molten Salts in Extreme Environments (MSEE) Energy Frontier Research Center, funded by the U.S. Department of Energy Office of Science.

Fast and Accurate High-dimensional Neural Network Interatomic Potentials for Lithium-based Fluoride Salts: Stephen Lam1; Qing-Jie Li2; Ronald Ballinger; Charles Forsberg2; Ju Li2; 1University of Massachusetts - Lowell; 2Massachusetts Institute of Technology
    Experimental data are difficult to collect for molten salts due to the complexities and cost in handling liquids at high temperatures. Computational modeling can elucidate physical mechanisms driving behavior and can thus provide predictive capacity and help guide experimental trials. In this work, density functional theory (DFT) was used to train neural networks potentials, which were used to run molecular dynamics simulations for common constituent LiF and prototypical salt Flibe (66.6%LiF-33.3BeF2). Neural network potentials accelerated computation by several orders of magnitude and allowed exploration of longer time scales and larger system sizes beyond hundreds of atoms. It was shown that neural network potentials can accurately reproduce multi-component liquid salt system energies with a mean average error of < 2 meV/atom, and atomic forces with an error of < 0.06 eV/Å. This enabled fast and accurate prediction of chemistry, transport properties, and local structure.

Fluoride Salt Purification Using Bifluoride Salt for Hydrogen Fluoride-generation: Ronald Laehn1; Dakotah Martinez2; Aaron Robison1; 1Abilene Christian University; 2ACU NEXT Project
    Fluoride salts are substantially less corrosive to structural materials if contaminants such as water and oxides are removed. Hydrofluorination, in which the molten fluoride salt is sparged with a combination of hydrogen and hydrogen fluoride, is the most effective process for removing oxides and water from the salt. Anhydrous hydrogen fluoride presents a unique challenge due to its corrosivity and toxicity, and the cost associated with safely storing and using this chemical presents a challenge for hydrofluorination implementation. This work will describe an alternative method for the on-demand production of hydrogen fluoride from the controlled thermal degradation of bifluoride salt. Storage of anhydrous hydrogen fluoride cylinders is not required with this approach and hydrogen fluoride is only present during the hydrofluorination process making this strategy a more accessible route to hydrofluorination. The efficacy of this approach will be described through chemical analysis of the fluoride salt both pre- and post-purification.

High-temperature, Air-compatible Molten Salts, and an Associated Corrosion-resistant Containment Strategy, for Cost-effective and Reliable Heat Transfer and Thermal Energy Storage: Adam Caldwell1; Grigorios Itskos1; Saeed Bagherzadeh1; Mario Caccia1; Kenneth Sandhage1; 1Purdue University
    Molten chlorides, such as MgCl2-KCl-based liquids, are being considered as cost-effective fluids for high-temperature (>750oC) heat transfer and thermal energy storage (TES) for Concentrated Solar Power (CSP) plants and other electricity-generating systems. Unfortunately, exposure of such liquids to air at >750oC results in MgCl2 oxidation and liquid contamination with oxygen-bearing species that, in turn, result in changes in the fluid properties and in enhanced corrosion of metal alloys in pipes and storage tanks. While such salt oxidation/contamination and alloy corrosion could be addressed by tight sealing of pipes and storage tanks from air, continuous removal of oxygen-bearing species from the molten salt (e.g., using magnesium as a gettering agent), and active salt monitoring and chemical adjustment, these steps would increase the design complexity and operational cost of CSP plants. In this talk, alternative, cost-effective, air-tolerant high-temperature TES fluids, and a strategy for corrosion-resistant containment of such fluids, will be discussed.

High-temperature, High-toughness, Corrosion-resistant Cermet Alloys (NiWC) for CSP Gen 3 Subsystem Component Design : Lewis Handy-Cardenas1; Mohamed Elbakhshwan1; Scott Lee1; Mark Anderson1; Joseph Hensel2; Gabriel Santillan2; 1University of Wisconsin-Madison; 2Powdermet
    Novel cermet alloys (Nickel-Tungsten Carbide) have been studied in efforts of finding solutions to the corrosion found in novel CSP Gen 3 systems featuring chloride salts (MgCl2-KCl-NaCl). These tests featured: The cermet in different compositions (NiWC3a, NiWC3b, NiWC3c), as a high velocity oxygen fuel (HVOF) coating, Inconel 617, Inconel 625 and Haynes 230. Corrosion rates from 250-hour molten salt tests (750 °C) were found tracking weight change, performing scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). The novel cermet performed well were the substrates exhibit grain boundary attack and Cr depletion. Pin-On-Disk testing was also performed (550 RPM & 960 RPM) to assess the friction and wear performance of materials (NiWC vs Haynes 230) in molten salt (725 °C) for up to 96 hours. The wear rate on the cermet was lower, and strong evidence of material deposition (Nickel) on the Haynes 230 disk was found.

Investigating Test Parameters for Isothermal Salt Compatibility Experiments: Cory Parker1; Dino Sulejmanovic1; James Kurley1; Stephen Raiman1; Bruce Pint1; 1Oak Ridge National Laboratory
    Isothermal capsule testing is a cheap and quick way to investigate corrosion behavior of structural alloys in molten salt and an important screening test before flowing experiments. Eliminating experimental variables in these tests is difficult, however, due to the complexity of the systems involved. Capsule tests of Fe-16Cr-20Ni and Ni-16Cr alloys exposed in Cl salts in Mo and quartz capsules at 700°C for 500h, showing that direct contact between the Fe samples and Mo capsules resulted in increased specific mass loss compared to Fe samples exposed in quartz capsules. Similar capsule tests were done for FLiNaK and FLiBe salts, comparing corrosion behavior of type 316H stainless steel in 316 stainless steel capsules and Mo capsules at 550 and 650°C. This work explores the connection between corrosion rates and salt purity, temperature, alloy composition and capsule material.

Performance of Corrosion Resistant Claddings on 316H Stainless Steel in Molten Fluoride Salt: Matthew Weinstein1; Will Doniger1; Cody Falconer1; Chuan Zhang2; Cem Topbasi3; Kumar Sridharan1; Adrien Couet1; 1University Of Wisconsin Madison; 2Computherm, LLC; 3Electric Power Research Institute
    All current structural alloys, code certified for the temperature ranges expected for MSRs, contain high levels of chromium, making them highly susceptible to salt corrosion. One potential solution to circumvent the need for code certification of new alloys is to design claddings that will protect the underlying code certified materials from corrosion damage during reactor operation. In this work, we examined a variety of Nickel-based, Molybdenum-based, and HEA based coating materials on SS316H. Introduction of a carburized layer is also investigated. We performed static corrosion tests in molten FLiNaK at 700 C up to 1000 hours to assess the corrosion resistance of the cladding systems. Pre and post corrosion SEM, EDS and GDOES were performed to characterize the cladding degradation. Additionally, four-point bend tests, thermal shock tests and thermal aging were performed in conjunction with thermo-kinetic modeling to assess the mechanical properties and high temperature performance of the claddings.

Cancelled
Prediction of Actinide Salt Compounds Using Density-Functional Theory and the Universal Structure Predictor: Evolutionary Xtallography (USPEX) Algorithm: Matthew Christian1; Theodore Besmann1; 1University of South Carolina
    The interest in molten salt reactors has resulted in the need for increased exploration of phase diagrams. Salt compositions of interest are typically mixtures of three or more components that can form ternary or higher crystals upon cooling. Modeling which salt compounds form upon cooling of a salt is important for understanding reactor behavior. This is typically done by careful study of re-solidified salt melts using different compositional ratios and different environmental conditions. Exploration of potential ternary and quaternary crystal structures can be streamlined using a crystalline structure predictor algorithm paired with density-functional theory (DFT). The U-K-Li-Cl compositional region was explored to predict possible stable ternary and quaternary crystals using the Universal Structure Predictor: Evolutionary Xtallography (USPEX) algorithm. Computationally predicted crystals and stability are discussed along with discussion to applications to additional salt compositions.

Purification of Molten NaCl-CaCl2 Using Anhydrous HCl: D. Hamilton1; 1University of Utah
    Molten NaCl-CaCl2 forms a eutectic with a melting temperature of about 500°C, making it an attractive base salt for a molten chloride fast reactor (MCFR). The salt is hygroscopic, and simple thermal dehydration results in hydrolysis and formation of oxygen containing anionic species such as oxides, hydroxides, and oxychlorides. This paper presents results of the study of water removal from NaCl-CaCl2 via thermal dehydration and hydrochlorination. The purity of the processed salt was tested through base titration, acid titration, cyclic voltammetry, and thermogravimetric analysis. Using 0.5% HCl in argon, salt purification appeared to go to completion in about 5 hours based on auto-titrator output. Salt sample titrations showed hydroxide removal between 76-93%. Cyclic voltammetry of the molten salt before and after hydrochlorination indicated a 69% reduction in the hydroxide concentration. This study demonstrates that MCFR salt can be produced starting with high water content chlorides.

Relevance and Methods of Fluoroacidity Quantification: Haley Williams1; Nicholas Winner1; Raluca O. Scarlat1; 1University of California - Berkeley
    Fluoroacidity, a measure of the activity of free fluoride ions in an ionic liquid, affects the physico-chemical properties of a molten fluoride mixture which are crucial for fundamental understanding and control of these systems. The effect of fluoroacidity on solute ion coordinancy can be seen in changes in properties such as viscosity and the diffusion coefficients of solutes. With such a relevance to the salt’s properties and with the ability to serve as a metric to generalize differences among various fluoride salts, fluoroacidity is an important metric for the study of fluoride salt systems. Since fluoroacidity is a result of the equilibrium established within a salt melt, multiple methods, both electrochemical and thermodynamic, have been employed to measure the fluoroacidity of various salt mixtures. This presentation will include an analysis of opportune applications of this metric and a review of existing methods used to measure relative fluoroacidity.

Short- and Medium-range Structure of Molten Fluorides with Cr Solutes: Nicholas Winner1; Haley Williams1; Raluca Scarlat1; Mark Asta1; 1University of California Berkeley
    Understanding molten salt chemistry is essential in ongoing research of the molten salt reactor (MSR). The interaction of common corrosion products, such as Cr, with molten salts is one of the pivotal domains of understanding from a technological standpoint, and it remains an active subject of research. One interesting area of research is the way that Cr impacts the local and extended structure of molten fluorides. In this work, we use ab-initio molecular dynamics simulations to study the short- and medium-range order in three different fluoride melts with and without Cr addition. We will show that, while the local structure of Cr is largely insensitive to the solvent, the incorporation of Cr into the medium-range structure depends on the solvent. We address connections between our work and fluoroacidity-based interpretations of solvation, and we also discuss research directions into understanding mechanisms of Cr dissolution.

Testing Setup to Analyze Particulates in 316 Stainless Steel Molten Salt Systems: Reuben Howe1; Josh Dowell1; Timothy Head1; Timothy Kennedy1; 1ACU NEXT Lab
    A testing apparatus was designed and built to aid the analysis of articulates filtered from molten fluoride salt and to test the properties of filter media in typical operating conditions. The testing unit was designed to flow salt through nickel 200 and 316 stainless steel filter media with varying pore size and thickness at temperatures up to 725 °C. Data was obtained to characterize the flow rate and pressure drop across the filters, and to analyze the particulates trapped on the filter media. Design parameters of the testing setup and preliminary results of testing will be presented.

Yellowjacket: A New MOOSE-based Corrosion Modelling Application for Molten Salt Reactors: Parikshit Bajpai1; Chaitanya Bhave2; Max Poschmann1; David Andrs3; Michael Tonks2; Markus Piro1; 1Ontario Tech University; 2University of Florida; 3Idaho National Laboratory
    Predicting the complex multiscale, multiphysics behaviour of nuclear materials requires simulating problems exhibiting very tight coupling between different physical phenomena. Such strong coupling of physical phenomena is especially demonstrated in the Molten Salt Reactors (MSR) posing a challenge in reactor design and development as hitherto insignificant effects become conspicuous. One such behaviour is the corrosion of structural materials by the molten salt. Corrosion is an electrochemical process driven by the thermodynamics and kinetics of the reactions and the material microstructure significantly affects the corrosion behaviour. Corrosion modelling at mesoscale requires coupling thermodynamic equilibrium calculations with the phase field method for microstructural evolution. A new application, Yellowjacket, is being developed and it is built on the Idaho National Laboratory's Multiphysics Object Oriented Simulation Environment (MOOSE). This work describes the recent progress towards development of Yellowjacket and presents some preliminary results demonstrating simulation capabilities of interest to the development of MSRs.