Materials and Chemistry for Molten Salt Systems: Corrosion & Chemistry
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
Monday 2:00 PM
March 15, 2021
Room: RM 49
Location: TMS2021 Virtual
Session Chair: Jinsuo Zhang, Virginia Tech
2:00 PM
Corrosion Control of 316H Stainless Steel and Nickel-Based Alloys in Molten Chloride Salts: Kasey Hanson1; Krishna Moorthi Sankar1; Remi Dingreville2; Joshua Sugar2; Chaitanya Deo1; Preet Singh1; 1Georgia Institute of Technology; 2Sandia National Laboratories
Molten chloride salts are used in various energy harvesting applications such as solar concentrators and molten salt reactors. Thermodynamically driven selective dissolution of alloying elements due to impurities present within the eutectic chloride salt mixture have been identified to be the main contributor to selective dissolution of active elements like chromium from structural alloys. Impurities in these salts, during salt preparation as well as during operation, are difficult to control. This work focused on the corrosion behavior of 316H stainless steel and nickel-based alloys in a KCl—MgCl2 eutectic mixture at 700°C. The effect of added impurities to control the redox potential of salt and hence the selective dissolution behavior of tested alloys was studied. Our results indicated that active metal additions like Mg can be very effective in controlling the redox behavior of salt, which in-turn can mitigate corrosion, but may also affect other material properties if incorrectly applied.
2:20 PM
Analysis of Particulate Properties of Commercial FLiNaK in a 316 Stainless Steel System.: Timothy Kennedy1; Timothy Head1; NEXT Lab2; 1Abilene Christian University; 2NEXT Lab
Molten salt cooled reactors and other systems will require means of mechanical filtration to ensure particulates forming from corrosion or precipitating fission fragments do not foul pumps and heat exchangers. Understanding the interaction of intended particulates and filter media begins with identification of both chemical and physical makeup of common impurities in the molten salt to predict interaction with the filter media. This work will present preliminary chemical and physical analysis of particulates trapped by sintered metal filter media as molten FLiNaK is passed between two 316 stainless steel heated storage containers. Results and planned research directions will be included.
2:40 PM
Chemical Interaction Between Molten Flibe and Nitrate Solar Salt: Michael Hanson1; Michael Zupan1; Augustus Merwin1; Francesco Carotti1; Alan Kruizenga1; 1Kairos Power
(LiF)0.67(BeF2)0.33 (denoted as “Flibe” when it meets Kairos Power's specifications) is the primary coolant for the Kairos Power - High Temperature Fluoride Reactor (KP-FHR), a Generation IV nuclear power reactor. The Flibe transports heat from solid nuclear fuel in the KP-FHR to a secondary nitrate solar salt [(NaNO3)0.64(KNO3)0.36] through a heat exchanger. Chemical reactions between these two salts is of interest because of possible leaks between the primary and secondary sides of the heat exchanger. This work observed an endothermic, kinetically slow, gas-evolving chemical reaction when Flibe and nitrate solar salt were melted separately and then rapidly combined. Thermodynamic modeling of this chemical interaction and the experimental confirmation of the modeling will be presented.
3:00 PM
Mechanistic Understanding of 3D Morphological Evolution of Metals in Molten Salts
by In Situ X-ray Nano-tomography: Xiaoyang Liu1; Arthur Ronne1; Lin-Chieh Yu1; Mingyuan Ge2; Lingfeng He3; Phillip Halstenberg4; Cheng-Hung Lin1; Bobby Layne2; Sheng Dai4; Wah-Keat Lee2; Shannon Mahurin4; James Wishart2; Xianghui Xiao2; Yu-chen Karen Chen-Wiegart5; 1Stony Brook University; 2Brookhaven National Laboratory; 3Idaho National Laboratory; 4Oak Ridge National Laboratory; 5Stony Brook University / Brookhaven National Laboratory
The work discusses underlying morphological evolution mechanisms of corrosion in molten salts. We investigated the 3D morphological evolution of Ni-Cr alloy in molten KCl-MgCl2 at 500-800 °C. The corrosion of the alloys was visualized and quantified via in situ X-ray nano-tomography at the National Synchrotron Light Source II. At lower temperatures, the progression of corrosion is consistent with intergranular attack; at higher temperatures, corrosion forms a characteristic bicontinuous structure, similar to those formed by dealloying for functional applications. Electron microscopy offers further insight into the chemistry and detailed microstructure. The results indicate a mechanistic transition from intergranular corrosion to percolation dealloying as the temperature increases, shedding light on the competing mechanisms responsible for morphological evolution in molten salt corrosion. 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.
3:20 PM
Effect of Impurities on Corrosion and Its Control in Molten FLiNaK: Krishna Moorthi Sankar1; Preet Singh1; 1Georgia Institute of Technology
One of the major issues in the design of MSRs is the significant corrosion of structural materials in FLiNaK. The corrosion in the form of selective dissolution of alloying elements in these molten salts depends on their redox potential, which in-turn depends on the type and amount of impurities present. Corrosion of a given alloy also depends on the alloy composition. In this study, corrosion behaviour of selected Ni and Fe based alloys were studied in molten FLiNaK at 700 oC. Various impurities such as Li2O, CrF3, CrF2, etc. were added to baseline FLiNaK to understand their effect on this corrosion. The effect of added Li metal as a reducing agent was also studied to understand its effect in inhibiting corrosion in FLiNaK with different impurity levels. This presentation will discuss our results on the effect of impurities on the mode and extent of corrosion of the candidate alloys.
3:40 PM
Complex Structure of Molten NaCl-CrCl2 and NaCl-CrCl3: Cr-Cl Octahedra Network and Intermediate-range Order: Boris Khaykovich1; Qing-Jie Li1; David Sprouster2; Guiqiu (Tony) Zheng1; Joerg Neuefeind3; Alex Braatz3; Joanna McFarlane3; Stephen Tsz Tang Lam1; Daniel Olds4; Matthew Marshall5; Ju Li1; 1Massachusetts Institute of Technology; 2Stony Brook University; 3Oak Ridge National Laboratory; 4Brookhaven National Laboratory; 5Radiation Monitoring Devices
As molten-salt nuclear reactors operate, chemical compositions and physical properties of salts change because of fission and corrosion. Since Cr is the most important corrosion product, we present detailed studies of the molten NaCl:CrCl3 and NaCl:CrCl2 by neutron and X-ray diffraction and spectroscopy. Although the corrosion results in small amounts of Cr in the melt, we used high Cr concentration to measure the structure around Cr ions with high fidelity. We found networks of Cr-Cl octahedra and an intermediate-range order with non-monotonic temperature behavior, and remarkable agreement between experiments and ab initio simulations. The availability of Cr isotopes with very different neutron-scattering properties makes them ideal ions to model local structures in molten salts containing multi-valent cations. Also, I will present the progress towards simultaneous electrochemical and X-ray absorption spectroscopies. These results will influence every molten-salt application where corrosion-born Cr impurities appear, including nuclear and solar energy.
4:10 PM
Electrochemistry and Corrosion Studies for Alloy Development for Molten Salt Reactors (MSRs): William Doniger1; Cody Falconer1; Matthew Weinstein1; Mohamed Elbakshwan1; Govindarajan Muralidharan2; Adrien Couet3; Kumar Sridharan3; 1University Of Wisconsin Madison; 2Oak Ridge National Laboratory; 3University of Wisconsin Madison
Alloys with a combination of good long-term corrosion performance in molten salt and high-temperature mechanical strength are required for structural components of MSRs. Two nickel-based alloys, with creep strength superior to Hastelloy-N, as well as TZM, a molybdenum-based alloy with Ti and Zr additions (<1wt.%), may be potential advanced alloys for MSR applications. The advanced alloys are evaluated for corrosion in molten FLiNaK (LiF-KF-NaF) at 700oC and compared to conventional alloys 316L and 316H stainless steels, and Hastelloy-N. The results of two concurrent experiments will be presented, namely the potentiodynamic polarization method for rapid measurements of corrosion parameters and the more long-term prototypical static corrosion tests. Comparisons of the materials will be made in terms of electrochemical performance, microstructure, and microchemistry to evaluate their suitability for deployment in MSRs.