Revealing 3D Morphological Evolution and Reaction Kinetics of Metals and Alloys in Molten Salts Via Synchrotron X-Ray Nano-Tomography and Multimodal Studies

The use of molten salts for large-scale solar concentrated power plants and molten salt reactors has been driving the research to better understand how metals and alloys interact with the molten salt. As the metals may undergo morphological, chemical, and structural change in molten salt environments, it is critical to understand the fundamental mechanisms in these changes. In this work, we will present how we utilized synchrotron X-ray nano-tomography to better understand the 3D morphological evolution of Ni, Cr, and their alloys in molten salt. The effects of temperature and additives in the salt on the morphological evolution will be discussed. At the higher temperature, a characteristic bicontinuous structure can form from molten salt dealloying a binary alloy. [1] This contrasts to the intergranular corrosion found in the same system reacted at a lower temperature. [2] Different additives in the salt were also found to alter the morphological changes of the alloys and can create planar corrosion, percolation dealloying, or redeposition. To complement the morphological studies by X-ray nano-tomography, a suite of X-ray and electron microscopy analyses were also carried out to better understand the chemical and structural (both short-and long-range ordering) evolution. Taking it as a multimodal approach, we will discuss how we couple the analysis from synchrotron operando X-ray absorption spectroscopy, diffraction, and imaging, as well as the multiscale imaging studies from both X-ray and electron microscopy. This work was supported as part of the Molten Salts in Extreme Environments (MSEE) Energy Frontier Research Center (EFRC), funded by the U.S. Department of Energy, Office of Science. References: [1] "Formation of three-dimensional bicontinuous structures via molten salt dealloying studied in real-time by in situ synchrotron X-ray nano-tomography" Xiaoyang Liu, Arthur Ronne*, Lin-Chieh Yu, Yang Liu, Mingyuan Ge, Cheng-Hung Lin, Bobby Layne, Phillip Halstenberg, Dmitry S. Maltsev, Alexander S. Ivanov, Stephen Antonelli, Sheng Dai, Wah-Keat Lee, Shannon M. Mahurin, Anatoly I. Frenkel, James F. Wishart, Xianghui Xiao & Yu-chen Karen Chen-Wiegart* Nature Communications (2021), DOI: 10.1038/s41467-021-23598-8 [2] "Visualizing time-dependent microstructural and chemical evolution during molten salt corrosion of Ni-20Cr model alloy using correlative quasi in situ TEM and in situ synchrotron X-ray nano-tomography" Kaustubh Bawane, Xiaoyang Liu, Ruchi Gakhar, Michael Woods, Mingyuan Ge, Xianghui Xiao, Wah-Keat Lee, Philip Halstenberg, Sheng Dai, Shannon Mahurin, Simon M. Pimblott, James F. Wishart, Yu-chen Karen Chen-Wiegart*, Lingfeng He* Corrosion Science (2021), DOI: 10.1016/j.corsci.2021.109962