Understanding how molten salt behaves is crucial, especially for its proposed use as a coolant in next-generation nuclear reactors and fusion energy systems, as it directly impacts safety for advanced energy production.
As researchers studied the matter, a puzzling question emerged: How did molten salt breach its metal container?
A collaborative team of U.S. researchers led by The Pennsylvania State University (Penn State) first examined a cross-section of the sealed container. Initially, they saw no clear path for the salt’s escape, according to the University Park-based school.
However, when researchers applied electron tomography, a three-dimensional (3-D) imaging technique, they uncovered minuscule, interconnected channels that bridged both sides of the solid container. This discovery sparked even more questions about this mysterious phenomenon.
The team has since shared its findings in Nature Communications.
Corrosion Resembles ‘Wormhole’
“Corrosion is a well-known cause of material failure, typically studied in three or two dimensions. However, these models couldn’t fully explain what was happening here,” says co-corresponding author Yang Yang, assistant professor of engineering science and mechanics and nuclear engineering at Penn State. “We discovered that the corrosion was so concentrated that it appeared in only one dimension—resembling a wormhole.”
Yang is also affiliated with the National Center for Electron Microscopy at Lawrence Berkeley National Laboratory and the Materials Research Institute at Penn State.
While wormholes in astrophysics are theoretical constructs, on Earth, they are often created by insects like worms or beetles, which dig through wood, soil, or fruits, leaving a trail of interconnected tunnels.
From the surface, it seems as though the creature disappears at one point and reappears at another. Electron tomography allowed the team to map out the tiny, hidden paths formed by the molten salt within the metal, showing a similar structure to these natural wormholes.
The researchers also observed that corrosion could occur in different dimensional forms—from three dimensions down to two and one. In one dimension, the corrosion predominantly travels along the grain boundaries of the metal material.
To better understand how molten salt could “bore” through the metal, Yang and his team developed innovative tools and new methods for analysis. The insights not only revealed an entirely new corrosion mechanism but also suggested the possibility of intentionally designing materials with such properties for future technologies.
Predicting Localized Corrosion
“Corrosion often occurs at specific sites due to material defects or local environmental variations, but identifying and predicting localized corrosion has always been a challenge,” says co-corresponding author Andrew M. Minor, professor of materials science and engineering at the University of California, Berkeley, and Lawrence Berkeley National Laboratory.
The researchers proposed that the formation of wormholes could be linked to an unusual concentration of vacancies—empty spaces left by missing atoms in the material.
To test this theory, the team combined four-dimensional (4-D) scanning transmission electron microscopy with theoretical modeling to pinpoint the vacancies in the material. This allowed them to map these atomic gaps at an extremely high resolution, about 10,000 times greater than traditional methods, according to Yang.
“Materials are inherently imperfect,” says co-corresponding author Michael Short, associate professor of nuclear science and engineering at the Massachusetts Institute of Technology (MIT). “As materials experience heating, irradiation, or corrosion, vacancy concentrations tend to increase. In this case, molten salt exacerbated the vacancy creation, setting the stage for the wormhole formation.”
Gaining a Deeper Understanding
Molten salt, already considered for use in various applications such as a medium for materials synthesis or as a recycling solvent in addition to being a coolant for nuclear reactors, contributes to corrosion by selectively removing atoms from the material.
This process results in one-dimensional wormholes forming along two-dimensional defects, known as grain boundaries, within the metal. The researchers found that molten salt interacted with different metal alloys in distinctive ways, affecting them in unique patterns.
“Understanding how the salt infiltrates the metal is crucial for controlling or even utilizing it for future technologies,” says co-first author Weiyue Zhou, postdoctoral associate at MIT. “This knowledge is critical for ensuring the safety of various advanced engineering systems.”
Having gained a deeper understanding of how molten salt interacts with various metals—and how different salts and metals affect this process—the researchers hope to apply their findings to predict material failures more accurately and design more resistant materials.
“The next step is to explore how this phenomenon develops over time and how we can simulate it to better understand the mechanisms at play,” says co-author Mia Jin, assistant professor of nuclear engineering at Penn State. “Once we combine modeling with experimental data, we’ll be able to more efficiently design new materials to either prevent or take advantage of this phenomenon.”
Research Support
Additional contributors include co-authors Jim Ciston, M.C. Scott, Sheng Yin, Qin Yu, Robert O. Ritchie, and Mark Asta from Lawrence Berkeley National Laboratory; co-authors Mingda Li and Ju Li from MIT; Sarah Y. Wang, Ya-Qian Zhang, and Steven E. Zeltmann from the University of California, Berkeley; and Matthew J. Olszta and Daniel K. Schreiber from the Pacific Northwest National Laboratory. Minor, Scott, Ritchie, and Asta are also affiliated with UC Berkeley.
This research was primarily supported by FUTURE (Fundamental Understanding of Transport Under Reactor Extremes), an Energy Frontier Research Center funded by the Department of Energy’s Office of Science, Basic Energy Sciences.
Source: Penn State College of Engineering, news.engr.psu.edu.
Editor’s note: This article first appeared in the June 2025 print issue of Materials Performance (MP) Magazine. Reprinted with permission.
