Formation of three-dimensional bicontinuous structures via molten salt dealloying studied in real-time by in situ synchrotron X-ray nano-tomography

Three-dimensional bicontinuous porous materials formed by dealloying contribute significantly to various applications including catalysis, sensor development and energy storage. This work studies a method of molten salt dealloying via real-time in situ synchrotron three-dimensional X-ray nano-tomography. Quantification of morphological parameters determined that long-range diffusion is the rate-determining step for the dealloying process. The subsequent coarsening rate was primarily surface diffusion controlled, with Rayleigh instability leading to ligament pinch-off and creating isolated bubbles in ligaments, while bulk diffusion leads to a slight densification. Chemical environments characterized by X-ray absorption near edge structure spectroscopic imaging show that molten salt dealloying prevents surface oxidation of the metal. In this work, gaining a fundamental mechanistic understanding of the molten salt dealloying process in forming porous structures provides a nontoxic, tunable dealloying technique and has important implications for molten salt corrosion processes, which is one of the major challenges in molten salt reactors and concentrated solar power plants. Understanding how pores evolve in metals submerged in molten salts is important for nanofabrication technology and molten salt corrosion in nuclear and solar power plants. Here, the authors present an in situ X-ray 3D imaging to directly visualize and quantify the process.

Automated summary

This study investigates a method of molten salt dealloying using real-time in situ synchrotron three-dimensional X-ray nano-tomography, revealing long-range diffusion as the rate-determining step for the process. It also shows that subsequent coarsening is primarily surface diffusion controlled, with Rayleigh instability leading to ligament pinch-off and isolated bubbles in ligaments. X-ray absorption near edge structure spectroscopic images characterize the chemical environments and demonstrate that molten salt dealloying prevents surface oxidation of the metal.