Custom-designed spectrophotometry system for optical absorption measurements of highly corrosive molten media in...

Optical absorption spectroscopy of halide molten salts enables the determination of the valence state and coordination properties of transition and rare-earth metals, as well as actinides which are present in these melts. However, a serious challenge arises from the highly corrosive behavior of the molten halides. Thus, the application of quartz cuvettes, commonly used for optical absorption spectroscopy as containers for liquid samples, is significantly limited because quartz can be easily dissolved by the melt. Herein, to overcome these issues, we present the design and verification results of a custom spectrophotometry system integrated into a glovebox, allowing for optical absorption measurements based on reflection registration geometry. Such registration geometry allows for utilizing a Pt or glassy carbon crucible as a container for the melt, with the Pt-Rh mirror on its bottom, which remains stable in numerous molten media. The absorption process occurs during vertical light transmission through the melt layer located above the mirror. The beam reflected back by the mirror and re-passed through the melt is detected by a spectrometer. An induction furnace provides the possibility for experiments at temperatures up to 2000 K. Integrating the system into a glovebox allows for convenient operation with materials under a controlled, pure inert atmosphere, which is crucial for halide melts. Verification was performed on KMnO4, PS-7 optical glass, and (LiF-NaF-KF)eut-2 mol. % NdF3 melt. The designed system is promising for measurements of highly corrosive (e.g., fluorides), highly hygroscopic (e.g., LiCl), and high-temperature (e.g., silicates) melts.