Infrared Spectra of N–H Compounds in LiCl-KCl-CsCl Molten Salts Using the Diffuse Reflectance Optical System

The in-situ Fourier transform infrared spectroscopy of molten eutectic LiCl-KCl-CsCl was conducted in order to identify the dissolved ions in the molten salt electrolytes. The transflectance spectrum of the melts could be easily obtained at temperatures higher than 350°C using the commercially available diffuse reflectance optical system and an air-tight chamber with a built-in heater. The sharp absorption peak attributable to the stretching vibration of OH− was observed in the melt containing LiOH, indicating the availability of identification of dissolved species in the melts. The intensities of transflection possibly assignable to N–H bonds in imide (NH2−) and amide (NH2−) anions in the melt containing Li3N changed during supplying H2 gas because of the progress of the protonation reactions of these anions to form NH3. The in-situ analysis of the dissolved ions in the melts under the reaction conditions by infrared spectroscopy with the diffuse reflectance optical system can be a simple and powerful tool for understanding the reaction mechanism.