LAUSR

Abstract To determine the synthesis conditions for NaI–NaBH4–LiI solid solutions in a single phase, the conversion reaction of NaBH4 ​+ ​LiI → NaI ​+ ​LiBH4 was investigated by preparing mixed pellets of NaBH4/LiI. The extent of the reaction was investigated under different reaction temperatures and pressures. Although it was not possible to completely suppress the conversion reaction in this study, the low temperature and high-pressure conditions were shown to be favorable to avoid the presence of LiBH4. A significant point is that the conversion reaction was investigated in a static condition in the form of pellets, whereas most of the metal borohydride-halide composites have been fabricated by ball-milling. The microstructure of NaBH4/LiI mixed pellets at different ageing times was observed by scanning electron microscope (SEM), Auger electron spectroscopy (AES), wavelength dispersive X-ray spectroscopy (WDS) and time of flight secondary ion mass spectroscopy (ToF-SIMS). The analysis revealed that the reaction interphase between NaBH4 and LiI occurs in the order of LiI/NaI/LiBH4/NaBH4. It was clearly confirmed that the growth of the NaI layer continued with time even at room temperature. In conjunction with the array of the interphase, the diffusion of Na+ in LiBH4 appears to be a necessary condition for the growth of the NaI layer. The present results suggest that a detailed investigation of the conversion reaction between other metal borohydrides and halides (for example, CeCl3/LiBH4, ZrCl4/KBH4, etc.) in the static condition would likely reveal the diffusion of the new ions in the existing compounds.