Sodium borohydride synthesis by reaction of Na2O contained sodium borate with Al and hydrogen

In this paper, sequential experiments were designed to explore the possibility of sodium borohydride synthesis by reaction of sodium borates with Al and hydrogen. It was found that NaBH4 cannot be formed by reaction of NaBO2 with Al and hydrogen but can be formed by reaction of Na4B2O5 with Al and hydrogen. NaBH4 formation was confirmed by X-ray diffraction analyses and morphology observations. It was found that Na2O in Na4B2O5 played an important role in NaBH4 formation due to the depression of Al2O3 formation. The highest sodium borohydride yield (65.8%) was obtained by reaction of a mixture of Na4B2O5, NaBO2, and Na2O with Al and hydrogen. However, NaBH4 formation was dependent upon the physical state of sodium borates. When sodium borates melted, NaBH4 formation was retarded due to the difficulty of hydrogen diffusion to Al surfaces.