Study of by-product of NaBH₄ hydrolysis and its behavior at a room temperature

We report here the observation of phase transitions within mixtures of NaBH₄ and various organic additives exposed to open air at a room temperature 22(±1) °C and air humidity 35(±5)%. During the exposure the phase composition of materials was monitored by X-ray diffraction. Also, we found that new crystal phases appear during the exposure. Initially the phase, which was identified as the orthorhombic phase with unit cell parameters a = 10.48Å , b = 6.91Å and c = 12.25Å and Pbca space group, was formed. It has been ascertained that orthorhombic phase is NaBH ₄·2H₂O - hydrated sodium boron hydride. Upon prolonged exposure this phase then finally transformed to the known crystalline tincalconite (Na₂B₄O₅(OH)₄· 3H₂O). We explained the observed phase transitions as hydrolysis of NaBH₄ and hydration of by-product due to absorption of air humidity. It was ascertained that kinetics of processes depends on kind of organic additives.