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 = 10.48 Å, b = 6.91 Å and c = 12.25 Å and Pbca space group, was formed. It has been ascertained that orthorhombic phase is NaBH4·2H2O – 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.