Structural phase transitions and adduct release in calcium borohydride

Ca(BH4)2 compounds were investigated above room temperature by anelastic spectroscopy (AS) and concomitant measurements of thermogravimetry and mass spectrometry (TGA/MS). Both AS and TGA/MS indicate that even after a thermal treatment at 125 °C for 20 h, a non-negligible residual of THF adduct is still present in the sample, which can be removed on a subsequent thermal treatment at temperatures lower than 250 °C. Above 250 °C dehydrogenation takes place. Moreover, AS sensitively detects the occurrence of the ? ? ?' structural phase transition around 180 °C, and the ?' ? ? transformation, which is completed around 330 °C. We also show that both transitions are irreversible and are not accompanied by a latent heat.