Hydrogen isotope effects on the structural phase transition of NH3BH3

✍ Scribed by Oriele Palumbo; Annalisa Paolone; Pasquale Rispoli; Rosario Cantelli; Tom Autrey; Abhijeet Karkamkar; Maria Assunta Navarra

• Publisher: Elsevier Science
• Year: 2011
• Tongue: English
• Weight: 430 KB
• Volume: 36
• Category: Article
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2010.12.076

✦ Synopsis

A systematic study of the structural phase transition of NH 3 BH 3 and of its fully deuterated analogue was performed combining DSC and anelastic spectroscopy measurements. The transition is accompanied by a latent heat, and therefore is of the 1st order. On the deuterated sample the enthalpy variation is reduced of more than 20%, from 1.29 to 1.01 kJ/mol and the transition is shifted by w1.5 K toward higher temperatures. Both NH 3 BH 3 and ND 3 BD 3 display a temperature hysteresis between cooling and heating, thus denoting that the phase transition is of first-order. In addition, this hysteresis is extremely small (w0.5 K) indicating that the coexistence region between the two phases is very narrow. During isothermal ageing, the transformation of the low-temperature orthorhombic phase into the hightemperature tetragonal one occurs with a time constant of w16 min in NH 3 BH 3 and w64 min in ND 3 BD 3 , evidencing a drastic slowing down of kinetics in the deuterated compound.