Thermochemical investigations on borazane (BH 3–NH 3) in the temperature range from 10 to 289 K

Abstract

The molar heat capacity of borazane BH 3–NH 3 was determined in the 10–289 K range. Two different adiabatic calorimeter systems, each using the classical heat-step method, were applied for the measurements. The molar standard entropy of borazane at T=298.15 K was determined to be S 0=96.34 J K −1 mol −1. For the phase transition at T=224 K, a transition entropy of Δ S=6.87 J K −1 mol −1 was calculated from the heat capacity data. The results of X-ray powder diffraction confirm an order–disorder transition with a change of the lattice structure from orthorhombic to tetragonal. From low-temperature differential scanning calorimetry, a transition enthalpy of Δ H=1.34 kJ mol −1 was found, the transition enthalpy derived from the heat capacity is Δ H=1.48 kJ mol −1