Calorimetric process monitoring of thermal decomposition of B–N–H compounds

Borazane BH3NH3 is a crystalline solid with a high hydrogen content. It decomposes thermally activated already at temperatures below 410 K. The thermal decomposition of BH3NH3 was studied by thermogravimetry (TG), differential scanning calorimetry (DSC), volumetric measurements and coupled TG/FTIR. Measurements were performed under isothermal conditions and in scanning mode. The enthalpy change at the exothermic decomposition reaction ΔrH was determined by use of DSC-technique. At different heating rates and temperatures a value of ΔrH = −(21.7 ± 1.2) kJ/mol BH3NH3 was obtained. It can be pointed out that under appropriate conditions borazane decomposes completely below the melting temperature of T = 385 K given in the literature. As a consequence of the low decomposition rate a separation of different steps is possible only at low heating rates. The decomposition reaction is accompanied by hydrogen evolution. During this first decomposition step borazane releases approximately 1 mol H2 per mol BH3NH3. The other decomposition products are a solid residue of polymeric aminoborane (BH2NH2)x and a small amount of the volatile borazine B3N3H6. The solid aminoborane was characterised by X-ray powder diffraction measurements, IR-spectroscopy and elemental analysis. The small amount of borazine formed was detected by the coupled TG/FTIR-investigations. The mass of the hydrogen released below T = 385 K is about 6.5% of the initial sample mass. Due to the significant amount of evolved hydrogen and the exothermic character of the decomposition process the use of borazane as a source for hydrogen seems to be possible and interesting.