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

Borazane BH3NH3 is a crystalline solid with a high hydrogen content. It dec omposes thermally activated already at temperatures below 410 K. The thermal decomposition of BH3NH3 was studied by thermogravimetry (TG), d ifferential scanning calorimetry (DSC), volumetric measurements and coupled TG/FTIR. Measurements were performed under isothermal conditions and in sc anning mode. The enthalpy change at the exothermic decomposition reaction Delta(r)H was determined by use of DSC-technique. At different heating rates and temperat ures a value of Delta(r)H = -(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 literat ure. As a consequence of the low decomposition rate a separation of differe nt steps is possible only at low heating rates. The decomposition reaction is accompanied by hydrogen evolution. During thi s first decomposition step borazane releases approximately 1 mol H-2 per mo l 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 measu rements, IR-spectroscopy and elemental analysis. The small amount of borazi ne 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 init ial 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. (C) 2000 Elsevier Science B.V. All rights reserved.