Thermal decomposition and spectroscopic studies of preheated ammonia borane

This paper presents enhanced dehydrogenation of solid ammonia borane (AB, NH₃BH₃) at 85 °C after it was preheated at 80 °C for 2-4 h. Thermal treatments and subsequent hydrogen release experiments were carried out in a Hastelloy cell mounted on a high-pressure differential scanning calorimeter. With increased preheating durations, not only does the induction period for hydrogen release shorten but also the hydrogen release becomes fast. It is deduced that diammoniate of diborane (DADB, [(NH₃) ₂BH₂]⁺[BH₄]^-), oligomers or polymers, and AB form a solid solution, shifting the melting temperature of AB to a low value. Hydrogen evolution, as the result of the initial stage of oligomerization, is observed after maintaining pristine AB at 80 °C for 20 min. FTIR-ATR spectra of thermally treated AB indicated that only linear dimers of aminoborane (LDAB, NH₃BH₂NH₂BH₃) are detected for preheating periods shorter than 3 h, whereas other oligomers and polymers form for the longer thermal treatment at 80 °C.