Thermal decomposition of hexanitrohexaazaisowurtzitane and its residues

Hexanitrohexaazaisowurtzitane (HNIW) particles were heated isothermally at (204.0±0.5), (208.0±0.5), (212.0±0.5), and (216.0±0.5)°C for 10, 20, 30, 40, 50, and 60 min under (2.0±0.1) MPa pressure in an argon atmosphere. Residues obtained at (208.0±0.5) °C were studied by elemental analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetry-differential scanning calorimetry-mass spectrometry (TG-DSC-MS) and thermogravimetry-Fourier transform infrared (TG-FTIR) spectroscopy. Results showed that after isothermal decomposition of HNIW crystals at about 210.0 °C for 60 min residues were formed with an average molecular formula of C₂H₂N ₂O. Unreacted HNIW is present in the residue and is more thermally unstable than the original HNIW. We confirmed that HNIW crystals decomposed stepwise under isothermal conditions. Three stages were found to exist during the thermal decomposition of HNIW residues. The first decomposition stage consists of an initial decomposition of unreacted HNIW, the second stage comprises an elimination reaction of five-membered ring amides and nitrogen heterocyclic compounds and in the third stage fivemembered ring amides are degraded and secondary reactions involving NO₂2 occur. The main gaseous products in every stage are discussed.