Thermal interactions between hybrid HMX/ANPyO cocrystals and commonly used propellant ingredients

Nitramine-based composite propellants (N-CPs) are receiving significant attention in the field of solid rocket propulsion. Cyclotetramethylene tetranitramine (HMX)/2,6-diamino-3,5-dinitropyridine-1-oxide (ANPyO) cocrystals are a novel insensitive energetic material that may replace the high-energy component HMX in insensitive formulations. This study used the DSC-TG coupling technique and the in-situ FTIR technique to investigate the effects of propellant ingredients (AP, n-Al, and nano-Fe₂O₃) on the thermal decomposition of hybrid HMX/ANPyO. The results show that there are strong interactions among the components of these mixtures. In particular, the peak thermal decomposition temperatures of HMX/ANPyO/AP decreased by about 38.1–42.6 ​°C. In addition, the activation energy (E_a) of hybrid HMX/ANPyO cocrystals was reduced under the effects of Al and nano-Fe₂O₃. The hybrid HMX/ANPyO cocrystals have different flame propagation speeds, whereas the two typical binary mixtures of HMX/ANPyO/nano-Fe₂O₃ each have the lowest flame propagation speeds of 0.9 ​mm·s⁻¹ and 1.0 ​mm·s⁻¹ at ambient conditions. The flame propagation speed of HMX/ANPyO/n-Al was barely dependent on pressure, but those of HMX/ANPyO/AP and HMX/ANPyO/nano-Fe₂O₃ decreased with an increase in pressure.