Combustion of CL-20 cocrystals

Combustion behavior, flame structure, and thermal decomposition of bimolecular crystals of hexanitrohexaazaisowurtzitane (CL-20) with glycerol triacetate (GTA), tris[1,2,5]oxadiazolo[3,4-b:3′,4′-d:3″,4″-f]azepine-7-amine (ATFAz), 4,4′′-dinitro-ter-furazan (BNTF), oxepino[2,3-c:4,5-c′:6,7-c′′]trisfurazan (OTF), oxepino[2,3-c:4,5-c′:6,7-c′′]trisfurazan-1-oxide (OTFO) have been studied by using a constant-pressure bomb, microthermocouple technique, and TG/DSC analysis. It has been found that the introduction of volatile and thermally stable compounds into the composition with CL-20 brought about unexpected results: first, the thermally stable component decreased the thermal stability of CL-20, and second, even twofold dilution of rapidly-burning CL-20 with slow-burning compound may practically does not change the burning rate of the former. It was suggested that a reason for the observed phenomena might be amorphous CL-20 which remains after evaporation of the volatile component in the combustion wave. The above assumption was confirmed by combustion modeling of bimolecular crystals in a wide pressure interval. It has been found that the combustion mechanism of the CL-20 cocrystals depends both on the burning rate of the second component and its volatility. Depending on these parameters, several combustion models of cocrystals are implemented: the burning rate is determined by (1) the CL-20 heat release kinetics at its boiling temperature, (2) the CL-20 heat release kinetics at the boiling point of the second component and (3) by the heat flow from the gas phase. It is abundantly clear that all these combustion mechanisms can be realized in real CL-20-based propellants.