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The thermal stability of 1,3,5,5-tetranitrohexahydropyrimidine (TNDA) in liquid phase under isothermal conditions was studied. It was established that the TNDA decomposition (k liq = 3.1 • 10 21 •exp(À 26865/T), E a = 223.4 kJ mol À 1) is accompanied by strong autocatalysis (k cat = 9.8 • 10 14 •exp(-18056/T), E a = 150.2 kJ mol À 1). The mechanism of autocatalysis was proposed. The essence of autocatalysis is the oxidation of TNDA by decomposition products, followed by the destruction of the molecule. An unusual feature of this autocatalysis is that, in contrast to autocatalysis of nitroesters, the process does not disappear at high temperatures, but rather determines the kinetics of heat release in the combustion wave. The surface temperature and combustion mechanism of TNDA were established through thermocouple studies. It was shown that the autocatalysis reaction at the surface temperature controls the burning rate.

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The combustion behavior and thermal stability of 4,6,8-trinitro-4,5,7,8-tetrahydro-6H-furazano[3,4-f]-1,3,5-triazepine (FRDX) and 1,4,5,8-tetranitrodifurazano[3,4-c][3,4-h]tetraazadecaline (FTNAD) were investigated and compared with analogs, where the furazan ring is substituted with CH 2 or C=O units. It has been shown that the furazan-fused unit reduces the thermal stability of azacyclic nitramines, probably due to the weakening of the NÀ NO 2 bond. The burning rates of FRDX and FTNAD are determined by the kinetics of heat release in the melt. There is the peculiar effect of the furazan unit on the burning rate: according to thermocouple measurements, the unit increases the volatility of cyclic nitramines and reduces the temperature of the burning surface, which should lead to a decrease in the burning rate, but on the other hand, it simultaneously increases the rate of heat release in the melt, and as a result, the burning rate increases rather than falls.

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