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Thermal Decomposition of NTO: An Explanation of the High Activation Energy
Author(s) -
Sinditskii Valery P.,
Smirnov Sergei P.,
Egorshev Viacheslav Yu.
Publication year - 2007
Publication title -
propellants, explosives, pyrotechnics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.56
H-Index - 65
eISSN - 1521-4087
pISSN - 0721-3115
DOI - 10.1002/prep.200700029
Subject(s) - thermal decomposition , decomposition , chemistry , activation energy , combustion , melting point , thermodynamics , reaction rate constant , analytical chemistry (journal) , vapor pressure , materials science , kinetics , organic chemistry , physics , quantum mechanics
Burning rate characteristics of the low‐sensitivity explosive 5‐nitro‐1,2,4‐triazol‐3‐one (NTO) have been investigated in the pressure interval of 0.1–40 MPa. The temperature distribution in the combustion wave of NTO has been measured at pressures of 0.4–2.1 MPa. Based on burning rate and thermocouple measurements, rate constants of NTO decomposition in the molten layer at 370–425 °C have been derived from a condensed‐phase combustion model ( k =8.08⋅10 13 ⋅exp(−19420/ T ) s −1 . NTO vapor pressure above the liquid (ln P =−9914.4/ T +14.82) and solid phases (ln P =−12984.4/ T +20.48) has been calculated. Decomposition rates of NTO at low temperatures have been defined more exactly and it has been shown that in the interval of 180–230 °C the decomposition of solid NTO is described by the following expression: k =2.9⋅10 12 ⋅exp(−20680 /T ). Taking into account the vapor pressure data obtained, the decomposition of NTO in the gas phase at 240–250 °C has been studied. Decomposition rate constants in the gaseous phase have been found to be comparable with rate constants in the solid state. Therefore, a partial decomposition in the gas cannot substantially increase the total rate. High values of the activation energy for solid‐state decomposition of NTO are not likely to be connected with a sub‐melting effect, because decomposition occurs at temperatures well below the melting point. It has been suggested that the abnormally high activation energy in the interval of 230–270 °C is a consequence of peculiarities of the NTO transitional process rather than strong bonds in the molecule. In this area, the NTO molecule undergoes isomerization into the aci ‐form, followed by C3‐N2 heterocyclic bond rupture. Both processes depend on temperature, resulting in an abnormally high value of the observed activation energy.