Thermal Decomposition of NTO: An Explanation of the High Activation Energy

Abstract

Burning rate characteristics of the low-sensitivity explosive 5nitro-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 8C have been derived from a condensed-phase combustion model (k ¼ 8.08 · 10 13 · exp(À 19420/T) s À1 . NTO vapor pressure above the liquid (ln P ¼ À 9914.4/T þ 14.82) and solid phases (ln P ¼ À 12984.4/T þ 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 8C the decomposition of solid NTO is described by the following expression: k ¼ 2.9 · 10 12 · exp(À 20680/T). Taking into account the vapor pressure data obtained, the decomposition of NTO in the gas phase at 240 -250 8C 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 submelting 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 8C 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.

Synthesis and Physicochemical Properties of Energetic 1,2,4,5‐Tetrazinyl Derivatives of 5‐Nitro‐2,4‐dihydro‐1,2,4‐triazol‐3‐one

“…Combustion at low pressures proceeds in a flameless mode; the dependence of the burning rate on pressure is described by the law r b (mm s -1 ) = 2.73p 0.71 in the pressure range of 2-10 MPa and r b = 7.43p 0.28 in the pressure range of 10-20 MPa (Figure 5). Compound NTO 2 Tz surpasses NTO [56] in the burning rate.…”

“…Note that the decomposition of NTO under similar conditions produces almost half the amount of gaseous products (2.75 moles per mole of NTO). [56] It turned out that the compound NTO 2 Tz, when stored in air, turns into crystalline hydrate. When a pressure gauge with NTO 2 Tz * H 2 O crystalline hydrate is placed in a thermostat (at 240-250°C), a rapid release of crystallization water is observed and the rate of decomposition increases (at 250°C, the dried product decomposes completely in 95 minutes, and the crystalline hydrate decomposes in 40 minutes).…”

“…[59] Such a high value of the activation energy is explained by the preliminary isomerization of the nitrotriazolone ring, which is hindered by the crystal lattice. [56] Obviously, in the case of NTO 2 Tz, the decomposition of the compound also begins with preliminary isomerization and decomposition of the nitrotriazolone ring (Scheme 4).…”

“…As seen from Figure 6, the NTO 2 Tz surface temperature is significantly higher than the NTO surface temperature. [56] The temperature gradient above the burning surface at 0.2 MPa is about 3 ⋅ 10 4 K cm À 1 and provides the heat feedback from the gas phase as 130 J g À 1 , given respective burningrates and an average thermal conductivity coefficient λ = 7.5 ⋅ 10 À 4 J cm À 1 s À 1 K À 1 are used in the calculation. At the same time, only for heating the substance to the surface temperature, the following amount of heat is needed: c p (T S -T 0 ) = 1.67*(713-298) = 693 J g À 1 .…”

Review on Promising Insensitive Energetic Materials

“…It is insensitive to spark and friction and has impact insensitivity (h 50% = 117 cm) approaching that of TATB (>177 cm) [65]. Amino-5-nitro-l,2,4-triazole (ANTA) 3-Amino-5-nitro-l,2,4-triazole (ANTA), an amino-nitro-heterocyclic compound has received some interest as an energetic material due to its greater heat of formation [66]. Explosives containing a triazole ring are of multipurpose interests because the heterocyclic ring system confers a high density, thermal stability, high nitrogen content, high volume of detonation products, and insensitivity to impact [67].…”