Multistep Thermolysis Mechanisms of Azido-s-triazine Derivatives and Kinetic Compensation Effects for the Rate-Limiting Processes

Abstract

The decomposition kinetics and mechanisms of 2-amino-4,6,-diazido-s-triazine and its derivatives have been investigated using TG techniques and quantum chemical calculations. The kinetic compensation effect for their rate-limiting steps are found, which is compared with some other group of materials. It has been found that the activation energy of DAAT is about 99.7 kJ.mol -1 , which is much lower than those of the first decomposition steps of its analogues. The activation energy of the first step of DANT is much higher than the second one, while the third and fourth ones have almost the same activation energy (127.2 kJ.mol -1 ). The decomposition of DAAT does not follow any ideal model due to strong interaction of overlapped reactions. All four decomposition steps of DANT as well as the first step of TAHT follow the same A2 model. The first two steps of TANDAzT decomposition are controlled by a "phase boundary controlled" mechanism, while the third and fourth steps roughly follow a "two-dimensional diffusion" model. It has been found that the first step of DANT decomposition is featured by scission of NH-NO2 bond via HONO elimination, which is very similar to nitramine decomposition. Decomposition of DAAT and DANT are featured by azido group scission, and the latter is greatly affected by elimination of HONO. As a comparison, the rate-limiting decomposition step of nitramine is featured by the bond rupture of N-NO2, while it is O-NO2 for nitric esters and C-NO2 for aromatic nitrocompounds, following on different kinetic compensation lines. The rate-limiting steps for involved materials are scission of azido group.Under the effect of the other function groups, the isokinetic temperatures for azido group scission are almost identical while their reaction rates are quite different.

Catalytic Reactivity of Graphene Oxide Stabilized Transition Metal Complexes of Triaminoguanidine on Thermolysis of RDX

“…Therefore, they could change the decomposition mechanism from the F1 model to what appears a two-dimensional Avrami–Erofeev nucleation and growth model . Similar results have been reported by showing the addition of clay nanoflakes produced a change of the thermal degradation mechanism toward a nucleation and growth model. −, The similarity of two works indicates such mechanism change is likely to be responsible for the increased stability of the composite because nucleation is an acceleratory mechanism that needs the formation of initiating decay centers before the degradation propagates through the bulk of the material. For pure RDX, as mentioned in the last section, its initial stage of decomposition in closed pans has activation energy of 206 kJ mol –1 , which is consistent with liquid phase RDX decomposition .…”

Critical Appraisal of Kinetic Calculation Methods Applied to Overlapping Multistep Reactions

“…The fitting function with the asymmetric peak shape is generally recommended, e.g., Fraser–Suzuki function [27]:F(t)=a0⋅exp(−ln2[ln(1+2a3t−a1a2)a3]2), where a 0 , a 1 , a 2 , a 3 are the amplitude, position, half-width and asymmetry of the curve, respectively. This approach has been successfully applied for real-life complex processes [49,50].…”

Sensitivity and Performance of Energetic Materials

“…The secondm ethod [ 149] uses an ew computer program, named EDPHT 2.0, which also embracest he prediction of the crystal density and enthalpy of formation and, in the case of activation energieso ft hermolysis, reflects the work reportedi nZ eman's papers [143,144,[149][150][151][152][153]; for predicting activation energiesthis program needs no experimental data and the conformity of its results with data from the Russian manometric methodi sg ood.T he experimental investigation of the relation of the molecular structure of 10 nitric esters and their thermal reactivity is addressedi n the papersb yY an et al [154,155].F or this purpose TGA and DSC were used. With the exception of the evaporable members of this series, the activation energies of decompositionc orrespond to those from using the Russian manometric method [ 154].T he results of an investigation,u sing thermogravimetry (TGA) techniquesa nd quantum chemical calculations, into the decomposition kinetics and mechanisms of 2-amino-4,6,-diazido-s-triazine and its five derivatives have beenr eported in paper [156].T he rate-limiting steps for the materials involved are the scission of the azido group, for which the kinetic compensation effect was found and compared with some other groups of EMs. Authors Yane tal.…”