TATB thermal decomposition: Expanding the molecular profile with cryo‐focused pyrolysis GC‐MS

Abstract

Understanding the molecular composition of high explosives during thermal decomposition is vital for predicting the sensitivity, safety, and performance of explosive materials. The thermal decomposition of 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) has been linked to the formation of furazans through a series of dehydration reactions of the NO2 and NH2 groups on the phenyl ring, along with breakdown into small molecules (≤120 amu). Molecular identification of compounds formed in this transformation of the furazans to light gases has been lacking. To address this, we have applied a pseudo‐confined sampling system in a cryo‐focused pyrolysis gas chromatography‐mass spectrometry (pyGC‐MS) system to molecularly identify these intermediates. By design, sublimation of TATB, which has complicated MS analyses of thermal degradation, was significantly reduced and additional compounds were identified with potential structural information. In addition to the known furazan compounds, one of these compounds forms from the loss of oxygen from benzo‐trifurazan (F3) and produces an open ring structure that may be the first step in the formation of lower molecular weight furazan breakdown products. The loss of a nitro group from benzo‐monofurazan (F1) was also discovered and implicates the formation of oxidizing NO2 gas in the thermal decomposition mechanism. These findings are vital for understanding the proper heat flow from energetic materials on a molecular level, necessary when measuring enthalpy and developing decomposition models based on kinetic parameters.

TATB thermal decomposition: An improved kinetic model for explosive safety analysis

“…To further elucidate the species formed during thermal decomposition, TATB of high chemical purity, as well as 13 C, D, 15 N, and 18 O isotopically-labeled TATB [21,22], were studied using PyGC-MS and Py-MS in EGA (evolved gas analysis) mode at elevated temperature (> 300 °C). These experiments are discussed in detail in Morrison, et al [13].…”

“…To further elucidate the species formed during thermal decomposition, TATB of high chemical purity, as well as 13 C, D, 15 N, and 18 O isotopically-labeled TATB [21,22], were studied using PyGC-MS and Py-MS in EGA (evolved gas analysis) mode at elevated temperature (> 300 °C). These experiments are discussed in detail in Morrison, et al [13]. In brief, samples of masses from 100 to 330 μg were studied in unconfined and foil-confined experiments under ramped and isothermal conditions, in which samples were loaded into a preheated oven.…”

“…In brief, samples of masses from 100 to 330 μg were studied in unconfined and foil-confined experiments under ramped and isothermal conditions, in which samples were loaded into a preheated oven. Figure 3 shows several of the primary masses measured at the highest total ion count near the end of thermal decomposition during 330 °C isothermal experiments with unlabeled, 15 N amine-labeled, 15 N amine-and nitro-labeled, and 13 C-labeled TATB. Unfortunately, due to exchange with environmental water, the D and 18 O labeled materials had much lower isotopic purities in the Py-MS experiments.…”

“…F I G U R E 3 Mass spectra and selected chemical structures at peak ion count for a) unlabeled TATB, b) 15 N amine-labeled TATB, c) 15 N amine-and nitro-labeled TATB, and d) 13 C-labeled TATB.…”

“…As the earlier focus of experiments has largely been on end-point data, we previously proposed a reduced form of the reaction network [12], excluding the furoxan species and later intermediates. However, recent PyGC-MS (pyrolysis gas chromatography mass spectrometry) [13], TGA (thermo-gravimetric analysis), and DSC (differential scanning calorimetry) experiments [14] have enabled a much more detailed analysis of thermal decomposition beyond those typically seen in (P)ODTX [15], where only a few percent of the starting material is typically converted to products before thermal runaway, as illustrated in Figure 2.…”