Comparative analysis of sublimation and thermal decomposition of TATB

Abstract

This experimental study investigated the effects of confinement, starting mass, and heating rate on TATB thermal decomposition and sublimation using a combined Thermo‐Gravimetric Analyzer and Differential Scanning Calorimetry (TGA/DSC) instrument. The confinement of volatile products was varied using different pinhole sizes with TGA/DSC pans. The measurements showed the open pan experiments without lids/pinholes resulted in complete sublimation of TATB between 320 °C and 360 °C. The heat of sublimation was determined to be 176 kJ/mol (42 kcal /mol), consistent with literature data obtained from other experimental techniques. The use of pinholes suppressed the sublimation of TATB such that the decrease in pinhole size resulted in 1) an increase in the enthalpy of reaction and an increase in the amount of carbonaceous material remaining at the end of decomposition, and 2) convergence of the two peak temperatures corresponding to maximum heat flow and maximum weight loss. Also, a transition from a two‐exotherm thermal decomposition behavior towards a single‐exotherm occurred as the pinhole size was decreased for a given starting mass or as the starting mass was increased for a given pinhole size. These results indicate the kinetics of TATB sublimation, TATB thermal decomposition, and gas diffusion out of a TGA/DSC pan can all compete and result in significantly different enthalpies, amounts of remaining materials, and peak temperatures depending on the pinhole size and starting mass used in the measurements. The results also indicate precise control of process variables (pinhole size, starting mass, and heating rate) in TGA/DSC measurements is required for thermal safety assessment of explosives.

Towards a heat‐ and mass‐balanced kinetic model of TATB decomposition

“…To avoid significant sublimation, the bulkheating experiments used 1.9-3.8 mg of powder in Mettler-Toledo 40-μL pans with crimped 50-μm pinhole lids, and the conventional thermal analysis experiments used TA 40-μL pans with crimped 75-μm pinhole lids. The ramped thermal analysis experiments used heating rates from 0.5 to 10 °C/min, and the sample size varied so that the product was between 1.1 and 2.8 mg × °C/min to both minimize sublimation and avoid self-heating [33]. Multiple runs were conducted at each heating rate, and the best at each rate was chosen for kinetic analysis based on optimum heat flow -close to but not exceeding the 8-mW limit [30] for any individual data point.…”

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

“…Figure 4 shows that of the small molecules measured in the MS, only CO 2 and NO 2 are present in the first phase of decomposition. Thus, we conclude that NO 2 is likely to be autocatalytic in early F I G U R E 6 Effect of pin hole size on reaction heat flow at 10 °C/min [32]. decomposition, once enough of the initial reactions have proceeded to form it.…”

“…Value Units Error ΔH r (J/g) is suppressed, as when using a small pinhole or a closed pan, no endotherm is seen [32].…”