Insights into the 5,5′-bis(1H-tetrazolyl)amine monohydrate (BTA·H2O) pyrolysis mechanism: integrated experimental and kinetic model analysis

Abstract

Nitrogen heterocycles as nitrogen-rich energetic materials have been widely popularized in energetic materials, especially in gun propellant application areas. Recently, bis-tetrazole compounds have attracted increasing focus for their various outstanding features, such as a high nitrogen content, insensitivity, and high thermal stability. In order to gain a greater in-depth understanding of the thermal decomposition behavior of such materials, the thermal decomposition process of BTA·H₂O was systematically studied through a series of analyses. The thermal decomposition process and gas products were analyzed using TG-DSC-FTIR analysis. The results revealed that the pyrolysis process of BTA·H₂O was a complex reaction, including three main mass loss stages. After the removal of crystal water in the BTA·H₂O molecule, the thermal decomposition mechanism of BTA also was investigated by condensed-phase thermolysis by multiple mode calorimetry (MMC) assisted by SEM, FTIR, and XPS. The results revealed that the pyrolysis process of BTA was most likely to begin with a ring-opening reaction of the tetrazole ring, and the main gaseous products, including HCN, HN₃, and NH₃, were then released from the decomposition of BTA. According to the condensed-phase kinetics, a kinetic model describing the thermal decomposition process of BTA was proposed. Based on the above results and the force constant of the chemical bonds in BTA, a detailed mechanism for the thermal decomposition of BTA was proposed. In addition, thermal hazard prediction was performed for BTA. When the value of φ decreased from 64.23 to 47.65, TD24 decreased from 193.0 °C to 187.2 °C and TD8 decreased from 197.1 °C to 192.4 °C.