A reduced mechanism with optimal rate-kinetics parameters for liquid-phase decomposition of bis(triaminoguanidinium) 5,5'-azotetrazolate (TAGzT): Quantum chemical calculations, thermolysis experiments and kinetic modeling

The development of reaction mechanisms is one of the crucial steps in formulating combustion models. In this study, quantum chemical calculations were performed to develop a detailed reaction mechanism for liquid-phase decomposition of bis(triaminoguanidinium) 5,5′-azotetrazolate (TAGzT). The developed mechanism has 495 elementary reactions and 355 species. Simultaneous thermal analysis experiments were also performed at three different heating rates: 5, 10, and 15 °C/min using a coupled TGA/DSC-FTIR system. The experimentally obtained mass loss and species evolution profiles were used to validate and optimize the developed mechanism. Due to a large number of elementary reactions and species in the detailed mechanism, its use in a combustion model becomes computationally challenging. Therefore, the detailed mechanism was reduced by identifying and removing elementary reactions whose rate-of-progress remained low throughout the decomposition process. The reduced mechanism has 90 elementary reactions and 70 species. The analysis leads to the conclusion that TAGzT decomposition occurs in two steps – 1) anion decomposition and 2) cation decomposition. The anionic part primarily decomposes via a single pathway, whereas the cationic part decomposes via five competing pathways. The experimentally observed rapid decomposition behavior of TAGzT is due to its highly exothermic decomposition pathways and the autocatalytic effects of HCN, CN⁻, and cyanamide on the decomposition process. The major residual products of TAGzT decomposition are identified as formoguanamine and melamine.