Ab Initio Molecular Dynamics Studies Of The Thermal Decomposition Mechanisms Of Cocrystal Explosives

In the thesis,ab initio molecular dynamics were used to simulate the decomposition processes of benzotrioxurazan(BTF)/1,3,3-trinitroazetidine(TNAZ),1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane(HMX)/pyridine-N-oxide(PNO),3,6-bis(1-hydro-1,2,3,4-tetrazole-5-amino)-1,2,4,5-tetrazine(BTATz)/pyrazine(PyA)cocrystals under high temperatures.The main contents including three parts are as follows:1.It is found that there are four initial reaction mechanisms involved in the decompositions of the BTF/TNAZ cocrystal at 3000 K.The TNAZ molecules are easier to decompose than the BTF ones.The hydrogen radicals and NO₂ as main decomposition products can accelerate the subsequent decompositions of the cocrystal.Main subsequent decomposition channels include the BTF-chain isomerization,C?NO₂ bond homolysis,and ring opening.The generated long chains can continue to decompose or after they formed nitrogen-rich heterocycle,they decomposed again.Main decomposition products are NO and NO₂ in the early decomposition stage,but CO₂ and N₂ become main products in the later decomposition stage.2.The initial decomposition mechanisms of the HMX/PNO cocrystal at 2000 K are slightly different from those at 3000 K.At 2000 K,the main decomposition mechanisms of the cocrystal are that the O and H radicals trigger subsequent decompositions.At 3000 K,the ring opening of the HMX molecules with the formation of NO₂ and H play a key role in promoting the subsequent decompositions.In the subsequent reaction stage,the PNO molecules are stable.The temperature does not produce important effects on the subsequent reaction mechanisms.But the decompositions of the PNO molecules are mainly due to the effects of the H,O,and the chained fragments formed by the decompositions of the HMX molecules.Its main decomposition products are H₂O,N₂,and CO₂ apart from a few of long and short chains and heterocycles with carbon and nitrogen.3.The decomposition processes of the HMX/PyA cocrystal at 2000 K are not obviously different from those at 3000 K.In the early reaction stage,the main decomposition mechanisms of the cocrystal are that the BTATz molecules break to release the H radicals,but the secondary ones are the ring opening of the tetrazine.In the later reaction stage,the main decomposition paths include the ring opening of the tetrazine and tetrazole,the release of N₂,and the cleavage of some long and short chains with carbon and nitrogen.The decompositions of the PyA molecules are mainly due to the effects of the H radicals and the fragments formed by the decompositions of the BTATz molecules.Its main decomposition products are the chained fragments and heterocycles with carbon and nitrogen in the later decomposition stage.N₂ are main small products.