P1-WEI Dongqing

Thermal Decomposition of the Solid Phase Nitromethane: Ab Initio Molecular Dynamics Simulations

Yan-Zhi Bai1, Yong-Kai Wei2, Yuan-Yuan Qi2, Jiao-Nan Yuan2, Jing-Xin Yu2, Kai Xu2, Dong-Qing Wei1,2*

1, State Key Laboratory of Microbial Metabolism, College of Life Science and Biotechnology and Research Center on New Aeronautics and Astronautics Materials, Shanghai Jiao Tong University, Shanghai 200240, China

2, Center For Interdisciplinary Research on Computational Science, Henan Institute of Technology, Zhengzhou, Henan, China

The Car-Parrinello molecular dynamics simulations were employed to investigate thermal decomposition of the solid nitromethane. It is found that it undergoes chemical decomposition at about 2200 K under ambient pressure. The initiation of reactions involves both proton transfer and commonly known C–N bond cleavage. About 75 species and 100 elementary reactions were observed with the final products being H2O, CO2, N2, and a long chain molecule consists of CNCNC. It represents the first complete simulation of solid-phase explosive reactions reported to date, which is of far-reaching implication for design and development of new energetic materials.

Static pressure is an alternative method to chemical pressure for tuning the crystal structure, bonds, and physical properties of materials, and is a significant technique for the synthesis of novel materials and fundamental research. The crystallization and phase transformation of p-xylene under high pressure are reported. Our optical micrographic observations and the appearance of lattice modes in the Raman and infrared (IR) spectra indicated that p-xylene crystallizes at ∼0.1 GPa. The X-ray diffraction (XRD) pattern at 0.84 GPa suggests that the crystallized p-xylene had a monoclinic phase with the Cc(9) space group. The sharp shrinkage of the lattice at ~13 GPa and the solid state of the decompressed sample we observed suggests a new crystalline phase of p-xylene. The in situ XRD showed that the new crystalline phase was still a monoclinic structure but with a different space group of C2(5), indicating that a phase transition occurred during further compression. The mass spectrometry experiment confirmed phase transition polymerization, with mainly trimer and tetramer polymers. Our findings suggest an easy and efficient method for crystallizing and polymerizing p-xylene under high pressure. It may be useful to understand formation of molecules with higher member of carbon chains in the condition deep inside the earth.