Thermal decomposition of ε-hexanitrohexaazaisowurtzitane (HNIW) was studied by thermogravimetrydifferential scanning calorimetry-mass spectrometry-Fourier transform infrared spectroscopy (TG-DSC-MS-FTIR) simultaneous analysis. It has been shown that there is a crystal transition point for ε-HNIW, and only a single decomposition process has been observed for HNIW. The kinetic parameters of thermal decomposition of HNIW were obtained by Kissinger and Flynn-Wall-Ozawa methods, indicating that HNIW has the higher reactivity compared to the other nitramines. The HNIW decomposition mechanism demonstrated by the non-isothermal kinetics conformed to Avrami-Erofeev equation with the factor of nucleus growth of n=1/3 and the conversion degree of α from 0.1 to 0.7. The MS and FTIR analyses indicated that the thermal decomposition of HNIW favors N-N bond cleavage over C-N bond cleavage as the rate determining step.

Density functional theory was employed to investigate the (111), (200), (210), (211) and (220) surfaces of CoS 2 . The surface energies were calculated with a sulfur environment using first-principle-based thermodynamics. It is founded that surfaces with metal atoms at their outermost layer have higher energy. The stoichiometric (220) surface terminated by two layer of sulfur atoms is most stable under the sulfur-rich condition, while the non-stoichiometric (211) surface terminated by a layer of Co atoms has the lower energy under the sulfur-poor environment. The electric structure results show that the front valence electrons of (200) surface are active, indicating that there may be some active sites on this face. There is an energy gap between the stoichiometric (220) and (211), which has low Fermi energy, indicating that their electronic structures are dynamically stable. Spin-polarized bands are calculated on the stoichiometric surfaces, and these two (200) and (210) surfaces are predicted to be noticeably spin-polarized. The Bravais–Friedel–Donnay–Harker (BFDH) method is adopted to predict crystal growth habit. The results show that the most important crystal planes for the CoS 2 crystal growth are (111) and (200) planes, and the macroscopic morphology of CoS 2 crystal may be spherical, cubic, octahedral, prismatic or plate-shaped, which have been verified by experiments.

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