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To investigate the catalytic decomposition performance of amorphous nano-sized oxides with short-range ordered and long-range disordered for energetic materials, amorphous nano-NiO was prepared by high-temperature calcination using nickel acetylacetonate as the raw material. The composition, structure and its catalytic decomposition properties on ammonium perchlorate (AP) and GAP-based propellant were investigated by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), N2 adsorption-desorption (BET) and differential scanning calorimetry (DSC). The results show that the amorphous nano-NiO can reduce the thermal decomposition peak temperature of AP from 406. 4°C to 309. 5°C, the apparent activation energy can be reduced from 158. 17 kj/mol to 129. 82 kj/mol, and the heat release increased from 747. 7 J/g to 1 780 J/g. Compared with crystalline nano-NiO nanoparticles, amorphous NiO increases the burning rate of GAP-based propellant by about 10% and reduces the pressure index by about 9. 7 %% . [ABSTRACT FROM AUTHOR]

To explore the difference in thermal stability of different CL-20 polymorphs, the initial thermal decomposition of four CL-20 polymorphs (α -, β-, γ-, and ε-) were depicted using longtime ReaxFF MD simulations at relative low temperatures of 600-900 K, which are close to the conventional thermal analysis experiments. The dynamic responses of varied CL-20 polymorphs under heating were characterized by the initial conformer transformation and thermal decomposition kinetics. The results show that under relative mild thermal stimulation conditions, conformer conversion dominates the initial responses of four CL-20 polymorphs. The molecular conformer stability of varied CL-20 polymorphs ranks as γ>β≈α>ε. Under heating conditions, ε -CL-20 converts to γ" or ϛ conformes, and γ-CL-20 converts to ϛ conformer. The above conformational transition phenomenons agree broadly with experimental phase diagram of Russell et al. Conformer conversion from ε to γ occurring very early in ε-CL-20 polymorph induces its fast initiation of decomposition reactions. In contrast, γ-CL-20 is rather stable and is conformer transformation and decomposion lags behind ε-CL-20. Once the decomposition initiates, the overall decomposition rate of γ-CL-20 polymorph is higher than that of ε-CL-20 polymorphs with increasing of thermolysis duration or tempeaatures. In terms of the reaction kinetics of weight loss and major bond cleavage during the entire thermolysis process, the thermal stability of ε-CL-20 polymorph is higher than that of γ-CL-20, which agrees with Nedelko's TG experiments. This work suggests that ReaxFF MD stimulations may be served as a computational prediction method for temperature phase diagram of polymorph conversion of energetic materials. [ABSTRACT FROM AUTHOR]

To more efficiently develop the single-atom catalysis, it is essential to deeply characterize the single-atom catalysis structure and study their catalytic mechanisms at the molecular and atomic scale. Herein, this paper reviews the advanced techniques for charactering the structure of single-atom combustion catalysis, including synchrotron-radiation based X-ray absorption spectroscopy (XAS) and spherical aberration-collected transmission electron microscopy. Meanwhile, synchrotron-tradiation based operando and in-situ techniques are introduced, including XAS, Fourier transform infrared (EQIR) and synchrotron vacuum ultraviolet radiation photoionization mass spectrometry (SVUV-PIMS), which could play vital roles in unravelling the reaction mechanisms. These advanced structural characterizations to investigate the existence of single-atom catalysis and their catalytic mechanisms would significantly provide a new vision for the design and synthesis of single-atom combustion catalysis. Furthermore, current challenges and future research directions of these characterization techniques in single-atom combustion catalysis are presented. 38 References are included. [ABSTRACT FROM AUTHOR]

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