Xiang Ke

A facile one-pot solvothermal synthesis of CoFe2O4/RGO and its excellent catalytic activity on thermal decomposition of ammonium perchlorate

CoFe2O4/RGO hybrids have been successfully fabricated via a facile one-pot solvothermal method, which were characterized by X-ray diffraction (XRD), Raman, Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). During this process, graphene oxide was reduced to graphene (RGO) and CoFe2O4 nanoparticles were deposited on the RGO. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the average size of CoFe2O4/RGO hybrids was 120 nm, which was smaller than that of bare CoFe2O4, implying that RGO could effectively prevent CoFe2O4 nanoparticles from aggregating. To investigate the catalytic activity of the as-synthesized CoFe2O4 particles and CoFe2O4/RGO hybrids, the thermal decomposition of ammonium perchlorate (AP) was characterized by differential thermal analyser (DTA). Both of the two exothermic processes were merged into a sole exothermic process with the addition of bare CoFe2O4 and CoFe2O4/RGO hybrids, though there was no change in the position of the phase transition temperature of AP. Moreover, the catalytic activity of CoFe2O4/RGO hybrids is higher than that of bare CoFe2O4, due to the large surface area and enhanced properties of RGO in the hybrids. The temperature programmed reduction (TPR) measurements showed that the reduction temperature of CoFe2O4/RGO decreased by 55 °C compared with bare CoFe2O4, which further confirmed the higher catalytic activity of CoFe2O4/RGO of than that of CoFe2O4 nanocomposites. Hence, CoFe2O4/RGO hybrids could be a promising additive in modifying the burning behaviour of AP-based composite propellant.

Synthesis and Characterization of a New Co-Crystal Explosive with High Energy and Good Sensitivity

ABSTRACT A new energetic co-crystal consisting of one of the most powerful explosive molecules 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and the military explosive cyclotrimethylenetrinitramine (RDX) was prepared with a simple solvent evaporation method. Scanning electron microscopy (SEM) revealed the morphology of the bar-shaped product, which differed greatly from the morphology of the individual components. Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction spectrum (XRD), and differential scanning calorimetry (DSC) proved the formation of the co-crystal at the molecular level. The result of mechanical sensitivity test indicated the sensitivity was effectively reduced compared to raw CL-20. Finally, a possible crystallization mechanism was discussed.

Aluminum/copper oxide nanostructured energetic materials prepared by solution chemistry and electrophoretic deposition

Nanostructured energetic materials benefit from improved spatial distribution and enhanced interfacial contact between reducing agents and oxidizing agents, and thus they have attracted increasing attention in the past decade. In this study Al/CuO nanostructured energetic materials were prepared by combining a solution chemistry method and electrophoretic deposition. A piece of clean Cu foil was first placed in a solution consisting of NaOH and (NH4)S2O8 to form a layer of copper hydroxide, which was then dehydrated in an oven at 180 °C for 4 h to obtain CuO nanostructures. Nano Al particles were integrated with the CuO nanostructures by electrophoretic deposition to form Al/CuO nanostructured energetic materials. Thermal analysis showed that the prepared nanostructured energetic materials had lower apparent activation energy than that of a randomly mixed counterpart thanks to the structural design.

Facile preparation of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane/glycidylazide polymer energetic nanocomposites with enhanced thermolysis activity and low impact sensitivity

1,3,5,7-tetranitro-1,3,5,7-tetrazocane/glycidylazide polymer (HMX/GAP) nanocomposites were successfully prepared via a facial sol–gel supercritical method. The as-synthesized HMX/GAP nanocomposites were characterized by X-ray diffraction (XRD), Raman, and Fourier-transform infrared spectroscopy (FT-IR), which indicated that HMX were successfully trapped in GAP gel skeleton. Scanning electron microscopy (SEM) images revealed that the GAP gel skeleton possessed nano-porous structure, which made it possible to load HMX particles. The thermal decomposition behaviours of GAP, raw HMX and HMX/GAP nanocomposites were determined by differential thermal analyser (DTA). The results indicated that GAP aerogel could promote the decomposition of HMX and enhance the interaction between GAP and HMX. The kinetic, thermodynamic and thermal stability parameters, such as activation energy (Ea), per-exponent factor (ln A), activation heat (ΔH≠), activation free energy (ΔG≠), activation entropy (ΔS≠), critical temperature of thermal explosion (Tb) and the self-accelerating decomposition temperature (TSADT) were calculated according to DTA analysis. The calculated results implied that HMX/GAP showed much lower activation energy than raw HMX. Similarly, the HMX/GAP presented a much lower Tb and TSADT than raw HMX. According to the impact sensitivity tests, the mechanical sensitivities of HMX/GAP nanocomposites were significantly lower than those of raw HMX.

Effect of aluminum morphology on thermal decomposition of ammonium perchlorate

In this paper, two kinds of flake aluminum powder are prepared by bidirectional rotation mill using the spherical aluminum powder (Al-1) as raw materials. The morphology and particle size distribution of Al powder are analyzed using scanning electron microscopy and laser particle size analyzer. At the same time, the catalytic performances of the Al-1 and as-prepared Al powder on the thermal decomposition of ammonium perchlorate (AP) are studied through thermogravimetric and differential scanning calorimetry analysis. The results revealed that compared with pure AP, the exothermic peak temperature of AP/Al-1, AP/thicker flake Al powder (Al-2) and AP/thinner flake Al powder (Al-3) mixtures are reduced. The activation energy of AP/Al-1, AP/Al-2 and AP/Al-3 mixtures is reduced by 3.7, 16.8 and 17.6%, respectively. The reaction rate constant of AP/Al-1, AP/Al-2 and AP/Al-3 mixtures grows by 3.3, 18.0 and 32.5%, respectively.

Safe preparation, energetic performance and reaction mechanism of corrosion-resistant Al/PVDF nanocomposite films

In this study, to improve the safety in the preparation process of energetic materials, vacuum freeze-drying technology is applied to develop nanoenergetic thin films in which Al nanoparticles (Al NPs) are used as the fuel and polyvinylidene fluoride (PVDF) powders act as the oxidant. The whole process effectively avoids high temperature and thus ensures operational safety. The morphology and composition characterizations confirm that Al NPs are dispersed uniformly in the hydrophobic energetic binder, endowing the films with increased water-proof, anti-aging and anti-corrosion characteristics. The results of thermal analysis show that a pre-ignition reaction (PIR) destroys the Al2O3 shell and a sharp exothermic peak from the reaction between the exposed Al core and PVDF is found before the melting point of Al. Combustion tests reveal that the film with the highest content of Al NPs possesses the fastest flame propagation speed. The preliminary reaction mechanism obtained by probing the reaction products and intermediates suggests that a two-step reaction exists when the film is slowly heated in N2, while a competitive reaction between oxidation and fluorination of Al NPs is observed when the film burns in air. These results indicate the promising potential of vacuum freeze-drying technology in manufacturing nanoenergetic materials.

Preparation and characterization of RDX/BAMO-THF energetic nanocomposites

ABSTRACT Novel 1,3,5-trinitro-1,3,5-triazine/3,3-bis (azidomethyl) oxetane-tetrahydrofuran copolymer (RDX/BAMO-THF) energetic nanocomposites were successfully prepared by a facile sol–gel freezing–drying method. The as-prepared RDX/BAMO-THF energetic nanocomposites were characterized by Raman and Fourier transform infrared spectroscopy, which revealed that RDX particles were incorporated into BAMO-THF gel matrix. Scanning electron microscopy was used to characterize the morphology and the particle size of the as-obtained samples. The results showed that RDX particles were trapped in the BAMO-THF gel matrix and the particle sizes were in nanoscale. Differential thermal analyzer (DTA) was performed to determine the thermal decomposition behaviors of BAMO-THF, raw RDX and RDX/BAMO-THF nanocomposites. The results indicated that the thermal decomposition process of RDX/BAMO-THF nanocomposites was enhanced compared with that of BAMO-THF and RDX. The kinetic, thermodynamic and thermal stability parameters were calculated according to DTA analysis. The calculated results revealed that RDX/BAMO-THF nanocomposites presented high thermal reactivity. The results of impact sensitivities for RDX/BAMO-THF nanocomposites indicated the sensitivity was effectively reduced compared to raw RDX.

Preparation and property of CL-20/BAMO-THF energetic nanocomposites

Abstract A sol-gel freezing-drying method was utilized to prepare energetic nanocomposites based on 2, 4, 6, 8, 10, 12-hexanitro-2, 4, 6, 8, 10, 12-hexaazaisowurtzitane (CL-20) with 3, 3-Bis (azidomethyl) oxetane-tetrahydrofuran copolymer (BAMO-THF) as energetic gel matrix. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman, Fourier-transform infrared spectroscopy (FT-IR) and differential thermal analyser (DTA) were utilized to characterize the structure and property of the resultant energetic nanocomposites. Compared with raw CL-20, the average particle sizes of CL-20 in CL-20/BAMO-THF energetic nanocomposites were decreased to nano scale and the morphologies of CL-20 were also changed from prismatic to spherical. FT-IR detection revealed that CL-20 particles were recrystallized in BAMO-THF gel matrix during the freezing-drying process. The thermal decomposition behaviors of the energetic nanocomposites were investigated as well. The thermolysis process of CL-20/BAMO-THF nanocomposites was enhanced and the activation energy was lower compared with that of raw CL-20, indicating that CL-20/BAMO-THF nanocomposites showed high thermolysis activity. The impact sensitivity tests indicated that CL-20/BAMO-THF energetic nanocomposites presented low sensitivity performance.

Intuitionistic study on the critical decomposition energy of ammonium perchlorate by SEM

The decomposition course of Ammonium Perchlorate (AP) particles under electron energy is observed using a G2 pro Desktop Scanning Electron Microscope. The state that the AP particle is starting to decompose exhibiting cracks on its surface is observed and recorded using the S-4800II Fielding Emission Scanning Electron Microscope (FESEM), the Image Pro Plus (IPP) System is employed to obtain the projected area of that decomposed AP particle in the FESEM image, and the critical decomposition energy of the AP particle is calculated. Results have shown that the critical decomposition energy is decreased with the reduction of AP particle size. Especially when the AP particle size is approximately under 20 μm, the critical decomposition energy is sharply decreased, and the critical decomposition energy is very small if under 3 μm. This result is very helpful to explain why the burning rate of propellants and the brisance of Fuel Air Explosives (FAE) are enhanced and the sensitivities of those AP-based energetic materials are increased with the reduction of AP particle size. Furthermore, this method can be used to calculate in an intuitionistic way the critical decomposition energies of other crystalline materials.

Preparation and characterization of an ultrafine HMX/NQ co-crystal by vacuum freeze drying method

In this paper a new energetic co-crystal consisting of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) and nitroguanidine (NQ) was prepared using a vacuum freeze drying method. Scanning electron microscopy (SEM) revealed that the particle size was under 500 nm and the morphology was spherical. Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy suggest that hydrogen bonds exist between HMX and NQ molecules. Powder X-ray diffraction spectra (PXRD) indicated the product was different from the single components and their mechanical mixture. Thermal gravimetric analysis and differential scanning calorimetry (TGA/DSC) were employed to characterize the thermal behavior of the co-crystal and then the related thermodynamic parameters were calculated, which indicated that after co-crystallization the molecule of the co-crystal needed more energy to activate. The result of an impact sensitivity test indicated that the sensitivity was effectively reduced compared to neat HMX and the mechanical mixture. The density of the product was found to be 1.80 g cm−3 and the storage performance was also investigated.