Abstract:

Abstract:In order to establish a precise combustion heat measurement system and method suitable for energetic materials， a method and device for measuring the heat of combustion of energetic materials with tiny doses has been developed. This device is based on the thermal principle of differential heat flux and uses a three-dimensional thermopile consisting of 960 pairs of thermocouples as the core measuring element. The device was calibrated by using standard material benzoic acid. The heat of combustion of six typical energetic materials， including cyclotetramethylene tetranitramine， hexanitrohexaazaisowurtzitane， cyclotrimethylene trinitramine， 3，4-bis（3-nitrofurazan-4-yl）furoxan， 1，1-diamino-2，2-dinitroethylene and nitroguanidine， was measured by this device. The results show that the calorimetric coefficient of the instrument is （64.804±0.071） μV·mW^-1 and the corresponding relative uncertainty is 0.109%. The solid-phase standard molar heats of combustion （Δ_cU） of these six energetic materials at 298.15 K are -（2749.1±4.5）， -（3593.6±6.0）， -（2115.2±3.4）， -（3040.8±4.8）， -（1211.4±2.3） and -（898.4±2.0） kJ·mol^-1， respectively. The measurement results are in good agreement with the values reported in the literature， indicating that the developed small-mass combustion measurement device can be widely used in the determination of the energy of combustion of substances containing C， H， O， and N， especially precious samples and explosive substances.

Abstract:To solve the problems of igniting difficulty and combustion agglomeration， modification of Al powder by alloying and oxidant coating was studied. AP@Al/Ni composite fuels were prepared by acoustic resonance mixing technique. The heats of reaction of the composite fuels with different ammonium perchlorate （AP） contents were measured using a bomb calorimeter. The morphology characteristics of the optimized AP@Al/Ni composite fuel were analyzed by SEM. The thermal reactivity of AP， Al/AP mixture， Ni/AP mixture， and AP@Al/Ni composite fuel were comparatively studied by DSC/TG. The effects of additives including Al， Ni， and Al/Ni composite on the thermal decomposition kinetic parameters of AP were evaluated by the non-isothermal kinetic method. The results show that the heat of reaction of the composite fuel reaches its maximum when the mass content of AP is 38.90%， which is considered as the optimal content of AP in the formula. Compared with Al and Ni， the Al/Ni composite has the most significant influence on the thermal decomposition of AP， which reduces the peak temperature of AP in high temperature decomposition by 76.9 ℃ and increases the heat release by 84.8%. The apparent activation energy of AP decomposition in AP@Al/Ni composite fuel that obtained by Friedman method is 103.9 kJ·mol^-1， and this process obeys the three-dimensional random nucleation and nucleus growth （A3） model.

Abstract:The particle size and morphology of energetic material crystal have a great influence on its performance. In order to study the relationship between crystal morphology， particle size and thermal decomposition performance of 1，1-diamino-2，2-dinitroethylene （FOX-7） explosive， FOX-7 explosive particles with different morphologies and particle sizes were prepared according to solvent/non-solvent method. Scanning electron microscope （SEM）， X-ray diffractometer （XRD）， differential scanning calorimeter （DSC） and impact sensitivity tester were used to investigate the crystal morphology and particle size， crystal form， thermal decomposition property and safety property of FOX-7 explosives， respectively. The results show that by changing the cooling rate， stirring rate and other process conditions， FOX-7 explosive particles with different morphologies such as sea urchin shape， spherical shape， flower shape and block shape can be obtained. The crystal form of prepared FOX-7 explosive is consistent with that of raw material as α-form. The crystal morphology and particle size of FOX-7 have a great influence on the breaking of intramolecular hydrogen bonds and the destruction of the conjugated system， and the spherical shape is beneficial to increase the thermal decomposition temperature. For the FOX-7 sample with a same shape， the larger the particle size， the better the thermal stability. Among the FOX-7 samples with diameters of tens of microns， the sample with spherical morphology has the best safety performance.

Abstract:To promote the stable production and wide application of silver acetylide-silver nitrate （Ag₂C₂·AgNO₃）， the structural morphology and thermal decomposition characteristics were systematically studied by X-ray powder diffractometry， Fourier tranform infrared spectrometer， scanning electron microscopy， differential scanning calorimeter and thermogravimetric-mass-infrar- ed spectrometry techniques. The results indicate that the prepared Ag₂C₂·AgNO₃ sample is in the form of nanospheres with particle sizes ranging from 400 to 500 nm. There is only one exothermal decomposition process of Ag₂C₂·AgNO₃ with a peak temperature of 234.9 ℃， a weight loss of 8.72%， and a heat release of 1449 J·g^-1，at a heating rate of 10 ℃·min^-1. The apparent activation energy and pre-exponential constant of decomposition process are obtained as 108.9 kJ·mol^-1 and10^8.94 s^-1， respectively. Moreover， the gaseous decomposition products of Ag₂C₂·AgNO₃ were NO， NO₂ and CO₂.

Abstract:To explore the detailed thermal decomposition properties of the mixture system consists of ammonium perchlorate-based molecular perovskite energetic material （H₂dabco）（NH₄）（ClO₄）₃ （DAP-4， where H₂dabco²⁺ refers to 1，4-diazabicyclo［2.2.2］octane-1，4-dianiumion） and dihydroxylammonium 5，5"-bistetrazole-1，1"-diolate （TKX-50）， the thermal decomposition characteristics and gas products of DAP-4 and DAP-4/TKX-50 mixtures were comparatively analyzed by using differential scanning calorimetry-thermogravimetry/mass spectrometry/fourier infrared spectroscopy； meanwhile， the changes of characteristic groups in the condensed phase of DAP-4 and DAP-4/TKX-50 mixtures with temperature were investigated by in-situ FTIR. Based on the explorations the thermal decomposition mechanism of DAP-4/TKX-50 mixture was proposed. The results showed that after mixing DAP-4 with TKX-50， DAP-4 had little effect on the thermal decomposition of TKX-50， while the heat generated by the thermal decomposition of TKX-50 made the reversible phase transition endothermic peak of DAP-4 disappeared， but hardly affected DAP-4′s thermal decomposition at high temperature. The thermal mass loss of DAP-4/TKX-50 mixture was divided into two stages. The mass loss of the first stage was 43.4% and the mass loss of the second stage was 52.4%， leaving 4.2% of the decomposition residue. The main gas products produced by thermal decomposition of DAP-4 and DAP-4/TKX-50 mixture were NH₃/H₂O/HNCO/HCN/CO/HCl/CO₂ and H₂O/NO/N₂O/HCl/NH₃/N₂/HNCO/HCN/CO/CO₂， respectively. The thermal decomposition mechanism of the DAP-4/TKX-50 mixture was proposed as follows： the reversible transfer of hydrogen ions occurs first in the molecule of TKX-50 to generate hydroxylamine and 1，1"-dihydroxy-5，5"-bitetrazole （BTO）， then hydroxylamine decomposed into small molecular gases at high temperature while the fragments generated by BTO decomposition partially polymerized into coupling products. Finally， the ionic bond of DAP-4 was broken， leading to instantaneous collapse of the cage-like skeleton. The strongly reducing and strongly oxidizing gas components underwent violent redox reactions at high temperatures and release a large amount of heat.

Abstract:（C₆H₁₄N₂）［Na（ClO₄）₃］ is a representative of energetic perovskite compounds. It is necessary to clarify the corresponding thermal decomposition behavior， thermal decomposition mechanism and sensitivity characteristics in order to promote the application in formulations. Thermal decomposition parameters， including heat release amount and decomposition temperatures， were obtained by simultaneous differential scanning calorimetric and thermogravimetric analyses methods. The relevant decomposition mechanism was analyzed by kinetic simulation calculations. The decomposition products and decomposition processes of （C₆H₁₄N₂）［Na（ClO₄）₃］ were explored by DSC/TG-FTIR-MS coupled technique combined with in-situ infrared technology. The parameters of thermal sensitivity， friction sensitivity and impact sensitivity were obtained by national military standard methods. The results show that the heat of decomposition of （C₆H₁₄N₂）［Na（ClO₄）₃］ is 4227 J·g^-1 at the heating rate of 10 ℃·min^-1 and the decomposition temperature reaches 345 ℃， which is higher than that of most active energetic materials， including Hexogen （RDX）， ogen （HMX） and hexanitrohexaazoisowuzane （CL-20）， indicating an outstanding thermal stability. The decomposition products analysis shows that the cubic cage-like skeleton effectively stabilizes the internal organic molecule， resulting in the high thermal stability of （C₆H₁₄N₂）［Na（ClO₄）₃］. In addition， the outgassing amount of （C₆H₁₄N₂）［Na（ClO₄）₃］ heated at 100 ℃ for 48 h is about 0.04 mL·g^-1， and the impact sensitivity and mechanical sensitivity are 32% and 80%， respectively， which are better than RDX and HMX.

Abstract:To investigate the effect of deuteration on the vibrational properties of chemical bonds of triacetone triperoxide （TATP） and its thermal decomposition behavior， TATP and deuterated triacetone triperoxide （TATP-d₁₈） were prepared by using acetone and acetone-d₆ as raw materials， respectively， with hydrogen peroxide acting as the oxidant source and sulfuric acid as the catalyst. TATP and TATP-d₁₈ were characterized by nuclear magnetic resonance spectroscopy （NMR）， Fourier transform infrared spectroscopy （FTIR） and differential scanning calorimetry （DSC）. The non-isothermal reaction kinetic parameters of TATP and TATP-d₁₈ were calculated with Kissinger， Ozawa， and Friedman methods. The results show that the deuteration of TATP results in an evident red-shift phenomenon， and the ratio of the stretching frequencies of C—H（D） bonds （ν_C—H/ν_C—D） is about 1.36. The apparent activation energy of TATP-d₁₈ （E_K=80.54 kJ·mol^-1， E_O=83.56 kJ·mol^-1， E_F=72.27 kJ mol^-1） is higher than that of TATP （E_K=67.91 kJ·mol^-1， E_O=71.01 kJ·mol^-1， E_F=63.79 kJ·mol^-1）， indicating that TATP-d₁₈ has higher thermal stability. The calculated thermal explosion critical temperatures for TATP （T_b=402.37 K） and TATP-d₁₈ （T_b=423.46 K） also confirm that deuteration improves the thermal stability of TATP-d₁₈. Finally， the calculated thermodynamic parameters for the non-isothermal decomposition processes of TATP and TATP-d₁₈ indicate that TATP and TATP-d₁₈ would not spontaneously undergo thermal explosions.

Abstract:3，3′-Diamino-4，4′-azofurazan （DAAzF） is one of the main impurities that produced during the synthesis of 3，3′-diamino-4，4′-azoxyfurazan （DAAF）. However， the effect of DAAzF on the thermal performance of DAAF remains unclear in the past. To this end， a doping strategy based on the dissolution-precipitation method was developed to prepare DAAF@DAAzF explosives by uniformly doping 0.5%-10% DAAzF into DAAF， and the effect of DAAzF on the thermal performance of DAAF@DAAzF explosives was investigated by using simultaneous thermogravimetry and differential scanning calorimetry. The doping of DAAzF decreases the melting point of DAAF-based explosives， with the greatest decrease from 246.4 ℃ to 239.3 ℃ occurring at 10% DAAzF content. For the first time， it is found that the eutectic mixture can be formed when the mass ratio of DAAzF/DAAF is 5/95. Further， the presence of DAAzF decreases the activation energies and pre-exponential factors of DAAF-based explosives during the initial decomposition. Therefore， DAAzF as an impurity accelerates the thermal decomposition of DAAF@DAAzF explosives and reduces their thermal stability.

Abstract:To prevent the agglomeration of cobalt ferrite （CoFe₂O₄） nanoparticles and improve their catalytic decomposition performance for Octogen （HMX） and HATO （TKX-50）， graphitic carbon nitride （g-C₃N₄） was applied as CoFe₂O₄ nanoparticles dispersant carrier. The in suit preparation of CoFe₂O₄/g-C₃N₄ binary nanocomposites were achieved through solvothermal method. Corresponding composition， structure morphology and catalytic decomposition performance of CoFe₂O₄/g-C₃N₄ were investigated through X-ray powder diffractometer， scanning electron microscopy， fourier transform infrared spectrometer and differential scanning calorimeter. The results showed that the morphology of CoFe₂O₄/g-C₃N₄ composites is uniform and dense， which reduces the thermal decomposition peak temperature of HMX and TKX-50 by 7.0 ℃ and 41.3 ℃， respectively， and the apparent activation energy by 341.1 kJ·mol^-1 and 21.0 kJ·mol^-1， respectively. Moreover， the introduction of g-C₃N₄ increases the heat release amount. The results of residue analysis showed that the catalytic decomposition of HMX was very complete， while TKX-50 presents incomplete catalytic decomposition， and its residua formed micron bulk mixtures with CoFe₂O₄/g-C₃N₄.

Abstract:The development of new combustion catalysts plays a key role in high performance propellants. Herein， the metal-organic complexes Mg（Salen） and Pb（Salen） were synthesized and characterized using X-ray diffraction， fourier transform infrared， and scanning electron microscope. Their catalytic effects on the thermal decomposition of 1，3，5，7-tetranitro-1，3，5，7-tetrazolidine （HMX） were further investigated by differential scanning calorimetry. The results indicate that the thermal decomposition of HMX is evidently enhanced by the introduction of Mg（Salen） and Pb（Salen）. Compared with HMX， the decomposition peak temperatures of HMX/Mg（Salen） and HMX/Pb（Salen） dropped by 3.0 ℃ and 34.0 ℃， and theoretical apparent activation energies decreased by 7.7 kJ·mol^-1 and 34.4 kJ·mol^-1， respectively. The catalytic decomposition mechanisms of Mg（Salen） and Pb（Salen） are also elucidated by exploring the decomposition kinetics and the reaction function models.

Abstract:To explore the curing reaction behavior of 3，3-bis（azidomethyl）oxetane-tetrahydrofuran copolyether （PBT） and toluene diisocyanate （TDI） binder system， the effects of curing temperature， curing ratio and plasticizer on the curing reaction of PBT-TDI system were investigated by microcalorimetry， and the curing reaction kinetics and thermodynamics of PBT-TDI system were studied and analyzed. The experimental results show that： （1） the higher the curing temperature and the higher the TDI content， the faster the curing reaction； （2） increasing the amount of plasticizer bis（2，2-dinitropropyl）acetal/bis（2，2-dinitropropyl）formal （A3） and dioctyl sebacate （DOS） would reduce the curing reaction speed of the PBT-TDI system； （3） the curing reaction of the PBT-TDI system fits well with the n-th order reaction kinetic model with an activation energy of 12.81 kJ·mol^-1 and a pre-exponential factor of 1.48×10^-2 s^-1.

Abstract:The performance prediction methods for high-throughput energetic molecule design and screening are required to balance accuracy and efficiency. In the present work， the suitability of three common theoretical methods on different levels， including semi-empirical PM6 method， density functional theory method B3LYP/6-31G（d，p）， and high-precision complete basis set CBS-4 method， for heat of formation （HOF） prediction under the atomization scheme for high-throughput energetic molecule design and screening were evaluated. The solid HOF of twenty energetic molecules were compared， and the results of different theoretical levels are found to differ greatly. Based on the predicted HOF， experimental density， and three models （K-J， BKW and VLW）， the detonation performance of ten common energetic molecules were predicted. The results show that B3LYP method possesses the best suitability and efficiency， and the predicted detonation performance is closed to that obtained by CBS method. For example， the average relative deviation of the detonation velocity and detonation pressure predicted by BKW are only 0.4% and 1.2%， respectively. However， both the low-precision PM6 method and the time-consuming CBS method are difficult to balance the requirements of precision and efficiency in high-throughput energetic molecule design and screening. It suggests that， for the high-throughput design of energetic molecules， a medium-precision method is adequate for rapid HOF prediction.

Abstract:Polymer Bonded Explosive （PBX） is a multiphase composite material composed of pure explosive particles occupying a high volume fraction and a little polymer binder. The interface debonding between particles and binder and the mesostructure play a critical role in the mechanical properties of the material. In this paper， according to the stochastic simulation method combined with the Voronoi method， the representative volume element model of PBXs is established at the mesoscale. When the particles generated by Voronoi method are multi-graded， the particles around the large ones show a strip-scattering shape. The method of mesostructure modeling of PBXs was improved based on Voronoi method. Considering the mesoscopic interface characteristics of PBX-9501， the interface damage evolution between particle and binder under static tension was numerically simulated by using the constitutive relationship of three-stage bonding interface. The results show that the macroscopic mechanical properties of PBX-9501 agree well with the experimental data. The relationship between convergence and the size of representative volume element is discussed. It is concluded that the larger the size of the representative volume element is， the worse the convergence of the interface debonding simulation is.

Abstract:In order to explore the characteristics of ignition and flame-propagation process of the modular charge， a small metal modular cartridge was designed and the ignition test was carried out. On this basis， the internal ballistic two-dimensional gas-solid two-phase flow model of the test was established， the model was solved by using CE/SE method. The variation characteristics of flow field parameters in the chamber are obtained， and the numerical results are in good agreement with the experimental results. The numerical results reveal the changing process of the pressure distribution of the ignition tube and main charge area during the flame-propagation process， the flow law of the gas phase and the influence of its radial propagation effect on the combustion of the propellant in main charge area； The rupture of the cartridge’s end cap will lead to the formation of a shock wave in free space of the chamber， the reason for the formation of the shock wave are discussed. In addition， the numerical simulation of the gas jet of the vent hole breaking-progress under the hypothetical working condition is carried out， the gas phase flow law and the pressure-boosting law of the main charge area are studied. The comprehensive results show that under the condition of modular charge， the radial effect of the gas phase in the ignition tube is obvious during the entire ignition and flame-propagation process， and the particularity of the charge structure can easily lead to the formation of shock waves.

Abstract:Meriting in green and pollution-free combustion products， large specific surface area， insensitive-safety ， large contact area with reactants and easy modification， nanocarbon has been widely focused on tuning the performances of energetic materials （EMs） such as high explosives， propellants and thermites. This work reviews the effects of nanocarbon on the decomposition characteristics， sensitivity， mechanical performances and combustion properties of EMs. In addition， it discloses the progresses in the detection， adsorption and degradation of EMs conducted by nanocarbon. The interaction mechanisms of typical nanocarbon materials （nano-diamond， fullerene， nanocarbon fiber， carbon nanotube and graphene） in EMs have been analyzed. Within this review， issues， challenges and promising research directions existing in the application of nanocarbon in EMs are highlighted and presented. （1） Optimizing the high-cost preparation processes of nano carbon. Easy agglomeration and large batch differences of nanocarbon. （2） Expanding the application scope of nanocarbon. Exploring the effects of new-type nanocarbon such as onion carbon and modified nanocarbon on the properties of energetic materials. （3） According to the specific environment and nanocarbon regulation mechanism， the application conditions of nanocarbon in improving the properties of energetic materials are optimized. It is expected that nanocarbon materials will provide a forum for future advancement in the modifications of multifunctional EMs.