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Co-crystallization of cyclic nitramines with sterically crowded molecules, i.e., ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-CL-20) with cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), is very difficult, but the co-agglomeration (slurry method) of their mixed micro-co-particles gives very good results. CL-20 is present in these co-agglomerates (CACs) in its β-form. Besides the medium of co-agglomeration, also the molar ratio is very important; it is possible to obtain β-CL-20/BCHMX (molar 1.8/1.0) with the impact sensitivity of 14.9 J. The density of these CACs approaches 99.6% of the density of the β-CL-20 crystals. Based on the application of the Raman, FTIR and PXRD techniques, it has been proved that the agglomeration of CL-20/BCHMX micro-co-particles leads to the formation of CACs mostly with the properties of co-crystals (CCs). This also seems to be confirmed by the relationships between the heat of formation and ring-deformation vibrations (in plane) and between the impact sensitivity and the difference in the asymmetric NO2 stretching vibrations in pure CL-20 and its CACs. The CACs studied have lower detonation energies than would be consistent with the percentage of individual coformers in these crystals. An examination of the most sensitive CACs (1.2 J) as a detonator primer has shown the absence of its required acceleration capabilities in the given detonator design. A comparison with literature data and our unpublished preliminary results indicates that the CACs and CCs of this type could have potential beneficial applications in propellants. [ABSTRACT FROM AUTHOR]

Graphical abstract The Diaminotriazole group has great effect on the physical models and activation energies of the initial decomposition of tetrazine derivatives. Highlights • The heat flow behaviour of three insensitive and thermostable s -tetrazine derivatives was evaluated. • The mass loss properties of these compounds were compared with DSC results. • Their decomposition kinetic parameters and physical models were determined. • The gaseous products were analyzed with proposed initial thermolysis mechanisms. Abstract The thermal behaviour, decomposition kinetics and mechanisms of three diaminotriazole-substituted tetrazine compounds have been investigated using simultaneous DSC-TG and TG/MS techniques. It has been found that TBDM-2NB is much more stable than TBDM-NB and TBDM, where the latter decomposes in two steps with different kinetic parameters. The TBDM decomposes with peak temperature of 379.0 °C, while it is 355.6 °C and 386.5 °C for TBDM-NB and TBDM-2NB, respectively. The activation energy of the first step of TBDM is much higher (176.2 kJ mol−1) than the second step (102.3 kJ mol−1). The decomposition of TBDM-NB follows 2-d diffusion model, while it is a first order reaction model for TBDM and nucleation growth model for TBDM-2NB. The rearrangement of s-tetrazine ring is typical for thermal decomposition of the title compounds, which may undergo a homo-scission to produce N 2 and followed by production of NH 3. [ABSTRACT FROM AUTHOR]

Several new photosensitive, yet mechanical insensitive energetic coordination hybrid crystals (ECHCs) containing nano-sheets of carbohydrazide functionalized graphene oxide (GO-CHZ), as a doping agent, were prepared and comprehensively characterized. It has been demonstrated that the transition metal centers in ECHCs are 6-coordinated with the GO-CHZ and CHZ as coligands. The SEM analyses show that the GO-CHZ-CuN-1 ECHC has irregular shapes, while its cobalt and nickel analogues are homogeneous crystalline embedded with layered GO-CHZ nano-sheets. Powder X-ray diffraction study indicates that the type of metals and doping of GO-CHZ would not change the space group and symmetry of the crystals of ECHCs. The doping of CHZ-CoP and CHZ-NiP by GO-CHZ significantly improves their impact sensitivity (from 1.0 J to over 10 J). Notably, by using GO-CHZ as a doping agent, the ignition delay of CHZ-CoP was also greatly improved (only 214 μs for GO-CHZ-CoP-3), which is much shorter than that of pristine CHZ-CoP (401 μs), even though the latter used a laser with 30 times higher energy density. It indicates that these new materials are highly attractive for future smart laser-ignition systems. [ABSTRACT FROM AUTHOR]

In this paper, the thermal stability and decomposition kinetics of 10 nitric esters including nitroglycerine (NG), pentaerythritol tetranitrate (PETN), trimethylolethane trinitrate (TMETN), dipentaerythritol hexanitrate (DiPEHN), trimethylolpropane trinitrate (TMPTN), xylitol pentanitrate (XPN), sorbitol hexanitrate (SHN), erythritol tetranitrate (ENT), mannitol hexanitrate (MHN) and nitroisobutylglycerol trinitrate (NiBGT) are investigated by non-isothermal TG and DSC. It has been shown that the mass loss processes of NG, TMETN and TMPTN are more dependent on the heating rate, and the simultaneous evaporation makes the initial temperatures for their mass loss lower than those of the other nitric esters. Based on the correlations among their thermal stability, activation energy, detonation velocity and heat of combustion, one could conclude that the oxygen coefficient (α) plays a positive role on the decomposition heat release efficiency (ηd) when it is less than one, whereas when the α is greater than or equals to one, the fuel elements such as C and H contents would play a decisive role on ηd. It has been further proved that the order of contribution rate of function groups on the tertiary carbon to the detonation velocity could be –CH3 < –NO2 < –C2H5 < –ONO2. In addition, the introduction of function groups to the tertiary carbon is in favor of increasing the thermal stability of nitric esters due to increase in symmetry and rigidity of their molecules. The proportion numbers (Cs) of methylene group (–CH2–) to tertiary carbon or quaternary carbon will, to some extent, determine the thermal stability of the nitric esters. [ABSTRACT FROM AUTHOR]

The RDX, HMX, and AP are currently the most widely used energetic ingredients in composite solid propellants, since the newly developed energetic compounds are still unable to replace them due to various bottleneck technical problems. In order to improve their combustion efficiency and performance, a common alternative way is to utilize novel nano-sized energetic additives. There are a great many nanomaterials that have been developed in the past decades, which include nanometal particles, metal oxides, metal salts, metallic composites, organometallic compounds, energetic nanocatalysts, and carbon nanomaterials. These additives could increase both the decomposition and the burning rate as well as enhance the combustion efficiency of the corresponding solid propellants by changing the thermal conductivity, energy barrier of thermolysis, heat of reaction, and gas-phase reaction mechanisms of the main ingredients such as RDX, HMX, and AP. This review paper discusses and summarizes the effects of abovementioned nano additives on decomposition kinetics, reaction models, decomposition mechanisms and burning rates, pressure exponents, combustion wave structures, and flame propagation of RDX-, HMX-, and AP-based energetic compositions. The catalytic mechanisms associated with different types of nanomaterials are explained and clarified. Owing to their extremely large specific surface areas, nano-sized energetic additives have significant catalytic effects in both condensed and gas phases during decomposition and subsequent combustion via activation of the reactants and acceleration of their transition state formations. The flame structures of AP-based composite propellants under the effect of some nanoadditives are presented showing the enhanced burning characteristics and stabilized combustion process. [ABSTRACT FROM AUTHOR]

Conceptually new cylindrical charges enveloped by Al foils have been designed and their thermobaric effects, due to simultaneous fragmentation and combustion of the foils, have been experimentally determined. The fragmentation processes of Al foil was supported by numerical simulations. It has been shown that the quasistatic pressures (QSP) for phlegmatized RDX (RDX ph ) enveloped with Al-coated plastic foils are higher than that of the pure RDX ph , due to combustion of these foil fragments in a thermobaric explosion. The QSP generated by Al–Ni foils enveloping RDX ph was found to be much lower than performance of other foils, possibly due to relatively inert nature of Ni. In a small detonation chamber, the charges of RDX ph /Al foil (RDX ph /Alf) produced even higher experimental maximum peak pressure (Δ p max ) than the charges that contained Al powder (Al p ). In a closed bunker, the impulse amplitudes of RDX ph enveloped by aluminized polyethylene (Al-PE) foils and RDX ph enveloped by 100 µm Alf (Alf100) charges are much lower than those of the other charges. It was found that the charges enveloped by Al foils have even larger Δ p max than that of RDX ph /Al p charges, indicating that the Alf could generate better blast performances than the Al p . The simulations indicate that the observed blast enhancement is dependent not on the thickness, but on the size of surrounding space. The thermobaric fire-ball generated by 40 g RDX/Alf charge could sustain combustion up to 40 ms, reaching a maximum radius of about 2.4 m. [ABSTRACT FROM AUTHOR]

Mixtures of 1,3,5-trinitroso-1,3,5-triazinane (TMTA) with 1,3,5-trinitro-1,3,5-triazinane (RDX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (BCHMX) and ɛ-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), respectively, have been investigated by DSC and TGA techniques. It has been found that there are two endothermic peaks at about 96 °C and 107 °C, due to polymorphic transition and melting of TMTA, whereas only small endothermic peaks were observed in the temperature region of 92.8–95.0 °C for mixtures of RDX-TMTA, BCHMX-TMTA and CL-20-TMTA. These differences in exothermic temperatures of the pristine TMTA versus its mixtures could be a result of co-crystals formation. Moreover, only one complex step for decomposition of TMTA and RDX-TMTA was observed, while at least two steps were found for BCHMX-TMTA and CL-20-TMTA mixtures. TGA measurements showed that a mass loss of TMTA begins at 89.3 °C and has a peak temperature of 185.9 °C. In contrast, the mass loss of RDX-TMTA mixture begins at 142.9 °C and has a peak temperature of 227.6 °C, evidently showing a behavior of a single compound. On the other hand, the activation parameters for the first step decomposition of the BCHMX-TMTA (2.355 J g −1 ) and CL-20-TMTA mixtures were found to be very close to that of TMTA (1.320 J g −1 ), strongly indicating that most probably TMTA undergoes decomposes during the first decomposition steps of these mixtures. [ABSTRACT FROM AUTHOR]

The project involves determination of the activation energies and physical models for thermolysis of BCHMX and its PBXs. The initial decomposition pathways were also proposed on the basis of molecular dynamic simulation. The goal is to find the mutual relationships among the physical models, decomposition pathways, and the impact sensitivities for BCHMX and its PBXs. It has been shown that the physical model of the first step of BCHMX thermolysis is close to first order and the second step is governed by a first order autocatalytic model, which turns to “2D or 3D Nucleation and Growth” models under the effect of polymeric binders probably due to their hindrances on topochemical reaction of BCHMX. Simulation results show that the scission of N-NO 2 is the initial step for BCHMX pyrolysis, followed by HONO and HNO eliminations, where the latter is due to nitro-nitrite rearrangement. Under the effect of hydrocarbon polymers, the HONO/HON elimination and collapse of ring structure of BCHMX occur earlier without changing the time for N-NO 2 scission, which might be the reason why those polymers have little effect on the thermal stability of BCHMX, while they could make it decompose almost in a single complex step. [ABSTRACT FROM AUTHOR]

The crystal morphologies, thermal behavior, sensitivity and performance of 2-amino-4,6,-diazido- s -triazine and its derivatives have been investigated using SEM, DSC, TG techniques and related theories. It has been shown that the DANT crystal is in 1–5 μm thickness layered regular hexagon structure with severe agglomeration. DAAT crystal is very hydrophobic and can be dispersed in water, which has layered rectangle structure with thickness less than 0.5 μm. The TAHT materials exist in a form of amorphous irregular particles with diameters of more than 200 μm while its analogue TAAT can be crystallized in needle shape with a length of 30 μm. TNADAzT crystal has a shape of regular polyhedron with average size of about 120 μm. The thermal analysis indicates that there is only one complex step for decomposition of DAAT, while at least three steps are included for the other materials. DAAT started to decompose at around 148.4 °C with a peak temperature of 197.0 °C, while TAHT started to decompose at 167.2 °C with shoulder-peak of 193.4–206.7 °C at the heating rate of 2.0 °C min −1 . DANT decomposes with a heat release of 2420–2721 J g −1 , which is much higher than that of DAAT indicating that the heat and its release rate are greatly enhanced by transformation of amino to nitroamino group. Different from the analogue TAHT, there is an obvious melting process at about 152 °C before TAAT decomposition covered by an enthalpy of fusion 93–100 J g −1 . The thermal stability of TNADAzT is slightly worse than that of DAAT, and it decomposes in liquid state with a melting point of about 171 °C. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nonisothermal decomposition kinetics of RDX and its PBXs has been investigated. [•] The kinetic models are determined by both master plot and combined kinetic analysis methods. [•] The constant rate temperature profiles and isothermal curves are predicted by obtained kinetic triplets. [•] The storage safety parameters are simulated based on thermal explosion theory. [ABSTRACT FROM AUTHOR]

Erythritol tetranitrate (butane-1,2,3,4-tetrayl tetranitrate, ETN) has become one of the most synthesized improvised explosives nowadays as it can be found on public internet discussion boards. However, the low melting point, nitrocellulose gelling ability, high energy content, and availability of its precursor make the substance potentially useful in industry as an energetic component or additive in certain gun propellants. Mixtures of ETN with other high explosives are also frequently discussed on web pages dealing with improvised explosives. This article describes thermal behavior and decomposition kinetics of pure ETN and its mixtures with pentaerythritol tetranitrate and cyclonite (1,3,5-trinitro-1,3,5-triazinane, RDX). The thermal behavior and decomposition kinetics of such mixtures are described using non-isothermal DSC and TG techniques. Kissinger method, Soviet manometric method, and modified Kissinger-Akahira-Sunose method were used for data evaluation. [ABSTRACT FROM AUTHOR]

Highlights: [•] The thermal behavior of Fluorel bonded explosives (PBXs) containing cyclic nitramines have been investigated. [•] Their decomposition kinetics parameters have been calculated by modified Kissinger–Akahira–Sunose (KAS) method. [•] It has been found that Fluorel matrix has a significant effect on the activation energy distribution of cyclic nitramines. [•] The Fluoropolymer is chemical incompatible cyclic nitramines with crowded molecule such as BCHMX. [Copyright &y& Elsevier]

Highlights: [•] The thermal behavior of a series of nitric esters has been firstly comprehensively investigated using non-isothermal TG and DSC techniques. [•] Their thermal decomposition kinetics parameters have been calculated by modified Kissinger–Akahira–Sunose (KAS) isoconversional method. [•] The order of molecular stability for involved nitric esters is found to be MHN

Highlights: [•] The effects of Viton A binder on the thermal behavior of cyclic nitramines have been investigated by using non-isothermal techniques. [•] The decomposition kinetics parameters have been calculated by modified Kissinger-Akahira-Sunose method. [•] As a thermostable polymer, Viton A could inhibit the initial autocatalysis effect of cyclic nitramines. [•] It would improve the thermal stability of corresponding PBXs containing RDX, β-HMX and ε-CL-20. [Copyright &y& Elsevier]

The crystal structure, thermal behavior, and decomposition kinetics of ε-CL-20, RS-ε-CL-20, α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4 were investigated by nonisothermal FTIR, TG, and DSC techniques. It was found that the thermal decomposition of α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4 could be considered as a two-step process and the initial step is partly controlled by crystal structure. However, the crystal structure could only affect the initial step of decomposition and the total heat release, and the heat release of RS-ε-CL-20 is the highest compared with α- and normal ε-CL-20. In addition, the activation energy of studied materials was calculated by Kissinger method and modified KAS method, which was compared with the results obtained by other researchers. It was indicated that the obtained activation energy of ε-CL-20 by Kissinger method is about 176.0 kJ mol, which is almost the same with the results from the literatures by STABIL and Noniso-TG methods. It was noticed that the crystal structure has significant effect on the initial activation energy distribution of CL-20, while in case of second stage (α = 0.30-0.85) this effect is relatively small, resulting in identical decomposition mechanism. Moreover, the kinetic compensation effects show that the studied materials could be divided into two groups, one including ε-CL-20, RS-ε-CL-20, α-CL-20, and ε-CL-20/C4 which decompose at solid state and another including ε-CL-20/Formex and RS-ε-CL-20/C4 which decompose at partial liquid state, resulting in different kinetic compensation effects. It reveals that the C4 base could affect the distribution of activation energy of ε-CL-20 and RS-ε-CL-20 in a totally different way. [ABSTRACT FROM AUTHOR]

The critical temperature and mechanism functions for thermal decomposition of ε-CL-20, RS-ε-CL-20, α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4 were evaluated based on non-isothermal TG data. A two-step mechanism has been found for thermal decomposition of α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4, where the initial step is partly controlled by crystal structure of CL-20. The more reasonable mean activation energies could be obtained after peak separation for each individual steps. In fact, the activation energy for the post integrated process is almost equivalent with that of the second step, indicating that the total activation energy at the main decomposition process is dominated by thermolysis of CL-20 molecular. Besides, it has been found that the decomposition of C4 matrix does not affect the decomposition of normal ε-CL-20, resulting in identical activation energy and reaction model. However, the interaction between the C4 matrix and RS-ε-CL-20 is significant especially at the initial stage, where the activation energy of RS-ε-CL-20/C4 was overestimated before peak separation, while the activation energy for the second step due to thermolysis of CL-20 molecular is underestimated. The first decomposition step for α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4 could be considered as autocatalytic process (AC model), whereas the second as JMA model, which is also applicable to that of pure ε-CL-20 and RS-ε-CL-20. Moreover, The critical temperatures of thermal explosion ( T) are obtained as 205.6, 205.5, 209.4, 214.4, and 227.5 °C for α-CL-20, ε-CL-20, RS-ε-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4, respectively. It proves that the C4 matrix could stabilize ε-CL-20 while the crystal form of CL-20 has little effect on its thermal stability. [ABSTRACT FROM AUTHOR]

Over the past 20 years, a number of scientists have conducted numerous fundamental investigations based on quantum chemistry theory into various mechanistic processes that seems to contribute to the sensitivity of energetic materials. A large number of theoretical methods that have been used to predict their mechanical and spark sensitivity are summarized in this article, in which the advantages and disadvantages of these methods, together with their scope of use are clarified. In addition, the theoretical models for thermal stability of explosives are briefly introduced as a supplement. It has been concluded that the current ability to predict sensitivity is merely based on a series of empirical rules, such as simple oxygen balance, molecular properties, and the ratios of C and H to oxygen for different classes of explosive compounds. These are valid only for organic classes of explosives, though some special models have been proposed for inorganic explosives, such as azides. An exact standard for sensitivity should be established experimentally by some new techniques for both energetic compounds and their mixtures. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: The thermal behavior and decomposition kinetics of C4-bonded PBXs based on some attractive cyclic nitramines were investigated by means of nonisothermal TG and DSC techniques. It has been shown that only a single decomposition process has been observed for RDX-C4 while an obvious two-step process for mixture of BCHMX-C4 CL-20-C4, and HMX-C4. The onset temperature of the exotherms were observed at 216.3, 238.7, 279.2 and 236.7°C with the peak temperatures of 235.1, 279.0, 231.2 and 233.7°C for RDX-C4, BCHMX-C4, HMX-C4 and CL-20-C4, respectively. Their corresponding exothermic decompostion processes were covered by energy changes of 1749, 1938, 1213 and 2639Jg−1, which are lower than that of their pure cyclic nitramines. It was also proved that C4 matrix has significant effect on the activation energy distribution of RDX, BCHMX and CL-20, whose initial autocatalysis effect was inhibited or weakened. With regard to HMX-C4, the activation energy of its initial step is much lower than that of the second step. [Copyright &y& Elsevier]

Thermal behavior and decomposition kinetics of Formex-bonded PBXs based on some attractive cyclic nitramines, such as 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Actually, cis-1,3,4,6-tetranitrooctahy droimidazo-[4,5-d]imidazole (BCHMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10, 12-hexaazaisowurtzitane (CL-20), was investigated by means of nonisothermal thermogravimetry (TG) and differential scanning calorimetry (DSC). It was found that the mass loss rate of PBXs involved in this research depends greatly on heating rate and the residue of the decomposition of these PBXs decreases with the heating rate. The onset of the exotherms was noticed at 215.4, 278.7, 231.2 and 233.7 °C with the peak maximum at 235.1, 279.0, 231.2 and 233.7 °C for RDX-Formex, HMX-Formex, CL-20-Formex, and BCHMX-Formex, respectively. Their corresponding exothermic changes were 1788, 1237, 691, and 1583 J g. It was also observed that the dependence on the heating rate for onset temperatures of HMX- and BCHMX-based PBXs was almost the same due to their similar molecular structure. In addition, based on nonisothermal TG data, the kinetic parameters for thermal decomposition of these PBXs were calculated by isoconversional methods. It was shown that the Formex base has great effects on the activation energy distribution of nitramines. It was further found that the kinetic compensation effects occurred during the thermal decomposition of nitramine-based PBXs, and they almost have the same compensation effects due to similar decomposition mechanism. [ABSTRACT FROM AUTHOR]

Abstract: As an attractive new energetic material, cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX) and its polymer bonded explosive (PBX) with styrene-butadiene rubber (SBR) binder (Formex type) have been investigated with regard to its thermal decomposition kinetics and reaction models by using DSC, TG and SEM techniques. It was found that the decomposition of BCHMX in dynamic nitrogen could be divided into two steps, while there is only one step for its Formex bonded explosive. The activation energy for decomposition of BCHMX/Formex was obtained to be 221.7±4.99kJmol−1 by modified KAS method, while the mean activation energies for pure BCHMX are calculated as 233.0±2.1kJmol−1 for first step and 186.0±0.92kJmol−1 for the second step. It was further proved that the first decomposition step of BCHMX is autocatalytic, during which the crystal of BCHMX could dissolve in the liquid phase of its thermolysis products on the surface. Besides, the JMA and AC models were found to be appropriate to interpret the two-step decomposition of pure BCHMX and JMA model for BCHMX/Formex, the parameterized reaction models for BCHMX could be established as f(α)= α 0.45(1− α)1.51 and f(α)=2.33×(1− α)[−ln(1− α)]0.57, while for BCHMX/Formex as f(α)=2×(1− α)[−ln(1− α)]1/2. [Copyright &y& Elsevier]

Abstract: In this paper, several fundamental investigations published over the past decades with regard to the thermal analysis of polymer-based explosives (PBXs) have been briefly reviewed. A number of explosive fillers and polymer bases that were used as their main ingredients of PBXs are summarized herein. In addition, the calculation methods for their decomposition kinetics and thermal stability parameters are also introduced in detail. It was concluded that only PBXs based on HMX, RDX and TATB have been widely investigated, and that some other PBXs containing innovative fillers, such as CL-20, TNAZ, NTO and BCHMX are at the design stage. The isoconversional methods and model fitting procedures are usually used to analyze the discrete thermolysis processes of PBXs. In addition, their thermal stability parameters such as shelf life, explosion delay, critical temperature, thermostability threshold, 500-day cookoff temperature and approximate time to explosion could be calculated easily from the kinetic data. [Copyright &y& Elsevier]

Abstract: The thermal decomposition process of a newly designed composite material KClO3–RDX (KC-RDX) was investigated by combined TG–DSC–FTIR technique and DSC technique. It was shown that KC-RDX began to decompose at about 209.9°C after melting, and the fast stage of mass loss at the temperature range of 209.9–259.8°C is considered to be the result of the thermolysis and complex reactions of KClO3 and RDX with energy release of 1887Jg−1, which exceeded that of pure RDX about 10%. The CO, CO2, HCN, NO2 and H2O were detected as the main gaseous products of KC-RDX decomposition, and occurred in initial stage of RDX decomposition are greatly affected by KClO3. In contrast to pure RDX, there was nearly no CH2O detected in thermolysis products of KC-RDX. In the presence of electronegative oxygen radical produced by thermolysis of KClO3 oxidized CH2O through gas-phase reaction CH2O+O2 →HCO+HO2, which might be one of the unique chemical reaction for KC-RDX. [Copyright &y& Elsevier]

Abstract: The combustion efficiency of metallized propellants are investigated and compared to the corresponding blank propellant in order to evaluate the actual effect of the metals in solid rocket applications. The image analysis coupled with energy dispersive spectrometry (EDS) analysis on a scanning electron microscope (SEM) and quantitative X-ray diffraction analysis were applied to the characterization of the original metal particles such as aluminum (Al), magnesium (Mg), boron (B), nickel (Ni), and Mg–Al alloy (Mg/Al) and their condensed combustion products. Under the explored operating conditions, the results confirm that the metallized propellants show heterogeneous diffusing flame, with significant change in pressure sensitivity, and larger aggregation/agglomeration phenomena in combustion products than that of the blank propellant. Besides, the chemical reactions in condensed phase and gas phase which control the burning process and combustion efficiency of the double-base propellant containing different metal particles were systematically investigated and descriptions of the detailed reaction mechanisms from solid phase to liquid phase or to gas phase are also included. It was indicated that the combustion efficiency is favored by the activity and melting points of the metals. [Copyright &y& Elsevier]

Abstract: In order to evaluate the actual pros and cons in the use of new nitroamines for solid rocket applications, the combustion properties of double-base propellants containing nitrogen heterocyclic nitroamines such as RDX, TNAD, HMX and DNP are experimentally investigated by means of high-speed photography technique, thermogravimetry (TG) and differential scanning calorimetry (DSC). It was indicated that DNP and TNAD can yield a lower pressure exponent than that of RDX and HMX, especially, TNAD-CMDB can give plateau burning at higher pressure with higher burning rates (, ) than that of RDX and HMX. It was also concluded that the rate of change in space of the temperature gradient is negligible for these propellants and the rate of mass diffusion is assumed to be small compared with the rate of mass convection. Furthermore, the reaction of CH2O + NO2 → CO + NO + H2O is probably the most important one in the foam layer of the propellants containing nitrogen heterocyclic nitroamines and the thermodynamic phase transition consisting of both evaporation and condensation of NC, HMX, TNAD, RDX and DNP, are considered to provide a complete description of the mass transfer process. [Copyright &y& Elsevier]

Abstract: In order to evaluate the actual pros and cons in the use of new nitroamines for solid rocket applications, the combustion properties of double-base propellants containing nitrogen heterocyclic nitroamines such as RDX, TNAD, HMX and DNP are investigated by means of high-speed photography technique, Non-contact wavelet-based measurement of flame temperature distribution. The chemical reactions in different combustion zone which control the burning characteristics of the double-base propellant containing nitrogen heterocyclic nitroamines were systematically investigated and descriptions of the detailed thermal decomposition mechanisms from solid phase to liquid phase or to gas phase are also included. It was indicated that the thermodynamic phase transition consisting of both evaporation and condensation of NC+NG, HMX, TNAD, RDX and DNP, are considered to provide a complete description of the mass transfer process in the combustion of these double-base propellants, and the combustion mechanisms of them are mainly involved with the oxidation mechanism of the NO2, formaldehyde (CH2O) and hydrogen cyanide (HCN). The entire oxidation reaction rate might be dependent on the pressure of the combustion chamber and temperature of the gas phase. [Copyright &y& Elsevier]

Abstract: The compatibility of trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin (TNAD) with some energetic components and inert materials of solid propellants was studied by using the pressure DSC method where, cyclotetramethylenetetranitroamine (HMX), cyclotrimethylenetrinitramine (RDX), 1,4-dinitropiperazine (DNP), 1.25/1-NC/NG mixture, lead 3-nitro-1,2,4-triazol-5-onate (NTO–Pb), aluminum powder (Al, particle size=13.6μm) and N-nitrodihydroxyethylaminedinitrate (DINA) were used as energetic components and polyethylene glycol (PEG), polyoxytetramethylene-co-oxyethylene (PET), addition product of hexamethylene diisocyanate and water (N-100), 2-nitrodianiline (2-NDPA), 1,3-dimethyl-1,3-diphenyl urea (C2), carbon black (C.B.), aluminum oxide (Al2O3), cupric 2,4-dihydroxy-benzoate (β-Cu), cupric adipate (AD-Cu) and lead phthalate (φ-Pb) were used as inert materials. It was concluded that the binary systems of TNAD with NTO–Pb, RDX, PET and Al powder are compatible, and systems of TNAD with DINA and HMX are slightly sensitive, and with 2-NDPA, φ-Pb, β-Cu, AD-Cu and Al2O3 are sensitive, and with PEG, N-100, C2 and C.B. are incompatible. The impact and friction sensitivity data of the TNAD and TNAD in combination with the other energetic materials under present study was also obtained, and there was no consequential affiliation between sensitivity and compatibility. [Copyright &y& Elsevier]

Abstract: DNP, a nitramine, has been studied with regard to the kinetics and mechanism of thermal decomposition, using thermogravimetry (TG), differential thermal analysis (DTA), infrared (IR) spectroscopy, and differential scanning calorimetry (DSC). The IR spectra of DNP have also been recorded and the kinetics of thermolysis has been followed by non-isothermal TG. The activation energy of the solid-state process was determined using Flynn–Wall–Ozawa method. The actual reaction mechanism obeyed nucleation and growth model, Avramie Erofeev function (n =1) with integral form G(α)=−ln(1− α) (α =0.10–0.65). E a and A were determined to be 116.51kJ/mol and 1010.52 s−1. The T/Jump FT-IR analysis showed that CH2O, NO2, and NO are produced in larger amounts than CO2 and HCN. The cleavage of the N–N and C–N bond appears to be the primary step in the thermolysis of DNP. [Copyright &y& Elsevier]

To improve the ignition and combustion behaviors of Al, the strategy of interfacial modification using transition metals (TMs) for the Al/AP composites to produce the multi-layered core-shell structured Al@TMs@AP composite fuels is provided. The relevant Al-based composite fuels are fabricated using spray granulation method and their morphologies are characterized by SEM and TEM techniques. The ignition and combustion of the solid propellants prepared with the core-shell structured composite fuels are evaluated and compared with that of reference propellant formulated with typical compositions using laser ignition setup and combustion diagnostic system. Results indicate that the heats of reaction measured for the Al@TMs@AP contained propellants are increased by as high as 13%, suggesting the completeness in combustion of Al is greatly improved by construction of Al composites with the multi-layered core-shell structure. The ignition delay times are apparently shortened from 421 ms to 373 ms for the propellants with Al@TMs@AP involved, which proves that the promoted ignition of Al is achieved by surface modification with transition metals. Additionally, the significantly increased burning velocity is monitored for the Al@TMs@AP contained propellants at low-pressure regime leading to the corresponding pressure exponents to be reduced by more than 20%, which is beneficial to the stability in operation of solid rocket motors. At last, the higher combustion wave temperature and finer particle size in CCPs are observed for the propellants containing surface modified Al, and the plausible combustion mechanism is proposed based on the phase composition analysis for the CCPs of studied propellants. [ABSTRACT FROM AUTHOR]

The nano-sized metal oxides (MOs) as combustion catalysts have been widely employed in solid rocket propellants, but the functionality of these materials is greatly restricted owing to their agglomeration. The catalytic activity of MOs on nanoscale was found to be significantly improved by the incorporation of MOs with carbon nanomaterials, which normally act as carriers allowing for well-distribution of MOs. In this paper, the CuO and Fe2O3 nanoparticles were produced by hydrothermal method and the CuO@C and Fe2O3@C nanocomposites with a uniform structure have been fabricated by an in-situ growth of corresponding MOs on the porous activated carbon (pAC). The morphology of the prepared MOs nanoparticles and resultant pAC carried ones were characterized using scanning electron microscope. It has been shown that the CuO and Fe2O3 nanoparticles are tightly adhered and dispersed on the surface of pAC. Their catalytic effects on the thermal decomposition of hexogen (RDX) were analyzed using thermal analysis techniques. Results indicate that the thermal decomposition of RDX was considerably promoted in the presence of these catalysts, where the CuO@C and Fe2O3@C were found to be capable of lowering the Tp for RDX by 14.8 °C and 12.4 °C, respectively. In addition, the decomposition kinetics of RDX in the presence of these catalysts have been evaluated with the DTG and DSC experimental data, and results show that the CuO@C and Fe2O3@C were able to reduce the Ea of RDX decomposition by 39.8 kJ mol−1 and 50.7 kJ mol−1, which is suggestive of an enhanced decomposition process for RDX by addition of carbon-loaded catalysts. The TG-FTIR analysis indicates that, in the presence of CuO@C and Fe2O3@C, the gaseous products are dominated by N2O in RDX decomposition. [ABSTRACT FROM AUTHOR]

ε-CL-20 is currently the most powerful commercially available explosive, but its high mechanical sensitivity and low phase stability limit its broad applications. In order to reduce the sensitivity of ε-CL-20, cross-linked graphene oxide (GO), using triaminoguanidine–glyoxal polymer (TAGP) as the bridging agent, was prepared in the ε-CL-20 solution, which could constrain the nano-sized ε-CL-20 crystals following a conventional solvent–nonsolvent in situ crystallization method. It was shown that the polymorphic transition temperature of the assembled CL-20/GO–TAGP crystals increased by about 36.0 °C at a maximum level compared with pristine ε-CL-20, and the polymorphic transformation temperature varied depending on the content of the cross-linked GO. Moreover, the heats of formation for the resulting modified products such as CL-20-2 (950.0 kJ kg−1) and CL-20-4 (848.3 kJ kg−1) were 26.9% and 13.3% higher than that of pure ε-CL-20 (748.9 kJ kg−1), respectively. The measured density of assembled CL-20 crystals was almost unchanged as 2.01 g cm−3 under a certain condition. The impact and friction sensitivities of the modified samples, such as CL-20-1, CL-20-3, and CL-20-6, were obviously reduced. More importantly, two of the assembled products even showed a certain improvement in specific impulse and detonation performance. [ABSTRACT FROM AUTHOR]

In this paper, the thermal degradation properties of Viton A and Fluorel are investigated by both isoconversional and combined kinetic analysis methods using non-isothermal thermogravimetry technique. It has been found that the heating rate has little affect on the degradation residue of Fluorel and Viton A, where around 1.3% char was formed for Fluorel and 3.5% for Viton A. Different from the literature, the decomposition of Viton A should be considered as an overlapped dehydrofluorination and carbon chain scission process, with activation energy of 214 ± 11 and 268 ± 13 kJ mol, respectively. The effect of dehydrofluorination on degradation of Fluorel is not so significant due to low content of H, and hence, it could be considered as a single-step mechanism with average activation energy of 264 ± 14 kJ mol. The thermal stability of Fluorel is much better than that of Viton A, and the predicted half-life is around 218 min for Fluorel and 49 min for Viton A at 420 °C, which are consistent with experimental values. If using a single-step model as in the literature for Viton A, its half-life at 420 °C would be underestimated for >20%. [ABSTRACT FROM AUTHOR]

• The combustion performance is significantly enhanced with the addition of integrated Al/oxidizers composites. • The burning rates of propellants can be well regulated in a wide range under 0.5–15 MPa with reduced pressure exponents. • The agglomeration of Al particles is greatly inhibited and the mechanism has been proposed and elucidated. Modulation of burning rates and inhibition of aluminum agglomeration in solid propellants have generated considerable research interest in the field of energetic materials. In this paper, integrated Al/oxidizer composites have been prepared by a spray-drying technique, which offer intimate contact between the fuel and oxidizers. The morphologies, thermal stability, density, heats of explosion and combustion performance of the resulted solid propellants containing these Al-based composites were systematically investigated, where the condensed combustion products (CCPs) analysis and the agglomeration behavior of Al particles have been focused. After well control of the Al/oxidizers structure, 9 % higher explosion heat, 58 % higher pressurization rate and 65 % stronger flame radiation intensity were achieved in comparison to the conventional solid propellants with the same formulation. The burn rate of the propellants can also be well controlled by using different type of Al/oxidizers composites, in the range of 3.6–5.9 mm s−1 under 0.5 MPa and 9.2–10.9 mm s−1 under 15 MPa. More importantly, very low burn rate pressure exponent of 0.1 within 0.5–15 MPa was obtained. Inspired by decreasing size of CCPs, the evolution of Al on the burning surface was studied and the agglomeration inhibition was observed, whose potential mechanism was then proposed and elucidated. [ABSTRACT FROM AUTHOR]

Energetic materials play an irreplaceable role in both civial and millitary applications. The development of new energetic materials with high energy but low sensitivity has become the major challenge for this community. The diagram describes the interdependence of detonation properties, thermal stability and sensitivity of existing energetic materials, and it clearly shows that L-HMX is the target idea product of EMs that balances all the performances. [Display omitted] • The strategy of hybridization or so-called host/guest is completely new. A new method of in-situ crosslinking macromolecular 2D materials in an organic explosive solution was developed. Layered high explosive crystals L-HMX have been prepared, which are presented in a single layer with a thickness of 6 nm. • The hybrid crystals have unexpected layered structures with permanent configuration changes, resulting in higher packing density. L-HMX shows great fluorescence characteristics with a laser at wavelengths less than 1024 nm. • The hybrid energetic crystals show great balance in energy density and sensitivity. The calculated VoD value of L-HMX was higher than that of pure HMX. Meantime, the mechanical sensitivity of L-HMX crystals is significantly lower than that of pure HMX. Low-sensitivity but high-energy layered HMX crystals have been prepared by using an in-situ crosslinked network as the templated confinement, following a solvent-antisolvent procedure. The as received layered-HMX (L-HMX) crystals have only three diffraction peaks at 13.8°, 28.0° and 42.6°. It reveals that the conformation of the HMX molecule was largely changed after the squeezing and templating effect of the high nitrogen layers. The endothermic peak was not observed prior to decomposition, as the polymorphic transition and melting processes were excluded. This suggests that a new phase of HMX has been achieved. Unexpectedly, the L-HMX also shows significant fluorescent properties with incident laser wavelength of less than 932 nm. L-HMX has a calculated VoD value of 9425 km·s−1 and a calculated P C-J value of 41.5 GPa even 5 % higher than that of pure HMX. It is worth mentioning that the mechanical sensitivity of L-HMX crystals has been significantly reduced, and the excitation energy required for impact initiation is greater than 50 J, whereas that of pure HMX is about 6 J. The friction sensitivity is greater than 200 N. This approach may offer an efficient means to significantly enhance mechanical and thermal safety performance, while still maintaining a high energy level. [ABSTRACT FROM AUTHOR]

• The interfacial controlled self-assembling technique has been used to prepare their co-particle with a minor content of nano-sized insensitive compound. By employing the spray drying technique, CL-20 and nanosized TATB@PDA could be easily assembled into spherical co-particles with different TATB contents (e.g. 1%, 5% and 10%). • As a typical example, with 10 % of nTATB@PDA, the co-particle exhibits 2 °C higher peak decomposition temperature than that of raw ε-CL-20. Furthermore, the TG results confirm the one-step thermal decomposition process of this co-particle, whereas the mixture at the same ratio would decompose in two steps due to very different thermal stability of CL-20 and TATB. • In terms of safety performance, the impact initiation energy of that co-particle is 16 J, which is five times higher than that of raw CL-20. Additionally, the friction sensitivity of co-TATB P10% /CL-20 is reduced from 100 % to 80 %. Notably, despite great improvements in sensitivity, the density of that co-particle remains almost the same as ε-CL-20. In this study, to effectively reduce the mechanical sensitivity of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaiso-wurtzitane (CL-20) while maintaining its high energy density, an interfacial controlled self-assembly technique was employed to prepare co-particles containing minimal amounts of nano-sized insensitive compounds. Herein, 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a commonly used insensitive energetic compound, was employed. Through the spray drying technique, CL-20 and nano-sized TATB@polydopamine (PDA) were effectively assembled into spherical co-particles with varying TATB contents (1, 5, and 10 %). The scanning electron microscopy images revealed the co-particles to have a football-shaped morphology. Notably, a part of the CL-20 had crystallised as a compact shell with a trace amount of nTATB@PDA on the surface, while most of CL-20 was embedded in the co-particles. The strong intermolecular interactions between the compact CL-20 shells and nTATB@PDA were confirmed through Raman and infrared spectroscopy analyses. For instance, the co-particles with 10 % nTATB@PDA exhibited 2 °C higher peak decomposition temperature compared to raw ε-CL-20, indicating improved thermal stability. Furthermore, thermal gravimetric analysis results revealed that the co-particles underwent one-step thermal decomposition, while the mixture decomposed in two steps (at the same ratio) due to the differing thermal stabilities of CL-20 and TATB. In terms of safety, the co-particles demonstrated an impact initiation energy of 16 J, which is five times higher than raw CL-20. Additionally, the friction sensitivity of co-TATB P10% /CL-20 decreased from 100 to 80 %. Despite great improvements in sensitivity, the density of the co-particles remained almost the same as that of ε-CL-20. Overall, these findings underscore the effectiveness of co-particle technology in reducing the mechanical sensitivity while enhancing the thermostability of CL-20, all whilst maintaining the energy density. [ABSTRACT FROM AUTHOR]

The 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is considered as the most promising energetic materials (EMs) in terms of its detonation performance. Nonetheless, its applications are limited due to high sensitivity and low phase stability. Thermal decomposition behavior especially for the initial reaction pathway determines its reactivity and sensitivity. An in-depth discernment of the innate decomposition pathways of CL-20 would facilitate the precision tailoring and augmentation of its performance. The thermal behavior and decomposition mechanisms of CL-20 are largely dependent on the experimental conditions and chemical environments. In this brief review, the effects of those factors on the thermal decomposition mechanisms of CL-20 are summarized from both theoretical and experimental perspectives. In particular, the interaction mechanisms between CL-20 and the other commonly used energetic compounds are simultaneously elucidated. • Environmental conditions and contact materials influence the thermal decomposition mechanism of CL-20. • High temperatures can weaken the influence of physical factors on the decomposition of CL-20. • The influence of contact materials on the decomposition mechanism of CL-20 varies depending on the material used. • Need to strengthen theoretical research on the decomposition mechanism of CL-20 under chemical environments. [ABSTRACT FROM AUTHOR]

As a novel high energy fuel, aluminum hydride (AlH 3) has great potential in the field of solid propellants because of its high hydrogen capacity, which can significantly improve the specific impulse of solid propellants. In order to improve the stability of α-AlH 3 , hydrochloric acid has been used to stabilize AlH 3 and the stabilization mechanism has been investigated. Various characterization techniques including scanning electron microscopy, X-ray electron spectrometer, X-ray diffraction, thermal analysis, and vacuum stability test have been employed to investigate the morphology, crystal structure, thermal stability, and decomposition kinetics of raw and passivated α-AlH 3. The results showed that the honeycomb-like structures could be formed on the surface of α-AlH 3 after passivation. First of all, the initial decomposition temperatures of the passivated samples were slightly increased. In particular, for the optimized sample with 105 min passivation time (AlH 3 -105min), the initial decomposition temperature (173.4 °C) is increased by 5.6 °C. Moreover, the total decomposition time (1652 min) is improved by about 50% than that of the raw sample (1098 min). Besides, the decomposition activation energies (E a) of passivated samples are much higher than that of the raw sample (84.8 kJ mol−1), in which the optimized sample (AlH 3 -105min) reaches 107.1 kJ. mol−1. The decomposition kinetics model may change from 3-D nucleation and nucleus growth model to 2-D nucleation and nucleus growth model. It demonstrates the passivated samples have a lower decomposition rate and higher thermal stability. The stabilization mechanism is as follows: removing the impurities on the surface and accelerating the hydrolysis reaction of AlH 3 to generate complete and dense oxide layers. [Display omitted] • The stabilization of AlH 3 has been achieved by surface passivation in acidic media. • The activation energy of the optimized sample has been improved by 22.3 kJ. mol−1. • The optimized passivation time was determined by the decomposition activation energy. • The decomposition kinetics models and stabilization mechanisms have been proposed. [ABSTRACT FROM AUTHOR]

• The chemical interactions between three typical pyrotechnics with cellulose as packing material have been studied. • The cellulose would interact with B/KNO 3 with exothermic reactions during the pyrolysis. • It is difficult for Mg/PTFE to undergo self-sustainable combustion at ambient pressure in presence of cellulose. • The cellulose has little effect on the flame temperature and reaction pathways of B/KNO 3. In order to study the effect of cellulose shell on the thermal behavior including pyrolysis gaseous products, ignition and combustion characteristics of typical pyrotechnics, three composites of pyrotechnics/cellulose were prepared in this paper. Various characterization techniques were used to investigate the prepared composites and their combustion condensed products (CCPs), including scanning electron microscopy (SEM), simultaneous thermal analysis (DSC-TG-FTIR), X-ray diffraction (XRD), bomb calorimetry, and home-made combustion diagnostic system. The results showed that the overall heat release of the black powder and Mg/PTFE decreased from 3108 J·g−1 and 1157.4 J·g−1 to 1045.4 J·g−1 and 810.4 J·g−1 in the presence of 33.3% cellulose, respectively. Moreover, the FTIR spectra showed that the cellulose did not change the reaction pathways of black powder and Mg/PTFE, which mainly include H 2 O, CO 2 , NO 2 for the black powder, and HF, H 2 O, CO 2 , CF 2 for Mg/PTFE. However, the condensed products of cellulose would interact with B/KNO 3 at a higher temperature, so that the heat release was largely increased by 339%. The cellulose has obviously impact on the energy release rate of Mg/PTFE in comparison to the other two composites. Moreover, the negative impact on ignition of Mg/PTFE composite is significant, when the content of cellulose reaches over 33.3%, resulting in difficult self-sustainable combustion at ambient pressure. The cellulose can largely reduce the maximum flame temperature of the black powder and Mg/PTFE, whereas it has little effect on B/KNO 3. The CCPs of the involved igniting pyrotechnics and their cellulose-based composites have different phases due to their strong thermal interactions with cellulose. [ABSTRACT FROM AUTHOR]

The surface functionalization of graphene oxide (GO) is always attractive in improving certain properties of the polymer. In this study, 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyl-trimethoxysilane (SPTES) have been used to make silane functionalized graphene oxides (SiGOs). The APTES-grafted GO (NH-SiGO), SPTES-grafted GO (SH-SiGO) and pure GO have been separately introduced into the nitrocellulose (NC) matrix. The morphology, thermal properties and energetic properties of the prepared nanocomposites (NH-SiGO and SH-SiGO) were investigated comprehensively. It is shown that the presence of GO and SiGOs have different influences on the thermal reactivity of NC with various contents, and NH-SiGO with 0.5 wt% content showed better catalytic performance on the thermal decomposition of NC than others and showed prominently higher efficiency in improving its heat of combustion. Adding 0.5 wt% of NH-SiGO to NC may decrease its decomposition temperature from 202.1 °C to 196.6 °C, and the residue was decreased from 10.61 wt% to 3.95 wt%, respectively. One isoconversional kinetic method was exploited to determine the kinetic parameters of NC and its nanocomposites. It was found that NH-SiGO had a strong catalytic action on the thermal decomposition of NC-based nanocomposites for which the activation energy and the pre-exponential factor were considerably lowered, while SH-SiGO exhibited an inverse effect. The heat of combustion from NC/GO/0.5, NC/NH-SiGO/0.5 and NC/SH-SiGO/0.5 were determined as 11 249.5, 11 675.1 and 11 491.5 J g−1, respectively, which are higher than that of the pure NC (10 908.4 J g−1). From the combustion process of NC/NH-SiGO/0.5, it was shown that the nanocomposite was combusted completely. [ABSTRACT FROM AUTHOR]

The zero-order reaction rates (specific rate constants) for isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) were measured by means of the Czech vacuum stability test, STABIL. The PBXs are based on 1,3,5-trinitro-1,3,5-triazinane (RDX), β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5- d] imidazole (BCHMX), and ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW, ε-CL-20) with 9 wt.% of the C4 type matrix, i.e., a matrix containing 25 wt.% of polyisobutylene, 59 wt.% of dioctyl sebacate and 16 wt.% of the oil HM46. Dependencies were found between the specific rate constants mentioned and the detonation velocities of the PBXs, and consequently between these constants and the impact of pure explosive fillers, i.e., RDX, β-HMX, ε-HNIW, RS-ε-HNIW, and BCHMX and, at the same time, the corresponding PBXs. The results obtained are compared with those from a recent analogous study of PBXs using an SBR (Formex P1) binder which could increase the PBXs' reactivity in comparison with C4 matrix. These results also help to dispel a widely held view about HNIW being a relatively sensitive explosive. [ABSTRACT FROM AUTHOR]

The zero-order reaction rates (specific rate constants) of isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) were measured by means of the Czech vacuum stability test, STABIL. The PBXs are based on 1,3,5-trinitro-1,3,5-triazinane (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5- d]imidazole (BCHMX), and ε 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW, ε-CL-20) with 13 wt% of the Formex P1 type matrix, i.e., a matrix of the explosive with pentaerythritol tetranitrate (PETN) bound by 13 wt% of a mixture of 25 wt% of styrene-butadiene rubber and 75 wt% of an oily material. Dependencies were found between the specific rate constants mentioned and the detonation velocities of PBXs, and consequently between these constants and the impact and electric spark sensitivities of pure explosive fillers, i.e., RDX, HMX, HNIW, BCHMX, and PETN. It is stated that the higher impact or electric spark sensitivity of their pure explosive fillers corresponds to the higher thermal reactivity of the given PBXs. [ABSTRACT FROM AUTHOR]

To demonstrate the discrepancies of the international standards on compatibility evaluation for energetic additives, a comparative study on compatibility of three typical graphene-based catalysts with common energetic ingredients has been done by using DSC and VST methods. Based on some unusual findings, further suggestions are proposed on improvement in the compatibility evaluation standard. The compatibility results from DSC and VST methods for HMX/GT-Ni, HMX/GC-Cu, AP/GC-Cu, AP/GT-Ni and RDX/GC-Cu systems are contradictory. The major discrepancies between DSC and VST results are caused by combination of contradictory nature of stabilization and catalytic effects of these additives on the corresponding energetic ingredients. It has been shown that the HMX/GC-Ni, HMX/GT-Ni, AP/GT-Ni, NC/GC-Ni, NC/GT-Ni, NC/GT-Cu and NC/GA-Cu mixtures have good compatibility, and the RDX/GC-Ni, AP/GC-Ni and NC/GC-Cu mixtures have moderate compatibility. In general, the copper-based additives even under the stabilization of graphene oxide are not so compatible with nitramine oxidizers and AP. These results indicate that each of the evaluation standards on compatibility has its own feature and limitation. The DSC standard is probably not suitable for the evaluation of the compatibility of GC-Ni, GC-Cu, GT-Ni, GT-Cu and GA-Cu with energetic ingredients. The compatibility assessment cannot simply rely on the available standards, and more comprehensive evaluation procedures need to be established according to the nature of the materials evaluated. [ABSTRACT FROM AUTHOR]

• Thermal reactivity of core–shell Al@AP and Al@AP/CuO composites were characterized. • The decomposition kinetics and gaseous products of composites were fully identified. • The Al@AP and Al@AP/CuO composites demonstrated better combustion performance. • Mutual interactions of Al@AP embedded with CuO under high temperature were clarified. Conventional solid propellants suffer from undesirable combustion performance due to the poor mass and heat transfer between metal fuels and oxidizers, as well as a lack of catalytic active sites between the catalyst and catalyzed objects. Embedding metal fuels and catalysts within the oxidizer has shown promise in improving the overall combustion performance of HTPB/AP/Al and HTPB/AP/RDX/Al composite solid propellants. However, the underlying mechanisms responsible for this enhancement remain to be further understood. In this study, we investigated the reactivities of core–shell Al@AP and Al@AP/CuO composites using thermal analysis and combustion diagnostic techniques. The results demonstrated that the decomposition of AP was promoted, as evidenced by a lower peak temperature (415.2–334.7 ℃), higher total heat release (116.4–720.8 J·g−1), a transition in the decomposition physical model from the random nucleation and 2D/3D growth of nuclei model to the auto-catalytic model, and increased generation of NO 2. Furthermore, the Al@AP/CuO propellant pellet exhibited a more stable flame without agglomeration, and the condensed combustion products (CCPs) contained a lower amount of unreacted Al compared to that of conventional mixtures. These findings highlighted the potential of core–shell Al@AP and Al@AP/CuO composites as replacements for discrete ingredients of solid propellants, thereby offering improved performance for next-generation propulsion systems. [ABSTRACT FROM AUTHOR]

Tailoring the combustion performance of propellant plays an important role in solid propellant design. Herein, we present that interfacial reaction (thermite reaction on Al surface) could be used for tuning the combustion performance of Al-based propellants. Two interfacial reactions included Al-based core-shell composites Al@PDA@CuO (Al@CuO) and Al@PDA@PVDF (Al@PVDF) were prepared and characterized. It is found that both Al@CuO and Al@PVDF have slightly decreased heat release and density, but significantly promote Al combustion, in comparison to the mechanically mixed ones without interfacial reaction. Experiments on ignition, combustion, agglomeration, and thermal property of those propellants containing core-shell Al-based composites have been carried out. The results show that both Al-CuO and Al-PVDF interfacial reactions could reduce the ignition delay time and improve the burn rate of propellant due to the low initial reaction temperature and generated high heat. In addition, it is also found that the interfacial reaction between Al and CuO could increase the size of condensed combustion products of the propellants due to the formation of AlCu 4. However, average condensed combustion product diameter of the propellant using Al@PVDF as the fuel is 0.47 µm, which is smaller than that of propellant using mechanically mixed Al/PVDF as the fuel (0.61 µm). This is a 23% decrease in agglomerate diameter compared with agglomerates formed from the propellant without interfacial reaction. These results reveal that different interfacial reaction may result in very different oxidation reaction mechanisms of Al that controls the combustion performances of the Al-based propellants. [ABSTRACT FROM AUTHOR]

Aluminum (Al) has been widely used in solid composite propellants (SCPs) to increase the specific impulse. However, Al always subjects to coalescence, sintering to large agglomerations during combustion of SCPs resulting in larger two-phase flow losses. Herein, core-shell μ-Al@M(IO 3) x composites have designed and synthesized as a replacement for micron-sized Al (μ-Al) in the Al/AP/RDX/HTPB propellant with tunable combustion behavior. The results show the thermal reactivity and heat releases of SCP are largely enhanced by using these novel metal-based composites. With the inclusion of μ-Al@EGCG@Fe(IO 3) 3 (EGCG: Epigallocatechin gallate), the major exothermic peak is reduced by 29.1 °C compared to the reference propellant with a heat release increase up to 5475 J g−1, exceeding that of the reference sample (86 J g−1 higher). The burn rates are increased with the inclusion of μ-Al@(MIO 3) x , while the pressure exponent is higher. The SCP-1 (0.3), SCP-2 (0.18) and SCP-4 (0.25) that have relatively low pressure exponent and high burn rates are good candidates for future applications. The major condensed combustion products (CCPs) of these SCPs are Al 2 O 3 , Al 2.81 O 3.56 N 0.44 , Al 4 C 3 , Al 2 OC, AlN and C 7 H 18 ClN. The agglomeration can be reduced with a minor inclusion of μ-Al@M(IO 3) x due to the enhanced interfacial reactions, and the average CCP sizes (0.5 μm for SCP-1 and SCP-4) are even smaller than that of initial μ-Al (1.2 μm). [ABSTRACT FROM AUTHOR]

Graphical abstract Core-shell n-Al@PDA@CuO MICs are constructed by the direction of polydopamine on the heterogeneous nucleation and growth of Cu(OH) 2 and CuO. Highlights • Core-shell structured MICs have been prepared and characterized. • The n-Al@PDA@CuO MIC shows an enhanced energy release. • Their formation and reaction mechanisms have been studied. • The improved combustion efficiency has been validated by the infrared thermographs. Abstract Over past few years, there has been increased interest in the development of metastable intermixed composites (MICs). As typical high energetic materials, MICs find important applications in aerospace and pyrotechnics. Newly developed methods based on the bioinspired surface modification enables advanced MICs with improved stability, higher energy content, and tunable performances. In this paper, the dopamine has been used to coat nano-sized Al (n-Al), forming a polydopamine (PDA) interfacial binding layer by in-situ polymerization. This interfacial binding layer makes it possible to prevent n-Al from further oxidation, and more importantly, functionalized n-Al with multiple chemical groups. Multiple oxidants could be synthesized on the coated n-Al surface under the direction of PDA on the heterogeneous nucleation and growth of crystals, affording exclusively the core-shell MICs. Typically, core-shell n-Al@PDA@CuO MICs have been fabricated. In comparison to the traditional n-Al/CuO MICs, the resulted n-Al@PDA@CuO showed an improved initial reaction temperature (528.4 °C), enhanced energy release (2934.8 J g−1) and lower combustion temperature (1606 °C). The infrared thermograph results also reveal that the n-Al@PDA@CuO has higher combustion efficiency since the n-Al core and CuO shell are better contacted at a nanoscale. [ABSTRACT FROM AUTHOR]

• Interfacial control Al@HMX composites with graphene-based carbohydrazide complexes as catalysts are prepared via spray-drying technique. • Enhanced heat release, reaction efficiency and ignition process between Al and HMX are realized. • A more complete oxidation reaction of Al by HMX is verified by reducing unreacted Al and increasing content of submicron-sized condensed products. • The synergy of interfacial control and GO-based catalysts on the decomposition mechanism of HMX is proposed and discussed. The incomplete combustion of aluminum in solid propellants leads to a low-level energy release. As a promising strategy, fuel/oxidizer interfacial control is proved to be effective for enhancing their reaction efficiency and less environmental dependence. In this paper, in order to investigate the effect of interfacial control on the reaction efficiency of Al and HMX, spherical Al@HMX composites with polydopamine as interfacial layer were prepared via spray-drying technique. The morphology, structure, heat of reaction, thermal stability, condensed/gaseous products, decomposition kinetics as well as the ignition performance of the composites under the catalytic effects of graphene-based carbohydrazide complexes (GO-CHZ-M, M = Co2+ or Ni2+) were comprehensively investigated. Results showed that the heat of reaction of Al@HMX increased by 220 J g−1 compared to corresponding physical mixture (5655 J g−1), which was further increased to 6210 J g−1 in presence of minor GO-CHZ-Co (1 wt%) as a catalyst. Moreover, the thermal decomposition temperature of HMX was slightly increased in Al@HMX composites. Under the synergy of interfacial control and GO-based catalysts, the enhanced reaction efficiency of Al with HMX was observed and verified by a shorter ignition delay time (reduced from 126 to 71 ms) and the condensed products analysis, with decreasing unreacted Al content and increasing content of submicron-sized particles. Gaseous products investigation illustrated that there were two main decomposition pathways for Al@HMX composites: the C N scission (dominant) and N N scission, where the latter could be enhanced by GO-CHZ-M catalysts. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical properties of a typical four-component composite solid propellants with various designed Al/oxidizer interfaces have been studied. The Al/oxidizer interfacial control is mainly realized by using the core-shell composites AP@Al and Al@RDX with different particle sizes, where Al powder was coated with a thin layer of polydopamine (PDA) as the binding sites, so that the oxidizers could crystalize on it during a rapid spray granulation process. The stress-strain curves of the above propellants at different temperatures and different tensile rates have been obtained. The dependence of the loss factor on temperature was studied by using a dynamic thermomechanical analysis (DMA). It has been shown that the fracture elongation of the interfacial modified propellants can reach 51.81% at room temperature, which is 127.3% higher than that of the blank formulation under the same formulation. Moreover, the temperature and strain rate sensitivity of interfacial controlled HTPB propellants is much less than that of traditional ones. The microstructure of these propellants at the crack sites was investigated by scanning electron microscopy (SEM) supported with micro-area in-situ tensile CT scanning technology, to clarify their damage and failure mechanisms. • Two types of core-shell Al-based composite fuels and corresponding solid propellants have been prepared. • The fracture elongation of the interfacial controlled solid propellants was improved significantly. • The temperature and strain rate sensitivity of these propellants are much less than those of traditional ones. • The fracture mode and damage evolution mechanisms of these propellants have been clarified. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Formulation of PVDF/CuO/Al is optimized on the basis of maximum heat of reaction. • Electrospinning is employed to fabricate high solid-loading MICs based on PVDF. • Electrospinning and doping of GO can improve the density, heat of reaction, etc. Abstract In this paper, the electrospinning technique has been employed to fabricate PVDF/CuO/Al nanocomposites, where the formulation was optimized on the basis of maximizing the reaction heat with increased efficiency. The graphene oxide (GO) has also been used as both lubricant and catalyst, which is well dispersed inside the PVDF matrix by the electrospinning process as well. It has been found that the smooth PVDF nano-fibers could be fabricated with GO content of 0.5 wt%, where the Al and CuO nanoparticles are also uniformly loaded. In comparison with the n-CuO/n-Al and PVDF/CuO/Al prepared by conventional mechanical mixing method, the GO-doped PVDF/CuO/Al nanocomposites via electrospinning improved heat of reaction, density as well as anti-oxidation capability. In addition, the electrospinning technique and doping of 0.5 wt% of GO can improve the reaction efficiency of PVDF/CuO/Al nanocomposites since they contribute to dispersion of components and homogeneous structure fabrication. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Various GO-doped complexes of triaminoguanidine have been prepared and evaluated. • The kinetics models governing the rate-limiting thermolysis reactions are obtained. • The significant stabilization effect of GO and corresponding mechanism are clarified. Abstract The graphene oxide (GO) was found to be able to stabilize organic molecules including energetic compounds. However, the inherent mechanisms of such stabilization effects are still not well-known. Herein, various transition metal complexes of triaminoguanidine nitrate (TAGN) using GO as a dopant have been prepared and evaluated. It has been shown that the presence of GO could great improve the thermal stability of the resulted TAG-based complexes. The physical models governing their thermolysis for their initial rate-limiting decomposition steps are obtained using the state-of-the-art evaluation methods. These physical models are further supported by analyses of the overall gaseous products. In addition, the reaction pathways are proposed to explain the stabilization mechanisms of GO. For instance, by interaction of GO, the release of N 2 from TAG-Ni was greatly postponed. There is a broad secondary peak at temperature of 378 °C due to decomposition of the nickel nitrides, as the primary thermolysis intermediates of TAG-Ni. The formation of cobalt nitrides plays a significant role on decomposition of TAG-Co and G-T-Co, which results in much less heat release and mass loss in comparison to TAG-Ni. [ABSTRACT FROM AUTHOR]

Development and molecular engineering of new highly-efficient energetic biocidal materials is a significant challenge and of a great importance. Until now this type of materials included mostly halogen-rich nano-thermites and iodine-rich organic materials. So far, no energetic coordination polymers were reported as precursors for combustion-generated biocidal agents. Here, we demonstrate for the first time the synthesis of uniquely-structured three-dimensional energetic coordination polymer ( ECP3 ) containing Zn metal centers and iodine- and nitrogen-rich bridging ligand ( 2 ). Upon its combustion, ECP3 is capable of generating gaseous reactive iodine species and elemental iodine-coated ZnO particles. ECP3 presents a novel approach for the design of efficient biocidal agents. [ABSTRACT FROM AUTHOR]