Probing on Mutual Interaction Mechanisms of the Ingredients of Al/CuO/PVDF Nanocomposites.

In this paper, several binary and ternary metastable intermixed nanocomposites Al/CuO, Al/PVDF, CuO/PVDF, and Al/CuO/PVDF have been prepared by simple mechanical mixing and ball milling followed by spray drying methods. In this way, the interfacial structure could be well tuned and compared in terms of reactivity. The nonisothermal DSC curves results showed that the exothermic reaction of Al/CuO/PVDF could be divided into three steps. In addition, it has been shown that for the same formulation, the reaction efficiency, pressurization capacity, and thermal reactivity are greatly dependent on the interfacial structure. As a typical example, composite Al@PVDF/CuO, where Al is fully covered with PVDF, exhibited a higher energy release of 10.7 kJ·cm-3 and pressurization rates of 22.79 MPa·s-1·g-1. The reaction between Al and PVDF has been facilitated in both extent of reaction and efficiency due to their intimate contact. Based on the thermal analysis, condensed combustion product analysis, and gaseous phase identification, the mutual reaction mechanisms of Al/CuO/PVDF have been proposed. The most likely reactions that occurred at each stage of the reaction are summarized, providing insight into the complicated underlying mechanisms. It shows that the regulation of energy release rates and improved efficiency could be easily realized by predesigned interfacial structures.

Thermal Reactivity of High-Density Hybrid Hexahydro-1,3,5-trinitro-1,3,5-triazine Crystals Prepared by a Microfluidic Crystallization Method.

In this paper, the two-dimensional (2D) high nitrogen triaminoguanidine-glyoxal polymer (TAGP) has been used to dope hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) crystals using a microfluidic crystallization method. A series of constraint TAGP-doped RDX crystals using a microfluidic mixer (so-called controlled qy-RDX) with higher bulk density and better thermal stability have been obtained as a result of the granulometric gradation. The crystal structure and thermal reactivity properties of qy-RDX are largely affected by the mixing speed of the solvent and antisolvent. In particular, the bulk density of qy-RDX could be slightly changed in the range from 1.78 to 1.85 g cm-3 as a result of varied mixing states. The obtained qy-RDX crystals have better thermal stability than pristine RDX, showing a higher exothermic peak temperature and an endothermic peak temperature with a higher heat release. Ea for thermal decomposition of controlled qy-RDX is 105.3 kJ mol-1, which is 20 kJ mol-1 lower than that of pure RDX. The controlled qy-RDX samples with lower Ea followed the random 2D nucleation and nucleus growth (A2) model, whereas controlled qy-RDX with higher Ea (122.8 and 122.7 kJ mol-1) following some complex model between A2 and the random chain scission (L2) model.

Precise Regulation of Combustion Characteristics of High-Energy Composite Propellants by Incorporation of CL-20 Crystals Intercalated with Energetic Burn Rate Modifiers.

In this study, a 2D structured triaminoguanidine-glyoxal polymer with a high nitrogen content has been coordinated with metal ions to produce energetic metal complexes (TAGP-Ms) employed as energetic burn rate inhibitors. The metal ions (Ba2+, K+, and Ca2+) are elaborately selected based on their ability of suppressing the burn rate of composite propellants. The CL-20 crystals were intercalated with prepared TAGP-Ms materials via a solvent-antisolvent method for realization of the precise control on burning behaviors of studied propellants. The influence of TAGP-Ms inhibitors on thermal decomposition and combustion characteristics of high-energy composite propellants was evaluated using thermal analysis and a combustion diagnostic method. Results of TGA/DSC-FTIR measurements suggest that the thermal decomposition of CL-20-containing composite propellants was found to be constrained by varied degrees as a result of TAGP-Ms additions, in which the TAGP-K displays a stronger effect on suppressing the thermal decomposition of CL-20 compared with that of other TAGP-Ms. The FTIR spectra indicate that the primary gaseous phase products are composed of N2O, H2O, and CO2 in CL-20 decomposition, as well as by HCl, H2O, NO2, and N2O in the decomposition of AP for all studied composite propellants. The combustion characterizations show that the TAGP-K-containing composite propellant exhibits a significantly reduced rate of heat release but is associated with a higher flame radiation intensity increased by 4.2% compared with that of the reference propellant, which clearly implies that the TAGP-K is capable of suppressing the energy release rate while ensuring the high energetic features of propellants to be well maintained. Moreover, the burn rate pressure exponents are considerably decreased by ∼10% for the TAGP-K-containing propellants in comparison with those of propellants with the typical formulation, which strongly suggests that TGAP-Ms are promising candidates for tuning the combustion behaviors of composite propellants by influencing the decomposition processes of CL-20 and AP collectively.

Hybrid RDX crystals assembled under constraint of 2D materials with largely reduced sensitivity and improved energy density.

In this paper, the widely used energetic material RDX had been modified with 2D high nitrogen polymer (TAGP). Various hybrid RDX crystals (qy-RDX) with higher detonation velocity and better thermostability had been obtained as a result of strong intermolecular interactions between TAGP and RDX molecules. The performance of the qy-RDX had been characterized to clarify the inherent mechanisms. It shows that the⊿Hf of qy-RDX could be largely changed in the range of 23.4 kJ kg-1 to 1343.6 kJ kg-1, whereas the density varies only from 1.81 g cm-3 to 1.86 g cm-3. The resulted detonation velocities are in the range of 8725.5 m·s-1 to 9251.8 m·s-1, depending on the content and state of the TAGP dopant. The sensitivity of the resulted qy-RDX is much better than pristine RDX due to improved crystal quality as well as higher concentration of hydrogen bonds. The impact energy is improved from 8.5 J (RDX) to 22 J (qy-RDX-1), whereas the friction sensitivity improves form 130 N to over 360 N for the same case. The Ea for thermal decomposition of qy-RDX-1has reduced from 147.8 kJ mol-1 (RDX) to (124.5 kJ mol-1), since TAGP dopant could be considered as active catalytic sites after melting of RDX.