RESUMEN

The combustion agglomeration of nano-aluminum (nAl) powder leads to incomplete combustion, which seriously hinders its application as metal fuel. In this work, nAl@AlF3 composites were produced by coating nAl with AlF3via a facile chemical deposition method. TEM and SEM analyses indicated that the AlF3 layer was evenly coated on the surface of nAl with a thickness of 4.6-9.1 nm, thereby varying the quantity of AlF3 applied. Experimental results from combustion indicated that the prepared nAl@AlF3 composites exhibit superior combustion efficiency, a higher combustion rate, and reduced combustion agglomeration as compared to raw nAl. Contrary to the widely accepted explanation that volatilization of AlF3 hinders Al combustion agglomeration, we proved that the gas-solid reaction between nAl and AlF3 plays an important role in inhibiting the sintering of nAl particles produced. The gaseous intermediate (i.e., AlOF and HF) released from the hydrolysis of AlF3 could reduce the diffusion barrier of Al2O3 to facilitate the reaction of Al core, which enhances the combustion reaction kinetics. More importantly, these gaseous products actively participate in the reaction cycle to continuously exert their catalytic effects.

RESUMEN

Ammonium perchlorate (AP) has been widely used as an oxidizer in propellants and military mixed explosives in recent years. However, its high characteristic signal, environmental pollution, and poor detonation performance have prompted the industry to seek alternatives to AP. Ammonium nitrate (AN) is a suitable substitute due to its low characteristic signal, lack of pollution, and excellent detonation performance. However, its room-temperature phase transition and hygroscopicity affect its practical use. In this work, we prepared mixed crystal coprecipitation (MCC) materials of AN and potassium perchlorate (KP) using the evaporative solvent method. The characterization of AN/KP MCCs was carried out by combining TG-DSC, XRD, FT-IR, and SEM analysis, revealing that the formation of MCCs by AN and KP is due to ion exchange between the two components. AN/KP MCCs not only solve the problem of room-temperature phase transition in AN but also reduce its hygroscopicity. Furthermore, AN/KP MCCs have mechanical sensitivity, explosive performance, and specific impulse similar to pure AN, but compared to AN, AN/KP MCCs have higher density, effective oxygen content, and thermal stability. Compared with existing oxidizers AN, AP, and KP, AN/KP MCCs with high density, low sensitivity, high oxygen content, and high safety have obvious advantages and have good prospects in the application of oxidizers in solid propellants and military mixed explosives.

RESUMEN

To examine the interactions between two binder systems-hydroxyl-terminated polybutadiene (HTPB) and hydroxyl-terminated block copolyether prepolymer (HTPE)-as well as between these binders and ammonium perchlorate (AP) at various temperatures for their susceptibility to varying degrees of thermal damage treatment, the thermal characteristics and combustion interactions of the HTPB and HTPE binder systems, HTPB/AP and HTPE/AP mixtures, and HTPB/AP/Al and HTPE/AP/Al propellants were studied. The results showed that the first and second weight loss decomposition peak temperatures of the HTPB binder were, respectively, 85.34 and 55.74 °C higher than the HTPE binder. The HTPE binder decomposed more easily than the HTPB binder. The microstructure showed that the HTPB binder became brittle and cracked when heated, while the HTPE binder liquefied when heated. The combustion characteristic index, S, and the difference between calculated and experimental mass damage, ΔW, indicated that the components interacted. The original S index of the HTPB/AP mixture was 3.34 × 10-8; S first decreased and then increased to 4.24 × 10-8 with the sampling temperature. Its combustion was initially mild, then intensified. The original S index of the HTPE/AP mixture was 3.78 × 10-8; S increased and then decreased to 2.78 × 10-8 with the increasing sampling temperature. Its combustion was initially rapid, then slowed. Under high-temperature conditions, the HTPB/AP/Al propellants combusted more intensely than the HTPE/AP/Al propellants, and its components interacted more strongly. A heated HTPE/AP mixture acted as a barrier, reducing the responsiveness of solid propellants.

RESUMEN

To study the thermal decomposition behavior of 4,4'-azobis(1,2,4-triazole) (ATRZ), the non-isothermal thermal decomposition kinetics of ATRZ were studied using the thermogravimetric-differential scanning calorimetry (TG-DSC) method. The TG-DSC of ATRZ was analyzed at heating rates of 5, 10, 15, and 20 K·min-1 in an argon atmosphere. The thermal decomposition kinetic parameters at peak temperature (Tp), such as apparent activation energy (Ea) and pre-exponential factor (lgA) of ATRZ, were calculated using the Kissinger, Ozawa, and Satava-Sestak methods. Ea and lgA calculated using the Kissinger, Ozawa, and Satava-Sestak methods are very close, at 780.2 kJ·mol-1/70.5 s-1, 751.1 kJ·mol-1/71.8 s-1, and 762.1 kJ·mol-1/71.8 s-1, respectively. Using a combination of three methods, the reaction mechanism function g(α) of ATRZ was obtained. The results show that the decomposition temperature of ATRZ is about 310 °C, and the decomposition is rapidly exothermic. The pyrolysis path of ATRZ was investigated through a pyrolysis-gas chromatography mass spectrometry (PY-GC/MS) experiment. ATRZ has three different decomposition paths and finally generates N2, HC-N-CH, N≡C-N, and HC=N-C≡N. The laser ignition combustion duration of ATRZ was 0.5033 s and the peak temperature was 1913 °C. The laser ignition combustion duration of ATRZ+CL-20 was 1.0277 s and the peak temperature was 2105 °C. The rapid energy release rate of ATRZ promotes the combustion energy release of CL-20.

Asunto(s)

Nitrógeno , Pirólisis , Argón , Cinética , Termogravimetría , Triazoles

RESUMEN

To deepen the oxidation depth and promote the exothermic reaction of aluminum nanoparticles (Al NPs), this work constructed perfluoropolyether-functionalized Al NPs by using a facile fabrication method. It was determined that perfluoropolyether (PFPE) was uniformly distributed on the surface of the Al NPs with no obvious agglomeration by micro-structure analysis. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), microcomputer automatic calorimeter (MAC), and combustion and ignition experiments were performed for varying percentages of PFPE blended with Al NPs to examine the reaction kinetics and combustion performance. It was revealed that the oxidation mechanism of PFPE-functionalized Al NPs at a slow heating rate was regulated by the reaction interface Fuel-Oxidizer ratio. Due to the enlarged Fuel-Oxidizer contact surface area, fluorine atoms could adequately decompose the inert alumina shell surrounding the Al NPs, optimizing the combustion process of Al NPs. The analytical X-ray diffraction (XRD) pattern results confirmed the existence of aluminum trifluoride in combustion products, providing insights into the oxidation mechanism of Al NPs. The obtained results indicated that PFPE participated in the oxidation of Al NPs and improved the overall reactivity of Al NPs.

RESUMEN

Determination of macroscale detonation parameters of energetic materials (EMs) in a safe and rapid way is highly desirable. However, traditional experimental methods suffer from tedious operation, safety hazards and high cost. Herein, we present a micro-scale approach for high-precision diagnosis of explosion parameters based on radiation spectra and dynamic analysis during the interaction between laser and EMs. The intrinsic natures of micro-explosion dynamics covering nanosecond to millisecond and chemical reactions in laser-induced plasma are revealed, which reveal a tight correlation between micro-detonation and macroscopic detonation based on laser-induced plasma spectra and dynamics combined with statistic ways. As hundreds to thousands of laser pulses ablate on seven typical tetrazole-based high-nitrogen compounds and ten single-compound explosives, macroscale detonation performance can be well estimated with a high-speed and high-accuracy way. Thereby, the detonation pressure and enthalpies of formation can be quantitatively determined by the laser ablation processes for the first time to our knowledge. These results enable us to diagnose the performance of EMs in macroscale domain from microscale domain with small-dose, low-cost and multiple parameters.

RESUMEN

In order to improve the thermal decomposition performances of ammonium perchlorate (AP), the laminated AP composite was prepared by ice-template induced self-assembly method. In this study, Iron-Konjac glucomannan (Fe3+-KGM) hydrosol rich in AP was selected as the freezing precursor. Through directional freezing of precursor and recrystallization of AP molecules, the laminated AP composite was obtained. The results showed that the thickness of the lamellar composite structure is about 10 to 30 µm, and the recrystallized AP particles are uniformly dispersed in the gel system. The oxygen bomb test results show that the micro-/nano-layered structure can significantly improve the sample's combustion heat value. Thermal analyses indicated that with the increasing Fe3+ content, the peak exothermic temperature of lamellar AP composite at different heating rates both showed a decreasing trend. With 10 wt% Fe(NO3)3·9H2O added, the decomposition peak temperature decreased from 433.0 to 336.2 °C at a heating rate of 5 °C/min, and the apparent activation energy (Ea) decreased dramatically from 334.1 kJ/mol to 255.4 kJ/mol. A possible catalytic thermal decomposition mechanism of lamellar AP composite catalyzed by Fe3+ was proposed. This work is beneficial to the structural design of other energetic materials.