Abstract:The dynamic compressive and reactive properties of two kinds of PTFE/Al reactive materials were studied by the split Hopkinson pressure bars (SHPB). The effects of Al content on yield stress, fragmented and reactive properties of PTFE/Al reactive materials were analyzed. Results show that PTFE/Al is sensitive to the strain rate. In the strain rate range of 1000-8000 s^-1, the yield stress of PA265 is 32-44 MPa and the yield stress of PA35 is 40-55 MPa; the yield stress increases with Al content; the fragmented stress is 143-153 MPa in the strain rate range of 3100-5800 s^-1 for the PTFE/Al reactive materials; the critical reactive stresses of PA265 and PA35 are 157 MPa and 163 MPa; partial reaction phenomena appear frequently due to lacking of enough oxidant polytetrafluorethylene (PTFE), if Al content is higher than 35%.

Abstract:PTFE/Al (polytetrafluoroethylene/aluminum) reactive multilayer films with different thickness and alternating deposition were prepared by a radio frequency magnetron sputtering method using Al as combustible and PTFE as oxidant. The influence rules of sputtering power on the film surface morphology was investigated by atomic force microscope (AFM) and X-ray diffraction (XRD).The appropriate preparation technology of the films was obtained. The mechanical property of PTFE/Al reactive multilayer films was measured by a nano-indentation apparatus. Results show that when the radio frequency sputtering power is 50 W and 150 W, the mean roughness and RMS roughness of PTFE film and Al film obtained are low. When the total thickness of PTFE/Al reactive multilayer films is about 300 nm, in comparison with pure PTFE film and Al film, PTFE/Al reactive multilayer films have higher hardness and elastic modulus: 5.8 GPa and 120.0 GPa, respectively.

Abstract:To improve the impact reaction damage effectiveness of Al/PTFE/W fluoropolymer-matrix reactive materials (RMs), quasi-static compression experiments of Al/PTFE/W RMs were carried out. The effects of W content(0%, 30%, 65%), Al particle size(13, 45, 75 μm) and PTFE particle size (25, 160 μm) on the quasi-static mechanical properties of the RMs were analyzed. The impact energy release test of the RMs was performed by quasi-sealed reaction vessel, the impact reaction pressure and duration of energy release of the RMs in the range of 750-1200 m·s^-1 were measured. The influence of Al particle size and PTFE particle size on the impact reaction energy release characteristics was analyzed. Results show that when the contents of W are 0%, 30% and 65%, the failure strength of the RMs is 55.6, 64.8 and 22.8 MPa respectively, and the change in W content has little effect on the yield strength. When the size of Al particles decreases from 75 μm to 13 μm, the failure strength of the RMs increases from 64.7 MPa to 83.1 MPa, the range increases by 28.4%. Increasing the particle size of the PTFE matrix material can also effectively improve the failure strength of the reactive material. The initial reaction pressure threshold and the duration of energy release of the RMs are affected by the particle size and quasi-static compressive mechanical properties of the materials.

Abstract:The Al-Ni-Ti-Zr non-equilibrium alloy powder was prepared by mechanical alloying method. The Al-Ni-Ti-Zr non-equilibrium alloy powder/polytetrafluoroethylene(PTFE) reactive materials were prepared via mixing/pressing using Al-based non-equilibrium alloy powders and PTFE micro powders. The phase composition and morphology characteristics of the powders during ball milling were characterized by X ray diffraction(XRD) and scanning electron microscopy(SEM). The phase structure of the milled alloy powders was analyzed by high resolution transmission electron microscopy(HRTEM) and selected area electron diffraction(SAED). The thermal behaviors of non-equilibrium Al/PTFE reactive materials were examined by differential scanning calorimetry(DSC). The results show that the Al-based non-equilibrium alloy powders can be prepared by mechanical alloying method. There is a nano scale micro-crystalline island area dispersed in amorphous phase matrix. The peak temperature and exothermic peak area of non-equilibrium Al/PTFE reactive materials at a heating rate of 10 K·min^-1 in air are 495 ℃ and 1775 J·g^-1, respectively. Under the continuous heating condition, the exothermic reaction of the non-equilibrium Al/PTFE reactive materials has the typical kinetic characteristics, and the activation energy E_c of the reaction is calculated as 309.1 kJ·mol^-1 by Kissinger method.

Abstract:To study the mechanical properties and reaction characteristics of aluminum/titanium hydride/polytetrafluoroethylene (Al/TiH₂/PTFE) reaction materials, four kinds of specimens with different content of TiH₂(0%, 5%, 10%, 20%) were prepared by cold isostatic pressing and vacuum sintering process.At the same time, TiH₂/PTFE specimens without active Al particles were also prepared as the control group, then all the specimens were subjected to quasi-static compression experiments. The stress-strain curves and the reaction rate data of the specimens with different TiH₂ content were obtained, and the reaction phenomena of the specimens were recorded.Moreover, the phase analyses of reaction residues were performed by XRD and the reaction mechanism of the materials was discussed.Results show that the content of TiH₂ has a significant effect on the material properties and the reaction rate.When the content of TiH₂ is 5%, the reaction rate is 90% and the material strength reaches the maximum value of 108 MPa, which is 15.1% higher than that of Al/PTFE type material.When the content of TiH₂ and Al is the same, the reinforcing effect of TiH₂ particles on PTFE matrix is greater than that of Al particles.Compared with Al/PTFE material, a special combustion flaming phenomenon appears in the reaction of TiH₂-containing samples, and the phenomenon gradually is obvious with the increasing of TiH₂ content.The high temperature of the crack tip of materials causes the reaction between Al and PTFE, which makes TiH₂ activate, hydrogen release and TiC generate, the energy of TiH₂ fully release and the purpose of using as a high-energy additive reach.

Abstract:To study the combustion and energy release characteristics of Zr-based amorphous alloys, the combustion heat of Zr_68.5-xAl_7.5+x(Cu+Ni)₂₄(x=0,2.5,5,7.5) under different oxygen pressures were tested by oxygen bomb calorimetry. The phase composition of combustion products were determined by X-ray diffractometer, and comparative analysis of various energetic materials was conducted. The results show that the combustion heat of Zr-based amorphous alloy is negatively correlated with the Zr∶Al atom ratio. The energy released mainly comes from the oxidation reaction of metal elements, and a very small amount of energy comes from the chemical reaction between metal elements. The combustion heat and reaction efficiency increase with the increase of oxygen pressure, according with the first-order decay index function. Zr-based amorphous alloy has higher chemical potentiality, compared with PTFE/Al and TNT, Its specific energy per unit mass is 10.981 kJ·g^-1，and the specific energy per unit volume is 72.035 kJ·cm^-3.

Abstract:To explore the effect of polytetrafluoroethylene（PTFE） content and sintering temperature on the morphology and combustion performances of aluminum powder （Al）/PTFE composites， the ball mill-sintering process was used to prepare Al/PTFE samples. These samples have been characterized by scanning electron microscopy（SEM） and X-ray diffractometer （XRD）， and the effect of PTFE content and sintering temperature on the microscopic morphology of the composites has been studied. The combustion processes have been analyzed using a confined combustion chamber， coupled with a high-speed camera and infrared thermal imager. The effects of PTFE content and sintering temperature on the combustion performances of the composites have been explored. The results show that sintering at 340 ℃ can make the composites form a regular core-shell structure. When the PTFE content is less than 35%， the integrity of the particle coating optimizes with the increasing of the PTFE content. However， when the PTFE content continues to increase， the shape of the composite particles becomes irregular， and the condensed products begin to agglomerate. With the increase of PTFE content and sintering temperature， the burning rate， radiation intensity， and the flame temperature of the samples all show a trend of first increase and then decrease. Compare the samples prepared under the optimal conditions （35% PTFE content， sintering temperature 340 ℃） with the ones prepared under other conditions， the combustion pressure can be increased by 16%， whereas the combustion time is shortened by up to 37%， so that the central flame temperature increases by 317.1 ℃. This indicates that the appropriate amount （35% optimal） of PTFE content and proper sintering temperature （340 ℃ optimal） will significantly improve the combustion performances of the composite particles.

Abstract:In order to investigate the dynamic behavior and ignition mechanism of Al/polytetrafluoroethylene（PTFE） reactive material under dynamic loading, a Split Hopkinson Pressure Bar (SHPB) was used to conduct the dynamic compression experiment on reactive materials with different molding pressure. Experimental results show that the Al/PTFE reactive material exhibits typical elastic-plastic mechanical behavior under dynamic loading at strain rate ranging from 2960 s^-1 to 5150 s^-1. The yield strength and hardening modulus of Al/PTFE reactive materials do not show strain rate effect when the molding pressure is 50-150 MPa. The velocity ignition threshold increases slowly from 28.77 m·s^-1 to 29.22 m·s^-1 with the molding pressure. When the molding pressure increases to 100 MPa, the velocity ignition threshold drops significantly to 26.60 m·s^-1. With the increase of the impact velocity, the ignition delay time for reactive materials with the molding pressure of 100-150 MPa decreases from 1000-1100 μs to 600-700 μs, while that of reactive materials with the molding pressure of 30-80 MPa maintains at 600-700 μs. Combining with results of Scanning Electron Microscopy, it is found that the local larger pores inside the reactive materials with higher molding pressure is the main factor for the sudden drop of the velocity ignition threshold. Therefore, the impact ignition characteristics of Al/PTFE reactive materials are mainly related to the external loading form and the internal micro-morphology.