Positive effects of PVP in MIC:Preparation and characterization of Al-Core heterojunction fibers

The core-shell metastable intermolecular composites(MIC)have attracted much attention in the past few years due to their unique properties.Here,the preparation of Al-Core heterojunction fibers using PVP as a template is proposed.The nano-Al was directly added to the precursor solution of cupric acetate monohydrate(CAM)/Polyvinylpyrrolidone(PVP),and the initial Al@CAM/PVP fibers were obtained via electrospinning.The core-shell MIC fibers are then obtained by calcining the initial fibers.The morphology,structure,and composition of Al-core MIC fibers were characterized,that the energetic fibers calcined at 300℃,350℃,and 400℃have a core-shell structure with shell compositions CuxO and PVP,CuxO and Cu O,respectively.The energy release characteristics of Al-core MIC were investigated,and preliminary ignition tests were performed using an ignition temperature measuring instrument and a pulsed laser.The energetic fibers calcined at 300℃exhibited unique properties.The decomposition of PVP in the shell layer promoted exotherm,and a low-temperature exothermic peak was shown at 372-458℃.Lower ignition temperatures and higher flame heights were observed in the combustion tests than calcination at 350℃and 400℃.An unexpected result was that PVP can play a positive role in Al/CuO nanothermites.Simultaneously,this preparation method provided an idea for the integrated preparation of core-shell Al-Core MIC fibers and tuning the properties of MIC.

Formation of explosively formed penetrator with fins and its flight characteristics

The ultimate goal of weapon system employing an explosively formed penetrator(EFP) is to defeat a target at the longest standoff.In order to do this,an EFP must be aerodynamically stable so as to strike the target at a small angle of obliquity,and the decay velocity per meter of EFP must be smaller at extended standoff.As the angle of attack increases,the penetration ability of EFP greatly reduces.The fins improve the EFP aeroballistic characteristics and decrease the flight drag of EFP as well.EFP with fins formed by three-point initiation is presented.The formation of EFP with fins is studied by LS-DYNA,and the aeroballistics is studied through experiment.The experimental results show that the decay velocity per meter of EFP with fins is much smaller than that of normal EFP.and the attitude angle steadily decreases.

Improving the energy release characteristics of PTFE/Al by doping magnesium hydride

Magnesium hydride(MgH2)was doped into PTFE/Al to improve the energy release characteristics of the material system and strive for better application in military engineering.Five types of PTFE/Al/MgH2 reactive materials with different MgH2 content were prepared by molding sintering method.The dynamic mechanical properties of the materials were studied by performing split-Hopkinson pressure bar(SHPB)tests and scanning electron microscope characterizations.The thermal behavior,reaction energy,reaction process and reaction mechanism were systematically investigated by conducting thermogravimetry-differential scanning calorimetry tests,oxygen bomb calorimeter measurements,Xray diffraction and SHPB tests.The results show that MgH2 particles less than 10%content contribute to heightening the dynamic mechanical properties of PTFE/Al system.The product Mg generated by decomposition of MgH2 can not only react with gas phase C2F4þbut also undergo a Grignard-type reaction with condensed PTFE.The reaction energy and ignition threshold of PTFE/Al/MgH2 reactive materials enhance monotonously as MgH2 content rose.With the increase of MgH2 content from 0%to 20%,the reaction time is prolonged as well as the reaction intensity is enhanced dramatically arising from the massive water vapour produced by the reaction between O2 and H2.The gaseous products generated can form a high pressure shortly after the reaction,which helps to elevate the damage effect of the PTFE/Al system.

The effect of al particle size on thermal decomposition,mechanical strength and sensitivity of Al/ZrH_(2)/PTFE composite

To study the thermal decomposition of Al/Zr H_(2)/PTFE with different Al particle size as well as mechanical strength and impact sensitivity under medium and low strain rates,molding-vacuum sintering was adopted to prepare four groups of power materials and cylindrical specimens with different Al particle size.The active decomposition temperature of Zr H_(2) was obtained by TG-DSC,and the quasi-static mechanics/reaction characteristics as well as the impact sensitivity of the specimen were studied respectively by quasi-static compression and drop-hammer test.The results show that the yield strength of the material decreased with the increase of the Al particle size,while the compressive strength,failure strain and toughness increased first and then decreased,which reached the maximum values of 116.61 MPa,191%,and 119.9 MJ/m respectively when the Al particle size is 12-14 mm because of particle size grading.The specimens with the highest strength and toughness formed circumferential open cracks and reacted partly when pressed.Those with developmental cracks formed inside did not react.It is considered that fracture of specimens first triggered initial reaction between Al and PTFE to release an amount of heat.Then ZrH_(2) was activated and decomposed,and participated in subsequent reaction to generate Zr C.The impact sensitivity of the specimens decreased with the increase of Al particle size.