Research On The Preparation And Properties Of Micro-nano Metal Oxides And Thermites And Their Applications In Composite Propellants

Micro/nano metal oxide and nano thermites possess good catalytic performance.Especially nanometer thermite,as a new type of high energy density material,has many potential performance advantages,such as anaerobic combustion,high heat release,the fast combustion wave propagation speed,etc.In recent years,researchers both in and abroad compete to apply the micro/nano metal oxide and nano thermite in the field of energetic materials.They control the particle size,morphology,dispersion degree,etc.,in order to obtain the catalytic materials with good performance.This work analyzes and investigates the interaction between the micro/nano metal oxide(nano thermite)and the nitrocellulose(NC,the main component of energetic materials),based on the preparation and properties characterization of micro/nano metal oxide and nano thermite.Also the influences of the micro/nano metal oxide and nano thermite on the combustion properties of the AP/HTPB(ammoniumperchlorate/hydroxyl-terminatedpolybutadiene)composite propellant are investigated in detail.The main research contents are as follows:(1)16 kinds of micro/nano metal oxides with different types,shapes and sizes were synthesized by the hydrothermal method,glycine-nitrate method,sol-gel method,including granular Fe2O3,olive Fe2O3,polyhedral Fe2O3,tubular Fe2O3,spindle Fe2O3,rod-like Fe2O3,small granular Fe2O3,CuO bulks,flower-like CuO,CuO microspheres,flaky CuO,bamboo leaf-like CuO,"shrimp head"-like CuO,ship type CuO,granular Cr2O3 and tubular MnO2.Their phase composition,shapes and particle size were characterized by scanning electron microscopy(SEM),energy spectrum analyzer(EDS),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM),X-ray powder diffraction(XRD)and Fourier transform infrared spectroscopy(FTIR).(2)Thermite Al/Fe2O3,Al/CuO,Al/Cr2O3 and Al/MnO2 were prepared using the ultrasonic dispersion method.By studying the structure and composition of various thermites,it can be found that Al nanoparticles adhered to metal oxide particles or embedded in metal oxide microstructure.Meantime,there was agglomerative phenomenon accompanying with them.(3)The thermal behaviors of micro/nano metal oxides-based NC composites and nano thermites-based NC composites were studied under a non-isothermal condition by the differential scanning calorimetry(DSC)method.The kinetic parameters,apparent activation energy(E)and the pre-exponential(A)in the exothermic processes of composite materials were carried out by combining the Kissinger equation,Ozawa equation,the differential equation and the integral equation.The thermal decomposition mechanism functions were obtained,and the self-accelerating decomposition temperature(Te0),thermal ignition temperature(Tbe0),critical temperatures of thermal explosion(Tb),entropy of activation(?S?),enthalpy of activation(?H?),Gibbs free energy of activation(?G?)and rate constant(k)of the exothermic decomposition reaction were obtained.It was found that both of the micro/nano metal oxides and nano thermites can decrease the thermal stability of the NC,and accelerate its decomposition.(4)TG-IR analysis indicated that Fe2O3 nanoparticles and Al/Fe2O3 play a crucial role in promoting the O-NO2 bond cleavage and secondary autocatalytic reactions in condensed phase,suggesting that introducing micro/nano metal oxides and nano thermites may be a promising way to accelerate the thermal decomposition of NC.(5)DSC method was employed to evaluate the compatibility of the micro/nano metal oxides(or nano thermites)with NC,which provided the feasible theoretical and experimental basis for the micro/nano metal oxides and nano thermites in application of solid propellants.(6)SDT Q600 synchronous thermal analyzer was used to characterize the thermal behaviors of the thermites Al/Fe2O3,Al/CuO,Al/Cr2O3,and Al/MnO2 by measuring the DSC curves at the heating rate of 10?-min-1.It can be found that the exothermic reaction of thermites happened before Al powder melted at 657?,then the molten Al powders continued to participate in the reaction.Among them,the bamboo leaf-like CuO(b)reacted with Al powders with the peak temperature of 561.02?,which is the lowest in 7 kinds of thermites under test,suggesting that the Al/CuO(b)possesses a higher reactivity.Thermite reaction between Cr2O3 nanoparticles and Al powders needed high reaction temperature,but released low quantity of heat,indicating that Al/Cr2O3 has the worst performance among the 7 kinds of tested thermites.Both of Al/Fe2O3 and Al/MnO2 possess lower exothermic temperatures and higher heat release,which can be used as combustion catalyst in application of propellant.(7)The effects of nanometer metal oxides(granular Fe2O3,olive Fe2O3,polyhedral Fe2O3,CuO bulks,granular Cr2O3 and tubular MnO2)and nano thermites on the combustion performance of AP-HTPB composite propellants.The results show that the burning rates and catalytic efficiencies of the formulations containing metal oxides and thermites are higher than that of the basic formulation,except the olive Fe2O3,Cr2O3 nanoparticles and the corresponding Al/Cr2O3.And all the formulations containing thermites possess the faster burning rates and higher catalytic efficiencies than the formulations containing the corresponding metal oxides.Thermites could enhance the combustion performance of propellants owing to the Al powders and the high heat release in short time of thermite reaction.The burning rate pressure exponents of composite propellants can be reduced by the combustion catalyst.Particle sizes of nanometer metal oxide are the important factors influencing the composite propellant combustion performance.The Fe2O3 nanoparticles prepared by the glycine-nitrate method possess small particle size and high specific surface area.And then the Fe2O3 combined with Al nanoparticles to produce Al/Fe2O3(G)thermite by ultrasonic mixing,which is the best combustion catalyst among all the above-mentioned metal oxides and thermites.