| Metal Al has the characteristics of high energy density,high calorific value of combustion,non-toxic combustion products and abundant raw materials.Adding aluminum to solid propellant can improve the energy density of the propellant and reduce the combustion instability of the propulsion system.Aluminum also plays an important role in fields such as explosives and welding.However,metal aluminum is easily oxidized under environmental conditions to form aluminum oxide that covers the surface of aluminum particles,hindering the oxidation process of aluminum.Through experimental research and theoretical analysis,this paper studies the slow oxidation and combustion processes of nano-aluminum(nAl)and its blends with different additives(oxides:CuO,MgO,Fe2O3,and SiO2;metals:Cu,Mg,Ni,and Mo)under different operating conditions.The effects of different gas atmospheres,heating rates,and additives on the slow oxidation process of nAl were studied through thermogravimetric experiments.In a vertical heating furnace,the effects of different gas atmospheres,ambient temperatures,and additive types on the combustion process of nAl were studied.Using digital image processing technology,the changes of luminous parameters in the combustion process of nAl under different conditions were analyzed.The main work is as follows:(1)The thermal weight gain process of nAl under different heating rates and gas atmospheres was studied using a thermal analyzer.Add different additives to nAl and analyze the changes in its thermal weight gain process in air atmosphere.The products from the oxidation process of nAl were detected by X-ray diffraction(XRD).The Kissinger Akahira Sunose(KAS)and Flynn Wall Ozawa(FWO)methods were used to calculate the kinetic and thermodynamic parameters of the thermal weight gain process of nAl.The results show that the slow oxidation process of nAl can be divided into three stages:the first stage is the initial oxidation stage(30℃～530℃),which mainly involves the volatilization of trace water in nAl and the production of a small amount of amorphous alumina;The second stage is a stage of intense combustion,with the second stage occurring at 530℃-705℃ and 530℃-758℃ in air and CO2 atmospheres,respectively.When the temperature is higher than 530℃,the aluminum oxide film gradually ruptures,leading to direct Al leakage in the oxidation atmosphere,and the sample quality rapidly increases;The third stage is the burnout stage until the end of the heating process.Compared to adding different oxides,the addition of different metals is more significant in enhancing the reaction activity of nAl,where Cu and Mo can effectively reduce the initial oxidation temperature.(2)A combustion experimental platform was established to carry out experimental research on the ignition and combustion processes of nAl under different operating conditions.The experimental results show that the combustion process of nAl exhibits a pattern of ignition at a certain point on the surface,followed by rapid flame spread around until the entire surface is ignited.During the combustion process,there is no obvious flame,but a bright white light is emitted.When the ambient gas is O2/N2,the ignition delay time becomes shorter and shorter as the oxygen concentration increases.When the ambient gas is CO2,the ignition delay time and oxygen concentration are 10 wt.%～20wt.%close.When the ambient temperature rises to 1000℃,the ignition delay time decreases rapidly.The combustion duration is influenced by ambient temperature and oxygen concentration,and its variation law is much more complex.At 1000℃,the average and peak values of the luminous intensity(Lf)of nAl combustion process gradually increase with the increase of oxygen concentration.(3)The effects of different additives on the ignition and combustion processes of nAl were studied on a combustion experimental platform in an air atmosphere and ambient temperature of 900℃.The study found that the addition of Cu,Fe2O3,and CuO can significantly shorten the combustion duration of nAl,and the light generated during the combustion process is very bright.As the content of Cu,Ni,and Mo in the mixed sample increases,the ignition delay time and combustion duration of nAl decrease,while the addition of Mg decreases.(4)Combining in situ resource utilization technology,the changes in ignition and combustion processes of different proportions of nAl/Mg mixed samples in a CO2 atmosphere and ambient temperature of 900℃ were studied on a combustion experimental platform.The results show that when the content of Mg in the mixed sample is 10wt.%～40wt.%During the combustion process,the combustion intensity decreases first and then increases during the middle period,indicating that the combustion of Mg and nAl is not completely synchronized.The ignition delay time first decreases and then increases with the increase of Mg content.Adding an appropriate amount of Mg powder to nAl can prolong its combustion duration and promote the combustion process.This promotion is achieved when the content of Mg is 30wt.%To achieve the best.(5)XRD,scanning electron microscopy and energy dispersive X-ray spectroscopy(SEM-EDS)were used to detect and analyze the micro morphology,element distribution on the micro surface,and crystal structure of the combustion products.The results show that when the ambient temperature rises from 800℃ to 1000℃,the content of a-Al2O3 is increasing.The combustion products of nAl、nAl+20wt.%MgO、nAl+20wt.%SiO2 are loosely distributed,while the particle size of combustion products of nAl+20wt.%CuO and nAl+20wt.%Fe2O3 is relatively large.Cu is oxidized to cuprous oxide,copper aluminide,and copper aluminate.After adding Ni to the mixed sample,Ni and NiO peaks can be observed in the product.When the additive is Mo,it reacts with oxygen and aluminum in the air to form aluminum molybdate.The MgO produced after combustion of Mg powder is less prone to agglomeration.The addition of different additives did not significantly improve the agglomeration phenomenon in the combustion process of nAl. |
PDF Full Text Request