Study On The Ignition And Combustion Performance Of Boron By Surface Functionalizing

Boron(B)has wide application in propellants,explosives,and pyrotechnics due to its high energy density.However,B has the problems of long ignition delay time and low combustion efficiency resulting from the limitation of its surface inert oxide(B₂O₃).Therefore,to improve the ignition and combustion properties,the surface functionalization technology was used in this paper.Nano-Al and Fluorographene(FG)were selected to functionalize the surface of boron.On this basis,the ignition and combustion performance of surface functionalized boron in potassium nitrate(KNO₃)and graphite fluoride(GF)oxidant environments were studied in detail.Based on the ignition and combustion performance of boron in two oxidants,we successfully constructed a B/Al/PTFE energetic composite with a microsphere-like structure by emulsion solvent evaporation method to improve the reactivity of B-containing energetic materials.The main research contents involved in this paper are as follows:1.The nano-Al/FG surface-functionalized boron with different coating amounts were successfully prepared by the solvent evaporation method.The surface-functionalized boron was characterized by SEM,XPS,EDS,and XRD,and it was proved that nano-Al and FG formed uniform shell structures on the surface of boron,which became more compact with the increase of coating amount.2.When the oxidant is KNO₃,the ignition and combustion performances of surface functionalized boron were systematically studied.DSC results show that the reaction heat of nano-Al and FG surface functionalized boron in KNO₃ is 1116.83 J/g and 862.69 J/g,respectively,which is higher than that of raw boron(823.39 J/g).The CO₂ laser ignition test shows that when the content of nano-Al coating is 8 wt%,the ignition delay time(75 ms)is lower than that of raw boron(109 ms).Ignition combustion test and closed bomb test results show that the flame height and peak pressure of surface-functionalized boron decrease first and then increase with the increase of nano-Al and FG content.In addition,the ignition and combustion properties of surface functionalized boron with different B/O mass ratios were explored.When the B/O ratio is 7:3,the surface functionalized boron has the minimum ignition delay time of 94 ms and 148 ms,respectively.When the B/O ratio is 4:6,the maximum pressure is 88 k Pa and 59 k Pa,respectively.3.When the oxidant is GF,the ignition and combustion performances of surface functionalized boron were studied in detail.DSC results show that when boron is coated with 6 wt%nano-Al and 2 wt%FG,respectively,the maximum reaction heats are 5.612 k J/g and 5.474 k J/g,which were higher than the raw boron(2.569 k J/g).The CO₂ laser ignition test shows that compared with the raw boron(120 ms),the ignition delay time of the surface-functionalized boron can be reduced to 116 ms and 88 ms,respectively.The ignition combustion test and closed bomb test show that FG is more conducive to enhancing the combustion and pressure output performance of boron than nano-Al.In addition,the ignition and combustion performances of surface functionalized boron under different B/GF mass ratios were studied.When B/GF mass ratio is 4:6,it has the shortest ignition delay time(85ms and 72 ms).When B/GF mass ratio is 2:8,it has the strongest combustion and fastest flame propagation.4.Based on the ignition and combustion performances of surface functionalized boron,the B/Al/PTFE composite microspheres with different B/Al mass ratios were prepared by the emulsion solvent evaporation method.Morphology and structure analysis shows that the components were evenly distributed and closely combined.The microspheres show a monodisperse and highly spherical structure with a diameter of about 400?m.Ignition combustion test and closed bomb test show that the shortest combustion duration time(200ms)of the microspheres is less than that of the physical mixture sample(315 ms),and the maximum peak pressure(821.25 k Pa)is higher than that of the physical mixture sample(632.43 k Pa).In addition,the energy density and reactivity of microspheres can be tuned by adjusting the B/Al mass ratio.DSC results show that with the decrease of the B/Al mass ratio,the heat release increases first and then decrease.When the B/Al mass ratio is 21/9,it has the maximum heat release(4.904 k J/g).The ignition combustion test and closed bomb test show that the reactivity increased gradually with the decrease of the B/Al mass ratio.When the B/Al mass ratio is 0/30,the microspheres had the lowest combustion duration time(200 ms)and the strongest pressure output performance(821.25 k Pa and 1831.18 MPa/s).The surface functionalization method proposed in this paper provides a new technical approach to improve the ignition and combustion performances of boron.The prepared nano-Al and FG surface functionalized boron have reduced ignition delay time and improved combustion performance.In addition,this paper proposed an emulsion-solvent evaporation method to construct the B/Al/PTFE composite microspheres with porous microstructure to achieve the improved combustion and pressure output performance of B-containing energetic materials.The surface functionalized boron and the microspheres prepared in this paper have good application prospects in the field of propellants and explosives.