Modification Of Amorphous Boron Powder And Preparation Of Composite Particles And Study On Ignition Performance

Boron（B）has great application value in solid propellants with the characteristics of high calorific value,clean combustion products and no pollution to the environment.However,the contaction between the internal active B and the oxidation component is hindered owing to the existence of boron oxide（B₂O₃）film on its surface.A using of flammable metal aluminum powder for composite treatment of B was introduced here to improve the ignition and combustion activity of B.After surface modification,B was combined with active aluminum powder to achieve the purpose of shortening the ignition delay time of B and improving the combustion efficiency.Firstly,B/Al composite material were prepared by mechanical planetary ball milling.The influences of ball milling process on the morphology,composite effect and thermal properties of B/Al composites were investigated.The research results showed that the B/Al composite particles hold the highest reactivity and the most excellent exothermic performance,when the planetary ball mill rotates at 300 rpm,anhydrous ethanol is used as the dispersion medium,the ratio of the total mass of the material to the mass of the ball milled zirconium beads is 1:10,the mass ratio of raw boron and raw aluminum is 5:1,and the ball milling time is 6 hours.Secondly,modified boron powder were prepared by solvent activation and surface modification,respectively.Among them,the boron powder activated with deionized water,absolute ethanol and ethyl acetate as solvents has no significant changes on the surface morphology and crystal structure.The element analysis in surface morphology and crystal structure.The elemental analysis of the sample revealed that the B₂O₃content on the surface of the boron powder after ethanol activation is the lowest（0.034%,51.43%lower than the raw material）.The results of thermal analysis displayed that the exothermic peak temperature（T_p）of boron powder（EB）treated with anhydrous ethanol was the smallest（760.29°C,0.23%lower than that of raw material）,and the heat release（Q）was the largest(10381 J·g^-1,24.37%higher than that of raw material).In addition,3-aminopropyltriethoxysilane(C₉H₂₃O₃NSi,KH550 for short)was added to modify the surface of B powder.When the amount of modifier added was3wt.%,the Q of the modified boron powder was largest(10533 J·g^-1,which is 26.19%higher than the raw material).Finally,flake aluminum powder（TF-Al）with larger specific surface area was gained by ball milling,and the modified B/Al composite particles were prepared by the best ball milling process.Furthermore,the results demonstrated that the B/Al composite particles prepared by using ethanol-activated B powder and KH550 modified B powder have closer contact with Al than that of raw material B.The thermal analysis data suggested that TF-Al will promote the combustion of B particles and make the high-temperature oxidation and exothermic stage of B proceed faster.Among them,the pre-exponential factor（A）of B/Al composite particles modified with ethanol was the largest.The ignition performance test indicated that the ignition energy of the composite sample of KH550 modified B powder（KH-B）and flake aluminum powder（TF-Al）has the smallest ignition energy（19.41 J,which is 16.66%lower than that of the unmodified composite B/Al sample and 29.06%lower than that of the raw material B）.