Characterization Of Agglomerated Boron Particles And Their Application In Fuel-Rich Propellants

The outstanding performance of the solid rocket ramjet depends on the energy performance and combustion efficiency of its fuel-rich propellant.The higher the energy of fuel-rich propellant and the higher the combustion efficiency,the higher the specific impulse of the solid rocket ramjet.The boron-based fuel-rich propellant is the only propulsion energy which can enable the theoretical specific impulse of solid rocket ramjet to reach more than 10000 N·s/kg.The addition of agglomerated boron is an effective means to improve the burning rate and burning rate pressure exponent of the fuel-rich propellant.During the kneading process of fuel-rich propellant slurry,the degree of crushing of the agglomerated boron particles affects the process performance.During the combustion process of propellant,the thermal dispersion of the agglomerated boron particles affects the combustion efficiency of the boron in the engine afterburner.Therefore,studying the degree of crushing of the agglomerated boron particles in the kneading process and the degree of thermal dispersion in the combustion process provide guiding for the optimization of the agglomerated boron formula and the engineering application of boron-based fuel-rich propellant.In this paper,the basic properties,reaction characteristics and the evaluation method of degree of crushing were studied;particle size,circularity,density,morphology,specific surface area and other parameters of different types of agglomerated boron particles were characterized;the compatibility of agglomerated boron and HTPB was tested.Thermal oxidation characterization of agglomerated boron particles was studied and the thermal oxidation exothermic peak was the same as the amorphous boron powder on the whole;the relative crushing index RBg was proposed,which can quantitatively characterize the degree of crushing of the agglomerated boron particles in the kneading process of slurry,and when the particle size of the agglomerated boron particles became smaller,the breaking degree would get lower;the influence of vibrating sieve method,pot milling method and ball milling method on RBg under different conditions were explored;adopting the ball milling method to mill the agglomerated boron particles directly,the crushing of the agglomerated boron particles during the kneading process of slurry can be simulated by controlling the ball milling conditions.The milling conditions of agglomerated boron particles of 450-860μm are:revolution speed is 280rpm,rotation speed is 560rpm,mass ratio of steel balls to materials is 7:4,the diameter of steel ball is 15.00mm and the time of ball milling is60min;the milling process of agglomerated boron particles of 255-450μm are:revolution speed is 280rpm,rotation speed is 560rpm,mass ratio of steel balls to materials is 7:4,the diameter of steel ball is 10.00mm and the time of ball milling is30min.The application of agglomerated boron in boron-based fuel-rich propellant was studied.The agglomerated boron-based fuel-rich propellant was prepared;the influence of the type and particle size of agglomerated boron particles on the combustion residue characteristics of boron-based fuel-rich propellant was studied;Adopting the thermal breakage rate index Bp,the degree of thermal dispersion of agglomerated boron particles during the combustion process was characterized semi-quantitatively.The results suggest that the order of different types of agglomerated boron particles’Bp from high to low is:AB1-40>AB1-20>AAB-20>AAB-40>AB2-40>AB2-20>AMB-40>AMB-20;the influence of particle size of agglomerated boron,the type of boride and the content of agglomerated boron on the combustion performance of boron-based fuel-rich propellants were studied.Among the 8 types of agglomerated boron particles,the burning rate of the FR-AAB-20 fuel-rich propellant with agglomerated boron containing aluminum diboride had the highest combustion rate that was 26.06mm?s^-1.The results show that agglomerated boron containing aluminum diboride can improve the combustion performance of the boron-based fuel-rich propellants,and had good application prospects.