Preparation Of Amorphous Boron?Evaluation And Application Of Agglomerated Boron

Compared to the traditional metal fuels,such as magnesium and aluminum,the volumetric and gravimetric heating values of boron is higher.Boron is considered as the preferred fuel in solid fuel-rich propellants.But there are two problems in the application of boron:?1?improving the preparation technology of the amorphous boron powder;?2?solving the difficulties in the processing of the fuel-rich propellants including the fine amorphous boron powder.To solve these problems,3 aspects of work were carried out in this paper:the efficient preparation technology of the amorphous boron powder,the rapid characterization methods for the agglomerated boron and the application of agglomerated boron in the fuel-rich propellants.To prepare the amorphous boron powder efficiently,a method combined with Self-propagating High-temperature Synthesis?SHS?and magnesium thermal reaction was developed.Sodium borohydride was introduced as active coolerant.The reaction conditions were optimized.Then the amorphous boron powder was prepared in the optimized reaction conditions.A series of rapid and effective characterization methods for the agglomerated boron was established,and an indication system was formed.By these methods,the agglomerated boron which meets the requirements of the propellant processing and other properties was selected.The fuel-rich propellants with the agglomerated boron were prepared.The influences of agglomerated boron's particle size and formulation on the energy property and the primary combustion property were investigated.By means of the adiabatic temperature calculation and the theoretical analysis,the initiating temperature of the SHS reaction for the amorphous boron powder preparation was determined.It is found that when the reactant ratio meets the theoretical stoichiometric ratio?NaBH₄:B₂O₃:Mg=4.0:5.0:9.0?,the initiating temperature is higher than 600?.Within the range of this paper,when the reactant ratio is NaBH₄:B₂O₃:Mg=4.0:7.5:9.9,the initiating temperature is 725?,and the reaction time is10min,the content of boron in the amorphous boron powder is highest.The amorphous boron powder prepared in this paper has smaller grain size,higher reactivity.According to the results of the oxygen bomb tests,the combustion efficiency of the amorphous boron powder prepared in this paper is 72.78%,and the combustion heat is-32143.61J?g^-1.To meet the application requirements of the fuel-rich propellants,a series of rapid and effective characterization methods for the agglomerated boron were established.The intrinsic properties and application properties of the agglomerated boron were characterized systematically.The compatibility of agglomerated boron and HTPB was characterized by measuring the viscosity characteristics of the mixed slurry of agglomerated boron/HTPB.The strength properties of agglomerated boron were characterized by measuring the breakage rate of agglomerated boron in a fixed can mill condition.Based on the test results,a reasonable indication system was established for the selecting the agglomerated boron.Then the agglomerated boron with better applicability in fuel-rich propellants was selected.The fuel-rich propellants containing 30%?mass fraction?agglomerated boron were prepared.And the burning rates,burning-rate pressure exponents,combustion heat,explosion heat of the propellant were tested.The results show that when the agglomerated boron with the same formulations are used in the propellants,in the mesh number range of 40¹00,the burning rate of propellant increases as the particle size of agglomerated boron increases.When the agglomerated boron containing the additive A,the burning rate,the burning-rate pressure exponent,the combustion heat and the explosion heat of the fuel-rich propellant were lower.With the same particle size and formulation,the shot blasted agglomerated boron decrease the burning rate of propellant,but increase the combustion heat and the explosion heat of the fuel-rich propellant.