Purification Of Amorphous Boron Powder And Study Of Its Propertie

At present,amorphous boron powder is considered as the best fuel for solid fuelrich propellant because of its extremely high volume calorific value and mass calorific value.However,the amorphous boron powder produced by magnesium thermal reduction method has many defects,such as many impurities,low purity,too large particle size,low tap density and poor chemical activity,which seriously hinders its large-scale application in military and aerospace fields.Aiming at the defects of amorphous boron powder produced by magnesium thermal reduction method,this paper takes cheap coarse boron powder as the research object,changes its composition structure by adding boron oxide,microwave heating pretreatment and ball milling,optimizes the physical and chemical properties of boron powder,and explores new ideas for modifying amorphous boron powder,aiming at solving the problems faced by cheap amorphous boron powder used in solid fuel-rich propellant.The specific research contents are as follows: The main results are as follows:(1)The influence of a large amount of heat released during the thermal reduction reaction of magnesium on the formation and occurrence distribution of boron powder impurities is analyzed.It is found that insoluble impurities magnesium borate and magnesium boride in amorphous boron powder are closely combined with boron to form a complex microstructure.A large number of impurities are in the reaction blind zone during acid leaching,which makes boron powder unable to be purified by simple acid leaching.It provides basic information for the selection of boron powder purification process.(2)The soluble transformation mechanism of insoluble boron and magnesium compounds in amorphous boron powder during roasting and the method of purifying boron powder were studied.In order to remove insoluble boron and magnesium compounds from amorphous boron powder,insoluble impurities Mg2B2O5 and Mg B4 were directionally transformed into soluble Mg B4O7 and Mg O during roasting with B2O3.The results show that the magnesium content in amorphous boron powder can be reduced to 0.96% and the purity can be improved to 97.34% by adding B2O3 roasting combined with water and acid leaching.(3)Using the characteristics of microwave selective heating,the shell of boron powder particles is cracked,resulting in a large number of cracks,which fully exposes impurities,facilitates the removal of impurities by reacting with acid solution,and increases the specific surface area of boron powder particles.The results show that the magnesium content of amorphous boron powder can be reduced to 0.85% by heating it to 800℃ by microwave for 5 hours and then acid leaching with ultrasonic assistance.The thermal properties of boron powder samples were tested by TG-DSC,and it was found that the activity of boron powder was significantly improved after microwave heating and purification,which opened up a new idea for unconventional modification of boron powder.(4)improving the tap density of boron powder by ball milling.Since the Boromohs hardness is as high as 9.3,Si O2 is 7.Therefore,a large amount of Si O2 impurities are introduced when using Si O2 ball milling tank and grinding ball to ball mill boron powder,which must be further removed by acid leaching.At the same time,long-term ball milling makes boron powder agglomerate and the particle size distribution widens.After ball milling,the particles of boron powder are spherical,and its space utilization rate and tap density are improved.(5)By comparing the effects of different processes on the properties of boron powder,the relationship between purity,morphology and activity of boron powder was studied,which provided a theoretical basis for preparing high-performance boron powder.It is found that microwave heating pretreatment combined with ultrasonic-assisted acid leaching treatment of amorphous boron powder can improve the purity of boron powder,reduce the impurity magnesium content and improve the activity.This process has the best effect and performance in purifying boron powder.The results show that the influence of different processes on the composition and structure of amorphous boron powder and the interaction between the composition and structure of boron powder and its properties are clear.It provides a theoretical basis for the preparation of high-quality amorphous boron powder.