Inclusion Analysis And Removal Mechanisms In Preparation Of Amorphous Boron Power By Self-propagating High-temperature Synthesis (SHS) Metallurgy

Preparation of Amorphous boron powder in magnesium thermal reduction exist the large size,quality defects of higher content of impurities magnesium, which seriously affecting its reactivity and burning speed, limiting its application as a high-energy fuel in solid rocket propellant and other areas. Our issue group developed new technology of SHS metallurgy method to prepare high activity amorphous boron powder of large-scale cleanly, successful prepared highly active amorphous boron powder of particle size less than 1.0μm. With the content magnesium of impurities in amorphous boron powder is not completely removed (the content of impurity magnesium is 4.50%～6.89%, the products only meet quality standards SB90～92), which seriously affect its performance.Based on preliminary studies, in this paper, systematic study the laws of thermodynamics law and existence state in SHS metallurgy method. Study the dynamic mechanism of different phases of impurities dissolved in the acid leaching process. The paper using orthogonal system studied impurities acid remove law in amorphous boron powder, optimize d the purification process conditions of removed impurity in acid leaching. Achieved the following major achievements:The thermodynamic calculations showed that:SHS reaction process will generate MgB2, MgB4, Mg3B2O6 and other impurities phase, range from 650-1200K, the trends of generat Mg3B2O6 is maximum; when the temperatures above 1300K, Not conducive the generation of MgB2, MgB4. With the Magnesium vapor partial pressure increases, will be promote the formation of MgB2, MgB4 reaction. Through XRD, SEM analysis showed that:with the boron oxide, magnesium powder as raw materials, the impurities obtained from SHS combustion products is a amount of MgO and a little Mg3B2O6, MgB2, MgB4, and dispersed throughout the matrix, which are consistent with thermodynamic calculation results.Using high-temperature solid-phase synthesis method for prepare Mg3B2O6 and MgB2 products. Using Mg3B2O6 and MgB2 as raw materials, study the influence of acid leaching process conditions on dissolution kinetics of Mg3B2O6 and MgB2 and other substances. The results showed that:with the temperature and the concentration of hydrochloric acid increases, the dissolution speed of Mg3B2O6 and MgB2 significantly increased. Dissolution process of Mg3B2O6 controled by chemical reaction and diffusion, the apparent activation energy is 35.00kJ/mol; reaction order of 1.88. Dissolution process of MgB2 mainly controlled by diffusion, the apparent activation energy is 13.30kJ/mol, the reaction order is 0.73. Through comparison found the dissolution speeed of magnesium hydrochloric acid is so fast. Solubility of Amorphous boron powder in hydrochloric acid is very small, only a maximum of 0.3%.Orthogonal experiment results of Acid leaching showed that:in the acid leaching process of remove impurity of SHS combustion products, the acid leaching conditions on the effect of significant influence is:temperature>Time>liquid to solid ratio>acid concentration. Combined with each phase dissolution kinetics test results to determine the best leaching conditions is:extraction temperature is 95℃, extraction time is 60min, liquid-solid ratiois 16:1, the concentration of hydrochloric acid is 5mol/L.After acid leaching process using the optimum leaching conditions impurity, prepared highly active amorphous boron powder with content of magnesium is only 3.55%, its quality meets quality standards SB92-95, the quality has been greatly improved. The particle size of amorphous boron powder dispersed uniformly, mean particle size less than 300nm.