Study On Preparation Of B/Al-B Alloys By Aluminothermic Reduction Processes

Boron has been widely used in material processing,automotive airbags,superconducting,semi-conductor,military and other fields because of its special physical and chemical properties.At the same time,it is one of the most potential fuel-rich solid propellant because of its high calorific value.AlB2 and AlB12 are the two most common Al-B alloys and commonly used as grain-refining agents in casting and substitutes of propellant fuel.At present,there are still many disadvantages in producing B/Al-B alloy,such as high preparation cost,low actual output,non-conforming product purity,etc.,which limit greatly the application of B and Al-B alloys.This paper put forward a novel process for preparing B/Al-B alloy,in which sodium fluoroborate was used as the raw material,aluminum powder as the reducing agent,and B/Al-B alloys were prepared through vacuum aluminothermic reduction.The reduction process was investigated and the results are as follows:Thermodynamic calculation of the possible reactions involved during the vacuum aluminothermic reduction for preparation single-mass B/Al-B alloy process was carried out,and the theoretical reduction sequence was determined.The saturated vapor pressure calculation of the raw materials and products participating in the reaction is calculated to determine that the reduction product.The obtained product can be separated by vacuum distillation.and Al-B alloy from NaBF4.Experiments indicated that the reduction temperature,insulation time and Al powder excess coefficient had a significant effect on the reduction degree of NaBF4 and the quality of the products.During preparation of B simple substance,the B powder containing 91.21%B can be obtained when the reduction temperature is 1100℃,the insulation time is 60 min and the reduction agent overdose coefficient is-6%,the particle size of which is evenly distributed and about 8.1μm.Here the yield rate of B simple substance is about 85.40%.During the preparation of Al-B alloy,an alloy containing about 92.6%AlB2 can be obtained when the reduction temperature is 900℃,insulation time is 60min and the reduction agent excess coefficient is-6%;and the alloy containing about 98.5%was obtained when the reduction temperature is 1100℃,the insulation time is 75 min,and the reduction agent overdose coefficient is-10%.Boron-containing ice crystals,which contain about 2.51%B,were obtained as the preparation of B/Al-B alloys.The B can be removed by secondary aluminothermic reduction.Meanwhile Al-B alloy and boron-free ice crystal can be obtained.The experimental results show that the B content in the ice crystal obtained after secondary aluminothermic reduction is below 0.030%,which meets the requirements of industrial ice crystal when the ratio of aluminum and boron-containing ice crystal is greater than 1:1 and the insulation time is greater than 30min.In present study,single-mass B and Al-B alloy(AlB2 and AlB12)were prepared using sodium fluoroborate as the raw material and Al powder as a reducing agent.After two-stage aluminothermic reduction,qualified ice crystal was obtained.The present process not only shortens the production flow of B/Al-B alloys,but also recycles qualified ice crystal.