Study On The Separation Of Free Carbon In Boron Carbide

The advantages of high hardness,low density,high melting point,high elastic modulus,high thermal neutron absorption cross section,acid and alkali resistance,and good thermal stability of boron carbide have made it a ceramic material with excellent performance.It is widely used in the fields of national defense industry,nuclear industry and industrial ceramics.At present,the main preparation method of boron carbide in the industry is the electric arc furnace carbothermal reduction method.Affected by the preparation method,the produced boron carbide powder contains a large amount of free carbon.The presence of free carbon will cause the boron carbide to be porous and poorly compact,and it will also reduce the hardness and elastic limit of the boron carbide and increase the probability of fracture.In addition,free carbon has a significant impact on the densification kinetics of boron carbide and the mechanical and electrophysical properties of the sintered product.Reducing the content of free carbon in boron carbide powder can greatly improve the purity of boron carbide,making it more widely used in cutting-edge fields.At present,the impurity removal of boron carbide at home and abroad is mainly aimed at impurities such as iron and silicon,there is no mature method for the separation of free carbon in boron carbide.In this paper,boron carbide powder prepared by electric arc furnace carbothermal reduction method is used as raw material,and analysis and detection equipment and methods such as laser particle size analyzer,X-ray diffractometer(XRD),scanning electron microscope(SEM),differential thermal analyzer,and chemical titration are used.The phase,morphology,oxidation characteristics and content of the impurity carbon in the raw material boron carbide were analyzed,and it was found that the impurity carbon in the boron carbide mainly existed in free form.Therefore,it is determined to use reverse flotation and static roasting methods to separate impurity carbon from boron carbide.Single factor experiments were used to study the influence of flotation parameters(slurry concentration,collector dosage,foaming agent dosage,slurry pH value)on the removal rate of free carbon in boron carbide powder by reverse flotation.The single factor experiment results show that the optimal slurry concentration range is 20%～30%,the optimal collector dosage range is 400～600g/t,the optimal foaming agent dosage range is 150～250g/t,the best pH value range of the slurry is 8-9.Orthogonal experiments are further used.The results indicate the slurry concentration of 25%,collector dosage of 600g/t,foaming agent dosage of 200 g/t,and slurry pH value of 8.5 were found to be the best process conditions for removing free carbon in boron carbide by reverse flotation.The experiment was repeated three times under optimal conditions.The percentage of free carbon was reduced from 2.98%to less than 0.6%.The removal rate of free carbon in boron carbide powder was up to about 80%,and the particle size of boron carbide powder before and after carbon removal was not significant changes,the reverse flotation process greatly improves the purity of boron carbide powder,and does not introduce new impurities.The effects of roasting temperature and roasting time on the carbon removal rate and structural characteristics of boron carbide powder were studied.The results show that the carbon removal rate increases with the increase of the roasting temperature and the extension of the roasting time.On the premise that the boron carbide is not oxidized,the best process conditions for the roasting method to remove free carbon in boron carbide are the roasting temperature of 400℃ and the roasting time of 3h.Under this technological condition,the removal rate of free carbon in boron carbide reaches about 32%.The properties of the boron carbide powder did not change significantly during the roasting process,and the average particle size change rate of the boron carbide powder was only 1.551%.