Impurity Of Boron Carbide Powder

Boron carbide with outstanding physicochemical characteristics has been extensively utilized in the fields of bullet resistant material, special acid and alkaline resisting material, atomic reactor controlling and shielding material, etc. However, its application and development are restricted due to there is a small quantity of impurity such as silicon, iron, etc. in Boron carbide powder which can make the hardness of Boron carbide on the decline resulting in great fall of its physical properties. Therefore, how to remove these impurities is to regard as have a greatly theoretical significance and applying prospect.According to the properties of silicon and iron, behaviors of silicon in the production process of Boron carbide were described in thermodynamic terms in this paper firstly. Subsequently, the shape of silicon is theoretically determined. Thermodynamic computations of some reactions possibly happened in the impurity removal process of applying these four methods—hydrofluoric acid process, leaching with alkali process, acid + fluoride process and high temperature roasting with alkali were depicted. The results show that the impurity removal with applying these four methods are all thermodynamically favorable in which high temperature roasting with alkali process is most favorable. The solution method of sample and optimum condition of measuring silicon and iron with color comparison method were determined respectively through experimentation.Experimental result indicates that impurity removal with hydrofluoric acid process, hydrochloric acid + fluoride process and roasting with NaOH process are all feasible. Reactions of Silicon removal involved in the processes of hydrofluoric acid process and hydrochloric acid + fluoride process are influenced by inner diffusion control, which have apparent activation energy of 5.97 and 11.12 kJ/mol respectively. Among these methods of impurity removal, the roasting with NaOH process has a greater effect on the Si and Fe removal from Boron carbide powder and removal efficiency of Si and Fe can reach 32.35% and 60% respectively. The high purity Boron carbide powder in which silicon and iron content are 0.046% and 0.044% respectively can be obtained when the roasting temperature is 500℃and roasting time is 10h.