Low-Temperature Synthesis of Boron Carbide Powder by Boric Acid-Polyvinyl Alcohol Gel Precursor

摘要

Polyvinyl borate polymer, which was employed as a precursor of boron carbide synthesized at low temperatures, was prepared with the condensation of polyvinyl alcohol and boric acid by a sol-gel method. Boron carbide powder was obtained by two steps, i.e., the pyrolysis of the polyvinyl borate precursor in air at 500-850 °C for 2 h and following the heat treatment of the pyrolyzed precursor in N_2 flow at 1200-1500 °C for 2 h. To get an insight into the low-temperature synthesis process of boron carbide, the effects of raw materials molar ratio, reaction time and temperature on the synthesis of boron carbide were investigated. The polymer-ceramic conversion process was characterized by element analysis, TG, FTIR, XRD, particle size distribution and SEM. The pyrolysis results of the polyvinyl borate precursor indicated that the synthesized polyvinyl borate with a molar ratio of 4:1 for polyvinyl alcohol and boric acid was pyrolyzed in air at 600 °C for 2 h to afford a mixture of B_2O_3 and C. The pyrolyzed precursor was then treated in N_2 flow at 1500 °C for 2 h to afford B_4C powder with a median diameter of 6.17 m.