Thermodynamic modeling and investigation of the oxygen effect on the sintering of B 4 C

Presence of oxygen in boron carbide (B4C) powder can result in deterioration of mechanical properties of the sintered sample. In this study, the potential effects of reaction between boron oxide (B2O3) and free carbon (C) as common impurities of commercial B4C powder were discussed. The emission of different gas species during B4C sintering, due to the reaction between B2O3 and C, was predicted. The importance of C/B2O3 ratio was also discussed and the ideal ratio was determined. It was shown that both B2O3 and C can be consumed completely by using the B4C powder with the ideal C/B2O3 ratio. It was also predicted that the B4C powder in carbon deficit region is highly prone to coarsening and the sintered product can have low density and hardness. It was suggested to adjust the C/B2O3 ratio in B4C powder slightly in carbon rich region, to keep the system away from carbon deficit region. The results of thermodynamic modeling were then applied in selected B4C sintering experiments. It was shown that thermodynamic modeling can provide critical clues to design more effective approaches and sintering parameters based on the sintering technique adopted.