Effect of citric acid on the adsorption behavior of polyethylene imine (PEI) and the relevant stability of SiC slurries

Polyethylene imine (PEI) proved to be effective for dispersing SiC particles in aqueous media. However, SiC suspensions with only PEI as dispersant exist in a flocculated state at high solid content. In this study, citric acid is introduced as the second dispersant for improving the slurry stability. The adsorption behavior of both dispersants and the relevant slurry properties were characterized in terms of zeta potential, sedimentation, adsorption, FTIR and rheology measurements. In the presence of citric acid, an increase in zeta potential of SiC particles was observed in neutral and acid pH ranges. Adsorption measurement showed that the addition of citric acid could effectively enhance the adsorption of PEI on SiC particle surface, which might come from the formation of complexation between citric acid and adsorbed PEI, as evidenced by FTIR. Sedimentation and rheological measurements further confirmed that SiC slurries exhibited an improvement in stability upon the addition of citric acid. Results showed that the combination of PEI and citric acid as dispersants could effectively stabilize SiC suspensions at high solid content.