Celation, consolidation, and rheological properties of boehmite-coated silicon carbide suspensions

We have studied the gelation, consolidation, and rheological properties of boehmite-coated SIC suspensions. A boehmite-coated SiC suspension consists of SiC particles covered with a boehmite layer of a few nanometers in thick ness in the suspension. Similar to boehmite suspensions, the boehmite-coate d SIC suspension can gel over time. The gelation, as well as the rheologica l behavior of the boehmite-coated SiC suspension with respect to pH, is sho wn to be similar to that of a boehmite suspension. However, because of the particle-size difference, a boehmite-coated SIC suspension gels more slowly than suspensions of smaller boehmite particles. The boehmite coating impro ves the consolidation density of SiC, increasing the sediment density from 39 to 52 vol% and the centrifuged density front 50 to 60 vol%. It, also, ma kes the consolidation behavior of a boehmite-coated SiC suspension with res pect to pH more consistent with the rheological behavior; i.e., lower suspe nsion viscosity and storage modulus correlate with a higher consolidated de nsity. In contrast, suspensions containing SiC particles partially covered with boehmite and individual boehmite particles in the suspensions show no improvement in the sediment density and no systematic correlation between t he consolidation density and the rheological properties. This indicates tha t the complete coating of boehmite on the SiC particles is critical to the improvement in consolidation density.