Interactions in the Silicon Carbide–Polyacrylic Acid–Yttrium Ion System

Interactions in the SiC powder–polyacrylic acid (PAA, dispersant)–Y³⁺ ion (sintering additive) system were investigated in the pH range from 2 to 6. The amount of Y³⁺ ions adsorbed on SiC particles increased with an increase of pH because of the electrostatic attraction between the negatively charged SiC surface and Y³⁺ ions. On the other hand, the amount of PAA adsorbed on SiC particles decreased with increasing pH because of the electrostatic repulsion between the negatively charged SiC surface and dissociated PAA. The addition of PAA to the SiC suspension with Y³⁺ ions increased the amount of Y³⁺ ions fixed to SiC particles through the strong interaction between Y³⁺ ions and PAA adsorbed on SiC particles. The above-described interactions in the SiC–PAA–Y³⁺ ions system were closely related to the coagulation of SiC particles and the rheology of SiC suspensions. The coagulation of SiC particles through the adsorbed Y³⁺ ions decreased the specific surface area of SiC powder after calcination in an argon atmosphere. The addition of PAA to the SiC suspensions with Y³⁺ ions kept the SiC particles separate during calcination, i.e., the PAA addition contributed to enhancement of the driving force of sintering (no decrease of specific surface area) and to control of the amount of Y³⁺ ions uniformly fixed to the SiC surface.