Effect of polyethylene glycol on the surface exfoliation of SiC green bodies prepared by gelcasting

The surface exfoliation of silicon carbide green bodies prepared by gelcasting in air was dramatically eliminated by adding polyethylene glycol (PEG) in the ceramic suspension. Thus, the size of silicon carbide green bodies could be precisely controlled. In this paper, the zeta potentials of silicon carbide powders dispersed in aqueous solution and the rheological property of the suspension were investigated to determine the effect of the addition of PEG. It was found that the addition of PEG did not affect the colloidal behavior of silicon carbide suspension markedly, but increased the viscosity of silicon carbide suspension because the macromolecular chains of PEG interfered with the fluidity of silicon carbide particles in the suspension. As the amount of PEG increased, the surfaces of silicon carbide green bodies became more and more rigid and the surface exfoliation was completely eliminated when the PEG was over 2.5 wt.% (based on silicon carbide weight) in silicon green body. The mechanism by which PEG inhibited the surface exfoliation of silicon carbide green bodies is probably because that this polymer prevents the reaction between oxygen and monomer free radical, RCH2, during the gelling procedure.