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Direct coagulation casting via urease-catalyzed hydrolysis of urea in SiC suspension was studied at room temperature. The results demonstrate that high-solids-loaded SiC slurries with low viscosity can be prepared at pH 9.5–10.5. The urease-catalyzed decomposition of urea can be used to shift the pH and to increase the ionic strength of the SiC slurry. The pH value decreased with the increase of coagulation time. The optimal coagulation temperature is 50 °C for 62 vol.% SiC slurry. The strength of wet green body after 1 h of coagulation at room temperature is high enough for demolding and handling without damage in the wet green stage. [Copyright &y& Elsevier]

Abstract: The effect of temperature on surface charge properties and rheological behavior (like pH, viscosity and zeta potential) of an aqueous SiC suspension were studied. Temperature significantly affected the rheological behavior of the aqueous SiC suspension. The pH and zeta potential of the SiC suspension all decreased with the increasing of temperature. Steady rate sweep experiments showed an increase in viscosity with increasing temperature and the effect was enhanced with increasing solid loading. These effects are attributed to a destabilizing effect of temperature, derived from the dissolution of a thin SiO2 layer on the SiC surface. [Copyright &y& Elsevier]

The hydrolysis assisted solidification (HAS) process was used in the slurry forming of SiC green bodies. AlN powder was added to aqueous SiC slurry prior to shaping. The addition of small amount of AlN powder causes a dramatic increase in the suspension viscosity or even solidification in the case of highly loaded suspension. Green bodies were successfully produced. Measurements of the changes in viscosity, the pH and the zeta potential measurements were performed to evaluate the process. Effects of the addition of AlN and solidification temperature on the process and the ceramic suspension were followed. [Copyright &y& Elsevier]