Reaction Induced Gelation Casting of SiC Ceramics

It was found that sol-gel transition may occur to electrostatically stabilized silicon carbide suspensions when their pH values are shifted from alkaline region to neutral. SiC slips may set when they are neutralized by the hydrolysis or esters or lactones. This process was used in the forming of SiC ceramics. Rheological studies on various factors influencing the setting process by small amplitude oscillatory measurements show that the gelation of the SiC suspensions depends not only on the final pH, but also on the initial pH and the pH-shifting rates of the systems. These effects indicate that this solidification is not a simple coagulation process but a gelation process that takes place by forming Si-O-Si bonds between the particles. SiC ceramic green bodies with complex shapes were prepared with this method.