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The chemorheological behavior of an aqueous suspension of monofunctional and difunctional monomers containing β-SiAlON was investigated for gelcasting process. The effect of various parameters on gel and processing times was also studied. The time–temperature–transformation (TTT) diagram was used to correlate the pertinent processing parameters (time and temperature) with the gelation and processing times during in situ polymerization. The significant difference noticed between TTT diagrams of gel system containing β-SiAlON and a pure gel system was a sharp shift of castable region to lower temperatures. This shift indicates that at the same monomers and initiator concentrations, the gelation can occur at lower temperature in the presence of SiAlON. These results clearly imply that the ingredient has accelerating effect on the polymerization reaction of acrylamide/methylene bisacrylamide. Reduction of polymerization activation energy from 72 kJ/mol for the monomer solution to 61 kJ/mol for a suspension containing SiAlON (35 vol%) confirmed this result. The impurities and surface groups of SiAlON are responsible for the accelerating effect of SiAlON. Furthermore, all suspensions showed shear thinning behavior, which were enhanced by β-SiAlON rate of concentration increase. POLYM. ENG. SCI., 53:2123–2128, 2013. © 2013 Society of Plastics Engineers