Studying the Role of Gelation Agents in Gelcasting Non-porous Si3N4 Bodies by Pressureless Sintering

The monomer content in the gelcasting process affects the kinetics of cross-linking reactions which determines the quality of the gel network structure and the final properties of the material. The main purpose of this study was to optimize the monomer contents in the gelcasting process to achieve a dense Si3N4 body by using pressureless sintering. Si3N4 bodies with a relative density of 95.9 +/- 0.5% and 605 +/- 4 MPa flexural strength were successfully prepared by employing the gelcasting technique using high-solid load slurry of 76 wt%. Acrylamide (AM) and N, N '-methylenebisarylamide (MBAM) were adopted as the monomeric system. The quality of gel structures was characterized by measuring idle time, green flexural strength, and linear shrinkage. Phase composition and microstructure of sintered samples were identified using XRD and SEM analysis, respectively. The linear drying shrinkage and Idle time decreased by increasing the monomer content. However, flexural green strength did not monotonically change with monomer content. The slurry with a 6 wt% monomer and AM/MBAM ratio of 3 produced the optimized gel structure. Besides, it resulted in a higher amount of beta-Si3N4 phase which gives better mechanical strength.