Effect of the molecular weight and concentration of PEG solution on microstructure and mechanical properties of Si3N4 ceramics fabricated by gel-casting

Gel-casting is a promising preparation technology of Si3N4 structural ceramics. The process involves drying of the "green" gel-cast parts before densification. And the drying of green gel-cast bodies is an important step in the gel-casting manufacturing process. In this work, the Si3N4 gel-cast green bodies were dried in polyethylene glycol (PEG) solution with the purpose of obtaining Si3N4 ceramics with good mechanical properties. The effect of the molecular weight and concentration of PEG solution on drying rate, microstructure and mechanical properties of Si3N4 ceramics was studied. The results indicated that with the increase of molecular weight of PEG, the drying rate increased obviously and the structure became more uniform and dense when the concentration of solution was 20 wt%. The Si3N4 ceramics after sintering have the excellent flexural strength (662.6 MPa) under PEG600 drying condition. Furthermore, the concentration of PEG600 solution had a positive effect on drying and sintering of the green body. Therefore, the bending strength reached 871.1 MPa under 65 wt % PEG 600 solution drying condition. Overall, the drying process (drying in 65 wt% PEG600 solution) promotes the efficiency and quality of drying of Si3N4 gel-cast green bodies, which is beneficial for the subsequent drying and sintering process.