Slip Casting of Silicon Nitride and Mechanical Properties of Sintered Body (Part 5)

Abstract

Vacuum-pressure-assisted slip casting was studied to develop a forming method for the fabrication of silicon nitride engineering ceramics with complicated shapes. A well-dispersed and high solid-content slurry was prepared, the consolidation kinetics of the slurry was studied by using a vacuum-pressure-assisted slip casting system with a porous resin mold, and the mechanical properties of sintered bodies were investigated. From a slurry containing 67mass% solid (92mass% α-Si3N4, 3mass% Al2O3, 5mass% Y2O3), 0.01mass% deflocculant, 0.1mass% defarmer, 4mass% binder, green bodies with densities of 1.55-1.62g/cm3 were prepared in the pressure range of 0.1-0.7MPa. The green body density gradually decreased with increasing slip casting pressure, while the density of sintered bodies was independent of the pressure. Based on the Adcock and McDowall's equation, calculated values of the rate of cake buildup (k) were well coincident with observed values by taking into account the green body density. The silicon nitride sintered at 1775°C for 10h at 0.9MPa N2 pressure showed a density of 3.25g/cm3, a flexural strength of 1.1GPa, and a Weibull modulus of 14. It was found that the vacuum-pressure-assisted slip casting was useful for the forming of silicon nitride.