The preparation of silicon nitride ceramics by gelcasting and pressureless sintering

A new gelling system based on the polymerization of hydantion epoxy resin and 3,3′-Diaminodipropylamine (DPTA) was successfully developed for fabricating silicon nitride (Si3N4) ceramics. The effects of pH value, the dispersant content, solid volume fraction and hydantion epoxy resin amount on the rheological properties of the Si3N4 slurries were investigated. The relative density of green body obtained from the solid loading of 52 vol% Si3N4 slurry reached up to 62.7%. As the concentration of hydantion epoxy resin increased from 5 wt% to 20 wt%, the flexural strength of Si3N4 green body enhanced from 5.3 MPa to 31.6 MPa. After pressureless sintering at 1780 °C for 80 min, the sintered samples exhibited the unique interlocking microstructure of elongated β-Si3N4 grains, which was beneficial to improve the mechanical properties of Si3N4 ceramics. The relative density, flexural strength and fracture toughness of Si3N4 ceramics reached 97.8%, 687 MPa and 6.5 MPa m1/2, respectively.