Formation mechanism of stereolithography of Si3N4 slurry using silane coupling agent as modifier and dispersant

Silicon nitride (Si3N4) ceramic slurry with high-solid loading, low-viscosity and high curing depth was prepared by using a surface modifier (silane coupling agent) directly as the dispersant. The effect of the interaction between modified Si3N4 powders and prepolymer on rheological property, kinetic stability, wettability and curing property of the slurry was investigated. The stereolithography forming mechanism of the modified Si3N4 ceramic slurry was elucidated. It is revealed that the epoxy group of KH560 can easily form an ether covalent bond with the hydroxyl group of bisphenol A epoxy acrylate (EA). This makes submicron sized Si3N4 powder well-dispersed in the premixed liquid and leads to improved rheological properties and kinetic stability of the ceramic slurry. In particular, the ether covalent bond formed between surface modified Si3N4 powder and EA reduces the surface tension of the slurry and enhances the wettability of the cured slurry layer. KH560 acts as a molecular bridge linking EA to Si3N4 powder surface and forms an EA shell structure. Therefore, the refractive index difference between the Si3N4 powder and prepolymer reduces significantly by two orders of magnitude, leading to an increase in the curing depth. These findings could be crucial for the stereolithographic fabrication of high refractive index ceramics parts with high precision and complex geometries.