Preparation and properties of Si3N4 3 N 4 ceramics via vat photopolymerization using Si3N4 3 N 4 powders coated with bowl-like boehmite

It is a significant challenge to fabricate Si3N4 ceramics due to the high refractive index (2.1) and UV absorbance (0.8903 at the wavelength of 405 nm) of Si3N4 powders. In this study, a method of filling Si3N4 powders into bowl-like hollow boehmite microspheres was proposed. And the effects of the boehmite coating content on the properties of Si3N4 ceramic slurries, green bodies and sintered samples were systematically investigated. Due to its low refractive index (1.7) and weak UV absorbance (0.2648 at the wavelength of 405 nm), boehmite can serve as a modifier to enhance the photocuring ability of Si3N4 ceramic slurries. At the same time, it can also be decomposed into Al2O3 at high temperature as a sintering aid of Si3N4 ceramics. As the boehmite coating content increased from 2.5 wt % to 10 wt %, the bulk density of Si3N4 ceramic samples decreased from 3.05 f 0.01 g/ cm3 to 2.79 f 0.03 g/cm3, while the porosity increased from 6.84 f 0.81 % to 13.23 f 0.93 %. The relative density (93.15 f 0.02 %) and flexural strength (406.5 f 18.3 MPa) of sintered Si3N4 ceramic samples revealed that both values peaked at 2.5 wt %. This study not only provides a constructive method for modifying Si3N4 powders to achieve photopolymerization, but also offers an innovative idea for other non-oxidation ceramics with poor photocuring ability.