Effect of polystyrene addition on properties of porous Si3N4 ceramics fabricated by digital light processing.

Porous Si 3 N 4 ceramics with high strength and high transmittance have been widely used in the field of defense and military. Additive manufacturing (AM) technology is one of the effective means to fabricate porous Si 3 N 4 ceramics. Nevertheless, it is difficult to prepare porous Si 3 N 4 ceramics by using digital light processing (DLP) because of the large refractive index difference between Si 3 N 4 powders and photosensitive resin. In this study, the effects of the amount of polystyrene (PS) powders on the properties of Si 3 N 4 ceramic slurries and sintered ceramics were systematically discussed. The addition of PS reduced the overall refractive index of powders and increased the average particle size of powders, thus improving the cure depth of Si 3 N 4 ceramic slurries from 11.0 ± 2.0 μm to 55.7 ± 1.8 μm. With the increase of PS content, the shrinkage and porosity of Si 3 N 4 ceramics gradually increased, and the bulk density and flexural strength showed the opposite trend. The slurry with low viscosity (2.38 Pa٠s at a shear rate of 30 s−1) and high cure depth (51.2 ± 4.6 μm) was obtained when the content of PS was 15 wt%, which met the thickness requirements for printing. The total porosity of Si 3 N 4 ceramics reached the maximum values at 28.21 ± 2.58%. The addition of PS solved the problem of low cure depth of slurries, and PS as a pore-forming agent could help Si 3 N 4 ceramics form porous structure. This research provides valuable insights into the fabrication of non-oxide ceramics with high refractive index using DLP technology. [ABSTRACT FROM AUTHOR]