Effect of Al2O3 coating on the properties of Si3N4 ceramics prepared by vat photopolymerization

The preparation of Si3N4 ceramics by vat photopolymerization (VPP) has motivated increasing research interest. However, it is challenging to prepare Si3N4 ceramics by VPP due to the high UV-light absorbance and refractive index of powder. In this paper, a method for Al2O3-coated Si3N4 powder was proposed. Combined with the boehmite-coated and high-temperature treatment, Al2O3 was successfully coated on the surface of Si3N4 powder. The effect of Al2O3 content on the properties of Si3N4 powders, slurry and the sintered Si3N4 samples were investigated. The Al2O3 coating layer not only improves the curing forming ability of Si3N4 slurries, but also can directly act as one of the sintering aids of Si3N4 ceramics. The bulk density of the samples decreases from 3.04 f 0.02 g/cm3 to 2.97 f 0.01 g/cm3 with the increase of coating content, while the porosity increases from 5.38 f 0.89 % to 7.54 f 0.63 %. The sample of 5 wt % Al2O3 coating content has the maximum flexural strength of 474.28 f 16.38 MPa and the highest relative density of 94.62 f 0.89 %. This work can not only obtain a great modification effect, but also promote the dense sintering of Si3N4 ceramics during subsequent stages, which provides a constructive method for modifying Si3N4 powders to achieve photopolymerization.