Vat photopolymerization 3D printing of Si₃N₄ceramics from submicron powders: dispersion, microstructure, mechanical and dielectric properties

Compared with micron-sized Si₃N₄powders, submicron powders offer significant advantages in sintering processes due to their higher sintering driving force. In this study, Si₃N₄ceramics were successfully fabricated using vat photopolymerization (VPP) combined with pressureless sintering, starting from submicron powders. In this research, an innovative combination of dispersant and plasticizer was utilized, achieving a substantial reduction in the viscosity of slurry. The rheological capability, curing ability, stability, and printing accuracy of slurries with varying solid loadings were thoroughly investigated. Among them, the Si₃N₄slurry with a solid loading of 40 vol% exhibits the optimal viscosity of approximately 0.9 Pa s and the best curing thickness of 30 μm. Subsequently, the effect of sintering temperature on the linear shrinkage, mechanical properties, microstructure, and dielectric properties of Si₃N₄ceramics was systematically examined. After sintering at 1650 °C for 2 h, the Si₃N₄ceramics achieve the highest relative density (80.20 ± 2.31 %) and flexural strength (355.73 ± 26.02 MPa). Moreover, the real part of permittivity of the samples is less than 4.0, the imaginary part is less than 1.6, and the dielectric loss is less than 1.0. Additionally, the transmittance of electromagnetic waves in the frequency range of 2.0–18.0 GHz through plates of different thicknesses was simulated. The samples sintered at 1700 °C demonstrate the best electromagnetic wave transmittance. This study holds great significance for reducing the viscosity of slurries containing submicron Si₃N₄powders and for the fabrication of Si₃N₄ceramics with excellent mechanical and dielectric properties via 3D printing.