Three dimensional (3D) printing technology by direct ink writing (DIW) is an innovative complex shaping technology, possessing advantages of flexibility in fabrication, high efficiency, low cost, and environmental-friendliness. Herein, 3D printing of complex alumina ceramic parts via DIW using thermally induced solidification with carrageenan swelling was investigated. The rheological properties of the slurry under different thermally-induced modes were systematically studied. The solidification properties of thermally-induced pastes with varying contents of carrageenan were optimized. The experimental results showed that the optimized paste consisting of 0.4 wt% carrageenan could be rapidly solidified at about 55 °C, which could print inclined-plane more than 60° in vertical without support, resulting in better homogeneity of the green body. A nearly pore-free structure was obtained after sintering at 1600 °C for 2 h.

The Si₃N₄ ceramics were prepared in this study by gas pressure sintering (GPS) and spark plasma sintering (SPS) techniques, using 5 wt.% Yb₂O₃–2 wt.% Al₂O₃ and 5 wt.% CeO₂–2 wt.% Al₂O₃ as sintering additives. Based on the difference in sintering methods and sintering additive systems, the relative density, phase composition, phase transition rate, microstructure, mechanical properties, and thermal conductivity were comparatively investigated and analyzed. SPS proved to be more efficient than GPS, producing higher relative density, bending strength, hardness, and thermal conductivity of Si₃N₄ ceramic with both additive systems; however, the phase transition rate and fracture toughness were lower. Similarly, higher bending strength, hardness, and thermal conductivity were achieved with Yb₂O₃–Al₂O₃ than CeO₂–Al₂O₃ in the case of GPS and SPS, and only the relative density, fracture toughness, and phase transition rate were lower.