Introducing a surface compressive stress layer is an effective way to enhance the strength of brittle ceramics, yet achieving such prestressing intrinsically in monolithic oxides ceramics remains challenging. Here, we report a novel method called oxygen-vacancy compensation prestressing (OVCP) to generate in situ surface prestressing in zirconia-toughened alumina (ZTA) ceramics. Oxygen-vacancy-rich ZTA was first produced by vacuum hot pressing, followed by air annealing to induce surface re-oxygenation and form an oxygen-charged layer (OCL). The optimized treatment increased the flexural strength to 1679 ± 78 MPa, representing a 31% improvement over the unannealed state. Oxygen-vacancy compensation during annealing induces lattice expansion in the near-surface region. Constrained by the less-oxidized interior, this lattice expansion is converted into a residual compressive stress field that suppresses bending-induced failure. A simplified bilayer model quantitatively supports the experimentally observed strengthening behavior. These findings establish oxygen-vacancy-regulated lattice expansion as an effective mechanism for intrinsic surface prestressing and provide a simple, interface-free route for strengthening oxide ceramics.

Silicon carbide (SiC) powders and silicon nitride (Si₃N₄) powders are critical raw materials for advanced ceramic technology and industry. There are two challenges in their synthesis and production: (ⅰ) phase formation of nano SiC powders due to harsh reaction temperature and (ⅱ) preparation of high-purity Si₃N₄ powders due to difficulties in removing trace oxygen impurities. Combustion synthesis is a cheap, scalable method for producing SiC and Si₃N₄ powders. However, there are two additional challenges: (ⅲ) combustion synthesis of SiC requires intense external energy input due to the weak exothermic reaction between Si and C and (ⅳ) combustion synthesis of Si₃N₄ requires a diluent to slow down the self-accelerated reaction and fully convert Si to Si₃N₄ due to the strong exothermic reaction between Si and N₂. Here, we reported a new combustion co-synthesis of nano SiC and high-purity Si₃N₄ powders in one chamber, which addressed all four challenges mentioned above: (ⅰ) the production of nano SiC powders resolved by fast synthesis, (ⅱ) purified pink-grade Si₃N₄ powders using carbon as an efficient high-temperature oxygen getter, (ⅲ) ignited Si–C combustion by a strongly exothermic Si–N₂ reaction, and (ⅳ) more controllable Si–N₂ combustion with less diluent usage and less residual Si. We demonstrated nano β-SiC powders with ~30 nm primary particle size and high-purity pink-colored β-Si₃N₄ powders with oxygen impurity content down to 0.46 wt%. This study not only offers practical solutions to the production of high-quality SiC and Si₃N₄ powders but also refreshes the design of combustion synthesis with new possibilities and improved controllability.

Porous silicon nitride ceramics have attracted a considerable attention due to their excellent overall performance, but poor porosity homogeneity and structural shrinkage induced by prolonged high temperature sintering limit its further application. Herein, as a three-in-one solution for the above issues, for the first time we develop a novel approach that integrates the merits of gelcasting-SHS (self-propagating high-temperature synthesis) to prepare porous Si₃N₄ ceramics to simultaneously achieve high porosity, high strength, high toughness, and low thermal conductivity across a wide temperature range. By regulating the solid content, porous Si₃N₄ ceramics with homogeneous pore structure are obtained, where the pore size falls inbetween 1.61 and 4.41 μm, and the elongated grains are interlaced and interlocked to form micron-sized coherent interconnected pores. At the same time, porous Si₃N₄ ceramics with porosity of 67.83% to 78.03% are obtained, where the compressive strength reaches 11.79 to 47.75 MPa and fracture toughness reaches 1.20 to 6.71 MPa·m^1/2.