•A single phase of the LZ7C3 ceramic with a pyrochlore structure was successfully fabricated.•The dense corrosion layer can effectively suppress further corrosion attacks by molten V2O5.•The lower concentration of V2O5 in the Na2SO4+V2O5 salt mixture is responsible for the development of t-ZrO2.The hot corrosion behavior of the La2(Zr0.7Ce0.3)2O7 ceramic with a pyrochlore structure was evaluated at selected temperatures of 800, 900 and 1000 °C. The phase constituents and microstructure of the corroded La2(Zr0.7Ce0.3)2O7 ceramic were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. The main corrosion products on the surface of the La2(Zr0.7Ce0.3)2O7 ceramic in V2O5 were (La,Ce)VO4 and m-ZrO2 at 800, 900 and 1000 °C, and the corrosion-layer thickness decreased whereas the size of the corrosion products increased gradually as the corrosion temperature increased. For the Na2SO4+V2O5 salt mixture, the main corrosion products were mainly (La,Ce)VO4 and t-ZrO2 at 800, 900 and 1000 °C on the surface of the La2(Zr0.7Ce0.3)2O7 ceramic; Na2SO4 may have remained on the ceramic surface after corrosion at 800 °C and reacted completely with the increase of the corrosion temperature. The chemical reactions between the La2(Zr0.7Ce0.3)2O7 ceramic and molten V2O5 or Na2SO4+V2O5 salt mixture are the primary corrosion mechanisms for the degradation of the La2(Zr0.7Ce0.3)2O7 ceramic. The lower concentration of V2O5 in the Na2SO4+V2O5 salt mixture compared to the case of V2O5 corrosion alone is significantly responsible for the development of t-ZrO2.La2O3 can readily react with V2O5 to form LaVO4, followed by CeO2 interacting with V2O5 to form CeVO4. La2O3 is easier to react with NaVO3 in compared with the reaction between La2Zr2O7 and V2O5. The calculated results are in good agreement with the experimental results.

The hot corrosion behaviors of Sr(Y0.05Yb0.05Zr0.9)O2.95 (SYYZ) ceramic were investigated in Na2SO4, V2O5, and Na2SO4 + V2O5 salts mixture, respectively. Na2SO4 did not react with SYYZ ceramic at 900, 950 and 1000 °C. m-ZrO2, YVO4 and YbVO4 were the main corrosion products on the SYYZ ceramic surface in V2O5 at 800 and 900 °C, whereas Sr3V2O8 and t-ZrO2 appeared at 1000 °C. In Na2SO4 + V2O5 salts mixture, the corrosion products were Sr3V2O8 and t-ZrO2 at 800 and 900 °C on the SYYZ ceramic surface, however, a new phase of SrZrO3 developed at 1000 °C. The phase transformation and chemical interaction are the primary corrosion mechanisms for degradation of SYYZ ceramic.

The joining of two pieces of SiC-based ceramic materials (SiC or Cf/SiC composite) was conducted using Ti3SiC2 as filler in vacuum in the joining temperatures range from 1200 °C to 1600 °C. The similar chemical reactions took place at the interface between Ti3SiC2 and SiC or Cf/SiC, and became more complete with joining temperature increases, and with the consequent increased joining strengths of the SiC and Cf/SiC joints. Based on the XRD and SEM analyses, it turns out that two reasons are most important for the high joining strengths of the SiC and Cf/SiC joints. One is the development of layered Ti3SiC2 ceramic, which has plasticity in nature and can contribute to thermal stress relaxation of the joints; the other is the chemical reactions between Ti3SiC2 and the base materials which result in good interface bonding.

•Both 4.5YSZ and 4.5YSZ+20 wt%Al2O3 powders are used as fillers to join SiC ceramic.•The SiC joint using 4.5YSZ+20 wt%Al2O3 filler possesses higher flexural strength.•Reaction and element diffusion occurred at the SiC/4.5YSZ+20 wt%Al2O3 interface.The SiC ceramic was joined via spark plasma sintering (SPS) using 4.5 wt% yttria partially stabilized zirconia (4.5YSZ) powder and 4.5YSZ+20 wt%Al2O3 powder mixture as fillers. The 4.5YSZ powder was synthesized by sol-gel method. The effects of different filler materials on the microstructure and mechanical properties of the SiC joints were investigated. Based on the X-ray diffraction and scanning electron microscope analyses, as well as three-point bend tests, the SiC joint with 4.5YSZ+20 wt%Al2O3 powder mixture as the filler material possesses higher flexural strength of 107.3 MPa at room temperature. The superior flexural strength of the SiC joint using the 4.5YSZ+20 wt%Al2O3 filler is attributed both to the carbothermic reaction and element diffusion at the SiC/4.5YSZ+20 wt%Al2O3 interface during the joining process.