Controllable sintering behaviors of Al2O3 green tapes and co-firing compatibility of Al2O3/YSZ ceramics

As a typical insulating material, Al2O3 serves as the signal isolation device in multi-layer ceramic NOx sensors. However, the application of Al2O3-based insulating materials is limited by the co-firing compatibility between Al2O3 and yttria-stabilized zirconia (YSZ). In the present study, Al2O3 green tapes with different contents of γ-Al2O3 and SiO2–B2O3 (Si–B) are developed to promote the integration of Al2O3-based insulating material and YSZ. The sintering shrinkage of the obtained Al2O3 green tapes is greatly influenced by the ratio of γ-Al2O3 to α-Al2O3 at 1450 °C, e.g., the maximum shrinkage reaches 17.34% when the γ-Al2O3 to α-Al2O3 ratio is 1:2. The addition of Si–B greatly increases the low density of Al2O3 tapes due to the pores generated during the firing process of the ultrafine γ-Al2O3 powders. The sintering density increases to 97.1% when the Si–B content is 15 wt. %, and the sintering shrinkage reaches a relatively higher value of 17.25%. The obtained Al2O3-based insulating materials show a greatly co-firing matching performance with the YSZ green tapes. This work will contribute to further investigation of ceramic co-firing studies.