Sealing Performance and Mechanism of a High-Temperature Near-Neutral Sealing Adhesive in the Ternary System of ZrO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>

A high-temperature sealing adhesive was prepared using kyanite, andalusite, and magnesia fully stabilized zirconia (Mg-FSZ) as raw materials and nanozirconia (ZrO2) sol as binder. The adhesive is chemically near-neutral and suitable for bonding acid, neutral, or alkaline materials at 1560 °C. The mineral composition, volume expansion, and air permeability of multiple thermal cycles were analyzed. Results showed that the volume expansion caused by the mullitization of kyanite and andalusite can compensate for the sintering shrinkage high temperature. MgO could gradually desolvatize from the Mg-FSZ particles and react with SiO2 and Al2O3 to produce a stable forsterite and magnesium aluminate spinel. Hence, Mg-FSZ became unstable, and cubic ZrO2 transformed into monoclinic ZrO2 when cooled, leading to a volume expansion of the adhesive, which ensured the sealing effect. A larger critical particle size of Mg-FSZ can provide the adhesive with a more persistent volume expansion during thermal cycles due to the more durable desolvatization of MgO. The nanoZrO2 sol binder can improve the sintering of the adhesive and bonding of the joint, resulting in a low gas permeability.