Preparation and performance analysis of an inorganic adhesive for alumina ceramic joining with a wide operating temperature range

In this study, a heat-resistant adhesive named APSB, designed for Al₂O₃ ceramics with a wide operating temperature range, was synthesized using Al(OH)₃ and H₃PO₄ as reaction precursors, and Cu, Si, and B₂O₃ as inorganic modifying fillers. The thermal stability, bonding strength, microstructure, and phase composition of adhesives with varying P/Al and filler ratios were systematically investigated. The results indicated that different P/Al ratios in the unmodified AP adhesive significantly affected its thermal stability and bonding performance. Within the temperature range of 600 °C–1200 °C, the AP binder with P/Al = 2.5 exhibited the best thermal stability, with a maximum mass loss of 57.4 %, while the adhesive with P/Al = 3.75 showed the poorest thermal stability, with a maximum mass loss of 85.6 %. Furthermore, at 600 °C, their shear strengths were 6.89 MPa and 3.02 MPa, respectively. At 1200 °C, the shear strength of the former decreased to 2.54 MPa, whereas the latter failed completely. For the APSB adhesive, after heat treatment at 1200 °C, the shear strength reached a maximum of 23 MPa. It maintained a shear strength of over 4 MPa across the temperature range of 600 °C–1500 °C, with a maximum mass loss of only 29.8 %. This demonstrates a significant improvement. The enhanced shear strength is primarily attributed to the addition of Si and B₂O₃, which inhibit the formation of metaphosphates and provide substantial mass and volume compensation, thereby improving the compositional stability of the adhesive matrix. Additionally, at high temperatures, intensified diffusion between the oxidation products in the binder and the Al₂O₃ ceramic substrate elements leads to the formation of effective chemical bonds. This adhesive shows great potential for applications in Al₂O₃ ceramic joining.