Preparation and Properties of Neodymium-Modified High-Temperature Resistant Phosphoaluminate Adhesive

To address the drawbacks of conventional aluminum phosphate high-temperature adhesives, including mismatched thermal expansion coefficients with alumina ceramics and severe performance degradation after repeated high-low temperature thermal cycles, neodymium doping was utilized to modify and optimize the aluminum phosphate-based adhesive in this work. Systematic mechanical property tests identified the optimal molar ratio of Nd/Al as 3:7. Combined with physical property characterization, phase evolution investigation and microstructure observation, the thermal reaction and bonding mechanisms of the modified adhesive were revealed. Upon high-temperature heat treatment, massive crystallization of AlPO₄ and NdPO₄ occurs above 900℃, giving rise to grain boundary pinning and dispersion strengthening effects. At 1300℃, a multi-phase skeleton consisting of monoclinic NdPO₄, orthorhombic AlPO₄ and orthorhombic Al₅BO₉ is constructed, which remarkably enhances the high-temperature mechanical performance and thermal stability of the adhesive. The bonding strength of the modified adhesive sintered at 1300℃ reaches 44.5MPa, representing a 92.6% improvement compared with the unmodified sample. After 20 thermal cycles between room temperature and 1300℃, the residual bonding strength is 27.89MPa with a retention rate of approximately 68.4%, demonstrating significantly improved thermal cycling resistance. Moreover, the thermal expansion coefficient of the modified adhesive stabilizes at (7–7.5)×10^-6K^-1, achieving greatly improved compatibility with alumina ceramics whose thermal expansion coefficient is 8.5×10^-6K^-1. The as-prepared modified adhesive can meet the service requirements of aerospace and other high-temperature industries, and provides experimental foundations for the further development and application of aluminum phosphate high-temperature resistant adhesives.