Reaction mechanism, hygroscopic behavior, and properties of aluminum phosphate adhesive

Abstract

The lack of basic research is a principal reason restricting the widespread application of aluminum phosphate adhesive, such as its reaction mechanism is not yet clear. Herein, we investigate the dissolution behavior of aluminum oxide (Al2O3) in acid aluminum phosphate (AAP) solution and the effects of Al2O3 addition, calcination temperature and phosphorus to aluminum (P/Al) ratio of the AAP solution on the thermal evolution, phase development and hygroscopic behavior of aluminum phosphate adhesive. The dissolution process of Al2O3 in AAP solution is controlled by external diffusion. The thermal evolution of aluminum phosphate adhesives is a complex process that is a function of Al2O3 addition and calcination temperature. Although it is a linear process, many of the reactions are largely coupled and occur simultaneously. The hygroscopic mechanism of aluminum phosphate adhesives is associated to the hydrophilicity of the hydroxyl groups (P–OH). Increasing the calcination temperature and the Al2O3 addition can improve the hygroscopicity resistance properties. Finally, the mechanical and dielectric properties of the quartz fiber cloth reinforced aluminum phosphate matrix composites (SiO2f/aluminum phosphate composites) were also investigated. The results demonstrate that the composites have the characteristics of light weight, high strength, and excellent dielectric properties, suggesting that they have attractive applications in radome materials.