New method for the protection of calcareous cultural heritage stones by aluminium phosphate modified hydroxyapatite

Carbonate stones are widely distributed, and there are numerous world cultural heritage sites composed of carbonate stones, which are highly susceptible to acid rain erosion and thermal stress due to the nature of calcium carbonate. In this study, three concentration gradients of diammonium phosphate and aluminium chloride solutions were employed to produce aluminum phosphate modified hydroxyapatite material. The compatibility and acid resistance of the material were evaluated by wettability, ultrasonic velocity, porosity, water vapor permeability, color change, and simulated acid rain corrosion, and the protection mechanism was clarified by microscopic analysis methods such as FTIR and SEM-EDS. It was found that the hydroxyapatite reinforcement coating modified with aluminum phosphate could improve the mechanical properties and the resistance to acid rain of the matrix, and the material has good compatibility with the reinforced carbonate matrix. Hydroxyapatite reinforcement coating modified with aluminum phosphate has good potential for application in the prevention of surface weathering of carbonate stones.