Infusion of Ag-Ion from Aqueous Solution into Solid Calcium Phosphate of Hydroxyapatite (HA) Crystal Structure

In contrast to extensive literature concerning Ag incorporation in hydroxyapatite, HA, while the phosphate approximated to stoichiometry of Ca10(PO4)6(OH)2, with added Ag has been precipitating from an aqueous solution, the paper presents Ag incorporation through Ag ion infusion from AgNO3 solution into solid HA pressed in pellet and ignited at 800°C. After Ag ions infused into the HA‐solid (crossed the interfacial solution‐solid boundary), they diffused across the crystal structure to a depth of time‐dependent several mm. The path of Ag diffusion in the solid HA was recorded using SEM‐EDS point analyses of Ag, Ca, P, EDS‐linear analyses of those elements, and elemental mapping. Time‐dependent concentrations of Ag+, Ca2+, and PO43− in AgNO3 solutions were also analyzed. The appearance of Ag in the crystalline HA with simultaneous local depletion in Ca and phosphate recorded as P, observed by EDS with simultaneous appearance of Ca2+ and PO43− ions and a decrease in Ag+ concentration in AgNO3 solution led the authors to a conclusion that Ag+ for Ca2+ substitution supported by PO43− charge balancing in the crystalline HA was in process. The HA particles in the section of the pellet without Ag had a uniform shape and size approximated to 300–400 nm. SEM image of the HA solid section, where Ag ions appeared was characterized by irregular aggregates of smaller crystals with sporadically present large, shaped in prism blocks identified by the XRD as Ag3PO4.