Calcium phosphate-encapsulated silver powder

Calcium phosphate encapsulated silver powder was obtained by heterogeneous nucleation during treatments of dispersed silver first with solutions of Ca(NO3)2 and then with Na2HPO4. Before treatment silver powders were functionalized with 3-mercaptopropionic acid and dispersed in a precipitation medium so the carboxylate groups could serve as nucleation sites. The ratio Ca/P in the coating increases with the number of treatment cycles. In contrast, calcium phosphate precipitation by slow release of phosphate ions via hydrolysis of tri(4-nitrophenyl)phosphate in a solution of Ca(NO3)2 results in homogeneous nucleation only; coating does not form on silver particles.