Dissolution mechanisms of β-tricalcium phosphate doped with monovalent metal ions

Abstract

The effects on solubility of the substitution of monovalent metal ions (Li+, Na+, and K+ ions) at the Ca sites in β-tricalcium phosphate (β-TCP) were investigated by immersion of β-TCP powder doped with metal ions in saline, and the dissolution mechanisms of these samples were inferred from the results of dissolution tests and from observations of the crystal structures. β- TCP powder doped with Li+, Na+, and K+ ions (Li-TCP, Na-TCP, and K-TCP) had a lower solubility than pure β-TCP powder, and the solubility decreased with an increase in the amount of metal ions. This decrease in solubility can be attributed to an improvement in crystal structure stabilization upon the substitution of monovalent metal ions at the Ca(4) sites and vacancies in β-TCP, and the resultant occupancy of Ca2+ and metal ions at all Ca sites in the β-TCP structure. However, the dissolution behavior of Li-TCP differed from that of Na-TCP and K-TCP because the atomic arrangement between the Li(4) sites and oxygen was less stable than that between the Na(4) or K(4) sites and oxygen. In addition, the solubility of β-TCP doped with divalent metal ions was lower than that of β-TCP doped with monovalent metal ions because the structural stability of β-TCP doped with divalent metal ions was higher than that of β-TCP doped with monovalent metal ions. These results show that the solubility and dissolution mechanisms of β-TCP doped with metal ions were significantly influenced by the crystal structure stabilization and atomic arrangement of doped β-TCP. © 2010 The Ceramic Society of Japan.