Kinetics of Dissolution of β-Tricalcium Phosphate

The dissolution kinetics of β-tricalcium phosphate (β-TCP) was investigated at 37 °C using the constant composition (CC) method over a range of undersaturation. The rates decreased markedly with time despite the sustained driving force and eventually approached zero, indicating a critical condition in the dissolution process. The calculated reaction order with respect to relative undersaturation, 5.5, suggested a surface-pit (polynucleation) mechanism of β-TCP dissolution. The interfacial tension between β-TCP and the solution phase obtained from this model, γSL = 3.8 mJ m-2, was consistent with its dissolution mechanism and relatively high solubility. The addition of magnesium or zinc ions retarded β-TCP dissolution; the latter completely suppressing the reaction at a concentration as low as 2 × 10-6 mol L-1.