Modeling of the hydrolysis of alpha-tricalcium phosphate

Some of the formulations of apatitic calcium phosphate bone cements are bas ed on the hydrolysis of alpha-tricalcium phosphate (alpha-Ca-3(PO4)(2), alp ha-TCP). In this work the hydrolysis kinetics of alpha-TCP are studied, tak ing into account the particle-size distribution of the initial powder, to i dentify the mechanisms that control the reaction in its successive stages. The temporal evolution of the depth of reaction is calculated from the degr ee of reaction data, measured by X-ray diffractometry. A kinetic model is p roposed, which suggests the existence of two rate-Limiting mechanisms: init ially, the surface area of the reactants and, subsequently, the diffusion t hrough the hydrated layer formed around the reactants. For the specific par ticle size and preparation used, the controlling mechanism changeover takes place after 16 h of reaction.