Some of the formulations of apatitic calcium phosphate bone cements are based on the hydrolysis of α-tricalcium phosphate (α-Ca3(PO4)2, α-TCP). In this work the hydrolysis kinetics of α-TCP are studied, taking into account the particle-size distribution of the initial powder, to identify the mechanisms that control the reaction in its successive stages. The temporal evolution of the depth of reaction is calculated from the degree of reaction data, measured by X-ray diffractometry. A kinetic model is proposed, which suggests the existence of two rate-limiting mechanisms: initially, the surface area of the reactants and, subsequently, the diffusion through the hydrated layer formed around the reactants. For the specific particle size and preparation used, the controlling mechanism changeover takes place after 16 h of reaction.
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