Modeling of the Hydrolysis of α‐Tricalcium Phosphate

Abstract

Some of the formulations of apatitic calcium phosphate bone cements are based on the hydrolysis of ␣-tricalcium phosphate (␣-Ca 3 (PO 4 ) 2 , ␣-TCP). In this work the hydrolysis kinetics of ␣-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.

Preparation of porous apatite granules from calcium phosphate cement

“…CaCO 3 Fig. 2 (a) characteristic XRD trace of granules immediately after production (*CaHPO 4 peaks, rest: apatitic CaP peaks), (b) FTIR spectrum of granules and (c) EXDS spectrum of granules present in the cement powder rapidly participated in this hydrolysis process facilitating the formation of carbonated, apatitic CaP [71]. Although a slow process, CaHPO 4 itself also underwent a similar hydrolysis procedure to the apatitic CaP, and the small amount of precipitated HA present in the cement formulation acted as an accelerator for those hydrolysis processes, which continued at the body temperature till the completion of the cement setting.…”

Influence of Si substitution on the reactivity of α-tricalcium phosphate

“…The crystalline phase composition at each time point was assessed by XRD, (including a JCPDS file #46-0905 for CDHA). The conversion rate was determined by XRD following the procedure proposed by Ginebra et al [39,40] and Rigo et al [41]. It is known that the mass fraction of a crystalline material present in a given sample is proportional to their XRD lines intensities.…”

“…Where I α is the integrated intensity of α-TCP (1 3 2), (1 1 3) or (1 0 7) XRD lines at a determined time, t; I α,0 is the integrated intensity of α-TCP (1 3 2), (1 1 3) or (1 0 7) XRD lines at initial time (t = 0h); M α is the is the mass absorption of α-TCP, 86.43 [40]; M CDHA is the mass absorption of CDHA, 84.97 [40]; w ß is the mass fraction of ß-TCP during setting reaction; w α is the mass fraction of α-TCP at a determined time, t and; w α,0 is the mass fraction of α-TCP at initial time (t = 0h). In this study, the external pattern method was employed [38].…”

“…In this study, the external pattern method was employed [38]. The external pattern used in this work was β-TCP which is present in all samples and do not participate on the setting reaction, thus, its mass fraction is constant during all the process [5,39,40].…”

In situ Synchrotron X-ray Powder Diffraction Study of the Early Hydration of α-tricalcium Phosphate/tricalcium Silicate Composite Bone Cement

“…Furthermore, setting times give us information related to the initial rates of reaction but not the extent of the cement reaction 13 ; therefore, the evolution of the hydrolysis at early stages could be followed by in situ X-ray diffraction (XRD) such as X-ray energy generated by a synchrotron source, which is a powerful tool in the Material Science and Engineering field had been poorly documented in the study of these kinds of reactions, and never employed in the case of α-TCP-based phosphate cements…”