Kinetics of hydroxyapatite precipitation at pH 7.4 to 8.4
1988; Elsevier BV; Volume: 52; Issue: 7 Linguagem: Inglês
10.1016/0016-7037(88)90012-9
ISSN1872-9533
AutoresWilliam P. Inskeep, J. C. Silvertooth,
Tópico(s)Crystallization and Solubility Studies
ResumoThe rate of hydroxyapatite (HAP) precipitation was studied using a reproducible seeded growth technique under pH stat conditions. Thirty different experiments were performed at initial Ca2+ and PO43− concentrations ranging from 0.37–0.86 and 0.29–1.0 mmol L−1, respectively, ionic strengths from 0.015–0.043 mol L−1, HAP seed concentrations from 7.1–28.4 m2 L−1, temperatures from 10–40°C, and pH from 7.4 to 8.4. Initial rates expressed as mole HAP L−1 s−1 were used to test several empirical rate equations and derive a rate equation based on experimentally determined reaction orders. The rate equation: R = kfsγ2γ3[Ca2+][PO43−], where R = rate of HAP precipitation (molHAPL−1s−1), kf = rate constant (L2 mol−1m−2s−1), γ2 and γ3 = divalent and trivalent ion activity coefficients, s = surface area (m2L−1), and brackets = concentrations of Ca2+ and PO43− (mol L−1), was derived based on the reaction orders with respect to S, [Ca2+] and [PO43−]. The equation was also verified using the integral method, and the average value for the precipitation rate constant was 173 ± 11 L2 mol−1m−2s−1. The Arrhenius activation energy was 186 ± 15 kJ mol−1, indicative of a surface controlled precipitation mechanism. We speculate that the rate limiting steps include migration of surface Ca2+ and HPO42− into lattice vacancies, with subsequent dehydration and incorporation into the crystal lattice.
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