Preparation and characterization of Na+, SiO44-, and CO32-Co-substituted hydroxyapatite

Abstract

The mechanism of Na+, SiO44-, and CO 32- cosubstitution in hydroxyapatite (HAP) crystal structure was investigated. Several powders were prepared by wet chemical precipitation at 37°C in the presence of different concentrations of sodium silicate in open atmosphere. The powders were characterized using chemical analysis, scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectrometry spectroscopy. Increasing of silicate ions substitutions were associated with increasing of carbonate ions substitutions for phosphates and vacancies of the OH- site. The crystallinity of HAP was reduced as the degree of substitution increased. Silicate substitution was dominated by two charge compensation mechanisms acting simultaneously. Firstly, SiO 44- and CO32- groups were substituted for two PO43- groups. Secondly, SiO 44- group was substituted for one PO43- group and a vacancy formed in the OH- site. A phenomenological relationship between the shift on O-H vibration bands and the degree of silicate substitution was established. This relationship indicated the presence of bent hydrogen bonding between O-H groups and silicate ions. The imperfections introduced by silicon substitution affected the OH- position and motion in the channel, which may play a role in enhancing bioactivity. © 2010 The American Ceramic Society.