Synthesis of silicon-substituted hydroxyapatite using hydrothermal process

Abstract

An alternative route for preparing silicon-substituted hydroxyapatite powders Ca10(PO4)6−x(SiO4)x(OH)2−x (Si-HAp); using different content of SiO4 (0.588–0.48M) in the aqueous solution of Si precursor was investigated. Tetramethylammonium silicate (TMAS) was used as a silicon precursor. The experiments were carried out via conventional hydrothermal treatments at 150°C for 10h. The Si-HAp nanoparticles obtained were characterized by X-ray diffraction (XRD), Fourier transform IR spectroscopy (FTIR), inductively coupled plasma AES (ICPAES) and scanning electron microscopy (SEM) techniques. A drastically decrease of the diffraction was not observed by increasing the Si content in the structure of the hydrothermally Si-Hap particles produced. A detailed structural analysis conducted by Rietveld refinement indicated that the incorporation of Si occurred in hydroxyapatite (HAp) lattice by partially replacing phosphate (PO43−) groups with silicate (SiO44−) groups. Raman and X-ray photoelectron spectroscopy (XPS) analysis confirmed the substitution of PO43− by SiO44− in the Si-HAp structure. The crystallite size decreases by increasing the Si molar content in the hexagonal HAp structure. TEM observations revealed that the Si-HAp produced have a high crystallinity. A slight decrease of the particle size of the Si-HAp compared to pure HAp was observed (from 60–100nm to 40–70nm). The morphological analysis revealed that all the SiHAp powders prepared have the rod-like shape. Additionally, a slight decrease in both length and diameter of nanorods was observed by increasing the silicon content, the minimum size obtained for the powders containing the largest amount of Si (20Si-HAp) 25 and 70nm. The presence of Si in the structure of the Si-HAp favored densification of the compacts treated at high temperature 1200°C in comparison with pure HAp.