STRUCTURAL AND OPTICAL PROPERTIES OF SOL-GEL DERIVED HYDROXYAPATITE FILMS IN DIFFERENT STAGES OF CRYSTALLIZATION AND DENSIFICATION PROCESSES

摘要

Hydroxyapatite (HAp) films, widely used as a biocompatible material for hard tissues repairing, are studied in this paper for a belter control and understanding of the crystallization and densification of sol-gel deposited layers. Calcium nitrate and triethyl phosphite diluted in alcohols were used as calcium and phosphorus precursors. HAp coatings were obtained by spinning method, followed by drying and annealing in the range 130-750 deg C. Specific temperatures of the chemical reactions of HAp formation have been revealed by thermogravimetric analysis (TG-DTA). Structural, chemical and optical characterizations of the films were performed by Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Analysis (EDX) facilities, X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Spectral Ellipsometry (SE). The film crystallinity increases with the annealing temperature above 550 deg C. XRD lines of HAp crystallographic planes become narrow at 750 deg, and correspond to a single crystallographic phase. The film morphology depends not only on annealing history but also on the synthesis parameters. Thus, layers with large grains of well sinterized HAp nano-crystals can be obtained. Using EDX measurements, the Ca/P ratio was found close to the stoichiometric value in the well sinterized HAp grain regions and slightly increased 1.82 for boundary regions between grains. The density of pores usually observed in sol-gel derived films was estimated for different samples using modeling of SE data.