Effect of Niobium Content on the Microstructure and Thermal Properties of Fluorapatite Glass-Ceramics

摘要

Niobium oxide has been shown to improve biocompatibility and promote bioactivity. The purpose of this study was to evaluate the effect of niobium oxide additions on the microstructure and thermal properties of fluorapatite glass-ceramics for biomedical applications. Four glass-ceramic compositions with increasing amounts of niobium oxide from 0 to 5 wt percent were prepared. The glass compositions were melted at 1525 deg C for 3 h, quenched, ground, melted again at 1525 deg C for 3 h and furnace cooled. The coefficient of thermal expansion was measured by dilatometry. The crystallization behavior was evaluated by differential thermal analysis. The nature of the crystalline phases was investigated by X-ray diffraction. The microstructure was studied by SEM. In addition, the cytotoxicity of the ceramics was evaluated according to the ASTM standard F895-84. The results from X-ray diffraction analyses showed that fluorapatite was the major crystalline phase in all glass-ceramics. Differential thermal analyses revealed that fluorapatite crystallization occurred between 800 and 934 deg C depending on the composition. The coefficient of thermal expansion varied from 7.6 to 9.4 X 10~(-6) deg C. The microstructure after heat treatment at 975 deg C for 30 min consisted of submicroscopic fluorapatite crystals (200-300 nm) for all niobium-containing glass-ceramics, whereas the niobium-free glass-ceramic contained needle-shaped fluorapatite crystals, 2 mu m in length. None of the glass-ceramics tested exhibited any cytotoxic activity as tested by ASTM standard F895-84.