Studies Of Bioactive Glass-ceramics With High Bioactivity And Low Coefficient Of Thermal Expansion

In this article seven kinds of bioactive glass-ceramics which designed for suitable mechanical properties and bioactivity were obtained by sol-gel method. As a typical type of Na2O-CaO-SiO2-P2O5bioglass,45S5was the basic component of the bioactive glass-ceramics. Then we replaced6mol%CaO of45S5by6mol%K2O, MgO, B2O3, TiO2, CaF2, NH4HF2to be the components of the other six kinds.Then the microstructures, mechanical properties were investigated by XRD, SEM, FTIR, thermal expansion instrument, micro hardness instrument, electron-tensile tester and the bioactivity when soaked in simulated body fluid for different time was also researched.The results showed that after stabilization, the glass powders which were not treated by crystallization were most made of amorphous phase with a small part of crystalline phase NaNO3due to the fact that the temperature of the stabilization treatment was under that of the decomposing temperature of NO3-1. Moreover, after the crystallization treatment, the seven kinds of bioactive glass-ceramics could all separate NaxCa6-0.5xSi6O18out, in which Na6Ca3Si6O18was the main crystal phase and x ranged from4to6. The grain in the crystal phase was granular, clumpy or strip. There were a large number of connected holes in the glass-ceramics due to sol-gel process.The addition of the seven various elements all improved the glass-ceramics’ bending strength. Meanwhile the increase of the bending strength was minimum with the addition of K2O while it was maximum with the addition of CaF2whose bending strength was6.7times as that of the original glass-ceramic. Although the elastic modulus was increased with the addition of MgO, the introduction of other elements had little effect on it. The fracture toughness of glass-ceramics all decreased due to the addition of other elements. At the same time, with the addition of other elements the microhardness of glass-ceramics had all been greatly increased while the microhardness of N6glass-ceramic achieved the maximum value that was7.3times as the original glass-ceramic. So the CaF2was efficiently in improving the micro hardness of glass-ceramics. The coefficient of thermal expansion of the seven kinds of bioactive glass-ceramics mainly ranged from9.1×10-6/℃to12.5×10-6/℃, approximately to that of titanium alloys. So these glass-ceramics are suitable to be used as coating material on titanium or titanium alloys surface.After immersed the powder of the seven kinds of bioactive glass-ceramics in simulated body fluid for2days, carbonated hydroxyapatite deposition was founded on their surfaces, which showed that their bioactivity was good enough while the bioactivity of N3was lower than other samples.21days later the surface of N6was almost completely covered by granular carbonated hydroxyapatites. After21days a thick layer of apatite appeared on the surface of N6glass-ceramic.Considered from mechanical properties, bioactivity and the coefficient of thermal expansion the N6glass-ceramic with the addition of6mol%CaF2is suitable to be used as titanium or titanium alloys coating material.