Study On Preparation And Bioactivity Of β-Ca₂SiO₄ Ceramics

Since the bioactive glass was invented by Hench in 1971, many Ca-Si-based ceramics and glasses have been widely investigated as bone repair and replacement materials. Among them,β-dicalcium silicate (β-Ca₂SiO₄) possesses good bioactivity, degradability and cytocompatibility, as well as the characteristics of hydration. Therefore, it is expected to be an excellent material for bone repair and replacement. However,β-Ca₂SiO₄ is the metastable phase at room temperature. In conventional means, theβ-Ca₂SiO₄ ceramics were usually prepared through the high-temperature calcination and quenching with stabilizer mixing, in which high energy and long time consumption are necessary. In this thesis, theβ-Ca₂SiO₄ ceramics were prepared by conventional and microwave-sintering methods, respectively. The raw materials, sintering temperature and stabilizer were examined. The bioactivity of the as-preparedβ-Ca₂SiO₄ ceramics were evaluated by soaking it in simulated body fluid (SBF) for various periods. Results obtained from this work are described as follows:(1) Theβ-Ca₂SiO₄ ceramics are firstly prepared by using conventional method. Their microstructure and phase compositions are examined. The results show that the addition of stabilizer (Ca3(PO4)2) is the key reason to the stabilization ofβ-Ca₂SiO₄ at room temperature. Theβ-Ca₂SiO₄ will transform toγ-Ca₂SiO₄ if the stabilizer was not added. With the stabilizer content increasing, the stability ofβ-Ca₂SiO₄ is enhanced. Theβ-Ca₂SiO₄ transforms toα'L-Ca₂SiO₄ when the stabilizer content is more than 1%. The sintering temperature is another important factor to the stabilization ofβ-Ca₂SiO₄. When the sintering temperature is below 1340℃, theβ-Ca₂SiO₄ transforms toα'L-Ca₂SiO₄. With the increasing of the sintering temperature, theβ-Ca₂SiO₄ phase in ceramic becomes stable. Meantime, the porosity and pore size of theβ-Ca₂SiO₄ ceramic are decrease. The density of ceramic increase and its surface tend to smooth.(2) A novel process to prepareβ-Ca₂SiO₄ ceramic is invented by combining the microwave-sintering and spray-drying technologies, which is fast, energy-saving and efficient. In the new process, the synthesis temperature of theβ-Ca₂SiO₄ ceramic is decreased to 900℃, and the sintering time is reduced to 30mins. In addition, the stabilizer is not the only factor contributing to the stability ofβ-Ca₂SiO₄. Both the nano-effect of materials and the nonthermal effect of microwave are very important to the stabilization ofβ-Ca₂SiO₄. As same as the conventional means, theβ-Ca₂SiO₄ also transforms toα'L-Ca₂SiO₄ when the stabilizer content is more than 1%.(3) The results obtained from the SBF soaking test confirm that theβ-Ca₂SiO₄ ceramics prepared using the new process can induce the deposition of hydroxyapatite on its surface, indicating good bioactivity.From the results described above, it can be seen that comparing with the conventional synthesis method, the new process to prepareβ-Ca₂SiO₄ ceramic is fast, energy-saving and efficient. In the new process, the synthesis temperature ofβ-Ca₂SiO₄ ceramic is significantly decreased, the sintering time is obviously shorten, theβ-Ca₂SiO₄ can be stabilized at room tempertaure even without the stabilizer.