Production of 45S5 bioactive glass obtained silica from rice husk ash doped with MgO,SrO and Al2O3 and its characterization

Silica (SiO2) is a basic raw material which is widely used in electronics, ceramics and polymer material industries. Recently silica is also used in biomaterial (bioactive glasses and dental composites) production. Silica is obtained from silicate solutions which are produced by high energy requiring processes such as smelting quartz at high temperatures at 1400-1500°C and ore enrichment. Pure silica also can be produced in laboratory conditions from precursor molecules like tetraethylorthosilicate (TEOS). However, the use of these precursor molecules is not economically viable. Recently, the use of agricultural waste materials containing SiO2 is considered as an alternative to these precursor. The most remarkable one of these agricultural waste materials is rice husk. Rice husks contain approximately 20% amorphous SiO2 and rice husk ash (RHA) which is obtained by burning the rice husks at different temperatures, contain approximately 87-97% SiO2. Pure silica can be produced from RHA by acid washing and alkali extraction processes, respectively. Burning rice husks cause environmental pollution and loss of valuable raw material which has use in different industrial and scientific applications. RHA is recycled in a low extent in metallurgical industry. Studies on the evaluation of rice husk and its ash as a silica source are in progress. Bioactive glasses, which contain silica, are used as bone defect fillers for bone repair and restoration, and bone grafting during maxillofacial surgery. Bioactive glasses basically consists of silicon, calcium, phosphorus and sodium oxides. Metal ions added affect the properties (mechanical, bioactivity, cell proliferation) of bioactive glasses. Bioactive glasses are inorganic glasses that can bond to living tissues (bone, ligament, muscle ) through the formation of hydroxyapatite layer at the glass/tissue interface. The levels of bioactivity, that is, the rate of apatite layer formation, and the apatite like layer thickness depend on the glass chemical composition and on the morphological parameters, such as surface area, pore size, and pore volume. Production of SiO2 from RHA will be done in a batch reactor by sodium hydroxide extraction and acidification of obtained silicate solution with hydrochloric acid. Produced SiO2 was used as SiO2 source in 45S5 bioactive glasses. These bioactive glasses were produced according to the melting method at 1450°C with CaO, P2O5, Na2O sources and RHA based SiO2. RHA SiO2 contains different metal ions (Mg, Mn, Ti, Fe, Cu) at 3% as impurity which are compatible to human body. Whereas, SiO2 which will be produced in this project contains clear majority of these ions. Within the aim of the project, mechanical properties (Vickers), bioactivity (SEM, XRD, behavior in artificial body fluid) of bioactive glasses, produced from RHA SiO2 that contain these metal ions, was investigated. Besides naturally occurring impurities of produced SiO2 Sr, Mg, Al that are investigated previously was added to bioactive glasses and their effects on mechanical and in vitro properties (mentioned above) of bioactive glasses will be studied. 45S5 bioactive glasses produced from commercial SiO2 and RHA SiO2, which are modified with these ions, will be compared according to their mechanical and chemical properties. In this study, valued SiO2 was produced from RHA, which is not an economically viable material, with purity and properties suitable to be used in bioactive glass. By doing so; recycling of RHA was provided and for the protection of the environment and economy contribution was done.