الفهرس 
Aim of the DissertationOnly 14 pages are availabe for public view
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Abstract
Borate based glasses are usually obtained by the conventional melt-quenching technique. The innovative sol-gel synthesis of glassy oxide materials has received great attention, particularly in the field of bioactive glass formation. Fabrication of borate glasses from sol-gel route has limited restrictions at high concentrations of modifier oxides because of difficulty in gel formation. In this dissertation, an aqueous solution route has been developed to prepare borate composites containing CaO, Na2O and P2O5. X-ray diffraction (XRD) and transmission (TEM) electron microscopy coupled with electron diffraction pattern (EDP) were used to identify the nature of products (borate networks) obtained from solution. XRD patterns show that the as-prepared compositions are crystalline matrices. TEM-EDP of selected regions exhibited diffuse intensity rings, in addition to halo diffuse intensity with bright spots. These features indicate that crystalline phases are dispersed in an amorphous phase. The effect of heat-treatment and melting-quench on the microstructure of composites obtained from solution and their physical properties was investigated using differential thermal analysis (DTA), XRD, TEM-EDP, FTIR spectroscopy, 11B MAS NMR and density. Dried powders were heat treated at temperatures 400‒800 ºC for 3 h. XRD patterns revealed formation of crystalline phases. Results of TEM-EDP proved that heat treatment at 700 ºC caused phase transformation with maintaining residual glassy borate network obtained from solution. Quenched solids obtained by melting powders are amorphous. FTIR spectra elucidate that CaO and Na2O modify the borate network forming BO4 and BO3 with non-bridging units, with concentration depending on the molar ratio and heat-treatment temperature. The fraction N4 of four coordinated boron atoms changes with R and can be predicted by treating the composites as if they were mixtures of Na2O‒B2O3 and CaO‒B2O3 matrices. N4 values have been used to calculate the fraction of all units in the glass structure. The results are confirmed by 11B MAS NMR spectra that show the presence of symmetric and asymmetric trigonal BO3 groups. There is a splitting in line shape of [4]B, assuming that different environments of four-coordinated boron are present. Density and molar volume obtained by using mixed matrices concept agree well with the experimental data. In the field of biomaterials, calcium sodium borate glasses with specific composition are applied as bio-scaffold to repair hard and soft tissue defects. Such materials are known as bioactive borate glasses. In the present study, microporous borate glass-ceramic could be obtained from solution route. Bioactivity and degradation were tested in simulated body fluid (SBF) at 37 ºC for different time intervals. Scanning (SEM) and transmission (TEM) electron microscopy, infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to examine the correlation between bioactivity and microstructure. Results of bioactivity testing indicated that the type and concentration of crystalline phases, in addition to concentration of bridging and non-bridging oxygen atoms, are the factors affecting the apatite forming ability and composition degradation. Further, the type of product after reaction in SBF is influenced by the nature of borate network. For melt-derived borate glasses, hydrous species of B‒OH and amorphous calcium phosphate are formed. Microporous borate glass-ceramics exhibited a good in vitro bioactive response through the formation of hydroxyapatite. TEM-EDP proved that the crystalline hydroxyapatite (HA) phase was formed on amorphous phase. The results of this study suggest that the solution-method can be used to prepare microporous bioactive borate glass-ceramics, such as three-dimensional porous scaffolds, which are of particular interest for the clinical application in bone regeneration.