2. Thesis and Dissertations
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Item Influence of Fe3+ and Mn2+ Ions on Structural, Thermal, Optical and Mechanical Properties of Mixed Alkali Zinc Borate Glass System(National Institute of Technology Karnataka, Surathkal, 2020) Subhashini; Shashikala, H D.; Udayashankar, N K.The thesis contains the systematic study on the synthesis and characterization of two and three alkali zinc borate glass systems prepared by melt-quenching method. The structural, optical, thermal and mechanical properties are studied in detail. The non-linearity observed in the mechanical, thermal and structural properties of alkali zinc borate glasses with nominal composition 5Li2O-(25-x)K2OxNa2O-60B2O3-10ZnO (x= 0, 5, 10, 15, 20 and 25 mol %) strongly suggests that there exists a strong mixed alkali effect (MAE) in this systems. It is also observed that the MAE is much stronger in three alkali doped system compared to that of two alkali doped glass system. The TMO doped 5Li2O-xK2O-(25-x)Na2O-60B2O3-(10-y) ZnOyTMO (x= 0 and 5 mol% and y= 0 and 0.1 mol%, TMO= Cr2CO3, MnO2, Fe2O3, Co3CO4, and Ni2CO3) glass system revealed the presence of transition metal ions in specific valence and coordination states in the glass matrix. This results in varied optical absorption and hence, is responsible for the colour of the prepared glasses. Chromium and cobalt in both two alkali and three alkali glass matrix favors high valence and coordination states and therefore exhibit the intense colour. The detailed comparative studies of Fe3+ and Mn2+ ions doping on the properties of two alkali 5Li2O-25Na2O-60B2O3-(10-y)ZnO-yTMO (y = 0, 0.1, 0.3, 0.5, 0.7 and 0.9 mol%, TMO= Fe2O3 and MnO2) glass system with that of the three alkali 5Li2O-xK2O-(25-x)Na2O-60B2O3-(10-y)ZnO-yTMO (x = 0 and 5 mol%, y= 0, 0.1, 0.3, 0.5, 0.7 and 0.9 mol%, TMO= Fe2O3 and MnO2) glass system is done. Fourier Transform Infrared (FTIR) and Raman spectroscopy studies reveal that both Fe2O3 and MnO2 act as network modifiers. Both Fe2O3 and MnO2 are observed to enhance the thermal stability of these system of glasses. These glass systems therefore are good host materials for optical fiber fabrication which yield a crystal-free fiber. Optical band gap energy, Eg, of the studied glass systems is found to reduce with increasing Fe2O3 and MnO2 content. Mechanical strength and fracture toughness of the prepared glass samples determined using Vickers micro-indentation technique, exhibit better mechanical properties with the incorporation of Fe2O3 and MnO2 content. The inclusion of Fe2O3 and MnO2 has proved to be of great importance intailoring the properties of the glass systems to make them promising candidates for optical filters.Item Synthesis, optimization and investigation of properties of BaO-P2O5 and BaO-CaF2-P2O5 glasses with and without silver nanoparticles(National Institute of Technology Karnataka, Surathkal, 2017) N, Manoj Kumar; Shashikala, H. D.This thesis reports synthesis, optimization and investigation of properties of metaphosphate BaO-P2O5 and BaO-CaF2-P2O5 host glasses and these glasses embedded with silver nanoparticles. Host glasses were prepared by conventional melt-quenching technique. Taguchi based grey relational analysis was used in the present study to simultaneously optimize the multiple performance characteristics of CaF2 added ternary barium phosphate glasses. This method helped to obtain optimal parametric combination for best performance characteristics of samples with minimum number of experiments. The investigated physical, structural, mechanical, optical and thermal properties of samples indicated that these properties strongly depended on CaF2 content. The sample with optimized composition, 30 mol% BaO–20 mol% CaF2–50 mol% P2O5 showed improved physical, elastic, mechanical, optical and thermal properties with thermal stability parameter above 100 ◦C. Hence, the above mentioned glass is suitable for fiber fabrication. Glasses doped with silver oxide and tin oxide were prepared by conventional melt-quenching technique but following a different synthesis route, in which silver nanoparticles of different sizes were embedded upon subsequent heat treatment at different temperatures and time durations. The formation, growth and distribution of silver nanoparticles in the glass matrix appeared to be both temperature and time dependent. Evolution in optical properties of prepared glasses were examined to understand the mechanism of cluster development and growth of silver nanoparticles. Size, morphology and distribution of embedded silver nanoparticles in the glass matrix were investigated using transmission electron microscope (TEM). Noticeable improvement was observed in elastic and mechanical properties of glass-metal nanoparticle composite with increase in concentration and size of embedded nanoparticles, which could be attributed to the improvement in strength of glass matrix and ease of plastic flow.