Faculty Publications
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Item Optical and mechanical properties of calcium phosphate glasses(Maik Nauka Publishing / Springer SBM compmg@maik.ru, 2014) Venkateswara Rao, G.V.; Shashikala, H.D.Binary calcium phosphate glasses in the system, xCaO-(100 - x) P 2O5 with x = 30, 35, 40, 45, and 50 mol % were prepared by conventional melt quenching technique. The density, molar volume and refractive index of the glasses were found to increase with the increase in CaO content. Structural investigation by FTIR spectroscopy revealed that the substitution of P2O5 by CaO depolymerizes the phosphate glass network by systematic conversion of Q3 structural units to Q2 structural units by breaking the P-O-P links. From the optical absorption studies, the optical band gap values were found to decrease with increasing CaO content which can be due to increase in the concentration of non-bridging oxygens in the glass network. Vickers hardness increased with the calcium oxide content due to densification. The fracture toughness decreases with the increase in CaO content due to the increase in the bond density between the modifying cations and the non-bridging oxygens in the glass network. It was observed that brittleness increases with the addition of CaO content which can be mainly attributed to the decrease in the molar volume. © 2014 Pleiades Publishing, Ltd.Item Structural, optical and mechanical properties of ternary CaO-CaF2-P2O5 glasses(Tsinghua University, 2014) Venkateswara Rao, G.V.; Shashikala, H.D.The ternary phosphate glass series (50?x)CaO-xCaF2-50P2O5 (x = 0–20 mol%) were synthesized using melt quench technique. Structural, optical and mechanical properties were investigated with increase in CaF2 content. Using X-ray diffraction (XRD), synthesized glasses were confirmed to be amorphous in nature. Replacement of oxygen ions by fluorine ions increased the values of density. Decrease in refractive index due to the low polarizability of fluorine ions in the glass matrix was observed. In Fourier transform infrared (FTIR) spectra, the slight variation in ?as (PO2) band position and intensity could be attributed to replacement of fluorine ions for oxygen ions in phosphate glass structure. These data were well supported by Raman spectra. Optical band gap energy increased from 3.44 eV to 3.64 eV with increase in CaF2 content, and Urbach energy decreased suggesting that the fluorine ions reduced the tail energy states in the band gap compared to the oxygen ions. Mechanical parameters such as Vickers hardness, fracture toughness and brittleness were evaluated from the Vickers micro indentation measurements. Increase in Vickers hardness, decrease in fracture toughness and increase in brittleness were observed with increase in CaF2 content. © 2014, The Author(s).Item Optical, dielectric and mechanical properties of silver nanoparticle embedded calcium phosphate glass(Elsevier, 2014) Venkateswara Rao, G.V.; Shashikala, H.D.Silver nanoparticles have been embedded in 50 mol% CaO-50 mol% P 2O5 glass using melt quenching technique. The quenched glasses were heat treated at 550 °C for different durations between 10 and 50 h. The growth of silver nanoparticles in glass matrix appeared to be time dependent. FTIR spectra revealed that silver nanocluster formation had not affected the position of vibration bands of basic phosphate tetrahedral network. The Ag nanoparticle embedded glass matrix showed the red shift and broadening of the surface plasmon resonance (SPR) peak in the visible region with the increase in the duration of the heat treatment. Results showed the increase in size of the nanoparticles in glass matrix with heat treatment which was further confirmed using transmission electron microscopy and XRD. X-ray diffraction studies indicated the presence of Ag crystalline peaks along with amorphous structure on heat treatment at 550 °C for 50 h. The dielectric constant of these glasses increased as the duration of the heat treatment increased. Increase in both Vickers hardness and fracture toughness, and decrease in brittleness were observed which can be attributed to the increase in size of the nanoparticles in glass matrix. © 2014 Elsevier B.V.Item Statistical optimization of melt-quenching process parameters for multiple properties of ternary barium phosphate glasses(Elsevier Ltd, 2015) Narayanan, M.K.; Shashikala, H.D.; Manjaiah, M.In the present work simultaneous optimization of density, refractive index and hardness (multiple performance characteristics) of ternary barium phosphate glasses has been carried out using Taguchi based grey relational analysis. Effect of the parameters such as CaF2 content, melting temperature and melting time on the response parameters of (50 - X)BaO-XCaF2-50P2O5 (X = 0, 10, 20 mol%) glasses prepared according to the experimental layout of Taguchi's standard orthogonal array has been studied. Highest grey relational grade is the performance criteria used in this study to indicate the optimum level of process parameters needed for the best multiple performance characteristics. Analysis of variance (ANOVA) conducted on grey relational grade shows that under 95% confidence level, CaF2 content is the only parameter significantly affecting multiple performance characteristics. Experimental values of response parameters obtained by conducting the confirmatory experiment at optimum level of process parameters are closer to the optimal set of predicted values. © 2014 Elsevier B.V. All rights reserved.Item Effect of heat treatment on optical, dielectric and mechanical properties of silver nanoparticle embedded CaOCaF2P2O5 glass(Elsevier Ltd, 2015) Venkateswara Rao, G.; Shashikala, H.D.Silver nanoparticle have been embedded in CaOCaF2P2O5 glass using melt quenching technique. The quenched glasses were heat treated at 550 °C for 10, 20, 30, 40 and 50 h. The growth of silver nanoparticle in the glass matrix appeared to be time dependent. FTIR spectra show that silver nanoparticle formation has not affected the vibration bands of basic phosphate tetrahedral network. The increase in compactness of the glass structure is confirmed by increase in measured density of the glasses with increase in the duration of the heat treatment. Glass containing spherical silver nanoparticle shows the red shift and increase in the full width half maxima (FWHM) of the surface plasmon resonance (SPR) in the visible region with increase in the duration of the heat treatment. X-ray diffraction pattern indicated the presence of Ag crystalline peaks along with amorphous structure on heat treating at 550°C for 50 h. For the glass samples, the increase in dielectric constant and low dielectric loss around 0.005 were observed with increase in duration of the heat treatment. Both Vickers hardness and fracture toughness increased while the brittleness decreased which can be attributed to the increase in size of the nanoparticles in glass matrix. © 2014 Elsevier B.V. All rights reserved.Item Thermal and optical properties of BaO-CaF2-P2O5 glasses(Elsevier B.V., 2015) Narayanan, M.K.; Shashikala, H.D.Thermal and optical properties of ternary phosphate glasses prepared by conventional melt-quenching technique, belonging to the series (50 - X)BaO-XCaF2-50P2O5 (X = 0 to 10 mol%) were investigated with increase in CaF2 content. Thermal stability and glass forming ability studied using differential thermal analysis (DTA) were found to increase with the increase in CaF2 content. Powder X-ray diffraction (XRD) analysis of heat treated samples also revealed that CaF2 addition improves the thermal stability against crystallization. Increase in both glass transition temperature and onset crystallization temperature with the increase in CaF2 content can be attributed to the partial substitution of Ba2 + ion with Ca2 + ion, which is having larger field strength. The observed decrease in the melting temperature of glass batch with the increase in CaF2 content indicates that CaF2 acts as a flux and reduces the viscosity of the glass melt. The decrease in refractive index of the glasses with the increase in CaF2 content can be attributed to replacement of lower field strength Ba2 + by Ca2 + or the partial substitution of more polarizable oxygen ion by fluorine. Optical band gap energy slightly increased and Urbach energy marginally reduced with the increase in CaF2 content. Increase in optical band gap energy was further confirmed by calculating theoretical optical basicity of glasses. Average anion polarizability (?O/F) of (50 - X)BaO-XCaF2-50P2O5 glasses calculated from refractivity data using Lorentz-Lorentz relation was correlated with its theoretical optical basicity (?th) using the previously established correlation for oxyfluoro phosphate glasses. © 2015 Elsevier B.V. All rights reserved.Item Mechanical properties of Nd3+-doped phosphate laser glasses(Society of Glass Technology christine@glass.demon.co.uk, 2015) Venkateswara Rao, G.; Vijaya, N.; Joshi, A.S.; Shashikala, H.D.; Jayasankar, C.K.The mechanical properties of P2O5+K2O+BaO+Al2O3+Nd2O3 (PKBANd) glasses were studied using the Vickers indentation technique. The values of Vickers hardness, fracture toughness and brittleness of the glass samples were evaluated. The surface morphology of the indentations were analyzed using scanning electron microscopy. An increase in Vickers hardness, fracture toughness and decrease in brittleness were observed with an increase in Nd2O3 concentration in the phosphate glass matrix. A decrease in the brittleness of the synthesized glass samples was confirmed by scanning electron microscopy of median/radial cracks generated due to Vickers indentation pattern with increase in Nd2O3 concentration.Item Physical, mechanical and structural properties of BaO-CaF2-P2O5 glasses(Elsevier, 2015) Narayanan, M.K.; Shashikala, H.D.Mechanical properties and structure of melt-quenched ternary barium phosphate glasses belonging to the composition (50 - X)BaO-XCaF2-50P2O5 (X = 0 to 10 mol%) were studied using Vickers indentation and vibrational spectroscopy. Elastic moduli of prepared samples were calculated using the Makishima and Mackenzie (M-M) model. Density of glasses was measured using the Archimedes method, while molar volume and atomic packing density were calculated from measured density to study structural changes in the glass matrix. Vickers hardness and brittleness increased and fracture toughness decreased with increase in CaF2 content. This can be attributed to increase in the compactness of phosphate bonds and reduction in the molar volume of glasses with partial substitution of Ba2 + with Ca2 +. Infrared and Raman spectroscopies revealed that the glass network mainly consisted of metaphosphate units arranged in chain and ring structures together with small amounts of ultraphosphate and pyrophosphate units. © 2015 Elsevier B.V. All rights reserved.Item Application of Taguchi method for optimization of process parameters of melt-quenching technique for microhardness(American Scientific Publishers, 2016) Narayanan, M.K.; Shashikala, H.D.Ternary barium phosphate glass of maximum hardness among the composition (50-X)BaO-XCaF2-50P2O5(X = 0, 10, 20 mol%) has been obtained by optimizing parameters of melt-quenching process such as CaF2 content, melting temperature and melting time. Optimization is carried out using Taguchi’s design of experiments. Optimum condition of process parameters needed to achieve highest hardness was obtained from main effects plot and response table. Reliability and repeatability of the method were confirmed by comparing experimental value of hardness obtained by conducting the confirmatory experiment at optimum level of process parameters with predicted value. © 2016 American Scientific Publishers. All rights reserved.Item Investigation of mixed alkali effect on mechanical, structural and thermal properties of three-alkali borate glass system(Elsevier Ltd, 2016) Subhashini, u.; Shashikala, H.D.; Udayashankar, N.K.In the present communication, the results of investigation on mixed alkali effect (MAE) in mechanical, structural and thermal investigation of alkali zinc borate glasses with nominal composition 5Li2O-(25-x)K2O-xNa2O-60B2O3-10ZnO (x = 0, 5, 10, 15, 20 and 25 mol%) are reported. The samples were prepared using standard melt quenching technique. Fourier transform infrared (FTIR) spectroscopy, differential scanning calarometry (DSC) and Vickers indentation studies were performed to investigate the mixed alkali effect in the samples. From the DSC studies, it was observed that the thermal parameters viz., glass transition temperature (Tg), glass melting temperature (Tm), glass crystallization temperature (Tc), glass stability (S) and fragility (F) exhibit a non linear variation with respect to increase in compositional parameter (RNa). This behavior clearly indicated the presence of strong MAE in the samples. FTIR studies confirmed the presence of both [BO3] and [BO4] units, indicating the present glass networks to be made up of these two units placed in different structural groups. The non linear variation of peak positions of B-O-B bending and stretching of [BO3] and [BO4] units of each glass sample explain the role of modifier alkali elements and validates the existence of strong MAE. The microhardness and fracture toughness of the samples were measured using Vickers micro indentation technique and non linear variation of both the properties have been observed confirming the presence of MAE in these glass samples. © 2015 Elsevier B.V.