Faculty Publications
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Item Dissolution studies of Na2O-BaO-CaO-P2O5 glasses in deionized water under semi-dynamic conditions for bioactive applications(Elsevier Ltd, 2018) Edathazhe, A.B.; Shashikala, H.D.The phosphate glasses of composition Na2O-CaO-P2O5 are widely accepted glass material for biomedical applications. The glass samples with composition (26-x)Na2O-xBaO-29CaO-45P2O5 (x = 0,5,10,15) are prepared at 1100°C by melt-quenching technique. In order to reduce the fast dissolution rate, which limits their application, BaO is added by reducing Na2O composition. The dissolution studies have been carried out in deionized water under semi-dynamic conditions at 37°C for 14 days. The properties are studied based on Barium composition and time of immersion. The samples are taken out at 24 hrs. intervals to carry out weight loss and pH measurements. The rates of cation (Na+ and Ca2+) release from the glass to the solution were found out using flame photometer. The release of orthophosphate (PO43-) anions is measured by UV-Visible spectrometer using phospho-molybdenum blue method. The weight losses linearly increase with time for all the compositions. The addition of barium decreases the weight loss in deionized water. The pH of the solutions varies with dissolution of ions. The dissolution rate has been found out from the slope of the weight loss vs time graph and it decreased with increase in barium content. © 2018 Elsevier Ltd. All rights reserved.Item Optical properties of BaO added bioactive Na2O-CaO-P2O5 glasses(American Institute of Physics Inc. subs@aip.org, 2018) Edathazhe, A.B.; Shashikala, H.D.This paper deals with the effect of BaO addition on the optical properties of bioactive Na2O-CaO-P2O5 glasses for biomedical optics applications. The phosphate glasses with composition (26-x)Na2O-xBaO-29CaO-45P2O5 (x = 0, 5, 10, 15 mol%) have been prepared by melt-quenching technique at 1100°C. The refractive index of glasses increased with BaO content. The optical band gap and Urbach energy of synthesized glasses were derived from the optical absorption spectra by using UV-Visible spectrometer. The addition of 5 mol% of BaO increased the band gap energy of glasses due to the formation of ionic cross-links in the glass structure. The defect and interstitial bonds formation in theglasses decreased with BaO additions as indicated by reductions in the Urbach energy values. No such variations in the band gap and Urbach energy values of glasses were observed with BaO content from 5 to 15 mol%. The molar and oxide ion polarizability values were calculated from the band gap and molar volume of glasses. The increase in the calculated optical basicity and metallization criteria of glasses supported the rise in band gap energy values with BaO additions. As the melting temperature of glasses decreased from 1200 to 1100°C, the refractive index increased as supported by the measured density values. The band gap energy is not changed with melting temperature. The Urbach energy decreased with decrease in melting temperature in case of BaO-free Na2O-CaO-P2O5 glasses, whereas it increased in case of BaO added glasses due to the role of BaO as modifying oxide. © 2018 Author(s).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 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 Effect of BaO addition on the structural and mechanical properties of soda lime phosphate glasses(Elsevier Ltd, 2016) Edathazhe, A.; Shashikala, H.D.The phosphate glasses of composition (26-x)Na2O-xBaO-29CaO-45P2O5 (x = 0,5,10,15 mol%) are prepared by melt-quenching technique. The variations in structural and mechanical properties are studied on glasses prepared at 1000, 1100 and 1200? C. The density of glasses increases with barium content for glasses prepared at different temperatures. The molar volume is nearly constant with compositional parameter. The amorphous nature of samples is confirmed by XRD. The calculated values of mass percentage of elements in the batch composition and EDS data are in a reasonable agreement. The FTIR spectra show that the main structural units in these glasses are Q1 and Q2 phosphate units. The frequency of the P[sbnd]O[sbnd]P band remains constant with barium substitution. The microhardness is measured using Vickers indentation method by applying 0.98 N for 10 s. The hardness and fracture toughness are independent of composition. The nature of crack formations is examined by SEM. The brittleness and crack length are correlated with plastic flow in the material. © 2016 Elsevier B.V.Item Dissolution and in vitro bioactive properties of BaO added Na2O-CaO-P2O5 glasses(Society of Glass Technology christine@glass.demon.co.uk, 2018) Edathazhe, A.B.; Shashikala, H.D.Na2O-CaO-P2O5 glasses with different additions of BaO were subjected to dissolution tests in deionised water and in vitro bioactivity tests in phosphate buffer saline (PBS) as well as Hank's balanced salt (HBS) solution. Phosphate glasses of composition (26-x)Na2O-xBaO-29CaO-45P2O5 (x=0, 5, 10, 15 mol%) were prepared by melt-quenching. The dissolution characteristics of these glasses were studied in deionised water under static conditions based on BaO composition. The dissolution rate of the glasses in deionised water decreased with BaO content. The in vitro bioactivity tests were carried out in PBS and HBSS for 28 days under static conditions. The bioactivity of the samples was verified by XRD, SEM/EDS and FTIR techniques. Hydroxyapatite phases were formed on all the glass samples within seven days of immersion in HBSS and the bioactivity was found to improve with BaO content. The glasses without BaO and with 15 mol% BaO showed the hydroxyapatite phases within the immersion of 14 days in PBS whereas the glasses with 5 and 10 mol% BaO showed formation of amorphous hydroxyapatite phases. © 2018 Society of Glass Technology. All rights reserved.