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 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 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 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 Influence of Fe3+ ions on optical, structural, thermal and mechanical properties of Li2O–Na2O–K2O–ZnO–B2O3 based glass system(Elsevier Ltd, 2020) Subhashini, u.; Shashikala, H.D.; Udayashankar, N.K.The effect of addition of Fe3+ ions in Li2O–Na2O–K2O–ZnO–B2O3 based glass system have been studied. The melt quenching technique is used to prepare the glass samples. The X-ray diffraction studies confirmed the amorphous nature of the samples. DSC thermographs indicate that the Tg is decreasing as the addition of Fe2O3 content. Increase in thermal stability is observed upon adding K2O to the F0 sample and increase in the Fe2O3 content further enhanced the thermal stability up to 187 °C. Optical band gap energy (Eg) of the studied glass system is found to reduce with increasing Fe2O3 content. A band observed around 450 nm in UV absorption spectra is due to the d-d transition of 6A1g(S) ? 4T2g(G) which indicates the presence of iron ion in trivalent state (Fe3+) with distorted octahedral symmetry. The oxide ion polarizability values determined using the refractive index and optical band gap energy are found to be increasing monotonically with partial incorporation of K2O content and with increasing Fe2O3 content. The FTIR and Raman spectroscopy studies confirmed the network modifier role of Fe2O3. The radial-median cracks produced due to Vickers indentation were studied and it confirmed the enhancement in brittleness of the samples as Fe2O3 content increased. Further efforts have been made to analyse and establish correlation between the physical and mechanical properties with the structural modification of the studied glass system. © 2019 Elsevier Ltd and Techna Group S.r.l.Item Mechanical and wetting properties of 25%NiCr-75%Cr2C3 cermet coated on low carbon steel using HVOF thermal spray technique(Elsevier B.V., 2021) Amudha, A.; Nagaraja, H.S.; Shashikala, H.D.The hydrophobic ceramic–metal composites with enhanced mechanical properties will have longer durability because of the embedded liquid-repellent properties, with low water and salt absorption. In this work, the 25%NiCr-75%Cr2C3 cermet powder has been coated on low carbon steel substrate, using High Velocity Oxy-fuel thermal spray technique. The SEM is employed to analyse the morphological characterization of the coating. The mechanical properties of the 25%NiCr-75%Cr2C3 coating is evaluated using the Vickers micro-indentation technique. The micro-hardness, fracture toughness and brittleness index of the coatings are obtained. Also, the wetting property of the coating in 3.5% NaCl salt solution is investigated using the contact angle measured by sessile drop method. The contact angle of the coating is observed to be hydrophobic in nature with a contact angle of 98.14?. Thus, 25%NiCr-75%Cr2C3 hydrophobic coatings helps in the improvement of brittleness, fracture toughness, and the microhardness. © 2020 Elsevier B.V.