Faculty Publications

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Author: search.filters.author.Shashikala, H.D.Subject: search.filters.subject.Brittleness

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    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).
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    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.
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    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.
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    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.