Browsing by Author "Bhat K, U.K."

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A single step unique microstructural growth of porous colossal dielectric constant titanium oxide
(Springer Verlag service@springer.de, 2019) Meti, S.; Hosangadi Prutvi, S.P.; Rahman, M.R.; Bhat K, U.K.
New microstructure of TiO 2 grown in hydrothermal process is reported on. The influence of hydrothermal process parameters, such as heating temperature, on growth dynamics is also reported. The improvement in surface area and crystallinity are reached by the hydrothermal process, as compared to other growth techniques. The synthesized TiO 2 is characterized by XRD technique and subjected to Rietveld analysis. The results indicate that the obtained TiO 2 is of tetragonal structure. The results of other characterization techniques such as micrography, Raman spectroscopy and TGA are also reported. The obtained TiO 2 is tested for its electrical properties and it shows good dielectric strength in the flat band region from 40 Hz to 1 MHz. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
Coating technologies for copper based antimicrobial active surfaces: A perspective review
(MDPI AG, 2021) Bharadishettar, N.; Bhat K, U.K.; Bhat Panemangalore, D.B.
Microbial contamination of medical devices and treatment rooms leads to several detrimental hospital and deviceâ€ associated infections. Antimicrobial copper coatings are a new approach to control healthcareâ€ associated infections (HAIâ€™s). This review paper focuses on the efficient methods for depositing highly adherent copperâ€ based antimicrobial coatings onto a variety of metal surfaces. Antimicrobial properties of the copper coatings produced by various deposition methods including thermal spray technique, electrodeposition, electroless plating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and sputtering techniques are compared. The coating produced using different processes did not produce similar properties. Also, process parameters often could be varied for any given coating process to impart a change in structure, topography, wettability, hardness, surface roughness, and adhesion strength. In turn, all of them affect antimicrobial activity. Fundamental concepts of the coating process are described in detail by highlighting the influence of process parameters to increase antimicrobial activity. The strategies for developing antimicrobial surfaces could help in understanding the mechanism of killing the microbes. Â© 2021 by the authors. Licensee MDPI, Basel, Switzerland.
Colossal dielectric permittivity of Nylon-6 matrix-based composites with nano-TiO2 fillers
(Springer, 2020) Meti, S.; Bhat K, U.K.; Rahman, M.R.
Herein, the nanocomposite films of Nylon-6 with reinforced nano-TiO2 were explored for their charge storage capacity. The high dielectric constant (?) of TiO2, along with its compatibility with Nylon-6, formed the basis for the present study. TiO2 nanoparticles were synthesized initially using hydrothermal technique. The microscopic uniformity and anatase-phase purity of the TiO2 nanoparticles were confirmed with the help of morphological and structural investigations. The effect of weight fraction of TiO2 in Nylon-6 was investigated to understand the robustness of the fabricated nanocomposites. The composite films with 5, 10 and 20 wt% of TiO2 in Nylon-6 matrix were prepared, and their dielectric behavior was explored by fabricating capacitors with parallel plate architecture. The composite film with 20 wt% TiO2 showed the highest dielectric parameters. The nanocomposite films have the exceptional dielectric quality with ? ~ 124 and low dielectric loss of 0.51 at 1 kHz. The colossal dielectric nature along with minimum sophistication in the film fabrication process makes the present nanocomposite to be a potential candidate for the various electronic devices. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Development of an industrial ferritic rolling process for IF grade steel
(Taylor and Francis Ltd., 2020) Kumar, D.S.; Sambandam, M.; Bhat K, U.K.
Interstitial free (IF) grade steels have high transformation temperatures and often results in non-uniform rolling and lower yields. In the present work, industrial ferritic rolling process is developed, where finish rolling is carried out below the Ar1 temperature for the IF grade steel. Offline simulation was carried out using a hot strip mill model (HSMM) software and full-scale ferritic rolling was carried out in a seven-stand hot strip mill under two different finishing and coiling temperatures and compared with austenitic rolling. Furnace drop-out temperature, mill speed and inter-stand cooling were controlled to achieve the desired low rolling temperatures. Both ferritic rolled coils had strained elongated grains and well-developed alpha (<110>//RD) and gamma (<111>//ND) textures. The lower finishing and coiling temperature processed coil shows higher microstructural and textural variation along with the thickness. This work established the optimum parameters for the industrial ferritic rolling process for IF grade steel. © 2020, © 2020 Institute of Materials, Minerals and Mining.
Eco-friendly ink formulation of column purified carbon dots from GABA for anticounterfeiting applications
(Elsevier B.V., 2023) Ullal, N.; Dhanya, D.; Kulkarni, S.D.; Sinha, R.K.; Anand, P.J.; Bhat K, U.K.
Forgery of valuable products causes a negative impact on the society as well as the economy of the country. There is a growing demand to not only differentiate or authenticate genuine documents/products but also to protect their integrity. Carbon dots (CDs) are a class of fluorescent nanomaterials that are well-known for their facile synthesis, good photostability and less toxicity profile. The current research work focuses on the preparation of CDs via hydrothermal method using γ-aminobutyric acid (GABA) that contains amino and carboxylic groups. Column chromatography technique is adopted to purify the GABA-derived CDs from the reactants and by-products. The fourth fraction obtained after column purification containing CDs with fluorescence emission in the visible region is chosen for further studies. The presence of spherical CDs confirmed through TEM imaging are chemically characterised using SAED, EDS, DLS, FTIR, XPS, Raman and XRD spectroscopy. The blue (λem = 490 nm) and green (λem = 538 nm) emitting CDs present in the fourth fraction displayed a fluorescence lifetime of 1.90 ns and 2.02 ns. Theoretical studies are performed using B3LYP/6-31G(d,p) theory level on different plausible structures. The HOMO-LUMO band gap of 2.3 eV deduced using DFT calculation is in close agreement with the optical band gap of 2.6 eV derived from Tauc plot. A complex forming mechanism is proposed for the fluorescence quenching of CDs upon examining the EDS data of the precipitate obtained upon addition of cupric ions. Further, the CDs are used as pigments to formulate a water-based ink for flexographic printing on UV-dull paper substrate. The printed samples exhibited good colorimetric values, lightfastness, and rub resistance. The security features of the ink film include an UV-induced yellow fluorescence, which will be known to the forger and a secondary quenching of fluorescence when exposed to cupric ions, which can be used by the user to validate document/product authenticity. This stimulus responsive optical property is also explored in the design of ionochromic security paper based on cupric ion induced fluorescence quenching of CDs for data storage and decryption. Moreover, the lesser surface roughness and electrical parameter values obtained for the print proofs could be further explored for the potential application of CD-derived ink in electronic anticounterfeiting. © 2023 Elsevier B.V.
Effect of High-Speed Dry Face Milling on Surface Integrity Characteristics of AZ91 Mg Alloy
(Springer, 2023) Marakini, V.; Pai, S.P.; Bhat K, U.K.; Thakur, D.S.; Achar, B.P.
In the present study, high-speed dry face milling is performed on AZ91 magnesium alloy using uncoated carbide inserts. The most influential surface integrity characteristics, such as surface roughness, hardness, microstructure and residual stresses, are investigated for a set of milling parameters chosen from the Taguchi design of experiments. The impact of machining conditions, such as feed rate, cutting speed and depth of cut on the surface integrity characteristics, are identified in order to improve the overall functionality of the alloy. Grey Relational Analysis optimization method is implemented to identify the optimal milling conditions. The results showed that high-speed dry face milling is very influential in improving the overall surface integrity characteristics of this alloy. © 2022, ASM International.
Enhancing the electrochemical performance of ZnO anode by novel additive of MoS2–SnO2 nanocomposite for the zinc alkaline battery application
(Springer, 2022) Prabukumar, C.; Meti, S.; Bhat K, U.K.
ZnO nanorods and ZnO microrods are synthesized as the anode material for the Zn alkaline battery application. The present work studies the electrochemical performance of ZnO with regard to its size, morphology and MoS2–SnO2 nanocomposite as its additive towards the alkaline battery application. The properties, such as oxidation–reduction reaction, anti-corrosion behaviour, charge-transfer resistance and suppression of hydrogen evolution reaction (HER), are studied in detail. The structural characterization of ZnO samples is performed by using X-ray diffractometry. The morphological analysis of ZnO and MoS2–SnO2 nanocomposite is performed by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. The atomic absorption spectroscopy (AAS) is employed to determine the solubility of ZnO samples in KOH solution. The electrochemical properties of the bare ZnO and the ZnO with MoS2–SnO2 additive (MoS2–SnO2/ZnO) samples are characterized by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), cathodic polarization and Tafel polarization techniques. The ZnO with nanorod morphology shows better electrochemical performance than ZnO microrods and ZnO nanoparticles with sphere-like or plate-like morphology. The addition of MoS2–SnO2 nanocomposite with the ZnO improved the electrochemical activity, suppressed the HER activity and improved the anti-corrosion behaviour of the ZnO samples. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Equal channel angular processing-a modern deforming technique for quality products
(Elsevier, 2021) Bhat K, U.K.; Bhat Panemangalore, D.B.; Bhat, S.
The grain size plays a significant role in determining the mechanical properties of the materials. Decreasing grain size increases strength, toughness, and ductility. Due to these, a lot of research has been executed to develop deforming techniques to produce ultrafine-grained materials. Among several plastic deformation techniques available, equal channel angular pressing or processing (ECAP) produces ultra-fine grained materials with substantial amount of high angle grain boundaries. ECAP produces ultra-fine grained material with typical substructural features, which are difficult to achieve using other severe deformation techniques. This chapter presents characteristics, variables, die design, and die materials employed in the process. The chapter also presents recent developments in the domain, such as, use of finite element techniques, etc. © 2021 Elsevier Inc. All rights reserved.
High-speed face milling of AZ91 Mg alloy: Surface integrity investigations
(KeAi Publishing Communications Ltd., 2022) Marakini, V.; Pai, S.P.; Bhat K, U.K.; Thakur, D.S.; Achar, B.P.
Magnesium (Mg) alloys are popular in the aerospace and automotive sector owing to their light-weight aspects. Amongst various Mg alloys, AZ91 alloy behaviour under machining has been trending and needs to be completely explored. The selection of optimal machining parameters is an important decision making process to achieve highest quality along with reduced cost and time. In this regard, this article describes experimental investigations to evaluate the performance of face milling operations on the surface characteristics of AZ91 magnesium alloy. The experiments were carried out with uncoated and PVD (Physical Vapour Deposition) coated carbide inserts at three levels of cutting speed (500, 700 and 900 m/min), feed rate (0.1, 0.2 and 0.3 mm/teeth) and depth of cut (0.5, 1.0 and 1.5 mm) under dry machining conditions. Major surface integrity indicators, such as roughness, hardness, residual stresses and microstructure are analysed. Chip morphology is also analysed and the correlation between chips and machined surface roughness is established. Face milling operation significantly improved surface roughness and microhardness of this alloy. Roughness improvement up to 85% (0.067 μm) and hardness improvement up to 33% (91.8 HV) is observed from the use of uncoated carbide inserts. Whereas, from PVD coated inserts, roughness improvement up to 81% (0.083 μm) and hardness improvement up to 60% (111.2 HV) is achieved. A similarity in behaviour between the two types of insert conditions are observed with increase in roughness from feed increase and decrease in hardness from cutting speed increase. Microstructural analysis showed PVD coated insert conditions producing surface with no defects, when compared to the crack observed in the surface from the use of uncoated carbide inserts. Marginally higher compressive residual stresses are detected at the surfaces from use of the uncoated inserts. Overall, due to no surface defect and the significant improvement in hardness and roughness from the PVD coated inserts, they are recommended for use in face milling operation for the cutting conditions investigated in this study. © 2022 The Authors
Improved fatigue crack growth resistance by retrogression and re-aging heat treatment in 7010 aluminum alloy
(Blackwell Publishing Ltd, 2019) Nandana, M.S.; Bhat K, U.K.; Manjunatha, C.M.
Aircraft grade 7010 aluminum alloy was heat treated to two different conditions: (1) standard peak aging (T6) and (2) retrogression and re-aging (RRA). The microstructures of these alloys were characterized by using transmission electron microscope. Fatigue crack growth rate (FCGR) tests were conducted using standard compact tension specimens, following ASTM standards. Tests were conducted at various stress ratios, R ranging from 0.1 to 0.7. The RRA-treated alloy was observed to contain coarsened ?? (MgZn2) precipitates with higher inter-particle spacing when compared with T6-treated alloy. The grain boundary precipitates (GBPs) were also coarsened and discontinuous in RRA-treated alloy as compared with continuous GBPs in T6 condition. The FCGR was lower and ?Kth was higher in RRA-treated alloy compared with T6-treated alloy at all the stress ratios investigated. Improved fatigue crack growth resistance in RRA-treated alloy was correlated to the modified microstructure and enhanced crack closure levels. © 2018 Wiley Publishing Ltd.
Improvement of third-order NLO properties of vacuum deposited Cd1-xPbxS nanostructured thin films for optoelectronic device applications
(Elsevier Ltd, 2023) Bairy, R.; Vijeth, H.; Kulkarni, S.D.; Murari, M.S.; Bhat K, U.K.
A polycrystalline nanostructured cadmium lead sulfide thin film was deposited using the thermal evaporation (PVD) technique (Cd1-xPbxS with x = 0.00, 0.01, 0.05 and 0.1 wt.% of Pb). Structural parameters of as-prepared Cd1-xPbxS thin films have been studied through X-ray diffraction. The optical investigation demonstrates that Cd1-xPbxS film's optical band gap (Eg) may be adjusted from the visible to the near-infrared region. (2.64 - 2.42 eV). The film is substantially more appropriate for absorbing layers in solar cells and optoelectronic applications due to the large decrease in ‘Eg.’ The enhanced Pb doping was found to have altered the surface morphology, verified by Field Emission Scanning Electron Microscopy (FESEM) images. The doped films also showed a significant red shift in the band edge and increased transmittance in the visible and NIR regions. The third-order nonlinear optical (TONLO) parameters of the samples were determined from the Q-switched Nd: YAG laser with 65-ps pulse duration at 1064 nm. The investigated TONLO components such as nonlinear absorption coefficient (β), nonlinear refractive index (n2) and the susceptibility χ(3)were found to be in the range from 1.16 × 10−3 to 4.12 × 10−3 (cmW−1), 1.06 × 10−8 to 3.32 × 10−8 (cm2 W−1) and 1.23 × 10−4 to 5.62 × 10−4 (esu) respectively. The results indicate that Pb-doping on CdS nanostructures on surface morphology can be used to modify NLO characteristics.Cd1-xPbxS thin film is a potential and able material for optoelectronic device applications, as seen by these encouraging NLO results. © 2023 Elsevier Ltd
Investigation of third-order nonlinear optical properties of nanostructured Ni-doped CdS thin films under continuous wave laser illumination
(Springer, 2019) Bairy, R.; Arasalike, A.; Shivakumar, G.K.; Radhakrishnan, K.; Bhat K, U.K.
We report the third-order nonlinear optical (NLO) properties and optical limiting (OL) thresholds of pure CdS and Ni-doped CdS thin films have been investigated with the Z-scan technique under continuous wave laser excitation. Nanocrystalline CdS thin films with various doping concentrations of Ni (0%, 1%, 3%, 5% and 10 at. %) are prepared by spray-pyrolysis technique. XRD patterns reveal that all the prepared films are polycrystalline and the incorporation of Ni does not lead to major changes in the crystalline phase of Cd1-xNixS thin films. The surface morphology of the prepared films is impacted by the Ni-doping and is indicated by Field Emission Scanning Electron Microscopy (FESEM) images. With an increase in Ni-doping concentration, the energy band-gap value decreased from 2.48 eV to 2.23 eV. From the Z-scan data, it is observed that the material show strong two-photon absorption (2PA) and with an increase in Ni-doping concentrations from 0 to 10 at. %, the nonlinear absorption coefficient (?) are enhanced from 0.92 x 10-5 to 4.46 x 10-5 (cm W-1), nonlinear refractive index (n2) from 0.2967 x 10-9 to 0.1297 x 10-8 (cm2 W-1) and thereby the third-order NLO susceptibility (?(3)) values also increased from 1.7075 x 10-6 to 7.4743 x 10-6 (esu). OL characteristics of the prepared films are studied at the experimental wavelength. The results propose that the Cd1-xNixS film is a capable material for nonlinear optical devices at 532 nm and optical power limiting applications. © Springer Science+Business Media, LLC, part of Springer Nature 2019.
Surface integrity investigation and VIKOR optimisation during the milling of aluminium–lithium alloy using uncoated and PVD-coated carbide tools
(Taylor and Francis Ltd., 2024) Marakini, V.; Pai, S.P.; Bhat K, U.K.; Thakur, D.; Achar, B.
In this study, the effect of face milling on the surface integrity of an aluminium–lithium alloy is investigated through an L27 Taguchi design of experiments. Uncoated and PVD-coated carbide inserts are used to investigate the material surface characteristics such as roughness, microhardness, microstructure and residual stresses. Both inserts showed their ability in achieving a better surface finish (Ra ∼ 0.04 µm) than the raw material (Ra ∼ 0.52 µm). Hardness improvement of up to 216.7 HV (uncoated) and 229.3 HV (PVD-coated) from the raw material (180.7 HV) surface is observed. Both inserts showed their ability to generate compressive residual stresses with uncoated inserts producing stresses on the surface. Microstructural changes from milling using both inserts are observed to be minimal. ANOVA showed the effect of process parameters on the surface roughness and microhardness. Furthermore, VIKOR statistical analysis technique is used to identify the optimal conditions for good roughness and microhardness of the alloy. © 2023 Canadian Institute of Mining, Metallurgy and Petroleum.
The role of cobalt doping in tuning the band gap, surface morphology and third-order optical nonlinearities of ZnO nanostructures for NLO device applications
(Royal Society of Chemistry, 2019) Bairy, R.; Patil, P.S.; Maidur, S.R.; Vijeth, H.; Murari, M.S.; Bhat K, U.K.
The work presented here reported the effect of doping cobalt (Co) in ZnO thin films. The thin films were prepared using the spray pyrolysis technique with 0, 1, 5 and 10 wt% cobalt doping concentrations to study the morphological, optical and third-order nonlinear optical (NLO) properties. X-ray diffraction revealed the crystalline nature of the prepared thin films, and the crystallite size was found to increase with the concentration of doped Co. The morphology and surface topography of the films were largely influenced by doping, as indicated by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). With an increase in Co-doping concentration, the direct optical energy band-gap value increased from 3.21 eV to 3.45 eV for pure to 10 at% of Co concentrations respectively. To study the NLO properties of the prepared thin films, the Z-scan technique was adopted; it was observed that with an increase in the doping concentration from 0 to 10 wt%, the nonlinear absorption coefficient (?) was enhanced from 4.68 × 10-3 to 9.92 × 10-3 (cm W-1), the nonlinear refractive index (n2) increased from 1.37 × 10-8 to 2.90 × 10-8 (cm2 W-1), and the third-order NLO susceptibility (?(3)) values also increased from 0.79 × 10-6 to 1.88 × 10-6 (esu). At the experimental wavelength, the optical limiting (OL) features of the prepared films were explored, and the limiting thresholds were calculated. The encouraging results of the NLO studies suggest that the Co:ZnO thin film is a capable and promising material for nonlinear optical devices and optical power limiting applications. © 2019 The Royal Society of Chemistry.
Triboelectric effect based self-powered compact vibration sensor for predictive maintenance of industrial machineries
(IOP Publishing Ltd, 2021) Hosangadi Prutvi, H.P.; Meti, S.; Bhat K, U.K.; Gupta, D.
This article showcases a compact self-powered contact-mode triboelectric (TE) phenomenon-based vibration sensor for predictive maintenance of industrial machinery. The sensor has a suspended proof-mass that oscillates under external vibration and causes contact-separation between Teflon and zinc oxide (ZnO) films creating tribo signals, which are used for both sensing and powering mechanisms. For these sensors to be implemented in real-time applications, the sensor must be cost-effective, reliable, and repeatable. Hence, the active layer (ZnO film) is fabricated by an efficient process of microwave-assisted thermal decomposition followed by the established screen printing method. The sensor operates up to 400 Hz and is highly robust with no significant decay in signal strength even after 120 000 cycles tested at elevated stress values. The device produces a maximum voltage (V) of ±30 V, short circuit current of ±3 ?A, and can deliver a maximum power density of 0.5 W m-2, at 8 M? load resistance. In the frequency domain, the device generates a maximum V at 55 Hz and can charge 1 µF capacitor to 3.5 V in 25 s. To demonstrate the functionality of the sensor in a real application, it is implemented on a lab-scale vacuum pump to capture the system faults by analyzing the harmonic signatures. Thus, in this article, we have showcased end-to-end development of the sensor from material synthesis to device testing along with its signal processing techniques and proved that the sensor can readily be implemented in industrial environments as is. This article thus emphasis bridging the lab-to-market gap for TE devices as a self-powering sensor. © 2021 IOP Publishing Ltd.