Faculty Publications
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Item Corrosion Characteristics of Metal Matrix Composites(Elsevier, 2021) Bhat Panemangalore, D.; Bhat K, U.To tackle significant challenges posed by industries and environment with respect to materials degradation, we need to have a clear understanding of the impact of corrosion in different components. Composites are designed for a specialized application using different material combinations. This article presents an overview on different corrosion characteristics of metal matrix composites. Several types of corrosion have been addressed along with different corrosion methodologies. Corrosion of aluminum MMCs, magnesium MMCs, etc., have been discussed, along with different processing related problems. Different aspects involved in determining the corrosion behavior of metal matrix composites have been addressed. © 2021 Elsevier Ltd. All rights reserved.Item Coating technologies for copper based antimicrobial active surfaces: A perspective review(MDPI AG, 2021) Bharadishettar, N.; Bhat K, U.; Bhat Panemangalore, D.B.Microbial contamination of medical devices and treatment rooms leads to several detrimental hospital and device‐associated infections. Antimicrobial copper coatings are a new approach to control healthcare‐associated infections (HAI’s). This review paper focuses on the efficient methods for depositing highly adherent copper‐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. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Item High strain rate behavior of GTM-900 titanium alloy(ASTM International, 2021) Thammaiah, B.R.; Fernando, C.D.; Majila, A.N.; Anil Chandra, A.R.; Nandana, M.S.; Bhat K, U.; Manjunatha, C.M.GTM-900 is an ?+? alloy of titanium used in low-pressure (LP) compressor blades of gas turbine (GT) engines. The maximum allowable operating temperature of this alloy is 500°C. Silicon is added to enhance the creep resistance at elevated temperatures. The aim of this work is to establish the microstructural stability of this alloy and determine the high strain rate Johnson-Cook (J-C) material parameters such as A, B, and n. The material parameters are subsequently used by designers to simulate the "blade-off"and "casing containment"capability of the LP compressor blade. Split Hopkinson tensile bar was used to conduct high strain rate tests at about 2,000 s-1, and at three different temperatures, viz., 25°C, 300°C, and 500°C, to simulate critical conditions. Data obtained from these testing were used to construct a J-C model. Flow stress increased with an increase in strain rate and decreased with an increase in temperature because of thermal softening. Characterization, using optical and electron microscopes, indicated that the microstructure was stable even after the deformation at 500°C. The presence of needle-like silicide phase was observed under transmission electron microscopy and the composition was verified with X-ray diffraction results. A high strain hardening rate was observed even at elevated temperatures in this alloy (n ? 0.54 at 2,000 s-1 and 500°C) compared to Ti-6Al-4V titanium alloy (n ? 0.28). Considering good strength and microstructural stability up to 500°C, the present material offers to be an attractive alternate to other contemporary titanium alloys currently used in GT engine applications. © © 2021 by ASTM International.Item Biological and Physical Characterization of Surface-Modified Grade v Titanium Alloy(Hindawi Limited, 2024) Kakunje, M.; Nambiar, S.; Isloor, A.M.; Kabekkodu, S.; Bhat K, U.Surface modification and biomimetic approaches have been widely used to enhance bioinert substances. It is not very clear whether surface alterations and polymer coatings on titanium make it more biologically active and enhance cell adhesion. We tried to focus on the physical and biological characterization of surface-modified titanium disks. Four different surface modifications were done for the titanium disks, ranging from acid etching, sandblasting, polydopamine coating, and polydopamine-based chitosan coating, and were compared with disks without any surface modification. The disks were studied for physical characteristics like surface roughness and contact angle. Human gingival fibroblasts were used to investigate the biological effects of surface modification of titanium alloy surfaces. The wettability of chitosan-coated, acid-etched, and polydopamine-coated titanium was much better than that of the sandblasted surface, indicating that surface energy was higher for acid-etched and coated surfaces than others. The cell seeding with fibroblasts showed increased adhesion to the smoother surfaces as compared to the rougher surfaces. Polydopamine coatings on titanium disks showed the most favorable physical and biological properties compared to others and can be a good surface coating for in vivo implants. © 2024 Mahesh Kakunje et al.Item Microstructural, electrochemical and immersion based corrosion analysis in milling induced magnesium alloy AZ91(Russian Association of Corrosion Engineers, 2024) Marakini, V.; Pai, S.; Achar, B.; Sahoo, B.; Bhat K, U.; Devadiga, R.; Rao, S.; Swamy, M.; Mesta, R.Present work discusses the effect of face milling operations on the corrosion characteristics of AZ91 alloy. A full factorial L27 design of experiment is prepared and face milling is performed to identify the optimal conditions with lowest roughness. The optimal surface of the alloy obtained from face milling has been compared with the slightly polished surface of as-cast alloy using weight loss and electrochemical polarization testing methods using 3.5% NaCl solution. In weight loss method, the alloy surfaces are solution treated for various time intervals ranging from 0.5 to 72 hours, to study the effect of surface finish obtained from face milling in comparison to polishing (as-cast). Whereas, in polarization method, the tests are conducted for only 0.5 hour on both specimens and compared. The corrosion rates are found to be in direct relation to the surface roughness, as the low roughness surface from face milling showed comparatively low corrosion rate. The polarization curves justified the better corrosion resistance of milled surface when compared to polished surface. Further, FESEM micrograph comparison between the before and after polarization test surfaces showed the severity of corrosion attack in both tested surfaces. Furthermore, the elemental analysis using EDAX test on the before and after polarization test surfaces showed the presence of less oxygen in the milled surface compared to polished surface, which established the better corrosion resistance of milled surfaces which has low surface roughness. © 2024, Russian Association of Corrosion Engineers. All rights reserved.Item Scratch and wear resistance of interstitial-free steel subjected to severe shot peening(SAGE Publications Inc., 2024) Sahoo, B.; Bhat K, U.; Rao, M.Surface integrity in terms of scratch and wear resistance is the major concern of any engineering component, which is attributed to most of the surface damages. A popular way of improving such behaviours is the mechanical treatment of the surface. The current investigation studied the improvement of scratch and wear properties by performing shot peening on the Ti–Nb stabilised interstitial free steel, a popular choice in automotive industries. The samples were shot-peened at different coverages. It was found that the shot-peened samples showed a superior scratch and wear behaviour as compared to as-received samples. The scratch hardness was improved by 2.4 times, the wear volume was decreased by 59.6%, and the wear rate was minimal for the 2000% peened sample. © Institute of Materials, Minerals and Mining 2024.Item Cost effective synthesis of sulfur and nitrogen co-doped graphene aerogel and application in binder free supercapacitor(American Institute of Physics, 2024) Muhiuddin, M.; Khan, A.Z.; Devi, N.A.; Bharadishettar, N.; Meti, S.; Siddique, A.B.; Bhat K, U.; Akhtar, W.; Rahman, M.R.Incorporating heteroatoms into graphene lattice results in enhanced electrical conductivity and electrochemically active sites and has significant importance in developing high-performance supercapacitors. In this study, sulfur and nitrogen co-doped graphene aerogel is synthesized via hydrothermal technique followed by a simple but effective freeze-thawing and ambient pressure drying process (referred to as SN-GA). The process requires low-cost raw materials and cost-effective equipment without the utilization of any special instrument that operates at ultra-low temperatures, under high pressure, or vacuum environment. Ammonium sulfate [(NH4)2SO4] and ethylenediamine are used as a source of sulfur and nitrogen and as a reducing agent. (NH4)2SO4 with different molarities (0, 12, 24, and 36 mM) are used to synthesize four different aerogel samples marked as GA, SN-GA1, SN-GA2, and SN-GA3. The electrode is prepared using an SN-GA2 sample, exhibiting an outstanding specific capacitance of 244 F g−1 at an applied current density of 1 A g−1 with almost 98.5% Coulomb efficiency. Furthermore, based on the SN-GA2 sample, the symmetrical supercapacitor is fabricated, displaying an energy density of 18.14 Wh kg−1 at a power density of 498.4 W kg−1. Hence, SN-GA2 renders a promising material for supercapacitor applications. © 2024 Author(s).Item Yellow emissive and high fluorescence quantum yield carbon dots from perylene-3,4,9,10-tetracarboxylic dianhydride for anticounterfeiting applications(Royal Society of Chemistry, 2024) Ullal, N.; Sahoo, B.; Dhanya, D.; Kulkarni, S.D.; Bhat K, U.; Anand, P.J.Forged products are widespread in the market and there is an immediate need to counter this growing menace. Anti-counterfeit techniques using fluorescent materials with covert features that appear hidden under daylight and display characteristic fluorescence upon specific source irradiation have gained popularity. Carbon dots (CDs) that can be prepared through facile synthesis from various raw materials are a class of fluorescent materials that provide tremendous opportunities to combat counterfeiting. This work focuses on the fabrication of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) derived CDs via the solvothermal approach and their subsequent purification using column chromatography. The fifth fraction obtained exhibited remarkable yellow emission (λem = 540 nm) with a high fluorescence quantum yield of 53.22% and a lifetime of 4 ns. The CDs appeared quasi-spherical during TEM imaging with an average diameter of 1-3 nm and appeared polycrystalline from the SAED pattern. The XPS and TEM-EDS results suggested carbon as the major element along with oxygen and nitrogen as the other heteroatoms. The water-based ecofriendly ink formulated using the CDs was printed on UV dull paper using the flexography technique. The print-proof paper samples appeared pale pink under daylight and fluorescent yellow upon 365 nm UV illumination. Moreover, the stability of the print was confirmed upon exposure to strong UV radiation cycles and abrasion resistance. Besides, the fluorescence emission remained unaltered even after 5 months of storage under room temperature conditions. The ink was used to print on PVC sheets and FBB boards with good stability against scuffing, suggesting its applicability in the packaging industry. The CDs could also serve as fluorescent markers for identifying post-consumer plastic packaging for a circular economy. © 2024 The Royal Society of Chemistry.Item Pyrene carbaldehyde derived carbon dots for detecting water in alcohol and security printing(Elsevier B.V., 2024) Ullal, N.; Sahoo, B.; Dhanya, D.; Kulkarni, S.D.; Bhat K, U.; AnandThis study focuses on preparing Carbon dots (CDs) from Pyrene-1-carbaldehyde (PCA) using a solvothermal method and further purification using column chromatography. The aggregation-induced emission (AIE) of CDs was systematically investigated in a THF/water medium. The CDs showed red shifts in their photoluminescence (PL) spectra upon increase in water content. Scanning electron microscopic (SEM) images revealed the formation of aggregates, while X-ray diffraction (XRD) confirmed that the d-spacing values remains unchanged. The NMR spectrum of the CDs displayed peaks corresponding to aromatic carbon, which disappeared upon addition of water due to ?-? stacking, indicating aggregate formation. Based on the aggregation-induced fluorescence emission mechanism, detection of water content in alcohol is demonstrated. Moreover, the synthesized CDs were used as fluorescent colorant in screen inks along with polyvinyl alcohol (PVA) and hydroxyethyl cellulose (HEC) as binders. The print proofs obtained on UV-dull paper using PVA-based screen ink exhibited fluorescence emission at longer wavelengths and showcased desirable photostability under prolonged UV exposure compared to the prints obtained using HEC-based ink. Moreover, though the PVA based print appeared blue or cyan fluorescent, the actual yellow emissions from the CDs can be visualised using UV block filter. Such features, masked to the forger, but known to the user can be utilised in checking the authenticity of the print. © 2024 The AuthorsItem Efficiency enhancement in dye-sensitized solar cells through neodymium-doped graphene quantum dot-modified TiO? photoanodes(Elsevier B.V., 2025) Senadeera, G.K.R.; Weerasekara, W.M.S.K.; Jaseetharan, T.; Sandunika, P.U.; Kumari, J.M.K.W.; Dissanayake, M.A.K.L.; Muhiuddin, M.; Rahman, M.R.; Bhat K, U.; Akhtar, M.W.; Udayakumar, U.; Siddique, A.B.; Ekanayake, P.This study explored the effects of Neodymium-doped graphene quantum dots (NdGQDs) on improving the performance efficiency of TiO2 based dye-sensitized solar cells (DSSCs). By employing in-situ physical assisted mixing, DSSCs with optimized NdGQDs in TiO2 photoanodes showed a power conversion efficiency of 8.76 %, a significant improvement compared to the 6.01 % efficiency of pristine TiO2-based DSSCs under 100 mW cm?2 illumination (AM 1.5). Notably, the short-circuit current density increased by 74 %. HRTEM analysis revealed that the NdGQDs have a size range of approximately 7–9 nm. UV–visible spectroscopy and Mott-Schottky analysis revealed a positive shift in the Fermi level, promoting better electron transfer and increased photocurrent density at the expenses of the open circuit voltage. Electrochemical impedance spectroscopy characterization of DSSCs incorporating NdGQD-modified photoanodes revealed a reduction in electron transfer resistance at the photoanode|dye|electrolyte interface, accompanied by an increase in recombination resistance within the device suppressing the electron recombination rate. © 2024 Elsevier B.V.