Faculty Publications
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Item Electrical Characterization of Hybrid Hetero Interface using n-ZnO and p-CuPc(Elsevier Ltd, 2015) Raveendra Kiran, M.R.; Ulla, H.; Fernandes, J.M.; Satyanarayan, M.N.; Umesh, G.In the present work we report the fabrication, current density-voltage (J-V) characteristics, capacitance-voltage characteristics and impedance measurements of the n-ZnO nanoparticles/ p-CuPc hybrid junction. ZnO nanoparticles were synthesized by sol-gel method. The J-V characteristics clearly show the diode like behaviour. The junction behaviour has been investigated using surface topography (AFM), capacitance and electrical impedance studies. © 2015 Elsevier Ltd.Item Synthesis and desalination performance of Ar+-N+ irradiated polysulfone based new NF membrane(2011) Hegde, C.; Isloor, A.M.; Padaki, M.; Wanichapichart, P.; Liangdeng, Y.In the last few years, membrane technology has gained more attention from polymer chemists throughout the globe. Nowadays, surface modification of membrane is very useful in biotechnology and food science. In the present investigation, we have synthesized polysulfone based composite nanofiltration (NF) membranes, and characterized these membranes by FT-IR, SEM and membrane performance studies. Surface plasma treatment was carried out by irradiation with argon and nitrogen beams in suitable conditions. It was observed that nitrogen beam caused surface roughness that was more severe than the Ar beam. After irradiation, water contact angle was slightly increased. For pure water permeability, flux increased linearly with the operating pressure. However, for the salt solution, the flux was decreased marginally and salt rejection increased after irradiation due to surface modification. The modification effect was characterized in terms of contact angle, AFM employed roughness measurement and dielectric property. It revealed that irradiated NF membranes showed higher salt rejection and lower flux as compared to the nonmodified membranes. Accordingly, the roughness of the membrane surface intensively affected the performance of RO membrane. © 2010 Elsevier B.V.Item Composition modulated multilayer Zn-Fe alloy coatings on mild steel for better corrosion resistance(2011) Venkatakrishna, K.; Hegde, A.C.Composition modulated alloy (CMA) of Zn-Fe coatings were developed on mild steel galvanostatically from chloride bath containing sulphanilic acid (SA) and ascorbic acid (AA) through single bath technique (SBT). The properties of CMA coatings were found to depend on the thickness of individual layers and switching cathode current densities (SCCDs). The CMA (Zn-Fe) coating, having 120 layers, deposited at 20 and 50mAcm-2, were found to show the least corrosion rate (1.545 × 10-2mmy-1) compared to monolithic alloy (32.5 × 10-2mmy-1) of the same thickness. The improved corrosion resistance of multilayered coatings was due to the fact that the defects and failures occurring in a single layer in the deposition process is covered by the successively deposited coating layers, and hence the corrosive agent path is extended or blocked. Further, the high corrosion resistance of CMA Zn-Fe coatings was attributed to the "dielectric barrier" of the coatings, evidenced by dielectric spectroscopy and Mott-Schottky's plot. The corrosion rate was found to increase at high degree of layering, and is attributed to less relaxation time for redistribution of metal ions in diffusion layer, during plating. In other words, at higher layer thickness, the CMA coating tends to become a monolithic. CMA coatings were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). © Taylor & Francis Group, LLC.Item Conversion of microfiltration membrane into nanofiltration membrane by vapour phase deposition of aluminium for desalination application(2011) Padaki, M.; Isloor, A.M.; Nagaraja, K.K.; Nagaraja, H.S.; Pattabi, M.Preparation and modification of NF membrane are challenging aspects in research. In the present work, we have synthesised Polysulfone (PSf) microfiltration membrane and reduced the pore size to nano level by physical vapour deposition (PVD) of aluminium metal. Membrane pore size was reduced from micro pore to nano pore, which rejected 42.22% of NaCl from the solution with 164L/m2h. And also water permeation decreases from 1.10324-10-10 to the 9.141-10-12. The SEM and AFM pictures showed the surface modification and metal deposition in the pores. The performance of the membrane was studied by dead end flow cell using 3.5% of NaCl solution, in which PVD membrane showed 42.22% of rejection with 16.4L/m2h flux. Thermal analysis from DSC showed Tg of 265°C. Contact angle measurement, and water uptake were also reported. © 2011 Elsevier B.V.Item Eclipta prostrata leaf aqueous extract mediated synthesis of titanium dioxide nanoparticles(2012) Govindasamy, G.; Rahuman, A.A.; Priyamvada, B.; Khanna, V.G.; Devarepally, D.K.; Jose, P.J.Eco-friendly, nontoxic, inexpensive, abundantly available hitherto unreported Eclipta prostrata leaf extract is used for the biosynthesis of titanium dioxide nanoparticles (TiO 2 NPs). The TiO 2 NPs were characterized by FTIR, XRD, AFM and FESEM analysis. FTIR peak implicated the role of carboxyl group OH stretching amine NH stretch in the formation of TiO 2 NPs. XRD characterized in crystallographic plane of rutile phase. AFM showed uneven surface morphology which indicates the presence of both individual and agglomerated nanoparticles. FESEM analysis showed shape in spherical clusters, quite polydisperse and it ranges in size from 36 to 68 nm with calculated average size of 49.5 nm. In this paper, we have demonstrated a novel biological route for the synthesis of TiO 2 NPs. © 2011 Elsevier B.V. All rights reserved.Item Magnetic domain studies of cobalt nanostructures(2012) Nagaraja, H.S.; Nagaraja, K.K.; Rossignol, F.; Dumas-Bouchiat, F.; Champeaux, C.; Catherinot, A.The pulsed laser deposition technique associated with a low energy cluster beam is used to deposit cobalt thin films with a thickness 100-200 nm and cobalt dots of a diameter 100-200 nm on silicon substrates. The deposited thin films of Co are composed of clusters of a size 10- 50 nm, with very few large grains as revealed by atomic force microscopy. The observations performed by magnetic force microscopy on as-grown thin films reveal randomly distributed out-of-plane magnetic domain structures. These magnetic domains are aligned linearly by applying an external magnetic field either perpendicular or parallel to the substrate during the deposition. In addition, the effect of film thickness and roughness on multidomains is reported. The increase of roughness resulted in the decrease of magnetic domain width from 200 to 100 nm. This decrease is accompanied by the appearance of instability in the stripe domain pattern. Well separated cobalt dots of diameter in the range of 100-200 nm are also deposited on silicon substrates, which show arc-like multidomains. The domains seem to be oriented along the long axis of the dots. The domain structure of Co nanodots is similar to that of Co thin films indicating strong magnetic coupling of clusters. © Springer Science+Business Media, LLC 2012.Item Magnetic complexity, magnetodielectric effect and DFT calculations on correlation driven Gd2CoMnO6 insulator(Elsevier B.V., 2022) Prashanth, C.H.; Reddy, I.; Tarafder, K.; Chandrasekhar Kakarla, D.; Yang, H.D.; Adyam, V.; Jyothinagaram, K.In the family of Re2CoMnO6 manganite double perovskites, in contrast to parent La2CoMnO6 compound, Gd2CoMnO6 exhibits multiple magnetic transitions; ferromagnetic (FM) ordering, TC ∼ 112 K followed by AFM transition, TN ∼ 47 K, Gd spins ordering for T < 10 K and large isothermal entropy changes. A study of DC field-superimposed AC magnetic susceptibility measurements revealed the field-induced magnetic glassy behavior below TC and enhancement of FM correlations above TC. From the analysis of Almeida-Thouless behavior and dynamical power-law fit to frequency dependent AC susceptibility, Gd2CoMnO6 exhibits a volume spin glass-like nature below the freezing temperature, Tf ∼ 117.5 K. The isothermal field-dependent magnetic and dielectric permittivity data and temperature dependent Raman measurements (reported in ref. R. X. Silva et al., J, Appl. Phys. 114 194,102 (2013)) confirms the spin-phonon coupling induced magnetodielectric effect. Further, the ground-state electronic structure and magnetic properties of Gd2CoMnO6 are investigated using DFT + U formalism with Vienna Ab-initio Simulation Package (VASP) code and predicted the material to be a correlation-driven insulator. The correlation value of the Hubbard U parameter at the 4f-Gd elements changes the stability of the magnetic state from Ferri to FM spin alignment for Ueff ≥ 3 eV and is correlated to the experimentally observed field-induced transformation of the short-range-order FiM/spin-glass-like phase into the long-range ordered FM phase. © 2022Item Surface Structure and Electrochemical Behavior of Zinc-Nickel Anti-Corrosive Coating(Center of Excellence in Electrochemistry, Univ. of Tehran, 2023) Bhat, R.S.; Venkatakrishna, K.; Hegde, A.C.We report on the electrodeposition of a zinc-nickel alloy using a sulphate bath on mild steel (MS) substrate. The Hull cell experiment was used to optimize the bath composition and operating conditions. Sulphanilic acid (SA) was used as an additive for the coatings. The bath demonstrated an abnormal co-deposition with more zinc being deposited over nobler nickel. The effect of temperature and current density on the coating thickness, hardness, corrosion resistance, and weight % of Ni content in the coating was investigated. The corrosion behaviour of coated zinc-nickel alloy film in sodium chloride (wt.% 3.5) solution was investigated using potentiodynamic polarization and electrochemical impedance spectroscopic approaches. The nickel content in the coatings was determined through the colorimetric method and verified by the energy dispersive X-ray spectroscopy (EDX) technique. Atomic force microscopy (AFM) and Scanning electron microscopy (SEM) techniques were used to determine the surface roughness and surface topography, of the coatings. The results show that the zinc-nickel coatings had the highest corrosion resistance (0.213 mm y-1) at optimal current density (3A dm-2). Thus, due to their superior corrosion resistance Zn-Ni coatings have been largely used to protect the mild steel components in many industries including the automotive, military, and aerospace segments. © 2023 by CEE (Center of Excellence in Electrochemistry).Item Single-Layered Zn-Fe Alloy Electrodeposition for The Protection of Mild Steel Structures(Center of Excellence in Electrochemistry, Univ. of Tehran, 2024) Bhat, R.S.; Hegde, A.Electrodeposition of Zinc-Iron alloy has been used to improve the corrosion resistance of mild steel. This alloy plating was successfully coated on mild steel using the electrodeposition technique. Under varied deposition conditions, the zinc-iron alloy films onto the steel plate were examined. The purpose of this study is to describe the corrosion characteristics of the coated sample in 3.5% NaCl for the application of novel, sacrificial coatings for the defence of steel structures. It has been thoroughly examined how plating variables including bath composition, pH, and current density affect the composition, morphology; and corrosion properties of the coatings were discussed. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used to analyze the morphological characteristics and phase structure of the coatings. The surface roughness of the coating was measured by Atomic Force Microscopy (AFM). The Vickers indenter was employed to measure the microhardness of the coated sample. The corrosion resistance of Zn-Fe alloy coatings was assessed using electrochemical impedance spectroscopy (EIS) and polarization techniques at different current densities. The new low-cost Zn-Fe alloy coating was used for automobile applications. © 2024 by CEE (Center of Excellence in Electrochemistry).