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Chaudhary A.,National Aerospace Laboratories, Bangalore | Barshilia H.C.,National Aerospace Laboratories, Bangalore
Journal of Physical Chemistry C | Year: 2011

An inexpensive and facile one-step method to develop a superhydrophobic coating on the copper surface is reported. Superhydrophobic CuO/Cu(OH) 2 surfaces were prepared by a simple solution-immersion process at room temperature, without using a low surface energy material. The structure and composition of as-prepared CuO/Cu(OH)2 hierarchical structure were confirmed by X-ray diffraction, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The growth stage was carefully examined by field emission scanning electron microscopy (FESEM), and it was observed that initially Cu(OH)2 nanoneedle arrays were formed on the copper surface and subsequently the CuO microflowers formed on the nanoneedle arrays. The contact angle as a function of immersion time was studied using a contact angle goniometer. The correlation between the microstructure of the immersed copper surface and the contact angle was examined carefully using FESEM and atomic force microscopy (AFM). Our results based on FESEM and AFM studies show that the CuO/Cu(OH)2 coatings demonstrate superhydrophobicity only for an optimal combination of the solid region (i.e., microflowers and nanoneedles) and air pockets (i.e., voids). The maximum static water contact angle on the prepared surface was 159°. The wettability transition of the CuO/Cu(OH) 2 surface from superhydrophobicity to superhydrophilicity was studied by the alteration of oxygen plasma treatment and dark storage. The FESEM, AFM, and XPS studies showed that this transformation was mainly due to the morphological changes that occur in addition to the chemical changes taking place on the CuO/Cu(OH)2 surface under the influence of oxygen plasma. XPS analysis demonstrated that the incorporation of oxygen species by oxygen plasma activation accounted for the highly hydrophilic character of the surface. © 2011 American Chemical Society.

Anandan C.,National Aerospace Laboratories, Bangalore | Bera P.,National Aerospace Laboratories, Bangalore
Applied Surface Science | Year: 2013

CeO2 thin films were deposited on silicon and silicon nitride substrates by magnetron sputtering at room temperature and annealed at 400 and 600 C in air and vacuum. Interaction between deposited CeO2 and Si in CeO2/Si and CeO2/Si3N4 systems was investigated by XPS. The results show that Ce is present as both Ce4+ and Ce3+ oxidation states in CeO2 film deposited on Si substrate, whereas Ce4+ is the main species in as-deposited CeO 2/Si3N4 film. Detailed analyses of Ce3d, Si2p and O1s core level spectra demonstrate that Ce2O3 and SiOx or cerium silicate type of species are formed at the interface of CeO2 and Si. Concentrations of Ce3+ species increase drastically in CeO2/Si thin films after annealing at 400 C in vacuum due to enhanced interfacial reaction. On the other hand, interfacial reaction between CeO2 and Si3N4 substrate is limited in as-deposited as well as heat treated films. © 2013 Elsevier B.V. All rights reserved.

Selvakumar N.,National Aerospace Laboratories, Bangalore | Barshilia H.C.,National Aerospace Laboratories, Bangalore
Solar Energy Materials and Solar Cells | Year: 2012

Solar energy is the most abundant source of renewable energy. The direct method of harnessing solar energy is the solar thermal conversion method using solar absorbers. The absorbers are coated with solar selective coatings with high absorptance and low thermal emittance. Spectrally selective coatings which are stable up to temperatures ≤300°C (in air and vacuum) have been developed in the past. These coatings are mainly deposited from wet chemical routes (e.g., electrodeposition) and have been reviewed widely in the literature. Because of the environmental issues as well as low thermal stability of these wet chemical deposited coatings, researchers all over the world started looking for other alternative routes such as physical vapor deposited (PVD) coatings. A great deal of research has been carried out since 1990s to develop PVD coatings for both mid- and high-temperature applications. The mid-temperature coatings are used mainly for solar hot water and industrial process heat applications, whereas, the high-temperature absorber coatings are used in concentrating solar power systems for solar thermal power generation. It is well recognized that in order to increase the efficiency of solar thermal power plants, solar selective coatings with high thermal stability are required. In recent years, significant efforts have been made in the field of solar selective coatings to achieve high solar absorptance and low thermal emittance at higher temperatures (T≥400°C). Transition metal based cermets have emerged as novel high temperature solar selective coatings, which are currently being used for solar thermal power plants for electricity generation. Solar selective coatings based on transition metal nitrides, oxides and oxynitrides also hold great potential for high-temperature applications because of their excellent mechanical and optical properties, which are yet to be commercialized. In this review, we present the state-of-the-art of the physical vapor deposited solar selective coatings used for solar thermal applications with an emphasis on sputter deposited coatings for high-temperature applications. A detailed survey, covering the period 1970-present, has been made for the PVD deposited solar selective coatings with high absorptance and low emittance. This review article also describes in detail about the commercially available PVD coatings for flat-plate/evacuated tube collectors and solar thermal power generation applications. © 2011 Elsevier B.V. All rights reserved.

Panda P.K.,National Aerospace Laboratories, Bangalore
Ceramics International | Year: 2013

Samaria nanofibers were prepared by electrospinning homogeneous viscous solutions of samarium citrate in polyvinyl alcohol (PVA) and calcining the nanofibers at 1000 °C for 2 h. PVA solutions of varied concentrations e.g. 19%, 23% and 25% (by weight) were used as polymer precursors. Electrospinning was carried out at 9 kV DC by maintaining tip to collector distance (TCD) of 7 cm. Thermogravimetric analysis (TGA) of nanofibers room temperature (RT) to 800 °C indicates the complete decomposition of organics below 750 °C with a weight loss of 55%. The morphology of nanofibers was observed under scanning electron microscope (SEM). The nanofibers are found cylindrical with fiber diameter in the range of 200-500 nm and aspect ratio>1000. The average diameter of the fibers increases with the increase in PVA concentration. The diameter of calcined Samaria nanofibers reduced by 43% due to loss of organics and shrinkage. © 2012 Elsevier Ltd and Techna Group S.r.l.

Kidambi R.,National Aerospace Laboratories, Bangalore
Physics of Fluids | Year: 2012

The frequency and damping of free lateral linear oscillations of a viscous non-cylindrical liquid bridge, formed between two axial disks of radii R 1 and R 2, are computed using a recently developed semi-analytic procedure [R. Kidambi, J. Fluid Mech.681, 597 (2011)]. A comparison with recent experimental results [E. J. Vega and J. M. Montanero, Phys. Fluids21, 092101 (2009)] for the first non-axisymmetric mode over a range of bridge volumes is good and the damping rate is better predicted than by a one-dimensional slice model especially for highly viscous bridges. The procedure can be used to calculate the oscillation characteristics of any desired mode for any region of the parameter space. © 2012 American Institute of Physics.

Barshilia H.C.,National Aerospace Laboratories, Bangalore
Solar Energy Materials and Solar Cells | Year: 2014

We describe the growth, characterization and performance evaluation of a multilayer solar selective coating useful for solar thermal power generation. The solar selective coating of the present work consists of Ti/chrome interlayer, two absorber layers of AlTiN and AlTiON, and an anti-reflection layer of AlTiO. All the layers have been deposited using reactive pulsed direct current sputtering of Ti and Al targets in Ar+N2, Ar+N 2+O2 and Ar+O2 plasmas, respectively. A large number of analytical tools have been used to characterize the structural and optical properties of the absorber coating. The optimized coating exhibited an absorptance of 0.930 and an emittance of 0.16-0.17 on stainless steel substrates and an absorptance of 0.933 and an emittance of 0.07 on copper substrates. The absorber coating displayed improved adhesion, UV stability, corrosion resistance and thermal stability in air and vacuum up to 350 and 450 °C, respectively under cyclic heating condition for more than 1000 h. © 2014 Elsevier B.V. All rights reserved.

Shri Prakash B.,National Aerospace Laboratories, Bangalore | Senthil Kumar S.,National Aerospace Laboratories, Bangalore | Aruna S.T.,National Aerospace Laboratories, Bangalore
Renewable and Sustainable Energy Reviews | Year: 2014

In recent times, synthesis, development and fabrication of anode component of solid oxide fuel cell (SOFC) have gained a significant importance, especially after the advent of anode supported SOFC. The function of the anode electrode involves the facilitation of fuel gas diffusion, oxidation of the fuel, transport of electrons and transport of by-product of the electrochemical reaction. Although impressive progress has been made in the development of alternative anode materials with mixed conducting properties and few of the other composite cermets, Ni/YSZ continues to be the most sought after anode for high temperature SOFC applications. Despite of its poor carburization and sulfidation capabilities during the operation of SOFC directly on hydrocarbons, Ni/YSZ continues to be the most opted anode electrode material due to its high catalytic activity for hydrogen oxidation, methane reforming, high electronic and ionic conductivity and stability. Present review focuses on the various aspects pertaining to Ni/YSZ as an anode in SOFC. Various factors that influence the ohmic, activation and the concentration polarization contribution of anode while using Ni/YSZ are discussed. Importance of optimizing the composition, microstructure and porosity to minimize the above mentioned polarizations are discussed extensively. Various synthesis methods that are used in the preparation of optimized NiO/YSZ composite powder and the methods that are adopted to fabricate anode component are provided in detail in the article. Information on Ni/YSZ anode failure and strategies to improve the long term stability are also discussed exhaustively. Parameters that influence the carburization and sulfidation of Ni/YSZ while using hydrocarbons as fuel are elaborated in this article and means to minimize the same are also discussed. © 2014 Elsevier Ltd.

Naidu V.P.S.,National Aerospace Laboratories, Bangalore
Journal of Optics (India) | Year: 2014

Multi sensor image fusion algorithm based on directional Discrete Cosine Transform (DDCT) - Principal Component Analysis (PCA) hybrid technique has been developed and evaluated. The input images were divided into non-overlapping square blocks and the fusion process was carried out on the corresponding blocks. The algorithm works in two stages. In first stage, modes 0 to 8 were performed on images to be fused. For each mode, the coefficients from the images to be fused are used in the fusion process. The same procedure is repeated for other modes. Three different fusion rules are used in fusion process viz., 1. Averaging the corresponding coefficients (DDCTav), 2. Choosing the corresponding frequency band with maximum energy (DDCTek) and 3. Choosing the corresponding coefficient with maximum absolute value (DDCTmx) between the images. After this stage, there are eight fused images, one from each mode. In second stage, these eight fused images are fused using PCA. Performance of these algorithms were compared using fusion quality evaluation metrics such as root mean square error (RMSE), quality index (QI), spatial frequency and fusion quality index (FQI). It was concluded from the results that DDCTav performs poor and DDCTek performs slightly better than DDCTmx. Moreover, DDCTek is computationally simple and easily implementable on target hardware. Matlab code has been provided for better understanding. © 2013 Optical Society of India.

Naidu V.P.S.,National Aerospace Laboratories, Bangalore
Defence Science Journal | Year: 2011

A novel image fusion technique based on multi-resolution singular value decomposition (MSVD) has been presented and evaluated. The performance of this algorithm is compared with that of well known image fusion technique using wavelets. It is observed that image fusion by MSVD perform almost similar to that of wavelets. It is computationally very simple and it could be well suited for real time applications. Moreover, MSVD does not have a fixed set of basis vectors like FFT, DCT and wavelet etc. and its basis vectors depend on the data set. © 2011, DESIDOC.

Singh A.K.,National Aerospace Laboratories, Bangalore
Journal of Physics: Conference Series | Year: 2012

Helium is commonly used as a pressure transmitting medium to render the sample pressure hydrostatic in high pressure experiments with diamond anvil cells. On solidification under pressure helium begins to develop strength that is characteristic of any solid. The estimation of the compressive strength of helium as a function of pressure is important as it helps in estimating the nonhydrostatic stresses that can develop in the sample even when it remains immersed in helium pressure transmitting medium. The x-ray diffraction data on polycrystalline samples obtained with the radial diffraction geometry are commonly used to determine the compressive strength of solids. This method fails in the case of helium because of it s low scattering power. The nonhydrostatic stresses that develop in crystalline solids immersed in helium pressure transmitting medium were used to estimate the strength of helium. The diffraction data available in the literature were selected for this study. It was important for this study to consider the data from the experiments that were conducted ensuring that the samples did not come in contact with the anvils. The analysis of these data suggests that the strength of helium remains low (< 0. 1 GPa) at pressures below 20 GPa and increases to ∼2 GPa at 100 GPa.

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