Papers by Harish C Barshilia, Ph D
International Journal of Energy Research, 2021
Reduced graphene oxide (RGO) based composite non‐selective solar absorber coatings (RGO/silicate)... more Reduced graphene oxide (RGO) based composite non‐selective solar absorber coatings (RGO/silicate) were developed using a simple spray technique. RGO powders were prepared using the modified Hummers' method. RGO‐silicate suspensions were obtained by adding an appropriate quantity of RGO in a sodium silicate solution. Transmission electron microscopy studies showed the corrugated morphology of reduced graphene oxide powders. The presence of RGO in the composite absorber coatings was confirmed by X‐ray photoelectron spectroscopy data. In order to study the thermal stability, the coatings were deposited on stainless steel (SS) and Inconel substrates. The composite nonselective coating exhibited an absorptance (α) of 0.96 and emittance (ε) of 0.88 at 82°C on SS and Inconel substrates. The coatings sprayed on SS substrates showed good thermal stability for 428 hours at 500°C in air. The coatings sprayed on Inconel substrates were thermally stable in air at 600°C for 96 hours. The performance evaluation tests revealed that these coatings can be used for concentrated solar power applications.
Zinc oxide (ZnO) is a very promising material for diverse applications in electronics, optoelectr... more Zinc oxide (ZnO) is a very promising material for diverse applications in electronics, optoelectronics, spintronics, transparent thin film transistors, high power devices and so on. ZnO and Mn doped ZnO nanostructures with different morphologies were grown via vapour-liquid-solid (VLS) method. Morphological, optical and magnetic behaviour studies were carried out using field emission scanning electron microscope (FE-SEM), micro-Raman, photoluminescence (PL) and vibrating sample magnetometer techniques, respectively. FE-SEM studies revealed the formation of nanowires, nanopillars, nanosheets of ZnO crystals. Raman measurements confirmed the formation of ZnO phase. PL measurements revealed a strong green emission at 536 nm exposing the oxygen deficiency in the ZnO nanostructures. Mn doping was found to affect the morphological, optical and magnetic properties of ZnO nanostructures. Mn doped ZnO nanoneedles exhibited ferromagnetism at room temperature. The significant changes in the properties of ZnO nanostructures after Mn doping are discussed in detail.
Graphene oxide was synthesized from graphite flakes using modified Hummers' method. The interlaye... more Graphene oxide was synthesized from graphite flakes using modified Hummers' method. The interlayer spacings of graphite, graphite oxide and graphene oxide were measured using X-ray diffraction technique. The C/O atomic ratios of graphite oxide and graphene oxide were calculated from XPS measurements. The transformation of graphite to graphite oxide and finally to graphene oxide was clearly observed from the micro-Raman spectroscopy data and was confirmed from the FESEM micrographs. UV-VIS-NIR spectrophotometer was used to study the absorbance of graphene oxide and reduced graphene oxide samples. Finally, the chemically reduced graphene oxide was heat-treated in air to obtain chemically modified graphene.
Micromachining techniques such as mechanical micro-drilling, electrical discharge machining (EDM)... more Micromachining techniques such as mechanical micro-drilling, electrical discharge machining (EDM) and laser beam machining (LBM) play an important role in the manufacturing of micro-devices used in mechanical, electronics, aerospace and medical applications. In this paper, an effort has been made to compare the performance of these micromachining techniques with regard to tool wear, burr formation and surface integrity. This is done by producing 20 micro-holes of approximately 800 μm diameter on a rectangular block (90×30×3 mm 3) of Nimonic 80A superalloy. TiAlN coated WC micro-drills, Cu electrodes and CO 2 laser beam are used to produce these holes in conventional micro-drilling, EDM and LBM, respectively. The quality of the drilled hole (diameter, surface roughness and micro-burr formation), tool diameter analysis, taper angle and material removal rate (MRR) are compared and reported. A comprehensive analysis is also carried out on overcut, which leads to hole inaccuracy. Results show that mechanical micro-drilling produces better results in the above mentioned characteristics in comparison to LBM and EDM techniques. The relatively better performance of mechanical micro-drilling is attributed to the usage of TiAlN coating on WC tool.
Cirp Journal of Manufacturing Science and Technology, 2017
Thin films of TiO 2 were grown on n-type Si substrate by thermal oxidation of Ti films deposited ... more Thin films of TiO 2 were grown on n-type Si substrate by thermal oxidation of Ti films deposited by dc sputtering. The phase purity of TiO 2 was confirmed by Raman spectroscopy, and secondary ion mass spectroscopy was used to analyze the interfacial and chemical composition of ...
Advancements in surface modification technologies have led to the development of various thin coa... more Advancements in surface modification technologies have led to the development of various thin coatings aimed at improving the tribological properties of materials in order to reduce losses due to friction and wear. Lubrication is indispensable for achieving reduced friction between two moving surfaces. The increasing demand for low friction and wear in aerospace and other tribological applications which involve severe sliding conditions and the limitations of fluid lubricants at extreme environmental conditions such as high vacuum, low and high temperature, radiation, etc. gave rise to the need for solid lubricant coatings. Solid lubricants such as transition metal dichalcogenides, soft metals, diamond like carbon films, polymers, etc. have been successful in providing low friction at a sliding interface. However, the use of these coatings is restricted to certain areas of application conditions and environments due to issues related to their structure and properties. In recent years, development of nanostructured coatings has received great attention since they exhibit exotic properties due to nano-scale engineering. Novel coating architectures such as nanocomposites and multilayered coatings have been areas of intense research since these nanostructured solid lubricant coatings exhibit improved tribological properties in combination with other desirable properties such as improved adhesion and hardness over a wide range of environmental conditions. In this review, we have described the deposition and characterization of nanostructured solid lubricant coatings which have great potential for enhancing the properties of traditional solid lubricant coatings. Various methods used for the preparation of the nanostructured solid lubricant coatings have been described in brief. We describe in detail, the structure, microstructure, adhesive strength, mechanical and tribological properties, and thermal stability of sputter deposited nanostructured solid lubricant coatings. We also present the potential applications of nanostructured solid lubricant coatings in aerospace, automotive and other engineering sectors.
Journal of Magnetism and Magnetic Materials, May 1, 2023
Graphene was grown on high purity Cu foils using hot-filament chemical vapor deposition method. T... more Graphene was grown on high purity Cu foils using hot-filament chemical vapor deposition method. The foils were kept directly below the tungsten filament and the whole assembly was kept inside a vacuum chamber. CH 4 and H 2 were used as precursor gases and were allowed to shower on a hot filament, which was kept at a predetermined temperature. The optimization of the process parameters such as gas flow rates, temperature, durations, etc. was done to grow single layer and multilayer graphene. The graphene was characterized using optical microscopy, field emission scanning electron microscopy and micro-Raman spectroscopy techniques. The graphene layers grown at different methane flow rates are shown in Figure 1. By varying the methane flow rates, graphene domains of different sizes and shapes were achieved and are clearly evident from Figures 1a-c. The curved white lines (Figure 1a) present in the FESEM micrographs correspond to Cu terraces. The graphene grown on Cu foils was successfully transferred to SiO 2 substrate and the micrograph of which is shown in Figure 1d. The presence of D, G and G' bands in the Raman spectrum confirmed the growth of graphene in the Cu foil (Figure 2).
Coatings
The properties of spectrally selective solar absorber coatings can be fine-tuned by varying the t... more The properties of spectrally selective solar absorber coatings can be fine-tuned by varying the thickness and composition of the individual layers. We have deposited individual layers of WAlSiN, SiON, and SiO2 of thicknesses ~940, 445, and 400 nm, respectively, for measuring the refractive indices and extinction coefficients using spectroscopic ellipsometer measurements. Appropriate dispersion models were used for curve fitting of Ψ and Δ for individual and multilayer stacks in obtaining the optical constants. The W/WAlSiN/SiON/SiO2 solar absorber exhibits a high solar absorptance of 0.955 and low thermal emissivity of 0.10. The refractive indices and extinction coefficients of different layers in the multilayer stack decrease from the substrate to the top anti-reflection layer. The graded refractive index of the individual layers in the multilayer stack enhances the solar absorption. In the tandem absorber, WAlSiN is the main absorbing layer, whereas SiON and SiO2 act as anti-refle...
Superalloys such as Nimonic 80A have high strength at elevated temperatures, which make them attr... more Superalloys such as Nimonic 80A have high strength at elevated temperatures, which make them attractive towards various applications in aerospace industry.
Sensors and Actuators A: Physical, 2021
Abstract The paper presents the development of a novel anisotropic magnetoresistive sensor for me... more Abstract The paper presents the development of a novel anisotropic magnetoresistive sensor for measurement of angle in the interval 0o to 180o. A sensor is comprised of two Wheatstone bridges arranged at 45o to each other. A unique design is proposed wherein each resistive element of the Wheatstone bridge was formed with strips of varying widths. It results in a substantial reduction in harmonics errors due to the dispersion of the shape anisotropy field values within each element. The reduced harmonic errors also lead to a drastic reduction of hysteresis error (60 %) and offer better accuracy with a signal amplitude of 18 mV/V even in weak fields of ≤ 80 G. Further, the sensor was employed in the development of a pedal position sensor. The preliminary results of the development are presented, indicating the usability for industrial and automotive applications.
Sensors and Actuators A: Physical, 2021
Journal of Applied Physics, 2020
Solid particle erosion is an unavoidable problem for gas turbine compressor blades, wind turbines... more Solid particle erosion is an unavoidable problem for gas turbine compressor blades, wind turbines, crude oil pipes, rovers in outer space, and other machine components operated in harsh conditions. Gas turbine components are usually operated in the temperature range of 100–1400 °C. However, the influence of temperature on the solid particle erosion mechanism has not been studied adequately. In this paper, the influence of temperature on the solid particle erosion properties of metals (Ti6Al4V, SS 304, Al-8011, and Ti/TiN multilayers) and non-metals (Al2O3, fused quartz, and Si) is studied. The erosion tests were conducted in the temperature range of 30–800 °C. The erosion rate of metallic and ionic solids (viz., Ti6Al4V, SS 304, Al-8011, Al2O3, and Ti/TiN multilayers with the thermal expansion coefficient α ≥ 8 μm/°C) initially decreased with increasing temperature and then increased at higher temperatures, whereas for covalently bonded materials such as fused quartz (α = 0.55 μm/°C...
Journal of Magnetism and Magnetic Materials, 2019
Journal of Magnetism and Magnetic Materials, 2019
The temperature dependent magnetoresistive behaviour of field cooled naturally oxidised specular ... more The temperature dependent magnetoresistive behaviour of field cooled naturally oxidised specular spin valve systems has been studied in the temperature range of 300-10 K. Inconsistent to the non-specular spin valve system, an anomalous behaviour was evolved with large exchange bias and higher coercivity, below 200 K. The structural investigations inferred the formation of magnetic oxides with higher density gradient in the pinned layer, and the observed anomalous behaviour at low temperatures was correlated with the antiferromagnetic ordering of these oxides in spin glass state. The uncompensated interfacial magnetism of the nano-oxide layer was further confirmed by comparing with low temperature magnetoresistive behaviour of non-magnetic oxide based specular spin valve systems.
Surface and Coatings Technology, 2019
Solid particle erosion is a very serious and inevitable issue faced by key components of modern m... more Solid particle erosion is a very serious and inevitable issue faced by key components of modern machinery in various applications such as compressor blades and vanes of turbine engines, and turbine blades of advanced aircraft engines. In this direction third generation Ti/TiN nanolayered multilayered erosion resistant coatings were developed using sputtering technique. Films of around 7-10 µm total thickness with bi-layer thicknesses from 7.5-115 nm were deposited. Structural and mechanical properties such as hardness, toughness and stress of the films were studied, and correlated with the bi-layer thickness and deposition conditions. Erosion test was carried out according to ASTM G76-13 standard parameters at 30, 45, 60, and 90 o impinging angles. Since the compressor blades of the gas turbine engines usually operate at 100 to 550°C, the erosion tests were conducted at 400 o C. Films with lower bi-layer thickness showed better erosion resistance in comparison with higher bi-layer thickness films. Further, effect of bi-layer thickness, annealing and internal stress of the films on erosion resistance performance is studied. Detailed studies revealed that the optimized coating exhibited an improvement in the erosion performance by a factor of 15.
Solar Energy Materials and Solar Cells, 2016
Ti/Al 2 O 3 coating was designed and developed for the growth of carbon nanotubes (CNTs)-based ta... more Ti/Al 2 O 3 coating was designed and developed for the growth of carbon nanotubes (CNTs)-based tandem absorber on stainless steel (SS) substrates. The aluminum and titanium target power densities and oxygen flow rates were optimized to deposit the Ti/Al 2 O 3 coatings. The optimized Ti/Al 2 O 3 coating with a Co catalyst on top was used as an underlying substrate to grow the CNT-based tandem absorber at 800°C in Ar þH 2 atmosphere (i.e., SS/Ti/Al 2 O 3 /Co/CNT). The formation of aluminum titanium oxide (AlTiO) was observed during the CNT growth process and this layer enhances the optical properties of the CNT based tandem absorber. At 0.36 mm CNT coating thickness, the tandem absorber exhibits an absorptance of 0.95 and an emittance of 0.20. The optical constants of Ti, Al 2 O 3 and AlTiO coatings were measured using phase modulated spectroscopic ellipsometry in the wavelength range of 300-900 nm. The experimentally measured ellipsometric parameters have been fitted with the simulated spectra using Tauc-Lorentz model for generating the dispersion of the optical constants of the Al 2 O 3 and the AlTiO layers. The Ti and Al 2 O 3 layer thicknesses play a major role in designing CNT based tandem absorber with good optical properties. The transmission electron microscopy studies showed that the as-grown CNTs were multiwalled in nature. The angular and the polarization dependence studies of the CNT based tandem absorber grown at different thicknesses were carried out using UV-VIS-NIR spectrophotometer.
International Journal of Sustainable Energy, 2017
ABSTRACT Significant research in the past decade has been focused on quantitatively and qualitati... more ABSTRACT Significant research in the past decade has been focused on quantitatively and qualitatively validating potential of solar thermoelectric modules to harness electricity. In the present study, we have experimentally analysed steady-state temperature variation of a spectrally selective solar absorber coating (α = 0.954, ε = 0.13) with variation in solar irradiation flux (concentration ratios = 39, 50 and 65) using Fresnel lens and vacuum enclosure pressure (200 mbar to 900 mbar in steps of 100 mbar). It is observed that the experimental results so obtained go hand in hand with a COMSOL simulation model of the set-up. Further, we have carried out performance analysis of a solar thermoelectric generator (STEG) set-up enclosed in vacuum conditions equipped with Fresnel lens and absorber set-up coupled to Bi2Te3 thermoelectric module array electrically connected in series. The results depict a maximum power output of 0.91 W and a peak efficiency of 2.21% at a hot-side temperature of 642 K.
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Papers by Harish C Barshilia, Ph D