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Aging studies on polymeric insulators under DC stress with controlled climatic conditions
No full textIn the present investigation, long term service performance of silicone rubber based polymeric insulators under DC stress with controlled climatic conditions is attempted. Simultaneous application of UV, thermal, humidity with DC electrical stress is applied to polymeric insulators enclosed in a specially fabricated climatic chamber. The stresses are applied for 1000 h for an adopted cycle to simulate close service life conditions. The leakage current is regularly monitored and recorded. After the experimentation, samples of the aged specimen are subjected for post analysis and psycho-chemical analysis like Scanning Electron Microscope (SEM) to monitor morphological changes, Energy Dispersive X-Ray analysis (EDAX) to observe elemental presence over the surface, Fourier Transform Infra-Red (FTIR) spectroscopy to examine chemical changes in the material, Thermogravimetric analysis (TGA) to understand the role of filler in aged insulator specimen and loss of Loss of hydrophobicity was measured. Investigations with long duration DC stress reveal material degradation, depolymerization and loss of ATH; this could result in low thermal stability and accelerate the thermal erosion and early failures
Self-Assembled Pd-6(II) Molecular Spheroids and Their Proton Conduction Property
No full textA series of molecular spheroids (SP1-SP4) was synthesized using pseudolinear bisimidazole and bisbenzimidazole donors in combination with Pd(NO3)(2) acceptor via coordination-driven self-assembly. They were characterized by NMR and mass spectrometry, and the solid-state structures of SP1 and SP3 were confirmed by X-ray diffraction. Crystal packing revealed the presence of molecular channels with water molecules in the channels as proton source. All the systems showed proton conductivity across a wide range of temperature and relative humidity. Furthermore, the mode of proton conduction in these molecular spheroids was explored by performing a control experiment using 2,4-dinitrophenol molecule, which indicates that the proton conductivity in the present case increases with increasing surface area of these molecular spheroids
Bubble dynamics and atomization mechanisms in burning multi-component droplets
No full textWe examine the complete sequence of events associated with the transition in the topology of a single droplet into multiple fragments of secondary droplets in the context of burning multi-component miscible mixtures. The multi-component blends consist of tetradecane as a lower volatile component, while butanol and acetone-butanol-ethanol (A-B-E) are used as the higher volatile constituents. In addition to the widely recognized theory of bubble growth via micro-bubble coalescence, we reveal that the vapor bubble growth also occurs through the merging of large bubbles during the combustion of droplets. The initial bubble growth (Regime I) and collapse cycles were found to increase the rate of bubble nucleation in the droplet, which in turn leads to the growth and merging of two or more vapor bubbles into a single larger bubble (Regime II). The final stage of bubble growth (Regime III) is associated with the Rayleigh-Taylor (RT) instability at the vapor-liquid interface. After the inception of the RT instability, capillary wave propagation is also witnessed on the droplet surface. The breakup of a vapor bubble results in the creation of a ligament that subsequently undergoes pinch-off into one or more secondary droplets. The ligament pinch-off mechanisms are categorized into two types, i.e., tip breakup and tip-base breakup, which govern the diameter and velocity of secondary droplets along with succeeding volumetric shape oscillations in the parent droplet. In particular, the ligament tip-base pinch-off mechanism results in a bimodal distribution of secondary droplets. After the initial breakup event, a vapor bubble may grow either in the secondary droplet or inside the developing ligament, leading to a sequential cascade of breakup events. Published by AIP Publishing
Effects of environmental and operational variability on the spectrally selective properties of W/WAlN/WAlON/Al2O3-based solar absorber coating
No full textThe stability of solar selective absorber coatings in hostile environments (e.g., humid condition, corrosive medium, longer exposure at elevated temperature) needs to be critically assessed to ensure durability of such coatings. In the present work, magnetron sputtered W/WAlN/WAlON/Al2O3-based absorber coating with a high absorptance (0.958) and low emittance (82 degrees C) has been tested in humid and corrosive environments. The selectivity (absorptance/emittance) of the coating did not change after keeping it in 95% humidity at 37 degrees C for 400 h. Corrosion study in 3.5% NaCl solution reveals that this novel multilayer coating has a better corrosion resistance than that of uncoated stainless steel (SS) substrate. The nanoindentation test on the coating indicates that it has a hardness of 9.6 +/- 0.5 GPa. The performance of the coating did not degrade after heat treatment at 350 degrees C in air for 1000 h. Additionally, the activation energy for degradation has been determined to predict the stability of the coating at high temperature. Further, the normal spectral emissivity of the tandem solar absorber was measured in the full angular range from 200 to 500 degrees C. The results of emissivity measurements by varying observation angles are analysed using numerical integration to obtain the total hemispherical emissivity. In summary, W/WAlN/WAlON/Al2O3 stack is an attractive candidate absorber coating for photo-thermal conversion systems
Assessment of Surface Water Storage trends for increasing groundwater areas in India
No full textRecent studies based on Gravity Recovery and Climate Experiment (GRACE) satellite mission suggested that groundwater has increased in central and southern parts of India. However, surface water, which is an equally important source of water in these semi-arid areas has not been studied yet. In the present study, the study areas were outlined based on trends in GRACE data followed by trend identification in surface water storages and checking the hypothesis of causality. Surface Water Extent (SWE) and Surface Soil Moisture (SSM) derived from Moderate-resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer -Earth Observing System (AMSR-E) respectively, are selected as proxies of surface water storage (SWS). Besides SWE and SSM, trend test was performed for GRACE derived terrestrial water storage (TWS) for the study areas named as R1, R2, GOR1 and KOR1. Granger-causality test is used to test the hypothesis that rainfall is a causal factor of the inter-annual variability of SWE, SSM and TWS. Positive trends were observed in TWS for R1, R2 and GOR1 whereas SWE and SSM show increasing trends for all the study regions. Results suggest that rainfall is the granger-causal of all the storage variables for R1 and R2, the regions exhibiting the most significant positive trends in TWS
Estimating the number density and energy distribution of electrons in a cold atmospheric plasma using optical emission spectroscopy
No full textCold atmospheric plasmas are generous sources of chemically active species, the reaction rates which can be predicted only if the electron number density and the electron energy distribution function are known. Here, the authors present a procedure for estimating both these parameters from the optical emission spectrum of an argon plasma. The peaks in the spectrum were curve fitted with Voigt profiles, and their widths and areas were mapped to the number density and energy distribution of electrons in the plasma, using the mathematical models for Stark broadening and Corona population, respectively. These plasma parameters were optimized to establish a good match between the simulated and the experimental peak attributes. This analysis estimated the value of the electron number density to be approximately 1.5 x 10(15) cm(-3) and the mean electron temperature to be approximately 0.37 eV in their plasma. It also predicted that the energy distribution of electrons can be closely approximated using a Maxwellian distribution. Published by the AVS
Citric acid assisted synthesis of manganese tungstate nanoparticles for simultaneous electrochemical sensing of heavy metal ions
No full textManganese tungstate nanoparticles (NPs) were successfully synthesized via a simple and cost effective citric acid assisted solution combustion method. Rietveld refinement of PXRD pattern indicates the formation of pure wolframite phase of manganese tungstate. Transmission electron microscope (TEM) analyses confirm the spherical shaped nanoparticles with average particle size ranging from 12 to 26 nm. The ultra-light combustion derived manganese tungstate NPs exhibits mesoporous nature with the estimated band gap 2.9 eV. The synthesized NPs were found to be an excellent electrode modifier for the simultaneous detection of Pb(II), Cd(II), Cu (II) and Hg(II) ions at nanomolar (nM) concentration. The present electrochemical sensor exhibits wide linearity of 10 - 500 nM with limit of detection based on 3 sigma method is 3.3, 3.5, 2.9 and 3.1 nM for Pb(II), Cd(II), Cu(II) and Hg(II) respectively. Additionally, room temperature photoluminescence emission spectrum exhibits an intense band at 445 nm that can be attributed to (1)A(1), ground-state to the high vibration T-1(2) energy levels of distorted WO6] octahedral groups
Effect of process optimization on electronic properties of conjugated small molecules
No full textIn this work, powders of a crystalline conjugated small molecule are thermally evaporated and electronic devices are fabricated to understand process property relationship. The conjugated small molecule possessing donor-acceptor-donor structure is deposited at various rates ranging from very low; 0.5 angstrom s(-1) to as high as 10 angstrom s(-1). It is observed that the chemical structure of 2,5-dithienyl-3,4-(1,8-naphthylene) cyclopentadienone (DTCPA) remains unaltered after thermal evaporation. It is also observed that there is a change in morphology and crystal orientation of the deposited films with a change in deposition rate. A growth mechanism concerning morphology is proposed based on the morphological and structural studies. As the deposition rate increases, there appears to be a gradual change in physical structure and molecular alignment. Optical properties such as UV-Visible absorption suggests that majority of the thermally evaporated films have considerable absorption spectra in the visible range. While photoluminescence studies suggest that 0.5 angstrom s(-1) film showed large emission at 700 nm whereas, all other films showed large emission at 540 nm. Current density versus voltage characteristics of DTCPA showed that at higher evaporation rate the curve no longer acts as rectifying diode, which is further explained by an increase in ideality factor. The photoelectric responses of these films indicate that deposition rates and therefore the film morphology has a profound effect on the energy band level of the film as indicated by the extracted device parameters. The DTCPA films deposited at 2 angstrom s(-1) exhibit the best response with an ideality factor of 3.8 and highest mobility of 0.27 cm(2) V-1 s(-1) suggesting optimum deposition rate is one of the critical parameters for device fabrication
Efficient Photosynthesis of Organics from Aqueous Bicarbonate Ions by Quantum Dots Using Visible Light
No full textWe synthesized CuAlS2/ZnS quantum dots (QDs) composed of biocompatible, earth-abundant elements that can reduce salts of carbon dioxide under visible light. The use of an asymmetric morphology at a type-II CuAlS2/ZnS heterointerface balances multiple requirements of a photoredox agent by providing a low optical bandgap (similar to 1.5 eV), a large optical cross section (>10(-16) cm(2) above 1.8 eV), spatial proximity of both semiconductor components to the surface, as well as photochemical stability. CuAlS2/ZnS QDs thus have an unprecedented photochemical activity in terms of reducing carbon dioxide in the form of aqueous sodium bicarbonate under visible light, without the need for a cocatalyst, promoter, or sacrificial reagent while maintaining large turnover numbers in excess of 7 x 10(4) per QD. Devices based on these QDs exhibit energy conversion efficiencies as high as 20.2 +/- 0.2%. These observations are rationalized through our spectroscopic studies that show short 550 fs electron dwell times in these structures. The high energy efficiency and the environmentally friendly composition of these materials suggest a future role in solar light harvesting