Current Resistivity Measurements Research Articles

Analysis of in-service composite insulators used in overhead railway traction

Polymeric based Composite insulators are extensively used for overhead rail electric traction system; these insulators play an important role in the traction electrification which supply power to the locomotives of train. Traction insulators are subjected to a variety of stresses, like mechanical, electrical, environmental, etc., these stresses act in unison, degradation and subsequent failure of traction insulator influences the safety of traction power supply system. To understand the phenomena of degradation and in-service aging, experimental investigations are conducted on in service traction insulators to identify and analyze the structural changes occurred in the field for a specified time, the insulators are of composite silicone polymeric materials rated for 25 kV. The electrical performance on the insulator samples is investigated using leakage current analysis and surface resistance measurements under normal and fog/moisture conditions using a specifically designed fog test chamber. The structural changes are studied by using Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDAX), Fourier Transform Infra-Red (FTIR) and wettability measurements. The study highlights the in-depth analysis conducted on the performance of service insulators compares with the fresh, also suggests mitigation methods to overcome the probable failures in the field. Some interesting results obtained from the study are analyzed and presented.

Short-Lived Electron Excitations in FeTe1 –xSex as Revealed by Microwave Absorption

The $\rm Fe_{1+y}Te_{1-x}Se_x$\ single crystals with the various Se/Te ratios were studied by the microwave absorption and direct current resistivity measurements. The comparison of the microwave absorption data and the resistivity versus temperature made it possible to separate the contributions of two types of spin fluctuations. One of them is due to the anisotropic magnetic (nematic) fluctuations. It is observed over the wide temperature range from 30K to 150 or 200K. In FeSe it has the maximum close to the structural transition temperature. Another MWA anomaly is located in the narrow temperature range above the superconducting transition. It is likely due to the antiferromagnetic fluctuations. Annealing of a sample at the temperature around 300 C in the oxygen atmosphere made it possible to exclude the effect of excess iron on the observed anomalies.

Failure analysis of BMC insulators used for third rail traction system

Bulk molding compound (BMC) or Glass Reinforced plastic (GRP) composite insulators are extensively used for the third rail electric traction system. The performance of these insulators primarily depends on the local environmental conditions that cause degradation over a period of time. Degradation leads to partial arcing which grow more severe and can generate combustion that ignites flammable debris, smoke including fires resulting in service interruptions and safety risks of the third rail traction system. In the present investigations, exhaustive analysis is conducted to understand the root cause of degradation and arcing on the field aged insulators rated for 750Vdc. Leakage current and surface resistance measurements are conducted under dry, wet and contaminated conditions. Further to better interpret Physico-chemical analysis are conducted using Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDAX) and Fourier Transform Infra-Red (FTIR) spectroscopy to investigate surface morphology and chemical changes in the samples, also Thermo-Gravimetric Analysis (TGA) is performed to find the thermal characteristics of the insulator. Interesting results obtained from the investigations clearly present evidence to loss of epoxy material from the bulk eventually leading to the exposure of glass fibers causing degradation, arcing and failure of the insulators. The study further highlights the essential procedures to be edopted to locate, isolate, and better anticipate failures of BMC insulators used in third rail traction system.

Mitigating the electromagnetic radiation by coupling use of waste cathode-ray tube glass and graphene oxide on cement composites

With technological development, the rapid growing numbers of electronic devices generate severe electromagnetic interference (EMI) and radiation to human environment. In this study, the coupling effect of graphene oxide (GO) addition (up to 0.10 wt.% of cement) and waste cathode-ray tube (CRT) glass replacement for fine aggregates (30 and 60 wt.%) in cement-based composites on mitigating EMI was studied. The electric permittivity obtained using a decoupling method was applied for evaluating the EMI shielding capacity of cement-based composites, while direct current (DC) electrical resistance measurement is conducted using four-probe method. The DC electrical resistivity of specimens increases insignificantly with increasing in GO content, but remarkably with increasing CRT glass content from 30 to 60 wt.%. The 60 wt.% replacement of waste CRT glass with 0.1 wt.% GO addition increases the relative permittivity by about 50% and 200% when the frequency is in the ranges of 104–5 × 106 Hz and 101–103 Hz, respectively. It is concluded that a significant increase in the permittivity can be obtained owing to the synergetic interaction between waste CRT glass and GO. The improvement in the EMI shielding ability of cement-based composites not only enables the applications of these composites in mitigating electromagnetic pollution, but also promotes large-volume recycling of toxic waste CRT glass.

Si-doped high-energy Li1.2Mn0.54Ni0.13Co0.13O2 cathode with improved capacity for lithium-ion batteries

Abstract

Microwave Absorption by Charge Density Waves in La2–xSrxCuO4

The results of studying the La2–xSrxCuO4 (x = 0.077−0.195) crystals with the microwave absorption, direct current resistance and magnetic susceptibility measurements are presented. The doping-temperature phase diagram with the boundaries of the areas with charge density waves, superconducting fluctuation and the bulk superconductivity state is plotted. The doping range of the charge density wave existence is found to be broader than that obtained from the X-Ray Diffraction study. It spreads at least down to x = 0.077.

Rhodium Oxide Surface-Loaded Gas Sensors

In order to increase their stability and tune-sensing characteristics, metal oxides are often surface-loaded with noble metals. Although a great deal of empirical work shows that surface-loading with noble metals drastically changes sensing characteristics, little information exists on the mechanism. Here, a systematic study of sensors based on rhodium-loaded WO3, SnO2, and In2O3—examined using X-ray diffraction, high-resolution scanning transmission electron microscopy, direct current (DC) resistance measurements, operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and operando X-ray absorption spectroscopy—is presented. Under normal sensing conditions, the rhodium clusters were oxidized. Significant evidence is provided that, in this case, the sensing is dominated by a Fermi-level pinning mechanism, i.e., the reaction with the target gas takes place on the noble-metal cluster, changing its oxidation state. As a result, the heterojunction between the oxidized rhodium clusters and the base metal oxide was altered and a change in the resistance was detected. Through measurements done in low-oxygen background, it was possible to induce a mechanism switch by reducing the clusters to their metallic state. At this point, there was a significant drop in the overall resistance, and the reaction between the target gas and the base material was again visible. For decades, noble metal loading was used to change the characteristics of metal-oxide-based sensors. The study presented here is an attempt to clarify the mechanism responsible for the change. Generalities are shown between the sensing mechanisms of different supporting materials loaded with rhodium, and sample-specific aspects that must be considered are identified.

Stretchability-The Metric for Stretchable Electrical Interconnects.

Stretchable circuit technology, as the name implies, allows an electronic circuit to adapt to its surroundings by elongating when an external force is applied. Based on this, early authors proposed a straightforward metric: stretchability—the percentage length increase the circuit can survive while remaining functional. However, when comparing technologies, this metric is often unreliable as it is heavily design dependent. This paper aims to demonstrate this shortcoming and proposes a series of alternate methods to evaluate the performance of a stretchable interconnect. These methods consider circuit volume, material usage, and the reliability of the technology. This analysis is then expanded to the direct current (DC) resistance measurement performed on these stretchable interconnects. A simple dead reckoning approach is demonstrated to estimate the magnitude of these measurement errors on the final measurement.

Influences of feedstock and plasma spraying parameters on the fabrication of tubular solid oxide fuel cell anodes

This study developed a tubular solid oxide fuel cell (SOFC) anode support layer via atmospheric plasma spraying, which is considered one of the most promising methods for producing SOFCs because of its faster deposition rate and lower cost compared with other film formation processes. Plasma spraying can replace the traditional use of extrusion technology to manufacture the anode base tube, eliminating the need for high-temperature sintering steps. In this study, commercially available powders were used to make the anode of a tubular SOFC from NiO/yttria-stabilized zirconia (YSZ) powder, and Na2CO3 and polymethyl methacrylate were tested as pore-forming agents. The anode composite powder was sprayed on the graphite base pipe, and the final product was changed by altering the spraying parameters and anode powder ratio. The direct current (DC) resistance measurements showed that the conductivity of the Ni/YSZ tubular anode formed with higher power plasma spraying could reach 428.55 S/cm at 800 °C. The experimental results showed that the power and parameters of atmospheric plasma spraying could affect the porosity and electron conductivity of tubular SOFC anodes.

In situ synthesis, characterization, conductivity studies of polypyrrole/silver doped zinc oxide nanocomposites and their application for ammonia gas sensing

The synthesis of polypyrrole (PPy)/silver doped zinc oxide (Ag–ZnO) nanocomposites have been carried out by employing a simple and environmentally benign in situ polymerisation strategy. The structural, morphological and thermal properties of nanocomposites were characterised through Fourier transform infrared spectra (FTIR), X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The FTIR spectra revealed the formation of nanocomposite by the shift in the characteristic peak of PPy to a lower wavenumber region in PPy/Ag–ZnO nanocomposite. The effective utilisation of the surface of the Ag–ZnO nanoparticles by PPy chains was also confirmed from X-ray diffraction. The SEM and TEM images revealed the good interaction between Ag–ZnO and PPy up to a loading of 10 weight percentage (wt%). TGA studies indicated the excellent thermal stability of the polymer nanocomposite. DSC results revealed that the glass transition temperature of the nanocomposite was increased with increase in the concentration of nanoparticles. The electrical properties of the nanocomposites were studied from the direct current (DC) and alternating current (AC) resistivity measurements. The dielectric properties, AC and DC conductivity of the nanocomposites were significantly increased with increase in content of nanoparticles. The sensitivity of ammonia gas through the nanocomposites was also evaluated with respect to different contents of nanoparticles. The ammonia sensing properties of nanocomposite was higher than that of pure PPy and the maximum sensor response was observed for 10 wt% of composite.

Structural, Electrical and Dielectric Properties of Li-Ni Ferrite–Polystyrene Thin Film Nano-Composites

Lithium nickel ferrite Li0.5Ni0.5Fe2O4 was synthesized by the sol–gel auto combustion method. The prepared ferrite was mixed with polystyrene with ratio 0.25:1(FP1), 0.50:1(FP2), 0.75:1(FP3) and 1:1(FP4) to get ferrite–polystyrene composite. The synthesized samples were characterized by x-ray diffraction, dielectric and direct current resistivity measurements. The x-ray diffraction pattern shows that the polystyrene is amorphous in nature. The diffraction peaks of ferrite–polystyrene composite become sharper and narrower by increasing the ferrite filler contents. Room temperature resistivity of the composites decreased significantly from 4.63 × 1013 Ω-cm to 3.67 × 109 Ω-cm with increasing ferrite content and temperature dependent resistivity decreased with increasing temperature. The dielectric constant increased as the concentration of ferrite was increased in the base sample. A maximum value of 23.60 was achieved for the last sample. Conversely, the increase in frequency results from the decrease in dielectric constant followed the Maxwell–Wagner model.

Control and materials characterization System for 6T Superconducting Cryogen Free Magnet Facility at IUAC, New Delhi

A system for carrying out automatic experimental measurements of various electrical transport characteristics and their relation to magnetic fields for samples mounted on the sample holder on a Variable Temperature Insert (VTI) of the Cryogen Free Superconducting Magnet System (CFMS) has been developed. The control and characterization system is capable of monitoring, online plotting and history logging in real-time of cryogenic temperatures with the Silicon (Si) Diode and Zirconium Oxy-Nitride sensors installed inside the magnet facility. Electrical transport property measurements have been automated with implementation of current reversal resistance measurements and automatic temperature set-point ramping with the parameters of interest available in real-time as well as for later analysis. The Graphical User Interface (GUI) based system is user friendly to facilitate operations. An ingenious electronics for reading Zirconium Oxy-Nitride temperature sensors has been used. Price to performance ratio has been optimized by using in house developed measurement techniques mixed with specialized commercial cryogenic measurement / control equipment.

Electrically Active Defects in Neutron Irradiated HPSI 4H-SiC X-ray Detectors Investigated by ZB-TSC Technique

Electrically active defects in high-purity semi-insulating (HPSI) 4H-silicon carbide (4H-SiC) X-ray detectors have been characterized before and after neutron irradiation by zero-bias thermally stimulated current (ZB-TSC) and high-temperature resistivity measurements. The ZB-TSC measurements prior to irradiation reveal nine hole traps in the energy range of 0.22–1.16 eV and two electron traps at $\text{E}_{c} -0.35$ eV and $\text{E}_{c} -0.44$ eV. For the same case, high-temperature resistivity measurements yield thermal activation energy in the range of 1–1.3 eV. It is considered that the hole traps at $\text{E}_{v}+ 0.83$ eV and $\text{E}_{v }+ 1.16$ eV along with defects located near the activation energies are possibly responsible for the substrate compensation. A poor resolution of 11.8-keV full-width at half-maximum (at 40 keV of 152Eu) with un-irradiated HPSI 4H-SiC detectors is attributed to the charge trapping and polarization effects. After neutron irradiation at the fluence of $10^{11}$ n/cm2, seven new traps ( $\text{E}_{v}+ 0.68$ eV, $\text{E}_{v} + 1.08$ eV, $\text{E}_{v} + 1.22$ eV, $\text{E}_{c} -0.72$ eV, $\text{E}_{c} - 0.9$ eV, $\text{E}_{c} - 1.04$ eV, and $\text{E}_{c} - 1.1$ eV) are identified with no significant changes in the activation energies. This indicates that the substrate resistivity is unaffected by the neutron-irradiation-induced defects. No considerable changes in the X-ray spectral response are noted at $10^{11}$ n/cm2.

Selectivity Enhancement by Using Double-Layer MOX-Based Gas Sensors Prepared by Flame Spray Pyrolysis (FSP).

Here we present a novel concept for the selective recognition of different target gases with a multilayer semiconducting metal oxide (SMOX)-based sensor device. Direct current (DC) electrical resistance measurements were performed during exposure to CO and ethanol as single gases and mixtures of highly porous metal oxide double- and single-layer sensors obtained by flame spray pyrolysis. The results show that the calculated resistance ratios of the single- and double-layer sensors are a good indicator for the presence of specific gases in the atmosphere, and can constitute some building blocks for the development of chemical logic devices. Due to the inherent lack of selectivity of SMOX-based gas sensors, such devices could be especially relevant for domestic applications.

Two‐dimensional joint inversions of cross‐hole resistivity data and resolution analysis of combined arrays

ABSTRACTIn this study, a new two‐dimensional inversion algorithm was developed for the inversion of cross‐hole direct current resistivity measurements. In the last decades, various array optimisation methods were suggested for resistivity tomography. However, researchers have still collected data by using classical electrode arrays in most cross‐hole applications. Therefore, we investigated the accuracy of both the individual and the joint inversion of the classical cross‐hole arrays by using both synthetic and field data with the developed algorithm. We showed that the joint inversion of bipole–bipole, pole–bipole, bipole–pole, and pole–tripole electrode arrays gives inverse solutions that are closer to the real model than the individual inversions of the electrode array datasets for the synthetic data inversion. The model resolution matrix of the suggested arrays was used to analyse the inversion results. This model resolution analysis also showed the advantage of the joint inversion of bipole–bipole, pole–bipole, bipole–pole, and pole–tripole arrays. We also used sensitivity sections from each of the arrays and their superpositions to explain why joint inversion gives better resolution than the any individual inversion result.

Effect of the eccentricity of normal resistivity borehole tools on the current field and resistivity measurement

Three-dimensional finite element numerical model calculations have been carried out to investigate the quantitative effect of the eccentric position of a normal resistivity borehole probe used in practice. Detailed calculations were done between the point-wise analytical solution and numerical solution to verify the results obtained from the finite element method for a normal probe with finite-length cylindrical electrodes. In the borehole the pattern of the current flowing out from current electrode A is efficiently influenced by the eccentricity. For high-resistivity rock the current density is decreased, while for low-resistivity rock it is increased toward the wall side. On the other hand, the eccentricity does not affect considerably the apparent resistivity calculated from electrode potentials. In most geological situations the deviation is less than 2%. However, in infrequent cases when the true resistivity of the rock is extremely low and/or the distance between the potential and current electrodes is very small the effect of the eccentricity can exceed even 10%.

Atomic and electronic structures evolution of the narrow band gap semiconductor Ag2Se under high pressure

Non-trivial electronic properties of silver telluride and other chalcogenides, such as the presence of a topological insulator state, electronic topological transitions, metallization, and the possible emergence of superconductivity under pressure have attracted attention in recent years. In this work, we studied the electronic properties of silver selenide (Ag2Se). We performed direct current electrical resistivity measurements, in situ Raman spectroscopy, and synchrotron x-ray diffraction accompanied by ab initio calculations to explore pressure-induced changes to the atomic and electronic structure of Ag2Se. The temperature dependence of the electrical resistivity was measured up to 30 GPa in the 4–300 K temperature interval. Resistivity data showed an unusual increase in the thermal energy gap of phase I, which is a semiconductor under ambient conditions. Recently, a similar effect was reported for the 3D topological insulator Bi2Se3. Raman spectroscopy studies revealed lattice instability in phase I indicated by the softening of observed vibrational modes with pressure. Our hybrid functional band structure calculations predicted that phase I of Ag2Se would be a narrow band gap semiconductor, in accordance with experimental results. At a pressure of ~7.5 GPa, Ag2Se underwent a structural transition to phase II with an orthorhombic Pnma structure. The temperature dependence of the resistivity of Ag2Se phase II demonstrated its metallic character. Ag2Se phase III, which is stable above 16.5 GPa, is also metallic according to the resistivity data. No indication of the superconducting transition is found above 4 K in the studied pressure range.

Fabrication of Nd3+ and Mn2+ ions Co-doped Spinal Strontium Nanoferrites for High Frequency Device Applications

Microemulsion method has been used for the synthesis of high resistive spinal nanoferrites with nominal composition Sr1−x Nd x Fe2−y Mn y O4 (0.0 ≤ x ≤ 0.1, 0.0 ≤ y ≤ 1.0) for high frequency device applications. It has been confirmed by x-ray diffraction (XRD) results that these ferrites have a cubic spinal structure with a mean crystallite size ranging from 34 mm to 47 nm. The co-substitution of Nd3+ and Mn2+ ions was performed, and its effect on electrical, dielectric and impedance properties was analyzed employing direct current (DC) resistivity measurements, dielectric measurements and electrochemical impedance spectroscopy (EIS). The DC resistivity (ρ) value was the highest for the composition Sr0.90Nd0.1FeMnO4, but for the same composition, dielectric parameters and alternating current (AC) conductivity showed their minimum values. In the lower frequency range, the magnitudes of dielectric parameters decrease with increasing frequency and show an almost independent frequency response at higher frequencies. Dielectric polarization has been employed to explain these results. It was inferred from the results of EIS that the conduction process in the studied ferrite materials is predominantly governed by grain boundary volume.

Effect of Au nano-particles doping on polycrystalline YBCO high temperature superconductor

In this research, we prepared different Au nanoparticles (0.1–2wt%) doped YBCO high temperature superconductor samples by sol-gel method. To characterize the samples, we used X-Ray diffraction (XRD) and scanning electron microscope (SEM) analysis. Results show the formation of orthorhombic phase of superconductivity for all prepared samples. We observed that by adding Au nanoparticles, the grains' size of the samples reduces from 76nm to 47nm as well. The critical current density (Jc) and transition temperature (Tc) were determined using current versus voltage (I–V) and resistivity versus temperature (ρ-T) measurements, respectively. We found that by increasing Au nanoparticles in the compound, in comparison to the pure YBCO sample, the transition temperature, pinning energy and critical current density will increase. Also, the highest Jc is for 1wt% Au doped YBCO compound that its critical current density is about 8 times more than the Jc of pure one in 0.7T magnetic field.

Electrochemical MEA Characterization: Area Specific Resistance Corrected to Fuel Utilization as Universal Characteristic for Cell Performance

Membrane-electrode-assembly (MEA) is a heart component of SOFC and defines the limits for power density, efficiency and durability available for exploitation in stacks and systems. MEA performance is often given as measure for possibilities of fuel cell technology. Most widespread way to communicate the MEA performance is to present the I-U-characteristic at a constant temperature and to estimate the area specific resistance from the slope of this curve. Other methods for characterization of performance like current density, impedance and local resistance measurement under defined operating conditions also have been used for this purpose. The fuel composition worldwide used for MEA tests (from dry hydrogen to H2:H2O=50:50) is connected with open circuit voltage which has great impact on measured performance. Moreover the realized fuel utilization strongly depends on operating conditions and varies in broad range. For these reasons it is difficult to compare results achieved by different researchers. It is beneficial to define unified value which would characterise electrochemical MEA performance. To resolve this challenge the voltage drop during the cell performance have been mathematically separated in two parts: (i) voltage drop due to change of Nernst voltage as a result of fuel utilization (and humidification) by current flow and (ii) voltage drop due to ohmic and polarization losses in the cell. This approach allows to separate the influence of non-linearity of Nernst voltage dependence from current on estimated cell resistance. It was found that at temperatures above 750°C the area specific resistance of the cell corrected to the Nernst voltage drop (fuel utilization) is a constant value, which only weakly depend on fuel composition. Favourable operating conditions as well as influence of operating conditions for estimation of cell resistance will be presented.