Variation Of Electrical Resistivity Research Articles

Effect of ammonia gas on electrical properties of boron nitride/nickel oxide (BN80/NiO20) nanocomposite

Hybrid materials exhibit excellent properties than their components. Herein, boron nitride and boron nitride/nickel oxide (BN80/NiO20) nanocomposite films were deposited by the drop-casting method. X-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy techniques have been utilized for determining structural, defect chemistry and morphological properties of deposited films. The structural analysis confirmed the formation of BN and NiO phases. Nelson–Riley Factor analysis and Raman analysis revealed the presence of defect states in BN80/NiO20 film. Electrical properties of films were studied in the presence of various concentrations of ammonia gas molecules at different temperatures. BN80/NiO20 composite film showed higher resistivity in the presence of ammonia gas than pure BN film. Variation of electrical resistivity with ammonia gas concentration has been explained through a proposed model. Also, to obtain the resistivity variation concerning ammonia gas concentrations at different temperatures, the linear regression method was used. This work insight the electrical behavior of composite material at different gas concentrations which opens these materials for exploration towards gas sensing and different functional applications.

Rapid detection of olive oil blends using a paper-based portable microfluidic platform

This paper presents an application of a portable microfluidic platform based on a filter paper on which multi-walled carbon nanotubes were deposited to quickly determine the quality of olive oil by measuring electrical resistance. Three different types of filter paper with different pore sizes and different filtration rates were used in the middle of the microfluidic platform, as a material for soaking a blend of olive and high-oleic sunflower oil. The rapid prototyping xurographic technique was used to fabricate the complete microfluidic platform. For testing purposes, oil blends in various proportions were deposited through the inlet on the top of the platform. The variation in electrical resistance at room temperature was measured, using the Chemical Impedance Analyzer, successfully indicating oil proportions in measured blends. We obtained the change of resistance in the range from 0.26 MΩ to 2.79 MΩ per percentage of olive oil content, for corresponding linearity index from 0.71 to 0.99, for papers labelled with 44–45, respectively. Additionally, a prototype of electronic device was developed for acquisition and displaying measured data, based on the created microfluidic platform.

Simultaneous Measurements in Shape Memory Alloy Springs to Enable Structural Health Monitoring by Self-Sensing Actuation

The vital sensing parameter on self-sensing actuation in the spring form of shape memory alloy (SMA) is determined through experimental analysis. A unique measurement technique is adopted that interlinks the electro–thermo–mechano features during the shape memory effect in NiTi, NiTiCu, and NiTiFe springs. The influence of the spring index, the number of active turns, material composition, and transition temperature is assessed. SMA spring’s effective functional behavior to be used as an actuator and or a sensor is ensured via the measurement of electrical parameters—the resistance, inductance, and impedance variations revealed during the solid–solid phase change, i.e., displacement. However, the spring form of SMA would exhibit variation in inductance and a variation in electrical resistance, which in turn is considered a variation in the electrical impedance, which may also be appropriate sensing information. The thermo-mechanical and thermo-electrical measurements are synchronized using an impedance analyzer and data acquisition module with a specific programming technique. The active spring is equivalently a series resistance–inductance circuit, since the collective effect of a decrease in resistance and increase in inductance with an increase in temperature offers increased $$\frac{L}{R}$$ and vice versa to support structural health monitoring.

COCONUT FIBER SENSOR FOR HUMIDITY / SENSOR DE FIBRA DE COCO PARA HUMIDADE

In this article we present the construction of a resistive humidity sensor making use of alternative materials of organic origin and source of renewable, coconut fiber. The hygroscopic film is obtained by deposition of the coconut fiber powder combined with carbon powder (graphite) on a substrate of polyester resin with short coconut fiber. Experimental results indicated that the sensor has characteristics expected from a humidity sensor, with adsorption in the time range of 45 seconds and variation in electrical resistance depending on the amount of water molecules in the air.

Electrical Conductivity‐Based Estimation of Unfrozen Water Content in Saturated Saline Frozen Sand

The salinity of the pore solution is closely associated with the unfrozen water content and can be reflected by variation in electrical conductivity in frozen soils. However, the influence of salinity was not considered in the existing models for estimation of unfrozen water content based on electrical conductivity measurement, and a model considering the effect of salt content was therefore developed to estimate the change of unfrozen water content of saline sands with variation of salt content (0%, 0.2%, and 1%). The unfrozen water content and the electrical resistivity were measured by nuclear magnetic resonance (NRM) and using resistance test equipment under a temperature ranging from 25°C to −15°C, respectively. The results indicated that the model using a cementation exponent expressed by a piecewise function with respect to temperature can produce a reasonable estimation on the content of unfrozen water. There was an essential difference between nonsaline and saline frozen sands in the increase of electrical resistivity due to the different reduction rates of unfrozen water content. The variation of electrical resistivity in nonsaline sand was mainly caused by the decrease of free water when temperature was higher than the freezing point and adsorbed water when temperature was lower than the freezing point, whereas the reduction of free water in two stages was the main reason for the variation of electrical resistivity in saline sand. The results and data obtained provided a basis for further developing a novel approach to measure the unfrozen water content in the field.

Modified WO3 nanosheets by N-GO nanocomposites to form NO2 sensor

In this work, WO3 nanosheets were synthesised and decorated with different percentages of N-GO nanocomposites to study gas sensing assets. The X-ray diffraction (XRD) and Raman spectra showed fine crystal quality. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) illustrated nanosheets morphology for WO3 and confirmed its decoration. The variation of the sensor electrical resistance was studied at various gas concentrations in the range of temperature intervals. The optimal operational temperature was 200 °C. The optimum response signal and recovery time for WO3–N-GO 6% at 200 ppm concentration were 90 s and 205 s, respectively. The selectivity of the WO3–N-GO samples was 53%, 46% and 60% for WO3–N-GO 3%, WO3–N-GO 6% and WO3–N-GO 9%, respectively at 200 °C. The highest response was found for WO3–N-GO 9% to NO2 (58%) and WO3–N-GO 6% to CO (28%) at 200 °C. Therefore, by selecting the optimum percentage of N-GO nanocomposites, the sensors can be fabricated with the highest response to NO2 or CO.

Electrical conductivity of MoS2 thin films and graphite under continuous injection to protons

The electrical conductivity of thin films of MoS2 and graphite has been studied under conditions of continuous injection of low-energy protons (∼ 1-4 keV). The effect of a sharp increase (by 3-4 orders of magnitude) in the electrical conductivity of substances with a layered structure (MoS2 and graphite) at T ∼ 293 K has been established. The observed effect increases (from 2 to 10 times) as the temperature decreases from room temperature to liquid nitrogen temperature (T ∼ 77 K) and with increasing number of protons injected into the sample. The established temperature variation of electrical resistance is typical for materials with a metallic type of conductivity. It is shown that a thin surface layer, onto which protons penetrate, is responsible for the change in the electrical conductivity of MoS2 and graphite films.

Fabrication of reduced graphene oxide modified poly(3,4-ethylenedioxythiophene) polystyrene sulfonate based transparent conducting electrodes for flexible optoelectronic application

Present article reports on reduced graphene oxide (rGO) modified poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) based transparent conducting electrodes for flexible optoelectronic applications. PEDOT: PSS samples embedded with different rGO concentrations i.e. 0, 1, 2, 3, 4, 5 wt% were prepared and later on, bar coated on polyethylene terephthalate substrate using a 30 μm wire size bar. Various parameters including sheet resistance, bending test (outside and inside bending), optical transmittance etc. were estimated. Our analysis indicates that the samples with 1 wt% rGO possess improved results i.e. low sheet resistance (315 ± 8 Ω/sq.) and high transmittance (~ 74%). Additionally, the sample shows low electrical resistance variation up to 12% (maximum increase) during outward bending and 9% (maximum decrease) during inward bending of the sample for bending curvature from 20 to 100 m−1.

Determination of the vacancy migration enthalpy in a ternary Fe54Cr16Ni30 alloy, by Monte Carlo simulation of ordering kinetic, using a vacancy diffusion mechanism

We determined the vacancy migration enthalpy in a Fe54Cr16Ni30 stainless steel with a face-centered cubic structure by Monte Carlo simulation of the kinetic ordering by a vacancy diffusion mechanism. We have calculated isothermal curves of electrical resistivity variation as a function of time, at two different temperatures T1 = 700 K and T2 = 800 K (Barkani et al., 2007) [1], (Belkadi et al., 2019) [2]. The vacancy migration enthalpy determined in our work ΔHVM = (1.10 ± 0.031) eV, is higher than that determined by Yoshihiro Sekio et al. [3] in an alloy with a composition close to that of our alloy, and which is 0.77 eV. It is slightly lower than that determined by Dimitrov et al. [4] who found a value of 1.17 eV, independent of nickel content for Fe-Cr-Ni steels containing 16% Cr and a nickel concentration ranging from 20%Ni to 45%Ni.

Thermoelectric performance of copper-rich β-Cu2Se films with Ag-doping by magnetron sputtering

The concept of “phonon-liquid electron-crystal” (PLEC) have attracted many researchers for thermoelectric materials. In this study, a series of Ag-doped β-Cu2Se films were prepared on single crystalline Si(111) substrate by magnetron sputtering and the influence of Ag doping on the phase composition, chemical component and thermoelectric performance of the deposited β-Cu2Se films were studied. An energy dispersive spectrometer (EDS) showed that the Cu-rich β-Cu2Se films in which the ratio of Cu to Se in β-Cu2Se lattice varied from 3.59 to 4.96 as Ag atomic percent content increased from 0 to 2.97 were obtained. The Ag existed in the form of CuAgSe phase which increased electrical resistivity and Seebeck coefficient. The phase transition from α to β phase of Cu2Se only took place at ~60 °C. The variation of electrical resistivity with Ag content relied on the combined action of the amounts of CuAgSe phase and the ratio of Cu to Se in β-Cu2Se lattice of deposited films. The power factor of 1.37 at% Ag samples at whole measured temperature was the highest in all samples due to high Seebeck coefficient. It was attributed to lower resistivity than that of bulk Ag-doped β-Cu2Se materials of references that the power factor of our deposited films reached the order of mW.m−1K−2.

Self-Sensing Properties of Green Alkali-Activated Binders with Carbon-Based Nanoinclusions

This paper is aimed at investigating the self-sensing properties of Portland-free alkali-activated binders doped with carbon-based nanofillers. Four different inclusions (carbon nanotubes, carbon nanofibers, carbon black and graphene nanoplatelets) were added into the matrix in the same amount. The physical and electromechanical properties were analyzed. The self-sensing capabilities of the samples were tested by applying a square wave voltage signal and measuring the variation of electrical resistance during cyclical compression tests. The results showed that the presence of nano-inclusions enhanced the sensing behavior of the materials, especially regarding the linearity and the hysteresis performances. Such results appear promising for the application of such novel and innovative nano-modified composites in the field of monitoring structures and infrastructures.

Study of the variations in apparent electrical resistivity of activated sludge during the electro-dewatering process

The high energy consumption of high apparent electrical resistivity (AER) in sludge during the later stages of the electro-dewatering (EDW) process is a difficult problem; however, analysis of sludge AER may contribute to a reduction in energy consumption. In this study, the variations in the AER of activated sludge and potential mechanisms related to sludge properties were systematically examined. First, a sludge cake was divided into four horizontal layers, in order to investigate the sludge AER in each layer. Then, the effects of variations in water distribution, oxidation-reduction potential (ORP), pH, metal ions, sludge conductivity, zeta potential, temperature, and sludge microstructure on the AER in each layer were explored. The results showed that the sludge AER began to increase from the bottom layers to the top layers when the moisture content (MC) was decreased to 60%. The formation of nonionic chemical systems and the gas barrier layer could increase the AER in the top layers, and the increase in sludge AER in the bottom layers was due to the decrease in MC and sludge conductivity. In addition, electrolyte release and electromigration had a significant effect on the sludge AER. This work identifies potential causes for the increase in AER, and provides a reference for solving problems related to high AER in sludge during the later stages of the EDW process.

Electric resistance as a sensitive measure for detecting graphene wear during macroscale tribological tests

Super-high mechanical strength and excellent lubrication property at the nanoscale render graphene a promising ultra-thin solid lubricant. However, macroscale friction tests have shown that wear of graphene often occurs resulting in failure of interface lubrication. As graphene coatings are atomically thin, a sensitive and reliable detection method for monitoring wear has been a great challenge to date. In this work, we performed tribological experiments on monolayer graphene on SiO2/Si while simultaneously measuring the in-plane electric resistance of graphene during the sliding tests. Our experiments showed that the electric resistance exhibited a sudden increase signifying the onset of graphene wear well before the macroscale friction increased rapidly. The variation of in-plane electric resistance was found to depend on the wear track length and relative orientation. Longer wear track and wear track perpendicular to the current would typically lead to higher increase in graphene electric resistance. Our work demonstrates that monitoring in-plane electric resistance can be a simple, sensitive and predictive method for detecting graphene wear, which makes it a useful inspecting technique for a wide range of mechanical applications.

Graphene and carbon nanotube-based high-sensitive film sensors for in-situ monitoring out-of-plane shear damage of epoxy composites

Graphene (GN) and carbon nanotube (CNT) have already been explored their potential crack-monitoring abilities in the field of composite materials, but a relatively low sensitivity to shear damage is still a practical problem. This work aims to improve the monitoring sensitivity to out-of-plane shear damage by constructing hybrid GN/CNT film sensors with a GN weight loading of 0–10%. The prepared GN/CNT sensors are integrated into epoxy composites and both quasi-static and cyclic shear loads are carried out. It is found from quasi-static testing that once the out-of-plane shear damage initiates, relative electrical resistance variation suddenly jumps about 34–191% from the GN/CNT film sensors. Also, the sensitivity coefficient in the crack growth stage could reach 124–684. Namely, the GN/CNT sensors show high monitoring sensitivity to the initiation and growth of out-of-plane shear damage. Moreover, results from cyclic loading further reveal that the GN/CNT sensors possess stable sensitivity to the shear deformation and damage. Meanwhile, similar response trends from an acoustic emission sensor prove the monitoring reliability of the GN/CNT film sensors. The obtained high sensitivity demonstrates that the GN/CNT hybrid film sensors are prospective in the field of structural health monitoring of composite materials.

Experimental research on electrical resistivity variation of coal under different loading modes

In order to investigate the variation regularity of coal mass electrical resistivity in a complex stress environment, a real-time testing system of resistivity variation regularities of coal under loading was established in this study. Through this testing system, resistivity variations of coal mass under uniaxial compression, cyclic loading, multi-stage loading, stress relaxation, and creep loading were tested, respectively. Also, field emission scanning electron microscopy (FE-SEM) was carried out on coal mass. Ultimately, the variation characteristics and micro-mechanism of coal mass resistivity under different loading modes were discussed in depth. The research results indicated that the electrical resistivity of the coal mass varies with stress under different loading modes. The results also suggested that there are great correlations between axial stress, axial strain, and resistivity. Furthermore, it was found that the variation regularity of coal mass electrical resistivity changes with the change of pore structure during mechanical loading. Considering the variations of the axial stress and porosity during uniaxial compression, it was also demonstrated that the electrical resistivity of the coal mass is dominated by its pore structure and characteristics.

A molecular dynamics study of the mechanical and electrical properties of Polydimethylsiloxane-Ni conductive nanocomposites

Molecular dynamics was applied to develop a novel PDMS and PDMS-Ni nanocomposite model. First, the PDMS model was validated in terms of the elastic and compressive moduli using available experimental data. The model was then used as a benchmark to add Ni nanoparticles and create a PDMS-Ni conductive nanocomposite model. This model was studied under uniaxial tensile and compressive loading conditions for different Ni filler ratios and mean particle diameters. The electrical resistivity of the model was then obtained as a function of pressure and the compressive stresses. The PDMS-Ni MD model was validated via the literature and shown to successfully predict electrical resistivity variations versus compressive stresses. The results show that as the Ni filler ratio increased from 3:1 to 6:1, the drop in initial electrical resistivity of the composites occurred much faster and at lower stresses. Furthermore, as the mean Ni particle diameter size was increased from 1 nm to 5 nm, the electrical conductivity of the PDMS-Ni improved at different filler ratios. The developed PDMS-Ni MD model can be used to study the electrical and mechanical behaviors of such materials in biosensor applications. It can further be used to study the effects of adding other fillers to PDMS matrix.

Room temperature ammonia gas sensing characteristics of copper oxide-tin oxide composite thin films prepared by radio frequency magnetron sputtering technique

In this work, thin films of composite copper oxide-tin oxide [CuO:SnO2 (1:1)] were prepared by radio frequency magnetron sputtering technique at room temperature on quartz glass substrates. X-ray diffraction study revealed that the as-deposited films were amorphous in nature and the crystallinity of the films was obtained by annealing the films at 1000 °C. The hexagon rod-like structure, dews-like particles and cylindrical-shaped particles were observed in surface morphological study. The X-ray photoelectron spectroscopic study confirmed the formation of Cu2+ and Sn4+ states in the deposited films. The decrease in optical energy band gap with increase in RF power and annealing temperature may be due to the creation of localized states near the band edges of CuO:SnO2. The gas sensing characteristics of the films were analysed by recording the electrical resistance variation of the films in the presence/absence of various concentrations of NH3 gas at room temperature. The CuO:SnO2 film exhibited a highest sensing response of 3838 for 125 ppm of NH3 gas at room temperature. The film sustained its initial sensor response even after 6 months period for 5 repeated cycles, which ascertained the stability and repeatability of CuO:SnO2 thin film based gas sensor.

About electrical resistivity variation during drying and improvement of the sensing behavior of carbon fiber-reinforced smart concrete

The addition of conductive fibers to a cementitious material reduces its electrical impedance, for monitoring purposes, based on the relationship between external stresses (mechanical or thermal) and changes in electrical properties. In this context, variations in the electrical properties due to drying prevent the application of this technique, unless such variations are negligible or precisely predictable. The aim of this paper, therefore, is to study the variation of the complex electrical impedance during drying, for measurement frequencies between 4 Hz and 1 MHz. Shrinkage, weight loss and electrical impedance spectrum were measured on three mortars with carbon fiber volume fractions (FVF) of 0, 0.1 and 0.5%. The results show that in the absence of conductive fibers, the real and imaginary parts of the impedance increase due to water loss. On the other hand, in the presence of a percolated carbon fiber network, the real impedance of the material decreases at low frequencies and increases at high frequencies during drying; for intermediate frequency ranges, quasi-constant values can be observed. In addition, as the material dries, the capacitive behavior of the material wanes, and the imaginary impedance values tend towards 0. The electrical behavior then approaches ideal resistive behavior with a real impedance value independent of the measurement frequency. Blind frequencies have been identified for fibrous mortars around 1 kHz and 40 kHz for 0.1% and 0.5% FVF, respectively. For monitoring purposes, coupling the presence of fibers with an appropriate measurement frequency would minimize the effects related to the variation of impedance as a function of time – i.e., allowing more precise monitoring of mechanical loads with time.

Surface Characteristics of Polymers with Different Absorbance after UV Picosecond Pulsed Laser Processing Using Various Repetition Rates.

We experimented with two polymer materials with different ultraviolet (UV) wavelength absorption characteristics, which are commonly used in flexible devices, by applying an ultrashort-pulsed laser of a 355-nm UV wavelength for 10 ps. The laser parameters studied were pulse repetition rate, laser irradiation method, and laser power condition. Previous studies using polyethylene terephthalate (PET), which does not exhibit linear absorption at a UV wavelength, have focused on processing trends resulting in minimal collateral damage around the laser-induced ablation. However, our results showed a trend of accumulating such damage irrespective of the laser parameters. Meanwhile, polyimide (PI) exhibited a completely different behavior depending on the laser parameters. At low pulse repetition rates, minimal collateral damage was observed, whereas at high repetition rates, the morphology varied considerably. The electrical characteristics of the laser-processed materials were found to be correlated with the variations in morphology. In the case of PI, such variations in electrical resistance and morphology indicated that the material was carbonized. The findings of this study are expected to provide a useful reference when selecting parameters for the laser processing of similar polymer materials.

Electrophysical Properties of 2 Co–Ti–Al Alloy Produced by SHS Pressing

This article investigates the microstructural features, phase composition, and electrophysical properties of Co2TiAl intermetallic alloy produced by self-propagating high-temperature synthesis (SHS) in combination with pressing. For the first time, a practically single-phase alloy based on the Co2TiAl Heusler compound with the weight content of at least 82% was produced using SHS; the synthesis products also contain TiCox intermetallic compounds of variable composition. The unit cell parameter of Co2TiAl was a = 5.8433 ± 0.0002 A. Metallographic analysis of the microstructure after SHS pressing demonstrated structure densification and decrease in porosity in comparison with samples produced by regular SHS without application of load to the combusted sample. The average microhardness of the synthesized alloy was Hμ = 5650 MPa, and the electrical resistance of the synthesized material at ambient temperature was 1.35 μΩ m. Variations of specific electrical resistance were studied in vacuum of 1.33 × 10–3 Pa in the temperature range of 77–1300 K. At temperatures above 600 K, the electrical resistance as a function of temperature ρ(T) in Co2TiAl alloy exhibits a decrease in slope; that is, for the given alloy, there exists the so-called effect of resistance saturation. The Curie point corresponding to transition from the magnetic to paramagnetic state was 133 K.