Increase In Impedance Research Articles

Micro–Macro-Analysis and Model Derivation of Electrical Resistivity of Ningxia Cement–Loess

In recent years, highway infrastructure in the Ningxia region of China has rapidly advanced. Cement–loess is extensively utilized in the roadbed and foundation reinforcement. It is necessary to conduct micro–macro-analysis and model derivation of the electrical resistivity on Ningxia cement–loess, which are beneficial for both the practical application of electrical resistivity and the evaluation of the geotechnical properties of cement–loess. Therefore, a series of electrical resistivity measurements, microstructural observations (scanning electron microscopy), mineral analyses (thermogravimetric analysis), and theoretical analyses were adopted on the cement–loess. The following conclusions can be drawn: The electrical resistivity is negatively related to dry density and water content, while it is positively related to cement dosage and curing age. A cement dosage of 6% exhibits a lower hydration reaction potential compared to 12%, causing a slower increase in electrical resistivity. The formation of calcium silicate gel around particles results in particle clustering and pore filling, reducing the pore area and increasing electrical resistivity. Increased hydration also decreases microscopic orientation, contributing to a higher electrical resistivity of cement–loess. Finally, a new three-dimensional electrical resistivity model was created, finding that the electrical resistivity of Ningxia cement–loess was determined by the dry density, water content (ρd·w), cement dosage, and curing age (aw·T) in an exponential function form. The new three-dimensional electrical resistivity model could be used in the high-efficiency evaluation of the cement–loess geotechnical parameter, offering valuable insights for the monitoring and maintenance of road infrastructure.

Effect of graphene on the key electrical, optical, and magnetic properties of polymethylmethacrylate: a study based on molecular modeling.

In this work, a new polymeric structure was designed consisting of a nanometric sheet of graphene (G) and a polymethylmethacrylate (PMMA) repeat unit, which was designated as PMMA-G. Three degrees of polymerization of PMMA-G were considered: monomer (PMMA-G1), dimer (PMMA-G2), and trimer (PMMA-G3). The effect of incorporating a nanometric sheet of graphene into the molecular structure of PMMA on the modification of some of its main optical, magnetic, and electrical properties was investigated. Currently, the study presented here is of great relevance since various areas of technology require new materials with specific properties for the development of new devices. The results of our study reveal that the dielectric constant of PMMA is reduced when graphene is incorporated. However, a percentage increase of 14.48% in the refractive index of PMMA when graphene is inserted to form the nanocomposite is observed. It is found that the absolute value of molar magnetic susceptibility of PMMA increases considerably when reinforced with graphene. Finally, when reinforcing PMMA with graphene to obtain the PMMA-G nanocomposite, the electrical resistivity increases by almost an order of magnitude. We used computational tools under Materials Studio (MS) software. We built a PMMA molecule with three degrees of polymerization, graphene sheet, and polymethylmethacrylate-graphene composite (PMMA-G) was built also with three degrees of polymerization using a concentration of 50% graphene over the PMMA polymer. For each structure, we used computational code DMol3 of MS, which is based on the Density Functional Theory, and the geometry optimization process was carried out to obtain the most stable structures. Finally, using the connectivity indices method together with topological properties of the molecular structures, implemented in Synthia computational code of MS software, we calculated the dielectric constant, magnetic susceptibility, refractive index, and electrical resistivity, for pure PMMA and PMMA-G structures for their three degrees of polymerization. The results were analyzed, and the changes in these properties were discussed in terms of the effect of an electric and magnetic field on the molecular structures of PMMA-G with respect to PMMA.

Effect of quenching and solubilization temperature on thermal, electrical, mechanical, and magnetic properties of a Heusler CuAlMnTiB alloy

We report a systematic investigation of the effect of quenching and solubilization temperature on the thermal, electrical, mechanical, and magnetic properties of the Heusler alloy CuAlMnTiB. The experimental procedure and the results obtained demonstrated that the tempering process can effectively adjust the physical properties of the CuAlMnTiB alloy. This treatment led to an increase in electrical resistivity, which went from 2.34×10−7Ω∙m in the raw melt sample (TBF) to 4.49×10−7Ω∙m in the sample quenching at 850 ºC (T850), in addition to an increase in the Curie temperature, from 297.5 ºC (TBF) to 305.85 ºC (T850). A decrease in remanent magnetization from 2.74 emu/g (TBF) to 0.31 emu/g (T850) and in the coercive field, which reduced from 54.15 Oe in the TBF to 4.55 Oe in the T850, was also observed. This makes tempering a viable alternative to adapt these properties to various technological applications, without requiring changes in the alloy composition. Here we were able to reach structural and magnetic properties compatible with those reported in the literature for CuMnAl alloys of different compositions.

Dissociative electrochemical analysis of materials degradation of an anion exchange membrane electrolyser

For anion exchange membrane (AEM) electrolysers, degradation studies provide valuable insights into how individual components degrade. Often, this presents a formidable challenge as each component significantly contributes to overall degradation. Here, we propose a methodology to individually compare the degradation of key components in AEM electrolysers: hydrogen evolution reaction (HER) catalyst, oxygen evolution reaction (OER) catalyst, and the AEM itself. First, to measure the degradation of catalyst-coated substrates (CCS) commonly used in AEM electrolysers, the AEM was replaced with a diaphragm (Zirfon Agfa UTP 500) permeable to OH− ions and stable in alkaline media. Subsequently, a cell with a stable catalytic layer (Nafion-coated Ni-felt substrates) was assembled to focus on membrane degradation with an AEM Sustainion X37-50 Grade 60. Chronopotentiometry and electrochemical impedance spectroscopy (EIS) revealed that the cell with the AEM experienced a threefold increase in ohmic resistance, attributed to the loss of functional groups. Additionally, an ion exchange capacity (IEC) analysis indicated that Sustainion lost approximately 20% of its ion exchange capacity. In contrast, the cell composed of CCS and Zirfon showed lower degradation. EIS data fitting demonstrated increased kinetic-related resistances while the ohmic resistance remained unchanged. This work presents a practical approach for comparing component degradation in AEM electrolysers.

Fabrication of conductive polyimide/metal composite fibers for high temperature EMI shielding

Surface metallization of high-performance polymer fibers via electroless plating represents a significant advancement in producing lightweight, flexible and durable electromagnetic interference (EMI) shielding fabrics. The conventional process for metallization of polyimide (PI) fibers faces challenges, including complex procedures and insufficient interfacial adhesion between the metal layer and fiber matrix. Herein, carboxylate-containing PI (PIC) fibers were developed to mitigate the mechanical degradation caused by traditional alkaline etching. Conductive composite fibers (PIC/Cu) were successfully produced through a continuous electroless copper plating process. The robust PIC/Cu interfacial bonding achieved based on nanoscale mechanical interlocking through Ni nanoparticles imparts excellent flexibility and durability, evidenced by only a 4 % increase in electrical resistance after 5000 bending cycles. The dense, uniform copper layer provides high conductivity (1.3 × 104 S/cm), resulting in an optimal EMI shielding efficiency of 63.4 dB for the corresponding fabric. Moreover, PIC/Cu-Ni fibers prepared by further electroless plating of nickel layer on the surface of PIC/Cu fibers demonstrate remarkable electrical stability across temperatures ranging from 50 to 350°C, with only a 1.2 % reduction in conductivity after exposure to 350°C for 1 h. These findings advance the development of high-performance conductive PI fibers for applications in aerospace vehicles and high-temperature environments.

DFT study of the brownmillerite-type strontium-based oxygen-deficient perovskites SrTMO2.5 (TM = Mn, Fe, Co and Cu)

DFT studies are performed to investigate the crystal structure and geometry, electronic and magnetic properties of brownmillerite-type strontium-based oxygen-deficient perovskites [Formula: see text] (TM = Mn, Fe, Co and Cu) in orthorhombic phase. The comparison of the calculated lattice parameters shows consistency with the experiments, and all these perovskites are thermodynamically stable as revealed by cohesive energy. The spin-dependent calculations of the electronic band profiles demonstrate the metallic behavior of all these deficient perovskites. The increase in electrical resistivity and electronic thermal conductivities with temperature also confirms the metallic behavior of these compounds. The optimized ground state energies in different magnetic phases and post-DFT treatment confirm that [Formula: see text] and [Formula: see text] are stable in C-type AFM, [Formula: see text] is in G-type AFM and [Formula: see text] in A-type AFM phase, respectively. The high specific heat of these deficient perovskites makes them good candidates for high-temperature technology. Based on the above physical properties, it is expected that these deficient perovskites are potential candidates for spintronics and magnetic storage devices.

Health monitoring of bonded joints through electrical measurements

The aim of this research work is to explore the possibility of continuously monitoring the presence of damage in bonded joints through electrical measurements. Initially, an analytical model for estimating the crack length based on the electric resistance increase measured across the bond area is presented. The model is successfully validated through finite element analyses and experimental tests on single lap joints made of a conductive adhesive and aluminium or carbon/epoxy adherends. For the last case, the model is extended to account for damage scenarios where a residual conductivity is present across crack faces, due, for instance, to fibre bridging. Eventually, a procedure for predicting the crack length and the stiffness reduction in bonded joint based on electrical measurement is developed.

Investigations on heat-generation stability and PTC effects of self-heating cement composites under diverse temperature conditions

In this study, the novel aspect lies in investigating heat-generation stability expressed as positive temperature coefficient (PTC) effects of self-heating cement under diverse temperature conditions. Self-heating cement composites were fabricated, and subjected to various types of heating tests including monotonic, cyclic, and long-term tests at three distinct temperatures: 25°C, 0°C, and −20°C. The results revealed a novel finding that the heat-generation performance decreased due to the increased electrical resistivity during the heating test, attributed to the PTC effect when high input voltage was applied. Conversely, the absence of PTC effect with low input voltage application resulted in a consistent temperature increase and negligible changes in electrical resistivity, particularly at low temperatures. These experimental findings provide valuable insights into the investigations on stability of heat-generation performance of self-heating cement composites, offering implications for their practical applications.

Fast fabrication of a hierarchical nanostructured multifunctional ferromagnet.

Materials with multifunctionality affect society enormously. However, the inability to surmount multiple functionality trade-offs limits the discovery of next-generation multifunctional materials. Departing from conventional alloying design philosophy, we present a hierarchical nanostructure (HNS) strategy to simultaneously break multiple performance trade-offs in a material. Using a praseodymium-cobalt (PrCo5) ferromagnet as a proof of concept, the resulting HNS outperforms contemporary high-temperature ferromagnets with a 50 to 138% increase in electrical resistivity while achieving their highest energy density. Our strategy also enables an exceptional thermal stability of coercivity (-0.148%/°C)-a key characteristic for device accuracy and reliability-surpassing that of existing commercial rare-earth magnets. The multifunctionality stems from the deliberately introduced nanohierarchical structure, which activates multiple micromechanisms to resist domain wall movement and electron transport, offering an advanced design concept for multifunctional materials.

Evaluation of the effect of hydrogen evolution reaction on the performance of all-vanadium redox flow batteries

The exceptional advantages of vanadium redox flow batteries (VRFBs) have garnered significant attention, establishing them as the preferred choice for large-scale and long-term energy storage solutions. However, side reactions such as hydrogen evolution reaction (HER) lead to suboptimal performance of VRFB parameters, resulting in an overall decrease in VRFB performance. Therefore, it is imperative to investigate the mechanism by which HER affects VRFB performance and identify effective methods to mitigate its impact. In light of this, critical parameters such as charge-discharge curve, internal resistance, pressure-drop, pump power consumption, efficiency, and capacity retention rate are selected to evaluate the impact of HER on VRFB performance. Experimental results demonstrate that HER causes an increases in voltage during charging and a decrease during discharging stages leading to voltage loss; additionally, bubble generation significantly increases pressure drop and pump power consumption; furthermore, blockage of flow channels and electrodes due to bubbles leads to an increase in ohmic resistance. Finally, HER has a substantial impact on efficiency and capacity with an average energy efficiency of 2.92 %. After 60 cycles, the capacity retention rate decreased by nearly 7.69 %.

Eulerian-Eulerian-VOF multifluid modelling of liquid–gas reacting flow for hydrogen generation in an alkaline water electrolyser

Alkaline water electrolysis is a promising technology for hydrogen production. However, its efficiency drops considerably at high current densities due to the mass transfer limitation and the increase in electrical resistivity arising from the complexity of the liquid–gas reacting flow behaviour within the electrolyser cell. In this work, a computational fluid dynamics (CFD) model is developed to describe the liquid–gas reactive flow behaviour. The model integrates the Eulerian-Eulerian two-fluid model and the multifluid Volume of Fluid (VOF) model, allowing the mathematical model to capture the electrochemical reaction effect on hydrogen gas formation and bulk flow bubble behaviour. The model is validated against prior experimental results. The simulation results suggest that, at higher current densities, the electrical performances and the mass transfer rates are highly influenced by the formation of gas bubbles, which may block the active sites for the electrochemical reaction to occur. Quantitatively, at 4000 A/m2, the mass transfer rate is reduced by 50% at regions above the cathode compared to electrode region, while electrical conductivity near the flow channel wall, drops by 17% compared to the bulk liquid electrical conductivity. The predicted electrical conductivity is comparable to the Bruggemann correlation with an average relative error of less than 2%, confirming the model’s validity in predicting the reacting flow behaviour and performance of the electrolyser. The numerical model offers a cost-effective tool for insightful understanding and refining the design and operation of hydrogen generation systems.

Evaluation of electrical resistivity of cement-based materials using time domain reflectometry

Time domain reflectometry (TDR) is a widely used electromagnetic wave–based technique for evaluating the volumetric water content of soils, although its use for moisture measurement in cement-based materials is limited. This paper presents a comprehensive analysis of the electrical properties of cement pastes and cement paste–slime mixtures using TDR. Both TDR and electrical resistivity probes are used to estimate the electrical resistivities of various cement-based materials over their curing period. The study reveals that these properties are significantly influenced by curing time, water–cement ratio, and water–solid ratio. The experimental results demonstrate a consistent increase in electrical resistivity with curing time, underscoring the significant role of hydration-induced water evaporation and microstructural changes. Furthermore, the interpretation of characteristic voltages on the TDR waveform significantly influences resistivity estimates. Thus, this study highlights the potential of TDR in accurately evaluating the electrical resistivity of cement-based materials.

Effects of particle surface modification on magnetic behavior of soft magnetic Fe@SiO2 composites and Fe compacts

The study aims to evaluate the influence of surface modification of Fe powder on the magnetic behavior of soft magnetic compacts and composites that can possibly enhance their properties. The smoothing of ferromagnetic particle surfaces led to a decrease in the total energy loss as the most evident positive impact in all investigated classes (max. by 11% for small, 63–125 μm particle-based annealed Fe compacts, at max. induction 0.5 T and frequency 100 Hz) and to a partial increase in specific electrical resistivity (max. by 47% for small particle-based Fe@SiO2 composites) and resonant frequency (max. by 48% for large, 200–400 μm particle-based Fe@SiO2 composites) as well as partial decrease in coercivity (max. by 14% for small particle-based annealed Fe compacts). Removing surface irregularities negatively affected the maximum total permeability (max. drop by 28% for large particle-based Fe@SiO2 composites) due to increased inner demagnetizing fields. Applying the Bertotti theory for loss separation, we obtained parameters of loss components and assumed the domain structure using simultaneously active magnetic objects as predictors. The total loss decrease observed after the smoothing process originates from the significantly increased numbers of active magnetic objects, facilitating AC magnetization reversal so that domain wall displacements are accompanied by lower energy loss, manifested as a decrease in the excess loss component (max. by 61% for small particle-based Fe@SiO2 composites).

Extracellular ATP/P2X7 receptor, a regulatory axis of migration in ovarian carcinoma-derived cells.

ATP is actively maintained at high concentrations in cancerous tissues, where it promotes a malignant phenotype through P2 receptors. In this study, we first evaluated the effect of extracellular ATP depletion with apyrase in SKOV-3, a cell line derived from metastatic ovarian carcinoma. We observed a decrease in cell migration and an increase in transepithelial electrical resistance and cell markers, suggesting a role in maintaining a mesenchymal phenotype. To identify the P2 receptor that mediated the effects of ATP, we compared the transcript levels of some P2 receptors and found that P2RX7 is three-fold higher in SKOV-3 cells than in a healthy cell line, namely HOSE6-3 (from human ovarian surface epithelium). Through bioinformatic analysis, we identified a higher expression of the P2RX7 transcript in metastatic tissues than in primary tumors; thus, P2X7 seems to be a promising effector for the malignant phenotype. Subsequently, we demonstrated the presence and functionality of the P2X7 receptor in SKOV-3 cells and showed through pharmacological approaches that its activity promotes cell migration and contributes to maintaining a mesenchymal phenotype. P2X7 activation using BzATP increased cell migration and abolished E-cadherin expression. On the other hand, a series of P2X7 receptor antagonists (A438079, BBG and OxATP) decreased cell migration. We used a CRISPR-based knock-out system directed to P2RX7. According to the results of our wound-healing assay, SKOV3-P2X7KO cells lacked receptor-mediated calcium mobilization and decreased migration. Altogether, these data let us propose that P2X7 receptor is a regulator for cancer cell migration and thus a potential drug target.

Micro-structured lateral thermal lens for increased output power and narrowed beam divergence in kilowatt-class 9xx nm diode laser bars

Local temperature non-uniformity is a critical limit to power in large-area semiconductor lasers, playing a larger role than the conversion efficiency and temperature sensitivity in the most efficient modern devices. For the specific case of kilowatt-level edge-emitting diode laser bars, we demonstrate that laterally re-distributing current locally within each emitter using a customized micro-structuring of the electrical contact can flatten the thermal profile, based on the thermal design using COMSOL. The concept is demonstrated experimentally in adapted bars that contain eight broad-area emitters, each having wide (∼1100 μm) stripes and a 4 mm long resonator. Each emitter in the laser bar has an electrical contact layer that is electrically structured into parallel sub-contacts using implantation, essential to prevent lateral lasing, implemented here with a period of 29 μm. The width of the individual sub-contacts is narrowed in the device center and then monotonically increased toward the emitter edges to collect a higher proportion of heat at the edges, for a fivefold reduction in the thermal lens, despite a significant (20%) overall increase in electrical and thermal resistance. Two performance benefits are observed. First, the slope varies more slowly with average temperature, recovering (here) around half of the efficiency penalty from in-stripe temperature non-uniformity, and hence increasing the power conversion efficiency at 800 W optical output power by around 5%. Second, the lateral far field (95% power content) is narrowed by around 2° at 800 W optical output power, corresponding to a reduction of around half of the thermal contribution.

Comprehensive study of high-temperature calendar aging on cylinder Li-ion battery

Calendar aging at high temperature is tightly correlated to the performance and safety behavior of lithium-ion batteries. However, the mechanism study in this area rarely focuses on multi-level analysis from cell to electrode. Here, a comprehensive study from centimeter-scale to nanometer-scale on high-temperature aged battery is carried out. After short-time high-temperature aging, measurements of electrochemical performance show notable decay of capacity and increase of internal resistance. The thermal safety behavior is studied through accelerating rate calorimeter (ARC), which indicates that the heat output of the aged battery during thermal runaway is largely increased. The aging mechanism of high temperature is investigated under various scales. Incremental capacity (IC) curves depict the deterioration of electrodes and increase of ohmic resistance. Computational Tomography (CT) reveals structure evolution of aged battery at millimeter scale, indicating gas generation after high-temperature aging. Scanning electron microscope (SEM) shows thickened solid-state-electrolyte (SEI) on anode and cracks on cathode at sub-micrometer scale. X-ray diffraction (XRD) patterns present crystallographic evolution of both anode and cathode. Thus, the cell degradation-mechanism after high-temperature aging is interpreted at multi-level, that high temperature induces deterioration of electrodes, formation of SEI and evolution of gas.

Nitrogen-Doped Carbon Nanothin Film as a Buffer Layer between Anodic Graphite and Solid Electrolyte Interphase for Lithium-Ion Batteries.

Lithium-ion batteries are essential batteries for electric vehicle drive systems. Such batteries must provide stable performance over a long period of time. Therefore, the degradation or aging of the battery capacity must be improved. In the case of the current graphite anodes, graphite coated with an amorphous layer is used. It is known that the amorphous layer can reduce the irreversible capacity loss caused by the solid electrolyte interphase (SEI) layer. The amorphous carbon layers reduce the initial capacity due to higher electrical resistance. In this study, we aim to develop a buffer layer using nitrogen-containing graphene that would prevent the increase in electrical resistance while maintaining the amorphous structure. Coatings with different film thicknesses were prepared by using the solution plasma method. The thinnest sample was oven sintered to optimize the structure, especially the surface and interface of the layer. The battery capacity from charge-discharge experiments and the resistance change of each part from electrochemical impedance measurements were evaluated. The results showed that the coating layer increased the electrical resistance of the graphite anode. On the other hand, the resistance of the SEI layer was reduced by the coating layer. It can be predicted that the addition of the coating layer will increase the total charge transfer resistance (R ct) of the cell but will also improve the period average capacity in the long run. To be used as a practical material, the film thickness would need to be further reduced, and the balance between the loss of charge transfer resistance and the gain of SEI layer resistance would need to be further optimized.

In Situ Electrical Resistance Measurement of Pure Titanium During Severe Plastic Deformation by High‐Pressure Sliding

In this study, in situ measurements of electrical resistance in pure Ti during severe plastic deformation (SPD) under high pressures are presented. The process of high‐pressure sliding (HPS) is adopted for the SPD so that straining is feasible under various pressures covering α to ω allotropic phase transformation in pure Ti. Anvil surfaces are coated by a plasma‐sprayed alumina layer to maintain electrical insulation between the sample and the anvils during HPS operation. The electrical resistance increases continuously with straining by the HPS processing but the increase in the electrical resistance is more pronounced as the applied pressure increases, particularly when the ω phase formation occurs. The phase transformation is evidenced by X‐Ray diffraction analysis as well as in situ static heating experiment. The continuous increase in the electrical resistance suggests that there is neither critical strain nor avalanche for the phase transformation to the ω phase.

Microwave-assisted hydrothermal synthesis and gas sensing properties of ZnSn(OH)6, ZnSnO3, and Zn2SnO4/SnO2 hierarchical nano-/hetero-structures

Although semiconducting metal oxide sensors present reasonable sensitivity, an improved lower detection limit and/or selectivity would allow broadening real-time monitoring applications. This work reports the growth mechanism and gas sensing performance of zinc tin oxide-based structures synthesised via a microwave-assisted hydrothermal route. The synthesised materials were characterised by X-ray diffraction (XRD), Raman and Fourier-transform infrared (FTIR) spectroscopy, scanning and scanning transmission electron microscopy (SEM and STEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and nitrogen adsorption/desorption experiments. Gas sensor measurements showed that ZnSnO3 presents an outstanding lower detection limit to nitrogen dioxide (NO2), in which a 10-fold increase in electrical resistance is expected in the presence of 1 ppb NO2 at an operating temperature of 150 ˚C. Moreover, the Zn2SnO4/SnO2 heterostructure exhibited superior selectivity to NO2 relative to hydrogen (H2) and carbon monoxide (CO), exhibiting a sensor response ∼1500 times higher for the oxidising gas. Hence, it is demonstrated that nanostructures’ growth engineering can realise lower detection limits and ultra-selective high-performance gas sensor devices through a greater surface area and enhanced contact potential barriers.

Effect of different quenching holding times on microstructure, texture and electrical resistivity of NiCrAlFe alloy

Quenching treatment can provide microstructure for subsequent tempering treatment in the production process of NiCrAlFe precision resistance alloy. However, the recrystallization texture formed during quenching will be inherited into the tempered alloy, causing anisotropy of resistance and affecting the final performance of precision resistors. In order to investigate the evolution of the texture and its influence on the anisotropy of resistance, the effect of various quenching holding times on the alloy were studied. The results indicate that certain rolling deformation texture is gradually transformed into recrystallization texture and the texture intensity decreases significantly during the holding process. At the same time, the formation of a large number of twins promotes the formation of Brass-R {111}<112> texture at twin boundaries. The electrical resistivity of the alloy changes from 1.360 μΩ·m to 1.427 μΩ·m, and it shows an increasing trend with the holding time. The large number of supersaturated vacancies generated by quenching is the main reason for the increase in alloy electrical resistivity, but there is no correlation between the orientation density of texture and the electrical resistivity, however the type and intensity of textures exhibit significant influence on the anisotropy of the electrical resistivity. The electrical resistivity of direction rolling, direction 45°, and direction 65° are mainly influenced by Goss {110}<001> texture, Goss {110}<001> texture and Brass-R {111}<112> texture, and S {123}<634> texture and R {124}<211> texture, respectively.