Volume Electrical Conductivity Research Articles

Subnanoscopically and homogeneously dispersed SiOx/C composite spheres for high-performance lithium ion battery anodes

Silicon suboxide (SiOx, x < 2) possesses high specific capacity as lithium ion battery anode. However, the cyclability and rate performance of SiOx are still unsatisfactory because of its huge volume change and low conductivity. Here, we report SiOx/C composite spheres with high cyclability and rate performance, which are synthesized by heating liquid mixture of polydimethylsiloxane and hexane in sealed vessels and subsequent heat treatment. High pressure generated in the sealed vessels at high temperature induces formation of the spherical morphology. The SiOx/C spheres consist of subnanoscopically and homogeneously dispersed SiOx and free carbon. Such dispersion structure increases tolerance for volume change and electrical conductivity. The spherical shape benefits uniform distribution of the SiOx/C spheres in electrodes, ensuring high electrical connectivity and uniform distribution of volume change. Consequently, the SiOx/C spheres exhibit outstanding cycle stability (96.1% capacity retention after 400 cycles), excellent rate performance (146.2 mAh g−1 at 10 A g−1), and high specific capacity (1667.3 mAh g−1). Particularly, at a high mass loading of 3.0 mg cm−2 the electrodes possess high areal capacities of 2.6-2.0 mAh cm−2 during 400 cycles, showing high promise for practical application.

An Anthraquinone/Carbon Fiber Composite as Cathode Material for Rechargeable Sodium‐Ion Batteries

AbstractThe transition from rare to natural abundant materials in rechargeable batteries is becoming a grand challenge in developing a resource sustainable power supply. Since decades, scientists attempt to circumvent the lithium's resource problem by innovating alternative active metal ions. A cost‐effective alternative to lithium is to use sodium (Na) as the carrier ion in rechargeable batteries. We present an electrode composite material comprising anthraquinone (AQ) and nanostructured carbon fibers, as a cathode material for Na‐ion batteries. These electrodes are characterized by a large surface area, ordered porous network, large pore volume and good electrical conductivity. The material is further compared to the water soluble, mono‐substituted anthraquinone derivative, sulfonated 9,10‐anthraquinone (SAQ). While the SAQ/carbon fiber composite demonstrates a moderate initial discharge capacity of ∼95 mAh g−1 accompanied by substantial, initial capacity fading, the AQ/carbon fiber composite shows a remarkably high discharge capacity of ∼307 mAh g−1 and exhibit reasonable cycling stability over 115 charge/discharge cycles in a Na containing electrolyte. This may be best explained by the well‐structured intermolecular π‐π stacking of the thermally evaporated AQ layers and with the subjacent carbon fibers. Since AQ and SAQ are widely‐used industrial pigments, they may offer a cost‐effective, abundant and environmentally benign cathode material for secondary Na‐ion and Na‐flow batteries.

Experimental study of water and salt migration in unsaturated loess

Water and salt migration properties are important in many disciplines, including engineering construction, natural disaster prevention, agricultural irrigation and wastewater disposal. Relevant research into unsaturated loess caters to the development needs of the cities located on it. The objective of this study is to identify the water flow dynamics and consequent salt migration and redistribution (as well as their influence on microstructure alteration of the soil) during long-term seepage in unsaturated loess. In this experimental study, a long-term and one-dimensional seepage simulation test is conducted in a loess column. Probes are buried at different depths along the vertical profile to monitor and record the variations of volume water content and electrical conductivity. After the seepage test, soils at different depths are analyzed with different methods to make further investigation, including use of a pressure-plate apparatus to obtain soil-water characteristic curves, ion chromatography to determine the soluble salt components, and scanning electron microscopy to observe the microstructure changes. Good consistency between the different tests is obtained. Based on those results, the water and salt migration patterns and their influence on loess are analyzed and concluded.

Ultralight, highly compressible and fire-retardant graphene aerogel with self-adjustable electromagnetic wave absorption

Macroscopic three-dimensional (3D) free-standing porous all-graphene aerogel with ultralight density and high compressibility is successfully fabricated through a mild in-situ self-assembly and thermal annealing processes. The formed interconnected 3D porous graphene network, high thermal stable all-graphene composition and large porosity of aerogels made it possible to remove heat quickly during combustion, exhibiting a conspicuous fire-retardancy. Meanwhile, excellent recoverable compressibility with high strain levels of up to 75% endowed the aerogel with high sensitive strain-responsive characteristic in volume electrical conductivity, thereby opening a new way for realizing the adjustment of internal free space and electrical conductivity of 3D architecture. Based on the results, the microwave absorption performance of the graphene aerogel was effectively self-adjusted via a simple mechanical compression. The optimal absorbing value was up to 61.09 dB with a broad qualified bandwidth of 6.30 GHz at the thickness of 4.81 mm when the compression strain ratio of the sample was controlled to be 30%.

Nonwoven fabrics with carbon nanotubes used as interleaves in CFRP

The goal of the present study was to implement thermoplastic nonwoven fabrics containing multi-walled carbon nanotubes as interlayers in Carbon Fiber Reinforced Polymers. These functional nonwovens were fabricated by a half-industrial scale melt-blown technique, starting with nanocomposite pellets of copolyamides doped with 3.5wt% of multi-walled carbon nanotubes. Three types of composite panels were fabricated using an out-of-autoclave technique (OoA): one without nonwovens and two with nonwovens. Incorporation of thermoplastic nonwovens doped with 3.5wt% of multi-walled carbon nanotubes increased the surface and volume electrical conductivity in direction Kz by about 2 and 3 orders of magnitude, respectively. Based on the images obtained from a Scanning Electron Microscope, it was found that melted nonwovens adhere well to the carbon fibers. It was also confirmed that carbon nanotubes are well dispersed in nonwovens, which results in an improvement of the overall electrical conductivity of the composite panels. The lack of homogenous layers of nonwovens between the carbon fiber layers decreased the interlaminar shear strength of the composite panels and affected the level of their electrical conductivity. Moreover, thermo-mechanical analysis showed an increase of the glass transition temperature of the resin in the presence of thermoplastic nonwovens and the appearance of an additional peak on the loss modulus curve caused by the polyamide 6 segments present in the copolyamides used.

Physico-chemical properties of the system (LiF-NaF)eut-LaF3 – Phase equilibria, density and volume properties, electrical conductivity and surface tension

A detailed physico-chemical investigation of molten system (LiF-NaF)eut-LaF3 up to 15 mol% of LaF3 has been done. The phase equilibria were measured by two independent methods (TA and DSC) and consequently Calphad modelling and calculation was performed in order to interpret obtained experimental data. Additional physico-chemical properties like density, electrical conductivity and surface tension were measured. It was found that all investigated properties reflect the ionic changes in the melt providing consistent data, i.e. the most significant changes in these properties are observed at ca. 10 mol% LaF3. The volume properties were calculated, as well, providing information about volume expansion. Also temperature anomalous behaviour was observed for the electrical conductivity and surface tension.

In Situ Synthesis of Mn3 O4 Nanoparticles on Hollow Carbon Nanofiber as High-Performance Lithium-Ion Battery Anode.

The practical applications of Mn3 O4 in lithium-ion batteries are greatly hindered by fast capacity decay and poor rate performance as a result of significant volume changes and low electrical conductivity. It is believed that the synthesis of nanoscale Mn3 O4 combined with carbonaceous matrix will lead to a better electrochemical performance. Herein, a convenient route for the synthesis of Mn3 O4 nanoparticles grown in situ on hollow carbon nanofiber (denoted as HCF/Mn3 O4 ) is reported. The small size of Mn3 O4 particles combined with HCF can significantly alleviate volume changes and electrical conductivity; the strong chemical interactions between HCF and Mn3 O4 would improve the reversibility of the conversion reaction for MnO into Mn3 O4 and accelerate charge transfer. These features endow the HCF/Mn3 O4 composite with superior cycling stability and rate performance if used as the anode for lithium-ion batteries. The composite delivers a high discharge capacity of 835 mA h g-1 after 100 cycles at 200 mA g-1 , and 652 mA h g-1 after 240 cycles at 1000 mA g-1 . Even at 2000 mA g-1 , it still shows a high capacity of 528 mA h g-1 . The facile synthetic method and outstanding electrochemical performance of the as-prepared HCF/Mn3 O4 composite make it a promising candidate for a potential anode material for lithium-ion batteries.

Does the Processing Method Resulting in Different States of an Interconnected Network of Multiwalled Carbon Nanotubes in Polymeric Blend Nanocomposites Affect EMI Shielding Properties?

Electromagnetic interference (EMI), an unwanted phenomenon, often affects the reliability of precise electronic circuitry. To prevent this, an effective shielding is prerequisite to protect the electronic devices. In this study, an attempt was made to understand how processing of polymeric blend nanocomposites involving multiwalled carbon nanotubes (MWCNTs) affects the evolving interconnected network structure of MWCNTs and eventually their EMI shielding properties. Thereby, the overall blend morphology and especially the connectivity of the polycarbonate (PC) component, in which the MWCNTs tend to migrate, as well as the perfectness of their migration, and the state of nanotube dispersion are considered. For this purpose, blends of varying composition of PC and poly(methyl methacrylate) were chosen as a model system as they show a phase diagram with lower critical solution temperature type of characteristic. Such blends were processed in two different ways: solution mixing (from the homogeneous state) and melt mixing (in the biphasic state). In both the processes, MWCNTs (3 wt %) were mixed into the blends, and the evolved structures (after phase separation induced by annealing in solution-mixed blends) and the quenched structures (as the blends exit the extruder) were systematically studied using transmission electron microscopy (TEM). Both the set of blends were subjected to the same thermal history, however, under different conditions such as under quiescent conditions (in the case of solution mixing) and under shear (in the case of melt mixing). The electrical volume conductivity and the evolved morphologies of these blend nanocomposites were evaluated and correlated with the measured EMI shielding behavior. The results indicated that irrespective of the type of processing, the MWCNTs localized in the PC component; driven by thermodynamic factors and depending on the blend composition, sea-island, cocontinuous, and phase-inverted structures evolved. Interestingly, the better interconnected network structures of MWCNTs observed using TEM in the solution-mixed samples together with larger nanotube lengths resulted in higher EMI shielding properties (−27 dB at 18 GHz) even if slightly higher electrical volume conductivities were observed in melt-mixed samples. Moreover, the shielding was absorption-driven, facilitated by the dense network of MWCNTs in the PC component of the blends, at any given concentration of nanotubes. Taken together, this study highlights the effects of different blend nanocomposite preparation methods (solution and melt) and the developed morphology and nanotube network structure in MWCNT filled blend nanocomposites on the EMI shielding behavior.

Measurement and Artificial Neural Network Modeling of Electrical Conductivity of CuO/Glycerol Nanofluids at Various Thermal and Concentration Conditions

In this work, the electrical conductivity of CuO/glycerol nanofluid was measured at a temperature range of 20–60 °C, volume fraction of 0.1–1.5% and nanoparticle size of 20–60 nm. The experimental data were predicted by the perceptron neural network. The results showed that the electrical conductivity increases with temperature, especially in higher volume fractions. These results are attributed to the accumulation of nanoparticles in the presence of the field and their Brownian motion at different temperatures and the reduction of electrical conductivity at higher nanoparticle sizes is attributed to the decreased mobility of nanoparticles as load carriers as well as to their decrease in volume unit per constant volume fraction. The results revealed that sonication time up to 70 min increases the nanofluid stability, while further increase in the sonication time decreases the nanofluid stability. In the modeling, input data to perceptron artificial neural network are nanofluid temperature, nanoparticle size, sonication time and volume fraction and electrical conductivity is considered as output. The results obtained from self-organizing map (SOM) showed that the winner neuron which has the most data is neuron 31. The values of the correlation coefficient (R2), the mean of squared errors (MSE) and maximum error(emax) used to evaluate the perceptron artificial neural network with 2 hidden layers and 31 neurons are 1, 2.3542 × 10−17 and 0 respectively, indicating the high accuracy of the network.

Enhancement of electrical conductivity of epoxy using graphene and determination of their thermo-mechanical properties

A three-roll mill processing technique was used to disperse graphene nanoplatelets into epon 828 epoxy system. As a first step of this research, processing of graphene/epoxy nanocomposites was explored with different weight percentages of graphene. After establishing an optimal and repeatable process to achieve good electrical properties, the materials were tested for thermal conductivity and mechanical properties. The xGnP-25 graphene nanoplatelet supplied by XG Science Inc. was used; the graphene average diameter was 25 μm and thickness was 6–10 nm. Mechanical mixing, sonication and three-roll mill dispersion techniques were investigated to disperse graphene in epon 828 epoxy. The study showed that the three-roll dispersion is effective, repeatable and potentially scalable to disperse graphene into epoxy to increase the electrical conductivity. The weight percentage of graphene used ranged from 0.5 to 5.0. Percolation threshold of graphene was found to be 1.0 wt%. Through-the-thickness or volume electrical conductivity increased by nine log cycles, thermal conductivity doubled and fracture toughness increased by one-third for 1.0 wt% addition of graphene to epon 828. However, the mechanical properties remained almost unchanged.

Electrical-based delamination crack monitoring in composites using z-pins

The in-situ, real-time detection of delamination cracks in composite materials using z-pins is reported. Carbon fibre-epoxy composites were reinforced in the through-thickness direction with different volume content (up to 4%) or material type (composite, metal) of z-pins. Z-pins can reduce the through-thickness electrical resistivity of composites by several orders of magnitude (up to ∼106), depending on their volume content and electrical properties. Z-pins create an electrically conductive pathway through-the-thickness of the otherwise resistive composite material (with an electrical resistivity of about 1.25 Ω m). Mode I interlaminar tests performed under static fracture and cyclic fatigue load conditions reveal that z-pins can be used to detect delamination cracking via changes to the electrical resistivity. The sensitivity of z-pins to changes in the resistivity caused by crack growth is influenced by their volume content, electrical conductivity and interfacial bonding with the composite material.

Graphene based biosensors for healthcare

Abstract

Hysteresis in the relation between moisture uptake and electrical conductivity in neat epoxy

Monitoring changes in electrical conductivity is a simple way to assess the water uptake from environmental moisture in polymers. However, the relation between water uptake and changes in conductivity is not fully understood. We monitored changes in the electrical volume conductivity of an anhydride-cured epoxy polymer during moisture sorption-desorption experiments. Gravimetric analysis showed that the polymer exhibits a two-stage sorption behavior resulting from the competition between diffusive and reactive mechanisms. As expected, the macroscopic electrical conductivity increases with the diffusion of water. However, our most surprising observation was severe hysteresis in the relation between water uptake and electrical conductivity during the sorption and desorption experiments. This indicates that change in the electrical conductivity depends on both the water uptake and the competition between the diffusive and reactive mechanisms. We studied samples with various thicknesses to determine the relative effects of the diffusive and reactive mechanisms. This is an important observation as it means that general electrical monitoring techniques should be used cautiously when it comes to measuring the moisture content of polymer or polymer-based composite samples.

Processing–morphology–property relationships of polypropylene–graphene nanoplatelets nanocomposites

ABSTRACTPolypropylene (PP) nanocomposites reinforced with graphene nanoplatelets (GNPs) were prepared via melt extrusion. A special sheet die containing with two shunt plates was designed. The relationships among the flow field of the special die, exfoliation, and dispersion morphology of the GNPs in PP and the macroscopic properties of the nanocomposites were analyzed. Flow field simulation results show that the die with shunt plates provided a high shear stress, high pressure, and high velocity. The differential scanning calorimetry, X‐ray scattering, and electron microscopy results reveal that the nanocomposites prepared by the die with the shunt plates had higher crystallinity values and higher exfoliation degrees of GNPs. The orientation of the GNPs parallel with the extrusion direction was also observed. The nanocomposites prepared by the die with shunt plates showed a higher electrical volume conductivity, thermal conductivity, and tensile properties. This indicated that the high shear stress exfoliated the GNPs effectively to a thinner layer and then enhanced the electrical, thermal, and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44486.

Poly dimethylsiloxane/carbon nanofiber nanocomposites: fabrication and characterization of electrical and thermal properties

ABSTRACTThis article presents the fabrication and characterization of poly dimethylsiloxane/carbon nanofiber (CNF)-based nanocomposites. Although silica and carbon nanoparticles have been traditionally used to reinforce mechanical properties in PDMS matrix nanocomposites, this article focuses on understanding their impacts on electrical and thermal properties. By adjusting both the silica and CNF concentrations, 12 different nanocomposite formulations were studied, and the thermal and electrical properties of these materials were experimentally characterized. The developed nanocomposites were prepared using a solvent-assisted method providing uniform dispersion of the CNFs in the polymer matrix. Scanning electron microscopy was employed to determine the dispersion of the CNFs at different length scales. The thermal properties, such as thermal stability and thermal diffusivity, of the developed nanocomposites were studied using thermogravimetirc and laser flash techniques. Furthermore, the electrical volume conductivity of each type of nanocomposite was tested using the four-probe method to eliminate the effects of contact electrical resistance during measurement. Experimental results showed that both CNFs and silica were able to impact on the overall properties of the synthesized PDMS/CNF nanocomposites. The developed nanocomposites have the potential to be applied to the development of new load sensors in the future.

Numerical computation of electrical conductivity of carbon nanotube-filled polymers

Abstract A Finite Element (FE) model, based on the tunneling effect, has been developed for simulating the electrical behavior of carbon nanotube-filled polymers. The geometry modeled belongs to a three-dimensional plate with an equivalent to the nanocomposite physical structure and electrical behavior evaluated using homogenization techniques. The FE model, after validated against experimental and numerical data from the literature, has been applied to conduct a parametric study on the effects of nanotube’s volume fraction, electrical conductivity and aspect ratio and polymer’s height of barrier. The numerical results show that with increasing the nanotube volume fraction, electrical conductivity and aspect ratio the electrical conductivity of the nanocomposite increases significantly. The height of barrier has effect only at large volume fractions where it varies conversely with electrical conductivity. The proposed FE model is simple compared to the existing numerical models, requires very low computational effort and may be potentially used for the design and optimization of multifunctional nanocomposites.

Dielectric barrier discharge in needle-to-plane configuration: Model of surface charge relaxation

Relaxation process of surface charge owing to dielectric barrier discharge (DBD) in “needle – air gap – polyethylene terephthalate film – plane” configuration is considered. Experimental data of the surface charge relaxation (SCR) are obtained by means of the rotating capacitive probe. Taking into account Gaussian radial distribution of accumulated charge density, effective surface and volume electrical conductivities of a barrier dielectric, phenomenological model of SCR for any dielectric thickness is proposed and exact solutions are obtained. The adequacy of the model is confirmed by the numerical computation. There is a good agreement between the experimental results and the model calculations.

Physicochemical Properties of the (LiF + CaF2)eut + LaF3 System: Phase Equilibria, Volume Properties, Electrical Conductivity, and Surface Tension

The physicochemical behavior of the molten system (LiF (1) + CaF2 (2))eut + LaF3 (3) has been studied and the phase equilibria, density and volume properties, electrical conductivity, and surface tension have been selected for investigation. Well-established methods for determination of these physicochemical properties of molten salts have been used, such as thermal analysis, the Archimedean method of hydrostatic weighing, and the phase shift and maximum bubble pressure methods. A significant change in all investigated properties was detected in the region of x3 = 0.04–0.06. In regard to phase equilibria, this region is close to and may contain the eutectic point; in volumetric properties, the initial volume contraction (on increasing mol %) starts to reverse. A sharp change of electrical conductivity reflects the changes in ionic composition, and surface tension also shows different behavior below and above this region.

Bond Formation Perspective: Effect of Sn Addition in Se-Te-Sn Chalcogenide Glasses

The aim of this study is to investigate the effect of Tin (Sn) addition on Band gap (Eg) and Dc conductivity of Se-Te-Sn semi-conducting glasses. This is an effort towards the understanding of physics of temperature dependence of dc electrical volume conductivity of Se75Te25-xSnx (X= 2, 4, 6 & 8) glasses in bulk form. These Chalcogenide glasses were prepared by melt quenching (rapid cooling of melt) technique. The amorphous nature of as prepared glass was confirmed by XRD. Using Keithley Electrometer / High resistance Meter 6517 A, the I-V characteristics of these glasses have been recorded in a temperature range from room temperature to 100˚C. Additionally, the Poole-Frenkel conduction mechanism has also been verified in order to investigate the good agreement with the established fact that most of Chalcogenide glasses obey Poole-Frenkel conduction mechanism. To calculate the Band gap, with the help of Ocean Optics Spectrophotometer, absorption spectra has been recorded. Analysis of these absorption spectra using Tauc relation reveals that these glasses are semiconducting and direct band gap material.

A Study on the Measurement of Volume and Surface Electrical Conductivity of Cryogenic Insulants for DC HTS Equipment

For the insulation design of dc high-temperature superconducting (HTS) equipment, dc electric field analysis should be performed. As the dc electric field distribution is mainly determined by the relative electrical conductivities of the various insulating materials used, the conductivities of these materials should be precisely measured. In particular, in cryogenic environment, the measurement of electrical conductivity could not be easily conducted due to the difficulty of measuring extremely low leakage current. In this paper, investigation on the measurement of volume and surface electrical conductivity of various cryogenic insulants, including polypropylene laminated paper (PPLP), Kraft, and glass fiber reinforced plastic (GFRP), was carried out. For the measurement of volume electrical conductivity in LN2, the infiltration of LN 2 into the specimen should be considered in order to avoid inaccurate measuring data. Thus, in order to increase the reliability for volume electrical conductivity, the PPLP specimen deposited by copper was adopted, and the comparison between ordinary PPLP and PPLP with copper deposition was made. As a result, it was suggested that the copper deposition could be a valid method to prevent the infiltration of LN 2 when the electrical conductivity of thin paper was measured. Consequently, volume and surface electrical conductivity values of PPLP, Kraft, and GFRP have been measured and summarized.