Non-conducting Matrix Research Articles

Variationally consistent magnetodynamic computational homogenization of particulate composites using an incremental potential

If composites made of conductive particles embedded in a nonconductive matrix are subject to highly dynamic magnetization processes, then microscopic eddy currents may lead to high magnetodynamic losses and heating of the material. Less obvious, the microscopic eddy currents also induce a dynamic macroscopic magnetization in accordance with Lenz’ law. Conventional homogenization theories based on volume averaging of the magnetic field strength disregard this effect and thus fail to properly predict the dynamic material response. In this work, the variationally consistent homogenization framework by Larsson et al. (2010), originally developed for transient heat conduction, is transferred to the aforementioned particulate composites, in order to properly reproduce this dynamic effect. It turns out that this approach predicts the macroscopic magnetization to be the volume averaged sum of the particles’ (conventional) magnetization and a non-standard dynamic magnetization due to microscopic eddy currents. Some first numerical examples illustrate the improved predictability of the variationally consistent homogenization method with respect to experimental complex permeability data. The resulting theory is shown to exhibit a two-scale incremental potential structure, which is exploited in several ways.

“Unveiling marigold assembled micro flowers of tungsten oxide towards solid-state flexible pouch and coin cell supercapacitors”

Marigold analogues micro flowers of tungsten oxide (WO3) have been grown in thin film form through simple and cost-effective solution chemistry approach on stainless steel substrate. Aqueous precursor involving WO4-2 ions agglomerated as self-sacrificing template growing initially into the nano-petal, followed by self-assembly; leading to marigold analogues micro flower surface architecture. This enthralling morphology motivated us not only to fabricate supercapacitive electrode but also to design complete solid-state supercapacitor devices in dual configurations: flexible pouch cell and coin cell. Interestingly, both devices even in symmetric configuration yields remarkable potential window of 1.82 V when sandwiched by gel inclusive of Li+ ions dispersed in non-conducting polyvinyl alcohol matrix. Solid-state flexible pouch cell and coin cell delivered specific capacitances of 103.98 ± 3.59 and 30.09 ± 1.03 F/g respectively at a scan rate of 5 mV/s. Assembled electrode, coin-cell and flexible pouch-cells have been well assessed in-depth through specific capacitances using cyclic voltammetry and galvanostatic charge discharge, diffusive and capacitive contributions, mechanical bending tests, electrochemical active surface area, and electrochemical impedance analysis. Practical applicability has been demonstrated for designed flexible pouch cell to run small fan and light emitting diode panel whereas coin cell to run light emitting diode panel.

Plasma bias homopolar sputtering technology and its application to enhance bioactivity of polyetheretherketone surface

Numerous strategies have been developed to deposit metal-based films on biomedical implants to improve their performances. As a promising strategy, vacuum plasma plating technology can introduce many bioactive metals on the implant surface and achieve strong interfacial bonding. However, there are still limitations in the surface modification of a non-conductive matrix. Here, a simple and universal plasma-based technique termed plasma bias homopolar sputtering (PBHS) was presented to modify the insulating and conductive materials. The technical principles and characteristics of PBHS were comprehensively studied. As a demonstration, the Fe-based film was prepared on the surface of an insulating polyetheretherketone (PEEK) by PBHS to improve its biological performance. The as-prepared Fe-based film exhibited low elasticity modulus and good hydrophilicity, enhancing the adhesion, proliferation, and osteogenic differentiation of rat bone marrow mesenchymal stem cells. This work provides a simple and universal technique for the preparation of metal-based films, holding great potential for the surface modification of biomedical implants.

Self-heating potential of geopolymer metashale mortars with graphite powder

Geopolymers are eco-friendly materials with favorable material properties and, therefore, suitable candidates for optimization in terms of electrical properties which broadens their potential in self-heating, self-sensing, or energy harvesting applications. The effectivity of self-heating function crucially depends on the presence of a sufficient number of conductive paths in a non-conductive material matrix corelating with the effective electrical conductivity of the material. The optimization of self-heating function, therefore, consists in appropriate dosing and homogenization of supplementing electrically conductive admixtures, as well as correct embedment of electrodes ensuring good contact with the material. The paper is focused on the design of multifunctional geopolymer mortar based on metashale precursor that was activated by a mix of potassium hydroxide and silicate. Electrical properties of the composite were optimized by graphite powder in the amount of 3 wt% and electrical experiments were performed using embedded copper grid electrodes. The material was characterized in terms of basic physical, mechanical, thermal, and electrical properties. The consecutive self-heating experiment was performed under the AC voltage of 130 V RMS with the initial power at the beginning of the measurement of 10 W. It was observed power increase of approximately 3 W and 25 °C rise of temperature during the 2 h lasting experiment.

Non-Isothermal Crystallization Kinetics of Polyether-Ether-Ketone Nanocomposites and Analysis of the Mechanical and Electrical Conductivity Performance.

High-performance polyether-ether-ketone (PEEK) is highly desirable for a plethora of engineering applications. The incorporation of conductive carbon nanotubes (CNTs) into PEEK can impart electrical conductivity to the otherwise non-conductive matrix, which can further expand the application realm for PEEK composites. However, a number of physical properties, which are central to the functionalities of the composite, are affected by the complex interplay of the crystallinity and presence of the nanofillers, such as CNTs. It is therefore of paramount importance to conduct an in-depth investigation to identify the process that optimizes the mechanical and electrical performance. In this work, PEEK/CNTs composites with different carbon nanotubes (CNTs) content ranging from 0.5 to 10.0 wt% are prepared by a parallel twin-screw extruder. The effects of CNTs content and annealing treatment on the crystallization behavior, mechanical properties and electrical conductivity of the PEEK/CNTs composites are investigated in detail. A non-isothermal crystallization kinetics test reveals a substantial loss in the composites' crystallinity with the increased CNTs content. On the other hand, mechanical tests show that with 5.0 wt% CNTs content, the tensile strength reaches a maximum at 118.2 MPa, which amounts to a rise of 30.3% compared with the neat PEEK sample after annealing treatment. However, additional annealing treatment decreases the electrical conductivity as well as EMI shielding performance. Such a decrease is mainly attributed to the relatively small crystal size of PEEK, which excludes the conductive fillers to the boundaries and disrupts the otherwise conductive networks.

Electrical Properties of Cadmium Telluride Films and the Al/CdTe Based Schottky Barrier

It is shown that with an increase in the thickness of cadmium telluride films from 0.4 to 1 μm, the resistivity decreases from 8·108 to 8,1·107 Ohm·cm. It is equivalent to an increase in conductivity from 1,25·10-9 to 1,23·10-8 Ohm-1· cm-1. The resistivity and conductivity change only slightly at thicknesses above 1 μm.
 One broad maximum is observed on the X-ray diffraction pattern at film thicknesses D=0.4 μm. This indicates the imperfection of the crystallites. As the thickness increases to 1 μm, a number of clear reflections with increasing intensity appear on the X-ray diffraction pattern, which is associated with the improvement of the crystal structure of the films.
 The current-voltage characteristic of the Schottky diode is obtained. It is shown that with an increase in the forward displacement, a significant increase in the forward current is observed, as well as a noticeable increase in the reverse current with a reverse displacement. The initial section of the forward characteristic at voltages up to 10 V is linear, which is inherent in Schottky barriers. However, the characteristic becomes non-linear at high voltages.
 The nonlinearity of the current-voltage characteristic of the Schottky barrier in a fairly wide range of applied voltage is related to the grain boundary effect in polycrystalline films. Namely, as the applied voltage increases to a certain value, the density of trap states in the region of the crystallite boundary decreases; holes begin to fill, which is usually observed in semiconductors containing conductive particles in a non-conductive matrix. We used this effect when studying the possibility of manufacturing nuclear radiation detectors with a metal — semiconductor — metal structure.

The Optimization of Dispersion and Application Techniques for Nanocarbon-Doped Mixed Matrix Gas Separation Membranes

In this work, supported cellulose acetate (CA) mixed matrix membranes (MMMs) were prepared and studied concerning their gas separation behaviors. The dispersion of carbon nanotube fillers were studied as a factor of polymer and filler concentrations using the mixing methods of the rotor–stator system (RS) and the three-roll-mill system (TRM). Compared to the dispersion quality achieved by RS, samples prepared using the TRM seem to have slightly bigger, but fewer and more homogenously distributed, agglomerates. The green γ-butyrolactone (GBL) was chosen as a polyimide (PI) polymer-solvent, whereas diacetone alcohol (DAA) was used for preparing the CA solutions. The coating of the thin CA separation layer was applied using a spin coater. For coating on the PP carriers, a short parameter study was conducted regarding the plasma treatment to affect the wettability, the coating speed, and the volume of dispersion that was applied to the carrier. As predicted by the parameter study, the amount of dispersion that remained on the carriers decreased with an increasing rotational speed during the spin coating process. The dry separation layer thickness was varied between about 1.4 and 4.7 μm. Electrically conductive additives in a non-conductive matrix showed a steeply increasing electrical conductivity after passing the so-called percolation threshold. This was used to evaluate the agglomeration behavior in suspension and in the applied layer. Gas permeation tests were performed using a constant volume apparatus at feed pressures of 5, 10, and 15 bar. The highest calculated CO2/N2 selectivity (ideal), 21, was achieved for the CA membrane and corresponded to a CO2 permeability of 49.6 Barrer.

A New Evaluation Method of Total Organic Carbon for Shale Source Rock Based on the Effective Medium Conductivity Theory

In the evaluation of source rocks, the total organic carbon (TOC) is an important indicator to evaluate the hydrocarbon generation potential of source rocks. At present, the commonly used methods for assessing TOC include △ log R and neural network method. However, practice shows that these methods have limitations in the application of unconventional intervals of sand-shale interbeds, and they cannot sufficiently reflect the variation of TOC in the vertical direction. Therefore, a total organic carbon (TOC) evaluation model suitable for shale and tight sandstone was established based on the effective medium symmetrical conduction theory. The model consists of four components: nonconductive matrix particles, clay minerals, organic components (solid organic matter and hydrocarbons), and pore water. The conductive phase in the model includes clay minerals and pore water, and other components are treated as nonconductive phases. When describing the conductivity of rock, each component in the model is completely symmetrical, and anisotropic characteristics of each component are considered. The model parameters are determined through the optimization method, and the bisection iteration method is used to solve the model equation. Compared with the classic TOC calculation method, the new model can evaluate the abundance of organic matter in shale and tight sandstone, which provides a new option to assess the TOC of rocks based on logging methods.

Thermal Modelling and Multi Decision Making Optimization of EDM of Non Conductive SiC-CNT Ceramic Composite Used for Li-ion Battery and Sensor

In this research work the thermal modeling of a nonconductive Silicon carbide Ceramic matrix composite (CMC) machined by Die Sinking Electric Discharge Machining (EDM) has been done. Though SiC is a non-conductive material but the presence of CNT makes it a conductive material which can be machined with EDM. The modeling procedure carried out by considering some realistic approach like Gaussian heat Flux, Specific Discharge Energy, Variable Latent heat etc. For this analysis a 2D continuum has been designed as work domain. By simulating the work domain model by a Finite Element Analysis (FEA) Software (COMSOL), material removal rate (MRR) has been estimated with variable thermal properties. Parametric analysis of effect of Variable Specific heat on MRR by considering different current, Voltage and Pulse-On time has been performed. The effect of different input parameters (peak current and Pulse-on time) on Crater geometry has been done. A new concept of Specific discharge energy has been introduced during modelling to make it a more realistic model which can also be used as electrode support for electrochemical energy devices as Polymer Electrolyte Membrane Fuel Cells on Li-ion battery. Desirability analysis has been done to get an optimize set of input parameters for I= 3A, V=30V, Ton= 75 µs for machining ceramic matrix composite by EDM. The optimized MRR at this setting is 7.25 mm3/min whereas PFE is 87%. The experimental analysis has been also performed to strengthen the thermal and mathematical modelling.

Percolation Conduction of Carbon Nanocomposites.

Carbon nanocomposites present a new class of nanomaterials in which conducting carbon nanoparticles are a small additive to a non-conducting matrix. A typical example of such composites is a polymer matrix doped with carbon nanotubes (CNT). Due to a high aspect ratio of CNTs, inserting rather low quantity of nanotubes (on the level of 0.01%) results in the percolation transition, which causes the enhancement in the conductivity of the material by 10–12 orders of magnitude. Another type of nanocarbon composite is a film produced as a result of reduction of graphene oxide (GO). Such a film is consisted of GO fragments whose conductivity is determined by the degree of reduction. A distinctive peculiarity of both types of nanocomposites relates to the dependence of the conductivity of those materials on the applied voltage. Such a behavior is caused by a non-ideal contact between neighboring carbon nanoparticles incorporated into the composite. The resistance of such a contact depends sharply on the electrical field strength and therefore on the distance between neighboring nanoparticles. Experiments demonstrating non-linear, non-Ohmic behavior of both above-mentioned types of carbon nanocomposites are considered in the present article. There has been a model description presented of such a behavior based on the quasi-classical approach to the problem of electron tunneling through the barrier formed by the electric field. The calculation results correspond qualitatively to the available experimental data.

Poly(phenylene sulfide) Graphite Composites with Graphite Nanoplatelets as a Secondary Filler for Bipolar Plates in Fuel Cell Applications

Graphite nanoplatelets (GNPs) have been used as a secondary filler to improve the electrical conductivity of poly(phenylene sulfide) (PPS)/graphite composites for use as bipolar plates in fuel cells, and the effects of adding small quantities of GNPs on the electrical, thermal, and mechanical properties of PPS/GNP/graphite composites have been extensively studied. The GNPs were compounded with PPS to produce master batch (MB) chips that were further ground to fine MB powder (MBg). PPS/MBg/graphite powders were compressed to fabricate 10-mm thick square samples. Composites containing a large quantity of graphite (~80 wt%) were then tested for use as a bipolar plate in phosphoric acid fuel cells. When 5 wt% GNP was added to the PPS/graphite composite, the in-plane electrical conductivity increased almost twofold from 643 to 1340 S·cm−1, the through-plane electrical conductivity increased from 19 to 54 S·cm−1, the through-plane thermal conductivity increased approximately two-fold from 60 to 129 W·(mK)−1, and the flexural strength decreased slightly from 32 to 26 MPa. The fractured surface of the compressed MBg sample revealed well-dispersed GNPs in the PPS matrix, which created electrical pathways and improved the electrical conductivity of the non-conducting PPS matrix material. Thus, the PPS/GNP/graphite composite is a promising system for bipolar plate applications because a higher amount of graphite (~93 wt%) is needed in PPS/graphite composites to reach the same level of electrical conductivity as the PPS/MBg(5 wt%)/graphite (75 wt%) composite, and such a large quantity of graphite is difficult to process and leads to weaker mechanical properties.

Silk Fibroin Based Magnetic Nanocomposites for Actuator Applications

The need for technologies based environmentally friendlier materials, able to minimize the global dependence on fossil fuel derivatives, promotes the development of new hybrid materials based on natural polymers, such as silk derivatives. This work reports on a new generation of magnetically active materials based on silk fibroin (SF) from Bombyx mori silkworm. Magnetic cobalt ferrite (CFO) nanoparticles are introduced in an SF polymer matrix to develop CFO/SF nanocomposites with filler contents of up to 20 wt%. It is shown that the inclusion of CFO nanoparticles affects the β‐sheet conformation of SF polymer having relevant effect on mechanical and thermal properties. The incorporation of conductive nanoparticles into nonconductive matrix, induces an increase in electric conductivity and also in dielectric constant. The primitive magnetic behavior of CFO nanoparticles is successfully maintained after their incorporation into SF, which has made possible the processing of magnetic SF. These results enable the design and fabrication of a fully functional magnetic actuator based on SF, proving the suitable natural polymer‐based magnetic materials for a new generation of environmental‐friendlier smart and multifunctional materials.

CoPt–Al2O3 Nanocomposite Films: Synthesis, Structure, and Magnetic Properties

The structure and magnetic properties of CoPt–Al2O3 nanocomposite films synthesized by the annealing of Al/(Co3O4 + Pt) bilayers on a MgO(001) substrate at 650°C in vacuum are investigated. The synthesized composite films contain ferromagnetic CoPt grains with an average size of 25–45 nm enclosed in a nonconducting Al2O3 matrix. The saturation magnetization (Ms ~ 330 G) and coercivity (Hc ≈ 6 kOe) of the films are measured in the film plane and perpendicular to it. The obtained films are characterized by a spatial rotational magnetic anisotropy, which makes it possible to arbitrarily set the easy magnetization axis in the film plane or perpendicular to it using a magnetic field stronger than the coercivity (H > Hc).

Conductive Electrospun Nanofiber Mats.

Conductive nanofiber mats can be used in a broad variety of applications, such as electromagnetic shielding, sensors, multifunctional textile surfaces, organic photovoltaics, or biomedicine. While nanofibers or nanofiber from pure or blended polymers can in many cases unambiguously be prepared by electrospinning, creating conductive nanofibers is often more challenging. Integration of conductive nano-fillers often needs a calcination step to evaporate the non-conductive polymer matrix which is necessary for the electrospinning process, while conductive polymers have often relatively low molecular weights and are hard to dissolve in common solvents, both factors impeding spinning them solely and making a spinning agent necessary. On the other hand, conductive coatings may disturb the desired porous structure and possibly cause problems with biocompatibility or other necessary properties of the original nanofiber mats. Here we give an overview of the most recent developments in the growing field of conductive electrospun nanofiber mats, based on electrospinning blends of spinning agents with conductive polymers or nanoparticles, alternatively applying conductive coatings, and the possible applications of such conductive electrospun nanofiber mats.

Percolation phenomena in nanocarbon composites

Nanocarbon composites present a new type of nanomaterials consisted of electric conducting carbon nanoparticles and a non-conducting matrix. A typical example of such composites is a polymer matrix doped with carbon nanotubes (CNT). Due to a high aspect ratio of nanotubes insertion of very small quantity of CNT (on the level of 0.01%) promotes the percolation transition resulting in an enhancement of the conductivity of the material by 10–12 orders of magnitude. Another type of nanocarbon composite is a film consisted of partially reduced graphene oxide (GO) produced as a result of thermal reduction of graphite oxide material. Distinctive peculiarity of both types of nanocomposites relates to the dependence of the specific resistivity of the materials on the applied voltage. Such a behavior is caused by non-ideal contacts between neighboring carbon particles involving into the composite. The resistance of this contact depends drastically on the intra-contact field, which promotes the dependence of the material resistivity on the applied voltage. The model description of such a non-linear dependence has been presented. The calculation results are compared with both literature data and the measured data obtained for reduced GO thermally treated at various temperatures.

Finite Element Modelling of Microelectrode Arrays of Mg and AA2024 Galvanic Couple

Aerospace aluminum alloys, such as AA2024-T3, are susceptible to microgalvanic corrosion and pitting due to its heterogeneous microstructure. Thus, they require additional corrosion protection methods. Magnesium rich primer coatings (MgRP) have emerged as an effective alternative to highly toxic chromate-based coatings. MgRP systems consist of an organic resin loaded with Mg pigment. The organic resin provides barrier protection, while metallic Mg pigment serves as a sacrificial anode by galvanic coupling with more noble Al alloy. The distance over which an active corrosion system can protect a defect exposing a metal surface is named galvanic throwing power and it is an important parameter used to evaluate the effectiveness of this type of protection method. Microelectrode array (MEA) is a technique commonly used to determine the galvanic throwing power. In this technique, wires of the metals of interest are mounted in a non-conductive matrix and the galvanic current distribution over the wires is measured. The wire diameter and the distance between the wires are important factors that affect the accuracy of MEA. While thin wires can provide finer spatial resolution, the experimental setup is challenging, and edge effects can decrease the representativeness of the measurement. Finite element analysis (FEA) is a tool used to predict both spatial and temporal potential and current distributions in electrochemical systems related to metal dissolution and cathodic reactions. FEA also can be used as an experimental design tool. In this work, FEA was used to assess important parameters and predict an optimal combination of wire diameters and distance between wires that result in higher accuracy of MEA. COMSOL Multiphysics (ver.5.4) was used to perform the finite element simulations. Potentiodynamic polarization scans of AA2024 and pure Mg immersed in 0.9 M NaCl solution were performed to generate E - i curves that were used as the electrochemical boundary conditions. Laplace equation was used to describe the current distribution that resulted from the galvanic coupling. The effect of the spacing between the wires and their diameters on the current distribution was studied. The results were compared to a reference solid plate configuration, where the two metals were in electrical contact.

Polymer composites containing dispersed VO2 of various polymorphs: Effects of polymer matrix on functional properties

VO2 (B), VO2 (A) and VO2 (M) polymorphs were obtained by energy efficient semi-industrial hydrothermal process. Synthesis of thermochromic VO2 (M) was performed in two steps and included thermal treatment in an inert atmosphere. The crystallographic peculiarities were observed by powder X-ray diffraction study. Scanning electron microscopy and specific surface area estimation showed the influence of recrystallization on the particles size and shape. The technique of VO2 surface modification with electrically conductive polymer (polyaniline) was developed and proved by infrared spectroscopy. The impact of the polymer on the composite properties was investigated in case of three different crystal phases of VO2 with different functionality. Vibrating-sample magnetometry, impedance spectroscopy, cyclic voltammetry and room condition modelling showed that polyaniline surface leads to competitive interactions but doesn't ruin optical switching abilities of VO2 (M). Polyethylene glycol as electrically nonconductive matrix demonstrated the difference in electrical conductivity between VO2 phases while conductive polyaniline eliminated them.

The role of the soft phase in rigidity enhancements in a particulate composite

Filling a non-conducting soft matrix with a hard conducting phase leads to two critical transitions: a percolation threshold with a drastic increase in conductivity and a rigidity threshold marking a substantial increase in the elastic modulus. A metal-particulate polymer composite has interpenetrating phases with substantial rigidity beyond the rigidity threshold. Experimental results show that the Young’s modulus of the composite is enhanced significantly when an entrapped incompressible polymer phase exerts high hydrostatic stresses in uniaxial compression at the rigidity threshold. Additional experiments beyond the glass transition temperature of the polymer reveal a substantial reduction in the modulus of the composite at the rigidity threshold, as the polymer compressibility is increased significantly, confirming the role of the soft phase in rigidity enhancements. The present investigation provides a potential new designing criterion for enhancing the Young’s modulus of an interpenetrating composite structure, by utilizing an incompressible second phase and negative volumetric strain.

Polymer composite for antistatic application in aerospace

Abstract The phenomenon of static electricity is unpredictable, particularly when an aircraft flying at high altitude that causes the accumulation of static charges beyond a threshold value leading to the failure of its parts and systems including severe explosion and radio communication failure. The accumulation of static charges on aircraft is generated by the virtue of interaction between the outer surface of aircraft and the external environmental attributes encompasses air particles, ice, hail, dust, volcanic ash in addition to its triboelectric charging. In the recent years, advanced polymer-based composites or nanocomposites are preferred structural constituents for aircrafts due to their light weight and comparable mechanical properties, but such composite systems do not render low impedance path for charge flow and are subsequently vulnerable to effect of lightning strike and precipitation static. In this context, it is essential to develop conductive composite systems from non-conductive polymer matrix by nanofiller embodiments. The advent of carbon-based nanocomposite/nanomaterials have adequately addressed such issues related to the nonconductive polymer matrix and further turned into an avant-garde genre of materials. The current review envisioned to illustrate the detailed exploitation of various polymer nanocomposites in addition to especially mentioned epoxy composites based on carbon fillers like carbon black, carbon nanotube (single walled carbon nanotube and multi walled carbon nanotube) and graphene the development of antistatic application in aircraft in addition to the static charge phenomenon and condition for its prevalence in avionic systems.

Prediction of electrical conductivity of carbon fiber-carbon nanotube-reinforced polymer hybrid composites

A two-step analytical electrical conductivity method is adopted to calculate the effective electrical conductivity of the carbon fiber (CF)-carbon nanotube (CNT)-polymer hybrid composite. First, CNTs are dispersed into the non-conducting polymer matrix and the electrical conductivity of the CNT-polymer composite is obtained. Then, CFs are randomly distributed in the CNT-polymer composite and the effective electrical conductivity of CF-CNT-polymer hybrid composite is estimated. The effect of critical parameters, including the volume fraction, alignment, agglomerated state and aspect ratio of the CNTs and the potential barrier height of the polymer on the hybrid composite electrical conductivity is evaluated. Also, the influence of the content and aspect ratio of CFs on the electric conductive behavior of the polymer hybrid composites is investigated. The results show that the polymer hybrid composite with larger aspect ratio and off alignment of CNTs presents a higher electrical conductivity.