Electrical Conductivity Of Composites Research Articles

Determination of type of honey produced in the different climatic regions of Bosnia and Herzegovina

The aim of this study was to investigate the impact of the environmental characteristics of a particular climate areas of Bosnia and Herzegovina on the type of honey produced in those areas. Physical, chemical and sensory characteristics of honey and pollen content in honey are the subject of ongoing research in the world, but still there is no universal method for classification of honey. Pollen analysis of honey in combination with other tests, e.g., pH, electrical conductivity and sensory properties, is often used for determination of type of honey. Acceptability of honey by consumers is based on the evaluation of sensory characteristics in the first place, which depend on the origin of plants from which the nectar (pollen) or honeydew was collected. Consumers and manufacturers are interested in classification of honeys because the most important characteristics of honey are dependent on its botanical and geographical origin. In this study were examined sensory properties, pH, electrical conductivity and pollen composition of honey samples collected from different climate regions, at different altitudes and at different vegetation season of Bosnia and Herzegovina. Laboratory analyses were carried out in three parallel determinations of the same sample of honey. In this research, 48 samples of honey were examined, out of which 29 were nectar (pollen) honey, 11 were mixed honey and 8 were honeydew.

Influence of Ultraviolet/Ozonolysis Treatment of Nanocarbon Filler on the Electrical Resistivity of Epoxy Composites.

In the present work, we have investigated concentration and temperature dependences of electrical conductivity of graphite nanoplatelets/epoxy resin composites. The content of nanocarbon filler is varied from 0.01 to 0.05 volume fraction. Before incorporation into the epoxy resin, the graphite nanoplatelets were subjected to ultraviolet ozone treatment at 20-min ultraviolet exposure. The electric resistance of the samples was measured by two- or four-probe method and teraohmmeter E6-13. Several characterization techniques were employed to identify the mechanisms behind the improvements in the electrical properties, including SEM and FTIR spectrum analysis.It is established that the changes of the relative intensities of the bands in FTIR spectra indicate the destruction of the carboxyl group –COOH and group –OH. Electrical conductivity of composites has percolation character and graphite nanoplatelets (ultraviolet ozone treatment for 20 min) addition which leads to a decrease of percolation threshold 0.005 volume fraction and increase values of electrical conductivity (by 2–3 orders of magnitude) above the percolation threshold in comparison with composite materials—graphite nanoplatelets/epoxy resin. The changes of the value and behavior of temperature dependences of the electrical resistivity of epoxy composites with ultraviolet/ozone-treated graphite nanoparticles have been analyzed within the model of effective electrical conductivity. The model takes into account the own electrical conductivity of the filler and the value of contact electric resistance between the filler particles of the formation of continuous conductive pathways.

Preliminary conceptual model of an Alpine carbonate aquifer (Pale di San Martino, Dolomites, Italy)

A hydrogeological and hydrochemical monitoring was conducted in the Pale di San Martino mountain ridge (Trento and Belluno Provinces, Italy) to build a preliminary conceptual model of the groundwater system. The model derives from a combination of new fieldwork and preexisting data provided by various public authorities. New data include geological and hydrogeological surveys, such as in situ measurements of the physical and chemical parameters, geochemical sampling and streamflow measurements. The lithologies outcropping in the area were grouped into seven hydrogeological complexes, each playing a different role in groundwater circulation. The dolomitic body of the ridges forms the main aquifer complex and is located above a terrigenous and evaporitic aquiclude. Due to this geometrical relationship, the site can be considered an isolated hydrostructure with well-defined no-flow boundaries. The main springs outcome near the aquifer-aquiclude boundary and in particular where the elevation of the contact is low and the tectonic pattern favors the drainage. Most of them have a calciumbicarbonate water composition, low temperature and low electrical conductivity, supporting the hypothesis of a fast flowing circulation in carbonate rocks and a high-altitude recharge. Seasonal streamflow measurements allowed the identification of linear springs and provided the first cumulative discharge data at the scale of the entire mountain group. The resulting model highlights a great spatial and temporal variability of the groundwater resources. Considering the geometry of the aquifer and the great seasonal variability of the discharge, it is possible to infer the absence of significant groundwater reserves at a regional scale. Thus, the hydrostructure shows a great capacity to supply water resources (mean discharge of 6 m3/s), but a low selfregulation capacity. It is necessary to consider this aspect when planning a long-term exploitation of the water resources that are used in the area for drinking purposes and hydropower generation.

The electric conductivity of composites based on various carbonaceous fillers and estimation of their percolation model parameters

We have studied the electric conductivity of composites with various carbonaceous fillers (multiwalled carbon nanotubes, colloidal graphite, and amorphous carbon) as a function of the filler content. The widths of critical regions of the percolation transition to the conducting state are determined and the percolation critical exponents are estimated. It is established that there is a tendency to increase in the width of transition region and values of critical exponents when the filler is varied in the following order: carbon nanotubes–colloidal graphite–amorphous carbon.

Microstructure characterization and thermal properties of Al-TiC sintered nano composites

Aluminium matrix infused with titanium carbide (TiC) particles was prepared by means of powder metallurgy process. The effect of TiC addition on microstructure, thermal properties, hardness and electrical conductivity of as-sintered Al-TiC with 2μm and ⩽200nm reinforcement were investigated. Microstructure studies reveal the even distribution of TiC particles in the aluminium matrix. Thermal analysis of TiC with varying particle size resulted in the formation of exothermic peak, due to the reduction in the oxidation of aluminium composites. Hardness and electrical conductivity of composites have been varied based on particle size variation of TiC.

The effect of mirabilite precipitation on the absolute and practical salinities of sea ice brines

The sea ice cover of high latitude oceans contains concentrated brines which are the site of in-situ chemical and biological reactions. The brines become supersaturated with respect to mirabilite (Na2SO4·10H2O) below −6.4°C, and the associated removal of Na+ and SO42− from the brine results in considerable non-conservative changes to its composition. The changes are reflected in the brine salinity, which is a fundamental physico-chemical parameter in the sea ice brine system. Here, measurements of electrical conductivity and brine composition in synthetic sea ice brines between −1.8 and −20.6°C, obtained during a comprehensive investigation of the brine-mirabilite equilibrium at below-zero temperatures reported elsewhere, are combined with modelled estimates to assess the behaviour of the absolute (SA) and practical (SP) salinities of sea ice brines. Results display substantial divergence of SP from SA below −6.4°C, reaching a 7.2% difference at −22.8°C. This is shown to create inaccuracies when SP is assumed to be equivalent to SA, firstly by misrepresenting the conditions inhabited by sea ice biota, whilst also creating errors in the calculation of physical sea ice parameters. Our measured and modelled data are used to refine the SA−T relationship for sea ice brines, implicit of mirabilite precipitation, which is crucial in estimating brine properties in absence of salinity data. Furthermore, because SP is the parameter measured in field studies, we provide an SP−T relationship for sea ice brines to −22.8°C, which aids in explaining the trends observed in available SP−T data from sea ice brines in the Southern Ocean, demonstrating the importance of the mirabilite-brine equilibrium in natural sea ice. Finally, we initiate the development of a conversion factor for the estimation of SA from SP measurement in sea ice brines, and produce an equation that can calculate SA from modelled brine density. This work ultimately highlights careful consideration of salinity concepts when applied to the sea ice system.

Constructing a segregated graphene network in rubber composites towards improved electrically conductive and barrier properties

A simple and effective approach, i.e. pre-construction method, was developed to fabricate a three-dimensional segregated graphene network (IL-3DGE) in a styrene butadiene rubber (SBR) matrix. Such segregated 3D-GE network dramatically enhanced the electrical conductivity, mechanical properties and gas barrier property of SBR composites. With the incorporation of 1.66 vol% IL-3DGE, the electrical conductivity of the composites was significantly enhanced by 10 orders of magnitude, the tensile strength was increased by 516%, and gas permeability was effectively reduced by 75.5%, as compared with those of neat SBR. Specifically, SBR/IL-3DGE with a segregated morphology showed a much low electrical percolation threshold (0.39 vol%), which is approximately 9-fold lower than that of the non-segregated SBR/IL-GE (3.78 vol%). The excellent properties of the composites were attributed to the construction of a 3D segregated conductive structure and strong interfacial interactions. This work provides a new insight into the fabrication of high-performance rubber composites for versatile practical applications.

Preparation, morphology and properties of natural rubber/carbon black/multi-walled carbon nanotubes conductive composites

Nature rubber (NR)/carbon black (CB)/multi-walled carbon nanotubes (MWNTs) electrical conductive composites were prepared through latex compounding technique assisted by anionic surfactants containing phenyl ring moieties, NR/MWNTs masterbatch treated with silane coupling agent containing polysulphide bond and mixed with commercial NR, CB, sulphur and other ingredients and vulcanization. When MWNTs were dispersed in sodium dodecylbenzene sulfonate (SDBS) water solution, SDBS assembly on the surface of MWNTs prevent aggregation of MWNTs in water forming a stable MWNTs suspension. After MWNTs suspension mixed with NR latex, NR-MWNTs latex compound was co-coagulated to obtain the well dispersed NR/MWNTs masterbatch. In order to strengthen interface bonding between MWNTs and NR matrix, MWNTs in the masterbatch were treated with silane coupling agent by melt mixing process. During rubber mixing process, MWNTs dispersed in masterbatch thoroughly mixed with all the components and MWNTs homogenously embedded in NR matrix. Owing to homogenous dispersion of MWNTs, interfacial bonding between MWNTs and NR matrix as well as synergistic reinforcing effect between MWNTs and CB, NR/CB/MWNTs composites exhibited improved mechanical properties, dynamical storage modulus, glass transition temperature, electrical and thermal conductivity. Tensile strength, stress at 300 % strain, tear strength and steady state thermal conductivity of NR/CB/MWNTs composite with 4 phr MWNTs loading were increased by 12.36, 26.02, 16.95 and 102 %, respectively, and volume resistivity at room temperature of the composite was decreased by four orders of magnitude compared with NR/CB composite.

Improvement of carbon black based polymer composite electrical conductivity with additions of MWCNT

Owing to their exceptional mechanical, electrical and thermal properties, carbon nanotubes (CNTs) are ideal candidates for improving the performances of polymer composites. In the present work, we investigated the effect of CNT addition on the electrical conductivity of two types of carbon black (CB) filled polymer. Also, two different methods of compounding were applied and their effects are compared: mixing by a laboratory compounder Haake Rheomix Polylab and mixing by a twin-roller mixer.Composites containing a total of 10% by weight of different carbon fillers (CB, CNTs and their mixtures in a ratio of 8/2) were thus obtained, characterized by scanning electron microscopy and their frequency dependence of the electrical conductivity was measured.It is shown that the alternating current (AC) conductivities display two regions: a low frequency region of constant conductivity and a higher frequency region of increasing conductivity with increasing frequency (following the percolation scaling law). It was also observed that the samples compounded with twin-roller mixer exhibit a higher electrical conductivity than those obtained with the laboratory compounder. Moreover, the conductivity of the composites containing CNTs in addition to CB is found to be higher than the conductivity of the composites containing only CB.

Karst hydrogeology of Karmustadj salt diapir, southern Iran

Karmustadj salt diapir (KSD) is located in the arid region of southern Iran. The karstic features of the KSD including vertical shafts, sinkholes, caves and brine springs, were investigated in order to characterize groundwater flow system in the diapir. KSD drains by three perennial and several temporary brine springs saturated with respect to halite. Electrical conductivity and chemical composition of three perennial brine springs were measured in wet and dry hydrological seasons. KSD consists of two hydrogeological units of Plug and Glacier districts. A conduit karst flow system is characterized for the Plug district including point recharge through sinkholes and discharge as several temporary brine springs. For the Glacier district, a diffuse flow system is proposed. Rainfall recharged to Glacier district discharges mainly via three brine springs throughout the year. The higher elevation of the springs of the diapir indicates that the elevation of base level of karstification is higher than the surrounding area, i.e. subsurface discharge of brine to the adjacent aquifers is unlikely. In this condition, construction of evaporite basins is proposed to prohibit re-infiltration of the emerged brine of the diapir into the surrounding aquifers which would increase water quality of the aquifers.

Carbon nanotube-epoxy composites: The role of acid treatment in thermal and electrical conductivity

Wet acid oxidation treatment methods have been widely reported as an effective method to purify and oxidize the surface of industrial multi-walled carbon nanotubes. This work examines the use of a concentrated HNO3/H2SO4 mixture in an attempt to optimize the purification procedure of industrial multi-walled carbon nanotubes with diameter distribution statistics. It is shown that acid treatments of several hours are enough to purify the nanotubes. The electrical and thermal conductivities of epoxy composites containing 0.05–0.25 wt% of an acid-treated multi-walled carbon nanotube have been studied. The electrical conductivity of the composites decreases by more than three orders, whereas the thermal conductivity of the same specimen increases very modestly as a function of the filler content.

S-doped carbon aerogels/GO composites as oxygen reduction catalysts

Composites of carbon aerogel and graphite oxide (GO) were synthesized using a self-assembly method based on dispersive forces. Their surface was modified by treatment in hydrogen sulfide at 650 and 800°C. The samples obtained were characterized by adsorption of nitrogen, TA-MS, XPS, potentiometric titration, and HRTEM and tested as catalysts for oxygen reduction reactions (ORR) in an alkaline medium. The synergistic effect of the composite (electrical conductivity, porosity and surface chemistry) leads to a good ORR catalytic activity. The onset potential for the composite of carbon aerogel heated at 800°C is shifted to a more positive value and the number of electron transfer was 2e− at the potential 0.68V versus RHE and it increased to 4e− with an increase in the negative values of the potential. An excellent tolerance to methanol crossover was also recorded.

Biochemical behavior of bean seeds and grains during storage

The development of researches about vigor provides greater insight about the physiological behavior of seeds over storage periods. The aim of this study was to evaluate the biochemical changes which occurred in beans stored for 360 days. Analyses were performed at 0, 30, 90, 180, 270, and 360 days after receiving the seeds (S1 and S2) and grains (G1 and G2) of BRS Splendor. The following tests were conducted: water content, electrical conductivity, and chemical composition of the soaking solution, where sugars and ions Fe 2+ , Zn, Ca 2+ , Mg 2+ and K + were quantified. The experimental design was completely randomized split-plot and means were compared through Tukey test (p>0.05). Water content decreased after 90 days, and after 180 days reached an average of 16%. The electrical conductivity showed the greatest loss of solute after 90 days. Larger amounts of soluble sugars were found in S1 and G1. The quantities of potassium and calcium decreased after 360 days, while magnesium increased after 90 days of storage. The electrical conductivity test showed no direct relation to the quantification of the investigated ions. The amount and behavior of amino acids and studied ions did not showed relation to the decrease in vigor of beans.

Electrical Conductivity and Chemical Composition of Soil Solution: Comparison of Solution Samplers in Tropical Soils

Soil solution samplers may have the same working principle, but they differ in relation to chemical and physical characteristics, cost and handling, and these aspects exert influence on the chemical composition of the soil solution obtained. This study was carried out to evaluate, over time, the chemical composition of solutions extracted by Suolo Acqua, with the hydrophilic membrane (HM) as a standard, using soils with contrasting characteristics, and to determine the relationship between electrical conductivity (EC) and concentration of ions and pH of soil solution samples. This study was carried out under laboratory conditions, using three soils samples with different clay and organic matter (OM) contents. Soil solution contents of F−, Cl−, NO−3, Br−, SO42−, Na+, NH4+, K+, Mg2+, Ca2+, were analyzed, as well as inorganic, organic, and total C contents, pH, and EC, in four successive sampling times. Soil solution chemical composition extracted by the Suolo Acqua sampler is similar to that collected by the HM, but the Suolo Acqua extracted more Na+ and soluble organic C than the HM solution. Solution EC, cation and anion concentrations, and soluble C levels are higher in the soil with greater clay and OM contents (Latossolo and Cambissolo in this case). Soil solution composition varied over time, with considerable changes in pH, EC, and nutrient concentrations, especially associated with soil OM. Thus, single and isolated sampling of the soil solution must be avoided, otherwise composition of the soil solution may not be correctly evaluated. Soil solution EC was regulated by pH, as well as the sum of cation and anion concentrations, and the C contents determined in the soil liquid phase.

Sensor-Enabled Geogrids for Performance Monitoring of Reinforced Soil Structures

Abstract Sensor-enabled geogrid (SEGG) technology has been introduced by the authors in the past few years as a new category of geogrid products that possess embedded strain-sensing capability in addition to their conventional reinforcement/stabilization function in geotechnical and transportation applications. In this technology, the strain-sensing function of modified geogrids (SEGG products) arises from their tensoresistivity, which is the sensitivity of the polymer composite electrical conductivity to tensile strain. An SEGG product is filled with a target concentration of conductive fillers such as carbon blacks and carbon nanotubes. The authors' previous studies on SEGG to date were focused on the in-isolation performance of the unitized SEGG and the coating of yarn-type SEGG samples. In the continuation of a long-term study, this paper reported the latest findings on both the in-isolation and in-soil tensoresistivity performance of polyethylene terephthalate (polyester) yarn SEGG specimens that were coated with a strain-sensitive carbon black-filled PVC composite. The formulation of the coating composite was presented and the influences of the soil confining pressure and loading (i.e., strain) rate on the tensoresistivity and tensile strength of SEGG specimens were investigated. It was found that greater confining pressures and strain rates both result in a reduction in the tensoresistivity of the SEGG samples. However, both the magnitude and reproducibility of the measured tensoresistivity in the in-soil tests carried out in this study were judged to be acceptable for civil engineering applications, given that the accuracy of strain distributions in geogrids can be improved by increasing the number of strain data points in each reinforcement layer at a significantly lower cost compared to the conventional methods. It was thus concluded that the SEGG technology holds promise to serve as an alternative to conventional instruments for the performance monitoring of geotechnical structures.

Microcombing enables high-performance carbon nanotube composites

A processing approach, microcombing, has been reported recently to produce dry carbon nanotube (CNT) films with superior mechanical and electrical properties by taking advantage of its efficiency in straightening the wavy CNTs and aligning the strands. Here, we report the fabrication of CNT composite films with aligned CNTs and CNT strands, reduced waviness, high CNT weight fraction, and relatively uniform CNT distribution, using poly(vinyl alcohol) (PVA) as a model matrix. These structural features give the micro-combed CNT/PVA composite films electrical conductivity of 1.84 × 105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which improve over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, and are also much higher than those obtained by other processing approaches. Moreover, this method is expected to be applicable to various polymer matrices as long as they can be dissolved in the solution.

Catchment‐Scale Permafrost Mapping using Spring Water Characteristics

AbstractThis study presents a method for mapping the spatial distribution of mountain permafrost based on the chemical‐physical characterisation of spring water in a 36 km2 high‐elevation catchment in the Eastern Italian Alps. Water temperature, electrical conductivity and isotopic composition (δ2H and δ18O) were measured in 45 springs during summer 2007, 2010 and 2012. Existing evidence of permafrost enabled the areas upslope of springs to be classified into two categories of permafrost occurrence (probable permafrost and no permafrost) and used to determine the most suitable tracer for permafrost mapping. Springs from probable permafrost areas have a specific water temperature signature. Spring water temperature was therefore used as a response variable in multiple linear regression, and mean elevation and mean clear sky radiation of spring upslope areas were used as predictors. The multiple regression models were statistically significant and used to map the potential spatial distribution of spring water temperature, which was reclassified into three permafrost categories (probable, possible and improbable). Cross‐validation and independent validation by ground surface temperature data provided evidence that the spring water temperature can be used alone for easy and low‐cost assessment of the catchment‐scale permafrost distribution in similar alpine catchments. Copyright © 2015 John Wiley & Sons, Ltd.

Electron Percolation In Copper Infiltrated Carbon

Abstract The work describes the dependence of the electrical conductivity of carbon materials infiltrated with copper in a vacuum-pressure autoclave on copper concentration and on the effective pore radius of the carbon skeleton. In comparison with non-infiltrated material the electrical conductivity of copper infiltrated composite increased almost 500 times. If the composite contained less than 7.2 vol% of Cu, a linear dependence of the electrical conductivity upon cupper content was observed. If infiltrated carbon contained more than 7.2 vol% of Cu, the dependence was nonlinear – the curve could be described by a power formula (x − xc ) t . This is a typical formula describing the electron percolation process in regions containing higher Cu fraction than the critical one. The maximum measured electrical conductivity was 396 × 104 Ω−1 m−1 for copper concentration 27.6 vol%. Experiments and analysis of the electrical conductivity showed that electron percolation occurred in carbon materials infiltrated by copper when the copper volume exceeded the critical concentration. The analysis also showed a sharp increase of electrical conductivity in composites with copper concentration higher than the threshold, where the effective radius of carbon skeleton pores decreased to 350 nanometres.

Fractal dendrite-based electrically conductive composites for laser-scribed flexible circuits.

Fractal metallic dendrites have been drawing more attentions recently, yet they have rarely been explored in electronic printing or packaging applications because of the great challenges in large-scale synthesis and limited understanding in such applications. Here we demonstrate a controllable synthesis of fractal Ag micro-dendrites at the hundred-gram scale. When used as the fillers for isotropically electrically conductive composites (ECCs), the unique three-dimensional fractal geometrical configuration and low-temperature sintering characteristic render the Ag micro dendrites with an ultra-low electrical percolation threshold of 0.97 vol% (8 wt%). The ultra-low percolation threshold and self-limited fusing ability may address some critical challenges in current interconnect technology for microelectronics. For example, only half of the laser-scribe energy is needed to pattern fine circuit lines printed using the present ECCs, showing great potential for wiring ultrathin circuits for high performance flexible electronics.

Conformal Pad-Printing Electrically Conductive Composites onto Thermoplastic Hemispheres: Toward Sustainable Fabrication of 3-Cents Volumetric Electrically Small Antennas.

Electrically small antennas (ESAs) are becoming one of the key components in the compact wireless devices for telecommunications, defence, and aerospace systems, especially for the spherical one whose geometric layout is more closely approaching Chu’s limit, thus yielding significant bandwidth improvements relative to the linear and planar counterparts. Yet broad applications of the volumetric ESAs are still hindered since the low cost fabrication has remained a tremendous challenge. Here we report a state-of-the-art technology to transfer electrically conductive composites (ECCs) from a planar mould to a volumetric thermoplastic substrate by using pad-printing technology without pattern distortion, benefit from the excellent properties of the ECCs as well as the printing-calibration method that we developed. The antenna samples prepared in this way meet the stringent requirement of an ESA (ka is as low as 0.32 and the antenna efficiency is as high as 57%), suggesting that volumetric electronic components i.e. the antennas can be produced in such a simple, green, and cost-effective way. This work can be of interest for the development of studies on green and high performance wireless communication devices.