Development of high performance EMI shielding material from EVA,NBR, and their blends: effect of carbon black structure

The conductive composites were prepared using two different types of conductive black (Conductex and Printex XE2) filled in matrices like EVA and NBR and their different blends. The electromagnetic interference shielding effectiveness (EMI SE) of all composites was measured in the X band frequency range 8–12 GHz. Both conductivity and EMI SE increase with filler loading. However, Printex black shows higher conductivity and better EMI SE at the same loading compared to Conductex black, and this can be used as a material having high EMI shielding effectiveness value. The conductivity of different blends with same filler loading generally found to increase slightly with the increase in NBR concentration. However, EMI SE has some dependency on blend composition. EMI SE increases linearly with thickness of the sample. EMI SE versus conductivity yields two master curves for two different fillers. EMI SE depends on formation of closed packed conductive network in insulating matrix, and Printex black is better than Conductex black in this respect. Some of the composites show appreciably high EMI SE (>45 dB).     

Conductive particulate films fabricated by electrospray deposition of candle soot suspensions with acid treatment

The electrical properties of carbon-based materials have attracted significant interest due to their wide range of potential applications. This study investigated the effect of nitric acid treatment on the electrical conductivity of candle soot particle films. Electrospray deposition was used to deposit the candle soot dispersion on a solid substrate. The electrical conductivity of the films increased as the concentration of nitric acid increased, with the highest conductivity of 27.65 S cm⁻¹ observed in the film treated with 5 M nitric acid. The increase in conductivity was attributed to the enhancement of interparticle bonding between soot particles after acid treatment. Functional groups such as carboxylic or nitro groups were observed in the films by Fourier transform infrared (FTIR) spectroscopy. Raman spectroscopy showed a broadening of the D bands, suggesting a defect in the crystalline structure due to the formation of functional groups on the soot structure. These results suggest that nitric acid treatment can be used to improve the electrical conductivity of candle soot particle films.     

Multiwavelength Raman microspectroscopy for rapid prediction of soot oxidation reactivity

Multiwavelength Raman microspectroscopy (MWRM) analysis for characterization of soot structure and reactivity was developed. This new method is based on the dispersive character of carbon D mode in Raman spectra (i.e., red shift and increase in intensity at higher excitation wavelength, λ(0)). The approach was proven by investigating various diesel soot samples and related carbonaceous materials at different λ(0) (785, 633, 532, and 514 nm). In order to compare the behavior of the D mode for various samples and to derive a single parameter characterizing the soot structure, the difference of integrals for pairs of spectra collected at different λ(0) was calculated. MWRM analysis revealed substantial differences in the structural ordering which decreases from graphite, over Printex XE2 and various diesel soot samples, to spark discharge soot. To obtain the relation between structure and reactivity of soot, MWRM analysis was combined with temperature-programmed oxidation (TPO). TPO allowed us to characterize the oxidation behavior of soot in terms of the maximum emission (CO + CO(2)) temperature and reactivity index. The latter was calculated by introducing the reactivity limits: spark discharge soot containing a large amount of disorder represents the upper limit, whereas the lower limit is given by graphite powder with high structural order. The comparison of MWRM (viz., the observed Raman difference integrals) and TPO data revealed a linear correlation between soot structure and oxidation reactivity. Thus, we demonstrated for the first time the potential of MWRM for a robust and rapid prediction of diesel soot reactivity based on the structure-reactivity correlation.     

Thermal conductivity measurement with a free floating molecule detector

“Zero‐pressure” elimination with Pirani principle for vacuum measurement and increase of the measurement range limit of thermal gas‐sensors and flow sensors Measurement of pressure in the medium vacuum range has been done via thermal conductivity. The literature on the Pirani principle has defined a lower range limit — the so‐called “zero pressure” until now [1]. The minimum power needed to hold a sensor up to operating temperature exceeds the useful signal, due to the conductivity of the sensor mounting and the resulting heat loss through the suspension. The author was able to eliminate the “zero pressure”, thereby expanding the measurement range of Pirani sensors significantly downwards. Measurement results confirmed an extension of the measurement range of two decades downwards with the coiled Pirani. Also with other sensors that use thermal conductivity and heatentrainment effects, e.g. gas sensors and sensors for flow measurement, the new principle can be applied and thus lower the lower range limit.     

Optical diagnostics on sooting laminar diffusion flames in microgravity

Laser-induced incandescence was successfully applied to the investigation of soot formation in both buoyant and non-buoyant laminar jet diffusion flames. Microgravity experiments were conducted in the Drop Tower Bremen, Germany. By the use of imaging laser-induced incandescence (LII) it was possible for the first time to obtain simultaneously two-dimensional information on soot concentration and primary particle size under microgravity. Additionally, temperature fields were measured by 2-color emission pyrometry. Results for the fuels propane and ethene show that soot formation and oxidation is drastically altered under microgravity. Maximum temperatures are reduced by roughly 220 K and 120 K, respectively, which in the case of ethene results in a termination of oxidation processes and the emission of soot. The distribution of soot within the non-buoyant flames is always concentrated in relatively small bands. For all non-buoyant flames investigated the maximum primary particle size roughly doubles compared to the buoyant ones.     

Electrical conductivity measurements of nanofluids and development of new correlations

In this study the electrical conductivity of aluminum oxide (Al2O3), silicon dioxide (SiO2) and zinc oxide (ZnO) nanoparticles dispersed in propylene glycol and water mixture were measured in the temperature range of 0 degrees C to 90 degrees C. The volumetric concentration of nanoparticles in these fluids ranged from 0 to 10% for different nanofluids. The particle sizes considered were from 20 nm to 70 nm. The electrical conductivity measuring apparatus and the measurement procedure were validated by measuring the electrical conductivity of a calibration fluid, whose properties are known accurately. The measured electrical conductivity values agreed within +/- 1% with the published data reported by the manufacturer. Following the validation, the electrical conductivities of different nanofluids were measured. The measurements showed that electrical conductivity of nanofluids increased with an increase in temperature and also with an increase in particle volumetric concentration. For the same nanofluid at a fixed volumetric concentration, the electrical conductivity was found to be higher for smaller particle sizes. From the experimental data, empirical models were developed for three nanofluids to express the electrical conductivity as functions of temperature, volumetric concentration and the size of the nanoparticles.     

Electrical conductivity of polyethylene-carbon-fibre composites mixed with carbon black

The study of electrical conductivity of high-density polyethylene-carbon-fibre composites mixed with different concentrations of carbon black is reported. The influence of the mixing procedure of the additives and material preparation is examined with regard to the conductivity values. The use of these two filler types in polyethylene composites combines the conducting features of both. Thus, while fibres provide charge transport over large distances (several millimetres), carbon black particles improve the interfibre contacts. Results are discussed with reference to simple electrical models. It is shown that for composites in which the segregated carbon black-polyethylene component lies above the percolation threshold the electrical interfibre contacts are activated through carbon black particle bridges, leading to a conductivity rise. This effect is more relevant in the case of shorter fibres. Processing of the material involving fibre orientation, such as in injection-moulding, decreases drastically the conductivity level reached.     

Investigations on coating durability and tenso-resistive effect of carbon black-coated polycaprolactam fibers

A novel coating method (dissolving-coating method) is designed to provide electrically conductive fibers with lower electrical resistivity and permanent conductivity. In the dissolving-coating method, no adhesive was used, but a solvent of fiber substrate was used. Carbon black (CB)-coated polycaprolactam (PA6) fibers application for electrically conducting sensor were prepared by the new coating method. The durability of CB coatings on PA6 fibers was tested through washing and stretching test. To make a study on the electromechanical behavior of the CB-coated PA6 fibers under tensile load, the effects of various factors that are responsible that correlates the resistance change with the applied strain, strain rate (S.R), the environmental temperature, and the relative humidity (RH) were discussed.     

An Experimental Study on Thermal and Electrical Properties of Packed Carbon Nanofibers

In the present study, the thermal and electrical properties of packed carbon nanofibers (P-CNFs) have been investigated. A short-hot-wire (SHW) technique was applied to determine simultaneously the thermal conductivity and thermal diffusivity of P-CNFs. In SHW measurements, a platinum wire coated with an alumina layer served as both the heating source and the thermometric sensor. A curve fitting method by matching the experimental data and numerical simulated values was proposed for determining the thermal conductivity and thermal diffusivity of P-CNFs with different packed densities. The electrical conductivities were measured by a four-terminal method where a special vessel with electrodes with circular plates was used. The results indicated that the electrical conductivity increases linearly with an increase in packed density. The thermal conductivity and thermal diffusivity also increase with an increase in packed density. The relation between the thermal conductivity and the electrical conductivity has been shown to be approximately linear. The SHW technique combined with the curve fitting method would be applicable to many kinds of materials.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

炭黑粒子表面改性及其电磁特性研究

采用溶胶-凝胶法制备钛酸钡改性炭黑的复合粒子,并观察和分析了改性后粒子的颗粒结构、体电阻率和介电性能.经XRD分析可知复合粒子中存在钛酸钡和炭黑;TEM和SEM研究表明,通过溶胶-凝胶法在炭黑表面包覆了钛酸钡绝缘层,从而使得改性后的炭黑粒子之间不能建立发达的导电网络,复合粒子导电性能降低.研究表明钛酸钡改性对复合粒子的电导率和介电性能有着重要影响.     

A variable pressure method for characterizing nanoparticle surface charge using pore sensors

A novel method using resistive pulse sensors for electrokinetic surface charge measurements of nanoparticles is presented. This method involves recording the particle blockade rate while the pressure applied across a pore sensor is varied. This applied pressure acts in a direction which opposes transport due to the combination of electro-osmosis, electrophoresis, and inherent pressure. The blockade rate reaches a minimum when the velocity of nanoparticles in the vicinity of the pore approaches zero, and the forces on typical nanoparticles are in equilibrium. The pressure applied at this minimum rate can be used to calculate the zeta potential of the nanoparticles. The efficacy of this variable pressure method was demonstrated for a range of carboxylated 200 nm polystyrene nanoparticles with different surface charge densities. Results were of the same order as phase analysis light scattering (PALS) measurements. Unlike PALS results, the sequence of increasing zeta potential for different particle types agreed with conductometric titration.     

DC conductivity and interfacial polarization in PMMA/nanotube and PMMA/soot composites

This work focuses on the DC conductivity and interfacial polarization of poly(methyl methacrylate) (PMMA) composites made with single wall nanotubes (SWNTs) and nanotube precursor soot. We aim to compare and contrast the behavior of the two nanofillers in an effort to determine if the precursor material imparts tunable electrical properties to PMMA. The DC activity of the polymers and composites was determined by extrapolating AC conductivity versus frequency plots to zero. Activation energies and DC conductivities were obtained through Arrhenius plots. The conductivity increased with temperature for all the samples in conjunction with viscous flow. Both nanotubes and nanosoot increased the DC conductivities. Activation energies for the SWNT decreased slightly upon the addition of nanotubes to the matrix. However, the activation energies increased with soot content in the matrix, indicating obstruction of motion or possible bridging caused by the soot. Cole-Cole plots were effectively used to determine the extent of interfacial polarization in the composite samples. Plots shifted toward the origin with the addition of carbon nanotubes or with soot concentration indicating a Maxwell-Wagner-Sillars process.     

A Novel Methodology for Spatial Damage Detection and Imaging Using a Distributed Carbon Nanotube-Based Composite Sensor Combined with Electrical Impedance Tomography

This paper describes a novel non-destructive evaluation methodology for imaging of damage in composite materials using the electrical impedance tomography (EIT) technique applied to a distributed carbon nanotube-based sensor. The sensor consists of a nonwoven aramid fabric, which was first coated with nanotubes using a solution casting approach and then infused with epoxy resin through the vacuum assisted resin transfer molding technique. Finally, this composite sensor is cured to become a mechanically-robust, electromechanically-sensitive, and highly customizable distributed two-dimensional sensor which can be adhered to virtually any substrate. By assuming that damage on the sensor directly affects its conductivity, a difference imaging-based EIT algorithm was implemented and tailored to offer two-dimensional maps of conductivity changes, from which damage location and size can be estimated. The reconstruction is based on a newly defined adjacent current–voltage measurement scheme associated with 32 electrodes located along the boundary of the sensor. In this paper, we evaluate our methodology first by introducing well-defined damage where sections are either removed or narrow cuts are made on a series of sensor specimens. Finally, a more realistic damage scenario was investigated to show the capability of our methodology to detect impact damage on a composite laminate. The resulting EIT maps are compared to visual inspection and thermograms taken with an infrared camera.     

Dual imaging modality of granular flow based on ECT sensors

In this study, a previously developed dual modality imaging system is applied to image the flow of granular matter with different electrical properties in cylindrical vessels. The imaging system is based on both capacitance and power measurements acquired by an electrical capacitance tomography (ECT) sensor located around the vessel. The measurement data are then used to reconstruct cross-sectional images of both permittivity and conductivity distributions. A neural network multi-criterion optimization reconstruction technique (NN-MOIRT) is used for the inverse (reconstruction) problem. The contribution of this technology to the field of granular matters is explored through review of research articles that can be a direct application of this development. We discuss the capabilities of this dual-modality acquisition system using synthetic data for granular matter with different electrical properties.     

扩散火焰中初始形成碳核的光学测量

根据米氏散射理论 ,推导出碳核的散射属于瑞利散射。介绍一种实验方法 ,该方法利用在入射光为偏振激光时碳核的瑞利散射光与碳核原始化合物 PAH辐射的荧光的差异 ,测量扩散火焰中形成的碳核     

Preparation and characterization of conducting polyaniline/silica nanosheet composites

A series of polyaniline/silica nanosheet composites (PANI/SNS) with different contents of the silica nanosheets derived from vermiculite via acid-leaching were prepared via the in situ chemical oxidation polymerization. The PANI/SNS composites were characterized with Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and electrical conductivity measurement. It is interesting that the electrical conductivities of the PANI/SNS composites increased with the increasing of the contents of the silica nanosheets added because of the moisture absorption. It was confirmed by the TGA analysis.     

Novel sucrose three-enzyme conductometric biosensor

For the first time a conductometric biosensor for sucrose determination has been developed using a complex three-enzyme (invertase, mutarotase, and glucose oxidase) containing membrane as a sensitive element immobilized on the conductometric interdigitated planar electrodes. The time of measurement of sucrose concentration in the solution was about 1–2 min. The dynamic range of biosensor depends on buffer capacity, being 2 μM–5 mM of sucrose in 5 mM phosphate buffer. The conductometric biosensor developed demonstrates high selectivity, operational stability and reproducibility. The dependence of sensor response on pH and ionic strength of tested solution has been studied in this work. Storage conditions have also been under investigation. The sensor appeared to be eligible towards application in practice.     

DC electrical conductivity of poly(methyl methacrylate)/carbon black composites at low temperatures

The study deals with the dc electrical conduction of poly(methyl methacrylate)/carbon black composites of different carbon black (CB) filler concentrations (2, 6, 12 wt%). The dc electrical conductivity was studied as a function of filler concentration, and temperature in the range (20–290 K). It was found that the composites exhibit negative temperature coefficient of resistivity (NTCR) at low temperatures and enhancement in the dc electrical conductivity with both temperature and CB concentration. The observed increase of conductivity with CB concentration was interpreted through the percolation theory. The dependence of the electrical conductivity of the composites in low temperatures was analyzed in term of a formula in consistence with Mott variable rang hopping (VRH) mechanism. The observed overall mechanism of electrical conduction has been related to the transfer of electrons through the carbon black aggregations distributed in the polymer matrix.     

热处理条件对氧化石墨结构和导电性能的影响

氧化石墨是石墨的氧化产物．由于它的碳层表面引入了很多极性功能团，使得很多分子都能够嵌入其层间形成纳米复合物，但也正是这些功能团使得它散失了石墨良好的导电性。为了考察氧化石墨受热处理后还原的可能性，通过X-射线衍射、扫描电镜、红外光谱分析以及元素分析等手段研究了氧化石墨在不同热处理条件下的结构变化。研究发现热处理时的升温速度对氧化石墨的结构影响很大，快速升温时，氧化石墨迅速分解，发生膨胀形成类似于膨胀石墨的含有丰富的50nm至5μm左右孔洞的一种结构；而当缓慢升温时，氧化石墨随着热处理温度的升高，逐渐恢复成类似于石墨的结构，同时电导率也随热处理温度的升高而提高，当热处理温度高于180℃时，电导率大于1S／cm。这些结果表明利用氧化石墨作为前驱体，通过先制备聚合物／氧化石墨纳米复合物后经热处理来得到导电性的聚合物／碳纳米复合材料是可行的。     

Assessment of percolation and homogeneity in ABS/carbon black composites by electrical measurements

In this study, composites consisting of an insulating poly(acrylonitrile-co-butadiene-co-styrene) polymer matrix and a conducting carbon black (CB) additive were produced by twin-screw extrusion. Both direct current and alternating current electrical measurements were used to evaluate the electrical properties of the composite and to assess whether sufficient mixing was achieved. Electrical measurement results and scanning electron micrographs show that once-extruded composites had a porous structure and poor conductivity while twice-extruded composites were much more homogeneous and had higher conductivity. The percolation threshold of the twice-extruded poly(acrylonitrile-co-butadiene-co-styrene)/CB composites was found to be between 8 and 10% CB. Electrical measurements provided a feedback loop for improving processing of the composite material.