Influence of the aggregate on the electrical conductivity of Portland cement concretes

The electrical conductivity and compressive strength of several high-performance Portland concretes with different amounts of crushed aggregate and sand have been measured at early age in isothermal conditions (20 °C). The total aggregate volume fraction varied from 0 (plain paste) to 0.75 and a constant weight ratio (1.2) between crushed aggregate and sand was used. The w/c ratio was 0.37 and microsilica (in slurry form) and a superplasticizer in water solution were used.The time taken before the electrical conductivity began to drop correlated very well with the induction period. The drop of conductivity was slightly delayed by the aggregate. The analysis of the electrical data, by means of different numerical and analytical models [hard core soft shell model (HCSS), differential effective medium theory (DEMT), Lu-Torquato, Maxwell], allowed an estimate of the properties of the interfacial transition zone (ITZ). In particular, an ITZ thickness of about 9 μm and an ITZ to bulk conductivity ratio of ∼2.5 were found. The existence of a percolating pathway through the interfacial regions was found by both electrical measurement and modeling when the aggregate volume fractions exceeded 60%. Finally, a new relationship among electrical conductivity, compressive strength, and aggregate amount was derived.     

Gas permeability and electrical conductivity of structural concretes: Impact of pore structure and pore saturation

This paper investigates the gas permeability and the electrical conductivity of structural concretes under different pore saturations. The gas permeability was measured by CemBureau device and the electrical conductivity by alternating current method. The pore structure was characterized by mercury intrusion porosimetry (MIP) and gravimetric methods. The Archie's law is used to interpret the tortuosity of the pore structure. The impact of pore saturation is evaluated through the Van Genuchten-Mualem (VGM) and Kozeny's models. The results show that (1) the global correlation between the gas permeability in dried state and the electrical conductivity in saturated sate is weak; (2) both VGM and Kozeny's models can describe the relative permeability/conductivity, but the VGM model gives more consistent exponents for permeability and conductivity; (3) as the pore gas and liquid phases are both percolated, the gas permeability is correlated to the electrical conductivity for arbitrary pore saturation.     

Determination of the electrical conductivity of carbon/carbon at high microwave frequencies

We present an accurate measurement of the electrical conductivity of carbon/carbon (C/C) composites in higher range of microwave frequencies. The composite is an 8 mm thick C/C laminate 2D woven fabric, machined to create a rectangular waveguide. Transmission and reflection parameters are acquired within a broad frequency band, ranging from 23 to 30 GHz, and used for the evaluation of the power loss in the waveguide and to extract the C/C electrical conductivity. The obtained conductivity values at microwave frequencies are about 10 times lower than those measured at very low frequencies. The effects of temperature are also investigated, and the variation of the conductivity with the temperature is reported.     

Electric conductivity and aggregation of anthracite and graphite particles in concretes

A statistical model of the electric conductivity of a heterogeneous system based on coal and a binding agent is presented. In this system, a conductive phase appears because of particle aggregation. The model was tested in the systems of anthracite and graphite in cement stone. The consistency between the experimental and calculated electric conductivities with a correlation coefficient higher than 0.9 was found on a linear interpolation of model parameters. It was found that the presence of a surfactant (cetylpyridinium chloride) and a high-molecular-weight compound (polyvinyl acetate) changed the number of particles in anthracite and graphite aggregates to affect the specific conductivity of the heterogeneous system.     

DC electrical conductivity of some oligoazomethines

Six aromatic oligoazomethines were synthesized containing seven benzene rings each. The terminal rings were substituted with different groups, namely, H, Cl, NO₂, OH, OCH₃ and CH₃. The synthesis was carried out by condensing the para‐substituted benzaldehydes with benzidine to give the three‐ring compound, which was then condensed with terephthaldehyde to give the respective seven‐benzene‐ring oligomers. The oligomers were characterized by elemental analysis, electronic spectra, Fourier‐transform infrared and thermal analysis. The oligomers were used to investigate the effects of their molecular structure on their electronic spectra, as well as their thermal, electronic and electrical properties. The different conformers were reported and compared. The DC electrical conductivity variation of oligoazomethines was studied in the temperature range 300–500 K after annealing for 24 h at 100 °C and after doping with 5% I₂. An attempt was made to relate the DC electrical conductivity, electronic properties and thermal properties to the chain length, substituted groups and coplanarity. The fairly low conductivity obtained was attributed to the non‐linearity of the rings in the chain. The different groups (neutral, electron withdrawing or electron donating) attached at the ends of the oligomer showed no influence upon the conductivity of the different oligomers. The action of doping gave almost the same enhancement as that noticed in the case of a long‐chain polymer. The DC electrical conductivity was interpreted using the band energy model. The seven‐benzene‐ring oligomer gave the same DC electrical conductivity as the long‐chain polymer. Copyright © 2004 Society of Chemical Industry     

Shock-induced electrical conductivity in some ferroelectrics

This paper gives the results of measurement of shock-induced electrical conductivity in ferroelectrics: PKR-1 lead zirconate-titanate piezoceramic, deuterated triglycerine sulphate single crystal, and polymer polyvinylidene fluoride.     

Ambient effects on the electrical conductivity of carbon nanotubes

We show that the electrical conductivity of single walled carbon nanotubes (SWCNT) networks is affected by oxygen and air humidity under ambient conditions by more than a magnitude. Later, we intentionally modified the electrical conductivity by functionalization with iodine and investigated the changes in the band structure by optical absorption spectroscopy.Measuring in parallel the tubes electrical conductivity and optical absorption spectra, we found that conduction mechanism in SWCNT is comparable to that of intrinsically conducting polymers. We identified, in analogy to conducting polymers, in the infrared spectra a new absorption band which is responsible for the increased conductivity, leading to a closing gap in semiconducting SWCNT.We could show that by different functionalizations of the same SWCNT starting material the properties like conductivity can be dramatically changed, leading to different imaginable applications. We investigated here, an ultraviolet sensor with weakly modified SWCNT.     

DC electrical conductivity of polyazomethinethiosemicarbazone metal complexes

Polyazomethinethiosemicarbazone (PATS) metal complexes of Ni(II), Co(II), Cu(II), Zn(II), Cd(II) and Hg(II) metal ions were prepared by reacting the polymer ligand (PATS) with the appropriate metal salt in refluxing DMSO. Elemental analyzes as well as FTIR and electronic spectral data are presented to confirm the formulation of the isolated materials. The spectral data show that the ligand polymer is bonded to the metal ions via the thiol sulfur atom and coordinated through the nitrogen of azomethine group. The DC electrical conductivity measurements of PATS and its metal complexes were measured in the range 300–500 K in the annealed and 5% iodine doped forms. The products gave electrical conductivity in the semiconducting region that increased by heat. The DC electrical conductivity is interpreted using the band gap theory using solitons, polarons and bipolarons. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The c-axis electrical conductivity of kish graphite

Measurements are reported on the temperature dependence of the d.c. conductivity in the c-direction of kish graphite. These results show that both the magnitude and temperature dependence of the c-axis conduction are similar to results reported in single crystal graphite, but qualitatively different from observations made in pyrolytic graphite. Because of differences in the impurity and defect density between kish graphite and single crystal graphite, the present results on kish graphite provide support for a band conduction model for c-axis conduction in graphite.     

四苯硼二烷基咪唑盐离子液体的合成及其电导性能

近十几年来,离子液体由于其显著的化学、物理特性以及作为一种环境友好的高效催化剂、良好的有机反应溶剂以及在分离及电化学等方面的应用,成为国内外学者研究的热点．在已报道的离子液体的组成中,阳离子主要是含有取代基团的咪唑、吡啶、喹啉、异喹啉等含氮有机杂环,     

Microwave absorption measurements of the electrical conductivity of small particles

A microwave absorption technique based on cavity perturbation theory is shown to be applicable for electrical conductivity measurements of both a small, single-crystal particle and finely divided powder samples when values fall in either the low (<0.1 ^–1 cm^–1) or the intermediate (0.1 100 ^–1 cm^–1) conductivity region. The results here pertain to semiconductors in the latter region. If the skin depth of the material becomes significantly smaller than the sample dimension parallel to theE-field, an appreciable error can be introduced into the calculated conductivity values; however, this discrepancy is eliminated by correcting for the field attenuation associated with the penetration depth of the microwaves. A modification of this approach utilizing the skin depth allows a first-order correction to be applied to powder samples which results in the accurate measurement of absolute values, and results with doped Si powders are compared to values obtained from one small single particle using this microwave technique as well as reported DC values determined with single crystals. The use of this microwave absorption technique with small particles having high surface/volume ratios, such as catalyst supports and oxide catalysts, under controlled environments can provide fundamental information about adsorption and catalytic processes on such semiconductor surfaces. An application to a ZnO powder demonstrates this capability.     

导电硅橡胶导电性和电热性的研究

对乙炔炭黑作导电填料的导电硅橡胶的导电性和电热性进行了研究。结果表明，由乙炔炭黑用量和渗滤阈可以预测和控制导电硅橡胶的体积电阻率；导电硅橡胶的电阻－温度变化规律符合隧道效应理论模型，导电硅橡胶的电压－电流特性呈非线性欧姆性，且乙炔炭黑用量越大，电压－电流特性的非线性欧姆性越显著；发热量与热损耗量达到平衡时，导电硅橡胶的表面温度可维持140℃，导电硅橡胶可作面状发热体使用；在满足导电性能的前提下，为保证导电硅橡胶良好的物理性能，应控制乙炔炭黑用量。     

Studies on the electrical conductivity of carbon black filled polymers

The conductivity mechanism for a carbon black (CB) filled high-density polyethylene (HDPE) compound was investigated in this work. From the experimental results obtained, it can be seen that the relation between electrical current density (J) and applied voltage across the sample (V) coincides with Simmons's equation (i.e., the electrical resistivity of the compound decreases with the applied voltage, especially at the critical voltage). The minimum electrical resistivity occurs near the glass transition temperature (T_g) of HDPE (198 K). It can be concluded that electron tunneling is an important mechanism and a dominant transport process in the HDPE/CB composite. A new model of carbon black dispersion in the matrix was established, and the resistivity was calculated by using percolation and quantum mechanical theories. © 1996 John Wiley & Sons, Inc.