Steady-state Electrical Conduction Research Articles

Frictional strength, electrical conductivity, and microstructure of calcite–graphite mixtures sheared at a subseismic slip rate

Calcite is a common mineral found in carbonate-bearing fault zones. Crystalline graphite (Gr) can be generated within calcite-bearing fault zones, which may contribute to their low strength and high electrical conductivity. To investigate the mixed effects of Gr on calcite gouges, a dedicated assembly was employed in a rotary-shear friction experiment, which enabled simultaneous measurement of friction and electrical conductivity. The experiments were conducted on synthetic dry calcite–Gr mixtures with 0–50 wt% Gr under a fixed normal stress of approximately 2 MPa at approximately 20 °C. A constant equivalent slip rate of 1 mm/s was imposed, with displacements ranging from 0.8 to 4.6 m. To resolve the microstructure evolution, four additional displacement-controlled experiments were performed on the 6 wt% Gr-bearing specimens under the same conditions. Following high peak friction, all Gr-bearing mixtures experienced dramatic slip weakening. The steady-state electrical conductivity of the specimens increased by over eight orders of magnitude when the Gr content exceeded 6 wt%. Microstructures indicated that the calcite particles initially formed a strong framework with distributed Gr, followed by the gradual development of conductive strain-localization zones (SLZs) and Gr-lubricated slip surfaces with increasing displacement. Even the mixtures with low-Gr content (< 2.4 vol%) developed smooth slip surfaces, sustaining low-level electrical conductivities throughout the experiments. For specimens with high electrical conductivities (Gr > 5.3 vol%), abundant Gr flakes were present in the SLZs, forming an interconnected structure. Combined with our companion study on quartz-Gr mixtures, we propose that the conductivity and frictional strength trends with displacement for Gr-bearing mixtures are not always consistent. Mineral crystal properties (e.g., hardness and crystal structure) may influence the frictional properties of these mixtures significantly, while the level of electrical conductivity of a fault zone cannot be used to infer its frictional strength.

Electromagnetic Response in an Expanding Quark–Gluon Plasma

The validity of conventional Ohm’s law is tested in the context of a rapidly evolving quark–gluon plasma produced in heavy-ion collisions. Here, we discuss the electromagnetic response using an analytical solution in kinetic theory. As conjectured previously, after switching on an electric field in a nonexpanding plasma, the time-dependent current is given by J(t)=(1−e−t/τ0)σ0E, where τ0 is the transport relaxation time and σ0 is the steady-state electrical conductivity. Such an incomplete electromagnetic response reduces the efficiency of the magnetic flux trapping in the quark–gluon plasma, and may prevent the observation of the chiral magnetic effect. Here, we extend the study to the case of a rapidly expanding plasma. We find that the decreasing temperature and the increasing transport relaxation time have opposite effects on the electromagnetic response. While the former suppresses the time-dependent conductivity, the latter enhances it.

The Effect of Quartz Particle Size on the Frictional and Electrically Conductive Properties of Mixed Graphite–Quartz Gouges

Mature faults usually contain fault rocks with a wide range of mineral grain sizes. Despite the importance of mineral grain sizes in affecting fault slip behaviors, little is known about the potential mechanism(s). To better understand this problem, electrical conductivity measurements on synthetic carbon-bearing gouges were conducted along a fault-parallel direction under progressive fault slip. All experiments were carried out under a slip rate of 1 mm/s, a normal stress of 2 MPa, ambient temperature, and a pure N2 atmosphere. The specimens that were used were mixtures of identical 6 wt% graphite (Gr) powders and 94 wt% quartz (Qz) particles with five different particle sizes (#100–12500 mesh). As Gr has a low friction coefficient and high electrical conductivity, the approach in this study may provide a favorable opportunity to examine the relation between the evolutions of friction and shear textures. The experimental results indicated that the reduction in Qz particle sizes causes gradual segregation of the Gr powders in the skeletal frame formed by granular Qz particles, resulting in the decreased interconnectivity of the anastomosing Gr-film networks and the destruction of Gr-lubricated slip surface(s). Then, it eventually manifests as an increase in the steady-state frictional coefficient (μss) and a logarithmic decrease in the steady-state electrical conductivity (σss) for Gr-bearing specimens. Furthermore, the Gr-bearing gouges containing &amp;gt;3 μm Qz particles first develop foliated layers, and subsequent Gr films penetrate around the boundary of the Qz particles to form conductive interconnected networks during a progressive fault slip. These experimental results implied that carbonaceous materials (CMs) represented by Gr may complicate the frictional properties of fine-grained fault gouges in mature faults.

Steady-State Conduction Current Performance for Multilayer Polyimide/SiO2 Films.

The steady-state electrical conduction current for single and multilayer polyimide (PI) nanocomposite films was observed at the low and high electric field for different temperatures. Experimental data were fitted to conduction models to investigate the dominant conduction mechanism in these films. In most films, space charge limited current (SCLC) and Poole–Frenkel current displayed dominant conduction. At a high electric field, the ohmic conduction was replaced by current–voltage dependency. Higher conduction current was observed for nanocomposite films at a lower temperature, but it declined at a higher temperature. PI nanocomposite multilayer films showed a huge reduction in the conduction current at higher electric fields and temperatures. The conclusions derived in this study would provide the empirical basis and early breakdown phenomenon explanation when performing dielectric strength and partial discharge measurements of PI-based nanocomposite insulation systems of electric motors.

A novel biosensor for detecting toxicity in water using sulfur-oxidizing bacteria

A novel toxicity detection methodology based on sulfur-oxidizing bacteria (SOB) has been developed for the rapid and reliable detection of toxic chemicals in water. The methodology exploits the ability of SOB to oxidize sulfur particles in the presence of oxygen to produce sulfuric acid according to the following equation: S + H 2O + 1.5O 2 → SO 4 2− + 2H +, Δ G°′ = −587.1 kJ/reaction. The reaction results in an increase in electrical conductivity (EC) and a decrease in pH as SOB convert insoluble sulfur particles to sulfate and protons. The proposed technique is validated using EC and pH data. Using a synthetic stream water (EC = 0.12 mS/cm and pH 7.2), the baseline steady-state EC and pH values were ∼1.0 mS/cm and ∼2.5 over 30 days of testing when hexavalent chromium (Cr 6+) was not added to the system. When Cr 6+ was added to the system, the effluent EC decreased and the pH increased due to inhibition of SOB. We found that the system can detect Cr 6+ at a concentration of 5 ppb which is lower than any method to date.

Simulating material inhomogeneities and defects in CIGS thin‐film solar cells

AbstractThin‐film CIGS solar cells are simulated using a hybrid model consisting of a distributed form of the analytical one diode model paired with a numerical finite element model of the d.c. conduction in the front contact layers. Variations in material quality over the substrate surface, from measured J–V curves, are incorporated into the model and the effects of cell width and window layer thickness are evaluated for homogeneous and inhomogeneous material quality. Furthermore, the effects of discrete shunt defects of different sizes are modelled, and in different positions on the cell surface. The results from optimizing cell width and window layer thickness show that the effects of material inhomogeneities include a small shift of the optimal parameters together with a less pronounced maximum. As expected, the defect size is important to the shunt conductance parameter of the resulting J–V curves. The passivating effect of the highly resistive ZnO layer is confirmed. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Influence from front contact sheet resistance on extracted diode parameters in CIGS solar cells

AbstractThe extraction of one‐diode model parameters from a current–voltage (J–V) curve is problematic, since the model is one‐dimensional while real devices are indeed three‐dimensional. The parameters obtained by fitting the model curve to experimental data depend on how the current is collected, and more specifically the geometry of the contact. This is due to the non‐uniform lateral current flow in the window layers, which leads to different parts of the device experiencing different front contact voltage drop, and hence different operating points on the ideal J–V curve. In this work, finite element simulations of three‐dimensional contact structures are performed and compared to experimental data on Cu(In,Ga)Se2‐based solar cell devices. It is concluded that the lateral current flow can influence the extracted parameters from the one‐diode model significantly if the resistivity of the front contact material is high, or if there is no current collecting grid structure. These types of situations may appear in damp heat‐treated cells and module type cells, respectively. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Wildfire plume electrical conductivity

Wildfires are weakly ionized gas. The ionization is mainly due to plant’s inorganic ash content species (more especially potassium), that are emitted from thermally decomposing plant structure into the flame during combustion. The amount of ionization in flames with potassium impurities is influenced by both the temperature and the amount potassium impurities in the flame. A numerical experiment was conducted using a local thermal equilibrium-based model to study the influence of inorganic wildfire contents on wildfire electrical conductivity. Simulated very high intensity wildfires (21–90 MW m-1) were used to quantify steady-state electrical conductivity. Its variation with wildfire plume height is important for high voltage power flashover research. In the simulation, vegetation potassium content was varied from 0.50% to 3.0% on dry weight basis, a reflection of its content in natural vegetation. The model predicted a maximum conductivity of 0.053 mho m-1 in 90 MW m-1 crown fire in vegetation with 3.0% potassium content. A 90 MW m-1 crown fire in vegetation with potassium content of 0.5% was predicted to produce a maximum conductivity of 0.022 mho m-1. Electrical conductivities were lower for a shrub fire with an intensity of 21 MW m-1. The model predicted conductivities of 0.0021 and 0.0009 mhom-1 for potassium content of 3.0 and 0.5% in vegetation, respectively.

A Study of Ionic Conductivity of Glasses in the PbCl2–PbO · B2O3 and PbCl2–2PbO · B2O3 Systems

The steady-state electrical conductivity of oxychloride glasses in the PbCl2–PbO · B2O3 and PbCl2–2PbO · B2O3 systems is investigated. In the temperature range from ∼190 to ∼380°C, the dependence of logσ on the reciprocal of the temperature exhibits a linear behavior. The nature of charge carriers is studied using the Hittorf technique. It is demonstrated that protons and chlorine ions are charge carriers in solid glasses. The concentration dependence of the transport numbers of chlorine ions is examined by the Tubandt method. The contribution of the electronic component to the total electrical conductivity is estimated with the use of the Liang–Wagner technique. The concentration dependences of the electrical conductivity and the transport numbers of chlorine ions are interpreted in terms of the microinhomogeneous glass structure associated with the selective interaction of components during synthesis of glasses.

Electrochemical Study of Glasses in the System Na2O-B2O3

The steady-state electrical conductivity and microhardness of glasses in the system Na2O-B2O3 was studied. IR spectroscopy was applied to determine the content of impurity hydrogen in the glasses studied.

Electroactive properties of flexible piezoelectric composites

A flexible piezoelectric composite with 0-3 connectivity, made from Lead Zirconate Titanate (PZT) powder and vegetable-based polyurethane (PU), was doped with small amount of semiconductor powder. As a result a composite with 0-0-3 connectivity was obtained. The nature of absorption and steady state electrical conduction and the dielectric behaviour have been studied for this ceramic/polymer composite. The dielectric loss processes of the composite were observed to be dominated by those the polymer. Adding a semiconductor phase in the composite the electrical conductivity can be controlled and a continuous electric flux path could be created between the PZT grains. This composite may be poled at low voltage and in shorter time compared with composites without a conductive phase.

Steady-state electrical conduction in the periodic Lorentz gas

We study nonequilibrium steady states in the Lorentz gas of periodic scatterers when an external field is applied and the particle kinetic energy is held fixed by a ``thermostat'' constructed according to Gauss' principle of least constraint (a model problem previously studied numerically by Moran and Hoover). The resulting dynamics is reversible and deterministic, but does not preserve Liouville measure. For a sufficiently small field, we prove the following results: (1) existence of a unique stationary, ergodic measure obtained by forward evolution of initial absolutely continuous distributions, for which the Pesin entropy formula and Young's expression for the fractal dimension are valid; (2) exact identity of the steady-state thermodyamic entropy production, the asymptotic decay of the Gibbs entropy for the time-evolved distribution, and minus the sum of the Lyapunov exponents; (3) an explicit expression for the full nonlinear current response (Kawasaki formula); and (4) validity of linear response theory and Ohm's transport law, including the Einstein relation between conductivity and diffusion matrices. Results (2) and (4) yield also a direct relation between Lyapunov exponents and zero-field transport (=diffusion) coefficients. Although we restrict ourselves here to dimension $d=2,$ the results carry over to higher dimensions and to some other physical situations: e.g. with additional external magnetic fields. The proofs use a well-developed theory of small perturbations of hyperbolic dynamical systems and the method of Markov sieves, an approximation of Markov partitions. In our context we discuss also the van Kampen objection to linear response theory, which, we point out, overlooks the ``structural stability'' of strongly hyperbolic flows.

Effect of rare-earth ion on electrical conductivity of ferroelectrics KVO3and LiVO3

Abstract The dc steady state electrical conductivity was measured by two terminal methods in the vicinity of phase transition point for pure and doped ferroelectric KVO3 and LiVO3. An exponential law is obeyed in both ferroelectric and paraelectric regions, with a change in activation energy at Tc . It was observed that the activation energy increases slowly with increasing dopant concentration up to 0.5 mol% Nd2O3, however decreases for higher concentrations, in both ferro and para states. The activation energy in the paraelectric phase is greater than that in the ferroelectric phase.

Electrical properties of ceramic/polymer composites

Three types of ceramic/polymer composites were prepared and their electrical, dielectric and pyroelectric properties analyzed. The composite PZT5/VDF-TrFE shows a significantly higher pyroelectric figure of merit than PZT (VDF=vinylidine fluoride, TrFE=trifluoroethylene). The dielectric loss of the ceramic/polymer composites is observed to be dominated by those of the polymer, whereas the ceramic phase has a significant contribution on the steady-state electrical conduction and low-frequency dielectric loss at high temperatures. >

I – V characteristics and electrical conductivity of synthetic melanin

AbstractI – V characteristics for synthetic melanin were investigated at – 10 and 25°C. It was found that the Ohm law is valid for low voltages whereas the Child law holds for higher ones. Furthermore, the steady state electrical conductivity was estimated. The change of activation energy from 0.76 eV for low temperatures to 1.58 eV was noticeable near 0°C.

Electroactive properties of polymer-ceramic composites

Abstract The nature of absorption and steady state electrical conduction as well as the dielectric and pyroelectric behaviour have been studied for polymer/ceramic composites. Experimentally observed values of pyroelectric coefficient and dielectric permittivity for various PZT content of PZT/PVDF composites seem to agree well with the calculated values. A high dielectric permittivity of polymer coupled with high pyroelectric activity of PZT may contribute to the high pyroelectric coefficient in the PZT/PVDF composites. The dielectric loss processes of the polymer-ceramic composites are observed to be dominated by those of the polymer whereas the ceramic phase may contribute significantly to the steady state electrical conduction which is suggested to be of ionic origin.

Dielectric and pyroelectric properties of polymer-ceramic composite

The dielectric and the pyroelectric behaviour and the nature of absorption and steady state of currents have been studied for a ceramic and a polymer-ceramic composite over wide ranges of frequency and poling field and a limited range of temperature. The relative permittivity and the pyroelectric coefficient of the composite are observed to be significantly higher than those of the polymer. The dielectric loss processes of the composite are observed to be dominated by those of the polymer whereas the ceramic phase contributes significantly to the steady state electrical conduction which is observed to be of ionic nature.

Dielectric properties of protein–methylglyoxal adducts. Interfacial and bulk effects

Steady-state electrical conduction and dielectric measurements over the frequency range 10–5–105 Hz are reported for polycrystalline samples of protein–methylglyoxal adducts. The results are found to be influenced by sample heterogeneity effects associated with a chemical instability that results in the formation of resistive layers at sample surfaces exposed to air. The conductivity data confirm earlier reports regarding the action of methylglyoxal in increasing the electrical conductivity of proteins, and an analysis of possible interfacial effects indicates that the increased conductivity and observed dielectric dispersions are associated with a true bulk phenomenon.

Electrical transport in doped and undoped polystyrene films in a cylindrical configuration

The steady state electrical conduction in films (about 30 μm thick) of polystyrene (PS) and of PS doped with acrylic acid (AA) was studied in the temperature range 35–115 °C. A mercury contact cylindrical electrode assembly was used in the conductivity measurements. Initially the conductivity decreases as a function of the dopant concentration but a higher concentrations it begins to increase with the dopant concentration. Different dopant concentrations were studied to attain an optimum doping concentration. The conduction behaviours for undoped and doped films were found to be different and a lowering of the activation energy due to doping with AA was also observed.

The effect of heat treatment on some electrical properties of polythene

The impulse electric strength of polythene film has been measured with and without a prestressing direct voltage of opposite polarity to that of the breakdown impulse after heating the polymer at several temperatures between 20 and 100 degrees C and quenching to room temperature. The steady-state electrical conduction through similar film specimens following identical heat treatment has also been measured. There was a correlation between breakdown strength with prestress, electrical conduction, and morphology as evinced by density changes.