Transport measurements, solids electrical conductivity

For salt aqueous solutions in the absence of any other chemical additives, the hydrate suppression temperature (i.e., dissociation temperature shift) can be determined by measuring the electrical conductivity (Mohammadi, et al, 2007) [16], To characterize liquid mixtures for industrial processes, an acoustic multi-sensor system was developed to measure the concentrations of the chemicals such as MeOH and MEG in the solutions without salts (Henning, et al, 2000) [10]. However, these methods may not be applicable to most hydrocarbon transport pipelines where salts and at least one inhibitor often coexist in the aqueous phase. (Sandengen and Kaasa, 2006) [18] developed an empirical correlation that determined the MEG and NaCl concentrations by measuring the density and electrical conductivity of water samples under examination. However, the critical weakness of this method is that it requires high accuracy of the density measurement, which prevents it from application to real produced water samples that usually contain solid particles (sands and clays) and oil droplets. 

Following the general trend of looldng for a molecular description of the properties of matter, self-diffusion in liquids has become a key quantity for interpretation and modeling of transport in liquids [5]. Self-diffusion coefficients can be combined with other data, such as viscosities, electrical conductivities, densities, etc., in order to evaluate and improve solvodynamic models such as the Stokes-Einstein type [6-9]. From temperature-dependent measurements, activation energies can be calculated by the Arrhenius or the Vogel-Tamman-Fulcher equation (VTF), in order to evaluate models that treat the diffusion process similarly to diffusion in the solid state with jump or hole models [1, 2, 7]. 

The experiments in the solid state are based on several techniques, including imaging, spectroscopy, and electrical transport measurements that reveal the electric current flux through the molecule under an external field. The results pertain to single molecules (or bundles) and can be remeasured many times. The roles of the donor and of the acceptor are in this case played either by the metal leads, or by the substrate and a metal tip. The interpretation is generally given in terms of conductivity, determined by the electronic energy levels (if the molecular structure supports the existence of localized... 

The electrical conductivity of a material is a macroscopic solid-state property since even in high molecular-weight polymers there is not just one conjugated chain which spans the distance between two electrodes. Then it is not valid to describe the conductivity by the electronic structure of a single chain only, because intra- and interchain charge transport are important. As with crystalline materials, some basic features of the microscopic charge-transport mechanism can be inferred from conductivity measurements [83]. The specific conductivity a can be measured as the resistance R of a piece of material with length d and cross section F within a closed electrical circuit,... 

The charged reactant for the sink electrochemical reaction is supplied by the solid electrochemical cell of a PEVD system. The solid phase (E) is an exclusive ionic conductor for (A +) or (A ), and serves as the solid electrolyte. (C) and (W) are solid electronic conducting phases, and contact (E) from both sides as counter and working electrodes, respectively. They coimect with the external electric circuit, which consists of a dc source and other possible measurement devices. Because the conductivity changes in nature from ionic to electronic at the electrode/electrolyte interfaces, the solid electrochemical cell in a PEVD system effectively separates the transport paths of ionic and electronic charged carriers... 

One current-based approach is referred to as impedancemetric sensing [32]. This is based on impedance spectroscopy, in which a cyclic voltage is applied to the electrode and an analysis of the resultant electrical current is used to determine the electrode impedance. As different processes have different characteristic frequencies, impedance spectroscopy can be used to identify and separate contributions from different processes, such as electron transfer at the interface from solid-state electronic conduction. The frequency range ofthe applied voltage in impedancemetric sensors is selected so that the measured impedance is related to the electrode reaction, rather than to transport in the electrode or electrolyte material. Thus, the response is different from that in resistance-based sensors, which are related to changes in the electrical conductivity of a semiconducting material in response to changes in the gas composition. 

Kinetic theory is introduced and developed as the initial step toward understanding microscopic transport phenomena. It is used to develop relations for the thermal conductivity which are compared to experimental measurements for a variety of solids. Next, it is shown that if the time- or length scale of the phenomena are on the order of those for scattering, kinetic theory cannot be used but instead Boltzmann transport theory should be used. It was shown that the Boltzmann transport equation (BTE) is fundamental since it forms the basis for a vast variety of transport laws such as the Fourier law of heat conduction, Ohm s law of electrical conduction, and hyperbolic heat conduction equation. In addition, for an ensemble of particles for which the particle number is conserved, such as in molecules, electrons, holes, and so forth, the BTE forms the basis for mass, momentum, and energy conservation equa-... 

Meyer, J.-P., Schlettwein, D., Wohrle, D and Jaeger, N.I. (1995) Charge Transport in thin films of molecular semiconductors as investigated by measurements of thermoelectric power and electrical conductivity. Thin Solid Films, 258, 317-324. 

T. Akashi, T. Maruyama, T. Goto, Transport of lanthanum ion and hole in LaCrOs determined by electrical conductivity measurements. Solid State Ionics 164,177-183 (2003)... 

Conventional two-electrode dc measurements on ceramics only yield conductivities that are averaged over contributions of bulk, grain boundaries and electrodes. Experimental techniques are therefore required to split the total sample resistance Rtot into its individual contributions. Four-point dc measurements using different electrodes for current supply and voltage measurement can, for example, be applied to avoid the influence of electrode resistances. In 1969 Bauerle [197] showed that impedance spectroscopy (i.e. frequency-dependent ac resistance measurements) facilitates a differentiation between bulk, grain boundary and electrode resistances in doped ZrC>2 samples. Since that time, this technique has become common in the field of solid state ionics and today it is probably the most important tool for investigating electrical transport in and electrochemical properties of ionic solids. Impedance spectroscopy is also widely used in liquid electrochemistry and reviews on this technique be found in Refs. [198 201], In this section, just some basic aspects of impedance spectroscopic studies in solid state ionics are discussed. 

Since the electronic conductivity of nanocrystalline ScSZ becomes significant in reducing atmosphere (Fig.3), its contribution to the electrical transport should be considered. This can be discussed based on the dependence of the ionic transference number, t,- = cr,- / (oxygen activity. Such information is important for the development of ScSZ solid electrolyte for Solid Oxide Fuel Cells. Figure 4 presents the relationship between the ionic transference number and oxygen activity, which has been determined based on the presented conductivity measurements and the defect model [13]. 

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