Steady-state electrical measurement conductivity

The multitude of transport coefficients collected can thus be divided into self-diffusion types (total or partial conductivities and mobilities obtained from equilibrium electrical measurements, ambipolar or self-diffusion data from steady state flux measurements through membranes), tracer-diffusivities, and chemical diffusivities from transient measurements. All but the last are fairly easily interrelated through definitions, the Nemst-Einstein relation, and the correlation factor. However, we need to look more closely at the chemical diffusion coefficient. We will do this next by a specific example, namely within the framework of oxygen ion and electron transport that we have restricted ourselves to at this stage. 

Of all existing methods to monitor electrical properties while using semiconductor sensors, only two [5] have become widely implemented both in experimental practice and in industrial conditions. These are kinetic method, i.e. measurement of various electrical parameters under kinetic conditions, and stationary (equilibrium) method based on the measurement of steady-state parameters (conductivity, work function. Hall s electromotive force, etc.). 

Thermal conductivity was measured by a steady-state technique. One end of the sample was fixed (see Fig. 11.13) onto a gold-plated copper platform (Pf) whose temperature 7 can be set by means of a heater (H0. The thermometer (R ), glued on the copper block (Bj), measured T1. The copper block (B2) held a carbon thermometer (R2), which measured T2, and a NiCr heater (H2) was glued on the top of the copper screw (Sc2) (see Fig. 11.12). Electrical connections were made of 0 50p,m, 35cm long manganin wires. 

Polar Cell Systems for Membrane Transport Studies Direct current electrical measurement in epithelia steady-state and transient analysis, 171, 607 impedance analysis in tight epithelia, 171, 628 electrical impedance analysis of leaky epithelia theory, techniques, and leak artifact problems, 171, 642 patch-clamp experiments in epithelia activation by hormones or neurotransmitters, 171, 663 ionic permeation mechanisms in epithelia biionic potentials, dilution potentials, conductances, and streaming potentials, 171, 678 use of ionophores in epithelia characterizing membrane properties, 171, 715 cultures as epithelial models porous-bottom culture dishes for studying transport and differentiation, 171, 736 volume regulation in epithelia experimental approaches, 171, 744 scanning electrode localization of transport pathways in epithelial tissues, 171, 792. 

A calorimetric method may be used where an electric heater is imbedded in the object of interest, and the power dissipated by the element is accurately calculated from voltage and current. Once steady state is established and the object is at constant temperature, the body must emit radiation at the same rate at which it is supplied. As long as conduction and convection are eliminated as mechanisms of heat transfer (e.g. vacuum conditions), the blackbody temperature is known by Rt = o"T4. The emittance can then be determined after py-rometric measurements of the brightness temperature of the object. 

As for the permeability measurements, most techniques based on the analysis of transient behavior of a mixed conducting material [iii, iv, vii, viii] make it possible to determine the ambipolar diffusion coefficients (- ambipolar conductivity). The transient methods analyze the kinetics of weight relaxation (gravimetry), composition (e.g. coulometric -> titration), or electrical response (e.g. conductivity -> relaxation or potential step techniques) after a definite change in the - chemical potential of a component or/and an -> electrical potential difference between electrodes. In selected cases, the use of blocking electrodes is possible, with the limitations similar to steady-state methods. See also - relaxation techniques. 

Local axial and radial gas-phase characteristic measurements were made at steady-state conditions in a 0.108-m-i.d. slurry bubble column apparatus with a two-point electrical conductivity probe. 

Two experimental procedures were carried out. In the first, a 100 1 (water and dye filtrate) dilution was concentrated to one-tenth its initial volume. Rejection based on color absorbance (HlO nm) and electrical conductivity, flux, pressure, temperature, and crossflow rate were measured at intervals during the concentration experiment. In the second, a slightly diluted dye filtrate (2 3) was used and the hyperfiltration at steady state was evaluated as in the first procedure. The test was repeated at dilutions reaching (100 1), with pH and temperature excursions at a dilution of 3 1. 

If a constant heat flux boundary condition is required, an electrical heating element, often a thin, metallic foil, can be stretched over an insulated wall. The uniform heat flux is obtained by Joule heating. If the wall is well insulated, then, under steady-state conditions, all of the energy input to the foil goes to the fluid flowing over the wall. Thermocouples attached to the wall beneath the heater can be used to measure local surface temperature. From the energy dissipation per unit time and area, the local surface temperature, and the fluid temperature, the convective heat transfer coefficient can be determined. Corrections to the total heat flow (e.g., due to radiation heat transfer or wall conduction) may have to be made. 

Under equilibrium conditions the electrical conductivity of many oxide phases, e.g., CugO, FeO, CoO, NiO, or ZnO at elevated temperatures is a function of the oxygen partial pressure in the ambient gas phase 12). The oxygen partial pressure determines the metal excess or deficit in the metal oxide and thereby the concentration of electrical carriers especially excess electrons and electron holes. Thus, after proper calibration, the steady-state oxygen activity ao(st) may be deduced from measurements of the conductance of a metal oxide foil used as catalyst while an oxygen transfer reaction, e.g., CO2 + H2 = CO -)- HjO or 2N2O = 2N2 + O2 proceeds at the surface of the metal oxide 13). 

Hayashi has investigated in some detail the ionic photopolymerization of styrene monomers. Free ion lifetimes measured by pulse electrical conductivity measurements were found to agree with those calculated from steady-state conductance measurements. Other studies of interest on radical addition polymerization include the photodimerization of polymers containing thymine bases, diene polymerization by terbium complexes, polymerization of vinyl acetate, and preparation of light-sensitive polyacrylates. 

Distinguishing between interface-dominated currents and bulk-dominated (ohmic) currents often requires a self-consistent interpretation of a variety of electrical conductivity measurements. These may be steady-state and transient, equilibrium and nonequilibrium, and can use a variety of electrode materials and sample geometries. 

The electrical conductivity of the foam was measured on-line to control the steady state of the process. Results were only accepted if they had been obtained under steady state conditions. The protein concentrations were determined by a photometer at 275.5 and 320 nm and the difference was used for to correct for the error due to the turbidity of the solution. 

Demonstration of the creation of multilayer line structures in the seal will result in the collection of physical measurement data on the change in seal features during heat up, steady state operation, transients, or on cool down. A radar type image of the signal characteristics will show build up or relaxation of stresses, discontinuities in seal structure including porosity, delamination of the seal from either the cell or interconnect, and ultimately the catastrophic failure of the seal. Additionally with the ability to use a metal interconnect as one of the plane references coupled with a trace on the oxide coating on the interconnect, electrical conductivity and structural integrity of the thin oxide film on the metal interconnect can be determined within the vicinity of the trace. 

The approximate experimental determination of xl), is based on measurement of the velocity of a charged particle in a solvent subjected to an applied voltage. Such a particle experiences an electrical force that initiates motion. Since a hydrodynamic frictional force acts on the particle as it moves, a steady state is reached, with the particle moving with a constant velocity U. To calculate this electrophoretic velocity U theoretically, it is, in general, necessary to solve Poisson s equation (Equation 3.19) and the governing equations for ion transport subject to the condition that the electric field is constant far away from the particle. The appropriate viscous drag on the particle can be calculated from the velocity field and the electrical force on the particle from the electrical potential distribution. The fact that the sum of the two is zero provides the electrophoretic velocity U. Actual solutions are complex, and the electrical properties of the particle (e.g., polarizability, conductivity, surface conductivity, etc.) come into play. Details are given by Levich (1962) (see also Problem 7.8). 

After finishing the electrical conductivity tests, a hydraulic permeability test was performed based on ASTM D 2434-68 [14]. 10 kg of agglomerates were placed into a 19.05 cm inner diameter test column. The test set up is shown schematically in Figure 2. The agglomerated bed was flooded by introducing water from the top. The flow rate was adjusted to achieve a steady state value. A difference in pressure or head was then measured across the agglomerate bed from the attached manometer. Head as a function of various flow rates were obtained. The values of... 

Thermal Conductivity. Conductivity measurements were made of tape candidates to determine whether or not they would satisfy the cable design requirements listed in Table I. The measurements were made for BNL by Jelinek of BCL using the apparatus illustrated in Fig. 7. The method was a modified steady-state conductivity technique where a temperature gradient was established between two copper plates separated by four layers of polymeric film. (Multilayer measurements were always made to approximate the series interfacial resistivity that would be present in lapped cable configurations.) One plate was attached to a controlled heat sink and a measured quantity of heat was added to the other plate by means of an electric heater. With the use of a liquid helium throttling dewar, the ambient temperature could be controlled to within 1 K. (Complete details of the conductivity measurement method are included in Appendix II of this paper.)... 

In the modified steady-state conductivity method employed in this experiment, a temperature gradient is established between two copper plates separated by the pol3nneric film. One plate is attached to a controlled temperature heat sink, and a measured quantity of heat is added to the other plate by means of an electric resistance heater. Conductivity is then calculated using a form of the Fourier equation ... 

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