Alternating current conductivity

Figure 2. Alternating current conduction electromagnetic pump...

The column is 18 inches in diameter by 21 feet in length, fabricated from 0.25-inch plates rolled and butt-welded with 720 inches of weld. Molten potassium chloride is introduced into the column through a trap. The 6-foot fractionating section of the column is equipped with a 6-inch vapor take-off line which serves as a condenser. Electromagnetic alternating current conduction pumps are used for reflux feed to the top of the column and continuous sodium feed to the bottom of the column. 

Cole, K.S., 1934. Alternating current conductance and direct current excitation of nerve. Science 79, 164—165. Cole, K.S., 1940. Permeability and impermeability of cell membranes for ions. Cold Spring Harb. Symp. 

Chemists often reason in terms of dielectric permittivity (e) or infrared spectra (a) while electrical engineers and physicists consider tangent loss (tg = e"/s ) and alternative current conductivity (free charges (where the complex impedance formalism is well-suited) and bound charges (where the description of the permittivity s = e (co) — ie"(co) is more suitable) can be distinguished. Such a distinction is not straightforward in superionic conductors, however, in which some conducting species are in a quasi-liquid state and in particular, for proton conductors. In the latter, the proton (attached... 

Sagar, M., and S. Sampath, 2005. Alternating current conductivity and spectroscopic studies on sol-gel derived, trivalent ion containing sUicate-tetra(ethylene glycol)-based composites. Macrvmolecules 38 134-44. 

The effect of doping on electrical properties such as (1) direct current conductivity ouc (dc conductivity), (2) thermoelectric power characterized by the Seebeck coefficient 5, and (3) alternating current conductivity cTac (ac conductivity) has until recently essentially been studied in the case of electroactive polymers doped by chemical or electrochemical processes. 

AKernating current conductivity The alternating current conductivity (trjc) measurements are usrraUy carried out in a frequency range between 10" and 10 Hz for the sandwich-type samples. The equivalent parallel capacitance C co) and conductance G co) are obtained from the experiments and then they are transformed into different representations, like complex resistivity p, complex conductivity a, complex modulus M, and complex permittivity ... 

As already indicated conductimetric measurements are normally made with alternating current of frequency 103Hz, and this leads to the existence of capacitance as well as resistance in the conductivity cell. If the frequency of the current is increased further to 106 — 107 Hz, the capacitance effect becomes even more marked, and the normal conductivity meter is no longer suitable for measuring the conductance. 

The conclusion regarding the fact that constant current conductivity involves not all microcrystals of the sample is proved by results of measurements of electric conductivity in sintered ZnO films in case of alternating current (Fig. 2.10). The availability of barrier-free ohmic pathways is proved by a low value of initial resistivity in sintered samples ( 1 - 5 kOhm) in addition to exponential dependence of electric conductivity plotted as a function of inverse temperature having activation energy 0.03 - 0.5 eV, which coincides with ionization energy of shallow dope levels. The same value is obtained from measurements of the temperature dependence of the Hall constant [46]. 

Electrolytes, like electronic conductors, obey Ohm s Law, except under such extreme conditions as those involving very high voltages and/or very high-frequency alternating currents. The conductance of an electrolyte is calculated from measurements of its resistance. 

Apart from use in metallurgical research and measurements, solid electrolytes have also been put to use as heating elements in electrical resistance furnaces. In order to prevent electrolysis from occurring, alternating currents must be used. In contrast to metallic heating elements, they may be used in air at around 2000 °C. In view of the fact that their conductivity must be very low at room temperature, there is a need for them either to be kept continuously warm, or to be preheated with an auxiliary heating element. 

Conductivity measurements were carried out by an alternating current method using 1 kHz, and measurements were taken at a current density in the range of 2,2-270 mA-cm 2. Six samples of each formula were... 

The conductivity of an ionic conductor can be assessed by direct current (dc) or alternating current (ac) methods. Direct current methods give the resistance R and the capacitance C. The corresponding physical quantity when ac is applied is the impedance, Z, which is the total opposition to the flow of the current. The unit of impedance is the ohm (fl). The impedance is a function of the frequency of the applied current and is sometimes written Z(to) to emphasize this point. Impedance is expressed as a complex quantity ... 

As an aside, benzotrifluoride is a slightly polar, non-Lewis basic solvent that has favorable properties for many kinds of organic reactions. A. Ogawa, D. P. Curran, Benzotrifluoride A useful alternative solvent for organic reactions currently conducted in dichloro-methane and related solvents , J. Org Chem. 1997, 62, 450. 

Conductance of a solution is a measure of its ionic composition. When potentials are applied to a pair of electrodes, electrical charge can be carried through solutions by the ions and redox processes at the electrode surfaces. Direct currents will result in concentration polarization at the electrodes and may result in a significant change in the composition of the solution if allowed to exist for a significant amount of time. Conductance measurements are therefore made using alternating currents to avoid the polarization effects and reduce the effect of redox processes if they are reversible. 

A Ogawa, DP Curran. Benzotrifluoride a useful alternative solvent for organic reactions currently conducted in dichloromethane. J Org Chem 62, 450, 1997. 

The techniques and apparatus which have been developed to measure electrolytic conductivities in nonaqueous solutions have been adapted from aqueous conductivity measurements with some modifications. Direct current measurements suffer the limitation of requiring reversible electrodes - a serious limitation in nonaqueous solvents. Although this problem can be circumvented U in some instances, virtually all precision conductance data have been taken using the alternating current method. General descriptions of this method are given in several sources. 2>3)... 

A Wheatstone bridge, modified for use with alternating current, forms the basis of the measuring system. Usually two arms of the bridge are matched resistors of approximately 1,000 ohms, the third arm is the conductance cell and the fourth... 

Kilbride et al. (2002 Andriotis et al., 2003) measured the alternating current (ac) and direct current (dc) conductivities of polymer-SWCNT composite thin films such as PMPV and polyvinylalcohol (PVA), the result showed that the ac conductivity... 

Kilbride BE, Coleman JN, Foumet P, Cadek A, Hutzler S, Roth S, Blau WJ (2002). Experimental observation of scaling laws for alternating current and direct current conductivity in polymer-carbon nanotube composite thin films. J. Appl. Phys. 92 4024—4030. 

---