Liquid conductivity measurements

Hamilton D C, Mitchell A C and Nellis W J 1986 Electrical conductivity measurements in shock compressed liquid nitrogen Shock M/aves in Condensed Matter (Proc. 4th Am. Phys. Soc. Top. Conf.) p 473... 

When a voltage is applied to a dielectric (insulator), a current passes that decays with time owing to various polarization mechanisms [ 133]. Conductivity is always time-dependent. This general time dependency affects conductivity measurement for nonconductive liquids, where the peak initial current is used to calculate conductivity. Test methods are given in 3-5.5 and... 

At present, the microwave electrochemical technique is still in its infancy and only exploits a portion of the experimental research possibilities that are provided by microwave technology. Much experience still has to be gained with the improvement of experimental cells for microwave studies and in the adjustment of the parameters that determine the sensitivity and reliability of microwave measurements. Many research possibilities are still unexplored, especially in the field of transient PMC measurements at semiconductor electrodes and in the application of phase-sensitive microwave conductivity measurements, which may be successfully combined with electrochemical impedance measurements for a more detailed exploration of surface states and representative electrical circuits of semiconductor liquid junctions. 

Molar conductivity measurements are equally applicable to both solid and liquid electrolytes. In contrast, the measurement of current flowing through an electrochemical cell on a time scale of minutes or hours while the cell is perturbed by a constant dc potential is only of value for solid solvents (Bruce and Vincent, 1987) where convection is absent. Because of the unique aspects of dc polarisation in a solid solvent this topic is treated in some detail in this chapter. Let us begin by considering a cell of the form ... 

Electrical conductivity measurements on silicate melts indicate an essentially ionic conductivity of unipolar type (Bockris et al., 1952a,b Bockris and Mellors, 1956 Waffe and Weill, 1975). Charge transfer is operated by cations, whereas anionic groups are essentially stationary. Transference of electronic charges (conductivity of h- and n-types) is observed only in melts enriched in transition elements, where band conduction and electron hopping phenomena are favored. We may thus state that silicate melts, like other fused salts, are ionic liquids. 

Controversial discussions ensued concerning the magiutude of the gap of the spin liquid state. Specific heat measurements suggested a gapless nature [358], while thermal conductivity measurements suggested a small gap [359]. Furthermore, there is an abnormality in lattice near 5-6 K which was detected by NMR [357] and thermal expansion [360] measurements, indicating that the lattice is not frozen even at 5-6 K. 

Jobs has carried out an extensive series of liquid thermal conductivity measurements over a wide range of temperature on a variety ot compounds. Data on butyraldehyde have been cororlaled with temperature Data ut individual temperature point have been compiled for acetaldehyde, pm-pionaldehyde. and hutyru)deh df > The Jain for formaldehyde were estimated by the method of Robbins and Kmgtea... 

Interpretation of the optimum metal content for these reactions. As already mentioned an optimum Pt content was found for dehydrogenation of liquid alcohols and cyclopentane-deuterium exchange in gas phase. Also, with Pt/Ti02 samples which had not been preoxidized and which were accordingly non-stoichiometric according to conductivity measurements, the same optimum content was found for the initial rate of OIE, whereas this rate decreased as a function of Pt content for preoxidized samples (44). 

Their major limitation is that they can be used only on electrically conductive fluids. This requirement eliminates their use on all gases and on most hydrocarbon fluids. If the liquid conductivity is 20 ps/cm or greater (Table 3.68), most of the conventional magnetic flowmeters can be used. Special designs are available to measure the flow of liquids with threshold conductivities as low as 0.1 ps/cm. 

However, Field, W. G. Gamer and Smith [138] had concluded earlier that proton transfers do not occur in liquid ammonia solutions of m- dinitrobenzene. On the basis of ultra-violet and visible absorption spectra and electrical conductance measurements of the products of interaction of polynitroaromatic compounds with a variety of amines, Miller and Wynne-Jones [139] came to the conclusion that ... 

The properties of a liquid mixture at or near a critical point (Stein and Allen, 1974) are complicated (Rowlinson, 1974) and will not be commented on further. Nevertheless, it seems likely that the kinetics of reactions in solvent mixtures near an LCST or a UCST may prove interesting in view of the report, admittedly not concerned with aqueous mixtures, that the rate of a Diels-Alder reaction increases by 30% within 0 01 K of the UCST for reaction in hexane + nitrobenzene mixtures (Wheeler, 1972). Measurement of the kinetics of reaction in such systems may prove difficult by spectrophoto-metric techniques because systems close to a critical point scatter light, but should be possible by electrical conductance measurements (Stein and Allen, 1973 Gammell and Angell, 1974). 

Sufficient experimental data from several laboratories now exist to describe the conditions under which the radiation-induced ionic propagation of many pure liquid vinyl monomers can be observed. The kinetic data and electrical conductivity measurements establish the ionic nature of the reaction scavenger studies appear to establish the preponderant role played by the carbonium ion in propagating the polymerization. On the basis of a single propagating species, it is possible to write a simple mechanism to describe the process. Limiting values of several of the kinetic rate constants can be estimated, notably the rate constant for reaction between a bare carbonium ion and a vinyl double bond. These rate constants are compared with similar constants arrived at in chemically initiated free radical, carbonium ion and carbanion polymerization. Several shortcomings of the present scheme are discussed. 

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