Total conductivities, dependence

The simplest equation for H2 permeation can be obtained from Eq. (14.42) by implementing the equilibrium condition described by Eq. (14.41) and by assuming that the total conductivity depends neither on the H2 nor on the O2 pressure. In such a situation, if we admit that the ionic mass transfer is essentially attributed to ions, a Wagner-type equation can be deduced for H2 permeation ... 

Figure 53. The total conductivity dependence on oxygen excess content for Al-doped ATLS at 700 °C.

Specific Conductance. The specific conductance depends on the total concentration of the dissolved ioni2ed substances, ie, the ionic strength of a water sample. It is an expression of the abiUty of the water to conduct an electric current. Freshly distilled water has a conductance of 0.5—2 ]lS/cm, whereas that of potable water generally is 50—1500 ]lS/cm. The conductivity of a water sample is measured by means of an a-c Wheatstone-bridge circuit with a null indicator and a conductance cell. Each cell has an associated constant which, when multiphed by the conductance, yields the specific conductance. 

Figure 22 The pressure dependence of conductance A plot of the ratio of the total conductance to the free molecular flow conductance as a function of the ratio of tube radius to mean free path.

Numerical experiments have shown that in many one dimensional systems with total momentum conservation, the heat conduction does not obey the Fourier law and the heat conductivity depends on the system size. For example, in the so-called FPU model, k IP, with (3 = 2/5, and if the transverse motion is introduced, / = 1/3. Moreover, in the billiard gas channels (with conserved total momentum), the value of P differs from model to model(Li and Wang, 2003). The question is whether one can relate / to the dynamical and statistical properties of the system. 

FIGURE1.27 Composition dependence of the apparent lattice conductivity, ag, grain- boundary conductivity, a and the total conductivity, at, for SmICe1 I02 l/2 measured at 300, 400, and 500°C [115].. 

FIGURE 1.39 Oxygen partial pressure dependency of (a) total conductivity and (b) electronic conductivity of Sm0 2Ce0 8O19 [160]. 

The dependence of the conductivity of this solution on the concentration and the temperature were studied during three days. The concentration was varied by distilling solvent out of the solution into a hanging burette, or into it from the burette. The resulting plots are shown in Figure 9. They are straight lines converging to a common intercept which represents the impurity contribution to the total conductivity. 

This expression is the general Wagner factor which includes the influence of all the motion of the other species on the motion of species i by the effect of the internal electric fields. W may be larger than 1 which indicates an enhancement of the motion by the simultaneous motions of other species, or W may be smaller than 1 which means that the species are slowed down because of the immobility of other species which are therefore unable to compensate for the electrical charges. The first situation is desirable for electrodes whereas the second one is required for electrolytes in which mobile species should not move except when electrons are provided through the external circuit. Since the transference numbers in Eqn (8.27) include the partial and total conductivities (tj = OjlYjk or the products of the diffusivities (or mobilities) and the concentrations, Eqn (8.27) shows that W depends both on kinetic... 

Typically, there is a predominate charge carrier in ionic solids. For example, in sodinm chloride, the mobility of sodium ions is much larger than the mobility of chloride ions. This phenomenon can be temperature-dependent, however. As shown in Table 6.6, the fraction of total conductivity attributable to positive ions (K+) in... 

As we shall see, the solution conductivity depends on the ion concentration and the characteristic mobility of the ions present. Therefore, conductivity measurements of simple, one-solute solutions can be interpreted to indicate the concentration of ions (as in the determination of solubility or the degree of dissociation) or the mobility of ions (as in the investigations of the degree of solvation, complexation, or association of ions). In multiple-solute solutions, the contribution of a single ionic solute to the total solution conductivity cannot be determined by conductance measurements alone. This lack of specificity or selectivity of the conductance parameter combined with the degree of tedium usually associated with electrolytic conductivity measurements has, in the past, discouraged the development of conductometry as a widespread electroanalyti-cal technique. Today, there is a substantial reawakening of interest in the practical applications of conductometry. Recent electronic developments have resulted in automated precision conductometric instrumentation and applications... 

Due to the very low dependence of the total conductivity a on the oxygen chemical potential, one may write... 

Both anions and cations take part in the transport of electricity so that the conductance of an electrolyte equals the sum of conductances of both species of ions. The conductance of each ion depends on the magnitude of elementary ionic charge e, the quantity of ions within the given volume of the solution (n+, n ), their respective valencies (z+, z ) and absolute velocities (t>+, ) at a potential gradient of 1 V/cm. The contribution of cations A to the total conductance of the solution is thus given by the product (en+z+jq) and the contribution of anions B by the product (en z v )- The summary equivalent conductance of the solution may then be expressed by following sum ... 

The class of ionic conductors is not unambiguously defined in literature. Depending on context, this term maybe used either for solid electrolytes where the ion transference number is higher than 0.99, or for any solid material where ions are mobile, including mixed ionic-electronic conductors where the partial ionic and electronic diffusivities are comparable. The latter term is used for materials where the ion transference numbers are lower than 0.95-0.99, and also in conditions when a minor contribution to the total conductivity (ionic or... 

The thermophysical properties of a foam heat capacity and thermal conductivity, depend on the total liquid content and its distribution in the foam. The bubbles shape and distribution of liquid between borders, films and vertexes also affect thermal conductivity. By definition the bulk heat capacity CV (at p - const) equals... 

This equation states that the electrical conductivity due to a free carrier is the product of the charge on the carrier, q, its concentration in the solid, and its mobility, fx. Since semiconductors have two different types of mobile charge carriers, electrons, and holes, the total sample conductivity, a, is simply the sum of the individual conductivities due to each carrier type. It should be noted that the conductivity depends only on the absolute number of carriers, and therefore is not affected by the signs of the carriers themselves. Carrier mobilities for electrons and holes in a variety of semiconductors can be measured experimentally. These values have been tabulated in various reference books and are available for many semiconductors of interest. Doping of a semiconductor therefore allows precise control over the conductivity of the semiconductor sample. 

The most important property for insulation is thermal conductivity. The following transport types participate in the transmission of heat heat conduction in PS, heat conduction in the filling gas (air), radiation heat transfer and heat convection by convection flows in the closed cells. The thermal conductivity of the air in the cells contributes the most to the total heat transport. The radiation fraction depends on the diameter of the cells formed. The thermal conductivity depends on the density of the foamed PS material. Thermal conductivity decreases with increasing bulk density, reaches a minimum and then rises again (Figure 9.15). The following processes are responsible for this characteristic. 

The conducting properties of a liquid in a porous medium can provide information on the pore geometry and the pore surface area [17]. Indeed, both the motion of free carriers and the polarization of the pore interfaces contribute to the total conductivity. Polymer foams are three-dimensional solids with an ultramacropore network, through which ionic species can migrate depending on the network structure. Based on previous works on water-saturated rocks and glasses, we have extracted information about the three-dimensional structure of the freeze-dried foams from the dielectric response. Let be d and the dielectric constant and the conductivity, respectively. Dielectric properties are usually expressed by the frequency-dependent real and imaginary components of the complex dielectric permittivity ... 

Ionic solutions are capable of conducting an electrical current. This ability is called conductance, G, and is measured in mhos. The total conductance of a solution depends on the number and kinds of ions in solution and the characteristics of the electrodes. To eliminate the latter variable, measurements are made in terms of specific conductance. This is defined as conductance of a solution contained between two platinum electrodes exactly 1 cm in area and 1 cm apart. Such an electrode assembly is shown in Figure 10-15. Test solutions are drawn into the... 

Khorkunov, B.A., Nafe, H., and Aldinger, F. 2006. Relationship between the ionic and electronic partial conductivities of co-doped LSGM ceramics from oxygen partial pressure dependence of the total conductivity. Journal of Solid State Electrochemistry 10, 479-487. 

The automated liquid-liquid extraction unit ALLEXis (Metder Toledo Myriad) uses a flow cell to monitor conductivity and thereby detect the phase boundary. The system is able to divert the upper and lower phases into individual vessels. The total volume depends on the size of the settling chamber and is of the order of 2 to 90 mL (Fig. 10). 

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