Log ionic conductivity

Figure 4. Log (ionic conductivity) versus time of an epoxy composite at various cure temperatures [15]. (With permission from Wiley Interscience).

By comparing log ionic conductivity profiles with loss factor measurements, the operator can identify the window in the process during which the material is fluid (and therefore workable), develops molecular weight and crosslinks (which is critical to product performance and appearance), and is completely cured (which identifies the proper time to demould the product or remove jigs). The dielectric analyser can also record the dielectric properties of the resin during cooling. 

Figure 10. Figure (a) shows the Arrhenius diagram for the inition time obtained from ionic conductivity measurements for the epoxy formulation cured at dlffo-ent temperatures. Figure (b) shows the Arrhenius diagram for the maximum rate of change of log ionic conductivity for the epoxy formulation cured at different temperatures. 

Fig. 4.2 Typical variations in ionic conductivity with composition. In all cases, variations in alkali or silver content are very low compared to the observed variation in log a (a) influence of the network modifier (LijS) (b) influence of a doping salt (c) mixed alkali effect (d) mixed anion effect. References for data are indicated in Souquet and Perera (1990).

The term oo now contains n and Ze, as well as the information on attempt frequency and Jump distance. This expression accounts for the fact that ionic conductivity increases with temperature. If we now take logs of Equation (5.10), we obtain ... 

The mechanism of the thermal decompn of unirradiated and of briefly preirradiated Ba azide was postulated by Mott (Ref 13) and studied by Thomas, Tompkins (Ref 20). However, on detailed examination of the photo and ionic conductivity of this salt, the latter authors found that their results did not agree with the mechanism postulated previously (Ref 21). Jacobs and Tompkins (Ref 23) in their study of the ionic conductance of solid metallic azides found that all salt obeyed the equation log k " log A... 

Na and K azides were detd in solns of varying concns by Petrikalns Ogrins (Ref 12).They also detd the density and refractive index for crystn Na and K azides. The ionic conductance of solid Li azide, as detd by Jacobs Tomkins (Ref 18), obeyed the general equation log k = log A - (E/2.303RT) where k is the specific conductivity in ohm-1 cm"1 A is a constant and E is activation energy in kcal/ mol. For Li azide log A 0.840, E is 19.1 and T, the temp range 300 370°K. The Raman Effect of crystn Li azide was detd by Kahovec Kohlrausch (Ref 14/, the observed frequency, 1368.7 cm-1, corresponded to the oscillation in a linear triatomic molecule. 

Although the motion of protons does not lead to electrical conduction in the case of benzoic acid, electronic and even ionic conductivity can be found in other molecular crystals. A well-studied example of ionic conduction is a film of polyethylene oxide (PEO) which forms complex structures if one adds alkaline halides (AX). Its ionic conductivity compares with that of normal inorganic ionic conductors (log [cr (Q cm)] -2.5). Other polymers with EO-units show a similar behavior when they are doped with salts. Lithium batteries have been built with this type of... 

Bulk ionic conductivities of the samples were measured by impedance analysis between room temperature and 545°C. The extrapolated ionic conductivity could be as high as 0.14-0.16 S/cm at 800°C. This value is very promising, however, caution should be exercised in interpreting this extrapolated ionic conductivity value. A change in the slope of log(cjT) versus 1/T plot is suspected in the literature above 550°C. 

These several assumptions do not lead to the same conclusions. For example, transfer activity coefficients obtained by the tetraphenylarsonium tetraphenyl borate assumption differ in water and polar aprotic solvents by up to 3 log units from those based on the ferrocene assumption. From data compiled by Kratochvil and Yeager on limiting ionic conductivities in many organic solvents, it is clear that no reference salt can serve for a valid comparison of all solvents. For example, the tetraphenylarsonium and tetraphenyl borate ions have limiting conductivities of 55.8 and 58.3 in acetonitrile. Krishnan and Friedman concluded that the solvation enthalpy of... 

The influence of the uranium content on the ionic conductivity of air-grown crystals is shown in Fig. 14. In this figure the temperature dependence of the ionic conductivity of the NaF-U crystals is presented as log aT versus T". The data reveal clearly that for the nominally pure crystals, three, and for the doped crystals... 

Sanyal and Cumming [1985] proposed an alternative method of determining the initial deformation temperature based on changes in the electrical resistivity of the ash as the temperature is raised. At a temperature where melting commences, ionic conduction markedly reduces ash resistivity. A plot of the log of resistivity against the reciprocal of the absolute temperature will show a discontinuity where melting commences. 

Arrhenius plot This plot provides direct information about ionic activation energy, phase transition, and electrical stability of nonelectronic conductors. Biomaterials are polymeric in nature and exhibit a certain Arrhenius nature. Hence, a review of the Arrhenius mechanism is needed. The plot of log a vs. 1/T provides a straight line for ionic conduction and from the slope of the curve the sum of the activation energies. The Arrhenius behaviour of amorphous gum Arabica specimen was measured with a.c. at frequency 1 KHz between room temperature, 20°C-80°C, which is a thermally stable temperature range for gum Arabica biopolymer (as indicated by TGA study). The... 

The influence of water on the poly(amide-iimde) was also determined with dielectric thermal analysis. Two samples were run one was as-received and the other was dried for 7 hours at 190 C. They are shown in Figures 4a and 4b. Figure 4a illustrates the effects of water on the low temperature loss between -100 and 0 C. There were also ionic conductivity losses between 0 and 70 C. The ionic conductive losses were determined from the slope (-1) of the loss maximum peak height versus log frequency plots. These were attributed to mobile ions. This ionic mobility was dependent on water. 

Advani, Gottling, and Osman, " and also Hacskaylo " have observed a region of field where log(///o) = pE. This law would correspond to thermal promotion over a barrier whose activation distance (to borrow a useful term from the ionic-conduction terminology) is not dependent on field. Hacskaylo claims that the... 

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