The influence of temperature on the electrical resistivity of the cellular polypropylene and the effect of activation energy
In this paper, we determine the surface and volume electrical resistivity of the 50 μm thick cellular polypropylen (VHD50), for the temperature range 393–453 K. For this we use a contemporary methodology, which consist of a voltage measurement across the sample, with a known current flowing through it. This methodology includes a three-electrode system, which allows us to estimate the resistivity of the samples, based on their corresponding total resistances. The electric fields applied for a time interval of 1 min are of the order of 200 kVm−1. The order of magnitude of surface and volume electrical resistivity is 1013 Ω and 1011 Ωm, respectively. For both types of the resistivity, the temperature dependence is an increasing or decreasing exponential function, depending on the type of the activation energy, (its average value for the temperature range mentioned above is 41,20 kJmol−1), totally confirmed by the corresponding theoretical interpretation, conditioned by the ionic conduction.The methodology and equipment used, as well as the satisfying accordance with the results, found out directly or indirectly with the consulted literature, confirm the high accuracy of experimental measurements.
A theoretical justification for the application of the Arrhenius equation to kinetics of solid state reactions (mainly ionic crystals)
Although the Arrhenius equation has been widely and successfully applied to innumerable solid state reactions, this use lacks a theoretical justification because the energy distribution amongst the immobilized constituents of a crystalline reactant is not represented by the Maxwell-Boltzmann equation. The present analysis focuses attention on the role of the reactant-product interface, the active zone within which chemical changes preferentially proceed in many solid state rate processes. We identify interface energy levels, that are the precursors to the bond redistribution step, as extensions to the band structure of the solid into the structurally less-regular reaction zone. These interface energy levels are analogous to impurity levels. Electron reorganization requires a locally high energy so that interface levels are appreciably above the Fermi level of the crystalline reactant (and product). Occupancy is determined by energy distribution functions based on Fermi-Dirac statistics for electrons and Bose-Einstein statistics for phonons. For the highest energies, necessary for reaction, both distributions approximate to the exponential energy term, thereby providing a theoretical justification for the application of the Arrhenius equation to reactions of solids. The treatment given here has been largely developed from the theory applicable to ionic solids and the conclusions are most directly relevant to reactions of this class of substance. It is intended, however, that the approach should be of value in extending theoretical understanding of all rate processes involving solids which require the preinvestment of energy in an electron reorganization step.
Ionic conductivity of silver chloride single crystals
Abstract The ionic conductivity of five single crystals of silver chloride has been measured from room temperature up to 25°C below the melting temperature. The experimental data for two of these crystals, one from the Harshaw Co. with total divalent impurity cation concentration of 4·8 × 10−6 and the other doped with Cd2+ at a concentration of 31·2 × 10−6, have been subjected to a non-linear least squares computer analysis to evaluate the thermodynamic parameters governing the formation, migration, and interaction of the point defects. The model used in this analysis includes migration of interstitial cations by both collinear and non-collinear interstitialcy mechanisms and includes long-range Coulombic interactions in the Debye-Huckel approximation. The parameters obtained have been tested by using them to predict (i) the conductivity of the remaining three crystals; (ii) the diffusion coefficient of silver in silver chloride; and (iii) conductivity isotherms. The quality of the non-linear least squares fits and the generally satisfactory nature of the above predictions lead to the conclusion that confidence may be placed in the numerical values of the parameters with the exception of the enthalpy and entropy of migration by the interstitialcy non-collinear mechanism. Possible reasons for the difficulty in resolving accurately this contribution to the total conductivity are discussed.