Maximum conductance phenomenon

Hydrated Zeolites. Figure 3 gives a typical plot of the conductivity vs. the reciprocal temperature for hydrated NaF86.5. The other samples behave qualitatively in the same way. Conduction and dielectric absorption are superposed. The position of the maximum of dielectric absorption is frequency dependent it shifts to higher temperatures with increasing frequency. In some favorable cases a second conduction phenomenon is observed on the low temperature side of the relaxation phenomenon (Figure 3). Because of a lack of reproducibility we cannot interpret it. 

Asymmetry of the response curve to the point of the exposition end reflects the different nature of the exposition and relaxation output signals. A transition from an exposition into relaxation phase corresponds to a return of gas-sensitive matter contact with the initial atmosphere. A variety of processes take place simultaneously in that phase. They may include oxidation of adsorbed molecules by the air oxygen, desorption of the previously adsorbed molecules, competitive adsorption of the ambient atmosphere components. These circumstances cause a complicated shape of the relaxation curve. In general, its course reflects the dynamics of the surface concentration of conductivity clusters. Almost all relaxation curves are characterized by presence of a maximum. It is often more prominent that the corresponding exposition maximum. The origin of this phenomenon is determined by higher conductivity of clusters formed by the oxidized molecules of compounds adsorbed during the exposition phase. 

It was noted that with the decrease in the rate of shift of the burning zone and with the reduction in the rate of air injection, the conductivity of the material medium of the bed tends to attain its maximum. Due to this phenomenon, something similar to heat energy accumulation takes place and, as a result, heat content (caloric power) of the burning zone increases. Apparently the rate of heat loss due to thermal conductivity of rocks is significandy smaller than the rate of advance of the burning front. 

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