The relation between electrical conductivity and temperature or voltage of sodalime glasses which underwent various heat treatments was studied. It is known that the heat of activation
ΔH* in Rasch-Hinrichsens' formula, log ρ=-
A+
ΔH*/
T where ρ is the specific resistivity,
A is a constant and
T is the absolute temperature, increases gradually in the course of the stabilization of the glass. It was found by the authors that the constant
A also increases in that interval and that it changes exactly linearly with
ΔH*. Similar relationship between
A and
ΔH* can be seen in some chemical reaction rate processes, namely in Mayer's rule for oxide semiconductors or in the change of Richardson's formula for electron emission of metals with the pressure of adsorbed gases, etc. Therefore, the stabilization of glass is thought to be caused by the mechanism of the same type common to these processes.
Also it was found that the inclination of the linear part of the curve which represents logarithm of the resistivity of glass
vs. voltage in the region of high field strength decreases slightly by annealing the glass. It shows that the width of the potential barrier for the alkali diffusion in glass decreases with the progress of the stabilization, and that the above mentioned change of
A is caused by the increase of the entropy of activation
ΔS*.
The free energy of activation
ΔF* was calculated on several assumptions. It was indicated that when the glass is treated at a constant temperature,
ΔF* changes little while
ΔH* and
ΔS* increase, and that when the glass is cooled by constant rate, the increase of
ΔF* becomes a little larger. The level of
ΔF* when the glass is treated at a constant temperature or cooled at a constant rate is not the same even for the parts of equal density.
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