Some Current-Time Relations in the Aluminum Cell

Abstract

The relation between current and time in an aluminum cell with the aluminum as anode and with d.c. applied voltage has been investigated. Apparatus and methods for obtaining data are described whereby many of the difficulties which have in the past hindered observers in obtaining consistent results have been overcome. The results obtained are in agreement with the theory of Guthe as modified by Fitch. After the lapse of a certain time ($t_0$), which was found to be about 300 seconds, from the moment of applying the voltage, the dependence of current on voltage conforms to the relation $\frac{E}{i^2}=Ct+D$. From this is deduced a linear relationship between $\frac{E}{i}$ and quantity of electricity passing through the cell, ($\frac{E}{i}-\frac{E}{i_0}=\frac{\mathrm{Cq}}{2}$). The slope, $\frac{\mathrm{Cq}}{2}$, is in the nature of a resistance and assuming that it represents the resistance of the oxide layer, the thickness and resistivity (3.403×${10}^{12}$ ohm cm) of the layer are computed. The data obtained show that the slopes of these lines vary inversely with the square of the anode area, which checks with the theory. Results obtained by Günther-Schulze with tantalum are compared and are shown to check the theory. After a short time of closed circuit the opposition to the flow of current when the aluminum is the anode is shown to be due primarily to the ohmic resistance of the solid layer which increases in value with time of closed circuit.