Capacity in the Aluminum Cell

Abstract

A new means of measuring the capacity of aluminum anode films is described in which the solid film capacity is measured without disconnection of the direct current used for film formation. The usual method of measurement has necessitated this disconnection and thus introduced an error in results due to the rapid recovery of the cell within the disconnection period. Results are obtained which verify the conclusions of A. L. Fitch and W. E. Meserve. It is found that the capacity of the solid film of oxide is inversely proportional to the quantity of electricity passed through the cell and that the resistance of the anode film in solid form is directly proportional to the quantity of electricity passed. If the film is composed of ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ its resistivity and dielectric constant are about 1.5\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ohm cm and 7.7\ensuremath{\mu}f/cm respectively. These values, because of the assumptions made in their calculation, are probably correct only in order of magnitude.