FEET Chapter 4

An electrochemical theory is proposed for rectification, as exemplified by the tantalum (or aluminum) electrolytic rectifier and capacitor. A detailed consideration of the mechanism of formation of the oxide film which constitutes the rectification barrier leads to the conclusion that this barrier consists of an electrolytic polarization, in the form of a concentration gradient of excess metal ions, permanently fixed or “frozen” in position in an otherwise insulating matrix of electrolytically‐formed oxide. The physical structure which has been described functions as (a) a current‐blocking ionic space charge or (b) a current‐passing electronic semiconductor, depending solely upon the direction of the applied voltage. The movement of electrons only is required. An explanation for breakdown of the barrier at excessively high voltages is suggested. This explanation may be applicable to dielectric breakdown of other kinds.