Film Characteristics of Electrolytic Condensers

Electrolytic condensers of the film-forming type have some interesting characteristics which have never been satisfactorily explained. Extremely thin oxide or hydroxide films formed on the surface of the metal anodes seem insufficient in themselves to explain the complete action. Likewise, an electromotive equilibrium is insufficient to explain the action. A résumé of former research reveals a great deal of information of large practical value in building electrolytic condensers but little of value from a theoretical standpoint. Reviewing the prominent papers, it appears that aluminum has been the chief subject of discussion for condenser anodes. Such anodes show small leakage currents in selected electrolytes at low temperatures. Increasing voltage, temperature, or electrolyte concentration cause increases in leakage; the addition of impurities also has a deleterious effect. The oxide-gas theory of rectification as applied to electrolytic condensers by Guntherschulze predicts changes in capacity for variations in pressure. Experiments do not substantiate the presence of gas. The oxide layer alone is unable to fulfil the necessary conditions found. Electrolytic condensers with extremely low applied voltages show large variations in measured capacity from high-voltage measurements. The results indicate a film in which ion penetration plays a large part. The presence of a film saturated with water as the dielectric overcomes a number of former obstacles, and lessens the necessity for the very thin films formerly assumed, due to the high dielectric constant of water.