Abstract: Aluminum electrolytic capacitor foil is treated after etching but before anodizing by first contacting it with a phosphate solution and then heat treating for 30 to 90 seconds to form a thermal oxide layer of controlled thickness. On subsequent anodization, the thermal oxide layer modifies the barrier oxide layer increasing its dielectric strength and hence capacitance and also stabilizes the barrier oxide layer.

Abstract: In the AC etching of aluminum foil in a hydrochloric acid electrolyte containing at least one additive, the presence of 200 to 500 ppm sulfate permits etching thicker foil for higher voltage use than is possible without the sulfate. The additive is chosen from phosphoric, nitric, and tartaric acids or salts. The presence of the relatively small amount of sulfate yields a foil with higher capacitance and generally allows lower temperatures and frequencies to be used.

Abstract: Aluminum electrolytic capacitor foil is etched in a bath containing 1.0 to 1.8 M hydrochloric acid, 0.25 to 0.5 M aluminum chloride, 0.2 to 1.0 M phosphoric acid, and 1.0 to 2.0 M chromium trioxide while subjected to the action of alternating current at 35.degree. to 55.degree. C.

Abstract: Aluminum electrolytic capacitor foil is etched in a bath containing 0.7 to 2.O M hydrochloric acid, 0.2 to 0.5 M hydrated aluminum trichloride, and 0.02 to 0.4 M phosphate ion while subjected to the action of alternating current at 35 to 55.degree. C.

Abstract: Aluminum electrolytic capacitor foil is treated prior to anodization in a two-step process in which a hydrous oxide film is first formed on the foil and the hydrous oxide is then modified. In the first step the foil is immersed in boiling water to form an appropriate thickness of hydrous oxide and in the second step it is immersed in a boiling aqueous solution containing phosphate, silicate, or tartrate ions, or combinations thereof. This treatment results in a decreased power consumption during anodization and produces a film having higher film capacitance.

Abstract: A dielectric oxide film is modified by the incorporation of a minor amount of carbonaceous material. The modified film is produced by anodizing an aluminum electrolytic capacitor anode in a conventional electrolyte containing a minor amount of an alpha- or ortho- hydroxy carboxylic acid or salt.

Abstract: Current efficiency is increased in the anodization of aluminum foil for electrolytic capacitors by carrying out the anodization below 90.degree. C. in a non-aqueous ethylene glycol-ammonium pentaborate bath containing a small amount of an orthophosphate source, e.g., ammonium dihydrogen phosphate.

Abstract: An electrolytic capacitor is provided with an electrode having a stable aluminum oxide dielectric by anodizing an aluminum foil in a process that includes depolarizing the foil in a bath containing a hydration inhibitor selected from tartrate or citrate or phosphate anions.

Abstract: Aluminum electrolytic capacitor foil is etched in a bath containing 0.7 to 2.0 M hydrochloric acid, 0.2 to 0.5 M hydrated aluminum trichloride, and 0.02 to 0.4 M phosphate ion while subjected to the action of alternating current at 35.degree. to 55.degree. C.