AC Etching of aluminum capacitor foil

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° to 55° C.

What is claimed is: .[.1. A process for the electrolytic etching of aluminum electrolytic capacitor foil comprising passing the foil between electrodes supplied with alternating current in a bath containing 0.7 to 2 moles/liter hydrochloric acid, 0.2 to 0.5 moles/liter hydrated aluminum trichloride, and 0.02 to 0.4 moles/liter phosphate ion at a temperature of 35° to 55° C..]. .[.2. A process according to claim 1 wherein the anodic current density is 1.6 to 4 amps/in 2  and the 
     
        frequency of the alternating current is 20 to 40 Hz..]. 3. A process according to claim .[.1.]. .Iadd.8 .Iaddend.wherein the concentration of said hydrochloric acid is 1.4 M, the concentration of said hydrated aluminum chloride is 0.4 M, the concentration of said phosphate ion is 0.2 
     
     
        M, and said temperature is 45° C. 4. A process according to claim .[.1.]. .Iadd.8 .Iaddend.wherein the etching time is 2 to 6 minutes. .Iadd.5. In a method for producing electrodes for use in an aluminum electrolytic capacitor whose effective surface area is enlarged by electrochemically etching aluminum foil in an aqueous solution consisting essentially of hydrogen chloride and an additive capable of anodizing said aluminum foil with electric power supplied in alternating current, an improvement characterized in that the concentration of the hydrogen chloride in said solution is set at a range between 0.7N and 2N, the concentration of said additive is set at a range between 0.02 mole/liter and 0.4 mole/liter, the frequency of said alternating current power supply is ranging from 20 Hz to 40 Hz and its current density is ranging from 1.6 A/in 2  to 4 A/in 2 , while the temperature of said solution is 
     
     
        being maintained at 30° to 45° C. .Iaddend. .Iadd.6.  A method as claimed in claim 5, further characterized in that said additive is selected from an inorganic acid capable of anodizing (forming an oxide protecting layer on the surface of) aluminum. .Iaddend. .Iadd.7. A method as claimed in claim 6, further characterized in that said additive is 
     
     
        phosphoric acid. .Iaddend. .Iadd.8.  A process for the electrolytic etching of aluminum electrolytic capacitor foil comprising passing the foil between electrodes supplied with alternating current in a bath consisting essentially of 0.7 to 2 moles/liter hydrochloric acid, 0.2 to 0.5 moles/liter hydrated aluminum trichloride, and 0.02 to 0.4 moles/liter phosphate ion at a temperature of 30° to 45° C. and an alternating current frequency of 20 to 40 Hz. .Iaddend. .Iadd.9. A process according to claim 1 wherein the anodic current density is 1.6 to 4 amps/in 2 . .Iaddend.