Use of nonafluorobutanesulfonic acid in a low PH etch solution to increase aluminum foil capacitance
Anode foil, preferably aluminum anode foil, is etched using a process of treating the foil in an electrolyte bath composition comprising a perfluoroalkylsulfonate, a sulfate, a halide, and an oxidizing agent. The anode foil is etched in the electrolyte bath composition by passing a direct current charge through the bath. The etched anode foil is suitable for use in an electrolytic capacitor.
1. An aqueous electrolyte bath composition for etching anode foil, comprising:
a sulfate;
a halide;
an oxidizing agent; and
a C 1 -C 8 perfluoroalkylsulfonate in an amount ranging from about 10 to 90 parts per million (ppm).
2. The composition of claim 1 , wherein said C 1 -C 8 perfluoroalkylsulfonate is present in the electrolyte bath composition in an amount ranging from about 20 to about 70 ppm.
3. The composition of claim 1 , wherein the C 1 -C 8 perfluoroalkylsulfonate comprises nonafluorobutanesulfonic acid (FBSA) and/or a salt thereof.
4. The composition of claim 1 , wherein the C 1 -C 8 perfluoroalkylsulfonate is an alkali metal nonafluorobutanesulfonate.
5. The composition of claim 4 , wherein the alkali metal is potassium.
6. The composition of claim 1 wherein:
the C 1 -C 8 perfluoroalkylsulfonate is selected from the group consisting of nonafluorobutanesulfonic acid (FBSA), potassium perfluoroalkylsulfonate (KFBS), and mixtures thereof,
the sulfate is sulfuric acid and said electrolyte bath composition comprises about 0.8% by weight to about 1.0% by weight sulfuric acid,
the halide is hydrochloric acid and said electrolyte bath composition comprises about 0.5% by weight to about 3% by weight hydrochloric acid, and
the oxidizing agent is sodium perchlorate and said electrolyte bath composition comprises about 2% by weight to about 6% by weight sodium perchlorate.
7. The composition of claim 6 , wherein said electrolyte bath composition comprises:
about 0.92% by weight sulfuric acid;
about 0.62% by weight hydrochloric acid; and
about 3.5% by weight sodium perchlorate.
8. The composition of claim 7 , wherein the C 1 -C 8 perfluoroalkylsulfonate is FBSA and/or KFBS.
9. The composition of claim 8 , further comprising diethanolamine (DEA).
10. A method of etching an anode foil, comprising:
passing a direct current (DC) charge through an anode foil while the anode foil is immersed in an aqueous electrolyte bath, wherein said aqueous electrolyte bath comprises:
a sulfate;
a halide;
an oxidizing agent; and
a C 1 -C 8 perfluoroalkylsulfonate in an amount ranging from about 10 to 90 parts per million (ppm); such that the anode foil is etched.
11. The method of claim 10 , wherein the C 1 -C 8 perfluoroalkylsulfonate is provided as an aqueous solution of C 1 -C 8 perfluoroalkylsulfonic acid and/or a salt thereof.
12. The method of claim 11 , wherein the C 1 -C 8 perfluoroalkylsulfonic acid or salt thereof is nonafluorobutanesulfonic acid (FBSA) and/or potassium nonafluorobutanesulfonate (KFBS).
13. The method of claim 10 , wherein the anode foil is etched so as to form branched tunnels in the anode foil.
14. The method of claim 10 , wherein the anode foil is etched so as to form tunnels in the anode foil, and further comprising:
widening the tunnels after etching the anode foil.
15. The method of claim 10 , further comprising:
making a capacitor that includes the etched anode foil as an anode.
16. The composition of claim 1 , wherein the foil is immersed in the bath.
17. The composition of claim 16 , wherein the bath etches tunnels in the foil.
18. The composition of claim 1 , wherein the bath further comprises: an amine base.
19. The composition of claim 18 , wherein the amine base is selected from a group consisting of: ethanolamine, diethanolamine, triethanolamine, ethylamine, diethylamine, triethyamine, methylamine, dimethylamine, trimethylamine, and ammonia.
20. The composition of claim 1 , wherein the bath has a composition of 4 to 9.