Electropolishing solution containing phosphorous pentoxide and methods of use thereof
Substantially anhydrous electropolishing electrolyte solutions. The substantially anhydrous electropolishing electrolyte solutions described herein do not use water as a solvent; instead, such electropolishing electrolyte solutions use anhydrous alcohols and/or glycols as a solvent. For example, an electropolishing electrolyte solution, as described herein, may include an alcohol, at least one mineral acid, and phosphorous pentoxide (“P 2 O 5 ”). Methods of electropolishing metal articles using such electropolishing electrolyte solutions are disclosed herein as well.
1. A method for scavenging water in an electropolishing electrolyte solution, comprising:
positioning a substantially anhydrous electropolishing electrolyte solution in an electropolishing cell;
adding a first quantity of phosphorous pentoxide to the substantially anhydrous electropolishing electrolyte solution;
electropolishing a metal article in the substantially anhydrous electropolishing electrolyte solution in the electropolishing cell at a substantially constant electrical current while monitoring voltage across the electropolishing cell, wherein water evolved during the electropolishing process is substantially scavenged by the phosphorous pentoxide and converted to phosphoric acid; and
adding a second quantity of phosphorous pentoxide to the electropolishing electrolyte solution when the voltage exceeds a selected value.
2. The method of claim 1 , wherein the substantially anhydrous electropolishing electrolyte solution includes about 5 volume % (“vol %”) to about 7 vol % sulfuric acid and about 3 vol % to about 14 vol % methanolic hydrochloric acid.
3. The method of claim 1 , wherein the substantially anhydrous electropolishing electrolyte solution further includes phosphoric acid.
4. The method of claim 1 , wherein the phosphorous pentoxide is encapsulated with an encapsulating agent selected from the group consisting of carrageenan, a polyethylene glycol (PEG), a cellulose gum, gelatin, a starch, and combinations thereof.
5. The method of claim 1 , further comprising adding a quantity of polyethylene glycol to the substantially anhydrous electropolishing electrolyte solution.
6. The method of claim 1 , wherein the substantially anhydrous electropolishing electrolyte solution comprises:
an alcohol including methanol added in an amount of about 79.5 vol %;
at least one mineral acid including concentrated methanolic hydrochloric acid added in an amount of about 14 vol % and concentrated sulfuric acid added in an amount of about 6.5 vol %; and
an encapsulated phosphorus pentoxide.
7. The method of claim 1 , wherein the metal article is an implantable stent fabricated from a tantalum alloy.
8. The method of claim 7 , wherein the tantalum alloy comprises:
about 75 to about 80 weight percent tantalum;
about 8 to about 12 weight percent niobium; and
about 2 to about 10 weight percent tungsten.
9. A method for electropolishing a metal article, comprising:
positioning a substantially anhydrous electropolishing electrolyte solution in an electropolishing cell,
wherein the electropolishing cell includes a reservoir configured to contain the substantially anhydrous electropolishing electrolyte solution, an anode and a cathode suspended in the substantially anhydrous electropolishing electrolyte solution and connected to an electrical power supply;
adding a first quantity of phosphorous pentoxide to the substantially anhydrous electropolishing electrolyte solution;
connecting a metal article to an anode and positioning the metal article in the reservoir in the substantially anhydrous electropolishing electrolyte solution;
running an electrical current through the substantially anhydrous electropolishing electrolyte solution via the anode and the cathode so as to electropolish the metal article, wherein water evolved during the electropolishing is substantially scavenged by the phosphorous pentoxide and converted to phosphoric acid so as to preserve the substantially anhydrous electropolishing electrolyte solution;
monitoring electrical current and voltage across the electropolishing cell during the electropolishing; and
adding a second quantity of phosphorus pentoxide to the substantially anhydrous electropolishing solution when the voltage exceeds a selected value.
10. The method of claim 9 , wherein the substantially anhydrous electropolishing electrolyte solution includes about 5 volume % (“vol %”) to about 7 vol % sulfuric acid, about 3 vol % to about 14 vol % methanolic hydrochloric acid, and a balance of methanol.
11. The method of claim 9 , wherein the metal article is a stent fabricated from a tantalum alloy.
12. The method of claim 11 , wherein the tantalum alloy comprises:
about 75 to about 80 weight percent tantalum;
about 8 to about 12 weight percent niobium; and
about 2 to about 10 weight percent tungsten.
13. The method of claim 9 , wherein the phosphorous pentoxide is encapsulated with an encapsulating agent selected from the group consisting of carrageenan, a polyethylene glycol (PEG), a cellulose gum, gelatin, a starch, and combinations thereof.
14. The method of claim 9 , further comprising adding at least one agent to the substantially anhydrous electropolishing electrolyte solution that is capable of sequestering water evolved during the electropolishing.
15. The method of claim 14 , wherein the at least one agent capable of sequestering water evolved during the electropolishing is PEG 1000.