Electrolytic generation of manganese (III) ions in strong sulfuric acid
An electrolytic cell and a method of electrochemical oxidation of manganese(II) ions to manganese(III) ions in the electrolytic cell are described. The electrolytic cell comprises (1) an electrolyte solution of manganese(II) ions in a solution of at least one acid; (2) a cathode immersed in the electrolyte solution; and (3) an anode immersed in the electrolyte solution and spaced apart from the cathode. Various anode materials are described including vitreous carbon, reticulated vitreous carbon, woven carbon fibers, lead and lead alloy. Once the electrolyte is oxidized to form a metastable complex of manganese(III) ions, a platable plastic may be contacted with the metastable complex to etch the platable plastic. In addition, a pretreatment step may also be performed on the platable plastic prior to contacting the platable plastic with the metastable complex to condition the plastic surface.
1. A method of etching a plastic part, the method comprising contacting the plastic part with a solution comprising manganese(III) ions and at least one acid,
wherein the solution is at least substantially free of permanganate; and
wherein prior to contacting the plastic part with the solution comprising manganese(III) ions and the at least one acid, the plastic part is contacted with a pretreatment composition to condition the surface of the plastic part, the pretreatment composition comprising an organic hydroxy acid and a solvent selected from the group consisting of propylene carbonate, gamma butyrolactone, and combinations thereof.
2. The method according to claim 1 wherein the at least one acid comprises sulfuric acid.
3. The method according to claim 2 , wherein the at least one acid further comprises methane sulfonic acid or methane disulfonic acid.
4. The method according to claim 3 , wherein the solution of acid comprises at least 8M sulfuric acid and between about 1M and about 6M methane sulfonic acid.
5. The method according to claim 1 , wherein the plastic part comprises acrylonitrile/butadiene/styrene.
6. The method according to claim 3 , wherein the manganese(III) ions are generated in the solution by electrolytic oxidation of manganese(II).
7. The method according to claim 6 wherein the electrolytic oxidation occurs at an anode in the solution and said anode comprises vitreous carbon, reticulated vitreous carbon, woven carbon fiber, lead or lead alloy.
8. The method according to claim 1 , wherein the organic hydroxy acid is selected from the group consisting of lactic acid, glycolic acid, gluconic acid and combinations of one or more of the foregoing.
9. The method according to claim 8 , wherein the pretreatment composition comprises about 100 to 500 mL/L of propylene carbonate and about 100 to 500 mL/L of the organic hydroxy acid.