Multi-step electrochemical stripping method

Abstract

A multi-step electrochemical stripping method includes providing a determined electrode potential between a reference electrode and an article submerged in an electrolyte; recording a current peak value of a current signal flowing through the article; removing the voltage provided to the article when the current signal falls to a determined first current value after passing the current peak value; refreshing the electrolyte; providing the determined electrode potential again for a determined time and determining whether the current signal is less than a determined second current value during the determined time, if not, goes back to the refreshing step; and if yes, the process ends.

1 . A multi-step electrochemical stripping method for stripping metallic coatings of a coated article, the method comprising:
 (a): providing a determined electrode potential between a reference electrode and the coated article submerged in an electrolyte;   (b): recording a current peak value of a current signal flowing through the coated article;   (c): removing the voltage provided to the coated article when the current signal falls to a determined first current value after passing the current peak value;   (d): refreshing the electrolyte;   (e): providing the determined electrode potential between the reference electrode and the coated article for a determined time and determining whether the current signal is less than a determined second current value during the determined time;   (f) repeating steps (d) and (e) if the current signal is not less than the determined second current value; and   (g): removing the voltage provided to the coated article if the current signal is less than the determined second current value, wherein the determined first current is greater than the determined second current value.   
     
     
         2 . The method of  claim 1 , wherein the electrolyte comprises a charge-carrying component in a solvent, the charge-carrying component comprising a first component, a second component, and a third component, wherein the first component comprises an alkali salt, the second component comprises an ammonium salt, the third component comprises an acid, the solvent comprises deionized water. 
     
     
         3 . The method of  claim 2 , wherein the first component comprises sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium nitrate, or combinations thereof;
 wherein the second component comprises of ammonium chloride, ammonium nitrate, or combinations thereof;   wherein the third component comprises hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, or combinations thereof; and   wherein the solvent comprises water.   
     
     
         4 . The method of  claim 3 , wherein the first component comprises sodium chloride in a range from 0-10 wt % of the solvent, potassium chloride in a range from 0-10 wt % of the solvent, sodium bromide in a range from 0-10 wt % of the solvent, potassium bromide in a range from 0-10 wt % of the solvent, sodium nitrate in a range from 3%-15 wt % of the solvent, or combinations thereof;
 wherein the second component comprises ammonium chloride in a range from 0-10 wt % of the solvent, ammonium nitrate in a range from 0-10 wt % of the solvent, or combinations thereof; and   wherein the third component comprises hydrochloric acid in a range from 0-10 wt % of the solvent, sulfuric acid in a range from 0-10 wt % of the solvent, nitric acid in a range from 0-10 wt % of the solvent, phosphoric acid in a range from 0-10 wt % of the solvent, or combinations thereof.   
     
     
         5 . The method of  claim 1 , wherein one metallic coating of the coated article comprises aluminide, platinum aluminide, nickel-aluminide, platinum-nickel-aluminide or combinations thereof; and
 wherein the substrate of the coated article comprises a nickel-based superalloy, a cobalt-based superalloy, an iron-based superalloy, or combinations thereof.   
     
     
         6 . The method of  claim 5 , wherein the coating of the coated article comprise platinum aluminide, and the substrate comprises nickel-based superalloy. 
     
     
         7 . The method of  claim 6 , wherein the electrolyte comprises a charge-carrying component in a solvent, wherein the charge-carrying component comprises about 3 wt % sodium chloride, 5 wt % ammonium chloride, and 3 wt % phosphoric acid, and wherein the solvent comprises distilled water. 
     
     
         8 . The method of  claim 7 , wherein the PH value of the electrolyte is about 0.8, and the temperature of the electrolyte is held at 30±3 degrees C. 
     
     
         9 . The method of  claim 7 , wherein the reference electrode is an Ag/AgCl reference electrode and the determined electrode potential is in range from 0.05V-0.3V. 
     
     
         10 . The method of  claim 9 , wherein the determined electrode potential is about 0.2V. 
     
     
         11 . The method of  claim 7 , wherein the determined time is about 10 minutes. 
     
     
         12 . The method of  claim 1 , wherein the determined first current value is in a range from 20%-90% of the current peak value. 
     
     
         13 . The method of  claim 12 , wherein the determined first current value is about 40%±5% of the current peak value. 
     
     
         14 . The method of  claim 12 , wherein the determined second current value is about 10% of the current peak value, or equal to about 0.002 A. 
     
     
         15 . The method of  claim 1 , wherein the electrolyte is circulated by a pump device circulating external electrolyte. 
     
     
         16 . The method of  claim 15 , wherein a circulating rate of the electrolyte is in range from 100 ml/min-800 ml/min. 
     
     
         17 . The method of  claim 16 , wherein a circulating rate of the electrolyte is about 400 ml/min. 
     
     
         18 . The method of  claim 17 , wherein refreshing the electrolyte comprises removing the voltage provided to the coated article for about 5 minutes. 
     
     
         19 . The method of  claim 1 , wherein providing a determined electrode potential between a reference electrode and the coated article comprises providing a controller to control a voltage regulator to regulate a cell voltage between an electrode and the coated article. 
     
     
         20 . The method of  claim 19 , wherein recording a current peak value of a current signal flowing through the coated article comprises providing a current sensor to sense the current signal received by the controller.