Solution for electrolytically removing chromium carbide coating and method for same

Abstract

A solution and method for electrolytically removing chromium carbide coatings from the surface of substrates are provided. The solution includes 20-200 g/L alkali, the alkali being soluble alkali metal hydroxides; 20-150 g/L accelerant, the accelerant being a complexant and can combine with chromium ion; and 0.5-10 g/L auxiliary agent, the auxiliary agent being soluble polyphosphates. The method for removing chromium carbide coating on the substrate mainly includes electrolysis using the substrate having the coating as the anode and using the solution as the electrolyte.

1 . An aqueous solution for electrolytically removing chromium carbide coatings from substrates, comprising:
 20-200 g/L alkali, the alkali being soluble alkali metal hydroxide;   20-150 g/L accelerant, the accelerant being a complexant capable of combining with chromium ions; and   0.5-10 g/L auxiliary agent, the auxiliary agent being soluble polyphosphate.   
     
     
         2 . The aqueous solution as claimed in  claim 1 , wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide, or a combination of the hydroxide and potassium hydroxide. 
     
     
         3 . The aqueous solution as claimed in  claim 1 , wherein the concentration of the alkali is about 50-100 g/L. 
     
     
         4 . The aqueous solution as claimed in  claim 1 , wherein the complexant comprises one or more of the group consisting of sodium potassium tartrate, sodium gluconate, sodium citrate, and ethylenediaminetetraacetic acid. 
     
     
         5 . The aqueous solution as claimed in  claim 4 , wherein the complexant is a combination of sodium gluconate and sodium citrate or a combination of sodium gluconate and ethylenediaminetetraacetic acid. 
     
     
         6 . The aqueous solution as claimed in  claim 1 , wherein the concentration of the accelerant is about 40-100 g/L. 
     
     
         7 . The aqueous solution as claimed in  claim 1 , wherein the polyphosphate is sodium tripolyphosphate or sodium pentapolyphosphate, or a combination of the tripolyphosphate and sodium pentapolyphosphate. 
     
     
         8 . The aqueous solution as claimed in  claim 1 , wherein the concentration of auxiliary agent is about 2-8 g/L. 
     
     
         9 . A method for removing a chromium carbide coating from a substrate, comprising:
 providing an aqueous solution containing 20-200 g/L alkali, the alkali being soluble alkali metal hydroxide, 20-150 g/L accelerant, the accelerant being complexant capable of combining with chromium ion, and 0.5-10 g/L auxiliary agent, the auxiliary agent being soluble polyphosphate; and   removing the chromium coating by electrolysis using the substrate as the anode, and the aqueous solution as the electrolyte.   
     
     
         10 . The method as claimed in  claim 9 , wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide, or a combination of the hydroxide and potassium hydroxide. 
     
     
         11 . The method as claimed in  claim 9 , wherein the concentration of the alkali is about 50-100 g/L. 
     
     
         12 . The method as claimed in  claim 9 , wherein the complexant comprises one or more of the group consisting of sodium potassium tartrate, sodium gluconate, sodium citrate, and ethylenediamine tetraacetic acid. 
     
     
         13 . The method as claimed in  claim 9 , wherein the concentration of the accelerant is about 40-100 g/L. 
     
     
         14 . The method as claimed in  claim 9 , wherein the polyphosphate is sodium tripolyphosphate or sodium pentapolyphosphate, or a combination of the tripolyphosphate and sodium pentapolyphosphate. 
     
     
         15 . The method as claimed in  claim 9 , wherein the concentration of auxiliary agent is about 2-8 g/L. 
     
     
         16 . The method as claimed in  claim 9 , wherein the electrolysis is carried out under an anodic current density of about 1-10 A/dm 2    
     
     
         17 . The method as claimed in  claim 16 , wherein the electrolysis is carried out under an anodic current density of about 4-6 A/dm 2 . 
     
     
         18 . The method as claimed in  claim 9 , wherein the solution is maintained at a temperature between about 50° C. and about 95° C. during electrolysis. 
     
     
         19 . The method as claimed in  claim 18 , wherein the solution is maintained at a temperature between about 60° C. and about 70° C. during electrolysis. 
     
     
         20 . The method as claimed in  claim 9 , wherein the substrate is selected from the group consisting of ferric-based alloy, copper, copper alloy, and plastic.