Colored trivalent chromate coating for zinc

Abstract

A zinc surface on a metal artifact may be colorized and rendered corrosion resistant by applying to the surface a solution of a trivalent chromium compound, plus at least one added metal salt selected from the group consisting of ferrous salts, nickel salts and cobalt salts capable of coloring the surface, along with the chromium compound in the presence of a phosphate at a pH of about 0.5 to 5, to provide a colored surface. Then, a top coat is provided to the colored surface, to achieve high corrosion resistance.

1 . A method for treating and protecting a zinc surface of a metal artifact, which comprises: 
 applying to the surface a solution of a trivalent chromium compound, plus at least one added metal salt selected from the group consisting of ferrous, nickel and cobalt salts capable of coloring the surface, along with a chromium compound, in the presence of a phosphate at a pH of about 0.5 to 5, to provide a colored surface; and    providing a top coat to said colored surface.    
   
   
       2 . The method of  claim 1  in which said top coat is selected from the group consisting of (1) an aqueous sealing solution of a lithium silicate, and a sodium or potassium silicate; (2) a sodium or potassium silicate dispersed in a coating polymer in a solvent; (3) an organosilane-silicate coating; (4) a sodium or potassium silicate dispersed in a polyethylene wax; (5) anodic or cathodic e-coats; and (6) organic paints.  
   
   
       3 . The method of  claim 1  in which said at least one added metal salt comprises a ferrous salt, to provide a black color.  
   
   
       4 . The method of  claim 1  in which said at least one added metal salt comprises at least one of a nickel salt and a cobalt salt to provide an olive drab color.  
   
   
       5 . The method of  claim 1  in which the trivalent chromium solution also comprises a chelating agent.  
   
   
       6 . The method of  claim 1  in which said solution contains acetic acid, the added salt is a ferrous salt, and the pH of the solution is from 2.1 to about 4.5, whereby the zinc surface acquires a yellow color.  
   
   
       7 . The method of  claim 1  which further includes a carbonate salt to suppress fading of the colored surface after it has formed.  
   
   
       8 . The method of  claim 1  in which from 0.5 to 10 grams per liter of said carbonate salt are present.  
   
   
       9 . The method of  claim 7  in which said carbonate salt is selected from the group consisting of sodium carbonate, calcium carbonate, and nickel carbonate.  
   
   
       10 . A zinc surface of a metal artifact treated in accordance with the method of  claim 1 .  
   
   
       11 . A method for treating and protecting a zinc surface of a metal artifact, which comprises: 
 applying to the surface a solution of a trivalent chromium compound, plus at least one added metal salt selected from the group consisting of ferrous salts, nickel salts and cobalt salts capable of coloring the surface along with the chromium compound, in the presence of a phosphorus-containing acid promoter, to provide a colored surface, and    applying to the colored surface an aqueous sealing solution of a lithium silicate plus a sodium or potassium silicate; and    allowing said surface to dry.    
   
   
       12 . The method of  claim 11  in which said at least one more metal salt comprises a ferrous salt to provide a black color.  
   
   
       13 . The method of  claim 11  in which said at least one more metal salt comprises at least one of a nickel salt and a cobalt salt to provide an olive drab color.  
   
   
       14 . The method of  claim 11  in which the trivalent chromium solution also comprises a chelating agent.  
   
   
       15 . The method of  claim 11  in which oxalic acid is present.  
   
   
       16 . The method of  claim 15  in which citric acid is present.  
   
   
       17 . The method of  claim 11  in which citric acid is present.  
   
   
       18 . The method of  claim 11  in which said solution contains acetic acid, the added salt is a ferrous salt, and the pH of the solution is from 2.1 to about 4.5, whereby the zinc surface acquires a yellow color.  
   
   
       19 . The method of  claim 11  in which oxalic acid is present.  
   
   
       20 . The method of  claim 19  in which citric acid is present.  
   
   
       21 . The method of  claim 11  in which citric acid is present.  
   
   
       22 . The method of  claim 11  which further includes a carbonate salt to suppress fading of the colored surface after it has formed.  
   
   
       23 . The method of  claim 22  in which from 0.5 to 10 grams per liter of said carbonate salt is present.  
   
   
       24 . The method of  claim 22  in which said carbonate salt is selected from the group consisting of sodium carbonate, calcium carbonate, and nickel carbonate.  
   
   
       25 . A zinc surface of a metal artifact treated in accordance with the method of  claim 11 .  
   
   
       26 . The method for treating and protecting a zinc surface of a metal artifact, which comprises: 
 applying to the surface a solution of a trivalent chromium compound plus at least one metal salt selected from the group consisting of ferrous salts, nickel salts, and cobalt salts capable of coloring the surface, along with the chromium compound in the presence of phosphate, and further in the presence of strontium chloride plus a chelating, solublizing agent for the strontium chloride, at a pH of 0.5 to 5, to provide a colored, corrosion resistant surface.    
   
   
       27 . The method of  claim 26  in which said solution further comprises a colloidal silicate.  
   
   
       28 . A solution which comprises a trivalent chromium compound plus at least one added metal salt selected from the group consisting of ferrous salts, nickel salts and cobalt salts, in the presence of a phosphate, at a pH of about 0.5 to 5, said solution being capable of providing color to a zinc surface.  
   
   
       29 . The solution of  claim 28  in which said at least one added metal salt comprises a ferrous salt.  
   
   
       30 . The method of  claim 28  in which said at least one added metal salt comprises at least one of a nickel salt and a cobalt salt.  
   
   
       31 . The solution of  claim 28  which also comprises a chelating agent.  
   
   
       32 . The solution of  claim 28  which also comprises a silicate corrosion protection agent.  
   
   
       33 . The solution of  claim 28  which further contains acetic acid, the added salt is a ferrous salt, and the pH of the solution is from 2.1 to about 4.5, whereby the zinc surface acquires a yellow color.  
   
   
       34 . The solution of  claim 28  which further includes a carbonate salt.  
   
   
       35 . The method of  claim 1  in which said solution contains from 1 g/L. to 100 g/L of trivalent chromium.  
   
   
       36 . The method of  claim 1  in which said solution contains from 0.5 g/L to 100 g/L. of ferrous ion.  
   
   
       37 . The method of  claim 1  in which said solution contains from 0.5 g/L to 50 g/L. of at least one of nickel and cobalt ions.  
   
   
       38 . The method of  claim 12  in which said trivalent chromium solution also comprises a chelating agent and a carbonate salt.  
   
   
       39 . The method of  claim 1  in which said solution contains from 1 g/l to 100 g/l of trivalent chromium, from 0.5 g/l to 100 g/l of ferrous ion.