Protective coating for metal surfaces

Abstract

A coating for a metal surface that provides excellent resistance to both electrochemical corrosion and mechanical insult is provided. The coating involves at least an inner coating that is a sacrificial anodic layer and an outer coating that is a protective dielectric material made of inorganic metal oxide. Some versions of the coating include an intermediate layer as well that serves to improve adhesion between the coatings and may provide additional galvanic protection. Although the coating can be made by a variety of methods, advanced methods of spray application are provided for making high-quality lightweight versions the coating.

I claim: 
     
         1 . A coated metal surface comprising:
 (a) a ductile iron substrate;   (b) a galvanic inner coating in direct contact with the substrate, wherein:
 (i) the inner coating comprises at least 85% w/w metallic zinc, 
 (ii) the inner coating functions as a sacrificial anode to the substrate, and 
 (iii) the inner coating is the product of thermally spraying metallic zinc onto the substrate; and 
   (c) a dielectric outer coating in direct contact with the inner coating, wherein:
 (i) said outer coating comprises at least 50% w/w Al 2 O 3 , and 
 (ii) the outer coating is the product of thermally spraying Al 2 O 3  directly onto the inner coating. 
   
     
     
         2 . A coated metal surface comprising:
 (a) a metallic substrate;   (b) a dielectric outer coating comprising an oxide of a second metal, wherein the outer coating is the product of thermally spraying the oxide of the second metal; and   (c) a galvanic inner coating disposed between the substrate and the outer coating, wherein
 (i) the inner coating comprises a first metal, and 
 (ii) the inner coating functions as a sacrificial anode to the substrate. 
   
     
     
         3 . The coated metal surface of  claim 2 , wherein the metallic substrate is a ferrous metal. 
     
     
         4 . The coated metal surface of  claim 2 , wherein the metallic substrate is ductile iron. 
     
     
         5 . The coated metal surface of  claim 2 , wherein the first metal selected is from the group consisting of: aluminum, zinc, magnesium, indium, gallium, and tellurium. 
     
     
         6 . The coated metal surface of  claim 2 , wherein the inner coating comprises at least 50% w/w of the first metal selected from the group consisting of: zinc, aluminum, magnesium, indium, gallium, and tellurium. 
     
     
         7 . The coated metal surface of  claim 2 , wherein the inner coating comprises at least 80% w/w zinc. 
     
     
         8 . The coated metal surface of  claim 2 , wherein the inner coating is in direct contact with the substrate. 
     
     
         9 . The coated metal surface of  claim 2 , wherein the outer coating comprises at least 50% w/w of the oxide of the second metal. 
     
     
         10 . The coated metal surface of  claim 2 , wherein the oxide of the second metal is selected from the group consisting of: an oxide of aluminum, an oxide of magnesium, and an oxide of titanium. 
     
     
         11 . The coated metal surface of  claim 2 , wherein the oxide of the second metal is Al 2 O 3 . 
     
     
         12 . The coated metal surface of  claim 2 , wherein the outer coating is in direct contact with the inner coating. 
     
     
         13 . The coated metal surface of  claim 2 , wherein the sum of the thicknesses of the inner coating and the outer coating does not exceed about 10 mils (254 μm). 
     
     
         14 . The coated metal surface of  claim 2 , comprising an organic dielectric topcoat. 
     
     
         15 . A coated metal surface comprising:
 (a) a metallic substrate;   (b) an outer coating comprising over 50% w/w of an oxide of a second metal, wherein the outer coating is the product of thermally spraying the oxide of the second metal; and   (c) a galvanic inner coating disposed between the substrate and the outer coating, wherein
 (i) the inner coating comprises a first metal that is anodic to the inner substrate, and 
 (ii) the inner coating functions as a sacrificial anode to the substrate. 
   
     
     
         16 . The coated metal surface of  claim 15 , wherein the metallic substrate is a ferrous metal. 
     
     
         17 . The coated metal surface of  claim 15 , wherein the metallic substrate is ductile iron. 
     
     
         18 . The coated metal surface of  claim 15 , wherein the first metal is selected from the group consisting of: aluminum, zinc, magnesium, indium, gallium, and tellurium. 
     
     
         19 . The coated metal surface of  claim 15 , wherein the inner coating comprises at least 50% w/w of the first metal selected from the group consisting of: zinc, magnesium, indium, gallium, and tellurium; and the outer coating is in direct contact with the inner coating. 
     
     
         20 . The coated metal surface of  claim 15 , wherein the inner coating comprises at least 80% w/w zinc. 
     
     
         21 . The coated metal surface of  claim 15 , wherein the inner coating is in direct contact with the substrate. 
     
     
         22 . The coated metal surface of  claim 15 , wherein the oxide of the second metal is selected from the group consisting of: an oxide of aluminum, an oxide of magnesium, and an oxide of titanium. 
     
     
         23 . The coated metal surface of  claim 15 , wherein the oxide of the second metal is Al 2 O 3 . 
     
     
         24 . The coated metal surface of  claim 15 , wherein the outer coating is in direct contact with the inner coating. 
     
     
         25 . The coated metal surface of  claim 15 , wherein the sum of the thicknesses of the inner coating and the outer coating does not exceed about 10 mils (254 μm). 
     
     
         26 . The coated metal surface of  claim 15 , comprising an organic dielectric topcoat. 
     
     
         27 . A coated metal surface comprising:
 (a) a metallic substrate;   (b) a galvanic inner coating that functions as a sacrificial anode to the substrate, comprising at least 50% w/w of a first metal selected from the group consisting of: zinc, magnesium, indium, gallium, and tellurium; and   (c) a thermally sprayed outer coating in direct contact with the inner coating comprising at least 50% w/w of an oxide of a second metal.   
     
     
         28 . The coated metal surface of  claim 27 , wherein the metallic substrate is a ferrous metal. 
     
     
         29 . The coated metal surface of  claim 27 , wherein the metallic substrate is ductile iron. 
     
     
         30 . The coated metal surface of  claim 27 , wherein the inner coating comprises at least 80% w/w zinc. 
     
     
         31 . The coated metal surface of  claim 27 , wherein the inner coating is in direct contact with the substrate. 
     
     
         32 . The coated metal surface of  claim 27 , wherein the outer coating is dielectric. 
     
     
         33 . The coated metal surface of  claim 27 , wherein the oxide of the second metal is selected from the group consisting of: an oxide of aluminum, an oxide of magnesium, and an oxide of titanium. 
     
     
         34 . The coated metal surface of  claim 27 , wherein the oxide of the second metal is Al 2 O 3 . 
     
     
         35 . The coated metal surface of  claim 27 , wherein the sum of the thicknesses of the inner coating and the outer coating does not exceed about 10 mils (254 μm). 
     
     
         36 . The coated metal surface of  claim 27 , comprising an organic dielectric topcoat. 
     
     
         37 . A coated metal surface comprising:
 (a) a metallic substrate;   (b) a galvanic inner coating that functions as a sacrificial anode to the substrate, comprising at least 50% w/w of a first metal selected from the group consisting of: zinc, magnesium, indium, gallium, and tellurium; and   (c) a thermally sprayed dielectric outer coating in direct contact with the inner coating comprising an oxide of a second metal.   
     
     
         38 . The coated metal surface of  claim 37 , wherein the metallic substrate is a ferrous metal. 
     
     
         39 . The coated metal surface of  claim 37 , wherein the metallic substrate is ductile iron. 
     
     
         40 . The coated metal surface of  claim 37 , wherein the inner coating comprises at least 80% w/w zinc. 
     
     
         41 . The coated metal surface of  claim 37 , wherein the inner coating is in direct contact with the substrate. 
     
     
         42 . The coated metal surface of  claim 37 , wherein the outer coating comprises at least 50% w/w of the oxide of the second metal. 
     
     
         43 . The coated metal surface of  claim 37 , wherein the oxide of the second metal is selected from the group consisting of: an oxide of aluminum, an oxide of magnesium, and an oxide of titanium. 
     
     
         44 . The coated metal surface of  claim 37 , wherein the oxide of the second metal is Al 2 O 3 . 
     
     
         45 . The coated metal surface of  claim 37 , wherein the sum of the thicknesses of the inner coating and the outer coating does not exceed about 10 mils (254 μm). 
     
     
         46 . The coated metal surface of  claim 37 , comprising an organic dielectric topcoat. 
     
     
         47 . A coated metal surface comprising:
 (a) a metallic substrate;   (b) a galvanic inner coating that functions as a sacrificial anode to the substrate, comprising at least 50% w/w of a first metal selected from the group consisting of: zinc, magnesium, indium, gallium, and tellurium; and   (c) a dielectric outer coating in direct contact with the inner coating comprising at least 50% w/w of an oxide of a second metal that is the product of spraying the oxide of the second metal onto the inner coating.   
     
     
         48 . The coated metal surface of  claim 47 , wherein the metallic substrate is a ferrous metal. 
     
     
         49 . The coated metal surface of  claim 47 , wherein the metallic substrate is ductile iron. 
     
     
         50 . The coated metal surface of  claim 47 , wherein the inner coating comprises at least 80% w/w zinc. 
     
     
         51 . The coated metal surface of  claim 47 , wherein the inner coating is in direct contact with the substrate. 
     
     
         52 . The coated metal surface of  claim 47 , wherein the oxide of the second metal is selected from the group consisting of: an oxide of aluminum, an oxide of magnesium, and an oxide of titanium. 
     
     
         53 . The coated metal surface of  claim 47 , wherein the oxide of the second metal is Al 2 O 3 . 
     
     
         54 . The coated metal surface of  claim 47 , wherein the sum of the thicknesses of the inner coating and the outer coating does not exceed about 10 mils (254 μm). 
     
     
         55 . The coated metal surface of  claim 47 , comprising an organic dielectric topcoat. 
     
     
         56 . A fluid conduit comprising the coated metal surface of  claim 2 . 
     
     
         57 . A fluid conduit comprising the coated metal surface of  claim 15 . 
     
     
         58 . A fluid conduit comprising the coated metal surface of  claim 27   
     
     
         59 . A fluid conduit comprising the coated metal surface of  claim 37 . 
     
     
         60 . A fluid conduit comprising the coated metal surface of  claim 47 .