Protective coating for metal surfaces
View Patent ↗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.
1. A coated metal surface comprising:
(a) a metallic substrate;
(b) an outer coating comprising a thermally sprayed oxide of a second metal, wherein the oxide of the second metal is dielectric, and whereto said outer coating is dielectric;
(c) a thermally sprayed inner coating disposed between the substrate and the outer coating, the inner coating comprising at least 99% wt metallic zinc, wherein the inner coating is substantially electrically connected to the metallic substrate; and
(d) further comprising an intermediate coating disposed between the inner and the outer coating, the intermediate coating comprising a third metal and the oxide of the second metal;
wherein the intermediate coating is a thermally co-sprayed composite; and
wherein the intermediate coating comprises metallic aluminum and aluminum oxide, and the outer coating comprises aluminum oxide.
2. A coated metal surface comprising:
(a) a metallic substrate;
(b) an outer coating comprising a thermally sprayed oxide of a second metal, wherein the oxide of the second metal is dielectric, and wherein said outer coating is dielectric;
(c) a thermally sprayed inner coating disposed between the substrate and the outer coating, the inner coating comprising at least 99% wt metallic zinc, wherein the inner coating is substantially electrically connected to the metallic substrate; and
(d) further comprising an intermediate coating disposed between the inner and outer coating, the intermediate coating comprising a third metal that is anodic to the metallic substrate, and wherein the third metal is substantially electrically connected to at least one of: the metallic substrate and inner coating, wherein:
(e) the inner coating has a thickness of about 2-3 mils;
(f) the intermediate coating has a thickness of about 2-3 mils;
(g) the outer coating has a thickness of about 2-6 mils; and
(h) the combined thickness of the inner coating, intermediate coating, and outer coating is no more than about 10 mils.
3. 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, an oxide of silicon, and an oxide of titanium.
4. The coated metal surface of claim 3 , wherein the oxide of the second metal is Al 2 O 3 .
5. The coated metal surface of claim 2 , wherein the third metal is anodic to metallic zinc.
6. The coated metal surface of claim 2 , wherein the third metal is an alloy comprising zinc and aluminum.
7. A coated metal surface comprising:
(a) a metallic substrate;
(b) an outer coating comprising a thermally sprayed oxide of a second metal, wherein the oxide of the second metal is dielectric, and wherein said outer coating is dielectric;
(c) a thermally sprayed inner coating disposed between the substrate and the outer coating, the inner coating comprising at least 99% wt metallic zinc, wherein the inner coating is substantially electrically connected to the metallic substrate; and
(d) further comprising an intermediate coating disposed between the inner and outer coating, the intermediate coating comprising a third metal that is anodic to the metallic substrate, and wherein the third metal is substantially electrically connected to at least one of: the metallic substrate and the inner coating;
wherein the third metal comprises at least 50% wt of zinc or aluminum.
8. The coated metal surface of claim 7 , wherein the third metal consists essentially of aluminum.
9. The coated metal surface of claim 7 , wherein the inner coating is in direct contact with the substrate, the intermediate coating is in direct contact with the inner coating, and the outer coating is in direct contact with the intermediate coating.
10. The coated metal surface of claim 7 , wherein the third metal is an alloy comprising a metal selected from the group consisting of: metallic zinc, the second metal, and a combination of the foregoing.
11. The coated metal surface of claim 7 , further comprising an organic topcoat.
12. The coated metal surface of claim 11 , wherein the organic topcoat is selected from the group consisting of: asphalt, wax, and paint.
13. The coated metal surface of claim 7 , wherein the intermediate coating is a composite of the third metal and a fourth metal.
14. A fluid conveyance comprising the coated metal surface of claim 7 .
15. The fluid conveyance of claim 14 , wherein the conveyance is of a type selected from the group consisting of: a pipe, a pipe fitting, a pipe valve, a pump component, a pipe fixture, and an appurtenance to a pipe.
16. A coated metal surface comprising:
(a) a metallic substrate comprising a ferrous metal;
(b) a thermally sprayed inner coating consisting essentially of metallic zinc, wherein the inner coating is about 2-3 mils thick, and wherein the inner coating is substantially electrically connected to the metallic substrate;
(c) a thermally sprayed intermediate coating consisting essentially of aluminum or an aluminum alloy, wherein the intermediate coating is about 2-3 mils thick, and wherein the intermediate coating is electrically connected to the inner coating;
(d) a thermally sprayed outer coating on the opposite side of the intermediate coating from the inner coating, said outer coating consisting essentially of thermally sprayed Al 2 O 3 and wherein the outer coating is about 2-6 mils thick; and
(e) an organic topcoat on the opposite side of the outer coating from the inner coating;
wherein the combined thickness of the inner coating, the intermediate coating, and the outer coating is no more than about 10 mils thick.