Corrosion inhibitor-incorporated layered double hydroxide and sol-gel coating compositions and related processes
A corrosion-resistant coating on an aluminum-containing substrate such as an aluminum substrate, an aluminum alloy substrate (e.g., AA 2024, AA 6061, or AA7075), or other aluminum-containing substrate includes a corrosion inhibitor-incorporated Zn—Al layered double hydroxide (LDH) layer and a sol-gel layer. A zinc salt and a corrosion inhibitor (e.g., a salt of an oxyanion of a transition metal such as a vanadate) is dissolved to form a zinc-corrosion inhibitor solution, and the substrate is immersed in or otherwise contacted with the solution to form the corrosion inhibitor-incorporated Zn—Al LDH layer on the substrate. A sol-gel composition is applied on the corrosion inhibitor-incorporated Zn—Al LDH layer of the substrate to form a sol-gel layer, and the sol-gel layer is cured.
1. A method for providing a corrosion-resistant coating on an aluminum-containing substrate, the method comprising:
preparing a zinc-corrosion inhibitor solution by dissolving a zinc salt and a corrosion inhibitor, the corrosion inhibitor comprising a salt of an oxyanion of a transition metal; and
contacting the aluminum-containing substrate with the zinc-corrosion inhibitor solution to form a corrosion inhibitor-incorporated Zn—Al layered double hydroxide (LDH) layer on the aluminum-containing substrate.
2. The method of claim 1 , wherein the preparing the zinc-corrosion inhibitor solution comprises:
dissolving the zinc salt in a first aqueous media to form a first solution;
adjusting the first solution to a pH ranging from about 6 to about 8;
dissolving the corrosion inhibitor in a second aqueous media to form a second solution;
adjusting the second solution to a pH ranging from about 8 to about 10; and
mixing the first and second solution to form the zinc-corrosion inhibitor solution.
3. The method of claim 1 , wherein the contacting comprises immersing the aluminum-containing substrate in the zinc-corrosion inhibitor solution at a temperature between 70° C. to about 90° C. for about 1 to about 6 hours.
4. The method of claim 3 , further comprising maintaining a pH of the zinc-corrosion inhibitor solution at a value between about 8 to about 10.
5. The method of claim 1 , further comprising contacting a sol-gel composition on the corrosion inhibitor-incorporated Zn—Al LDH layer of the aluminum-containing substrate to form a sol-gel layer.
6. The method of claim 5 , further comprising preparing the sol-gel composition.
7. The method of claim 6 , wherein preparing the sol-gel composition comprises:
contacting an alkoxysilane with water and an inorganic acid to form a first composition;
contacting a zirconium alkoxide with a first organic acid to form a second composition; and
mixing the first composition with the second composition to form the sol-gel composition.
8. The method of claim 7 , further comprising adding an additional alkoxysilane and methacrylic acid to the sol-gel composition.
9. The method of claim 7 , further comprising adding a corrosion inhibiting compound to the sol-gel composition.
10. The method of claim 9 , wherein the adding the corrosion inhibiting compound comprises adding a vanadate, a molybdate, a phosphate, a manganate, a permanganate, a titanate, titania, an aluminate, alumina, ceria, a ceric salt, a cerous salt, or combination thereof.
11. The method of claim 5 , further comprising curing the sol-gel layer.
12. The method of claim 11 , wherein the curing the sol-gel layer comprises exposing the sol-gel layer to a temperature ranging from about 70° C. to about 90° C. for about 30 to about 120 min in a hot air circulated oven, or exposing the sol-gel layer to infrared (IR) radiation and/or near IR radiation.
13. The method of claim 11 , further comprising applying a primer or a paint on the sol-gel layer of the substrate, the sol-gel layer facilitating adherence of the primer or the paint to the substrate.
14. A corrosion-resistant coating comprising the corrosion inhibitor-incorporated Zn—Al LDH layer and the sol-gel layer formed by the method of claim 5 .
15. A corrosion-resistant coated product, comprising:
a corrosion inhibitor-incorporated Zn—Al layered double hydroxide (LDH) layer on an aluminum-containing substrate, the corrosion inhibitor comprising an inorganic corrosion inhibitor; and
a sol-gel layer on the corrosion inhibitor-incorporated Zn—Al LDH layer of the substrate, the sol-gel layer comprising a polymer composite of one or more alkoxysilanes and a zirconium alkoxide.
16. The corrosion-resistant coated product of claim 15 , wherein the inorganic corrosion inhibitor comprises a vanadate, a manganate, a permanganate, a molybdate, or a tungstate.
17. The corrosion-resistant coated product of claim 15 , wherein the alkoxysilanes comprise:
an alkoxysilane having the formula R A —Si—(R B ) 3 , where R A is methacryloxyalkyl or glycidyloxyalkyl and R B is a methoxy or ethoxy, or
an alkoxysilane having the formula R D —Si—(R E ) 3 , where R D is aryl, aminoalkyl, or glycidoxyalkyl and R E is methoxy or ethoxy.
18. The corrosion-resistant coated product of claim 15 , wherein the zirconium alkoxide comprises a zirconium alkoxide having the formula Zr—(R C ) 4 , where R C is ethoxy, n-propoxy, isopropoxy, n-butyloxy, or tert-butyloxy.
19. The corrosion-resistant coated product of claim 15 , wherein the sol-gel layer further comprises a corrosion inhibiting compound.
20. The corrosion-resistant coated product of claim 19 , wherein the corrosion inhibiting compound comprises a vanadate, a molybdate, a phosphate, a manganate, a permanganate, a titanate, titania, an aluminate, alumina, ceria, a ceric salt, a cerous salt, or combination thereof.