Chromate-free ceramic coating compositions
A novel chromate-free multi-layer coating system composed of a lithium-doped potassium silicate binder based basecoat composition that is sealed with an aluminum phosphate-based top coat composition is described. The multi-layer coating system exhibits superior corrosion and heat oxidation resistance which can replace traditional chromate-containing coating systems.
1. Aqueous slurries compositions for the production of a multilayer coating system on a substrate comprising:
a basecoat slurry, comprising:
a binder comprising an aqueous solution of lithium doped potassium silicate, the binder characterized by an absence of chromium; and
an aluminum or aluminum alloy powder incorporated into the binder, wherein the aluminum or the aluminum alloy powder and the binder are contained as a one-part composition;
wherein the aluminum or aluminum alloy powder comprises a particle size distribution characterized in that the 50 th percentile of the particle size distribution has a diameter of between about 4 to 7 microns and the 90 th percentile of the particle size distribution has a diameter of less than or equal to about 11.5-15.5 microns; and
a topcoat slurry wherein said topcoat slurry comprises an aqueous solution of an aluminum phosphate based binder having a molar ratio of Al:PO 4 of higher than about 1:3.
2. The aqueous slurries compositions for the production of a multilayer coating system of claim 1 , wherein said topcoat slurry has molar ratio of Al:PO 4 in the range from about 1:2.2 to about 1:2.8.
3. The aqueous slurries compositions for the production of a multilayer coating system of claim 1 , wherein said topcoat slurry has molar ratio of Al:PO 4 in the range from about 1:2.4 to about 1:2.7.
4. The aqueous slurries compositions for the production of a multilayer coating system of claim 1 , wherein said aluminum phosphate based binder comprises aluminum dihydrogen phosphate.
5. The aqueous slurries compositions for the production of a multilayer coating system of claim 1 , wherein said topcoat slurry further comprises metallic oxide particles.
6. The aqueous slurries compositions for the production of a multilayer coating system of claim 1 , wherein said basecoat slurry contains the lithium doped potassium silicate and aluminum or aluminum alloy powder in a weight ratio of about 0.18:1 to 0.46:1 silicate to aluminum or aluminum alloy powder.
7. The aqueous slurries compositions for the production of a multilayer coating system of claim 1 , wherein said basecoat slurry contains aluminum or aluminum alloy powder between about 35-45 weight percent (wt %) based on the total weight of the slurry and the silicate to aluminum is contained in a ratio of about 0.22:1 to 0.37:1 by weight.
8. Aqueous slurries compositions for the production of a multilayer coating system on a substrate comprising:
a basecoat slurry, comprising:
a binder comprising an aqueous solution of lithium doped potassium silicate, the binder characterized by an absence of chromium; and
an aluminum or aluminum alloy powder incorporated into the binder, wherein the aluminum or the aluminum alloy powder and the binder are contained as a one-part composition;
wherein the aluminum or aluminum alloy powder content in the slurry is between about 30-50 weight percent (wt %) based on the total weight of the slurry and further comprises a particle size distribution characterized in that the 50 th percentile of the particle size distribution has a diameter of between about 3.9 to 4.5 microns and the 90 th percentile of the particle size distribution has a diameter of less than or equal to about 9.0 microns and
a topcoat slurry , wherein said topcoat slurry comprises an aqueous solution of an aluminum phosphate based binder having a molar ratio of Al:PO 4 of higher than about 1:3.
9. The aqueous slurries compositions for the production of a multilayer coating system of claim 8 , wherein said topcoat slurry has molar ratio of Al:PO 4 in the range from about 1:2.2 to about 1:2.8.
10. The aqueous slurries compositions for the production of a multilayer coating system of claim 8 , wherein said topcoat slurry has molar ratio of Al:PO 4 in the range from about 1:2.4 to about 1:2.7.
11. The aqueous slurries compositions for the production of a multilayer coating system of claim 8 , wherein said aluminum phosphate based binder comprises aluminum dihydrogen phosphate.
12. The aqueous slurries compositions for the production of a multilayer coating system of claim 8 , wherein said topcoat slurry further comprises metallic oxide particles.
13. The aqueous slurries compositions for the production of a multilayer coating system of claim 8 , wherein said basecoat slurry contains the lithium doped potassium silicate and aluminum or aluminum alloy powder in a weight ratio of about 0.18:1 to 0.46:1 silicate to aluminum or aluminum alloy powder.
14. The aqueous slurries composition for the production of a multilayer coating of claim 8 , wherein said basecoat slurry contains aluminum or aluminum alloy powder between about 35-45 weight percent (wt %) based on the total weight of the slurry and the silicate to aluminum is contained in a ratio of about 0.22:1 to 0.37:1 by weight.
15. Aqueous slurries compositions for the production of a multilayer coating system on a substrate, comprising:
a basecoat slurry, comprising:
a binder comprising an aqueous solution of lithium doped potassium silicate, the binder characterized by an absence of chromium; and
an aluminum or aluminum alloy powder incorporated into the binder, wherein the aluminum or the aluminum alloy powder and the binder are contained as a one-part composition;
wherein the lithium-doped potassium silicate comprises potassium and lithium in a ratio of about 3:1 to 20:1 by weight as K 2 O:Li 2 O, and further wherein the ratio of silicate to potassium is in a ratio of about 2:1 to 3:1 by weight as SiO 2 :K 2 O; and
a topcoat slurry , wherein said topcoat slurry comprises an aqueous solution of an aluminum phosphate based binder having a molar ratio of Al:PO 4 of higher than about 1:3.
16. The aqueous slurries compositions for the production of a multilayer coating system of claim 15 , wherein said topcoat slurry has molar ratio of Al:PO 4 in the range from about 1:2.2 to about 1:2.8.
17. The aqueous slurries compositions for the production of a multilayer coating system of claim 15 , wherein said topcoat slurry has molar ratio of Al:PO 4 in the range from about 1:2.4 to about 1:2.7.
18. The aqueous slurries compositions for the production of a multilayer coating system of claim 15 , wherein said aluminum phosphate based binder comprises aluminum dihydrogen phosphate.
19. The aqueous slurries composition for the production of a multilayer coating of claim 15 , wherein said topcoat slurry further comprises metallic oxide particles.
20. The aqueous slurries compositions for the production of a multilayer coating system of claim 15 , wherein said basecoat slurry contains the lithium doped potassium silicate and aluminum or aluminum alloy powder in a weight ratio of about 0.18:1 to 0.46:1 silicate to aluminum or aluminum alloy powder.
21. A multilayer coating substrate, comprising:
a substrate,
a basecoat on said substrate, comprising:
a ceramic matrix not containing chromium, said matrix formed by a silicate binder and a plurality of aluminum powder particles embedded within said matrix;
wherein said silicate binder is potassium silicate doped with lithium;
wherein the aluminum powder comprises a particle size distribution characterized in that the 50 th percentile of the particle size distribution has a diameter of between about 4 to 7 microns and the 90 th percentile of the particle size distribution has a diameter of less than or equal to about 11.5-15.5 microns; and
a topcoat on said basecoat comprising a matrix formed by curing an aluminum phosphate based binder having a molar ratio of Al:PO 4 of higher than about 1:3.
22. The multilayer coating composition of claim 21 , wherein said topcoat further comprises metallic oxide particles embedded in the matrix.
23. A multilayer coating substrate comprising:
a substrate,
basecoat on said substrate, comprising:
a ceramic matrix not containing chromium, said matrix formed by a silicate binder and a plurality of aluminum powder particles embedded within said matrix;
wherein said silicate binder is potassium silicate doped with lithium;
wherein the aluminum powder comprises a particle size distribution characterized in that the 50 th percentile of the particle size distribution has a diameter of between about 3.9 to 4.5 microns and the 90 th percentile of the particle size distribution has a diameter of less than or equal to about 9.0 microns; and
a topcoat on said basecoat comprising a matrix formed by curing an aluminum phosphate based binder having a molar ratio of Al:PO 4 of higher than about 1:3.
24. The multilayer coating composition of claim 23 , wherein said topcoat further comprises metallic oxide particles embedded in the matrix.