Protective internal coatings for porous substrates
A material contains open pores in which the channels and pores that are internally coated with at least one layer of phosphorus-containing alumina. Such material is formed by infiltrating a porous material one or more times with a non-colloidal, low-viscosity liquid coating precursor, drying, and curing the coating precursor to form a phosphorus-containing alumina layer within pores of the material.
1. A method of conformally coating pore walls of a porous inorganic substrate comprising:
providing a porous inorganic substrate;
forming a liquid film having a thickness of 5 to 250 nm on pore walls of the porous inorganic substrate, wherein the liquid film consists of a non-colloidal solution of a phospho-alumina precursor having an aluminum-to-phosphorous atomic ratio of 0.5:1 to 15:1;
drying the liquid film to yield a dried film; and then
curing the dried film to form a phosphorus-containing alumina sublayer having a thickness of 1 to 50 nm conformally coating the pore walls of the porous inorganic substrate;
and
wherein the conformally coated porous inorganic substrate has an open porosity that is at least 50% of an open porosity of the provided porous inorganic substrate.
2. The method of claim 1 , wherein the liquid film comprises a non-colloidal solution of a phospho-alumina precursor carried in an alcohol solvent selected from the group consisting of methanol, ethanol, n-propanol, i-propanol, n-butanol, 2-butanol, t-butanol, and a mixture thereof.
3. The method of claim 1 , further comprising providing the non-colloidal solution by admixing an aluminum salt solution and a phosphate ester solution, wherein the phospho-alumina precursor has a Al:P ratio of 4:1 to 15:1.
4. The method of claim 1 , wherein the porous inorganic substrate carrying the conformal coating has a higher flexural mechanical strength than the same porous inorganic substrate without the conformal coating.
5. The method of claim 1 , wherein the porous inorganic substrate is a ceramic thermal barrier coating.
6. The method of claim 1 , wherein the porous inorganic substrate is a ceramic coating produced by an electron beam physical vapor deposition process.
7. The method of claim 1 , wherein the porous inorganic substrate is a ceramic coating produced by a plasma spray process.
8. The method of claim 1 , wherein the phosphorus-containing alumina sublayer has an aluminum-to-phosphorous atomic ratio of less than about 10.
9. The method of claim 1 , wherein the phospho-alumina precursor has an aluminum-to-phosphorous atomic ratio of 4:1 to 15:1.
10. The method of claim 9 , wherein the phosphorus-containing alumina sublayer has an aluminum-to-phosphorous atomic ratio less than 12:1.
11. The method of claim 1 , wherein the phosphorus-containing alumina sublayer has an aluminum-to-phosphorous atomic ratio less than 12:1.
12. The method of claim 1 , wherein the provided porous inorganic substrate includes mesopores that constitute 25% to 99.99% of a measured porosity.
13. A method of conformally coating pore walls of a porous inorganic substrate comprising:
providing a porous inorganic substrate;
a plurality of coating steps which provide a conformal coating consisting of two to five phosphorus-containing alumina sublayers carried on the pore walls of the provided porous inorganic substrate, the coating steps include
first forming a liquid film having a thickness of 5 to 250 nm on the pore walls of the provided porous inorganic substrate, wherein the liquid film comprises a non-colloidal solution of a phospho-alumina precursor having an Al:P ratio of 0.5:1 to 15:1; drying the liquid film; and then curing the dried film to provide a first phosphorus-containing alumina sublayer, where the phosphorus-containing alumina sublayer has a thickness of 1 to 50 nm; then
forming a liquid film having a thickness of 5 to 250 nm on the first phosphorus-containing alumina sublayer, wherein the liquid film comprises a non-colloidal solution of a phospho-alumina precursor having an Al:P ratio of 0.5:1 to 15:1; drying the liquid film; and then curing the dried film to provide a second phosphorous-containing alumina sublayer having a thickness of 1 to 50 nm;
wherein the conformally coated porous inorganic substrate has a remaining open porosity of at least 50% and a remaining volumetric porosity of at least 90%;
wherein each phosphorus-containing alumina sublayer has an aluminum-to-phosphorous ratio of less than 12:1.
14. The method of claim 13 , wherein the porous inorganic substrate is a ceramic thermal barrier coating on a gas turbine engine component.
15. The method of claim 13 , wherein the conformally coated porous inorganic substrate resists sintering and promotes retention of an original pore structure when exposed to temperatures which promote pore deterioration and/or sintering of the provided porous inorganic substrate.
16. The method of claim 13 , wherein the first phosphorus-containing alumina sublayer and the second phosphorus-containing alumina sublayer have different Al/P ratios.
17. The method of claim 13 , wherein the provided porous inorganic substrate includes mesopores that constitute 25% to 99.99% of a measured porosity.
18. A method comprising:
providing a porous inorganic substrate;
forming a liquid film having a thickness of 5 to 250 nm on pore walls of the provided porous inorganic substrate, wherein the liquid film is a non-colloidal solution of a phospho-alumina precursor having an aluminum-to-phosphorous atomic ratio of 4:1 to 15:1;
drying the liquid film to yield a dried film; and then
forming a cured phosphorus-containing alumina layer, with a thickness of 1 to 50 nm, conformally coating the pore walls;
the coated substrate having an open porosity that is at least 90% of an open porosity of the provided porous inorganic substrate.
19. The method of claim 18 , wherein the provided porous inorganic substrate includes mesopores that constitute 25% to 99.99% of a measured porosity.