Environmental barrier coatings for high temperature ceramic components

1. An environmental barrier coating for high temperature ceramic components, the barrier coating comprising:

a bond coat layer comprising silicon;

an optional silica layer;

at least one transition layer consisting of about 85% to about 99% by volume of a primary transition material comprising mullite or a mullite/BSAS mixture, optionally a first sintering aid dissolved in the primary transition material and 1% to about 15% by volume of a first secondary material;

an outer layer consisting of about 1% to about 15% by volume of a second secondary material, about 85% to about 100% by volume of a primary outer material comprising BSAS, and optionally a second sintering aid dissolved in the primary outer material; and

the first and second sintering aids being selected from water soluble sintering aids and solvent soluble sintering aids, the water soluble sintering aids being chosen from the group consisting of rare earth nitrate, rare earth acetate, rare earth chloride, rare earth oxide, ammonium phosphate, phosphoric acid, polyvinyl phosphonic acid, and combinations thereof, the solvent soluble sintering aids being chosen from the group consisting of solvent soluble rare earth sources and solvent soluble phosphorous sources, and the first and second secondary materials being chosen from the group consisting of rare earth oxides, rare earth disilicates, rare earth monosilicates, rare earth elements, rare earth containing aluminosilicate glasses, rare earth and alkaline earth containing aluminosilicate glasses, rare earth aluminates, phosphorous pentoxide, phosphorous containing aluminosilicate glasses, phosphorous and alkaline earth containing aluminosilicate glasses, aluminum orthophosphate, aluminum oxide, and combinations thereof;

wherein the transition layer is produced by sintering a transition layer slurry comprising particles of the primary transition material and particles of the first sintering aid, and the sintering step consolidates the particles of the primary transition material in the presence of the first sintering aid and forms the first secondary material as a reaction product of the first sintering aid and the primary transition material;

wherein the outer layer is produced by sintering an outer layer slurry comprising particles of the primary outer material and particles of the second sintering aid, and the sintering step consolidates the particles of the primary outer material in the presence of the second sintering aid and forms the second secondary material as a reaction product of the second sintering aid and the primary outer material; and

wherein the transition layer has a porosity of less than 10% by volume, and the outer layer has a porosity of less than 10% by volume.

2. The coating of claim 1 wherein the bond coat layer comprises a thickness of about 2.5 to about 150 micrometers; the transition layer comprises a thickness of about 2.5 to about 150 micrometers; and the outer layer comprises a thickness of about 2.5 to about 1000 micrometers.

3. The coating of claim 1 comprising more than one transition layer.

4. The coating of claim 1 wherein the high temperature ceramic component comprises a ceramic matrix composite or a monolithic ceramic turbine engine component selected from the group consisting of combustor components, turbine blades, shrouds, nozzles, heat shields, and vanes.

5. The coating of claim 1 wherein the first and second secondary materials are at least one of the rare earth disilicates and rare earth monosilicates.

6. An environmental barrier coating for high temperature ceramic components, the barrier coating comprising:

a bond coat layer comprising silicon;

an optional silica layer;

at least one transition layer consisting of about 85% to about 99% by volume of a primary transition material consisting of mullite or a mullite/BSAS mixture, optionally a first sintering aid dissolved in the primary transition material, and 1% to about 15% by volume of a first secondary material, the first secondary material being chosen from the group consisting of rare earth oxide, rare earth disilicate, rare earth monosilicate, rare earth elements, rare earth containing aluminosilicate glass, rare earth and alkaline earth containing aluminosilicate glass, rare earth aluminates, phosphorous pentoxide, phosphorous containing aluminosilicate glass, phosphorous and alkaline earth containing aluminosilicate glass, aluminum orthophosphate, aluminum oxide, and combinations thereof; and

an outer layer containing about 85% to about 100% by volume of a primary outer material comprising BSAS and 0% to about 15% by volume of a second secondary material;

wherein the transition layer is produced by sintering a transition layer slurry comprising particles of the primary transition material and particles of the first sintering aid, and the sintering step consolidates the particles of the primary transition material in the presence of the first sintering aid and forms the first secondary material as a reaction product of the first sintering aid and the primary transition material;

wherein the outer layer is produced by sintering an outer layer slurry comprising particles of the primary outer material, and the sintering step consolidates the particles of the primary outer material in the presence of the first sintering aid and forms the second secondary material as a reaction product of the first sintering aid and the primary outer material; and

wherein the transition layer has a porosity of less than 10% by volume.

7. The coating of claim 6 wherein the outer layer contains the secondary material in an amount of at least 1 volume percent.

8. The coating of claim 6 wherein the bond coat layer comprises a thickness of about 2.5 to about 150 micrometers; the transition layer comprises a thickness of about 2.5 to about 150 micrometers; and the outer layer comprises a thickness of about 2.5 to about 1000 micrometers.

9. The coating of claim 6 comprising more than one transition layer.

10. The coating of claim 6 wherein the high temperature ceramic component comprises a ceramic matrix composite or a monolithic ceramic turbine engine component selected from the group consisting of combustor components, turbine blades, shrouds, nozzles, heat shields, and vanes.

11. The coating of claim 6 wherein the secondary material is at least one of the rare earth disilicates and rare earth monosilicates.

12. The coating of claim 7 , wherein the first sintering aid is:

a water soluble salt sintering aid selected from the group consisting of rare earth nitrate, a rare earth acetate, and a rare earth chloride; or

a solvent soluble salt sintering aid selected from the group consisting of solvent soluble rare earth sources.

13. An environmental barrier coating for high temperature ceramic components, the barrier coating comprising:

a bond coat layer comprising silicon;

an optional silica layer;

at least one transition layer consisting of about 85% to about 99% by volume of a primary transition material consisting of mullite or a mullite/BSAS mixture, and 1% to about 15% by volume of a first secondary material, the first secondary material being chosen from the group consisting of rare earth oxide, rare earth disilicate, rare earth monosilicate, rare earth elements, rare earth containing aluminosilicate glass, rare earth and alkaline earth containing aluminosilicate glass, rare earth aluminates, phosphorous pentoxide, phosphorous containing aluminosilicate glass, phosphorous and alkaline earth containing aluminosilicate glass, aluminum orthophosphate, aluminum oxide, and combinations thereof; and

an outer layer containing about 85% to about 99% by volume of a primary outer material comprising BSAS, optionally a sintering aid dissolved in the primary outer material, and 1% to about 15% by volume of a second secondary material;

wherein the transition layer is produced by sintering a transition layer slurry comprising particles of the primary transition material, and the sintering step consolidates the particles of the primary transition material in the presence of the sintering aid and forms the first secondary material as a reaction product of the sintering aid and the primary transition material;

wherein the outer layer is produced by sintering an outer layer slurry comprising particles of the primary outer material and particles of the sintering aid, and the sintering step consolidates the particles of the primary outer material in the presence of the sintering aid and forms the second secondary material as a reaction product of the sintering aid and the primary outer material; and

wherein the transition layer has a porosity of less than 10% by volume, and the outer layer has a porosity of less than 10% by volume.

14. The coating of claim 13 wherein the bond coat layer comprises a thickness of about 2.5 to about 150 micrometers; the transition layer comprises a thickness of about 2.5 to about 150 micrometers; and the outer layer comprises a thickness of about 2.5 to about 1000 micrometers.

15. The coating of claim 13 comprising more than one transition layer.

16. The coating of claim 13 wherein the high temperature ceramic component comprises a ceramic matrix composite or a monolithic ceramic turbine engine component selected from the group consisting of combustor components, turbine blades, shrouds, nozzles, heat shields, and vanes.

17. The coating of claim 13 wherein the secondary material is at least one of the rare earth disilicates and rare earth monosilicates.

18. The coating of claim 13 wherein the sintering aid is:

a water soluble salt sintering aid selected from the group consisting of rare earth nitrate, a rare earth acetate, and a rare earth chloride; or

a solvent soluble salt sintering aid selected from the group consisting of solvent soluble rare earth sources.