Slurry compositions for making environmental barrier coatings and environmental barrier coatings comprising the same

1. An environmental barrier coating comprising:

at least one transition layer made from a transition layer slurry composition comprising:

water;

a primary transition material; and

a first slurry sintering aid in an amount that exceeds solubility of the first slurry sintering aid in the primary transition material so that the amount of the first slurry sintering includes an insoluble portion; and

an outer layer made from an outer layer slurry composition comprising:

water;

a primary outer material; and

a second slurry sintering aid in an amount that exceeds solubility of the second slurry sintering aid in the primary outer material so that the amount of the second slurry sintering aid includes an insoluble portion,

wherein the primary transition material is selected from the group consisting of mullite, BSAS, and a mullite/BSAS mixture, and the primary outer material comprises BSAS, and

wherein the transition layer consists of the primary transition material, any of the first slurry sintering aid dissolved therein, and a first secondary material as a reaction product of the primary transition material and the insoluble portion of the first slurry sintering aid, the outer layer consists of the primary outer material, any of the second slurry sintering aid dissolved therein, and a second secondary material as a reaction product of the primary outer material and the insoluble portion of the second slurry sintering aid, the first and second slurry sintering aids increase rates of diffusion of, respectively, the primary transition material and the primary outer material such that surface area reduction occurs within the transition layer and the outer layer at lower temperatures than would occur absent the first and second slurry sintering aids, and the first and second secondary materials are 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.

2. The coating of claim 1 , wherein 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 100 micrometers.

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

4. The coating of claim 1 , wherein the environmental barrier coating is on a component formed of a ceramic matrix composite material or a monolithic ceramic material and the component is selected from the group consisting of combustor components, turbine blades, shrouds, nozzles, heat shields, and vanes.

5. An environmental barrier coating comprising:

a bond coat layer comprising silicon;

a silica layer;

at least one transition layer made from a transition layer slurry composition comprising:

from about 9 wt % to about 81 wt % water;

from about 3 wt % to about 72 wt % of a primary transition material; and

a first slurry sintering aid in an amount that exceeds solubility of the first slurry sintering aid in the primary transition material so that the amount of the first slurry sintering includes an insoluble portion; and

an outer layer made from a slurry composition comprising:

from about 9 wt % to about 81 wt % water;

from about 3 wt % to about 72 wt % of a primary outer material; and

a second slurry sintering aid in an amount that exceeds solubility of the second slurry sintering aid in the primary outer material so that the amount of the second slurry sintering aid includes an insoluble portion;

wherein the transition layer comprises a porosity of from about 0.01% to about 30% by volume of the transition layer, and the outer layer comprises a porosity of from about 0.01% to about 15% by volume of the outer layer, and

wherein the first and second slurry sintering aids are selected 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, and

wherein the primary transition material is selected from the group consisting of mullite, BSAS, and a mullite/BSAS mixture, and the primary outer material comprises BSAS, and

wherein the transition layer consists of the primary transition material, any of the first slurry sintering aid dissolved therein, and a first secondary material as a reaction product of the primary transition material and the insoluble portion of the first slurry sintering aid, the outer layer consists of the primary outer material, any of the second slurry sintering aid dissolved therein, and a second secondary material as a reaction product of the primary outer material and the insoluble portion of the second slurry sintering aid, the first and second slurry sintering aids increase rates of diffusion of, respectively, the primary transition material and the primary outer material such that surface area reduction occurs within the transition layer and the outer layer at lower temperatures than would occur absent the first and second slurry sintering aids, and the first and second secondary materials are chosen from the group consisting of rare earth disilicates, rare earth monosilicates, rare earth aluminates, and combinations thereof.

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

7. The coating of claim 5 , wherein 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 100 micrometers.

8. The coating of claim 5 , wherein the environmental barrier coating is on a component formed of a ceramic matrix composite material or a monolithic ceramic material and the component is selected from the group consisting of combustor components, turbine blades, shrouds, nozzles, heat shields, and vanes.