Dense environmental barrier coating compositions

1. A coated substrate, comprising:

a substrate defining a surface; and

an environmental barrier coating on the surface of the substrate, wherein the environmental barrier coating comprises a barrier layer having a refractory material phase and a silicon-containing glass phase,

wherein the refractory material phase comprises a rare earth component at a first atomic percent, and wherein the silicon-containing glass phase is a continuous phase and comprises the rare earth component at a second atomic percent with the second atomic percent being less than the first atomic percent.

2. The coated substrate as in claim 1 , wherein the barrier layer further comprises a dopant, the dopant having a greater atomic percentage in the silicon-containing glass phase than in the refractory material phase.

3. The coated substrate as in claim 1 , wherein the silicon-containing glass phase is permeable to CO gas, CO 2 gas, N 2 gas, NO gas, NO 2 gas, or a mixture thereof.

4. The coated substrate as in claim 1 , wherein the barrier layer is directly on the surface of the substrate.

5. The coated substrate as in claim 1 , wherein the silicon-containing glass phase is a continuous phase within the barrier layer, and wherein the silicon-containing glass phase comprises about 10% to about 65% of a total volume of the barrier layer.

6. The coated substrate as in claim 5 , wherein the silicon-containing glass phase defines a boundary layer at the surface of the substrate, and wherein the refractory material phase includes a plurality of microcracks extending from the silicon-containing glass phase to an opposite surface of the barrier layer.

7. The coated substrate as in claim 1 , wherein the silicon-containing glass phase comprises a Ca—Yb-silicate glass.

8. The coated substrate as in claim 1 , wherein the barrier layer has a thickness of about 130 μm or less, and wherein the silicon-containing glass phase defines about 10% to less than 100% of the thickness of the barrier layer, and further wherein the barrier layer has a porosity of less than about 10%.

9. The coated substrate as in claim 1 , wherein the barrier layer comprises Ln 2 SiO 5 where Ln is a rare earth element or a mixture of rare earth elements doped at the Ln site with a dopant, Ln 2 Si 2 O 7 where Ln is a rare earth element or a mixture of rare earth elements doped at the Ln site with the dopant, or a mixture thereof; and wherein the dopant comprises an alkali metal cation, Cu 1+ , Au 1+ , Ag 1+ , a noble metal cation, an alkaline earth metal cation, Cu 2+ , Ni 2+ , Fe 2+ , Mn 2+ , Zn 2+ , Sn 2+ , or a mixture thereof, and further wherein the dopant has a greater atomic percentage in the silicon-containing glass phase than in the refractory material phase.

10. The coated substrate as in claim 1 , wherein the refractory material phase comprises a doped monosilicate compound having a formula:

Ln 2-x-y (D 1+ )x(D 2+ ) y Si 1-z (D 4+ ) z O 5−δ

where

D 1+ is an alkali metal cation, Cu 1+ , Au 1+ , Ag 1+ , a noble metal cation, or a mixture thereof;

D 2+ is an alkaline earth metal cation, Cu 2+ , Ni 2+ , Fe 2+ , Mn 2+ , Zn 2+ , Sn 2+ , or a mixture thereof;

0≤x≤1;

0≤y≤1;

D 4+ is Sn 4+ , Ge 4+ , Hf 4+ , Zr 4+ , Ti 4+ , Ce 4+ , or a mixture thereof;

0≤z≤1;

0≤δ≤0.2; and

0<(x+y+z),

with the conditions:

if y>0 and D 2+ is an alkaline earth metal cation, then Ln is Yb, Lu, Tm or a mixture thereof; and

if not both y>0 and D 2+ is an alkaline earth metal cation, then Ln is a rare earth element or a mixture of rare earth elements.

11. The coated substrate as in claim 1 , wherein the refractory material phase comprises a doped disilicate compound having the formula:

Ln 2-x-y (D 1+ ) x (D 2+ ) y Si 2-z (D 4+ ) z O 7−δ

where

D 1+ is an alkali metal cation, Cu 1+ , Au 1+ , Ag 1+ , a noble metal cation, or a mixture thereof;

D 2+ is an alkaline earth metal cation, Cu 2+ , Ni 2+ , Fe 2+ , Mn 2+ , Zn 2+ , Sn 2+ , or a mixture thereof;

0≤x≤1;

0≤y≤1;

D 4+ is Sn 4+ , Ge 4+ , Hf 4+ , zr 4+ , Ti 4+ , Ce 4+ , or a mixture thereof;

0≤z≤1;

0≤δ≤0.2; and

0<(x+y+z),

with the conditions:

if y>0 and D 2+ is an alkaline earth metal cation, then Ln is Yb, Lu, Tm or a mixture thereof; and

if not both y>0 and D 2+ is an alkaline earth metal cation, then Ln is a rare earth element or a mixture of rare earth elements.

12. The coated substrate as in claim 1 , wherein a rare earth silicate material of the refractory material phase comprises a disilicate compound having a formula Yb 2−x Ca x Si 2 O 7−δ where 0.01≤x≤0.1 and 0≤δ≤0.2, or a mixture thereof, and wherein the silicon-containing glass phase contains a higher atomic percentage of calcium than the rare earth silicate material of the refractory material phase.

13. A method of forming a barrier layer, comprising:

forming a barrier layer on a substrate, wherein the barrier layer includes a refractory material phase and a silicon-containing glass phase,

wherein the refractory material phase comprises a rare earth component at a first atomic percent, and wherein the silicon-containing glass phase is a continuous phase and comprises the rare earth component at a second atomic percent with the second atomic percent being less than the first atomic percent.

14. The method of claim 13 , wherein the barrier layer is formed by:

over-doping a rare earth silicate material of a precursor powder such that a secondary breathable silicon-containing glass phase emerges in the precursor powder as a glass; and

thereafter, applying the precursor powder onto a substrate to form the barrier layer.

15. The method of claim 14 , wherein the precursor powder is applied in a slurry or as a plasma spray.