WE CLAIM
1. A method of removing a bond coat from a ceramic matrix composite,
said method comprising: contacting a ceramic matrix composite comprising a
bond coat with at least one hydroxide for a sufficient time necessary for said
hydroxide to react; and removing the bond coat from said ceramic matrix
composite.
2. The method of claim 1, wherein substantially all of the bond coat is removed from the ceramic matrix composite component without damaging the ceramic matrix composite component.
3. The method of claim 1, wherein said hydroxide is selected from a group consisting of potassium hydroxide, sodium hydroxide, ammonium hydroxide, lithium hydroxide, and tetramethylammonium hydroxide.
4. The method of claim 1, wherein said hydroxide is sodium hydroxide.
5. The method of claim 1, wherein said ceramic matrix composite comprises oxide or non-oxide fibers in nonoxide matrices.
6. The method of claim 5, wherein the ceramic matrix composite comprises SiC fibers in SiC matrices, SiC fibers in silicide containing matrices, SiC fibers in Si-SiC matrices, carbon fibers in carbon matrices, carbon fibers in SiC matrices, or Alumina fibers in SiC matrices.

7. The method of claim 6, wherein the ceramic matrix composite comprises SiC fibers in Si-SiC matrices.
8. The method of claim 1, wherein said bond coat comprises silicon or a silicon-containing substrate.
9. The method of claim 1, wherein the hydroxide comprises at least 5 weight % of an hydroxide and the balance essentially water.
10. The method of claim 1, wherein the hydroxide comprises about 10
weight % to about 40 % of sodium hydroxide.
11. The method of claim 1, wherein the contacting and removing steps are performed at an elevated temperature and pressure above ambient.
12. The method of claim 11, wherein an elevated temperature is at least about 120 degrees Celsius and an elevated pressure of about 0.1 to 1 MPa.
13. The method of claim 1, wherein the solution is at a temperature of at least about 50 degrees Celsius.
14. The method of claim 1, wherein the contacting and removing steps are performed simultaneously with providing ultrasonic energy to said liquid.
15. The method of claim 1, wherein the ceramic matrix composite with the barrier coating and/or bond coat is contacted with the hydroxide for 30 seconds or

more.
16. The method of claim 1, further including the step of contacting the substrate with water at a lower temperature than the temperature of said caustic liquid following the step of contacting with said hydroxide.
17. The method of claim 1, wherein the coated substrate is immersed in a caustic liquid contained in a vessel open to ambient atmosphere.
18. The method of claim 1, further comprising removing an oxide layer from the ceramic matrix composite.
19. A method of removing a barrier coating from a ceramic matrix composite,
said method comprising: contacting a coated ceramic matrix composite with a
caustic liquid comprising at least one hydroxide for a sufficient time necessary for
said liquid to chemically attack the bond coat beneath the barrier coating, causing
detachment of said barrier coating from said ceramic matrix composite, thereby
removing the barrier coating.
20. The method of claim 19, wherein said hydroxide is selected from a
group consisting of potassium hydroxide, sodium hydroxide, ammonium
hydroxide, lithium hydroxide, and tetramethylammonium hydroxide.
21. The method of claim 19, wherein said liquid is sodium hydroxide.
22. The method of claim 19, wherein said ceramic matrix composite

comprises oxide or non-oxide fibers in nonoxide matrices.
23. The method of claim 22, wherein the ceramic matrix composite comprises SiC fibers in SiC matrices, SiC fibers in silicide containing matrices, SiC fibers in Si-SiC matrices, carbon fibers in carbon matrices, carbon fibers in SiC matrices, or Alumina fibers in SiC matrices.
24. The method of claim 23, wherein the ceramic matrix composite comprises SiC fibers in Si-SiC matrices.
25. The method of claim 19, wherein said bond coat comprises silicon or a silicon-containing substrate.
26. The method of claim 19, wherein the method is performed at an elevated temperature and pressure above ambient.
27. The method of claim 19, wherein the step of removing the barrier coating from the surface of the component is performed at an elevated temperature of about 120 degrees Celsius and an elevated pressure of about 0.1 to 1 MPa.
28. The method of claim 19, wherein the contacting step is performed simultaneously with providing ultrasonic energy to said liquid.
29. The method of claim 19, wherein substantially all of the bond coat is removed from the ceramic matrix composite component without damaging the ceramic matrix composite component.

30. The method of claim 19, wherein the liquid comprises about 10 weight % to about 40 % of sodium hydroxide.
31. The method of claim 19, wherein the caustic liquid is at a temperature of at least about 50 degrees Celsius.
32. The method of claim 19, wherein the ceramic matrix composite with the barrier coating and/or bond coat is contacted with the caustic liquid for 30 seconds or more.
33. The method of claim 19, further including the step of contacting the substrate with water at a lower temperature than the temperature of said caustic liquid following the step of contacting with said caustic liquid.
34. The method of claim 19, wherein the coated substrate is immersed in a said caustic liquid contained in a vessel open to ambient atmosphere.
35. The method of claim 19, further comprising removing an oxide layer from the ceramic matrix composite.
36. A method of removing an oxide layer from a ceramic matrix composite,
said method comprising: contacting a ceramic matrix composite comprising an
oxide layer with at least one hydroxide for a sufficient time necessary for said
hydroxide to react; and removing the oxide layer from said ceramic matrix
composite.

37. The method of claim 36, wherein said hydroxide is sodium hydroxide.
38. The method of claim 36, wherein the oxide is a silicate.
39. The method of claim 36, where the oxide is formed by oxidation of the CMC surface during processing or use.
40. A method of removing a bond coat from a ceramic matrix composite, said method comprising: contacting a ceramic matrix composite comprising a bond coat with an aqueous solution of at least one nitrogen containing base for a sufficient time necessary for said solution to react; and removing the bond coat from said ceramic matrix composite.
41. The method of claim 40, wherein substantially all of the bond coat is removed from the ceramic matrix composite component without damaging the ceramic matrix composite component.
42. The method of claim 40, wherein said nitrogen containing base is selected from a group consisting of ethylene diamine, pyrazine, ethanolamine, and hydrazine.
43. The method of claim 40, wherein said nitrogen containing base is ethylene diamine.
44. The method of claim 40, wherein said ceramic matrix composite comprises oxide or non-oxide fibers in nonoxide matrices.

45. The method of claim 44, wherein the ceramic matrix composite comprises SiC fibers in SiC matrices, SiC fibers in silicide containing matrices, SiC fibers in Si-SiC matrices, carbon fibers in carbon matrices, carbon fibers in SiC matrices, or Alumina fibers in SiC matrices.
46. The method of claim 45, wherein the ceramic matrix composite comprises SiC fibers in Si-SiC matrices.
47. The method of claim 40, wherein said bond coat comprises silicon or a silicon-containing substrate.
48. The method of claim 40, wherein the solution comprises at least 50 weight % of a nitrogen containing base.
49. The method of claim 40, wherein the hydroxide comprises about 50
weight % to about 80 weight % of ethylene diamine, 5 weight % to about 20
weight % pyrocatechol, and 5 weight % to about 50 weight % water.
50. The method of claim 40, wherein the contacting and removing steps are performed at an elevated temperature and pressure above ambient.
51. The method of claim 50, wherein an elevated temperature is at least about 115 degrees Celsius and an elevated pressure of about 0.1 to 1 MPa.
52. The method of claim 40, wherein the solution is at a temperature of at least about 50 degrees Celsius.

53. The method of claim 40, wherein the contacting and removing steps are performed simultaneously with providing ultrasonic energy to said liquid.
54. The method of claim 40, wherein the ceramic matrix composite with the barrier coating and/or bond coat is contacted with the solution for 30 seconds or more.
55. The method of claim 40, further including the step of contacting the
substrate with water at a lower temperature than the temperature of said caustic
liquid following the step of contacting with said solution.
56. The method of claim 40, wherein the coated substrate is immersed in a
caustic liquid contained in a vessel open to ambient atmosphere.