Method of treating ceramic fibers by phosphating

1. A method of treating silicon carbide fibers, the method comprising phosphating heat treatment in a reactive gas so as to form a coating around each fiber for protection against oxidation, the coating comprising a surface layer of silicon pyrophosphate crystals and at least one underlying bilayer system comprising a layer of a phosphosilicate glass and a layer of microporous carbon.

2. A method according to claim 1 , wherein before the phosphating heat treatment in a reactive gas, a micro-mesoporous or microporous carbon layer is formed on the surface of each fiber, and after the phosphating heat treatment said micro-mesoporous or microporous carbon layer is interposed between the surface layer of silicon pyrophosphate crystals and said at least one bilayer system comprising a layer of a phosphosilicate glass and a layer of microporous carbon.

3. A method according to claim 2 , wherein the micro-mesoporous carbon layer is formed by etching the surface of each fiber with a phosphorus-containing agent in a gas followed by treatment to eliminate the phosphosilicate glass and the silicon pyrophosphate formed during the etching with the phosphorus-containing agent in a gas.

4. A method according to claim 3 , wherein the treatment for eliminating the phosphosilicate glass and the silicon pyrophosphate is performed by etching the surface of the fibers with a basic compound.

5. A method according to claim 2 , wherein the microporous carbon layer formed before phosphating heat treatment is formed by heat treatment in a reactive gas performed with at least one reactive gas comprising a halogen atom.

6. A method according to claim 5 , wherein the reactive gas comprising a halogen atom further comprises chlorine gas, fluorine gas, or hydrogen chloride.

7. A method according to claim 1 , wherein the protective coating against oxidation presents thickness lying in the range 50 nm to 1 μm.

8. A method according to claim 1 , wherein the phosphating heat treatment in a reactive gas is performed at temperatures lower than the thermal stability temperature of silicon carbide fibers.

9. A method of fabricating a fiber preform comprising forming a fiber structure at least from silicon carbide fibers, wherein the fibers are treated in accordance with the treatment method of claim 1 .

10. A method according to claim 9 , wherein the fibers are treated before forming the fiber structure.

11. A method according to claim 9 , wherein the fibers are treated after forming the fiber structure.

12. A method of fabricating a composite material part comprising making a fiber preform according to the method of claim 9 , and densifying said preform.