High temperature oxidation protection for carbon-carbon composites

1. A method for forming an oxidation protection system on a composite structure, comprising:

preparing a ceramic layer slurry by combining only an aluminum powder and a silicon powder in a solvent or a carrier fluid, wherein the aluminum powder and the silicon powder comprise between 40% and 60% by weight of the ceramic layer slurry;

applying the ceramic layer slurry to the composite structure, wherein the ceramic layer slurry comprises the aluminum powder and the silicon powder in the solvent or the carrier fluid; and

heating the composite structure in an environment comprising nitrogen gas and oxygen gas to form a ceramic layer on the composite structure, wherein the ceramic layer consists of between 50% and 94% alumina by weight, between 5% and 50% aluminum nitride, pure silicon between 1% and 30% by weight, and optionally a binder having a remaining weight.

2. The method of claim 1 , further comprising:

applying a sealant slurry to the composite structure, wherein the sealant slurry comprises a sealant pre-slurry composition and a sealant carrier fluid, wherein the sealant pre-slurry composition comprises a sealant phosphate glass composition; and

heating the composite structure to form a sealant layer on the composite structure.

3. The method of claim 2 , wherein the ceramic layer is disposed between the sealant layer and the composite structure.

4. The method of claim 3 , further comprising preparing the sealant slurry by combining the sealant pre-slurry composition with the sealant carrier fluid.

5. The method of claim 1 , wherein the composite structure is heated to a temperature between 500° C. and 1500° C. to form the ceramic layer.

6. The method of claim 5 , wherein the composite structure is heated to a temperature of at least 900° C.

7. The method of claim 1 , wherein the ceramic layer is a continuous layer comprising the alumina.

8. The method of claim 1 , further comprising applying a boron compound slurry to the composite structure prior to the applying the ceramic layer slurry to the composite structure.

9. The method of claim 8 , further comprising allowing the boron compound slurry to dry on the composite structure to form a boron compound layer.

10. The method of claim 9 , wherein the boron compound slurry comprises boron carbide, and wherein the ceramic layer further comprises aluminum boron carbide.

11. The method of claim 1 , wherein the ceramic layer slurry further comprises silicon oxycarbide.

12. The method of claim 11 , wherein the ceramic layer further comprises silicon carbide.

13. The method of claim 1 , wherein the aluminum and the silicon, together, comprise between 10% and 50% by weight of the ceramic layer slurry.

14. The method of claim 2 , wherein the sealant phosphate glass composition is represented by the formula a(A′ 2 O) x (P 2 O 5 ) y1 b(G f O) y2 c(A″O) z :

A′ is selected from: lithium, sodium, potassium, rubidium, cesium, and mixtures thereof;

G f is selected from: boron, silicon, sulfur, germanium, arsenic, antimony, and mixtures thereof;

A″ is selected from: vanadium, aluminum, tin, titanium, chromium, manganese, iron, cobalt, nickel, copper, mercury, zinc, thulium, lead, zirconium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium, uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin, bismuth, cadmium, and mixtures thereof;

a is a number in the range from 1 to about 5;

b is a number in the range from 0 to about 10;

c is a number in the range from 0 to about 30;

x is a number in the range from about 0.050 to about 0.500;

y 1 is a number in the range from about 0.100 to about 0.950;

y 2 is a number in the range from 0 to about 0.20; and

z is a number in the range from about 0.01 to about 0.5;

(x+y 1 +y 2 +z)=1; and

x<(y 1 +y 2 ).