High temperature oxidation protection for composites

1. An oxidation protection system disposed on an outer surface of a substrate, comprising:

a base layer comprising a first pre-slurry composition comprising a first phosphate glass composition; and

a sealing layer comprising a second pre-slurry composition comprising a second phosphate glass composition and a strengthening compound comprising boron nitride, wherein the sealing layer is disposed on the base layer.

2. The oxidation protection system of claim 1 , wherein the second phosphate glass composition comprises a glass frit, and wherein a weight ratio of boron nitride to the glass frit in the sealing layer is between 5:100 to 15:100.

3. The oxidation protection system of claim 1 , wherein the base layer further comprises a silicon compound comprising at least one of silica and a silica former.

4. The oxidation protection system of claim 3 , wherein the silica former is at least one of a metal silicide, silicon, fumed silica, silicon carbide, and silicon carbonitride.

5. The oxidation protection system of claim 1 , wherein at least one of the first phosphate glass composition and the second 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, ytterbium, actinium, thorium, uranium, yttrium, gallium, magnesium, calcium, strontium, barium, 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 ).

6. An aircraft brake disk, comprising:

a carbon-carbon composite structure comprising a non-wear surface; and

an oxidation protection system disposed on the non-wear surface, the oxidation protection system comprising:

a base layer comprising a first pre-slurry composition disposed on the non-wear surface, wherein the first pre-slurry composition comprises a first phosphate glass composition; and

a sealing layer comprising a second pre-slurry composition comprising a second phosphate glass composition and a strengthening compound comprising boron nitride disposed on the base layer, wherein the sealing layer comprises between 5 and 15 percent weight boron nitride.