High temperature oxidation protection for composites
An oxidation protection system disposed on a substrate is provided, which may comprise a base layer comprising a first pre-slurry composition comprising a first phosphate glass composition, and/or a sealing layer comprising a second pre-slurry composition comprising a second phosphate glass composition and a strengthening compound comprising boron nitride, a metal oxide, and/or silicon carbide.
1. A method for forming an oxidation protection system on a composite structure, comprising:
forming a first slurry by combining a first pre-slurry composition with a first carrier fluid, wherein the first pre-slurry composition comprises a first phosphate glass composition;
applying the first slurry to the composite structure;
heating the composite structure to a temperature sufficient to form a base layer on the composite structure;
forming a second slurry by combining a second pre-slurry composition with a second carrier fluid, wherein the second pre-slurry composition comprises a second phosphate glass composition and a strengthening compound comprising boron nitride;
applying the second slurry to the composite structure; and
heating the composite structure to a temperature sufficient to form a sealing layer on the composite structure.
2. The method of claim 1 , wherein the strengthening compound further comprises at least one of a metal oxide or silicon carbide.
3. The method of claim 2 , wherein the metal oxide comprises at least one of aluminum oxide, silicon dioxide, and titanium oxide.
4. The method of claim 1 , wherein the second slurry comprises between 0.1 and 6 weight percent boron nitride.
5. The method of claim 1 , wherein the second slurry comprises between 2 and 5 weight percent boron nitride.
6. The method 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 second slurry is between 5:100 to 15:100.
7. The method 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 second slurry is between 10:100 to 12:100.
8. The method of claim 1 , wherein the first pre-slurry composition further comprises a silica compound comprising at least one of silica and a silica former.
9. The method of claim 8 , wherein the silica former comprises at least one of a metal silicide, silicon, fumed silica, silicon carbide, and silicon carbonitride.
10. The method of claim 1 , wherein the first pre-slurry composition of the base layer comprises between about 15 weight percent and about 30 weight percent boron nitride.
11. The method of claim 1 , wherein the first pre-slurry composition comprises a first acid aluminum phosphate wherein a first molar ratio of aluminum to phosphate is between 1 to 2 and 1 to 3.
12. The method of claim 1 , further comprising applying a pretreating composition, wherein the applying comprises:
applying a first pretreating composition to an outer surface of the composite structure before the applying the first slurry, wherein the first pretreating composition comprises aluminum oxide and water;
heating the pretreating composition; and
applying a second pretreating composition comprising at least one of a phosphoric acid or an acid phosphate salt, and an aluminum salt on the first pretreating composition, wherein the composite structure is porous and the second pretreating composition penetrates at least a portion of a plurality of pores of the composite structure.
13. The method of claim 1 , wherein at least one of the first phosphate glass composition or 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, 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 ).