Process for protecting fiber-reinforced carbon-containing composites against oxidation
Process for protecting fiber-reinforced, carbon-containing composites whose matrix comprises, at least in the outer layer, silicon carbide (SiC) and also silicon (Si) and/or silicon alloys against oxidation, which comprises the steps a) impregnation of the composite with an aqueous, phosphate-containing solution, b) drying, c) heat treatment at a temperature which is at least sufficient to convert the dried solution into insoluble compounds which are suitable for forming a self-healing glass, wherein the composite is treated oxidatively to form silicon oxide (SiO 2 ) either prior to step a), between steps a) and b) or during or after step b) and/or c).
1. A process for protecting fiber-reinforced, carbon-containing composites whose matrix comprises silicon carbide (SiC) at least in the outer layer against oxidation, which comprises the following steps:
a) impregnating the composite with an aqueous, phosphate-containing solution,
b) after drying, carrying out a heat treatment at a temperature which is at least sufficient to convert the dried solution into insoluble compounds which are suitable for forming a self-healing glass,
c) oxydatively treating the composite at a temperature in excess of 480° C. whereby silicon in the matrix is reacted to silicon dioxide, and
d) forming a silicate glass by reaction of the silicon dioxide with the material of the phosphation layer,
wherein the oxidation protection is generated on a fiber-reinforced, carbon-containing composite material whose matrix comprises, at least in the outer layer, silicon (Si) and/or silicon alloys in addition to silicon carbide (SiC).
2. The process of claim 1 , wherein the composite is treated oxidatively prior to step a).
3. The process of claim 1 , wherein the composite is treated oxidatively between steps a) and b).
4. The process of claim 1 , wherein the composite is treated oxidatively during step b).
5. The process of claim 1 , wherein the composite is treated oxidatively after step b).
6. The process as claimed in claim 1 , wherein the silicon content of the matrix at least in the outer layer is above 1% by weight and preferably in the range from 1 to 30% by weight, based on the total weight of the composite or based on the weight of the outer layer permeated by the SiC-containing matrix.
7. The process of claim 6 , wherein the silicon content of the matrix in the outer layer is from 1 to 30% by weight.
8. The process of claim 1 , wherein the oxidative treatment takes place in air.
9. The process of claim 1 , wherein the heat treatment of step b) is effected at a temperature above 480° C.
10. A fiber-reinforced, carbon-containing composite produced by the process of claim 1 .
11. A shaped body produced from a composite as claimed in claim 10 .
12. A brake disk produced from a composite as claimed in claim 10 .
13. A brake lining produced from a composite as claimed in claim 10 .
14. A clutch disk produced from a composite as claimed in claim 10 .
15. A lining element for lining furnaces produced from a composite as claimed in claim 10 .
16. A lining element for lining combustion chambers produced from a composite as claimed in claim 10 .
17. A heat shield produced from a composite as claimed in claim 10 .
18. A fiber-reinforced, carbon-containing composite produced by the process of claim 1 , whose matrix comprises silicon carbide (SiC) at least in the outer layer and has a phosphate-containing glass in the pores and/or on the surface, wherein the matrix further comprises free silicon (Si) and/or free silicon alloys.
19. A composite as claimed in claim 18 , wherein the silicon content of the matrix at least in the outer layer is above 1% by weight, based on the total weight of the material or based on the weight of the outer layer permeated by the SiC-containing matrix.
20. A composite as claimed in claim 18 , wherein the glass comprises one or more of the group consisting of aluminum oxide, silicon oxide, phosphorus oxide, zinc oxide, zinc phosphate, and boron oxide.
21. A fiber-reinforced, carbon-containing composite produced by the process of claim 1 which is covered at least partly by a layer of a glass comprising one or more of aluminum oxide, silicon oxide, phosphorus oxide, zinc oxide, zinc phosphate, and boron oxide.
22. A process for protecting fiber-reinforced, carbon-containing composites whose matrix comprises silicon carbide (SiC) at least in the outer layer against oxidation, which comprises the following steps:
a) impregnating the composite with an aqueous, aluminium phosphate-containing solution to form a coating after drying,
b) heating at a temperature sufficient to decompose the aluminium phosphate containing water of crystallisation and to convert the said coating into insoluble compounds,
c) carrying out a wet chemical treatment using oxidising agents, whereby silicon in the matrix is reacted to silicon dioxide, and
d) forming a silicate glass by heating the coating to a temperature significantly above about 480° C. to react the silicon dioxide formed in step c) with the layer comprising aluminium phosphate.
23. The process of claim 22 , wherein the wet chemical oxidation is carried out by means of perborates, peroxophosphoric acid.
24. The process of claim 22 , wherein the wet chemical oxidation is carried out by means of anodic oxidation.
25. The process of claim 22 , wherein the aqueous solution comprises at least 15% by mass of monoaluminium phosphate (AI(H2P04)3).
26. The process of claim 22 , wherein the aqueous solution comprises soluble compounds of the elements Zn, Cu and/or B.