Silicon carbide coated article with ceramic topcoat

Claim 2

An article comprising (1) a silicon carbide-coated carbonaceous substrate which is normally susceptible to oxidative deterioration and (2) a ceramic topcoat derived by the application, drying, and pyrolysis of an organoborosilazane polymer solution containing 0-60% by weight of dispersed ceramic or preceramic powdered solids; said polymer being the product obtained by reacting about 0.25-20 parts by weight of a trialkoxy-, triaryloxy-, or tri(arylalkoxy)boroxine with one part by weight of a polysilazane in an organic solvent.

Claim 3

The article of claim 1 wherein the carbonaceous substrate is a carbon-carbon composite.

Claim 4

The article of claim 1 wherein the organoborosilazane polymer is the product obtained by reacting about 1-6 parts by weight of a trialkoxyboroxine with one part by weight of a polysilazane prepared by reacting an organodihalosilane with ammonia, treating the ammonolysis product with a basic catalyst which is capable of deprotonating an NH group that is adjacent to an SiH group, and quenching the resultant product with an electrophilic quenching reagent.

Claim 5

The article of claim 3 wherein the organoborosilazane polymer is the product obtained by reacting about 3-4 parts by weight of trimethoxyboroxine with one part by weight of a polysilazane prepared by reacting methyldichlorosilane with ammonia, treating the ammonolysis product with potassium hydride, and quenching the resultant product with an electrophilic quenching reagent.

Claim 6

The article of claim 1 comprising: (A) a silicon carbide-coated carbonaceous substrate that is normally susceptible to oxidative deterioration, (B) at least one ceramic coating layer derived by (1) coating the silicon-carbide-coated carbonaceous substrate with a solution of 5-75% by weight of an organoborosilazane polymer in 95-25% by weight of an organic solvent and (2) drying and pyrolyzing the organoborosilazane polymer coating, (C) at least one ceramic overcoat derived by (1) overcoating the thus-coated substrate with a dispersion of about 0-1.0 part by weight of a Group IIa metal salt and about 0.1-5.0 parts by weight of ceramic or preceramic powdered solids in a solution of about 1.25-20 parts by weight of an organoborosilazane polymer in about 0.5-400 parts by weight of an organic solvent and (2) drying and pyrolyzing the coating, (D) at least one ceramic overcoat derived by (1) overcoating the thus-coated substrate with a buffer composition which is a dispersion of about 1-35% by weight of ceramic or preceramic powdered solids in a solution of (a) a Group IIIb metal hydrocarbyloxide, (b) a Group IVa metal hydrocarbyloxide, (c) a bis-, tris-, or tetrakis(dialkylamino)metal of Group IVa, (d) a polysilazane and/or a bis-, tris-, or tetrakis(dialkylamino)silane, and (e) optionally a cyclopentadienyl Group IVa metal halide in an organic solvent; each of ingredients a-d constituting 1-50% of their combined weights, and ingredient e constituting 0-20% of the combined weights of ingredients a-e, (2) overcoating the buffer composition with a solution of 5-75% by weight of a polysilazane in 95-25% by weight of an organic solvent, and (3) drying the pyrolyzing the buffer and polysilazane compositions separately or simultaneously, (E) at least one ceramic overcoat derived by (1) overcoating the thus-coated substrate with a dispersion of about 0.1-5.0 parts by weight of ceramic or preceramic powdered solids in a solution of one part by weight of a polysilazane in about 1.3-20 parts by weight of an organic solvent and (2) drying and pyrolyzing the coating, and (F) optionally (1) an overcoat derived by (a) overcoating the thus-coated substrate with the buffer composition of (D) and (b) drying and optionally pyrolyzing the coating and/or (2) at least one ceramic overcoat derived by (a) overcoating the thus-coated substrate with a solution of 5-75% by weight of a polysilazane in 95-25% by weight of an organic solvent and (b) drying and pyrolyzing the coating.

Claim 7

A process which comprises (1) overcoating a silicon carbide-coated carbonaceous substrate with an organoborosilazane polymer solution containing 0-60% by weight of dispersed ceramic or preceramic powdered solids, said polymer being the product obtained by reacting about 0.25-20 parts by weight of a trialkoxy-, triaryloxy-, or tri(arylalkoxy)boroxine with one part by weight of a polysilazane in an organic solvent, (2) drying the coating, and (3) pyrolyzing the polymer at a temperature of about 675° C.-900° C.

Claim 8

A process which comprises (1) overcoating a silicon carbide-coated carbonaceous substrate with an organoborosilazane polymer solution containing 0-60% by weight of dispersed ceramic or preceramic powdered solids, said polymer being the product obtained by reacting about 0.25-20 parts by weight of a trialkoxy-, triaryloxy-, or tri(arylalkoxy)boroxine with one part by weight of a polysilazane in an organic solvent, (2) drying the coating, and (3) pyrolyzing the polymer at a temperature of about 675° C.-900° C.

Claim 9

The process of claim 6 wherein the organoborosilazane polymer is the product obtained by reacting about 3-4 parts by weight of trimethoxyboroxine with one part by weight of a polysilazane prepared by reacting methyldichlorosilane with ammonia, treating the ammonolysis product with potassium hydride, and quenching the resultant product with an electrophilic quenching reagent.