High temperature carbonaceous cement

Details High temperature carbonaceous cement High temperature carbonaceous cement

1999-02-26

2001-04-10

Gallagher, John J. (Department: 1733)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C106S287240, C156S331100, C252S510000, C528S351000, C528S405000

Reexamination Certificate

active

06214158

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to a high temperature carbonaceous cement for bonding large carbon bodies which is curable at a low temperature while being capable of retaining strength and stability at extremely high temperatures.
2. Description of Related Art
Large machined graphite shapes have many uses and may be subject to extreme temperature conditions and/or thermal cycling. For example, in the aerospace industry graphite is used in large molds for the production of composite structures. Such large shapes, due to their sheer size, are made from smaller parts and assembled together. The assembly of the graphite shapes requires carbonaceous bonding agents which must withstand extreme temperatures and thermal cycling while retaining the strength of the joint. The strength of the joints between the individual graphite shapes should be sufficient to avoid failure of the mold.
An example of a conventional carbonaceous cement is disclosed in U.S. Pat. No. 5,002,981 ('981 patent) to Chiu and is assigned to the assignee of the current invention. The cement of the '981 patent is made from a binder comprising a pre-imidized oligomeric precursor which polymerizes at the acetylenic end-caps of the molecule. Dynamic Mechanical Analysis (DMA) of the binder phase of the '981 patent after curing at 240° C. for 2 hours shows a glass transition temperature of 274° C. It also partially softens when heated above the 240° C. cure temperature indicating that it had not completely gelled. Gelation of the binder occurs when it will no longer melt when heated above the initial cure temperature. Gelation indicates further cross-linking of the binder phase producing a stronger binder, thus a stronger cement. Thus, it is desirable to provide a carbonaceous cement for use at high service temperatures which is more completely gelled during its initial cure and substantially gels with less softening during subsequent heating.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a carbonaceous cement having superior strength and stability at high service temperatures.
It is another object of the present invention to provide a carbonaceous cement having a low curing temperature while retaining its strength at high service temperatures.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a curable cement paste composition comprising a catalyst; a carbon filler present in an amount of about 20 to about 60 wt. %; a polymerizable monomeric system present in an amount of about 7 to about 30 wt. % comprising a dialkyl ester of an aromatic tetracarboxylic acid, an aromatic diamine, and a monoalkyl ester of an acid selected from the group consisting of 5-norbornene-2,3-dicarboxylic acid and phthalic acid; and a furan solvent present in an amount of about 20 to about 60 wt. %.
Preferably, the dialkyl ester of an aromatic tetracarboxylic acid comprises a dimethylester of 3,3′,4,4′-benzophenonetetracarboxylic acid, the aromatic diamine is selected from the group consisting of 4,4′-methylenedianiline, 4,4′-oxydianiline, &rgr;phenylenediamine, 2,2′-bis(4-[4-aminophenoxyl]phenyl)propane, and 3,5-diaminobenzotrifluoride, and the monoalkyl ester comprises a monomethyl ester of 5-norbornene-2,3-dicarboxylic acid.
The preferred embodiment of the cement paste composition upon curing maintains a strength of at least about 2000 psi at room temperature after heat treatment at about 3000° C. even when cured at a substantially lower temperature of at least about 200° C.
The present invention is directed to, in another aspect, a carbonaceous bonding composition comprising an effective amount of furfuryl alcohol; a carbon filler comprising pitch coke flour, petroleum coke flour, carbon black or mixtures thereof; a polymerizable monomeric binder comprising a dimethylester of 3,3′,4,4′-benzophenonetetracarboxylic acid, 2,2′-bis(4-[4-aminophenoxyl]phenyl)propane and a monomethyl ester of 5-norbornene-2,3-dicarboxylic acid, the monomeric binder dissolved in an effective amount of furfuryl alcohol and admixed with the carbon filler to a uniform consistency; and a catalytic solution comprising an aqueous solution of zinc chloride admixed with furfuryl alcohol, the catalytic solution added to the monomeric binder and the carbon filler. The carbonaceous bonding composition is curable at a temperature of at least about 200° C., produces a carbon yield of about 70% at about 900° C. and, preferably, maintains a strength of at least about 2000 psi at room temperature after heat treatment at about 3000° C. even when cured at a substantially lower temperature.
Preferably, the carbonaceous bonding composition comprises carbon filler present in an amount of about 40 wt. %, furfuryl alcohol present in an amount of about 41 wt. %, and polymerizable monomeric system present in an amount of about 15 wt. % based upon the weight of the bonding composition.
The present invention is directed to, in yet another aspect, a method of making a carbonaceous cement composition by admixing the following materials: a catalyst; a furan solvent in an amount of about 20 to about 60%; a carbon filler in an amount of about 20 to about 60 wt. %; and a polymerizable monomeric binder in an amount of about 7 to about 30 wt. % comprising a dialkyl ester of an aromatic tetracarboxylic acid, an aromatic diamine, and a monoalkyl ester of an acid selected from the group consisting of 5-norbornene-2,3dicarboxylic acid and phthalic acid; and curing the admixture at a temperature of at least about 200° C.
The present invention is directed to, in still another aspect, a method of bonding carbon bodies comprising the steps of: (a) providing two or more carbon bodies to be bonded together; (b) coating the carbon bodies with a pre-oat at a bonding site until the bonding site is substantially saturated with the pre-coat, the pre-coat comprising a furan solvent, a polymerizable monomeric system comprising a dialkyl ester of an aromatic tetracarboxylic acid, an aromatic diamine, and a monoalkyl ester of an acid selected from the group consisting of 5-norbornene-2,3-dicarboxylic acid and phthalic acid, the monomeric system dissolved in an effective amount of the furan solvent, and a catalyst, the catalyst added to the polymerizable monomeric system dissolved in an effective amount of the furan solvent; (c) applying an effective amount of a carbonaceous cement composition to the bonding site, the carbonaceous cement composition comprising a furan solvent in an amount of about 20 to about 60 wt. %, a catalyst admixed with a first effective amount of the furan solvent, carbonaceous particles in an amount of about 20 to about 60 wt. %, and a polymerizable monomeric binder in an amount of about 7 to about 30 wt. % comprising a dialkyl ester of an aromatic tetracarboxylic acid, an aromatic diamine, and a monoalkyl ester of an acid selected from the group consisting of 5-norbornene-2,3-dicarboxylic acid and phthalic acid, the monomeric binder dissolved in a second effective amount of the furan solvent and admixed with the carbonaceous particles and the catalyst to form the cement composition; (d) setting the carbon bodies together at the bonding site forming a joined carbon body; and (e) heating the joined carbon body.
Preferably, the pre-coat comprises a monomeric system comprising a dimethylester of 3,3′,4,4′-benzophenonetetracarboxylic acid, 2,2′-bis(4-[4 aminophenoxyl]phenyl)propane and a monomethyl ester of 5-norbornene-2,3-dicarboxylic acid dissolved in an effective amount of furfuryl alcohol to which is added about 50 wt. % aqueous zinc chloride solution.
Preferably the carbonaceous ce

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