JPH0242790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to high strength, oxidation resistant carbon/carbon composites formed by diffusing antioxidants into a composite matrix. The antioxidant is placed inside the composite matrix and diffused into the composite matrix.

BACKGROUND OF THE INVENTION The use of boron in the manufacture of carbon materials such as graphite made from graphite powder and fillers such as graphitizable materials such as pitch or resins is known. Boron enhances the bonding of the material and its conversion into graphite.

It is also known in the art to use boron in the manufacture of carbon/carbon composites made of fibrous carbon materials such as carbon or graphite fabrics. The boron or boron-containing material is placed onto the fiber form and the fiber is then densified by one or more impregnations with furan/furfural resin.
An example of this type of composite is Leo C. Ehrenreich
It is disclosed in US Pat. No. 3,672,936 and US Pat. No. 4,119,189. These patents recognize that there are certain improvements in interlaminar strength and oxidation resistance when boron-containing compounds are added to the fibrous carbon material prior to resin impregnation and subsequent carbonization of the resin.

Robert C. Shaffer U.S. Patent No. 4164601 and
No. 4,101,354 discloses that the interlaminar tensile strength of boron-containing carbon/carbon composites is greatly improved when the composite is heated to at least 2160° C. during carbonization and graphitization, and further discloses that at such temperatures disclose that the tensile strength in the fiber direction of fibrous carbon materials is typically significantly reduced, apparently due to degradation of the fibrous carbon material in the composite caused by reaction with boron at high temperatures. are doing. According to the teachings of this patent, significant reductions in the fiber direction tensile strength of fibrous carbon materials are prevented by the use of a protective coating on the fibers. The protective coating includes a thermosetting material that remains flexible after being exposed to curing temperatures. The coating is applied to the fiber and cured prior to application of the resin and boron-containing compound. The resin and boron-containing compound are then applied and the resin is at least partially cured during the "B" stage process. After forming the laminate and heating the laminate to a temperature sufficient to carbonize and at least partially graphitize the resin, the composite tensile strength in the fiber direction of the fibrous carbon material of the laminate is determined. It has been found that the interlaminar tensile strength is greatly improved without significant reduction.

U.S. Pat. No. 4,321,298 to Robert C. Shaffer and William L. Tarasen discloses carbon/carbon composites with higher oxidation resistance, improved high temperature stability, higher density and improved laminate tensile strength. Discloses the formation of. According to the teachings of this patent, a mixture is formed that includes a refractory metal and a thermoset resin that remains flexible after being exposed to curing temperatures. The metal can be in the form of particulate metal or atomically dispersed metal or both. This metal can react with boron at high temperatures in a ternary system of carbon. The fibrous carbon material is coated with this mixture and the thermosetting resin is cured. The coated fibrous carbon material is then re-impregnated with a second thermoset resin containing a boron compound and an optional refractory metal capable of reacting with boron to form a stable metal boride.

Regarding the refractory metal in the first coating, if present, it can be in the form of particulate metal or atomically dispersed metal or both. The second thermoset resin is at least partially cured and the multiple layers of fibrous material are then assembled to form a composite. The composite is then heated to a temperature sufficient to carbonize and graphitize the thermoset resin. Carbon/carbon composites made by the methods described in US Pat. No. 4,164,601 and US Pat. No. 4,321,298 have virtually no inherent voids.

Composites formed in this manner are desirable for surfaces exposed to oxygen attack, and the oxidation rate of the composite was significantly reduced.

Structure and Effects of the Present Invention The mechanical properties of carbon/carbon composites formed by the methods described in US Pat. Nos. 4,164,601 and 4,321,298 are improved by the following method.

The present invention is a method of manufacturing a carbon/carbon composite including the following steps.

(a) applying a coating of a flexible thermosetting resin to a fibrous carbon material that remains flexible after hardening; (b) curing the flexible thermosetting resin; (c) impregnating the carbon material with a second thermosetting resin containing a boron compound; (d) at least partially curing the second thermosetting resin; (e) impregnating a plurality of the fibrous carbon materials. assembling the layers to form a laminate; (f) heating said laminate to a temperature sufficient to carbonize the thermosetting resin to form a carbon/carbon composite; (g) step ( f) treating the carbon/carbon composite to fill the characteristic voids in the carbon/carbon composite obtained in step (g) with a carbon-containing material; and (h) the carbon/carbon obtained in step (g). Heating the composite material to cause the boron contained therein to diffuse into the deposited carbon-containing material.

The present invention will be explained in more detail below.

(a) The fibrous carbon material is first coated with a flexible thermosetting resin that remains flexible after curing. The thermoset resin can optionally include a refractory metal that can react with boron to form a metal boride.

Here, "flexible" means having a stiffness smaller than that of the fibrous carbon material.
The thermosetting resin is deposited around the fibrous carbon material to protect it from boron migration that occurs during the diffusion process.

(b) The thermosetting resin is then cured. This prevents the first resin coated in step (a) from dissolving during coating with the second thermosetting resin. When the first resin dissolves, the effectiveness of the resin coating is compromised.

(c) this first resin-coated fibrous carbon material is then recycled with a second thermoset resin containing a boron compound and an optional refractory metal capable of reacting with boron to form a metal boride; coated. Regarding the optional refractory metal in the first coating, this metal, if present, can be in the form of particulate metal or atomically dispersed metal or both. This second thermosetting resin spaces the boron compound contained therein from the fibrous carbon material. In other words, since the first resin is cured first, in the subsequent lamination process,
The boron will be spaced from the fibrous carbon material during curing.

(d) the second thermoset resin is at least partially cured; That is, it is heated at a temperature and for a time that subjects the second thermoset resin coating to a "B" stage. Generally, this resin system has high fluidity, so it is difficult to layer the resins to form a composite material without going through this step.

(e) Assembling multiple layers of fibrous carbon material to form a laminate.

(f) The laminate is heated to carbonize the thermosetting resin. A carbon/carbon composite is thus obtained from the polymer matrix composite, ie a composite with a carbonaceous matrix containing boron. This matrix has a large number of voids formed by thermal decomposition of the matrix polymer. This voided composite material is further densified by the method described below, and serves as a base for producing densified carbon/carbon composite materials suitable for various uses.

(g) Filling the voids of the carbon/carbon composite material with the voids thus obtained with a carbon-containing substance. “Carbon-containing material” means “a material capable of filling the characteristic voids in a carbon/carbon composite and capable of forming a carbonaceous or graphitic material upon subsequent heat treatment.” do. This void can be filled, for example, by the following two methods.

(a) Impregnation method (a-) Impregnate with a polymer containing boron and carbon.

(a-) Impregnating with carbon-containing polymer.

(B-) Impregnate carbon-containing coal tar pitch.

(b) Filling with carbon-containing gas molecules by CVD (chemical vapor deposition).

In the present invention, it is necessary to fill the voids and increase the density, which can be done by any of the processes (a), (i), (a) and (b) above. Alternatively, it can be carried out by a method combining two or more methods. When it is desired to increase the amount of boron, it is desirable to impregnate a polymer containing boron and carbon as shown in (a). This allows boron to be selectively spaced from the fibrous carbon material. Sky =
As a method of filling, (I-), (I-)
and (b) are preferred, but as appropriate for the purpose,
Resin, coal tar pitch, or CVD are selected.

As mentioned above, to densify composite materials,
Two or more of the above methods may be combined, for example, after (i) the boron-carbon containing polymer is impregnated, the CVD method (b) may be performed.

(h) The carbon/carbon composite material filled with carbon-containing material in this way is heated, subjected to a heating cycle to carbonize the filling material, and the resulting composite material is further heat-treated to form the carbon/carbon composite material in step (g). boron is diffused into the carbon-containing material.

The composite obtained in step (f) is then re-impregnated with a resin containing atomically dispersed boron and optionally an atomically dispersed refractory metal capable of reacting with the boron to form a metal boride. It is possible to achieve higher density. This step is an optional step. Thereafter, the composite material is subjected to a void filling process in step (g). Specifically, it is densified, for example, by the use of carbon chemical vapor deposition, or by further treatment with a reimpregnating resin. This is then subjected to a heating cycle to carbonize the re-impregnated material and the resulting carbon/
The carbon composite is heat treated to diffuse boron into the composite matrix formed by the last filled carbon-containing material, such as carbon chemical vapor deposition or the last applied reimpregnated resin.

Reimpregnation with a resin containing atomically dispersed boron is an optional preferred step. The total boron content of the composite can be contained in the second thermosetting resin added during the pre-prescribing operation, but some of the boron can be removed from the fibers and the boron-free final density Preferably, the carbon from the chemical vapor deposition is placed close to the carbon from the final reimpregnation. This provides the best diffusion of boron into the final densified carbon and reduces the possibility of sheathing around the fibers.

According to the invention, the fibrous carbon material initially comprises:
Coated with a flexible thermoset that remains flexible after curing. The thermoset resin optionally includes a refractory metal that can react with boron to form a metal boride. The refractory metal can be atomically dispersed in the resin, i.e. the refractory metal can be part of the molecular structure of the resin; or it can be a particulate metal; or both can be used. be able to.

Thermosetting resins such as those disclosed in Robert C. Shaffer, US Pat. No. 3,544,530, can be used in the present invention and are incorporated herein by reference. This patent describes furfuryl alcohol copolymers, which are made by reacting maleic acid or maleic anhydride with polyhydroxy compounds such as ethylene glycol. it is,
Forming an ethylenically unsaturated polycarboxylic ester prepolymer. The ester prepolymer is then copolymerized with furfuryl alcohol to form a furfuryl alcohol copolymer.

Thermosetting resins containing atomically dispersed metals can be made by incorporating refractory metals into the resin in the form of reaction products of tungsten carbonyl and/or molybdenum carbonyl and pyrrolidine. An example of such a thermosetting resin is
Mention may be made of copolymers of furfuryl alcohol and polyester prepolymers which have been reacted with complexes that are the reaction products of tungsten carbonyl and/or molybdenum carbonyl and pyrrolidine. Such copolymers are described in Robert C. Shaffer's U.S. patent
It is disclosed in more detail in the specification of No. 4087482.
Other thermoset polymers containing chemically bonded metal atoms made by reacting monomers and prepolymers with complexes that are the reaction products of tungsten carbonyl and/or molybdenum carbonyl and pyrrolidine are Robert C. Shaffer US Pat. Nos. 4,185,043 and 4,302,392. After the resin is prepared, it can be diluted with a suitable solvent such as dimethylformamide to a solids content of, for example, 70%.

Fibrous carbon materials that can be used in the present invention include any carbon material in the form of fibrous filaments or other forms. Examples include fabrics such as carbon fabrics or graphite fabrics. The term carbon herein refers to all forms of carbon including graphite.

The flexible first coating is applied to the fibrous carbon material in a suitable manner and cured. One method that may be used is to dip the fibrous carbon material into an open container of coating material, then remove excess coating material by passing the fibrous carbon material through a pressure roller, and then remove the fibrous carbon material by passing it through a pressure roller. The coating is dried by hanging it in air at ambient temperature to evaporate some of the solvent in the coating material.
Curing of the coating material is then accomplished, for example, by placing the fibrous carbon material in a circulating air oven to allow polymerization of the resin and further removal of remaining solvent.
The solids content of the thermosetting coating material is adjusted to provide a cured coating comprising about 5 to 200% by weight of the fibrous carbon material.

Following application of the flexible coating, the fibrous carbon material is then re-impregnated with a second thermoset resin, which is partially cured or "B-staged"("B-staged"). ”-staged). This resin may be the same as a flexible thermoset resin. The resin may or may not contain suitable amounts of atomically dispersed or particulate refractory metals, or both, as described above. The resin also contains boron compounds, the amount of boron preferably being balanced on a molecular basis with the metal content present in the overall system. The boron-containing compound is preferably amorphous boron.
Impregnation and curing of the second coating of thermoset resin is accomplished by any suitable method such as dipping the coated fibrous carbon material into an open container of thermoset resin containing boron and, if desired, a refractory metal. can. Excess material is removed by passing the fibrous carbon material between pressure rollers, after which the material is suspended in air at ambient temperature to vaporize some of the solvent contained in the resin. dry.
Preferably, the amount of amorphous boron blended with the resin is selected such that the amorphous boron comprises about 2-9% by volume of the laminate. The dry fibrous carbon material is then
The thermosetting resin is treated to at least partially cure, for example by placing it in a circulating air oven to drive polymerization of the resin.

The resulting laminate is then preferably combined and densified with a resin matrix that is further cured. In one process to do this, the laminate is placed in a mold in an electrically heated platen press at elevated pressure and temperature to give the laminate a relatively hard fiber-resin matrix bond. It is left in place for a sufficient time to make it sufficiently self-supporting to maintain its shape and size during subsequent processing.

The laminate is then carbonized and preferably at least partially graphitized by heating, for example at a temperature of 1400-2200°C. For example, carbon-organic resin composites are first shaped by molding and at least partially precured. After that, the composite material is 1000〓
(538°C) to essentially decompose the resin without delamination or other damage to the composite. To perform this carbonization, the carbonization time is 14
It can last up to days. The laminate is then
The resin is further heated in a furnace to a higher temperature to further carbonize and/or graphitize. This high temperature can be between 1400°C and 2200°C. The characteristic voids in the resulting carbon/carbon composite are at least partially filled with carbon-containing material. This void can be filled, for example, by impregnating with (a) a polymer containing boron and carbon, (i) a carbon-containing polymer, or (i) carbon-containing coal tar pitch, as described above, or (b) This is done by CVD of carbon-containing gas molecules or by a combination of these methods. An example of the polymer (A-) is
It is described in US Pat. No. 4,412,064.
Chemical vapor deposition deposits pyrolytic type carbon-containing materials inside and on the surface of the cavity. Surfaces can be sealed in this way, which results in composites with considerably lower surface areas. Mesophase coal tar pitch can be used to deposit a carbon-containing material matrix and densify the composite.

However, this method is not a preferred embodiment since the composite still retains a relatively large amount of porosity after densification. This carbon-containing material is
Whether deposited by chemical vapor deposition or coal tar pitch reimpregnation, they are sensitive to oxygen attack. However, composite materials can now be processed at temperatures such as 3500-4500°C and evaporated by chemical vapor deposition or coal tar pitch treatments.
The boron contained in the boron-containing re-impregnated resin is diffused into the carbon filled in the carbon.

This diffused boron changes the properties of the chemically vapor deposited carbon or coal tar pitch carbon so that subsequent silicon carbide coatings or other surface coatings are no longer susceptible to attack in the range of 1200 to 1400. do not. That is, the practice of the present invention not only provides fiber protection from boron attack, but also provides uniform oxidation resistance throughout the composite, and allows the chemical vapor deposited carbon or coal tar pitch carbon to be modified to provide protection against other coatings. Provides a synergistic surface that promotes improved oxidation resistance for.

Example 1 A resin made according to Example 1 of Shaffer US Pat. No. 4,087,482 was placed in an open container and a carbon fabric was immersed in the resin. The solids content of the resin was adjusted to produce a coating that comprised approximately 28% of the weight of the fabric. The fabric was passed through a pressure roller to remove excess coating material and hung in air to dry at ambient temperature.
The fabric is then placed in a circulating air oven maintained at approximately 325㎓.
Leave it for 30 minutes. This temperature treatment cured the resin sufficiently to avoid intermixing with the resin in the second coating.

The coated fabric was then further impregnated by dipping into an open container containing a grind consisting of 82.2% by weight phenolic resin and 17.8% by weight amorphous boron. Enough milling material was added to give approximately 55% by weight of the original weight of the fabric. The fabric was passed through a pressure roller to remove excess resin and the prepreg was hung in air at ambient temperature to dry. The fabric is then placed in a circulating air oven at a temperature of approximately 180°C.
Leave it for 60 minutes, then increase the temperature to 200〓 for about 30 minutes,
Next, raise the temperature to 225〓 for about 10 minutes. This temperature treatment advances the resin to the "B" stage. The impregnated fabric is then cut into pieces of selected size and shape,
This piece was then constructed into the desired shape. The laminate is integrated, densified, and the matrix material is heated to approximately 21.1 kg/cm ² in a conforming mold using an electrically heated platen press.
(300 psi) and about 177° C. (350°) for about 90 minutes.

It has been found that the time required for curing depends on various factors including wall thickness and the shape of the part.
When removed from the press, the parts had a high degree of fabric-matrix adhesion. The part has sufficient self-supporting properties to maintain this shape and dimensions during subsequent processing steps. The laminate is then placed in a furnace and heated to approximately 260
By slowly raising the temperature to approximately 538°C (1000°C) over time, this was fully carbonized. The part was then cooled to ambient temperature over approximately 36 hours.
The carbonized laminate was placed in a container in a vacuum oven and evacuated to 29 inches for approximately 1 hour. This part then approx.
Heat to 185°C (365°C) for approximately 1 hour and allow the reimpregnated resin to melt and flow over the part. The reimpregnated resin is a resin made according to Example 7 of U.S. Pat. heated to ℃. A transparent prepolymer was produced. This was a thermoplastic that was solid at room temperature. 508.6 g of this boron prepolymer was solvated in approximately 800 ml of DMF. heating the solution to 65°C for 30 minutes;
At this time, in 500 ml of DMF at 40℃ prepared in the same way.
A solvated solution of 640.84 g of DowDEN-438 epoxy resin was added. Approximately 80℃ for 2 hours
Copolymerization was carried out at a temperature of . During this time, 500ml of DMF was added to maintain proper viscosity. The resin produced was a thermosetting epoxide with a curing temperature of about 200°C.

A resin was produced in this way. The vacuum is then released and the re-impregnated composite is then heated to approximately 224°C (435〓).
The mixture was further heated for about 14 hours. This further heat treatment cured the reimpregnated resin enough to prevent it from flowing in the next carbonization step.

The laminate was then placed in a furnace and carbonized by heating to about 538°C (1000°C) for about 48 hours. The laminate was heated to about 3800°C for about 2 hours to further carbonize and graphitize the composite matrix. The laminate was then placed in a furnace and densified by chemical vapor deposition of carbon in the matrix for approximately 125 hours. The laminate was then machined to the desired size and shape and then densified a second time by chemical vapor deposition for approximately 125 hours. The densified part is then heated to about 4250°C for about 3 hours and maintained at this temperature for about 1 hour. This additional heat treatment was found to diffuse boron into the chemical vapor deposited carbon. The laminate was then tested and found to have the following mechanical properties.

Tensile strength 1442Kg/cm ² (20510psi) Flexural strength 2025Kg/cm ² (28800psi) Compressive strength 1469Kg/cm ² (20890psi) Short beam shear (4-1)
171Kg/cm ² (2431psi) Izotsu impact strength
14.4 ft-lb/in Tensile Strength/Fabric Volume 2787 Kg/cm ² (39648 psi) Example 2 A carbon/carbon composite was made as in Example 1. However, the first carbonization was completed in about 48 hours, the first pyrolysis was limited to 3500°, and the final heat treatment to diffuse boron was limited to 3500°. The laminate was then tested and found to have the following mechanical properties.

Tensile strength 1565Kg/cm ² (22260psi) Flexural strength 1946Kg/cm ² (27680psi) Compressive strength 1312Kg/cm ² (18660psi) Short beam shear (4-1)
118Kg/cm ² (1684psi) Izotsu impact strength
8.7 ft-lb/in tensile strength/fabric volume 3433 Kg/cm ² (48830 psi) Example 3 A carbon/carbon composite was made as in Example 1, except that the first carbonization was completed in approximately 48 hours. . The laminate was then tested and found to have the following mechanical properties.

Tensile strength 1157Kg/cm ² (16460psi) Flexural strength 1802Kg/cm ² (25630psi) Compressive strength 1402Kg/cm ² (19940psi) Short beam shear (4-1)
133Kg/cm ² (1889psi) Izotsu impact strength
7.9 ft-lb/in Tensile Strength/Fabric Volume 2513 Kg/cm ² (35750 psi) Example 4 A carbon/carbon composite was made as in Example 3. However, the amount of boron in the second coated crushed material is
It was limited to 8.9% by weight. The laminate was tested and found to have the following mechanical properties.

Tensile strength 1230Kg/cm ² (17490psi) Flexural strength 2832Kg/cm ² (40280psi) Compressive strength 1263Kg/cm ² (27960psi) Short beam shear (4-1)
170Kg/cm ² (2418psi) Izotsu impact strength
13.0 ft-lbs/in tensile strength/fabric volume 2358 Kg/cm ² (33540 psi) Example 5 A carbon/carbon composite was made as in Example 3. However, the first composite was re-impregnated three times with resin-containing boron, and between each re-impregnation the 48
With time carbonization cycle. Test the laminate and
It was found to have the following mechanical properties.

Tensile strength 1365Kg/cm ² (19420psi) Flexural strength 1805Kg/cm ² (25670psi) Compressive strength 1863Kg/cm ² (26500psi) Short beam shear (4-1)
164Kg/cm ² (2336psi) Izotsu impact strength
9.6 ft-lb/inch tensile strength/fabric volume 2679 Kg/cm ² (38110 psi) Example 6 (Comparative) Using the same high strength carbon fabric used in the previous example, the method described in U.S. Pat. Therefore, a carbon/carbon composite was made. The laminate was then tested and found to have the following mechanical properties.

Tensile strength 680Kg/cm ² (9666psi) Flexural strength 1450Kg/cm ² (21331psi) Compressive strength 1202Kg/cm ² (17098psi) Short beam shear (4-1)
127 Kg/cm ² (1811 psi) Tensile strength/fabric volume 1095 Kg/cm ² (15575 psi) Therefore, the tensile, deflection,
The mechanical properties in terms of compressive and normalized tensile strength were shown to be better than those obtained with known methods.

These composites were also found to exhibit significantly improved oxidation resistance. In a test in an oxidizing atmosphere of about 1,800㎓, the product of Example 2 had a temperature of 45.4 after 3 hours.
Example 3 lost 32.03% by weight. On the other hand, a conventional carbon/carbon composite made by chemical vapor deposition has a loss of 84.92% by weight.

When coated with silicon carbide or other coatings, these composites exhibit the ability to work synergistically with the coatings by repairing the coatings at lower temperatures where these coatings are susceptible to oxidation.

Claims (1)

Claims: 1. (a) applying a coating of a flexible thermoset resin to a fibrous carbon material that remains flexible after being cured; (b) curing the flexible thermoset resin; (c) impregnating the fibrous carbon material with a second thermosetting resin containing a boron compound; (d) at least partially curing the second thermosetting resin; (e) a plurality of assembling the layers of said fibrous carbon material to form a laminate; (f) heating said laminate to a temperature sufficient to carbonize the thermosetting resin to form a carbon/carbon composite; (g) treating the carbon/carbon composite to fill the characteristic voids in the carbon/carbon composite obtained in step (f) with a carbon-containing material; and (h) step (g). 1. A method for producing a carbon/carbon composite comprising the steps of heating the carbon/carbon composite obtained above to diffuse the boron contained therein into a deposited carbon-containing material. 2. The method according to claim 1, wherein the carbon/carbon composite material obtained in step (f) is treated with a resin containing atomically dispersed boron. 3. The method of claim 2, wherein the carbon/carbon composite obtained in step (f) is further densified by chemical vapor deposition or coal tar pitch re-impregnation. 4. The carbon/carbon composite is further heat treated to carbonize the re-impregnated material prior to the heat treatment to diffuse the boron into the carbon.
The method described in section. 5. The method according to any one of claims 1 to 4, wherein at least one of the resins includes a refractory metal capable of reacting with boron to form a metal boride.