CN103266470A - Carbon fiber antioxidation coating and preparation method thereof - Google Patents

Abstract

The invention discloses a carbon fiber anti-oxidation coating and a preparation method thereof. The carbon fiber anti-oxidation coating is a SiO2-doped SiC coating, and the SiO2 _- doped SiC coating is covered on the surface of the carbon fiber with a pyrolytic carbon coating. The carbon fiber prefabricated body with a carbon fiber diameter of 6-8μm and a pyrolytic carbon coating with a thickness of 400-700nm is used, and the precursor is impregnated and cracked, with xylene as the solvent and ethyl orthosilicate doped with polycarbosilane as the precursor. , the SiO ₂ doped SiC coating was prepared through pressure impregnation, curing treatment and high temperature cracking steps. Oxidation properties.

Description

A kind of carbon fiber anti-oxidation coating and preparation method thereof

technical field

The invention relates to a carbon fiber surface coating and a preparation method thereof, in particular to a carbon fiber anti-oxidation coating and a preparation method thereof.

Background technique

Carbon fiber has a series of advantages such as high specific strength, high specific modulus, low linear expansion coefficient, and excellent thermoelectric properties. It is not only an indispensable structural material and corrosion-resistant material for manufacturing rockets, missiles, satellite space shuttles, and space stations. , heat insulation materials and special functional materials, and is also the main reinforcing fiber for lightweight and high performance of fighter jets, civil aviation airliners and helicopters, so it is widely used in high-tech industries. However, the oxidation of carbon fiber in an oxidizing environment with a temperature higher than 400 ° C gradually reduces its mechanical properties, which has become an Achilles' heel that limits the use of carbon fiber at higher temperatures. At the same time, carbon fiber is widely used as a reinforcing material in a variety of composite materials, and different composite materials have different requirements for the fiber-matrix interface. Preparing coatings on the surface of carbon fibers is a commonly used method to solve the above problems. At present, the interface coating materials that are relatively mature and have entered the practical field include boron nitride (BN), silicon carbide (SiC) and so on. Among them, SiC has high melting point, high temperature resistance, corrosion resistance, oxidation resistance and other properties, so it is widely used in composite materials and fiber coatings. At present, the preparation methods of SiC coating mainly include chemical vapor deposition (CVD) method, precursor impregnation pyrolysis (PIP) method, physical vapor deposition (PVD) method, sol-gel (Sol-Gel) method and in-situ reaction method. wait. Among them, the process of preparing SiC coating on the surface of carbon fiber using PIP method with polycarbosilane (PCS) as the precursor is relatively mature, and has the advantages of low process temperature, controllable composition and structure of the product, and low equipment requirements. However, due to the shrinkage and thermal stress caused by the discharge of small molecular substances during the pyrolysis process of PCS, the coating is prone to cracks and peeling off, which affects its oxidation resistance.

Contents of the invention

Aiming at the deficiencies of the above-mentioned prior art, the present invention provides a carbon fiber anti-oxidation coating and a preparation method thereof, which solves the problems that the coating is prone to cracks, easy to fall off, and the oxidation resistance is not high.

The present invention adopts following technical scheme:

A carbon fiber anti-oxidation coating, the carbon fiber anti-oxidation coating is a SiO ₂ doped SiC coating, wherein, wherein the mass fraction of SiO ₂ is 1% to 10%, and the SiO ₂ doped SiC coating Coated on the carbon fiber surface of a carbon fiber preform with a pyrolytic carbon (PyC) coating.

Further, the thickness of the SiO ₂ -doped SiC coating is greater than 0 and less than 1 μm.

Further, the carbon fiber diameter of the carbon fiber preform with pyrolytic carbon coating is 6-8 μm, and the thickness of the pyrolytic carbon coating is 400-700 nm.

The preparation method of the above-mentioned carbon fiber anti-oxidation coating comprises the following steps:

Step 1. Add polycarbosilane and tetraethyl orthosilicate to xylene, stir and dissolve to obtain a precursor solution, wherein the mass fraction of polycarbosilane is 2.5% to 20%, and the mass fraction of tetraethyl orthosilicate is 1.25%. ~20%;

Step 2. Pressure-impregnate the carbon fiber prefabricated body with pyrolytic carbon coating with the precursor solution obtained in Step 1, wherein the immersion pressure is 1-2.5Mpa, and the immersion time is 10-60min;

Step 3, performing curing treatment on the carbon fiber prefabricated body obtained in step 2, wherein the curing treatment temperature is 160-220° C., the curing treatment atmosphere is air, and the curing treatment time is 1-2 hours;

Step 4. The carbon fiber prefabricated body obtained in step 3 is subjected to high-temperature pyrolysis, wherein the pyrolysis temperature is 1000-1300°C, the heating rate is 2-10°C/min, the pyrolysis atmosphere is argon or vacuum, and the pyrolysis holding time is 1-10°C. 2h, that is to prepare a complete SiO ₂ doped SiC coating on the carbon fiber surface of the carbon fiber preform with pyrolytic carbon coating.

Further, the carbon fiber diameter of the carbon fiber preform with pyrolytic carbon coating in the step 2 is 6-8 μm, and the thickness of the pyrolytic carbon coating is 400-700 nm.

Further, step 2 to step 4 are repeated multiple times, wherein the number of cycles is 1 to 4 times.

The principle of the present invention is that the high temperature of ethyl orthosilicate produces glassy SiO ₂ , and the high temperature process can heal cracks. At the same time, the _SiO2 produced by doping tetraethyl orthosilicate in the precursor solution improves the bonding performance between the SiC coating and the PyC coating, so the quality of the coating is significantly improved, providing an obstacle for the diffusion of oxygen, that is, anti-oxidation Improved performance.

Beneficial effects of the present invention: the present invention prepares a complete _SiO2- doped SiC coating on the surface of the PyC coated carbon fiber, which solves the problem of peeling off of the SiC coating prepared by the PIP method. The oxidation resistance of coated carbon fiber is significantly improved, and at the same time, the problem of interfacial wettability and compatibility between carbon fiber and some composite material matrix is solved. The method for preparing the anti-oxidation coating on the carbon fiber surface of the carbon fiber prefabricated body of the present invention is simple and easy, and the cost is not high. The coated carbon fiber prefabricated body can be compounded with metals, ceramics, polymers, etc. to obtain a composite material with good oxidation resistance, which reduces the damage to the coating during the process of preparing the composite material from the monofilament coated carbon fiber and the fiber weaving process.

In summary, the present invention prepares a complete _SiO2 doped SiC coating on the surface of PyC coated carbon fiber, the coating thickness is less than 1 μm, and the thickness is controllable, the coating is smooth and complete, not easy to fall off, the preparation process is simple, and it has better Antioxidant properties.

Description of drawings

Fig. 1 is the scanning electron micrograph of 8000 times of the PyC/SiC coated carbon fiber prefabricated body prepared by embodiment 1;

Fig. 2 is the scanning electron micrograph of 8000 times of the PyC/SiC coated carbon fiber prefabricated body prepared by embodiment 5;

Fig. 3 is the scanning electron micrograph of 20000 times of the PyC/SiC coated carbon fiber prefabricated body prepared by embodiment 5;

Fig. 4 is the scanning electron micrograph of the PyC/SiC coated carbon fiber preform prepared in Example 5 after being oxidized in air at 700° C. for 10 min;

Fig. 5 is the static oxidation curves of carbon fibers with no coating, PyC coating and PyC/SiC coating prepared by different cracking temperatures of the present invention.

Detailed ways:

The present invention will be further explained below in conjunction with the embodiments and accompanying drawings. It should be understood that the following embodiments are only intended to illustrate and should not be regarded as limiting the scope of the present invention.

A carbon fiber anti-oxidation coating is a SiO ₂ doped SiC coating, the thickness of which is greater than 0 μm and less than 1 μm, wherein the mass fraction of SiO ₂ is 1% to 10%. The SiO ₂ doped SiC coating is coated on the carbon fiber surface of the carbon fiber preform with pyrolytic carbon (PyC) coating, wherein the carbon fiber diameter of the carbon fiber preform with pyrolytic carbon coating is 6-8 μm, and the pyrolytic carbon The coating thickness is 400-700nm.

The above-mentioned carbon fiber anti-oxidation coating is prepared by the precursor impregnation pyrolysis (PIP) method, including the following steps:

Step 1. Add polycarbosilane and tetraethyl orthosilicate to xylene, stir and dissolve to obtain a precursor solution, wherein the mass fraction of polycarbosilane is 2.5% to 20%, and the mass fraction of tetraethyl orthosilicate is 1.25%. ~20%;

Step 2. Pressure impregnation: Pressure impregnate the carbon fiber prefabricated body with pyrolytic carbon coating with the precursor solution obtained in step 1. During the impregnation process, pressurization of the mold is used to promote the penetration of the precursor solution, wherein the height of the precursor solution is greater than The height of the carbon fiber preform ensures that the pressurization process will not directly pressurize the preform. The impregnation pressure is 1-2.5Mpa, the impregnation time is 10-60min, and the carbon fiber diameter of the carbon fiber preform with PyC coating is 6-8μm. The chemical vapor infiltration (CVI) method is used to prepare the PyC coating on the carbon fiber preform, and the thickness of the PyC coating is 400-700nm;

Step 3, curing treatment: curing the carbon fiber prefabricated body obtained in step 2, wherein the curing treatment temperature is 160-220°C, the curing treatment atmosphere is air, and the curing treatment time is 1-2 hours;

Step 4, pyrolysis: pyrolyze the carbon fiber preform obtained in step 3, wherein the pyrolysis temperature is 1000-1300°C, the heating rate is 2-10°C/min, the pyrolysis atmosphere is argon or vacuum, and the pyrolysis holding time is 1 to 2 hours, that is, a complete SiO ₂ doped SiC coating is prepared on the carbon fiber surface of the carbon fiber preform with a pyrolytic carbon coating, and the thickness is greater than 0 μm and less than 1 μm.

In the present invention, after the carbon fiber prefabricated body pressurized and impregnated with the precursor solution is solidified and pyrolyzed, the carbon fiber prefabricated body is cooled to room temperature, and the process of pressure impregnation-solidification treatment-high-temperature pyrolysis is repeated, and the process can be carried out 1 to 4 times. Example 1

Using a mortar to grind PCS into a fine powder can speed up its dissolution rate in solvents. Add PCS and tetraethyl orthosilicate (TEOS) into xylene in a certain proportion, stir and dissolve to prepare a precursor solution, in which the mass fraction of PCS is 10%, and the mass fraction of TEOS is 5%. The carbon fiber diameter of the carbon fiber preform with the PyC coating is 6-8 μm, and the thickness of the PyC coating is 400-700 nm. The carbon fiber preform was pressure impregnated with the above precursor solution for 20 minutes at a pressure of 2 MPa. After the carbon fiber preform is taken out, it is cured at a constant temperature of 180° C. in an air atmosphere for 1.5 hours. Then put the preform in a graphite crucible and put them into the furnace together. The furnace used is an atmosphere furnace. The temperature is raised from room temperature to 1000°C at a rate of 4°C/min, kept for 1 hour, and high-temperature cracking is carried out under the protection of argon atmosphere. , so as to prepare SiO ₂ doped SiC coating on the surface of PyC coated carbon fiber. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 20-100 nm, and the mass fraction of SiO ₂ is 2%-5%.

Example 2

The difference between this example and Example 1 is that the pyrolysis process adopts a vacuum environment, and the furnace used is a vacuum furnace, and the temperature is raised to 1200° C. at a rate of 8° C./min, and the temperature is kept for 1 hour. Other steps are identical with embodiment 1. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 20-100 nm, and the mass fraction of SiO ₂ is 2%-5%.

Example 3

The difference between this example and Example 1 is that the mass fraction of modified PCS in the precursor solution is 15%, and the mass fraction of TEOS is 10%. Other steps are identical with embodiment 1. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 50-240 nm, and the mass fraction of SiO ₂ is 2.4%-6%.

Example 4

The difference between this example and Example 3 is that the pyrolysis process adopts a vacuum environment, the furnace used is a vacuum furnace, and the temperature is raised to 1200° C. at a speed of 8° C./min, and the temperature is kept for 1 hour. Other steps are identical with embodiment 3. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 50-240 nm, and the mass fraction of SiO ₂ is 2.4%-6%.

Example 5

PCS was ground into fine powder with a mortar, PCS and TEOS were added into xylene in a certain proportion, stirred and dissolved to prepare a precursor solution, wherein the mass fraction of PCS was 10%, and the mass fraction of TEOS was 5%. The carbon fiber preform with PyC coating has a carbon fiber diameter of 6-8 μm and a PyC coating thickness of 400-700 nm. The carbon fiber preform was pressure impregnated with the above precursor solution for 20 minutes at a pressure of 2 MPa. After the carbon fiber preform is taken out, it is cured in an air atmosphere at 180°C for 1.5 hours at a constant temperature. Then the preform is placed in a graphite crucible and put into a furnace together, and the furnace used is an atmosphere furnace. The temperature was raised from room temperature to 1000°C at a rate of 4°C/min, kept for 1 hour, and pyrolysis was carried out under the protection of an argon atmosphere. Repeat pressure impregnation-curing treatment-high temperature cracking once to prepare SiO ₂ doped SiC coating on the surface of PyC coated carbon fiber. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 30-150 nm, and the mass fraction of SiO ₂ is 2%-5%.

Example 6

The difference between this implementation and Example 5 is that the pyrolysis process adopts a vacuum environment, the furnace used is a vacuum furnace, and the temperature is raised to 1200 ° C at a speed of 8 ° C / min, and the temperature is kept for 1 hour. Other steps are identical with embodiment 5. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 30-150 nm, and the mass fraction of SiO ₂ is 2%-5%.

Example 7

The difference between this example and Example 5 is that the mass fraction of PCS in the precursor solution is 6%, and the mass fraction of TEOS is 2%. Other steps are identical with embodiment 5. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 20-100 nm, and the mass fraction of SiO ₂ is 1.5%-3.7%.

Example 8

The difference between this implementation and Example 7 is that the pyrolysis process adopts a vacuum environment, and the furnace used is a vacuum furnace, which is heated to 1200° C. at a speed of 8° C./min and kept for 1 hour. Other steps are the same as in Embodiment 7. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 20-100 nm, and the mass fraction of SiO ₂ is 1.5%-3.7%. Example 9

The difference between this example and Example 5 lies in the pyrolysis process, the temperature is raised to 1000° C. at a rate of 4° C./min, kept for 2 hours, and the pyrolysis is carried out under the protection of an argon atmosphere. Other steps are identical with embodiment 5. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 30-150 nm, and the mass fraction of SiO ₂ in the SiC coating is 2%-5%. Example 10

The difference between this example and Example 6 is that the pyrolysis process adopts a vacuum environment, the temperature is raised to 1200°C at a rate of 8°C/min, and the temperature is kept for 2 hours. Other steps are identical with embodiment 6. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 30-150 nm, and the mass fraction of SiO ₂ is 2%-5%.

Example 11

PCS was ground into fine powder with a mortar, PCS and TEOS were added to xylene in a certain proportion, stirred and dissolved to prepare a precursor solution, wherein the mass fraction of PCS was 20%, and the mass fraction of TEOS was 20%. The carbon fiber preform with PyC coating has a carbon fiber diameter of 6-8 μm and a PyC coating thickness of 400-700 nm. The carbon fiber preform was pressure impregnated with the above precursor solution for 60 minutes at a pressure of 2.5 MPa. After the carbon fiber preform is taken out, it is cured in an air atmosphere at 220°C for 2 hours at a constant temperature. Then put the preform in a graphite crucible and put them into the furnace together. The furnace used is an atmosphere furnace. The temperature is raised from room temperature to 1300°C at a rate of 10°C/min, and kept for 1 hour, and then high-temperature cracking is carried out under the protection of an argon atmosphere. , so as to prepare SiO ₂ doped SiC coating on the surface of PyC coated carbon fiber. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 60-400 nm, and the mass fraction of SiO ₂ is 3%-7.5%.

Example 12

PCS was ground into fine powder with a mortar, PCS and TEOS were added into xylene in a certain proportion, stirred and dissolved to prepare a precursor solution, wherein the mass fraction of PCS was 2.5%, and the mass fraction of TEOS was 1.25%. The carbon fiber preform with PyC coating has a fiber diameter of 6-8 μm and a PyC coating thickness of 400-700 nm. The above precursor solution was used to pressure impregnate the carbon fiber preform for 10 minutes at a pressure of 1 MPa. After the carbon fiber preform is taken out, it is cured in an air atmosphere at 160°C for 1 hour. Then put the preform in a graphite crucible and put them into the furnace together. The furnace used is an atmosphere furnace. The temperature is raised from room temperature to 1300°C at a rate of 2°C/min, kept for 1 hour, and high-temperature cracking is carried out under the protection of argon atmosphere. , so as to prepare SiO ₂ doped SiC coating on the surface of PyC coated carbon fiber. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is about 10-50 nm, and the mass fraction of SiO ₂ is 2%-5%.

Example 13

PCS was ground into fine powder with a mortar, PCS and TEOS were added into xylene in a certain proportion, stirred and dissolved to prepare a precursor solution, wherein the mass fraction of PCS was 10%, and the mass fraction of TEOS was 5%. The carbon fiber preform with PyC coating has a carbon fiber diameter of 6-8 μm and a PyC coating thickness of 400-700 nm. The carbon fiber preform was pressure impregnated with the above precursor solution for 20 minutes at a pressure of 2 MPa. After the carbon fiber preform is taken out, it is cured in an air atmosphere at 180°C for 1.5 hours at a constant temperature. Then the preform is placed in a graphite crucible and put into a furnace together, and the furnace used is an atmosphere furnace. The temperature was raised from room temperature to 1000°C at a rate of 4°C/min, kept for 1 hour, and pyrolysis was carried out under the protection of an argon atmosphere. Repeat pressure impregnation-curing treatment-high temperature cracking 4 times to prepare SiO ₂ doped SiC coating on the surface of PyC coated carbon fiber. The thickness of the SiO ₂ -doped SiC coating prepared in this embodiment is 60-300 nm, and the mass fraction of SiO ₂ is 2%-5%.

The PyC/SiC coated carbon fiber preforms prepared in Example 1 and Example 5 were subjected to a scanning electron microscope, as shown in Figures 1-3. The SiC coating doped with SiO ₂ in Figure 1 is very thin, and the SiC coating doped with SiO ₂ in Figure 2 is significantly thicker. At the same time, the coating is completely coated on the carbon fiber with PyC, without obvious cracks, voids, etc. Defects, visible, repeated pressure impregnation-curing treatment-pyrolysis steps can increase the thickness of the coating, and at the same time, can fill the cracks and voids in the SiC coating doped with _SiO2 in the previous layer to improve the coating quality. The higher magnification SEM in Figure 3 shows that the SiC coating is very complete without macroscopic defects such as obvious cracks and voids. The PyC/SiC coated carbon fiber preform prepared in Example 5 was oxidized in air at 700° C. for 10 minutes and then subjected to a scanning electron microscope, as shown in FIG. 4 . Oxidation occurs at the interface between carbon fiber and PyC coating, but the coating is still relatively complete at this time, which can hinder the diffusion of oxygen. The present invention statically oxidizes uncoated carbon fibers, PyC-coated carbon fibers, and PyC/SiC-coated carbon fibers (Examples 5 and 6) prepared by different pyrolysis temperatures according to the present invention, and the graphs thereof are shown in FIG. 5 . It can be seen from the figure that the oxidation resistance of PyC-coated carbon fiber and PyC/SiC-coated carbon fiber is significantly improved, and the initial oxidation temperature is significantly increased. Among them, the oxidation resistance of PyC/SiC-coated carbon fiber is the best, and the initial oxidation At the highest temperature, the oxidation rate decreased significantly. At the same time, the oxidation resistance of coated carbon fibers cracked at 1200°C is higher than that at 1000°C, because the coating cracked at 1200°C has a crystalline structure and has higher oxidation stability; while the coating cracked at 1000°C is amorphous , poor oxidation stability.

Claims (6)

1. a carbon fiber ORC is characterized in that, described carbon fiber ORC is SiO ₂The SiC coating of mixing, wherein, SiO ₂Mass fraction be 1%～10%, SiO ₂The SiC coating of mixing overlays on the carbon fiber surface of the prefabricated carbon fiber body of being with pyrocarbon coating.

2. carbon fiber ORC according to claim 1 is characterized in that, described SiO ₂The SiC coating layer thickness that mixes is greater than 0 μ m and less than 1 μ m.

3. carbon fiber ORC according to claim 1 is characterized in that, the carbon fiber diameter of the prefabricated carbon fiber body of described band pyrocarbon coating is 6～8 μ m, and pyrocarbon coating thickness is 400～700nm.

4. a method for preparing the described carbon fiber ORC of claim 1 is characterized in that, may further comprise the steps:

Step 1, Polycarbosilane and ethyl orthosilicate added stirring and dissolving makes precursor solution in the dimethylbenzene, wherein, the mass fraction of Polycarbosilane is 2.5%～20%, and the mass fraction of ethyl orthosilicate is 1.25%～20%;

Step 2, with the prefabricated carbon fiber body of the precursor solution pressure impregnation band pyrocarbon coating that obtains in the step 1, wherein impregnation pressure is 1～2.5Mpa, dip time 10～60min;

Step 3, the prefabricated carbon fiber body that obtains in the step 2 is cured processing, wherein, solidifying the temperature of handling is 160～220 ℃, and solidifying the atmosphere of handling is air, and solidifying the time of handling is 1～2h;

Step 4, the prefabricated carbon fiber body that obtains in the step 3 is carried out Pintsch process, wherein, cracking temperature is 1000～1300 ℃, heating rate is 2～10 ℃/min, cracking atmosphere is argon gas or vacuum, the cracking temperature retention time is 1～2h, and namely the carbon fiber surface at the prefabricated carbon fiber body of being with pyrocarbon coating prepares complete SiO ₂The SiC coating of mixing.

5. the preparation method of carbon fiber ORC according to claim 4 is characterized in that, the carbon fiber diameter of the prefabricated carbon fiber body of band pyrocarbon coating is 6～8 μ m in the described step 2, and pyrocarbon coating thickness is 400～700nm.

6. the preparation method of carbon fiber ORC according to claim 4 is characterized in that, repeatedly circulation step two is to step 4, and wherein cycle-index is 1～4 time.

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