Preparation method of porous carbon intermediate

Abstract

The invention relates to the technical field of ceramic-based composite materials, and particularly discloses a preparation method of a porous carbon intermediate. According to the preparation method of the porous carbon intermediate, regulation and control of the pore structure of the porous carbon intermediate are realized on the basis of a sol-gel method in combination with a molecular control technology. During preparation, the carbon element-containing resin with specific composition and a resin monomer are adopted to form gel with a high-concentration net structure, and then the gel is carbonized to form a stable carbon skeleton. On the basis of a carbon skeleton, a thermosetting resin carbon source and inorganic particles with different functions are added to realize the effects of uniform dispersion, specific surface area increase and pore channel fixation, so that a porous carbon intermediate structure with uniform pores and uniform size is prepared.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic-based composite materials, and in particular to a method for preparing a porous carbon intermediate. Background Art

[0002] With the upgrade of service conditions of components such as aerospace vehicles, engines and other power systems and hot end components of thermal protection systems, higher requirements are placed on service materials. Materials need to have better heat resistance, oxidation resistance and other characteristics to meet service needs. Continuous SiC fiber reinforced SiC ceramic matrix composites (i.e., SiC / SiC composites) are composite materials with SiC fibers as reinforcement phase and SiC matrix as continuous phase formed by introducing SiC fibers as reinforcement materials into SiC matrix. SiC / SiC composites retain the high temperature resistance, oxidation resistance, corrosion resistance and other characteristics of SiC matrix, and improve the brittleness of SiC ceramics. They are important component materials in the aviation field and have been promoted in military and civilian fields.

[0003] The preparation of SiC / SiC composites by melt infiltration has the advantages of short preparation cycle and low cost. It is a ceramic-based composite preparation process with significant engineering advantages. In the process of preparing SiC / SiC ceramic composites by melt infiltration, the porous carbon intermediate first reacts with molten Si, fills the pores of the porous carbon intermediate by silicon infiltration, and prepares the SiC matrix by silicon-carbon reaction, and then further prepares high-density SiC / SiC composites. The porous carbon intermediate is the key structure in the melt infiltration process. The porous carbon intermediate has a specific pore microstructure. In the melt infiltration process, on the one hand, it provides a channel for Si infiltration, and on the other hand, the porous carbon skeleton serves as a triggering place for the silicon-carbon reaction of the SiC / SiC composite forming. The elemental Si contacts the internal C through the pore channel, reacts to produce SiC, fills the carbon pores to a certain extent, and achieves densification. Therefore, it is of great significance to prepare and regulate porous carbon intermediates with suitable microstructure pores.

[0004] At present, researchers have proposed many solutions to obtain a uniform porous carbon intermediate structure. However, the means of controlling the structure of porous carbon are relatively simple, and the structural control and technology need to be further studied and improved. Since the porous carbon intermediate structure of the infiltration process has a direct impact on the permeability of molten metal Si and the degree of silicon-carbon reaction, when the pore size of the porous carbon is not conducive to the penetration of molten Si and the degree of reaction between the porous carbon and molten Si is low, it will lead to problems such as high residual carbon and residual silicon content in the matrix, low intrinsic density of the composite material, and poor mechanical properties.

[0005] Based on the above existing problems, the present invention aims to develop a method for preparing a porous carbon intermediate, in order to solve the current technical difficulties in controlling the structure of porous carbon intermediates and obtain a porous carbon intermediate structure with uniform and suitable pore size. Summary of the invention

[0006] The main technical problem solved by the present invention is to provide a method for preparing a porous carbon intermediate, in which pores are evenly distributed and have uniform sizes.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a porous carbon intermediate, comprising the steps of:

[0008] S1: impregnating a fiber preform having an interface phase with a porous carbon precursor slurry to obtain an impregnated fiber preform;

[0009] S2: the impregnated fiber preform is subjected to a sol-gel treatment and then to a carbonization treatment to obtain a porous carbon intermediate;

[0010] The porous carbon precursor slurry comprises a carbon source, a solvent, a dispersant, reaction-promoting particles and a flux.

[0011] As an embodiment of the present invention, the carbon source is phenolic resin and / or phenolic resin monomer; the solvent is ethanol; the dispersant is sodium hydroxymethyl cellulose; the reaction-promoting particles are nano-SiC; and the fluxing agent is carbon black.

[0012] As an embodiment of the present invention, the mass fractions of the carbon source, solvent, dispersant, reaction-promoting particles, and fluxing agent in the porous carbon precursor slurry are arranged as follows:

[0013]

[0014] As a preferred embodiment of the present invention, the mass fractions of the carbon source, solvent, dispersant, reaction-promoting particles, and fluxing agent in the porous carbon precursor slurry are arranged as follows:

[0015]

[0016] As a further preferred embodiment of the present invention, the mass fractions of the carbon source, solvent, dispersant, reaction-promoting particles, and fluxing agent in the porous carbon precursor slurry are arranged as follows:

[0017]

[0018] Still more preferably, the mass fractions of the carbon source, solvent, dispersant, reaction-promoting particles and fluxing agent in the porous carbon precursor slurry are arranged as follows:

[0019]

[0020] As an embodiment of the present invention, the carbon source is a mixture of phenolic resin and phenolic resin monomer, wherein the mass ratio of the phenolic resin to the phenolic resin monomer is (1-5):1.

[0021] Preferably, the phenolic resin is a thermosetting phenolic resin.

[0022] Preferably, the mass ratio of the phenolic resin to the phenolic resin monomer is (2-5): 1. For example, the phenolic resin and the phenolic resin monomer can be mixed in a ratio of 2:1, 3:1, 4:1 or 5:1 and used as a carbon source.

[0023] More preferably, the mass ratio of the phenolic resin to the linear phenolic resin monomer is (3-5):1.

[0024] As an embodiment of the present invention, in step S1, the impregnation treatment comprises: vacuum impregnating the fiber preform having the interface phase in the porous carbon precursor slurry for 20-24 hours.

[0025] As an embodiment of the present invention, in step S2, the sol-gel treatment comprises: heating the impregnated fiber preform to 70-90° C. under vacuum conditions for 18-22 hours.

[0026] As an embodiment of the present invention, in step S2, the carbonization treatment comprises: subjecting the impregnated fiber preform after the sol-gel treatment to a stepwise temperature-raising heat treatment under an inert atmosphere.

[0027] Preferably, the staged temperature increase heat treatment comprises: firstly heating the temperature to 170-185° C. for treatment for 0.5-1.5 h, and then heating the temperature to 850-910° C. for treatment for 0.5-1.5 h.

[0028] As an embodiment of the present invention, when the temperature is raised to 170-185°C, the heating rate is controlled to be 1-3°C / min.

[0029] As an embodiment of the present invention, when the temperature is raised to 850-910°C, the heating rate is controlled to be 4-6°C / min.

[0030] The present invention provides a porous carbon intermediate obtained by the method of the present invention.

[0031] The present invention also provides application of the porous carbon intermediate in preparing a SiC matrix of a SiC / SiC composite material.

[0032] The present invention further provides a SiC matrix material, which is obtained by subjecting the porous carbon intermediate of the present invention to a melt infiltration process using molten Si.

[0033] In the present invention, the fiber preform having the interface phase can be obtained by the following steps:

[0034] (1) placing the woven fiber preform into a high-temperature pyrolysis furnace for heat treatment to remove the sizing agent on the fiber surface to ensure good wettability between the interface phase and the fiber;

[0035] (2) A fiber preform is treated by a chemical vapor deposition process to obtain a fiber preform having an interface phase; the specific steps are as follows:

[0036] The fiber preform treated in step (1) is placed in a vapor deposition furnace, and vacuum is drawn to ensure that the gas in the furnace is completely exhausted. At a set temperature and pressure, a gas source gas is introduced to start the CVI interface deposition process. An interface phase of suitable thickness and type is prepared on the fiber preform through a chemical vapor deposition process to achieve a protective effect on the fiber.

[0037] The fiber preform with the interface phase described in the present invention is obtained by conventional techniques and can be obtained by using known methods reported in the prior art.

[0038] The method for preparing a porous carbon intermediate provided by the present invention is based on the sol-gel method and combines molecular control technology to achieve the regulation of the pore structure of the porous carbon intermediate. During the preparation, a resin containing carbon elements and a resin monomer of a specific composition are used to form a gel with a high concentration network structure, which is then carbonized to form a stable carbon skeleton. Based on the carbon skeleton, a thermosetting phenolic resin carbon source and inorganic particles with different functionalities are added to achieve uniform dispersion, increase specific surface area, and fix pore channels, thereby preparing a porous carbon intermediate structure with uniform pores and uniform size.

[0039] The present invention proposes a molecular-level porous carbon intermediate structure control preparation technology combined with a sol-gel method. Compared with the prior art, the present invention has the following characteristics:

[0040] (1) Through the sol-gel method, the linear resin monomers are fully cross-linked to form a cross-linked macromolecular skeleton with a stable structure, and a uniform porous carbon structure is obtained through the carbonization process, which can achieve stable and controllable pore formation;

[0041] (2) The pores formed during the carbonization of the dispersant are used as channels for the escape of small molecules generated during the cracking of the resin, ensuring that the pore formation position is controllable and the pore distribution is uniform;

[0042] (3) Using inorganic nano-SiC powder to increase the specific surface area of ​​porous carbon, increase the contact area between porous carbon and Si, and improve the degree of silicon-carbon reaction;

[0043] (4) Linear phenolic resin monomer and thermosetting phenolic resin are mixed as carbon sources to ensure that the slurry contains sufficient carbon source and the carbon content after carbonization ensures that the silicon-carbon reaction is sufficient.

[0044] The present invention obtains a porous carbon intermediate structure with uniform pore distribution and uniform pore size through porous carbon structure control technology. Undertaking the infiltration and silicon-carbon reaction in the melt infiltration process, the appropriate pore structure has a good infiltration effect on molten Si. The porous carbon intermediate obtained by the method of the present invention is conducive to obtaining a high-density SiC / SiC composite material, and the silicon-carbon reaction degree is high.

[0045] The intrinsic density of the SiC / SiC composite material further obtained by using the porous carbon intermediate structure provided by the present invention can reach 2.7g / cm 3 The above, porosity 2.3 ~ 2.6%, process densification cycle only takes 15 days, the melt infiltration process is realized to quickly prepare high-density SiC / SiC composite materials, giving full play to the engineering advantages of the melt infiltration process. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a 100-fold scanning electron microscope photograph of the porous carbon intermediate prepared in Example 1 of the present invention;

[0047] Figure 2 This is a 3000-fold scanning electron microscope photograph of the porous carbon intermediate prepared in Example 1 of the present invention;

[0048] Figure 3 is a CT image of the porous carbon intermediate prepared in Example 1 of the present invention;

[0049] Figure 4 This is a 1000-fold scanning electron microscope photograph of the porous carbon intermediate prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is described in detail below through specific embodiments. The following embodiments are intended to further illustrate the content of the present invention in detail, but are not intended to limit the scope of protection of the claims of the present invention.

[0051] In the following examples, unless otherwise specified, all reagents used are commercially available products.

[0052] Example 1

[0053] This embodiment provides a method for preparing a porous carbon intermediate, comprising the steps of:

[0054] (1) The woven fiber preform is placed in a high-temperature pyrolysis furnace and heat treated at 800°C in an inert atmosphere for 30 minutes to remove the sizing agent on the fiber surface and ensure good wettability between the interface phase and the fiber;

[0055] (2) placing the fiber preform processed in step (1) into a vapor deposition furnace, evacuating the furnace for 3 times to ensure that the gas in the furnace is completely exhausted, introducing BCl3, NH3 and H2 gases at a temperature of 1050°C and a pressure of 200 Pa, and starting CVI interface deposition. The chemical vapor deposition process was used for 60 minutes to prepare a boron nitride interface phase with a thickness of 800 nm, thereby achieving high-temperature protection for the fiber;

[0056] (3) impregnating the fiber preform with the interface phase prepared in step (2) into the porous carbon precursor slurry, and vacuum impregnating for 24 hours to ensure that the precursor components are fully introduced into the fiber preform, thereby obtaining an impregnated fiber preform;

[0057] The preparation process of the porous carbon precursor slurry is as follows: 150 g of thermosetting phenolic resin, 30 g of linear phenolic resin monomer, 30 g of ethanol, 5 g of sodium hydroxymethyl cellulose, 15 g of nano-SiC powder, and 5 g of carbon black are weighed, and then mixed and magnetically stirred for 10 hours to prepare a porous carbon precursor slurry solution;

[0058] (4) heating the impregnated fiber preform obtained in step (3) to 80° C. for 20 h under vacuum conditions to fully gel the sol in the slurry and remove small molecular substances;

[0059] (5) The impregnated fiber preform after the solvent-gelation treatment in step (4) is heated to 180°C at a heating rate of 2°C / min for 1 hour in a nitrogen atmosphere, and then heated to 900°C at a heating rate of 5°C / min for 1 hour to obtain a porous carbon intermediate.

[0060] Example 2

[0061] This embodiment provides a method for preparing a porous carbon intermediate, comprising the steps of:

[0062] (1) The woven fiber preform is placed in a high-temperature pyrolysis furnace and heat treated at 800°C in an inert atmosphere for 30 minutes to remove the sizing agent on the fiber surface and ensure good wettability between the interface phase and the fiber;

[0063] (2) placing the fiber preform processed in step (1) into a vapor deposition furnace, evacuating the furnace for 3 times to ensure that the gas in the furnace is completely exhausted, introducing BCl3, NH3 and H2 gases at a temperature of 1050°C and a pressure of 200 Pa, and starting CVI interface deposition. The chemical vapor deposition process was used for 60 minutes to prepare a boron nitride interface phase with a thickness of 800 nm, thereby achieving high-temperature protection for the fiber;

[0064] (3) impregnating the fiber preform with the interface phase prepared in step (2) into the porous carbon precursor slurry, and vacuum impregnating for 24 hours to ensure that the precursor components are fully introduced into the fiber preform, thereby obtaining an impregnated fiber preform;

[0065] The preparation process of the porous carbon precursor slurry is as follows: 100 g of thermosetting phenolic resin, 50 g of linear phenolic resin monomer, 50 g of ethanol, 1 g of sodium hydroxymethyl cellulose, 15 g of nano-SiC powder, and 5 g of carbon black are weighed, then mixed, and magnetically stirred for 10 hours to prepare a porous carbon precursor slurry solution;

[0066] (4) heating the impregnated fiber preform obtained in step (3) to 80° C. for 20 h under vacuum conditions to fully gel the sol in the slurry and remove small molecular substances;

[0067] (5) The impregnated fiber preform after the solvent-gelation treatment in step (4) is heated to 180°C at a heating rate of 2°C / min for 1 hour in a nitrogen atmosphere, and then heated to 900°C at a heating rate of 5°C / min for 1 hour to obtain a porous carbon intermediate.

[0068] Example 3

[0069] This embodiment provides a method for preparing a porous carbon intermediate, comprising the steps of:

[0070] (1) The woven fiber preform is placed in a high-temperature pyrolysis furnace and heat treated at 800°C in an inert atmosphere for 30 minutes to remove the sizing agent on the fiber surface and ensure good wettability between the interface phase and the fiber;

[0071] (2) placing the fiber preform processed in step (1) into a vapor deposition furnace, evacuating the furnace for 3 times to ensure that the gas in the furnace is completely exhausted, introducing BCl3, NH3 and H2 gases at a temperature of 1050°C and a pressure of 200 Pa, and starting CVI interface deposition. The chemical vapor deposition process was used for 60 minutes to prepare a boron nitride interface phase with a thickness of 800 nm, thereby achieving high-temperature protection for the fiber;

[0072] (3) impregnating the fiber preform with the interface phase prepared in step (2) into the porous carbon precursor slurry, and vacuum impregnating for 24 hours to ensure that the precursor components are fully introduced into the fiber preform, thereby obtaining an impregnated fiber preform;

[0073] The preparation process of the porous carbon precursor slurry is as follows: 150 g of thermosetting phenolic resin, 50 g of linear phenolic resin monomer, 50 g of ethanol, 3 g of sodium hydroxymethyl cellulose, 15 g of nano-SiC powder, and 5 g of carbon black are weighed, and then mixed and magnetically stirred for 10 hours to prepare a porous carbon precursor slurry solution;

[0074] (4) heating the impregnated fiber preform obtained in step (3) to 80° C. for 20 h under vacuum conditions to fully gel the sol in the slurry and remove small molecular substances;

[0075] (5) The impregnated fiber preform after the solvent-gelation treatment in step (4) is heated to 180°C at a heating rate of 2°C / min for 1 hour in a nitrogen atmosphere, and then heated to 900°C at a heating rate of 5°C / min for 1 hour to obtain a porous carbon intermediate.

[0076] The porous carbon intermediates prepared in the above Examples 1-3 were tested.

[0077] Among them, the low-magnification scanning electron microscope photo of the porous carbon intermediate prepared in Example 1 of the present invention is shown in Figure 1 As shown in the figure, it can be seen that the resin monomers are fully cross-linked to build a complete carbon skeleton, and there are uniform pores between the carbon skeletons, which meets the requirements of the porous structure.

[0078] A high-magnification scanning electron microscope photograph of the porous carbon intermediate prepared in Example 1 of the present invention is shown in Figure 2 As shown in the figure, it can be seen that there are spherical particles on the surface of the carbon skeleton formed by the polymerization of resin monomers. Analysis shows that they are mainly formed by the carbonization of thermosetting phenolic resin and the attachment of inorganic particles, which can effectively increase the specific surface area and total carbon content of the porous carbon intermediate.

[0079] The CT scan of the porous carbon intermediate prepared in Example 1 of the present invention is shown in Figure 3 As shown, the distribution and size of the pores can be observed from the CT image, and the pores in the porous carbon intermediate are evenly distributed and uniform in size.

[0080] A high-magnification scanning electron microscope photograph of the porous carbon intermediate prepared in Example 2 of the present invention is shown in Figure 4 As shown in the figure, it can be seen that there are relatively few pores in the carbon skeleton formed by the polymerization of resin monomers. The main reason is that the proportion of phenolic resin monomer components in the carbon source is high and the proportion of dispersant is low, which reduces the porosity. It can be seen that the porous carbon results can be regulated by adjusting the proportion of components in the porous carbon precursor slurry.

[0081] Example 1

[0082] This example is based on the porous carbon intermediate prepared in Example 1, and a subsequent melt infiltration treatment is performed to prepare a SiC / SiC composite material. The specific process is as follows:

[0083] (1) Based on the SiC fiber reinforced carbon-based composite material with a specific porous structure prepared in Example 1, that is, the porous carbon intermediate prepared in Example 1, the porous carbon matrix is ​​converted into silicon carbide by Si melt infiltration treatment, thereby preparing a SiC fiber reinforced SiC-based composite material;

[0084] (2) placing the composite material obtained in step (1) into a high temperature resistant graphite crucible coated with BN powder, adding micron-sized silicon powder, and ensuring that the composite material sample is completely embedded in the silicon powder;

[0085] (3) placing the sample-containing graphite crucible of step (2) into an infiltration furnace, evacuating the furnace to ensure that all gases in the furnace are exhausted, and performing infiltration treatment at a temperature of 1450° C. and standard atmospheric pressure for 1 h to prepare a SiC / SiC composite material.

[0086] In this example, the preparation period of SiC / SiC composite material is 15 days, and the intrinsic density of SiC / SiC composite material is 2.79g / cm 3 , porosity 2.3%. The ceramic-based composite materials prepared by this process have the characteristics of short preparation cycle and high product density.

[0087] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a porous carbon intermediate, characterized in that: Includes steps: S1: impregnating a fiber preform having an interface phase with a porous carbon precursor slurry to obtain an impregnated fiber preform; S2: the impregnated fiber preform is subjected to a sol-gel treatment and then to a carbonization treatment to obtain a porous carbon intermediate; Wherein, the porous carbon precursor slurry comprises a carbon source, a solvent, a dispersant, reaction-promoting particles, and a flux; Preferably, the carbon source is phenolic resin and / or phenolic resin monomer; and / or the solvent is ethanol; and / or the dispersant is sodium hydroxymethyl cellulose; and / or the reaction-promoting particles are nano-SiC; and / or the fluxing agent is carbon black.

2. The method according to claim 1, characterized in that The mass fractions of the carbon source, solvent, dispersant, reaction-promoting particles and fluxing agent in the porous carbon precursor slurry are arranged as follows: Preferably, the mass fractions of the carbon source, solvent, dispersant, reaction-promoting particles and fluxing agent in the porous carbon precursor slurry are arranged as follows:

3. The method according to claim 1 or 2, characterized in that: The carbon source is a mixture of phenolic resin and phenolic resin monomer, wherein the mass ratio of the phenolic resin to the phenolic resin monomer is (1-5):1, and preferably the mass ratio is (2-5):

1.

4. The method according to any one of claims 1 to 3, characterized in that: In step S1, the impregnation treatment includes: vacuum impregnating the fiber preform having the interface phase in the porous carbon precursor slurry for 20-24 hours.

5. The method according to any one of claims 1 to 4, characterized in that: In step S2, the sol-gel treatment includes: heating the impregnated fiber preform to 70-90° C. under vacuum conditions for 18-22 hours.

6. The method according to claim 5, characterized in that In step S2, the carbonization treatment includes: subjecting the impregnated fiber preform after the sol-gel treatment to a staged temperature-raising heat treatment under an inert atmosphere; Preferably, the staged temperature increase heat treatment comprises: firstly heating the temperature to 170-185°C for treatment for 0.5-1.5h, and then heating the temperature to 850-910°C for treatment for 0.5-1.5h.

7. The method according to claim 6, characterized in that When the temperature is raised to 170-185°C, the heating rate is controlled to be 1-3°C / min; and / or, when the temperature is raised to 850-910°C, the heating rate is controlled to be 4-6°C / min.

8. A porous carbon intermediate obtained by the method according to any one of claims 1 to 7.

9. Use of the porous carbon intermediate according to claim 8 in preparing a SiC matrix for a SiC / SiC composite material.

10. A SiC matrix material, characterized in that: The porous carbon intermediate according to claim 8 is subjected to a melt infiltration process using molten Si to obtain a SiC matrix material.

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