Preparation method and application of ultrahigh-temperature-resistant tantalum carbide ceramic aerogel

Abstract

The invention discloses a preparation method and application of ultrahigh-temperature-resistant tantalum carbide ceramic aerogel, and belongs to the field of ultrahigh-temperature ceramic aerogel preparation. The preparation method of the ultrahigh-temperature-resistant tantalum carbide ceramic aerogel comprises the following steps: mixing a complexing agent and tantalum alkoxide in a polyol solvent for reaction, then adding organic acid for catalytic polymerization, then adding phenolic resin and a gel catalyst to obtain a tantalum carbide precursor solution, and carrying out sol-gel reaction to obtain tantalum carbide precursor wet gel; performing drying treatment on the tantalum carbide precursor wet gel to obtain tantalum carbide precursor aerogel, and performing pyrolysis to obtain the tantalum carbide ceramic aerogel. The tantalum alkoxide is modified by using the complexing agent, the polyhydric alcohol and the organic acid, the precursor solution in which the raw materials can stably coexist at room temperature is obtained, an oxide ceramic gel network does not need to be synthesized in the preparation process, normal-pressure drying can be performed, and the obtained tantalum carbide ceramic aerogel has the characteristics of high purity and low residual carbon content.

Description

Technical Field

[0001] The present invention relates to the field of preparation of ultra-high temperature ceramic aerogels, and particularly to a method for preparing and applying tantalum carbide ceramic aerogels with ultra-high temperature resistance. Background Art

[0002] The special structure of aerogels endows them with extremely low density and thermal conductivity, making them ideal thermal insulation materials for thermal protection systems in the aerospace field. Currently, the aerogel materials applied to aerospace thermal protection systems mainly include oxide ceramic aerogels, organic aerogels, carbon aerogels, and silicon carbide ceramic aerogels, etc. However, these aerogels generally have problems such as poor high-temperature stability and are difficult to be competent for the thermal insulation task in ultra-high temperature environments above 1500 °C. Although the carbon aerogel can withstand temperatures as high as 2500 °C in a vacuum or inert atmosphere, its oxidation temperature is relatively low, and it will undergo severe oxidation at 450 °C in an oxidizing atmosphere, resulting in structural collapse and performance degradation, making it difficult to be applied in an aerobic environment. Therefore, developing a ceramic aerogel with excellent high-temperature stability and high-temperature oxidation resistance is the key to achieving ultra-high temperature thermal insulation in extreme working condition fields such as aerospace.

[0003] Tantalum carbide is a typical carbide ultra-high temperature ceramic with a melting point as high as 3880 °C, having outstanding high-temperature thermal stability, excellent high-temperature oxidation resistance, and thermal shock resistance. It is an excellent candidate material for ultra-high temperature applications such as high-performance cutting tools, rocket nozzles, and aircraft propulsion systems. Therefore, tantalum carbide ceramic aerogels based on tantalum carbide are expected to combine the excellent high-temperature stability and high-temperature oxidation resistance of tantalum carbide itself and the low thermal conductivity of aerogels, and become an efficient thermal insulation material for applications in extreme high-temperature environments such as aerospace.

[0004] Existing carbide ultra-high temperature ceramic aerogels are mainly prepared by carbothermal reduction using oxide ceramic aerogels containing carbon sources as the skeleton; however, the relatively low skeleton strength of oxide aerogels severely restricts the drying methods that can be used, and only supercritical drying can be used, which requires high equipment requirements and has potential safety hazards. Although adding phenolic resin can improve the skeleton strength of oxide gels, in order to avoid the destruction of the skeleton structure of oxide aerogels during the drying process, an excessive amount of phenolic resin often needs to be added, which will result in a relatively high residual carbon content in the obtained carbide ceramic aerogels, being unfavorable for the high-temperature oxidation resistance of ceramic aerogels. Therefore, it is necessary to develop a method for preparing high-purity tantalum carbide ultra-high temperature ceramic aerogels by atmospheric pressure drying without using oxide ceramic aerogels as the skeleton.

[0005] In addition, metal halides and metal alkoxides are two common metal sources. Metal halides are usually processed into oxide precursor sols and then mixed with carbon sources, but an oxide gel network is easily formed during the preparation process. Metal alkoxides, on the other hand, have the problem of high reactivity. They easily react with most carbon sources at room temperature, which is not conducive to the formation of a gel network with a uniform structure. Therefore, using appropriate means to reduce the reactivity of metal alkoxides to obtain a precursor solution in which metal alkoxides and carbon sources can coexist stably at room temperature is still a key problem to be solved in the preparation of tantalum carbide ultra-high temperature ceramic aerogels. Summary of the Invention

[0006] The object of the present invention is to provide a preparation method and application of a tantalum carbide ceramic aerogel resistant to ultra-high temperature to solve the above problems in the background technology. The present invention uses tantalum alkoxide as the metal source and phenolic resin capable of forming a high-strength gel skeleton as the carbon source. A complexing agent, polyol, and organic acid are used to modify the tantalum alkoxide to obtain a precursor solution in which the raw materials can coexist stably at room temperature. The tantalum carbide ceramic aerogel is prepared by a sol-gel, atmospheric drying, and carbothermal reduction method, and has the characteristics of high purity and low residual carbon content.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the technical solutions of the present invention: Provide a preparation method of a tantalum carbide ceramic aerogel resistant to ultra-high temperature, including the following steps:

[0009] Mix a complexing agent and tantalum alkoxide in a polyol solvent, stir and react to obtain an alcohol solution of a tantalum alkoxide complex;

[0010] Add an organic acid to the alcohol solution of the tantalum alkoxide complex, catalyze polymerization to obtain an alcohol solution of a tantalum alkoxide oligomer;

[0011] Mix phenolic resin with the alcohol solution of the tantalum alkoxide oligomer, add a gel catalyst to obtain a tantalum carbide precursor solution, and perform a sol-gel reaction (curing treatment) to obtain a wet gel of the tantalum carbide precursor;

[0012] Perform a drying treatment on the wet gel of the tantalum carbide precursor to obtain a tantalum carbide precursor aerogel, and pyrolyze to obtain the tantalum carbide ceramic aerogel.

[0013] Preferably, the phenolic resin is added in the form of a polyol solution of phenolic resin, and the mass fraction of the phenolic resin therein is 10-30%.

[0014] Preferably, the tantalum alkoxide is tantalum isopropoxide, tantalum n-propoxide, or tantalum n-butoxide.

[0015] Preferably, the molar ratio of the complexing agent to the tantalum alkoxide is 1.2-3.2:1.

[0016] Preferably, the complexing agent is any one of acetylacetone, methyl acetoacetate, ethyl acetoacetate, and ethyl benzoylacetate.

[0017] Preferably, the mass ratio of the polyol solvent to the tantalum alkoxide is 0.6 - 1.5:1.

[0018] Preferably, the polyol solvent is one or more of ethylene glycol, propylene glycol, butylene glycol, and glycerol.

[0019] Preferably, the temperature of the stirring reaction is 80 - 120 °C, and the time is 1 - 2 h.

[0020] Preferably, the addition amount of the organic acid is 15 - 25% of the mass of the tantalum alkoxide.

[0021] Preferably, the temperature of the catalytic polymerization is 80 - 110 °C, and the time is 1 - 2 h.

[0022] Preferably, the organic acid is an organic acid that is soluble in the polyol, has a boiling point higher than 110 °C, and a decomposition temperature higher than 200 °C.

[0023] More preferably, the organic acid is one or more of acetic acid, adipic acid, salicylic acid, benzoic acid, and terephthalic acid.

[0024] Preferably, the mass ratio of the phenolic resin to the amount of substance of the tantalum alkoxide is 154 - 320 g:1 mol.

[0025] Preferably, the phenolic resin is a thermosetting phenolic resin.

[0026] Preferably, the addition amount of the gel catalyst is 10 - 20% of the mass of the tantalum carbide precursor solution.

[0027] Preferably, the gel catalyst is one or more of acetic acid, benzoic acid, salicylic acid, and hexamethylenetetramine.

[0028] Furthermore, while the gel catalyst contains hexamethylenetetramine, it also contains an acidic catalyst that is one or more of acetic acid, benzoic acid, and salicylic acid, and the mass ratio of the hexamethylenetetramine to the acidic catalyst is 1:5 - 20.

[0029] Preferably, the temperature of the sol - gel reaction is 160 - 200 °C, and the time is 10 - 20 h.

[0030] Preferably, the drying treatment is to first perform solvent replacement on the wet gel of the tantalum carbide precursor with ethanol, and then dry it at 20 - 80 °C under normal pressure for 5 - 48 h.

[0031] Preferably, the temperature of the pyrolysis is 1300 - 1500 °C, and the time is 1 - 2 h.

[0032] The second technical solution of the present invention: Provide a tantalum carbide ceramic aerogel resistant to ultra-high temperature obtained according to the above preparation method.

[0033] The third technical solution of the present invention: Provide an application of the above tantalum carbide ceramic aerogel resistant to ultra-high temperature in the field of high-temperature thermal insulation materials.

[0034] Preferably, the field of high-temperature thermal insulation materials is the field of high-temperature thermal insulation materials used in the aerospace field or the nuclear industry field.

[0035] The technical principle of the present invention is as follows:

[0036] In the present invention, tantalum alkoxide and phenolic resin are used as the tantalum source and carbon source respectively. The tantalum alkoxide is modified by using a complexing agent, polyol and organic acid. The polyol is used to replace the alkoxy groups that cannot be replaced by the complexing agent due to steric hindrance effect. Subsequently, the organic acid is used to catalyze the polymerization of the tantalum alkoxide, further consuming the highly active alkoxy groups in the tantalum alkoxide, effectively inhibiting the rapid reaction between the tantalum alkoxide and the phenolic resin at room temperature, and obtaining a precursor mixed solution in which the tantalum source and the carbon source can coexist stably for a long time at room temperature; and using polyol as the solvent, the precursor mixed solution is cured at high temperature. During the curing process, the phenolic resin undergoes a cross-linking reaction to form a gel skeleton with a certain strength. The modified tantalum alkoxide undergoes a substitution reaction with the phenolic hydroxyl groups in the phenolic resin at high temperature, so that the tantalum element is uniformly distributed on the phenolic resin gel skeleton, and a tantalum carbide precursor wet gel with a certain strength that can be used for atmospheric drying is obtained. Subsequently, through solvent replacement, atmospheric drying and high-temperature pyrolysis, a tantalum carbide ceramic aerogel resistant to ultra-high temperature is obtained. The purpose of the present invention is to provide a preparation method of a tantalum carbide ultra-high temperature ceramic aerogel with simple operation and low residual carbon content, which can be applied to the field of ultra-high temperature thermal insulation materials. The tantalum carbide ceramic aerogel uses phenolic resin that can form a high-strength gel skeleton as the carbon source, and is prepared by a method combining atmospheric drying and carbothermal reduction, and has the characteristics of high purity and low residual carbon content.

[0037] The beneficial technical effects of the present invention are as follows:

[0038] (1) In the present invention, a complexing agent, polyol and organic acid are used to modify the tantalum alkoxide, effectively reducing its reaction activity and inhibiting the rapid reaction between the tantalum alkoxide and the phenolic resin at room temperature. And thermosetting phenolic resin is selected as the carbon source, excluding the influence of the substitution reaction between free phenol and tantalum alkoxide, and obtaining a tantalum carbide precursor solution with good fluidity in which the tantalum alkoxide and the phenolic resin can coexist stably at room temperature.

[0039] (2) The present invention uses a high-boiling polyol solvent to replace the ethanol solvent in the preparation of traditional ceramic aerogels, which can increase the reaction temperature during the gelation process, promote the cross-linking and curing of polymers, enhance the strength of the wet gel skeleton, ensure that the wet gel can be dried at atmospheric pressure, and significantly shorten the gel reaction time, effectively improving the preparation efficiency.

[0040] (3) The present invention uses a phenolic resin gel skeleton with higher strength to replace the low-strength oxide gel skeleton in the traditional ultra-high temperature ceramic preparation process to achieve atmospheric drying; and by adjusting the ratio of tantalum alkoxide to phenolic resin, a high-purity tantalum carbide ceramic aerogel with a residual carbon content of less than 10 wt% can be obtained. Brief Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 It is the XRD pattern of the products of Example 1 and Comparative Example 1;

[0043] Figure 2 It is the SEM image of the tantalum carbide ceramic aerogel pyrolyzed at 1500 °C in Example 1;

[0044] Figure 3 It is the compression curve of the tantalum carbide precursor aerogel obtained in Example 2;

[0045] Figure 4 It is the SEM-EDS image of the tantalum carbide ceramic aerogel obtained in Example 2; among them, (a) is the SEM photo, and (b)-(d) are the EDS images;

[0046] Figure 5 It is the XRD pattern of the tantalum carbide ceramic aerogel obtained in Example 3;

[0047] Figure 6 It is the SEM image of the tantalum carbide ceramic aerogel obtained in Example 3;

[0048] Figure 7 It is the real-time photos of the tantalum carbide ceramic aerogel obtained in Example 3 before and after heat treatment in a vacuum atmosphere at 1800 °C for 1 h; among them, (a) is before heat treatment, and (b) is after heat treatment;

[0049] Figure 8 It is the physical picture of the tantalum carbide precursor solution in Comparative Example 2;

[0050] Figure 9It is a physical picture of the tantalum carbide precursor solution in Comparative Example 3;

[0051] Figure 10 It is a physical picture of the tantalum carbide precursor solution in Comparative Example 4;

[0052] Figure 11 It is a physical picture of the tantalum carbide precursor solutions in Example 1 and Comparative Example 5; wherein, (a) is Comparative Example 5, and (b) is Example 1;

[0053] Figure 12 It is a physical picture of the tantalum carbide precursor solutions in Example 1 and Comparative Example 6;

[0054] Figure 13 It is a physical picture of the tantalum carbide precursor wet gels in Example 1 and Comparative Example 7; wherein, (a), (b), and (c) are Comparative Example 7, and (d) is Example 1;

[0055] Figure 14 It is a physical picture of the tantalum carbide precursor aerogels in Example 2 and Comparative Example 8; wherein, (a) is Comparative Example 8, and (b) is Example 2;

[0056] Figure 15 It is the SEM image and XRD pattern of the tantalum carbide ceramic aerogel in Comparative Example 8; wherein, (a) is the SEM image, and (b) is the XRD pattern;

[0057] Figure 16 It is a physical picture of the tantalum carbide precursor solutions in Example 2 and Comparative Example 9; wherein, (a) is Comparative Example 6, and (b) is Example 2. Detailed implementation manners

[0058] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation to the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention.

[0059] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0060] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of this invention. It should be noted that those aspects not detailed in this invention are common operating means in the art and are not the focus of this invention.

[0061] Regarding the use of "comprising", "including", "having", "containing", etc. in this invention, they are all open-ended terms, meaning including but not limited to.

[0062] This invention provides a method for preparing a tantalum carbide ceramic aerogel resistant to ultra-high temperature, comprising the following steps:

[0063] (1) Drop a complexing agent into tantalum alkoxide, then add a polyol solvent and stir at 80 - 120 °C for 1 - 2 h to obtain an alcohol solution of tantalum alkoxide complex; wherein, the molar ratio of the complexing agent to tantalum alkoxide can vary from 1.2 - 3.2:1, and the mass ratio of polyol to tantalum alkoxide can vary from 0.6 - 1.5:1;

[0064] (2) Add an organic acid to the above solution, stir at 80 - 110 °C for 1 - 2 h for catalytic polymerization, and perform vacuum distillation to obtain an alcohol solution of tantalum alkoxide oligomer; wherein, the addition amount of the organic acid can vary between 15 - 25% of the mass of tantalum alkoxide;

[0065] (3) After uniformly mixing the polyol solution of thermosetting phenolic resin with the polyol solution of tantalum alkoxide oligomer, add a gel catalyst and stir evenly to obtain a tantalum carbide precursor solution; wherein, the mass ratio of phenolic resin to the amount of substance of tantalum alkoxide can vary from 154 - 320 g:1 mol; the mass fraction of phenolic resin in the alcohol solution of phenolic resin can vary from 10 - 30%; the addition amount of the gel catalyst can vary from 10 - 20% of the mass of the tantalum carbide precursor solution;

[0066] (4) Keep the tantalum carbide precursor solution at 160 - 200 °C for 10 - 20 h to obtain a wet gel of tantalum carbide precursor;

[0067] (5) After performing solvent replacement on the wet gel of tantalum carbide precursor with ethanol for 3 - 4 days, perform atmospheric drying at 20 - 80 °C for 5 - 48 h to obtain a tantalum carbide precursor aerogel;

[0068] (6) Pyrolyze the tantalum carbide precursor aerogel in an inert or vacuum atmosphere at 1300 - 1500 °C for 1 - 2 h to obtain a tantalum carbide ceramic aerogel.

[0069] In the present invention, "atmospheric pressure" refers to standard atmospheric pressure if not specified otherwise.

[0070] In the present invention, "room temperature" refers to 10 - 30 °C if not specified otherwise.

[0071] The thermosetting phenolic resin (model: JYPF2130) and thermoplastic phenolic resin (model: JYPF2123B) used in the present invention are both purchased from Jiayuan New Materials Co., Ltd.

[0072] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0073] Example 1

[0074] A preparation method of tantalum carbide ceramic aerogel resistant to ultra-high temperature is as follows:

[0075] (1) Drop the complexing agent acetylacetone into tantalum propoxide, then add ethylene glycol solvent and stir at 120 °C for 2 h to obtain an ethylene glycol solution of tantalum propoxide complex; wherein, the molar ratio of acetylacetone to tantalum propoxide is 3.2:1, and the mass ratio of ethylene glycol to tantalum propoxide is 0.6:1;

[0076] (2) Add acetic acid with a mass of 15% of the mass of tantalum propoxide to the above solution, stir at 110 °C for 2 h for catalytic polymerization, and carry out vacuum distillation to obtain an ethylene glycol solution of tantalum propoxide oligomer;

[0077] (3) After uniformly mixing an ethylene glycol solution of thermosetting phenolic resin with a mass fraction of 30% of phenolic resin and the ethylene glycol solution of tantalum propoxide oligomer, add acetic acid with a mass of 10% of the mixed solution and stir evenly to obtain a tantalum carbide precursor solution; wherein, the mass ratio of phenolic resin to the amount of substance of tantalum propoxide is 320 g:1 mol;

[0078] (4) Keep the tantalum carbide precursor solution at 180 °C for 10 h to obtain a wet gel of tantalum carbide precursor;

[0079] (5) Use ethanol to carry out solvent replacement on the wet gel of tantalum carbide precursor for 4 days, and carry out atmospheric drying at 60 °C for 48 h to obtain a tantalum carbide precursor aerogel;

[0080] (6) Take the tantalum carbide precursor aerogel, pyrolyze it at 1300 °C and 1500 °C for 2 h respectively under an argon atmosphere to obtain tantalum carbide ceramic aerogel pyrolyzed at 1500 °C (measured, its density is 0.84 g / cm 3 , and the room temperature thermal conductivity is 0.181 W·m -1 ·K -1 ) and tantalum carbide ceramic aerogel pyrolyzed at 1300 °C.

[0081] Comparative Example 1

[0082] The difference from Example 1 is only that the pyrolysis temperatures are modified to 900 °C and 1100 °C respectively, and tantalum carbide ceramic aerogels pyrolyzed at 900 °C and 1100 °C are obtained respectively.

[0083] Figure 1 It is the XRD pattern of the products of Example 1 and Comparative Example 1.

[0084] As Figure 1 shown, the phase of the tantalum carbide ceramic aerogel prepared in Example 1 is only TaC, and there are no oxide impurities.

[0085] Figure 2 It is the SEM image of the tantalum carbide ceramic aerogel pyrolyzed at 1500 °C in Example 1.

[0086] Example 2

[0087] A preparation method of a tantalum carbide ceramic aerogel resistant to ultra-high temperature is as follows:

[0088] (1) Drop acetylacetone methyl ester as a complexing agent into tantalum isopropoxide, then add ethylene glycol solvent and stir at 80 °C for 2 h to obtain an ethylene glycol solution of tantalum isopropoxide complex; wherein, the molar ratio of acetylacetone methyl ester to tantalum isopropoxide is 1.2:1, and the mass ratio of ethylene glycol to tantalum isopropoxide is 1.5:1;

[0089] (2) Add acetic acid with a mass of 25% of the mass of tantalum isopropoxide to the above solution, stir at 80 °C for 2 h for catalytic polymerization, and perform vacuum distillation to obtain an ethylene glycol solution of tantalum isopropoxide oligomer;

[0090] (3) After uniformly mixing an ethylene glycol solution of thermosetting phenolic resin with a mass fraction of 20% of phenolic resin and an ethylene glycol solution of tantalum isopropoxide oligomer, add 20% of acetic acid based on the mass of the mixed solution and stir evenly to obtain a tantalum carbide precursor solution; wherein, the mass ratio of phenolic resin to tantalum alkoxide is 200 g:1 mol;

[0091] (4) Keep the tantalum carbide precursor solution at 160 °C for 10 h to obtain a tantalum carbide precursor wet gel;

[0092] (5) Use ethanol to perform solvent replacement on the tantalum carbide precursor wet gel for 4 days, and then perform atmospheric drying at 60 °C for 48 h to obtain a tantalum carbide precursor aerogel;

[0093] (6) Pyrolyze the tantalum carbide precursor aerogel in an argon atmosphere at 1500 °C for 2 h to obtain a tantalum carbide ceramic aerogel (measured, its density is 0.58 g / cm 3 , and the room temperature thermal conductivity is 0.137 W·m-1 ·K -1 ).

[0094] Figure 3 It is the compression curve of the tantalum carbide precursor aerogel obtained in Example 2.

[0095] As Figure 3 shown, the compressive strength of the tantalum carbide precursor aerogel prepared in Example 2 is 0.62 MPa.

[0096] Figure 4 It is the SEM-EDS diagram of the tantalum carbide ceramic aerogel obtained in Example 2. Among them, (a) is the SEM photo, and (b)-(d) are the EDS diagrams.

[0097] As Figure 4 shown, the tantalum carbide ceramic aerogel is composed of only two elements, tantalum and carbon, and is evenly distributed, without other elements such as oxygen. Among them, the atomic ratio of tantalum and carbon elements is close to the stoichiometric ratio of tantalum carbide 1:1, and the residual carbon content in the aerogel is low. After testing, it is only 2.43 wt%.

[0098] Example 3

[0099] A preparation method of a tantalum carbide ceramic aerogel resistant to ultra-high temperature is as follows:

[0100] (1) Drop the complexing agent acetylacetone into tantalum butoxide, then add glycerol solvent and stir at 120 °C for 2 h to obtain a glycerol solution of tantalum butoxide complex; among them, the molar ratio of the complexing agent to tantalum butoxide is 2:1, and the mass ratio of glycerol to tantalum butoxide is 0.6:1;

[0101] (2) Add salicylic acid with a mass of 20% of the mass of tantalum butoxide to the above solution, stir at 100 °C for 2 h for catalytic polymerization, and perform vacuum distillation to obtain a glycerol solution of tantalum butoxide oligomer;

[0102] (3) After uniformly mixing the glycerol solution of thermosetting phenolic resin with a mass fraction of 10% of phenolic resin and the glycerol solution of tantalum butoxide oligomer, add a catalyst with a mass of 10% of the mixed solution and stir evenly to obtain a tantalum carbide precursor solution; among them, the mass ratio of phenolic resin to the amount of substance of tantalum alkoxide is 154 g:1 mol; the catalyst is hexamethylenetetramine and salicylic acid with a mass ratio of 1:10;

[0103] (4) Keep the tantalum carbide precursor solution at 200 °C for 20 h to obtain a tantalum carbide precursor wet gel;

[0104] (5) After using ethanol to perform solvent replacement on the tantalum carbide precursor wet gel for 4 days, perform atmospheric drying at 60 °C for 48 h to obtain a tantalum carbide precursor aerogel;

[0105] (6) Pyrolyze the tantalum carbide precursor aerogel in an argon atmosphere at 1500 °C for 2 h to obtain a tantalum carbide ceramic aerogel (as measured, its density is 0.41 g / cm 3 , and the room temperature thermal conductivity is 0.092 W·m -1 ·K -1 ).

[0106] Figure 5 It is the XRD pattern of the tantalum carbide ceramic aerogel obtained in Example 3.

[0107] As Figure 5 shown, the phase composition of the tantalum carbide ceramic aerogel prepared in Example 3 is only TaC, and there are no oxide impurities.

[0108] Figure 6 It is the SEM image of the tantalum carbide ceramic aerogel obtained in Example 3.

[0109] Heat-treat the tantalum carbide ceramic aerogel of Example 3 in a vacuum atmosphere at 1800 °C for 1 h to test the ultra-high temperature resistance of the product. The test results are as Figure 7 shown.

[0110] Figure 7 They are the real-time photos of the tantalum carbide ceramic aerogel obtained in Example 3 before and after heat treatment in a vacuum atmosphere at 1800 °C for 1 h; among them, (a) is before heat treatment, and (b) is after heat treatment.

[0111] Test the shrinkage rate of the tantalum carbide ceramic aerogel of Example 3 at an ultra-high temperature of 1800 °C. The specific test method is as follows:

[0112] Use a visual high-temperature deformation analyzer (model: TA-Z20, manufacturer: Tianjin Zhonghuan Electric Furnace Co., Ltd.) and the supporting visual high-temperature deformation analysis software to test the high-temperature resistance of the sample; place the sample on the sample stage of the visual high-temperature deformation analyzer, and wait until the vacuum degree drops to 10 -3 Pa and below, then heat it up to 1800 °C at a heating rate of 10 °C / min and hold for 1 h. During the heating and holding process, the visual high-temperature deformation analyzer detects the deformation of the sample in real time, and the supporting high-resolution camera takes pictures every 5 s to record the shape change of the sample. Use the supporting software to process the image data, extract the size data of the sample at different temperatures, and calculate the shrinkage rate of the sample at 1800 °C according to the following formula:

[0113]

[0114] Among them, S is the linear shrinkage rate of the sample, L0 is the initial height or width of the sample before testing, L TIt is the height or width of the sample at the corresponding temperature (the obtained dimensional data is the relative value processed by the visualization high-temperature deformation analysis software and has no unit).

[0115] It is measured that the shrinkage rate of the tantalum carbide ceramic aerogel in Example 3 is only 7.62% at the ultra-high temperature of 1800 °C, indicating that it has good ultra-high temperature resistance.

[0116] Comparative Example 2

[0117] The difference from Example 1 is only that the ethylene glycol in steps (1) and (3) is adjusted to ethanol with the same addition amount, and the addition of acetic acid in step (2) is omitted.

[0118] Comparative Example 3

[0119] The difference from Example 1 is only that the addition of acetylacetone in step (1) is omitted, and the addition of acetic acid in step (2) is omitted.

[0120] Comparative Example 4

[0121] The difference from Example 1 is only that the addition of acetylacetone in step (1) is omitted, and the ethylene glycol in steps (1) and (3) is adjusted to ethanol with the same addition amount.

[0122] Comparative Example 5

[0123] The difference from Example 1 is only that the addition of acetylacetone in step (1) is omitted.

[0124] Comparative Example 6

[0125] The difference from Example 1 is only that the addition of acetic acid in step (2) is omitted or replaced with formic acid with the same addition amount, and samples without acid addition and with formic acid addition are obtained respectively.

[0126] Comparative Example 7

[0127] The difference from Example 1 is only that the acetic acid in step (2) is respectively replaced with oxalic acid, malonic acid or citric acid with the same addition amount, and 3 different samples are obtained.

[0128] Comparative Example 8

[0129] The difference from Example 2 is only that the ethylene glycol in steps (1) and (3) is adjusted to ethanol with the same addition amount, and the sol-gel reaction conditions in step (4) are adjusted to keep warm at 75 °C for 12 h.

[0130] Comparative Example 9

[0131] The difference from Example 3 is only that the thermosetting phenolic resin in step (3) is replaced with a thermoplastic phenolic resin containing free phenol with the same addition amount.

[0132] Figure 8 It is a physical picture of the tantalum carbide precursor solution in Comparative Example 2.

[0133] From Figure 8 it can be seen that when only using the complexing agent acetylacetone to modify tantalum n-propoxide, the resulting modified tantalum source reacts with phenolic resin at room temperature to form a solid product, and a precursor solution in which the tantalum source and carbon source can coexist stably cannot be obtained. Due to the influence of steric hindrance, acetylacetone cannot completely replace all alkoxy groups of tantalum n-propoxide, and some highly reactive alkoxy groups remain.

[0134] Figure 9 It is a physical picture of the tantalum carbide precursor solution in Comparative Example 3.

[0135] From Figure 9 it can be seen that when only using ethylene glycol to modify tantalum n-propoxide, the modified tantalum source reacts with phenolic resin at room temperature to form a solid product, and a precursor solution in which the tantalum source and carbon source can coexist stably cannot be obtained. Ethylene glycol reacts with tantalum n-propoxide to form a chelate ring, resulting in a relatively high molecular association, which reduces the reactivity of tantalum n-propoxide. However, this chelate ring is an alkoxy group with low stability, and it is difficult to completely avoid the reaction between tantalum alkoxide and phenolic resin.

[0136] Figure 10 It is a physical picture of the tantalum carbide precursor solution in Comparative Example 4.

[0137] From Figure 10 it can be seen that when only using acetic acid to modify tantalum n-propoxide, the resulting modified tantalum source reacts with phenolic resin at room temperature to form a solid product, and a precursor solution in which the tantalum source and carbon source can coexist stably cannot be obtained. Acetate can form a bidentate ligand with tantalum n-propoxide to reduce the reactivity of tantalum n-propoxide. However, due to the influence of steric hindrance, acetic acid is difficult to completely replace all alkoxy groups of tantalum n-propoxide, and in the absence of water, the self-condensation degree of tantalum n-propoxide is limited, resulting in highly reactive alkoxy groups still existing in the modified tantalum n-propoxide.

[0138] Figure 11 It is a physical picture of the tantalum carbide precursor solutions in Example 1 and Comparative Example 5.

[0139] Figure 11 Among them, the leftmost one is the physical picture of the tantalum carbide precursor solution without the addition of acetylacetone in Comparative Example 5, and the second from the left is the physical picture of the tantalum carbide precursor solution in Example 1.

[0140] From Figure 11It can be seen that when no complexing agent acetylacetone is added and tantalum propoxide is modified only with ethylene glycol and acetic acid, the modified tantalum propoxide reacts violently with phenolic resin at room temperature to form solid products, and the two cannot coexist. When tantalum propoxide is modified with complexing agent acetylacetone, ethylene glycol and acetic acid together, the modified tantalum propoxide and phenolic resin can coexist stably at room temperature.

[0141] Figure 12 It is a physical picture of the tantalum carbide precursor solution in Example 1 and Comparative Example 6.

[0142] Figure 12 Among them, the leftmost and the second left are the physical pictures of the tantalum carbide precursor solution without acid addition and with formic acid addition in Comparative Example 6, and the third left is the physical picture of the tantalum carbide precursor solution in Example 1.

[0143] It can be seen from Figure 12 that when no organic acid is added and tantalum propoxide is modified only with acetylacetone and ethylene glycol, the modified tantalum propoxide reacts with phenolic resin at room temperature to produce precipitation, and the two cannot coexist stably. When tantalum propoxide is modified with acetylacetone, ethylene glycol and formic acid with a boiling point lower than 110°C together, precipitation is generated when the modified tantalum source and carbon source are mixed at room temperature, and they cannot coexist stably. When tantalum propoxide is modified with acetylacetone, ethylene glycol and acetic acid with a boiling point higher than 110°C together, the modified tantalum source and carbon source can coexist stably at room temperature.

[0144] Figure 13 It is a physical picture of the wet gel of the tantalum carbide precursor in Example 1 and Comparative Example 7. Among them, (a), (b) and (c) are Comparative Example 7, and (d) is Example 1.

[0145] It can be seen from Figure 13 that when oxalic acid, malonic acid and citric acid with a decomposition temperature lower than 200°C are added, after high-temperature curing, the obtained wet gel of the tantalum carbide precursor is a mud-like substance without strength and cannot be dried at normal pressure. When acetic acid with a decomposition temperature higher than 200°C is added, after high-temperature curing, the obtained wet gel of the tantalum carbide precursor is a block with certain strength.

[0146] Figure 14 It is a physical picture of the aerogel of the tantalum carbide precursor in Example 2 and Comparative Example 8. Among them, (a) is Comparative Example 8, and (b) is Example 2.

[0147] It can be seen from Figure 14 that when ethanol with a low boiling point is used as the solvent, the obtained tantalum carbide precursor aerogel after curing is difficult to resist the surface tension generated by solvent volatilization, and the aerogel block is severely fragmented after drying at normal pressure. When ethylene glycol with a high boiling point is used as the solvent, the obtained tantalum carbide precursor aerogel after curing can effectively resist the surface tension generated by solvent volatilization, and the aerogel block can still maintain its shape after drying at normal pressure.

[0148] Figure 15 SEM images and XRD patterns of the tantalum carbide ceramic aerogel in Comparative Example 8. Among them, (a) is the SEM image and (b) is the XRD pattern.

[0149] It can be seen from Figure 15 that when polyol is not added and only acetylacetone and acetic acid are used to modify tantalum isopropoxide, the obtained tantalum carbide aerogel has an uneven microstructure, there are a large number of particles with a size above 200 nm, and the phase is impure, with oxide impurities.

[0150] Figure 16 Pictures of the tantalum carbide precursor solutions in Example 3 and Comparative Example 9. Among them, (a) is Comparative Example 9 and (b) is Example 3.

[0151] It can be seen from Figure 16 that when thermoplastic phenolic resin is used as the carbon source, the modified tantalum source and the carbon source react after being mixed at room temperature, resulting in a sludge and it is difficult to coexist stably. When thermosetting phenolic resin is used as the carbon source, the modified tantalum source and the carbon source can coexist stably after being mixed at room temperature, and the mixture remains a transparent liquid.

[0152] The above-described embodiments are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of tantalum carbide ceramic aerogel resistant to ultra-high temperature, characterized in that, It includes the following steps: Mix a complexing agent and tantalum alkoxide in a polyol solvent, stir and react to obtain an alcoholic solution of a tantalum alkoxide complex; Add an organic acid to the alcoholic solution of the tantalum alkoxide complex, catalyze the polymerization to obtain an alcoholic solution of a tantalum alkoxide oligomer; Mix phenolic resin with the alcoholic solution of the tantalum alkoxide oligomer, add a gel catalyst to obtain a tantalum carbide precursor solution, carry out a sol-gel reaction to obtain a wet gel of the tantalum carbide precursor; Carry out a drying treatment on the wet gel of the tantalum carbide precursor to obtain an aerogel of the tantalum carbide precursor, and pyrolyze to obtain the tantalum carbide ceramic aerogel.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the complexing agent to the tantalum alkoxide is 1.2 - 3.2:1; and / or, the complexing agent is any one of acetylacetone, methyl acetoacetate, ethyl acetoacetate and ethyl benzoylacetate; and / or, the mass ratio of the polyol solvent to the tantalum alkoxide is 0.6 - 1.5:1; and / or, the polyol solvent is one or more of ethylene glycol, propylene glycol, butylene glycol and glycerol.

3. The preparation method according to claim 1, characterized in that, The temperature of the stirring reaction is 80 - 120 °C, and the time is 1 - 2 h.

4. The preparation method according to claim 1, characterized in that, The addition amount of the organic acid is 15 - 25% of the mass of the tantalum alkoxide; and / or, the temperature of the catalytic polymerization is 80 - 110 °C, and the time is 1 - 2 h; and / or, the organic acid is one or more of acetic acid, adipic acid, salicylic acid, benzoic acid and terephthalic acid.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the phenolic resin to the amount of substance of the tantalum alkoxide is 154 - 320 g:1 mol; and / or, the phenolic resin is a thermosetting phenolic resin; and / or, the addition amount of the gel catalyst is 10 - 20% of the mass of the tantalum carbide precursor solution; and / or, the gel catalyst is one or more of acetic acid, benzoic acid, salicylic acid and hexamethylenetetramine.

6. The preparation method according to claim 1, characterized in that, The temperature of the sol-gel reaction is 160 - 200 °C, and the time is 10 - 20 h.

7. The preparation method according to claim 1, characterized in that, The drying treatment is to first carry out solvent replacement on the wet gel of the tantalum carbide precursor with ethanol, and then carry out atmospheric drying at 20 - 80 °C for 5 - 48 h.

8. The preparation method according to claim 1, wherein, The temperature of the pyrolysis is 1300 - 1500 °C, and the time is 1 - 2 h.

9. A tantalum carbide ceramic aerogel with ultra-high temperature resistance obtained by the preparation method according to any one of claims 1 - 8.

10. An application of the tantalum carbide ceramic aerogel with ultra-high temperature resistance according to claim 9 in the field of high-temperature thermal insulation materials.

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