Heat prevention and insulation integrated porous ceramic composite material and preparation method thereof

Abstract

The invention relates to a heat prevention and insulation integrated porous ceramic composite material and a preparation method thereof. The porous ceramic composite material is composed of a silicon carbide fiber felt, a (BN / SiC) n composite interface layer wrapping silicon carbide fibers, a SiCO porous ceramic matrix and a heat-proof coating, and the heat-proof coating is composed of a hole sealing layer and a compact layer; according to the heat prevention and heat insulation integrated porous ceramic composite material, a stable ablation-resistant oxidation ceramic layer can be formed on the surface within the temperature range of 800-1800 DEG C, meanwhile, the internal SiCO porous ceramic achieves the heat insulation function, and the heat prevention and heat insulation integrated function under the conditions of medium and low heat flux density and weak scouring is achieved; compared with an existing low-density heat-proof and heat-insulation material, the heat-proof and heat-insulation material is more excellent in oxidation resistance and ablation resistance, and the optimal use temperature can be designed; the material can realize integration of heat insulation and heat prevention functions, and is suitable for a large-area thermal protection material in a medium-low heat flow environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of porous ceramic composites, and particularly relates to a heat insulation and heat prevention integrated porous ceramic composite material and a preparation method thereof. Background Art

[0002] The Toughened Uni-piece Fibrous Reinforced Oxidation-resistant Composite (TUFROC) consists of a heat protection cap with a gradient coating on the surface and an internal heat insulation matrix. Among them, the internal heat insulation material is the ceramic fiber rigid heat insulation tile AETB, which has a very low thermal conductivity; the heat protection cap is composed of a refractory oxidation resistant ceramics carbon insulation (ROCCI). ROCCI is prepared by impregnating short carbon fibers with a SiCO ceramic precursor and pyrolyzing at high temperature in an inert environment. Its cooperation with the surface coating enables TUFROC to have good high-temperature stability. TUFROC has many advantages such as low density, high temperature resistance, good mechanical properties, reusability, short manufacturing cycle, and low cost, and the temperature that the outer surface can withstand reaches about 1700°C. At the same time, TUFROC also overcomes the brittleness problem of a simple ceramic heat insulation tile and has excellent oxidation resistance and thermal shock resistance, and is a new type of lightweight heat insulation and heat prevention integrated material. However, for ROCCI with short carbon fibers as the skeleton, since carbon is easily oxidized (the initial oxidation temperature is 450°C) and the thermal conductivity of carbon fibers is strong, it is necessary to modify the surface of the carbon fibers with an oxidation-resistant coating, which undoubtedly increases the process complexity. Silicon carbide fibers have the advantage of high oxidation resistance temperature (1300°C). Replacing carbon fibers with them will further improve the oxidation resistance, heat insulation performance, and temperature resistance of ROCCI.

[0003] CN118003709A discloses a silicon carbide fiber felt laminate with adjustable high strength electrical properties and a preparation method thereof. However, the silicon carbide fiber felt used therein has a low oxidation resistance temperature and low skeleton strength because gaseous silica powder is incorporated as a dispersant during the preparation process and there are few overlapping sites between the short silicon carbide fibers. Summary of the Invention

[0004] Aiming at the deficiencies of the short carbon fiber skeleton used in the existing ROCCI, such as poor oxidation resistance, high thermal conductivity, short service life, and weak ablation resistance of the heat protection layer, the first object of the present invention is to provide a preparation method of a heat insulation and heat prevention integrated porous ceramic composite material.

[0005] The second object of the present invention is to provide a porous ceramic composite material with integrated anti-heat and heat insulation functions. The porous ceramic composite material with integrated anti-heat and heat insulation functions provided by the present invention can form a stable ablation-resistant oxidation ceramic layer on the surface in the temperature range of 800-1800 °C. At the same time, the internal SiCO porous ceramic realizes the heat insulation function, achieving the integrated anti-heat and heat insulation function under medium and low heat flux density and weak erosion conditions.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a preparation method of a porous ceramic composite material with integrated anti-heat and heat insulation functions. After degumming the silicon carbide fiber felt, the degummed silicon carbide fiber felt is obtained. The degummed silicon carbide fiber felt is first subjected to surface pre-oxidation treatment, and then treated with an acidic liquid medium to obtain a pretreated silicon carbide fiber felt. Then, a (BN / SiC) n composite interface layer is deposited on the surface of the pretreated silicon carbide fiber felt to obtain a self-supporting silicon carbide fiber skeleton. The self-supporting silicon carbide fiber skeleton is impregnated in a SiCO ceramic precursor, and a wet gel felt is formed through gelation and aging. The wet gel felt is then dried and pyrolyzed to obtain a porous ceramic composite material, and multiple anti-heat coatings are provided on the surface of the porous ceramic composite material to obtain the product.

[0008] For the porous ceramic composite material of the present invention, after degumming the silicon carbide fiber felt, the surface pre-oxidation treatment is first carried out on it to completely or partially eliminate the carbon existing on the fiber surface, and all or part of the carbon oxides containing elements Si, O, and C existing on the fiber surface are converted into silicon dioxide. Then, the silicon dioxide is washed and removed with an acidic liquid medium to obtain silicon carbide fibers with a pure surface, which is beneficial to the deposition of the composite interface. Then, a supporting silicon carbide fiber skeleton is obtained by depositing a (BN / SiC) n composite interface layer. The self-supporting silicon carbide fiber skeleton is impregnated in a SiCO ceramic precursor, and a wet gel felt is formed through gelation and aging. The wet gel felt is then dried and pyrolyzed to obtain a porous ceramic composite material, and multiple anti-heat coatings are provided on the surface of the porous ceramic composite material to prepare a porous ceramic composite material with integrated anti-heat and heat insulation functions.

[0009] Preferably, the thickness of the silicon carbide fiber felt is 0.5-200 mm.

[0010] Preferably, the density of the silicon carbide fiber felt is 0.05-0.085 g / cm 3 .

[0011] Preferably, the silicon carbide fiber felt is obtained by wet forming of chopped silicon carbide fibers, and the length of the chopped silicon carbide fibers is 4-15 mm. The inventor found that the silicon carbide fiber felt with high porosity, low density and strong heat resistance can be obtained by wet forming of the chopped silicon carbide fibers with the above length. If the fibers are too long, the isotropy of the silicon carbide fiber felt will be reduced, and if the fibers are too short, the ability of the fiber skeleton to overlap and form self-support will be reduced.

[0012] The inventor found that it is crucial to use the silicon carbide fiber felt obtained by wet forming of chopped silicon carbide fibers as the raw material. If the silicon carbide fiber felt is prepared by the method of first forming and then sintering the polycarbosilane precursor pre-oxidized fiber, volume shrinkage and pore collapse are likely to occur, and it does not have the characteristics of low density, controllable pore structure and grammage, and cannot be used as a skeleton connecting material.

[0013] Preferably, the silicon carbide fiber felt is degummed by soaking in acetone or oxidizing in air atmosphere at 500-650 °C for 1-1.5 h.

[0014] Preferably, the pre-oxidation treatment process is to heat-treat the degummed silicon carbide fiber felt in air, the temperature of the heat treatment is 650 °C - 1000 °C, and the time of the heat treatment is 1-2 h.

[0015] Preferably, the treatment time of the acidic liquid medium is 10-60 min.

[0016] Further preferably, the acidic liquid medium is a mixed aqueous solution containing hydrofluoric acid and nitric acid. In the mixed aqueous solution, the mass fraction of dissolved HF is 4 wt% - 8 wt%, and the concentration of nitric acid is 0.5-5 mol / L.

[0017] After pretreatment, a silicon carbide fiber felt (SiC f -O-HF) suitable for deposition is obtained.

[0018] Preferably, the interface layer is a (BN / SiC) n composite interface, where n≥1, preferably 2-4.

[0019] Further preferably, in the (BN / SiC) n composite interface, the total thickness of BN is 150-650 nm, and the total thickness of SiC is 50-500 nm.

[0020] Controlling the total thickness of BN and the total thickness of SiC within the scope of the present invention, such that the relative ratio of BN and SiC is within the above-mentioned range, the final performance is optimal. Because when the BN / SiC composite interface oxidizes at high temperature, a borosilicate glass phase will be formed, which can play a role in self-healing cracks. The self-healing effect is determined by the relative ratio of BN and SiC. On the one hand, in terms of the thickness of the interface, when BN is less (i.e., the thickness of BN is thinner), BN can react with silicon carbide fibers and at the BN and SiC interface in a timely manner to form borosilicate to block cracks; when BN is more (i.e., the thickness of BN is thicker), in an oxygen environment, especially in a water-oxygen environment, B 2 O 3 will form volatile substances HxByOz, leading to an increase in the gasification of oxidation products, and the borosilicate formed by the reaction at the BN and silicon carbide fibers and the BN and SiC interface cannot block cracks in a timely manner. On the other hand, from the perspective of the composition of borosilicate, when the content of B element is low, the viscosity of the formed borosilicate is low and the oxygen permeability is high, which is beneficial for blocking cracks but not for antioxidation. When the B element is higher, the viscosity of the formed borosilicate is high and the oxygen permeability is low, which is beneficial for antioxidation but not for blocking cracks.

[0021] Further preferably, the process for obtaining the (BN / SiC) n composite interface is as follows: By chemical vapor deposition, deposit the BN layer, heat treatment, and deposit the SiC layer in sequence cyclically;

[0022] During the deposition process of the BN layer, the flow rate of boron trichloride (BCl 3 ) is 1 - 3 L / min, the flow rate of ammonia (NH 3 ) is 3 - 7 L / min, the flow rate of hydrogen (H 2 ) is 3 - 4.8 L / min, the flow rate of argon (Ar) is 3 - 6 L / min. Control the pressure in the deposition furnace to be 0.5 - 4 kPa, the deposition temperature to be 650°C - 1050°C, and the single-layer deposition time to be 15 - 30 min;

[0023] The heat treatment is carried out in a vacuum environment, the heat treatment temperature is 1000 - 1200°C, and the heat treatment time is 1 - 2 h;

[0024] During the deposition process of the SiC layer, control the flow rate of trichloromethylsilane (CH 3 SiCl 3 ) to be 1 - 3 L / min, the flow rate of hydrogen (H 2 ) to be 1 - 2 L / min, and the flow rate of argon (Ar) to be 1.5 - 2.5 L / min; the pressure in the furnace is 0.5 - 4 kPa, the deposition temperature is 1000 - 1100°C, and the single-layer deposition time is 20 - 40 min.

[0025] More preferably, the (BN / SiC) n in the composite interface, the BN layer is successively composed of a BN 1 layer and a BN 2 layer. The BN 1 is isotropic BN, and the BN 2 is anisotropic BN.

[0026] When the BN layer is successively composed of a BN 1 layer and a BN 2 layer, the BN 1 can protect the chopped silicon carbide fibers from oxidation, and the outer BN 2 can achieve crack deflection and play a toughening role, making the comprehensive performance of the material better.

[0027] Even more preferably, during the deposition process of the BN 1 layer, the flow rate of boron trichloride (BCl 3 ) is 1 - 3 L / min, the flow rate of ammonia (NH 3 ) is 3 - 7 L / min, the flow rate of hydrogen (H 2 ) is 3 - 4.8 L / min, the flow rate of argon (Ar) is 3 - 6 L / min. Control the pressure in the deposition furnace to be 0.5 - 4 kPa, the deposition temperature to be 650 °C - 750 °C, and the single-layer deposition time to be 15 - 30 min. During the deposition process of the BN 2 layer, the flow rate of boron trichloride (BCl 3 ) is 1 - 3 L / min, the flow rate of ammonia (NH 3 ) is 3 - 7 L / min, the flow rate of hydrogen (H 2 ) is 3 - 4.8 L / min, the flow rate of argon (Ar) is 3 - 6 L / min. Control the pressure in the deposition furnace to be 0.5 - 4 kPa, the deposition temperature to be 850 °C - 1050 °C, and the single-layer deposition time to be 15 - 30 min.

[0028] When the BN layer is successively composed of a BN 1 layer and a BN 2 layer, heat treatment is carried out after the deposition of the BN 2 layer is completed.

[0029] In a preferred embodiment, the SiCO precursor sol is prepared by an acid-base two-step catalysis method.

[0030] Further preferably, the preparation process of the SiCO precursor sol is as follows: Using silane A and silane B together as raw materials, adding them into an ethanol aqueous solution, then adding a nitric acid solution as an acid catalyst, stirring and then sealing and standing still, so that silane A and silane B are fully hydrolyzed under acidic conditions to obtain a standing solution; Then slowly add a mixed solution of ethanol and ammonia water into the standing solution, and stir evenly to make it undergo a polycondensation reaction under alkaline conditions to obtain the SiCO precursor sol;

[0031] The silane A is methyltrimethoxysilane (MTMS), and the silane B is dimethyldiethoxysilane (DMDES), or the silane A is methyltrimethoxysilane and the silane B is dimethyldimethoxysilane.

[0032] In the actual operation process, the SiCO precursor sol can also be obtained by using two SiOC ceramic precursors, polymethylhydrogensiloxane (PHMS) and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (TMTV), and undergoing an addition reaction of C═C / Si-H bonds under the catalysis of Pt, or by mixing hydrogen-containing polymethylsiloxane, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, chloroplatinic acid and acetone evenly and then placing them in a hydrothermal reaction kettle for reaction.

[0033] In a preferred scheme, the impregnation is vacuum impregnation, and the time of the vacuum impregnation is 1 to 2 h. In the actual operation process, the impregnation process is to place the SiCO precursor sol in an impregnation tank, immerse the self-supporting silicon carbide fiber skeleton into the impregnation tank, the SiCO precursor sol submerges the self-supporting silicon carbide fiber skeleton, and negative pressure makes the SiCO precursor sol immerse into the fiber felt, and the SiCO precursor sol combined with the fiber felt in the impregnation tank gels to form SiC f / BN / SiC-SiCO wet gel felt.

[0034] In a preferred scheme, the aging temperature is 65 °C to 75 °C, and the aging time is 1 to 3 days.

[0035] In the actual operation process, put the SiC f / BN / SiC-SiCO wet gel felt into an aging tank in a sealed manner, gel and age at 65 °C to 75 °C for a total of 1 to 3 days to make the gel fully undergo a polycondensation reaction.

[0036] In a preferred scheme, the drying process is to dissolve and displace the ethanol in the wet gel felt through supercritical CO 2 to obtain it.

[0037] Preferably, the pyrolysis is carried out under a protective atmosphere. The pyrolysis temperature is 1000 - 1200 °C, the pyrolysis time is 1 - 2 h, and the heating rate is 2 - 5 °C / min. By controlling the heating rate between 2 - 5 °C / min and the pyrolysis temperature between 1000 - 1200 °C, it is possible to prevent pore collapse caused by excessive shrinkage stress during the pyrolysis of the ceramic precursor polymer.

[0038] During the actual operation process, the obtained SiC f / BN / SiC - SiCO ceramic precursor is placed in a pyrolysis furnace. After evacuating the air, argon is filled, and pyrolysis is carried out at 1000 - 1200 °C for 1 h under an inert atmosphere according to the set heating program. After natural cooling to room temperature, the porous ceramic composite material is obtained.

[0039] Preferably, the self - supporting silicon carbide fiber skeleton is impregnated in the SiCO ceramic precursor, and after gelation and aging, a wet gel felt is formed. The wet gel felt is then dried and pyrolyzed; then the impregnation - aging - drying - pyrolysis cycle is repeated, and the number of cycles is 1 - 4 times.

[0040] Preferably, the surface layer of 1 - 3 mm of the porous ceramic composite material is subjected to a selective treatment with a hydrophilic coupling agent first, and then multiple layers of thermal insulation coatings are provided.

[0041] Further preferably, the process of the selective treatment with the hydrophilic coupling agent is as follows: The porous ceramic composite material is lifted by hoisting, and the surface layer of 1 - 3 mm of the porous ceramic composite material is immersed in a hydrophilic silane coupling agent solution, then the immersed part is subjected to ultrasonic hydrolysis reaction for 1 - 3 h, and finally dried to obtain the product.

[0042] Even more preferably, the solvent in the silane coupling agent solution is a mixed solvent of ethanol and water, and the mass ratio of ethanol to water is 9 - 12:1;

[0043] Even more preferably, in the silane coupling agent solution, the mass fraction of the silane coupling agent is 4 - 6%;

[0044] Even more preferably, the silane coupling agent is selected from at least one of γ - aminopropyltriethoxysilane, γ - (2,3 - epoxypropoxy)propyltrimethoxysilane, and γ - methacryloxypropyltrimethoxysilane.

[0045] By immersing the surface layer of 1 - 3 mm of the porous ceramic composite material in the hydrophilic coupling agent and controlling the immersion depth during hoisting, the modification depth of the coupling agent is controlled, so that the immersed part is hydrophilic while the other part is hydrophobic, thereby controlling the depth range of the coating slurry entering the porous material, and enabling the coating to be only compounded on the surface of the porous ceramic composite material and showing a gradient distribution, thus effectively avoiding the increase in the density and thermal conductivity of the thermal insulation material.

[0046] In a preferred embodiment, the process of setting a multi-layer thermal protection coating on the surface of the porous ceramic composite material is as follows: The porous ceramic composite material is hoisted, and the surface layer of 1-3 mm in the porous ceramic composite material is immersed in the sealant coating slurry. After drying, pre-oxidation sintering is carried out. Then, the dense layer slurry is painted on the surface of the porous ceramic composite material, and then sintered to obtain. The temperature of the pre-oxidation sintering is 1350-1500 °C, the time is 10-40 min, the sintering temperature is 1350-1500 °C, and the time is 40-90 min.

[0047] On the one hand, the multi-layer thermal protection coating is beneficial to reducing the thermal mismatch between the matrix material and the coating and effectively relieving the thermal stress; on the other hand, it is difficult for a single-layer coating to meet the service environment of current aircraft. Therefore, in the present invention, a composite multi-layer coating is set. First, the SiC f / BN / SiC-SiCO porous ceramic composite material is hoisted in the sealant coating slurry, and only the surface layer of 1-3 mm is immersed. The slurry enters the porous composite material through capillary force and forms a gradient distribution. Then, a dense layer coating is set on its surface to play the function of anti-ablation.

[0048] Further preferably, the sealant coating slurry is obtained by adding molybdenum silicide, SiC whiskers, and borosilicate glass to the ceramic precursor slurry; the solid content of the sealant coating slurry is 20-40%; in the solid phase of the sealant coating slurry, by volume percentage, SiC whiskers are 1-5 vol%, molybdenum silicide is 40-60 vol%, and borosilicate glass is 35-59 vol%;

[0049] The dense layer slurry is obtained by adding ultra-high temperature ceramics, SiC whiskers, molybdenum silicide, and borosilicate powder to the ceramic precursor slurry. The solid content of the dense layer slurry is 20-40%. In the solid phase of the dense layer slurry, by volume percentage, SiC whiskers are 1-5 vol%, molybdenum silicide is 40-60 vol%, ultra-high temperature ceramics are 5-25 vol%, and borosilicate glass is 20-54 vol%;

[0050] The ceramic precursor slurry is composed of a ceramic precursor and xylene, and the volume fraction of xylene in the ceramic precursor slurry is 10-50 vol%;

[0051] The ceramic precursor is selected from at least one of polycarbosilane, polysilazane, polyhafnosilane, and polyborosilane;

[0052] The ultra-high temperature ceramics are selected from at least one of hafnium carbide, zirconium carbide, hafnium boride, and zirconium boride.

[0053] In the present invention, the hole-sealing coating slurry is obtained by dissolving three solid-phase components, namely molybdenum silicide, SiC whiskers, and borosilicate glass, in a ceramic precursor slurry. After impregnation, it is pre-oxidized and sintered in an oxygen-containing atmosphere to form a dense hole-sealing layer. Among them, silicides such as molybdenum silicide can form silicon dioxide oxide at about 1000 °C, thereby playing a role in forming an oxide layer. The addition of SiC whiskers, on the one hand, improves the interfacial bonding strength between the coating and the porous ceramic and can effectively prevent the coating from cracking. On the other hand, it also forms a silicon dioxide oxide layer in an oxidation environment to protect the substrate. Borosilicate glass has a low oxygen diffusion rate and can form a liquid with a certain fluidity at high temperatures, which can play a self-healing role.

[0054] The dense layer slurry is obtained by adding three solid-phase components, namely ultra-high temperature ceramics, SiC whiskers, and borosilicate glass powder, to a ceramic precursor slurry. The dense layer mainly plays a role in heat protection. Using the synergistic mechanism of ultra-high temperature ceramics and borosilicate glass, the ultra-high temperature oxide skeleton formed after the ultra-high temperature ceramics are oxidized can resist the erosion of high-temperature ablation gas flow. The liquid borosilicate glass between the ultra-high temperature ceramic skeletons has a low oxygen diffusion rate and can form a liquid oxide with a certain fluidity at high temperatures, which can form a sealed oxide layer phase between the ultra-high temperature ceramic skeletons and play a role in self-healing cracks. In addition, SiC whiskers are incorporated into the slurry in the present invention. The addition of SiC whiskers, on the one hand, improves the interfacial bonding strength between the dense coating and the hole-sealing coating and can effectively prevent the coating from cracking. On the other hand, it also forms a silicon dioxide oxide layer in an oxidation environment to protect the substrate.

[0055] Further preferably, the particle size of the ultra-high temperature ceramics is 20 nm to 800 nm. In the actual operation process, the selection of the particle size of the ultra-high temperature ceramics is determined by the pore distribution on the surface of the porous ceramic composite material. The size of the ceramic particles should match the pore size to facilitate the formation of an infiltration area with a controllable thickness and form a gradient distribution, which can effectively alleviate the coating peeling caused by the mismatch of thermal expansion coefficients.

[0056] Further preferably, the volume content of boron in the borosilicate glass in the dense layer slurry and the hole-sealing coating slurry is 20 to 40 vol%. Using borosilicate glass with a boron content of 20 to 40 vol% as the glass phase in the coating has the best antioxidant performance.

[0057] The present invention also provides a heat-insulating and heat-protecting integrated porous ceramic composite material prepared by the above preparation method. The porous ceramic composite material is composed of a silicon carbide fiber felt, an (BN / SiC) n interface layer wrapping the silicon carbide fiber, a SiCO porous ceramic matrix, and a heat-protecting coating. The heat-protecting coating is composed of a hole-sealing layer and a dense layer.

[0058] In the integrated anti - heat - insulation porous ceramic composite material provided by the present invention, the skeleton is a silicon carbide fiber felt deposited with an interface layer, which plays the role of antioxidant and toughening; the SiCO porous ceramic matrix plays the role of improving antioxidant and heat - insulation properties; the anti - heat layer is an ultra - high - temperature ceramic - SiC whisker - borosilicate, which mainly plays the function of anti - ablation.

[0059] The technical solution provided by the present invention has the following beneficial effects compared with the prior art:

[0060] The integrated anti - heat - insulation porous ceramic composite material of the present invention can form a stable anti - ablation oxidation ceramic layer on the surface in the temperature range of 800 - 1800 °C. At the same time, the internal SiCO porous ceramic realizes the heat - insulation function, achieving the integrated function of anti - heat and heat - insulation under the conditions of medium - low heat - flux density and weak erosion; compared with the existing low - density anti - heat - insulation materials, it has more excellent antioxidant and anti - ablation properties, and the optimal use temperature can be designed; moreover, the material can realize the integration of anti - heat and heat - insulation functions and is suitable for large - area thermal protection materials in medium - low heat - flux environments. Brief Description of the Drawings

[0061] Figure 1 The morphology of the integrated anti - heat - insulation porous ceramic composite material after ablation in Example 1.

[0062] Figure 2 The microscopic morphology of the integrated anti - heat - insulation porous ceramic composite material after ablation in Example 2.

[0063] Figure 3 The morphology diagram of the porous silicon carbide fiber felt containing a BN / SiC composite interface in Example 3.

[0064] Figure 4 The macroscopic morphology of the integrated anti - heat - insulation porous ceramic composite material after ablation in Example 3.

[0065] Figure 5 The microscopic morphology of the integrated anti - heat - insulation porous ceramic composite material after ablation in Example 3.

[0066] Figure 6 The microscopic morphology of the integrated anti - heat - insulation porous ceramic composite material after ablation in Example 4.

[0067] From the above microscopic images, it can be clearly seen that the white phase is the ultra - high - temperature phase and the gray phase is the borosilicate glass phase. Due to the different proportions of the two, the surface morphology after ablation is different. The more the ultra - high - temperature ceramic phase, the stronger the ability to resist ablation and erosion, and the more the borosilicate glass phase, the stronger the antioxidant ability. Detailed Embodiments

[0068] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0069] Example 1

[0070] This embodiment provides a method for preparing an integrated heat-insulating and heat-proof porous ceramic composite material, including the following steps:

[0071] (1) Prepare a SiCO precursor sol: First, use methyltrimethoxysilane (MTMS) and dimethyldiethoxysilane (DMDES) together as raw materials and mix them in an ethanol-aqueous solution; then add a 0.1 mol / L nitric acid solution as an acid catalyst, stir for 30 min and then seal and stand for 3 h to allow MTMS and DMDES to hydrolyze fully under acidic conditions; then slowly add a mixed solution of ethanol and 1 mol / L ammonia water to the above standing solution and stir evenly for 20 min to cause a polycondensation reaction under alkaline conditions to obtain a SiCO precursor sol;

[0072] (2) Prepare a silicon carbide fiber felt with a BN / SiC composite interface: First, cut short the silicon carbide fibers to a length of 4 mm, a thickness of 10 mm, and a density of 0.05 g / cm 3 of the silicon carbide fiber felt and treat it in a muffle furnace at 500 °C for 1 h to remove the sizing agent on the surface, then pre-oxidize the degummed silicon carbide fiber felt at 650 °C for 1 h, and finally place the pre-oxidized silicon carbide fiber felt in an acidic medium (a mixed aqueous solution of hydrofluoric acid and nitric acid, where the mass fraction of dissolved HF is 4 wt% and the concentration of nitric acid is 3 mol / L) and treat it for 1 h to obtain a silicon carbide fiber felt for deposition (SiC f -O-HF). Place the treated silicon carbide fiber felt (SiC f -O-HF) in a chemical vapor infiltration furnace to deposit a boron nitride / silicon carbide composite interface BN / SiC to obtain a silicon carbide fiber felt with a BN / SiC composite interface (SiC f / BN / SiC). During the deposition process of the BN layer, the flow rate of boron trichloride (BCl 3 ) is 1 L / min, and the flow rate of ammonia gas (NH 3 ) is 3 L / min, and the flow rate of hydrogen gas (H 2) The flow rate of [substance] is 3 L / min, the flow rate of argon (Ar) is 3 L / min, the pressure inside the deposition furnace is controlled at 0.5 kPa, the deposition temperature is 650 °C, and the single-layer deposition time is 20 min; after the single-layer BN layer deposition is completed, heat treatment is carried out in a vacuum environment, the heat treatment temperature is 1100 °C, and the heat treatment time is 1 h;

[0073] During the deposition process of the SiC layer, control the flow rate of trichloromethylsilane (CH 3 SiCl 3 ) to be 1 L / min, the flow rate of hydrogen (H 2 ) to be 1 L / min, and the flow rate of argon (Ar) to be 1.5 L / min; the pressure inside the furnace is 0.5 kPa, the deposition temperature is 1000 °C, and the single-layer deposition time is 20 min. BN and SiC are each deposited once, and the thickness of the obtained BN interface is 191 nm, and the thickness of the SiC interface is 87 nm.

[0074] (3) Impregnation, gelation, and aging: Immerse SiC f / BN / SiC in the SiCO precursor sol, keep it under vacuum for 1 h to obtain the SiC f / BN / SiC-SiCO sol complex gel, and then age the sol complex gel at 75 °C for 3 days to allow the gel to fully undergo polycondensation reaction and ensure the strength of its skeleton structure.

[0075] (4) Drying: Dissolve and displace the ethanol in the obtained SiC / BN / SiC-SiCO wet gel with supercritical CO 2 to obtain the SiC f / BN / SiC-SiCO ceramic precursor. f / BN / SiC-SiCO ceramic precursor.

[0076] (5) Pyrolysis: Place the SiC f / BN / SiC-SiCO ceramic precursor in a pyrolysis furnace, evacuate and then fill with argon, and carry out pyrolysis at 1000 °C for 1 h under an inert atmosphere according to the set heating program. After naturally cooling to room temperature, take out the sample. The number of cycles of SiCO precursor sol impregnation - aging - drying - pyrolysis is 1 time to obtain the SiC f / BN / SiC-SiCO porous ceramic composite.

[0077] (6) SiC fThe surface of the / BN / SiC-SiCO porous ceramic composite material is subjected to selective hydrophilic treatment, and the surface layer of the porous ceramic composite material with a thickness of 1 mm is immersed in γ-aminopropyltriethoxysilane (KH-550). Due to the hydrophilicity of the surface of the porous ceramic composite material, the slurry mixed with the ceramic precursor and the nano-ultrahigh temperature ceramic powder can be effectively prevented from entering the porous material, so that the coating matrix is ​​only compounded on the surface of the porous ceramic composite material, thereby effectively avoiding the increase of the density of the thermal insulation material and the increase of the thermal conductivity.

[0078] (7) Preparation of heat-resistant coating: It is divided into the preparation of surface sealing layer and dense layer. First, SiC f / BN / SiC-SiCO porous ceramic composite material is hoisted, and the surface layer of 1mm of the porous ceramic composite material is immersed in the sealing coating slurry, wherein the sealing coating slurry is obtained by adding molybdenum silicide, SiC whisker and borosilicate glass into the ceramic precursor slurry, and the solid phase content of the sealing coating slurry is 35%, and the volume content of SiC whisker in the solid phase is 1vol%, the volume content of molybdenum silicide is 40vol%, and the volume content of borosilicate glass is 59vol%. After the impregnation is completed, the composite material is dried at 25°C for 24h, and then pre-oxidized and sintered at a temperature of 1350°C for 10min, and then the dense layer slurry is brushed on the surface of the porous ceramic composite material. The dense layer slurry is obtained by adding zirconium boride with a particle size of 200nm, SiC whiskers, and borosilicate powder into polycarbosilane slurry. The solid phase content of the dense layer slurry is 35%. In the solid phase, the volume content of SiC whiskers is 1vol%, the volume content of ultra-high temperature ceramics is 5vol%, the volume content of molybdenum silicide is 40vol%, and the volume content of borosilicate glass is 54vol%. The above-mentioned ceramic precursor slurries are all composed of ceramic precursors and xylene, wherein the volume fraction of xylene in the ceramic precursor slurry is 20vol.%. After the coating is completed, it is sintered (sintering temperature 1350°C, time 40min) to obtain a heat-insulating integrated porous ceramic composite material.

[0079] The thermal insulation integrated porous ceramic composite material obtained in this embodiment was subjected to an ablation test at a high temperature of 1600°C using an oxyacetylene flame method. The morphology after ablation is as follows: Figure 1 shown.

[0080] Example 2

[0081] This embodiment provides a method for preparing a thermal insulation integrated porous ceramic composite material, comprising the following steps:

[0082] (1) Preparation of SiCO precursor sol: First, methyltrimethoxysilane and dimethyldiethoxysilane are used as raw materials together and mixed in an ethanol-water solution. Then, a 0.5 mol / L nitric acid solution is added as an acid catalyst, and after stirring for 30 min, it is sealed and left standing for 1 h to allow methyltrimethoxysilane and dimethyldiethoxysilane to hydrolyze fully under acidic conditions. Then, a mixed solution of ethanol and 0.5 mol / L ammonia water is slowly added to the above standing solution, and stirred evenly for 30 min to cause a polycondensation reaction under alkaline conditions, obtaining the SiCO precursor sol;

[0083] (2) Preparation of silicon carbide fiber felt with a BN / SiC composite interface: First, the chopped silicon carbide fibers with a length of 6 mm, a thickness of 20 mm, and a density of 0.05 g / cm 3 are degummed at 500 °C for 1 h to remove the sizing agent on the surface. Then, the silicon carbide fiber felt is pre-oxidized at 850 °C for 1 h. Finally, the pre-oxidized silicon carbide fiber felt is placed in an acidic medium (a mixed aqueous solution of hydrofluoric acid and nitric acid, where the mass fraction of dissolved HF is 5 wt%, and the concentration of nitric acid is 2 mol / L) for 1 h to obtain the silicon carbide fiber felt for deposition (SiC f -O-HF). The treated silicon carbide fiber felt (SiC f -O-HF) is placed in a chemical vapor infiltration furnace to deposit a boron nitride / silicon carbide composite interface BN / SiC, obtaining a silicon carbide fiber felt with a BN / SiC composite interface (SiC f / BN / SiC). During the deposition process of the BN layer, the flow rate of boron trichloride (BCl 3 ) is 2 L / min, the flow rate of ammonia (NH 3 ) is 7 L / min, the flow rate of hydrogen (H 2 ) is 4.2 L / min, and the flow rate of argon (Ar) is 5 L / min. The pressure inside the deposition furnace is controlled at 1.0 kPa, the deposition temperature is 850 °C, and the single-layer deposition time is 25 min. After the single-layer BN layer deposition is completed, heat treatment is carried out in a vacuum environment. The heat treatment temperature is 1100 °C, and the heat treatment time is 1.5 h;

[0084] During the deposition process of the SiC layer, the flow rate of trichloromethylsilane (CH 3 SiCl 3 ) is controlled at 2 L / minL / min, the flow rate of hydrogen (H 2 ) is 2 L / min, and the flow rate of argon (Ar) is 2.5 L / min; the pressure inside the furnace is 2 kPa, the deposition temperature is 1100 °C, and the single-layer deposition time is 20 min. BN and SiC are each deposited once. The thickness of the obtained BN interface is 250 nm, and the thickness of the SiC interface is 150 nm.

[0085] (3) Impregnation, gelation, and aging: Immerse SiC f / BN / SiC in the SiCO precursor sol, evacuate and hold for 1 h to obtain the SiC f / BN / SiC-SiCO sol complex gel. Then age the sol complex gel at 60 °C for 2 days to allow sufficient polycondensation reaction of the gel and ensure the strength of its framework structure.

[0086] (4) Drying: The obtained SiC f / BN / SiC-SiCO wet gel is dried by supercritical CO 2 to dissolve and displace ethanol in the SiC f / BN / SiC-SiCO wet gel to obtain the SiC f / BN / SiC-SiCO ceramic precursor.

[0087] (5) Pyrolysis: Place the SiC f / BN / SiC-SiCO ceramic precursor in a pyrolysis furnace, evacuate and then fill with argon. Carry out pyrolysis at 1200 °C for 1 h under an inert atmosphere according to the set heating program. After naturally cooling to room temperature, take out the sample. Repeat the cycle of SiCO precursor sol impregnation - aging - drying - pyrolysis 2 times to obtain the SiC f / BN / SiC-SiCO porous ceramic composite.

[0088] (6) Selective hydrophilic treatment of the surface of the SiC f / BN / SiC-SiCO porous ceramic composite is carried out so that the surface layer 2 mm of the porous ceramic composite is impregnated with γ-methacryloxypropyltrimethoxysilane. Since the hydrophilicity of the surface of the porous ceramic composite can effectively prevent the slurry composed of the ceramic precursor and the nano ultra-high temperature ceramic powder from entering the porous material, the coating matrix is only compounded on the surface of the porous ceramic composite, thereby effectively avoiding the increase in the density and thermal conductivity of the thermal insulation material.

[0089] (7) Preparation of the thermal protection coating: It is divided into the preparation of the surface sealing layer and the dense layer. First, the SiC fLifting of the / BN / SiC-SiCO porous ceramic composite material, dipping the surface layer of 2 mm in the porous ceramic composite material into the sealing hole coating slurry, wherein the sealing hole coating slurry is obtained by adding molybdenum silicide, SiC whiskers, and borosilicate glass to the ceramic precursor slurry. The solid content of the sealing hole coating slurry is 25%. In its solid phase, the volume content of SiC whiskers is 2 vol%, the volume content of molybdenum silicide is 50 vol%, and the volume content of borosilicate glass is 48 vol%. After dipping, the composite material is dried at 25 °C for 24 h. After drying, pre-oxidation sintering is carried out at a temperature of 1350 °C for 20 min. Then, the dense layer slurry is brushed on the surface of the porous ceramic composite material. The dense layer slurry is obtained by adding hafnium boride with a particle size of 200 nm, SiC whiskers, and borosilicate powder to the polycarbosilane slurry. The solid content of the dense layer slurry is 25%. In the solid phase, the volume content of SiC whiskers is 2 vol%, the volume content of ultra-high temperature ceramics is 10 vol%, the volume content of molybdenum silicide is 50 vol%, and the volume content of borosilicate glass is 38 vol%. The ceramic precursor slurry is composed of a ceramic precursor and xylene, wherein the volume fraction of xylene in the ceramic precursor slurry is 30 vol.%. Then, sintering (sintering temperature: 1350 °C, time: 50 min) is carried out to obtain the product.

[0090] For the integrated thermal insulation and ablation-resistant porous ceramic composite material obtained in this example, at a high temperature of 1600 °C, the oxyacetylene flame method is used to carry out an ablation test on it. The microscopic morphology after ablation is as Figure 2 shown.

[0091] Example 3

[0092] This example provides a preparation method for an integrated thermal insulation and ablation-resistant porous ceramic composite material, including the following steps:

[0093] (1) Preparation of SiCO precursor sol: First, use methyltrimethoxysilane and dimethyldiethoxysilane as raw materials and mix them in an ethanol-aqueous solution; then add a 0.2 mol / L nitric acid solution as an acid catalyst, stir and seal for static placement to allow methyltrimethoxysilane and dimethyldiethoxysilane to fully hydrolyze under acidic conditions; then slowly add a mixed solution of ethanol and 0.8 mol / L ammonia water to the above static solution, and stir evenly to cause a polycondensation reaction under alkaline conditions to obtain the SiCO precursor sol;

[0094] (2) Preparation of silicon carbide fiber felt with a BN / SiC composite interface: First, cut the silicon carbide fibers to a length of 8 mm, a thickness of 30 mm, and a density of 0.06 g / cm 3The silicon carbide fiber felt is degummed at 500 °C for 1 h to remove the sizing agent on the surface, and then the silicon carbide fiber felt is pre-oxidized at 1000 °C for 1 h. Finally, the pre-oxidized silicon carbide fiber felt is placed in an acidic medium (a mixed aqueous solution of hydrofluoric acid and nitric acid, where the mass fraction of dissolved HF is 5 wt%, and the concentration of nitric acid is 3.5 mol / L) and treated for 40 min to obtain a silicon carbide fiber felt (SiC f -O-HF) for deposition. The treated silicon carbide fiber felt (SiC f -O-HF) is placed in a chemical vapor infiltration furnace to deposit a boron nitride / silicon carbide composite interface BN / SiC, and a silicon carbide fiber felt (SiC f / BN / SiC) containing a BN / SiC composite interface is obtained. During the deposition of the BN layer, the flow rate of boron trichloride (BCl 3 ) is 2 L / min, the flow rate of ammonia gas (NH 3 ) is 4 L / min, the flow rate of hydrogen gas (H 2 ) is 3.5 L / min, and the flow rate of argon gas (Ar) is 3 L / min. The pressure in the deposition furnace is controlled to be 1.0 kPa, where the deposition temperature of BN1 is 750 °C, the deposition temperature of BN2 is 1000 °C, and the single-layer deposition time is 20 - 30 min; after the single-layer BN layer deposition is completed, heat treatment is carried out in a vacuum environment, the heat treatment temperature is 1200 °C, and the heat treatment time is 1 h; during the deposition of the SiC layer, the flow rate of trichloromethylsilane (CH 3 SiCl 3 ) is controlled to be 1 L / min, the flow rate of hydrogen gas (H 2 ) is 1.5 L / min, and the flow rate of argon gas (Ar) is 1.5 L / min; the pressure in the furnace is 2 kPa, the deposition temperature is 1000 °C, and the single-layer deposition time is 20 - 40 min. BN and SiC are each deposited three times, and the thickness of the obtained BN interface is 300 nm (where the thickness of the BN1 interface is 100 nm and the thickness of the BN2 interface is 200 nm), 150 nm (where the thickness of the BN1 interface is 100 nm and the thickness of the BN2 interface is 50 nm), 200 nm (where the thickness of the BN1 interface is 100 nm and the thickness of the BN2 interface is 100 nm). The thickness of the SiC interface is 150 nm, 200 nm, 50 nm.

[0095] (3) Impregnation, gelation, and aging: The SiC f / BN / SiC is impregnated in the SiCO precursor sol, and vacuum is maintained for 1 h to obtain a SiC f / BN / SiC-SiCO sol complex gel. Then, the sol complex gel is aged at 70 °C for 2 days to allow the gel to fully undergo a polycondensation reaction and ensure the strength of its skeleton structure.

[0096] (4) Drying: The obtained SiC f / BN / SiC-SiCO wet gel is dissolved and the ethanol in the SiC 2 / BN / SiC-SiCO wet gel is replaced by supercritical CO f to obtain the SiC f / BN / SiC-SiCO ceramic precursor.

[0097] (5) Pyrolysis: The SiC / BN / SiC-SiCO ceramic precursor is placed in a pyrolysis furnace. After evacuating, argon is filled. Pyrolysis is carried out at 1250 °C for 1 h under an inert atmosphere according to the set heating program. After naturally cooling to room temperature, the sample is taken out. The cycle of SiCO precursor sol impregnation - aging - drying - pyrolysis is repeated 3 times to obtain the SiC f / BN / SiC-SiCO porous ceramic composite.

[0098] (6) Selective area hydrophilization treatment is carried out on the surface of the SiC f / BN / SiC-SiCO porous ceramic composite, so that the surface layer 3 mm of the porous ceramic composite is impregnated in γ-(2,3-epoxypropoxy) propyltrimethoxysilane. Since the hydrophilicity of the surface of the porous ceramic composite can effectively prevent the slurry composed of the ceramic precursor and the nano ultra-high temperature ceramic powder from entering the porous material, the coating matrix is only compounded on the surface of the porous ceramic composite, thereby effectively avoiding the increase in the density and thermal conductivity of the thermal insulation material.

[0099] (7) Preparation of the thermal protection coating: It is divided into the preparation of the surface sealing layer and the dense layer. First, the SiC fLifting of the / BN / SiC-SiCO porous ceramic composite material, immersing the surface layer of 3 mm in the porous ceramic composite material in the sealant coating slurry. The sealant coating slurry is obtained by adding molybdenum silicide, SiC whiskers, and borosilicate glass to the ceramic precursor slurry. The solid content of the sealant coating slurry is 40%. In its solid phase, it contains a mixed slurry of molybdenum silicide, SiC whiskers, and borosilicate glass. Among them, the volume content of SiC whiskers is 3 vol%, the volume content of molybdenum silicide is 50 vol%, and the volume content of borosilicate glass is 47 vol%. After immersion, the composite material is dried at 25 °C for 24 h. (After drying, pre-oxidation sintering is carried out at a temperature of 1350 °C for 60 min. Then, the dense layer slurry is brushed on the surface of the porous ceramic composite material, and then the dense coating is brushed on the surface of the sealant layer. The dense layer slurry is obtained by adding zirconium carbide with a particle size of 500 nm, SiC whiskers, and borosilicate powder to the polycarbosilane slurry. The solid content of the dense layer slurry is 40%. In the solid phase, the volume content of SiC whiskers is 2 vol%, the volume content of ultra-high temperature ceramics is 15 vol%, the volume content of molybdenum silicide is 30 vol%, and the volume content of borosilicate glass is 53 vol%. The ceramic precursor slurry is composed of a ceramic precursor and xylene, and the volume fraction of xylene in the ceramic precursor slurry is 50 vol.%. After brushing, sintering is carried out (sintering temperature 1350 °C, time 60 min) to obtain the product.)

[0100] The morphology diagram of the porous silicon carbide fiber felt with a BN / SiC composite interface contained in the heat insulation and heat protection integrated porous ceramic composite material obtained in this example is as follows Figure 3 shown. At a high temperature of 1600 °C, an ablation test is carried out on it by the oxyacetylene flame method. The macroscopic morphology after ablation is as follows Figure 4 shown, and the microscopic morphology after ablation is as follows Figure 5 shown. It can be seen from the figure that the ablation situation on its surface is not obvious.

[0101] Example 4

[0102] This example provides a preparation method for a heat insulation and heat protection integrated porous ceramic composite material, including the following steps:

[0103] (1) Preparation of SiCO precursor sol: First, use methyltrimethoxysilane and dimethyldiethoxysilane as raw materials and mix them in an ethanol-aqueous solution; then add a 1 wt% nitric acid solution as an acid catalyst, stir and seal for standing, so that methyltrimethoxysilane and dimethyldiethoxysilane are fully hydrolyzed under acidic conditions; then slowly add a mixed solution of ethanol and 1 wt% ammonia water to the above standing solution, and stir evenly to make it undergo a polycondensation reaction under alkaline conditions to obtain the SiCO precursor sol;

[0104] (2) Preparation of silicon carbide fiber felt with BN / SiC composite interface: First, cut short the silicon carbide fibers to a length of 10 mm, a thickness of 50 mm, and a density of 0.07 g / cm 3 The silicon carbide fiber felt is degummed at 500 °C for 1 h to remove the sizing agent on the surface. Then, the silicon carbide fiber felt is pre-oxidized at 950 °C for 1 h. Finally, the pre-oxidized silicon carbide fiber felt is placed in an acidic medium (a mixed aqueous solution of hydrofluoric acid and nitric acid, where the mass fraction of dissolved HF is 8 wt%, and the concentration of nitric acid is 3.5 mol / L) and treated for 1 h to obtain a silicon carbide fiber felt (SiC f -O-HF) for deposition. The treated silicon carbide fiber felt (SiC f -O-HF) is placed in a chemical vapor infiltration furnace to deposit a boron nitride / silicon carbide composite interface BN / SiC, obtaining a silicon carbide fiber felt (SiC f / BN / SiC). During the deposition process of the BN layer, the flow rate of boron trichloride (BCl 3 ) is 3 L / min, the flow rate of ammonia (NH 3 ) is 7 L / min, the flow rate of hydrogen (H 2 ) is 4.8 L / min, and the flow rate of argon (Ar) is 6 L / min. The pressure in the deposition furnace is controlled at 3 kPa, the deposition temperature is 950 °C, and the single-layer deposition time is 15 - 30 min; after the single-layer BN layer deposition is completed, heat treatment is carried out in a vacuum environment, the heat treatment temperature is 1100 °C, and the heat treatment time is 2 h; during the deposition process of the SiC layer, the flow rate of trichloromethylsilane (CH 3 SiCl 3 ) is controlled at 2 L / min, the flow rate of hydrogen (H 2 ) is 2 L / min, and the flow rate of argon (Ar) is 2.5 L / min; the pressure in the furnace is 4 kPa, the deposition temperature is 1100 °C, and the single-layer deposition time is 20 - 40 min. BN and SiC are each deposited twice, and the thicknesses of the obtained BN interfaces are 350 nm and 200 nm, and the thicknesses of the SiC interfaces are 200 nm and 100 nm.

[0105] (3) Impregnation, gelation, and aging: Immerse the SiC f / BN / SiC in the SiCO precursor sol, evacuate and hold for 1 h to obtain a SiC f / BN / SiC-SiCO sol complex gel. Then, age the sol complex gel at 70 °C - 75 °C for 3 days to allow the gel to fully undergo polycondensation reactions and ensure the strength of its skeleton structure.

[0106] (4) Drying: The obtained SiC f / BN / SiC-SiCO wet gel is dissolved and replaced by SiC 2 by supercritical CO f dissolving and replacing ethanol in the / BN / SiC-SiCO wet gel to obtain SiC f / BN / SiC-SiCO ceramic precursor.

[0107] (5) Pyrolysis: Place the SiC f / BN / SiC-SiCO ceramic precursor in a pyrolysis furnace, evacuate and then fill with argon. Carry out pyrolysis at 1100 °C for 1 h under an inert atmosphere according to the set heating program. After natural cooling to room temperature, take out the sample. Repeat the cycle of SiCO precursor sol impregnation - aging - drying - pyrolysis 4 times to obtain SiC f / BN / SiC-SiCO porous ceramic composite.

[0108] (6) Selective hydrophilic treatment is carried out on the surface of the SiC f / BN / SiC-SiCO porous ceramic composite, so that the surface layer 3 mm of the porous ceramic composite is impregnated with γ-(2,3-epoxypropoxy) propyltrimethoxysilane. Since the hydrophilicity of the porous ceramic composite surface can effectively prevent the slurry composed of the ceramic precursor and the nano ultra-high temperature ceramic powder from entering the porous material, the coating matrix is only compounded on the surface of the porous ceramic composite, thereby effectively avoiding the increase in the density and thermal conductivity of the thermal insulation material.

[0109] (7) Preparation of the thermal protection coating: It is divided into the preparation of the surface sealing layer and the dense layer. First, place the SiC fLifting of the / BN / SiC-SiCO porous ceramic composite material, immersing the surface layer of 3 mm in the porous ceramic composite material in the sealant coating slurry. The sealant coating slurry is obtained by adding molybdenum silicide, SiC whiskers, and borosilicate glass to the ceramic precursor slurry. The solid content of the sealant coating slurry is 15%. In its solid phase, the volume content of SiC whiskers is 5 vol%, the volume content of molybdenum silicide is 50 vol%, and the volume content of borosilicate glass is 45 vol%. After immersion, the composite material is dried at 25 °C for 24 h. After drying, pre-oxidation sintering is carried out at a temperature of 1250 °C for 20 min. Then, the dense layer slurry is brushed on the surface of the porous ceramic composite material, and then the dense coating is brush-coated on the surface of the sealant layer. The dense layer slurry is obtained by adding hafnium carbide with a particle size of 500 nm, SiC whiskers, and borosilicate powder to the polycarbosilane slurry. The solid content of the dense layer slurry is 15%. In the solid phase, the volume content of SiC whiskers is 5 vol%, the volume content of ultra-high temperature ceramics is 25 vol%, the volume content of molybdenum silicide is 20 vol%, and the volume content of borosilicate glass is 50 vol%. The ceramic precursor slurry is composed of a ceramic precursor and xylene, and the volume fraction of xylene in the ceramic precursor slurry is 50 vol.%. After brushing, sintering is carried out (sintering temperature 1350 °C, time 50 min) to obtain the integrated thermal insulation and heat protection porous ceramic composite material.

[0110] For the integrated thermal insulation and heat protection porous ceramic composite material obtained in this example, at a high temperature of 1600 °C, the oxyacetylene flame method is used to carry out an ablation test on it, and the microscopic morphology after ablation is as Figure 6 shown.

[0111] Example 5

[0112] This example provides a preparation method for an integrated thermal insulation and heat protection porous ceramic composite material, including the following steps:

[0113] (1) Preparation of SiCO precursor sol: First, methyltrimethoxysilane and dimethyldiethoxysilane are used as raw materials together and mixed in an ethanol-aqueous solution; then, 1 wt% nitric acid solution is added as an acid catalyst, and after stirring, it is sealed and left standing to allow methyltrimethoxysilane and dimethyldiethoxysilane to hydrolyze fully under acidic conditions; then, a mixed solution of ethanol and 1 wt% ammonia water is slowly added to the above standing solution, and stirred evenly to cause a polycondensation reaction under alkaline conditions to obtain the SiCO precursor sol;

[0114] (2) Preparation of silicon carbide fiber felt with a BN / SiC composite interface: First, the chopped silicon carbide fibers have a length of 15 mm, a thickness of 100 mm, and a density of 0.08 g / cm 3The silicon carbide fiber felt is degummed at 500 °C for 1 h to remove the sizing agent on the surface. Then, the silicon carbide fiber felt is pre-oxidized at 850 °C for 1 h. Finally, the pre-oxidized silicon carbide fiber felt is treated in an acidic medium (a mixed aqueous solution of hydrofluoric acid and nitric acid, where the mass fraction of dissolved HF is 7 wt% and the concentration of nitric acid is 0.5 mol / L) for 1 h to obtain a silicon carbide fiber felt (SiC f -O-HF) for deposition. The treated silicon carbide fiber felt (SiC f -O-HF) is placed in a chemical vapor infiltration furnace to deposit a boron nitride / silicon carbide composite interface BN / SiC, obtaining a silicon carbide fiber felt (SiC f / BN / SiC) containing the BN / SiC composite interface. During the deposition of the BN layer, the flow rate of boron trichloride (BCl 3 ) is 2 L / min, the flow rate of ammonia (NH 3 ) is 5 L / min, the flow rate of hydrogen (H 2 ) is 3.5 L / min, and the flow rate of argon (Ar) is 5 L / min. The pressure in the deposition furnace is controlled at 3 kPa, the deposition temperature is 850 °C, and the single-layer deposition time is 15 - 30 min; after the single-layer BN layer deposition is completed, heat treatment is carried out in a vacuum environment, the heat treatment temperature is 1050 °C, and the heat treatment time is 1.5 h; during the deposition of the SiC layer, the flow rate of trichloromethylsilane (CH 3 SiCl 3 ) is 1 - 2 L / min, the flow rate of hydrogen (H 2 ) is 2 L / min, and the flow rate of argon (Ar) is 2.5 L / min; the pressure in the furnace is 2 kPa, the deposition temperature is 1100 °C, and the single-layer deposition time is 20 - 40 min. BN and SiC are each deposited twice, and the thicknesses of the obtained BN interfaces are 400 nm and 200 nm, and the thicknesses of the SiC interfaces are 200 nm and 100 nm.

[0115] (3) Impregnation, gelation, and aging: The SiC f / BN / SiC is impregnated in the SiCO precursor sol, and vacuum is maintained for 1 h to obtain a SiC f / BN / SiC-SiCO sol complex gel. Then, the sol complex gel is aged at 70 °C - 75 °C for 1 day to allow the gel to fully undergo a polycondensation reaction and ensure the strength of its framework structure.

[0116] (4) Drying: The obtained SiC f / BN / SiC-SiCO wet gel is dissolved and replaced with ethanol in the SiC 2 / BN / SiC-SiCO wet gel by supercritical CO f to obtain a SiC f / BN / SiC-SiCO ceramic precursor.

[0117] (5) Pyrolysis: Place the SiC f / BN / SiC-SiCO ceramic precursor in a pyrolysis furnace, evacuate and then fill with argon. Carry out pyrolysis at 1150 °C for 1 h under an inert atmosphere according to the set heating program. After natural cooling to room temperature, take out the sample. Repeat the cycle of SiCO precursor sol impregnation - aging - drying - pyrolysis 2 times to obtain SiC f / BN / SiC-SiCO porous ceramic composite.

[0118] (6) Perform selective area hydrophilic treatment on the surface of the SiC f / BN / SiC-SiCO porous ceramic composite, so that the surface layer 3 mm of the porous ceramic composite is impregnated in γ-methacryloxypropyltrimethoxysilane. Since the hydrophilicity of the porous ceramic composite surface can effectively prevent the slurry composed of the ceramic precursor and the nano ultra-high temperature ceramic powder from entering the porous material, the coating matrix is only compounded on the surface of the porous ceramic composite, thereby effectively avoiding the increase in the density and thermal conductivity of the thermal insulation material.

[0119] (7) Preparation of the thermal protection coating: It is divided into the preparation of the surface sealing layer and the dense layer. First, lift and suspend the SiC f / BN / SiC-SiCO porous ceramic composite, so that the surface layer 3 mm of the porous ceramic composite is impregnated in the sealing coating slurry. The sealing coating slurry is obtained by adding molybdenum silicide, SiC whiskers, and borosilicate glass to the ceramic precursor slurry. The solid content of the sealing coating slurry is 27%. In its solid phase, the volume content of SiC whiskers is 5 vol%, the volume content of molybdenum silicide is 50 vol%, and the volume content of borosilicate glass is 45 vol%. After impregnation, dry the composite at 25 °C for 24 h. After drying, carry out pre-oxidation sintering at a temperature of 1250 °C for 40 min. Then brush the dense layer slurry on the surface of the porous ceramic composite, and then brush the dense coating on the surface of the sealing layer. The dense layer slurry is obtained by adding hafnium carbide with a particle size of 200 nm, SiC whiskers, and borosilicate powder to the polycarbosilane slurry. In the dense layer slurry, the solid content of the dense layer slurry is 27%. In the solid phase, the volume content of SiC whiskers is 4 vol%, the volume content of the ultra-high temperature ceramic is 20 vol%, the volume content of molybdenum silicide is 50 vol%, and the volume content of borosilicate glass is 26 vol%. The ceramic precursor slurry is composed of a ceramic precursor and xylene, and the volume fraction of xylene in the ceramic precursor slurry is 40 vol.%. Then, through sintering (sintering temperature 1300 °C, time 30 min), the thermal insulation and protection integrated porous ceramic composite is obtained.

[0120] Comparative Example 1

[0121] All other conditions were the same as in Example 1, and only the BN interface phase led to a decrease in the skeleton strength.

[0122] Comparative Example 2

[0123] All other conditions were the same as in Example 2, and only the volume content of the ultra-high temperature ceramic phase in the dense layer was 4 vol%, resulting in a decrease in the ablation resistance.

[0124] Comparative Example 3

[0125] All other conditions were the same as in Example 4, and only the volume content of the ultra-high temperature ceramic phase in the dense layer was 30 vol%, resulting in a decrease in the ablation resistance.

[0126] The mechanical properties of the integrated thermal insulation and ablation resistant porous ceramic composites obtained from the examples and comparative examples were tested, and the performance data of the ablation test using the oxyacetylene flame method at 1600 °C are shown in Table 1.

[0127] Table 1 Performance data results of examples and comparative examples

[0128]

Claims

1. A method for preparing a porous ceramic composite material with integrated heat insulation, characterized in that: After degumming the silicon carbide fiber felt, a degummed silicon carbide fiber felt is obtained, the degummed silicon carbide fiber felt is first subjected to surface pre-oxidation treatment, and then treated with an acidic liquid medium to obtain a pre-treated silicon carbide fiber felt, and then (BN / SiC) is deposited on the surface of the pre-treated silicon carbide fiber felt. n The composite interface layer is obtained by obtaining a self-supporting silicon carbide fiber skeleton, which is impregnated in a SiCO ceramic precursor, and a wet gel felt is formed through gelation and aging, and the wet gel felt is dried and cracked to obtain a porous ceramic composite material, and a multi-layer heat-resistant coating is then arranged on the surface of the porous ceramic composite material.

2. The method for preparing a thermal insulation integrated porous ceramic composite material according to claim 1, characterized in that: The thickness of the silicon carbide fiber felt is 0.5 to 200 mm; The density of the silicon carbide fiber felt is 0.05-0.085 g / cm 3 ; The silicon carbide fiber felt is prepared by wet felting short-cut silicon carbide fibers, and the length of the short-cut silicon carbide fibers is 4 to 15 mm.

3. The method for preparing a thermal insulation integrated porous ceramic composite material according to claim 1 or 2, characterized in that: The method of degumming the silicon carbide fiber felt is to remove it by soaking it in acetone, or to oxidize it in an air atmosphere at 500-650°C for 1-1.5h; The pre-oxidation process is to heat-treat the degummed silicon carbide fiber felt in air at a temperature of 650° C. to 1000° C. for 1 to 2 hours. The acidic liquid medium treatment time is 10 to 60 minutes; The acidic liquid medium is a mixed aqueous solution containing hydrofluoric acid and nitric acid. In the mixed aqueous solution, the mass fraction of dissolved HF is 4wt% to 8wt%, and the concentration of nitric acid is 0.5 to 5 mol / L.

4. The method for preparing a thermal insulation integrated porous ceramic composite material according to claim 1 or 2, characterized in that: The interface layer is (BN / SiC) n Composite interface, where n ≥ 1; The (BN / SiC) n In the composite interface, the total thickness of BN is 150-650 nm, and the total thickness of SiC is 50-500 nm; The (BN / SiC) n The process of obtaining the composite interface is: by chemical vapor deposition, cyclically depositing a BN layer, heat treatment, and depositing a SiC layer in sequence; During the deposition of the BN layer, the flow rate of BCl3 is 1-3 L / min, the flow rate of NH3 is 3-7 L / min, the flow rate of H2 is 3-4.8 L / min, the flow rate of Ar is 3-6 L / min, the pressure in the deposition furnace is controlled to be 0.5-4 kPa, the deposition temperature is 650°C-950°C, and the single layer deposition time is 15-30 min; The heat treatment is carried out in a vacuum environment at a temperature of 1000 to 1200° C. for a time of 1 to 2 hours; During the deposition of the SiC layer, the flow rate of CH3SiCl3 is controlled to be 1-3 L / min, the flow rate of H2 is 1-2 L / min, and the flow rate of Ar is 1.5-2.5 L / min; the pressure in the furnace is 0.5-4 kPa, the deposition temperature is 1000-1100°C, and the single-layer deposition time is 20-40 min.

5. The method for preparing a porous ceramic composite material with integrated heat insulation according to claim 4, characterized in that: The (BN / SiC) n The BN layer in the composite interface is composed of a BN1 layer and a BN2 layer in sequence, wherein the BN1 is an isotropic BN and the BN2 is an anisotropic BN; During the deposition of the BN1 layer, the flow rate of BCl3 is 1-3L / min, the flow rate of NH3 is 3-7L / min, the flow rate of H2 is 3-4.8L / min, the flow rate of Ar is 3-6L / min, the pressure in the deposition furnace is controlled to be 0.5-4kPa, the deposition temperature is 650℃-750℃, and the single-layer deposition time is 15-30min. During the deposition of the BN2 layer, the flow rate of BCl3 is 1-3L / min, the flow rate of NH3 is 3-7L / min, the flow rate of H2 is 3-4.8L / min, the flow rate of Ar is 3-6L / min, the pressure in the deposition furnace is controlled to be 0.5-4kPa, the deposition temperature is 850℃-1050℃, and the single-layer deposition time is 15-30min.

6. The method for preparing a thermal insulation integrated porous ceramic composite material according to claim 1 or 2, characterized in that: The preparation process of the SiCO precursor sol is as follows: silane A and silane B are used as raw materials, added into an ethanol aqueous solution, and then a nitric acid solution is added as an acid catalyst, and then the mixture is sealed and allowed to stand still, so that the silane A and the silane B are hydrolyzed under acidic conditions to obtain a standing solution; then a mixed solution of ethanol and ammonia water is added into the standing solution, and the mixture is stirred to cause a polycondensation reaction under alkaline conditions to obtain a SiCO precursor sol; The silane A is methyltrimethoxysilane, and the silane B is dimethyldiethoxysilane, or the silane A is methyltrimethoxysilane, and the silane B is dimethyldimethoxysilane.

7. The method for preparing a thermal insulation integrated porous ceramic composite material according to claim 1 or 2, characterized in that: The impregnation is vacuum impregnation, and the time of the vacuum impregnation is 1 to 2 hours; The aging temperature is 65°C to 75°C, and the aging time is 1 to 3 days; The drying process is to dissolve the wet gel felt by supercritical CO2 and replace the ethanol in the wet gel felt; The pyrolysis is carried out under a protective atmosphere, the pyrolysis temperature is 1000-1200°C, the pyrolysis time is 1-2h, and the heating rate is 2-5°C / min. The self-supporting silicon carbide fiber skeleton is impregnated in a SiCO ceramic precursor, and a wet gel felt is formed through gelation and aging. The wet gel felt is then dried and cracked. Then, the impregnation-aging-drying-cracking cycle is repeated for 1 to 4 cycles.

8. The method for preparing a thermal insulation integrated porous ceramic composite material according to claim 1 or 2, characterized in that: Firstly, the surface layer of the porous ceramic composite material (1 to 3 mm) is selectively treated with a hydrophilic coupling agent, and then a multi-layer heat-resistant coating is provided; The process of the hydrophilic coupling agent selective treatment is as follows: the porous ceramic composite material is hoisted, and the surface layer of the porous ceramic composite material of 1 to 3 mm is immersed in the hydrophilic silane coupling agent solution, and then the immersed part is subjected to ultrasonic hydrolysis reaction for 1 to 3 hours, and finally dried to obtain the result; The solvent in the silane coupling agent solution is a mixed solvent of ethanol and water, and the mass ratio of the ethanol to water is 9 to 12:1; In the silane coupling agent solution, the mass fraction of the silane coupling agent is 4-6%. The silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropyloxy)propyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane.

9. The method for preparing a thermal insulation integrated porous ceramic composite material according to claim 1 or 2, characterized in that: The process of setting a multi-layer heat-resistant coating on the surface of a porous ceramic composite material is as follows: the porous ceramic composite material is hoisted, 1 to 3 mm of the surface layer of the porous ceramic composite material is immersed in a sealing coating slurry, and then pre-oxidation sintering is performed after drying, and then a dense layer slurry is brushed on the surface of the porous ceramic composite material, and then sintered to obtain the coating, wherein the pre-oxidation sintering temperature is 1350 to 1500° C., the time is 10 to 40 minutes, and the sintering temperature is 1350 to 1500° C., and the time is 40 to 90 minutes; The sealing coating slurry is obtained by adding molybdenum silicide, SiC whiskers, and borosilicate glass into a ceramic precursor slurry; the solid phase content of the sealing coating slurry is 20-40%; in the solid phase of the sealing coating slurry, by volume percentage, SiC whiskers are 1-5 vol%, molybdenum silicide is 40-60 vol%, and borosilicate glass is 35-59 vol%; The dense layer slurry is obtained by adding ultra-high temperature ceramics, SiC whiskers, molybdenum silicide, and borosilicate powder into ceramic precursor slurry, wherein the solid phase content of the dense layer slurry is 20-40%, and the solid phase of the dense layer slurry contains, by volume percentage, 1-5 vol% SiC whiskers, 40-60 vol% molybdenum silicide, 5-25 vol% ultra-high temperature ceramics, and 20-54 vol% borosilicate glass; The ceramic precursor slurry is composed of a ceramic precursor and xylene, wherein the volume fraction of xylene in the ceramic precursor slurry is 10 to 50 vol%; The ceramic precursor is selected from at least one of polycarbosilane, polynitrogen silane, polyhafnium silane and polyborosilane; The ultra-high temperature ceramic is selected from at least one of hafnium carbide, zirconium carbide, hafnium boride and zirconium boride; The particle size of the ultra-high temperature ceramic is 20nm-800nm.

10. A porous ceramic composite material with integrated heat insulation prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The porous ceramic composite material is composed of silicon carbide fiber felt, (BN / SiC) wrapped with silicon carbide fiber n The composite interface layer, the SiCO porous ceramic matrix and the heat-resistant coating are composed, wherein the heat-resistant coating is composed of a sealing layer and a dense layer.

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