A method for preparing gradient thermal insulation material for thermal protection systems

Abstract

This application discloses a method for preparing a gradient thermal insulation material for a thermal protection system, comprising: pretreating ceramic fibers to obtain ceramic fiber A and ceramic fiber B; performing surface treatment on ceramic fiber A and ceramic fiber B respectively to obtain primary ceramic fiber A and primary ceramic fiber B; preparing ceramic fiber A solution and ceramic fiber B solution based on primary ceramic fiber A and primary ceramic fiber B respectively; preparing a primary gradient thermal insulation layer matrix based on ceramic fiber A solution and ceramic fiber B solution; performing surface treatment on the primary gradient thermal insulation layer matrix, followed by drying and heat treatment to obtain a gradient thermal insulation layer matrix; preparing an organic precursor, impregnating the gradient thermal insulation layer matrix with the organic precursor, pyrolyzing it, and then performing supercritical drying; thereby achieving that the gradient thermal insulation material for the thermal protection system simultaneously possesses high thermal insulation, high strength, low weight, high surface mechanical strength, and protective performance to avoid the impact of environmental heat flow on the material.

Description

Technical Field

[0001] This invention belongs to the field of heat insulation materials technology, specifically relating to a method for preparing a gradient heat insulation material for a thermal protection system. Background Technology

[0002] Currently, thermal protection systems possess both thermal insulation properties and mechanical fastening capabilities, making this material widely in demand in the aviation and aerospace fields. Traditional thermal protection systems are mainly combined systems, which possess both thermal insulation properties and mechanical connections. However, existing mechanically connected thermal protection materials suffer from problems such as high density and weight, complex connection structures, and low thermal insulation efficiency, failing to meet the thermal protection requirements of new aircraft.

[0003] The existing technology mainly uses rigid thermal insulation materials with composite molding process. These materials have the function of mechanical connection on the surface and surface protection to avoid the impact of environmental heat flow on the material. The internal thermal insulation layer has the function of thermal insulation performance. However, the thermal insulation layer has low strength and the thermal insulation performance decreases significantly if the thermal insulation strength is increased. The mechanical connection layer has poor thermal insulation performance and low connection strength with the thermal insulation layer, which reduces the thermal insulation effect of the thermal insulation layer. Ultimately, the thermal protection system material has poor thermal insulation performance and low connection strength.

[0004] Therefore, how to prepare a thermal insulation material for thermal protection systems that has high surface mechanical connection strength, strong resistance to thermal shock, high thermal insulation performance, and light weight has become a technical challenge in this field. Summary of the Invention

[0005] To overcome the shortcomings of the above-mentioned technical problems, this invention provides a method for preparing a gradient thermal insulation material for a thermal protection system. By performing surface treatment on ceramic fibers A and B respectively, the gradient thermal insulation layer matrix is ​​prepared with high strength and high thermal insulation performance. At the same time, the gradient structure of the gradient thermal insulation layer matrix is ​​conducive to the connection with the protective layer on the surface. Thus, the gradient thermal insulation material for the thermal protection system simultaneously has high thermal insulation, high strength, low weight, high surface mechanical strength, and protective performance to avoid the impact of environmental heat flow on the material.

[0006] This invention provides a method for preparing a gradient thermal insulation material for a thermal protection system, comprising the following steps:

[0007] Ceramic fibers are pretreated to obtain ceramic fiber A and ceramic fiber B;

[0008] Ceramic fiber A and ceramic fiber B are respectively surface treated to obtain primary ceramic fiber A and primary ceramic fiber B.

[0009] Ceramic fiber A solution and ceramic fiber B solution were prepared based on primary ceramic fiber A and primary ceramic fiber B, respectively.

[0010] Primary gradient thermal insulation layer matrix prepared based on ceramic fiber A solution and ceramic fiber B solution;

[0011] The primary gradient insulation layer substrate is surface treated, then dried and heat-treated to obtain the gradient insulation layer substrate.

[0012] An organic precursor is prepared, and the organic precursor is impregnated with the gradient insulation layer matrix, pyrolyzed, and then supercritically dried to obtain the gradient insulation material for the thermal protection system.

[0013] The thermal protection system uses a gradient thermal insulation material comprising a protective layer and a thermal insulation layer. The internal porosity of the thermal insulation layer varies with a gradient, and the density of the side of the protective layer connected to the thermal insulation layer is higher than that of the side away from the thermal insulation layer. The thermal insulation layer has high internal porosity and a density of 0.15–0.25 g / cm³. 3 The density of the protective layer is 1.8-2.0 g / cm³. 3 The protective layer has a high degree of densification on the side away from the insulation layer, and the compressive strength of the protective layer is greater than 3MPa and the tensile strength is greater than 1MPa; the overall thermal conductivity of the gradient thermal insulation material used in the thermal protection system is less than 0.05W / m·K at room temperature and 0.1W / m·K at 800℃.

[0014] Preferably, the density of the insulation layer is 0.15–0.20 g / cm³. 3 The protective layer includes a surface protective layer and a thermal insulation connecting layer, which are connected to the protective layer and the thermal insulation layer respectively; the protective layer has a compressive strength greater than 4 MPa and a tensile strength greater than 1.5 MPa; the overall thermal conductivity of the gradient thermal insulation material used in the thermal protection system is less than 0.035 W / m·K at room temperature and 0.06 W / m·K at 800℃.

[0015] Preferably, the ceramic fiber includes one or more of quartz fiber, alumina fiber, zirconium oxide fiber, and aluminosilicate fiber;

[0016] The beneficial effect of adopting the above-mentioned further technical solution is that ceramic fiber A and ceramic fiber B are obtained through ceramic fiber pretreatment, and the gradient heat insulation layer matrix prepared by ceramic fiber A and ceramic fiber B has a gradient porosity, which is beneficial to have a high porosity and to have a high bonding strength between the gradient heat insulation layer matrix and the surface layer obtained by surface impregnation.

[0017] By performing surface treatments on ceramic fibers A and B respectively, the components of the binder are uniformly adhered to the surfaces of ceramic fibers A and B, and the components of the binder are prevented from being dispersed in the pores of the gradient insulation layer matrix. This is beneficial for a significant increase in the sintering strength of the ceramic fiber overlap points during subsequent sintering without reducing the strength of the gradient insulation layer matrix. Thus, it is possible to increase the porosity of the gradient insulation layer matrix without reducing its strength, ultimately improving the thermal insulation performance of the gradient insulation layer without reducing its strength.

[0018] By performing surface treatment on the primary gradient insulation layer matrix, other components of the adhesive are dispersed at the fiber overlap points in the primary gradient insulation layer matrix and do not remain in the pores, thereby further improving the thermal insulation performance of the gradient insulation layer matrix without reducing its strength.

[0019] By impregnating and pyrolyzing the gradient insulation layer matrix with the organic precursor, and then supercritically drying it, a protective layer is attached to the surface of the gradient insulation layer matrix. The pyrolysis of the organic precursor achieves high densification strength of the protective layer. At the same time, the high strength of the fiber overlap points in the gradient insulation layer matrix avoids problems such as matrix shrinkage, deformation or cracking during the densification process of the organic precursor.

[0020] The high-gradient insulation layer is transformed into the insulation layer of the gradient heat insulation material for the thermal protection system, and the organic precursor impregnated on the surface of the high-gradient insulation layer is transformed into a protective layer; thus, the gradient heat insulation material for the thermal protection system simultaneously possesses high heat insulation, high strength, low weight, high surface mechanical strength, and protective properties to avoid the impact of environmental heat flow on the material.

[0021] Furthermore, the pretreatment of ceramic fibers includes shaving the ceramic fibers at different aspect ratios to obtain ceramic fiber A and ceramic fiber B.

[0022] The aspect ratio of the ceramic fiber A is (100-500):1; the aspect ratio of the ceramic fiber B is (10-50):1.

[0023] The beneficial effect of adopting the above-mentioned further technical solution is that the gradient heat insulation layer matrix prepared by the above-mentioned technical features has a gradient porosity, which is beneficial to the high porosity and the high bonding strength between the gradient heat insulation layer matrix and the surface layer obtained by surface impregnation.

[0024] Furthermore, the specific process of surface treatment of ceramic fiber A is as follows: ceramic fiber A is impregnated in silica sol, and after impregnation, it is dried and cured to obtain primary ceramic fiber A, wherein the mass ratio of ceramic fiber A to silica sol is (10-50):1.

[0025] The specific process for surface treatment of ceramic fiber B is as follows:

[0026] Ceramic fiber B is impregnated in silica sol, and then dried and cured to obtain primary ceramic fiber B, wherein the mass ratio of ceramic fiber B to silica sol is (5-50):1.

[0027] The beneficial effect of adopting the above-mentioned further technical solution is that it enables the uniform adhesion of silica sol to the surface of ceramic fiber A and ceramic fiber B, thereby obtaining primary ceramic fiber A and primary ceramic fiber B with silicon element uniformly attached to their surface.

[0028] Furthermore, the step of preparing ceramic fiber A solution includes: dispersing the primary ceramic fiber A in a dispersion medium to obtain the ceramic fiber A solution;

[0029] The steps for preparing ceramic fiber B solution include: dispersing the primary ceramic fiber B in a dispersion medium to obtain the ceramic fiber B solution;

[0030] The mass ratio of primary ceramic fiber A to dispersant in the ceramic fiber A solution is (10-40):1; the mass ratio of primary ceramic fiber B to dispersant in the ceramic fiber B solution is (40-100):1; the dispersant is water.

[0031] The beneficial effect of adopting the above-mentioned further technical solution is that it enables the preparation of ceramic fiber A solution and ceramic fiber B solution by primary ceramic fiber A and primary ceramic fiber B respectively; and the silicon element attached to the surface of primary ceramic fiber A and primary ceramic fiber B will not dissolve into the dispersant.

[0032] Furthermore, the primary ceramic fiber A undergoes a secondary treatment before being used to prepare the ceramic fiber A solution. The specific process is as follows: the primary ceramic fiber A is coated with paraffin or an organic modification solution is coated on the surface of the primary ceramic fiber A to complete the secondary treatment. The organic modification solution includes a reaction monomer and an initiator. The reaction monomer is one of a mixture of triethylene glycol and ethylene oxide monomer, acrylate, or methacrylate.

[0033] The primary ceramic fiber B is used for secondary treatment before preparing the ceramic fiber B solution. The specific process is as follows: the primary ceramic fiber B is coated with paraffin, or an organic modification solution is coated on the surface of the primary ceramic fiber B to complete the secondary treatment. The organic modification solution includes a reaction monomer and an initiator. The reaction monomer is a mixture of triethylene glycol and ethylene oxide monomer, acrylate, or methacrylate.

[0034] Preferably, the mass ratio of the paraffin or organic modified solution to ceramic fiber A is (0.1-0.8):1;

[0035] The mass ratio of the paraffin or organic modified solution to ceramic fiber B is (0.1-0.8):1;

[0036] Preferably, the primary ceramic fibers A and B are subjected to heat treatment after the organic modification solution is applied to their surfaces, and the heat treatment temperature is 50-150℃.

[0037] Preferably, the initiator is a peroxide; preferably, paraffin or an organic modification solution is sprayed or coated onto the surface of primary ceramic fiber A and primary ceramic fiber B;

[0038] The beneficial effect of adopting the above-mentioned further technical solution is that by attaching paraffin or organic modification solution to the surface of primary ceramic fiber A and primary ceramic fiber B, the silicon attached to the surface of primary ceramic fiber A and primary ceramic fiber B is protected, and the silicon attached to the surface of primary ceramic fiber A and primary ceramic fiber B is prevented from being dispersed into the dispersant when preparing ceramic fiber solution A and ceramic fiber solution B.

[0039] Furthermore, the paraffin or organic matter adhering to the surface will evaporate during subsequent high-temperature treatment, without affecting the reaction of the silicon adhering to the surface with other binder components, thus not affecting the increase in the strength of the ceramic fiber overlap.

[0040] Furthermore, the preparation process of the primary gradient heat insulation layer matrix is ​​as follows: the ceramic fiber A solution is poured into a porous mold with a sieve at the bottom, and then the solvent in the ceramic fiber A solution is filtered out;

[0041] When all or part of the solvent in the ceramic fiber A solution is filtered out, the ceramic fiber B solution is poured into a porous mold with a screen at the bottom, and the solvent is removed by suction filtration and pressure filtration to obtain the primary gradient insulation layer matrix.

[0042] The mass ratio of primary ceramic fiber A to primary ceramic fiber B in the primary gradient insulation layer matrix is ​​(1-4)(5-9);

[0043] Preferably, when the solvent in the ceramic fiber A solution is filtered out to a level 5 mm below the primary ceramic fiber A, the ceramic fiber B solution is then poured into a porous mold with a screen at the bottom.

[0044] The beneficial effect of adopting the above-mentioned further technical solution is that the prepared gradient thermal insulation layer matrix has a gradient porosity, which is beneficial to both the high porosity and the high bonding strength between the gradient thermal insulation layer matrix and the surface layer obtained by surface impregnation.

[0045] Furthermore, the process of surface treatment of the primary gradient heat insulation layer substrate is as follows: a first solution is prepared, and the primary gradient heat insulation layer substrate is impregnated with the first solution; the first solution is a mixture of sintering aid and water or ethanol, and the sintering aid is one or two of boron nitride and boron carbide;

[0046] The mass ratio of primary ceramic fiber A, primary ceramic fiber B, and sintering aid in the primary gradient insulation layer matrix is ​​(1-4):(6-9):(0.2-0.8).

[0047] The beneficial effect of adopting the above-mentioned further technical solution is that the sintering aid is dispersed on the overlap points of ceramic fibers and has very low residual amount in the pores of the primary gradient insulation layer matrix. This allows the boron in the sintering aid to react and generate silicon boron compounds during the high-temperature treatment of the primary gradient insulation layer matrix, thereby increasing the strength of the ceramic fiber overlap points without reducing the porosity of the primary gradient insulation layer matrix. This avoids the increase in insulation layer density in the finished product, thus preventing a reduction in the insulation effect of the finished insulation layer and reducing the weight of the finished product.

[0048] Furthermore, the primary gradient insulation layer substrate after surface treatment is dried at room temperature for 10-30 hours, and then subjected to segmented heat treatment.

[0049] The first stage of heat treatment is at a temperature of 65-75℃ for 8-24 hours; the second stage is at a temperature of 135-145℃ for 4-24 hours; and the third stage is at a temperature of 1100℃-1500℃ for 1-4 hours.

[0050] The beneficial effect of adopting the above-mentioned further technical solution is that it realizes the sintering of ceramic fibers and the reaction of silicon and boron on the surface of ceramic fibers to generate borosilicate compounds, thereby enhancing the strength of the ceramic fiber overlap points.

[0051] Furthermore, the organic precursor includes: polycarbosilane and ultra-high temperature ceramic precursor; the ultra-high temperature ceramic precursor includes one or two of the liquid-phase precursors of polyboronzirconium, polycarbosilane, hafnium boride, and hafnium carbide; the volume ratio of polycarbosilane to ultra-high temperature ceramic precursor is 1:3-6.

[0052] And / or,

[0053] After impregnating the gradient insulation layer matrix with the organic precursor, it is pyrolyzed under an inert atmosphere at a temperature of 1100-1500℃ for 2-5 hours.

[0054] and / or

[0055] The supercritical drying process is carried out at a drying temperature of 250-300℃, a pressure of 5-12MPa, and a time of 2-5h.

[0056] The beneficial effects of adopting the above-mentioned further technical solution are that a protective layer is attached to the surface of the gradient insulation layer substrate, and the protective layer is densified with high strength through the pyrolysis of the organic precursor; at the same time, due to the high strength of the fiber overlap points in the gradient insulation layer substrate, problems such as substrate shrinkage and deformation or cracking during the pyrolysis and densification process of the organic precursor are avoided.

[0057] Simultaneously, the inclusion of boron, zirconium, and hafnium elements in the protective layer enables it to possess high thermal insulation performance, thereby improving the heat resistance and thermal shock resistance of the finished product during use.

[0058] Furthermore, before impregnating the gradient insulation layer substrate with the organic precursor, the surface of the gradient insulation layer substrate is first impregnated with the aerogel precursor. After impregnation, the side of the gradient insulation layer substrate impregnated with the aerogel precursor is then impregnated with the organic precursor.

[0059] The beneficial effect of adopting the above-mentioned further technical solution is that it realizes the aerogel conforming to the substrate surface of the gradient insulation layer, while increasing the connection strength with the protective layer formed on the surface, and also increasing the insulation performance of the finished product. Attached Figure Description

[0060] Figure 1 The microstructure of the protective layer in the gradient thermal insulation material for the thermal protection system prepared in this invention;

[0061] Figure 2 The microstructure of the insulation layer in the gradient thermal insulation material for the thermal protection system prepared in this invention;

[0062] Figure 3 The microstructure of the insulation layer in gradient thermal insulation materials used in conventionally prepared thermal protection systems. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0064] Example 1:

[0065] This embodiment 1 provides a method for preparing a gradient thermal insulation material for a thermal protection system, including the following steps: pre-treating ceramic fibers to obtain ceramic fiber A and ceramic fiber B; the ceramic fibers include quartz fiber and alumina fiber.

[0066] The pretreatment of ceramic fibers includes shaving the ceramic fibers at different aspect ratios to obtain ceramic fiber A and ceramic fiber B; the aspect ratio of ceramic fiber A is 300:1; the aspect ratio of ceramic fiber B is 30:1.

[0067] Ceramic fiber A and ceramic fiber B are respectively surface treated to obtain primary ceramic fiber A and primary ceramic fiber B.

[0068] Ceramic fiber A solution and ceramic fiber B solution were prepared based on primary ceramic fiber A and primary ceramic fiber B, respectively.

[0069] The specific process for surface treatment of ceramic fiber A is as follows:

[0070] Ceramic fiber A is impregnated in silica sol, and then dried and cured to obtain primary ceramic fiber A, wherein the mass ratio of ceramic fiber A to silica sol is 30:1.

[0071] The specific process for surface treatment of ceramic fiber B is as follows:

[0072] Ceramic fiber B is impregnated in silica sol, and then dried and cured to obtain primary ceramic fiber B, wherein the mass ratio of ceramic fiber B to silica sol is 20:1.

[0073] The primary gradient thermal insulation layer matrix is ​​prepared based on ceramic fiber A solution and ceramic fiber B solution. The specific process is as follows: The step of preparing ceramic fiber A solution is to disperse the primary ceramic fiber A in a dispersion medium to obtain the ceramic fiber A solution;

[0074] The steps for preparing ceramic fiber B solution are as follows: the primary ceramic fiber B is dispersed in a dispersion medium to obtain the ceramic fiber B solution;

[0075] The mass ratio of primary ceramic fiber A to dispersant in the ceramic fiber A solution is 25:1; the mass ratio of primary ceramic fiber B to dispersant in the ceramic fiber B solution is 70:1; the dispersant is water.

[0076] The ceramic fiber A solution is poured into a porous mold with a sieve at the bottom, and then the solvent in the ceramic fiber A solution is filtered out.

[0077] When the solvent in the ceramic fiber A solution is partially filtered out; when the solvent level in the ceramic fiber A solution is filtered out to a height of 5 mm below the primary ceramic fiber A, the ceramic fiber B solution is then poured into a porous mold with a screen at the bottom; then it is filtered to obtain the substrate of the contact gradient heat insulation layer.

[0078] The mass ratio of primary ceramic fiber A to primary ceramic fiber B in the primary gradient insulation layer matrix is ​​2.5:7;

[0079] The primary gradient heat insulation layer substrate is surface treated by: preparing a first solution and impregnating the primary gradient heat insulation layer substrate with the first solution; the first solution is a mixture of sintering aid and water or ethanol, and the sintering aid is boron nitride;

[0080] The mass ratio of primary ceramic fiber A, primary ceramic fiber B, and sintering aid in the primary gradient insulation layer matrix is ​​2.5:7:0.5.

[0081] The primary gradient insulation layer substrate is surface treated, then dried and heat-treated to obtain the gradient insulation layer substrate.

[0082] The primary gradient insulation layer substrate after surface treatment is dried at room temperature for 20 hours, and then subjected to segmented heat treatment.

[0083] The first heat treatment stage was at 70℃ for 16 hours; the second heat treatment stage was at 140℃ for 14 hours; and the third heat treatment stage was at 1300℃ for 2.5 hours.

[0084] An organic precursor is prepared, and the organic precursor is impregnated with a gradient insulation layer matrix, pyrolyzed, and then supercritically dried to obtain the gradient insulation material for the thermal protection system. The organic precursor includes: polycarbosilane and ultra-high temperature ceramic precursor; the ultra-high temperature ceramic precursor includes a liquid-phase precursor of polyboronzirconium; the volume ratio of polycarbosilane to ultra-high temperature ceramic precursor is 2-6.

[0085] The gradient insulation layer substrate is impregnated with the organic precursor and then pyrolyzed under an inert atmosphere at a temperature of 1300°C for 3.5 hours. The supercritical drying process is carried out at a temperature of 270°C, a pressure of 8 MPa, and a time of 3 hours.

[0086] The thermal protection system uses a gradient thermal insulation material comprising a protective layer and a thermal insulation layer. The internal pores of the thermal insulation layer exhibit a gradient change, with the side connected to the thermal insulation layer having a higher density than the side furthest from it. The thermal insulation layer has high internal porosity and a density of 0.2 g / cm³. 3 The density of the protective layer is 1.9 g / cm³. 3 The protective layer has a high degree of densification on the side away from the insulation layer, with a compressive strength of 3.2 MPa and a tensile strength greater than 1.2 MPa. The overall thermal conductivity of the gradient thermal insulation material used in the thermal protection system is 0.045 W / m·K at room temperature and 0.09 W / m·K at 800℃.

[0087] Example 2:

[0088] The features that are the same as those in Embodiment 1 will not be repeated here. The features that differ from those in Embodiment 1 are as follows:

[0089] The ceramic fibers include quartz fibers and aluminosilicate fibers;

[0090] The primary ceramic fiber A is used for secondary treatment before preparing the ceramic fiber A solution. The specific process is: the primary ceramic fiber A is coated with paraffin wax; the primary ceramic fiber B is used for secondary treatment before preparing the ceramic fiber B solution. The specific process is: the primary ceramic fiber B is coated with paraffin wax.

[0091] The mass ratio of paraffin wax to ceramic fiber A is 0.45:1; the mass ratio of paraffin wax to ceramic fiber B is 0.45:1.

[0092] Paraffin wax is applied to the surfaces of primary ceramic fibers A and B; specifically, molten paraffin wax is applied to the surfaces of primary ceramic fibers A and B.

[0093] The aspect ratio of the ceramic fiber A is 480:1; the aspect ratio of the ceramic fiber B is 45:1.

[0094] The mass ratio of ceramic fiber A to silica sol is 30:1; the mass ratio of ceramic fiber B to silica sol is 45:1; the mass ratio of primary ceramic fiber A to dispersant in the ceramic fiber A solution is 12:1; and the mass ratio of primary ceramic fiber B to dispersant in the ceramic fiber B solution is 43:1.

[0095] The mass ratio of primary ceramic fiber A to primary ceramic fiber B in the primary gradient insulation layer matrix is ​​2:8.5;

[0096] The first solution is a mixture of sintering aid and water, wherein the sintering aid is boron carbide; the mass ratio of primary ceramic fiber A, primary ceramic fiber B and sintering aid in the primary gradient insulation layer matrix is ​​2.8.5:0.25;

[0097] The primary gradient insulation layer substrate after surface treatment was dried at room temperature for 11 hours, and then subjected to segmented heat treatment.

[0098] The first heat treatment was carried out at 68℃ for 9 hours; the second heat treatment was carried out at 138℃ for 20 hours; and the third heat treatment was carried out at 1150℃ for 3 hours.

[0099] The ultra-high temperature ceramic precursor includes a liquid-phase precursor of polyboronzirconium and hafnium carbide; the volume ratio of the polycarbosilane to the ultra-high temperature ceramic precursor is 1:2.

[0100] The pyrolysis temperature was 1150℃ and the pyrolysis time was 2.5h; the supercritical drying process had a drying temperature of 260℃, a pressure of 6MPa, and a time of 4.5h.

[0101] The insulation layer has high internal porosity and a density of 0.16 g / cm³. 3 The density of the protective layer is 1.95 g / cm³. 3 The protective layer has a compressive strength of 5 MPa and a tensile strength greater than 1.8 MPa; the overall thermal conductivity of the gradient thermal insulation material used in the thermal protection system is less than 0.03 W / m·K at room temperature and 0.06 W / m·K at 800℃.

[0102] Example 3:

[0103] The features that are the same as those in Embodiment 2 will not be repeated here. The features that differ from those in Embodiment 2 are as follows:

[0104] The primary ceramic fiber A is used for secondary treatment before preparing the ceramic fiber A solution. The specific process is as follows: the primary ceramic fiber A is attached with an organic modification solution to complete the secondary treatment. The organic modification solution includes a reactive monomer and an initiator. The reactive monomer is acrylate.

[0105] The primary ceramic fiber B is used for secondary treatment before preparing the ceramic fiber B solution. The specific process is as follows: the primary ceramic fiber B is attached with an organic modification solution to complete the secondary treatment. The organic modification solution includes a reaction monomer and an initiator. The reaction monomer is methacrylate.

[0106] The mass ratio of the organic modification solution to ceramic fiber A is 0.25:1; the mass ratio of the paraffin or organic modification solution to ceramic fiber B is 0.25:1; the primary ceramic fibers A and B are subjected to heat treatment after the organic modification solution is applied to their surfaces, and the heat treatment temperature is 80℃.

[0107] The initiator is a peroxide, specifically hydrogen peroxide; the organic modification solution is sprayed onto the surface of primary ceramic fiber A and primary ceramic fiber B; the ceramic fibers include zirconium oxide fiber and aluminosilicate fiber;

[0108] The aspect ratio of ceramic fiber A is 150:1; the aspect ratio of ceramic fiber B is 15:1; the mass ratio of ceramic fiber A to silica sol is 15:1; the mass ratio of ceramic fiber B to silica sol is 10:1; the mass ratio of primary ceramic fiber A to dispersant in the ceramic fiber A solution is 35:1; the mass ratio of primary ceramic fiber B to dispersant in the ceramic fiber B solution is 90:1.

[0109] The mass ratio of primary ceramic fiber A to primary ceramic fiber B in the primary gradient insulation layer matrix is ​​3.5:6.5; the first solution is a mixture of sintering aid and water, and the sintering aid is boron nitride;

[0110] The mass ratio of primary ceramic fiber A, primary ceramic fiber B, and sintering aid in the primary gradient insulation layer matrix is ​​3.5:6.5:0.75.

[0111] The primary gradient insulation layer substrate after surface treatment is dried at room temperature for 28 hours, and then subjected to segmented heat treatment.

[0112] The first heat treatment stage was at 72℃ for 22 hours; the second heat treatment stage was at 143℃ for 6 hours; and the third heat treatment stage was at 1450℃ for 1.5 hours.

[0113] The ultra-high temperature ceramic precursor includes a liquid-phase precursor of polyboron zirconium ether and hafnium boride; the volume ratio of polycarbosilane to the ultra-high temperature ceramic precursor is 1:5; the pyrolysis temperature is 1450℃ and the pyrolysis time is 4.5h; the supercritical drying process has a drying temperature of 290℃, a pressure of 11MPa, and a time of 2.5h.

[0114] The insulation layer has high internal porosity and a density of 0.18 g / cm³. 3 The density of the protective layer is 185 g / cm³. 3 The protective layer has a compressive strength of 4 MPa and a tensile strength of 1.7 MPa; the overall thermal conductivity of the gradient thermal insulation material used in the thermal protection system is less than 0.032 W / m·K at room temperature and 0.08 W / m·K at 800℃.

[0115] Example 4:

[0116] The features that are the same as those in Embodiment 2 will not be repeated here. The features that differ from those in Embodiment 2 are as follows:

[0117] Before impregnating the gradient insulation layer substrate with the organic precursor, the surface of the gradient insulation layer substrate is first impregnated with the aerogel precursor. After impregnation, the side of the gradient insulation layer substrate impregnated with the aerogel precursor is then impregnated with the organic precursor.

[0118] pass Figure 1 It can be shown that the protective layer of the gradient thermal insulation material for the thermal protection system prepared by the present invention has high density and low porosity, and the porosity of the protective layer changes in a gradient.

[0119] pass Figure 1 It can be shown that the ceramic fiber overlap of the thermal insulation layer of the gradient thermal insulation material for the thermal protection system prepared by the present invention is connected with borosilicate compound, and other impurities remain in the pores of the ceramic fibers, and the pores are uniform.

[0120] pass Figure 2 It can be seen that the pores of the thermal insulation layer of ceramic fibers prepared by conventional methods contain other impurities and the pore distribution is uneven.

[0121] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a gradient thermal insulation material for a thermal protection system, characterized in that, Includes the following steps: Ceramic fibers are pretreated to obtain ceramic fiber A and ceramic fiber B; The pretreatment of ceramic fibers includes shaving the ceramic fibers at different aspect ratios to obtain ceramic fiber A and ceramic fiber B. Ceramic fiber A and ceramic fiber B are respectively surface treated to obtain primary ceramic fiber A and primary ceramic fiber B. Ceramic fiber A solution and ceramic fiber B solution were prepared based on primary ceramic fiber A and primary ceramic fiber B, respectively. Primary gradient thermal insulation layer matrix prepared based on ceramic fiber A solution and ceramic fiber B solution; The primary gradient insulation layer substrate is surface treated, then dried and heat-treated to obtain the gradient insulation layer substrate. An organic precursor is prepared, and the organic precursor is impregnated with the gradient thermal insulation layer matrix, pyrolyzed, and then supercritically dried to obtain the gradient thermal insulation material for the thermal protection system. The specific process for surface treatment of ceramic fiber A is as follows: Ceramic fiber A is impregnated in silica sol, and then dried and cured to obtain primary ceramic fiber A, wherein the mass ratio of ceramic fiber A to silica sol is (10-50):

1. The specific process for surface treatment of ceramic fiber B is as follows: Ceramic fiber B is impregnated in silica sol, and then dried and cured to obtain primary ceramic fiber B, wherein the mass ratio of ceramic fiber B to silica sol is (5-50):

1. The primary ceramic fiber A is used for secondary treatment before preparing the ceramic fiber A solution. The specific process is as follows: the primary ceramic fiber A is coated with paraffin or an organic modification solution is coated on the surface of the primary ceramic fiber A to complete the secondary treatment. The organic modification solution includes a reaction monomer and an initiator. The reaction monomer is a mixture of triethylene glycol and ethylene oxide monomer, acrylate, or methacrylate. The primary ceramic fiber B is used for secondary treatment before preparing the ceramic fiber B solution. The specific process is as follows: the primary ceramic fiber B is coated with paraffin or an organic modification solution is coated on the surface of the primary ceramic fiber B to complete the secondary treatment. The organic modification solution includes a reactive monomer and an initiator. The reactive monomer is a mixture of triethylene glycol and ethylene oxide monomer, acrylate, or methacrylate.

2. The method for preparing gradient thermal insulation material for thermal protection systems according to claim 1, characterized in that, The aspect ratio of the ceramic fiber A is (100-500):1; the aspect ratio of the ceramic fiber B is (10-50):

1.

3. The method for preparing gradient thermal insulation material for thermal protection systems according to claim 1, characterized in that, The steps for preparing ceramic fiber A solution include: dispersing the primary ceramic fiber A in a dispersion medium to obtain the ceramic fiber A solution; The steps for preparing the ceramic fiber B solution include: dispersing the primary ceramic fiber B in a dispersion medium to obtain the ceramic fiber B solution; The mass ratio of primary ceramic fiber A to dispersant in the ceramic fiber A solution is (10-40):1; The mass ratio of primary ceramic fiber B to dispersant in the ceramic fiber B solution is (40-100):1; The dispersant is water.

4. The method for preparing gradient thermal insulation material for thermal protection systems according to claim 1, characterized in that, The preparation process of the primary gradient thermal insulation layer substrate is as follows: The ceramic fiber A solution is poured into a porous mold with a sieve at the bottom, and then the solvent in the ceramic fiber A solution is filtered out. When all or part of the solvent in the ceramic fiber A solution is filtered out, the ceramic fiber B solution is poured into a porous mold with a screen at the bottom, and the solvent is removed by suction filtration and pressure filtration to obtain the primary gradient insulation layer matrix. The mass ratio of primary ceramic fiber A to primary ceramic fiber B in the primary gradient insulation layer matrix is ​​(1-4):(6-9).

5. The method for preparing gradient thermal insulation material for thermal protection systems according to claim 1, characterized in that, The process of surface treatment of the primary gradient heat insulation layer substrate is as follows: a first solution is prepared, and the primary gradient heat insulation layer substrate is impregnated with the first solution; the first solution is a mixture of sintering aid and water or ethanol, and the sintering aid is one or two of boron nitride and boron carbide. The mass ratio of primary ceramic fiber A, primary ceramic fiber B, and sintering aid in the primary gradient insulation layer matrix is ​​(1-4):(6-9):(0.2-0.8).

6. The method for preparing gradient thermal insulation material for thermal protection systems according to claim 1, characterized in that, The primary gradient insulation layer substrate after surface treatment is dried at room temperature for 10-30 hours, and then subjected to segmented heat treatment. The first stage of heat treatment is at a temperature of 65-75℃ for 8-24 hours; the second stage is at a temperature of 135-145℃ for 4-24 hours; and the third stage is at a temperature of 1100℃-1500℃ for 1-4 hours.

7. The method for preparing gradient thermal insulation material for thermal protection systems according to claim 1, characterized in that, The organic precursor includes: polycarbosilane and ultra-high temperature ceramic precursor; the ultra-high temperature ceramic precursor includes one or two of the following: polyboronzirconium, polycarbosilane, hafnium boride, and hafnium carbide liquid-phase precursor; the volume ratio of the polycarbosilane to the ultra-high temperature ceramic precursor is 1:3-6. and / or After impregnating the gradient insulation layer matrix with the organic precursor, it is pyrolyzed under an inert atmosphere at a temperature of 1100-1500℃ for 2-5 hours. and / or The supercritical drying process is carried out at a drying temperature of 250-300℃, a pressure of 5-12MPa, and a time of 2-5h.

8. The method for preparing gradient thermal insulation material for thermal protection systems according to claim 1, characterized in that, Before impregnating the gradient insulation layer substrate with the organic precursor, the surface of the gradient insulation layer substrate is first impregnated with the aerogel precursor. After impregnation, the side of the gradient insulation layer substrate impregnated with the aerogel precursor is then impregnated with the organic precursor.

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