A continuous gradient thermal insulation tile based on dynamic slurry adsorption molding, its preparation method and application

Abstract

This invention relates to a continuous gradient thermal insulation tile based on dynamic slurry adsorption molding, its preparation method, and its application, belonging to the field of thermal protection material preparation technology. To address the problems of poor functional matching, easy interface cracking, low molding efficiency, and poor structural adjustability of existing thermal insulation tiles, this invention provides a method for preparing a continuous gradient thermal insulation tile based on dynamic slurry adsorption molding. By mixing high-density and low-density slurries online at independently controlled flow rates and then introducing them into a vacuum adsorption mold, a three-stage dynamic slurry adsorption molding process—from loose to dense—is achieved, realizing a continuous gradient transition from a loose layer to a dense layer in the thermal insulation tile, eliminating macroscopic interfaces and solving the problem of delamination and cracking. The fine powder in the high-density slurry penetrates into the loose layer skeleton to form a microscopic interlocking structure, significantly improving interlayer bonding and thermal shock resistance. This invention offers strong process designability, and the product possesses excellent properties such as high-efficiency thermal insulation, resistance to airflow erosion, and structural integration.

Description

Technical Field

[0001] This invention belongs to the field of thermal protection material preparation technology, and particularly relates to a continuous gradient thermal insulation tile based on dynamic slurry adsorption molding, its preparation method and application. Background Technology

[0002] Hypersonic vehicles face intense aerodynamic heating during cruise and reentry phases. Ceramic fiber thermal insulation tiles, with their advantages of low density, low thermal conductivity, high temperature resistance, high strength, and reusability, have become a key material for thermal protection in aerospace and high-temperature industrial furnaces. Traditional rigid ceramic thermal insulation tiles are mostly homogeneous structures, making it difficult to simultaneously meet the requirements of high density and high strength for surface resistance to airflow erosion and low density and high porosity for efficient internal thermal insulation, resulting in poor functional matching.

[0003] To resolve this contradiction, existing technologies generally employ a layered preparation + high-temperature bonding process, separately preparing a high-density erosion-resistant layer and a low-density thermal insulation layer, which are then bonded together with an adhesive at high temperature. For example, patent CN117902886B uses a mixture of fiber and sintering aid, precipitation filtration, and sintering to produce a homogeneous thermal insulation tile, which cannot achieve a functional gradient design; patent CN119078305B introduces a buffer layer through layered impregnation molding, which improves interfacial thermal matching, but still relies on multi-layer bonding molding.

[0004] The aforementioned process interface defects are significant. The layered bonding forms a clear macroscopic interface with abrupt changes in the coefficient of thermal expansion, making it prone to cracking and peeling under high-temperature thermal shock, severely affecting service stability. Moreover, the interlayer bonding force is weak, relying solely on physical adhesion with adhesives, lacking a microscopic interlocking structure, resulting in insufficient shear and thermal shock resistance. Furthermore, traditional vacuum adsorption molding processes suffer from low molding efficiency when preparing gradient structures. Direct filtration of high-density fine powder easily clogs the filter screen, resulting in slow drainage, long molding cycles, and poor compactness and uniformity of the preform. Structural adjustability is also poor, with fixed layer thickness and transition morphology, making it unsuitable for customized needs in complex thermal environments.

[0005] Therefore, there is an urgent need to develop a method for preparing heat-insulating tiles that can achieve continuous transition of composition and structure, no macroscopic interface, and high molding efficiency, so as to meet the dual requirements of material performance and process controllability in high-end thermal protection fields such as hypersonic aircraft. Summary of the Invention

[0006] To address the problems of poor functional matching, easy interface cracking, low molding efficiency, and poor structural adjustability of existing thermal insulation tiles, this invention provides a continuous gradient thermal insulation tile based on dynamic slurry adsorption molding, its preparation method, and its application.

[0007] The technical solution of this invention:

[0008] A method for preparing continuous gradient thermal insulation tiles based on dynamic slurry adsorption molding includes the following steps:

[0009] Step 1: Prepare high-density slurry and low-density slurry respectively; the high-density slurry comprises short-cut ceramic fibers, ceramic powder filler, light-blocking agent and inorganic binder; the low-density slurry comprises long ceramic fibers, pore-forming agent and inorganic binder.

[0010] Step 2: High-density slurry and low-density slurry are fed into the mixing unit for online mixing at independently controlled flow rates. The mixed slurry is then fed into a vacuum adsorption mold with filters on the bottom and side walls. The vacuum pump of the vacuum adsorption mold is started. The total flow rate Q0 of the low-density and high-density slurries is kept constant. The flow rates of the high-density and low-density slurries are controlled in the following three stages:

[0011] Stage 1: Only low-density slurry is conveyed at a flow rate of Q0, and a layer of pure low-density fiber skeleton is deposited at the bottom of the mold;

[0012] Phase 2: The flow rate of the low-density slurry gradually decreases from Q0 to 0, while the flow rate of the high-density slurry gradually increases from 0 to Q0, so that the deposition composition continuously transitions from long fiber-dominated to short fiber / powder-dominated.

[0013] Phase 3: Only high-density slurry is transported at a flow rate of Q0, and pure high-density slurry is deposited on the top of the layer;

[0014] Step 3: After vacuum adsorption is completed, the wet blank is pressed, shaped, dried and sintered at high temperature to obtain a continuous gradient heat insulation tile.

[0015] Furthermore, the high-density slurry in step one comprises the following components in parts by weight: 10-40 parts of chopped ceramic fibers, 5-15 parts of ceramic powder filler, 1-5 parts of opacifier, 5-15 parts of inorganic binder, and 30-60 parts of water; the low-density slurry comprises the following components in parts by weight: 5-30 parts of long ceramic fibers, 1-10 parts of pore-forming agent, 3-10 parts of inorganic binder, and 60-85 parts of water.

[0016] Furthermore, in step one, the chopped ceramic fibers and long ceramic fibers are both combinations of one or more of mullite fibers, quartz fibers, or alumina fibers, wherein the length of the chopped ceramic fibers is less than 100 μm, and the length of the long ceramic fibers is 1~6 mm; the ceramic powder filler is a combination of one or more of fumed silica, alumina, mullite powder, magnesium oxide, or yttrium oxide, and the particle size of the ceramic powder filler is 0.1~5 μm; the light-blocking agent is a combination of one or more of zirconium oxide, titanium oxide, silicon carbide, cerium oxide, or zirconium silicate; the inorganic binder is silica sol or alumina sol; and the pore-forming agent is a combination of one or more of starch, cellulose powder, wood flour, or rice husk powder.

[0017] Furthermore, in step two, the total transport flow rate Q0 is kept constant at 1~3 L / min; the total adsorption time is T, and the time allocation for stages 1, 2 and 3 is 0.4T : 0.4T : 0.2T;

[0018] Phase 2 Vacuum Adsorption Process High-Density Slurry Delivery Flow Rate Q A The conveying flow rate Q of the low-density slurry is (2.5Q0 / T)·t-Q0. B For Q0-Q A In the formula, t is the adsorption time, 0.4T≤t≤0.8T;

[0019] Furthermore, in step two, the total flow rate Q0 of the low-density slurry and the high-density slurry is kept constant at 2 L / min, and the total adsorption time T is 10 min; in stage 1 from the start of adsorption to the 4th minute, the flow rate of the low-density slurry is 2 L / min; in stage 2 from the 4th minute to the 8th minute of adsorption, the flow rate of the high-density slurry is (0.5t-2) L / min, and the flow rate of the low-density slurry is (4-0.5t) L / min; in stage 3 from the 8th minute to the 10th minute, the flow rate of the high-density slurry is 2 L / min.

[0020] Furthermore, in step two, the vacuum degree in stages 1 and 2 is -0.01 to -0.03 MPa, and after the dense layer begins to deposit in stage 3, the vacuum degree gradually increases to -0.06 to -0.09 MPa.

[0021] Furthermore, in step three, the compression ratio of the pressing and shaping is 5-15%, and the holding time is 20-50 seconds; the drying is carried out using microwave drying with a microwave frequency of 2450 MHz, a drying temperature of 100℃, a microwave power of 1.5 kW, and a drying time of 30 min, until the moisture content of the green body is less than 2%; the high-temperature sintering temperature is 1100-1500℃, and the sintering time is 1-3 h.

[0022] A continuous gradient heat insulation tile prepared by the method provided by the present invention comprises a loose layer, a gradient transition layer and a dense layer in sequence from the cold side to the hot side along the thickness direction. There is no macroscopic interface between the loose layer and the dense layer, and it has a microscopic rooted interlocking structure formed by the infiltration of fine powder particles in the high-density slurry into the long fiber skeleton pores of the loose layer.

[0023] Furthermore, the density of the loose layer is 0.10~0.25 g / cm³. 3 The density of the dense layer is 0.35~0.55 g / cm³. 3 .

[0024] Furthermore, the thickness of the loose layer is 6-10 cm, the thickness of the gradient transition layer is 5-10 cm, and the thickness of the dense layer is 1-3 cm.

[0025] The application of a continuous gradient thermal insulation tile provided by the present invention in the preparation of thermal protection components for aerospace vehicles or thermal insulation components for high-temperature industrial kilns.

[0026] The beneficial effects of this invention are:

[0027] This invention achieves a continuous gradient transition in the composition and structure of thermal insulation tiles. Employing a dynamic slurry adsorption molding method, and through a three-stage flow control strategy of first loose and then dense, the composition of the low-density and high-density slurries continuously changes during deposition. Along the thickness direction, the low-density loose layer naturally transitions through a gradient transition layer to a high-density dense layer, with no macroscopic interface present, fundamentally eliminating the macroscopic interface problem of traditional layered bonding processes. Simultaneously, the fine powder particles in the high-density slurry infiltrate into the pores of the long fiber skeleton in the loose layer with the filtrate, forming a microscopic, rooted, two-way mechanically interlocking structure. This effectively avoids problems such as interface cracking and peeling caused by abrupt changes in the coefficient of thermal expansion in traditional processes, significantly improving the thermal shock resistance, interlayer bonding strength, and overall mechanical properties of the thermal insulation tiles. Testing shows that the continuous gradient thermal insulation tiles produced by this invention have a compressive strength of 2.5~3.5 MPa and a shear strength of 0.45~0.65 MPa. This invention achieves an integrated design of heat insulation tile functions. The hot side is dense and resistant to radiation and erosion, while the cold side is loose and provides heat insulation and weight reduction. Furthermore, the continuous gradient structure effectively alleviates the concentration of thermal stress at high temperatures.

[0028] This invention optimizes the vacuum adsorption molding process by employing a first-sparse, then-dense adsorption sequence. First, a pure, low-density, loose layer is deposited, utilizing its high-porosity framework as a natural filter medium. This prevents fine powder in the high-density slurry from directly contacting the filter screen and causing clogging, ensuring smooth discharge of the filtrate. This solves the industry-wide problem of high-density fine powder clogging the filter screen and significantly improves molding efficiency. Combined with a constant total flow control strategy and a low-to-high vacuum control method, rapid and uniform adsorption molding is achieved, shortening the molding cycle while ensuring the uniformity of density and structural integrity of the preform.

[0029] This invention offers highly designable processes, allowing for flexible control of the thickness ratio and gradient morphology of the loose layer, gradient transition layer, and dense layer through programming adjustment of the flow curves, time allocation, and total delivery flow at each stage. This enables customized designs to meet diverse thermal environment requirements. The resulting continuous gradient thermal insulation tiles achieve a cold-surface density of 0.10~0.25 g / cm³. 3 The surface density can reach 0.35~0.55 g / cm³. 3It possesses excellent properties such as high-efficiency heat insulation, resistance to airflow erosion, thermal shock resistance, and structural integration, and can be widely used in fields such as thermal protection components for hypersonic aircraft and heat insulation components for high-temperature industrial kilns. Attached Figure Description

[0030] Figure 1 The images shown are characterization images of the continuous gradient thermal insulation tile prepared in Example 1. (a) is a macroscopic photograph of the actual object, (b) is a microstructure diagram of the loose layer, (c) is a microstructure diagram of the gradient transition layer, and (d) is a microstructure diagram of the dense layer.

[0031] Figure 2 This is a perspective view of the molding device for the gradient heat insulation tile in Example 5;

[0032] Figure 3 This is a diagram showing the usage state of the gradient heat insulation tile forming device in Example 5;

[0033] Figure 4 This is a front view of the molding apparatus for the gradient heat insulation tile in Example 5;

[0034] Figure 5 This is a schematic diagram of the molding device for gradient heat insulation tiles in Example 5;

[0035] Figure 6 This is a schematic diagram of the baffle assembly in Example 5;

[0036] In the diagram: 1-slurry tank, 2-peristaltic pump, 3-inner spiral static mixing tube, 31-tube body, 32-spiral body, 4-molded filter component, 41-shell, 42-piston, 43-first electric push rod, 44-filter base plate, 45-through hole, 46-feed hole, 5-baffle, 51-guide rail, 52-second electric push rod, 6-frame. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, the process equipment or apparatus not specifically specified are all conventional equipment or apparatus in the art. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0038] Example 1

[0039] This embodiment provides a method for preparing continuous gradient thermal insulation tiles based on dynamic slurry adsorption molding, including the following steps:

[0040] Step 1: Prepare high-density slurry and low-density slurry separately;

[0041] Preparation of high-density slurry: 20 parts by weight of short-chopped mullite fibers (<100 μm in length), 10 parts of ceramic powder filler, 5 parts of zirconium oxide opacifier, 10 parts of silica sol, and 55 parts of water were weighed. The ceramic powder filler was a mixture of fumed silica, alumina, and magnesium oxide in a mass ratio of 6:3:1, with an average particle size of 1 μm; the opacifier was zirconium oxide. Water was first added to a mixing container, and the silica sol was slowly added under stirring. After stirring until homogeneous, the opacifier and ceramic powder filler were added, and stirring continued until the powder was fully dispersed. Finally, the short-chopped mullite fibers were added, and stirring at low speed until the fibers were uniformly dispersed to obtain the high-density slurry.

[0042] Preparation of low-density slurry: Weigh out 12 parts by weight of long chopped mullite fibers (1-6 mm in length), 5 parts by weight of starch (pore-forming agent), 6 parts by weight of silica sol, and 77 parts by weight of water. First, add water to a mixing container, then add silica sol and starch under stirring conditions, and stir until homogeneous. Finally, add the long chopped mullite fibers and stir at low speed until the fibers are uniformly dispersed to obtain the low-density slurry.

[0043] Step 2: Dynamic mixing and adsorption molding:

[0044] High-density and low-density slurries are fed into an inner spiral static mixing tube for online mixing at independently controlled flow rates. The mixed slurry is then passed into a vacuum adsorption mold with 200-mesh filters on the bottom and side walls. The vacuum pump is started, with the total delivery flow rate Q0 kept constant at 2 L / min and the total adsorption time T set to 10 min.

[0045] The conveying flow rate is controlled in the following three stages:

[0046] Phase 1 (0~4 min): Only low-density slurry is conveyed, with a conveying flow rate Q. B The flow rate is 2 L / min, and the vacuum degree is -0.02 MPa;

[0047] Stage 2 (4-8 min): Delivery flow rate Q of low-density slurry B The flow rate Q of the high-density slurry is gradually reduced from 2 L / min to 0. A The flow rate was gradually increased from 0 to 2 L / min, Q A = (0.5t-2) L / min, Q B = (4-0.5t) L / min, where t is the adsorption time, 4≤t≤8; vacuum degree maintained at -0.02 MPa;

[0048] Phase 3 (8-10 min): Only high-density slurry is delivered, with a delivery flow rate Q. AThe flow rate was 2 L / min, and the vacuum level was gradually increased to -0.08 MPa.

[0049] Step 3, Post-processing:

[0050] After vacuum adsorption, the wet blank is shaped by limiting and pressing using a top mold at a compression ratio of 10% and a holding time of 30 seconds to remove residual moisture. The wet blank is then fed into a microwave drying device at a microwave frequency of 2450 MHz, a drying temperature of 100℃, a microwave power of 1.5 kW, and a drying time of 30 minutes, until the moisture content of the blank is below 2%. Finally, it is sintered in a high-temperature furnace at 1400℃ for 1.5 hours and cooled with the furnace to obtain a continuous gradient heat-insulating tile.

[0051] The continuous gradient thermal insulation tile prepared in this embodiment comprises, from the cold side to the hot side, a loose layer, a gradient transition layer, and a dense layer along the thickness direction. The loose layer has a thickness of 8 cm, the gradient transition layer has a thickness of 7 cm, and the dense layer has a thickness of 2 cm. There is no macroscopic interface between the loose layer and the dense layer, and it has a microscopic rooted interlocking structure formed by the infiltration of fine powder particles from the high-density slurry into the pores of the long fiber skeleton of the loose layer.

[0052] The density of the porous layer was measured to be 0.18 g / cm³. 3 The density of the dense layer is 0.45 g / cm³. 3 The compressive strength is 3.0 MPa, the shear strength is 0.55 MPa, and after 20 cycles of thermal shock from 1200℃ to room temperature, no peeling or cracking occurred.

[0053] Figure 1 Characterization images of the continuous gradient thermal insulation tiles prepared in this embodiment. Figure 1 (a) is a macroscopic photograph of the actual product, showing that the heat insulation tile is a complete white block structure with a uniform and flat surface, free from defects such as cracks, delamination, and peeling. Macroscopically, there are no traces of interlayer interfaces, which intuitively proves that the present invention achieves the effect of integrated molding and no macroscopic interfaces, which is different from the delamination of traditional bonding processes. Figure 1 (b) is a microstructure diagram of the loose layer. Under the microscopic level, it presents a three-dimensional porous skeleton structure formed by the interlocking of long ceramic fibers. The fibers are long, loosely arranged, with large pore size and good connectivity, forming a low-density network dominated by fibers. This structure has high porosity, which is the key to achieving excellent thermal insulation performance. Figure 1 (c) is a microstructure diagram of the gradient transition layer, and... Figure 1(b) In contrast, a large number of ceramic powder / short fiber particles were clearly observed in the fiber skeleton. The particles began to fill some of the pores, and the fibers were uniformly coated and connected by the powder. The porosity and pore size showed a continuous decreasing trend. This microscopic change corresponds to the process of decreasing the flow rate of low-density slurry and increasing the flow rate of high-density slurry in the process. It realizes a continuous and gradual transition of composition and structure without abrupt interfaces, providing direct evidence for the "rooted interlocking structure". Figure 1 (d) shows the microstructure of the dense layer. At the microscopic level, powder / short fibers dominate, with long fibers only sparsely distributed in the matrix. The pores are filled with a large amount of powder, resulting in a dense and uniform overall structure with almost no large pores. This powder-dominated dense structure significantly improves the material's density and mechanical strength, effectively resisting the erosion of hot surfaces by airflow and high-temperature oxidation.

[0054] Example 2

[0055] This embodiment provides a method for preparing continuous gradient thermal insulation tiles based on dynamic slurry adsorption molding, including the following steps:

[0056] Step 1: Prepare high-density slurry and low-density slurry separately;

[0057] Preparation of high-density slurry: 10 parts by weight of short-cut silica fibers (<100 μm in length), 5 parts of ceramic powder filler, 1 part of silicon carbide opacifier, 5 parts of aluminum sol, and 60 parts of water were weighed. The ceramic powder filler was a mixture of fumed silica and alumina in a 1:1 mass ratio, with an average particle size of 0.2 μm. Water was first added to a mixing container, and then the aluminum sol was slowly added under stirring. After stirring until homogeneous, the opacifier and ceramic powder filler were added, and stirring continued until the powder was fully dispersed. Finally, the short-cut silica fibers were added, and stirring at low speed until the fibers were uniformly dispersed to obtain the high-density slurry.

[0058] Preparation of low-density slurry: Weigh out 5 parts by weight of long-cut quartz fibers (1-6 mm in length), 1 part by weight of cellulose powder (pore-forming agent), 3 parts by weight of aluminum sol, and 80 parts by weight of water. First, add water to a mixing container, then add aluminum sol and cellulose powder under stirring conditions, and stir until homogeneous. Finally, add the long-cut quartz fibers and stir at low speed until the fibers are uniformly dispersed to obtain the low-density slurry.

[0059] Step Two: Dynamic Mixing and Adsorption Molding

[0060] High-density and low-density slurries are fed into an inner spiral static mixing tube for online mixing at independently controlled flow rates. The mixed slurry is then passed into a vacuum adsorption mold with 200-mesh filters on the bottom and side walls. The vacuum pump is started, with the total delivery flow rate Q0 kept constant at 1 L / min and the total adsorption time T set to 20 min.

[0061] The conveying flow rate is controlled in the following three stages:

[0062] Phase 1 (0~8min): Only low-density slurry is conveyed, with a conveying flow rate Q. B The flow rate is 1 L / min, and the vacuum degree is -0.01 MPa;

[0063] Stage 2 (8~16 min): Delivery flow rate Q of low-density slurry B The flow rate Q of the high-density slurry is gradually reduced from 1 L / min to 0. A The flow rate was gradually increased from 0 to 1 L / min, Q A = (0.125t-1) L / min, Q B = (2-0.125t) L / min, where t is the adsorption time, 8≤t≤16; vacuum degree maintained at -0.01MPa;

[0064] Phase 3 (16-20 min): Only high-density slurry is delivered, with a delivery flow rate Q. A The flow rate was 1 L / min, and the vacuum level was gradually increased to -0.06 MPa.

[0065] Step 3: Post-processing

[0066] After vacuum adsorption, the wet blank is shaped by limiting and pressing using a top mold at a compression ratio of 5% and a holding time of 50 seconds to remove residual moisture. The wet blank is then fed into a microwave drying device at a microwave frequency of 2450 MHz, a drying temperature of 100℃, a microwave power of 1.5 kW, and a drying time of 30 minutes, until the moisture content of the blank is below 2%. Finally, it is sintered in a high-temperature furnace at 1100℃ for 3 hours and cooled with the furnace to obtain a continuous gradient heat-insulating tile.

[0067] The continuous gradient thermal insulation tile prepared in this embodiment comprises, from the cold side to the hot side, a loose layer, a gradient transition layer, and a dense layer along the thickness direction, wherein the density of the loose layer is 0.10 g / cm³. 3 The density of the dense layer is 0.35 g / cm³. 3 The compressive strength is 2.5 MPa, and the shear strength is 0.45 MPa. The thickness of the loose layer is 9 cm, the thickness of the gradient transition layer is 8 cm, and the thickness of the dense layer is 2.5 cm. There is no macroscopic interface between the loose and dense layers, and it has a microscopic rooted interlocking structure formed by the infiltration of fine powder particles from the high-density slurry into the pores of the long fiber skeleton in the loose layer. It did not crack after 20 thermal shocks at 1000℃.

[0068] Example 3

[0069] This embodiment provides a method for preparing continuous gradient thermal insulation tiles based on dynamic slurry adsorption molding, including the following steps:

[0070] Step 1: Prepare high-density slurry and low-density slurry separately;

[0071] Preparation of high-density slurry: 30 parts by weight of chopped alumina fibers (<100 μm in length), 12 parts by weight of ceramic powder filler, 5 parts by weight of a mixture of titanium dioxide and zirconium silicate (in a 1:1 mass ratio), 15 parts by weight of silica sol, and 30 parts by weight of water. The ceramic powder filler is a mixture of mullite powder and yttrium oxide in a 4:1 mass ratio, with an average particle size of 5 μm. First, water is added to a mixing container. Then, silica sol is slowly added under stirring. After stirring until homogeneous, the opacifier and ceramic powder filler are added, and stirring continues until the powder is fully dispersed. Finally, the chopped alumina fibers are added, and the mixture is stirred at low speed until the fibers are uniformly dispersed to obtain the high-density slurry.

[0072] Preparation of low-density slurry: Weigh out 20 parts by weight of long-cut alumina fibers (1-6 mm in length), 1 part by weight of a mixture of wood flour and rice husk powder (1:1 by weight), 10 parts by weight of silica sol, and 60 parts by weight of water. First, add water to a mixing container, then add silica sol and the pore-forming agent while stirring, and stir until homogeneous. Finally, add the long-cut alumina fibers and stir at low speed until the fibers are uniformly dispersed to obtain the low-density slurry.

[0073] Step Two: Dynamic Mixing and Adsorption Molding

[0074] High-density and low-density slurries are fed into an inner spiral static mixing tube for online mixing at independently controlled flow rates. The mixed slurry is then passed into a vacuum adsorption mold with 200-mesh filters on the bottom and side walls. The vacuum pump is started, with the total delivery flow rate Q0 kept constant at 3 L / min and the total adsorption time T set to 6.7 min.

[0075] The conveying flow rate is controlled in the following three stages:

[0076] Phase 1 (0~2.7 min): Only low-density slurry is conveyed, with a conveying flow rate Q. B The flow rate is 3 L / min, and the vacuum degree is -0.03 MPa;

[0077] Phase 2 (2.7~5.4 min): Delivery flow rate Q of low-density slurry B The flow rate Q of the high-density slurry is gradually reduced from 3 L / min to 0. A The flow rate was gradually increased from 0 to 3 L / min, Q A = (1.11t-3) L / min, Q B = (6-1.11t) L / min, where t is the adsorption time, 2.7≤t≤5.4; vacuum degree maintained at -0.03MPa;

[0078] Phase 3 (5.4~6.7 min): Only high-density slurry is delivered, with a delivery flow rate Q.A The flow rate was 3 L / min, and the vacuum level was gradually increased to -0.09 MPa.

[0079] Step 3: Post-processing

[0080] After vacuum adsorption, the wet blank is shaped by limiting and pressing with a top mold at a compression ratio of 15% and a holding time of 20 seconds to remove residual moisture. The wet blank is then fed into a microwave drying device at a microwave frequency of 2450 MHz, a drying temperature of 100℃, a microwave power of 1.5 kW, and a drying time of 30 minutes, until the moisture content of the blank is below 2%. Finally, it is sintered in a high-temperature furnace at 1500℃ for 1 hour and cooled with the furnace to obtain a continuous gradient heat-insulating tile.

[0081] The continuous gradient thermal insulation tile prepared in this embodiment comprises, from the cold side to the hot side, a loose layer, a gradient transition layer, and a dense layer along the thickness direction, wherein the density of the loose layer is 0.25 g / cm³. 3 The density of the dense layer is 0.55 g / cm³. 3 The compressive strength is 3.5 MPa, and the shear strength is 0.65 MPa. The thickness of the loose layer is 6 cm, the thickness of the gradient transition layer is 6 cm, and the thickness of the dense layer is 1.5 cm. There is no macroscopic interface between the loose layer and the dense layer, and it has a microscopic rooted interlocking structure formed by the infiltration of fine powder particles from the high-density slurry into the pores of the long fiber skeleton in the loose layer. It did not crack after 20 thermal shocks at 1200℃.

[0082] Example 4

[0083] This embodiment provides a method for preparing continuous gradient thermal insulation tiles based on dynamic slurry adsorption molding, including the following steps:

[0084] Step 1: Prepare high-density slurry and low-density slurry separately;

[0085] Preparation of high-density slurry: 25 parts by weight of a mixture of mullite fibers and alumina fibers (length <100 μm) in a 1:1 mass ratio, 15 parts by weight of ceramic powder filler, 3 parts by weight of cerium oxide opacifier, 12 parts by weight of alumina sol, and 45 parts by weight of water were weighed. The ceramic powder filler was a mixture of fumed silica and mullite powder in a 2:1 mass ratio, with an average particle size of 0.5 μm. First, water was added to a mixing container. Then, the alumina sol was slowly added under stirring. After stirring until homogeneous, the opacifier and ceramic powder filler were added, and stirring continued until the powder was fully dispersed. Finally, the mixture of chopped mullite fibers and chopped alumina fibers in a 1:1 mass ratio was added, and the mixture was stirred at low speed until the fibers were uniformly dispersed, yielding the high-density slurry.

[0086] Preparation of low-density slurry: Weigh out 15 parts by weight of a mixture of mullite fibers and alumina fibers (1-6 mm in length, mass ratio 1:1), 8 parts by weight of a mixture of starch and cellulose powder (pore-forming agent, mass ratio 1:1), 8 parts by weight of alumina sol, and 69 parts by weight of water. First, add water to a mixing container, then add the alumina sol and pore-forming agent while stirring, and stir until homogeneous. Finally, add the mixture of mullite fibers and alumina fibers (mass ratio 1:1) and stir at low speed until the fibers are uniformly dispersed to obtain the low-density slurry.

[0087] Step 2: Dynamic mixing and adsorption molding:

[0088] High-density and low-density slurries are fed into an inner spiral static mixing tube for online mixing at independently controlled flow rates. The mixed slurry is then passed into a vacuum adsorption mold with 200-mesh filters on the bottom and side walls. The vacuum pump is started, with the total delivery flow rate Q0 kept constant at 2 L / min and the total adsorption time T set to 8 min.

[0089] The conveying flow rate is controlled in the following three stages:

[0090] Phase 1 (0~3.2 min): Only low-density slurry is conveyed, with a conveying flow rate Q. B The flow rate is 2 L / min, and the vacuum degree is -0.02 MPa;

[0091] Phase 2 (3.2~6.4 min): Delivery flow rate Q of low-density slurry B The flow rate Q of the high-density slurry is gradually reduced from 2 L / min to 0. A The flow rate was gradually increased from 0 to 2 L / min, Q A = (0.625t-2) L / min, Q B = (4-0.625t) L / min, where t is the adsorption time, 3.2≤t≤6.4; vacuum degree maintained at -0.02 MPa;

[0092] Phase 3 (6.4~8 min): Only high-density slurry is delivered, with a delivery flow rate Q A The flow rate was 2 L / min, and the vacuum level was gradually increased to -0.075 MPa.

[0093] Step 3, Post-processing:

[0094] After vacuum adsorption, the wet blank is shaped by limiting and pressing using a top mold at a compression ratio of 12% and a holding time of 40 seconds to remove residual moisture. The wet blank is then fed into a microwave drying device at a microwave frequency of 2450 MHz, a drying temperature of 100℃, a microwave power of 1.5 kW, and a drying time of 30 minutes, until the moisture content of the blank is below 2%. Finally, it is sintered in a high-temperature furnace at 1300℃ for 2 hours and cooled with the furnace to obtain a continuous gradient heat-insulating tile.

[0095] The continuous gradient thermal insulation tile prepared in this embodiment comprises, from the cold side to the hot side, a loose layer, a gradient transition layer, and a dense layer along the thickness direction, wherein the density of the loose layer is 0.20 g / cm³. 3 The density of the dense layer is 0.50 g / cm³. 3 The compressive strength is 3.2 MPa, and the shear strength is 0.58 MPa. The thickness of the loose layer is 7 cm, the thickness of the gradient transition layer is 6.5 cm, and the thickness of the dense layer is 1.8 cm. There is no macroscopic interface between the loose and dense layers, and it has a microscopic rooted interlocking structure formed by the infiltration of fine powder particles from the high-density slurry into the pores of the long fiber skeleton in the loose layer. It did not crack after 20 thermal shocks at 1200℃.

[0096] Example 5

[0097] This embodiment provides a molding device for gradient heat insulation tiles, used for dynamic mixing and adsorption molding to prepare the gradient heat insulation tiles of the present invention.

[0098] Combination Figures 2-6 This embodiment provides a molding device for gradient heat insulation tiles, which includes a slurry tank 1, a peristaltic pump 2, an inner spiral static mixing pipe 3, a molding filter component 4, and a frame 6.

[0099] The molded filter component 4 includes a housing 41, a piston 42, and a first electric push rod 43. The housing 41 has an internal cavity, and the piston 42 is slidably disposed within the cavity, its sidewall fitting against the cavity sidewall. The bottom plate of the housing 41 is a filter bottom plate 44, on which multiple through holes 45 are formed. The diameter of the through holes 45 is 0.5~3mm, preferably 1mm or 2mm in this embodiment. A feed hole 46 is provided on the sidewall of the housing 41. The housing 41 is made of transparent acrylic sheet, allowing operators to observe the filling status and molding process of the slurry inside the cavity in real time. The piston 42 is made of acrylic sheet, which is lightweight and corrosion-resistant.

[0100] The housing 41 is placed on the frame 6. The first electric push rod 43 is fixedly installed on the top of the housing 41. Its output end extends downward into the cavity of the housing 41 and is fixedly connected to the piston 42, which is used to drive the piston 42 to perform vertical lifting and lowering movements inside the cavity.

[0101] A baffle 5 is provided below the filter base plate 44 for opening or closing the through hole 45. A sealing gasket is provided between the baffle 5 and the filter base plate 44 to ensure that the slurry does not leak from the through hole 45 when closed. The left and right sides of the baffle 5 are mounted to the bottom of the housing 41 via guide rails 51. The guide rails 51 are L-shaped and serve both as guides and vertical supports for the baffle 5. A second electric actuator 52 is fixedly mounted on the frame 6, and its output end is fixedly connected to the baffle 5 via a connecting seat. The installation direction of the second electric actuator 52 is parallel to the guide rail 51, and it is used to drive the baffle 5 to reciprocate along the direction of the guide rail 51, thereby opening and closing the through hole 45.

[0102] The inner spiral static mixing tube 3 includes a tube body 31 and a spiral body 32 fixed inside the tube body 31. Its outlet is connected to the cavity through the feed hole 46 on the side wall of the shell 41.

[0103] There are multiple slurry tanks 1, and each slurry tank 1 is independently equipped with a peristaltic pump 2. The discharge pipes of each peristaltic pump 2 are connected in parallel to the inlet of the inner spiral static mixing pipe 3, and the slurry tank 1 is connected to the inner spiral static mixing pipe 3 through the peristaltic pump 2.

[0104] The slurry tank 1, peristaltic pump 2, internal spiral static mixing pipe 3, and molded filter component 4 are all connected by pipelines. The pipelines are ceramic-lined composite pipes, which are wear-resistant and corrosion-resistant. Each connection is equipped with a sealing strip to ensure the airtightness and leak-proof performance of the delivery pipeline.

[0105] The work process is as follows:

[0106] First, the second electric push rod 52 drives the baffle 5 to move forward along the L-shaped guide rail 51, so that the baffle 5 completely covers the bottom of the filter base plate 44 and closes the through hole 45. The high-density slurry and low-density slurry are then poured into their respective slurry tanks 1.

[0107] The peristaltic pump 2 is turned on, and the slurry in each slurry tank 1 is delivered to the inner spiral static mixing tube 3 at a preset flow rate. As the slurry flows through the spiral 32 inside the tube 31, it is continuously divided, turned, and merged, achieving uniform mixing of multiple components. By programming and controlling the power curve of each peristaltic pump 2, the real-time flow rate of different slurries can be precisely adjusted, thereby obtaining a mixed slurry with continuously changing composition over time.

[0108] The mixed slurry is continuously filled into the cavity of the housing 41 through the feed hole 46. After the slurry level is lower than the feed hole 46, the peristaltic pump 2 is stopped to terminate the feeding.

[0109] Subsequently, the second electric push rod 52 drives the baffle 5 to move backward along the guide rail 51, opening the through hole 45. Free water in the slurry is naturally discharged through the through hole 45 on the filter base plate 44 under gravity. After most of the free water has been discharged, the first electric push rod 43 is activated, driving the piston 42 to move downward, applying pressure to the wet blank inside the cavity for molding, further removing residual moisture and improving the density and uniformity of the blank. After reaching the preset holding time, the first electric push rod 43 drives the piston 42 to move upward and reset, removing the molded gradient insulation tile wet blank, which is then transferred to the subsequent drying and sintering processes to obtain an integrated gradient insulation tile.

Claims

1. A method for preparing continuous gradient thermal insulation tiles based on dynamic slurry adsorption molding, characterized in that, Includes the following steps: Step 1: Prepare high-density slurry and low-density slurry respectively; the high-density slurry comprises short-cut ceramic fibers, ceramic powder filler, light-blocking agent and inorganic binder; the low-density slurry comprises long ceramic fibers, pore-forming agent and inorganic binder. Step 2: High-density slurry and low-density slurry are fed into the mixing unit for online mixing at independently controlled flow rates. The mixed slurry is then fed into a vacuum adsorption mold with filters on the bottom and side walls. The vacuum pump of the vacuum adsorption mold is started. The total flow rate Q0 of the low-density and high-density slurries is kept constant. The flow rates of the high-density and low-density slurries are controlled in the following three stages: Stage 1: Only low-density slurry is conveyed at a flow rate of Q0, and a layer of pure low-density fiber skeleton is deposited at the bottom of the mold; Phase 2: The flow rate of the low-density slurry gradually decreases from Q0 to 0, while the flow rate of the high-density slurry gradually increases from 0 to Q0, so that the deposition composition continuously transitions from long fiber-dominated to short fiber / powder-dominated. Phase 3: Only high-density slurry is transported at a flow rate of Q0, and pure high-density slurry is deposited on the top of the layer; Step 3: After vacuum adsorption is completed, the wet blank is pressed, shaped, dried and sintered at high temperature to obtain a continuous gradient heat insulation tile.

2. The method for preparing continuous gradient thermal insulation tiles according to claim 1, characterized in that, The high-density slurry in step one comprises the following components in parts by weight: 10-40 parts of chopped ceramic fibers, 5-15 parts of ceramic powder filler, 1-5 parts of opacifier, 5-15 parts of inorganic binder, and 30-60 parts of water; the low-density slurry comprises the following components in parts by weight: 5-30 parts of long ceramic fibers, 1-10 parts of pore-forming agent, 3-10 parts of inorganic binder, and 60-85 parts of water.

3. The method for preparing continuous gradient thermal insulation tiles according to claim 1 or 2, characterized in that, The short-cut ceramic fibers and long ceramic fibers mentioned in step one are all combinations of one or more of mullite fibers, quartz fibers, or alumina fibers, wherein the length of the short-cut ceramic fibers is less than 100 μm, and the length of the long ceramic fibers is 1~6 mm; the ceramic powder filler is one or more of fumed silica, alumina, mullite powder, magnesium oxide, or yttrium oxide, and the particle size of the ceramic powder filler is 0.1~5 μm; the light-blocking agent is one or more of zirconium oxide, titanium oxide, silicon carbide, cerium oxide, or zirconium silicate; the inorganic binder is silica sol or alumina sol; and the pore-forming agent is one or more of starch, cellulose powder, wood flour, or rice husk powder.

4. The method for preparing continuous gradient thermal insulation tiles according to claim 3, characterized in that, In step two, the total transport flow rate Q0 is kept constant at 1~3 L / min; the total adsorption time is T, and the time allocation for stages 1, 2 and 3 is 0.4T : 0.4T : 0.2T; Phase 2 Vacuum Adsorption Process High-Density Slurry Delivery Flow Rate Q A The conveying flow rate Q of the low-density slurry is (2.5Q0 / T)·t-Q0. B For Q0-Q A In the formula, t is the adsorption time, and 0.4T≤t≤0.8T.

5. The method for preparing continuous gradient thermal insulation tiles according to claim 4, characterized in that, In step two, the total flow rate Q0 of the low-density slurry and the high-density slurry is kept constant at 2L / min, and the total adsorption time T is 10min; in stage 1, from the start of adsorption to the 4th minute, the flow rate of the low-density slurry is 2L / min. In stage 2, from the 4th to the 8th minute of adsorption, the flow rate of the high-density slurry was (0.5t-2) L / min, and the flow rate of the low-density slurry was (4-0.5t) L / min; in stage 3, from the 8th to the 10th minute, the flow rate of the high-density slurry was 2 L / min.

6. The method for preparing continuous gradient thermal insulation tiles according to claim 5, characterized in that, In step two, the vacuum level in stages 1 and 2 is -0.01 to -0.03 MPa. After the dense layer begins to deposit in stage 3, the vacuum level gradually increases to -0.06 to -0.09 MPa.

7. The method for preparing continuous gradient thermal insulation tiles according to claim 6, characterized in that, The compression ratio of the pressing and shaping in step three is 5~15%, and the holding time is 20~50 seconds; the drying is carried out by microwave drying, with a microwave frequency of 2450 MHz, a drying temperature of 100℃, a microwave power of 1.5 kW, and a drying time of 30 min, until the moisture content of the green body is less than 2%; the high-temperature sintering temperature is 1100~1500℃, and the sintering time is 1~3 h.

8. A continuous gradient thermal insulation tile prepared by the method according to any one of claims 1-7, characterized in that, Along the thickness direction from the cold side to the hot side, it includes a loose layer, a gradient transition layer and a dense layer in sequence. There is no macroscopic interface between the loose layer and the dense layer, and it has a microscopic rooted interlocking structure formed by the infiltration of fine powder particles in the high-density slurry into the long fiber skeleton pores of the loose layer.

9. The continuous gradient thermal insulation tile according to claim 8, characterized in that, The density of the loose layer is 0.10~0.25 g / cm³. 3 The density of the dense layer is 0.35~0.55 g / cm³. 3 .

10. The application of a continuous gradient thermal insulation tile as described in claim 8 or 9 in the manufacture of thermal protection components for aerospace vehicles or thermal insulation components for high-temperature industrial kilns.

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