Alumina fiber porous insulating tile based on aluminum phosphate binder and method

Abstract

The application discloses a kind of based on aluminum phosphate binder preparation alumina fiber porous heat insulating tile and method, short-cut alumina fiber is obtained by standard mesh screen to screen under alumina fiber;Polyacrylamide is mixed with deionized water to prepare polyacrylamide aqueous solution;Phosphoric acid and aluminum hydroxide are reacted in oil bath with certain molar ratio, to obtain aluminum phosphate binder;Screened short-cut fiber, polyacrylamide aqueous solution, aluminum phosphate binder are mixed, stirred and dispersed uniformly, to obtain fiber slurry;Fiber slurry is dehydrated, polymerized, glued and cured, to obtain ceramic heat insulating tile dry embryo;Ceramic heat insulating tile dry embryo is degassed and sintered, to obtain alumina fiber porous heat insulating tile.The application overcomes the technical problems of adhesive thermal migration and reaction with fiber matrix at high temperature in alumina fiber heat insulating tile, has the advantages of low density, porosity and high strength, and can withstand high temperature, and has good application prospect in high-speed spacecraft thermal protection system.

Description

Technical Field

[0001] This invention relates to the field of high-temperature thermal insulation material preparation, and in particular to a method for preparing porous alumina fiber thermal insulation tiles based on aluminum phosphate binder. Background Technology

[0002] New high-speed spacecraft operate at high speeds and for extended periods, facing severe aerodynamic heating environments. Thermal protection materials are crucial for maintaining the spacecraft's normal operation. Fiber porous thermal insulation tiles utilize adhesives to bond randomly distributed high-temperature resistant ceramic fibers, forming a bird's nest-like porous material with numerous three-dimensional interconnected pores. These tiles offer advantages such as lightweight, high strength, efficient thermal insulation, and high operating temperature. While providing excellent thermal protection for spacecraft, fiber porous thermal insulation tiles can significantly reduce their weight and launch costs, making them a highly promising candidate material for large-area thermal protection systems in spacecraft.

[0003] The most widely used high-temperature resistant ceramic fibers are currently quartz fiber, mullite fiber, and alumina fiber. Quartz fiber has a maximum operating temperature of only 1200℃, which cannot meet the temperature resistance requirements of new high-speed spacecraft. Compared with mullite fiber, alumina fiber has higher strength and a higher operating temperature, with a maximum operating temperature of up to 1800℃, and has important applications in the field of high-temperature thermal protection.

[0004] The choice of adhesive is crucial to the structural integrity of thermal insulation tiles. Traditional thermal insulation tiles primarily use silica sol and its composite systems. On one hand, silica sol itself lacks adhesive properties at room temperature and diffuses and migrates with moisture evaporation, meaning it is prone to thermal migration during curing, leading to uneven bonding between internal and external nodes. On the other hand, the introduction of silica sol can cause it to react with alumina fibers at higher temperatures, forming a mullite phase that damages the integrity of the alumina fibers and affects the sample's performance.

[0005] Therefore, there is an urgent need to provide a porous thermal insulation tile with higher operating temperature, good density, porosity and compressive strength to meet the temperature resistance requirements of high-speed aerospace vehicle materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing porous alumina fiber thermal insulation tiles based on aluminum phosphate binder. Alumina fiber is selected as the fiber matrix, and aluminum phosphate binder is used as a room temperature and high temperature dual-use binder through dehydration polymerization and curing at low temperature and phase change sintering at high temperature. This allows the preparation of alumina fiber thermal insulation tiles, thereby achieving higher operating temperatures for high-speed aerospace materials and meeting the requirements for good density, porosity and compressive strength.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] One aspect of the present invention provides a method for preparing porous alumina fiber thermal insulation tiles based on aluminum phosphate binder, comprising the following steps:

[0009] Step 1: Pass the chopped alumina fibers through a standard sieve to obtain undersized chopped alumina fibers;

[0010] Step 2: Mix polyacrylamide with deionized water to prepare a polyacrylamide aqueous solution;

[0011] Step 3: Mix phosphoric acid and aluminum hydroxide at a molar ratio of (2.5-3.5):1, and react them in an oil bath to obtain aluminum phosphate binder;

[0012] Step 4: Mix the chopped alumina fibers, polyacrylamide aqueous solution, and aluminum phosphate binder at a mass ratio of 10:(15-30):(2.5-10), stir and disperse evenly to obtain fiber slurry;

[0013] Step 5: Pour the fiber slurry into the mold and dehydrate, polymerize, and cure the wet fiber slurry blank to obtain the dry ceramic heat insulation tile blank;

[0014] Step 6: Remove the adhesive from the dry ceramic heat insulation tile blank and sinter it to obtain the alumina fiber porous heat insulation tile.

[0015] A further improvement of the present invention is that:

[0016] Preferably, the standard sieve mesh size is 20-120 mesh.

[0017] Preferably, the mass concentration of the prepared polyacrylamide aqueous solution is 1-3 wt.%.

[0018] Preferably, phosphoric acid and aluminum hydroxide are reacted in an oil bath at a temperature of 90-95℃ for 1-2 hours.

[0019] Preferably, the chopped alumina fibers, polyacrylamide aqueous solution, and aluminum phosphate binder are stirred and dispersed evenly at a speed of 50-1500 r / min.

[0020] Preferably, the curing temperature of the fiber pulp wet blank is 50-150℃, and the curing time is 24-72h.

[0021] Preferably, the dry blank of the ceramic heat insulation tile is placed in a muffle furnace for debinding and sintering. The sintering process of the dry blank is to raise the temperature to 600°C at a heating rate of 5-10°C / min, hold for 1-2 hours for debinding, then raise the temperature to 900-1500°C at a heating rate of 3-5°C / min, hold for 2-4 hours for sintering, and then cool with the furnace.

[0022] In another aspect, the present invention provides a porous alumina fiber heat insulation tile prepared based on aluminum phosphate binder obtained by the method described above.

[0023] The alumina fiber porous thermal insulation tile prepared by the present invention based on aluminum phosphate binder has a porosity of greater than 70%.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The method of the present invention uses aluminum phosphate, an inorganic binder, to replace the traditional silica sol system. The low-temperature dehydration polymerization adhesive curing and high-temperature sintering properties of aluminum phosphate are used to ensure the connection of fiber skeleton nodes and the uniformity of the product.

[0026] 2. This invention overcomes the technical problems of thermal migration and high-temperature reaction with the fiber matrix in traditional alumina fiber porous thermal insulation tile adhesives. Compared with silica sol and its composite system, the use of aluminum phosphate adhesive effectively increases the service temperature of the thermal insulation tile from 1200℃ to 1500℃, while ensuring better bonding of the adhesive to the alumina fibers, further improving mechanical properties.

[0027] 3. The alumina fiber porous heat insulation tile prepared by this invention has high porosity and mechanical properties, and can be used at a high temperature of 1500℃. It can be applied to high-temperature fields such as furnace insulation and thermal protection systems for new high-speed aerospace vehicles. Attached Figure Description

[0028] Figure 1 These are electron scanning images of the alumina fiber porous thermal insulation tiles prepared in Example 1;

[0029] Figure 2 This is an electron scanning image of the fiber overlap of the alumina fiber porous thermal insulation tile prepared in Example 1. Detailed Implementation

[0030] To better understand the present invention, the following description, in conjunction with the accompanying drawings and specific embodiments, further clarifies the content of the present invention, but the content of the present invention is not limited to the described embodiments.

[0031] The method for preparing porous alumina fiber thermal insulation tiles based on aluminum phosphate binder provided in this invention includes the following steps:

[0032] Step 1: Pass the chopped alumina fibers through a standard sieve with a mesh size of 20-120 to obtain undersized chopped alumina fibers;

[0033] Step 2: Mix polyacrylamide with deionized water to prepare a polyacrylamide aqueous solution with a mass concentration of 1-3 wt.%.

[0034] Step 3: Phosphoric acid and aluminum hydroxide are reacted in an oil bath at 90-95℃ for 1-2 hours at a P:Al molar ratio of (2.5-3.5):1 to obtain aluminum phosphate binder;

[0035] Step 4: Mix the chopped fibers, polyacrylamide aqueous solution and aluminum phosphate binder at a mass ratio of 10:(15-30):(2.5-10) and stir and disperse them evenly with a stirrer at a speed of 150-500 r / min to obtain fiber slurry;

[0036] Step 5: Pour the above fiber slurry into the mold, transfer the wet fiber slurry blank to a forced-air drying oven for curing, the curing temperature of the wet blank is 50-150℃, the curing time is 24-72h, and the dry blank of ceramic heat insulation tile is obtained.

[0037] Step 6: Place the above-mentioned ceramic heat insulation tile blank into a muffle furnace for debinding and sintering. The sintering process of the blank is to raise the temperature to 600℃ at a heating rate of 5-10℃ / min, hold for 1-2 hours for debinding, then raise the temperature to 900-1500℃ at a heating rate of 3-5℃ / min, hold for 2-4 hours for sintering, and then cool with the furnace to obtain alumina fiber porous heat insulation tile.

[0038] The resulting porous alumina fiber insulation tile has a porosity greater than 70%.

[0039] In the above method, the chopped alumina fibers are sieved to control the fiber length to 100μm-0.1mm, and the mass concentration of polyacrylamide is reasonably controlled at 1-3wt%. This facilitates fiber dispersion without causing the binder to accumulate at the fibers, ensuring the lightweight and high-porosity characteristics of the insulation tile. The aluminum phosphate binder is used for dehydration polymerization and curing at low temperature, controlling the binder to bond at the fiber nodes in situ, forming a uniform bird's nest-like overlapping structure with superior mechanical properties. At temperatures above 900℃, the aluminum phosphate binder can generate stable type A aluminum metaphosphate and aluminum phosphate, with stable ceramic phase chemical properties and higher temperature resistance, further improving the service temperature of the insulation tile.

[0040] The present invention will be further illustrated below through different embodiments.

[0041] Example 1:

[0042] (1) Pass 10g of alumina fiber through a 20-mesh standard sieve to obtain undersized alumina fiber;

[0043] (2) Mix 1g of polyacrylamide with 99g of deionized water to obtain a polyacrylamide aqueous solution with a mass concentration of 1wt.%;

[0044] (3) Phosphoric acid and aluminum hydroxide were placed in an oil bath at 95°C for 1 hour with a molar ratio of P:A = 3:1 to obtain aluminum phosphate binder;

[0045] (4) Add 10g of sieved alumina fiber obtained in step (1) to 20g of polyacrylamide aqueous solution obtained in step (2), and stir continuously for 1 hour with a fixed speed of 500r / min until it is evenly dispersed. Then add 2.5g of aluminum phosphate binder and continue stirring with a stirrer for 3 hours until it is evenly dispersed to obtain fiber slurry.

[0046] (5) Pour the above fiber slurry into the mold and transfer it to an 80°C forced-air oven to cure for 3 days to obtain a dry blank of ceramic fiber heat insulation tile;

[0047] (6) The above-mentioned ceramic heat insulation tile blank is placed in a muffle furnace and heated to 600°C at a heating rate of 10°C / min. The temperature is maintained for 1 hour to remove the glue. Then the temperature is increased to 1300°C at 5°C / min and maintained for 2 hours for sintering. Then the furnace is cooled to obtain the alumina fiber porous heat insulation tile.

[0048] Scanning electron images of the prepared alumina fiber porous thermal insulation tiles are shown below. Figure 1 As shown, the electron scanning image of the fiber overlap of the alumina fiber porous insulation tile is shown below. Figure 2 As shown.

[0049] The sample density is 0.482 g / cm³. 3 It has a porosity of 83%, a compressive strength of 2.04 MPa, and a long-term operating temperature of up to 1500℃.

[0050] Example 2:

[0051] (1) Pass 10g of alumina fiber through a 120-mesh standard sieve to obtain undersized alumina fiber;

[0052] (2) Mix 1.5g of polyacrylamide with 98.5g of deionized water to obtain a polyacrylamide aqueous solution with a mass concentration of 1.5 wt.%;

[0053] (3) Phosphoric acid and aluminum hydroxide were reacted in an oil bath at 95°C for 2 hours with a molar ratio of P:A = 2.8:1 to obtain aluminum phosphate binder;

[0054] (4) Add 10g of sieved alumina fiber obtained in step (1) to 22g of polyacrylamide aqueous solution obtained in step (2), and stir continuously for 1 hour with a fixed speed of 400r / min until it is evenly dispersed. Then add 4g of aluminum phosphate binder and continue stirring with a stirrer for 3 hours until it is evenly dispersed to obtain fiber slurry.

[0055] (5) Pour the above fiber slurry into the mold and transfer it to a forced-air oven at 100°C for 36 hours to cure and obtain a dry blank of ceramic fiber heat insulation tile;

[0056] (6) The above-mentioned ceramic heat insulation tile blank is placed in a muffle furnace and heated to 600°C at a heating rate of 5°C / min. The temperature is maintained for 1 hour to remove the glue. Then the temperature is increased to 1100°C at 5°C / min and maintained for 2 hours for sintering. Then the furnace is cooled to obtain the alumina fiber porous heat insulation tile.

[0057] The sample density is 0.762 g / cm³. 3 It has a porosity of 73%, a compressive strength of 5.42 MPa, and a long-term operating temperature of up to 1500℃.

[0058] Example 3:

[0059] (1) Pass 10g of alumina fiber through a 60-mesh standard sieve to obtain undersized alumina fiber;

[0060] (2) Mix 2g of polyacrylamide with 98g of deionized water to obtain a polyacrylamide aqueous solution with a mass concentration of 2wt.%;

[0061] (3) Phosphoric acid and aluminum hydroxide were placed in an oil bath at 90°C for 2 hours with a molar ratio of P:A = 3.5:1 to obtain aluminum phosphate binder;

[0062] (4) Add 10g of sieved alumina fiber obtained in step (1) to 15g of polyacrylamide aqueous solution obtained in step (2), and stir continuously for 1 hour with a fixed speed of 200r / min until it is evenly dispersed. Then add 2g of aluminum phosphate binder and continue stirring with a stirrer for 3 hours until it is evenly dispersed to obtain fiber slurry.

[0063] (5) Pour the above fiber slurry into the mold and transfer it to a 50°C forced-air oven to cure for 3 days to obtain a dry blank of ceramic fiber heat insulation tile;

[0064] (6) The above-mentioned ceramic heat insulation tile blank is placed in a muffle furnace and heated to 600°C at a heating rate of 10°C / min. The temperature is maintained for 1 hour to remove the glue. Then the temperature is increased to 900°C at 3°C / min and maintained for 4 hours for sintering. Then the furnace is cooled to obtain the alumina fiber porous heat insulation tile.

[0065] The sample density is 0.642 g / cm³. 3 It has a porosity of 77%, a compressive strength of 3.82 MPa, and a long-term operating temperature of up to 1500℃.

[0066] Example 4:

[0067] (1) Pass 10g of alumina fiber through a 100-mesh standard sieve to obtain undersized alumina fiber;

[0068] (2) Mix 3g of polyacrylamide with 97g of deionized water to obtain a polyacrylamide aqueous solution with a mass concentration of 3wt.%;

[0069] (3) Phosphoric acid and aluminum hydroxide were placed in an oil bath at 95°C for 2 hours with a molar ratio of P:A = 2.5:1 to obtain aluminum phosphate binder;

[0070] (4) Add 10g of sieved alumina fiber obtained in step (1) to 30g of polyacrylamide aqueous solution obtained in step (2), and stir continuously for 1 hour with a fixed speed of 150r / min until it is evenly dispersed. Then add 10g of aluminum phosphate binder and continue stirring with a stirrer for 3 hours until it is evenly dispersed to obtain fiber slurry.

[0071] (5) Pour the above fiber slurry into the mold and transfer it to a forced-air oven at 150°C for 24 hours to cure and obtain a dry blank of ceramic fiber heat insulation tile;

[0072] (6) The above-mentioned ceramic heat insulation tile blank is placed in a muffle furnace and heated to 600°C at a heating rate of 10°C / min. The temperature is maintained for 2 hours to remove the glue. Then the temperature is increased to 1500°C at 5°C / min and maintained for 2 hours for sintering. Then the furnace is cooled to obtain the alumina fiber porous heat insulation tile.

[0073] The sample density is 0.596 g / cm³. 3 It has a porosity of 81.4%, a compressive strength of 3.13 MPa, and a long-term operating temperature of up to 1500℃.

[0074] As can be seen from the above embodiments, the alumina fiber porous thermal insulation tile prepared by the present invention has a density of not less than 0.482 g / cm³. 3 With a porosity of not less than 73% and a compressive strength of not less than 2.04 MPa, it possesses good density, porosity, and compressive strength, and also has a higher operating temperature, making it a high-speed aerospace thermal protection material with excellent processing performance.

[0075] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A method for preparing porous alumina fiber thermal insulation tiles based on aluminum phosphate binder, characterized in that, Includes the following steps: Step 1: Pass the chopped alumina fibers through a standard sieve to a mesh size of 20-120 to obtain the undersized chopped alumina fibers; Step 2: Mix polyacrylamide with deionized water to prepare a polyacrylamide aqueous solution; Step 3: Mix phosphoric acid and aluminum hydroxide at a molar ratio of (2.5-3.5):1, and react them in an oil bath to obtain aluminum phosphate binder; Step 4: Mix the chopped alumina fibers, polyacrylamide aqueous solution, and aluminum phosphate binder at a mass ratio of 10:(15-30):(2.5-10), stir and disperse evenly to obtain fiber slurry; The mass concentration of the prepared polyacrylamide aqueous solution is 1-3 wt.%. Step 5: Pour the fiber slurry into the mold and dehydrate, polymerize, and cure the wet fiber slurry blank to obtain the dry ceramic heat insulation tile blank; Step 6: Place the dry ceramic insulation tile blank into a muffle furnace for debinding and sintering. The dry blank is sintered by heating to 600℃ at a rate of 5-10℃ / min and holding for 1-2 hours for debinding; then heating to 1100-1500℃ at a rate of 3-5℃ / min and holding for 2-4 hours for sintering. After that, it is cooled with the furnace to obtain the alumina fiber porous insulation tile. The alumina fiber porous insulation tile has a porosity of more than 70%.

2. The method for preparing porous alumina fiber thermal insulation tiles based on aluminum phosphate binder according to claim 1, characterized in that, Phosphoric acid and aluminum hydroxide react in an oil bath at 90-95℃ for 1-2 hours.

3. The method for preparing porous alumina fiber thermal insulation tiles based on aluminum phosphate binder according to claim 1, characterized in that, Short-cut alumina fibers, polyacrylamide aqueous solution, and aluminum phosphate binder are stirred and dispersed evenly at a speed of 50-1500 r / min.

4. The method for preparing porous alumina fiber thermal insulation tiles based on aluminum phosphate binder according to claim 1, characterized in that, The curing temperature of the fiber pulp wet preform is 50-150℃, and the curing time is 24-72h.

5. An alumina fiber porous heat insulation tile obtained by the method of any one of claims 1-4.

6. The application of the alumina fiber porous thermal insulation tile as described in claim 5 in the thermal protection system of a spacecraft.

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