High Temperature Gradient Composite Aerogel Materials and Preparation Methods for Directional Solidification Single Crystal Furnaces

Abstract

This invention discloses a high-temperature gradient composite aerogel material for directional solidification single-crystal furnaces and its preparation method. The composite aerogel material comprises the following components in the following proportions: 76-91 wt% composite precursor, 0.5-3 wt% catalyst, 0.5-3 wt% dispersant, 1-4 wt% carbon nanotubes, 1-5 wt% fiber component, 1-5 wt% whisker component, and 0.5-5 wt% graphene. The preparation method includes the following steps: preparing a wet gel; aging and supercritical drying the wet gel to obtain a semi-finished composite aerogel material; and carbonizing the semi-finished composite aerogel material. The composite aerogel material of this invention has good thermal insulation properties, a soft texture, excellent mechanical properties, and a long service life. Using this composite aerogel material to make a baffle for a single-crystal furnace can create a high temperature gradient on the mold shell, thereby improving the integrity of the single crystal.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature thermal insulation material design and preparation technology, specifically relating to a high temperature gradient composite aerogel material and preparation method for directional solidification single crystal furnace. This composite aerogel material is particularly suitable for making baffles for directional solidification single crystal furnace, used to form a high temperature gradient on the blade shell during the melting and casting process. Background Technology

[0002] In the manufacturing of high-end equipment such as aerospace and energy, single-crystal blades are core components, and their performance directly determines the operating efficiency and reliability of the equipment. The superior performance of single-crystal blades largely depends on the complete and uniform single-crystal structure formed during the directional solidification process, which places extremely stringent requirements on the temperature field distribution within the single-crystal furnace.

[0003] During the melting and casting process, the directional solidification of single-crystal blades requires precise control of the temperature gradient. When the high-temperature molten metal cools within the mold shell, a sufficiently high and stable temperature difference—a temperature gradient—must be formed on the shell to ensure crystal growth along a single direction and prevent the formation of impurities. In this process, the baffle of the single-crystal furnace plays a crucial role, acting as a precise thermal barrier to effectively isolate the heat generated by the heating coils in the melting chamber from the casting chamber, thereby creating the required temperature gradient in the mold shell region. However, traditional baffle materials for single-crystal furnaces are mainly carbon felt and graphite, which have many insurmountable defects that severely restrict the production quality and efficiency of single-crystal blades.

[0004] From a thermal insulation perspective, traditional baffle materials are ineffective. The thermal conductivity of carbon felt is typically 0.04-0.06 W / (m·K), while graphite materials have even higher thermal conductivity of 0.1-0.3 W / (m·K), making them ineffective at blocking heat transfer. In actual production, when using these traditional baffle materials, the temperature gradient within the single-crystal furnace can only reach 5-10℃ / cm. Such a low temperature gradient leads to unstable crystal growth direction, easily generating impurities during growth. These impurities directly cause blade failure, resulting in severe smelting losses.

[0005] In terms of service life, traditional baffle materials have a relatively short lifespan. Carbon felt and graphite materials undergo oxidation and sintering at high temperatures, resulting in structural damage after each use. This damage accumulates with each use. Generally, the thermal insulation performance of carbon felt baffles decreases by more than 30% after 20-30 uses, while that of graphite baffles decreases by more than 40% after about 50 uses. Because of this rapid decline in thermal insulation performance, frequent baffle replacements are necessary when manufacturing single-crystal blades. This not only increases production costs but also causes downtime due to baffle replacements, reducing production efficiency.

[0006] Furthermore, traditional baffle materials are brittle and lack flexibility. When manufacturing irregularly shaped baffles that conform to the shell's shape, traditional baffle materials cannot adapt well to the complex contours of the shell, making processing difficult. Moreover, these irregularly shaped baffles are often only usable once; they can be easily scratched during the shell's drawing process, which not only increases the manufacturing cost of irregularly shaped baffles but also extends the production cycle due to frequent replacements.

[0007] In summary, the shortcomings of traditional baffle materials in terms of thermal insulation performance, service life, and flexibility have become key bottlenecks restricting the improvement of the production quality and efficiency of monocrystalline blades. Therefore, the development of new baffle materials with excellent thermal insulation performance, long service life, and good flexibility is of great significance to the manufacturing of monocrystalline blades. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a high temperature gradient composite aerogel material for directional solidification single crystal furnaces. The composite aerogel material comprises the following components by mass percentage: composite precursor 76-91 wt%, catalyst 0.5-3 wt%, dispersant 0.5-3 wt%, carbon nanotubes 1-4 wt%, fiber component 1-5 wt%, whisker component 1-5 wt%, and graphene 0.5-5 wt%, with a total content of 100 wt%. The composite precursor is composed of a silicon source, a carbon source, and a zirconium source, with a mass ratio of 3-4.2:1.5-2.3:1.

[0009] Preferably, the silicon source comprises, by mass percentage, 45-52 wt% tetraethyl orthosilicate, 30-43 wt% methyl orthosilicate, and 12-20 wt% silica sol; the carbon source comprises, by mass percentage, 50-65 wt% phenolic resin, 20-35 wt% furfuryl alcohol, and 15-20 wt% resorcinol-formaldehyde resin; and the zirconium source comprises, by mass percentage, 15-25 wt% zirconium sol, 35-45 wt% zirconium chloride, and 35-45 wt% zirconium nitrate.

[0010] In any of the above embodiments, it is preferred that the catalyst is hydrochloric acid or ammonia; the dispersant is a compound of polyvinyl alcohol and polyethylene glycol, wherein the mass ratio of polyvinyl alcohol to polyethylene glycol is 1.5-2:1.

[0011] In any of the above embodiments, it is preferred that the polyethylene glycol is a compound system designed with a molecular weight gradient, wherein the polyethylene glycol in the low molecular weight range of 1000-2000, the medium molecular weight range of 6000-8000, and the high molecular weight range of 10000-14000 accounts for 40-50 wt%, 30-40 wt%, and 20-30 wt% of the total polyethylene glycol, respectively.

[0012] In any of the above embodiments, it is preferred that, in the low molecular weight polyethylene glycol (1000-2000), the mass ratio of polyethylene glycol with a molecular weight of 1000 to that with a molecular weight of 2000 is 2:1; in the medium molecular weight polyethylene glycol (6000-8000), the mass ratio of polyethylene glycol with a molecular weight of 6000 to that with a molecular weight of 8000 is 2:1; and in the high molecular weight polyethylene glycol (10000-14000), the mass ratio of polyethylene glycol with a molecular weight of 10000, a molecular weight of 12000, and a molecular weight of 14000 is 3:2:1.

[0013] In any of the above embodiments, it is preferred that the mass percentage of each substance in the fiber component is 28-42 wt% chopped carbon fiber, 28-42 wt% chopped ceramic fiber, and 20-30 wt% chopped nylon fiber; the diameter of the chopped carbon fiber, the chopped ceramic fiber, and the chopped nylon fiber are all controlled at 10-15 μm, and the aspect ratio is controlled at 50-80:1.

[0014] In any of the above embodiments, it is preferred that the mass percentage of each substance in the whisker component is 25-38 wt% silicon carbide whiskers, 30-42 wt% alumina whiskers, and 28-35 wt% mullite whiskers; the diameters of the silicon carbide whiskers, the alumina whiskers, and the mullite whiskers are all controlled at 1-3 μm, and the aspect ratios are all controlled at 150-200:1.

[0015] In any of the above embodiments, it is preferred that the diameter of the carbon nanotubes is controlled in the range of 10-20 nm and the aspect ratio is controlled in the range of 50-100:1; and the particle size of the graphene is controlled in the range of 100-500 nm.

[0016] This invention also provides a method for preparing a high temperature gradient composite aerogel material for a directional solidification single crystal furnace, the preparation method comprising the following steps in sequence:

[0017] Step 1: According to the designed material ratio, addition order and process parameters, add each substance in the composite aerogel material into the reaction vessel and mix with an appropriate amount of solvent to obtain a wet gel;

[0018] Step 2: Place the prepared wet gel into a water bath containing an aging solution for aging treatment to further cross-link and strengthen the network structure of the wet gel.

[0019] Step 3: Place the aged wet gel into an autoclave for supercritical drying. First, liquid carbon dioxide is introduced into the autoclave to replace the solvent in the wet gel. Then, the temperature and pressure inside the autoclave are increased to convert the carbon dioxide into a supercritical state and maintain it for a certain period of time. Finally, the pressure is slowly released to gradually release the supercritical carbon dioxide until the pressure inside and outside the autoclave is balanced, thus obtaining a semi-finished composite aerogel material.

[0020] Step 4: Place the semi-finished composite aerogel material into a vacuum furnace for carbonization treatment to remove impurities and enhance the orderliness of carbon components. After the carbonization treatment is completed, the composite aerogel material is obtained.

[0021] Preferably, in step one, the preparation method of the wet gel includes the following steps in sequence:

[0022] Step 1.1: Weigh each raw material according to the designed material ratio and set aside;

[0023] Step 1.2: Add ethanol to the reactor as a reaction solvent. The amount of ethanol added is 5-10 wt% of the composite aerogel material. Add the composite precursor while stirring. The stirring temperature is 25-35℃ and the stirring speed is 50-80 r / min. First, add all the substances from the silicon source, including tetraethyl orthosilicate, methyl orthosilicate, and silica sol, to the reactor and stir for 30-40 min. Then, add all the substances from the carbon source, including phenolic resin, furfuryl alcohol, and resorcinol-formaldehyde resin, to the reactor and continue stirring for 30-40 min. Finally, add all the substances from the zirconium source, including zirconium sol, zirconium chloride, and zirconium nitrate, to the reactor and continue stirring for 1-2 h to allow the substances to fuse together.

[0024] Step 1.3: Keep the stirring temperature and stirring speed constant, add all the catalyst and pre-prepared dispersant into the reactor, and continue stirring for 1-2 hours to allow the substances to mix together and form a homogeneous mixture.

[0025] Step 1.4: Keep the stirring temperature constant and increase the stirring speed to 150-200 r / min. Add all the materials in the fiber component (short carbon fiber, short ceramic fiber, short nylon fiber) and the materials in the whisker component (silicon carbide whiskers, alumina whiskers, mullite whiskers and carbon nanotubes) to the reactor. Continue stirring for 3-5 hours to form a multi-size reinforcement system and uniformly disperse the fiber component, whisker component and carbon nanotubes in the mixture.

[0026] Step 1.5: Keep the stirring temperature and stirring speed constant, add graphene to the reactor, and continue stirring for 5-8 hours to allow the composite precursor to be fully hydrolyzed and form a sol. Then continue stirring for 10-15 hours to promote the condensation reaction of the sol and gradually transform it into a wet gel.

[0027] In any of the above embodiments, it is preferred that, in step 1.3, the dispersant needs to be prepared in advance. The preparation method is as follows: First, polyethylene glycol with molecular weights of 10,000, 12,000, and 14,000 is placed in a mixer and heated while stirring at a speed of 100-200 r / min. After the temperature reaches 70-90°C, stirring is continued for 20-50 min. Then, while maintaining the stirring temperature and speed, polyethylene glycol with molecular weights of 1,000, 2,000, 6,000, and 8,000 is added to the mixer and stirred for another 20-50 min. Finally, polyvinyl alcohol is added to the mixer and heated while stirring at a speed of 200-300 r / min. After the temperature reaches 150-200°C, stirring is continued for another 30-80 min to obtain the dispersant.

[0028] In any of the above schemes, it is preferred that in step two, the aging solution is an ethanol solution, the amount of which is added is 50-60 wt% of the mass of the wet gel, the aging temperature is 55-65℃, and the aging time is 45-50 h.

[0029] In any of the above schemes, preferably, in step three, the initial temperature inside the autoclave is 25-35℃ and the initial pressure is 4-6MPa. Liquid carbon dioxide is introduced into the autoclave at a flow rate of 4-6mL / min. The temperature inside the autoclave is raised to 38-42℃ and the pressure is raised to 7.5-8.5MPa. The pressure is maintained for 1.5-2.5h to convert the carbon dioxide into a supercritical state. The depressurization rate is no higher than 0.5MPa / min to gradually release the supercritical carbon dioxide.

[0030] In any of the above schemes, the preferred method is that, in step four, the carbonization process is as follows: the semi-finished composite aerogel material is placed in a vacuum furnace and protected by an inert gas. The temperature is first raised from room temperature to 400-600℃ at a heating rate of 5-10℃ / min and held for 2-4 hours; then the temperature is further raised to 800-1200℃ at a heating rate of 3-5℃ / min and held for 2-4 hours; and then the temperature is lowered to room temperature at a cooling rate of 8-15℃ / min.

[0031] The composite aerogel material prepared by this invention has excellent thermal insulation properties, making it particularly suitable for fabricating baffles in directional solidification single crystal furnaces. During the melting and casting process of the single crystal furnace, this baffle acts to create a high temperature gradient on the mold shell. Depending on the structure of the single crystal furnace and the shape of the mold shell, the prepared composite aerogel material is cut, processed, or molded into a suitable shape for the directional solidification baffle. This baffle is then installed between the heating and cooling zones of the single crystal furnace to ensure effective heat transfer isolation and provide a favorable temperature environment for the directional solidification of single crystals. For example, for common cylindrical single crystal furnaces, the composite aerogel material is processed into a ring-shaped baffle; for single crystal furnaces with special mold shell shapes, the composite aerogel material is molded to fit the shape of the mold shell to create an irregularly shaped baffle.

[0032] In this invention, the chopped ceramic fibers used include any one of chopped alumina fibers, chopped mullite fibers, chopped zirconia fibers, and chopped quartz fibers, which have good thermal insulation properties.

[0033] In this invention, the selection and proportion of each component, the proportion of polyethylene glycol of different molecular weight ranges, the selection and proportion of various fibers and whiskers, the limitation of fiber and whisker size, the order of addition of each component, and process parameters are all very important in the entire preparation process of the composite aerogel material. The material proportion parameters and process parameters need to work together to achieve the technical effect expected by this invention.

[0034] The present invention relates to a high-temperature gradient composite aerogel material and its preparation method for a directional solidification single crystal furnace, which has the following beneficial effects:

[0035] (1) The composite aerogel material prepared by this invention has good thermal insulation effect. The composite aerogel material has low thermal conductivity and a nanoporous structure. The synergistic effect of graphene, carbon nanotubes, fiber components, and whisker components can greatly hinder heat transfer. The carbonization treatment further optimizes the pore structure of the composite aerogel material. Experimental verification shows that at a high temperature of 1500℃, the thermal conductivity of the composite aerogel baffle is only 0.012W / (m·K), which can provide a higher temperature gradient for melting and casting in a directional solidification single crystal furnace. The temperature gradient in the single crystal furnace can be increased to 25-35℃ / cm, thereby greatly improving the integrity of the single crystal and reducing the generation of impurities.

[0036] (2) The composite aerogel material prepared by this invention has the effects of high temperature resistance and long service life. The composite aerogel baffle can withstand high temperatures up to 1800℃, and its structure and performance remain stable after multiple high-temperature uses. The addition of graphene, carbon nanotubes, fiber components, whisker components and carbonization treatment enhance the high-temperature stability and oxidation resistance of the material. After experimental verification, after 100 high-temperature cycles (from room temperature to 1600℃ and then cooled back to room temperature), its heat insulation performance only decreased by 3%, and it can be reused repeatedly, greatly reducing the frequency and cost of replacing the baffle. (3) The composite aerogel material prepared by this invention is soft and has excellent mechanical properties, and can be used to make irregularly shaped baffles and reused multiple times. The composite aerogel material is soft and has good flexibility. At the same time, the addition of graphene, carbon nanotubes, fiber components, whisker components and carbonization treatment improve the strength, fatigue resistance and wear resistance of the material, which is conducive to making irregularly shaped baffles that conform to the shape of the shell. During the shell pulling process, it is not easily scratched and can be used multiple times. Tests have shown that the same irregularly shaped aerogel baffle remains intact after 70 cycles of shell pulling and stretching, and its thermal insulation performance does not decrease significantly. Attached Figure Description

[0037] Figure 1 This is a photograph of a semi-finished composite aerogel material (before carbonization treatment) prepared according to a preferred embodiment of the high temperature gradient composite aerogel material and preparation method for directional solidification single crystal furnace of the present invention.

[0038] Figure 2 for Figure 1 Photograph of the composite aerogel material (after carbonization treatment) prepared in the illustrated embodiment;

[0039] Figure 3 for Figure 1 The macroscopic microstructure of the single-crystal blade prepared using a composite aerogel baffle in the illustrated embodiment is shown in the photograph. Detailed Implementation

[0040] To further understand the invention, the following detailed description of the invention will be provided in conjunction with specific embodiments.

[0041] Example 1:

[0042] According to a preferred embodiment of the high temperature gradient composite aerogel material for directional solidification single crystal furnace of the present invention, the mass percentage of each substance in the composite aerogel material is as follows: composite precursor 84wt%, catalyst 2.3wt%, dispersant 2.3wt%, carbon nanotubes 2.6wt%, fiber component 3wt%, whisker component 3wt%, and graphene 2.8wt%, with a total content of 100wt%. The composite precursor is composed of silicon source, carbon source, and zirconium source, and the mass ratio of silicon source, carbon source, and zirconium source is 3.6:1.9:1.

[0043] The silicon source comprises, by mass percentage, 48 wt% tetraethyl orthosilicate, 36 wt% methyl orthosilicate, and 16 wt% silica sol; the carbon source comprises, by mass percentage, 56 wt% phenolic resin, 26 wt% furfuryl alcohol, and 18 wt% resorcinol-formaldehyde resin; and the zirconium source comprises, by mass percentage, 20 wt% zirconium sol, 40 wt% zirconium chloride, and 40 wt% zirconium nitrate.

[0044] The catalyst is hydrochloric acid or ammonia; the dispersant is a compound of polyvinyl alcohol and polyethylene glycol, with a mass ratio of polyvinyl alcohol to polyethylene glycol of 1.8:1.

[0045] The polyethylene glycol is a molecular weight gradient compound system, wherein the low molecular weight polyethylene glycol (1000-2000), medium molecular weight polyethylene glycol (6000-8000), and high molecular weight polyethylene glycol (10000-14000) account for 45 wt%, 35 wt%, and 20 wt% of the total polyethylene glycol by mass, respectively. In the low molecular weight polyethylene glycol (1000-2000), the mass ratio of polyethylene glycol with a molecular weight of 1000 to 2000 is 2:1; in the medium molecular weight polyethylene glycol (6000-8000), the mass ratio of polyethylene glycol with a molecular weight of 6000 to 8000 is 2:1; and in the high molecular weight polyethylene glycol (10000-14000), the mass ratio of polyethylene glycol with a molecular weight of 10000, 12000, and 14000 is 3:2:1.

[0046] The fiber composition comprises, by mass percentage, 35 wt% chopped carbon fiber, 35 wt% chopped ceramic fiber, and 30 wt% chopped nylon fiber; the diameters of the chopped carbon fiber, chopped ceramic fiber, and chopped nylon fiber are all controlled within 10-15 μm, and their aspect ratios are all controlled within 50-80:1. The chopped ceramic fiber used in this embodiment includes any one of chopped alumina fiber, chopped mullite fiber, chopped zirconia fiber, and chopped quartz fiber.

[0047] The mass percentage of each substance in the whisker component is 32wt% for silicon carbide whiskers, 36wt% for alumina whiskers, and 32wt% for mullite whiskers; the diameters of the silicon carbide whiskers, alumina whiskers, and mullite whiskers are all controlled within 1-3μm, and the aspect ratios are all controlled within 150-200:1.

[0048] The diameter of the carbon nanotubes is controlled within the range of 10-20 nm, and the aspect ratio is controlled within the range of 50-100:1; the particle size of the graphene is controlled within the range of 100-500 nm.

[0049] This embodiment also provides a method for preparing a high-temperature gradient composite aerogel material for a directional solidification single crystal furnace, the preparation method comprising the following steps in sequence:

[0050] Step 1: According to the designed material ratio, addition order and process parameters, add each substance in the composite aerogel material into the reaction vessel and mix with an appropriate amount of solvent to obtain a wet gel;

[0051] Step 2: Place the prepared wet gel into a water bath containing an aging solution for aging treatment to further cross-link and strengthen the network structure of the wet gel.

[0052] Step 3: Place the aged wet gel into an autoclave for supercritical drying. First, liquid carbon dioxide is introduced into the autoclave to replace the solvent in the wet gel. Then, the temperature and pressure inside the autoclave are increased to convert the carbon dioxide into a supercritical state and maintain it for a certain period of time. Finally, the pressure is slowly released to gradually release the supercritical carbon dioxide until the pressure inside and outside the autoclave is balanced, thus obtaining a semi-finished composite aerogel material.

[0053] Step 4: Place the semi-finished composite aerogel material into a vacuum furnace for carbonization treatment to remove impurities and enhance the orderliness of carbon components. After the carbonization treatment is completed, the composite aerogel material is obtained.

[0054] In step one, the preparation method of the wet gel includes the following steps in sequence:

[0055] Step 1.1: Weigh each raw material according to the designed material ratio and set aside;

[0056] Step 1.2: Add ethanol to the reactor as a reaction solvent. The amount of ethanol added is 8 wt% of the composite aerogel material. Add the composite precursor while stirring. The stirring temperature is 30℃ and the stirring speed is 65 r / min. Specifically, first, add all the substances from the silicon source, including tetraethyl orthosilicate, methyl orthosilicate, and silica sol, to the reactor and stir for 35 min. Then, add all the substances from the carbon source, including phenolic resin, furfuryl alcohol, and resorcinol-formaldehyde resin, to the reactor and continue stirring for 35 min. Finally, add all the substances from the zirconium source, including zirconium sol, zirconium chloride, and zirconium nitrate, to the reactor and continue stirring for 1.5 h to allow the substances to fuse together.

[0057] Step 1.3: Keep the stirring temperature and stirring speed constant, add all the catalyst and pre-prepared dispersant into the reactor, and continue stirring for 1.5 hours to allow the substances to mix together and form a homogeneous mixture.

[0058] Step 1.4: Keep the stirring temperature constant and increase the stirring speed to 180 r / min. Add all the materials in the fiber component (short carbon fiber, short ceramic fiber, short nylon fiber) and the materials in the whisker component (silicon carbide whiskers, alumina whiskers, mullite whiskers and carbon nanotubes) to the reactor. Continue stirring for 4 hours to form a multi-size reinforcement system of fiber component, whisker component and carbon nanotubes and disperse them evenly in the mixture.

[0059] Step 1.5: Keep the stirring temperature and stirring speed constant, add graphene to the reactor, and continue stirring for 6.5 h to allow the composite precursor to be fully hydrolyzed and form a sol. Then continue stirring for 12.5 h to promote the condensation reaction of the sol and gradually transform it into a wet gel.

[0060] In step 1.3, the dispersant needs to be prepared in advance. The preparation method is as follows: First, polyethylene glycol with molecular weights of 10,000, 12,000, and 14,000 is placed in a mixer and heated while stirring at a speed of 150 r / min. After the temperature reaches 80°C, stirring is continued for 35 min. Then, while keeping the stirring temperature and speed constant, polyethylene glycol with molecular weights of 1,000, 2,000, 6,000, and 8,000 is added to the mixer and stirred for another 35 min. Finally, polyvinyl alcohol is added to the mixer and heated while stirring at a speed of 250 r / min. After the temperature reaches 180°C, stirring is continued for another 55 min to obtain the dispersant.

[0061] In step two, the aging solution is an ethanol solution, the amount of which is added is 55 wt% of the wet gel mass, the aging temperature is 60℃, and the aging time is 48 h.

[0062] In step three, the initial temperature inside the autoclave is 30℃ and the initial pressure is 5MPa. Liquid carbon dioxide is introduced into the autoclave at a flow rate of 5mL / min. The temperature inside the autoclave is raised to 40℃ and the pressure is raised to 8MPa. The pressure is maintained for 2 hours to allow the carbon dioxide to transform into a supercritical state. The depressurization rate is no higher than 0.5MPa / min to allow the supercritical carbon dioxide to be released gradually.

[0063] In step four, the carbonization process is as follows: the semi-finished composite aerogel material is placed in a vacuum furnace and protected by inert gas. The temperature is first raised from room temperature to 500°C at a rate of 8°C / min and held for 3 hours; then the temperature is raised to 1000°C at a rate of 4°C / min and held for 3 hours; and then the temperature is lowered to room temperature at a rate of 12°C / min.

[0064] The composite aerogel material prepared in this embodiment is used to fabricate a baffle for a directional solidification single crystal furnace. During the melting and casting process of the single crystal furnace, this baffle serves to create a high temperature gradient on the mold shell. Based on the structure of the single crystal furnace and the shape of the mold shell, the prepared composite aerogel material is cut, processed, or molded to form a suitable directional solidification baffle shape, and then installed between the heating and cooling zones of the single crystal furnace to ensure effective heat transfer isolation and provide a favorable temperature environment for directional solidification of single crystals.

[0065] The composite aerogel material semi-finished product prepared in this embodiment (before carbonization treatment) is as follows: Figure 1 As shown, the prepared composite aerogel material (after carbonization treatment) is as follows: Figure 2 As shown in the figure. The macroscopic microstructure of the single-crystal blade prepared using composite aerogel baffles is as follows. Figure 3 As shown, no impurities were generated.

[0066] The prepared composite aerogel baffle was installed between the heating and cooling zones of the single crystal furnace. During the actual melting and casting process, the temperature gradient inside the furnace was measured to reach 35℃ / cm. No impurities were generated during the single crystal growth process. After 100 high-temperature cycles, the heat insulation performance of the baffle decreased by only 3%, and the edges of the baffle remained intact without damage during the shell pulling process.

[0067] The high temperature gradient composite aerogel material and preparation method for directional solidification single crystal furnace in this embodiment have the following beneficial effects: (1) The composite aerogel material has good heat insulation effect. The synergistic effect of graphene, carbon nanotubes, fiber components and whisker components can greatly hinder heat transfer. The carbonization treatment optimizes the pore structure of the composite aerogel material. (2) The composite aerogel material has the effect of high temperature resistance and long service life. It can withstand high temperatures up to 1800℃. After multiple high-temperature uses, its structure and performance remain stable. The addition of graphene, carbon nanotubes, fiber components and whisker components and the carbonization treatment enhance the high temperature stability and oxidation resistance of the material. (3) The composite aerogel material is soft and has excellent mechanical properties. It can be used to make irregular baffles and can be used multiple times. The addition of graphene, carbon nanotubes, fiber components and whisker components and the carbonization treatment improve the strength, fatigue resistance and wear resistance of the material, which is conducive to making irregular baffles with conformal shell shape.

[0068] Example 2:

[0069] Another preferred embodiment of the high temperature gradient composite aerogel material and preparation method for directional solidification single crystal furnace according to the present invention is basically the same as that in Embodiment 1 in terms of material selection and proportioning, process flow and parameters, technical principle, and beneficial effects, except that:

[0070] The composite aerogel material comprises the following components by mass percentage: 76 wt% composite precursor, 2 wt% catalyst, 3 wt% dispersant, 4 wt% carbon nanotubes, 5 wt% fiber component, 5 wt% whisker component, and 5 wt% graphene. The composite precursor is composed of silicon source, carbon source, and zirconium source, with a mass ratio of 3:1.5:1.

[0071] The silicon source comprises, by mass percentage, 45 wt% tetraethyl orthosilicate, 43 wt% methyl orthosilicate, and 12 wt% silica sol; the carbon source comprises, by mass percentage, 50 wt% phenolic resin, 35 wt% furfuryl alcohol, and 15 wt% resorcinol-formaldehyde resin; and the zirconium source comprises, by mass percentage, 15 wt% zirconium sol, 43 wt% zirconium chloride, and 42 wt% zirconium nitrate.

[0072] The catalyst is hydrochloric acid or ammonia; the dispersant is a compound of polyvinyl alcohol and polyethylene glycol, with a mass ratio of polyvinyl alcohol to polyethylene glycol of 1.5:1. The polyethylene glycol is a molecular weight gradient compound system, wherein the low molecular weight range (1000-2000), the medium molecular weight range (6000-8000), and the high molecular weight range (10000-14000) of polyethylene glycol account for 40 wt%, 30 wt%, and 30 wt% of the total polyethylene glycol mass, respectively.

[0073] The fiber components comprise, by mass percentage, 38 wt% chopped carbon fiber, 42 wt% chopped ceramic fiber, and 20 wt% chopped nylon fiber. The whisker components comprise, by mass percentage, 25 wt% silicon carbide whiskers, 40 wt% alumina whiskers, and 35 wt% mullite whiskers.

[0074] In step one, the preparation method of the wet gel includes the following main parameters: Step 1.2: Add ethanol to the reaction vessel, the amount of ethanol added is 5 wt% of the mass of the composite aerogel material, and add the composite precursor while stirring. The stirring temperature is 25℃ and the stirring speed is 50 r / min. That is, first add the substances in the silicon source to the reaction vessel and stir for 40 min, then add the substances in the carbon source to the reaction vessel and continue stirring for 40 min, and finally add the substances in the zirconium source to the reaction vessel and continue stirring for 2 h. Step 1.3: Keep the stirring temperature and stirring speed constant, add the catalyst and the pre-prepared dispersant to the reaction vessel and continue stirring for 2 h. Step 1.4: Keep the stirring temperature constant, increase the stirring speed to 150 r / min, add the substances in the fiber component, the substances in the whisker component, and the carbon nanotubes to the reaction vessel and continue stirring for 5 h. Step 1.5: Keep the stirring temperature and stirring speed constant, add graphene to the reactor and continue stirring for 8 hours to allow the composite precursor to be fully hydrolyzed and form a sol. Then continue stirring for 15 hours to promote the condensation reaction of the sol and gradually transform it into a wet gel.

[0075] In step 1.3, the preparation method of the dispersant includes the following main parameters: polyethylene glycol with molecular weights of 10000, 12000, and 14000 is placed in a mixer, the stirring speed is 100 r / min, the temperature is heated to 70℃ and then stirred for 50 min; polyethylene glycol with molecular weights of 1000, 2000, 6000, and 8000 is added to the mixer and stirred for 50 min; polyvinyl alcohol is added to the mixer, the stirring speed is 200 r / min, the temperature is raised to 150℃ and then stirred for 80 min.

[0076] In step two, the amount of aging solution added is 50 wt% of the wet gel mass, the aging temperature is 55℃, and the aging time is 50 h.

[0077] In step three, the initial temperature inside the autoclave is 25℃ and the initial pressure is 4MPa. Liquid carbon dioxide is introduced into the autoclave at a flow rate of 4mL / min. The temperature inside the autoclave is raised to 38℃ and the pressure is raised to 7.5MPa. The pressure is maintained for 1.5h to allow the carbon dioxide to transform into a supercritical state. The depressurization rate is no higher than 0.5MPa / min to allow the supercritical carbon dioxide to be released gradually.

[0078] In step four, the carbonization process is as follows: first, the temperature is increased from room temperature to 400℃ at a heating rate of 5℃ / min and held for 4 hours; then, the temperature is increased to 800℃ at a heating rate of 3℃ / min and held for 4 hours; and then, the temperature is reduced to room temperature at a cooling rate of 8℃ / min.

[0079] The composite aerogel material prepared in this embodiment is used to make a baffle for a directional solidification single crystal furnace. During the melting and casting process of the single crystal furnace, the baffle plays the role of forming a high temperature gradient on the shell.

[0080] Example 3:

[0081] Another preferred embodiment of the high temperature gradient composite aerogel material and preparation method for directional solidification single crystal furnace according to the present invention is basically the same as that in Embodiment 1 in terms of material selection and proportioning, process flow and parameters, technical principle, and beneficial effects, except that:

[0082] The composite aerogel material comprises the following components by mass percentage: 91 wt% composite precursor, 1.5 wt% catalyst, 1.5 wt% dispersant, 1.5 wt% carbon nanotubes, 1.5 wt% fiber component, 1.5 wt% whisker component, and 1.5 wt% graphene. The composite precursor is composed of silicon source, carbon source, and zirconium source, with a mass ratio of 4.2:2.3:1.

[0083] The silicon source comprises, by mass percentage, 50 wt% tetraethyl orthosilicate, 30 wt% methyl orthosilicate, and 20 wt% silica sol; the carbon source comprises, by mass percentage, 60 wt% phenolic resin, 20 wt% furfuryl alcohol, and 20 wt% resorcinol-formaldehyde resin; and the zirconium source comprises, by mass percentage, 25 wt% zirconium sol, 37 wt% zirconium chloride, and 38 wt% zirconium nitrate.

[0084] The catalyst is hydrochloric acid or ammonia; the dispersant is a compound of polyvinyl alcohol and polyethylene glycol, with a mass ratio of polyvinyl alcohol to polyethylene glycol of 2:1. The polyethylene glycol is a molecular weight gradient compound system, wherein the low molecular weight range (1000-2000), the medium molecular weight range (6000-8000), and the high molecular weight range (10000-14000) of polyethylene glycol account for 43 wt%, 37 wt%, and 20 wt% of the total polyethylene glycol mass, respectively.

[0085] The fiber components comprise, by mass percentage, 28 wt% chopped carbon fiber, 42 wt% chopped ceramic fiber, and 30 wt% chopped nylon fiber. The whisker components comprise, by mass percentage, 38 wt% silicon carbide whiskers, 34 wt% alumina whiskers, and 28 wt% mullite whiskers.

[0086] In step one, the preparation method of the wet gel includes the following main parameters: Step 1.2: Add ethanol to the reaction vessel, the amount of ethanol added is 10 wt% of the mass of the composite aerogel material, and add the composite precursor while stirring. The stirring temperature is 35℃ and the stirring speed is 80 r / min. That is, first add the substances in the silicon source to the reaction vessel and stir for 30 min, then add the substances in the carbon source to the reaction vessel and continue stirring for 30 min, and finally add the substances in the zirconium source to the reaction vessel and continue stirring for 1 h. Step 1.3: Keep the stirring temperature and stirring speed constant, add the catalyst and the pre-prepared dispersant to the reaction vessel and continue stirring for 1 h. Step 1.4: Keep the stirring temperature constant, increase the stirring speed to 200 r / min, add the substances in the fiber component, the substances in the whisker component, and the carbon nanotubes to the reaction vessel and continue stirring for 3 h. Step 1.5: Keep the stirring temperature and stirring speed constant, add graphene to the reactor and continue stirring for 5 hours to allow the composite precursor to be fully hydrolyzed and form a sol. Then continue stirring for 10 hours to promote the condensation reaction of the sol and gradually transform it into a wet gel.

[0087] In step 1.3, the preparation method of the dispersant includes the following main parameters: polyethylene glycol with molecular weights of 10000, 12000, and 14000 is placed in a mixer, stirred at a speed of 200 r / min, heated to 90°C and stirred for 20 min; polyethylene glycol with molecular weights of 1000, 2000, 6000, and 8000 is added to the mixer and stirred for 20 min; polyvinyl alcohol is added to the mixer, stirred at a speed of 300 r / min, heated to 200°C and stirred for 30 min.

[0088] In step two, the amount of aging solution added is 60 wt% of the wet gel mass, the aging temperature is 65℃, and the aging time is 45 h.

[0089] In step three, the initial temperature inside the autoclave is 35℃ and the initial pressure is 6MPa. Liquid carbon dioxide is introduced into the autoclave at a flow rate of 6mL / min. The temperature inside the autoclave is raised to 42℃ and the pressure is raised to 8.5MPa. The pressure is maintained for 2.5h to convert the carbon dioxide into a supercritical state. The depressurization rate is no higher than 0.5MPa / min to gradually release the supercritical carbon dioxide.

[0090] In step four, the carbonization process is as follows: first, the temperature is increased from room temperature to 600℃ at a heating rate of 10℃ / min and held for 2 hours; then, the temperature is increased to 1200℃ at a heating rate of 5℃ / min and held for 2 hours; and then, the temperature is reduced to room temperature at a cooling rate of 15℃ / min.

[0091] The composite aerogel material prepared in this embodiment is used to make a baffle for a directional solidification single crystal furnace. During the melting and casting process of the single crystal furnace, the baffle plays the role of forming a high temperature gradient on the shell.

[0092] Comparative Example 1:

[0093] The baffle of the single crystal furnace was made using traditional carbon felt, with the same shape as in Example 1, and was installed between the heating and cooling zones of the same model of single crystal furnace. During actual melting and casting, the measured temperature gradient inside the furnace was only 8℃ / cm. Impurities generated during single crystal growth led to a blade scrap rate of 28%. After 30 uses, the baffle's heat insulation performance decreased by 35%, and the baffle edges broke during the shell pulling process, rendering it unusable.

[0094] Comparative Example 2:

[0095] Based on the composite aerogel material of Example 1, graphene, carbon nanotubes, fiber components, and whisker components were removed. These substances were directly added to the composite precursor, and the preparation process and parameters were the same as in Example 1. The prepared aerogel material was used to fabricate a baffle for a single-crystal furnace, with the same shape as in Example 1, and installed between the heating and cooling zones of the same model of single-crystal furnace. During actual melting and casting, the temperature gradient inside the furnace was measured to be 15℃ / cm. After 30 uses, the thermal insulation performance of the baffle decreased by 18%.

[0096] The composite precursors, catalysts, dispersants, carbon nanotubes, fiber components, whisker components, graphene and other raw materials used in the above embodiments were purchased from Aladdin Reagent Co., Ltd. and Sinopharm Chemical Reagent Co., Ltd.

[0097] Special Note: The technical solution of this invention involves numerous parameters, and the synergistic effects between these parameters must be comprehensively considered to achieve the beneficial effects and significant progress of this invention. Furthermore, the value ranges of each parameter in the technical solution were obtained through extensive experimentation. For each parameter and its combinations, the inventors recorded a large amount of experimental data; however, due to space limitations, the specific experimental data is not disclosed here. Those skilled in the art will readily understand that this invention includes any combination of the inventive content and specific embodiments described in the foregoing specification and the various parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, each of these combined solutions has not been described in detail. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A high temperature gradient composite aerogel material for directional solidification single crystal furnaces, characterized in that, The composite aerogel material comprises the following components by mass percentage: composite precursor 76-91 wt%, catalyst 0.5-3 wt%, dispersant 0.5-3 wt%, carbon nanotubes 1-4 wt%, fiber component 1-5 wt%, whisker component 1-5 wt%, and graphene 0.5-5 wt%, with a total content of 100 wt%. The composite precursor is composed of a silicon source, a carbon source, and a zirconium source, with a mass ratio of 3-4.2:1.5-2.3:

1. The mass percentage of each substance in the fiber component is 28-42 wt% of chopped carbon fiber, 28-42 wt% of chopped ceramic fiber, and 20-30 wt% of chopped nylon fiber; the diameter of the chopped carbon fiber, the chopped ceramic fiber, and the chopped nylon fiber are all controlled at 10-15 μm, and the aspect ratio is controlled at 50-80:

1. The mass percentage of each substance in the whisker component is as follows: silicon carbide whiskers 25-38 wt%, alumina whiskers 30-42 wt%, and mullite whiskers 28-35 wt%. The diameters of the silicon carbide whiskers, alumina whiskers, and mullite whiskers are all controlled at 1-3 μm, and the aspect ratios are all controlled at 150-200:

1.

2. The high temperature gradient composite aerogel material for directional solidification single crystal furnaces according to claim 1, characterized in that, The silicon source comprises, by mass percentage, 45-52 wt% tetraethyl orthosilicate, 30-43 wt% methyl orthosilicate, and 12-20 wt% silica sol; the carbon source comprises, by mass percentage, 50-65 wt% phenolic resin, 20-35 wt% furfuryl alcohol, and 15-20 wt% resorcinol-formaldehyde resin; and the zirconium source comprises, by mass percentage, 15-25 wt% zirconium sol, 35-45 wt% zirconium chloride, and 35-45 wt% zirconium nitrate.

3. The high temperature gradient composite aerogel material for directional solidification single crystal furnaces according to claim 2, characterized in that, The catalyst is hydrochloric acid or ammonia; the dispersant is a compound of polyvinyl alcohol and polyethylene glycol, with a mass ratio of polyvinyl alcohol to polyethylene glycol of 1.5-2:

1.

4. The high temperature gradient composite aerogel material for directional solidification single crystal furnaces according to claim 3, characterized in that, The polyethylene glycol is a compound system designed with a molecular weight gradient, wherein the polyethylene glycol in the low molecular weight range of 1000-2000, the medium molecular weight range of 6000-8000, and the high molecular weight range of 10000-14000 accounts for 40-50 wt%, 30-40 wt%, and 20-30 wt% of the total polyethylene glycol, respectively. In the low molecular weight polyethylene glycol (1000-2000), the mass ratio of polyethylene glycol with a molecular weight of 1000 to that with a molecular weight of 2000 is 2:1; in the medium molecular weight polyethylene glycol (6000-8000), the mass ratio of polyethylene glycol with a molecular weight of 6000 to that with a molecular weight of 8000 is 2:1; and in the high molecular weight polyethylene glycol (10000-14000), the mass ratio of polyethylene glycol with a molecular weight of 10000, 12000, and 14000 is 3:2:

1.

5. The high temperature gradient composite aerogel material for directional solidification single crystal furnace according to claim 4, characterized in that, The diameter of the carbon nanotubes is controlled within the range of 10-20 nm, and the aspect ratio is controlled within the range of 50-100:1; the particle size of the graphene is controlled within the range of 100-500 nm.

6. A method for preparing a high temperature gradient composite aerogel material for a directional solidification single crystal furnace according to any one of claims 1-5, characterized in that, The preparation method includes the following steps in sequence: Step 1: According to the designed material ratio, addition order and process parameters, add each substance in the composite aerogel material into the reaction vessel and mix with an appropriate amount of solvent to obtain a wet gel; Step 2: Place the prepared wet gel into a water bath containing an aging solution for aging treatment to further cross-link and strengthen the network structure of the wet gel. Step 3: Place the aged wet gel into an autoclave for supercritical drying. First, liquid carbon dioxide is introduced into the autoclave to replace the solvent in the wet gel. Then, the temperature and pressure inside the autoclave are increased to convert the carbon dioxide into a supercritical state and maintain it for a certain period of time. Finally, the pressure is slowly released to gradually release the supercritical carbon dioxide until the pressure inside and outside the autoclave is balanced, thus obtaining a semi-finished composite aerogel material. Step 4: Place the semi-finished composite aerogel material into a vacuum furnace for carbonization treatment to remove impurities and enhance the orderliness of carbon components. After the carbonization treatment is completed, the composite aerogel material is obtained.

7. The method for preparing high temperature gradient composite aerogel material for directional solidification single crystal furnace according to claim 6, characterized in that, In step one, the preparation method of the wet gel includes the following steps in sequence: Step 1.1: Weigh each raw material according to the designed material ratio and set aside; Step 1.2: Add ethanol to the reactor as a reaction solvent. The amount of ethanol added is 5-10 wt% of the composite aerogel material. Add the composite precursor while stirring. The stirring temperature is 25-35℃ and the stirring speed is 50-80 r / min. First, add all the substances from the silicon source, including tetraethyl orthosilicate, methyl orthosilicate, and silica sol, to the reactor and stir for 30-40 min. Then, add all the substances from the carbon source, including phenolic resin, furfuryl alcohol, and resorcinol-formaldehyde resin, to the reactor and continue stirring for 30-40 min. Finally, add all the substances from the zirconium source, including zirconium sol, zirconium chloride, and zirconium nitrate, to the reactor and continue stirring for 1-2 h to allow the substances to fuse together. Step 1.3: Keep the stirring temperature and stirring speed constant, add all the catalyst and pre-prepared dispersant into the reactor, and continue stirring for 1-2 hours to allow the substances to mix together and form a homogeneous mixture. Step 1.4: Keep the stirring temperature constant and increase the stirring speed to 150-200 r / min. Add all the materials in the fiber component (short carbon fiber, short ceramic fiber, short nylon fiber) and the materials in the whisker component (silicon carbide whiskers, alumina whiskers, mullite whiskers and carbon nanotubes) to the reactor. Continue stirring for 3-5 hours to form a multi-size reinforcement system and uniformly disperse the fiber component, whisker component and carbon nanotubes in the mixture. Step 1.5: Keep the stirring temperature and stirring speed constant, add graphene to the reaction vessel, and continue stirring for 5-8 hours to allow the composite precursor to be fully hydrolyzed and form a sol. Then continue stirring for 10-15 hours to promote the condensation reaction of the sol and gradually transform it into a wet gel. In step 1.3, the dispersant needs to be prepared in advance. The preparation method is as follows: First, polyethylene glycol with molecular weights of 10,000, 12,000, and 14,000 is placed in a mixer and heated while stirring at a speed of 100-200 r / min. After the temperature reaches 70-90℃, stirring is continued for 20-50 min. Then, while maintaining the stirring temperature and speed, polyethylene glycol with molecular weights of 1,000, 2,000, 6,000, and 8,000 is added to the mixer and stirred for another 20-50 min. Finally, polyvinyl alcohol is added to the mixer and heated while stirring at a speed of 200-300 r / min. After the temperature reaches 150-200℃, stirring is continued for another 30-80 min to obtain the dispersant.

8. The method for preparing high temperature gradient composite aerogel material for directional solidification single crystal furnace according to claim 7, characterized in that, In step two, the aging solution is an ethanol solution, and its addition amount is 50-60 wt% of the wet gel mass. The aging temperature is 55-65℃, and the aging time is 45-50 h.

9. The method for preparing high temperature gradient composite aerogel material for directional solidification single crystal furnace according to claim 8, characterized in that, In step three, the initial temperature inside the autoclave is 25-35℃ and the initial pressure is 4-6MPa. Liquid carbon dioxide is introduced into the autoclave at a flow rate of 4-6mL / min. The temperature inside the autoclave is then increased to 38-42℃ and the pressure is increased to 7.5-8.5MPa. The pressure is maintained for 1.5-2.5h to allow the carbon dioxide to transform into a supercritical state. The depressurization rate is no higher than 0.5MPa / min to allow the supercritical carbon dioxide to be released gradually.

10. The method for preparing high temperature gradient composite aerogel material for directional solidification single crystal furnace according to claim 9, characterized in that, In step four, the carbonization process is as follows: the semi-finished composite aerogel material is placed in a vacuum furnace and protected with inert gas. The temperature is first raised from room temperature to 400-600℃ at a rate of 5-10℃ / min and held for 2-4 hours. Then, the temperature is raised to 800-1200℃ at a rate of 3-5℃ / min and held for 2-4 hours. Finally, the temperature is lowered to room temperature at a rate of 8-15℃ / min.

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