Alumina aerogel composite material as well as preparation method and application thereof

Abstract

The invention provides an aluminum oxide aerogel composite material as well as a preparation method and application thereof, and belongs to the technical field of aluminum oxide aerogel preparation. The preparation method provided by the invention comprises the following steps: (1) preparing aluminum sol by taking coal gangue as an aluminum source; (2) mixing the aluminum sol obtained in the step (1) with aluminum silicate fibers, and performing gelation to obtain composite hydrogel; and (3) mixing the composite hydrogel obtained in the step (2) with ethanol, aging, mixing with a modifier, modifying, and carrying out graded normal-pressure drying to obtain the aluminum oxide aerogel composite material, the modifier in the step (3) is one or more of absolute ethyl alcohol, tetraethoxysilane and normal hexane. The alumina aerogel composite material prepared by the preparation method provided by the invention has the characteristics of low density, low heat conductivity coefficient and high strength, and is suitable for the high-temperature processing field of special materials and the aerospace field.

Description

Technical Field

[0001] This invention relates to the field of alumina aerogel preparation technology, and in particular to an alumina aerogel composite material, its preparation method, and its application. Background Technology

[0002] The resource utilization of coal-based solid waste has become an increasingly hot research topic. Taking coal gangue as an example, the valuable elements such as aluminum and silicon contained in coal gangue can be used to prepare high-value materials such as aluminum-based chemical raw materials, aerogels, and porous ceramics. This can not only effectively reduce and harmlessly treat solid waste coal gangue, but also alleviate the problem of insufficient energy and resources in my country.

[0003] Alumina aerogels, due to the numerous micropores and mesopores within their nanoparticles, possess excellent thermal, optical, electrical, acoustic, catalytic, and hydrogen storage properties, making them a highly valuable porous material. Traditional alumina aerogels typically use organoaluminate alkoxides as the aluminum source for the sol, but these raw materials are not only costly but also toxic, hindering their further industrial application. While the chemical composition of coal gangue is complex, its main components are aluminum and silicon, making it an effective aluminum source for synthesizing alumina aerogels and also compensating for the shortage of bauxite resources in my country. Therefore, synthesizing alumina aerogel composite materials using inexpensive coal-based solid waste as raw material can achieve high-value utilization of coal-based solid waste and solve the problems of high synthesis costs and insufficient bauxite resources for alumina aerogels.

[0004] However, although alumina aerogel has good high temperature resistance, its low strength and tendency to collapse make it difficult to be widely used. At the same time, the alumina aerogel prepared by coal gangue in the existing technology also has the problems of high density and high thermal conductivity.

[0005] Therefore, how to utilize coal gangue to prepare alumina aerogel composite materials with low density, low thermal conductivity and high strength has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide an alumina aerogel composite material, its preparation method, and its applications. The preparation method provided by this invention uses coal gangue as raw material, and the prepared alumina aerogel composite material has the characteristics of low density, low thermal conductivity, and high strength.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing alumina aerogel composite material, comprising the following steps:

[0009] (1) Aluminum sol was prepared using coal gangue as the aluminum source;

[0010] (2) The aluminum sol obtained in step (1) is mixed with aluminum silicate fiber and then gelled to obtain a composite hydrogel;

[0011] (3) The composite hydrogel obtained in step (2) is mixed with ethanol for aging, then mixed with a modifier for modification, and then dried under normal pressure in stages to obtain an alumina aerogel composite material.

[0012] The modifier in step (3) is one or more of anhydrous ethanol, tetraethyl orthosilicate and n-hexane.

[0013] Preferably, the particle size of the coal gangue is ≤80μm.

[0014] Preferably, step (2) further includes pretreatment of the aluminum silicate fiber before mixing the aluminum sol with the aluminum silicate fiber.

[0015] Preferably, the pretreatment step includes: ultrasonically mixing aluminum silicate fibers with an acidic solution, followed by sequential cleaning and drying.

[0016] Preferably, in step (2), the mass ratio of aluminum silicate fiber to aluminum sol is 1:(13-21).

[0017] Preferably, the aging and modification temperatures in step (3) are independently 40–80°C, and the aging and modification times are independently 24–72 h.

[0018] Preferably, the graded atmospheric pressure drying in step (3) is performed sequentially as follows: drying at 60°C for 4-8 hours, drying at 80°C for 4-8 hours, drying at 100°C for 8-12 hours, and drying at 120°C for 8-12 hours.

[0019] Preferably, the modifier in step (3) is a mixed solution of tetraethyl orthosilicate and anhydrous ethanol.

[0020] The present invention provides an alumina aerogel composite material prepared by the preparation method described in the above technical solution.

[0021] This invention also provides the application of the alumina aerogel composite material described above in the field of high-temperature processing of special materials and in the aerospace field.

[0022] This invention provides a method for preparing alumina aerogel composite material, comprising the following steps:

[0023] (1) Aluminum sol is prepared using coal gangue as the aluminum source; (2) The aluminum sol obtained in step (1) is mixed with aluminum silicate fiber and then gelled to obtain a composite hydrogel; (3) The composite hydrogel obtained in step (2) is mixed with ethanol for aging, then mixed with a modifier for modification, and then dried under graded atmospheric pressure to obtain an alumina aerogel composite material; the modifier in step (3) is one or more of anhydrous ethanol, tetraethyl orthosilicate, and n-hexane. This invention uses coal gangue as the aluminum source to prepare aluminum sol, and achieves low density and low thermal conductivity of alumina aerogel composite material by aging and modifying the gelled aluminum sol; the strength of alumina aerogel composite material is improved by adding aluminum silicate fiber as a reinforcing phase to the aluminum sol; and the thermal conductivity of alumina aerogel composite material is reduced by using graded atmospheric pressure drying. The results of the examples show that the density of the alumina aerogel composite material provided by this invention is 0.18~0.26g / cm³. 3 With a deformation of 25%–94%, its compressive strength is 0.08–13.4 MPa and its thermal conductivity is 0.047–0.081 W / (m·K). After heat treatment at 400℃ to 1200℃, its thermal conductivity is 0.053–0.077 W / (m·K). It has the characteristics of low density, low thermal conductivity and high strength, and is suitable for high-temperature processing of special materials and aerospace. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the preparation process of the alumina aerogel composite material in this embodiment of the invention.

[0025] Figure 2 This is a SEM image of the pretreated aluminosilicate fibers in Example 1 of the present invention;

[0026] Figure 3 This is a SEM image of the alumina aerogel composite material in Example 1 of the present invention;

[0027] Figure 4 This is a SEM image of the alumina aerogel of aluminum silicate fibers without pretreatment in Example 2 of the present invention;

[0028] Figure 5 This is a graph showing the compressive strength of the alumina aerogel composite material in Example 2 of the present invention.

[0029] Figure 6 The infrared spectrum of the alumina aerogel composite material in Example 2 of this invention;

[0030] Figure 7 This is a line graph showing the thermal conductivity of the alumina aerogel composite material at different temperatures in Example 2 of the present invention. Detailed Implementation

[0031] This invention provides a method for preparing alumina aerogel composite material, comprising the following steps:

[0032] (1) Aluminum sol was prepared using coal gangue as the aluminum source;

[0033] (2) The aluminum sol obtained in step (1) is mixed with aluminum silicate fiber and then gelled to obtain a composite hydrogel;

[0034] (3) The composite hydrogel obtained in step (2) is mixed with ethanol for aging, then mixed with a modifier for modification, and then dried under normal pressure in stages to obtain an alumina aerogel composite material.

[0035] This invention uses coal gangue as the aluminum source to prepare aluminum sol.

[0036] In this invention, the step of preparing aluminum sol using coal gangue as the aluminum source preferably includes:

[0037] 1) After activating the coal gangue, mix it with an acid solution to carry out a metathesis reaction, then filter to obtain the supernatant;

[0038] 2) The supernatant obtained in step 1) is mixed with an alkaline solution to carry out a metathesis reaction, and then filtered to obtain an aluminate solution;

[0039] 3) The aluminate solution and acid solution obtained in step 2) are mixed and subjected to a metathesis reaction to obtain aluminum hydroxide powder;

[0040] 4) The aluminum hydroxide powder obtained in step 3) is mixed with an acidic solution, ethanol and a desiccant to carry out a hydrolysis polymerization reaction to obtain aluminum sol.

[0041] In this invention, coal gangue is activated, mixed with an acid solution, subjected to a metathesis reaction, and then filtered to obtain a supernatant.

[0042] In this invention, the particle size of the coal gangue is preferably ≤80μm. Limiting the particle size of the coal gangue to this range facilitates subsequent activation.

[0043] In this invention, when the particle size of the coal gangue is greater than 80 μm, it is preferable to crush the coal gangue so that the particle size of the coal gangue is ≤80 μm.

[0044] In this invention, the coal gangue is preferably coal gangue from Xingxian County, and the composition of the coal gangue from Xingxian County is shown in Table 1.

[0045] Table 1. Main chemical components of Xingxian coal gangue

[0046] chemical composition <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO <![CDATA[TiO2]]> <![CDATA[K2O]]> <![CDATA[Na2O]]> other percentage 51.72 35.66 4.45 2.59 2.11 1.25 0.13 2.09

[0047] In this invention, the activation is preferably calcination activation; the calcination activation temperature is preferably 600–850°C, more preferably 650–800°C; and the calcination activation time is preferably 30–180 min, more preferably 60–120 min. By setting the activation temperature and time within the above ranges, this invention can achieve a complete conversion of alumina in coal gangue into active alumina.

[0048] In this invention, the acid solution is preferably a hydrochloric acid solution; the mass concentration of the hydrochloric acid solution is preferably 20%. Limiting the type and concentration of the acid solution to the above range ensures the complete progress of the reaction.

[0049] In this invention, the preferred temperature for the metathesis reaction of activated coal gangue with acid solution is 80–120°C, more preferably 100–120°C; the preferred time for the metathesis reaction is 2–6 hours, more preferably 4–6 hours. Limiting the temperature and time of the metathesis reaction to the above ranges ensures that the aluminum element in the activated coal gangue is fully dissolved.

[0050] In this invention, the solid-liquid mass ratio of the coal gangue to the acid solution is preferably 1:(3-5), more preferably 1:4. This invention limits the solid-liquid mass ratio of the coal gangue to the acid solution to within the above range to ensure sufficient extraction of aluminum from the coal gangue.

[0051] After obtaining the supernatant, the present invention preferably mixes the supernatant with an alkaline solution to carry out a metathesis reaction and then filters it to obtain an aluminate solution.

[0052] In this invention, the alkaline solution is preferably a sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is preferably 20%. Limiting the type and concentration of the alkaline solution to the above range ensures the complete progress of the reaction.

[0053] In this invention, during the metathesis reaction of the supernatant and the alkaline solution, it is preferable to add an excess of alkaline solution. This invention does not have a particular limitation on the amount of alkaline solution added, as long as the pH of the mixture is greater than 12. This invention obtains aluminate by adding an excess of alkaline solution.

[0054] After obtaining the aluminate solution, the present invention preferably mixes the aluminate solution and the acid solution to carry out a metathesis reaction to obtain aluminum hydroxide powder.

[0055] In this invention, during the metathesis reaction of the aluminate solution and the acid solution, there is no particular limitation on the amount of acid solution added, as long as the pH of the mixture is 4-5. This invention generates aluminum hydroxide precipitate by adding acid solution.

[0056] In this invention, after the metathesis reaction is completed by mixing aluminate solution and acid solution, the reaction products are preferably filtered, washed and dried sequentially to obtain aluminum hydroxide powder.

[0057] The present invention does not impose any special limitations on the filtering operation; any filtering operation commonly used by those skilled in the art can be used.

[0058] In this invention, the solvent used for washing is preferably deionized water. This invention does not impose any special limitations on the washing operation; washing operations commonly used by those skilled in the art can be employed.

[0059] In this invention, the drying temperature is preferably 80–100°C, and the drying time is preferably 8–12 hours. Limiting the drying temperature and time to these ranges ensures that the aluminum hydroxide precipitate is thoroughly dried.

[0060] After obtaining aluminum hydroxide powder, the present invention preferably mixes the aluminum hydroxide powder with an acidic solution, ethanol and a desiccant to carry out a hydrolysis polymerization reaction to obtain aluminum sol.

[0061] In this invention, the solid-liquid mass ratio of the aluminum hydroxide powder to the acidic solution, ethanol, and desiccant is preferably 1:(6-7):(4.7-5.9):(1.4-1.7); more preferably 1:(6-6.5):(5-5.5):(1.5-1.7); and even more preferably 1:6.3:5.3:1.7. Limiting the solid-liquid mass ratio of the aluminum hydroxide powder to the acidic solution, ethanol, and desiccant to the above range ensures the formation of an aluminum sol.

[0062] In this invention, the acidic solution is preferably a hydrochloric acid solution; the mass concentration of the hydrochloric acid solution is preferably 20%. Limiting the type and concentration of the acidic solution to the above range in this invention is beneficial for the preparation of aluminum sol.

[0063] In this invention, the desiccant is preferably N,N-dimethylformamide (DMF). Limiting the type of desiccant to the above-mentioned type in this invention is beneficial for the preparation of aluminum sol.

[0064] In this invention, the mixing of the aluminum hydroxide powder with the acidic solution, ethanol, and desiccant is preferably carried out under heating and stirring; the heating and stirring temperature is preferably 40–80°C, more preferably 50–60°C; the heating and stirring time is preferably 1–4 hours, more preferably 2–3 hours; the mixing is preferably carried out in a constant temperature oil bath. Limiting the heating and stirring temperature and time to the above ranges allows for a more complete sol-gelation process.

[0065] After obtaining the aluminum sol, the present invention mixes the aluminum sol with aluminum silicate fiber and then gels it to obtain a composite hydrogel.

[0066] In this invention, the mass ratio of aluminum silicate fiber to aluminum sol is preferably 1:(13-21), more preferably 1:(13-18), and even more preferably 1:(13-15). Limiting the mass ratio of aluminum silicate fiber to aluminum sol to the above range allows the resulting composite material to have good strength.

[0067] In this invention, the aluminum sol is preferably further subjected to pretreatment of the aluminum silicate fiber before mixing with the aluminum silicate fiber.

[0068] In this invention, the pretreatment step preferably includes: ultrasonically mixing aluminum silicate fibers with an acidic solution, followed by sequential cleaning and drying.

[0069] In this invention, the acidic solution in the ultrasonic mixing of the aluminum silicate fiber and the acidic solution is preferably a hydrochloric acid solution; the molar concentration of the hydrochloric acid solution is preferably 0.1 to 1 mol / L.

[0070] In this invention, the frequency of the ultrasound is preferably 20-60 Hz, and the duration of the ultrasound is preferably 2-4 hours.

[0071] In this invention, the solvent used for cleaning is preferably anhydrous ethanol; the number of cleaning cycles is preferably 3 to 4. This invention does not impose any particular limitation on the cleaning operation; any operation well-known to those skilled in the art can be used.

[0072] In this invention, the drying temperature is preferably 70–80°C. This invention does not have a specific limitation on the drying time, as long as the aluminum silicate fibers are completely dried.

[0073] This invention can ensure the removal of impurities and slag balls from fibers through pretreatment.

[0074] In this invention, the mixing of the aluminum sol and aluminum silicate fibers is preferably carried out in a magnetic stirrer; the mixing speed is preferably 1500-2500 r / min, more preferably 2000 r / min; and the mixing time is preferably 5-20 min. This invention can stir the fibers in the sol into a cotton-like state through mixing.

[0075] In this invention, the solvent used for gelation is preferably propylene oxide.

[0076] In this invention, the solid-liquid mass ratio of the aluminum hydroxide powder to the propylene oxide is preferably 1:(3.7-5.3), more preferably 1:(4.5-5.3). By limiting the solid-liquid mass ratio of the aluminum hydroxide powder to the propylene oxide to the above range, a hydrogel can be obtained.

[0077] In this invention, the gelation method is preferably static standing; the static standing temperature is preferably 30–60°C, and the static standing time is preferably 5–20 minutes. This invention utilizes static standing to promote the formation of alumina hydrogels.

[0078] After obtaining the composite hydrogel, the present invention mixes the composite hydrogel with ethanol for aging, then mixes it with a modifier for modification, and then performs graded drying at normal pressure to obtain an alumina aerogel composite material.

[0079] In this invention, the volume ratio of the composite hydrogel to ethanol is preferably 1:(1.5-2.5), more preferably 1:2. Limiting the volume ratio of the composite hydrogel to ethanol to the above range in this invention is more conducive to the aging of the composite hydrogel.

[0080] In this invention, the volume ratio of the composite hydrogel to the modifier is preferably 1:(0.2-0.8), more preferably 1:0.5. Limiting the volume ratio of the composite hydrogel to the modifier to the above range in this invention is more beneficial to the modification of the composite hydrogel.

[0081] In this invention, the modifier is one or more of anhydrous ethanol, tetraethyl orthosilicate, and n-hexane; preferably, it is a mixed solution of tetraethyl orthosilicate and anhydrous ethanol; the volume concentration of tetraethyl orthosilicate in the mixed solution of tetraethyl orthosilicate and anhydrous ethanol is preferably 80%. This invention limits the type and concentration of the modifier to the above range to achieve low density and low thermal conductivity in alumina aerogel composite materials.

[0082] In this invention, the aging and modification temperature is preferably 40-80°C, more preferably 50-60°C; the aging and modification time is preferably 24-72h, more preferably 36-48h.

[0083] In this invention, the ethanol is preferably replaced every 12 hours during the aging process. This invention replaces the ethanol to displace water and reaction byproducts.

[0084] In this invention, the modifier is preferably replaced every 12 hours during the modification process. This invention, by replacing the modifier, can displace residual modifier, water, and other byproducts.

[0085] In this invention, the staged atmospheric pressure drying is preferably performed sequentially at 60°C for 4–8 hours, 80°C for 4–8 hours, 100°C for 8–12 hours, and 120°C for 8–12 hours; more preferably, it is performed sequentially at 60°C for 4–6 hours, 80°C for 4–6 hours, 100°C for 8–10 hours, and 120°C for 8–10 hours. This invention improves the thermal stability and reduces the thermal conductivity of alumina aerogel composite materials through staged atmospheric pressure drying.

[0086] This invention uses coal gangue as an aluminum source to prepare aluminum sol. By aging and modifying the gelled aluminum sol, the low density and low thermal conductivity of the alumina aerogel composite material are achieved. The strength of the alumina aerogel composite material is improved by adding aluminum silicate fiber as a reinforcing phase to the aluminum sol. The thermal conductivity of the alumina aerogel composite material is reduced by using staged atmospheric pressure drying.

[0087] The present invention provides an alumina aerogel composite material prepared by the preparation method described in the above technical solution.

[0088] This invention also provides the application of the alumina aerogel composite material described above in the field of high-temperature processing of special materials and in the aerospace field.

[0089] In embodiments of the present invention, such as Figure 1 As shown, the preparation process of the alumina aerogel composite material is as follows:

[0090] After mixing coal gangue powder with hydrochloric acid, the mixture is stirred, impurities are removed and filtered in sequence, and then mixed with anhydrous ethanol, DMF and aluminum silicate fiber to obtain aluminum sol.

[0091] Aluminum sol was mixed with propylene oxide to obtain a hydrogel (composite hydrogel);

[0092] The hydrogel (composite hydrogel) was aged and modified to obtain an alumina aerogel composite material (alumina silicate fiber / alumina aerogel composite material);

[0093] Thermal conductivity of alumina aerogel composite material (alumina silicate fiber / alumina aerogel composite material) was tested.

[0094] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0095] Example 1

[0096] A method for preparing an alumina aerogel composite material comprises the following steps:

[0097] (1) 25g of activated coal gangue with a particle size ≤80μm was placed in 100mL of 20% hydrochloric acid solution and stirred at 120℃ for 6h. Excess sodium hydroxide solution with a mass concentration of 20% was added to the supernatant after filtration until pH >12. After filtration, 20% hydrochloric acid solution was added dropwise to the supernatant until pH 4.7 was obtained to obtain aluminum hydroxide precipitate. After drying at 80℃ for 12h, aluminum hydroxide powder was obtained.

[0098] (2) 6g of aluminum hydroxide powder, 38mL of 20% hydrochloric acid solution, 44mL of anhydrous ethanol, and 10mL of DMF are heated and stirred at 60℃ for 2h to obtain aluminum sol; the pH of the aluminum sol is 3-4; the preferred solid-liquid mass ratio of the aluminum hydroxide powder to the hydrochloric acid solution, anhydrous ethanol, and DMF is 1:6.3:5.3:1.7;

[0099] (3) Soak 10g of aluminosilicate fiber in 60mL of 0.2mol / L hydrochloric acid solution, sonicate at 40HZ for 1h, filter and wash with ethanol 3 times, and dry at 80℃ for pretreatment to obtain pretreated aluminosilicate fiber. Mix the aluminum sol obtained in step (2) with the pretreated aluminosilicate fiber in a stirrer at 2000r / min for 10min until the fiber is in the form of cotton wool to obtain aluminum sol containing aluminosilicate fiber; the mass ratio of the pretreated aluminosilicate fiber to the aluminum sol is 1:13.

[0100] (4) The aluminum silicate fiber aluminum sol obtained in step (3) is mixed with 42 mL of propylene oxide and then left to stand at 30 °C for 15 min to obtain a composite hydrogel.

[0101] (5) The composite hydrogel obtained in step (4) is mixed with ethanol at 60°C. The ethanol is replaced every 12 hours. After aging for 48 hours, the hydrogel is soaked in ethanol and then soaked in a mixture of tetraethyl orthosilicate and ethanol at 60°C. The modifier is replaced every 12 hours. After 48 hours, the modified composite gel is soaked in anhydrous ethanol at 60°C for 48 hours. The ethanol is replaced every 12 hours. After completion, the gel is placed in a forced-air drying oven and dried at 60°C for 6 hours, 80°C for 6 hours, 100°C for 8 hours, and 120°C for 8 hours to obtain an alumina aerogel composite material. The volume ratio of the alumina hydrogel to ethanol is 1:2. The volume ratio of the alumina hydrogel to the modifier is 1:0.5.

[0102] The preferred solid-liquid mass ratio of aluminum hydroxide powder in step (2) to propylene oxide in step (4) is 1:5.2.

[0103] The density of the alumina aerogel composite material obtained in Example 1 was tested and found to be 0.26 g / cm³.3 ;

[0104] The thermal conductivity of the alumina aerogel composite material obtained in Example 1 was measured to be 0.068 W / (m·K) using the transient flat plate heat source method. The thermal conductivity of the composite material after modification with the modifier decreased significantly, and the thermal insulation performance was improved.

[0105] Comparative Example 1

[0106] A method for preparing an alumina aerogel composite material comprises the following steps:

[0107] (1) 25g of activated coal gangue with a particle size ≤80μm was placed in 100mL of 20% hydrochloric acid solution and stirred at 120℃ for 6h. Excess sodium hydroxide solution with a mass concentration of 20% was added to the supernatant after filtration until pH >12. After filtration, 20% hydrochloric acid solution was added dropwise to the supernatant until pH 4.7 was obtained to obtain aluminum hydroxide precipitate. After drying at 80℃ for 12h, aluminum hydroxide powder was obtained.

[0108] (2) 6g of aluminum hydroxide powder, 38mL of 20% hydrochloric acid solution, 44mL of anhydrous ethanol, and 10mL of DMF are heated and stirred at 60℃ for 2h to obtain aluminum sol; the pH of the aluminum sol is 3-4; the preferred solid-liquid mass ratio of the aluminum hydroxide powder to the hydrochloric acid solution, anhydrous ethanol, and DMF is 1:6.3:5.3:1.7;

[0109] (3) Soak 7g of aluminosilicate fiber in 60mL of 0.2mol / L hydrochloric acid solution, sonicate at 40Hz for 1h, filter and wash with ethanol 3 times, and dry at 80℃ for pretreatment to obtain pretreated aluminosilicate fiber. Mix the aluminum sol obtained in step (2) with the pretreated aluminosilicate fiber in a stirrer at 2000r / min for 10min until the fiber is in the form of cotton wool to obtain aluminum sol containing aluminosilicate fiber; the mass ratio of the pretreated aluminosilicate fiber to the aluminum sol is 1:13.

[0110] (4) The aluminum silicate fiber aluminum sol obtained in step (3) is mixed with 42 mL of propylene oxide and then left to stand at 30 °C for 15 min to obtain a composite hydrogel.

[0111] (5) The composite hydrogel obtained in step (4) is mixed with ethanol at 60°C, and the ethanol is replaced every 12 hours. After aging for 48 hours, it is placed in a forced-air drying oven and dried at 60°C for 6 hours, 80°C for 6 hours, 100°C for 8 hours, and 120°C for 8 hours to obtain an alumina aerogel composite material; the volume ratio of the composite alumina hydrogel to ethanol is 1:2.

[0112] The preferred solid-liquid mass ratio of aluminum hydroxide powder in step (2) to propylene oxide in step (4) is 1:5.2.

[0113] The density of the alumina aerogel composite material obtained in Comparative Example 1 was tested and found to be 0.18 g / cm³. 3 ;

[0114] The thermal conductivity of the alumina aerogel composite material obtained in Comparative Example 1 was measured to be 0.081 W / (m·K) using the transient flat plate heat source method.

[0115] Example 2

[0116] A method for preparing an alumina aerogel composite material comprises the following steps:

[0117] (1) 25g of activated coal gangue with a particle size ≤80μm was placed in 100mL of 20% hydrochloric acid solution and stirred at 120℃ for 6h. Excess sodium hydroxide solution with a mass concentration of 20% was added to the supernatant after filtration until pH >12. After filtration, 20% hydrochloric acid solution was added dropwise to the supernatant until pH 4.7 was obtained to obtain aluminum hydroxide precipitate. After drying at 80℃ for 12h, aluminum hydroxide powder was obtained.

[0118] (2) 6g of aluminum hydroxide powder, 38mL of 20% hydrochloric acid solution, 44mL of anhydrous ethanol, and 10mL of DMF are heated and stirred at 60℃ for 2h to obtain aluminum sol; the pH of the aluminum sol is 3-4; the preferred solid-liquid mass ratio of the aluminum hydroxide powder to the hydrochloric acid solution, anhydrous ethanol, and DMF is 1:6.3:5.3:1.7;

[0119] (3) Soak 7g of aluminosilicate fiber in 60mL of 0.2mol / L hydrochloric acid solution, sonicate at 40Hz for 1h, filter and wash with ethanol 3 times, and dry at 80℃ for pretreatment to obtain pretreated aluminosilicate fiber. Mix the aluminum sol obtained in step (2) with the pretreated aluminosilicate fiber in a stirrer at 2000r / min for 10min until the fiber is in the form of cotton wool to obtain aluminum sol containing aluminosilicate fiber; the mass ratio of the pretreated aluminosilicate fiber to the aluminum sol is 1:13.

[0120] (4) The aluminum silicate fiber aluminum sol obtained in step (3) is mixed with 42 mL of propylene oxide and then left to stand at 30 °C for 15 min to obtain a composite hydrogel.

[0121] (5) The composite hydrogel obtained in step (4) is mixed with ethanol at 60°C. The ethanol is replaced every 12 hours. After aging for 48 hours, the hydrogel is soaked in ethanol and then soaked in a mixture of tetraethyl orthosilicate and ethanol at 60°C. The modifier is replaced every 12 hours. After 48 hours, the modified composite gel is soaked in anhydrous ethanol at 60°C for 48 hours. The ethanol is replaced every 12 hours. After completion, the gel is placed in a forced-air drying oven and dried at 60°C for 6 hours, 80°C for 6 hours, 100°C for 8 hours, and 120°C for 8 hours to obtain an alumina aerogel composite material. The volume ratio of the alumina hydrogel to ethanol is 1:2. The volume ratio of the alumina hydrogel to the modifier is 1:0.5.

[0122] The preferred solid-liquid mass ratio of aluminum hydroxide powder in step (2) to propylene oxide in step (4) is 1:5.2.

[0123] The density of the alumina aerogel composite material obtained in Example 2 was tested and found to be 0.20 g / cm³. 3 ;

[0124] The thermal conductivity of the alumina aerogel composite material obtained in Example 1 was measured to be 0.047 W / (m·K) using the transient flat plate heat source method.

[0125] Test case

[0126] The microstructure of the alumina aerogel composite material prepared in Example 2 was examined using scanning electron microscopy. The test results are as follows: Figure 3 As shown;

[0127] The microstructure of the untreated alumina aerogel prepared in Example 2 was examined using scanning electron microscopy. The test results are as follows: Figure 4 As shown;

[0128] The compressive strength of the alumina aerogel composite material obtained in Example 2 was tested using a universal testing machine. The test results are as follows: Figure 5 As shown;

[0129] Infrared spectroscopy was performed on the alumina aerogel composite material prepared in Example 2, and the test results are as follows: Figure 6 As shown;

[0130] The alumina aerogel composite material obtained in Example 2 was heat-treated in an air atmosphere. The heating rate in the tube furnace was 5℃ / min, and two samples were held at 400℃, 600℃, 800℃, 1000℃, and 1200℃ for 2 hours each. The thermal conductivity of the heat-treated alumina aerogel composite material as a function of temperature was measured using the transient flat plate heat source method as shown below. Figure 7As shown.

[0131] from Figure 3 and Figure 4 It can be seen that alumina aerogel is attached to the aluminum silicate fibers in the alumina aerogel composite material.

[0132] from Figure 5 It can be seen that the compressive strength of alumina aerogel composite material is 0.085-13.4 MPa when the deformation is 25-94%.

[0133] from Figure 6 It can be seen that 1637cm -1 The absorption band at 2025 cm⁻¹ is caused by the rotational vibration of hydroxyl groups (HOH) on the aerogel surface. The peak intensities of all peaks decreased after modification with tetraethyl orthosilicate, indicating that modification reduces the physically adsorbed water and surface hydroxyl groups on the aerogel surface, which is beneficial for reducing the thermal conductivity. -1 1073cm -1 The structure is an Al-O-Al bond; 743cm -1 The nearby absorption peak is the absorption peak of tetrahedral Al-O; 964 cm⁻¹ -1 The peak at that point corresponds to the stretching vibration of Si-OH, indicating that the material contains Si-O-Al bonds.

[0134] from Figure 7 It can be seen that the thermal conductivity is as low as 0.077 W / (m·K) at 1200℃, and the prepared alumina aerogel composite material has excellent thermal stability and has the potential to be applied in the field of high-temperature processing of special materials and aerospace.

[0135] This invention uses coal gangue as the aluminum source to prepare alumina sol. By aging and modifying the gelled alumina sol, low density and low thermal conductivity of the alumina aerogel composite material are achieved. The strength of the alumina aerogel composite material is improved by adding aluminum silicate fibers as a reinforcing phase. The thermal conductivity of the alumina aerogel composite material is reduced by using staged atmospheric pressure drying. The results of the examples show that the density of the alumina aerogel composite material provided by this invention is 0.18–0.26 g / cm³. 3 With a deformation of 25%–94%, its compressive strength is 0.08–13.4 MPa, and its thermal conductivity is 0.047–0.081 W / (m·K). After heat treatment at 400℃ to 1200℃, its thermal conductivity is 0.053–0.077 W / (m·K). It has the characteristics of low density, low thermal conductivity and high strength, and is suitable for high-temperature processing of special materials and aerospace.

[0136] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an alumina aerogel composite material, comprising the following steps: (1) Aluminum sol was prepared using coal gangue as the aluminum source; (2) The aluminum sol obtained in step (1) is mixed with aluminum silicate fiber and then gelled to obtain a composite hydrogel; (3) The composite hydrogel obtained in step (2) is mixed with ethanol for aging, then mixed with a modifier for modification, and then dried under normal pressure in stages to obtain an alumina aerogel composite material. The modifier in step (3) is one or more of anhydrous ethanol, tetraethyl orthosilicate and n-hexane.

2. The preparation method according to claim 1, characterized in that: The particle size of the coal gangue is ≤80μm.

3. The preparation method according to claim 1, characterized in that: The step (2) before mixing the aluminum sol with the aluminum silicate fiber also includes pretreatment of the aluminum silicate fiber.

4. The preparation method according to claim 3, characterized in that: The pretreatment steps include: ultrasonically mixing aluminum silicate fibers with an acidic solution, followed by sequential cleaning and drying.

5. The preparation method according to claim 1, 3 or 4, characterized in that: In step (2), the mass ratio of aluminum silicate fiber to aluminum sol is 1:(13-21).

6. The preparation method according to claim 1, characterized in that: In step (3), the aging and modification temperatures are independently 40–80°C, and the aging and modification times are independently 24–72 h.

7. The preparation method according to claim 1, characterized in that: In step (3), the graded atmospheric pressure drying is carried out sequentially at 60℃ for 4-8 hours, 80℃ for 4-8 hours, 100℃ for 8-12 hours, and 120℃ for 8-12 hours.

8. The preparation method according to claim 1, characterized in that: In step (3), the modifier is a mixed solution of tetraethyl orthosilicate and anhydrous ethanol.

9. The alumina aerogel composite material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the alumina aerogel composite material according to claim 9 in the field of high-temperature processing of special materials and in the aerospace field.

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