A high-temperature-resistant, high-flame-retardant silicon-aluminum aerogel composite material and its preparation method

Abstract

This invention relates to the field of aerogel materials technology, specifically to a silicon-aluminum aerogel composite material with high temperature resistance and high flame retardancy, and its preparation method. The preparation method of this composite material includes: Step 1, mixing aluminum dihydrogen phosphate, water, alcohol, and a stabilizer, stirring until the aluminum source is completely hydrolyzed to obtain an aluminum sol, and then adding a silicon source dropwise to the obtained aluminum sol to prepare a silicon-aluminum sol; Step 2, combining a fiber substrate with the silicon-aluminum sol obtained in Step 1 and then gelling to obtain a silicon-aluminum gel-fiber substrate composite material; Step 3, aging and solvent replacement of the silicon-aluminum gel-fiber substrate composite material obtained in Step 2; Step 4, drying the silicon-aluminum gel-fiber substrate composite material obtained after solvent replacement in Step 3 to obtain a silicon-aluminum aerogel composite material with high temperature resistance and high flame retardancy. The final prepared silicon-aluminum aerogel composite material exhibits good high-temperature thermal insulation performance, high-temperature flame retardant performance, and high-temperature stability.

Description

Technical Field

[0001] This invention relates to the field of aerogel materials technology, specifically to a silicon-aluminum aerogel composite material with high temperature resistance and high flame retardancy and its preparation method. Background Technology

[0002] Aerogels are nanoporous solid materials with a three-dimensional network structure formed by the cross-linking of colloidal particles or polymer molecules. They are characterized by extremely low density, high specific surface area, high porosity, and low thermal conductivity, making them the most ideal lightweight thermal insulation materials currently available. Currently, the most widely used silica aerogel, due to its maximum operating temperature generally not exceeding 650℃, is gradually failing to meet the requirements of aerospace, refining, and metallurgical industries for high-temperature resistance and high flame retardancy in thermal insulation materials. Alumina aerogel, while maintaining the general characteristics of aerogels, has a higher operating temperature (theoretically up to 950℃). However, under prolonged high-temperature environments, the pore structure of alumina aerogel will significantly collapse, leading to a substantial decrease in the material's thermal insulation performance.

[0003] To prepare aerogels with low thermal conductivity, high temperature resistance, and high thermal conductivity, those skilled in the art have made a series of beneficial attempts. The main approach involves combining silica aerogels and aluminum aerogels to prepare silica-alumina aerogel composites with excellent heat resistance and insulation properties. However, conventional preparation methods involve cumbersome processes, and expensive aluminum alkoxides are generally used as the aluminum source, resulting in high preparation costs and limiting the application of silica-alumina composite aerogels. To address these issues, Chinese patent application CN110627475A discloses a method for preparing aluminum-silicon aerogel insulation materials. This method utilizes inorganic aluminum sources, silicon sources, and propylene oxide as raw materials to prepare aluminum-silicon aerogel insulation materials with excellent high temperature resistance and mechanical properties. However, the aerogel prepared by this method lacks flame-retardant properties, and because it uses inorganic aluminum sources (anhydrous aluminum chloride, aluminum chloride hexahydrate, anhydrous aluminum nitrate, and aluminum nitrate nonahydrate), the network inducer propylene oxide needs to be added to promote or accelerate gelation. Furthermore, the introduction of carbon into the aerogel skeleton structure leads to uneven pore structure, ultimately resulting in decreased thermal insulation performance, reduced flame retardancy, and decreased thermal stability of the material.

[0004] To enhance the flame retardant properties of materials, adding flame retardants is often the obvious first thought. Commonly used flame retardants include phosphates, such as phosphates and dihydrogen phosphates. However, directly adding phosphates to the system during aerogel preparation introduces impurities. Furthermore, phosphates and dihydrogen phosphates tend to precipitate in the aluminosilicate aerogel preparation system, hindering the formation of a three-dimensional network structure and affecting the thermal insulation performance of the final aluminosilicate aerogel composite material. Summary of the Invention

[0005] To address the issues of poor high-temperature insulation, high-temperature stability, and flame retardant properties in the aforementioned silicon-aluminum composite aerogel materials, this invention utilizes aluminum dihydrogen phosphate as the aluminum source and adds stabilizers to control the degree of hydrolysis and agglomeration, thereby preparing a high-temperature resistant and highly flame-retardant silicon-aluminum aerogel composite material. The specific technical solution of this invention is as follows:

[0006] A method for preparing a high-temperature resistant and high-flame-retardant silicon-aluminum aerogel composite material, comprising:

[0007] Step 1: Mix aluminum dihydrogen phosphate, water, alcohol and stabilizer, and stir until the aluminum source is completely hydrolyzed to obtain aluminum sol. Then add silicon source dropwise to the obtained aluminum sol to prepare silicon-aluminum sol.

[0008] Step 2: After the fiber substrate is combined with the silicon-aluminum sol obtained in Step 1, a gel is formed to obtain a silicon-aluminum gel-fiber substrate composite material.

[0009] Step 3: Aging and solvent replacement of the silica-alumina gel-fiber substrate composite material obtained in Step 2;

[0010] Step 4: Dry the silicon-aluminum gel-fiber substrate composite material obtained after solvent replacement in Step 3 to obtain a silicon-aluminum aerogel composite material with high temperature resistance and high flame retardancy.

[0011] The alcohol mentioned in step 1 is selected from at least one of methanol, ethanol, propanol and isopropanol.

[0012] The stabilizer mentioned in step 1 is at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, and sodium hexadecyl sulfonate. The stabilizer is added to reduce phase separation, enhance the uniform distribution of the system, control the degree of hydrolysis and agglomeration of the aluminum source (aluminum dihydrogen phosphate), and enable the sol-gel process to proceed smoothly.

[0013] The molar ratio of aluminum dihydrogen phosphate, water, alcohol and stabilizer mentioned in step 1 is 1:(10-20):(20-50):(0.004-0.005).

[0014] In aluminum-silicon composite aerogels, if the molar ratio of aluminum source to silicon source is higher than this ratio, the silicon source content is lower, which reduces the structural retention effect of the aerogel at high temperatures and leads to a decrease in the high-temperature thermal insulation performance of the composite material. If it is lower than this ratio, the silicon source content is higher, and the silicon oxide structure is prone to softening and collapse at high temperatures, resulting in the loss of the high-temperature thermal insulation performance of the composite material.

[0015] The hydrolysis in step 1 is carried out at a temperature of 15–40°C for 1.5–4 hours.

[0016] The silicon source mentioned in step 1 is selected from at least one of alkaline water glass, alkaline silica sol, tetraethyl orthosilicate, acidic silica sol, and neutral silica sol.

[0017] The SiO2 content in alkaline water glass, alkaline silica sol, acidic silica sol, and neutral silica sol is 15 wt%.

[0018] Preferably, the pH value of the silica-alumina sol in step 1 is 7 to 9.

[0019] Specifically, the pH value of the silica-alumina sol can be adjusted to 7-9 by adding an alkaline catalyst;

[0020] The alkaline catalyst comprises one or a combination of sodium hydroxide, potassium hydroxide, and ammonia water.

[0021] The molar ratio of aluminum dihydrogen phosphate, water, alcohol and stabilizer mentioned in step 1 is 1:(10-20):(20-50):(0.004-0.005);

[0022] The molar ratio of aluminum dihydrogen phosphate to silicon source (based on SiO2) in step 1 is 1:(0.10-0.14).

[0023] The fiber substrate mentioned in step 2 is selected from one of pre-oxidized fiber felt, basalt fiber felt, or ceramic fiber felt.

[0024] The fiber substrate mentioned in step 2 is selected from any two or more fiber felts formed by blending pre-oxidized fiber, basalt fiber, and ceramic fiber. The fiber materials vary in melting point, flatness, tensile strength, and bending strength, allowing for the selection of appropriate substrates for composite processing based on different application scenarios. The various materials listed in this case demonstrate strong process adaptability and a wide range of applications.

[0025] The composite process described in step 2 is carried out under vacuum conditions, with a vacuum pressure of -0.1 to -0.05 MPa.

[0026] The aging solvent in step 3 is a mixture of silicon source and water, wherein the mass ratio of silicon source to water in the mixture is (0.05-0.2):1, and the silicon source is selected from at least one of alkaline water glass, alkaline silica sol, acidic silica sol and neutral silica sol.

[0027] In step 3, the volume ratio of the silica-alumina gel-fiber substrate composite material to the aged solvent is 1:(0.2~1);

[0028] The aging process described in step 3 is carried out at 35–60°C for 6–16 hours.

[0029] The solvent used for solvent replacement in step 3 is an organic solvent, which is selected from at least one of methanol, ethanol, propanol and isopropanol, with ethanol being preferred;

[0030] The volume ratio of the silica-alumina gel-fiber substrate composite material to the organic solvent in step 3 is 1:(2-3);

[0031] The solvent replacement in step 3 is performed 2 to 3 times.

[0032] The drying process described in step 4 is supercritical drying, using carbon dioxide as the medium, at a temperature of 50–65°C and a pressure of 13–20 MPa.

[0033] A silicon-aluminum aerogel composite material with high temperature resistance and high flame retardancy prepared using any of the above methods.

[0034] This invention uses aluminum dihydrogen phosphate as a raw material to prepare a silicon-aluminum composite aerogel material. Aluminum ions hydrolyze to produce aluminum hydroxide ions, which then self-polymerize to form dimer and trimer colloidal particles. With the help of a stabilizer, further self-polymerization and precipitation of aluminum hydroxide are prevented. The added silicon source, containing or forming silica colloidal particles, also contains a large number of silanol groups, which condense and crosslink with the hydroxyl groups on the surface of the dimer and trimer colloidal particles, forming a strongly crosslinked three-dimensional network structure. Compared with the prior art, this invention has the following beneficial effects:

[0035] (1) In this invention, aluminum dihydrogen phosphate is used as the aluminum source. After controlling the degree of hydrolysis and aggregation of the aluminum source by a stabilizer, it is condensed with silanol. Without the need to add an additional crosslinking agent, a strong crosslinked three-dimensional network structure can be formed quickly. Moreover, the influence of adding carbon-containing network inducing agents such as propylene oxide on the gel skeleton structure is avoided. In the end, the prepared silicon-aluminum aerogel composite material has excellent high temperature resistance and high temperature insulation performance, as well as good high temperature stability and high flame retardant performance.

[0036] (2) The present invention uses aluminum dihydrogen phosphate as raw material. On the one hand, aluminum dihydrogen phosphate can be used as an aluminum source, which reduces the preparation cost. On the other hand, dihydrogen phosphate can provide flame retardant properties to the material, eliminating the need to add additional flame retardants and reducing the introduction of impurity ions. Detailed Implementation

[0037] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] Example 1

[0039] 1) Preparation of silicon-aluminum sol:

[0040] Weigh 317.94 g of aluminum dihydrogen phosphate, 360 g of water, 1612 g of ethanol, and 1.46 g of hexadecyltrimethylammonium bromide into a reaction vessel, keep the reaction vessel sealed, and stir at 25 °C for 2.5 h. Then, add 37.8 g of alkaline silica sol (SiO2 content 15 wt%) dropwise to the system to prepare a silica-alumina sol. The final pH of the silica-alumina sol is 8.

[0041] In the above process, the molar ratio of aluminum dihydrogen phosphate, water, and ethanol is 1:20:35, and the molar ratio of aluminum dihydrogen phosphate and alkaline silica sol (calculated as SiO2) is 1:0.11. The alkaline silica sol can adjust the pH of the system, promote the cross-linking of aluminum and silicon sources after hydrolysis, accelerate the sol-gel state conversion, and shorten the process cycle.

[0042] 2) Sol-fiber substrate composite:

[0043] As needed, the pre-oxidized fiber felt is rolled into rolls or cut into sheets of a certain size and placed in a container. The silica-alumina sol obtained in step 1) is poured into the container to completely impregnate the fiber substrate. The container is kept sealed and defoamed under a vacuum of -0.07 MPa. Then, it is left to stand for 3 hours to allow gelation, thus obtaining the silica-alumina gel-fiber substrate composite gel.

[0044] 3) Aging of composite materials:

[0045] Add 2000g of water glass solution (SiO2 content 10wt%) to the silica-alumina gel-fiber matrix composite material in step 2), accelerate aging at 45℃, and obtain the aged silica-alumina gel-fiber matrix composite material after aging for 10h. Add 4000ml of ethanol to the aged silica-alumina gel-fiber matrix composite material for solvent replacement for 6h, and repeat 3 times.

[0046] 4) Supercritical drying:

[0047] Using carbon dioxide as a medium, the solvent-displaced silicon-aluminum gel-fiber substrate composite material obtained in step 3) was subjected to supercritical drying at a temperature of 60℃ and a pressure of 16MPa to obtain a silicon-aluminum aerogel composite material with high temperature resistance and high flame retardancy.

[0048] Example 2

[0049] In this embodiment, the silicon source used in the preparation of silicon-aluminum sol is acidic silica sol. After adding the acidic silica sol, sodium hydroxide is added to adjust the pH of the silicon-aluminum sol to 8. Other features are the same as in Example 1.

[0050] Example 3

[0051] In this embodiment, the molar ratio of aluminum dihydrogen phosphate, water, and ethanol in the preparation process of silicon-aluminum sol is 1:10:50; other characteristics are the same as in Example 1.

[0052] Example 4

[0053] In this embodiment, the molar ratio of aluminum dihydrogen phosphate, water, and ethanol in the preparation process of silicon-aluminum sol is 1:20:30; other characteristics are the same as in Example 1.

[0054] Example 5

[0055] In this embodiment, the molar ratio of aluminum dihydrogen phosphate to silicon source in the preparation process of silicon-aluminum sol is 1:0.13; other characteristics are the same as in Example 1.

[0056] Example 6

[0057] In this embodiment, the stabilizer added during the preparation of the silicon-aluminum sol is hexadecylpyridine bromide; other characteristics are the same as in Example 1.

[0058] Comparative Example 1

[0059] No stabilizer was added in Comparative Example 1; other characteristics were the same as in Example 1.

[0060] Comparative Example 2

[0061] In Comparative Example 2, the aluminum source used in the preparation of silica-alumina sol was aluminum chloride (the molar ratio of aluminum chloride, water, and ethanol was 1:20:35). After adding the silica sol, propylene oxide was added as a network inducer to avoid excessive gelation time or failure to gel. The amount of propylene oxide added was 6 mol. Other characteristics were the same as in Example 1.

[0062] Test Results

[0063]

[0064]

[0065] Examples 1-6 demonstrate the preparation of carbon-silicon composite aerogel materials using the method of this invention. Comparative Example 1 uses aluminum dihydrogen phosphate as the aluminum source without adding a stabilizer, while Comparative Example 2 uses aluminum chloride as the aluminum source and adds a network inducing agent to promote gelation. The test results show that the carbon-silicon aerogel prepared by the method of this invention exhibits relatively small changes in thermal conductivity under high-temperature conditions, maintaining a relatively low thermal conductivity and demonstrating good high-temperature stability. Furthermore, it possesses a high flame retardant rating and low linear shrinkage, indicating good flame retardancy and high-temperature resistance, which can well meet the application requirements under high-temperature conditions and shows promising application prospects.

Claims

1. A method for preparing a silicon-aluminum aerogel composite material with high temperature resistance and high flame retardancy, characterized in that, include: Step 1: Mix aluminum dihydrogen phosphate, water, alcohol and stabilizer, and stir until the aluminum source is completely hydrolyzed to obtain aluminum sol. Then add silicon source dropwise to the obtained aluminum sol to prepare silicon-aluminum sol. The stabilizer is sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide and sodium hexadecyl sulfonate. Step 2: After the fiber substrate is combined with the silicon-aluminum sol obtained in Step 1, a gel is formed to obtain a silicon-aluminum gel-fiber substrate composite material. Step 3: Aging and solvent replacement of the silica-alumina gel-fiber substrate composite material obtained in Step 2; Step 4: Dry the silicon-aluminum gel-fiber substrate composite material obtained after solvent replacement in Step 3 to obtain a silicon-aluminum aerogel composite material with high temperature resistance and high flame retardancy.

2. The method for preparing a high-temperature resistant and high-flame-retardant silicon-aluminum aerogel composite material as described in claim 1, characterized in that, The molar ratio of aluminum dihydrogen phosphate, water, alcohol and stabilizer mentioned in step 1 is 1: (10~20): (20~50): (0.004~0.005).

3. The method for preparing a high-temperature resistant and high-flame-retardant silicon-aluminum aerogel composite material as described in claim 1, characterized in that, The molar ratio of aluminum dihydrogen phosphate to silicon source mentioned in step 1, based on SiO2, is 1:(0.10~0.14).

4. The method for preparing a high-temperature resistant and high-flame-retardant silicon-aluminum aerogel composite material as described in claim 1, characterized in that, The hydrolysis temperature in step 1 is 15~40℃, and the hydrolysis time is 1.5~4h.

5. The method for preparing a high-temperature resistant and high-flame-retardant silicon-aluminum aerogel composite material as described in claim 1, characterized in that, The silicon source mentioned in step 1 is selected from at least one of alkaline water glass, alkaline silica sol, tetraethyl orthosilicate, acidic silica sol, and neutral silica sol.

6. The method for preparing a high-temperature resistant and high-flame-retardant silicon-aluminum aerogel composite material as described in claim 1, characterized in that, The pH value of the silica-alumina sol described in step 1 is 7~9.

7. The method for preparing a high-temperature resistant and high-flame-retardant silicon-aluminum aerogel composite material as described in claim 1, characterized in that, The fiber substrate mentioned in step 2 is selected from one or more combinations of pre-oxidized fiber felt, basalt fiber felt, or ceramic fiber felt.

8. The method for preparing a high-temperature resistant and high-flame-retardant silicon-aluminum aerogel composite material as described in claim 1, characterized in that, The drying process described in step 4 is supercritical drying.

9. A silicon-aluminum aerogel composite material with high temperature resistance and high flame retardancy prepared by the method according to any one of claims 1 to 8.

Images