Preparation method of low-temperature molecular ceramic mullite sol

Abstract

The invention belongs to the technical field of mullite preparation, and relates to a preparation method of low-temperature molecular ceramic mullite sol. The preparation method comprises the following steps: dissolving formic acid and citric acid in deionized water, uniformly mixing to obtain a mixed acid solution, adding aluminum powder, uniformly mixing to obtain a reaction solution, heating the reaction solution, and reacting in a condensation reflux state; filtering, adding a silicon source, adding a sorbitol solution, uniformly mixing, adding 1, 6-hexamethylenediamine, and uniformly mixing to obtain the mullite sol. The mullite sol provided by the invention can be subjected to self-propagating combustion to form a phase through a solvent combustion method, and compared with the traditional solid-phase temperature, the temperature is greatly reduced. The mullite sol prepared by the process disclosed by the invention does not contain chloride ions or nitrate ions, can prevent generation of strong acid during calcination, is environment-friendly, and has relatively low damage to equipment in the production process. The prepared mullite crystal grains are nanoscale, uniform in particle size, stable in chemical property and suitable for being used as a catalyst or a matrix of a composite material.

Description

Technical Field

[0001] The invention belongs to the technical field of mullite preparation, and relates to a method for preparing low-temperature molecular ceramic mullite sol. Background Art

[0002] Mullite sol has attracted considerable attention as a matrix material for alumina fiber-reinforced mullite ceramic-based composites. Its excellent formability and plasticity allow its properties to be tuned by manipulating its chemical composition and structural structure. It can also be combined with other materials to optimize the overall performance of components. Mullite sol exhibits excellent high-temperature resistance, maintaining stability in high-temperature environments and thus extending its service life. High-performance mullite sol is an important raw material for the development of new high-performance materials. Mullite phase materials prepared from high-performance mullite sol exhibit excellent physical properties, such as high fracture toughness, high-temperature resistance, oxidation resistance, thermal shock resistance, creep resistance, low thermal conductivity, strong electrical insulation, and low dielectric constant. Furthermore, mullite phases prepared from high-performance mullite sol exhibit high chemical stability and excellent corrosion resistance in both alkaline and carbonated solvents. Traditional mullite sol preparation typically requires high temperatures, which not only consumes significant energy but also increases production costs, hindering energy conservation, emission reduction, and sustainable development. On the other hand, traditional mullite sols are made from aluminum salts containing Cl and N. The byproducts released during the reaction pose a significant environmental risk. Especially with increasingly stringent environmental regulations, the environmental impact of traditional preparation processes has become a major bottleneck. Furthermore, the mullitization temperature of mullite sols currently reaches 1200°C. This excessively high mullitization temperature can cause thermal damage to fibers or interfacial reactions during composite material preparation, thereby compromising the performance of ceramic-based composite products. Furthermore, the sintering process of mullite sols poses certain risks, and the byproducts released during the reaction of aluminum salts containing Cl and N can significantly pollute the environment. Summary of the Invention

[0003] Aiming at the problems existing in traditional mullite sol and mullite sol sintering process, the present invention proposes a novel preparation method of low-temperature molecular ceramic mullite sol.

[0004] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions: A method for preparing low-temperature molecular ceramic mullite sol, the preparation steps are as follows: (1) Formic acid and citric acid are added to deionized water, dissolved and mixed uniformly to obtain a mixed acid solution, aluminum powder is added and mixed uniformly to obtain a reaction solution, and the reaction solution is heated and maintained under condensation reflux to carry out the reaction.

[0005] (2) After the reaction is completed, filter to obtain aluminum carboxylate sol.

[0006] (3) Add a silicon source to the aluminum carboxylate sol, mix and stir thoroughly to obtain sol A.

[0007] (4) Add sorbitol solution to sol A and mix well to obtain sol B.

[0008] (5) Add 1,6-hexanediamine to sol B and mix well to obtain mullite sol.

[0009] Preferably, in step (3), the silicon source is obtained by mixing tetraethyl orthosilicate (TEOS) and ethanol and stirring the mixture to react.

[0010] Preferably, in step (1), the aluminum powder contains 20-30% aluminum oxide by mass after complete decomposition; the heating reaction temperature is 93-96° C., and the reaction time is 9-12 h.

[0011] Preferably, the molar ratio of silicon atoms to aluminum atoms in the sol A in step (3) is 3:1, and after the silicon source is added to the aluminum carboxylate sol, the stirring time is 2-10 hours.

[0012] Preferably, the mass fraction of the sorbitol aqueous solution in the sol B in step (4) is 2-5%.

[0013] Preferably, in step (5), the mass fraction of the 1,6-hexanediamine aqueous solution in the mullite sol is 3-6%.

[0014] The role of sorbitol in the above process mainly includes the following aspects: the six hydroxyl groups (-OH) in sorbitol can react with the metal ions of aluminum and silicon sources (Al³⁺, Si 4 ⁺) forms a complex, slowing the hydrolysis rate of metal ions in the precursor solution, preventing localized precipitation and improving the uniformity of the sol. Steric hindrance disperses particles, inhibits agglomeration, and forms a nanoscale precursor structure. 1,6-Hexanediamine, as a nitrogen-containing organic fuel, undergoes oxidative decomposition at high temperatures, releasing large amounts of heat and gases (such as NH3, H2O, and CO2), providing the energy required for self-propagating combustion. The reducing gases (such as NH3) produced by decomposition inhibit excessive oxidation of metal ions and promote the formation of a metastable mullite phase at low temperatures. The complexing effects of sorbitol and 1,6-Hexanediamine complement each other. 1,6-Hexanediamine provides strong complexation to stabilize the sol, while sorbitol enhances dispersion through steric hindrance, significantly improving the uniformity and stability of the sol. The combustion characteristics of the two are complementary. 1,6-Hexanediamine provides high-temperature combustion energy, and sorbitol forms a porous structure through foaming, synergistically lowering the crystallization temperature of mullite. The two work together to generate a multi-level pore structure (mesoporous structure), which is suitable for catalysis, adsorption and other fields. Nitrogen doping gives the material new functional properties (such as enhanced catalytic activity), and the carbon template refines the grains and improves the mechanical properties of the composite material.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are: 1. The mullite sol provided by the present invention can be self-propagatingly burned into a phase at a relatively low temperature by a solvent combustion method, which is significantly lower than the traditional solid phase temperature.

[0016] 2. The mullite sol produced by this process contains no chloride or nitrate ions, preventing the generation of strong acids during calcination. This is environmentally friendly and causes minimal damage to equipment during production. Biomass-derived fuels can be used as combustion agents, reducing harmful gas emissions (NOx / SOx), aligning with the trend toward carbon neutrality.

[0017] 3. The resulting mullite has nanoscale grains, uniform particle size, and stable chemical properties, making it suitable as a matrix for catalysts or composite materials. The resulting bulk material, obtained by pressing and calcining the powder, exhibits a compressive strength exceeding 200 MPa and a thermal conductivity below 1.5 W / m•K. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 TEM image of mullite grains.

[0019] Figure 2 This is the SEM image of mullite grains. DETAILED DESCRIPTION

[0020] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below in conjunction with specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0021] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0022] Example 1 5 mL of formic acid (National Pharmaceutical Group, analytical grade) and 4 g of citric acid (National Pharmaceutical Group, analytical grade) were added to 20 mL of deionized water and mixed and dissolved uniformly to obtain a mixed acid solution. Subsequently, 5 g of aluminum powder (Shandong Fuwang Chemical Co., Ltd., particle size 40-50 μm) was added and stirred at 200 rpm for 1 h to mix uniformly. The mixture was heated to 95°C at 200 rpm and stirred at a constant temperature for reaction. The condensation reflux state was maintained during the reaction. After 10 h of reaction, the mixture was naturally cooled to room temperature. Filtration was performed to obtain a transparent and clear carboxylate aluminum sol. 27 g of tetraethyl orthosilicate (TEOS, Sinopharm, analytical grade) and 27 mL of ethanol (Sinopharm, analytical grade) were stirred at 200 rpm for 3 h to form an unhydrolyzed silica sol. 26 mL of the unhydrolyzed silica sol and 30 mL of the carboxylate aluminum sol were then mixed and stirred at 300 rpm for 3 h to form mullite sol A. 1.5 g of a 20% (mass fraction) sorbitol aqueous solution was then added to mullite sol A and stirred at 200 rpm for 20 min to obtain mullite sol B. 2.5 g of 1,6-hexanediamine was then added and stirred at 200 rpm for another 20 min. The mixture was then concentrated at a constant temperature of 80°C and stirring at 200 rpm to obtain a transparent mullite sol with a solid content of 37.5%. The mullite sol was placed in a muffle furnace and heated to 980°C at a rate of 25°C / min. It was then calcined at this temperature for 2 h and then naturally cooled to room temperature to form a mullite phase.

[0023] The mullite phase was manually ground for 10 min to obtain mullite sol powder. After testing, the mullite sol powder prepared in this embodiment had a nano-scale grain size (such as Figure 1 and Figure 2 The sintered mullite-phase bulk material has a flexural strength of 200 MPa. Thanks to the densification effect of the nano-grains, the bulk material has a uniform texture, making it suitable for catalytic or composite material matrices. Its thermal conductivity has been tested to be 1.3 W / m·K (superior to traditional mullite bricks).

[0024] Example 2 Unless otherwise specified, this Example is consistent with Example 1. 5 mL of formic acid (Chinese herbal medicine, analytical grade) and 4 g of citric acid (Chinese herbal medicine, analytical grade) were added to 20 mL of deionized water and mixed and dissolved uniformly to obtain a mixed acid solution. Subsequently, 5 g of aluminum powder (Shandong Fuwang Chemical Co., Ltd., particle size 40-50 μm) was added and stirred at 200 rpm for 1 h to mix uniformly. The mixture was then heated to 93°C at 200 rpm and stirred at constant temperature to react. The reaction was maintained in a condensation reflux state during the reaction. After 10 h of reaction, the mixture was naturally cooled to room temperature. The mixture was filtered to obtain a transparent and clear aluminum carboxylate sol. 27 g of tetraethyl orthosilicate (TEOS, Sinopharm, analytical grade) and 27 mL of ethanol (Sinopharm, analytical grade) were stirred at 200 rpm for 3 h to form an unhydrolyzed silica sol. 26 mL of the unhydrolyzed silica sol and 30 mL of the aluminum carboxylate sol were then mixed and stirred at 300 rpm for 3 h to form mullite sol A. 2 g of a 20% (mass fraction) sorbitol aqueous solution was then added to mullite sol A and stirred at 200 rpm for 20 min to obtain mullite sol B. 3 g of 1,6-hexanediamine was then added and stirred at 200 rpm for another 20 min. The mixture was then concentrated at a constant temperature of 80°C and stirring at 200 rpm to obtain a transparent mullite sol with a solid content of 37.5%. The mullite sol was placed in a muffle furnace and heated to 1020°C at a rate of 25°C / min. The mixture was kept warm for 2 h and then naturally cooled to room temperature to form a mullite phase.

[0025] The mullite phase was manually ground for 10 minutes to obtain a mullite sol powder. Testing showed that the sintered mullite bulk material had a flexural strength of 195 MPa. Thanks to the densification effect of the nanocrystals, the bulk material had a uniform texture, making it suitable for catalytic or composite matrix applications. Testing also showed a thermal conductivity of 1.38 W / m·K.

[0026] Example 3 Unless otherwise specified, this example is consistent with Example 1. 5 mL of formic acid and 4 g of citric acid were added to 20 mL of deionized water and mixed and dissolved uniformly to obtain a mixed acid solution. 5 g of aluminum powder was then added and stirred uniformly. The solution was heated to 96° C. at 200 rpm and stirred at this temperature to react. The reaction was maintained in a condensation reflux state during the reaction. After 9 hours of reaction, the solution was naturally cooled to room temperature. Filtration was performed to obtain a transparent and clear carboxylate aluminum sol; 27 g of ethyl silicate (TEOS, Sinopharm, analytical grade) and 27 mL of ethanol (Sinopharm, analytical grade) were stirred at 200 rpm for 3 h to form an unhydrolyzed silica sol; then 26 mL of unhydrolyzed silica sol and 30 mL of carboxylate aluminum sol were mixed and stirred at 300 rpm for 3 h to form mullite sol A; then 1.8 g of a 20% mass fraction sorbitol aqueous solution was added to the mullite sol and stirred evenly, and concentrated at a constant temperature of 80°C to obtain a transparent mullite sol B with a solid content of 37.5%, which was calcined at 1100°C for 2 h to form a mullite phase.

[0027] The mullite phase was ground to produce a mullite sol powder. Testing showed that the mullite grains produced in this example were nanoscale, and the flexural strength of the sintered block material was 185 MPa. Testing also showed that its thermal conductivity was 1.42 W / m·K (superior to conventional mullite bricks).

[0028] In order to verify the calcination temperature requirement of the mullite grains obtained in Example 1, the calcination performance of the mullite sol A prepared in Example 1 was verified.

[0029] 1. The repeatedly prepared transparent mullite sol was calcined at 1150°C for 2 hours to form a mullite phase. The mullite phase was ground to obtain a mullite sol powder. Testing showed that the mullite grains prepared in this example were nanoscale, and the flexural strength of the sintered bulk material was 175 MPa.

[0030] 2. The repeatedly prepared transparent mullite sol was calcined at 1200°C for 2 hours to form a mullite phase. The mullite phase was ground to obtain a mullite sol powder. Testing showed that the mullite grains prepared in this example were nanoscale, and the flexural strength of the sintered bulk material was 160 MPa.

[0031] It can be seen from this that the flexural strength of the transparent mullite sol prepared by the process of Example 1 will decrease when calcined at high temperature.

[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that sorbitol and 1,6-hexanediamine are not added, and the formed mullite sol is directly tested. It is verified that the calcination temperature of the sol in this comparative example needs to reach 1300°C. After sintering, the flexural strength of the bulk material is 120 MPa, the grain size is large (micrometer level), and the thermal conductivity is 2.8 W / m·K.

[0033] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing low-temperature molecular ceramic mullite sol, characterized in that: The preparation steps are as follows: (1) Formic acid and citric acid are added to deionized water, dissolved and mixed uniformly to obtain a mixed acid solution, aluminum powder is added and mixed uniformly to obtain a reaction solution, and the reaction solution is heated and maintained under condensation reflux to carry out the reaction; (2) After the reaction is completed, filter to obtain aluminum carboxylate sol; (3) Adding a silicon source to the aluminum carboxylate sol, mixing and stirring thoroughly to obtain sol A; (4) Add sorbitol solution to sol A and mix well to obtain sol B; (5) Add 1,6-hexanediamine to sol B and mix well to obtain mullite sol.

2. The method for preparing the low-temperature molecular ceramic mullite sol according to claim 1, characterized in that: In step (3), the silicon source is prepared by a mixed reaction of TEOS and ethanol.

3. The method for preparing the low-temperature molecular ceramic mullite sol according to claim 1, characterized in that: In step (1), the aluminum powder contains 20-30% by mass of aluminum oxide; the heating reaction temperature is 93-96° C., and the reaction time is 9-12 hours.

4. The method for preparing the low-temperature molecular ceramic mullite sol according to claim 1, characterized in that: In step (3), the molar ratio of silicon atoms to aluminum atoms in sol A is 3:

1. After the silicon source is added to the aluminum carboxylate sol, the mixture is fully mixed and stirred for 2-10 hours.

5. The method for preparing the low-temperature molecular ceramic mullite sol according to claim 1, characterized in that: In step (4), the mass fraction of sorbitol in sol B is 2-5%.

6. The method for preparing the low-temperature molecular ceramic mullite sol according to claim 1, characterized in that: In step (5), the mass fraction of 1,6-hexanediamine in the mullite sol is 3-6%.

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