Alumina-based ceramic material and preparation method thereof

Abstract

The invention relates to the field of ceramic materials, in particular to an aluminum oxide-based ceramic material and a preparation method thereof.The preparation method comprises the steps that sulfonic polyferrocene modified carbon nanotubes, magnesium oxide and aluminum oxide are mixed and subjected to ball milling to obtain slurry, the slurry is dried, and then the slurry is subjected to granulation, blank pressing and sintering to obtain the aluminum oxide-based ceramic material. The method has wide application prospects in the fields of machinery, electronics, chemical engineering, biomedicine and the like.

Description

An alumina-based ceramic material and its preparation method Technical Field

[0001] This invention relates to the field of ceramic materials, specifically to an alumina-based ceramic material and its preparation method. Background Technology

[0002] Alumina ceramics are widely used in machinery, electronics, chemical engineering, and biomedicine due to their high hardness, excellent wear resistance, good chemical stability, and high mechanical strength. However, traditional alumina ceramics suffer from problems such as high brittleness, insufficient toughness, and poor thermal shock resistance, which limit their application in harsh environments.

[0003] To improve the performance of alumina ceramics, researchers have tried various methods, such as adding one-dimensional reinforcements like carbon nanotubes. Due to their excellent mechanical properties, high aspect ratio, and unique electrical characteristics, carbon nanotubes can improve the toughness and thermal shock resistance of alumina ceramics to a certain extent. However, carbon nanotubes are prone to agglomeration and generally suffer from problems such as difficulty in dispersion and poor bonding with the matrix, making it difficult to fully exert their reinforcing effect.

[0004] Ball milling can mechanically disperse carbon nanotube aggregates in alumina slurry or powder. However, current ball milling techniques often require approximately 20 hours of milling time. Prolonged milling not only results in low production efficiency but can also lead to carbon nanotube breakage or structural damage, reducing their aspect ratio and mechanical properties. Insufficient milling time can cause uneven dispersion of carbon nanotubes, both of which limit their reinforcing effect in alumina ceramics. Summary of the Invention

[0005] Purpose of the invention: To address the above-mentioned technical problems, this invention proposes an alumina-based ceramic material and its preparation method.

[0006] The technical solution adopted is as follows: This invention provides a method for preparing alumina-based ceramic materials: the slurry obtained by ball milling sulfonate-based polyferrocene-modified carbon nanotubes, magnesium oxide and alumina is dried, then granulated, pressed into a green body and sintered.

[0007] Furthermore, the mass ratio of the sulfonate-based polyferrocene-modified carbon nanotubes, magnesium oxide, and aluminum oxide is 1%-5%:0.5%-1%:1.

[0008] Furthermore, the preparation method of the sulfonate-based polyferrocene-modified carbon nanotubes is as follows: first, polyferrocene is prepared on the surface of carbon nanotubes; sulfonate fatty acids are acylated to obtain sulfonate-based fatty acyl chlorides; finally, under Lewis acid catalysis, the sulfonate-based fatty acyl chlorides undergo an acylation reaction with the polyferrocene on the surface of the carbon nanotubes.

[0009] Lewis acids are substances (including ions, atomic groups, or molecules) that can accept electron pairs. Their core characteristic is that they have empty orbitals or an extended electronic structure, enabling them to form coordinate bonds with Lewis bases (electron pair donors). Aluminum trichloride is a common Lewis acid, and aluminum trichloride is selected as a catalyst in this invention.

[0010] Furthermore, before polyferrocene is prepared on the surface of carbon nanotubes, the carbon nanotubes need to undergo oxidation treatment with mixed acid solution and annealing treatment.

[0011] Oxidation treatment with mixed acid solutions can introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups onto the surface of carbon nanotubes. These functional groups can enhance the activity of carbon nanotubes and decompose amorphous carbon impurities in the carbon nanotubes, reducing structural defects and improving the uniformity of subsequent coating.

[0012] Annealing promotes graphitization of carbon nanotube walls, reduces lattice defects, and enhances their conductivity and chemical stability. After annealing, the surface of carbon nanotubes is smoother and the diameter distribution is more uniform, which is beneficial for ferrocene molecules to uniformly cover the surface through chemical bonds or physical adsorption. An inert gas such as argon should be used for protection during annealing.

[0013] Furthermore, the mixed acid solution is composed of concentrated sulfuric acid and concentrated nitric acid.

[0014] Furthermore, the annealing process is carried out under an argon atmosphere at a temperature of 800℃-1000℃.

[0015] Further, the sulfonic acid fatty acid has ≥5 carbon atoms. Preferably, the sulfonic acid fatty acid has a straight-chain structure with the sulfonic acid group and carboxyl group located at opposite ends of the carbon chain. Preferably, the sulfonic acid fatty acid is 5-sulfovaleric acid.

[0016] Furthermore, sulfonate dispersants are added during ball milling to further improve the dispersion uniformity of each component.

[0017] The sulfonic acid groups on the surface of carbon nanotubes are negatively charged, as are the sulfonate groups in sulfonate dispersants. However, their long-chain alkyl groups can intertwine to form specific electrostatic adsorption. This adsorption causes the dispersant to form a negatively charged interfacial layer on the surface of carbon nanotubes, preventing direct contact between carbon nanotubes through electrostatic repulsion. At the same time, the hydrophilicity of sulfonates can increase the zeta potential on the surface of carbon nanotubes, further enhancing the dispersion stability.

[0018] Meanwhile, sulfonate dispersants (such as SDBS) have long-chain structures, which form a steric hindrance layer after adsorption on the surface of carbon nanotubes. This steric hindrance layer can effectively prevent the aggregation of carbon nanotubes by van der Waals forces, especially during ball milling, when the aggregates are broken up by mechanical force, the steric hindrance layer can prevent them from re-aggregating.

[0019] Furthermore, the mixing and ball milling time is ≤2h.

[0020] Furthermore, the sintering temperature is 1300℃-1400℃. Within this temperature range, sufficient densification of the material can be achieved without causing excessive grain growth.

[0021] On the other hand, the present invention also provides an alumina-based ceramic material, which is prepared by the above-described method for preparing alumina-based ceramic materials.

[0022] The beneficial effects of this invention are as follows: This invention provides a method for preparing alumina-based ceramic materials. In the prior art, carbon nanotubes are prone to agglomeration when used to reinforce alumina ceramics, and generally suffer from problems such as difficulty in dispersion and poor bonding with the matrix, making it difficult to fully exert their reinforcing effect. In this invention, polyferrocene is first prepared on the surface of carbon nanotubes. Then, under Lewis acid catalysis, it can react with sulfonic acid fatty acyl chlorides to generate acyl cations. The acyl cations attack the electron cloud of the cyclopentadienyl ring in the polyferrocene structure, resulting in electrophilic substitution. Long-chain sulfonic acid groups are introduced into the surface of carbon nanotubes, thereby promoting the dispersion of carbon nanotubes during ball milling, shortening the ball milling time, avoiding the breakage or structural damage of carbon nanotubes caused by prolonged ball milling, reducing their aspect ratio and mechanical properties, and improving production efficiency.

[0023] Polyferrocene undergoes thermal decomposition at sintering temperatures, releasing elemental iron, iron oxide, or iron carbide. These iron-based species act as "pinning" agents during alumina grain growth, hindering grain boundary migration and thus suppressing excessive grain growth. This keeps the grain size within a smaller range, increasing the number of grain boundaries, which are crucial for crack propagation, thereby enhancing the strength and toughness of the ceramic. The decomposition products of polyferrocene can also react with magnesium oxide to form a magnesium-iron-aluminum composite spinel phase. This reaction is accompanied by volume expansion, which effectively counteracts the shrinkage during alumina sintering, reducing microcracks and porosity within the material, increasing density. The dense structure reduces thermal stress concentration points, thereby improving mechanical properties and thermal shock resistance.

[0024] The ceramic materials prepared by this invention have excellent mechanical properties and thermal shock resistance, and have broad application prospects in the fields of machinery, electronics, chemical engineering, and biomedicine. Detailed Implementation

[0025] Unless otherwise specified in the examples, the conditions were performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products. Techniques not mentioned in this invention refer to existing technologies. Unless otherwise specified, the following examples and comparative examples are parallel experiments, using the same processing steps and parameters.

[0026] Example 1: A method for preparing an alumina-based ceramic material: 10g of carbon nanotubes were added to a mixed acid solution consisting of 90ml of concentrated sulfuric acid and 30ml of concentrated nitric acid. After stirring and oxidizing at room temperature for 30min, the solution was filtered out, washed with water until neutral, and dried. Then, the solution was annealed at 900℃ for 2h under argon protection to obtain pretreated carbon nanotubes. 10g of pretreated carbon nanotubes were dispersed in 100ml of DMF and sonicated for 30min. Then, 5g of vinyl ferrocene and 0.05g of azobisisobutyronitrile were added. After removing dissolved oxygen by purging with nitrogen for 30min, the solution was stirred and reacted at 65℃ for 48h. After the reaction was completed, the solution was cooled to room temperature, centrifuged, washed with DMF, and dried to obtain polyferrocene-coated carbon nanotubes. 18.2g of... 5-Sulfonovalerate (CAS: 89211-38-1) was added to 200 ml of dichloromethane, and 25 ml of sulfonyl chloride was added dropwise under an ice bath. After stirring for 30 min, the ice bath was removed, and the reaction was carried out at 45 °C for 6 h. After the reaction was completed, dichloromethane and unreacted sulfonyl chloride were removed by vacuum distillation to obtain 5-sulfonovalerate chloride. 4 g of aluminum trichloride and 5 g of 5-sulfonovalerate chloride were added to 100 ml of dichloromethane, and the mixture was stirred at room temperature for 30 min. Then, 10 g of polyferrocene-coated carbon nanotubes were added to the dispersion obtained by dispersing in 100 ml of dichloromethane. The mixture was stirred at 45 °C for 3 h, and the reaction was stopped. After cooling to room temperature and centrifugation, the product was washed successively with dichloromethane, 5 wt% sodium bicarbonate solution, and deionized water, and then dried to obtain sulfonate-based polyferrocene-modified carbon nanotubes.

[0027] Add 3g of sulfonated polyferrocene-modified carbon nanotubes, 0.75g of magnesium oxide and 100g of aluminum oxide to the ball mill jar of a planetary ball mill. Use 1g of sodium dodecylbenzenesulfonate as a dispersant and 50ml of deionized water as the ball milling medium. Mix and ball mill for 2 hours. Dry the resulting slurry and mix it with 5wt% polyvinyl alcohol to form granules. Then press the granules into green bodies under a pressure of 20MPa in a mold. Finally, place the green bodies in a sintering furnace and heat them to 1350℃ at a rate of 2℃ / min. Hold the temperature for 2 hours.

[0028] Example 2: A method for preparing an alumina-based ceramic material: 10g of carbon nanotubes were added to a mixed acid solution consisting of 90ml of concentrated sulfuric acid and 30ml of concentrated nitric acid. After stirring and oxidizing at room temperature for 30min, the solution was filtered out, washed with water until neutral, and dried. Then, the solution was annealed at 1000℃ for 2h under argon protection to obtain pretreated carbon nanotubes. 10g of pretreated carbon nanotubes were dispersed in 100ml of DMF and sonicated for 30min. Then, 5g of vinyl ferrocene and 0.05g of azobisisobutyronitrile were added. After purging with nitrogen for 30min to remove dissolved oxygen, the mixture was stirred at 65℃ for 48h. After the reaction was completed, the solution was cooled to room temperature, centrifuged, washed with DMF, and dried to obtain polyferrocene-coated carbon nanotubes. 18.2g of… 5-Sulfonovalerate (CAS: 89211-38-1) was added to 200 ml of dichloromethane, and 25 ml of sulfonyl chloride was added dropwise under an ice bath. After stirring for 30 min, the ice bath was removed, and the reaction was carried out at 45 °C for 6 h. After the reaction was completed, dichloromethane and unreacted sulfonyl chloride were removed by vacuum distillation to obtain 5-sulfonovalerate chloride. 4 g of aluminum trichloride and 5 g of 5-sulfonovalerate chloride were added to 100 ml of dichloromethane, and the mixture was stirred at room temperature for 30 min. Then, 10 g of polyferrocene-coated carbon nanotubes were added to the dispersion obtained by dispersing in 100 ml of dichloromethane. The mixture was stirred at 45 °C for 3 h, and the reaction was stopped. After cooling to room temperature and centrifugation, the product was washed successively with dichloromethane, 5 wt% sodium bicarbonate solution, and deionized water, and then dried to obtain sulfonate-based polyferrocene-modified carbon nanotubes.

[0029] Add 5g of sulfonated polyferrocene-modified carbon nanotubes, 1g of magnesium oxide, and 100g of aluminum oxide to the ball mill jar of a planetary ball mill. Use 1g of sodium dodecylbenzenesulfonate as a dispersant and 50ml of deionized water as the ball milling medium. Mix and ball mill for 2 hours. Dry the resulting slurry and mix it with 5wt% polyvinyl alcohol to form granules. Then press the granules into green bodies under a pressure of 20MPa in a mold. Finally, place the green bodies in a sintering furnace and heat them to 1400℃ at a rate of 2℃ / min. Hold the temperature for 2 hours.

[0030] Example 3: A method for preparing an alumina-based ceramic material: 10g of carbon nanotubes were added to a mixed acid solution consisting of 90ml of concentrated sulfuric acid and 30ml of concentrated nitric acid. After stirring and oxidizing at room temperature for 30min, the solution was filtered out, washed with water until neutral, and dried. Then, the solution was annealed at 800℃ for 2h under argon protection to obtain pretreated carbon nanotubes. 10g of pretreated carbon nanotubes were dispersed in 100ml of DMF and sonicated for 30min. Then, 5g of vinyl ferrocene and 0.05g of azobisisobutyronitrile were added. After purging with nitrogen for 30min to remove dissolved oxygen, the solution was stirred and reacted at 65℃ for 48h. After the reaction was completed, the solution was cooled to room temperature, centrifuged, washed with DMF, and dried to obtain polyferrocene-coated carbon nanotubes. 18.2g of… 5-Sulfonovalerate (CAS: 89211-38-1) was added to 200 ml of dichloromethane, and 25 ml of sulfonyl chloride was added dropwise under an ice bath. After stirring for 30 min, the ice bath was removed, and the reaction was carried out at 45 °C for 6 h. After the reaction was completed, dichloromethane and unreacted sulfonyl chloride were removed by vacuum distillation to obtain 5-sulfonovalerate chloride. 4 g of aluminum trichloride and 5 g of 5-sulfonovalerate chloride were added to 100 ml of dichloromethane, and the mixture was stirred at room temperature for 30 min. Then, 10 g of polyferrocene-coated carbon nanotubes were added to the dispersion obtained by dispersing in 100 ml of dichloromethane. The mixture was stirred at 45 °C for 3 h, and the reaction was stopped. After cooling to room temperature and centrifugation, the product was washed successively with dichloromethane, 5 wt% sodium bicarbonate solution, and deionized water, and then dried to obtain sulfonate-based polyferrocene-modified carbon nanotubes.

[0031] 1g of sulfonated polyferrocene-modified carbon nanotubes, 0.5g of magnesium oxide and 100g of aluminum oxide were added to the ball mill jar of a planetary ball mill. 1g of sodium dodecylbenzenesulfonate was used as the dispersant and 50ml of deionized water was used as the ball milling medium. The mixture was ball milled for 2 hours. The resulting slurry was dried and mixed with 5wt% polyvinyl alcohol to form granules. The granules were then pressed into green bodies under a pressure of 20MPa in a mold. Finally, the green bodies were placed in a sintering furnace and heated to 1300℃ at a rate of 2℃ / min and sintered for 2 hours.

[0032] Comparative Example 1: Basically the same as Example 1, except that it does not undergo an acylation reaction.

[0033] A method for preparing an alumina-based ceramic material: 10g of carbon nanotubes are added to a mixed acid solution consisting of 90ml of concentrated sulfuric acid and 30ml of concentrated nitric acid. After stirring and oxidizing at room temperature for 30min, the solution is filtered out, washed with water until neutral, and dried. Subsequently, the solution is annealed at 900℃ for 2h under argon protection to obtain pretreated carbon nanotubes. 10g of pretreated carbon nanotubes are dispersed in 100ml of... After ultrasonic treatment in DMF for 30 min, 5 g of vinyl ferrocene and 0.05 g of azobisisobutyronitrile were added. Nitrogen gas was purged for 30 min to remove dissolved oxygen, and the mixture was stirred at 65 °C for 48 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and the collected solid was washed with DMF and dried to obtain polyferrocene-coated carbon nanotubes. 3 g of polyferrocene-coated carbon nanotubes, 0.75 g of magnesium oxide, and 100 g of aluminum oxide were added to the ball mill jar of a planetary ball mill. 1 g of sodium dodecylbenzenesulfonate was used as the dispersant, and 50 ml of deionized water was used as the milling medium. The mixture was ball milled for 2 h. The resulting slurry was dried and mixed with 5 wt% polyvinyl alcohol to form granules. The granules were then pressed into green bodies under a pressure of 20 MPa in a mold. Finally, the green bodies were placed in a sintering furnace and sintered at 1350 °C at a rate of 2 °C / min for 2 h.

[0034] Comparative Example 2: Basically the same as Example 1, except that carbon nanotubes were added directly.

[0035] A method for preparing an alumina-based ceramic material: 3g of carbon nanotubes, 0.75g of magnesium oxide and 100g of alumina are added to the ball mill jar of a planetary ball mill. 1g of sodium dodecylbenzenesulfonate is used as a dispersant and 50ml of deionized water is used as the ball milling medium. The mixture is ball milled for 2 hours. The resulting slurry is dried and mixed with 5wt% polyvinyl alcohol to form granules. The granules are then pressed into a green body under a pressure of 20MPa in a mold. Finally, the green body is placed in a sintering furnace and heated to 1350℃ at a rate of 2℃ / min and sintered for 2 hours.

[0036] Comparative Example 3: Basically the same as Example 1, except that polyethylene glycol 400 was used instead of sodium dodecylbenzenesulfonate as a dispersant.

[0037] Comparative Example 4: Basically the same as Example 1, except that sodium polyacrylate was used instead of sodium dodecylbenzenesulfonate as a dispersant.

[0038] The ceramic materials prepared in Examples 1-3 and Comparative Examples 1-4 were used as samples for performance testing.

[0039] The three-point bending strength of the specimen was tested using an electronic universal testing machine (GB / T6569-2006). The specimen size was 35mm×4mm×3mm, and the loading speed was 0.5mm / min.

[0040] The fracture toughness KIC of the specimen was calculated using the indentation method.

[0041] The sample was placed in a sintering furnace at 1200℃ and held for 20 minutes. Then it was taken out and placed in cold water at 25℃ for rapid cooling. The thermal shock was repeated multiple times until macroscopic cracks appeared. The number of thermal shocks experienced by different samples when cracks appeared was recorded to characterize the thermal shock resistance of ceramics.

[0042] The test results are shown in Table 1 below: As shown in Table 1 above, the ceramic material prepared by this invention has excellent mechanical properties and thermal shock resistance.

[0043] A comparison between Example 1 and Comparative Example 1 shows that the various properties of the ceramic material are improved after the introduction of long-chain sulfonic acid groups through acylation reaction.

[0044] The comparison between Example 1 and Comparative Example 2 shows that, compared with the direct addition of carbon nanotubes, the addition of sulfonate-based polyferrocene-modified carbon nanotubes in this invention can significantly improve the various properties of ceramic materials.

[0045] The comparison between Example 1 and Comparative Examples 3-4 shows that, compared with polyethylene glycol 400 and sodium polyacrylate, the use of sulfonate dispersants can effectively improve the various properties of ceramic materials. It is possible that sulfonate dispersants have a better dispersion effect under the same ball milling time.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an alumina-based ceramic material, characterized in that, The slurry obtained by ball milling sulfonate-based polyferrocene-modified carbon nanotubes, magnesium oxide, and aluminum oxide is dried, then granulated, pressed into a green body, and sintered.

2. The method for preparing alumina-based ceramic materials as described in claim 1, characterized in that, The mass ratio of the sulfonate-based polyferrocene-modified carbon nanotubes, magnesium oxide, and aluminum oxide is 1%-5%:0.5%-1%:

1.

3. The method for preparing the alumina-based ceramic material as described in claim 1, characterized in that, The preparation method of the sulfonate-based polyferrocene-modified carbon nanotubes is as follows: first, polyferrocene is prepared on the surface of carbon nanotubes; sulfonate fatty acids are acylated to obtain sulfonate fatty acyl chlorides; finally, under Lewis acid catalysis, the sulfonate fatty acyl chlorides undergo an acylation reaction with the polyferrocene on the surface of the carbon nanotubes.

4. The method for preparing the alumina-based ceramic material as described in claim 3, characterized in that, Before polyferrocene can be prepared on the surface of carbon nanotubes, the carbon nanotubes need to undergo oxidation treatment with mixed acid solution and annealing treatment.

5. The method for preparing the alumina-based ceramic material as described in claim 4, characterized in that, The mixed acid solution consists of concentrated sulfuric acid and concentrated nitric acid.

6. The method for preparing the alumina-based ceramic material as described in claim 4, characterized in that, The annealing process is carried out under an argon atmosphere at a temperature of 800℃-1000℃.

7. The method for preparing the alumina-based ceramic material as described in claim 3, characterized in that, The sulfonic acid fatty acid has ≥5 carbon atoms.

8. The method for preparing the alumina-based ceramic material as described in claim 1, characterized in that, Sulfonate dispersants are added during ball milling.

9. The method for preparing the alumina-based ceramic material as described in claim 1, characterized in that, The sintering temperature is 1300℃-1400℃.

10. An alumina-based ceramic material, characterized in that, The alumina-based ceramic material is prepared by any one of the preparation methods of claims 1-9.

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