Nanometer zirconium oxide toughened aluminum oxide composite powder prepared based on sol-gel method and preparation method thereof

Abstract

The application relates to the technical field of powder materials, and particularly discloses a nano zirconium oxide toughened aluminum oxide composite powder prepared based on a sol-gel method and a preparation method thereof. Solvent replacement is combined with supercritical drying technology, so that the gel network collapse and inter-particle hard agglomeration caused by capillary force in a conventional drying process are effectively eliminated, and a nano powder with loose structure and excellent dispersibility is obtained. The obtained ZTA composite powder has uniform two-phase distribution, high specific surface area and sintering activity, is favorable for reducing the sintering temperature of subsequent ceramics, and is favorable for obtaining ZTA ceramic products with uniform microstructure and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of powder materials technology, and in particular to a nano-zirconia toughened alumina composite powder prepared by the sol-gel method and its preparation method. Background Technology

[0002] Traditional alumina ceramics, with their significant advantages of high hardness, high wear resistance, and low cost, have found applications in many fields. However, their application range is limited by their relatively low flexural strength and fracture toughness. To overcome this core shortcoming, researchers have successfully prepared zirconia-toughened alumina (ZTA) ceramics by introducing a specific proportion of nano-zirconia into an alumina matrix. This material cleverly utilizes the synergistic effects of multiple mechanisms, including phase transformation toughening, microcrack toughening, crack deflection, and bridging, to achieve a significant improvement in flexural strength and fracture toughness while fully retaining the original excellent properties of alumina ceramics. The overall reliability of the material is also significantly optimized. Thanks to these outstanding advantages, ZTA ceramics have shown broad application prospects in emerging fields such as electronics, biomedicine, and semiconductors, and have been widely applied in practice.

[0003] Currently, the main methods for preparing ZTA powder include mechanical mixing, co-precipitation, hydrothermal methods, and sol-gel methods. Mechanical mixing is difficult to achieve uniform mixing at the molecular level and easily introduces impurities. Co-precipitation is easy to scale up, but controlling the pH and ion concentration during the co-precipitation process is crucial; otherwise, component segregation can easily occur. Hydrothermal methods can obtain well-crystallized powders, but require sophisticated equipment and are expensive. The sol-gel method has advantages such as low reaction temperature, high product purity, and good component uniformity, making it particularly suitable for preparing multi-component nanocomposite powders.

[0004] CN102451764A discloses a method for preparing a zirconium oxide-alumina composite oxide support. This method involves first preparing aluminum hydroxide sol and zirconium-containing sol separately, then mixing the two and subjecting them to aging, washing, filtration, and drying to obtain a composite oxide dry gel. This preparation method allows most of the zirconium oxide to be distributed on the alumina surface, reducing the impact on the alumina pore structure and enhancing the co-catalytic effect of zirconium oxide. It fully leverages the inherent advantages of both oxides. The resulting composite oxide support exhibits large pore volume, high specific surface area, concentrated pore distribution, and controllable acidity, making it suitable for use as a hydrogenation catalyst support.

[0005] CN104556968A relates to a method for preparing a ternary composite aerogel of alumina-silica-zirconia for thermal insulation. The method uses inorganic aluminum salt, silicate, and inorganic zirconium salt as precursors, alcohol solvent and water as reaction solvents, and epoxide as a gelation promoter. A high-performance blocky ternary aerogel is prepared through a supercritical fluid drying process. The aerogel sample exhibits low density, good elasticity, and stable performance. Compared to single alumina, silica, and zirconium oxide aerogels, it has superior high-temperature resistance and more stable quality. This excellent high-temperature stability further expands the applicability of the aerogel, enabling its effective application in the field of thermal insulation.

[0006] Currently, the sol-gel method for preparing ZTA faces several challenges: 1) the hydrolysis rates of aluminum and zirconium alkoxides differ significantly, easily leading to component inhomogeneity; 2) during gelation and drying, capillary forces can cause severe hard agglomerations, affecting subsequent sintering densification and the final product performance; and 3) process control is relatively complex. Therefore, developing a novel sol-gel process that overcomes these drawbacks and achieves uniform and controllable preparation of ZTA nanopowder is of great significance. Summary of the Invention

[0007] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a nano-zirconia toughened alumina composite powder prepared by the sol-gel method and the preparation method thereof.

[0008] Aluminum alkoxide sols form amorphous aluminum hydroxide, typically with larger particle sizes and requiring a series of transition phases, resulting in lower activity. Nanoparticles are prone to self-aggregation. After mixing, ZrO2 and Al2O3 clusters intertwine, and the traditional alumina exhibits low activity, with grain boundary migration rates not significantly different from ZrO2. During sintering, ZrO2 particles have sufficient time and energy to be "pushed away" by Al2O3 grain boundaries, ultimately ending up almost entirely located at the grain boundaries, forming a traditional intergranular structure. Large-sized intergranular ZrO2 undergoes a phase transformation during cooling, losing its stress-induced phase transformation ability, potentially limiting the toughening effect. Furthermore, agglomeration leads to uneven shrinkage during sintering, easily forming micropores or cracks at the original agglomerates, affecting the composite powder properties.

[0009] This invention utilizes boehmite sol, which possesses a huge specific surface area, extremely high surface energy, and strong sintering driving force. A self-made polymer is used as a surfactant to modify the boehmite sol and zirconium oxide sol. The polymer strongly anchors and isolates the particles, and the steric hindrance effect ensures that ZrO2 nanoparticles are uniformly embedded in the boehmite network. The highly active boehmite derivative exhibits extremely rapid grain boundary migration at high temperatures, effectively fixing the previously polymer-immobilized, uniformly distributed ZrO2 particles within the Al2O3 grains.

[0010] The modified boehmite and zirconia surfaces are both anchored to the same polymer molecules via phosphate groups, and both have hydrophilic PEG chains extending outwards. When these two types of polymer-modified particles approach each other, the PEG chains on their periphery generate a strong steric hindrance effect, allowing the zirconia and boehmite particles to coexist stably and uniformly in solution, each maintaining its independent nanoscale size without uncontrolled aggregation. After sintering, the polymer decomposes, and atomic diffusion becomes active. These closely contacted interfaces form strong chemical bonds through solid-state reactions and grain boundary diffusion, thus achieving a truly strong and tight bond.

[0011] To achieve the above objectives, the present invention provides a method for preparing nano-zirconia-toughened alumina composite powder based on the sol-gel method, comprising the following steps:

[0012] S1. Disperse boehmite in water, add dilute nitric acid to adjust the pH, stir to obtain boehmite sol, add polymer surfactant, heat and stir evenly, then add ethylene glycol to obtain modified boehmite sol.

[0013] S2. Add concentrated ammonia to the zirconium oxychloride solution, adjust the pH to 9-10, heat and stir to age, then redisperse in water after post-treatment, add acid to adjust the pH to 3-4, and then perform dialysis purification. Concentrate to obtain 10wt% zirconium oxide sol, add polymer surfactant, heat and stir evenly to obtain modified zirconium oxide sol.

[0014] S3. Add the modified zirconia sol to the modified boehmite sol and carry out a hydrothermal reaction. After cooling, adjust the pH to 9-10, allow it to stand and age to obtain a composite gel, then perform solvent replacement, and finally obtain nano-zirconia toughened alumina composite powder through supercritical drying and heat treatment.

[0015] The method for preparing the polymer surfactant includes the following steps:

[0016] X1. Mix polyethylene glycol monomethyl ether methacrylate with monomers evenly, deoxygenate the system, heat it under nitrogen atmosphere, add initiator and stir for 4-8 hours, and then perform post-treatment to obtain copolymer;

[0017] X2. Phosphorus pentoxide was added to anhydrous ethanol under ice bath conditions. The copolymer was then added and the temperature was raised to 70-90°C and stirred for 3-5 hours to induce phosphorylation. The resulting polymer surfactant was obtained after post-treatment.

[0018] Furthermore, the mass ratio of the polyethylene glycol monomethyl ether methacrylate to the monomer and the initiator is 1:0.2~0.3:0.01~0.03.

[0019] Furthermore, the monomer is one of hydroxyethyl acrylate, p-vinylbenzyl alcohol, hydroxypropyl acrylate, or 2-methyl-2-acrylate-2,3-dihydroxypropyl ester.

[0020] Furthermore, the temperature range for the heating is 60~80℃.

[0021] Furthermore, the mass ratio of phosphorus pentoxide to anhydrous ethanol and copolymer is 1:3~5:8~12.

[0022] Preferably, the method for preparing the polymer surfactant includes the following steps:

[0023] X1. Polyethylene glycol monomethyl ether methacrylate and monomer are mixed evenly in water. After deoxygenating the system, it is heated to 60~80℃ under a nitrogen atmosphere. After adding the initiator, it is stirred for 4~8h. The mass ratio of polyethylene glycol monomethyl ether methacrylate to monomer, water and initiator is 1:0.2~0.3:2~3:0.01~0.03. The copolymer is obtained after post-treatment.

[0024] X2. Phosphorus pentoxide was added to anhydrous ethanol under ice bath conditions. The copolymer was added and the temperature was raised to 70-90°C and stirred for 3-5 hours for phosphorylation. The mass ratio of phosphorus pentoxide to anhydrous ethanol and copolymer was 1:3-5:8-12. The polymer surfactant was obtained after post-treatment.

[0025] Furthermore, the mass ratio of boehmite to water, polymer surfactant, and ethylene glycol is 1:8~12:0.02~0.05:0.8~1.

[0026] Furthermore, in step S1, the temperature range for heating is 60~70℃, and the stirring time is 2~4 hours.

[0027] Furthermore, in step S2, the temperature range for heating is 60~70℃, and the stirring time is 1~2 hours.

[0028] Furthermore, in step S2, the amount of polymer surfactant added is 2-4 wt% of zirconium oxide.

[0029] Furthermore, the hydrothermal reaction is carried out at 120~140℃ for 6~10 hours.

[0030] Furthermore, the supercritical drying medium is liquid CO2, at 40-50°C and a pressure of 10-15 MPa.

[0031] Furthermore, the heat treatment involves heating to 500-700℃ at a rate of 1-5℃ / min, holding at that temperature for 1-3 hours, then continuing to heat to 800-1000℃ and holding for 1-4 hours, and finally heating to 1100-1200℃ and holding for 1-2 hours.

[0032] The present invention also provides a nano-zirconia toughened alumina composite powder prepared by the sol-gel method, which is prepared by the above method.

[0033] The beneficial effects of this invention are:

[0034] 1. Compared with the prior art, the present invention modifies boehmite sol and zirconium oxide sol by using a self-made polymer as a surfactant. The polymer strongly anchors and isolates the particles, thereby avoiding agglomeration and affecting the toughening effect.

[0035] 2. Compared with existing technologies, this invention uses solvent replacement combined with supercritical drying technology, which effectively eliminates the collapse of gel network and hard agglomeration between particles caused by capillary forces during conventional drying, and obtains nanoparticles with loose structure and excellent dispersibility.

[0036] 3. The ZTA composite powder obtained by this invention has a uniform two-phase distribution, a high specific surface area and sintering activity, which is beneficial to reducing the subsequent sintering temperature of ceramics and obtaining ZTA ceramic products with uniform microstructure and excellent mechanical properties. Attached Figure Description

[0037] Figure 1 This is a SEM image of the composite powder obtained in this invention. Detailed Implementation

[0038] Boehmite, particle size: 50~100nm.

[0039] Polyethylene glycol monomethyl ether methacrylate, CAS: 26915-72-0, average molecular weight 2000, sourced from Xiamen Sainuobang Biotechnology.

[0040] p-Vinylbenzyl alcohol, CAS: 1074-61-9.

[0041] Example 1

[0042] A method for preparing nano-zirconia-toughened alumina composite powder based on the sol-gel method includes the following steps:

[0043] S1. Disperse boehmite in water, add 0.3 mol / L dilute nitric acid to adjust the pH to 4, stir to obtain boehmite sol, add polymer surfactant, heat to 65℃ and stir for 3 hours, then add ethylene glycol to obtain modified boehmite sol; the mass ratio of boehmite to water, polymer surfactant and ethylene glycol is 1:9:0.03:0.9.

[0044] S2. 25 wt% concentrated ammonia solution was added dropwise to a 0.3 mol / L zirconium oxychloride solution until the pH reached 9. The solution was then heated to 60°C and stirred for 2 hours to age. After aging, the solution was filtered, washed, and dried. The filter cake was redispersed in water, and the pH was adjusted to 4 by adding 0.3 mol / L dilute nitric acid. The solution was then purified by dialysis. Partial solvent removal was achieved by concentrating the solution to obtain 10 wt% zirconium oxide sol. A polymer surfactant was added, and the solution was heated to 60°C and stirred for 2 hours to obtain modified zirconium oxide sol. The amount of polymer surfactant added was 3 wt% of the zirconium oxide.

[0045] S3. Add the modified zirconia sol to the modified boehmite sol and perform a hydrothermal reaction at 130℃ for 8 hours. After cooling, adjust the pH to 9 and allow it to stand for 36 hours to obtain a composite gel. Then, replace the solvent with anhydrous ethanol and use liquid CO2 as a medium to perform supercritical drying at 45℃ and 12MPa to obtain a precursor. After grinding the precursor, raise the temperature to 600℃ at 2℃ / min in a 1% weak oxygen atmosphere and hold for 2 hours. Then raise the temperature to 900℃ at 5℃ / min and hold for 3 hours. Finally, raise the temperature to 1200℃ in air and hold for 1 hour to obtain nano-zirconia toughened alumina composite powder.

[0046] The method for preparing the polymer surfactant includes the following steps:

[0047] X1. Polyethylene glycol monomethyl ether methacrylate and hydroxyethyl acrylate were mixed evenly in water. After deoxygenating the system, it was heated to 70°C under a nitrogen atmosphere. A 10wt% potassium persulfate solution was added dropwise, and the mixture was stirred for 6 hours. The mass ratio of polyethylene glycol monomethyl ether methacrylate to hydroxyethyl acrylate, water, and potassium persulfate was 1:0.25:2.5:0.02. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was poured into 3 times its volume of anhydrous ethanol. After precipitation, the mixture was filtered, washed, and dried to obtain the copolymer.

[0048] X2. Phosphorus pentoxide was added to anhydrous ethanol at 0°C, and the copolymer was added. The temperature was raised to 80°C and stirred for 4 hours for phosphorylation. The mass ratio of phosphorus pentoxide to anhydrous ethanol and copolymer was 1:4:10. After the reaction was completed, the mixture was cooled, and 2 times the volume of water was added. After stirring at 80°C for 1 hour, 0.1 mol / L ammonia was added to adjust the pH to 7, and then 5 times the volume of anhydrous ethanol was added. After the precipitate was formed, it was filtered, washed, and dried to obtain the polymer surfactant.

[0049] Example 2

[0050] It is basically the same as Example 1, except that hydroxyethyl acrylate is replaced with p-vinylbenzyl alcohol.

[0051] Example 3

[0052] It is basically the same as Example 1, except that hydroxyethyl acrylate is replaced with hydroxypropyl acrylate.

[0053] Example 4

[0054] It is basically the same as Example 1, except that hydroxyethyl acrylate is replaced with 2-methyl-2-acrylate-2,3-dihydroxypropyl acrylate.

[0055] Compare with Example 1

[0056] A method for preparing nano-zirconia-toughened alumina composite powder based on the sol-gel method includes the following steps:

[0057] S1. Disperse boehmite in water, add 0.3 mol / L dilute nitric acid to adjust the pH to 4, and stir to obtain boehmite sol;

[0058] S2. Add 25wt% concentrated ammonia solution dropwise to 0.3mol / L zirconium oxychloride solution until the pH reaches 9. Then, heat to 60℃ and stir for 2 hours to age. After filtration, washing, and drying, the filter cake is redispersed in water. Add 0.3mol / L dilute nitric acid dropwise to adjust the pH to 4 and then perform dialysis purification. Concentrate to remove some of the solvent to obtain 10wt% zirconium oxide sol.

[0059] S3. Zirconia sol was added to boehmite sol and hydrothermally reacted at 130℃ for 8 hours. After cooling, the pH was adjusted to 9 and allowed to stand for 36 hours to obtain a composite gel. The gel was then replaced with anhydrous ethanol as solvent and supercritically dried at 45℃ and 12MPa using liquid CO2 as the medium to obtain a precursor. The precursor was then ground and heated to 600℃ at 2℃ / min in a 1% weak oxygen atmosphere and held for 2 hours. The temperature was then increased to 900℃ at 5℃ / min and held for 3 hours. Finally, the temperature was increased to 1200℃ in air and held for 1 hour to obtain nano-zirconia toughened alumina composite powder.

[0060] Test Example 1

[0061] The composite powders prepared in the examples and control examples were pressed into samples with dimensions of 50mm × 50mm × 5mm using a mold. These samples were then sintered without pressure at 1400℃ in air for 6 hours, followed by hot isostatic pressing at 1300℃ for 1 hour under an Ar atmosphere of 180MPa. Vickers hardness was then tested using the indentation method. Before testing, it was ensured that the test surface and bottom surface of the sample were parallel, and the surface was polished. The loading load was set to 10 kgf, and the holding time was 10 s. When selecting the load, a larger load value was preferred, provided that no obvious cracks were generated in the sample. During testing, after complete unloading, the lengths of the two diagonals of the indentation were measured and recorded. Five different points were selected for testing each sample, and the average value of the data from each test point was taken as the final hardness value of the sample. The Vickers hardness calculation formula is Hv = 1.8544 × (P / d²), where Hv is the hardness value (GPa), P is the loading load (N), and d is the average length of the indentation diagonal (mm).

[0062] Table 1

[0063]

[0064] As shown in Table 1, the composite powder of the examples exhibits higher hardness compared to the control example. This is likely due to the presence of polyethylene glycol hydrophilic chains in the polymer surfactant, which reduces van der Waals forces between precursor particles through steric hindrance, preventing agglomeration and laying the foundation for subsequent sintering densification. The polymer chemically anchors zirconium oxide and boehmite via phosphate groups. The long polymer chains provide sustained steric hindrance throughout the mixing, hydrothermal, and gelation processes, resulting in a large number of uniformly distributed intracrystalline structures after sintering. The stable structure provided by the polymer ensures the perfect preservation of the three-dimensional network structure of the gel during supercritical drying. The resulting precursor is fluffy and porous. The absence of large agglomerates prevents microcracks or large pores during sintering due to inconsistent shrinkage between agglomerates and the matrix, leading to a more uniform densification process and higher mechanical reliability of the final product.

[0065] Compared to other embodiments, the monomer in Embodiment 2 has a rigid benzene ring, which can provide greater steric hindrance. Furthermore, the carbon residue during sintering in a weak oxygen atmosphere at <600°C can inhibit the growth of Al2O3 grains at high temperatures to a certain extent, and the internal residual carbon will form a skeleton for support and structure. Although the skeleton carbon disappears after experiencing a high temperature of 1200°C, due to these effects, a stable internal structure has been formed, resulting in the highest hardness.

[0066] Test Example 2

[0067] The composite powders prepared in the examples and control examples were pressed into samples with dimensions of 50mm×50mm×5mm using a mold. These samples were then sintered without pressure at 1400℃ in air for 6 hours, followed by hot isostatic pressing at 1300℃ for 1 hour in an Ar atmosphere of 180MPa. A four-point bending test was then performed on the samples according to ISO 6474-2 to determine their bending strength. The samples were machined to standard dimensions of 3×4×45mm, with all four sides polished and chamfered at 45° to minimize experimental errors introduced by machining. The test conditions were set as follows: indenter descent speed 0.5mm / min, lower span 40mm, upper span 20mm. The bending strength value was determined by averaging the test results of 5 samples, σ=3FL / (2bd²), where σ is the four-point bending strength (MPa·m). 1 / 2 F is the load (N) at which the specimen breaks, L is the lower span length (mm), b is the specimen width (mm), and d is the specimen thickness (mm).

[0068] Table 2

[0069]

[0070] Flexural strength is an effective measure of a ceramic material's ability to prevent fracture under bending conditions, and it is highly sensitive to defects such as porosity, agglomerates, and grain size. Example 2 exhibits a more uniform structure due to its maximum steric hindrance. Furthermore, during crack propagation, the crack encounters the ductile carbon phase, causing deflection, bridging, and branching, consuming a significant amount of energy and thus significantly increasing the fracture load. These two factors work synergistically to achieve the highest flexural strength.

[0071] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a nano-zirconia toughened alumina composite powder based on a sol-gel method, characterized in that, It comprises the following steps: S1, dispersing boehmite in water, adding dilute nitric acid dropwise to adjust pH to 3-4, stirring to obtain boehmite sol, then adding polymer surfactant, stirring uniformly after heating, and then adding ethylene glycol to obtain modified boehmite sol; S2, adding concentrated ammonia to zirconium oxychloride solution, adjusting pH to 9-10 after heating and stirring, and then aging, re-dispersing in water after post-treatment, adjusting pH to 3-4 after adding acid, and then performing dialysis purification to obtain 10wt% zirconia sol, adding polymer surfactant, and stirring uniformly after heating to obtain modified zirconia sol; S3, adding modified zirconia sol to modified boehmite sol to perform hydrothermal reaction, adjusting pH to 9-10 after cooling, and then aging to obtain composite gel, and then performing solvent replacement, and then performing supercritical drying and heat treatment to obtain nano zirconia toughened alumina composite powder; The preparation method of the polymer surfactant comprises the following steps: X1, uniformly mixing polyethylene glycol monomethyl ether methacrylate and monomers in water, removing oxygen from the system, heating to 60-80℃ under nitrogen atmosphere, adding initiator after stirring for 4-8h, and the mass ratio of polyethylene glycol monomethyl ether methacrylate, monomers, water and initiator being 1:0.2-0.3:2-3:0.01-0.03, and then performing post-treatment to obtain copolymer; X2, adding phosphorus pentoxide to anhydrous ethanol in an ice bath, adding copolymer, heating to 70-90℃ and stirring for 3-5h to perform phosphorylation, and the mass ratio of phosphorus pentoxide, anhydrous ethanol and copolymer being 1:3-5:8-12, and then performing post-treatment to obtain polymer surfactant; The monomer is one of hydroxyethyl acrylate, p-vinylbenzyl alcohol, hydroxypropyl acrylate or 2-methyl-2-acrylic acid-2,3-dihydroxypropyl ester.

2. The method for preparing the nano zirconium oxide toughened aluminum oxide composite powder based on sol-gel method according to claim 1, characterized in that, The mass ratio of boehmite, water, polymer surfactant and ethylene glycol is 1:8-12:0.02-0.05:0.8-1.

3. The method for preparing the nano zirconium oxide toughened aluminum oxide composite powder based on sol-gel method according to claim 1, characterized in that, The temperature range of the heating in step S1 is 60-70℃, and the stirring time is 2-4h; the temperature range of the two heating in step S2 is both 60-70℃, and the stirring time is 1-2h.

4. The method for preparing the nano zirconium oxide toughened aluminum oxide composite powder based on sol-gel method according to claim 1, characterized in that, The addition amount of the polymer surfactant in step S2 is 2-4wt% of zirconia.

5. The method for preparing the nano zirconium oxide toughened aluminum oxide composite powder based on sol-gel method according to claim 1, characterized in that, The hydrothermal reaction is performed at 120-140℃ for 6-10h.

6. A nano-zirconia toughened alumina composite powder prepared based on a sol-gel method, characterized in that, Prepared by the method of any one of claims 1-5. Prepared by the method of any one of claims 1-5.

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