High-temperature-stable nano-zirconia-based thermal insulation ceramic material and preparation method thereof

Abstract

The invention discloses a high-temperature-stable nano-zirconia-based thermal insulation ceramic material and a preparation method thereof. The method comprises the following steps: mixing a ZrOCl2. 8H2O solution with a Y (NO3) 3 solution, adding a citric acid complexing agent and high-valence transition metal alkoxide (Nb or Ta), and adjusting the pH value to 8.5-10.5 to form polymerized complexed nano sol; la or Gd rare earth components are introduced; performing one-way freeze drying to obtain a closed nanopore precursor; and after pre-sintering at 500-700 DEG C, sintering at 1250-1350 DEG C to obtain the ceramic.

Description

Technical Field

[0001] This invention relates to the technical field of thermal insulation ceramic materials, and in particular to a high-temperature stable nano-zirconia-based thermal insulation ceramic material and its preparation method. Background Technology

[0002] Zirconia-based thermal insulation ceramics are widely used in aero-engines, gas turbines, and high-temperature industrial kilns due to their excellent high-temperature mechanical properties and relatively low thermal conductivity. Among them, the stabilized zirconia system, represented by Y₂O₃-stabilized ZrO₂ (YSZ), introduces 3–8 mol% Y₂O₃ solution into the ZrO₂ lattice, stabilizing the tetragonal or cubic phase structure within the room temperature to medium-high temperature range, significantly suppressing the volume expansion instability problem caused by martensitic phase transformation. This system also possesses a high coefficient of thermal expansion, good compatibility with metal matrices, and exhibits certain fracture toughness advantages due to the phase transformation toughening effect generated by stress-induced tetragonal-to-monoclinic phase transformation. Furthermore, the YSZ powder preparation, molding, and sintering processes are mature and easily scalable, making it the mainstream technology in the field of high-temperature thermal insulation ceramics for a long time. With the development of nanotechnology, the application of nano-zirconia powder and its ceramic bodies has gradually emerged. The increased number of grain boundaries and enhanced interfacial phonon scattering effect brought about by the nanostructure make the material exhibit lower thermal conductivity and better microstructure uniformity in the initial state, thereby further enhancing its thermal insulation potential.

[0003] However, existing zirconia-based nano-insulating ceramics with YSZ as the core still suffer from significant structural stability issues under long-term service conditions above 1200℃. First, nanomaterials possess high specific surface area and interfacial energy, making them prone to grain boundary migration and accelerated mass diffusion at high temperatures. This leads to rapid grain growth and pore shrinkage, disrupting the original nanoscale interfacial structure and weakening phonon scattering capabilities, causing thermal conductivity to gradually increase over service time. Second, under prolonged high-temperature thermal exposure, oxygen vacancy distribution tends towards thermodynamic equilibrium, altering the local stress field. Some tetragonal phases may still transform into monoclinic phases, inducing volume effects and microcrack initiation, affecting structural reliability. Furthermore, with grain coarsening and a reduction in defect structures, the interfacial thermal resistance effect within the material weakens, making it difficult to maintain thermal insulation performance over long periods. Therefore, how to suppress abnormal grain growth, stabilize the tetragonal phase structure, and maintain low thermal conductivity microstructure characteristics in zirconia-based nano-insulating ceramics under high-temperature long-term service conditions, achieving a synergistic improvement in thermal insulation performance and structural stability, has become a critical technical problem urgently needing to be solved in the field of zirconia-based insulating ceramic materials. Summary of the Invention

[0004] This application provides a method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, including the following steps: S1. Dissolve ZrOCl2·8H2O in deionized water to form a 0.5-1.5 mol / L zirconium salt solution, add Y(NO3)3 solution so that Y2O3 accounts for 3-8 mol% of the molar amount of ZrO2, then add a multidentate organic acid complexing agent and introduce a high-valence transition metal alkoxide, heat and stir at 60-80℃ to form a polymeric complex nanosol precursor with adjustable surface electrochemical properties; S2. Introduce rare earth components into the sol system that can undergo a solid-phase reaction with zirconium oxide during sintering to generate a pyrochlore structure; S3. The obtained system is subjected to unidirectional freeze-drying to form a nanoporous precursor structure; S4. The obtained precursor is pre-fired at 500-700℃ and then sintered at 1250-1350℃ to obtain a high-temperature stable nano-zirconia-based thermal insulation ceramic material.

[0005] It should be noted that in step S1, Zr 4+ With Y 3+ Under the action of multidentate organic acids, a stable polymeric complex network is formed, inhibiting the rapid hydrolysis and disordered condensation of Zr species, thus enabling Y... 3+ The high-valence transition metal alkoxides are uniformly distributed at the molecular scale. They participate in complexation and condensation to construct organic-inorganic hybrid precursors, and undergo controllable hydroxylation under pH 8.5–10.5 conditions, avoiding the effects of Zr under acidic conditions. 4+ The problem of suppressed hydrolysis, resulting in the presence of mainly hydrated ions or simple complexes, allows for controlled hydroxylation of the system, forming nano-sol particles rich in active hydroxyl groups and coordination sites. This facilitates the uniform enrichment of subsequent components at grain boundaries and improves the homogeneity of the precursor structure. In step S2, the rare earth component undergoes a solid-state diffusion reaction with ZrO2 during sintering to generate a pyrochlore-type rare earth zirconate phase, constructing a stable second phase with low thermal conductivity. Step S3 involves unidirectional freeze-drying to form a nanoporous structure, disrupting the continuous heat transfer path in the solid and enhancing interfacial phonon scattering. In step S4, pre-sintering removes organic components, and during high-temperature sintering, the formation of the Y-stable ZrO2 main phase, the segregation of high-valence transition metals to grain boundaries and their transformation into a high-melting-point oxide stable layer, and the formation of the pyrochlore phase are completed. This increases the grain boundary migration activation energy, inhibits abnormal grain growth, and constructs a multi-scale thermal resistance network, ultimately yielding a nano-zirconia-based insulating ceramic material with both high-temperature structural stability and low thermal conductivity.

[0006] In a preferred embodiment of a method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, the ZrOCl2·8H2O solution is 0.5–1.5 mol / L.

[0007] It should be noted that this method helps to ensure the reactivity and complexation efficiency of the system while avoiding rapid hydrolysis and aggregation caused by excessive concentration, thereby obtaining a nanosol precursor with uniform particle size and stable structure.

[0008] In a preferred embodiment of a high-temperature stable nano-zirconia-based thermal insulation ceramic material preparation method, the multidentate organic acid is citric acid, and the citric acid reacts with Zr... 4+ and Y 3+ The ratio of total molar amounts is 1.2 to 1.8:1.

[0009] It should be noted that citric acid was selected as the multidentate organic acid, and citric acid was combined with Zr. 4+ and Y 3+ The total molar ratio is controlled at 1.2 to 1.8:1, which is beneficial for utilizing the multiple carboxyl and hydroxyl groups in citric acid molecules to form a stable multi-coordinate complex structure for metal ions. This effectively inhibits the rapid hydrolysis and aggregation of metal ions, promotes the uniform dispersion and synergistic complexation of Zr and Y elements in the sol system, and provides conditions for the formation of a uniform nanosol precursor.

[0010] In a preferred embodiment of a method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, the high-valence transition metal alkoxide is Nb(OEt)5 or Ta(OEt)5, and the mass ratio of the high-valence transition metal alkoxide to citric acid is 0.1 to 0.8:1.

[0011] It should be noted that the polycarboxyl and hydroxyl groups in citric acid molecules can coordinate with high-valence transition metal ions to form stable metal-organic complex structures, thereby regulating the hydrolysis and condensation processes of metal alkoxides. In subsequent heat treatment, this complex structure can achieve uniform dispersion of high-valence transition metal elements in the system and promote their entry into the oxide lattice or the formation of a refined second-phase structure, thereby improving the structural stability and microstructure uniformity of the material.

[0012] In a preferred embodiment of a method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, the rare earth component is La or Gd, and its addition amount is 5 to 20 wt% of the final ceramic mass.

[0013] It should be noted that rare earth ions can enter the oxide lattice or be distributed at the grain boundaries, inhibiting abnormal grain growth through lattice distortion and grain boundary pinning, while improving the structural stability and densification of the material. When the content is below 5 wt%, the stabilizing and refining effects are insufficient, while when the content is above 20 wt%, too many second phases are easily formed and the continuity of the matrix is ​​affected. Therefore, controlling it within the above range is beneficial to obtaining a uniform and stable ceramic microstructure and excellent comprehensive performance.

[0014] In a preferred embodiment of a method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, the unidirectional freezing treatment temperature is -20℃ to -60℃, the freezing time is 4 to 12 hours, and the freeze-drying time is 24 to 48 hours.

[0015] It should be noted that this facilitates the formation of directional ice crystal templates during the freezing process and the retention of a uniform and stable nanoporous structure during subsequent sublimation, thus providing a structural basis for obtaining zirconia-based insulating ceramics with low thermal conductivity.

[0016] In a preferred embodiment of a high-temperature stable nano-zirconia-based thermal insulation ceramic material preparation method, the sintering heating rate is 5–15 °C / min.

[0017] It should be noted that the sintering heating rate is controlled at 5-15℃ / min, which is beneficial to achieve the gradual decomposition of organic complexes in the precursor structure and the uniform formation of crystal phase, avoiding structural collapse or abnormal grain growth caused by excessive heating, thereby obtaining a zirconia-based thermal insulation ceramic material with stable structure and uniform pore distribution.

[0018] The high-temperature stable nano-zirconia-based thermal insulation ceramic material prepared by this invention has significant beneficial effects: through the synergistic effect of a polymeric complex sol precursor, a high-valence transition metal grain boundary stabilizing layer, a pyrochlore-type rare-earth zirconate second phase, and a closed nanoporous structure formed by unidirectional freeze-drying, it successfully solves the core problems of abnormal grain growth, tetragonal phase instability, and increased thermal conductivity of traditional YSZ nanoceramics during long-term service above 1200℃. The room temperature thermal conductivity is as low as 0.55–0.78 W·m. -1 ·K -1 Meanwhile, its flexural strength reaches 82–108 MPa and its fracture toughness is 4.2–5.1 MPa·m. 1 / 2 It combines excellent high-temperature structural stability and mechanical reliability, significantly outperforming control examples that do not contain high-priced metal alkoxides, have improper pH adjustment, lack rare earth components, or are conventionally dried. It achieves a synergistic improvement in thermal insulation performance and long-term service reliability, providing an ideal thermal insulation material solution for extreme environments such as aero-engines, gas turbines, and high-temperature industrial kilns. Attached Figure Description

[0019] Figure 1 Infrared spectrum of the polymeric complex nanosol precursor prepared in Example 1; Figure 2 The image shows the XRD pattern of the nano-zirconia-based thermal insulation ceramic material prepared in Example 1. Figure 3 The pore size distribution curves are for the nano-zirconia-based thermal insulating ceramic materials prepared in Examples 1 to 4; Detailed Implementation

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0022] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0023] Example

[0024] Example 1

[0025] This embodiment provides a method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, which specifically includes the following steps: S1. First, dissolve ZrOCl2·8H2O in deionized water to form a zirconium salt solution with a concentration of 0.5 mol / L. Then, add a Y(NO3)3 solution (approximately 0.5 mol / L) to the above zirconium salt solution, so that Y2O3 accounts for 3 mol% of the molar amount of ZrO2. Next, add citric acid, a multidentate organic acid complexing agent, to react the citric acid with ZrO2. 4+ and Y 3+ The total molar ratio was 1.2:1. Subsequently, a high-valence transition metal alkoxide Nb(OEt)5 was introduced, with a mass ratio of 0.1:1 to citric acid. The mixture was heated and stirred at 60°C for 2 hours to promote the complexation reaction. Subsequently, the pH of the solution was adjusted to 8.5 with an ammonia solution to form a polymeric complex nanosol precursor.

[0026] S2. Introduce rare earth component La (in the form of La(NO3)3) into the above sol system, the amount of which is 5 wt% of the final ceramic mass. Stir evenly to ensure that the rare earth component is uniformly dispersed in the sol.

[0027] S3. Pour the obtained system into a mold and perform unidirectional freezing treatment: freeze at -20°C for 4 hours to form a directional ice crystal template. Subsequently, perform freeze-drying: place the frozen sample in a vacuum freeze dryer and dry for 24 hours to sublimate the ice crystals and retain the nanoporous precursor structure.

[0028] S4. The obtained precursor was placed in a muffle furnace and pre-fired at 500°C for 2 hours (heating rate 5°C / min) to remove organic components and initially form an oxide structure. Then, the temperature was increased to 1250°C at a heating rate of 5°C / min and held for 2 hours for sintering. After cooling, a high-temperature stable nano-zirconia-based thermal insulation ceramic material was obtained.

[0029] Example 2

[0030] This embodiment provides a method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, which specifically includes the following steps: S1. First, dissolve ZrOCl2·8H2O in deionized water to form a zirconium salt solution with a concentration of 1.0 mol / L. Then, add a Y(NO3)3 solution (approximately 1.0 mol / L) to the above zirconium salt solution, so that Y2O3 accounts for 5.5 mol% of the molar amount of ZrO2. Next, add citric acid, a multidentate organic acid complexing agent, to react the citric acid with ZrO2. 4+ and Y 3+ The total molar ratio was 1.5:1. Subsequently, a high-valence transition metal alkoxide, Ta(OEt)5, was introduced at a mass ratio of 0.45:1 to citric acid. The mixture was heated and stirred at 70°C for 3 hours to promote the complexation reaction. The pH of the solution was then adjusted to 9.5 with NaOH solution to form a polymeric complex nanosol precursor.

[0031] S2. Introduce rare earth component Gd (in the form of Gd(NO3)3) into the above sol system, the amount of which is 12.5 wt% of the final ceramic mass. Stir evenly to ensure that the rare earth component is uniformly dispersed in the sol.

[0032] S3. Pour the obtained system into a mold and perform unidirectional freezing treatment: freeze at -40℃ for 8 hours to form a directional ice crystal template. Subsequently, perform freeze drying: place the frozen sample in a vacuum freeze dryer and dry for 36 hours to sublimate the ice crystals and retain the nanoporous precursor structure.

[0033] S4. The obtained precursor was placed in a muffle furnace and pre-fired at 600℃ for 3 hours (heating rate 10℃ / min) to remove organic components and preliminarily crystallize. Then, the temperature was increased to 1300℃ at a heating rate of 10℃ / min and held for 3 hours for sintering. After cooling, a high-temperature stable nano-zirconia-based thermal insulation ceramic material was obtained.

[0034] Example 3

[0035] This embodiment provides a method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, which specifically includes the following steps: S1. First, dissolve ZrOCl2·8H2O in deionized water to form a zirconium salt solution with a concentration of 1.5 mol / L. Then, add a Y(NO3)3 solution (concentration approximately 1.5 mol / L) to the above zirconium salt solution, so that Y2O3 accounts for 8 mol% of the molar amount of ZrO2. Next, add citric acid, a multidentate organic acid complexing agent, to react the citric acid with ZrO2. 4+ and Y 3+ The total molar ratio was 1.8:1. Subsequently, a high-valence transition metal alkoxide Nb(OEt)5 was introduced, with a mass ratio of 0.8:1 to citric acid. The mixture was heated and stirred at 80°C for 4 hours to promote the complexation reaction. The pH of the solution was then adjusted to 10.5 with an ammonia solution to form a polymeric complex nanosol precursor.

[0036] S2. Introduce the rare earth component La (in the form of La(NO3)3) into the above sol system, the amount of which is 20 wt% of the final ceramic mass. Stir evenly to ensure that the rare earth component is uniformly dispersed in the sol.

[0037] S3. Pour the obtained system into a mold and perform unidirectional freezing treatment: freeze at -60℃ for 12 hours to form a directional ice crystal template. Subsequently, perform freeze drying: place the frozen sample in a vacuum freeze dryer and dry for 48 hours to sublimate the ice crystals and retain the nanoporous precursor structure.

[0038] S4. The obtained precursor was placed in a muffle furnace and pre-fired at 700℃ for 4 hours (heating rate 15℃ / min) to remove organic components and form a stable oxide phase. Then, the temperature was increased to 1350℃ at a heating rate of 15℃ / min and held for 4 hours for sintering. After cooling, a high-temperature stable nano-zirconia-based thermal insulation ceramic material was obtained.

[0039] Example 4

[0040] This embodiment provides a method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, which specifically includes the following steps: S1. First, dissolve ZrOCl2·8H2O in deionized water to form a zirconium salt solution with a concentration of 0.75 mol / L. Then, add a Y(NO3)3 solution (approximately 0.75 mol / L) to the above zirconium salt solution, so that Y2O3 accounts for 4 mol% of the molar amount of ZrO2. Next, add citric acid, a multidentate organic acid complexing agent, to react the citric acid with ZrO2. 4+ and Y 3+The total molar ratio was 1.4:1. Subsequently, a high-valence transition metal alkoxide, Ta(OEt)5, was introduced at a mass ratio of 0.3:1 to citric acid. The mixture was heated and stirred at 65°C for 2.5 hours to promote the complexation reaction. The pH of the solution was then adjusted to 9.0 with an ammonia solution to form a polymeric complex nanosol precursor.

[0041] S2. Introduce rare earth component Gd (in the form of Gd(NO3)3) into the above sol system, the amount of which is 10 wt% of the final ceramic mass. Stir evenly to ensure that the rare earth component is uniformly dispersed in the sol.

[0042] S3. Pour the obtained system into a mold and perform unidirectional freezing treatment: freeze at -30°C for 6 hours to form a directional ice crystal template. Subsequently, perform freeze-drying: place the frozen sample in a vacuum freeze dryer and dry for 30 hours to sublimate the ice crystals and retain the nanoporous precursor structure.

[0043] S4. The obtained precursor was placed in a muffle furnace and pre-fired at 550℃ for 2.5 hours (heating rate 7.5℃ / min) to remove organic components and initially stabilize the structure. Then, the temperature was increased to 1275℃ at a heating rate of 7.5℃ / min and held for 2.5 hours for sintering. After cooling, a high-temperature stable nano-zirconia-based thermal insulation ceramic material was obtained.

[0044] Comparison Example

[0045] Compare with Example 1

[0046] Compared with the embodiment, the difference is that Nb(OEt)5 is not added in step S1, and the rest of the steps are exactly the same as in embodiment 1.

[0047] Compare with Example 2

[0048] The difference from the example is that the pH of the solution is adjusted to 3.0 in step S1.

[0049] Compare with Example 3

[0050] The difference from the example is that the La component is not introduced in step S2.

[0051] Compare with Example 4

[0052] Compared with the example, the difference is that in step S3, unidirectional freezing is not performed, and the sol is directly dried by conventional heat at 100°C.

[0053] Performance testing methods

[0054] 1. Thermal conductivity testing method: The sintered ceramic material is processed into circular samples with a diameter of 10-12 mm and a thickness of 1-3 mm. The surface of the sample is polished to ensure a flat test surface. A laser flash thermal conductivity meter is used to test the sample. The thermal diffusivity of the material is determined within the range from room temperature to a set high temperature. At the same time, the specific heat capacity of the material is measured using a differential scanning calorimeter. Combined with the bulk density measured by the Archimedes method, the thermal conductivity of the material is calculated according to the formula λ=α·Cp·ρ, where λ is the thermal conductivity, α is the thermal diffusivity, Cp is the specific heat capacity, and ρ is the bulk density.

[0055] 2. Bending strength test method: The sintered ceramic sample was processed into a strip specimen with dimensions of 3 mm × 4 mm × 36 mm, and the surface of the specimen was polished to eliminate processing defects. A three-point bending test was performed using an electronic universal testing machine, with a span of 20–30 mm and a loading rate of 0.5–1 mm / min. The maximum load value at which the specimen fractured was recorded during the loading process. The bending strength of the material was calculated according to the three-point bending strength calculation formula.

[0056] 3. Fracture Toughness Testing Method: The ceramic sample is processed into a polished, flat block. An indentation test is performed by applying a certain load to the sample surface using a Vickers hardness tester. Radial cracks will appear at the four corners of the indentation. The diagonal length of the indentation and the crack propagation length are measured using an optical microscope. Combined with the Vickers hardness value of the material, the fracture toughness value K_IC of the material is calculated according to the indentation fracture mechanics model. This method reflects the material's ability to resist crack initiation and propagation, thereby evaluating the fracture resistance of ceramic materials.

[0057] 4. Pore Size Distribution Testing Method: The prepared samples were subjected to vacuum degassing at 80–120℃ for 4–6 h to remove adsorbed water and impurity gases from the pores. Subsequently, the samples were tested using a nitrogen adsorption-desorption specific surface area and pore structure analyzer, and the nitrogen adsorption-desorption isotherm was measured at liquid nitrogen temperature (77 K). Based on the obtained adsorption-desorption data, the desorption branch was calculated and analyzed using the BJH (Barrett–Joyner–Halenda) model to obtain the pore size distribution curve, average pore size, pore volume, and other parameters of the samples.

[0058] Table 1

[0059]

[0060] In conjunction with Example 1 and Figure 1 It can be seen that 3400 cm -1 The broad and strong OH stretching vibration peak originates from the residual water molecule and the hydroxyl group at the center of citric acid; 2925 cm⁻¹ -1With 2850 cm -1 The asymmetric / symmetric stretching vibrations of CH originate from the citric acid -CH2 group and the -CH2CH3 group of the Nb(OEt)5 residual ethoxy group, respectively; 1630 cm -1 H2O bending vibration and 1580 cm -1 (COO) - (Asymmetric stretching) and 1400 cm -1 (COO) - The symmetric stretching peaks coexist, with Δν≈180 cm⁻¹. -1 This proves that all three carboxyl groups of citric acid have been deprotonated and reacted with Zr. 4+ Y 3+ 、Nb 5+ Formation of stable bidental bridging coordination complex structure (without 1710 cm) -1 (Free carboxylic acid peak); 1380 cm⁻¹ -1 The weak peak is attributed to residual nitrate ions (from Y(NO3)3); 1100 cm⁻¹ -1 The CO stretching vibration encompasses both the citrate-CO bond and the Nb-OC framework; 950 cm -1 The moderate intensity peak is a characteristic stretching vibration of the residual alkoxy group in Nb-OEt, indicating that a small amount of ethoxy group remains after partial hydrolysis of the alkoxide; 550 cm⁻¹ -1 The nearby broad MO vibrational band directly confirms the initial formation of Zr-O, Nb-O, and YO metal-oxygen bonds. The overall spectrum exhibits symmetrical peak shapes, a smooth background, and is free of extraneous peaks, fully validating the Zr... 4+ With Y 3+ A stable polymeric complex network is formed under the action of multidentate organic acids... The molecular-scale uniformity of high-valence transition metal alkoxides participating in complexation and condensation provides a reliable precursor structure basis for subsequent unidirectional freeze-sintering to obtain high-temperature stable nano-zirconia-based thermal insulation ceramics.

[0061] In conjunction with Example 1 and Figure 2It can be seen that the main crystalline phase is the tetragonal ZrO2 (t-ZrO2) stabilized by Y2O3, with its strongest peak located at 30.18° (corresponding to the 101 crystal plane), accompanied by a series of characteristic peaks at 34.85°, 35.28°, 50.25°, and 59.85°. The slightly broadened peak shape reflects the nanocrystal size effect, and there is no 28.2° / 31.5° peak of monoclinic ZrO2, which fully proves that Y2O3 has achieved high-temperature tetragonal phase stability; the second phase is the La group formed during sintering. The La2Zr2O7 pyrochlore structure formed by the solid-state reaction of ZrO2 exhibits moderate intensity at its strongest peak of 28.55° (222 crystal plane) and other peaks at 33.05°, 47.85°, and 56.75°. Due to the extremely small amount of Nb added, it exists only as grain boundary segregation and does not show independent diffraction peaks. The overall spectrum has a smooth background and symmetrical peaks, confirming the nanoporous structure formed by unidirectional freeze-freeze-freeze drying and the high-temperature structural stability and low thermal conductivity characteristics obtained after sintering at 1250℃.

[0062] As can be seen from Examples 1 to 4 and Table 1, the nano-zirconia-based thermal insulating ceramic material prepared by this invention exhibits stable and excellent performance across the entire parameter range: its room temperature thermal conductivity ranges from 0.55 to 0.78 W·m. -1 ·K -1 Flexural strength 82–108 MPa, fracture toughness 4.2–5.1 MPa·m 1 / 2 This indicates that through the synergistic effect of polymerized complex sol, pyrochlore second phase, closed nanopores, and grain boundary stabilizing layer, the material achieves long-term high-temperature thermal insulation performance far lower than that of traditional YSZ, while maintaining high mechanical reliability, verifying the robustness and optimal matching of process parameters.

[0063] Combining Example 1, Comparative Example 1, and Table 1, it can be seen that the room temperature thermal conductivity of Example 1 is 0.78 vs 0.85 W·m. -1 ·K -1 ), flexural strength (95 vs 78 MPa) and fracture toughness (4.5 vs 3.8 MPa·m) 1 / 2 All of these results were significantly better than those of Control Example 1. In Control Example 1, Nb(OEt)5 was not introduced in step S1, which prevented the high-valence transition metal from segregating at the grain boundaries during sintering to form a high-melting-point oxide stable layer. This prevented the grain boundary migration activation energy from being increased, resulting in abnormal grain growth, destruction of the nano-interface, weakened phonon scattering ability, and increased thermal conductivity at a high temperature of 1250℃. At the same time, the inhomogeneous microstructure led to a decrease in mechanical properties.

[0064] Combining Example 1, Comparative Example 2, and Table 1, it can be seen that the room temperature thermal conductivity of Example 1 is 0.78 vs 0.92 W·m. -1 ·K -1), flexural strength (95 vs 65 MPa) and fracture toughness (4.5 vs 3.2 MPa·m) 1 / 2 This is superior to Control Example 2 in all aspects. The reason is that Control Example 2 adjusted the pH to 3.0 in step S1, and the acidic environment inhibited Zr... 4+ Controllable hydroxylation and polymerization complexation lead to non-uniformity of nanosol particles, collapse of the closed nanoporous structure formed by subsequent freeze-drying, failure to effectively destroy the continuous heat transfer path of the solid, significant reduction in interfacial phonon scattering, and poor precursor uniformity which exacerbates grain growth, resulting in deterioration of overall thermal conductivity and mechanical properties.

[0065] Combining Example 1, Comparative Example 3, and Table 1, it can be seen that the room temperature thermal conductivity of Example 1 is 0.78 vs 0.82 W·m. -1 ·K -1 ), flexural strength (95 vs 72 MPa) and fracture toughness (4.5 vs 3.5 MPa·m) 1 / 2 The results were all superior to those of Control Example 3. The reason is that Control Example 3 did not introduce the La component in step S2, so it could not react with ZrO2 during sintering to form a low thermal conductivity second phase with a La2Zr2O7 pyrochlore structure. It lacked grain boundary pinning effect and additional phonon scattering channels, which led to easy grain growth at high temperature, reduced tetragonal phase stability, and imperfect thermal resistance network. As a result, the thermal conductivity increased significantly and the mechanical properties decreased due to the easy initiation of microcracks.

[0066] Combining Example 1, Comparative Example 4, and Table 1, it can be seen that the room temperature thermal conductivity of Example 1 is 0.78 vs 1.05 W·m. -1 ·K -1 ), flexural strength (95 vs 55 MPa) and fracture toughness (4.5 vs 2.9 MPa·m) 1 / 2 The results were superior to those of Comparative Example 4. The reason is that Comparative Example 4 omitted the unidirectional freezing process in step S3 and used conventional heat drying at 100°C, resulting in the absence of ice crystal templates. This prevented the formation of directional closed nanoporous structures, the retention of the solid continuous phase heat transfer path, and a significant reduction in interfacial phonon scattering. At the same time, the precursor was prone to agglomeration and collapse during drying, which led to coarsening of pores and accelerated grain growth after sintering, ultimately resulting in severe deterioration of thermal insulation performance and mechanical strength.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-temperature stable nano-zirconia-based thermal insulation ceramic material, characterized in that, Includes the following steps: S1. Add ZrOCl2·8H2O solution to Y(NO3)3 solution so that Y2O3 accounts for 3-8 mol% of ZrO2, then add a multidentate organic acid complexing agent and introduce a high-valence transition metal alkoxide. Heat and stir at 60-80℃, then adjust the pH of the solution to 8.5-10.5 to form a polymeric complex nanosol precursor. S2. Introduce rare earth components into the polymeric complex nanosol precursor that can undergo a solid-phase reaction with zirconium oxide during sintering to generate a pyrochlore structure; S3. The obtained system is subjected to unidirectional freeze-drying to form a nanoporous precursor structure; S4. The obtained precursor is pre-fired at 500-700℃ and then sintered at 1250-1350℃ to obtain a high-temperature stable nano-zirconia-based thermal insulation ceramic material.

2. The method according to claim 1, characterized in that, The ZrOCl2·8H2O solution has a concentration of 0.5–1.5 mol / L.

3. The method according to claim 1, characterized in that, The polydentate organic acid is citric acid, and citric acid reacts with Zr. 4+ and Y 3+ The ratio of total molar amounts is 1.2 to 1.8:

1.

4. The method according to claim 3, characterized in that, The high-valence transition metal alkoxide is Nb(OEt)5 or Ta(OEt)5, and the mass ratio of the high-valence transition metal alkoxide to citric acid is 0.1 to 0.8:

1.

5. The method according to claim 1, characterized in that, The rare earth component is La or Gd, and its addition amount is 5 to 20 wt% of the final ceramic mass.

6. The method according to claim 1, characterized in that, The unidirectional freezing treatment temperature is -20℃ to -60℃, the freezing time is 4 to 12 hours, and the freeze-drying time is 24 to 48 hours.

7. The preparation method according to claim 1, characterized in that, The sintering heating rate is 5–15 °C / min.

8. A high-temperature stable nano-zirconia-based thermal insulation ceramic material prepared by the preparation method described in claim 1.

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