A method for preparing highly dispersed zirconium dioxide

Abstract

The application provides a method for preparing high-dispersion zirconium dioxide, comprising the following steps: dissolving a zirconium salt in water, adding a composite directing agent, and mixing to obtain a precursor solution; the composite directing agent comprises an imidazole ionic liquid and a non-ionic surfactant; dropwise adding the precursor solution into a mixed bottom solution containing an alkaline precipitator and a cationic surfactant, maintaining the pH of the reaction system at 10.5-11.5 to form a zirconium hydroxide precipitate, and obtaining a zirconium hydroxide slurry; filtering and washing the zirconium hydroxide slurry to remove impurity ions, and then replacing and dispersing with a low-carbon alcohol to obtain an alcohol gel precursor; dispersing the alcohol gel precursor in an azeotrope agent to perform azeotrope rectification, removing the azeotrope agent and the solvent, and obtaining a dry powder; and mixing the dry powder with an inorganic salt, and then performing a step-by-step controlled calcination treatment to obtain high-dispersion zirconium dioxide.

Description

Technical Field

[0001] This application relates to the field of inorganic material preparation technology, specifically to a method for preparing highly dispersed zirconium dioxide. Background Technology

[0002] Zirconium dioxide is an important inorganic non-metallic material. Due to its high melting point, high refractive index, low thermal conductivity, corrosion resistance, and excellent electrochemical properties, it is widely used in precision ceramics, catalyst supports, solid oxide fuel cells, biomedical implants, and optical coatings.

[0003] The preparation of highly dispersed zirconium dioxide is key to improving the performance of related products; however, during the preparation of nano zirconium dioxide, particles are very prone to forming hard agglomerates through hydrogen bonds and chemical bonds; these hard agglomerates are difficult to eliminate by mechanical means in subsequent application processing, which will seriously affect the functional characteristics of the final product.

[0004] Currently, the main methods for preparing zirconium dioxide include hydrothermal method, sol-gel method and chemical precipitation method; Although chemical precipitation has advantages such as simple process, low cost and easy industrial production, the powder obtained by conventional process has poor dispersibility and wide particle size distribution.

[0005] To suppress agglomeration, existing technologies often employ methods such as adding a single surfactant or replacing organic solvents. However, during high-temperature calcination, simple surface coatings are prone to deactivation, leading to the growth of sintered necks in primary particles and the formation of agglomerated structures that are difficult to break down. In addition, the traditional one-step calcination method is prone to causing the gel pores to collapse, which will exacerbate aggregation.

[0006] Therefore, how to achieve precise control over the morphology and dispersibility of zirconium dioxide throughout the entire process through multiple synergistic effects, and prepare a zirconium dioxide powder with high dispersibility and relatively uniform particle size, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] This application provides a method for preparing highly dispersed zirconium dioxide, which can produce zirconium dioxide powder with high dispersibility and relatively uniform particle size.

[0008] In a first aspect, this application provides a method for preparing highly dispersed zirconium dioxide, comprising the following steps: S1: Dissolve zirconium salt in water, add a composite directing agent, and mix to obtain a precursor solution; the composite directing agent includes imidazole ionic liquids and nonionic surfactants; S2: The precursor solution is added dropwise to a mixed substrate containing an alkaline precipitant and a cationic surfactant, and the pH of the reaction system is maintained at 10.5-11.5 to form zirconium hydroxide precipitate, thus obtaining zirconium hydroxide slurry; S3: The zirconium hydroxide slurry is filtered and washed to remove impurity ions, and then dispersed and replaced with low-carbon alcohols to obtain an alcohol gel precursor. S4: Disperse the alcohol gel precursor in an azeotropic agent and perform azeotropic distillation to remove the azeotropic agent and solvent, and obtain a dry powder; S5: The dried powder is mixed with inorganic salt and then subjected to step-controlled calcination to obtain highly dispersed zirconium dioxide.

[0009] According to the above implementation method, by introducing imidazole ionic liquids and nonionic surfactants, the initial distribution state of the obtained precursor is optimized by utilizing the physical compatibility between the components; combined with a specific feeding sequence, the precursor generates rapid physical interaction when entering the mixed bottom liquid, and the disordered aggregation of nascent zirconium hydroxide particles is suppressed through the physical barrier effect; the low surface tension characteristics of the azeotropic agent are used to alleviate the capillary pressure during the azeotropic drying process, which can protect the skeletal structure of the alcohol gel precursor from collapse; finally, with the participation of inorganic salts in the step-controlled calcination treatment, the inorganic salt medium is used to construct a physical isolation environment, which effectively limits the interfacial migration and sintering between zirconium dioxide grains under high temperature conditions; Specifically, in step S1, the imidazole ionic liquid in the precursor solution, due to its polarity and cyclic structure, may interact to a certain extent with the hydrated zirconium ions and polynuclear complexes formed after zirconium salt dissolves in water through coordination and intermolecular forces. Simultaneously, the nonionic surfactant is relatively uniformly dispersed in the liquid phase. When the reaction enters the initial nucleation stage of step S2, the nonionic surfactant generates a steric hindrance effect through adsorption, and its interaction with the imidazole ionic liquid synergistically affects the formation of primary zirconium hydroxide nuclei, to some extent slowing down the diffusion of zirconium ions in the liquid phase and forming a coating layer on the surface of the primary zirconium hydroxide nuclei. This synergistic effect helps improve the dispersion of the primary zirconium hydroxide nuclei and reduces the possibility of abnormal growth. Step S2 ensures that zirconium ions are always in an environment of excess alkali, which accelerates the precipitation rate, reduces redeposition, and minimizes the dissolution-reprecipitation phenomenon caused by local pH fluctuations. Specifically, by adding the precursor solution dropwise to a mixed substrate containing an alkaline precipitant and a cationic surfactant, the zirconium ions react instantly upon the addition of the slightly acidic precursor solution. 4+The mixture rapidly transforms into negatively charged hydroxyl complexes and nascent zirconium hydroxide nuclei. At this point, the cationic surfactant in the substrate can be adsorbed onto the surface of the zirconium hydroxide nuclei through electrostatic attraction. Simultaneously, the composite directing agent in the precursor solution diffuses with the droplets to the interface of the nascent zirconium hydroxide nuclei. The hydrophobic tail chains of the nonionic surfactant interact with the hydrophobic groups of the anchored cationic surfactant, while the imidazole ionic liquid is interspersed among them. Driven by both electrostatic attraction and hydrophobic interaction, the three components help to form a micelle-like structure during the mixing process, thereby inhibiting aggregation, reducing the aggregation of precipitates, improving the uniformity of precipitates, and controlling the particle size of the primary zirconium hydroxide particles formed from the nascent zirconium hydroxide nuclei to the nanoscale, exhibiting good dispersibility. If a cationic surfactant is added to the precursor solution beforehand, due to Zr 4+ The electrorepulsive force between cationic surfactants and zirconium hydroxide primary crystal nuclei prevents the cationic surfactants from being effectively adsorbed during the formation stage of zirconium hydroxide primary crystal nuclei. This specific feeding sequence allows the components in the precursor solution to form an interaction environment with the active components upon entering the mixed substrate. This stepwise introduction process helps maintain the stability of the system at each stage of precipitation formation, avoiding disordered aggregation of nascent zirconium hydroxide particles due to excessively high local concentrations. This has a stronger anti-agglomeration ability than a single mixed micelle formed by mixing imidazole ionic liquids, nonionic surfactants, and cationic surfactants, allowing primary zirconium hydroxide particles to exist in a highly monodisperse state in the zirconium hydroxide slurry. Step S3, through washing, helps to reduce impurity ions in the system, thereby reducing the risk of them forming inorganic salts and inducing particle sintering during subsequent high-temperature calcination; the use of low-carbon alcohols can effectively disperse and replace free water in the gel pores, reduce the surface tension of the system, and provide a relatively pure alcohol gel precursor with low tension for subsequent steps. Step S4 utilizes the azeotropic agent to form an azeotrope with water, which helps to reduce the residue of low-carbon alcohols and pore water during azeotropic distillation and reduces the risk of hard agglomeration caused by capillary pressure due to the high surface tension of water. Since the surface tension of the azeotropic agent is lower than that of water, the pressure fluctuation in the pores is smaller during azeotropic distillation, which allows the framework structure of zirconium hydroxide to be maintained relatively intact and form dry powder. In step S5, inorganic salts act as a physical barrier medium, which can increase the mass transfer resistance between grains and reduce the strong chemical bond connections that may occur between dry powder particles to a certain extent, thereby reducing the risk of zirconium dioxide grain growth and sintering under high temperature conditions. Combined with the step-by-step controlled calcination treatment, it is beneficial to achieve the gradual removal of organic matter and reduce the particle crushing or local thermal agglomeration caused by intense heating or sudden gas release during conventional calcination. In summary, by connecting the various steps in the spatiotemporal dimension, it is helpful to form an overall anti-agglomeration process from molecular precursors to macroscopic powders; it can be reasonably inferred that this process is beneficial to improving the dispersibility of the final zirconium dioxide powder to a certain extent.

[0010] In some embodiments, in step S1, the mass ratio of the imidazole ionic liquid to the nonionic surfactant is 1:(2.5-3.5); the total mass of the composite directing agent is 4%-6% of the mass of the zirconium salt; the zirconium salt includes at least one of zirconium oxychloride octahydrate and zirconium nitrate pentahydrate; the imidazole ionic liquid includes at least one of 1-butyl-3-methylimidazolium bromide and 1-butyl-3-methylimidazolium tetrafluoroborate; and the nonionic surfactant is polyethylene glycol.

[0011] Through the above implementation methods, imidazole ionic liquids help provide electrostatic repulsion in the system, while nonionic surfactants mainly produce steric hindrance effects. Those skilled in the art can reasonably infer that when the ratio of the two is controlled between 1:(2.5-3.5), it is beneficial to form a dual stabilizing trend of electrostatics and steric hindrance on the surface of the nascent zirconium nucleus. If the proportion of imidazole ionic liquids is too high, it may affect the preparation of subsequent zirconium hydroxide slurry due to excessive charge density. If the proportion of nonionic surfactants is too high, it may increase organic residues during the heat treatment process. Furthermore, when the total mass of the composite directing agent is controlled within the range of 4%-6% of the zirconium salt mass, it helps to ensure that the surface of the nascent zirconium nucleus is adequately covered by the composite directing agent, thereby reducing agglomeration and lowering the risk of local overheating caused by excessive organic matter in subsequent heat treatment processes, which is beneficial to maintaining the purity of the final highly dispersed zirconium dioxide. The selected zirconium salt has high solubility, which is beneficial for preparing high-concentration precursor solutions and improving production efficiency; The selected imidazole ionic liquid can utilize its imidazole ring structure and cationic properties to generate strong coordination or electrostatic interaction with zirconium ions, thus solving the problem of easy desorption of protective agents in traditional processes. The selected nonionic surfactant has excellent water solubility and mild steric hindrance; and the thermal decomposition characteristics of polyethylene glycol are highly matched with the crystallization temperature range of zirconium dioxide, so it can be decomposed into gas more uniformly and completely in the subsequent heat treatment process without introducing metal ion impurities.

[0012] In some embodiments, in step S2, the concentration of the alkaline precipitant in the mixed base liquid is 3-8 mol / L; the concentration of the cationic surfactant is 0.01-0.05 mol / L; the alkaline precipitant includes at least one of ammonia, tetramethylammonium hydroxide, and triethanolamine; and the cationic surfactant includes at least one of hexadecyltrimethylammonium bromide and hexadecylpyridine chloride.

[0013] Through the above implementation methods, in the mixed substrate, the 3-8 mol / L alkaline precipitant exhibits a high buffering tendency in the pH range of 10.5-11.5, which helps neutralize the hydrogen ions released when the precursor solution is added, thereby promoting the nucleation of zirconium ions and keeping the primary zirconium hydroxide crystal nuclei at a small scale; Zr 4+ When it enters a strongly alkaline environment, it will transform into a negatively charged hydroxyl complex. At this time, the pre-placed cationic surfactant will change from a mutually repulsive state to a capture of the primary zirconium hydroxide crystal nuclei due to electrostatic interaction. This will help to form directional coating and reduce the aggregation between primary zirconium hydroxide crystal nuclei during the precipitation process. Furthermore, the selected alkaline precipitant reduces the impact of metal impurities on the dispersibility of subsequent heat treatment stages to some extent; the alkane segments of the cationic surfactant provide steric hindrance, which helps to improve the uniformity of the zirconium hydroxide slurry and maintain the high dispersibility of the dried powder in subsequent processes.

[0014] In some embodiments, in step S3, the washing conditions include: washing until the conductivity of the filtrate is ≤50μS / cm; the low alcohol includes at least one of ethanol and isopropanol.

[0015] Through the above implementation method, when the conductivity of the filtrate is ≤50μS / cm, the process helps to achieve a deeper washing effect, thereby reducing impurity ions in the system to a certain extent and reducing the risk of agglomeration caused by residual inorganic salts in subsequent heat treatment processes. At the same time, low-carbon alcohols, with their lower surface tension and better permeability, are beneficial to initially replace the water inside the gel, thereby providing a more compatible solvent environment for subsequent azeotropic distillation.

[0016] In some embodiments, in step S3, the alcohol gel precursor is immersed in a low-carbon alcohol solution containing 1-3 wt% surface modifier for 2-4 hours and then dispersed and replaced once; the surface modifier includes at least one of acetylacetone and ethyl acetoacetate; the low-carbon alcohol includes at least one of ethanol and isopropanol.

[0017] Through the above embodiments, the coordination and chelation of the surface modifier with the active sites in the gel precursor helps to form an in-situ chemical grafting tendency and introduces organic cross-linking points to a certain extent, thereby enhancing the network structure of the gel precursor. This surface modification can change the surface of the gel skeleton from hydrophilic to hydrophobic, which is beneficial to reduce the interfacial tension between it and the azeotropic agent, and reduce the damage to the structure caused by capillary stress during subsequent azeotropic distillation and drying.

[0018] In some embodiments, in step S4, the azeotropic agent includes at least one of n-butanol, isobutanol, n-pentanol, and isopentanol.

[0019] Through the above implementation methods, the azeotropic agent, with a surface tension much lower than that of water, helps to reduce capillary stress during azeotropic distillation and drying, and to a certain extent maintains the integrity of the skeletal structure of the alcohol gel precursor. The azeotrope formed by alcohol and water is beneficial for removing residual water in the system to a greater extent, so that the resulting dried powder is in a low moisture content state before entering the heat treatment process, reducing the oxygen bridging and hard agglomeration phenomena that water molecules may induce.

[0020] In some embodiments, the conditions for the stepped controlled calcination in step S5 include: calcining at 250-300℃ for 1-2 hours at a rate of 1-2℃ / min under an oxidizing atmosphere; then calcining at 450-500℃ for 2-3 hours at a rate of 1-2℃ / min; and then calcining at 700-800℃ for 2-3 hours at a rate of 4-6℃ / min; wherein the oxidizing atmosphere is air.

[0021] Through the above implementation method, when calcined at 250-300℃ for 1-2 hours under an oxidizing atmosphere at a rate of 1-2℃ / min, imidazole ionic liquids, nonionic surfactants and cationic surfactants will gradually undergo desorption, chain scission and oxidative decomposition; low-rate heating is conducive to the relatively stable escape of organic gases, thereby reducing the risk of particle bursting or pore structure collapse caused by the instantaneous generation of a large amount of gas to a certain extent. When the temperature is increased to 450-500℃ at 1-2℃ / min and calcined for 2-3 hours, the long chains of imidazole ionic liquids, nonionic surfactants, and cationic surfactants tend to carbonize and oxidize, which helps to reduce residual organic matter and reduce the possibility of carbon residue in the subsequent high-temperature calcination stage. Then, the temperature is increased to 700-800℃ and calcined for 2-3 hours at a rate of 4-6℃ / min. Zirconium dioxide exhibits a tendency to transform from amorphous to crystalline in this temperature range and obtains a high degree of crystallinity. At the same time, it reduces the grain coarsening phenomenon that may be caused by excessively high temperature to a certain extent. In summary, this process helps to suppress the growth of sintering necks to a certain extent, which is beneficial for maintaining the high dispersibility of zirconium dioxide products.

[0022] In some embodiments, step S5 specifically involves: mixing the dried powder with inorganic salt at a mass ratio of 1:(1.8-2.2), performing a stepped controlled calcination treatment, and then washing with water to remove salt to obtain highly dispersed zirconium dioxide; the inorganic salt includes at least one of NaCl and KCl.

[0023] Through the above implementation methods, the superior thermal conductivity of inorganic salts helps to absorb and disperse the heat released in the preceding processes during the oxidative decomposition process, thereby reducing the risk of grain coarsening or cracking caused by local thermal runaway to a certain extent. The step-by-step controlled calcination strategy facilitates the gradual removal of organic components and reduces the adverse effects of violent decomposition. Furthermore, as a solid diluent and barrier medium, inorganic salts can isolate zirconium dioxide grains in the dry powder to a certain extent, and increase the interfacial mass transfer resistance between grains by utilizing the spatial confinement effect, which helps to inhibit grain migration and sintering neck development during calcination and reduce hard agglomeration. Since NaCl and KCl have high water solubility, the salt matrix can be easily removed through the washing process after calcination, which helps to maintain the dispersibility and chemical purity of the final zirconium dioxide product.

[0024] In some embodiments, the inorganic salt includes NaCl and KCl, wherein the mass ratio of NaCl to KCl is 1:(0.8-1.5).

[0025] Through the above implementation methods, the melting points of pure NaCl and KCl are 801℃ and 770℃, respectively. The binary salt system constructed using NaCl and KCl exhibits low eutectic properties under proportional adjustment, resulting in a lower eutectic point for the mixed salt compared to the pure component. During the stepped controlled calcination heat treatment process, this binary salt system is conducive to early transformation into a liquid-phase molten salt environment, thereby enhancing the coating and wetting effect in the molten state to a certain extent and improving the isolation efficiency of inorganic salt for zirconium dioxide grains. Compared with a single component, the binary salt system exhibits more stable chemical potential and vapor pressure during heating, which helps to buffer temperature fluctuations in the high-temperature zone. At the same time, it has lower viscosity and better wetting properties in the molten state, allowing the molten inorganic salt to penetrate and coat zirconium dioxide grains more uniformly, forming a relatively continuous protective film. While enhancing the physical spatial isolation effect, it also reduces the risk of local sintering that may be caused by a single inorganic salt phase to a certain extent.

[0026] The second aspect is the application of highly dispersed zirconium dioxide prepared by the method according to any embodiment of the first aspect in optical coatings.

[0027] Through the above embodiments, highly dispersed zirconium dioxide exhibits high dispersibility and a low tendency for particle agglomeration, which is conducive to forming a uniform and dense coating structure and improves the light transmittance and stability of the coating to a certain extent. At the same time, the high dispersibility also helps to reduce local defects, which is beneficial to extending the service life of the coating in optical devices and improving performance to a certain extent.

[0028] Compared with the prior art, the beneficial effects of this application are at least as follows: The directional adsorption of imidazole ionic liquids, the steric hindrance effect of nonionic surfactants, and the formation of micelle-like structures by cationic surfactants facilitate the formation of a composite guiding system with both electrostatic repulsion and physical isolation functions on the surface of nascent zirconium hydroxide crystal nuclei during the precipitation reaction. This helps maintain the dispersion of primary particles in the zirconium hydroxide slurry to a certain extent, providing conditions for the subsequent preparation of zirconium dioxide with higher dispersion. Subsequently, in the azeotropic distillation and drying stages, the synergistic effect of surface modifiers and the azeotropic distillation process helps reduce the agglomeration tendency of zirconium dioxide. In the stepped controlled calcination stage, the introduction of a specific proportion of inorganic salt media can construct a spatially confined environment. Combined with the stepped controlled calcination process, while gradually removing organic components, the physical shielding and thermal conduction buffering effect of the salt matrix helps reduce the interfacial migration of zirconium dioxide nanocrystals at high temperatures, thereby obtaining zirconium dioxide products with better dispersion to a certain extent. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of the embodiments of this application and constitute a part of this application, do not constitute a limitation on the embodiments of this application.

[0030] Figure 1 This is a SEM image of the highly dispersed zirconium dioxide synthesized in Example 1 of this application; Figure 2 This is a graph showing the dynamic light scattering test results of highly dispersed zirconium dioxide synthesized in Example 1 of this application. Detailed Implementation

[0031] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0032] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0034] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0035] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0036] Polyethylene glycol, number average molecular weight 2000.

[0037] Example 1 Preparation of a highly dispersed zirconium dioxide: S1: Dissolve 32.2 parts of zirconium oxychloride octahydrate in 200 parts of high-purity water, then add 0.4 parts of a composite directing agent composed of 1-butyl-3-methylimidazolium bromide and 1.2 parts of polyethylene glycol, and stir continuously at 400 rpm for 30 min at 25°C to obtain a precursor solution. S2: The precursor solution was added dropwise at a rate of 2 ml / min to 360 parts of a mixed base solution containing an alkaline precipitant and a cationic surfactant (ammonia concentration of 5 mol / L and cetyltrimethylammonium bromide concentration of 0.03 mol / L). The mixture was continuously stirred at 850 rpm at 25°C. During the addition process, the pH was monitored in real time and adjusted to 11.0 with 25 wt% ammonia. After the addition was completed, the mixture was aged for 2 hours to obtain zirconium hydroxide slurry. S3: Filter the zirconium hydroxide slurry and wash it repeatedly with high-purity water until the conductivity of the filtrate is 30 μS / cm; then perform three dispersion replacements with 250 parts of isopropanol. During the fourth replacement, soak the resulting filter cake in 250 parts of isopropanol solution containing 2 wt% acetylacetone, let it stand for 3 hours, and then filter to obtain the alcohol gel precursor. S4: Disperse the alcohol gel precursor in 500 parts of n-butanol, transfer it to a distillation apparatus equipped with a water separator for azeotropic distillation; continue heating until the distillation temperature stabilizes at 117.7℃, then stop distillation; vacuum dry the residue at 80℃ to remove residual azeotropic agent, and obtain dry powder; S5: Mix 15.5 parts of the above-mentioned dried powder with 31 parts of inorganic salt (14.1 parts of NaCl and 16.9 parts of KCl) and grind thoroughly. Then place the mixture in a muffle furnace and perform the following stepwise heating program under an air atmosphere: heat to 280℃ at 1.5℃ / min and calcine at a constant temperature for 1.5h; continue to heat to 480℃ at 1.5℃ / min and calcine at a constant temperature for 2.5h; finally heat to 750℃ at 5℃ / min and calcine at a constant temperature for 2.5h; after calcine, cool with the furnace and wash the product repeatedly with water until the conductivity of the washing liquid is 30μS / cm; finally bake in a forced-air oven at 100℃ to constant weight to obtain highly dispersed zirconium dioxide.

[0038] The scanning electron microscope image of the highly dispersed zirconium dioxide is as follows: Figure 1 As shown, the dynamic light scattering test results are as follows: Figure 2 As shown.

[0039] Example 2 It is largely the same as Example 1, except that the inorganic salt in step S5 is KCl.

[0040] Example 3 It is largely the same as Example 1, except that the inorganic salt in step S5 is NaCl.

[0041] Comparative Example 1 Similar to Example 1, except that step S1 no longer involves adding a composite directing agent consisting of an imidazole ionic liquid and a nonionic surfactant.

[0042] Comparative Example 2 Similar to Example 1, except that in step S3, during the fourth replacement, 250 parts of isopropanol solution containing 2wt% acetylacetone are replaced with 250 parts of isopropanol.

[0043] Comparative Example 3 It is largely the same as Example 1, except that the 1.2 parts of polyethylene glycol in step S1 are replaced with 0.8 parts of polyethylene glycol.

[0044] Comparative Example 4 It is largely the same as Example 1, except that in step S1, 1.2 parts of polyethylene glycol are replaced with 1.6 parts of polyethylene glycol.

[0045] Comparative Example 5 It is largely the same as Example 1, except that inorganic salts are no longer mixed in step S5.

[0046] Comparative Example 6 S1: It is roughly the same as Example 1, except that: the same amount of hexadecyltrimethylammonium bromide as in step S2 of Example 1 is added directly after the composite directing agent is added in step S1, and the mixture is continuously stirred at 400 rpm for 30 min at 25°C to obtain the precursor solution. S2: It is largely the same as Example 1, except that the base solution is only 360 parts of 5mol / L ammonia water; S3-S5: Same as steps S3-S5 in Example 1.

[0047] Test section Dispersion stability test: At 25°C, equal amounts (0.1 g) of the examples and comparative samples were added to equal volumes (50 ml) of isopropanol, and then treated with an ultrasonic cleaner at an ultrasonic frequency of 40 kHz for 20 min to ensure thorough dispersion. The dispersion was then transferred to a standard graduated colorimetric tube with a diameter of 25 mm and a height of 150 mm. The time it took for the clear layer (the first visible clear liquid) to appear 5 mm below the liquid surface was recorded.

[0048] Particle size and polydispersity index (PDI) testing: The particle size distribution of the samples was quantitatively analyzed using a Malvern laser particle size analyzer based on the principle of dynamic light scattering (DLS). Take 0.05g of the zirconium dioxide sample to be tested from the examples and comparative examples, add it to 50mL of isopropanol, and treat it continuously in an ice-water bath for 20min using an ultrasonic cleaner (frequency 40kHz, power 200W) to obtain the initial dispersion; set the test temperature to 25℃, the equilibration time to 120s, select isopropanol as the dispersant, and set the refractive index to 2.15; record the average value of the hydrodynamic diameter (i.e., average particle size) and the polydispersity index (PDI).

[0049] The test results are shown in Table 1: Table 1

[0050] As shown in Table 1, the time for the clear layer of the highly dispersed zirconium dioxide dispersion prepared in each comparative example is shorter than that in each embodiment. The reason may be that in comparative example 1, since the composite directing agent composed of imidazole ionic liquid and nonionic surfactant is no longer added in step S1, the hydrated zirconium ions and polynuclear complexes formed after zirconium salt dissolves in water lack the directional adsorption of polar ring structure and the steric hindrance synergistic effect of long chain molecules, resulting in the diffusion rate of zirconium ions in the liquid phase being unrestricted. When the reaction enters the nucleation stage of step S2, the primary zirconium hydroxide nuclei undergo uncontrolled abnormal growth and initial physical accumulation, which increases the particle size and widens the distribution of the primary zirconium hydroxide nuclei. In Comparative Example 2, since no surface modifiers such as acetylacetone were added in step S3, the active sites of the gel precursor failed to achieve effective coordination and chelation with the surface modifiers, and the surface of the gel skeleton remained in a high-energy hydrophilic state. In the subsequent azeotropic distillation process, the system could not resist the huge capillary pressure generated by the high surface tension of water, which may lead to severe collapse of the gel pore structure. In Comparative Example 3, the lack of nonionic surfactant in the composite directing agent resulted in insufficient steric hindrance effect strength in the instantaneous microenvironment where the precursor solution and the mixed substrate come into contact, making it difficult to form a relatively complete physical barrier on the surface of the nascent zirconium hydroxide crystal nuclei. Consequently, some nascent zirconium hydroxide crystal nuclei in the early stage of nucleation were exposed to high-energy active sites due to incomplete surface coating, resulting in disordered aggregation. In Comparative Example 4, the excessively high proportion of nonionic surfactant in the composite directing agent, while providing sufficient steric hindrance during the nucleation stage, resulted in negative thermodynamic effects on the subsequent heat treatment process in step S5 due to the excessively encapsulated organic components. Under an oxidizing atmosphere, the excessive surfactant underwent violent oxidative decomposition, leading to excessively high instantaneous pressure of the generated organic gas, which eroded and destroyed the nanoscale pore structure maintained by azeotropic distillation, causing micropore collapse. Furthermore, the intense local exothermic reaction accompanying the concentrated oxidation of a large amount of organic matter caused a sudden increase in the surface energy of the zirconium dioxide grains, weakening the physical barrier effect of the inorganic salt medium, which could induce interfacial migration and sintering neck growth between zirconium dioxide grains, leading to secondary thermal agglomeration. In Comparative Example 5, since no inorganic salt medium was mixed during the calcination stage, the zirconium dioxide grains in the dry powder lost the physical isolation of the inorganic salt, and the interfacial mass transfer resistance was greatly reduced. In the high-energy state crystallization temperature range of 700-800℃ during the stepped controlled calcination, adjacent zirconium dioxide grains are prone to undergo violent interfacial migration and induce sintering neck growth, causing zirconium dioxide to evolve from a loose state into a highly dense sintered agglomerate structure. Comparative Example 6 lacked the cationic surfactant in the mixed substrate, which affected the Zr content in the precursor solution immediately upon droplet introduction. 4+ The rapid conversion of negatively charged hydroxyl complexes or the instantaneous electrostatic attraction of primary nuclei prevents the active sites on the surface of nascent zirconium hydroxide crystal nuclei from being effectively physically isolated, leading to uncontrolled collisional aggregation; this change in the feeding sequence avoids the optimal kinetic window for achieving in-situ coating.

[0051] Based on Examples 1-3 in Table 1, it can be reasonably inferred that Example 1 uses a binary mixed salt composed of NaCl and KCl in a specific ratio. Due to its low eutectic effect, the inorganic salt medium tends to transform into a liquid phase earlier when the temperature is below the final calcination temperature. This liquid phase medium has a certain fluidity, which helps to smooth out local thermal fluctuations and, to a certain extent, blocks direct contact between zirconia grains, thereby reducing the risk of interface migration at high temperatures. In contrast, Examples 2 and 3 use single KCl or NaCl, respectively. Since their melting points are higher than or close to the calcination temperature of this process, the inorganic salt medium mainly exists in solid or semi-solid form during the critical crystallization period. It lacks the fluidity and wettability of liquid molten salt, which to a certain extent reduces the inhibitory effect on the contact sintering of zirconia grains.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing highly dispersed zirconium dioxide, characterized in that, Includes the following steps: S1: Dissolve zirconium salt in water, add a composite directing agent, and mix to obtain a precursor solution; the composite directing agent includes imidazole ionic liquids and nonionic surfactants; S2: The precursor solution is added dropwise to a mixed substrate containing an alkaline precipitant and a cationic surfactant, and the pH of the reaction system is maintained at 10.5-11.5 to form zirconium hydroxide precipitate, thus obtaining zirconium hydroxide slurry; S3: The zirconium hydroxide slurry is filtered and washed to remove impurity ions, and then dispersed and replaced with low-carbon alcohols to obtain an alcohol gel precursor. S4: Disperse the alcohol gel precursor in an azeotropic agent and perform azeotropic distillation to remove the azeotropic agent and solvent, and obtain a dry powder; S5: The dried powder is mixed with inorganic salt and then subjected to step-controlled calcination to obtain highly dispersed zirconium dioxide; In step S3, the alcohol gel precursor is immersed in a low-carbon alcohol solution containing 1-3 wt% surface modifier for 2-4 hours and then dispersed and replaced once; the surface modifier includes at least one of acetylacetone and ethyl acetoacetate; the low-carbon alcohol includes at least one of ethanol and isopropanol.

2. The method according to claim 1, characterized in that, In step S1, the mass ratio of the imidazole ionic liquid to the nonionic surfactant is 1:(2.5-3.5); the total mass of the composite directing agent is 4%-6% of the mass of the zirconium salt; the zirconium salt includes at least one of zirconium oxychloride octahydrate and zirconium nitrate pentahydrate; the imidazole ionic liquid includes at least one of 1-butyl-3-methylimidazolium bromide and 1-butyl-3-methylimidazolium tetrafluoroborate; and the nonionic surfactant is polyethylene glycol.

3. The method according to claim 1, characterized in that, In step S2, the concentration of the alkaline precipitant in the mixed base liquid is 3-8 mol / L; the concentration of the cationic surfactant is 0.01-0.05 mol / L; the alkaline precipitant includes at least one of ammonia, tetramethylammonium hydroxide, and triethanolamine; and the cationic surfactant includes at least one of hexadecyltrimethylammonium bromide and hexadecylpyridine chloride.

4. The method according to claim 1, characterized in that, In step S3, the washing conditions include: washing until the conductivity of the filtrate is ≤50μS / cm.

5. The method according to claim 1, characterized in that, In step S4, the azeotropic agent includes at least one of n-butanol, isobutanol, n-pentanol, and isopentanol.

6. The method according to claim 1, characterized in that, In step S5, the conditions for the stepped controlled calcination include: calcining at 250-300℃ for 1-2 hours at a rate of 1-2℃ / min under an oxidizing atmosphere; then calcining at 450-500℃ for 2-3 hours at a rate of 1-2℃ / min; and then calcining at 700-800℃ for 2-3 hours at a rate of 4-6℃ / min; wherein the oxidizing atmosphere is air.

7. The method according to claim 1, characterized in that, Step S5 specifically involves mixing the dried powder with inorganic salt at a mass ratio of 1:(1.8-2.2), then subjecting it to a step-controlled calcination process. After washing with water to remove salt, highly dispersed zirconium dioxide is obtained. The inorganic salt includes at least one of NaCl and KCl.

8. The method according to claim 7, characterized in that, The inorganic salts include NaCl and KCl, wherein the mass ratio of NaCl to KCl is 1:(0.8-1.5).

9. The application of the highly dispersed zirconium dioxide prepared by the method according to any one of claims 1-8 in optical coatings.

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