Tetragonal nano-barium titanate powder and its manufacturing method and application

Abstract

The present invention relates to the technical field of a dielectric ceramic powder manufacturing process, and particularly relates to tetragonal nanometer barium titanate powder, a manufacturing method thereof, and an application. The manufacturing method includes: (S.1) manufacturing a mesoporous titanium dioxide precursor with controllable crystal phase, adding it to a barium salt solution so that the molar ratio of barium to titanium is 2 to 4, then adding ethanol and aqueous ammonia to obtain a barium titanate precursor suspension in which the volume ratio of ethanol is 40% to 60%; (S.2) subjecting the barium titanate precursor suspension to a hydrothermal reaction to obtain a barium titanate suspension; and (S.3) centrifugally washing, drying, and pulverizing the barium titanate suspension to obtain tetragonal nanometer barium titanate powder. In the present application, by simultaneously controlling the molar ratio of barium to titanium between the anatase-type mesoporous titanium dioxide precursor and the barium salt in the hydrothermal reaction process and the ratio of ethanol in the hydrothermal medium in the hydrothermal reaction process, barium titanate powder having a higher c / a value and particle size uniformity can be obtained.

Description

[Technical Field]

[0001] The present invention relates to the technical field of dielectric ceramic powder manufacturing process, and in particular to tetragonal nano barium titanate powder and its manufacturing method and application. [Background technology]

[0002] Due to its excellent dielectric and ferroelectric properties, barium titanate is expected to have a wide range of applications in the dielectric ceramic industry, especially in multilayer ceramic capacitors (MLCCs). As electronic devices become more compact, the need for thin dielectric layers and large capacitance MLCCs is increasing significantly. This has led to higher requirements for the tetragonality (measured by the crystal axis ratio c / a value) and particle size of nano-barium titanate powder, the main raw material for the dielectric layer.

[0003] Currently, there are many methods used to synthesize barium titanate, among which the hydrothermal method has been widely studied due to its advantages of controllable synthesis process and simple operation. However, barium titanate powder synthesized by the conventional hydrothermal method is often cubic or tetragonal with a low c / a value, and usually requires subsequent high-temperature heat treatment to increase the c / a value, but this process is prone to agglomeration of barium titanate particles.

[0004] Therefore, the synthesis of tetragonal nano-barium titanate powders with high c / a values ​​by hydrothermal method is an important and worth exploring task. Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to overcome the drawback of the prior art that it is difficult to directly obtain tetragonal barium titanate having a high c / a value by a hydrothermal method. Therefore, the present invention provides a method for directly obtaining tetragonal barium titanate having a high c / a value by a one-step hydrothermal method. [Means for solving the problem]

[0006] In order to achieve the above object of the invention, the present invention is realized by the following technical solutions. According to a first aspect, the present invention provides a method for manufacturing a semiconductor device comprising: (S.1) adding a mesoporous titanium dioxide precursor capable of controlling the crystal phase to a barium salt solution so that the molar ratio of barium to titanium is 2 to 4, and then adding ethanol and aqueous ammonia to obtain a barium titanate precursor suspension having a volume ratio of ethanol of 40% to 60%; (S.2) subjecting the barium titanate precursor suspension to a hydrothermal reaction to obtain a barium titanate suspension; (S.3) centrifugal washing the barium titanate suspension, drying and pulverizing the same to obtain tetragonal nano barium titanate powder.

[0007] The inventors of the present application have found through research that in the process of producing nanobarium titanate powder by hydrothermal method, by controlling the reaction conditions in the hydrothermal process, the morphology of the final nanobarium titanate powder can be adjusted, and the barium titanate can have a relatively high c / a value. In further research, the inventors have found that the key factors affecting the c / a value of tetragonal nanobarium titanate powder include: (1) the morphology and particle size characteristics of the mesoporous titanium dioxide precursor, (2) the molar ratio of barium to titanium between the titanium dioxide precursor and the barium salt in the hydrothermal reaction process, and (3) the ratio of ethanol in the hydrothermal medium in the hydrothermal reaction process.

[0008] However, in terms of the morphology and particle size characteristics of the mesoporous titanium dioxide precursor, the anatase mesoporous titanium dioxide prepared by the present invention offers the dual benefits of having both anatase and mesoporous structures. The mesoporous structure further increases the specific surface area of ​​the anatase structure in the hydrothermal medium, providing more reactive sites and higher reaction activity, facilitating the subsequent hydrothermal synthesis of barium titanate. This improves the C / A value of the barium titanate powder, helping to obtain a barium titanate powder with high purity and low impurity content. Furthermore, the mesoporous structure, composed of a large number of small nanoparticles, not only increases the solubility of titanium dioxide in the hydrothermal reaction, allowing the hydrothermal reaction to proceed smoothly to obtain a tetragonal structure, but also reduces the non-uniformity of barium titanate nucleation and growth caused by differences in solubility, ensuring the uniformity and dispersion of the barium titanate nanoparticles subsequently synthesized by the hydrothermal method.

[0009] Regarding the molar ratio of barium to titanium, the inventors found that when the molar ratio of barium to titanium is within the range of 2 to 4, the c / a values ​​of the nanobarium titanate powder are all higher than 1.008, which is sufficient to meet the needs of practical applications. Further research into the principles behind this ratio revealed that, in theory, it is sufficient to ensure a barium to titanium molar ratio of 1:1 to form nanobarium titanate particles. However, in this application, the inventors found that when the molar ratio of barium to titanium is within the range of 2 to 4, sufficient barium ions are available around the mesoporous titanium dioxide dissolved in the hydrothermal medium to rapidly react with it, further increasing the probability of barium titanate nucleation, thereby efficiently producing fine, uniformly sized tetragonal barium titanate nanoparticles. On the other hand, when the molar ratio of barium to titanium is less than 2, the probability of forming barium titanate crystal nuclei is greatly reduced, resulting in a significant reduction in the yield of barium titanate, and at the same time, the number of barium titanate crystal nuclei is reduced, resulting in a significant increase in the particle size of the produced barium titanate, which is not useful for final use.On the other hand, after further increasing the molar ratio of barium to titanium, the inventors found that the concentration of barium ions in the reaction system is too high, resulting in the synthesis of barium titanate containing barium carbonate impurities, which significantly reduces its performance and makes it inapplicable to practical applications.

[0010] Regarding the ratio of ethanol in the hydrothermal solvent during the hydrothermal reaction, the inventors found that a high level of ethanol in the hydrothermal solvent significantly affected the formation of tetragonal nanobarium titanate powder with a high c / a value. This is due to the adsorption of hydroxyl groups on titanium sites or the catalytic oxidation of ethanol during the hydrothermal reaction. These side reactions intensify the hydroxylation process and further reduce the c / a value of the barium titanate. After extensive research into the ethanol ratio in the hydrothermal solvent, the inventors found that when the ethanol ratio in the hydrothermal solvent is between 40% and 60%, the hydroxylation process is suppressed due to competition between side reactions, thereby ensuring the c / a value of the tetragonal nanobarium titanate powder product. At the same time, by reducing the polarity of the hydrothermal solvent under these conditions, the tetragonal nanobarium titanate powder product has good particle size uniformity.

[0011] Therefore, in this application, by using an anatase mesoporous titanium dioxide precursor and simultaneously controlling the molar ratio of barium to titanium between the titanium dioxide precursor and the barium salt in the hydrothermal reaction process and the ratio of ethanol in the hydrothermal medium in the hydrothermal reaction process, it is possible to obtain barium titanate powder with a higher c / a value and particle size uniformity, and there is a synergistic effect between the three, and both are essential.

[0012] Preferably, the method for producing the mesoporous titanium dioxide precursor in step (S.1) includes: (1) simultaneously dropping a titanium source and a pH adjuster into an ethanol aqueous solution containing a template agent, a pH stabilizer, and a dispersant, dispersing the titanium source and the pH adjuster uniformly, and then subjecting the resulting solution to a hydrothermal reaction to obtain a reaction product; (2) washing and drying the resulting reaction product, followed by calcining to remove residual organic matter; (3) grinding and homogenizing the calcined product to obtain a powder crystal phase-controllable anatase or rutile mesoporous titanium dioxide precursor; However, the pH adjuster in the step (1) is concentrated hydrochloric acid or aqueous ammonia, and after adding the pH adjuster, the pH value of the system is controlled to be 0.5 to 10.

[0013] To better control the synthesis cost and tetragonality of barium titanate, the inventors have found that the selection of the titanium source is also crucial. Titanium dioxide has attracted much attention due to its advantages of easy availability, low storage requirements, and ease of scalability. However, its complex crystalline structure and solubility under mild hydrothermal conditions affect the properties of the final synthesized barium titanate powder, which must be further considered. In this application, the inventors surprisingly discovered that the crystalline structure of titanium dioxide can be adjusted by controlling the type of pH adjuster and pH conditions during the hydrothermal reaction. The applicants have found that different pH values ​​are key to obtaining mesoporous titanium dioxide with different crystalline structures. A higher pH value favors the synthesis of anatase mesoporous titanium dioxide, while a lower pH value favors the synthesis of rutile mesoporous titanium dioxide.

[0014] In the present application, the addition of a template and a dispersant in the hydrothermal production process of mesoporous titanium dioxide precursors can produce mesoporous titanium dioxide precursors composed of a large amount of small nanoparticles. In the same way, more uniform and fine titanium dioxide nanoparticle precursors increase the solubility of the titanium dioxide precursor in the subsequent hydrothermal reaction to produce barium titanate. At the same time, the mesoporous structure further increases the specific surface area of ​​the anatase structure in the hydrothermal medium, providing more reactive sites and higher reaction activity, which facilitates the subsequent hydrothermal reaction to produce barium titanate, improves the c / a value, and helps to obtain barium titanate powder with high product purity and low impurity content. In the subsequent hydrothermal barium titanate production process, the previously synthesized mesoporous titanium dioxide is first dissolved in the hydrothermal medium to form seeds, which are then further reacted with barium ions to produce barium titanate crystal nuclei. The increased solubility not only facilitates sufficient hydrothermal reaction to obtain a tetragonal structure, but also reduces the unevenness of barium titanate nucleation and growth caused by solubility differences, ensuring the uniformity and dispersion of the subsequently hydrothermally synthesized barium titanate nanoparticles.

[0015] Preferably, the mesoporous titanium dioxide precursor described in step (S.1) is an anatase mesoporous titanium dioxide precursor.

[0016] Compared with rutile titanium dioxide, which has a more stable thermodynamic crystalline structure, anatase titanium dioxide has a higher solubility in hydrothermal processes, and the formation of mesoporous titanium dioxide further increases the specific surface area in contact with the hydrothermal medium, facilitating the formation of more barium titanate crystal nuclei and resulting in tetragonal barium titanate nanoparticles with fine and uniform particle size. Therefore, anatase mesoporous titanium dioxide is preferably used as a precursor.

[0017] Preferably, the titanium source in step (1) is any one of tetrabutyl titanate, titanium tetrachloride, and titanium isopropoxide.

[0018] Preferably, the pH stabilizer is any one of urea, acetylacetone, acetic acid, and thioglycolic acid; the template agent is any one of glucose, carbonaceous polysaccharide microspheres, polyethylene glycol, organic amine, and soluble starch; The dispersant is any one of cetyltrimethylammonium bromide, polyvinylpyrrolidone, and O-xylene.

[0019] Preferably, the hydrothermal conditions in the step (1) are heating to 160 to 190°C by a method of heating a mantle, a heat transfer oil, or a molten salt, and carrying out a hydrothermal reaction for 2 to 6 hours; The firing temperature in the step (3) is 400 to 700° C., and the firing time is 2 to 4 hours.

[0020] Preferably, the barium source in step (S.1) is any one of barium hydroxide, barium chloride, and barium acetate.

[0021] Preferably, the pH of the barium titanate precursor suspension in step (S.1) is ≥ 13; Preferably, the hydrothermal temperature in step (S.2) is 220°C to 260°C, and the hydrothermal time is 12 to 40 hours.

[0022] According to a second aspect, the present invention further provides a tetragonal nano barium titanate powder produced by the above method, The tetragonal nano barium titanate powder has a c / a value of greater than 1.008; The average particle size of the tetragonal nano barium titanate powder is less than 200 nm.

[0023] According to a third aspect, the present invention further provides an application of the above tetragonal nano barium titanate powder in dielectric ceramic industry. [Effects of the Invention]

[0024] Therefore, the present invention has the following beneficial effects. The hydrothermal method used in the present invention has simple production conditions, is easy to operate, low cost, and allows for mass production. The barium titanate powder synthesized from the anatase mesoporous titanium dioxide precursor produced by this method has a high c / a value of 1.0095, a narrow particle size distribution, and an average particle size of approximately 95 nm. This is because the anatase structure has greater solubility in the hydrothermal process and further increases the specific surface area of ​​the mesoporous structure, making the hydrothermal reaction faster and more efficient, resulting in a narrow particle size distribution for the resulting tetragonal barium titanate. When the hydrothermal medium contains an appropriate ethanol ratio of 40% to 60%, the hydroxylation process is suppressed, resulting in a high c / a value. [Brief explanation of the drawings]

[0025] [Figure 1] 1 shows XRD patterns of mesoporous titanium dioxide powders whose crystal phases are controllable and produced by a hydrothermal method in Examples 1 to 4 of the present invention.

[0026] [Figure 2] 1 shows XRD patterns of tetragonal barium titanate powders produced by a hydrothermal method in Examples 1 to 4 of the present invention.

[0027] [Figure 3] 1 is a SEM image of an anatase mesoporous titanium dioxide powder prepared in Example 1 of the present invention.

[0028] [Figure 4] 1 is a TEM image of an anatase mesoporous titanium dioxide powder prepared in Example 1 of the present invention.

[0029] [Figure 5]1 is an SEM image of the tetragonal barium titanate powder produced in Example 1 of the present invention.

[0030] [Figure 6] 1 is a locally enlarged XRD pattern of the tetragonal barium titanate powder prepared in Example 1 of the present invention.

[0031] [Figure 7] 1 is a SEM image of the tetragonal barium titanate powder produced in Example 5 of the present invention.

[0032] [Figure 8] 1 is an SEM image of the tetragonal barium titanate powder produced in Example 6 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be further described below in conjunction with the drawings and specific examples. Those skilled in the art can realize the present invention based on these descriptions. In addition, the embodiments of the present invention related to the following description are generally only a part of the embodiments of the present invention, and not all of the embodiments. Therefore, based on the embodiments of the present invention, those skilled in the art can easily realize all other embodiments without any creative effort, and all other embodiments are included in the scope of the present invention.

[0034] Example 1: (1) Barium precursor: 18.93 g of barium hydroxide octahydrate was added to 20 mL of deionized water and heated and stirred in a water bath at 80°C until dissolved, to obtain a barium salt solution.

[0035] (2) Titanium precursor: 0.6 M glucose and 0.6 M urea were added to 30 mL of a 1:2 deionized water / ethanol mixture and magnetically stirred until all solids dissolved. Then, 3.64 g of cetyltrimethylammonium bromide was added. Under vigorous stirring in an ice-water bath, 4 mL of tetrabutyl titanate was added dropwise at a constant rate using a fixed double-ended dropping funnel. Simultaneously, aqueous ammonia was added dropwise to adjust the solution's pH to 10, yielding an anatase structure. After uniform stirring, the mixture was heated to 190 °C using a heating mantle or heat transfer oil for 3 hours for hydrothermal reaction. The reaction product was washed several times with absolute ethanol and deionized water, dried in a drying box at 80 °C for at least 12 hours, and then calcined at 400 °C for 3 hours to remove residual organic matter. The calcined powder was dispersed in ethanol and homogenized using an ultrasonic cell disrupter to obtain a well-dispersed suspension. The suspension was then dried in a vacuum drying cabinet and finally pulverized to obtain a mesoporous titanium dioxide precursor with controllable crystal phase. The XRD pattern of the resulting mesoporous titanium dioxide powder is shown in Figure 1, its SEM image in Figure 3, and its TEM image in Figure 4.

[0036] (3) Mixing: A predetermined amount of mesoporous titanium dioxide precursor with controllable crystal phase was weighed and transferred to a barium salt solution so that the molar ratio of barium to titanium was 4. The mixture was stirred uniformly, and then ethanol (the ratio of ethanol in the hydrothermal medium was 50%) and 15 mL of aqueous ammonia were added. The solution pH was adjusted to ≥ 13, yielding a barium titanate precursor suspension.

[0037] (4) Synthesis: The barium titanate precursor suspension was added to 50 mL of a hydrothermal reaction vessel, heated to 260°C by heating a mantle, heat transfer oil, or molten salt, and subjected to a hydrothermal reaction for 30 hours. The vessel was then cooled to room temperature along with the furnace, and the vessel was opened to obtain a barium titanate suspension.

[0038] (5) Washing: The hydrothermally synthesized barium titanate suspension was centrifuged and washed several times with acetic acid, deionized water, and ethanol, and the supernatant was discarded, leaving the white precipitate at the bottom.

[0039] (6) Drying: The washed product was placed in a drying cabinet at 80°C and dried for more than 12 hours. The resulting product was then pulverized to obtain barium titanate powder. The XRD pattern of the produced tetragonal barium titanate powder is shown in Figure 2. The split peaks, which clearly show the tetragonal structure shown in the locally enlarged XRD pattern, are shown in Figure 6, and its SEM image is shown in Figure 5.

[0040] Example 2: A mesoporous titanium dioxide precursor with controllable crystal phase was prepared by hydrothermal method using the method of Example 1, except that in step (2), 6 mL of the initial titanium source was added dropwise at a constant rate and heated to 160°C using a heating mantle, heat transfer oil, or molten salt, and allowed to hydrothermally react for 6 hours. The XRD pattern of the prepared mesoporous titanium dioxide powder is shown in Figure 1, and the XRD pattern of the final tetragonal barium titanate powder is shown in Figure 2.

[0041] Example 3: A mesoporous titanium dioxide precursor with controllable crystal phase was prepared by hydrothermal method using the method of Example 1, except that in step (2), concentrated hydrochloric acid was added dropwise to adjust the pH of the solution to 4, resulting in a mixed phase structure of anatase and rutile. The XRD pattern of the obtained mesoporous titanium dioxide powder is shown in Figure 1, and the XRD pattern of the final tetragonal barium titanate powder is shown in Figure 2.

[0042] Example 4: A mesoporous titanium dioxide precursor with controllable crystal phase was prepared by hydrothermal processing using the method described in Example 1, except that in step (2), concentrated hydrochloric acid was added dropwise to adjust the pH of the solution to 0.5 to obtain the rutile structure, and the dried product was calcined at 700°C for 3 hours to remove residual organic matter. The XRD pattern of the resulting mesoporous titanium dioxide powder is shown in Figure 1, and the XRD pattern of the final tetragonal barium titanate powder is shown in Figure 2.

[0043] Example 5: Tetragonal nano-barium titanate powder was prepared by hydrothermal method using the method of Example 1, except that in steps (1), (2), and (3), the barium source was barium chloride, the titanium source was titanium tetrachloride, and the Ba / Ti ratio was 3. The SEM image of the final barium titanate powder is shown in Figure 7.

[0044] Example 6: Tetragonal nano-barium titanate powder was prepared by hydrothermal method using the method of Example 1, except that in steps (1), (2), and (3), the barium source was barium acetate, the titanium source was titanium isopropoxide, and the Ba / Ti ratio was 2. The SEM image of the final barium titanate powder is shown in Figure 8.

[0045] Example 7: The method of Example 1 was used to prepare tetragonal nano barium titanate powder by hydrothermal method, with the difference that in step (3), the ratio of ethanol in the hydrothermal medium was 40%.

[0046] Example 8: The method of Example 1 was used to prepare tetragonal nano barium titanate powder by hydrothermal method, with the difference that in step (3), the ratio of ethanol in the hydrothermal medium was 60%.

[0047] Example 9: Tetragonal nano-barium titanate powder was produced by hydrothermal method using the method of Example 1, except that in step (4), the powder was heated to 220°C by heating a mantle, heat transfer oil, or molten salt, and subjected to hydrothermal reaction for 40 hours.

[0048] Example 10: Tetragonal nano-barium titanate powder was produced by hydrothermal method using the method of Example 1, except that in step (4), the powder was heated to 250°C by heating a mantle, heat transfer oil, or molten salt, and subjected to hydrothermal reaction for 12 hours.

[0049] Comparative Example 1: The crystal phase-controllable mesoporous titanium dioxide precursor was prepared by a hydrothermal method using the method of Example 1, with the difference that in step (2), 2 mL of the initial titanium source was added dropwise at a constant rate.

[0050] Comparative Example 2: A mesoporous titanium dioxide precursor with controllable crystal phase was prepared by hydrothermal method using the method of Example 1, except that in step (2), 8 mL of the initial titanium source was added dropwise at a constant rate, and the mixture was heated to 160°C using a heating mantle, heat transfer oil, or molten salt, and subjected to hydrothermal reaction for 12 hours.

[0051] Comparative Example 3: The crystal phase-controllable mesoporous titanium dioxide precursor was prepared by a hydrothermal method using the method of Example 1, except that in step (2), a mixed solution of deionized water and ethanol in a ratio of 1:1 was used.

[0052] Comparative Example 4: The crystal phase-controllable mesoporous titanium dioxide precursor was prepared by a hydrothermal method using the method of Example 1, except that in step (2), a mixed solution of deionized water and ethanol in a ratio of 2:1 was used.

[0053] Comparative Example 5: Tetragonal nano-barium titanate powder was prepared by hydrothermal method using the method of Example 1, except that in steps (1), (2), and (3), the barium source was barium chloride, the titanium source was titanium tetrachloride, and the Ba / Ti ratio was 1.

[0054] Comparative Example 6: Tetragonal nano-barium titanate powder was prepared by hydrothermal method using the method of Example 1, except that in steps (1), (2), and (3), the barium source was barium chloride, the titanium source was titanium tetrachloride, and the Ba / Ti ratio was 5.

[0055] Comparative Example 7: The method of Example 1 was used to prepare tetragonal nano barium titanate powder by hydrothermal method, with the difference that in step (3), the ratio of ethanol in the hydrothermal medium was 20%.

[0056] Comparative Example 8: The method of Example 1 was used to prepare tetragonal nano barium titanate powder by hydrothermal method, with the difference that in step (3), the ratio of ethanol in the hydrothermal medium was 80%.

[0057] Comparative Example 9: Tetragonal nano-barium titanate powder was produced by hydrothermal method using the method of Example 1, except that in step (4), the powder was heated to 200°C by heating a mantle, heat transfer oil, or molten salt, and subjected to hydrothermal reaction for 60 hours.

[0058] Comparative Example 10: Tetragonal nano-barium titanate powder was produced by hydrothermal method using the method of Example 1, except that in step (4), the powder was heated to 270°C by heating a mantle, heat transfer oil, or molten salt, and subjected to hydrothermal reaction for 10 hours.

[0059] Comparative Example 11: Tetragonal nanobarium titanate powder was prepared by hydrothermal method using the method of Example 1, except that in step (2), the titanium dioxide precursor used was a non-mesoporous commercial anatase titanium dioxide precursor.

[0060] <Performance test and result analysis> (1) The effect of pH on the crystal phase-controllable mesoporous titanium dioxide precursor prepared by hydrothermal method is shown in Table 1.

[0061] Table 1. Effect of pH on the crystal phase-controllable mesoporous titanium dioxide precursor prepared by the hydrothermal method. JPEG0007798273000001.jpg37164

[0062] As can be seen from Table 1, different pH values ​​are key to obtaining different crystalline types of mesoporous titanium dioxide. The higher the pH value, the easier it is to synthesize anatase mesoporous titanium dioxide. Compared with rutile titanium dioxide, which has a more stable thermodynamic crystalline structure, anatase titanium dioxide has a higher solubility in the hydrothermal process. Furthermore, the formation of mesoporous titanium dioxide further increases the specific surface area in contact with the hydrothermal medium, facilitating the formation of more barium titanate crystal nuclei and resulting in fine, uniformly sized tetragonal barium titanate nanoparticles. Therefore, anatase mesoporous titanium dioxide is preferred as the precursor.

[0063] (2) The influence of the initial amount of titanium source on the crystalline phase-controllable mesoporous titanium dioxide precursor prepared by the hydrothermal method is shown in Table 2.

[0064] Table 2. Effect of the amount of initial titanium source used on the crystal phase-controllable mesoporous titanium dioxide precursors produced by the hydrothermal method. JPEG0007798273000002.jpg44164

[0065] As can be seen from Table 2, the crystalline phase of the mesoporous titanium dioxide obtained using different initial titanium source amounts was anatase. However, the mesoporous titanium dioxide synthesized using an initial titanium source amount in the range of 4 to 6 mL had finer, more uniform particle sizes. This is because as the reactant concentration increased, the number of nucleation sites for titanium dioxide nanoparticles increased, resulting in finer mesoporous titanium dioxide. When the initial titanium source amount was 2 mL, there were fewer initial nucleation sites, and titanium dioxide tended to grow on the already formed nucleation sites, resulting in a relatively large particle size of the resulting anatase titanium dioxide. On the other hand, when the initial titanium source amount was increased to 8 mL, the particle size of the resulting titanium dioxide was not significantly different from that of 6 mL. Therefore, it is recommended that the initial titanium source amount be 4 to 6 mL.

[0066] (3) The effect of the ratio of deionized water to ethanol on the crystal phase-controllable mesoporous titanium dioxide precursor prepared by hydrothermal method is shown in Table 3.

[0067] Table 3. Effect of the ratio of deionized water to ethanol on the crystal phase-controllable mesoporous titanium dioxide precursor prepared by the hydrothermal method. JPEG0007798273000003.jpg36164

[0068] As can be seen from Table 3, when the deionized water to ethanol ratio is 1:2, the initial particle size of the titanium dioxide precursor obtained under these conditions is finer than that of the other comparative examples, which further increases the solubility of the titanium dioxide precursor in the hydrothermal process, helping to obtain tetragonal barium titanate nanoparticles with fine and uniform particle size. Furthermore, because glucose is slightly soluble in ethanol, the ethanol content should not be too high; a higher deionized water to ethanol ratio makes it difficult to dissolve the glucose, requiring a longer stirring time. Therefore, a deionized water to ethanol ratio of 1:2 is preferred.

[0069] (4) The influence of Ba / Ti ratio on the tetragonal nano-barium titanate powder prepared by hydrothermal method is shown in Table 4.

[0070] Table 4. Effect of Ba / Ti ratio on tetragonal nano-barium titanate powder produced by hydrothermal method JPEG0007798273000004.jpg46163

[0071] As can be seen from Table 4, when the Ba / Ti ratio is between 2 and 4, the c / a values ​​of the nanobarium titanate powders prepared by the hydrothermal method are all higher than 1.008, sufficient to meet the needs of practical applications. A relatively high Ba / Ti ratio increases the probability of forming barium titanate crystal nuclei, which helps to obtain tetragonal barium titanate nanoparticles with fine and uniform particle size. If the Ba / Ti ratio is further increased to 5, the concentration of barium ions becomes too high, resulting in the synthesis of barium titanate containing barium carbonate impurities. Therefore, a Ba / Ti ratio between 2 and 4 is preferred.

[0072] (5) The tetragonal nano-barium titanate powder prepared by hydrothermal method according to the ratio of ethanol in step (3) is shown in Table 5.

[0073] Table 5. Effect of ethanol ratio on tetragonal nano-barium titanate powder prepared by hydrothermal method. JPEG0007798273000005.jpg45163

[0074] As can be seen from Table 5, when the ethanol content is relatively high or low, the c / a value of the barium titanate obtained in the comparative example is relatively low, and the adsorption of hydroxyl groups or catalytic oxidation of ethanol occurs at the titanium site, which causes the hydroxylation process to become more severe. Only when the ethanol content in the hydrothermal medium is in the appropriate range of 40% to 60%, is the hydroxylation process inhibited by competition between side reactions. Therefore, it is preferable to set the ethanol content to 40% to 60%.

[0075] (6) See Table 6 for the effect of hydrothermal temperature and time on the tetragonal nano barium titanate powder prepared by hydrothermal method.

[0076] Table 6. Effect of hydrothermal temperature and time on tetragonal nano-barium titanate powder produced by hydrothermal method JPEG0007798273000006.jpg46163

[0077] As can be seen from Table 6, when the hydrothermal temperature was low (200°C), the ideal c / a value could not be achieved even with extended hydrothermal time. This exacerbated the effects of dissolution differences, resulting in poor particle size uniformity for the resulting barium titanate. Prolonged hydrothermal treatment consumed time and energy. Furthermore, considering the operating temperature requirements of the hydrothermal reactor, excessively high temperatures increase reactor wear. To provide sufficient driving force for the formation of tetragonal crystals within a short time, more appropriate temperatures and times were selected for the experiments of this invention. Therefore, it is preferred to conduct the reaction at a hydrothermal temperature of 220°C to 260°C for a time of 12 to 40 hours.

[0078] (7) The effect of mesoporous and non-mesoporous titanium dioxide precursors on the tetragonal nano-barium titanate powder prepared by hydrothermal method is shown in Table 7.

[0079] Table 7. Effect of mesoporous and non-mesoporous titanium dioxide precursors on tetragonal nano-barium titanate powders produced by hydrothermal method. JPEG0007798273000007.jpg25164

[0080] As can be seen from Table 7, under the same experimental conditions as in Example 1, barium titanate powder obtained using a non-mesoporous commercial anatase titanium dioxide precursor had a low c / a value and large particle size. This is because the specific surface area of ​​non-mesoporous titanium dioxide in contact with the hydrothermal medium is not as large as that of mesoporous titanium dioxide, resulting in a lower dissolution rate and reaction activity of titanium dioxide, and an insufficient driving force for crystalline structure change, resulting in an undesirable c / a value. Furthermore, the rate of barium titanate nucleation is slow, resulting in a large particle size. Furthermore, in an experiment to synthesize barium titanate by hydrothermal method using a titanium dioxide precursor, as disclosed in the invention patent publication number CN111762810A entitled "Method for Producing Tetragonal Nano Barium Titanate," the resulting tetragonal nano barium titanate particles had a particle size in the range of 60-200 nm and a c / a value of 1.0082, which is also lower than the effect of the mesoporous titanium dioxide precursor of the present invention.

[0081] In summary, the present invention demonstrates synergistic effects among the various parameters. For example, the mesoporous structure of anatase mesoporous titanium dioxide, composed of fine, uniformly sized particles, increases the specific surface area and reactivity, further improving the solubility of the titanium dioxide precursor in the hydrothermal reaction. Meanwhile, the use of a relatively high Ba / Ti ratio in the subsequent reaction provides sufficient barium ions to react with the dissolved titanium species in a timely manner, increasing the nucleation rate of barium titanate and achieving a high c / a value while also contributing to the production of fine, uniformly sized barium titanate powder. Furthermore, the synergistic effect of the relatively high reaction temperature range (220-260°C) and the ethanol ratio in the hydrothermal medium (40%-60%) helps to suppress the formation of hydroxyl groups during the hydrothermal reaction, thereby ensuring a high c / a value for the barium titanate powder.

[0082] The above content (combined with the drawings) describes preferred embodiments of the present invention, but the present invention is not limited to the above specific embodiments, which are merely illustrative and not limiting. Those skilled in the art can, under the teachings of the present invention, make various specific modifications without departing from the spirit of the present invention and the scope claimed by the claims, and all of these are included in the scope of the claims of the present invention.

Claims

1. (S.1) adding a crystal phase-controllable anatase mesoporous titanium dioxide precursor to a barium salt solution so that the molar ratio of barium to titanium is 2-4, and then adding ethanol and ammonia water to obtain a barium titanate precursor suspension with a volume ratio of ethanol of 40%-60%; (S.2) subjecting the barium titanate precursor suspension to a hydrothermal reaction at a hydrothermal temperature of 220°C to 260°C for a hydrothermal time of 12 to 40 hours to obtain a barium titanate suspension; (S.3) centrifugal washing, drying and pulverization of the barium titanate suspension to obtain tetragonal nano barium titanate powder; The method for preparing an anatase mesoporous titanium dioxide precursor in step (S.1) includes: (1) simultaneously adding a titanium source and a pH adjuster dropwise to an ethanol aqueous solution containing a template agent, a pH stabilizer, and a dispersant, dispersing the titanium source and the pH adjuster uniformly, and then subjecting the resulting mixture to a hydrothermal reaction to obtain a reaction product; (2) washing and drying the resulting reaction product, and then baking it at a baking temperature of 400 to 700°C to remove residual organic matter; (3) grinding and homogenizing the calcined product to obtain an anatase mesoporous titanium dioxide precursor; The pH adjuster in step (1) is concentrated hydrochloric acid or aqueous ammonia, and after adding the pH adjuster, the pH value of the system is controlled to be 0.5 to 10; A method for producing tetragonal nano barium titanate powder.

2. The method for producing tetragonal nano-barium titanate powder according to claim 1, characterized in that the titanium source in step (1) is any one of tetrabutyl titanate, titanium tetrachloride, and titanium isopropoxide.

3. the template agent is any one of glucose, carbonaceous polysaccharide microspheres, polyethylene glycol, organic amine, and soluble starch; the pH stabilizer is any one of urea, acetylacetone, acetic acid, and thioglycolic acid; 2. The method for producing tetragonal nano barium titanate powder according to claim 1, wherein the dispersant is any one of cetyltrimethylammonium bromide, polyvinylpyrrolidone, and o-xylene.

4. The hydrothermal conditions in the step (1) are to heat the mixture to 160-190°C by heating a mantle, heat transfer oil, or molten salt, and then carry out a hydrothermal reaction for 2-6 hours; The method for producing tetragonal nano barium titanate powder according to claim 1, 2 or 3, characterized in that the firing time in step (2) is 2 to 4 hours.

5. The method for producing tetragonal nano barium titanate powder according to claim 1, characterized in that the barium source in step (S.1) is any one of barium hydroxide, barium chloride, and barium acetate.

6. The method for producing tetragonal nano barium titanate powder according to claim 1 or 5, characterized in that the pH of the barium titanate precursor suspension in step (S.1) is ≥ 13.

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