Cubic system barium titanate nano-powder, its manufacturing method, and applications

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 the production process of dielectric ceramic powder, and particularly relates to tetragonal barium titanate nanometer powder, its production method and application.

Background Art

[0002] Due to its excellent dielectric properties and ferroelectricity, barium titanate has broad application prospects in the dielectric ceramic industry, especially in multilayer ceramic capacitors (MLCCs). With the development of the miniaturization of electronic devices, the demand for MLCCs with thin dielectric layers and large capacitance has increased significantly. Therefore, higher requirements are imposed on indicators such as the tetragonality (measured by the c / a value of the crystal axis ratio) and particle size of barium titanate nanometer powder, which is the main raw material of the dielectric layer.

[0003] Currently, there are many methods used for the synthesis of barium titanate. Among them, the hydrothermal method has been widely studied because of its advantages such as controllable synthesis process and simple operation method. However, barium titanate powder synthesized by the conventional hydrothermal method mostly has a cubic crystal phase or a tetragonal system with a low c / a value. Usually, it is necessary to increase its c / a value by subsequent high-temperature heat treatment, but this process is likely to cause aggregation of barium titanate particles.

[0004] Therefore, the synthesis of tetragonal barium titanate nanometer powder with a high c / a value by the hydrothermal method is an important and valuable work to explore.

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0006] To achieve the above object of the present invention, the present invention is realized by the following technical solutions. According to a first aspect, the present invention (S.1) adding a mesoporous titanium dioxide precursor with controllable 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 in which the volume ratio of ethanol is 40% to 60%; (S.2) hydrothermally reacting the barium titanate precursor suspension to obtain a barium titanate suspension; (S.3) centrifugally washing, drying and pulverizing the barium titanate suspension to obtain orthorhombic nanobarium titanate powder, and providing a method for producing orthorhombic nanobarium titanate powder.

[0007] According to the research of the inventors of the present application, in the process of producing nanobarium titanate powder by the hydrothermal method, by controlling the reaction conditions in the hydrothermal process, the morphology of the finally formed nanobarium titanate powder can be adjusted, and it is found that barium titanate can have a relatively high c / a value. In the further research process of the inventors, it is found that the important factors affecting the c / a value of orthorhombic 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, regarding the morphology and particle size characteristics of the mesoporous titanium dioxide precursor, the anatase-type mesoporous titanium dioxide produced in the present invention provides a dual merit of having an anatase and a mesoporous structure. The mesoporous structure further increases the specific surface area of the anatase structure in the hydrothermal medium, provides more reaction sites and higher reaction activity, promotes the sufficient progress of the subsequent reaction for producing barium titanate by the hydrothermal method, improves the c / a value of the barium titanate powder, and helps to obtain barium titanate powder with high product purity and low impurity content. And the mesoporous structure is composed of a large number of small-sized nano-titanium dioxide particles. The uniform and fine titanium dioxide nanoparticle precursor not only helps to increase the solubility of titanium dioxide in the hydrothermal reaction and allows the hydrothermal reaction to proceed sufficiently to obtain a tetragonal crystal structure, but also reduces the non-uniformity of the nucleation and growth of barium titanate caused by the difference in solubility, and guarantees the uniformity and dispersibility of the barium titanate nanoparticles synthesized by the subsequent 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 barium titanate nano-powders are all higher than 1.008 and sufficient to meet the needs of practical applications. Further studying the principle behind this ratio, it was found that theoretically, it is only necessary to ensure that the molar ratio of barium to titanium is 1:1 to form barium titanate nano-particles. On the other hand, in the present application, the inventors found that when the molar ratio of barium to titanium is within the range of 2 to 4, there are sufficient barium ions around the mesoporous titanium dioxide dissolved in the hydrothermal medium that can rapidly react with it, ensuring that the probability of forming barium titanate crystal nuclei can be further increased, and thus it is possible to efficiently obtain orthorhombic barium titanate nano-particles with fine and uniform particle sizes. 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 significantly reduced, so the yield of barium titanate is significantly reduced. At the same time, since the barium titanate crystal nuclei decrease, the particle size of the produced barium titanate is significantly increased, making it useless for final utilization. On the other hand, after further increasing the molar ratio of barium to titanium, the inventors found that because the concentration of barium ions in the reaction system is too high, the synthesized barium titanate contains barium carbonate impurities, so its performance is significantly reduced and not applicable to the needs of practical applications.

[0010] Regarding the ratio of ethanol in the hydrothermal medium in the hydrothermal reaction process, the inventors have found that the level of the ratio of ethanol in the hydrothermal medium has a significant impact on the formation of orthorhombic barium titanate powder with a high c / a value. The reason is that in the hydrothermal reaction process, the adsorption of hydroxyl groups or the catalytic oxidation reaction of ethanol occurs on the titanium site, and these side reactions intensify the hydroxylation process and further reduce the c / a value of barium titanate. After deeply studying the ratio of ethanol in the hydrothermal medium, the inventors have found that when the ratio of ethanol in the hydrothermal medium is 40% - 60%, the hydroxylation process in the hydrothermal reaction process is suppressed due to the competition between side reactions, thereby ensuring the c / a value of the orthorhombic barium titanate powder product. At the same time, by reducing the polarity of the hydrothermal solvent under this condition, the orthorhombic barium titanate powder product has good particle size uniformity.

[0011] Therefore, in the present application, by using anatase-type 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, barium titanate powder with a higher c / a value and particle size uniformity can be obtained, and there is a synergistic effect among the three, and both are indispensable.

[0012] Preferably, the method for producing the mesoporous titanium dioxide precursor in the step (S.1) is (1) A step of simultaneously dropping a titanium source and a pH adjuster into an ethanol aqueous solution containing a template agent, a pH stabilizer, and a dispersant, uniformly dispersing them, and then subjecting them to a hydrothermal reaction to obtain a reaction product; (2) A step of washing the obtained reaction product, drying it, and then calcining it to remove residual organic substances; (3) A step of pulverizing and homogenizing the product after calcination to obtain an anatase-type or rutile-type mesoporous titanium dioxide precursor capable of controlling the powder crystal phase, and However, the pH regulator in the step (1) is concentrated hydrochloric acid or ammonia water, and after adding the pH regulator, the pH value of the system is controlled to be 0.5 - 10.

[0013] In order to better control the synthesis cost and the tetragonality of barium titanate, the inventors have found that the selection of the titanium source is also extremely important. Titanium dioxide has attracted much attention due to its advantages of easy availability, low requirements for storage, and easy scale-up. However, under mild hydrothermal conditions, it is necessary to further consider the influence of its complex crystal structure and solubility on the characteristics of the finally synthesized barium titanate powder. In this application, the inventors surprisingly found that the crystal structure of titanium dioxide can be adjusted by controlling the type and pH conditions of the pH regulator in the hydrothermal reaction. The applicant has found that different pH values are the key to obtaining mesoporous titanium dioxide with different crystal forms. The higher the pH value, the easier it is to synthesize anatase-type mesoporous titanium dioxide, while the lower the pH value, the easier it is to synthesize rutile-type mesoporous titanium dioxide.

[0014] In this application, in the manufacturing process of the mesoporous titanium dioxide precursor by the hydrothermal method, by adding a templating agent and a dispersing agent, a mesoporous titanium dioxide precursor composed of a large number of nano-titanium dioxide particles with small particle sizes can be obtained. In the same case, a more uniform and finer titanium dioxide nanoparticle precursor increases the solubility of the titanium dioxide precursor in the subsequent hydrothermal reaction for the formation of barium titanate. At the same time, the mesoporous structure further increases the specific surface area of the anatase structure in the hydrothermal medium, provides more reaction sites and higher reaction activity, promotes the sufficient progress of the subsequent reaction for manufacturing barium titanate by the hydrothermal method, improves the c / a value, and helps to obtain barium titanate powder with high purity and low impurity content. In the subsequent hydrothermal process for the formation of barium titanate, the previously synthesized mesoporous titanium dioxide first dissolves in the hydrothermal medium to form seeds, and then further reacts with barium ions to generate barium titanate crystal nuclei. The increased solubility not only helps to obtain a tetragonal crystal structure by fully performing the hydrothermal reaction, but also reduces the non-uniformity of the nucleation and growth of barium titanate caused by the difference in solubility, and guarantees the uniformity and dispersibility of the barium titanate nanoparticles synthesized by the subsequent hydrothermal method.

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

[0016] Compared with rutile-type titanium dioxide with a more stable thermodynamic crystal structure, the solubility of anatase-type titanium dioxide in the hydrothermal process is higher, and the formation of mesopores further increases the specific surface area in contact with the hydrothermal medium, facilitating the formation of more barium titanate crystal nuclei to obtain tetragonal barium titanate nanoparticles with fine and uniform particle sizes. Therefore, it is preferable to use anatase-type mesoporous titanium dioxide as the precursor.

[0017] Preferably, the titanium source in the 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 condition in the step (1) is to heat to 160 - 190°C by a method of heating mantle or heat medium oil or molten salt and carry out hydrothermal reaction for 2 - 6 h, the firing temperature in the step (3) is 400 - 700°C, and the firing time is 2 - 4 h.

[0020] Preferably, the barium source in the 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 the step (S.1) is ≧13, Preferably, the hydrothermal temperature in the step (S.2) is 220°C - 260°C, and the hydrothermal time is 12 - 40 h.

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

[0023] According to a third aspect, the present invention further provides the application of the barium titanate nanometer powder of the tetragonal system in the dielectric ceramic industry.

Advantages of the Invention

[0024] Therefore, the present invention has the following beneficial effects. The hydrothermal method used in the present invention has simple manufacturing conditions, is easy to operate, has low costs, and enables mass production. The barium titanate powder synthesized from the anatase-type mesoporous titanium dioxide precursor produced by this method has a c / a value reaching as high as 1.0095, a narrow particle size distribution, and an average particle size of about 95 nm. The reason is that the anatase structure has greater solubility in the hydrothermal process and further increases the specific surface area of the mesopores, making the reaction in the hydrothermal process faster and more sufficient. As a result, the particle size distribution of the obtained tetragonal barium titanate becomes narrow. When ethanol in the hydrothermal medium exhibits an appropriate ratio of 40% - 60%, the hydroxylation process is suppressed, and a high c / a value is obtained.

Brief Description of the Drawings

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Mode for Carrying Out 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 implement the present invention based on these descriptions. In addition, the examples of the present invention related to the following description are usually only a part of the examples of the present invention, not all examples. Therefore, based on the examples of the present invention, those skilled in the art can obtain all other examples without creative effort, and all of them are included in the claims 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 mixed solution of deionized water and ethanol with a ratio of 1:2, and magnetically stirred until all the solids were dissolved. Then, 3.64 g of cetyltrimethylammonium bromide was added, and 4 mL of tetrabutyl titanate was added dropwise at a constant rate using a fixed double dropping funnel device under the condition of vigorously stirring in an ice water bath. At the same time, ammonia water was added dropwise to adjust the pH of the above solution to 10 to obtain anatase structure. After uniformly stirring, it was heated to 190 °C by heating with a mantle or hot medium oil for 3 h of hydrothermal reaction. The reaction product was washed several times with anhydrous ethanol and deionized water, placed in a drying oven at 80 °C for drying for more than 12 h, and the dried product was calcined at 400 °C for 3 h to remove residual organic matter. The calcined and pulverized powder was dispersed in ethanol, and subjected to subdivision and homogenization treatment using an ultrasonic cell crusher to obtain a well-dispersed suspension, which was placed in a vacuum drying oven for drying, and finally pulverized to obtain a mesoporous titanium dioxide precursor with controllable crystal phase. The XRD pattern of the obtained mesoporous titanium dioxide powder is shown in Figure 1, its SEM image is shown in Figure 3, and its TEM image is shown in Figure 4.

[0036] (3) Mixing: A predetermined amount of the 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, and uniformly stirred. Then, ethanol (the ratio of ethanol in the hydrothermal medium was 50%) and 15 mL of ammonia water were added, and the solution pH was controlled to be ≥ 13 to obtain a barium titanate precursor suspension.

[0037] (4) Synthesis: The barium titanate precursor suspension was added to a 50 mL hydrothermal reaction kettle, heated to 260 °C by heating with a mantle or hot medium oil or molten salt for 30 h of hydrothermal reaction, cooled to room temperature together with the furnace, and the kettle 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, the supernatant was discarded, and the white precipitate at the bottom was left.

[0039] (6) Drying: The washed product was placed in a drying oven at 80 °C and dried for 12 h or more. After the obtained product was pulverized, barium titanate powder was obtained. The XRD pattern of the produced tetragonal barium titanate powder is shown in Fig. 2, and the split peaks showing the obvious tetragonal structure shown in the locally enlarged XRD pattern are shown in Fig. 6, and its SEM image is shown in Fig. 5.

[0040] Example 2: Using the method of Example 1, a mesoporous titanium dioxide precursor with controllable crystal phase was produced by hydrothermal method. The difference is that in step (2), 6 mL of the initial titanium source was dropped at a constant speed and heated to 160 °C by heating with a mantle or heat transfer oil or molten salt for a hydrothermal reaction for 6 h. The XRD pattern of the produced mesoporous titanium dioxide powder is shown in Fig. 1, and the XRD pattern of the finally produced tetragonal barium titanate powder is shown in Fig. 2.

[0041] Example 3: Using the method of Example 1, a mesoporous titanium dioxide precursor with controllable crystal phase was produced by hydrothermal method. The difference is that in step (2), concentrated hydrochloric acid was dropped and the pH of the above solution was adjusted to 4 to obtain a mixed phase structure of anatase and rutile. The XRD pattern of the obtained mesoporous titanium dioxide powder is shown in Fig. 1, and the XRD pattern of the finally produced tetragonal barium titanate powder is shown in Fig. 2.

[0042] Example 4: Using the method of Example 1, a mesoporous titanium dioxide precursor with controllable crystal phase was produced by hydrothermal method. The difference is that in step (2), concentrated hydrochloric acid was dropped and the pH of the above solution was adjusted to 0.5 to obtain a rutile structure, and the dried product was calcined at 700 °C for 3 h to remove residual organic matter. The XRD pattern of the obtained mesoporous titanium dioxide powder is shown in Fig. 1, and the XRD pattern of the finally produced tetragonal barium titanate powder is shown in Fig. 2.

[0043] Example 5: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference is that in steps (1), (2), and (3), the barium source was barium chloride and the titanium source was titanium tetrachloride, and the Ba / Ti ratio value was used as 3. The SEM image of the finally obtained barium titanate powder is shown in Figure 7.

[0044] Example 6: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference is that in steps (1), (2), and (3), the barium source was barium acetate and the titanium source was titanium isopropoxide, and the Ba / Ti ratio value was used as 2. The SEM image of the finally obtained barium titanate powder is shown in Figure 8.

[0045] Example 7: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference is that in step (3), the ratio of ethanol in the hydrothermal medium was 40%.

[0046] Example 8: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference is that in step (3), the ratio of ethanol in the hydrothermal medium was 60%.

[0047] Example 9: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference is that in step (4), it was heated to 220 °C by a method of heating a mantle or heat transfer medium oil or molten salt and subjected to a hydrothermal reaction for 40 h.

[0048] Example 10: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference is that in step (4), it was heated to 250 °C by a method of heating a mantle or heat transfer medium oil or molten salt and subjected to a hydrothermal reaction for 12 h.

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

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

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

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

[0053] Comparative Example 5: Orthorhombic barium titanate nanopowder was prepared by a hydrothermal method using the method of Example 1. The difference is that in steps (1), (2), and (3), the barium source was barium chloride and the titanium source was titanium tetrachloride, and the Ba / Ti ratio value was used as 1.

[0054] Comparative Example 6: Orthorhombic barium titanate nanopowder was prepared by a hydrothermal method using the method of Example 1. The difference is that in steps (1), (2), and (3), the barium source was barium chloride and the titanium source was titanium tetrachloride, and the Ba / Ti ratio value was used as 5.

[0055] Comparative Example 7: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference was that in step (3), the ratio of ethanol in the hydrothermal medium was 20%.

[0056] Comparative Example 8: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference was that in step (3), the ratio of ethanol in the hydrothermal medium was 80%.

[0057] Comparative Example 9: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference was that in step (4), it was heated to 200 °C by a method of heating a mantle or heat transfer oil or molten salt and subjected to a hydrothermal reaction for 60 h.

[0058] Comparative Example 10: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference was that in step (4), it was heated to 270 °C by a method of heating a mantle or heat transfer oil or molten salt and subjected to a hydrothermal reaction for 10 h.

[0059] Comparative Example 11: Using the method of Example 1, tetragonal barium titanate nanometer powder was prepared by a hydrothermal method. The difference was that in step (2), the titanium dioxide precursor used was a non-mesoporous commercial anatase-type titanium dioxide precursor.

[0060] <Performance Test and Result Analysis> (1) Refer to Table 1 for the influence of the pH value on the mesoporous titanium dioxide precursor with controllable crystal phase prepared by the hydrothermal method.

[0061] Table 1 Influence of the pH value on the mesoporous titanium dioxide precursor with controllable crystal phase prepared by the hydrothermal method. JPEG2025522242000002.jpg37164

[0062] As can be seen from Table 1, different pH values are the key to obtaining mesoporous titanium dioxide with different crystal forms. The higher the pH value, the easier it is to synthesize anatase-type mesoporous titanium dioxide. Compared with rutile-type titanium dioxide with a more stable thermodynamic crystal structure, the solubility of anatase-type titanium dioxide in the hydrothermal process is higher, and the formation of mesopores further increases the specific surface area in contact with the hydrothermal medium, thus easily forming more barium titanate crystal nuclei and obtaining cubic barium titanate nanoparticles with fine and uniform particle sizes. Therefore, it is preferable to use anatase-type mesoporous titanium dioxide as the precursor.

[0063] (2) Refer to Table 2 for the influence of the initial usage amount of the titanium source on the mesoporous titanium dioxide precursor with controllable crystal phase prepared by the hydrothermal method.

[0064] Table 2 Influence of the initial usage amount of the titanium source on the mesoporous titanium dioxide precursor with controllable crystal phase prepared by the hydrothermal method JPEG2025522242000003.jpg44164

[0065] As can be seen from Table 2, the crystal phases of the mesoporous titanium dioxide obtained with different initial usage amounts of the titanium source are all anatase. However, the mesoporous titanium dioxide synthesized within the range of 4 - 6 mL of the initial usage amount of the titanium source has fine and uniform particle sizes. The reason is that as the concentration of the reactants increases, the nucleation sites of titanium dioxide nanoparticles increase, resulting in finer mesoporous titanium dioxide. When the initial usage amount of the titanium source is 2 mL, the initial nucleation sites are few, and titanium dioxide is likely to grow at the already formed nucleation sites, so the particle size of the obtained anatase-type titanium dioxide is relatively large. On the other hand, when the initial usage amount of the titanium source increases to 8 mL, there is no obvious difference in the particle size of the obtained titanium dioxide compared with that of 6 mL. Therefore, it is preferable to set 4 - 6 mL as the optimal usage amount of the initial titanium source.

[0066] (3) Refer to Table 3 for the influence on the mesoporous titanium dioxide precursor with controllable crystal phase prepared by the hydrothermal method according to the ratio of deionized water to ethanol.

[0067] Table 3 Influence on the mesoporous titanium dioxide precursor with controllable crystal phase prepared by the hydrothermal method according to the ratio of deionized water to ethanol JPEG2025522242000004.jpg36164

[0068] As can be seen from Table 3, when the ratio of deionized water to ethanol is 1:2, compared with other cases of the comparative examples, the initial particle size of the titanium dioxide precursor obtained under this condition is fine, which further increases the solubility of the titanium dioxide precursor in the hydrothermal process. This is helpful for obtaining cubic barium titanate nanoparticles with fine and uniform particle sizes. Also, since glucose is slightly soluble in ethanol, the ethanol content should not be too high. When the ratio of deionized water to ethanol is larger, it becomes difficult to dissolve glucose and a longer stirring time is required. Therefore, it is preferable to set the ratio of deionized water to ethanol to 1:2.

[0069] (4) Refer to Table 4 for the influence on the cubic barium titanate powder prepared by the hydrothermal method according to the Ba / Ti ratio value.

[0070] Table 4 Influence on the cubic barium titanate powder prepared by the hydrothermal method according to the Ba / Ti ratio value JPEG2025522242000005.jpg46163

[0071] As can be seen from Table 4, when the Ba / Ti ratio value is between 2 and 4, the c / a values of the barium titanate nano-powders produced by the hydrothermal method are all higher than 1.008, which are sufficient to meet the needs of practical applications. A relatively high Ba / Ti ratio value increases the probability of forming barium titanate crystal nuclei. This helps to obtain cubic barium titanate nano-particles with fine and uniform particle sizes. When the Ba / Ti ratio value further increases to 5, the concentration of barium ions is too high, and the synthesized barium titanate contains barium carbonate impurities. Therefore, it is preferable to set the Ba / Ti ratio value between 2 and 4.

[0072] (V) For the cubic nano-barium titanate powder produced by the hydrothermal method according to the ratio of ethanol in step (3), refer to Table 5.

[0073] Table 5 Influence on the cubic nano-barium titanate powder produced by the hydrothermal method according to the ratio of ethanol. JPEG2025522242000006.jpg45163

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

[0075] (VI) For the influence on the cubic nano-barium titanate powder produced by the hydrothermal method by the hydrothermal temperature and time, refer to Table 6.

[0076] Table 6 Influence on the cubic nano-barium titanate powder produced by the hydrothermal method by the hydrothermal temperature and time JPEG2025522242000007.jpg46163

[0077] As can be seen from Table 6, when the hydrothermal temperature was low (200 °C), even if the hydrothermal time was extended, an ideal c / a value could not be obtained. Instead, the influence caused by the difference in dissolution was amplified, resulting in poor uniformity of the particle size of the obtained barium titanate, and long-term hydrothermal reaction consumed both time and energy. Also, considering the requirements for the operating temperature of the hydrothermal reaction kettle, too high a temperature would increase the wear of the reaction kettle. To provide sufficient driving force for generating the tetragonal phase within a short time, more appropriate temperatures and times were investigated and selected according to the experiments of the present invention. Therefore, it is preferable to react with the hydrothermal temperature set at 220 °C to 260 °C and the time set at 12 h to 40 h.

[0078] (VII) Refer to Table 7 for the influence on the tetragonal barium titanate powder produced by the hydrothermal method using mesoporous and non-mesoporous titanium dioxide precursors.

[0079] Table 7 Influence on the tetragonal barium titanate powder produced by the hydrothermal method using mesoporous and non-mesoporous titanium dioxide precursors JPEG2025522242000008.jpg25164

[0080] As can be seen from Table 7, under the same experimental conditions as in Example 1, the barium titanate powder obtained from a non-mesoporous commercial anatase-type titanium dioxide precursor has a low c / a value and a large particle size. The reason is that the specific surface area of the non-mesoporous titanium dioxide in contact with the hydrothermal medium is not as large as that of the mesoporous titanium dioxide. Therefore, the dissolution rate and reaction activity of titanium dioxide decrease, and the driving force for changing the crystal structure is insufficient, so an ideal c / a value cannot be obtained. And since the formation rate of barium titanate crystal nuclei becomes slow, the particle size becomes large. Also, in the experiment of synthesizing barium titanate by hydrothermal method using a titanium dioxide precursor disclosed in the invention patent with the publication number CN111762810A and the name "Method for producing tetragonal nanobarium titanate", the particle size of the provided tetragonal nanobarium titanate particles is in the range of 60 to 200 nm, and the c / a value is 1.0082, which is also lower than the effect of the mesoporous titanium dioxide precursor of the present invention.

[0081] Summarizing the above, there is a synergistic effect among the adjustments of multiple parameters in the present invention. For example, the mesoporous structure of anatase-type mesoporous titanium dioxide composed of particles with fine and uniform particle size increases the specific surface area and reaction activity, and further improves the solubility of the titanium dioxide precursor in the hydrothermal reaction. On the other hand, by using a relatively large Ba / Ti ratio value in the subsequent reaction, sufficient barium ions are further provided to react with the titanium species after dissolution in a timely manner, increasing the nucleation probability of barium titanate and obtaining a high c / a value, while at the same time helping to obtain barium titanate powder with fine and uniform particle size. Also, the synergistic effect between the relatively high reaction temperature range (220 - 260 °C) and the ratio of ethanol in the hydrothermal medium (40% - 60%) helps to control the defect of the formation of hydroxy groups in the hydrothermal reaction and ensure that the barium titanate powder obtains a high c / a value.

[0082] The above content (in combination with the drawings) has described the preferred embodiments of the present invention. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Those skilled in the art can, under the inspiration of the present invention, make various specific transformations without departing from the spirit of the present invention and the scope claimed by the claims, and all of these are included within the scope of the claims of the present invention.

Claims

1. (S.1) Adding a mesoporous titanium dioxide precursor with controllable crystal phase, where the molar ratio of barium to titanium is 2 - 4, to a barium salt solution, then adding ethanol and aqueous ammonia to obtain a barium titanate precursor suspension with an ethanol volume ratio of 40% - 60%; (S.2) Hydrothermally reacting the barium titanate precursor suspension to obtain a barium titanate suspension; (S.3) Centrifugally washing, drying, and pulverizing the barium titanate suspension to obtain orthorhombic barium titanate nano - powder. A method for manufacturing orthorhombic barium titanate nano - powder, characterized by comprising the above steps.

2. The method for manufacturing the mesoporous titanium dioxide precursor in step (S.1) is as follows: (1) Simultaneously dropping a titanium source and a pH regulator into an ethanol aqueous solution containing a template agent, a pH stabilizer, and a dispersant, uniformly dispersing them, and then subjecting them to a hydrothermal reaction to obtain a reaction product; (2) Washing and drying the obtained reaction product, and then calcining it to remove residual organic substances; (3) Pulverizing and homogenizing the product after calcination to obtain anatase - type or rutile - type mesoporous titanium dioxide precursor with controllable powder crystal phase. The pH regulator in step (1) is concentrated hydrochloric acid or aqueous ammonia, and after adding the pH regulator, the pH value of the system is controlled to be 0.5 - 10. The method for manufacturing orthorhombic barium titanate nano - powder according to Claim 1.

3. The mesoporous titanium dioxide precursor described in step (S.1) is anatase - type mesoporous titanium dioxide precursor. The method for manufacturing orthorhombic barium titanate nano - powder according to Claim 1 or 2.

4. The titanium source in step (1) is any one of tetrabutyl titanate, titanium tetrachloride, and titanium isopropoxide. The method for manufacturing orthorhombic barium titanate nano - powder according to Claim 2.

5. The template agent is any one of glucose, carbonaceous polysaccharide microspheres, polyethylene glycol, organic amines, and soluble starch; The pH stabilizer is any one of urea, acetylacetone, acetic acid, and thioglycolic acid; The dispersant is any one of cetyltrimethylammonium bromide, polyvinylpyrrolidone, and o-xylene, and the method for producing orthorhombic barium titanate powder according to claim 2 is characterized in this.

6. The hydrothermal conditions in step (1) are to heat to 160 - 190 °C by a method of heating a mantle or heat transfer oil or molten salt and perform a hydrothermal reaction for 2 - 6 h. The firing temperature in step (3) is 400 - 700 °C, and the firing time is 2 - 4 h. The method for producing orthorhombic barium titanate powder according to claim 2 or 4 or 5 is characterized in this.

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

8. The pH of the barium titanate precursor suspension in step (S.1) is ≧ 13. The hydrothermal temperature in step (S.2) is 220 °C - 260 °C, and the hydrothermal time is 12 - 40 h. The method for producing orthorhombic barium titanate powder according to claim 1 or 7 is characterized in this.

9. Produced by the method according to any one of claims 1 - 8. The c / a value of the orthorhombic barium titanate powder is greater than 1.

008. The average particle size of the orthorhombic barium titanate powder is less than 200 nm. The orthorhombic barium titanate powder is characterized in this.

10. Application of the orthorhombic barium titanate powder according to claim 9 in the dielectric ceramic industry.

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