Preparation method of monodisperse, crystal phase controllable nanoscale barium titanate powder

Abstract

The application discloses a preparation method of monodisperse, crystal phase controllable nanoscale barium titanate powder, and the nanoscale barium titanate powder is prepared by a microwave-assisted hydrothermal method, and different crystal phase nanoscale barium titanate powders can be controllably synthesized. The preparation method of the monodisperse, crystal phase controllable nanoscale barium titanate powder utilizes the synergistic effect of citric acid and oleic acid, can realize controllable synthesis of monodisperse, different crystal phase and nanoscale (below 200 nm) barium titanate powder, and has the advantages of simple overall preparation process, easily obtained raw materials, low equipment requirement and low cost, and can meet the industrial production requirement.

Description

Technical Field

[0001] This invention belongs to the field of nanoscale barium titanate powder preparation technology, specifically, it relates to a method for preparing monodisperse, controllable crystal phase nanoscale barium titanate powder. Background Technology

[0002] With increasing demands for capacity in communication equipment, there is an urgent need for the mass production of high-capacity energy storage capacitors. Barium titanate (BaTiO3), a perovskite-structured metal oxide, possesses excellent dielectric and ferroelectric properties, making it a primary raw material for the fabrication of multilayer ceramic chip capacitors (MLCCs). However, high-dielectric-performance ceramics require barium titanate powder particles with a size below 100 nm. Therefore, the controllable fabrication of nanoscale barium titanate (BT) powder that meets international high standards for MLCCs is one of the key technologies for applications in functional ceramics.

[0003] Currently, the main methods for preparing barium titanate powder are divided into solid-phase methods and liquid-phase methods. Traditional solid-phase methods mostly use barium carbonate and titanium dioxide as raw materials, synthesized at high temperatures. Although this technology is relatively mature, the synthesized samples exhibit severe agglomeration, large size, and difficult morphology control. Furthermore, the high temperatures result in high energy consumption and high costs. Liquid-phase methods include sol-gel methods, co-precipitation methods, and hydrothermal methods. Sol-gel methods have stringent experimental conditions, requiring high purity of raw materials and high reaction temperatures, making them unsuitable for industrial production. Co-precipitation methods result in low purity and large particle radii, failing to meet the requirements of MLCCs. Hydrothermal methods, on the other hand, are widely favored due to their small particle size, high purity, and good uniformity.

[0004] Additives play a crucial role in the hydrothermal synthesis of barium titanate. Studies have shown that the addition of surfactants can effectively regulate the morphology and crystal structure of barium titanate. During hydrothermal synthesis, the addition of surfactants can alter the growth active sites of barium titanate in solution, thereby affecting the particle morphology and size distribution. By selecting and controlling appropriate surfactants, the crystal morphology of barium titanate can be regulated, enabling the synthesis of nanomaterials and the control of particle size. Secondly, surfactants can also affect the crystal structure and lattice parameters of barium titanate. By adjusting the concentration and type of surfactant, the growth direction and crystal structure of barium titanate crystals can be effectively controlled during hydrothermal synthesis. This regulation can alter the lattice parameters of barium titanate crystals, thus affecting their physicochemical properties. Furthermore, surfactants can also regulate the nucleation and growth rate of barium titanate crystals during hydrothermal synthesis. By changing the method and concentration of surfactant addition, the nucleation density and growth rate of barium titanate crystals can be adjusted, thereby controlling the crystal size. This regulation is of great significance for synthesizing barium titanate materials with specific properties and application requirements.

[0005] Currently, many domestic patents involve the use of additives to regulate the synthesis of barium titanate nanoparticles. For example, CN101891466A discloses a method for preparing plate-shaped barium titanate nanoparticles, which ultimately produces cubic phase barium titanate powder by adding citric acid as a dispersant; CN109399700A discloses a method for preparing monodisperse cubic barium titanate nanoparticles, which can synthesize small-sized monodisperse cubic phase BT powder by adding an appropriate amount of oleic acid; CN103449512A discloses a method for preparing monodisperse, cuboid barium titanate nanoparticles by microwave hydrothermal method, which produces barium titanate powder with a cubic structure, a particle size of about 10 nm, and good dispersibility.

[0006] In summary, barium titanate powder synthesized by using citric acid and oleic acid alone as additives often has a cubic phase structure. However, this patent successfully synthesizes small-sized tetragonal barium titanate by simultaneously adding citric acid and oleic acid and adjusting the appropriate ratio using a microwave hydrothermal method. Conventional small-sized tetragonal barium titanate powder often requires doping to achieve this. Therefore, this method provides a new reference for the development of MLCCs. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to synthesize barium titanate with different crystal forms by adjusting the special additives, so as to achieve fine control of the properties of barium titanate, thereby providing a method for preparing monodisperse, crystal phase-controllable nanoscale barium titanate powder.

[0008] The technical solution of this invention to solve the above-mentioned technical problems is as follows: a method for preparing monodisperse, controllable crystal phase nanoscale barium titanate powder, which is prepared by microwave-assisted hydrothermal method, including the following steps: For precursor preparation, barium source and titanium source are dissolved in deionized water under magnetic stirring and mixed thoroughly until a milky white sol is formed to obtain the precursor solution. Adjust the pH value, keep the magnetic stirring, and add the mineralizer dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution until the solution is homogeneous. The pH-adjusted precursor solution was transferred to the liner of the autoclave, and oleic acid and citric acid were added at the same time. The autoclave was then sealed. Hydrothermal reaction: The sealed autoclave is placed in a high-temperature microwave hydrothermal oven to carry out the reaction at the reaction temperature. After the reaction is completed, it is naturally cooled to room temperature. In the post-processing stage, the autoclave cooled to room temperature was opened, the reactants were removed, the supernatant was removed to obtain the crude product, the crude product was centrifuged to obtain the precipitate, the precipitate was washed, then filtered and centrifuged, and then dried to obtain nano-sized barium titanate powder. The magnetic stirring speed is 700 rpm, the reaction temperature is 160~200℃, the barium-to-titanium ratio in the precursor solution is 1.5~2.5, the barium source is barium hydroxide octahydrate, the titanium source is titanium dioxide, the amount of oleic acid is 5~20 mL, and the amount of citric acid is 0.1~0.4 g.

[0009] The present invention has the following beneficial effects: (1) By adding oleic acid and citric acid, the surface energy of barium titanate powder particles is increased by oleic acid, thereby reducing the attraction between particles and preventing particle aggregation. Then, citric acid promotes the formation of complexes between barium and titanium ions. The adsorption selectivity of oleic acid and citric acid affects the anisotropic growth of crystals. Finally, by adjusting the amount of oleic acid and citric acid added, the crystal phase of barium titanate powder is controlled, thereby obtaining small-sized tetragonal barium titanate powder. (2) Microwave-assisted hydrothermal method is used to achieve rapid and uniform heating of the solution, avoiding the thermal gradient problem in traditional heating; (3) The overall preparation process is simple, the raw materials are easy to obtain, the equipment requirements are not high and the cost is low. The prepared barium titanate powder has high purity and controllable crystal phase, and the particle size is uniformly dispersed, which is conducive to industrial production and application. Attached Figure Description

[0010] Figure 1 In the middle (1)~(4), the SEM images of the nano-sized barium titanate powder prepared in Examples 1-4 of the present invention are shown, and (5)~(8) are the SEM images of the nano-sized barium titanate powder prepared in Comparative Examples 1-4 are shown.

[0011] Figure 2 The image shows the XRD pattern of the nano-sized barium titanate powder prepared in Example 1 of this invention.

[0012] Figure 3 The image shows the XRD pattern of the nano-sized barium titanate powder prepared in Example 2 of this invention.

[0013] Figure 4 The image shows the XRD pattern of the nano-sized barium titanate powder prepared in Example 3 of this invention.

[0014] Figure 5 The image shows the XRD pattern of the nano-sized barium titanate powder prepared in Example 4 of this invention.

[0015] Figure 6 The image shows the XRD pattern of the nano-sized barium titanate powder prepared in Comparative Example 1 of this invention.

[0016] Figure 7 The image shows the XRD pattern of the nano-sized barium titanate powder prepared in Comparative Example 2 of this invention.

[0017] Figure 8The image shows the XRD pattern of the nano-sized barium titanate powder prepared in Comparative Example 3 of this invention.

[0018] Figure 9 The image shows the XRD pattern of the nano-sized barium titanate powder prepared in Comparative Example 4 of this invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the embodiments. Example

[0020] The present invention provides a method for preparing monodisperse, crystal-phase-controllable nanoscale barium titanate powder using a microwave-assisted hydrothermal method, comprising the following steps: For precursor preparation, barium and titanium sources were dissolved in deionized water under magnetic stirring and thoroughly mixed. Specifically, 8.5174 g of barium hydroxide octahydrate (Ba(OH)2·8H2O) with a purity of 99.9% and a molecular weight of 315.46 was poured into a beaker, and 30 mL of deionized water was added. The beaker was then placed on a magnetic stirrer and stirred at a speed of 700 rpm for 1 h. Subsequently, 1.4378 g of titanium dioxide with a purity of 99.9% and a molecular weight of 79.88 (rutile powder was used in this embodiment) was taken and stirred for another 1 h until a milky white sol was formed, thus obtaining the precursor solution. At this time, the barium-to-titanium ratio in the precursor solution was 1.5.

[0021] Adjust the pH value, maintain magnetic stirring at a speed of 700 rpm, and add 10 mL of (5M) sodium hydroxide aqueous solution dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution for 30 min until the solution is homogeneous. In this embodiment, the (5M) sodium hydroxide aqueous solution is prepared by dissolving 2.0 g of solid flake sodium hydroxide (NaOH) with a purity of 99.5% and a molecular weight of 40.0 into deionized water.

[0022] The pH-adjusted precursor solution was transferred to the liner of an autoclave. In this embodiment, a polytetrafluoroethylene (PTFE) autoclave was used. During the transfer, the magnetic stir bar was removed, and 5 mL of oleic acid and 0.1 g of citric acid were added. The autoclave was then sealed. Oleic acid is a long-chain polymer, and its molecules consist of long carbon chains and terminal carboxylic acid groups. The carboxyl groups react with metal ions (such as Ba) on the particle surface. 2+The formation of coordination bonds through chemical adsorption, with the hydrophobic long carbon chains extending into the solution, increases the surface energy of the barium titanate powder particles, thereby reducing the attractive force between particles and preventing particle aggregation. Citric acid, being a short-chain small molecule, has carboxyl groups that can form complexes with barium and titanium ions. The selective adsorption of citric acid and oleic acid can affect the anisotropic growth of crystals; for example, it may cause the growth rate of certain crystal orientations to be greater than that of other orientations, thus leading to different crystal shapes synergistically controlling the growth rate and orientation of the crystal. In this invention, oleic acid and citric acid are adsorbed on the (002) crystal plane of barium titanate particles, enabling controllable adjustment of the barium titanate crystal phase. In this embodiment, rutile is used as the titanium source, which can synthesize cubic barium titanate powder.

[0023] For the hydrothermal reaction, the sealed autoclave was placed in a high-temperature microwave hydrothermal oven and reacted for 6 hours at a microwave frequency of 1 kHz-1 MHz and a reaction temperature of 180°C. After the reaction was completed, it was allowed to cool naturally to room temperature. The microwave frequency was 1 kHz.

[0024] For post-processing, the autoclave cooled to room temperature was opened, the reactants were removed, and the supernatant was removed to obtain the crude product. The crude product was centrifuged to obtain the precipitate, which was then washed 2-3 times sequentially with acetic acid, ultrapure water, and ethanol. After filtration, the filtered product was placed in a centrifuge and centrifuged at a speed of 2000-8000 rpm for at least 3 minutes. Then it was placed in a dryer and dried at a drying temperature of 60°C for 12 hours to obtain nano-sized barium titanate powder.

[0025] The prepared nano-sized barium titanate powder was analyzed, and the XRD pattern was obtained as follows: Figure 2 As shown, all the diffraction peaks of the BaTiO3 powder correspond precisely to the cubic phase standard PDF card (JCPDS number 89-2475), indicating that the cubic phase purity of the sample is high. Figure 1 (1) SEM images show that the BaTiO3 powder has good dispersibility and a relatively uniform particle size distribution. The average particle size of barium titanate is 80-110 nm. Example

[0026] The present invention, in Example 2, discloses a method for preparing monodisperse, crystal-phase-controllable nanoscale barium titanate powder, which employs a microwave-assisted hydrothermal method and includes the following steps: For precursor preparation, barium and titanium sources were dissolved in deionized water under magnetic stirring and thoroughly mixed. Specifically, 11.3566 g of barium hydroxide octahydrate (Ba(OH)2·8H2O) with a purity of 99.9% and a molecular weight of 315.46 was poured into a beaker, and 30 mL of deionized water was added. The beaker was then placed on a magnetic stirrer and stirred at a speed of 700 rpm for 1 h. Subsequently, 1.4378 g of titanium dioxide with a purity of 99.9% and a molecular weight of 79.88 (anatase powder was used in this embodiment) was taken and stirred for another 1 h until a milky white sol was formed, obtaining the precursor solution. At this time, the barium-to-titanium ratio in the precursor solution was 2.0.

[0027] Adjust the pH value, maintain magnetic stirring at a speed of 700 rpm, and add 10 mL of (5M) sodium hydroxide aqueous solution dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution for 30 min until the solution is homogeneous. In this embodiment, the (5M) sodium hydroxide aqueous solution is prepared by dissolving 2.0 g of solid flake sodium hydroxide (NaOH) with a purity of 99.5% and a molecular weight of 40.0 into deionized water.

[0028] The precursor solution with adjusted pH value is transferred to the liner of a high-pressure reactor. In this embodiment, a polytetrafluoroethylene reactor is used. During the transfer process, the magnetic stir bar is removed, and 10 mL of oleic acid and 0.2 g of citric acid are added. Then the high-pressure reactor is sealed. In this embodiment, anatase is used as the titanium source, which can synthesize cubic phase barium titanate powder.

[0029] For the hydrothermal reaction, the sealed autoclave was placed in a high-temperature microwave hydrothermal oven and reacted for 6 hours at a microwave frequency of 1 kHz-1 MHz and a reaction temperature of 200°C. After the reaction was completed, it was naturally cooled to room temperature. The microwave frequency was 1 MHz.

[0030] For post-processing, the autoclave cooled to room temperature was opened, the reactants were removed, and the supernatant was removed to obtain the crude product. The crude product was centrifuged to obtain the precipitate, which was then washed 2-3 times sequentially with acetic acid, ultrapure water, and ethanol. After filtration, the filtered product was placed in a centrifuge and centrifuged at a speed of 2000-8000 rpm for at least 3 minutes. Then it was placed in a dryer and dried at a drying temperature of 60°C for 12 hours to obtain nano-sized barium titanate powder.

[0031] The prepared nano-sized barium titanate powder was analyzed, and the XRD pattern was obtained as follows: Figure 3 As shown, all the diffraction peaks of the BaTiO3 powder correspond precisely to the cubic phase standard PDF card (JCPDS number 89-2475), indicating that the cubic phase purity of the sample is high. Figure 1(2) The SEM image shows that the product BaTiO3 powder has good dispersibility and a relatively uniform particle size distribution. The average particle size of barium titanate is 80-140 nm. Example

[0032] The present invention, in Example 3, discloses a method for preparing monodisperse, crystal-phase-controllable nanoscale barium titanate powder, which employs a microwave-assisted hydrothermal method and includes the following steps: For precursor preparation, barium and titanium sources were dissolved in deionized water under magnetic stirring and thoroughly mixed. Specifically, 14.1957 g of barium hydroxide octahydrate (Ba(OH)2·8H2O) with a purity of 99.9% and a molecular weight of 315.46 was poured into a beaker, and 30 mL of deionized water was added. The beaker was then placed on a magnetic stirrer and stirred at a speed of 700 rpm for 1 h. Subsequently, 1.4378 g of titanium dioxide with a purity of 99.9% and a molecular weight of 79.88 (rutile powder was used in this embodiment) was taken and stirred for another 1 h until a milky white sol was formed, thus obtaining the precursor solution. At this time, the barium-to-titanium ratio in the precursor solution was 2.5.

[0033] Adjust the pH value, maintain magnetic stirring at a speed of 700 rpm, and add 10 mL of (5M) sodium hydroxide aqueous solution dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution for 30 min until the solution is homogeneous. In this embodiment, the (5M) sodium hydroxide aqueous solution is prepared by dissolving 2.0 g of solid flake sodium hydroxide (NaOH) with a purity of 99.5% and a molecular weight of 40.0 into deionized water.

[0034] The precursor solution with adjusted pH value is transferred to the liner of an autoclave. In this embodiment, a polytetrafluoroethylene reactor is used. During the transfer process, the magnetic stir bar is removed, and 15 mL of oleic acid and 0.3 g of citric acid are added. The autoclave is then sealed. In this embodiment, rutile is used as the titanium source, which can synthesize tetragonal barium titanate powder.

[0035] For the hydrothermal reaction, the sealed autoclave is placed in a high-temperature microwave hydrothermal oven and reacted for 2 hours at a microwave frequency of 1 kHz-1 MHz and a reaction temperature of 160°C. After the reaction is completed, it is naturally cooled to room temperature. The preferred microwave frequency is 0.1 MHz.

[0036] For post-processing, the autoclave cooled to room temperature was opened, the reactants were removed, and the supernatant was removed to obtain the crude product. The crude product was centrifuged to obtain the precipitate, which was then washed 2-3 times sequentially with acetic acid, ultrapure water, and ethanol. After filtration, the filtered product was placed in a centrifuge and centrifuged at a speed of 2000-8000 rpm for at least 3 minutes. Then it was placed in a dryer and dried at a drying temperature of 60°C for 12 hours to obtain nano-sized barium titanate powder.

[0037] The prepared nano-sized barium titanate powder was analyzed, and the XRD pattern was obtained as follows: Figure 4 As shown, all the diffraction peaks of the BaTiO3 powder correspond precisely to the tetragonal phase standard PDF card (JCPDS number 79-2264), indicating that the sample has high cubic phase purity. Figure 1 (3) The SEM image shows that the BaTiO3 powder has good dispersibility and a relatively uniform particle size distribution. The average particle size of barium titanate is 90-120 nm. Example

[0038] The present invention, in Example 4, discloses a method for preparing monodisperse, crystal-phase-controllable nanoscale barium titanate powder, which employs a microwave-assisted hydrothermal method and includes the following steps: For precursor preparation, barium and titanium sources were dissolved in deionized water under magnetic stirring and thoroughly mixed. Specifically, 11.3566 g of barium hydroxide octahydrate (Ba(OH)2·8H2O) with a purity of 99.9% and a molecular weight of 315.46 was poured into a beaker, and 30 mL of deionized water was added. The beaker was then placed on a magnetic stirrer and stirred at a speed of 700 rpm for 1 h. Subsequently, 1.4378 g of titanium dioxide with a purity of 99.9% and a molecular weight of 79.88 (anatase powder was used in this embodiment) was taken and stirred for another 1 h until a milky white sol was formed, obtaining the precursor solution. At this time, the barium-to-titanium ratio in the precursor solution was 2.0.

[0039] Adjust the pH value, maintain magnetic stirring at a speed of 700 rpm, and add 10 mL of (5M) sodium hydroxide aqueous solution dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution for 30 min until the solution is homogeneous. In this embodiment, the (5M) sodium hydroxide aqueous solution is prepared by dissolving 2.0 g of solid flake sodium hydroxide (NaOH) with a purity of 99.5% and a molecular weight of 40.0 into deionized water.

[0040] The precursor solution with adjusted pH value is transferred to the liner of an autoclave. In this embodiment, a polytetrafluoroethylene reactor is used. During the transfer process, the magnetic stir bar is removed, and 20 mL of oleic acid and 0.4 g of citric acid are added. The autoclave is then sealed. In this embodiment, anatase is used as the titanium source, which can synthesize tetragonal barium titanate powder.

[0041] For the hydrothermal reaction, the sealed autoclave was placed in a high-temperature microwave hydrothermal oven and reacted for 4 hours at a microwave frequency of 1 kHz-1 MHz and a reaction temperature of 200°C. After the reaction was completed, it was allowed to cool naturally to room temperature. The microwave frequency was 0.1 MHz.

[0042] For post-processing, the autoclave cooled to room temperature was opened, the reactants were removed, and the supernatant was removed to obtain the crude product. The crude product was centrifuged to obtain the precipitate, which was then washed 2-3 times sequentially with acetic acid, ultrapure water, and ethanol. After filtration, the filtered product was placed in a centrifuge and centrifuged at a speed of 2000-8000 rpm for at least 3 minutes. Then it was placed in a dryer and dried at a drying temperature of 60°C for 12 hours to obtain nano-sized barium titanate powder.

[0043] The prepared nano-sized barium titanate powder was analyzed, and the XRD pattern was obtained as follows: Figure 5 As shown, all the diffraction peaks of the BaTiO3 powder correspond precisely to the tetragonal phase standard PDF card (JCPDS number 79-2264), indicating that the sample has high tetragonal phase purity. Figure 1 (4) The SEM image shows that the product BaTiO3 powder has good dispersibility and a relatively uniform particle size distribution. The average particle size of barium titanate is 80-130 nm.

[0044] Comparative Example 1: The preparation method of nano-sized barium titanate powder in Comparative Example 1, using a microwave-assisted hydrothermal method, includes the following steps: For precursor preparation, barium and titanium sources were dissolved in deionized water under magnetic stirring and thoroughly mixed. Specifically, 8.5174 g of barium hydroxide octahydrate (Ba(OH)2·8H2O) with a purity of 99.9% and a molecular weight of 315.46 was poured into a beaker, and 30 mL of deionized water was added. The beaker was then placed on a magnetic stirrer and stirred at a speed of 700 rpm for 1 h. Subsequently, 1.4378 g of titanium dioxide with a purity of 99.9% and a molecular weight of 79.88 (rutile powder was used in this embodiment) was taken and stirred for another 1 h until a milky white sol was formed, thus obtaining the precursor solution. At this time, the barium-to-titanium ratio in the precursor solution was 1.5.

[0045] Adjust the pH value, maintain magnetic stirring at a speed of 700 rpm, and add 10 mL of (5M) sodium hydroxide aqueous solution dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution for 30 min until the solution is homogeneous. In this embodiment, the (5M) sodium hydroxide aqueous solution is prepared by dissolving 2.0 g of solid flake sodium hydroxide (NaOH) with a purity of 99.5% and a molecular weight of 40.0 into deionized water.

[0046] The precursor solution with adjusted pH value is transferred to the liner of a high-pressure reactor. In this embodiment, a polytetrafluoroethylene reactor is used. During the transfer process, the magnetic stir bar is removed, and then the high-pressure reactor is sealed. In this embodiment, rutile is used as the titanium source, which can synthesize cubic barium titanate powder.

[0047] For the hydrothermal reaction, the sealed autoclave is placed in a high-temperature microwave hydrothermal oven and reacted for 6 hours at a microwave frequency of 1 kHz-1 MHz and a reaction temperature of 200°C. After the reaction is completed, it is naturally cooled to room temperature. The preferred microwave frequency is 1 kHz.

[0048] For post-processing, the autoclave cooled to room temperature was opened, the reactants were removed, and the supernatant was removed to obtain the crude product. The crude product was centrifuged to obtain the precipitate, which was then washed 2-3 times sequentially with acetic acid, ultrapure water, and ethanol. After filtration, the filtered product was placed in a centrifuge and centrifuged at a speed of 2000-8000 rpm for at least 3 minutes. Then it was placed in a dryer and dried at a drying temperature of 60°C for 12 hours to obtain nano-sized barium titanate powder.

[0049] The prepared nano-sized barium titanate powder was analyzed, and the XRD pattern was obtained as follows: Figure 6 As shown, all the diffraction peaks of the BaTiO3 powder correspond precisely to the cubic phase standard PDF card (JCPDS number 89-2475), indicating that the cubic phase purity of the sample is high. Figure 1 (5) The SEM image shows that the BaTiO3 powder product is severely agglomerated, with uneven particle size distribution, and large solid particles are also present. The average particle size of barium titanate is 200-300 nm.

[0050] Comparative Example 2: The preparation method of nano-sized barium titanate powder in Comparative Example 2, using a microwave-assisted hydrothermal method, includes the following steps: For precursor preparation, barium and titanium sources were dissolved in deionized water under magnetic stirring and thoroughly mixed. Specifically, 11.3566 g of barium hydroxide octahydrate (Ba(OH)2·8H2O) with a purity of 99.9% and a molecular weight of 315.46 was poured into a beaker, and 30 mL of deionized water was added. The beaker was then placed on a magnetic stirrer and stirred at a speed of 700 rpm for 1 h. Subsequently, 1.4378 g of titanium dioxide with a purity of 99.9% and a molecular weight of 79.88 (anatase powder was used in this embodiment) was taken and stirred for another 1 h until a milky white sol was formed, obtaining the precursor solution. At this time, the barium-to-titanium ratio in the precursor solution was 2.0.

[0051] Adjust the pH value, maintain magnetic stirring at a speed of 700 rpm, and add 10 mL of (5M) sodium hydroxide aqueous solution dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution for 30 min until the solution is homogeneous. In this embodiment, the (5M) sodium hydroxide aqueous solution is prepared by dissolving 2.0 g of solid flake sodium hydroxide (NaOH) with a purity of 99.5% and a molecular weight of 40.0 into deionized water.

[0052] The precursor solution with adjusted pH value is transferred to the liner of a high-pressure reactor. In this embodiment, a polytetrafluoroethylene reactor is used. During the transfer process, the magnetic stir bar is removed, and then the high-pressure reactor is sealed. In this embodiment, anatase is used as the titanium source, which can synthesize cubic barium titanate powder.

[0053] For the hydrothermal reaction, the sealed autoclave is placed in a high-temperature microwave hydrothermal oven and reacted for 6 hours at a microwave frequency of 1 kHz-1 MHz and a reaction temperature of 200°C. After the reaction is completed, it is naturally cooled to room temperature. The preferred microwave frequency is 1 kHz.

[0054] For post-processing, the autoclave cooled to room temperature was opened, the reactants were removed, and the supernatant was removed to obtain the crude product. The crude product was centrifuged to obtain the precipitate, which was then washed 2-3 times sequentially with acetic acid, ultrapure water, and ethanol. After filtration, the filtered product was placed in a centrifuge and centrifuged at a speed of 2000-8000 rpm for at least 3 minutes. Then it was placed in a dryer and dried at a drying temperature of 60°C for 12 hours to obtain nano-sized barium titanate powder.

[0055] The prepared nano-sized barium titanate powder was analyzed, and the XRD pattern was obtained as follows: Figure 7 As shown, all the diffraction peaks of the BaTiO3 powder correspond precisely to the cubic phase standard PDF card (JCPDS number 89-2475), indicating that the cubic phase purity of the sample is high. Figure 1(6) SEM images show that the BaTiO3 powder exhibits severe agglomeration and poor particle size uniformity. The average particle size of the barium titanate is 250-300 nm.

[0056] Comparative Example 3: The preparation method of nano-sized barium titanate powder in Comparative Example 3, using a microwave-assisted hydrothermal method, includes the following steps: For precursor preparation, barium and titanium sources were dissolved in deionized water under magnetic stirring and thoroughly mixed. Specifically, 14.1957 g of barium hydroxide octahydrate (Ba(OH)2·8H2O) with a purity of 99.9% and a molecular weight of 315.46 was poured into a beaker, and 30 mL of deionized water was added. The beaker was then placed on a magnetic stirrer and stirred at a speed of 700 rpm for 1 h. Subsequently, 1.4378 g of titanium dioxide with a purity of 99.9% and a molecular weight of 79.88 (rutile powder was used in this embodiment) was taken and stirred for another 1 h until a milky white sol was formed, thus obtaining the precursor solution. At this time, the barium-to-titanium ratio in the precursor solution was 2.5.

[0057] Adjust the pH value, maintain magnetic stirring at a speed of 700 rpm, and add 10 mL of (5M) sodium hydroxide aqueous solution dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution for 30 min until the solution is homogeneous. In this embodiment, the (5M) sodium hydroxide aqueous solution is prepared by dissolving 2.0 g of solid flake sodium hydroxide (NaOH) with a purity of 99.5% and a molecular weight of 40.0 into deionized water.

[0058] The precursor solution with adjusted pH value is transferred to the liner of an autoclave. In this embodiment, a polytetrafluoroethylene reactor is used. During the transfer process, the magnetic stir bar is removed, and 20 mL of oleic acid is added. The autoclave is then sealed. In this embodiment, rutile is used as the titanium source, which can synthesize cubic barium titanate powder.

[0059] For the hydrothermal reaction, the sealed autoclave is placed in a high-temperature microwave hydrothermal oven and reacted for 6 hours at a microwave frequency of 1 kHz-1 MHz and a reaction temperature of 200°C. After the reaction is completed, it is naturally cooled to room temperature. The preferred microwave frequency is 1 kHz.

[0060] For post-processing, the autoclave cooled to room temperature was opened, the reactants were removed, and the supernatant was removed to obtain the crude product. The crude product was centrifuged to obtain the precipitate, which was then washed 2-3 times sequentially with acetic acid, ultrapure water, and ethanol. After filtration, the filtered product was placed in a centrifuge and centrifuged at a speed of 2000-8000 rpm for at least 3 minutes. Then it was placed in a dryer and dried at a drying temperature of 60°C for 12 hours to obtain nano-sized barium titanate powder.

[0061] The prepared nano-sized barium titanate powder was analyzed, and the XRD pattern was obtained as follows: Figure 7 As shown, all the diffraction peaks of the BaTiO3 powder correspond precisely to the cubic phase standard PDF card (JCPDS number 89-2475), indicating that the cubic phase purity of the sample is high. Figure 1 (5) SEM images show that the BaTiO3 powder has slight agglomeration. The average particle size of barium titanate is 200-250 nm.

[0062] Comparative Example 4: The preparation method of nano-sized barium titanate powder in Comparative Example 4, which adopts a microwave-assisted hydrothermal method, includes the following steps: For precursor preparation, barium and titanium sources were dissolved in deionized water under magnetic stirring and thoroughly mixed. Specifically, 11.3566 g of barium hydroxide octahydrate (Ba(OH)2·8H2O) with a purity of 99.9% and a molecular weight of 315.46 was poured into a beaker, and 30 mL of deionized water was added. The beaker was then placed on a magnetic stirrer and stirred at a speed of 700 rpm for 1 h. Subsequently, 1.4378 g of titanium dioxide with a purity of 99.9% and a molecular weight of 79.88 (anatase powder was used in this embodiment) was taken and stirred for another 1 h until a milky white sol was formed, obtaining the precursor solution. At this time, the barium-to-titanium ratio in the precursor solution was 2.0.

[0063] Adjust the pH value, maintain magnetic stirring at a speed of 700 rpm, and add 10 mL of (5M) sodium hydroxide aqueous solution dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution for 30 min until the solution is homogeneous. In this embodiment, the (5M) sodium hydroxide aqueous solution is prepared by dissolving 2.0 g of solid flake sodium hydroxide (NaOH) with a purity of 99.5% and a molecular weight of 40.0 into deionized water.

[0064] The precursor solution with adjusted pH value is transferred to the liner of an autoclave. In this embodiment, a polytetrafluoroethylene reactor is used. During the transfer process, the magnetic stir bar is removed, 0.4g of citric acid is added, and then the autoclave is sealed. In this embodiment, anatase is used as the titanium source, which can synthesize cubic barium titanate powder.

[0065] For the hydrothermal reaction, the sealed autoclave is placed in a high-temperature microwave hydrothermal oven and reacted for 6 hours at a microwave frequency of 1 kHz-1 MHz and a reaction temperature of 200°C. After the reaction is completed, it is naturally cooled to room temperature. The preferred microwave frequency is 1 kHz.

[0066] For post-processing, the autoclave cooled to room temperature was opened, the reactants were removed, and the supernatant was removed to obtain the crude product. The crude product was centrifuged to obtain the precipitate, which was then washed 2-3 times sequentially with acetic acid, ultrapure water, and ethanol. After filtration, the filtered product was placed in a centrifuge and centrifuged at a speed of 2000-8000 rpm for at least 3 minutes. Then it was placed in a dryer and dried at a drying temperature of 60°C for 12 hours to obtain nano-sized barium titanate powder.

[0067] The prepared nano-sized barium titanate powder was analyzed, and the XRD pattern was obtained as follows: Figure 9 As shown, all the diffraction peaks of the BaTiO3 powder correspond precisely to the cubic phase standard PDF card (JCPDS number 89-2475), indicating that the cubic phase purity of the sample is high. Figure 1 (8) SEM images show that the product BaTiO3 powder is slightly agglomerated. The average particle size of barium titanate is 250-300 nm.

[0068] As can be seen from the above comparative examples, when oleic acid and citric acid are not added to the reaction simultaneously, the nano-sized barium titanate powder produced, regardless of whether rutile or anatase is used as the titanium dioxide, is cubic in phase and cannot form tetragonal nano-sized barium titanate powder. Furthermore, the particle size of the generated nano-barium titanate is above 200 nm. However, using the preparation method provided by this invention, under the premise of adding oleic acid and citric acid to the reaction simultaneously, and using rutile or anatase as the titanium source, tetragonal nano-sized barium titanate powder can be generated. Regardless of whether cubic or tetragonal nano-sized barium titanate powder is obtained, its particle size is less than 150 nm.

[0069] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the inventive concept, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing monodisperse, controllable-crystal-phase nanoscale barium titanate powder, comprising a microwave-assisted hydrothermal method, characterized in that, Includes the following steps: For precursor preparation, barium source and titanium source were dissolved in 30 mL of deionized water under magnetic stirring and mixed thoroughly until a milky white sol was formed to obtain the precursor solution. Adjust the pH value, keep the magnetic stirring, and add the mineralizer dropwise to the precursor solution until the pH value of the precursor solution reaches above 13. Continue stirring the solution until the solution is homogeneous. The pH-adjusted precursor solution was transferred to the liner of the autoclave, and oleic acid and citric acid were added at the same time. The autoclave was then sealed. Hydrothermal reaction: The sealed autoclave is placed in a high-temperature microwave hydrothermal oven to carry out the reaction at the reaction temperature. After the reaction is completed, it is naturally cooled to room temperature. In the post-processing stage, the autoclave cooled to room temperature was opened, the reactants were removed, the supernatant was removed to obtain the crude product, the crude product was centrifuged to obtain the precipitate, the precipitate was washed, then filtered and centrifuged, and then dried to obtain nano-sized barium titanate powder. The magnetic stirring speed is 700 rpm, the reaction temperature is 160~200℃, the barium-to-titanium ratio in the precursor solution is 1.5~2.5, the barium source is barium hydroxide octahydrate, the titanium source is titanium dioxide, the amount of oleic acid is 15~20 mL, and the amount of citric acid is 0.3~0.4 g.

2. The method for preparing monodisperse, crystal-phase-controllable nanoscale barium titanate powder according to claim 1, characterized in that, The precursor preparation steps include: pouring a barium source into a beaker, adding deionized water, then placing the beaker on a magnetic stirrer for magnetic stirring for 1 hour; then, pouring a titanium source into the beaker and continuing to stir for 1 hour until a milky white sol is formed, thus obtaining a precursor solution.

3. The method for preparing monodisperse, crystal-phase-controllable nanoscale barium titanate powder according to claim 1, characterized in that: In the step of adjusting the pH value, the mineralizing agent is an aqueous solution of sodium hydroxide. After the pH value of the precursor solution reaches above 13, stirring is continued for 30 minutes.

4. The method for preparing monodisperse, crystal phase-controllable nanoscale barium titanate powder according to claim 1, characterized in that: In the hydrothermal reaction step, the hydrothermal reaction time is 2-6 hours, and the microwave frequency is 1kHz-1MHz.

5. The method for preparing monodisperse, crystal phase-controllable nanoscale barium titanate powder according to claim 1, characterized in that: In the post-processing step, the washing process involves centrifugation and washing with acetic acid, ultrapure water, and ethanol 2-3 times in sequence.

6. The method for preparing monodisperse, crystal phase-controllable nanoscale barium titanate powder according to claim 5, characterized in that: The centrifugation speed is 2000~8000 rpm, and the centrifugation time is at least 3 minutes.

7. The method for preparing monodisperse, crystal phase-controllable nanoscale barium titanate powder according to claim 6, characterized in that: The drying temperature is 40~80℃, and the drying time is at least 12 hours.

8. The method for preparing monodisperse, crystal phase-controllable nanoscale barium titanate powder according to any one of claims 1-7, characterized in that: The autoclave is a polytetrafluoroethylene (PTFE) reactor.

9. The method for preparing monodisperse, crystal-phase-controllable nanoscale barium titanate powder according to any one of claims 1-7, characterized in that: The titanium dioxide is made from rutile or anatase powder that has been pulverized.

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