Method for preparing nano barium titanate powder by sol-gel-hydrothermal method

Abstract

The invention discloses a method for preparing nano barium titanate based on sol-gel synergistic hydrothermal reaction, which comprises the following steps: (1) dissolving barium acetate in an acetic acid aqueous solution to obtain a barium source solution; weighing tetrabutyl titanate according to the molar ratio of barium to titanium being greater than 1.25, and dissolving the tetrabutyl titanate in alcohol to obtain a titanium source solution; (2) uniformly mixing the barium source solution and the titanium source solution, preserving heat at 20-80 DEG C to obtain gel, drying and grinding to obtain white powder of the barium titanate precursor: (3) preparing a 2-4mol / L inorganic strong alkali aqueous solution, adding the white powder and a dispersing agent into the inorganic strong alkali aqueous solution, and fully stirring to obtain a barium titanate precursor suspension; and (4) transferring the barium titanate precursor suspension into a reaction kettle for hydrothermal reaction, and after the reaction is completed, washing, drying and grinding to obtain the nano barium titanate powder. The preparation method is low in cost, and the prepared nano barium titanate powder is uniform in distribution, spherical or sphere-like in morphology, small in particle size, 80-150nm in average particle size and good in particle crystallinity.

Description

Technical Field

[0001] The present invention relates to the field of barium titanate powder preparation, and in particular to a new method for preparing nanometer barium titanate powder by sol-gel coordinated hydrothermal method. Background Art

[0002] BaTiO3, a key research target in the field of electronic ceramics, is widely used in multilayer ceramic capacitors (MLCCs), thermistors, ferroelectric and piezoelectric devices due to its excellent dielectric, ferroelectric, piezoelectric, and insulation properties. It is known as the "pillar of the electronic ceramics industry." The rapid development of electronic information technology requires BaTiO3 ceramic materials to perform even better, and their performance is inextricably linked to the quality of the BaTiO3 powder used.

[0003] Barium titanate can be synthesized using a variety of methods, including solid-phase, hydrothermal, and sol-gel methods. The traditional solid-phase method uses titanium dioxide and barium titanate as raw materials, ball-milled, and then synthesized at 800-1200°C. The resulting powders are large and lack uniformity. Wet chemical methods are widely used due to their advantages, such as high purity and small particle size. The hydrothermal and sol-gel methods are the primary wet chemical methods. The sol-gel method uses an organic metal salt solution (such as acetate, citrate, or alkoxide) as raw material. This solution is dissolved in a solvent (water or an organic solvent) and undergoes hydrolysis and condensation to form a sol. The sol is then gelled, dried, and heat-treated to produce a powder. The sol-gel method enables uniform doping of multiple components, has a simple process flow, and produces high-purity powders. However, gels often require high-temperature calcination, which can easily cause particle agglomeration and the introduction of impurities, resulting in large particle size and incomplete grain development. Furthermore, the reaction cycle is long, and later cracking or residual porosity in the product can occur.

[0004] Therefore, BaTiO3 powders prepared by these traditional methods often suffer from defects such as large particle size, particle agglomeration, and hydroxyl groups, making them unable to meet the performance requirements of modern precision devices. Therefore, there is an urgent need to develop innovative methods for preparing BaTiO3 powders with good crystallinity, fine size, and excellent dispersion to promote technological advancements in electronic ceramic materials. Summary of the Invention

[0005] The present invention addresses the shortcomings of the prior art by providing a method for preparing nano-barium titanate powder using a sol-gel-hydrothermal process. This method produces nano-barium titanate powder with a well-developed crystal structure. The barium titanate particles are spherical or nearly spherical, with a small average particle size between 80 and 150 nm and good crystallinity.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is: A method for preparing nano-barium titanate powder by a sol-gel-hydrothermal method comprises the following steps: (1) dissolving barium acetate in an acetic acid aqueous solution to obtain a barium source solution; weighing tetrabutyl titanate so that the molar ratio of barium to titanium is greater than 1.25, and dissolving the mixture in a solvent alcohol to obtain a titanium source solution; (2) mixing the barium source solution and the titanium source solution and stirring them uniformly, and keeping them warm at 20-80° C. to obtain a gel, which is then dried and ground to obtain a white powder of a barium titanate precursor; (3) Preparation of OH - An inorganic strong base aqueous solution with a concentration of 2-4 mol / L, then adding the white powder of the barium titanate precursor and a dispersant to the inorganic strong base aqueous solution and stirring thoroughly to obtain a barium titanate precursor suspension; (4) The barium titanate precursor suspension is transferred to a reactor for hydrothermal reaction. After the reaction is completed, the suspension is washed with water for multiple times, and then dried and ground to obtain nano-barium titanate powder.

[0007] According to the above scheme, in step (1), the acetic acid aqueous solution is prepared by mixing glacial acetic acid and water, and the glacial acetic acid accounts for between 30% and 50% of the total volume.

[0008] According to the above scheme, in step (1), the molar concentration of barium acetate in the acetic acid aqueous solution is between 1-2 mol / L.

[0009] According to the above scheme, in step (1), the alcohol is one or more of ethylene glycol, ethanol and methanol; and the molar concentration of tetrabutyl titanate in the titanium source is about 2 mol / L.

[0010] According to the above scheme, in step (2), when the barium source solution and the titanium source solution are mixed, the ratio of barium acetate to tetrabutyl titanate is between 1.25 and 1.75 in terms of the molar ratio of barium to titanium.

[0011] According to the above scheme, in step (2), the drying temperature of the gel is 100-110°C and the drying time is 12-24h.

[0012] According to the above scheme, in step (3), KOH is used as the inorganic strong base, and water is used as the solvent to prepare the inorganic strong base aqueous solution. The white powder of the barium titanate precursor is added to the inorganic strong base aqueous solution at a mass concentration of 50-150 g / L; the dispersant is polyethylene glycol (PEG) with a molecular weight of 15000-25000, and the mass of the dispersant is 2%-5% of the barium titanate precursor (i.e., the white powder of the barium titanate precursor).

[0013] According to the above scheme, in step (4), the hydrothermal reaction conditions are: hydrothermal reaction at 100-180°C for 8-24h.

[0014] The nano-barium titanate powder prepared by the above method is white powder in macroscopic form and spherical or nearly spherical nanoparticles in microscopic form. The particle size is small, with an average particle size between 80-150nm. At the same time, the crystal form is well developed, the number of hydroxyl defects generated on the surface of the barium titanate powder is small, and the dispersibility is good.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention utilizes a sol-gel-hydrothermal method to prepare nano-barium titanate powder. This hydrothermal method replaces the traditional calcination process of the barium titanate precursor, allowing the reaction to proceed at a lower temperature. This is environmentally friendly and avoids particle agglomeration and impurity introduction caused by high-temperature heat treatment. First, barium acetate is dissolved in an aqueous acetic acid solution, replacing the traditional solvent water. This allows the barium acetate to dissolve in the aqueous acetic acid solution during heating and directly bond with the titanium phase by replacing the alkoxy group in the alkoxide in a di-coordinated manner. Furthermore, the acetic acid acts as a chelating agent, reacting with tetrabutyl titanate to form a chelate complex, reducing reaction activity and controlling the hydrolysis rate, thereby matching the hydrolysis rates of the titanium and barium source precursors. At the same time, the molar ratio of barium to titanium is controlled to be greater than 1.25. Properly increasing Ba / Ti is beneficial to increasing the supersaturation concentration of the system and increasing the number of nucleations per unit time. In this way, the growth rate of the crystal cannot keep up with the nucleation rate, which reduces the particle size of the barium titanate powder and increases the specific surface area. At the same time, increasing the proportion of barium source is beneficial to reducing the generation of barium vacancies. In the crystal electrical neutrality balance mechanism, hydroxyl defects need to achieve charge balance through a charge compensation mechanism. Barium vacancies can serve as effective charge compensation centers. Therefore, the reduction of barium vacancies is beneficial to the elimination of hydroxyl defects.

[0016] BaTiO3(s)+2xH2O=Ba 1-x TiO 3-2x OH 2x (s)+xBa 2+ (aq.)+2xOH - (aq.) Formula 1 Furthermore, in the subsequent hydrothermal reaction of the barium titanate precursor, the present invention selects to control the concentration of the KOH mineralizer to be between 2 mol / L and 4 mol / L. The presence of the mineralizer can promote or control the formation of the crystalline compound. According to the chemical reaction formula 1, the reaction can induce the Ba in the lattice to 2+ The removal process leads to an increase in the concentration of hydroxide. Therefore, when there is a certain amount of OH in the system - When the concentration is too high, the forward reaction will be significantly inhibited, resulting in the hydroxylation process being blocked and the hydroxyl defects being reduced. However, too high KOH concentration means that OH -Higher concentrations make it easier to adsorb carbon dioxide from the air, leading to the formation of barium carbonate impurities. Therefore, the present invention uses a 2-4 mol / L inorganic strong base aqueous solution, which can effectively control the formation of crystalline compounds and reduce hydroxyl defects on the one hand, and on the other hand, can ensure the purity of the crystal phase and avoid the formation of impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is an X-ray diffraction (XRD) spectrum and a local magnified view of the nano-barium titanate powder prepared in Example 1 of the present invention; Figure 2 is a scanning electron microscope photograph and particle size distribution diagram of the nano-barium titanate powder prepared in Example 1 of the present invention; Figure 3 This is an infrared spectrum of the nano-barium titanate powder prepared in Example 1 of the present invention; Figure 4 1 is an X-ray diffraction (XRD) spectrum and a local magnified view of the nano-barium titanate powder prepared in Example 2 of the present invention; Figure 5 This is a scanning electron microscope photograph and particle size distribution diagram of nano-barium titanate powder prepared in Example 2 of the present invention; Figure 6 This is an infrared spectrum of the nano-barium titanate powder prepared in Example 2 of the present invention; Figure 7 It is the scanning electron microscope photograph and particle size distribution diagram of the nano-barium titanate powder of the comparative example. DETAILED DESCRIPTION

[0018] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with examples, but the present invention is not limited to the following examples.

[0019] In the following examples, the mass fraction of glacial acetic acid is 99.5%.

[0020] Example 1 A method for preparing nano-barium titanate powder by a sol-gel-hydrothermal method comprises the following steps: (1) Mix 8 ml of glacial acetic acid and 12 ml of deionized water to obtain 20 ml of acetic acid aqueous solution, add 7.7425 g (0.03 mol) of barium acetate, and heat in a water bath at 80°C with stirring for 30 min to prepare a barium source solution; Weigh 6.8752 g (0.02 mol) of tetrabutyl titanate and add it to 10 ml of anhydrous ethanol. Stir for 30 minutes to prepare a titanium source solution. (2) slowly dripping the titanium source solution into the barium source solution under vigorous stirring at a rate of 10-20 drops / min, and heating in a water bath at 40°C for 3 hours to obtain a light yellow transparent gel; transferring the gel to a 105°C oven and drying it for 24 hours, and then grinding it to obtain a white powder of a barium titanate precursor; (3) Add 80 ml of 2 mol / L KOH solution to the polytetrafluoroethylene liner, then add 8 g of white powder of barium titanate precursor powder and PEG (the mass of PEG is 5% of the white powder of barium titanate precursor; the molecular weight of PEG is 15000), stir evenly, and obtain a barium titanate precursor suspension; (4) The barium titanate precursor suspension was transferred into a high-pressure reactor, sealed, and placed in a high-temperature oven, and kept at constant temperatures of 120°C, 140°C, and 160°C for 12 hours (i.e., hydrothermal reaction was performed at different temperatures); after the reaction was completed, the reactor was taken out, filtered and rinsed repeatedly with deionized water, and then placed in a 105°C oven to dry for 12 hours and ground to obtain nano-barium titanate powder.

[0021] The XRD pattern of the barium titanate powder obtained in Example 1 is as follows: Figure 1 As shown in Figure 2, the temperature range from 120℃ to 160℃ is uniform cubic phase barium titanate with no obvious impurity phase; SEM photos of nano-barium titanate prepared under hydrothermal conditions of 120℃, 140℃ and 160℃ are shown in Figure 2. Figure 2 As shown in the figure, the average particle size is between 100 and 130 nm (the proportion of particles larger than 150 nm is less than 20%, and the proportion of particles smaller than 80 nm is less than 10%), the morphology is nearly spherical, and the particle size increases further with increasing temperature.

[0022] The infrared spectrum of the barium titanate powder prepared in Example 1 is as follows: Figure 3 As shown in the figure, the hydroxyl defect content is small at 120℃ to 160℃, and there are no other impurities, which is consistent with XRD.

[0023] Example 2 A method for preparing nano-barium titanate powder by a sol-gel-hydrothermal method comprises the following steps: (1) Mix 8 ml of glacial acetic acid and 12 ml of deionized water to obtain 20 ml of acetic acid aqueous solution, add 7.7425 g (0.03 mol) of barium acetate, and heat in a water bath at 80°C with stirring for 30 min to prepare a barium source solution; Weigh 6.8752 g (0.02 mol) of tetrabutyl titanate and add it to 10 ml of anhydrous ethanol. Stir for 30 minutes to prepare a titanium source solution. (2) slowly dripping the titanium source solution into the barium source solution under vigorous stirring at a rate of 10-20 drops / min, and heating in a water bath at 40°C for 3 hours to obtain a light yellow transparent gel; transferring the gel to a 105°C oven and drying it for 24 hours, and then grinding it to obtain a white powder of a barium titanate precursor; (3) 80 ml of KOH aqueous solutions with concentrations of 2 mol / L, 3 mol / L, and 4 mol / L were added to the polytetrafluoroethylene liner, respectively (only one concentration of KOH aqueous solution was added, i.e., experiments were conducted using KOH aqueous solutions with different concentrations), and then 8 g of white powder of barium titanate precursor powder and PEG (the mass of PEG was 5% of the white powder of barium titanate precursor; the molecular weight of PEG was 15,000) were added, and after stirring evenly, a barium titanate precursor suspension was obtained; (4) Each barium titanate precursor suspension obtained in step (3) was transferred into a high-pressure reactor, sealed, and placed in a high-temperature oven, and maintained at a constant temperature of 140°C for 12 hours; after the reaction was completed, the reactor was taken out, filtered and rinsed repeatedly with deionized water, and then placed in a 105°C oven for drying for 12 hours and ground to obtain nano-barium titanate powder.

[0024] The XRD pattern of the barium titanate powder obtained in Example 2 is as follows: Figure 4 As shown in the SEM photos Figure 5 As shown, the barium titanate prepared with a KOH concentration between 2-4 mol / L is a uniform cubic phase without obvious impurities, and the average particle size is between 100 and 130 nm, and the morphology is nearly spherical.

[0025] The infrared spectrum of Example 2 is as follows Figure 6 As shown in the figure, the peak height of hydroxyl group of barium titanate powder prepared with KOH concentration between 2-4 mol / L is suppressed with the increase of KOH concentration, indicating that OH - The increase in concentration is beneficial to the reduction of hydroxyl defects.

[0026] Comparative Example A method for preparing nano-barium titanate powder by a sol-gel-hydrothermal method comprises the following steps: (1) Mix 8 ml of glacial acetic acid and 12 ml of deionized water to obtain 20 ml of acetic acid aqueous solution, add 5.1617 g (0.02 mol) of barium acetate, and heat in a water bath at 80°C with stirring for 30 min to prepare a barium source solution; Weigh 6.8752 g (0.02 mol) of tetrabutyl titanate and add it to 10 ml of anhydrous ethanol. Stir for 30 minutes to prepare a titanium source solution. (2) slowly dripping the titanium source solution into the barium source solution under vigorous stirring at a rate of 10-20 drops / min, and heating in a water bath at 40°C for 3 hours to obtain a light yellow transparent gel; transferring the gel to a 105°C oven and drying it for 24 hours, and then grinding it to obtain a white powder of a barium titanate precursor; (3) Add 80 ml of 2 mol / L KOH solution to the polytetrafluoroethylene liner, then add 8 g of white powder of barium titanate precursor powder and PEG (the mass of PEG is 5% of the white powder of barium titanate precursor; the molecular weight of PEG is 15000), stir evenly, and obtain a barium titanate precursor suspension; (4) The barium titanate precursor suspension was transferred into a high-pressure reactor, sealed, and placed in a high-temperature oven, maintained at a constant temperature of 140°C for 12 hours; after the reaction was completed, the reactor was taken out, filtered and rinsed repeatedly with deionized water, and then placed in a 105°C oven for 12 hours and ground to obtain nano-barium titanate powder.

[0027] Comparative Example: Ba / Ti=1 titanium source and barium source were used to prepare nano-barium titanate powder. Figure 7 As shown, the average particle size is about 153 nm and the morphology is hexahedral.

[0028] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, several improvements and changes can be made without departing from the creative concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A method for preparing nano-barium titanate powder by a sol-gel-hydrothermal method, characterized in that: The following steps are involved: (1) dissolving barium acetate in an acetic acid aqueous solution to obtain a barium source solution; weighing tetrabutyl titanate so that the molar ratio of barium to titanium is greater than 1.25, and dissolving the mixture in a solvent alcohol to obtain a titanium source solution; (2) mixing the barium source solution and the titanium source solution and stirring them uniformly, and keeping them warm at 20-80° C. to obtain a gel, which is then dried and ground to obtain a white powder of a barium titanate precursor; (3) Preparation of OH - An inorganic strong base aqueous solution with a concentration of 2-4 mol / L, then adding the white powder of the barium titanate precursor and a dispersant to the inorganic strong base aqueous solution and stirring thoroughly to obtain a barium titanate precursor suspension; (4) The barium titanate precursor suspension is transferred to a reactor for hydrothermal reaction. After the reaction is completed, the suspension is washed and dried to obtain nano-barium titanate powder.

2. The method for preparing nano-barium titanate powder by sol-gel-hydrothermal method according to claim 1, characterized in that: In step (1), the acetic acid aqueous solution is prepared by mixing glacial acetic acid and water, and the glacial acetic acid accounts for between 30% and 50% of the total volume.

3. The method for preparing nano-barium titanate powder by sol-gel-hydrothermal method according to claim 1, characterized in that: In step (1), the molar concentration of barium acetate in the acetic acid aqueous solution is between 1-2 mol / L.

4. The method for preparing nano-barium titanate powder by sol-gel-hydrothermal method according to claim 1, characterized in that: In step (1), the alcohol is one or more of ethylene glycol, ethanol and methanol; and the molar concentration of tetrabutyl titanate in the titanium source solution is 1.5-2.5 mol / L.

5. The method for preparing nano-barium titanate powder by sol-gel-hydrothermal method according to claim 1, characterized in that: In step (2), when the barium source solution and the titanium source solution are mixed, the ratio of barium acetate to tetrabutyl titanate is between 1.25 and 1.75 in terms of the molar ratio of barium to titanium.

6. The method for preparing nano-barium titanate powder by sol-gel-hydrothermal method according to claim 1, characterized in that: In step (3), the inorganic strong alkali aqueous solution is a mixture of KOH and water; the white powder of the barium titanate precursor is added to the inorganic strong alkali aqueous solution at a mass concentration of 50-150 g / L.

7. The method for preparing nano-barium titanate powder by sol-gel-hydrothermal method according to claim 1, characterized in that: In step (3), the dispersant is polyethylene glycol with a molecular weight of 15,000-25,000, and the mass of the dispersant is 2%-5% of the white powder of the barium titanate precursor.

8. The method for preparing nano-barium titanate powder by sol-gel-hydrothermal method according to claim 1, characterized in that: In step (4), the hydrothermal reaction conditions are: hydrothermal reaction at 100-180° C. for 8-24 h.

9. The nano-barium titanate powder prepared by the method according to any one of claims 1 to 8, characterized in that: The nano-barium titanate powder is white powder in macroscopic view and spherical or nearly spherical nano-particles in microscopic view, with an average particle size between 80-150 nm.

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