Preparation method of barium titanate powder

Abstract

The invention relates to the technical field of preparation of barium titanate, and discloses a preparation method of barium titanate powder, which comprises the following steps: (1) adding a 15% ammonia water solution into a stirring tank, weighing a certain amount of TiCl4, slowly dripping into the ammonia water solution, and continuously stirring for 1 hour to obtain a titanium source solution; (2) adding pure water into a heatable stirring tank, stirring all the time, weighing a certain amount of Ba (OH) 2.8 H2O, putting the Ba (OH) 2.8 H2O into the stirring tank, heating and raising the temperature to 100 DEG C, keeping the temperature for 2 hours, and adjusting the pH value to 13.5 by using a 15% ammonia water solution to obtain a barium source solution; (3) slowly adding the titanium source solution into the barium source solution, transferring the mixed solution into a hydrothermal reaction kettle, adding a reaction regulator into the reaction kettle, washing and drying for multiple times, collecting to obtain a solid, and calcining the solid at high temperature to obtain barium titanate powder; the method has the effect of improving the tetragonal phase content of the barium titanate powder.

Description

Technical Field

[0001] The present invention relates to the technical field of barium titanate preparation, and in particular to a method for preparing barium titanate powder. Background Art

[0002] Barium titanate, a typical perovskite-type crystal, is a key raw material for multilayer ceramic capacitors (MLCCs). As MLCCs evolve toward miniaturization, thinness, and higher capacitance, higher requirements are placed on the purity, particle size, and dispersibility of barium titanate powders. Currently, high-end nano-barium titanate materials rely on imports, creating a bottleneck restricting the development of high-end MLCCs.

[0003] Among the many methods for synthesizing barium titanate powder, the hydrothermal method has attracted much attention due to its mild reaction conditions, small size, controllable particle size, and uniform composition. However, during the hydrothermal reaction, when Ti(OH)6 4－ with Ba 2+ When the combination is insufficient and the dehydration is incomplete, hydroxyl groups will be retained at the free end of the TiO6 octahedron. In order to maintain electrical neutrality, hydroxyl defects and barium vacancies form barium titanate crystal defects in a 1:2 ratio, resulting in defects inside the barium titanate. The purity of the tetragonal phase of the prepared barium titanate powder is not high. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing barium titanate powder, which has the effect of increasing the tetragonal phase content of the barium titanate powder.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions: a method for preparing barium titanate powder, comprising the following steps:

[0006] (1) Preparation of titanium source solution: Add 15% ammonia solution to a stirring tank, weigh a certain amount of TiCl4 and slowly drop it into the stirring tank, and continue stirring for 1 hour to obtain a titanium source solution;

[0007] (2) Preparation of barium source solution: pure water was added to a heated stirring tank, and a certain amount of Ba(OH)2·8H2O was weighed and added thereto while stirring continuously. The mixture was heated to 100°C and maintained for 2 h. The pH was adjusted to 12.5 using a 25% ammonia solution to obtain a barium source solution.

[0008] (3) Preparation of barium titanate powder: The titanium source solution is slowly added to the barium source solution, and stirring is continued during the addition process. Stirring is continued for 1 hour after the addition is completed. The mixed solution is then transferred to a hydrothermal reactor, sealed and slowly stirred and quickly heated to 80°C, then stopped stirring and kept warm for 2 hours, and then a reaction regulator is added to the reactor, stirred for 60 minutes, sealed, heated to 160°C and kept warm for 12 hours. After multiple washing and drying, the solid is collected and then calcined at high temperature to obtain the barium titanate powder.

[0009] The present invention is further configured as follows: the reaction regulator is prepared by adding a certain amount of phenolic resin to a 20% by mass ethanol solution, stirring to dissolve, then adding an appropriate amount of barium stearate, heating to 60° C. and stirring for 30 minutes to obtain the reaction regulator.

[0010] The present invention is further configured as follows: the mass ratio of the phenolic resin, the ethanol and the barium stearate is 3:20:4.

[0011] The present invention is further configured as follows: the amount of the reaction regulator added in step (3) is 15% of the volume of the titanium source solution.

[0012] The present invention is further configured as follows: the molar ratio of titanium in the titanium source solution to barium in the barium source solution is 4:5, and the volume ratio of the titanium source solution to the barium source solution in step (3) is 1:1.

[0013] The present invention is further configured as follows: the temperature of the high-temperature calcination in step (3) is 1000° C. and the time is 6 hours.

[0014] The beneficial effects of the present invention are:

[0015] 1. The present invention adopts a two-step hydrothermal calcination method to prepare barium titanate powder. First, a barium source and a titanium source are mixed in a certain proportion and subjected to a hydrothermal reaction. After cooling, the obtained precipitate is washed, filtered, and dried to obtain a precursor of the barium titanate powder. Finally, the obtained barium titanate powder precursor is placed in a heating furnace for calcination. By calcining at a certain temperature and time, the defects of the powder are eliminated and the tetragonal phase content in the barium titanate powder is increased.

[0016] 2. The present invention adds TiCl4 to the ammonia solution. During the reaction, Ti 4+ First, Ti(OH)4 colloid is generated in an alkaline environment, and the barium source (Ba 2+ ) can quickly move to the Ti-O group (Ti(OH) x 4-x) surface, which is the nucleation site of BaTiO3 crystal, thus quickly promoting the growth of crystal nuclei. Therefore, ammonia water is used as the solvent of titanium source solution and the pH of barium source solution is adjusted to 12.5. Under high alkalinity conditions, Ba2 + It is not easy to be replaced and basically no barium vacancies are generated, so the crystal growth is relatively sufficient. Therefore, the alkaline environment can not only promote the formation of BaTiO3, but also compensate for the hydroxyl defects in the synthesis process, eliminate the internal defects of the barium titanate crystal, and further increase the tetragonal phase content in the barium titanate powder.

[0017] 3. In the present invention, after the titanium source solution and the barium source solution react for a period of time, a reaction regulator is added. On the one hand, after the phenolic resin is dissolved in the ethanol solution, barium stearate is added to promote the dissolution of barium stearate through the hydrophobic interaction between the long-chain alkyl and the benzene ring structure of the phenolic resin, so that the barium stearate can perform a secondary barium filling on the barium titanate particles to repair the barium vacancy defects of the barium titanate material. After the secondary barium filling treatment, the concentration of barium vacancy defects in the crystal can be reduced, the stability of the crystal structure can be improved, and the abnormal growth of particles caused by the disappearance of vacancies in the powder at high temperature can be suppressed. The charge characteristics of the particle surface can also be changed, and the mutual attraction between particles can be reduced to prevent the occurrence of agglomeration. On the other hand, after the ionization of the phenolic resin and barium stearate, the free groups and the negative charges on the surface of the barium titanate particles form specific bonds through Ba bridges, and form a protective layer on the surface of the barium titanate particles by coordinating with the surface ions or forming hydrogen bonds. The protective layer That is, it acts as a growth inhibitor, limiting the growth of barium titanate particles at high temperatures, and can also act as an isolation between barium titanate particles to prevent the fusion and growth of barium titanate particles at high temperatures. At the same time, the protective layer can slowly decompose, carbonize and oxidize as the temperature rises during high-temperature calcination, and no solid phase remains. In summary, by adding a reaction regulator during the reaction process, not only can barium be supplemented for the second time through barium stearate, further repairing the barium vacancy defects of the barium titanate material, inhibiting the abnormal growth of particles during subsequent calcination, and avoiding agglomeration, but also through the interaction between phenolic resin, ethanol and barium stearate to promote dissolution, so that the ionized free groups can form a protective layer on the surface of the barium titanate particles, further inhibiting the abnormal growth of particles during calcination, and avoiding agglomeration, ensuring that the barium titanate powder after high-temperature calcination has the advantages of good dispersibility, small particle size, uniform composition and high tetragonal phase content, meeting the application requirements of high-end MLCC.

[0018] 4. The barium titanate powder prepared by the present invention has good dispersibility, small particle size, uniform composition, high tetragonality, and has good application prospects. DETAILED DESCRIPTION

[0019] The technical solutions of the present invention will be described clearly and completely below with reference to specific embodiments. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0020] 1. Experimental process

[0021] Example 1

[0022] (1) Preparation of titanium source solution: pure water was added to a stirring tank, and a certain amount of TiCl4 was slowly added dropwise thereto, and stirring was continued for 1 h to obtain a 0.8 mol / L titanium source solution;

[0023] (2) Preparation of barium source solution: pure water was added to a heated stirring tank, and a certain amount of Ba(OH)2·8H2O was weighed and added thereto. The mixture was heated to 100°C and maintained for 2 h to obtain a 1.0 mol / L barium source solution.

[0024] (3) Preparation of reaction regulator: A certain amount of phenolic resin was added to a 20% by mass ethanol solution and stirred to dissolve. Then, an appropriate amount of barium stearate was added and heated to 60°C and stirred for 30 minutes to obtain a reaction regulator, wherein the mass ratio of phenolic resin, ethanol and barium stearate was 3:20:4;

[0025] (4) Preparation of barium titanate powder: The titanium source solution is slowly added to an equal volume of the barium source solution, and stirring is continued during the addition process. Stirring is continued for 1 hour after the addition is completed. The mixed solution is then transferred to a hydrothermal reactor, sealed, slowly stirred, and quickly heated to 80°C. Stirring is then stopped and kept warm for 2 hours. A reaction regulator with a volume fraction of 15% of the titanium source solution is then added to the reactor, stirred for 30 minutes, sealed, heated to 160°C, and kept warm for 12 hours. After multiple washing and drying, the solid is collected and then calcined at 1000°C for 6 hours to obtain barium titanate powder.

[0026] It should be noted that in step (4), the pressure of the hydrothermal reactor is always controlled at 1.6-1.7 MPa.

[0027] Example 2

[0028] (1) Preparation of titanium source solution: Add 15% ammonia solution to a stirring tank, weigh a certain amount of TiCl4 and slowly drop it into it, and continue stirring for 1 hour to obtain a 0.8 mol / L titanium source solution;

[0029] (2) Preparation of barium source solution: Pure water was added to a heated stirring tank, and a certain amount of Ba(OH)2·8H2O was weighed and added thereto while stirring continuously. The mixture was heated to 100°C and maintained for 2 h. The pH was adjusted to 12.5 using a 25% ammonia solution to obtain a 1.0 mol / L barium source solution.

[0030] (3) Preparation of barium titanate powder: The titanium source solution is slowly added to an equal volume of the barium source solution, and stirring is continued during the addition process. Stirring is continued for 1 hour after the addition is completed. The mixed solution is then transferred to a hydrothermal reactor, slowly stirred in a sealed container, and quickly heated to 80°C. Stirring is then stopped and kept warm for 2 hours. The temperature is then raised to 160°C and kept warm for 12 hours. After multiple washing and drying, the solid is collected and then calcined at 1000°C for 6 hours to obtain barium titanate powder.

[0031] It should be noted that in step (3), the pressure of the hydrothermal reactor is always controlled at 1.6-1.7 MPa.

[0032] Example 3

[0033] (1) Preparation of titanium source solution: Add 15% ammonia solution to a stirring tank, weigh a certain amount of TiCl4 and slowly drop it into it, and continue stirring for 1 hour to obtain a 0.8 mol / L titanium source solution;

[0034] (2) Preparation of barium source solution: Pure water was added to a heated stirring tank, and a certain amount of Ba(OH)2·8H2O was weighed and added thereto while stirring continuously. The mixture was heated to 100°C and maintained for 2 h. The pH was adjusted to 12.5 using a 25% ammonia solution to obtain a 1.0 mol / L barium source solution.

[0035] (3) Preparation of reaction regulator: A certain amount of phenolic resin was added to a 20% by mass ethanol solution and stirred to dissolve. Then, an appropriate amount of barium stearate was added and heated to 60°C and stirred for 30 minutes to obtain a reaction regulator, wherein the mass ratio of phenolic resin, ethanol and barium stearate was 3:20:4;

[0036] (4) Preparation of barium titanate powder: The titanium source solution is slowly added to an equal volume of the barium source solution, and stirring is continued during the addition process. Stirring is continued for 1 hour after the addition is completed. The mixed solution is then transferred to a hydrothermal reactor, sealed, slowly stirred, and quickly heated to 80°C. Stirring is then stopped and kept warm for 2 hours. A reaction regulator with a volume fraction of 15% of the titanium source solution is then added to the reactor, stirred for 30 minutes, sealed, heated to 160°C, and kept warm for 12 hours. After multiple washing and drying, the solid is collected and then calcined at 1000°C for 6 hours to obtain barium titanate powder.

[0037] It should be noted that in step (4), the pressure of the hydrothermal reactor is always controlled at 1.6-1.7 MPa.

[0038] Comparative Example 1

[0039] (1) Preparation of titanium source solution: pure water was added to a stirring tank, and a certain amount of TiCl4 was slowly added dropwise thereto, and stirring was continued for 1 h to obtain a 0.8 mol / L titanium source solution;

[0040] (2) Preparation of barium source solution: pure water was added to a heated stirring tank, and a certain amount of Ba(OH)2·8H2O was weighed and added thereto. The mixture was heated to 100°C and maintained for 2 h to obtain a 1.0 mol / L barium source solution.

[0041] (3) Preparation of barium titanate powder: The titanium source solution is slowly added to an equal volume of the barium source solution, and stirring is continued during the addition process. Stirring is continued for 1 hour after the addition is completed. The mixed solution is then transferred to a hydrothermal reactor, sealed, slowly stirred, and quickly heated to 80°C. Stirring is then stopped and kept warm for 2 hours. A reaction regulator with a volume fraction of 15% of the titanium source solution is then added to the reactor, stirred for 30 minutes, sealed, heated to 160°C, and kept warm for 12 hours. After multiple washing and drying, the barium titanate powder is collected.

[0042] It should be noted that in step (3), the pressure of the hydrothermal reactor is always controlled at 1.6-1.7 MPa.

[0043] 2. Characterization method of barium titanate powder

[0044] (1) Morphology and microstructure characterization

[0045] Field emission scanning electron microscopy (SEM) was used to characterize the surface morphology and particle size of the powder generated by the reaction. The particles in the SEM image were counted using ImageJ software to calculate their average size D SEM .

[0046] (2) Specific surface area (S) measurement

[0047] The specific surface area of ​​the powder is measured using a specific surface area and pore size analyzer, and then the agglomeration coefficient (AF) of the powder is calculated.

[0048] (3) Particle size distribution measurement

[0049] Laser particle size analyzer and potentiometer were used to characterize the particle size distribution of barium titanate powder, and then the particle size distribution non-uniformity coefficient (MD) was calculated.

[0050] (4) Barium titanate lattice constant and tetragonality value (c / a)

[0051] X-ray powder diffractometer (XRD) can be used to characterize whether the synthesized barium titanate powder is pure phase, and then calculate the tetragonal phase content of BaTiO3 crystals.

[0052] 3. Experimental results

[0053] Table 1

[0054] <![CDATA[D SEM ]]> AF MD c / a Example 1 145 1.25 0.45 1.0094 Example 2 342 1.65 0.63 1.0065 Example 3 132 1.10 0.41 1.0108 Comparative Example 1 125 1.24 0.56 1.0044

[0055] By comparing Example 3 with Comparative Example 1, it can be seen that the tetragonal phase of the powder increases from 1.0044 to 1.0108, while the uniformity coefficient MD decreases from 0.56 to 0.41, and the agglomeration coefficient AF decreases from 1.24 to 1.10. This shows that by adjusting the alkaline environment of the titanium source solution and the barium source solution and adding a reaction regulator to calcine the barium titanate powder at high temperature, the tetragonal phase content of the powder can be significantly increased without significantly increasing the powder particle size, while reducing the uniformity coefficient and agglomeration coefficient of the powder, thereby obtaining barium titanate powder with good dispersibility, small particle size, uniform composition and high tetragonal phase content, which meets the application requirements of high-end MLCC.

[0056] By comparing Example 1 with Example 3, it can be seen that the tetragonal phase content of the powder obtained by the reaction of the titanium source solution and the barium source solution in an alkaline environment is significantly increased, while the uniformity coefficient MD and the agglomeration coefficient AF are reduced, indicating that the alkaline environment can not only promote the formation of BaTiO3, but also compensate for the hydroxyl defects in the synthesis process, eliminate the internal defects of the barium titanate crystal, and further increase the tetragonal phase content in the barium titanate powder.

[0057] By comparing Example 2 with Example 3, it can be seen that the addition of a reaction regulator during the hydrothermal reaction of barium titanate can greatly reduce the particle size of the obtained barium titanate powder and increase the content of the tetragonal phase of the powder, indicating that the addition of a reaction regulator can perform secondary barium supplementation and form a protective layer on the surface of the barium titanate particles, thereby improving the stability of the crystal structure, inhibiting the abnormal growth of particles caused by the disappearance of vacancies at high temperatures, and playing an isolating role between the particles to prevent the fusion and growth of the barium titanate particles at high temperatures, thereby avoiding the problems of poor dispersibility, significant increase in particle size, and severe agglomeration caused by high-temperature calcination, and obtaining a barium titanate powder with a high tetragonal phase content, good dispersibility, and uniform composition.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing barium titanate powder, characterized in that: The following steps are involved: (1) Preparation of titanium source solution: Add 15% ammonia solution to a stirring tank, weigh a certain amount of TiCl4 and slowly drop it into the stirring tank, and continue stirring for 1 hour to obtain a titanium source solution; (2) Preparation of barium source solution: pure water was added to a heated stirring tank, and a certain amount of Ba(OH)2·8H2O was weighed and added thereto while stirring continuously. The mixture was heated to 100°C and maintained for 2 h. The pH was adjusted to 12.5 using a 25% ammonia solution to obtain a barium source solution. (3) Preparation of barium titanate powder: The titanium source solution is slowly added to the barium source solution, and stirring is continued during the addition process. Stirring is continued for 1 hour after the addition is completed. The mixed solution is then transferred to a hydrothermal reactor, sealed and slowly stirred and quickly heated to 80°C, then stopped stirring and kept warm for 2 hours, and then a reaction regulator is added to the reactor, stirred for 60 minutes, sealed, heated to 160°C and kept warm for 12 hours. After multiple washing and drying, the solid is collected and then calcined at high temperature to obtain the barium titanate powder.

2. The method for preparing barium titanate powder according to claim 1, wherein: The reaction regulator is prepared by adding a certain amount of phenolic resin to a 20% by mass ethanol solution, stirring to dissolve, then adding an appropriate amount of barium stearate, heating to 60° C. and stirring for 30 minutes to obtain the reaction regulator.

3. The method for preparing barium titanate powder according to claim 2, wherein: The mass ratio of the phenolic resin, the ethanol and the barium stearate is 3:20:

4.

4. The method for preparing barium titanate powder according to claim 3, wherein: The amount of the reaction regulator added in step (3) is 15% of the volume of the titanium source solution.

5. The method for preparing barium titanate powder according to claim 1, wherein: The molar ratio of titanium in the titanium source solution to barium in the barium source solution is 4:5, and the volume ratio of the titanium source solution to the barium source solution in step (3) is 1:

1.

6. The method for preparing barium titanate powder according to claim 1, wherein: The high temperature calcination in step (3) is carried out at a temperature of 1000° C. and for a time of 6 hours.