A spherical barium titanate powder with controllable particle size and a high tetragonal ammonium salt and its hydrothermal synthesis method.

Abstract

This invention relates to the field of electronic ceramic powder technology, and discloses a spherical barium titanate powder with controllable ammonium salt high tetragonal phase particle size and its hydrothermal synthesis method. The method includes: preparing a titanium-containing precursor solution from titanium tetrachloride under cooling conditions; preparing a barium-containing alkaline solution from barium hydroxide; controlling the Ba / Ti molar ratio at 0.998-1.003 after mixing; adding ammonia to adjust the strong alkaline system; and adding a composite dispersant for ammonium salt-assisted hydrothermal reaction. The resulting slurry is washed, filtered, dehydrated, dried, and depolymerized; a heat-treatment dispersant is added; and the slurry is heat-treated at 900-1000℃. After crushing, grinding, and classification, spherical barium titanate powder is obtained. The obtained powder has a d50 of 100-200 nm and a tetragonality c / a greater than 1.008. It features narrow particle size distribution, good sphericity, low agglomeration, and low risk of alkali metal impurity introduction, making it suitable for electronic ceramic materials such as multilayer ceramic capacitors.

Description

Technical Field

[0001] This invention relates to the field of electronic ceramic powder technology, specifically to a spherical barium titanate powder with controllable ammonium salt high tetragonal phase particle size and its hydrothermal synthesis method. Background Technology

[0002] Barium titanate is a typical perovskite-structured electronic ceramic material with high dielectric constant, low dielectric loss, and good ferroelectric, piezoelectric, and insulating properties. It is widely used in multilayer ceramic capacitors, thermistors, piezoelectric ceramic components, and dielectric ceramic materials. As electronic components develop towards miniaturization, higher capacitance, and higher reliability, the requirements for barium titanate powder used in multilayer ceramic capacitors are continuously increasing regarding particle size, particle size distribution, sphericity, purity, crystal phase stability, and batch consistency.

[0003] Existing industrial methods for preparing barium titanate powder mainly include solid-state and hydrothermal methods. Solid-state methods typically use barium carbonate and titanium dioxide as raw materials, which are mixed, calcined, and pulverized to obtain barium titanate powder. This method has advantages such as mature technology and low cost. However, during the solid-state reaction, uneven particle contact and limited local diffusion easily lead to uneven distribution of barium and titanium components in the microscopic region. Furthermore, high-temperature sintering easily causes particle growth and hard agglomeration, resulting in a wider particle size distribution, which is difficult to meet the requirements of high-end electronic ceramics for nanoscale, narrow-distribution, and highly dispersed powders.

[0004] The hydrothermal method involves reacting barium and titanium sources in a closed reactor under a strong alkaline environment in the liquid phase to produce barium titanate. This method offers advantages such as lower reaction temperatures, better particle uniformity, and higher batch stability. However, barium titanate powder prepared by the conventional hydrothermal method is prone to hydroxyl defects and insufficient lattice distortion, resulting in insufficient tetragonal phase content. Furthermore, using strong alkalis such as sodium or potassium to adjust the pH of the system can easily introduce alkali metal impurities, adversely affecting subsequent dielectric properties and reliability. In addition, if the dispersion system is poorly designed during the hydrothermal reaction, uneven particle nucleation and growth can easily lead to problems such as agglomeration, irregular morphology, and uncontrollable particle size.

[0005] Therefore, it is necessary to provide a hydrothermal synthesis method that can improve the tetragonality and sphericity of barium titanate powder and achieve controllable particle size while reducing the risk of introducing alkali metal impurities. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a spherical barium titanate powder with controllable ammonium salt high tetragonal phase particle size and its hydrothermal synthesis method, thereby solving the problems of numerous hydroxyl defects, insufficient tetragonality, wide particle size distribution, and obvious particle agglomeration in existing hydrothermal barium titanate powders.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a hydrothermal synthesis method for spherical barium titanate powder with controllable ammonium salt tetragonal phase particle size, comprising the following steps: S1. Under cooling and stirring conditions, titanium tetrachloride is added to deionized water to obtain a titanium-containing precursor solution. S2. Dissolve barium hydroxide in deionized water to obtain a barium-containing alkaline solution; S3. Mix the titanium-containing precursor solution with the barium-containing alkaline solution, control the Ba / Ti molar ratio to be 0.998-1.003, add ammonia to adjust the pH of the system to be greater than 13, and add a composite dispersant to obtain an ammonium salt-assisted hydrothermal reaction solution. S4. The ammonium salt-assisted hydrothermal reaction solution is placed in a reaction vessel for hydrothermal reaction to obtain barium titanate slurry. S5. The barium titanate slurry is washed, filtered, dehydrated, dried and depolymerized to obtain primary barium titanate powder; S6. Add heat treatment dispersant to the primary barium titanate powder, mix and heat treat at 900-1000℃, then crush, grind and classify to obtain spherical barium titanate powder. The spherical barium titanate powder has a d50 of 100-200 nm and a tetragonality c / a greater than 1.008.

[0008] Further, in step S1, the titanium tetrachloride is added dropwise to deionized water at 0-10℃, and the system temperature is controlled not to exceed 15℃ during the dropwise addition process, to obtain a titanium-containing precursor solution with a Ti concentration of 0.1-1.0 mol / L.

[0009] Further, in step S2, the barium hydroxide is barium hydroxide or barium hydroxide octahydrate, the dissolution temperature is 60-90℃, and the concentration of Ba in the resulting barium-containing alkaline solution is 0.1-1.0 mol / L.

[0010] Furthermore, in step S3, the mass concentration of the ammonia water is 20-28%, and the pH of the adjusted system is 13.1-14.2.

[0011] Further, in step S3, the composite dispersant is composed of ammonium polyacrylate, ammonium citrate, polyethylene glycol and polyvinylpyrrolidone in a mass ratio of 1:(0.1-0.5):(0.1-0.4):(0.05-0.3).

[0012] Further, in step S3, the amount of the composite dispersant added, based on its effective complexing and dispersing groups, is 1.0-1.5% of the molar amount of Ti in the titanium source.

[0013] Furthermore, in step S4, the hydrothermal reaction temperature is 160-220℃, the reaction time is 3-12h, the stirring speed is 100-500r / min, and the reactor filling rate is 60-80%.

[0014] Further, in step S5, the filtrate is washed until its conductivity is not higher than 80 μS / cm and its chloride ion content is not higher than 50 mg / L; the drying temperature is 80-120℃ and the drying time is 4-12 h.

[0015] Further, in step S6, the heat treatment dispersant is one or more of ammonium polyacrylate, ammonium citrate, and polyethylene glycol, and the amount added is 0.2-1.0% of the mass of the primary barium titanate powder; the heat treatment holding time is 1-4 hours, and the heating rate is 2-5℃ / min.

[0016] Furthermore, the spherical barium titanate powder has a d50 of 100-200 nm, a tetragonality c / a of 1.008-1.012, a Ba / Ti molar ratio of 0.998-1.003, and the powder is spherical.

[0017] Furthermore, the d50 of the primary barium titanate powder is 10-100 nm, and the d50 of the spherical barium titanate powder obtained after heat treatment is 100-200 nm, with D90 / D10 not exceeding 3.0.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: This invention employs ammonia water to construct a strongly alkaline ammonium salt-assisted hydrothermal system. By precisely controlling the Ba / Ti molar ratio, the barium and titanium sources are uniformly nucleated and grown in a liquid phase environment, avoiding the impact of residual alkali metal impurities on dielectric properties and reliability found in traditional sodium and potassium strong alkaline systems. Simultaneously, the ammonium salt environment helps reduce the risk of introducing impurity ions into the powder, improves the lattice integrity and tetragonal phase stability of barium titanate, and results in a powder with a high tetragonality, meeting the requirements of high-end electronic ceramic powders for phase stability and compositional consistency.

[0019] This invention utilizes the synergistic effect of a composite dispersant and a heat treatment dispersant to suppress disordered particle agglomeration and promote uniform particle growth during the hydrothermal reaction stage. In the subsequent heat treatment stage, it inhibits hard agglomeration and abnormal growth, enabling the powder to maintain a controllable particle size of 100-200 nm and a good spherical morphology while improving its tetragonality. This method features clear process steps, well-defined parameter windows, and produces barium titanate powder with a narrow particle size distribution, good dispersibility, high sphericity, and excellent batch stability, which is beneficial for improving its application performance in multilayer ceramic capacitors, dielectric ceramics, and piezoelectric ceramic materials. Attached Figure Description

[0020] Figure 1This is a SEM image of the spherical barium titanate powder from Example 1. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The reagents used in the following specific embodiments are analytical grade. In addition, titanium tetrachloride, barium hydroxide octahydrate, ammonia, ammonium polyacrylate, ammonium citrate, polyethylene glycol and polyvinylpyrrolidone are all commercially available.

[0023] The ammonium polyacrylate has a weight-average molecular weight of 5000, the polyethylene glycol is PEG-1000, and the polyvinylpyrrolidone is PVP K30. By selecting dispersants within the above molecular weight range, the ammonium polyacrylate can provide electrostatic repulsion and complexation dispersion effects of the carboxylic acid ammonium groups, the polyethylene glycol can form a flexible steric hindrance layer on the particle surface, and the polyvinylpyrrolidone can improve the dispersion stability of barium titanate precursor particles in the hydrothermal system, thereby inhibiting particle agglomeration and abnormal growth, which is beneficial to obtaining barium titanate powder with concentrated particle size and high sphericity.

[0024] Example 1 This embodiment describes a method for preparing spherical barium titanate powder under the upper limit of process parameters, specifically including the following steps: S1. Preparation of titanium-containing precursor solution: Under cooling and stirring conditions at 0-10℃, 37.94g of titanium tetrachloride was slowly added dropwise to deionized water. During the dropwise addition, the system temperature was controlled not to exceed 15℃. After the dropwise addition was completed, stirring was continued for 40min, and deionized water was added to prepare a titanium-containing precursor solution with a Ti concentration of 1.0mol / L.

[0025] S2. Preparation of barium-containing alkaline solution: 63.28g of barium hydroxide octahydrate was added to deionized water and stirred at 90℃ to dissolve, resulting in a barium-containing alkaline solution with a Ba concentration of 1.0mol / L.

[0026] S3. Preparation of ammonium salt-assisted hydrothermal reaction solution: The titanium-containing precursor solution obtained in step S1 is slowly added to the barium-containing alkaline solution obtained in step S2, controlling the Ba / Ti molar ratio to be 1.003; then, 28% ammonia solution is added to adjust the pH of the system to 14.2, and then a composite dispersant is added to obtain the ammonium salt-assisted hydrothermal reaction solution. The composite dispersant is composed of ammonium polyacrylate, ammonium citrate, polyethylene glycol, and polyvinylpyrrolidone in a mass ratio of 1:0.5:0.4:0.3, and the amount of composite dispersant added, based on its effective complexing and dispersing groups, is 1.5% of the molar amount of Ti in the titanium source.

[0027] S4. Hydrothermal reaction: The ammonium salt-assisted hydrothermal reaction solution obtained in step S3 is transferred to the reactor, and the reactor filling rate is controlled at 80%. The hydrothermal reaction is carried out at 220℃ and 500r / min for 12h. After the reaction is completed, it is cooled to room temperature to obtain barium titanate slurry.

[0028] S5. Washing, drying and depolymerization: The barium titanate slurry obtained in step S4 is washed, filtered and dehydrated with deionized water until the conductivity of the filtrate is 52 μS / cm and the chloride ion content is 35 mg / L. Then it is dried at 120℃ for 12 h. After drying, it is depolymerized to obtain primary barium titanate powder.

[0029] S6. Heat treatment and post-treatment: Add 1.0 wt% of heat treatment dispersant to the primary barium titanate powder obtained in step S5. The heat treatment dispersant is composed of ammonium polyacrylate, ammonium citrate and polyethylene glycol in a mass ratio of 1:0.3:0.2. After mixing evenly, put it into a sagger, heat it to 1000℃ at 5℃ / min, keep it at the temperature for 4h, cool it, and then crush, grind and classify it to obtain spherical barium titanate powder.

[0030] Depend on Figure 1 It can be seen that the obtained spherical barium titanate powder has a regular spherical or near-spherical morphology, with clear particle outlines and high sphericity. No obvious flaky, needle-like, or irregular blocky particles were observed. Only slight soft agglomeration existed between particles, without obvious hard agglomeration or large-scale sintering. This indicates that the composite dispersant can regulate the nucleation and growth of barium titanate crystals during the hydrothermal reaction through complexation, electrostatic repulsion, and steric hindrance, inhibiting disordered particle agglomeration. Simultaneously, the subsequent heat treatment dispersant, while improving the crystallinity and crystal integrity of the powder, can reduce sintering bridging between particles, maintaining good spherical morphology and dispersibility. The particle surface is relatively dense, with locally visible fine rough structures, indicating that the grains further grow and tend to become denser after heat treatment. In summary, this powder has the characteristics of high sphericity, relatively uniform particle size, good dispersibility, and low agglomeration, which is beneficial for improving the dispersibility, powder filling properties, and sintering uniformity of subsequent ceramic slurries.

[0031] Example 2 This embodiment describes a method for preparing spherical barium titanate powder under the lower limit of process parameters, specifically including the following steps: S1. Preparation of titanium-containing precursor solution: Under cooling and stirring conditions at 0-10℃, 18.97g of titanium tetrachloride was slowly added dropwise to deionized water. During the dropwise addition, the system temperature was controlled not to exceed 15℃. After the dropwise addition was completed, stirring was continued for 30min, and deionized water was added to prepare a titanium-containing precursor solution with a Ti concentration of 0.1mol / L.

[0032] S2. Preparation of barium-containing alkaline solution: 31.48g of barium hydroxide octahydrate was added to deionized water and stirred at 60℃ to dissolve, resulting in a barium-containing alkaline solution with a Ba concentration of 0.1mol / L.

[0033] S3. Preparation of ammonium salt-assisted hydrothermal reaction solution: The titanium-containing precursor solution obtained in step S1 is slowly added to the barium-containing alkaline solution obtained in step S2, controlling the Ba / Ti molar ratio to be 0.998; then, 20% ammonia solution is added to adjust the pH of the system to 13.1, and then a composite dispersant is added to obtain the ammonium salt-assisted hydrothermal reaction solution. The composite dispersant is composed of ammonium polyacrylate, ammonium citrate, polyethylene glycol, and polyvinylpyrrolidone in a mass ratio of 1:0.1:0.1:0.05, and the amount of composite dispersant added, based on its effective complexing and dispersing groups, is 1.0% of the molar amount of Ti in the titanium source.

[0034] S4. Hydrothermal reaction: The ammonium salt-assisted hydrothermal reaction solution obtained in step S3 is transferred to the reactor, and the reactor filling rate is controlled at 60%. The hydrothermal reaction is carried out at 160℃ and 100r / min for 3 hours. After the reaction is completed, it is cooled to room temperature to obtain barium titanate slurry.

[0035] S5. Washing, drying and depolymerization: The barium titanate slurry obtained in step S4 is washed, filtered and dehydrated multiple times with deionized water until the conductivity of the filtrate is 68 μS / cm and the chloride ion content is 46 mg / L; then it is dried at 80℃ for 4 hours, and after drying, it is depolymerized to obtain primary barium titanate powder.

[0036] S6. Heat treatment and post-treatment: Add 0.2wt% of ammonium polyacrylate as a heat treatment dispersant to the primary barium titanate powder obtained in step S5; after mixing evenly, load it into a sagger, heat it to 900℃ at 2℃ / min, keep it at that temperature for 1h, and after cooling, crush, grind and classify it to obtain spherical barium titanate powder.

[0037] Example 3 This embodiment describes a method for preparing spherical barium titanate powder under intermediate process parameter conditions, specifically including the following steps: S1. Preparation of titanium-containing precursor solution: Under cooling and stirring conditions at 0-10℃, 37.94g of titanium tetrachloride was slowly added dropwise to deionized water. During the dropwise addition, the system temperature was controlled not to exceed 15℃. After the dropwise addition was completed, stirring was continued for 40min, and deionized water was added to prepare a titanium-containing precursor solution with a Ti concentration of 0.5mol / L.

[0038] S2. Preparation of barium-containing alkaline solution: 63.09g of barium hydroxide octahydrate was added to deionized water and stirred at 75℃ to dissolve, resulting in a barium-containing alkaline solution with a Ba concentration of 0.5mol / L.

[0039] S3. Preparation of ammonium salt-assisted hydrothermal reaction solution: The titanium-containing precursor solution obtained in step S1 is slowly added to the barium-containing alkaline solution obtained in step S2, and the Ba / Ti molar ratio is controlled to be 1.000; then, 25% ammonia solution is added to adjust the pH of the system to 13.6, and then a composite dispersant is added to obtain the ammonium salt-assisted hydrothermal reaction solution; the composite dispersant is composed of ammonium polyacrylate, ammonium citrate, polyethylene glycol and polyvinylpyrrolidone in a mass ratio of 1:0.3:0.25:0.15, and the amount of composite dispersant added, based on its effective complexing and dispersing groups, is 1.25% of the molar amount of Ti in the titanium source.

[0040] S4. Hydrothermal reaction: The ammonium salt-assisted hydrothermal reaction solution obtained in step S3 is transferred to the reactor, and the reactor filling rate is controlled at 70%. The hydrothermal reaction is carried out at 190℃ and 300r / min for 7h. After the reaction is completed, it is cooled to room temperature to obtain barium titanate slurry.

[0041] S5. Washing, drying and depolymerization: The barium titanate slurry obtained in step S4 is washed, filtered and dehydrated multiple times with deionized water until the conductivity of the filtrate is 41 μS / cm and the chloride ion content is 28 mg / L; then it is dried at 100℃ for 8 hours, and after drying, it is depolymerized to obtain primary barium titanate powder.

[0042] S6. Heat treatment and post-treatment: Add 0.5 wt% of heat treatment dispersant to the primary barium titanate powder obtained in step S5. The heat treatment dispersant is composed of ammonium polyacrylate and polyethylene glycol in a mass ratio of 1:0.2. After mixing evenly, put it into a sagger, heat it to 950°C at 3°C / min, keep it at that temperature for 2.5 h, and after cooling, crush, grind and classify it to obtain spherical barium titanate powder.

[0043] Comparative Example 1 The main difference between this comparative example and Example 3 is that ammonia is not added in step S3, but sodium hydroxide solution is used to adjust the pH of the system to 13.6. The remaining steps and parameters are the same as in Example 3.

[0044] Comparative Example 2 The main difference between this comparative example and Example 3 is that no composite dispersant is added in step S3, while the remaining steps and parameters are the same as in Example 3.

[0045] Comparative Example 3 The main difference between this comparative example and Example 3 is that the heat treatment at 900-1000℃ is not performed in step S6. Instead, the primary barium titanate powder obtained in step S5 is dried and depolymerized and used directly as the final product. The remaining steps and parameters are the same as in Example 3.

[0046] Comparative Example 4 The main difference between this comparative example and Example 3 is that no heat treatment dispersant is added in step S6, and the heat treatment temperature is increased to 1050°C. The remaining steps and parameters are the same as in Example 3.

[0047] Test methods To verify the controllability of particle size, tetragonal crystal phase, elemental ratio, impurity residue, and morphological dispersion of the spherical barium titanate powder obtained in this invention, the powders obtained in Examples 1-3 and Comparative Examples 1-4 were subjected to the following tests. Each sample was taken from the same batch of powder, and the tests were performed in triplicate. The average value of the results was taken.

[0048] 1. Particle size distribution test The particle size distribution of the powder was tested using a laser particle size analyzer. 0.10 g of the barium titanate powder to be tested was weighed and added to 100 mL of deionized water. 0.05 wt% ammonium polyacrylate was added as a dispersion medium, and the mixture was ultrasonically dispersed for 5 min at 300 W ultrasonic power. The powder was then transferred to the circulating tank of the laser particle size analyzer for testing. During the test, water was used as the dispersion medium, the refractive index of barium titanate was set to 2.40, the refractive index of water to 1.333, the circulation pump speed was set to 1800-2200 r / min, and the shading rate was controlled at 8%-15%. The d10, d50, and d90 values ​​were obtained, and the width of the particle size distribution was calculated according to D90 / D10. d50 is used to characterize the median particle size of the powder; a smaller D90 / D10 ratio indicates a more concentrated particle size distribution.

[0049] 2. XRD phase and tetragonality test X-ray diffraction was used to perform crystal phase analysis on the powder.

[0050] 3. SEM morphology and sphericity test The microstructure of the powder was observed using a scanning electron microscope.

[0051] 4. Ba / Ti molar ratio and impurity element test Inductively coupled plasma atomic emission spectrometry (ICP-OES) was used to determine the contents of Ba, Ti, and impurity elements. 0.0500 g of powder sample was weighed and placed in a polytetrafluoroethylene digestion vessel. Nitric acid, hydrofluoric acid, and a small amount of hydrochloric acid were added for sealed digestion. After digestion, boric acid solution was added to complex residual fluoride ions. The volume was adjusted to 100 mL before ICP-OES analysis. The Ba / Ti molar ratio was calculated using the following formula: Ba / Ti molar ratio = (Ba element mass concentration / 137.33) / (Ti element mass concentration / 47.87).

[0052] Simultaneously, the contents of alkali metal impurities such as Na and K were tested to evaluate the inhibitory effect of the ammonia-ammonium salt auxiliary system on the introduction of alkali metal impurities.

[0053] 5. Chloride ion residue test The residual chloride ion content in the powder was determined by ion chromatography. 2.000 g of powder sample was weighed and added to 100 mL of deionized water. The mixture was stirred and extracted in an 80℃ water bath for 30 min. After cooling, it was filtered through a 0.22 μm filter membrane, and the filtrate was injected to determine the chloride ion content. The residual chloride ion content in the powder was calculated based on the chloride ion concentration in the filtrate and the sample mass. A lower residual chloride ion content indicates more thorough washing and desalination.

[0054] 6. Hydroxyl defect and thermogravimetric analysis Thermogravimetric analysis was used to test the mass loss of powder during the heating process, which was used to indirectly evaluate the content of adsorbed water and hydroxyl defects in hydrothermal powder.

[0055] 7. Specific surface area test The specific surface area of ​​powder was tested using the BET nitrogen adsorption method.

[0056] Table 1: Test results of particle size, crystal phase and elemental composition Ba / Ti molar ratio 1.003 0.998 1.000 1.000 1.001 1.000 1.002 D10 / nm 112 66 88 75 112 47 150 <![CDATA[D500 / nm]]> 192 108 146 158 318 72 426 D90 / nm 294 184 207 239 506 102 762 <![CDATA[D900 / D10]]> 2.63 2.79 2.35 3.19 4.52 2.17 5.08 Four-square law c / a 1.0108 1.0083 1.0095 1.0067 1.0082 1.0046 1.0098 Impurity phase situation No obvious heterogeneous features were observed. No obvious heterogeneous features were observed. No obvious heterogeneous features were observed. No obvious heterogeneous features were observed. No obvious heterogeneous features were observed. No obvious heterogeneous features were observed. No obvious heterogeneous features were observed. As shown in Table 1, the d50 values ​​of the spherical barium titanate powders obtained in Examples 1-3 are 192 nm, 108 nm, and 146 nm, respectively, all within the range of 100-200 nm. Furthermore, the D90 / D10 ratios are all less than 3.0, indicating that the present invention can achieve controlled particle size distribution by controlling the Ba / Ti molar ratio, ammonia pH, the amount of composite dispersant added, the hydrothermal reaction conditions, and the heat treatment conditions. The tetragonality c / a values ​​of Examples 1-3 are 1.0108, 1.0083, and 1.0095, respectively, all greater than 1.008, indicating that the barium titanate powders obtained after the combined hydrothermal reaction and heat treatment exhibit high tetragonal phase characteristics.

[0057] Comparative Example 1 used sodium hydroxide instead of ammonia to adjust the pH of the system. Although its d50 was 158 nm, its tetragonality c / a was only 1.0067, lower than the requirements of this invention, indicating that the ammonia-ammonium salt-assisted environment is beneficial to improving the tetragonality of the powder. Comparative Example 2 did not add a composite dispersant, and its d50 increased to 318 nm, while its D90 / D10 increased to 4.52, indicating that the lack of a composite dispersant leads to particle agglomeration and a wider particle size distribution. Comparative Example 3 did not undergo heat treatment at 900-1000℃, and its d50 was 72 nm, but its tetragonality c / a was only 1.0046, indicating that although the primary hydrothermal powder had a small particle size, its tetragonality was insufficient. Comparative Example 4 did not add a heat treatment dispersant and the heat treatment temperature was increased to 1050℃, and its d50 increased to 426 nm, while its D90 / D10 increased to 5.08, indicating that when the heat treatment temperature is too high and there is a lack of dispersion protection, the powder is prone to sintering, agglomeration, and abnormal growth.

[0058] Table 2: Results of tests on residual impurities, hydroxyl defects, and morphology Na content / ppm 8 7 6 126 9 6 8 K content / ppm 5 4 4 6 5 4 5 Chloride ion residue / mg / kg 42 51 35 39 44 32 37 200-600℃ thermal weight loss / % 0.23 0.31 0.20 0.38 0.29 1.18 0.18 BET specific surface area / m² / g 8.4 13.8 10.7 9.6 5.2 19.6 3.1 Mean sphericity 0.89 0.86 0.91 0.79 0.62 0.88 0.54 SEM morphology Spherical or nearly spherical, with a small amount of soft aggregates Spherical shape, with fine particles High sphericity and good dispersion Indistinct particle boundaries in some areas Significant hard agglomeration and particle adhesion. The particles are relatively fine, but lack tetragonality. Sintering adhesion and abnormal growth are obvious. As shown in Table 2, the Na content in Examples 1-3 was all below 10 ppm, and the K content was all below approximately 5 ppm. This indicates that using ammonia as a pH adjuster and ammonium salt as an auxiliary reaction environment can effectively avoid the introduction of large amounts of alkali metal impurities such as sodium and potassium. In Comparative Example 1, the pH of the system was adjusted using sodium hydroxide, and the Na content increased to 126 ppm. This indicates that using a sodium-alkali system significantly increases the risk of alkali metal residue, which is detrimental to the preparation of high-purity electronic ceramic powders.

[0059] The weight loss at 200-600℃ in Examples 1-3 was 0.23%, 0.31%, and 0.20%, respectively, significantly lower than the 1.18% in Comparative Example 3. This indicates that heat treatment at 900-1000℃ can effectively reduce hydroxyl defects and structural water residue in hydrothermal barium titanate powder, thereby improving its tetragonality. Although Comparative Example 3 has finer particles and a higher specific surface area, it has more hydroxyl defects due to the lack of heat treatment, resulting in a significantly lower tetragonality.

[0060] Based on the SEM morphology and average sphericity test results, the average sphericity of Examples 1-3 was not less than 0.86, the particles were spherical or nearly spherical, and no obvious hard agglomeration was observed. In Comparative Example 2, due to the absence of a composite dispersant, the average sphericity decreased to 0.62, and obvious particle adhesion was observed. In Comparative Example 4, due to excessively high heat treatment temperature and the absence of a heat treatment dispersant, the average sphericity decreased to 0.54, and the powder exhibited sintering, adhesion, and abnormal growth. This demonstrates that the composite dispersant and heat treatment dispersant in this invention can synergistically inhibit particle agglomeration, enabling the powder to maintain controllable particle size and spherical morphology while improving tetragonality.

[0061] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hydrothermal synthesis method for spherical barium titanate powder with controllable ammonium salt tetragonal phase particle size, characterized in that, Includes the following steps: S1. Under cooling and stirring conditions, titanium tetrachloride is added to deionized water to obtain a titanium-containing precursor solution. S2. Dissolve barium hydroxide in deionized water to obtain a barium-containing alkaline solution; S3. Mix the titanium-containing precursor solution with the barium-containing alkaline solution, control the Ba / Ti molar ratio to be 0.998-1.003, add ammonia to adjust the pH of the system to be greater than 13, and add a composite dispersant to obtain an ammonium salt-assisted hydrothermal reaction solution. S4. The ammonium salt-assisted hydrothermal reaction solution is placed in a reaction vessel for hydrothermal reaction to obtain barium titanate slurry. S5. The barium titanate slurry is washed, filtered, dehydrated, dried and depolymerized to obtain primary barium titanate powder; S6. Add heat treatment dispersant to the primary barium titanate powder, mix and heat treat at 900-1000℃, then crush, grind and classify to obtain spherical barium titanate powder. The spherical barium titanate powder has a d50 of 100-200 nm and a tetragonality c / a greater than 1.

008.

2. The hydrothermal synthesis method of ammonium salt high tetragonal phase spherical barium titanate powder with controllable particle size according to claim 1, characterized in that, In step S1, titanium tetrachloride is added dropwise to deionized water at 0-10℃, and the system temperature is controlled not to exceed 15℃ during the dropwise addition process to obtain a titanium-containing precursor solution with a Ti concentration of 0.1-1.0 mol / L.

3. The hydrothermal synthesis method of ammonium salt high tetragonal phase spherical barium titanate powder with controllable particle size according to claim 1, characterized in that, In step S2, the barium hydroxide is barium hydroxide or barium hydroxide octahydrate, the dissolution temperature is 60-90℃, and the concentration of Ba in the resulting barium-containing alkaline solution is 0.1-1.0 mol / L.

4. The hydrothermal synthesis method of ammonium salt high tetragonal phase spherical barium titanate powder with controllable particle size according to claim 1, characterized in that, In step S3, the mass concentration of the ammonia water is 20-28%, and the pH of the adjusted system is 13.1-14.

2.

5. The hydrothermal synthesis method of ammonium salt high tetragonal phase spherical barium titanate powder with controllable particle size according to claim 1, characterized in that, In step S3, the composite dispersant is composed of ammonium polyacrylate, ammonium citrate, polyethylene glycol and polyvinylpyrrolidone in a mass ratio of 1:(0.1-0.5):(0.1-0.4):(0.05-0.3).

6. The hydrothermal synthesis method of ammonium salt high tetragonal phase spherical barium titanate powder with controllable particle size according to claim 1, characterized in that, In step S3, the amount of the composite dispersant added, based on its effective complexing and dispersing groups, is 1.0-1.5% of the molar amount of Ti in the titanium source.

7. The hydrothermal synthesis method of ammonium salt high tetragonal phase spherical barium titanate powder with controllable particle size according to claim 1, characterized in that, In step S4, the hydrothermal reaction temperature is 160-220℃, the reaction time is 3-12h, the stirring speed is 100-500r / min, and the reactor filling rate is 60-80%.

8. The hydrothermal synthesis method of ammonium salt high tetragonal phase spherical barium titanate powder with controllable particle size according to claim 1, characterized in that, In step S5, the filtrate is washed until its conductivity is not higher than 80 μS / cm and its chloride ion content is not higher than 50 mg / L; the drying temperature is 80-120℃ and the drying time is 4-12 h.

9. The hydrothermal synthesis method of ammonium salt high tetragonal phase spherical barium titanate powder with controllable particle size according to claim 1, characterized in that, In step S6, the heat treatment dispersant is one or more of ammonium polyacrylate, ammonium citrate, and polyethylene glycol, and the amount added is 0.2-1.0% of the mass of the primary barium titanate powder; The heat treatment holding time is 1-4 hours, and the heating rate is 2-5℃ / min.

10. A spherical barium titanate powder with controllable ammonium salt high tetragonal phase particle size, characterized in that, The spherical barium titanate powder is prepared by the hydrothermal synthesis method according to any one of claims 1-10; the d50 of the spherical barium titanate powder is 100-200 nm, the tetragonality c / a is 1.008-1.012, the Ba / Ti molar ratio is 0.998-1.003, and the powder is spherical.

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