Multilayer ceramic capacitor, high-activity nano barium titanate powder for multilayer ceramic capacitor and preparation method of high-activity nano barium titanate powder

Abstract

The invention relates to the technical field of dielectric ceramic powder preparation processes, in particular to a multilayer ceramic capacitor, high-activity nano barium titanate powder for the multilayer ceramic capacitor and a preparation method of the high-activity nano barium titanate powder, and the method comprises the following steps: (1) reacting soluble barium salt with a precipitator to obtain barium carbonate precursor particles with high specific surface area; (2) uniformly coating the surfaces of the barium carbonate precursor particles with nano titanium dioxide particles by using a supercritical fluid flash evaporation technology to form a composite precursor; and (3) carrying out solid-phase synthesis reaction on the composite precursor, and sintering to obtain the nano barium titanate powder. Through the synergistic effect of two means of high-activity precursor preparation and nanoscale uniform coating, the composite precursor with extremely high specific surface area, surface energy and microcosmic uniformity is prepared, the thermal sintering temperature is effectively reduced, abnormal growth of crystal grains and lattice distortion are restrained, and the preparation method has the advantages that the preparation process is simple, and the preparation cost is low. The tetragonality of the nano barium titanate powder is obviously improved.

Description

Technical Field

[0001] This invention relates to the field of dielectric ceramic powder preparation technology, and in particular to multilayer ceramic capacitors, highly active nano-barium titanate powder for multilayer ceramic capacitors, and their preparation methods. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are cornerstone components of modern electronic devices. With the explosive growth of 5G communications, new energy vehicles, and wearable devices, the market has placed almost stringent demands on MLCCs for miniaturization and high capacitance. Barium titanate is a key functional material for manufacturing its core dielectric layer. Its high dielectric properties are the physical basis for achieving miniaturization and high capacitance in MLCCs. The degree of nano-sizing of its powder, the purity of its crystal structure, and its chemical homogeneity directly determine the performance, reliability, and technological ceiling of MLCCs. Therefore, precise control of barium titanate materials and breakthroughs in its preparation processes are essentially the core competitive advantage driving the progress of MLCCs and even the entire electronics industry.

[0003] The traditional solid-state method, widely used in the industry for preparing barium titanate powder, relies on the mechanical mixing and high-temperature calcination of barium carbonate and titanium dioxide micron-sized powders. While this method offers advantages such as low cost and simple process, it suffers from fundamental defects in atomic-scale mixing uniformity. During mechanical ball milling, raw material particles of different densities and hardness struggle to achieve molecular-level contact, leading to significant deviations in the barium-titanium ratio from the stoichiometric ratio in localized areas. This uneven mixing necessitates raising the reaction temperature to above 1200℃, which in turn causes abnormal grain coarsening and the formation of hard agglomerates. More problematic is that impurities (such as Zr and Al ions) introduced by prolonged ball milling can disrupt the integrity of the barium titanate lattice, ultimately causing batch-to-batch fluctuations in the electrical properties of the ceramic dielectric. Numerous studies have shown that powders prepared by the traditional solid-state method typically have an average particle size exceeding 400 nanometers, and the tetragonal phase content (c / a ratio) is generally below 1.008, making it difficult to meet the stringent requirements of high-end MLCCs for dielectric constant temperature stability.

[0004] To overcome the limitations of solid-phase methods, liquid-phase methods (such as co-precipitation and hydrothermal methods) have been developed for the preparation of nanoscale barium titanate. These methods can achieve atomic-level mixing, significantly improving the controllability of product particle size and crystal form. However, their inherent drawbacks are equally prominent: expensive organic titanium sources (such as tetrabutyl titanate) lead to a surge in raw material costs; the treatment of large amounts of wastewater containing heavy metals brings severe environmental pressure; and the difference in precipitation rates between barium and titanium ions during the reaction process can easily cause stoichiometric drift. More importantly, the powder synthesized by liquid-phase methods has extremely high surface energy, and the unavoidable hard agglomeration during drying and calcination often negates the initial uniformity advantage. In actual production, the equipment investment intensity and energy consumption level of liquid-phase methods far exceed those of solid-phase methods, making it difficult to promote large-scale applications.

[0005] In recent years, the industry has attempted to achieve breakthroughs through improved approaches. For example, adding dispersants to solid-state precursors improves mixing, but residual organic components can form amorphous phases at high temperatures, hindering grain growth. Other studies have used high-energy ball milling to activate raw materials, but excessive mechanical energy input damages the crystal lattice, leading to decreased sintering activity. These improvements have failed to fundamentally resolve the deep-seated contradiction between "mixing uniformity" and "reaction kinetics." Uniform mixing requires reducing particle size, but the high surface energy resulting from nano-sizing exacerbates high-temperature agglomeration. Low-temperature reactions can inhibit grain growth, but traditional mixing methods cannot provide sufficient reaction driving force. This technological deadlock means that existing processes are constantly making difficult compromises between particle size control, crystal phase purity, and production costs. Summary of the Invention

[0006] The present invention aims to address the shortcomings of the existing solid-phase method for preparing barium titanate powder, which suffers from uneven mixing and high reaction temperature. Therefore, it provides a highly active nano-barium titanate powder, its preparation method, and its application to overcome the above-mentioned deficiencies.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing highly active nano-barium titanate powder for multilayer ceramic capacitors, comprising the following steps: (1) A soluble barium salt solution and a carbonate-containing precipitant solution are instantaneously mixed and controlled to nucleate the reactants under the condition of applying a high-energy physical field to obtain barium carbonate precursor particles. (2) Using supercritical fluid flash evaporation technology, nano-titanium dioxide particles are uniformly coated on the surface of the barium carbonate precursor particles to form a composite precursor. (3) The composite precursor is subjected to a solid-state synthesis reaction and sintered to obtain barium titanate nanoparticles.

[0008] As described in the background section, the core contradiction currently facing the field of electronic ceramic materials lies in the irreconcilable conflict between the nanoscale particle size, high tetragonal phase purity, and batch consistency requirements of barium titanate powder for high-end multilayer ceramic capacitors and the inherent defects of traditional preparation processes in terms of mixing uniformity, reaction temperature, and cost control. Solid-phase methods are constrained by the microscopic inhomogeneities of mechanical mixing, forcing reliance on high-temperature reactions that lead to grain coarsening; while liquid-phase methods achieve molecular-level mixing, their complex processes and high costs make them difficult to scale up. The industry has attempted compromises, such as adding dispersants to solid-phase mixing, which has resulted in residual contamination, or pre-activating raw materials which has damaged lattice activity. These improvements have consistently failed to overcome the fundamental technical barrier that "uniform mixing" and "low-temperature reaction" cannot coexist.

[0009] The technological breakthrough of this application begins with a re-examination of the fundamental nature of the reaction. Traditional approaches focus on optimizing existing mixing or reaction steps, while this invention addresses the contradictions at their source by reconstructing the properties of precursors and the mixing mechanism. The first key step of this application focuses on the reactivation of barium carbonate precursors: achieving instantaneous mixing and controlled nucleation of soluble barium salts and precipitant solutions in an environment with a high-energy physical field. This design directly addresses the pain point of insufficient activity in traditional barium carbonate, namely, the limited specific surface area and low surface energy of micron-sized particles obtained by mechanical crushing. This application achieves homogeneous collisions at the molecular scale of reactants within milliseconds using high-energy physical fields (such as ultrasonic cavitation or microfluidic shearing), forcing the nucleation process to proceed explosively far from equilibrium. The resulting barium carbonate particles no longer rely on subsequent mechanical crushing to obtain small sizes, but instead become "active carriers" with intrinsic reaction driving force due to their high specific surface area and surface defects formed in situ. This shift from "passive crushing" to "active construction" lays an indispensable kinetic foundation for low-temperature reactions.

[0010] However, highly active precursors are only the first step in solving this problem. If traditional mechanical mixing methods are used to composite with titanium dioxide, the agglomeration tendency of nanoparticles will still lead to microscopic component segregation. This is precisely the core innovation of the second step in this application: This application utilizes supercritical fluid flash evaporation technology to achieve atomically precise coating of nano-titanium dioxide. When a supercritical fluid (such as carbon dioxide) carries dispersed titanium dioxide nanoparticles through a fluidized bed of barium carbonate precursor, the instantaneous release of pressure triggers fluid flash evaporation. This phase transition process produces two key effects: first, the rapid expansion from the supercritical state to the gaseous state "sprays" titanium dioxide nanoparticles onto the barium carbonate surface in single or multiple layers; second, the enormous energy released during flash evaporation promotes a tight physical-chemical bond between the two types of particles. This method fundamentally overturns the random contact mode of mechanical mixing, replacing it with a directional and quantitative coating logic, ensuring that each barium carbonate particle surface receives a stoichiometrically precise titanium dioxide coating. This "core-shell" structured composite precursor achieves, for the first time in a solid-phase system, atomic-level mixing homogeneity comparable to that of the liquid-phase method.

[0011] Finally, due to the high reactivity of barium carbonate providing ample reaction driving force, and the nanoscale coating of titanium dioxide shortening the diffusion distance to its limit, the traditional BaCO3-TiO2 solid-phase reaction, which requires temperatures above 1200℃, can now be fully carried out in a temperature range of over 100℃ below this. The low-temperature environment provides a dual benefit to the final product performance: on the one hand, it fundamentally inhibits abnormal grain growth, resulting in a breakthrough reduction in the average particle size of the powder to the nanoscale; on the other hand, the extreme mixing uniformity achieved by this invention allows for sufficient crystal transformation to be completed at a relatively lower temperature, yielding a tetragonal phase structure with few lattice defects and high purity (high c / a ratio). Crucially, this method fully retains the advantages of the solid-phase method—simple equipment and low cost—while avoiding the environmental and cost burdens of the liquid-phase method.

[0012] Therefore, this application constructs a novel paradigm for barium titanate powder preparation technology through a three-tiered innovation: "precursor activation regeneration—supercritical precision coating—low-temperature synergistic synthesis." This creates a positive feedback loop: the active precursor provides an ideal carrier for supercritical coating, precision coating creates a uniform reaction interface for the low-temperature reaction, and low-temperature synthesis, in turn, preserves the high activity imparted by the precursor. This closed-loop technology ultimately yields nano-barium titanate powder with finer particle size, superior crystal structure, and higher batch consistency, clearing material obstacles for the mass production of next-generation ultra-miniature, high-capacity MLCCs.

[0013] Preferably, the high-energy physical field in step (1) includes at least one of ultrasound, microwave or high-intensity shear field.

[0014] Preferably, step (1) is carried out in a continuous flow microreactor with a reaction residence time of less than 100 milliseconds.

[0015] Preferably, the barium carbonate precursor particles prepared in step (1) have a specific surface area of ​​6 m². 2 / g -15m 2 / g.

[0016] Preferably, step (2) includes: dispersing nano-sized titanium dioxide in supercritical carbon dioxide to form a highly dispersed suspension, and then injecting the suspension into barium carbonate precursor particles, thereby making the titanium dioxide nanoparticles uniformly coated on the surface of the barium carbonate precursor particles by rapid depressurization flash evaporation.

[0017] Preferably, the supercritical carbon dioxide temperature is 35℃-60℃ and the pressure is 10 MPa-25 MPa.

[0018] Preferably, after the supercritical fluid flash evaporation is completed, the composite precursor is further subjected to wet milling and spray drying in sequence to produce micron-sized spherical particles.

[0019] Preferably, the solid-phase synthesis reaction includes a two-stage heat preservation process: first, pre-decomposition and interface activation are carried out at 680℃-860℃, and then the final synthesis is completed at 1050℃-1250℃.

[0020] Secondly, the present invention also provides a highly active nano-barium titanate powder for multilayer ceramic capacitors, which is prepared by the method described above. The highly active nano barium titanate powder has a particle size of 100nm~400nm; The highly active nano-barium titanate powder has a tetragonal crystal form and a c / a ratio of 1.008 to 1.011.

[0021] Thirdly, the present invention also provides a multilayer ceramic capacitor prepared from highly active nano-barium titanate powder for multilayer ceramic capacitors as described above.

[0022] Therefore, the present invention has the following beneficial effects: (1) Improved reactivity from the source: The barium carbonate precursor prepared by the continuous flow microreaction technology in this application has extremely high specific surface area and surface energy, which lays the kinetic foundation for subsequent low-temperature solid-phase reactions; (2) Achieving ultimate mixing uniformity: This application innovatively adopts supercritical fluid flash evaporation technology for coating, which fundamentally solves the problem of micro-uniformity that traditional mechanical mixing cannot achieve, and ensures the accuracy of the Ba / Ti stoichiometric ratio on each particle; (3) Significantly reduce synthesis temperature and improve product performance: Due to the high activity of the precursor and the extreme uniformity of the mixture, the temperature of the solid-phase reaction can be reduced by 100-150℃ compared with the traditional process, which effectively inhibits grain growth. The final product has the advantages of small and uniform particle size, high tetragonality and good dispersibility. Attached Figure Description

[0023] Figure 1 This is a scanning electron microscope (SEM) image of the barium titanate nanoparticles prepared in Example 1.

[0024] Figure 2 The image shows a scanning electron microscope (SEM) image of the barium titanate nanoparticles prepared in Comparative Example 1.

[0025] Figure 3 The image shows the specific surface area of ​​barium titanate powder prepared by the traditional high-temperature solid-state method in Comparative Example 1.

[0026] Figure 4 The image shows the specific surface area of ​​the barium titanate powder prepared by the method of the present invention in Example 1.

[0027] Figure 5This is a test chart of the specific surface area of ​​barium titanate powder prepared by the method of the present invention in Example 5. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0029] Example 1 (1) Precursor preparation: Prepare a 1.0 mol / L barium chloride solution and a 1.0 mol / L ammonium carbonate solution. Pump the two solutions into a reactor with a power density of 30 W / cm³ at a total flow rate of 2 L / min. 2 An online mixing chamber using ultrasonic energy (residence time approximately 50 ms) was used to mix the slurry, which then entered a tubular reactor with an inner diameter of 2 mm. The slurry was collected, washed, and dried to obtain a BET of 12 m. 2 / g of highly active barium carbonate powder.

[0030] (2) Coating and homogenization: Take 1 kg of the above-mentioned highly active barium carbonate powder and place it in a fluidized bed. Separately, take nano-titanium dioxide (D) with a stoichiometric ratio (Ba / Ti = 1.000). 50 (≈30nm) dispersed in supercritical carbon dioxide at 40℃ and 15 MPa, and injected into a fluidized bed through a nozzle. The pressure drops instantaneously, causing the supercritical carbon dioxide to flash evaporate. The titanium dioxide nanoparticles carried are uniformly and firmly coated on the surface of the highly active barium carbonate powder particles, forming a composite precursor powder.

[0031] (3) Grinding and sintering: The composite precursor is made into a slurry with a solid content of 50% and wet-ground to a D50 of 80nm. After spray drying, it is kept at 840℃ for 3 hours in a roller kiln, and then heated to 1080℃ for 2 hours.

[0032] (4) Finished product processing: After secondary wet milling and drying, the sintered material is used to obtain the final barium titanate nanoparticles. The scanning electron microscope (SEM) image of the final product, barium titanate powder, is shown below. Figure 1 .

[0033] Example 2 (1) Precursor preparation: Prepare a 1.5 mol / L barium nitrate solution and a 1.5 mol / L sodium carbonate solution. Pump the two solutions into a reactor with a power density of 30 W / cm³ at a total flow rate of 2 L / min. 2An online mixing chamber using ultrasonic energy (residence time approximately 50 ms) was used to mix the slurry, which then entered a tubular reactor with an inner diameter of 2 mm. The slurry was collected, washed, and dried to obtain a BET of 11 m. 2 / g of highly active barium carbonate powder.

[0034] (2) Coating and homogenization: Take 1 kg of the above-mentioned highly active barium carbonate powder and place it in a fluidized bed. Separately, take nano-titanium dioxide (D) with a stoichiometric ratio (Ba / Ti = 1.000). 50 (≈50nm) dispersed in supercritical carbon dioxide at 35℃ and 10MPa, and injected into a fluidized bed through a nozzle. The pressure drops instantaneously, causing the supercritical carbon dioxide to flash evaporate. The titanium dioxide nanoparticles carried are uniformly and firmly coated on the surface of the highly active barium carbonate powder particles, forming a composite precursor powder.

[0035] (3) Grinding and sintering: The composite precursor is made into a slurry with a solid content of 45% and wet-ground to a D50 of 110 nm. After spray drying, it is kept at 780℃ for 5 hours in a roller kiln, and then heated to 1150℃ for 2 hours.

[0036] (4) Finished product processing: After the sintered material is wet-milled and dried twice, the final nano barium titanate powder is obtained.

[0037] Example 3 (1) Precursor preparation: Prepare 2 mol / L barium nitrate solution and 2 mol / L sodium carbonate solution. Pump the two solutions into a microwave generator (frequency 2.45 GHz, power density 50 W / cm³) at a total flow rate of 2.5 L / min. 3 The mixture is placed in a microreactor (residence time approximately 200 ms), and after mixing, the slurry enters a tubular reactor with an inner diameter of 2 mm. The slurry is collected, washed, and dried to obtain a BET of 9 m. 2 / g of highly active barium carbonate powder.

[0038] (2) Coating and homogenization: Take 1 kg of the above-mentioned highly active barium carbonate powder and place it in a fluidized bed. Separately, take nano-titanium dioxide (D) with a stoichiometric ratio (Ba / Ti = 1.000). 50 (≈30nm) dispersed in supercritical propane at 120℃ and 8 MPa, and injected into a fluidized bed through a nozzle. The pressure drops instantaneously, causing the supercritical propane to flash evaporate. The titanium dioxide nanoparticles carried are uniformly and firmly coated on the surface of the highly active barium carbonate powder particles, forming a composite precursor powder.

[0039] (3) Grinding and sintering: The composite precursor is made into a slurry with a solid content of 45% and wet-ground to a D50 of 85nm. After spray drying, it is kept at 850℃ for 3 hours in a roller kiln, and then heated to 1100℃ for 2 hours.

[0040] (4) Finished product processing: After the sintered material is wet-milled and dried twice, the final nano barium titanate powder is obtained.

[0041] Example 4 (1) Precursor preparation: Prepare 0.8 mol / L barium chloride solution and 0.8 mol / L ammonium carbonate solution. Pump the two solutions into a reactor with a power density of 50 W / cm³ at a total flow rate of 1 L / min. 2 An online mixing chamber using ultrasonic energy (residence time approximately 300 ms) was used to mix the slurry, which then entered a tubular reactor with an inner diameter of 2 mm. The slurry was collected, washed, and dried to obtain a BET of 6 m. 2 / g of highly active barium carbonate powder.

[0042] (2) Coating and homogenization: Take 1 kg of the above-mentioned highly active barium carbonate powder and place it in a fluidized bed. Separately, take nano-titanium dioxide (D) with a stoichiometric ratio (Ba / Ti = 1.000). 50 (≈30nm) dispersed in supercritical carbon dioxide at 50℃ and 20 MPa, and injected into a fluidized bed through a nozzle. The pressure drops instantaneously, causing the supercritical carbon dioxide to flash evaporate. The titanium dioxide nanoparticles carried are uniformly and firmly coated on the surface of the highly active barium carbonate powder particles, forming a composite precursor powder.

[0043] (3) Grinding and sintering: The composite precursor is made into a slurry with a solid content of 50% and wet-ground to a D50 of 100 nm. After spray drying, it is kept at 680℃ for 4 hours in a roller kiln, and then heated to 1250℃ for 3 hours.

[0044] Example 5 (1) The preparation of the precursor is the same as in Example 1.

[0045] (2) Coating and homogenization: Take 1 kg of the above-mentioned highly active barium carbonate powder and place it in a fluidized bed. Separately, take stoichiometric amounts of nano-titanium dioxide (D... 50 (≈30nm) dispersed in supercritical carbon dioxide at 60℃ and 25 MPa, and injected into a fluidized bed through a nozzle. The pressure drops instantaneously, causing the supercritical carbon dioxide to flash evaporate. The titanium dioxide nanoparticles carried are uniformly and firmly coated on the surface of the highly active barium carbonate powder particles, forming a composite precursor powder.

[0046] (3) Grinding and sintering: The composite precursor is made into a slurry with a solid content of 55% and wet-milled to a D50 of 60nm. After spray drying, it is kept at 860℃ for 1 hour in a roller kiln, and then heated to 1050℃ for 4 hours.

[0047] (4) Finished product processing: After the sintered material is wet-milled and dried twice, the final nano barium titanate powder is obtained.

[0048] Comparative Example 1 Take commercially available ordinary barium carbonate powder (BET≈2 m 2 Barium titanate powder (Ba / Ti = 1.000) and anatase titanium dioxide powder were dry-mixed in a ball mill for 8 hours at a stoichiometric ratio. The mixed powder was then calcined at 1250°C for 4 hours. The remaining processing steps were the same as in Example 1. A scanning electron microscope (SEM) image of the final product, barium titanate powder, from Comparative Example 1 is shown below. Figure 2 .

[0049] Comparative Example 2 The highly active barium carbonate powder prepared in step 1 of Example 1 was used, but it was mixed with titanium dioxide powder using a conventional dry mechanical mixing method for 8 hours, and then calcined at 1080°C for 2 hours. The remaining steps were the same as in Example 1.

[0050] Comparative Example 3 Commercially available ordinary barium carbonate powder (BET≈2 m) was used. 2 / g), but coated with titanium dioxide using the supercritical fluid flash evaporation technique described in step 2 of Example 1. Then calcined at 1080°C for 2 hours. The remaining steps are the same as in Example 1.

[0051] The performance of the barium titanate nanoparticles prepared in Examples 1-5 and Comparative Examples 1-3 was tested, and the test results are shown in Table 1 below.

[0052] Table 1 sample Synthesis temperature (°C) Final powder particle size (nm) Tetragonality (c / a) <![CDATA[Specific surface area (m 2 / g)]]> Example 1 1080 200 1.0105 5.2 Example 2 1150 235 1.0101 4.2 Example 3 1100 210 1.0103 4.7 Example 4 1250 350 1.0104 2.9 Example 5 1050 180 1.0104 5.8 Comparative Example 1 1250 450 1.0103 2.5 Comparative Example 2 1080 280 1.0082 3.3 Comparative Example 3 1080 250 1.0085 3.8 As shown in Table 1 above, the continuous flow micro-reaction technology and supercritical fluid flash evaporation technology in this application can be used to prepare composite precursors with extremely high specific surface area, surface energy and extremely high microscopic uniformity, thereby effectively reducing the hot sintering temperature, thus effectively suppressing the abnormal grain growth caused by high temperature, making the average particle size of the powder break through to the nanoscale, and reducing lattice distortion, significantly improving the tetragonality of the nano barium titanate powder.

[0053] from Figure 3 It can be seen that Comparative Example 1, prepared using the traditional high-temperature solid-state method, has an extremely low specific surface area, only 2.5 μm. 2 / g. This is related to... Figure 2 The morphological characteristics observed in Example 1, such as coarse particles, severe sintering, and the presence of numerous hard agglomerates, are completely consistent, indicating that a large amount of surface area is destroyed during the high-temperature sintering process. In contrast, the sample prepared using the method of this invention (Example 1) Figure 4 At a synthesis temperature of 1080℃, a particle size as high as 5.2 m was obtained. 2The specific surface area is / g. This is thanks to the unique "in-situ conversion of precursors - rapid sintering" mechanism of this invention, which effectively inhibits particle agglomeration, thereby preserving the high specific surface area characteristics of the nanoparticles. Furthermore, when the synthesis temperature is optimized to 1050℃, Example 5 ( Figure 5 The specific surface area reached 5.8 m². 2 / g, which is the highest value among all samples. This clearly demonstrates that the present invention can not only prepare barium titanate powder with a high specific surface area far superior to traditional methods, but also that its properties have good process controllability.

[0054] Comparing Comparative Example 1 with Example 1, we can see that Comparative Example 1 uses a traditional process that requires extremely high temperatures to carry out the reaction, and the final product has large particle size, unsatisfactory crystal form, and the worst performance.

[0055] Comparing Comparative Example 2 with Example 1, we can see that even though a highly active precursor was used in Comparative Example 2, the reaction was still insufficient if the mixing was uneven, and although the performance of the final product was improved, it was far inferior to that of the present invention. This proves the necessity of supercritical coating homogenization.

[0056] Comparing Comparative Example 3 with Example 1, we can see that even if the mixture in Comparative Example 3 is very homogeneous, if the precursor itself is not sufficiently active, the reaction kinetics are still limited, and the product performance cannot reach its optimal level. This demonstrates the necessity of preparing highly active precursors.

[0057] In summary, this invention achieves a synergistic effect of 1+1>2 through the combined use of "highly active precursor preparation" and "nanoscale uniform coating," which is key to the preparation of high-performance barium titanate powder. This provides a foundation for multilayer ceramic capacitors (MLCCs) requiring miniaturization and high capacitance.

[0058] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing highly active nano-barium titanate powder for multilayer ceramic capacitors, characterized in that, Includes the following steps: (1) A soluble barium salt solution and a carbonate-containing precipitant solution are instantaneously mixed and controlled to nucleate the reactants under the condition of applying a high-energy physical field to obtain barium carbonate precursor particles. (2) Using supercritical fluid flash evaporation technology, nano-titanium dioxide particles are uniformly coated on the surface of the barium carbonate precursor particles to form a composite precursor. (3) The composite precursor is subjected to a solid-state synthesis reaction and sintered to obtain barium titanate nanoparticles.

2. The method according to claim 1, characterized in that, The high-energy physical field mentioned in step (1) includes at least one of ultrasound, microwave or high-intensity shear field.

3. The method according to claim 1, characterized in that, Step (1) is carried out in a continuous flow microreactor with a reaction residence time of less than 500 milliseconds.

4. The method according to any one of claims 1-3, characterized in that, The barium carbonate precursor particles prepared in step (1) have a specific surface area of ​​6 m². 2 / g -15 m 2 / g.

5. The method according to claim 1, characterized in that, Step (2) includes: dispersing nano-sized titanium dioxide in a supercritical fluid to form a highly dispersed suspension, and then injecting the suspension into barium carbonate precursor particles, thereby making the titanium dioxide nanoparticles uniformly coated on the surface of the barium carbonate precursor particles by rapid depressurization flash evaporation.

6. The method according to claim 5, characterized in that, The supercritical fluid is supercritical carbon dioxide, with a temperature of 35℃-60℃ and a pressure of 10 MPa-25 MPa.

7. The method according to claim 1, 5, or 6, characterized in that, After the supercritical fluid flash evaporation is completed, the composite precursor is then subjected to wet milling and spray drying in sequence to produce micron-sized spherical particles.

8. The method according to claim 1, characterized in that, The solid-phase synthesis reaction includes a two-stage heat preservation process: first, pre-decomposition and interface activation are carried out at 680℃-860℃, and then the final synthesis is completed at 1050℃-1250℃.

9. A highly active nano-barium titanate powder for use in multilayer ceramic capacitors, characterized in that, It is prepared by any one of the methods described in claims 1-8 above; The highly active nano barium titanate powder has a particle size of 100nm~400nm; The highly active nano-barium titanate powder has a tetragonal crystal form and a c / a ratio of 1.008 to 1.

011.

10. A multilayer ceramic capacitor, which is prepared from the highly active nano-barium titanate powder for multilayer ceramic capacitors as described in claim 9.

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