Multilayer ceramic capacitor, highly active nano-barium titanate powder for multilayer ceramic capacitor, and method for manufacturing the same

Abstract

The present application relates to the technical field of dielectric ceramic powder preparation, and particularly relates to a multilayer ceramic capacitor, a high-activity nano-barium titanate powder for the multilayer ceramic capacitor and a preparation method of the high-activity nano-barium titanate powder, the method comprising the following steps: (1) reacting a soluble barium salt with a precipitator to obtain barium carbonate precursor particles with high specific surface area; (2) uniformly coating nano-titanium dioxide particles on the surface of the barium carbonate precursor particles by using a supercritical fluid flash technology to form a composite precursor; and (3) performing a solid-phase synthesis reaction on the composite precursor and sintering to obtain nano-barium titanate powder. The present application, through the synergistic effect of the two means of "high-activity precursor preparation" and "nano-level uniform coating", prepares a composite precursor with extremely high specific surface area, surface energy and micro-uniformity, effectively reduces the heat sintering temperature, suppresses abnormal grain growth and lattice distortion, and significantly improves the tetragonality of the nano-barium titanate powder.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dielectric ceramic powder preparation, and particularly relates to a multilayer ceramic capacitor, a high-activity nano-barium titanate powder for the multilayer ceramic capacitor and a preparation method thereof. BACKGROUND

[0002] The multilayer ceramic capacitor (MLCC) is a cornerstone component of modern electronic devices. With the explosive growth of 5G communication, new energy vehicles and wearable devices, the market has put forward almost stringent requirements for miniaturization and high capacitance of the MLCC. Barium titanate is a key functional material for manufacturing the core dielectric layer thereof, and its high dielectric property is the physical basis for realizing miniaturization and large capacity of the MLCC. The nanocrystallization degree, crystal structure purity and chemical uniformity of the powder directly determine the performance, reliability and technical upper limit of the MLCC. Therefore, the precise regulation of the barium titanate material and the breakthrough of the preparation process are essentially the core competition for promoting the progress of the MLCC and even the entire electronic industry.

[0003] At present, the traditional solid-phase method is widely used in the preparation of barium titanate powder in the industry, which depends on the mechanical mixing and high-temperature calcination of barium carbonate and titanium dioxide micropowder. Although this method has the advantages of low cost and simple process, it has a fundamental defect in the uniformity of atomic-scale mixing. During mechanical ball milling, particles of different densities and hardnesses are difficult to contact at the molecular level, resulting in a serious deviation of the barium-titanium ratio in local areas from the stoichiometric ratio. This uneven mixing problem forces the reaction temperature to be raised to above 1200°C, and the high-temperature environment causes abnormal coarsening of the crystal grains and formation of hard agglomerates. More troublesome is that the ball wear impurities (such as Zr and Al ions) introduced by long-time ball milling will damage the integrity of the barium titanate lattice, ultimately causing batch fluctuations in the electrical properties of the ceramic dielectric. A large number of studies have shown that the average particle size of the powder prepared by the traditional solid-phase method is usually above 400 nanometers, and the tetragonal phase content (c / a ratio) is generally lower than 1.008, which is difficult to meet the stringent requirements of high-end MLCCs for temperature stability of the dielectric constant.

[0004] To overcome the limitations of the solid-phase method, liquid-phase methods (such as coprecipitation and hydrothermal method) are developed for the preparation of nano-sized barium titanate. These methods can achieve atomic-level mixing, and the controllability of the product particle size and crystal form is significantly improved. However, their inherent defects are also prominent: the use of expensive organic titanium sources (such as tetrabutyl titanate) leads to a sharp increase in raw material costs, and the treatment of a large amount of heavy metal-containing wastewater brings severe environmental pressure. Moreover, the difference in precipitation rates of barium and titanium ions during the reaction process easily causes the stoichiometric ratio to deviate. More importantly, the surface energy of the powder synthesized by the liquid-phase method is extremely high, and the hard agglomeration phenomenon during the drying and calcination stages is difficult to avoid, which often offsets the advantages of uniformity in the early stage. In actual production, the equipment investment intensity and energy consumption level of the liquid-phase method far exceed those of the solid-phase method, making it difficult to popularize in large-scale applications.

[0005] In recent years, the industry has tried to seek breakthroughs by improving the route. For example, adding a dispersing agent in the solid phase method precursor to improve the mixing effect, but the residual organic components will form amorphous phase at high temperature to hinder grain growth; there are also studies that use high-energy ball milling to activate raw materials, but excessive mechanical energy input damages the lattice and leads to a decrease in sintering activity. These improvements have not fundamentally solved the deep-seated contradiction between "mixing uniformity" and "reaction kinetics", that is, uniform mixing requires reducing particle size, and the high surface energy brought by nanocrystallization will exacerbate high-temperature agglomeration; low-temperature reaction can inhibit grain growth, but traditional mixing methods cannot provide enough driving force for the reaction. This technical closed-loop dilemma has led to the existing process always being difficult to compromise between particle size control, phase purity and production cost. SUMMARY

[0006] The present application is to solve the defects of uneven mixing and high reaction temperature in the preparation of barium titanate powder by solid phase method in the prior art, and therefore provides a high-activity nanobarium titanate powder and a preparation method and application thereof to overcome the above-mentioned deficiencies.

[0007] To achieve the above-mentioned application purposes, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application first provides a preparation method of a high-activity nanobarium titanate powder for a multilayer ceramic capacitor, comprising the following steps:

[0009] (1) The soluble barium salt solution and the precipitant solution containing carbonate are reacted under the condition of applying a high-energy physical field to realize instantaneous mixing of reactants and controlled nucleation, so as to obtain barium carbonate precursor particles;

[0010] (2) The nanometer titanium dioxide particles are uniformly coated on the surface of the barium carbonate precursor particles by using supercritical fluid flash technology to form a composite precursor;

[0011] (3) The composite precursor is subjected to a solid phase synthesis reaction, and nanobarium titanate powder is obtained by sintering.

[0012] As described in the background, the core contradiction faced by the current electronic ceramic material field is that the high-end multilayer ceramic capacitor requires nanoscale particle size, high tetragonal phase purity and batch consistency of barium titanate powder, which forms an irreconcilable conflict with the inherent defects of traditional preparation process in mixing uniformity, reaction temperature and cost control. The solid phase method is forced to rely on high-temperature reaction due to the micro-uniformity of mechanical mixing, leading to grain coarsening; although the liquid phase method realizes molecular-level mixing, it is difficult to scale up due to complex process and high cost. The industry has tried to take a compromise route, that is, adding a dispersing agent in solid phase mixing, which causes residual pollution, or pre-activating raw materials, which damages the lattice activity. These improvements have not been able to break through the bottom-line technical barrier that "uniform mixing" and "low-temperature reaction" cannot coexist.

[0013] The technical breakthrough of the present application starts from re-examining the origin of the reaction. The traditional approach focuses on how to optimize the existing mixing or reaction steps, while the present application breaks the contradiction chain from the source by reconfiguring the precursor properties and mixing mechanism. The first key step of the present application focuses on the reactivation of barium carbonate precursor: soluble barium salt and precipitator solution are mixed instantaneously and controlled nucleation is achieved in the environment of applying high-energy physical field. This design directly targets the pain point of the low activity of traditional barium carbonate, i.e. the micron-sized particles obtained by mechanical crushing have limited specific surface area and low surface energy. The present application completes the homogeneous collision of reactant molecules at the molecular scale within milliseconds by high-energy physical field (such as ultrasonic cavitation or microfluidic shear), forcing the nucleation process to occur explosively under conditions far from equilibrium. The barium carbonate particles generated in this way no longer rely on mechanical crushing to obtain small size, but rely on the high specific surface area and surface defects formed in situ to become "active carriers" with intrinsic reaction driving force. This transformation from "passive crushing" to "active construction" lays an indispensable kinetic foundation for low-temperature reaction.

[0014] But the high-activity precursor is only the first step. If the traditional mechanical mixing method is used to compound with titanium dioxide, the agglomeration tendency of nanoparticles will still cause composition segregation at the microscale. This is the core innovation of the second step of the present application: the present application uses supercritical fluid flash technology to realize the atomic-level precise coating of nanometer titanium dioxide. When the supercritical fluid (such as carbon dioxide) carries dispersed titanium dioxide nanoparticles through the barium carbonate precursor fluidized bed, the instantaneous release of pressure triggers the flash of the fluid. This phase change process produces two key effects: first, the sharp expansion from supercritical state to gaseous state "sprays" titanium dioxide nanoparticles in single or multiple layers on the surface of barium carbonate; second, the huge energy released by flash evaporation promotes the formation of close physical-chemical bonds between the two particles. This method fundamentally overturns the random contact mode of mechanical mixing, and instead uses a directional and quantitative coating logic to ensure that each barium carbonate particle surface has a stoichiometrically accurate titanium dioxide coating layer. This "core-shell" composite precursor first realizes atomic-level mixing uniformity comparable to liquid-phase methods in the solid-phase system.

[0015] Finally, due to the high activity of barium carbonate providing sufficient reaction driving force, and the nanoscale coating of titanium dioxide shortening the diffusion distance to the limit, the traditional BaCO3-TiO2 solid phase reaction which needs to be carried out at 1200℃ or above can now be fully carried out in a temperature range of more than 100 degrees below this temperature. The low temperature environment produces a double gain on the performance of the final product: on the one hand, it fundamentally inhibits the abnormal growth of the crystal grains, and makes the average particle size of the powder break through to the nanometer level; on the other hand, the extreme mixing uniformity achieved by the present application enables sufficient crystal type conversion to be completed at a relatively lower temperature, and a tetragonal phase structure (high c / a ratio) with few lattice defects and high purity is obtained. What is particularly key is that the method completely retains the simple equipment and low cost gene of the solid phase method, avoiding the environmental and cost burden of the liquid phase method.

[0016] Therefore, through the three-level innovation of "precursor activity re-creation - supercritical precise coating - low-temperature collaborative synthesis", the present application constructs a new paradigm for the preparation of barium titanate powder, so that the three form a positive positive cycle: the active precursor provides an ideal carrier for supercritical coating, precise coating creates a uniform reaction interface for low-temperature reaction, and low-temperature synthesis in turn preserves the high activity of the precursor. This technical closed loop ultimately gives birth to nanometer barium titanate powder with finer particle size, better crystal type, and higher batch consistency, which sweeps away the material obstacles for mass production of the next generation of ultra-micro, high-capacity MLCC.

[0017] As a preferred, the high-energy physical field in step (1) comprises at least one of ultrasonic wave, microwave or high-intensity shear field.

[0018] As a preferred, step (1) is carried out in a continuous flow microreactor with a reaction residence time less than 100 milliseconds.

[0019] As a preferred, the specific surface area of the barium carbonate precursor particles prepared in step (1) is 6 m 2 / g - 15 m 2 / g.

[0020] As a preferred, step (2) comprises: dispersing nanoscale titanium dioxide in supercritical carbon dioxide to form a highly dispersed suspension, and then injecting the suspension into the barium carbonate precursor particles, so that the titanium dioxide nanoparticles are uniformly coated on the surface of the barium carbonate precursor particles by rapid pressure reduction flash evaporation.

[0021] As a preferred, the temperature of the supercritical carbon dioxide is 35℃-60℃, and the pressure is 10 MPa-25 MPa.

[0022] As a preferred, after the supercritical fluid flash evaporation, the step of sequentially carrying out wet grinding and spray drying on the composite precursor to prepare micron-sized spherical particles is further included.

[0023] As preferred, the solid phase synthesis reaction comprises a two-stage holding procedure: pre-decomposition and interface activation at 680-860℃, and final synthesis at 1050-1250℃.

[0024] In a second aspect, the present application further provides a high-activity nano-barium titanate powder for multilayer ceramic capacitors, which is prepared by the method as described above.

[0025] The high-activity nano-barium titanate powder has a particle size of 100-400 nm.

[0026] The high-activity nano-barium titanate powder has a tetragonal crystal form, and a c / a value ratio of 1.008-1.011.

[0027] In a third aspect, the present application further provides a multilayer ceramic capacitor prepared from the high-activity nano-barium titanate powder for multilayer ceramic capacitors as described above.

[0028] Therefore, the present application has the following beneficial effects:

[0029] (1) The reaction activity is improved from the source: the barium carbonate precursor prepared by the continuous flow micro-reaction technology has a very high specific surface area and surface energy, which lays a kinetic foundation for the subsequent low-temperature solid phase reaction;

[0030] (2) The mixing uniformity is achieved: the supercritical fluid flash technology is used for coating in the present application, which fundamentally solves the micro-uniformity problem that cannot be achieved by traditional mechanical mixing, and ensures the accuracy of Ba / Ti stoichiometric ratio on each particle;

[0031] (3) The synthesis temperature is significantly reduced, and the product performance is improved: due to the high activity of the precursor and the extreme uniformity of the mixing, the temperature of the solid phase reaction can be reduced by 100-150℃ compared with the traditional process, which effectively inhibits the grain growth, and the final product has the advantages of small and uniform particle size, high tetragonality, good dispersity, etc. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 FIG. 1 is a scanning electron microscope (SEM) image of the nano-barium titanate powder prepared in Example 1.

[0033] Figure 2 FIG. 2 is a scanning electron microscope (SEM) image of the nano-barium titanate powder prepared in Comparative Example 1.

[0034] Figure 3 FIG. 3 is a specific surface area test chart of the barium titanate powder prepared by the traditional high-temperature solid phase method in Comparative Example 1.

[0035] Figure 4This is a test chart of the specific surface area of ​​barium titanate powder prepared by the method of the present invention in Example 1.

[0036] Figure 5 This 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

[0037] 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.

[0038] Example 1

[0039] (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.

[0040] (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.

[0041] (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.

[0042] (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 .

[0043] Example 2

[0044] (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. 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 11 m. 2 / g of highly active barium carbonate powder.

[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 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.

[0046] (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.

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

[0048] Example 3

[0049] (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.

[0050] (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.

[0051] (3) Milling and sintering: The composite precursor was made into a slurry with solid content of 45%, wet-milled to D50 of 85 nm. After spray drying, it was sintered in a roller hearth kiln at 850°C for 3 hours, and then heated to 1100°C for 2 hours.

[0052] (4) Product processing: After secondary wet-milling and drying, the sintered material obtained the final nano-barium titanate powder.

[0053] Example 4

[0054] (1) Precursor preparation: A 0.8 mol / L barium chloride solution and a 0.8 mol / L ammonium carbonate solution were prepared. The two solutions were pumped into an online mixing chamber with a power density of 50 W / cm 2 supplied ultrasonic energy (residence time of about 300 ms) at a total flow rate of 1 L / min and an equal volume flow rate. After mixing, the slurry entered a 2 mm inner diameter tubular reactor. The slurry was collected, washed, and dried to obtain a high-activity barium carbonate powder with a BET of 6 m 2 / g.

[0055] (2) Coating and homogenization: 1 kg of the above high-activity barium carbonate powder was placed in a fluidized bed. Another stoichiometric ratio (Ba / Ti = 1.000) of nano-titanium dioxide (D 50 ≈30 nm) was dispersed in supercritical carbon dioxide at 50°C and 20 MPa, and injected into the fluidized bed through a nozzle. The pressure was instantaneously reduced, causing the supercritical carbon dioxide to flash, and the carried titanium dioxide nanoparticles uniformly and firmly coated on the surface of the high-activity barium carbonate powder particles, forming a composite precursor powder.

[0056] (3) Milling and sintering: The composite precursor was made into a slurry with a solid content of 50%, wet-milled to D50 of 100 nm. After spray drying, it was sintered in a roller hearth kiln at 680°C for 4 hours, and then heated to 1250°C for 3 hours.

[0057] Example 5

[0058] (1) Precursor preparation: The same as Example 1.

[0059] (2) Coating and homogenization: 1 kg of the above high-activity barium carbonate powder was placed in a fluidized bed. Another stoichiometric ratio of nano-titanium dioxide (D 50 ≈30 nm) was dispersed in supercritical carbon dioxide at 60°C and 25 MPa, and injected into the fluidized bed through a nozzle. The pressure was instantaneously reduced, causing the supercritical carbon dioxide to flash, and the carried titanium dioxide nanoparticles uniformly and firmly coated on the surface of the high-activity barium carbonate powder particles, forming a composite precursor powder.

[0060] (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.

[0061] (4) Finished product processing: After the sintered material is wet-milled and dried twice, the final nano barium titanate powder is obtained.

[0062] Comparative Example 1

[0063] 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 .

[0064] Comparative Example 2

[0065] 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.

[0066] Comparative Example 3

[0067] 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.

[0068] 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.

[0069] Table 1

[0070] Sample Synthesis temperature (°C) Final powder particle size (nm) Tetragonality (c / a) 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

[0071] 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.

[0072] from Figure 3It 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. 2 The 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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 nucleated under the condition of applying a high-energy physical field to obtain barium carbonate precursor particles. The high-energy physical field mentioned in step (1) includes at least one of ultrasound and microwave, and step (1) is carried out in a continuous flow microreactor with a reaction residence time of less than 500 milliseconds; (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-phase synthesis reaction and sintered to obtain nano-barium titanate powder.

2. The method according to any one of claims 1, 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.

3. 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.

4. The method according to claim 3, characterized in that, The supercritical fluid is supercritical carbon dioxide, with a temperature of 35℃-60℃ and a pressure of 10 MPa-25 MPa.

5. The method according to claim 1, 3, or 4, 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.

6. 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℃.

7. 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 1-6 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 value of 1.008~1.

011.

8. A multilayer ceramic capacitor, which is prepared from the highly active nano-barium titanate powder for multilayer ceramic capacitors as described in claim 7.

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