Multilayer ceramic capacitor, method for preparing high-performance nano-barium titanate powder for multilayer ceramic capacitor

Abstract

The present application relates to the technical field of dielectric ceramic powder preparation, and particularly relates to a multilayer ceramic capacitor and a method for preparing high-performance nano-barium titanate powder used for the multilayer ceramic capacitor, the method comprising the following steps: high-purity titanium hydroxide precursor and solid-state barium source are mixed under the condition of deep cold medium at low temperature, so as to form an amorphous composite precursor with high reactivity, and finally, the nano-barium titanate powder is generated through a hydrothermal synthesis reaction. The present application realizes the forced mixing of the titanium hydroxide precursor and the solid-state barium source at the solid state through the low-temperature cryogenic grinding, so as to physically ensure that the Ba / Ti ratio is highly consistent in each micro area, and the problem of the out-of-control stoichiometric ratio is solved from the source. Meanwhile, the high activation of the precursor shortens the hydrothermal reaction time, greatly reduces the calcination temperature, effectively inhibits the abnormal growth of the crystal grains, and makes the product particle size distribution narrower and the performance better.

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 and a method for preparing high-performance nano-barium titanate powder for the multilayer ceramic capacitor. BACKGROUND

[0002] The multilayer ceramic capacitor (MLCC) is an extremely important basic electronic component, which is internally composed of hundreds or even thousands of layers of ceramic dielectric and metal electrodes alternately stacked to store a large amount of electric charge in a small volume. Barium titanate is the core raw material for the ceramic dielectric layer of the MLCC, and its unique crystal structure makes it have extremely high dielectric properties, which is the physical basis for the MLCC to achieve ultra-high capacitance. It can be said that the quality (such as purity, particle size and crystal form) of the barium titanate powder directly determines the performance, reliability and miniaturization level of the MLCC. However, in industrial production, the industry has long been faced with a difficult contradiction: the existing process cannot simultaneously achieve the three key requirements of low-temperature synthesis, accurate composition control and high purity.

[0003] The current mainstream preparation methods include solid phase method and liquid phase method. Among them, the solid phase method is to mechanically mix barium carbonate and titanium dioxide powders, and then complete the reaction by calcining at a high temperature of 1200 DEG C or above. Although this method is simple in equipment, it has a fundamental limitation: the raw materials cannot be uniformly mixed at the molecular level, resulting in inconsistent barium-titanium ratio in different areas. In order to compensate for this unevenness, it is necessary to add excess barium salt in production, which in turn leads to the formation of impurity phases at the grain boundaries due to excess components, resulting in unstable electrical properties of the final product. More seriously, the high-temperature environment will promote the excessive growth of the crystal grains, and subsequent strong crushing is necessary, but the crushing process will introduce foreign impurities such as iron and silicon, thereby significantly reducing the insulation performance of the product.

[0004] The hydrothermal synthesis technology was once highly expected. This method allows barium salt and titanium salt solutions to react directly in an autoclave at a moderate temperature of 150-200 DEG C. In theory, this liquid phase reaction should be more uniform, but in practice, new problems are found: (1) Because the dissolution rate of barium ions is much faster than that of titanium ions, the reaction rates of the two are seriously mismatched, and this difference leads to a difference of more than 5% in the barium-titanium ratio in different areas of the product. (2) More troublesome is that if chloride-containing raw materials (such as titanium tetrachloride) are used, chloride ions will be firmly adsorbed on the surface of the crystal. Conventional water washing cannot completely remove them. These residual chlorides will form pores when volatilized during subsequent sintering, directly affecting the service life of the capacitor. (3) In addition, the nanoparticles generated by the hydrothermal reaction are prone to clumping and agglomeration, forming hard agglomerates after drying, forcing downstream manufacturers to perform secondary crushing, which in turn damages the crystal structure.

[0005] Currently, the industry has tried various improvement solutions: such as adding a wet mixing step to the solid-state method, or equipping the hydrothermal method with an ultrasonic vibration device. However, the actual effects are limited. Although premixing can improve uniformity, it cannot solve the grain coarsening caused by high temperature; although ultrasound can temporarily break up particles, it accelerates ion dissolution, which amplifies the compositional deviation. This technical bottleneck makes it difficult to meet the requirements for insulation performance and particle size uniformity of the 200-500nm high-purity barium titanate powder required for high-end MLCCs. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of existing nano-barium titanate powders in meeting the requirements of insulation performance and particle size uniformity. Therefore, it provides a multilayer ceramic capacitor and a method for preparing high-performance nano-barium titanate powder for multilayer ceramic capacitors to overcome the above-mentioned deficiencies.

[0007] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing high-performance barium titanate nanoparticles for multilayer ceramic capacitors, comprising the following steps:

[0009] (a) Titanium hydroxide was washed with pure water in multiple countercurrent stages under membrane filtration conditions until the conductivity of the filtrate was less than 1000 μS / cm, thus obtaining a high-purity titanium hydroxide precursor.

[0010] (b) A high-purity titanium hydroxide precursor and a solid barium source were cryogenically ground in the presence of a cryogenic medium at an environment of -100°C to -196°C, with a molar ratio of barium atoms to titanium atoms of 1.000. This forced the materials to achieve embedded mixing at the nanoscale, thereby forming an amorphous composite precursor with high reactivity.

[0011] (c) The amorphous composite precursor obtained in step (b) is subjected to a hydrothermal synthesis reaction to generate barium titanate nanoparticles.

[0012] As described in the background section, the preparation of high-performance barium titanate nanoparticles has always been a core challenge in the field of electronic materials, with controlling the mixing state of the precursors being a particularly difficult aspect. In traditional wet mixing, the solvation layer prevents atomic-level contact between barium and titanium ions; while dry mechanical mixing, due to the plastic deformation of the material at room temperature, results in particles only adhering to the surface and failing to penetrate deeply. Therefore, neither of these apparent mixing methods can achieve uniform dispersion at the molecular scale. Even more challenging is that the difference in dissolution rates between barium and titanium ions during the hydrothermal reaction initiation rapidly amplifies the initial inhomogeneity, ultimately leaving permanent compositional defects during crystal growth.

[0013] To address this technical problem in existing technologies, this application creatively introduces a solid-state forced homogenization technology under cryogenic conditions. Its core breakthrough lies in utilizing the embrittlement effect of cryogenic media (e.g., cooling materials to below -100°C with liquid nitrogen) to transform the originally ductile precursor filter cake into a brittle state. At this point, high-energy mechanical grinding is no longer merely physical pulverization; it creates a large number of fresh, active interfaces at the moment of fracture, thereby enabling the micro-regions of titanium hydroxide and solid barium sources (such as barium hydroxide octahydrate) to be strongly dispersed and intercalated at the nanoscale, forming a unique three-dimensional interpenetrating structure. This amorphous composite precursor overturns the traditional reaction pathway: it avoids solvent interference in wet mixing, overcomes the insufficient dispersion in dry mixing, and, more importantly, locks in the precise spatial distribution of the barium-titanium atomic ratio before the reaction.

[0014] When this pre-homogenized amorphous precursor enters the reactor, the surface energy activated by cryogenic grinding significantly enhances its reactivity. This drastically shortens the hydrothermal process, which would normally take several hours, and ensures that the reaction occurs entirely within a homogeneous microenvironment. This means that barium-titanium ions can bond directly without long-range diffusion, thus fundamentally eliminating regional concentration fluctuations. Experiments have demonstrated that the barium-titanium molar ratio deviation of the powder obtained using the method described in this application can be controlled within the ten-thousandths range, far superior to the fluctuation range of several percent in traditional processes.

[0015] From an industry perspective, the technology in this application is the first to successfully bridge the performance triangle of "ultra-fine particle size, precise stoichiometry, and high purity." Traditional processes require difficult trade-offs among these three objectives, while this method achieves synergistic optimization through innovative control of the precursor state. It avoids the energy consumption of high-temperature routes and fundamentally overcomes the inherent defects of wet processing methods, providing underlying technological support for the localization of high-end MLCC materials.

[0016] Preferably, the cryogenic medium includes liquid nitrogen or liquid helium.

[0017] In step (a), the temperature of the high-purity water in the multi-stage countercurrent washing is 30℃-60℃.

[0018] This application involves washing titanium hydroxide under membrane filtration conditions with high-purity hot water in multiple stages of countercurrent washing until the conductivity of the filtrate is below 1000 μS / cm, thereby completely removing impurity ions (such as chloride ions) and laying a high-purity foundation for subsequent cryogenic grinding and hydrothermal synthesis.

[0019] In traditional processes, residual impurities are a persistent problem. Simple water washing can only remove surface-adsorbed ions, but cannot eradicate chloride ions embedded in the micropores or interstices of the precursor. These impurities are like lurking destroyers, volatilizing into pores or reducing insulation performance in subsequent reactions.

[0020] This method innovatively achieves deep purification through a combination of multi-stage countercurrent washing and membrane filtration: the countercurrent design allows fresh hot water to continuously contact materials with high impurity concentrations, desorbing ions layer by layer like a highly efficient "wash"; membrane filtration physically blocks impurities from backmixing, ensuring purification efficiency; and the conductivity threshold (<1000 μS / cm) serves as an objective monitoring point, accurately quantifying the degree of impurity removal and avoiding the randomness of traditional experience-based judgments.

[0021] Preferably, the hydrothermal synthesis reaction in step (c) is carried out at 150°C to 200°C.

[0022] Preferably, the process also includes calcining the generated barium titanate nanoparticles to control grain growth and crystal transformation.

[0023] Preferably, the calcination treatment is carried out in an inert or oxidizing atmosphere at a temperature of 800°C to 1200°C.

[0024] Preferably, the nano-barium titanate powder after hydrothermal synthesis or calcination is further subjected to wet grinding to deagglomerate, followed by spray drying to obtain the final nano-barium titanate powder product.

[0025] Secondly, the present invention also provides a high-performance barium titanate nanopowder for multilayer ceramic capacitors, which is prepared by the above method.

[0026] The average particle size of the high-performance nano barium titanate powder is 100nm-400nm.

[0027] The molar ratio of Ba atoms to Ti atoms in the high-performance nano-barium titanate powder is 1.000 ± 0.005.

[0028] The c / a value of the high-performance nano barium titanate powder is 1.008-1.011.

[0029] Thirdly, the present invention also provides a multilayer ceramic capacitor prepared from the aforementioned high-performance nano-barium titanate powder.

[0030] Therefore, the present invention has the following beneficial effects:

[0031] (1) Intrinsic stoichiometric accuracy: By “low-temperature cryogenic grinding”, the titanium hydroxide precursor and the solid barium source are forcibly mixed in the solid state, thus physically ensuring that the Ba / Ti ratio is highly consistent in each micro-region, without the need for subsequent complex online compensation, thus solving the problem of stoichiometric ratio runaway from the source;

[0032] (2) Strong controllability of product particle size: This process can directly obtain ultrafine (<100nm) powder prepared by hydrothermal method, and can also obtain a series of products with larger particle size and better crystal form through subsequent controllable calcination steps, with a wide range of applications;

[0033] (3) Significantly improve reaction efficiency and product performance: The high activation of the precursor shortens the hydrothermal reaction time and the subsequent calcination temperature is also lower than that of the traditional method, which effectively inhibits abnormal grain growth, resulting in a narrower particle size distribution and better performance of the product. Attached Figure Description

[0034] Figure 1 This is an electron microscope image of the barium titanate nanoparticles obtained by hydrothermal reaction in Example 1 of the present invention.

[0035] Figure 2 This is an electron microscope image of the barium titanate nanoparticles obtained after calcination in Example 1 of the present invention. Detailed Implementation

[0036] 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.

[0037] Example 1

[0038] Step (1): In a 20L reactor, mix 10L of pure water cooled to 5℃ with 1.7Kg of titanium tetrachloride, and add ammonia water dropwise to adjust the pH to alkaline conditions to obtain titanium hydroxide precursor slurry.

[0039] Step (2): Filter the slurry using a small ceramic membrane filtration system and wash it with pure water at 50°C until the conductivity of the filtrate is below 700 µs / cm.

[0040] Step (3): Freeze homogenization: The purified titanium hydroxide filter cake and barium hydroxide octahydrate were added together in a 20L cryogenic grinder pre-cooled with liquid nitrogen at a molar ratio of barium atoms to titanium atoms of 1.000. The mixture was then ground at -150℃ for 2 hours to obtain a uniform composite precursor powder.

[0041] Step (4): The above powder is mixed with pure water to form a slurry, wherein the mass ratio of water to composite precursor powder is 10:1. The slurry is pumped into a 20L autoclave, heated to 170℃, and held at that temperature for 3 hours for hydrothermal synthesis to obtain nano-barium titanate powder. The morphology of the obtained powder is as follows:Figure 1 As shown, the primary particle size is between 70-80 nm and the distribution is very uniform.

[0042] Step (5): Calcination: After filtration and drying, the hydrothermal product is placed in a roller kiln and calcined at 950°C for 2 hours in air. The morphology of the calcined powder is as follows: Figure 2 As shown, the grains grew uniformly to approximately 220 nm. The calcined powder was then subjected to wet sand milling to break up the sintered agglomerates, followed by spray drying to obtain the final product.

[0043] Example 2

[0044] Step (1) is the same as in Example 1.

[0045] Step (2): Filter the slurry using a small ceramic membrane filtration system and wash it with pure water at 30°C until the conductivity of the filtrate is less than 1000 µs / cm.

[0046] Step (3) Freeze homogenization: The purified titanium hydroxide filter cake and barium hydroxide octahydrate were added together in a 20L cryogenic grinder pre-cooled with liquid nitrogen at a molar ratio of barium atoms to titanium atoms of 1.000. The mixture was then ground at -100℃ for 5 hours to obtain a uniform composite precursor powder.

[0047] Step (4) The above powder is made into a slurry and pumped into a 20L high-pressure reactor. The temperature is raised to 150℃ and kept at the temperature for 5 hours for hydrothermal synthesis to obtain nano barium titanate powder.

[0048] Step (5) Calcination: After filtering and drying, the hydrothermal product is placed in a roller kiln and calcined at 800°C for 5 hours under a nitrogen atmosphere. The calcined powder is then wet-milled to break up the sintered agglomerates, and subsequently spray-dried to obtain the final product.

[0049] Example 3

[0050] Step (1) is the same as in Example 1.

[0051] Step (2): Filter the slurry using a small ceramic membrane filtration system and wash it with pure water at 60°C until the conductivity of the filtrate is below 600 µs / cm.

[0052] Step (3) Freezing and homogenization: The purified titanium hydroxide filter cake and barium hydroxide octahydrate were added together in a 20L cryogenic grinder pre-cooled with liquid nitrogen at a molar ratio of barium atoms to titanium atoms of 1.000. The mixture was then ground at -196℃ for 2 hours to obtain a uniform composite precursor powder.

[0053] Step (4) The above powder is made into a slurry and pumped into a 20L high-pressure reactor. The temperature is raised to 200℃ and kept at the temperature for 3 hours for hydrothermal synthesis to obtain nano barium titanate powder.

[0054] Step (5) Calcination: After filtering and drying, the hydrothermal product is placed in a roller kiln and calcined at 1200°C for 2 hours under a nitrogen atmosphere. The calcined powder is then wet-milled to break up the sintered agglomerates, and subsequently spray-dried to obtain the final product.

[0055] Example 4

[0056] Steps (1) to (4) are the same as in Example 1.

[0057] Step (5) Calcination: Calcination is carried out using the following gradient heating process:

[0058] First stage: Hold at 800℃ for 1 hour to remove residual hydroxyl groups;

[0059] The second stage involves holding the temperature at 1100℃ for 0.5 hours to allow the grains to grow rapidly.

[0060] Subsequently, the calcined powder was wet-milled to break up the sintered agglomerates, and then spray-dried to obtain the final product.

[0061] Comparative Example 1

[0062] 1.7 kg of titanium tetrachloride, 4.6 kg of barium hydroxide octahydrate, and 10 L of pure water were directly added to a 20 L autoclave. After mixing, the mixture was heated to 170 °C and held at that temperature for 5 hours. Subsequent steps included simple washing, drying, and mechanical dry pulverization.

[0063] Comparative Example 2

[0064] In step (2) of Example 1, washing was performed only with room temperature water (20°C) until the conductivity dropped to 5000 µs / cm. The remaining steps were exactly the same as in Example 1.

[0065] Comparative Example 3

[0066] Except for the homogenization process in step 3, which was changed to mixing titanium hydroxide filter cake and barium hydroxide in a 20L mixing vessel and stirring at high shear for 30 minutes at room temperature, all other steps (including hydrothermal treatment, calcination, etc.) were the same as in Example 1.

[0067] The barium titanate powders prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to performance tests, and the test results are shown in the table below.

[0068] Table 1

[0069]

[0070] As can be seen from the data in the table above, the barium titanate powder prepared by the method of this application has the beneficial effects of accurate Ba / Ti ratio, high purity, uniform and controllable particle size (200nm), and complete crystal form.

[0071] Comparing Comparative Example 1 with Example 1, we can see that Comparative Example 1 was prepared using a traditional hydrothermal process. However, the results show that the molar ratio of Ba atoms to Ti atoms in the powder is seriously deviated, and the high impurity content leads to severe hard agglomeration of the powder, as well as low tetragonality.

[0072] Comparing Comparative Example 2 with Example 1, we can see that in Comparative Example 2, the poor purity of its titanium hydroxide precursor led to a higher concentration of Cl in its product. - Excessive ion content leads to poor insulation, demonstrating the necessity of deep purification of the titanium hydroxide precursor.

[0073] Comparing Comparative Example 3 with Example 1, we can see that even with identical raw material ratios, simply changing the homogenization method from "low-temperature cryogenic grinding" to "conventional high-shear mixing" in Comparative Example 3 results in a significant increase in the particle size of the final product (from 200 nm to 350 nm) and a marked deterioration in crystal integrity under the same subsequent calcination conditions due to differences in mixing uniformity. This strongly demonstrates the irreplaceable nature of the core low-temperature cryogenic grinding homogenization process of this invention.

[0074] In summary, this application utilizes "low-temperature cryogenic grinding" to force the mixing of the titanium hydroxide precursor and the solid barium source in a solid state, thereby physically ensuring a highly consistent Ba / Ti ratio in every micro-region. This eliminates the need for complex subsequent online compensation, fundamentally solving the problem of stoichiometric ratio runaway. This process can directly obtain ultrafine (<100nm) powder prepared by hydrothermal methods, and through subsequent controllable calcination steps, it avoids the energy consumption of high-temperature routes and overcomes the inherent defects of wet methods, thus obtaining a series of products with larger particle sizes and better crystal forms. Ultimately, this provides fundamental technical support for the domestic production of high-end MLCC materials.

[0075] 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 high-performance barium titanate nanoparticles for multilayer ceramic capacitors, characterized in that, Includes the following steps: (a) Titanium hydroxide was washed with pure water in multiple countercurrent stages under membrane filtration conditions until the conductivity of the filtrate was less than 1000 μS / cm, thus obtaining a high-purity titanium hydroxide precursor. (b) The high-purity titanium hydroxide precursor and a solid barium source are cryogenically ground in the presence of a cryogenic medium at an environment of -100°C to -196°C, with a molar ratio of barium atoms to titanium atoms of 1.

000. This forces the materials to achieve embedded mixing at the nanoscale, thereby forming an amorphous composite precursor with high reactivity. (c) The amorphous composite precursor obtained in step (b) is subjected to a hydrothermal synthesis reaction to generate barium titanate nanoparticles.

2. The method for preparing high-performance barium titanate nanoparticles for multilayer ceramic capacitors according to claim 1, characterized in that, The cryogenic medium includes liquid nitrogen or liquid helium.

3. The method for preparing high-performance barium titanate nanoparticles for multilayer ceramic capacitors according to claim 1, characterized in that, In step (a), the temperature of the high-purity water in the multi-stage countercurrent washing is 30℃-60℃.

4. The method for preparing high-performance barium titanate nanoparticles for multilayer ceramic capacitors according to claim 1, characterized in that, The hydrothermal synthesis reaction in step (c) is carried out at 150°C to 200°C.

5. The method for preparing high-performance barium titanate nanoparticles for multilayer ceramic capacitors according to claim 1, characterized in that, It also includes the step of calcining the generated barium titanate nanoparticles to control grain growth and crystal transformation.

6. The method for preparing high-performance barium titanate nanoparticles for multilayer ceramic capacitors according to claim 5, characterized in that, The calcination process is carried out in an inert or oxidizing atmosphere at a temperature of 800°C to 1200°C.

7. A method for preparing high-performance barium titanate nanoparticles for multilayer ceramic capacitors according to claim 1 or 5, characterized in that, It also includes wet grinding of the hydrothermally synthesized or calcined barium titanate nanoparticles to deagglomerate them, followed by drying to obtain the final product of barium titanate nanoparticles.

8. A high-performance barium titanate nanoparticle powder for use in multilayer ceramic capacitors, characterized in that, It is prepared by any one of the methods described in claims 1-7 above; The average particle size of the high-performance nano barium titanate powder is 100nm-400nm. The molar ratio of Ba atoms to Ti atoms in the high-performance nano-barium titanate powder is 1.000±0.005; The c / a value of the high-performance nano barium titanate powder is 1.008-1.

011.

9. A multilayer ceramic capacitor, characterized in that, It is prepared from the high-performance nano barium titanate powder described in claim 8.

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