KR102529316B1 - Preparation of nano size BNT ceramic powder for MLCC - Google Patents

Abstract

The present invention includes the steps of pulverizing sodium carbonate in anhydrous alcohol among the starting materials of the solid phase reaction, removing the anhydrous alcohol from the pulverized sodium carbonate using a dryer and drying it in a powder state, the pulverized sodium carbonate powder and Mixing a mixture of bismuth oxide powder and titanium oxide powder with a solvent zirconia ball, mixing the mixture at high speed using a milling device, drying the mixed powder mixture at high speed, heat-treating the dried powder mixture to obtain a solid state It provides a method for producing BNT-based nano-sized powder for MLCC, comprising the steps of reacting and pulverizing the heat-treated solid reactant using a planetary mill.

Description

Manufacturing method of BNT-based nano-size powder for MLCC {Preparation of nano-size BNT ceramic powder for MLCC}

The present invention relates to a method for manufacturing nano-sized ceramic powder, and more particularly, proposes a new method for synthesizing nano-powder of BNT-based ceramics that can be used for MLCC.

Multi-layer Ceramic Capacitor (MLCC) is a typical passive element that accounts for 60% of passive components in IT electronic circuits such as mobile phones, personal PCs, and digital displays, and isolates noise from power supply circuits of active elements such as ICs. Its roles, such as decoupling function that removes the dc component from the signal and signal flattening function, are as important as semiconductors, which are representative active elements.

As the trend of miniaturization and multifunctionality of electronic devices is rapidly progressing, miniaturization and performance improvement of electronic components are also progressing rapidly. It is increasing. Competition for technology development of passive components (Inductor, Capacitor, Resistor) to meet such market demands is accelerating, and in the case of MLCC, the use and usage of which is increasing as a general-purpose passive component, the dielectric layer and the thin layer of the internal electrode layer Many attempts and efforts are being made to preoccupy the market with the development of ultra-high-capacity products based on chemical technologies.

In particular, when used in major parts such as ECUs that may affect human life in automotive MLCCs, robust design must be made from the MLCC design stage to process and shipment inspection to prevent failures due to internal shorts even in harsh environments. It can be said that securing reliability that can cope with the external environment is the key. The closest product that can be used as an automotive MLCC is X9R, and a BT-based material (BaTiO ₃ ) has been proposed as a material that can be used in a temperature range of -55℃ to 175℃.

Since the MLCC process is optimized for BT-based materials, the development of process technology is essential for the application of new compositions, such as the formation of new nanoparticles, the manufacture of highly stable slurries, and the synthesis of nanoparticles for the manufacture of high-strength sheets. It is becoming. In particular, the development of high-strength and high-permittivity ferroelectric nanopowder is becoming a key element technology.

Because the specific surface area of nano-sized particles increases rapidly, the reactivity is greatly different from that of micro-scale materials, and the change in the properties of these materials gives a large difference in macroscopic results as well as microscopic effects. Since these nano-sized particles greatly change electrical, chemical, and physical properties, etc., they act as a factor resulting from performance improvement in industrial fields such as batteries, semiconductors, and multi-layer ceramic capacitors (MLCCs). There are two methods of manufacturing nanoparticles: top-down and bottom-up. The top-down method is to grind large particles to make them into smaller sizes, and the bottom-up method uses a solution or vapor state. method to synthesize it.

In order to obtain powder in a top-down method when manufacturing ceramic materials for nano-level MLCC, process control at each stage, induction of uniform solid-phase reaction, optimization of grinding process, etc. are required. However, in the prior art, there is a lack of proposals for these element technologies.

For example, according to Patent Publication No. 10-2017-0078123, a dielectric composition and a multilayer electronic component including the same include BaTiO3 as a first main component, PbTiO3 as a second main component, and (Bi0.5Na0.5)TiO3 as a third main component. The dielectric composition has been proposed, but the process of obtaining nanoparticles is silent, focusing only on the composition of the material.

As another example, in the case of Patent Publication No. 10-2020-0072400, a ceramic raw material powder for a multilayer ceramic capacitor is proposed, and a ceramic raw material powder capable of obtaining both a donor action and an acceptor action is proposed, but it is difficult to synthesize nanoparticles. No specific process is proposed for this.

In order to develop ceramic parts that can be used in extreme conditions such as automotive MLCC, it is necessary to secure functionality through particle control and process control in addition to composition development.

The present invention was conceived under the above technical background, and an object of the present invention is to provide a new method for synthesizing nano-sized ceramic powder.

Another object of the present invention is to provide a nanopowder synthesis method capable of producing high-quality, highly functional ceramic products.

Another object of the present invention is to provide a new method for manufacturing a BNT-based ceramic powder for MLCC that can satisfy extreme conditions such as electrical components.

Other objects and technical features of the present invention will be presented in more detail in the following detailed description.

In order to achieve the above object, the present invention is a step of pulverizing sodium carbonate (Na ₂ CO ₃ ) of the starting material of the solid phase reaction in anhydrous alcohol, removing anhydrous alcohol from the pulverized sodium carbonate using a dryer and drying it in a powder state Mixing a mixture of the pulverized sodium carbonate powder, bismuth oxide (Bi ₂ O ₃ ) powder, and titanium oxide (TiO ₂ ) powder with anhydrous alcohol and zirconia balls as a starting material for a solid phase reaction, using a milling device to mix the mixture mixing at high speed, drying the powder mixture mixed at high speed, heat-treating the dried powder mixture to cause a solid phase reaction, and pulverizing the heat-treated solid phase reactant using a milling device, wherein sodium carbonate among the starting materials Grinding provides a method for producing BNT-based nano-sized powder for MLCC, characterized in that sodium carbonate, solvent and zirconia balls are mixed in a high-purity zirconia container, filled in a zirconia container, and pulverized at 250 to 400 RPM for 1 to 2 hours.

In the present invention, the nano-sized powder is a solid solution represented by the following chemical formula, Bi _{1 - x} Na _x TiO ₃ , where 0≤x<0.5, and the particle size of the nano-sized powder prepared is in the range of 300 to 500 nm on average. It is characterized by being

In addition, in the present invention, the powder mixture is heat treated in the range of 700 ~ 900 ℃ after drying to proceed with the solid phase reaction, and the heat treated solid reactant is subjected to high-speed milling using planetary mill equipment using 1 ~ 2 mm zirconia balls and anhydrous alcohol. It is desirable to do

According to the present invention, in the manufacture of ceramic nanoparticles, it is possible to synthesize several hundred nanoscale ceramic powders by controlling the particle size of the initial material.

In addition, according to the present invention, nanoparticles applicable to various industrial fields can be manufactured, and it can contribute to securing original technology for high-quality and highly functional ceramic products such as MLCC for electric vehicles.

1a and 1b show the particle size of BNT-based ceramic powder synthesized without controlling the particle size of the starting material.
2 is a flowchart of a BNT-based ceramic nanopowder synthesis process according to the present invention
3 is an XRD graph of the BNT-based ceramic nanopowder obtained by the present invention
4a and 4b are particle size distribution diagrams of BNT-based ceramic nanopowders obtained according to Examples 1 and 2 of the present invention;
5 is a graph of span change according to zirconia ball size during grinding
6a to 6d are photographs of microstructure changes of BNT-based ceramics according to zirconia ball sizes;

The present invention proposes a new method of synthesizing nano-sized ceramic powder through a solid-state reaction after controlling the particle size of some of the starting materials.

The solid phase reaction can be further promoted by controlling the particle size of the starting material, and as a result of pulverization of the heat-treated reactant, the size of the final nanopowder can be more finely controlled. Through such a top-down method of synthesizing nanoparticles, a highly functional BNT-based ceramic solid solution powder for MLCC can be obtained.

The nano-sized ceramic powder manufacturing method of the present invention can control the average particle diameter (D50) of the BNT-based nano-ceramic powder to a level of less than 500 nm, and can be used in a BNT-based MLCC manufacturing process using a top-down process. In the present invention, in particular, the possibility of nano-sized grinding of the final solid-state reactant was confirmed using the milling process of the starting material, and the particle size distribution of the particles obtained while changing the process conditions such as ball size, mixture content, solvent, etc. at each manufacturing step was evaluated. Through this, optimal grinding conditions were derived.

Through the particle size control process of the starting material proposed in the present invention, various processors for manufacturing ceramic nanoparticles in a top-down type can be developed, and other than multilayer ceramic capacitors, it can be applied to the manufacture of other ceramic products requiring nanosize. .

The ceramic solid solution powder completed according to the present invention may be represented by the following chemical formula, Bi _{1 - x} Na _x TiO ₃ (0≤x<0.5), starting material particle size control, heat treatment for solid-state reaction, and solid-state reactant The particle size of the final ceramic nanoparticles obtained through grinding has an average size in the range of 300 to 500 nm, and can be used as a high-strength, high-functional MLCC material. In particular, it is suitable for MLCC materials that can withstand extreme conditions such as battlefield conditions.

The solid-state reaction method is the most widely used method in manufacturing ceramic raw materials. Since the reaction starts when a sample in the solid state is hit with strong energy, the degree of reaction varies depending on the contact area of the initial material, and the size between particles is evenly distributed to obtain a uniform It should elicit a reaction. The more constant the particle size of the starting material, the more uniformly sized material can be obtained during synthesis. As a result of checking the particle size of Bi ₂ O ₃ , Na ₂ CO ₃ , and TiO ₂ , which are the initial starting materials of BNT-based ceramics, the average particle size D50 of Bi ₂ O ₃ and TiO ₂ is less than 8.6㎛ and 6.0㎛, respectively, but Na ₂ CO ₃ was 18.6 μm or more and the particles were not uniform. As a result of synthesizing the BNT ceramic powder with these starting materials and confirming the particle size, overall micro-level powder was obtained although there was a slight difference depending on the milling time (see FIGS. 1a and 1b).

Therefore, in the present invention, sodium carbonate among the starting materials was primarily pulverized to control the particle size first and then to uniformly promote the solid phase reaction. As a result of grinding Na ₂ CO ₃ using a planetary mill at 300 RPM for 2 hours, the average particle size was 4 μm, indicating a particle size of 10 μm or less. Synthesis was performed using materials whose starting materials were all 10 μm or less, and high-quality ceramic powder at the nano level was completed by changing the milling conditions during final grinding for the solid solution in which the solid phase reaction was completed after heat treatment. 2 is a flowchart of a BNT-based ceramic nanopowder synthesis process according to the present invention.

Among the starting materials of the solid phase reaction, sodium carbonate (Na ₂ CO ₃ ) is pulverized. Sodium carbonate is pulverized by mixing sodium carbonate, anhydrous alcohol, and zirconia balls in a volume ratio of 1: 1.5: 2 in a high-purity zirconia container, and filling the zirconia container to 1/3 to 1/4 level, and 1 to 2 at 250 to 400 RPM. It may include a process of crushing for a period of time. Anhydrous alcohol is removed from the pulverized sodium carbonate using a dryer and dried in a powder state.

Next, the pulverized sodium carbonate powder, bismuth oxide (Bi ₂ O ₃ ) powder, and titanium oxide (TiO ₂ ) powder are mixed as starting materials for the solid phase reaction. A mixture of starting materials is mixed with anhydrous alcohol and zirconia balls in a volume ratio of 1:1.5:2, and the mixture is mixed at high speed using a planetary mill, and then dried. In the process of mixing at high speed, the first solid state reaction occurs. Through the solid phase reaction, surface collision occurs due to strong energy between the starting materials in the form of oxides, and this surface reaction helps to obtain finer nanoparticles in the subsequent heat treatment process and final grinding process.

The powder mixture mixed at high speed is dried, heat-treated, and the solid-state reaction is finally pulverized to obtain nano ceramic particles. The powder mixture may be heat treated in the range of 700 ~ 900 ℃ after drying. The heat-treated solid reactant can be milled at high speed using planetary mill equipment with 1 to 2 mm zirconia balls and absolute alcohol.

Hereinafter, the synthesis process and results of the BNT-based nano ceramic powder according to the present invention will be described in more detail through Examples and Comparative Examples.

Example One

As an initial material for the manufacturing process of lead-free piezoelectric ceramics, Bi _{1 - x} Na _x TiO ₃ (BNT), a process of pulverizing sodium carbonate was first performed.

Sodium carbonate was pulverized by mixing sodium carbonate powder, anhydrous alcohol, and zirconia balls in a volume ratio of 1: 1.5: 2 in a milling container, filling it with 1/4 of the high-purity zirconia container used for grinding, and proceeding at 300 rpm for 2 hours. The pulverized sodium carbonate was dried in a circulation dryer at 80° C. for about 12 hours.

The crushed and dried sodium carbonate, bismuth oxide (Bi ₂ O ₃ ), and titanium oxide (TiO ₂ ) were put in a zirconia container, and the total volume of the starting material, anhydrous alcohol, and zirconia balls were mixed at a ratio of 1: 1.5: 2. Then, the total volume of the starting material, anhydrous alcohol, and zirconia were mixed in such a state that the total volume was less than 1/4 of the zirconia container. The mixed materials were mixed for 2 hours at 300 rpm using a high-speed milling machine, and then dried at 80° C. for about 12 hours in a circulation dryer.

The dried powder was heat-treated at 700° C. for 2 hours to complete the solid phase reaction. The heat-treated BNT-based ceramic powder was mixed with anhydrous alcohol and 1 mm zirconia balls at a volume ratio of 1:1.5:2 in a milling container, and final grinding was performed at 300 rpm for 3 hours using a high-speed mill. Table 1 shows the particle size according to the grinding time of the BNT-based ceramic powder after grinding. It can be seen that the particle size of the powder is on the order of hundreds of nanometers.

3 is a graph showing XRD of the BNT-based ceramic nanopowder by the method according to the present embodiment. As shown, it can be confirmed that the ceramic powder according to the present invention exists in a state with almost no secondary phase. FIG. 4a is a particle size distribution graph of the BNT-based ceramic nanopowder obtained according to this embodiment. It can be seen that the particle size is uniformly distributed around the average particle size (D50) as a whole, and as the grinding time increases, the average particle size is uniformly distributed. You can see that the size has decreased.

Example 2

BNT-based ceramic powder was synthesized in the same process as in Example 1, and unlike Example 1, 2 mm zirconia balls were used for grinding in the final grinding process of the heat-treated ceramic powder. Table 2 shows the particle size according to the pulverization time of the pulverized BNT-based ceramic powder. It can be seen that the particle size of the powder is on the order of hundreds of nanometers. 4B is a particle size distribution graph of the BNT-based ceramic nanopowder obtained according to the present embodiment, and it can be seen that the particle size is uniformly distributed around the average particle size (D50) as a whole.

comparative example One

BNT-based ceramic powder was synthesized in the same process as in Example 1, and a grinding process for controlling the initial particle size of sodium carbonate in the starting material was not performed. Table 3 shows the particle size according to the grinding time of the BNT-based ceramic powder after grinding. It can be seen that the particle size of the obtained powder is larger than that of Example 1.

comparative example 2

BNT-based ceramic powder was synthesized in the same process as in Example 2, and a grinding process for controlling the initial particle size of sodium carbonate in the starting material was not performed. Table 4 shows the particle size according to the grinding time of the BNT-based ceramic powder after grinding. It can be seen that the particle size of the obtained powder is larger than that of Example 2.

zirconia ball size effect

The ball size is an important factor in grinding using a planetary mill, and the particle size of the material can be affected by the ball size and rotation speed. In this example, in order to manufacture BNTs of 500 nm or less, heat treatment at 700 ° C. for 2 hours was compared with the case of synthesizing BNTs using 1 mm and 2 mm balls when pulverizing with conventional 5 mm balls. At this time, the powder: solvent: zirconia ball volume ratio was maintained at the same 1: 1.5: 2, and the process was performed at a speed of 300 rpm using a planetary mill.

As a result of obtaining the span value using D10, D90, and D50 values representing 10%, 50%, and 90% of the particle size of the particle size distribution, the case using a 1mm zirconia ball showed the best value (see FIG. 5). The span value indicates how close the particle distribution is to the midpoint size, and the smaller this value is, the more uniformly sized the particle is.

Smaller balls provide lower impact energy, but as grinding progresses, finer grinding is possible because the specific surface area in contact with the powder is larger. On the other hand, larger balls cause particle aggregation along the space between balls After a certain level of pulverization is achieved, the effect of reducing the particle size by pulverization does not increase significantly. When 1mm zirconia balls and 2mm zirconia balls were used, 500nm class BNTs could be produced, and in particular, when 1mm zirconia balls were used, particles of about 446nm were obtained as a result of pulverization for 3 hours. On the other hand, when grinding for 3 hours using a 5mm zirconia ball, it was confirmed that the D50 remained at the micro-level particle size as 1.43㎛, as shown in Table 5.

When the heat-treated BNT-based solid solution was pulverized, the microstructure change of the final powder according to the size of the zirconia ball was confirmed. FIG. 6a shows the microstructure of the BNT-based ceramic powder synthesized without controlling the particle size of sodium carbonate among the starting materials, as in Comparative Example 1 described above. On the other hand, FIGS. 6b to 6d show that BNT-based ceramic powder was prepared after grinding sodium carbonate. FIGS. 6b and 6c show that 1mm and 2mm zirconia balls were used when grinding the final solid reactant, respectively, and uniform and small solid solution particles were obtained. distribution can be seen. Meanwhile, FIG. 6D shows that zirconia balls having a size of 5 mm are used, and although the particle size is somewhat reduced, it can be seen that the solid solution particles are not uniform throughout.

From the results of these Examples and Comparative Examples, BNT-based high-quality nanoparticles can be manufactured through control of the particle size of the starting material and process control during grinding after the heat treatment process, and these high-quality nano-sized ceramic powders can be sintered at high density as well as It was confirmed that the non-uniformity of ceramic molding density can be controlled. Through the technical characteristics of the ceramic powder synthesis process of the present invention, it is expected that it will be possible to develop highly reliable MLCCs because it can be used to manufacture multi-layered ceramic ferroelectric sheets having high strength.

Although the present invention has been illustratively described through preferred embodiments above, the present invention is not limited to such specific embodiments, and various forms are provided within the scope of the technical idea presented in the present invention, specifically, the claims. may be modified, changed, or improved.

Claims (3)

Grinding sodium carbonate (Na ₂ CO ₃ ) in anhydrous alcohol among the starting materials of the solid phase reaction;
Removing anhydrous alcohol from the pulverized sodium carbonate using a dryer and drying it in a powder state;
Mixing a mixture of the pulverized sodium carbonate powder, bismuth oxide (Bi ₂ O ₃ ) powder, and titanium oxide (TiO ₂ ) powder with a solvent and zirconia balls as a starting material for a solid phase reaction;
Mixing the mixture at high speed using a milling device;
drying the high speed blended powder mixture;
Solid state reaction by heat treatment of the dried powder mixture;
Preparing a nano-sized powder by pulverizing the heat-treated solid reactant using a milling device,
The pulverization of sodium carbonate among the starting materials is performed by mixing sodium carbonate, solvent, and zirconia balls in a high-purity zirconia container, filling the zirconia container, and pulverizing at 250 to 400 RPM for 1 to 2 hours to have an average particle size of 10 μm or less,
The nano-sized powder is a solid solution represented by the following chemical formula,
Bi _1-x Na _x TiO ₃ , where 0≤x<0.5
Characterized in that the particle size of the prepared nano-sized powder ranges from 300 to 500 nm on average.
Manufacturing method of BNT-based nano-sized powder for MLCC.
delete According to claim 1,
The powder mixture is heat-treated in the range of 700 ~ 900 ℃ after drying to proceed with the solid-phase reaction, and the heat-treated solid-phase reactant is a BNT-based nano-size powder manufacturing method for MLCC, characterized in that high-speed milling using 1-2 mm zirconia balls .

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