KR102661174B1 - Preparation of ceramic nanoparticle - Google Patents

Abstract

In the present invention, a solution of bismuth, sodium, and titanium metal compounds is prepared by mixing titanium peroxo compound, bismuth nitrate, and sodium nitrate as starting materials in a solution state, and adding a precipitant to the solution of bismuth, sodium, and titanium metal compounds to produce bismuth, A method for synthesizing ceramic nanoparticles is provided, including the steps of preparing a sodium and titanium mixed metal precipitate, drying the bismuth, sodium, and titanium mixed metal precipitate, and then heat treating the precipitate to obtain perovskite-type oxide powder.

Description

Ceramic nanoparticle synthesis method {Preparation of ceramic nanoparticle}

The present invention relates to ceramic nanoparticles used in ferroelectrics and their manufacturing method, and proposes a new method of manufacturing BiNaTiO ₃ (BNT) ceramic powder with a perovskite structure by a wet method.

A multilayer ceramic capacitor (MLCC) is a key component that regulates current flow or prevents electromagnetic interference between components so that electronic circuits can operate stably in electronic devices such as laptops, mobile phones, and TVs.

Recently, MLCCs for automotive semiconductors, telematics, displays, batteries, motors, camera modules, and other electronic devices have been attracting attention, and the background is the expanding supply of electric vehicles, which are replacing internal combustion engine vehicles that have been the mainstream to date. This is because the demand for semiconductors used in various sensors, electronic control units (ECUs), motors, and driving devices used in electric vehicles is rapidly increasing. Automotive MLCCs have a similar role to existing IT MLCCs, but because the operating environment such as temperature, voltage, vibration, and humidity is harsh, and automobiles are closely related to human life, different electrical characteristics are required than before, especially safety. In terms of securing and increasing lifespan, a higher level of reliability and durability is required than the current MLCC.

MLCC is a green sheet made by manufacturing a slurry using atomized ferroelectric powder, typically BaTiO ₃ powder, an organic binder, and a solvent, then forming a green sheet on a carrier film using a die coater method or a doctor blade method, and printing internal electrodes. It is manufactured by stacking to create a multi-layer structure and then firing at high temperature. Since the capacitance of an MLCC increases in proportion to the number of ferroelectric and internal electrode layers at a given volume, it is essential to make the MLCC more multi-layered by making the ferroelectric layer thinner in order to increase capacitance. Meanwhile, in order to manufacture a thin ferroelectric layer, it is very important to nanosize the ferroelectric powder used as a raw material.

Generally, ferroelectric powder is manufactured through solid-phase synthesis. In the solid-phase synthesis method, starting materials as raw materials are uniformly mixed using mixing equipment such as a ball mill or planetary mill, and then calcinated and pulverized to produce ferroelectric powder. Meanwhile, in order to obtain a ferroelectric material with the desired composition using solid-state synthesis, calcination (heat treatment) at high temperature is essential. This causes particle growth or agglomeration of particles, so a long-time grinding process is essential to obtain nanoparticles. . The grinding process using a ball mill or planetary mill has been pointed out to have problems with impurities mixed in due to wear of the grinding medium, and the size of nanoparticles that can be obtained through grinding is also relatively limited.

Meanwhile, the method of producing ferroelectric powder from a solution containing raw materials is called wet synthesis, and includes hydrothermal synthesis, hydrolysis, and oxalic acid methods. These synthesis methods can omit the heat treatment process at high temperature, so nanoparticles are produced. It is advantageous for synthesizing.

For example, Registered Patent No. 10-2297718 proposes a method of synthesizing piezoelectric ceramic powder by obtaining a precursor polymer using reduced pressure distillation from a piezoelectric precursor solution synthesized by chemical solution synthesis and then calcining and heat treating it to remove the organic polymer. It has been reported that in order to obtain piezoelectric ceramic nanopowder, a process of pulverizing the calcined heat-treated piezoelectric ceramic powder using ball milling for 20 to 30 hours is necessary.

Japanese Patent Publication No. JP2018095524 proposes a wet process method for producing a perovskite-type composite oxide with a high specific surface area, by adding a dicarboxylic acid compound as an additive to the acetate solution of the metal as the starting raw material, without going through a grinding process. It has been reported that perovskite-type oxides with a large specific surface area can be manufactured. However, the above process uses metal acetate as a starting material. Metal acetate is expensive among metal salts, and when mixed with water, it creates a highly corrosive liquid. Therefore, for mass production, it is necessary to use inexpensive and non-corrosive metal salt raw materials. There is.

The present invention was created under the above-mentioned technical background, and the purpose of the present invention is to provide an advanced method compared to the conventional method for producing perovskite-type powder with a small particle size.

Another object of the present invention is to provide nanoparticles that can manufacture capacitors with better electrical performance using high sintering density.

The objects of the present invention are not limited to the above, but will be applied to various cases using devices using perovskite-type ceramics having a fine size.

In order to achieve the above object, the present invention prepares a bismuth, sodium, and titanium metal compound solution by mixing titanium peroxo compound, bismuth nitrate, and sodium nitrate as starting materials in a solution state, and preparing the bismuth, sodium, and titanium metal compound solution. Adding a precipitant to prepare a bismuth, sodium, and titanium mixed metal precipitate, drying the bismuth, sodium, and titanium mixed metal precipitate, and then heat treating to obtain perovskite-type oxide powder, wherein the perovskite-type oxide is It is a ceramic material represented by the following chemical formula,

Bi _1-x Na _x TiO ₃ , where x is 0<x<1

The starting material is prepared in a stoichiometric amount to satisfy the above chemical formula, and the heat treatment is performed at a temperature of 500 to 800°C for 2 to 8 hours.

In the present invention, the titanium peroxo compound is obtained by adding water to a titanium isopropoxide solution to obtain a titanium hydroxide precipitate, dissolving the titanium hydroxide precipitate in an aqueous nitric acid solution to obtain a titanium nitrate solution, and adding a hydrogen peroxide solution to the titanium nitrate solution. It can be produced as a titanium peroxo compound in a solution state by adding it.

In addition, in the present invention, the bismuth, sodium, and titanium mixed metal precipitate uses sodium hydroxide, potassium hydroxide, ammonia, or urea as a precipitant while maintaining the pH of the bismuth, sodium, and titanium mixed metal solution in the range of 7 to 11. It can be manufactured.

According to the present invention, it is possible to provide perovskite-type oxide powder having a finer particle size than powder obtained by existing methods without going through a grinding process.

According to the present invention, it is possible to provide ceramics with a high relative density even when fired at a low temperature, thereby providing a capacitor with better electrical characteristics. Ceramic nanoparticles manufactured according to the present invention can be effectively applied to cutting-edge products that require ferroelectrics, such as MLCC for electronics.

Figure 1 is a flow chart showing the manufacturing process of the perovskite-type oxide of the present invention.
2A and 2B are XRD graphs showing the crystallinity of ceramic powder according to examples and comparative examples of the present invention.
3A to 3D are electron micrographs of nanoparticles according to an embodiment of the present invention.
4A to 4D are electron micrographs of nanoparticles of comparative examples.

The present invention relates to ceramic nanoparticles used in ferroelectric products such as multilayer ceramic capacitors (MLCC) and a method of manufacturing the same. BiNaTiO ₃ (BNT) ceramic powder with a perovskite structure is manufactured by the sol-gel method, using a conventional method. Compared to the solid-state reaction method of , we propose ceramic nanoparticles with a fine size and narrow and uniform distribution without a grinding process, and a method for manufacturing the same.

Conventionally, in order to manufacture perovskite-type oxide powder, for example, in the case of piezoelectric ceramic nanopowder having an average particle diameter of 150 nm or less, heat treatment for solid-state synthesis must be followed by pulverization to obtain fine particles again, and nano-level fine particles. Not only does it require a lot of energy and time to obtain particles, but agglomeration may occur during the drying process, which may require additional processes to resolve it. In addition, wet processes also have limitations in that expensive raw materials are required or corrosive liquids are generated during the manufacturing process.

On the other hand, in the present invention, titanium peroxo complex (TiO(OH) _n ) is used as a raw material to obtain perovskite-type BNT nanopowder, and the entire process is performed wet. It was confirmed that by using a titanium peroxo compound, it is possible to produce perovskite-type oxide powder with a small particle size without performing a fine grinding process. In manufacturing perovskite-type oxide powder, the desired crystal phase can be obtained even through a wet process and low-temperature heat treatment, so there is no need for a grinding process to obtain fine particles after heat treatment, and the perovskite-type powder obtained from the present invention can be used at low temperature. Even after firing, a ferroelectric perovskite-type oxide with high density can be produced.

The present invention proposes a new method for producing perovskite-type oxide powder composed of fine particles. This perovskite-type oxide is a ceramic material represented by the following formula (1), and the perovskite-type powder according to the present invention is composed of fine particles in the range of 100 to 200 nm.

[Formula 1]

Bi _1-x Na _x TiO ₃ , where x is 0<x<1

The titanium peroxo compound (TiO(OH) _n ), 0.1≤n≤10 ) used to produce the perovskite-type oxide powder of the present invention has various chemical formulas, and in the examples of the present invention, TiO(OH) ₂ was synthesized. . In addition, titanium peroxo compound is not a commercially available material and requires synthesis. In an example of the present invention, titanium hydroxide obtained by hydrolyzing titanium isopropoxide was dissolved in nitric acid and then synthesized by adding hydrogen peroxide, and commercial titanium hydroxide was synthesized. It is also possible to manufacture from .

The perovskite-type oxide powder of the present invention can be manufactured, for example, according to the process shown in Figure 1, and in this case, titanium isopropoxide, bisbose nitrate, and sodium nitrate can be used as starting raw materials. The starting material is prepared in a stoichiometric amount according to the above-mentioned Chemical Formula 1.

To synthesize a titanium peroxo compound, titanium isopropoxide is first dissolved homogeneously in a solvent, and then water is added to the titanium isopropoxide solution to produce titanium hydroxide precipitate. At this time, the solvent for dissolving titanium isopropoxide can be methanol, ethanol, isopropanol, normal propanol, butanol, etc. Additionally, in order to obtain titanium hydroxide precipitation, water is added to the titanium isopropoxide solution, and the pH of the solution is preferably in the range of 7 to 11.

Next, the titanium hydroxide powder is dissolved in an aqueous nitric acid solution to prepare a titanium nitrate solution, and an aqueous hydrogen peroxide solution is added to the titanium nitrate solution to complete the titanium peroxo compound in a solution state.

After synthesizing the titanium peroxo compound, perovskite-type oxide powder is prepared with other starting materials. First, prepare a bismuth, sodium, and titanium metal compound solution by mixing a titanium peroxo compound solution with a bismuth nitrate solution and a sodium nitrate solution. Next, a precipitant is added to the bismuth, sodium, and titanium metal compound solution to prepare a bismuth, sodium, and titanium mixed metal precipitate. In order to obtain a mixed metal precipitate, the pH of the bismuth, sodium, and titanium mixed metal solution is preferably in the range of 7 to 11. At this time, sodium hydroxide, potassium hydroxide, ammonia, urea, etc. can be used as precipitants.

Afterwards, the bismuth, sodium, and titanium mixed metal precipitate is dried and then heat treated to obtain perovskite-type oxide powder. In the present invention, heat treatment can be performed at a temperature of 500 to 800°C. Additionally, heat treatment is preferably performed for 2 to 8 hours. In order to produce a perovskite-type oxide powder having the formula 1 through a solid-state reaction method, heat treatment must be performed at a high temperature of at least 700°C. However, in the present invention, a perovskite single phase can be formed without any remaining organic matter even at a low temperature of 500°C. , it is possible to produce oxide powder with a particle size in the range of 100 to 200 nm.

Hereinafter, the technical features and effects of the present invention will be described in more detail through specific examples. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms.

Example I - Powder preparation by wet synthesis

Perovskite-type oxide in the case of x = 0.5 in the above-mentioned Chemical Formula 1 was manufactured using the process shown in FIG. 1.

A titanium isopropoxide solution was prepared by adding 0.01 mole of titanium isopropoxide into 200 ml of isopropanol and stirring it using a magnetic stirrer for 1 hour until completely dissolved. Then, 0.04 mol of distilled water with the pH adjusted to 9 as a precipitant was added to the titanium isopropoxide solution to prepare a titanium hydroxide precipitate. The titanium hydroxide precipitate was washed twice with distilled water using filter paper to remove residual isopropanol.

Next, the titanium hydroxide precipitate was placed in 200 ml of nitric acid aqueous solution containing 0.02 mol of nitric acid, stirred using a magnetic stirrer until completely dissolved, and then 0.04 mol of hydrogen peroxide was added to prepare a titanium peroxo compound solution. .

To the titanium peroxo compound solution prepared in this way, 0.005 mol of bismuth nitrate and 0.005 mol of sodium nitrate were added to prepare a composite metal solution composed of titanium, bismuth, and sodium, and then caustic soda was used as a precipitant to prepare the composite metal solution. A composite metal precipitate of titanium, bismuth, and sodium was synthesized by adjusting the pH to 11.

The composite metal precipitate was washed twice with distilled water using a filter, dried in an electric oven at 100°C for 2 hours, and then calcined and heat-treated in air for 2 hours in an electric furnace at 500°C to produce single-phase Bi _0.5 Na _0.5 TiO ₃ PerovSky. A t-type oxide powder was prepared (Example 1).

As shown in the The sample was obtained as a perovskite single phase. Although a perovskite phase can be obtained when heat treated at 400°C, it was confirmed that a small amount of impurity phase exists, so calcining heat treatment at 500°C or more is necessary to obtain a single-phase perovskite-type oxide.

Bi0.5Na0.5TiO3 perovskite was prepared in the same manner as in Example 1 by varying the heat treatment temperature at 600°C for 2 hours to 600°C (Example 2), 700°C (Example 3), and 800°C (Example 4), respectively. A t-type oxide powder was prepared. In each example, a single-phase perovskite-type oxide was obtained. Figures 3a to 3d show the microstructure of the oxide powder according to each example, and it was confirmed that nanoparticles with a uniform size in the range of 100 to 200 nm were formed.

Comparative Example - Powder production by solid phase reaction

Prepare sodium carbonate (NaCO ₃ ), bismuth oxide (Bi ₂ O ₃ ), and titanium oxide (TiO ₂ ) as starting materials, place the starting materials in a zirconia container, and adjust the total volume of the starting materials to the volume ratio of anhydrous alcohol and zirconia balls. After mixing at a ratio of 1:1.5:2, the total volume of the starting materials, anhydrous alcohol, and zirconia balls was mixed so that it was less than 1/4 of the zirconia container. The mixed materials were mixed at 300 rpm for 2 hours using a high-speed mill, and then dried in an electric oven at 80°C for 12 hours. The dried powder was calcined and heat treated at 700°C for 2 hours to complete the solid phase reaction of the starting material (Comparative Example 1). In addition, Bi _0.5 Na _0.5 TiO ₃ perovskite-type oxide powder was prepared in the same manner as above, except that it was heat treated at 800°C for 2 hours (Comparative Example 2).

In the You can see that the size is very large (scale bar difference). The present invention synthesizes the powder by a wet method, making it possible to produce particles of 100 to 200 nanometers even in heat treatment at 500°C without grinding, whereas in the comparative example, not only was the heat treatment temperature as high as 700°C or more, but grinding after heat treatment was required to produce particles of about 500 nm. particles can be obtained.

Example II - Ceramic Sample Preparation and Relative Density Determination

The Bi _0.5 Na _0.5 TiO ₃ perovskite powder prepared in Example 1 was uniaxially press-molded in a metal circular mold with a diameter of 20 mm to produce a molded body, and then heated at 1000°C, 1050°C, 1100°C, and 1150°C for 2 hours. A ceramic sample was prepared by sintering (Example 5). In the same way, the Bi _0.5 Na _0.5 TiO ₃ perovskite powder prepared in Example 2, Example 3, and Example 4, respectively, was uniaxially pressed and molded in a metal circular mold with a diameter of 20 mm to produce a molded body, and then 1000 Ceramic samples were prepared by sintering at ℃, 1050℃, 1100℃, and 1150℃ for 2 hours (Example 6, Example 7, Example 8).

In addition, the powder prepared in Comparative Example 1 was mixed in a milling container so that the volume ratio of absolute alcohol and 1 mm zirconia balls was 1:1.5:2, and grinding was performed at 300 rpm for 3 hours using a high-speed milling machine (Comparison Example 3).

The Bi0.5Na0.5TiO3 perovskite powder prepared in Comparative Example 3 was uniaxially press-molded in a metal circular mold with a diameter of 20 mm to produce a molded body, and then heated at 1000°C, 1050°C, 1100°C, and 1150°C for 2 hours. A ceramic sample was prepared by sintering (Comparative Example 4).

The relative density measurement results of Examples to Comparative Examples are shown in Table 1, and it was confirmed that the ceramic samples of each Example of the present invention could obtain a higher relative density even when sintered at low temperature compared to the Comparative Examples.

The method for synthesizing ferroelectric ceramic nanoparticles according to the present invention does not use expensive raw materials and reduces process time and cost by not performing low-temperature heat treatment and grinding processes. However, the particle size is small and density is high, so it is effective for high-quality ferroelectric products such as MLCC for electronics. can be used

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

Claims (3)

As starting materials, titanium peroxo compound, bismuth nitrate, and sodium nitrate are mixed in solution to prepare a bismuth, sodium, and titanium metal compound solution,
Adding a precipitant to the bismuth, sodium and titanium metal compound solution to prepare a bismuth, sodium and titanium mixed metal precipitate,
A step of drying the bismuth, sodium, and titanium mixed metal precipitate and then heat-treating it to obtain perovskite-type oxide powder,
The perovskite-type oxide is a ceramic material represented by the following chemical formula,
Bi _1-x Na _x TiO ₃ , where x is 0<x<1
The starting material is prepared in a stoichiometric amount to satisfy the above chemical formula, and the heat treatment is performed at a temperature of 500 to 800 ° C. for 2 to 8 hours.
Ceramic nanoparticle synthesis method.
According to paragraph 1,
The bismuth, sodium, and titanium mixed metal precipitate is prepared by using sodium hydroxide, potassium hydroxide, ammonia, or urea as a precipitant while maintaining the pH of the bismuth, sodium, and titanium mixed metal solution in the range of 7 to 11. Ceramic nanoparticle synthesis method using.
According to paragraph 1,
The titanium peroxo compound is
Add water to the titanium isopropoxide solution to obtain titanium hydroxide precipitate,
Dissolving the titanium hydroxide precipitate in an aqueous nitric acid solution to obtain a titanium nitrate solution,
A method of synthesizing ceramic nanoparticles, characterized in that a titanium peroxo compound in a solution state is produced by adding a hydrogen peroxide solution to the titanium nitrate solution.