KR20060030230A - Method for producing calsium-modified barium titanate powder and the calsium-modified barium titanate powder obtained, multilayer ceramic capacitor using same - Google Patents

Abstract

The present invention relates to a method for preparing barium calcium titanate (BaCaTiO ₃ ) powder which precipitates nano-sized calcium hydroxide salt on the surface of BaTiO ₃ powder and heat-treats it to synthesize BaCaTiO ₃ powder. Method for producing barium calcium titanate powder of the present invention, the step of preparing a mixed aqueous solution of BaTiO ₃ powder and Ca salt,

Precipitating calcium hydroxide salt on the surface of the BaTiO ₃ powder in the mixed aqueous solution,

The powder obtained by drying from the mixed aqueous solution is calcined and synthesized into BaCaTiO ₃ powder and then pulverized. In the present invention, there is also provided a barium calcium titanate powder and a laminated ceramic capacitor using the powder.

Barium Calcium Titanium Powder, Precipitation, Calcium Hydroxide, Multilayer Ceramic Capacitor, Urea

Description

METHOD FOR PRODUCING CALSIUM-MODIFIED BARIUM TITANATE POWDER AND THE CALSIUM-MODIFIED BARIUM TITANATE POWDER OBTAINED, MULTILAYER CERAMIC CAPACITOR USING

Figure 1 is a graph showing the pH change with the reaction time when the addition of urea and KOH.

2 shows the results of EPMA analysis of barium calcium titanate powder.

Figure 2a is a case using a conventional solid phase synthesis method,

Figure 2b is the case of using KOH

2C and 2D show a case where 1 mol% and 3 mol% of urea are used.

3 is a graph showing the results of XRD analysis.

Figure 4 is a photograph showing the SEM analysis results.

The present invention relates to a manufacturing method of barium calcium titanate (BaCaTiO ₃ ) powder and a laminated ceramic capacitor having a powder obtained therefrom as a main component, and more particularly to producing barium calcium titanate powder by chemical adsorption. Moreover, it is related with the barium calcium titanate powder obtained by this manufacturing method, and the laminated ceramic capacitor which has this powder as a main component.

Recently, with the rapid development of electronic technology, miniaturization of electronic components has progressed, along with high capacity and miniaturization, in multilayer ceramic capacitors (MLCC). This requires the thinning and multilayering of the dielectric layer.

Multilayer ceramic capacitors are mainly made of barium titanate (BaTiO ₃ ) powder as a main component of ceramic raw materials. This is because barium titanate powder is a ferroelectric material with a high dielectric constant and a relatively low price. However, when barium titanate is calcined in a reducing atmosphere due to the use of inexpensive non-metals such as Ni as the internal electrode of the multilayer ceramic capacitor, it loses insulation due to semiconductor formation during firing. As a result, if the shell sugar having a reduction resistance is not uniformly formed in all particles in the capacitor, the product's natural resistance may be lowered and its life may be drastically reduced. In addition, even if a large shell is formed, when the thickness is very small, the barium titanate in the particles may be semiconductorized to lower the insulation resistance and to drastically reduce the lifetime. This tendency becomes a bigger problem as the particle size of the dielectric composition is atomized for the production of thin multilayer ceramic capacitors.

In order to solve this problem, barium calcium titanate (BaCaTiO ₃ ) is used instead of barium titanate powder as a ceramic raw material of a multilayer ceramic capacitor. Since barium calcium titanate has reduction resistance due to lattice defects formed by Ca replacing Ti sites, it has an advantage of maintaining high insulation resistance even when a shell is not formed or is thinly formed during firing in a reducing atmosphere.

Solid phase synthesis and hydrolysis methods are known for producing barium calcium tartarate powder.

The solid phase synthesis method is prepared by mixing and calcining starting materials of BaCO ₃ powder, CaCO ₃ powder, and TiO ₂ powder in an appropriate molar ratio. Calcination is carried out at a high temperature of about 1200 ℃ for the solid phase reaction, the calcination reaction temperature is high, the average particle size is increased. In addition, the chemical uniformity of the obtained barium calcium titanate powder is low.

In the hydrolysis method, barium hydroxide aqueous solution, alkoxy solution of titanium alkoxide and alcohol solution of calcium salt are mixed and the mixed solution is reacted at an appropriate temperature to prepare barium calcium titanate powder. The obtained hydrolysis method shows excellent characteristics for the entrants, but due to the high unit cost of the raw material powder of the component and the high reactivity of the alkoxide material, there is a technical difficulty in mass production.

It is an object of the present invention to provide a method for producing barium calcium titanate powder in which Ca is uniformly dissolved and Ba is eluted, chemical uniformity is high, and grain growth is suppressed.

Method for producing a barium calcium titanate powder of the present invention for achieving the above object, the step of preparing a mixed aqueous solution of BaTiO ₃ powder and Ca salt,

Precipitating calcium hydroxide salt on the surface of the BaTiO ₃ powder in the mixed aqueous solution,

The powder obtained by drying from the mixed aqueous solution is calcined and synthesized into BaCaTiO ₃ powder and then pulverized.

In the present invention, the precipitation of the calcium hydroxide salt is preferably obtained by increasing the pH change rate of the mixed aqueous solution to 0.3pH / min or less up to the initial 10 minutes, at a rate of 0.005pH / min or less up to 900 minutes in the initial stage. The increase in pH may be due to decomposition of the amine compound, and the amine compound may include urea (Co (NH ₂ ) ₂ ).

In addition, the method for producing a barium calcium titanate powder of the present invention for achieving the above object comprises the steps of preparing a mixed aqueous solution of BaTiO ₃ powder and Ca salt,

Mixing and pyrolyzing urea in the mixed aqueous solution,

The powder obtained by drying from the mixed aqueous solution is calcined and then synthesized into BaCaTiO ₃ powder.

In the present invention, pyrolysis of urea (Co (NH ₂ ) ₂ ) may be performed at 60-80 ° C. for 15-24 hours, and urea (Co (NH ₂ ) ₂ ) may be mixed with 1.0-10 mol with respect to 100 mol of BaTiO _3. desirable.

In the present invention, the Ca salt is one selected from the group of CaCO ₃ , Ca (NO ₃ ) ₂ , Ca (COOCH ₃ ) ₂ , Ca (OH) ₂ , CaCl ₂ , 0.5 ~ 2.5mol mixed with 100 mol of BaTiO ₃ One is preferable.

It is preferable to perform calcination at 800-1100 degreeC in this invention.

According to the present invention, a BaCaTiO ₃ powder having a Ba / Ti ratio of 0.995 to 1.005 is obtained, which is a ratio of Ba / Ti of BaTiO ₃ powder as starting material (X) to Ba / Ti of BaCaTiO ₃ (Y ) Difference (XY) is 0.003 to 0.0002, elution of Ba is suppressed.

The present invention relates to a multilayer ceramic capacitor using such BaCaTiO ₃ powder as a main component of the dielectric ceramic layer.

Hereinafter, the present invention will be described in detail.

The present invention is characterized by depositing a nano-sized calcium hydroxide salt on the surface of BaTiO ₃ powder and heat-treating it to synthesize BaCaTiO ₃ powder.

The present inventors have focused on the fact that BaCaTiO ₃ powder having high chemical uniformity can be obtained by chemically coating (chemical adsorption) Ca on the surface of BaTiO ₃ particles in the form of calcium hydroxide using BaTiO ₃ particles as seeds. The invention is completed. According to the results of the present invention, calcium hydroxide is precipitated on the surface of the BaTiO ₃ powder, wherein the reaction is preferably performed while supplying hydroxide ions. The supply of hydroxide ions causes the pH to increase gradually, resulting in even higher chemical uniformity.

The present invention completed in this technical aspect will be described in detail with reference to the accompanying drawings.

[Preparation process of mixed aqueous solution of BaTiO ₃ powder and Ca salt]

BaTiO ₃ powder is produced by various methods such as solid phase method, grinding method, wet method, hydrolysis method, hydrothermal synthesis method, alkoxide method, sol gel method and the like. BaTiO ₃ powder to be used in the present invention is not limited to the production method, but the powder produced by the hydrothermal synthesis method is most preferred. This is because the hydrothermal synthesis method can provide finer BaTiO ₃ powder. The Ba / Ti ratio in the BaTiO ₃ powder can also be used under normal conditions, preferably 0.995 to 1.005. The particle size of the BaTiO ₃ powder to be used is preferably 0.05 ~ 0.3㎛ when considering the calcining heat treatment for dispersion and synthesis.

Mixing BaTiO ₃ powder and Ca salt as described above, Ca salt may be one selected from the group of CaCO ₃ , Ca (NO ₃ ) ₂ , Ca (COOCH ₃ ) ₂ , Ca (OH) ₂ , CaCl _2, etc. . Ca is preferably doped 0.5 ~ 2.5mol% compared to BaTiO ₃ , for this purpose Ca is preferably mixed 0.5 ~ 2.5mol with respect to 100mol BaTiO ₃ . If the mixing amount of Ca salt is less than 0.5mol, the doping amount of Ca in the BaCaTiO ₃ powder obtained does not contribute to the reduction resistance and improve the reliability, and if it exceeds 2.5mol, the dielectric constant may be lowered.

Preferable examples of mixing BaTiO ₃ powder and Ca salt will be described. First, BaTiO ₃ powder is dispersed in an aqueous phase. Dispersion should be optimized without aggregation of BaTiO ₃ powders so that Ca ions can be evenly wrapped around the BaTiO ₃ powder. A suitable dispersant may be used for this purpose, or other dispersing methods may be used to physically disperse the agglomerated powder using a device such as a sonicator. Ca salt is mixed with BaTiO ₃ powder dispersed in this way to prepare a mixed aqueous solution. Ca salt is preferably used in the form of a hydrate (Ca (NO ₃ ) ₂ .4H ₂ O).

[Precipitation Process of Calcium Hydroxide on the Surface of BaTiO ₃ Powder]

In the mixed aqueous solution of BaTiO ₃ powder and Ca salt, calcium hydroxide is deposited on the surface of BaTiO ₃ powder. At this time, it is recommended to supply hydroxide ions from the mixed aqueous solution. The supply of hydroxide ions is preferably such that the pH of the mixed aqueous solution is gradually increased. As the pH increases gradually, the chemical uniformity of the BaCaTiO ₃ powder obtained by synthesis increases.

In the present invention, the rate of change of pH is gradually increased rather than abruptly, and the condition of the rate of change of appropriate pH calculated through experiments is 0.3pH / min or less up to 10 minutes at the beginning of the reaction (start time of addition of hydroxide ion feed material). , 900 minutes from the beginning of the reaction is to be less than 0.005pH / min. Figure 1 shows the rate of pH change when supplying hydroxide ions using urea and KOH. In the case of supplying hydroxide ions using urea in FIG. 1, the pH change rate is 0.3pH / min or less from the initial reaction to 10 minutes, and the pH change rate is less than 0.005pH / min or less from the initial reaction to 900 minutes. In one case, the chemical uniformity of BaCaTiO ₃ powder is considerably better than when the pH change rate is too rapid (KOH). Since the rate of pH change becomes slow after 900 minutes at the beginning of the reaction, it is not particularly limited.

In the present invention, the supply of hydroxide ions may utilize decomposition of an amine compound. The supply reaction of hydroxide ions through urea (Co (NH ₂ ) ₂ ), which is a representative example of an amine compound, will be described.

Urea generates a pyrolysis reaction as in Scheme 1 at a temperature of 60 ° C. or higher. In acidic aqueous solution, decomposition products are produced as in Scheme 2 and Scheme 3 in a basic aqueous solution.

Scheme 1

_{CO (NH 2) 2 → NH} 4+ + OCN -

Scheme 2

_{CO (NH 2) 2 + 3H} 2 O → 2NH 4+ + CO 2 + 2OH -

Scheme 3

_{CO (NH 2) 2 + 3H} 2 O → 2NH 4+ + HCO 3- + OH -

As in Schemes 2 and 3, urea decomposes to generate ammonia and hydroxide ions. When ammonia and hydroxide ions are generated, the concentration of hydroxide ions in the entire solution may be increased slowly and uniformly as shown in FIG. 1. In the present invention, an amine-based compound decomposing in an aqueous solution to generate ammonia, such as urea, may be applied. Slowly increasing the concentration of hydroxide ions can precipitate Ca ions in the form of calcium hydroxide salts.

In general, precipitation can take place in 1) the nucleation of new particles in a supersaturated aqueous solution, or 2) the ostwald ripening of already existing particles. Therefore, in order to precipitate the nano-sized calcium hydroxide salt, it inhibits its own growth reaction, and instead, the surface of the activated BaTiO ₃ particles as a seed serves as a nucleating agent.

Therefore, each calcium hydroxide salt generated by hydrolysis through urea pyrolysis may be coated (chemical adsorption) by inducing precipitation in nano size on the surface of BaTiO ₃ particles.

According to the invention, the precipitation of calcium salts on the surface of the BaTiO ₃ powder and BaTiO ₃ powder, Ca salt mixed aqueous solution. At this time, the hydroxide ions are supplied under the condition that the rate of change of pH does not increase rapidly. The most preferable example is pyrolysis of urea. When using pyrolysis of urea, it is desirable to optimize the concentration of urea, pyrolysis temperature and reaction time of urea in order to optimize the adsorption amount compared to the supply of Ca ions and to minimize leaching of Ba ²⁺ ions from BaTiO ₃ powder. .

The concentration of urea (Co (NH ₂ ) ₂ ) is preferably mixed 1.0 to 10 mol with respect to 100 mol of BaTiO ₃ . When the concentration of urea is 1 mol or more, the amount of adsorption compared to the supply of Ca ions can be secured at an appropriate level or more. If the concentration of the urea exceeds 10 mol, carbon of the urea may be xanthan and the characteristics of the BaCaTiO ₃ powder may be reduced.

Pyrolysis of the urea (Co (NH ₂ ) ₂ ) is preferably performed at 60-80 ° C. For pyrolysis of urea, it is preferable to be 60 ° C. or higher, but if it exceeds 80 ° C., it may be eluted into an aqueous solution of Ba ions. Pyrolysis time should be more than 15 hours to ensure the adsorption amount of Ca ions compared to the appropriate level or more, but if more than 24 hours can be eluted into the aqueous solution of Ba ions.

[Drying and Synthesis Process]

The mixed aqueous solution reacted as above is dried immediately or dried after solid-liquid separation to obtain a powder. Solid-liquid separation may use a filter (centrifuge filter or membrane filter).

The dry powder is calcined to synthesize BaCaTiO ₃ powder and then ground. As for calcining, 800-1100 degreeC is preferable. If the calcination temperature is less than 800 ℃ unreacted unreacted phase may occur, and if the calcination temperature is higher than 1100 ℃ may cause excessive growth of the particles to obtain the desired particle size. In the calcination process, the temperature increase time is 1 ~ 10 ℃ / min, the calcination time may be applied 1 to 4 hours. The powder obtained by calcining is ground to a desired particle size.

[Barium calcium titanate powder and laminated ceramic capacitor]

Together of Ba / Ti in BaCaTiO ₃ powder which is synthesized by the present invention, ratio of 0.995 ~ 1.005 are preferred, non-(Y) of the starting material of BaTiO ₃ powder of Ba / Ti ratio (X) and the BaCaTiO ₃ of Ba / Ti The difference XY is about 0.003 to 0.0002, and it can be obtained that the elution of Ba is suppressed.

In the present invention, the BaCaTiO ₃ powder may be used as a main component of the dielectric ceramic layer in the multilayer ceramic capacitor. That is, the dielectric ceramic layer in the multilayer ceramic capacitor including a plurality of stacked dielectric ceramic layers and a plurality of internal electrodes arranged to form capacitance between the dielectric ceramic layers and external electrodes electrically connected to the internal electrodes. The main ingredient is barium calcium titanate powder obtained according to the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

100 nm-class BaTiO ₃ (100 mol) and Ca (NO ₃ ) ₂ (0.5 to _2.5 mol) prepared by hydrothermal synthesis were dispersed in an aqueous phase using an aqueous dispersant. When mixing on an aqueous system, the materials were mixed while stirring with a mechanical stirrer so as to be dispersed in small amounts in order.

The mixed aqueous solution was added at 1.0-5.0 mol% of CO (NH ₂ ) ₂ while maintaining the temperature at 60-80 ° C. under an oil-bath, followed by stirring for 15-24 hours using a mechanical stirrer. After completion of the reaction, the slurry was allowed to settle and then filtered through a membrane filter. The powder finally obtained was dried at a temperature of 100 to 120 ° C. in a dry oven. On the other hand, using 2 mol% KOH instead of urea (urea) to measure the pH change according to the mixing time and the results are shown in FIG.

As shown in Figure 1, when using urea (urea) was confirmed that the pH change gradually increases. Table 1 shows the change and rate of pH at 10 minutes and 1000 minutes after the injection time of urea and KOH in the graph of FIG.

Solution holding time Add KOH Urea addition pH change pH change rate pH change pH change rate 10min 6.0 0.6 (pH / min) 1.5 0.15 (pH / min) 1000min 6.0 0.006 (pH / min) 4.0 0.004 (pH / min)

2 shows the results of EPMA analysis, which can determine the dispersion degree of BaTiO ₃ powder and Ca as the uniformity of color. In the case of urea (Fig. 2c, d) having a slower pH change rate than KOH (Fig. 2b) having a rapid pH change rate, the components are evenly dispersed. Figure 2a is for the powder prepared by the conventional solid-phase synthesis method, it was found that the dispersion of the components is not very good.

Example 2

BaCaTiO ₃ powders prepared in the same manner as in Example 1 but obtained by mixing 1 mol% of Ca (NO ₃ ) ₂ were subjected to XRD analysis, SEM analysis, ICP analysis, and XRF analysis.

XRD analysis results are shown in FIG. 3. In FIG. 3B, the left peak is the (002) plane and the right peak is the (200) plane, and the (002) plane and the (200) plane are separated from the peaks, thereby confirming that the electrical characteristics can be properly implemented. there was. In FIG. 3A, 2θ is 10 to 110 °, and in FIG. 3B, 2θ is an enlarged 45 ° region. K factor is 7.026 and crystallinity (c / a) is 1.010.

SEM analysis results are shown in FIG. 4. It can be seen from FIG. 4 that particle growth is greatly suppressed.

The results of ICP analysis and XRF analysis are shown in Tables 2 and 3.

ICP Analysis Results Urea concentration 1mol% 2mol% 3mol% 5mol% Ca content 0.145 wt% 0.151% by weight 0.159% by weight 0.169% by weight

In the case of mixing 1 mol% of Ca (NO ₃ ) ₂ , the theoretical content corresponds to 0.17 wt%. When pyrolysis of urea was used, most of Ca was adsorbed, and as the concentration of urea was increased, it was found to be closer to the theoretical content of Ca.

XRF analysis result Urea concentration 1mol% 2mol% 3mol% 5mol% Ba / Ti 0.9945 0.9956 0.9969 0.9973

In the BaTiO ₃ powder used in Example 2, the Ba / Ti ratio was 0.9975. As shown in Table 3, the elution of Ba is not large when pyrolysis of urea is used, and the elution of Ba is suppressed as the urea concentration increases.

In the accompanying drawings and the detailed description of the present invention, it was confirmed that BaCaTiO ₃ powder having excellent chemical uniformity could be obtained by suppressing a sharp increase in pH through pyrolysis of urea. However, this embodiment is one of the most preferred examples, and any thing having substantially the same configuration as the technical idea described in the claims of the present invention and achieving the same effect is included in the technical scope of the present invention. For example, if a calcium hydroxide salt is precipitated on the surface of BaTiO ₃ powder by suppressing a sudden increase in pH without using pyrolysis of urea, and synthesized into BaCaTiO ₃ powder having excellent chemical uniformity through heat treatment, the technical scope of the present invention is obvious. It should be interpreted as being included in.

As described above, according to the present invention, there is a useful effect of obtaining a barium calcium titanate powder having high chemical uniformity and suppressing grain growth even after heat treatment.

Claims (14)

Preparing a mixed aqueous solution of BaTiO ₃ powder and Ca salt, Precipitating calcium hydroxide salt on the surface of the BaTiO ₃ powder in the mixed aqueous solution, A method for producing barium calcium titanate powder comprising calcining the powder obtained by drying from the mixed aqueous solution to synthesize the BaCaTiO ₃ powder and then grinding. The method of claim 1, wherein the precipitation of the calcium hydroxide is obtained by increasing the rate of change of the pH of the mixed aqueous solution to 0.3pH / min or less up to the initial 10 minutes, and mixing at a rate of 0.005pH / min or less from the initial to 900 minutes A method for producing barium calcium titanate powder. The method of claim 1, wherein the increase in pH is caused by decomposition of the amine compound. The method of claim 3, wherein the amine compound is urea (Co (NH ₂ ) ₂ ). Preparing a mixed aqueous solution of BaTiO ₃ powder and Ca salt, Mixing and pyrolyzing urea in the mixed aqueous solution, A method for producing barium calcium titanate powder comprising calcining the powder obtained by drying from the mixed aqueous solution to synthesize BaCaTiO ₃ powder and then grinding the powder. The method for producing barium calcium titanate powder according to claim 4 or 5, wherein the pyrolysis of the urea (Co (NH ₂ ) ₂ ) is performed at 60-80 ° C. 6. The method of claim 4, wherein the urea (Co (NH ₂ ) ₂ ) is mixed in an amount of 1.0 to 10 mol with respect to 100 mol of BaTiO _{3. 7} . The method for producing barium calcium titanate powder according to claim 4 or 5, wherein the pyrolysis of the urea is performed for 15 to 24 hours. The titanic acid according to claim 1 or 5, wherein the Ca salt is one selected from the group consisting of CaCO ₃ , Ca (NO ₃ ) ₂ , Ca (COOCH ₃ ) ₂ , Ca (OH) ₂ and CaCl ₂ . Method for producing barium calcium powder. The method for preparing barium calcium titanate powder according to claim 1 or 5, wherein the Ca salt in the mixed aqueous solution of BaTiO ₃ powder and Ca salt is 0.5 to 2.5 mol with respect to 100 mol of BaTiO ₃ . The method for producing barium calcium titanate powder according to claim 1 or 5, wherein the calcination is performed at 800 to 1100 ° C. A barium calcium titanate powder obtained by synthesizing a powder of BaTiO ₃ by the method of claim 1 or 5, wherein a Ba / Ti ratio of BaCaTiO ₃ is 0.995 to 1.005. 13. The barium calcium titanate powder according to claim 12, wherein a difference (XY) between the ratio (X) of Ba / Ti of the BaTiO ₃ powder and the ratio (Y) of Ba / Ti of BaCaTiO ₃ is 0.003 to 0.0002. 12. A dielectric material comprising a plurality of stacked dielectric ceramic layers and a plurality of internal electrodes arranged to form capacitance between the dielectric ceramic layers and external electrodes electrically connected to the internal electrodes. Multilayer ceramic capacitor mainly composed of barium calcium titanate powder.

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