JPH11335177A - Production of ceramic powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a ceramic raw material powder containing a uniformly dispersed ceramic additive by effectively suppressing a reduction in pH when drying a ceramic slurry and preventing the segregation of the dispersion of the additive in the ceramic principal component raw material powder in the ceramic raw material powder. SOLUTION: This ceramic powder contains ceramic particles having a perovskite type structure represented by ABO3 such as BaTiO3 used as a principal raw component of the ceramic powder, a difference in the ratio of density of an element A to an element B of the ABO3 between the particle surfaces and the particle central part and further a lower density of the element A on the surface than that in the interior. The ratio of the density of the element A to the element B on the surfaces of the ceramic particles having the perovskite type structure is preferably lower at a depth up to at least 5% of the particle diameter than that of the central part by >=5/1,000. The ceramic particles having the perovskite type structure contain the element A more sparsely on the surface than in the center of the particles and thereby have unevennesses on the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic powder containing perovskite-type structural ceramic particles represented by ABO ₃ and a method for producing the same. More particularly, the present invention relates to a perovskite-type structural ceramic particle represented by ABO ₃ as a main ceramic component. The present invention relates to a method for producing the ceramic particles and a method for producing a ceramic powder in which an additive component is coated on the surface of the perovskite-type structured ceramic particles.

[0002]

2. Description of the Related Art For example, dielectric ceramics mainly composed of a perovskite-type structural ceramic such as BaTiO ₃ used for a multilayer ceramic capacitor, etc. are prepared by adding Mg, Mn, Ca, Sr, etc. to BaTiO _3. The characteristics are improved. More specifically, the purpose of adding the ceramic additive to the ceramic raw material powder is roughly divided into two purposes. One is to improve the temperature characteristics, and as additives to be added for such a purpose, there are a shifter that changes the Curie point of a dielectric material serving as a base material and a defresor that suppresses the dielectric constant near the Curie point. Working metal compounds can be mentioned. Such additives can significantly alter the electrical properties of the ceramic. The other is to improve the low-temperature sinterability of the composite powder. As an additive to be added for such a purpose, a low melting point compound such as silica can be used.

In recent years, ceramic electronic components such as multilayer ceramic capacitors have been significantly reduced in size and performance. For example,
In the case of a multilayer ceramic capacitor, the size and the capacity are remarkably reduced. Along with this, the thickness of the dielectric layer forming the base of the multilayer ceramic capacitor has been significantly reduced. Under such circumstances, if the dispersion of the additive components in the dielectric layer is non-uniform, the electrical characteristics of the dielectric layer are locally different and non-uniform, and the temperature characteristics and quality of the multilayer ceramic capacitor are reduced. , Significantly lowering the reliability. Therefore, in order to maintain the characteristics, quality, and reliability of the multilayer ceramic capacitor, it is essential to uniformly disperse the additive components in the dielectric layer.

Conventionally, in order to manufacture such a dielectric porcelain, the main ingredient component powder and the additive ingredient powder are wet-mixed to disperse the additive ingredient powder in the main ingredient component powder. I was According to this method, a main raw material component powder and an additive component powder are added as a raw material powder of an oxide or a carbonate to a dispersion medium, and wet-mixed with a pulverizing medium.

However, in this method, because of mechanical dispersion, the dispersion limit is naturally determined by the dispersion device and the diameter of the medium, and uniform mixing at the micron level is impossible.
When the dispersion state becomes non-uniform, a difference occurs in the doping effect of the additive component on the individual main raw material component particles, the non-uniformity of the sintered body increases, and the electrical characteristics, reliability, and mechanical strength decrease. Bring. Therefore, in order to further increase the dispersion, a coating method in which an additive is added in a form soluble in a solvent and deposited on the surface of the main raw material has been studied. For example, adding a hydrolyzable metal organic compound to the main raw material component powder,
A method of performing coating in an organic solvent is disclosed in JP-A-8-87.
No. 039.

[0006]

However, when ammonia or the like is used to adjust the pH of the ceramic slurry during mixing and dispersion, the ammonia evaporates during heating and drying after the dispersion,
In some cases, the pH of the ceramic slurry decreased, and the additive coated only by chemisorption redissolved, resulting in poor dispersibility of the additive. In addition, when the dispersion is performed after the coating, the peel strength of the coating layer is weak, so that the coating layer is easily missing and the dispersion is deteriorated.

Accordingly, the present invention has been made in view of the above-mentioned problems of the conventional method for producing a ceramic raw material powder, and effectively suppresses a decrease in pH during drying of ceramic slurry, and disperses the additive in the ceramic raw material powder with respect to the ceramic main raw material powder. An object of the present invention is to provide a ceramic powder capable of preventing segregation and obtaining a ceramic raw material powder in which additives are uniformly dispersed, and a method for producing the same.

[0008]

In order to achieve the above object, the present invention relates to a method for uniformly coating an additive component on the surface of a perovskite-type structural ceramic particle represented by ABO _3. Of the density of the element A and the density of the element B (hereinafter referred to as “A
/ B ratio ”. ), The particle surface has a smaller density of the element A than the inside of the particle, that is, a structure of a perovskite-type structure ceramic particle that forms an A site pore, and this is used as a ceramic main raw material powder.

[0009] That is, the ceramic powder according to the invention, in a ceramic powder comprising a perovskite-type structure ceramic particles represented by ABO _3, and A elements wherein at the surface and the particle center portion of the perovskite-type structure ceramic particles ABO ₃ It is characterized in that the density ratio of the element B is different and the density of the element A is smaller on the surface than on the inside. The ratio between the density of the A element and the density of the B element on the surface of the ceramic particles having a perovskite structure is at least 5% of the particle size.
%, It is preferably at least 5/1000 smaller than the central part. The surface of the ceramic particles having such a perovskite structure has an element A which is less sparse than the center of the particles, thereby having irregularities on the surface.

In such a ceramic powder, the surface of perovskite particles, which is a main raw material component, is activated,
The surface area due to the unevenness is increased, and the physical adsorption of the additive component is promoted. For this reason, the mechanical peel strength after coating can be increased. Further, in such perovskite-type structured ceramic particles, A
Since the density of the element is small and the element is diluted, chemical adsorption of the additive component is promoted, and the physical adsorption becomes better due to the uneven surface state. As a result, a stronger additive component can be coated, the peel strength of the coating layer can be improved, and the dispersibility of the additive component in a drying step or the like can be prevented from being deteriorated, and the dispersibility can be improved.

According to the method of the present invention for producing a ceramic powder containing such perovskite-type structured ceramic particles, the surface of the perovskite-type structured ceramic particles is chemically etched to remove the A element of ABO _{3 on} the surface of the particles. It is characterized by being removed. Also,
Another manufacturing method involves mechanically rubbing the surface of the perovskite-type structured ceramic particles and causing the ABO ₃
It is characterized by removing elements.

In such a method for producing a ceramic powder, it is preferable that the change rate of the specific surface area of the perovskite-type ceramic particles before and after chemical etching or mechanical friction is 1.5 to 3.0 times. Furthermore, ceramic powder obtained by dispersing an additive in ceramic powder containing perovskite-type structural ceramic particles is dispersed in a dispersion medium into the ceramic powder by dispersing the perovskite-type structural ceramic particles in which the element A on the surface is diluted. An additive is added therein, and the additive component is coated on the surface of the perovskite-type structure ceramic particles, and then the ceramic slurry is dried,
It is obtained by precipitating ceramic particles.

[0013]

Embodiments of the present invention will now be described specifically and in detail with reference to the drawings.
As described above, the main raw material component powder contained in the ceramic powder according to the present invention is, for example, BaTiO ₃ , PbTi
In order to uniformly coat and disperse an additive on the surface of perovskite-type structural ceramic particles represented by ABO ₃ such as O ₃ , PbZrO ₃ , and YFeO ₃ , a perovskite-type structural ceramic which is a main raw material component powder is used. When the concentration of the element A and the concentration of the element B are compared between the surface of the particle and the inside of the particle, the particle surface has a lower concentration of the element A than the inside of the particle, that is, a perovskite-type structural ceramic particle having an A site pore. Use

In order to produce such perovskite particles, the surface of the main raw material is chemically modified by etching the surface with nitric acid or the like. Thereby, fine irregularities can be formed on the surface of the main raw material, and when the additive component is coated on the surface of the perovskite-type structural ceramic particles in order to activate the surface of the main raw material, not only chemical adsorption but also chemical adsorption. It promotes physical adsorption and improves mechanical peel strength after coating.

In general, since element A has a property of being easily soluble in water, the element A is eluted from the particle surface by etching, and the concentration of element A on the surface of the perovskite particles becomes low, resulting in chemical adsorption. Is promoted,
The strength of the coating is improved. Further, as described above, as another means for producing a perovskite particle having a low concentration of the element A on the surface of the particle, a perovskite particle which is a main raw material before coating is mechanically pulverized in advance so that physical Is to perform a good surface modification. In other words, a new surface of the perovskite particles, which is a main component of the ceramic, is increased, and the surface is made uneven.

This activates the surface of the perovskite particles, which are the main raw material components, and promotes physical adsorption.
For this reason, the mechanical peel strength after coating can be increased. Further, by mechanical pulverization, the element A is eluted from the surface of the perovskite particles, and the element A is diluted on the surface of the perovskite particles, thereby promoting chemical adsorption. For this reason, the strength of the coating is improved.

It is desirable that the rate of change of the specific surface area of the perovskite-type structured ceramic particles before and after chemical etching or mechanical friction is 1.5 to 3.0 times. The A / B ratio of the surface of the perovskite-type structured ceramic particles after such chemical etching or mechanical friction is at least 5% of the particle size, more than 5% of the central A / B ratio. It is preferably smaller than / 1000.

In such perovskite-type structured ceramic particles, the chemical adsorption of the additive is promoted by elution of the element A on the surface thereof, and the physical adsorption is enhanced by the unevenness of the surface state. It will be good. This makes it possible to more strongly coat the additive component, and the peel strength of the coating layer is improved. For this reason, it is possible to prevent the dispersion of the additive component from being deteriorated in the drying process or the like, and the dispersibility is improved.

[0019]

Next, embodiments of the present invention will be described in detail with specific numerical values. (Example 1) Example 1 and Comparative Example 1 using a B characteristic multilayer ceramic capacitor using barium titanate as a main raw material
Will be described. First, as the main component raw material component powder,
BaTiO ₃ having a purity of 99% or more was used. This main raw material component powder and 3φ zirconia beads were charged into a ball mill, and a 2.0 wt% aqueous nitrate solution was added thereto.
Stirred for minutes and then dried. As a comparative example, BaTiO ₃ was stirred with pure water for 10 minutes without adding a nitrate aqueous solution, and then dried. Table 1 shows the specific surface area of BaTiO ₃ before and after stirring. This indicates that the specific surface area of BaTiO ₃ in Example 1 subjected to the nitric acid etching treatment was 2.4 times that before the treatment. On the other hand, BaTiO in Comparative Example 1 dispersed in pure water without adding an aqueous nitrate solution was used.
The specific surface area of ₃ was almost unchanged.

The A / B ratio between the surface and the center of the BaTiO ₃ particles was examined by a transmission electron microscope and EDS. Here, the central part of the particles is BaTiO
_The surface is substantially near the center of the _three particles, and the surface refers to a portion having a depth of about 10 nm (about 5% of the particle diameter) from the surface of the BaTiO ₃ sliced. Table 1 shows the difference between the A / B ratio between the surface of the BaTiO ₃ particles and the central part measured in this manner.
Shown in

In the BaTiO ₃ particles in Example 1 etched with nitric acid, the A / B ratio at the surface is smaller by 6/1000 in molar ratio than the A / B ratio at the center, that is, the A element on the particle surface It was found that the density was smaller than that inside the particles, and the element A was diluted. On the other hand, in the BaTiO ₃ particles in Comparative Example 1 not subjected to the etching treatment with nitric acid, A / A
Little difference in B ratio was observed. Table 1 shows the specific surface area before and after stirring.

[0022]

[Table 1]

Next, after stirring these ceramic slurry in a ball mill, Mg acetate, Mn acetate and C acetate were added.
The solution in which a was dissolved was put into a ceramic slurry in a ball mill, and the ceramic slurry was further stirred for 3 hours. After the stirring, ammonia was added to the ceramic slurry to adjust the pH. The eluted components of the ceramic slurry prepared in this manner are converted to ICP (Inductive).
Table 2 shows the results of the analysis using the above method (e.g., coupled Coupled Plasma).

[0024]

[Table 2]

As a result, in both Example 1 and Comparative Example 1, the elution of the additive component in the ceramic slurry was hardly detected, and the additive component was BaTi which was the main raw material component.
It can be seen that the surface of the O ₃ particles is almost completely coated. Next, the ceramic slurry thus prepared was dried with a spray dryer. Dispersion of the additive component in the ceramic powder obtained by drying was determined by EPMA (El
electric Probe Micro Analysis
is) Table 2 shows the results obtained using color mapping. As shown in Table 2, in the ceramic powder in Example 1 dispersed in the nitric acid solution, a good dispersion state was obtained. On the other hand, in the ceramic powder of Comparative Example 1, segregation of the additive component was confirmed, and the dispersion state was poor.

This can be attributed to the following causes.
In both the case of Example 1 and the case of Comparative Example 1, the additive component was completely adsorbed on the surface of BaTiO _{3 in} the ceramic slurry. However, the ceramic powder in Comparative Example 1, which was dispersed in pure water, changed the pH due to the evaporation of ammonia in the process of applying heat and drying, the coating components eluted, and the dispersion of the additive components deteriorated. I think that the. On the other hand, in the ceramic powder in Example 1 dispersed in nitric acid, the surface of the BaTiO ₃ particles is eroded by the acid, so that the surface becomes uneven, the surface activity increases, and the physical adsorption is promoted. It is supposed to be. In addition, since the element A on the surface of the BaTiO ₃ particles is diluted, it is considered that chemical adsorption was promoted, and as a result, a strong coating was enabled.
It is presumed that the dispersion was good because the coating layer did not peel off irrespective of the change in pH during the drying process.

Example 2 Next, a mechanical ceramic powder was used.
Example 2 and Comparative Example 2 for confirming the effect of crushing
Will be described. In the same manner as above,
BaTiO with a purity of 99% or more as powder _ThreeUsing
Of the main raw material component powder and 3φ zirconia beads
And stirred in pure water for 10 hours, and then dried.
On the other hand, for comparison, zirconi
BaTiO in pure water without using beads_ThreeInput
And stirred for the same time and then dried.

Table 3 shows the specific surface area of BaTiO ₃ before and after stirring.
Shown in From this, it can be seen that the BaTiO ₃ specific surface area in Example 2 in which the zirconia beads and the zirconia beads were stirred by a ball mill was 2.6 times that before the treatment. On the other hand, Comparative Example 2 in which water was dispersed without using zirconia beads.
The specific surface area of BaTiO ₃ was almost unchanged.

In the same manner as in Example 1, the A / B ratio between the surface and the inside of these BaTiO ₃ particles was examined by a transmission electron microscope and EDS. BaTiO in Example 2 stirred in a ball mill with zirconia beads
_{The three} particles have a surface whose molar ratio is 7/100 from the center.
It was found that the A / B ratio was reduced by 0, the density of the element A on the particle surface was smaller than that inside the particle, and the element A was diluted. On the other hand, Ba in Comparative Example 2 dispersed only with water without using zirconia beads was used.
In the TiO ₃ particles, almost no difference in A / B ratio was observed between the surface and the center. Table 3 shows the specific surface area before and after stirring.

[0030]

[Table 3]

Next, acetic acid M was added to these ceramic slurry.
g, Mn acetate, and Ca acetate were dissolved therein, and the ceramic slurry was further stirred in a ball mill for 3 hours. After the stirring, ammonia was added to the ceramic slurry to adjust the pH. Table 4 shows the results of ICP analysis of the components eluted from the ceramic slurry thus prepared.

As a result, in both of Example 2 and Comparative Example 2, the elution of the additive component in the ceramic slurry was hardly detected, and the additive component was BaTi which was the main raw material component.
It can be seen that the surface of the O ₃ particles is almost completely coated. Next, the ceramic slurry thus prepared was dried with a spray dryer. As a result of examining the dispersion of the additive component in the ceramic powder obtained by drying using EPMA color mapping, as shown in Table 4, the ceramic powder in Example 2 dispersed using zirconia beads showed good dispersion. The condition was obtained. On the other hand, in the ceramic powder of Comparative Example 2, segregation of the additive component was confirmed, and the dispersion state was poor.

[0033]

[Table 4]

The reason for this is that the zirconia beads
It is considered that the pH of the ceramic powder in Comparative Example 2 in which TiO ₃ was not stirred was changed in the course of heating and drying due to evaporation of ammonia, the coating components were eluted, and the dispersion was deteriorated. On the other hand, in the ceramic powder in Example 2 in which BaTiO ₃ was previously stirred with zirconia beads, the element A was eluted from the surface of the BaTiO ₃ particles by mechanical pulverization, the surface became uneven, and the surface activity was increased, and physical adsorption was observed. Is presumed to be promoted. In addition, since the element A on the surface of the BaTiO ₃ particles is diluted, it is considered that chemical adsorption was promoted, and as a result, a strong coating was enabled. It is presumed that the dispersion was good because the coating layer did not peel off irrespective of the change in pH during the drying process.

Example 3 Next, the surface modification of ceramic particles
Examples 3 to 5 for confirming the effect of quality and comparative examples
3 and 4 will be described. First, change the concentration of nitric acid
As shown in Table 5, the main raw material BaTiO _Threeparticle
Of the specific surface area and the concentration of element A on the surface
And a ceramic slurry was obtained from this. these
BaTiO_ThreeCeramic slurry powder with 3φ zirconi
It is put into a ball mill together with the beads and the ceramics
A solution of Mg acetate, Mn acetate, and Ca acetate
After the addition, the mixture was stirred with a ball mill for 3 hours. End of stirring
After that, ammonia was added to adjust the pH of the ceramic slurry.
It was adjusted.

[0036]

[Table 5]

The results of ICP analysis of the components eluted from the ceramic slurry thus prepared are shown in Table 6. From Table 6, it can be seen that the elution of the additive component was hardly detected in any case, and the additive component was almost completely coated. Next, the ceramic slurry thus prepared was dried with a spray dryer. The results of examining the dispersion of the additive component in the dried ceramic powder by using EPMA color mapping are shown in Table 6. Further, the specific surface area of BaTiO ₃ before and after stirring, the ratio thereof, and the obtained BaT
Table 5 shows the A / B ratio between the surface and the center of the iO ₃ particles.
It was shown to.

[0038]

[Table 6]

The specific surface area is increased by a factor of 1.2,
The A / B ratio of the surface of the _three particles is 3/1000 compared to the center.
Comparative Example 3, which was only small, had poor dispersibility of the additive component. However, when the increase in specific surface area is 1.5 times or more, BaTi
The A / B ratio of the surface of O ₃ particles is 5/100
In Example 3, which was smaller than 0, the dispersibility of the additive component was good.

Table 6 shows the electrical characteristics of the multilayer ceramic capacitor made from this ceramic powder. In Comparative Example 4, in which the specific surface area of the main raw material was 3.3 times, the electrical characteristics were deteriorated. Since the A / B ratio of BaTiO ₃ particles does not seem to have a significant effect on the electrical characteristics, even if the A / B ratio of the surface is smaller than the center by 10/1000 or more, the specific surface area increases. It is considered that the electrical characteristics can be satisfied unless accompanied by.

From the above results, it can be seen that in performing the surface modification of the main raw material, it is desirable that the ratio of the specific surface area of the main raw material is 1.5 to 3.0 times. At this time, BaTiO
The A / B ratio of the surface of the _three grains is 5/1000 m compared to the center.
From the above, it can be seen that it is desirable to be small. As described above, by making the surface of the main raw material uneven by acid or mechanical pulverization, the peel strength of the coating layer was increased and the dispersion was improved.

In each of the above embodiments, the ceramic powder for a multilayer ceramic capacitor using BaTiO ₃ has been described. However, the present invention is not limited to the ceramic powder for a multilayer ceramic capacitor using BaTiO _3. For example, PbTiO ₃ , PbZrO ₃ , YF
As with eO ₃ , particles having a perovskite structure represented by ABO ₃ are used as a main raw material, and the same effects can be obtained in the production of ceramic powders used for all electronic components and functional components requiring high dispersion and the like. is there.

[0043]

As described above, in the ceramic powder according to the present invention, the density of the element A is smaller and the element A is diluted as compared with the inside of the surface of the perovskite structure ceramic particles represented by ABO ₃ . Thereby, the chemical adsorption of the additive is promoted, and the physical state becomes better due to the unevenness of the surface state. As a result, a stronger coating is possible, and the peel strength of the coating layer is increased. Therefore, it is possible to prevent deterioration of the dispersion of the additive components in a drying process or the like, and to improve the dispersibility. As a result, uniform dispersibility of the additive component in the perovskite-type ceramic particles represented by ABO ₃ can be obtained.

Claims (7)

[Claims] 1. A ceramic powder containing a perovskite-type structural ceramic particle represented by ABO ₃ , wherein the ratio of the density of the A-element to the B-element of ABO ₃ is between the surface of the perovskite-type structural ceramic particle and the particle center. A ceramic powder characterized in that the density of the element A is different from that of the inside of the ceramic powder. 2. The method according to claim 1, wherein the ratio of the density of the element A to the density of the element B on the surface of the perovskite-type structured ceramic particles is at least 5/1000 smaller than the central portion at a depth of at least 5% of the particle size. Item 7. The ceramic powder according to Item 1. 3. The surface of the perovskite-structured ceramic particles is characterized in that the element A is less sparse than the center of the particles, thereby having irregularities on the surface.
Or the ceramic powder according to 2. 4. The method for producing a ceramic powder containing the perovskite-type structured ceramic particles according to claim 1, wherein the surface of the perovskite-type structured ceramic particles is chemically etched. Removing the element A of ABO ₃ . 5. The method for producing a ceramic powder containing perovskite-type structural ceramic particles according to claim 1, wherein the surface of the perovskite-type structural ceramic particles is mechanically rubbed, and A method for producing a ceramic powder, wherein the element A of ABO ₃ is removed. 6. The method according to claim 4, wherein the change rate of the specific surface area of the perovskite type ceramic particles before and after chemical etching or mechanical friction is 1.5 to 3.0 times. Production method of ceramic powder. 7. A method for producing a ceramic powder in which an additive is dispersed in a ceramic powder containing perovskite-type structural ceramic particles according to any one of claims 1 to 3, wherein the perovskite has a surface in which the element A is diluted. The ceramic particles are dispersed in a dispersion medium to form a ceramic slurry, and an additive is added to the ceramic slurry, and the additive component is coated on the surface of the perovskite-type ceramic particles, and then the ceramic slurry is dried. And a method for producing ceramic powder, wherein ceramic particles are precipitated.