JP5354213B2 - Composite oxide particles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide fine dielectric particles having uniform particle size and particle characteristics, particularly a precursor material capable of producing barium titanate particles. <P>SOLUTION: The compound oxide particle which is the precursor material of barium titanate particles consists substantially of 75-25 mol% barium titanate phase and 25-75 mol% titanium dioxide phase. In this compound oxide particle, the ratio of a different phase comprising unreacted barium compound and excess titanium phase is 1 mol% or less. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to composite oxide particles preferably used as a precursor of dielectric particles typified by barium titanate particles. In particular, the present invention relates to composite oxide particles suitable as a precursor for producing barium titanate particles that are fine and have uniform particle properties.

Barium titanate (BaTiO ₃ ) is widely used as the dielectric layer of the ceramic capacitor. The dielectric layer is obtained by preparing a green sheet from a paste containing barium titanate particles and sintering it. The barium titanate particles used for such applications are generally produced by a solid phase synthesis method. In the solid-phase synthesis method, barium carbonate (BaCO ₃ ) particles and titanium oxide (TiO ₂ ) particles are mixed in a wet manner, and after drying, the mixed powder is fired at a temperature of about 900 to 1200 ° C. Barium titanate particles are obtained by chemical reaction with titanium particles in a solid phase.

In general, firing of a mixed powder of barium carbonate particles and titanium dioxide particles is performed at the above firing temperature by raising the temperature from around normal temperature. When the mixed powder of barium carbonate particles and titanium dioxide particles is fired, the production of barium titanate starts from around 500 ° C. under reduced pressure (under vacuum) and from around 550 ° C. in the air atmosphere. On the other hand, it is known that the raw material barium carbonate grows around 400-800 ° C. Titanium dioxide grows from around 700 ° C.

For this reason, the grain growth of barium carbonate particles and titanium dioxide particles proceeds in the temperature rising process of the mixed powder. Thereafter, when the reaction is carried out at a predetermined firing temperature, the barium carbonate particles and the titanium oxide particles having a large particle size react with each other, so that the particle size of the generated barium titanate powder inevitably increases. Further, in the mixed powder used in the solid phase method, the dispersion of barium carbonate particles and titanium dioxide particles is not necessarily uniform. For this reason, the density of barium carbonate particles is present in the mixed powder. In the portion where the concentration of barium carbonate particles is high, the growth of barium carbonate particles proceeds and large barium carbonate particles are generated. However, in the portion where the concentration of barium carbonate particles is low, the growth of barium carbonate particles hardly occurs. A similar phenomenon appears for titanium dioxide. Furthermore, irregularly shaped particles are generated by the particle bonding between the barium carbonate particles or the titanium dioxide particles. As a result, the particle sizes and particle properties of the titanium dioxide particles and barium carbonate particles involved in the reaction become non-uniform, and the particle size and particle properties of the resulting barium titanate powder also vary.

In recent years, there has been a demand for miniaturization of capacitors, but pastes containing barium titanate particles having a large particle size have a limit in thinning the dielectric layer. Therefore, in order to reduce the thickness of the dielectric layer, the barium titanate powder obtained as described above is pulverized to prepare a powder having a desired particle size. However, it takes time and cost to grind, and the particle properties of the obtained powder are not uniform. Further, when a capacitor is made using barium titanate particles having large particle size variations and non-uniform particle properties, the electrical characteristics of the capacitor become unstable. Therefore, a simple method for obtaining a homogeneous barium titanate powder with a small particle size is desired.

There is a possibility that the barium titanate powder to be produced can be refined and the particle size and particle properties can be made uniform by suppressing the growth and bonding of barium carbonate particles and titanium dioxide particles in the temperature rising process of the mixed powder. . In Patent Document 1, in order to suppress grain growth of barium carbonate particles, barium carbonate particles having a relatively large particle diameter and titanium dioxide particles having a small particle diameter are mixed to form a mixed powder, and titanic acid for firing the mixture powder. A method for producing barium powder is disclosed. Specifically, barium carbonate particles having a specific surface area of 10 m ² / g or less and titanium dioxide particles having a specific surface area of 15 m ² / g or more are used. According to this method, since the barium carbonate particles having a large particle size are surrounded by the titanium oxide particles having a small particle size, the contact between the barium carbonate particles is inhibited, and the particle growth of the barium carbonate powder is suppressed.

However, since barium carbonate particles having a relatively large particle diameter are used as the raw material powder, there is a limit to miniaturization of the barium titanate powder. In addition, since the progress of the reaction is slow for particles having a large particle size, firing for a long time or at a high temperature is necessary in order to obtain homogeneous barium titanate, and there is also a problem in terms of energy efficiency. In addition, the above-described method cannot suppress grain bonding and grain growth between titanium dioxide particles, and irregularly shaped and large-sized titanium dioxide particles may be produced prior to the production of barium titanate. For this reason, there is a limit to the control of the particle size and particle properties of the barium titanate particles.

Further, in Patent Document 2, barium carbonate particles and titanium dioxide particles having a specific surface area of 5 m ² / g or more are mixed so that the molar ratio of Ba / Ti is 1.001 to 1.010, and then fired. A method for producing barium titanate is disclosed. However, even in this method, it is impossible to suppress grain bonding and grain growth between titanium dioxide particles in the firing process, and irregular and large titanium dioxide particles are produced prior to the production of barium titanate. There was a limit to the control of the particle size and particle properties of barium acid particles.

Patent Document 3 and Patent Document 4 disclose a technique in which a titanium oxide particle is coated with a barium compound such as barium nitrate and the resulting composite powder is fired in order to control the particle size of the barium titanate powder. Similarly, Patent Document 5 discloses a technique in which a barium alkoxide compound is coated on the surface of titanium oxide particles and calcined to obtain barium titanate. However, in the methods described in Patent Documents 3 to 5, the process of forming the barium compound layer on the titanium oxide surface is complicated, and the uniformity of the obtained barium compound layer is not necessarily good. Furthermore, the grains may be deformed or enlarged due to grain bonding through the barium compound layer.

In general, the production reaction of barium titanate using barium carbonate and titanium dioxide as raw materials is represented by BaCO ₃ + TiO ₂ → BaTiO ₃ + CO ₂ , but the reaction is known to occur in two stages (non-patent document). Reference 1). That is, the first-stage reaction is a reaction for producing barium titanate on the particle surface of titanium dioxide particles (contact point between barium carbonate and titanium dioxide) at 500 to 700 ° C., and the second-stage reaction is performed at a temperature of 700 ° C. or higher. This is a reaction in which barium ion species diffuses into titanium dioxide in the first stage product.

Therefore, as in Patent Documents 1 and 2, when the heat treatment of the mixed powder is performed at a temperature of 900 ° C. or more in one stage, the grain growth of the raw material particles, the barium titanate formation reaction on the titanium dioxide particle surface, Diffusion of ionic species and grain growth of barium titanate particles occur in a short time. As a result, the resulting barium titanate particles vary in particle size and particle properties.

JP-A-10-338524 JP 11-199318 A JP-A-6-227816 JP-A-8-239215 JP 2002-265278 A J. Mater. Rev. 19, 3592 (2004)

It is an object of the present invention to provide a precursor material capable of producing fine dielectric particles having a uniform particle size and particle property, particularly barium titanate particles.

As a result of diligent studies to achieve this object, the present inventors have noted that grain growth of barium titanate occurs at 900 ° C. or higher.

By generating a barium titanate phase on the surface of the titanium dioxide particles, contact between the titanium dioxide particles is reduced, and grain growth and grain bonding of the titanium dioxide particles are suppressed. In addition, since the barium titanate phase present on the surface of titanium dioxide particles is involved in grain bonding and grain growth at a relatively high temperature, the grain growth and grain bonding of titanium dioxide powder having a barium titanate phase formed on the surface is at a high temperature. Hard to happen until it reaches. Therefore, a titanium dioxide powder having a barium titanate phase formed on the surface is obtained, and then an alkaline earth compound and a rare earth compound are added so that the entire composition falls within the target composition range of the dielectric particles. By performing the heat treatment, the grain growth of the raw material titanium dioxide particles and the product dielectric particles (barium titanate particles, etc.) in the initial stage of the heat treatment process is suppressed, and it has uniform particle properties and crystallinity. It has been found that dielectric particles having a high thickness can be obtained. Based on this finding, the inventors have come up with the following invention.

The present invention for solving the above-mentioned problems includes the following matters as a gist.
(1) Composite oxide particles substantially consisting of 75 to 25 mol% of a barium titanate phase and 25 to 75 mol% of a titanium dioxide phase.

(2) The composite oxide particle according to (1), wherein a barium titanate phase is formed on the surface of the titanium dioxide particle.

(3) The composite oxide particle according to (1) or (2), wherein the ratio of the unreacted barium compound and the excess phase in which titanium is excessive is 1 mol% or less.

According to the present invention, composite oxide particles used as a precursor material for barium titanate particles having high crystallinity, which are suppressed in grain growth during the production of barium titanate, have a fine particle and uniform particle properties, are provided. Provided.

Although not theoretically constrained at all, the present inventors believe that the above-described effect is exhibited by the following reaction mechanism.

That is, first, when obtaining the composite oxide particles of the present invention, by generating a barium titanate phase on the surface of the titanium dioxide particles (hereinafter referred to as “first heat treatment step”), Contact between the titanium dioxide particles is suppressed. As a result, the grain growth (necking, grain bonding) of the titanium dioxide particles is suppressed, and the generation of impurity intermediate substances (Ba ₂ TiO ₄ ) due to the heterogeneity of the reaction is also reduced.

Subsequently, alkaline earth ions (barium ions) and rare earth ion species are diffused into the composite oxide particles to further expand the dielectric phase (barium titanate phase), and finally the dielectric particles (titanate). Barium particles) (hereinafter referred to as “second heat treatment step”). This step is performed at a relatively high temperature. At this time, if the barium titanate phase is not formed on the surface of the titanium dioxide particles, necking and grain bonding may occur through the exposed titanium dioxide sites, and irregular grain growth may occur. In this case, the obtained barium titanate particles are also made amorphous, and uniform barium titanate particles cannot be obtained. However, in the present invention, since the surface of the titanium dioxide particles is coated with the barium titanate phase, the barium ion species is diffused without causing grain growth of the titanium dioxide particles. As a result, fine barium titanate particles having uniform particle properties can be obtained.

Moreover, since the barium titanate particles obtained using the composite oxide particles of the present invention are fine particles, they can be grown to a desired size through the second heat treatment step. As a result of further heat treatment during the grain growth process, barium titanate particles having high crystallinity are obtained.

Hereinafter, the present invention will be described more specifically, including its best mode. In the following description, an example in which barium titanate is produced as a dielectric particle will be described. However, the production method of the present invention is (Ba, Sr) TiO ₃ , (Ba, Ca) TiO ₃ , (Ba, Sr). Manufacturing method of various dielectric particles having a step of heat-treating mixed powder containing titanium dioxide particles and barium compound particles such as (Ti, Zr) O ₃ , (Ba, Ca) (Ti, Zr) O ₃ Applicable to.

The composite oxide particle of the present invention, which is preferably used as a precursor for producing dielectric particles, is substantially composed of only a barium titanate phase and a titanium dioxide phase.
The proportion of the barium titanate phase in the composite oxide particles is 75 to 25 mol%, preferably 75 to 40 mol%, more preferably 75 to 50 mol%, and the proportion of the titanium dioxide phase is 25 to 75 mol%. , Preferably 25 to 60 mol%, more preferably 25 to 50 mol%. The composite oxide particles are substantially composed of only the two phases described above, and are substantially free of an unreacted barium compound phase and a hetero phase with excessive titanium (BaTi ₂ O ₅ , BaTi ₄ O _9, etc.). The ratio of the unreacted phase and the heterogeneous phase is 1 mol% or less.

The barium titanate phase as described above is considered to be formed as a film on the surface of the titanium dioxide particles from the generation mechanism. The titanium dioxide particles are considered to have a barium titanate phase with a thickness of 3 nm or more on the surface, and the titanium dioxide phase is not exposed.

When the proportion of the barium titanate phase in the composite oxide particles is too small, the proportion of the barium titanate phase on the titanium dioxide particle surface becomes insufficient, and the shielding effect of the titanium dioxide particle surface by the barium titanate phase is reduced. To do. As a result, when the titanium dioxide particles come into contact with each other, the titanium dioxide particles may sinter and cause irregular grain growth.

The ratio and average thickness of the barium titanate phase can be controlled by appropriately selecting the charging ratio of titanium dioxide particles and barium compound particles in the first heat treatment step described later. That is, as the proportion of the barium compound increases, the proportion of the barium titanate phase and its average thickness increase.

The formation of a predetermined barium titanate phase in the composite oxide particles of the present invention can be confirmed by X-ray diffraction analysis and transmission electron microscope analysis of the composite oxide particles.

Next, the manufacturing method of said composite oxide particle is demonstrated.
The composite oxide particles are a mixed powder containing titanium dioxide particles and barium compound particles that generate barium oxide by thermal decomposition at a predetermined ratio (hereinafter sometimes referred to as “first mixed powder”), 500 It is obtained by heat treatment (first heat treatment step) at a temperature not lower than 900 ° C and lower than 900 ° C.

The titanium dioxide particles used as a raw material are not particularly limited, but the BET specific surface area is preferably 20 m ² / g or more, more preferably 25 m ² / g or more, and particularly preferably 30 m ² / g or more. From the viewpoint of improving the reactivity and obtaining fine barium titanate particles, the higher the BET specific surface area of the titanium dioxide particles, that is, the smaller the particle diameter of the particles, the better. It can be difficult. Therefore, in order to improve productivity, it is preferable to keep it at about 20 to 80 m ² / g.

The production method of the titanium dioxide particles used in the present invention is not particularly limited, and a commercially available product may be used, or a product obtained by pulverizing a commercially available product may be used. In particular, since the rutileization is low and fine titanium dioxide fine particles can be obtained, titanium dioxide particles obtained by a vapor phase method using titanium tetrachloride as a raw material are preferably used.

A general method for producing titanium dioxide by a vapor phase method is known, and when titanium tetrachloride as a raw material is oxidized using an oxidizing gas such as oxygen or water vapor under a reaction condition of about 600 to 1200 ° C., dioxide dioxide is obtained. Titanium fine particles are obtained. When the reaction temperature is too high, the amount of titanium dioxide having a high rutile ratio tends to increase. Therefore, the reaction is preferably performed at about 1000 ° C. or lower.

As the barium compound that generates barium oxide by thermal decomposition, barium carbonate (BaCO ₃ ), barium hydroxide (Ba (OH) ₂ ), or the like can be used, and two or more barium compounds may be used in combination. However, barium carbonate particles are particularly preferably used from the viewpoint of easy availability. Barium carbonate particles are not particularly limited, and known barium carbonate particles are used. However, in order to promote the solid phase reaction and obtain fine barium titanate particles, it is preferable to use raw material particles having a relatively small particle size. Therefore, BET specific surface area of the barium compound particles used as a raw material is preferably ^{10 m} 2 / g or more, more preferably 10 to 40 m ² / g.

The mixing ratio of the raw material powder in the first mixed powder is set according to the composition of the target composite oxide particles, and is 25 to 75 mol%, preferably 40 to 75 mol%, and more preferably 40 to 75 mol% with respect to 100 mol% of titanium. Preferably, titanium dioxide and barium compound are mixed at a ratio of 50 to 75 mol%.

The method for preparing the first mixed powder is not particularly limited, and a conventional method such as a wet method using a ball mill may be adopted. The obtained first mixed powder is dried and then heat-treated under a predetermined condition (first heat treatment step) to obtain composite oxide particles.

In the first heat treatment step, the mixed powder is heat treated to generate a barium titanate phase on the surface of the titanium dioxide particles. Note that the binder removal step may be performed prior to the first heat treatment step.

The heat treatment temperature in the first heat treatment step varies depending on the heat treatment atmosphere and the like, but is lower than the heat treatment temperature in the second heat treatment step, and a barium titanate phase is formed on the surface of the titanium dioxide particles due to the reaction between the titanium dioxide particles and the barium compound. It is a temperature to be formed, and is 500 ° C or higher and lower than 900 ° C. The heat treatment time is sufficient for all the barium compounds to react and produce barium titanate. The heat treatment atmosphere is not particularly limited, and may be an air atmosphere, a gas atmosphere such as nitrogen, a reduced pressure, or a vacuum.

When the heat treatment temperature is too high, grain growth occurs before the barium compound particles and titanium dioxide particles as raw materials react, and there is a limit to miniaturizing the finally obtained barium titanate particles. In this case, a heterogeneous phase (BaTi ₂ O ₅ , BaTi ₄ O _9, etc.) in which titanium is excessive may be generated. On the other hand, when the heat treatment temperature is too low or the heat treatment time is too short, the barium compound may remain and a predetermined barium titanate phase may not be generated.

When performing a 1st heat processing process using a normal baking furnace, Preferably it is 500-900 degreeC, More preferably, it is 500-700 degreeC, Most preferably, it performs at 600-700 degreeC. Here, the normal firing furnace refers to a furnace for firing the mixed powder in a stationary state, such as a batch furnace. The temperature increase may be performed from room temperature, or after the mixed powder is preheated, the above temperature increase operation may be performed. In this case, the holding time at the heat treatment temperature is 0.5 to 4 hours, preferably 0.5 to 3 hours.

In the temperature raising process up to the heat treatment temperature, the rate of temperature rise is preferably about 1.5 to 20 ° C./min. The atmosphere in the temperature raising process is not particularly limited, and may be an air atmosphere, a gas atmosphere such as nitrogen, a reduced pressure, or a vacuum.

Further, the first heat treatment step may be performed in a firing furnace in which powder is fluidly fired. In this case, the heat treatment is preferably performed at 500 to 900 ° C, more preferably 500 to 700 ° C, particularly preferably 600 to 700 ° C. Here, examples of the firing furnace for fluidly firing the powder include a rotary kiln. The rotary kiln is an inclined heating tube and has a mechanism that rotates around the central axis of the heating tube. The mixed powder charged from the upper part of the heating tube is heated in the process of moving downward in the tube. Therefore, by controlling the temperature of the heating tube and the passing speed of the mixed powder, the ultimate temperature and the heating rate of the mixed powder can be appropriately controlled. In this case, the holding time at the heat treatment temperature is 0.1 to 4 hours, preferably 0.2 to 2 hours.

The first heat treatment step can be performed at 450 to 600 ° C., preferably 450 to 550 ° C. under a reduced pressure of less than atmospheric pressure, for example, at a pressure of about 8 × 10 ⁴ Pa. In this case, the holding time at the heat treatment temperature is 0.5 to 4 hours, preferably 0.5 to 3 hours. According to the reduced pressure firing, the reaction can be performed at a low temperature, and the reaction rate for the growth of the raw material particles can be increased.

The composite oxide particles according to the present invention are obtained by the first heat treatment step as described above. As described above, this composite oxide particle is particularly preferably used as a precursor for producing dielectric particles. When producing dielectric particles using the composite oxide particles of the present invention, a predetermined additional component is added to the composite oxide particles, and the composition of the entire mixed powder is almost equal to the intended dielectric particles. Then, a second heat treatment step described later is performed.

The additional component added to the composite oxide particles varies depending on the composition of the target dielectric particles, but is generally an alkaline earth compound and / or a rare earth compound.

For example, when producing barium titanate (BaTiO ₃ ), a barium compound may be added. The molar ratio of Ba / Ti in barium titanate that is stably obtained by ordinary one-step firing is about 0.990 to 1.010, but according to the production method of the present invention, 0.985 to 1 An unexpected effect is obtained that barium titanate is obtained in the range of .015.

Moreover, when manufacturing (Ba, Sr) TiO ₃ and (Ba, Ca) TiO ₃ , a predetermined amount of barium carbonate, strontium carbonate, calcium carbonate, or the like is added. Further, in the case of synthesizing (Ba, Sr) (Ti, Zr) O ₃ , (Ba, Ca) (Ti, Zr) O _3, etc., in addition to the above, a compound serving as a zirconium source such as ZrO ₂ is added. To do.

Further, in order to impart various characteristics to the finally obtained dielectric, a rare earth compound serving as a rare earth source may be added. The rare earth compound is not particularly limited, and may be various rare earth oxides (Re ₂ O ₃ ). As a rare earth oxide, an oxide of each element of Y, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb can be exemplified.

An additional component as described above is added to the composite oxide particles and mixed in the same manner as the first mixed powder, thereby preparing a second mixed powder and performing a second heat treatment step.
The heat treatment temperature in the second heat treatment step is 850 to 1000 ° C, preferably 850 to 950 ° C. As described above, since the second heat treatment step is performed after the composite oxide particles having the barium titanate phase are formed by the first heat treatment step, the tetragonal crystallinity is good even at a low temperature of 1000 ° C. or lower. In addition, fine particles of barium titanate having high crystallinity and uniform particle properties can be obtained. The heat treatment time is a time sufficient for the solid phase reaction between the composite oxide particles and the additional component to be substantially completed. Generally, the holding time at the heat treatment temperature is 0.5 to 4 hours, Preferably it is 0.5 to 2 hours. The atmosphere during the heat treatment is not particularly limited, and may be an air atmosphere, a gas atmosphere such as nitrogen, a reduced pressure, or a vacuum. If the heat treatment temperature is too low or the heat treatment time is too short, there is a possibility that homogeneous barium titanate particles cannot be obtained.

In the temperature raising process up to the heat treatment temperature, the rate of temperature rise is preferably about 1.5 to 20 ° C./min. The atmosphere in the temperature raising process is not particularly limited, and may be an air atmosphere, a gas atmosphere such as nitrogen, or a reduced pressure or vacuum.

The second heat treatment step may be performed using a general electric furnace such as a batch furnace, and a rotary kiln may be used when a large amount of mixed powder is continuously heat-treated.

Due to the second heat treatment step, additional components (barium ion species, etc.) diffuse through the barium titanate phase of the composite oxide particles formed in the first heat treatment step, and the dielectric particles have a small particle size at the initial stage of the heat treatment. (Barium titanate particles) are obtained. The fine dielectric particles grow by continuing the heat treatment. Therefore, dielectric particles having a desired particle size can be easily obtained by appropriately setting the heat treatment time in the second heat treatment step. In particular, by using the composite oxide particles of the present invention, dielectric particles having uniform particle properties can be obtained, so that abnormal grain growth is suppressed even when the particles are grown. After the heat treatment, the temperature is lowered to obtain dielectric particles. The temperature lowering rate at this time is not particularly limited, and may be about 3 to 100 ° C./min from the viewpoint of safety.

By using the composite oxide particles of the present invention, grain growth during the production of dielectric particles is suppressed, and particularly in the initial stage of heat treatment, dielectric particles having high crystallinity and uniform particle properties, typically Fine particles of barium titanate are obtained.

In the obtained barium titanate particles, c / a serving as a tetragonal index is determined by X-ray diffraction analysis, and is preferably 1.008 or more, more preferably 1.009 or more.

The particle property can be evaluated by obtaining the particle size by X-ray diffraction analysis or a scanning electron microscope and calculating the variation in particle size. The variation in particle diameter can be confirmed from, for example, the average particle diameter and the standard deviation of the particle diameter. The particle properties can also be confirmed from the specific surface area by the BET method.

Further, the obtained barium titanate powder is substantially free of unreacted additional components and heterogeneous phases containing excessive titanium (BaTi ₂ O ₅ , BaTi ₄ O _9, etc.), and has extremely high uniformity.

The obtained dielectric particles (barium titanate particles) are pulverized as necessary, and then used as a co-material added to a raw material for manufacturing dielectric ceramics and a paste for forming an electrode layer. Various known methods can be employed without particular limitation for the production of dielectric ceramics. For example, the subcomponents used for the production of dielectric ceramics can be appropriately selected according to the target dielectric characteristics. Moreover, the preparation of the paste, the green sheet, the formation of the electrode layer, and the sintering of the green body may be appropriately performed according to known methods.

As mentioned above, although the example which manufactures barium titanate as a dielectric particle was demonstrated about the usage aspect of the composite oxide particle of this invention, the said manufacturing method heat-processes the mixed powder containing a titanium dioxide particle and a barium compound particle. The present invention can be applied to various dielectric particle manufacturing methods having a process. For example, when synthesizing (Ba, Sr) TiO ₃ , (Ba, Ca) TiO ₃ , (Ba, Sr) (Ti, Zr) O ₃ , (Ba, Ca) (Ti, Zr) O _3, etc. In the above solid-phase reaction, a compound that becomes a Sr source, a Ca source, and a Zr source is added, or a compound that becomes a Sr source, a Ca source, and a Zr source is further added after the synthesis of barium titanate, and heat treatment is performed. (Baking) may be performed.

Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

As starting materials, titanium dioxide powder having a BET specific surface area of 31 m ² / g and barium carbonate powder having 26 m ² / g were used.

(Comparative Example 1 and Examples 1 and 2)
[Preparation of first mixed powder]
The barium carbonate particles and titanium dioxide particles are weighed so that BaCO ₃ / TiO ₂ (molar ratio) is 60/100, and wet-mixed for 24 hours in a 500 cc polypot using zirconia (ZrO ₂ ) media. Then, it dried with the dryer and obtained mixed powder. In the wet mixing, the slurry concentration was 20% by weight.

[First heat treatment step]
In the electric furnace (batch furnace), the first mixed powder was heated from room temperature to the first heat treatment temperature (T ₀ ) shown in Table 1 at a heating rate of 3.3 ° C./min (200 ° C./hour). Thereafter, the temperature was maintained at the heat treatment temperature for 2 hours, and the temperature was decreased at 3.3 ° C./min (200 ° C./hour).

In Example 1, heat treatment is performed at a first heat treatment temperature (T ₀ = 500 ° C.) under reduced pressure (8 × 10 ⁴ Pa). In Example 2, the first heat treatment temperature is obtained in an atmospheric pressure atmosphere. Heat treatment was performed at (T ₀ = 550 ° C.), and in Comparative Example 1, heat treatment was performed at the first heat treatment temperature (T ₀ = 450 ° C.) in an atmospheric pressure atmosphere.

Particle X-ray diffraction analysis of the product in the first heat treatment step was performed, and the amount of barium titanate produced and the amount of residual raw material powder were measured. The measurement was performed under the following conditions. The results are shown in Table 1.

(Particle X-ray diffraction analysis)
Measured with Cu-Kα, 40 kV, 40 mA, 2θ: 20-120 deg using a fully automatic multipurpose X-ray diffractometer D8 ADVANCE manufactured by BRUKER AXS, one-dimensional high-speed detector LynxEye, divergence slit 0.5 deg, scattering slit 0.5 deg was used. Further, scanning was performed at a scan rate of 0.01 to 0.02 deg and a scan speed of 0.3 to 0.8 s / div. For the analysis, Rietvelt analysis software (Topas (manufactured by Bruker AXS)) was used to calculate the weight concentration of barium titanate and unreacted raw material powder.

(Examples 3 to 6, Comparative Examples 2 and 3)
In the same manner as in Example 2 except that the composition [BaCO ₃ / TiO ₂ (molar ratio)] and the first heat treatment temperature (T ₀ ) of the first mixed powder were changed as shown in Table 1, in an atmospheric pressure atmosphere A heat treatment was performed. Particle X-ray diffraction analysis of the product in the first heat treatment step was performed, and the amount of barium titanate produced and the amount of residual raw material powder were measured. The results are shown in Table 1.

Moreover, the X-ray diffraction pattern of the composite oxide particles obtained in Example 4 and Comparative Example 3 is shown in FIG. From the above, it can be seen that when the first heat treatment temperature is 450, the reaction is incomplete and a large amount of unreacted raw material powder remains. It can also be seen that when the first heat treatment temperature is 900 ° C. or higher, a heterogeneous phase in which titanium is excessive is generated.

(Examples 4-1 to 4-6)
[Preparation of second mixed powder]
Barium carbonate particles were further added to the composite oxide particles obtained in Example 4 so as to have a Ba / Ti ratio shown in Table 2, and mixed in the same manner as in Example 1 to prepare a second mixed powder. .

[Second heat treatment step]
In the electric furnace (batch furnace), the second mixed powder was heated from room temperature to the second heat treatment temperature (T ₁ ) shown in Table 2 at a temperature rising rate of 3.3 ° C./min (200 ° C./hour). Then, it hold | maintained at the heat processing temperature in atmospheric pressure atmosphere for 2 hours, and fell at 3.3 degreeC / min (200 degreeC / hour).

About the obtained barium titanate particles, the specific surface area is measured by the BET method, and X-ray diffraction analysis is performed to obtain a c / a value that is an index of tetragonality, and the presence or absence of a heterogeneous phase is confirmed. The crystal grain size was determined and the variation in grain size was evaluated. The results are shown in Table 2.

(Specific surface area)
Using NOVA2200 (high-speed specific surface area meter), the measurement was performed under the conditions of a powder amount of 1 g, nitrogen gas, one-point method, deaeration condition of 300 ° C. and 15 minutes holding.

(Particle X-ray diffraction analysis)
The a-axis and c-axis were determined by X-ray diffraction analysis of the obtained barium titanate powder, and the c / a ratio and crystal grain size, which are tetragonal indices, were determined. Further, from the quantitative value of barium carbonate obtained from the analysis software, 1% by weight or more was regarded as a different phase of barium carbonate.

Specifically, using a fully automatic multi-purpose X-ray diffractometer D8 ADVANCE manufactured by BRUKER AXS, measurement is performed with Cu-Kα, 40 kV, 40 mA, 2θ: 20 to 120 deg, a one-dimensional high-speed detector LynxEye, and a diverging slit 0 0.5 deg and a scattering slit of 0.5 deg were used. For the analysis, Rietvelt analysis software (Topas (manufactured by Bruker AXS)) was used.

The particle size variation is evaluated by electron microscope observation (SEM) of the powder. “A” has a CV value of 25% or less, “B” has a CV value of more than 25% and 30% or less, and “C” has a CV value of 25% or less. More than 31%.

The CV value was determined as CV (%) = (standard deviation / average value) × 100 from the average value and standard deviation by measuring the particle diameter of 200 or more particles from the SEM image.

Further, the barium titanate powder having little variation in particle diameter, good tetragonal crystal, and no heterogeneous phase was evaluated as “good”.

(Comparative Examples 4-7)
[Preparation of mixed powder]
Barium carbonate particles and titanium dioxide particles were weighed so that BaCO ₃ / TiO ₂ (molar ratio) was in the ratio shown in Table 2, and 72 hours by a ball mill with a capacity of 50 liters using zirconia (ZrO ₂ ) media. Wet mixing was performed, and then drying was performed by spray drying to obtain a mixed powder. The wet mixing was performed under the condition that the slurry concentration was 40% by weight and 0.5% by weight of a polycarboxylate-based dispersant was added.

[Heat treatment process]
Using an electric furnace (batch furnace), the mixed powder was heated from room temperature to the heat treatment temperature (T ₁ ) shown in Table 2 at a heating rate of 3.3 ° C./min (200 ° C./hour). Thereafter, the temperature was maintained at the heat treatment temperature for 2 hours, and the temperature was decreased at 3.3 ° C./min (200 ° C./hour). The results are shown in Table 2.

Furthermore, the scanning electron micrograph (SEM image) of the barium titanate powder obtained in Example 4-3 and Comparative Example 4 is shown in FIG.
From the above, by using the composite oxide particles of the present invention as a precursor for the production of barium titanate powder, it is possible to obtain a barium titanate powder with little variation in particle diameter, good tetragonal crystal, and no heterogeneous phase. all right.

The X-ray diffraction pattern of the composite oxide particles obtained in Example 4 and Comparative Example 3 is shown. The scanning electron micrograph (SEM image) of the barium titanate powder obtained in Example 4-3 and Comparative Example 4 is shown.

Claims (2)

Substantially, and 75 to 25 mol% of barium titanate phase, 25 to 75 mole% of the Ri Do from titanium dioxide phase alone, the composite oxide particles ing is barium titanate phase is formed on the titanium dioxide particle surface. 2. The composite oxide particle according to claim 1, wherein the proportion of the unreacted barium compound and the excess phase in which titanium is excessive is 1 mol% or less.

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