KR20090110261A - Method for producing dielectric particle - Google Patents

Abstract

PURPOSE: A method for producing dielectric particles is provided to suppress the growth of particles in a process of manufacturing barium titanate in order to secure minute and uniform dielectric particles. CONSTITUTION: A method for producing dielectric particles comprises the following steps of: preparing titanium dioxide particles with rutilation of 30% and BET specific surface area of 20 m^2/g or greater; preparing barium carbonate particles of BET specific surface area of 10 m^2/g or greater; mixing the titanium dioxide particles and barium carbonate particles to obtain mixed powder; and heat-treating the mixed powder to generate barium titanate on the surface of the titanium dioxide particles.

Description

Method for producing dielectric particles {METHOD FOR PRODUCING DIELECTRIC PARTICLE}

The present invention relates to a method for producing a dielectric particle represented by barium titanate particles.

The dielectric of the magnetic capacitor includes BaTiO ₃ , (Ba, Sr) TiO ₃ , (Ba, Ca) TiO ₃ , (Ba, Sr) (Ti, Zr) O ₃ , (Ba, Ca) (Ti, Zr) O _3, etc. Ceramics are widely used. The dielectric layer is obtained by producing a green sheet from a paste containing dielectric particles and sintering it. Dielectric particles used for such use are generally manufactured by a solid phase synthesis method. For example, barium titanate (BaTiO ₃ ) is wet mixed with barium carbonate (BaCO ₃ ) particles and titanium dioxide (TiO ₂ ) particles and dried, and then heat-treated (plasticized) the mixed powder to a temperature of about 900 to 1200 ℃ Viii)), the barium carbonate particles and the titanium dioxide particles are chemically reacted in a solid phase to obtain barium titanate particles. When (Ba, Sr) TiO ₃ , (Ba, Ca) TiO ₃ , (Ba, Sr) (Ti, Zr) O ₃ , (Ba, Ca) (Ti, Zr) O _3, and the like are synthesized, In the solid phase reaction, a compound serving as an Sr source, a Ca source, or a Zr source is added, or a barium titanate is synthesized, and then a compound serving as an Sr source, a Ca source, or a Zr source is further added, followed by heat treatment (firing).

The barium titanate particles used as ceramic raw material particles for obtaining a dielectric in such a multilayer ceramic capacitor have a finer grain, uniform particle size, and high tetragonality with the thinning of the ceramic layer between internal electrodes. Is required.

As the titanium dioxide in the solid phase reaction, in order not to deteriorate the characteristics of the obtained dielectric ceramic, a high purity one obtained by pyrolyzing titanium tetrachloride is typically used. In this case, the crystal form of the obtained titanium dioxide is different depending on the thermal decomposition conditions, but when the usual heat treatment conditions are applied, the rutile rate becomes high, and the rutile type generally dominates.

However, rutile titanium dioxide particles are poor in reactivity, and the tetragonality of the obtained barium titanate becomes low. And when the tetragonality of barium titanate is low, when used as a raw material particle of the dielectric provided in a multilayer ceramic capacitor, for example, the solid solution to the barium titanate of the additive component added to the raw material particle in a baking process advances. In this case, it is difficult to obtain a sintered body having a core-shell structure after firing. For this reason, the problem that the temperature characteristic of the electrostatic capacitance of the obtained multilayer ceramic capacitor worsens is caused.

Further, even if the tetragonality of barium titanate is high, if the primary particle diameter of the raw material particles is large, the reliability of the multilayer ceramic capacitor is reduced when the dielectric ceramic layer is thinned. In addition, in thinning, not only the size of the primary particle diameter of the raw material particles but also the distribution becomes an important factor, and the particle size distribution of barium titanate should be good while having high crystallinity.

On the other hand, in order to increase the tetragonality of barium titanate, it is effective to increase the heat treatment temperature at the time of synthesizing barium titanate by mixing and heat-treating a barium compound such as barium carbonate and titanium dioxide in the solid phase reaction method. There is a problem that growth of the lower surface particles and condensation of the particles occur, which makes it difficult to atomize the obtained barium titanate particles. For this reason, the obtained barium titanate is granulated and used by grinding (patent document 1). However, in order to obtain fine particles by pulverizing barium titanate having high crystallinity, for example, by wet crushing, in addition to the particle size distribution before pulverization, dispersion factors at the time of pulverization are taken into account, thereby uniformizing the particle diameter. Is difficult, and it is not easy to avoid deterioration of dielectric properties due to crushing damage.

In order to solve this problem, a method of producing barium titanate using titanium dioxide particles having low rutileization rate (high anatase conversion rate) and highly reactive barium compounds that produce barium oxide by thermal decomposition and X-ray diffraction A method is disclosed in which heat treatment (calcination) is carried out by mixing titanium dioxide having a rutile ratio obtained by the method of 30% or less and a specific surface area of 5 m 2 / g or more obtained by the BET method (Patent Document 2).

According to this method, since the highly reactive and fine grained anatase type titanium dioxide is used, the barium titanate powder with high tetragonality and small particle diameter is obtained. Since the anatase type titanium dioxide is metastable compared with the rutile type, it is generally known to transition to the rutile type around 700 ° C.

However, in recent years, miniaturization of electronic devices has been accelerated, and even in a multilayer ceramic capacitor, it is required to further thin a dielectric layer. For this reason, also in barium titanate particle | grains, it is calculated | required that it is finer and uniform particle size.

In the method of patent document 2, the heat processing of the mixed powder is performed in one step at high temperature of 950 degreeC or more. Under such firing conditions, grain growth occurs before the barium compound particles or titanium dioxide particles as the raw material react, and there is a limit to making the barium titanate particles fine. In the case of titanium dioxide particles having a relatively large specific surface area of 5 to 10 m 2 / g, even though the heat treatment is performed at 700 to 800 ° C., no significant decrease in the specific surface area due to particle growth occurs, but the specific surface area of not less than 20 m 2 / g is 700. It was a problem that the specific surface area remarkably decreased above ° C. Since this has a large specific surface area, particle surface energy becomes high, and it shows that particle growth and particle | grain bonding (necking of adjoining particle | grains are induced even after 700 degreeC).

In general, the production reaction of barium titanate using barium carbonate and titanium dioxide as a raw material is represented by BaCO ₃ + TiO ₂ → BaTiO ₃ + CO ₂ , which is known to occur in two steps (Non-Patent Document 1). ). That is, the first reaction is the production reaction of barium titanate on the particle surface (barium carbonate and titanium dioxide contact) of the titanium dioxide particles at 500 to 700 ° C., and the second reaction is barium in the first stage product at a temperature of 700 ° C. or higher. It is a reaction in which ionic species diffuse into titanium dioxide. The reaction on the particle surface of the titanium dioxide particles needs to sufficiently mix and disperse the powder of the raw material. Non-Patent Document 1 describes that a raw material having a specific surface area of 26.5 m 2 / g is used, but the behaviors of thermogravimetric analysis and differential thermal analysis differ greatly depending on the mixing dispersion time. Therefore, it is disclosed that when titanium dioxide particles are fine particles of 20 m 2 / g or more, aggregation of titanium dioxide particles is likely to occur, so that the characteristics and particle size distribution of barium titanate produced depending on the dispersion conditions are greatly affected.

For this reason, as in Patent Document 2, when the heat treatment of the mixed powder is performed in one step at a temperature of 950 ° C or higher, particle growth of raw material particles, formation reaction of barium titanate on the surface of titanium dioxide particles, diffusion of barium ion species, and titanic acid Particle growth of barium particles occurs in a short time. As a result, a variation occurs in the particle properties of the barium titanate particles obtained.

When barium carbonate is used as a raw material, it is influenced by carbon dioxide (CO ₂ ) generated during the reaction process. Therefore, when a large amount of mixed powder (for example, 1 kg or more) is to be heat treated, the influence of carbon dioxide generated cannot be ignored. .

In the prior art, for example, Patent Document 2 discloses that crystallinity is improved by performing heat treatment under reduced pressure. However, when barium carbonate is used as a raw material, it is necessary to continuously inhale carbon dioxide generated in the reaction process. Therefore, a large facility is needed.

[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-345230

[Patent Document 2] Japanese Patent Application Laid-Open No. 2002-255552

[Non-Patent Document 1] J. Mater. Rev. 19, 3592 (2004)

The present invention has been made in view of the prior art as described above. Using fine titanium dioxide particles having a low rutileization rate (high anatase rate) and high reactivity, fine and uniform dielectric particles, particularly barium titanate particles, are prepared. It aims to provide a way to do it.

As a result of earnestly examining in order to achieve such an objective, the present inventors made the raw material titanium dioxide particle in a heat processing process by heat-processing at high temperature after uniformly growing the barium titanate phase continuously formed on the surface of a titanium dioxide particle. Particle growth of barium titanate particles as a product was suppressed, and it was reached that barium titanate particles having a uniform particle shape and high crystallinity were obtained. Based on this view, the inventors came up with the following production method.

MEANS TO SOLVE THE PROBLEM This invention which solves the said subject includes the following matter as a summary.

Preparing titanium dioxide particles having a rutileization rate of 30% or less and a BET specific surface area of 20 m 2 / g or more, preparing a barium carbonate particle having a BET specific surface area of 10 m 2 / g or more, mixing titanium dioxide particles and barium carbonate particles To prepare a mixed powder, a first heat treatment step of heat treating the mixed powder to form a barium titanate phase on the surface of the titanium dioxide particles, and a second heat treatment step of performing heat treatment at 800 to 1000 ° C. after the first heat treatment step; The heat treatment temperature in the first heat treatment step is lower than the heat treatment temperature in the second heat treatment step, and at least 15% by weight of the mixed powder after the first heat treatment step becomes barium titanate, and the barium titanate having an average thickness of 3 nm or more on the surface of the titanium dioxide particles. A method of making a dielectric particle that is allowed to react for a time sufficient to produce a phase.

In the first heat treatment step, at least 75% of the total titanium dioxide particles are formed to continuously produce a barium titanate phase having an average thickness of 4 nm or more on the surface of the titanium dioxide particles, and at least 20% by weight of the mixed powder becomes barium titanate. It is preferable.

The heat treatment temperature of the 2nd heat treatment process is 850-950 degreeC, and it is preferable that c / a value of the produced barium titanate particle is 1.008 or more.

The heat treatment temperature of the second heat treatment step is 850 to 950 ° C., and the resulting barium titanate particles have X-ray intensity at the midpoint between the peak point of the (200) plane and the (002) plane in powder X-ray diffraction of X-ray CuKα rays. to (I _b) and at least a non-(I ₍₂₀₀₎ / I _b) 4 (200) diffraction ray intensity I (200) of the surface is preferred.

It is preferable that 1st heat processing processes are performed at 575-650 degreeC in air | atmosphere in the pressure of 1x10 <^3> Pa or more and 1.0133x10 <^5> Pa, and it is preferable that 25 weight% or more and 55 weight% or less in mixed powder become barium titanate. .

The first heat treatment step is performed at 600 to 700 ° C. in an air atmosphere at a pressure of 1 × 10 ³ Pa or more and 1.0133 × 10 ⁵ Pa or less in a calcining furnace for flow-firing the powder, and at least 20% by weight to 75% by weight in the mixed powder. It is preferable to become a barium titanate.

In the first heat treatment step, the concentration of the CO ₂ gas in the atmosphere is preferably 15 mol% or less.

It is preferable to include the process of cooling to 550 degrees C or less after a 1st heat processing process, and to perform a 2nd heat processing process after that.

You may perform a 1st heat processing process at 450-600 degreeC in the pressure of 1 * 10 <^3> Pa or less.

It is preferable to include the process of evaluating the weight concentration of a barium titanate phase by confirming the progress of a 1st heat processing process by powder X-ray diffraction analysis of the product in a 1st heat processing process.

It is preferable to include the process of observing the product in a 1st heat processing process by a transmission electron microscope analysis, confirming the barium titanate phase on the surface of a titanium dioxide particle, and confirming progress of a 1st heat processing process.

According to the present invention, grain growth during the production of barium titanate is suppressed, so that barium titanate particles having fine and uniform grain properties, good tetragonality and high crystallinity are obtained.

Although not theoretically restricted, the inventors believe that the above effects are exhibited by the following reaction mechanism.

That is, in the first heat treatment step, by continuously growing the barium titanate phase on the surface of the titanium dioxide particles more than a predetermined level, the contact between the titanium dioxide particles in the first heat treatment step or after the step is suppressed. As a result, particle growth (necking, particle bonding) of the titanium dioxide particles is suppressed, and the production of impurity intermediate (Ba ₂ TiO ₄ ) due to the heterogeneity of the reaction is also reduced. In Non-Patent Document 1, it is disclosed that the barium titanate phase produced on the surface in the first step is not a continuous surface layer but a discontinuous particulate state, but the present invention can form a continuous barium titanate phase on the surface.

In the 1st heat processing process of this invention, in 75% or more of all the titanium dioxide particles, it becomes possible to produce the barium titanate phase more than average thickness 4nm on the titanium dioxide particle surface continuously. At this time, it can be confirmed by powder X-ray diffraction analysis that at least 20% by weight of the mixed powder becomes barium titanate, and the barium titanate phase on the surface can be confirmed by transmission electron microscope analysis.

Subsequently, in the second heat treatment step, barium ion species is diffused to further expand the barium titanate phase, and finally barium titanate particles are obtained. This process is performed at a relatively high temperature. At this time, when the barium titanate phase is not sufficiently formed on the surface of the titanium dioxide particles, necking and particle bonding may occur through the exposed titanium dioxide site, resulting in irregular grain growth. In this case, barium titanate particles obtained are also deformed to obtain uniform barium titanate particles. However, in the present invention, since the surface of the titanium dioxide particles is covered by the barium titanate phase, diffusion of barium ion species occurs without causing particle growth of the titanium dioxide particles. As a result, barium titanate particles having fine and uniform particle properties are obtained. Decision by the effect of the first heat treatment step which is different from a barium titanate uniformly on the surface is formed, the second is not an intermediate product, such as Ba ₂ TiO ₄ in the heat treatment step is OK, from around 850 to 900 ℃ barium titanate (BaTiO ₃₎ You can see an improvement in sex. In addition, it is possible to produce particles with high crystallinity even when not under reduced pressure such as 1 × 10 ² Pa or less.

In addition, since the obtained barium titanate particles are fine, the particles can be grown to a desired size through the second heat treatment step. As a result of further heat treatment in the grain growth process, barium titanate particles having good tetragonality and high crystallinity can be obtained.

Hereinafter, the present invention will be described in more detail, including the best mode thereof. In the following description, an example of producing barium titanate as a dielectric particle will be described. In particular, the production method of the present invention includes (Ba, Sr) TiO ₃ , (Ba, Ca) TiO ₃ , (Ba, Sr) (Ti, Zr It is applicable to the production method of various dielectric powders having a step of heat-treating a mixed powder containing titanium dioxide particles and barium compound particles such as) O ₃ , (Ba, Ca) (Ti, Zr) O _3, and the like.

The manufacturing method of the barium titanate of this invention includes the process of heat-processing the mixed powder of a titanium dioxide particle and a barium compound particle.

The rutile rate of the titanium dioxide particles used as the raw material is 30% or less, preferably 20% or less, and even more preferably 10% or less. From the viewpoint of improving the reactivity, the lower the rutile rate of the titanium dioxide particles, that is, the higher the anatase rate, the better. However, in achieving the object of the present invention, there is no significant difference in the effect even if the rutile rate is excessively lowered. Therefore, in improving productivity, it is desirable to set it as about 10%. Rutile rate is calculated | required from the X-ray-diffraction analysis of titanium dioxide particle.

Further, the BET specific surface area of the titanium dioxide particles is 20 m 2 / g or more, preferably 30 m 2 / g or more, more preferably 40 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 is, the more difficult it is to handle if the particles are excessively atomized. . Therefore, in order to improve productivity, it is preferable to set it as about 20-40 m <2> / g.

As long as the titanium dioxide particles used in the present invention satisfy the above physical properties, the production method is not particularly limited, and may be a commercially available product, or may be obtained by pulverizing a commercially available product. In particular, since fine titanium dioxide fine particles are obtained with a low rutylation rate, titanium dioxide particles obtained by a gas phase method using titanium tetrachloride as a raw material are preferably used.

A general method for producing titanium dioxide by the gas phase method is known, and fine titanium dioxide is obtained by oxidizing titanium tetrachloride as a raw material under reaction conditions of about 600 to 1200 ° C using an oxidizing gas such as oxygen or water vapor. If the reaction temperature is too high, the amount of titanium dioxide having a high rutylation rate tends to increase. Therefore, it is preferable to perform reaction at about 1000 degreeC or less.

The titanium dioxide particles used as the raw material preferably have a residual chlorine content of 1200 ppm or less, more preferably 600 ppm or less, and even more preferably 300 ppm or less. The lower the amount of residual chlorine, the better. However, heating for low chlorination causes sintering of titanium dioxide particles and transition to rutile type. Therefore, even when reducing the amount of residual chlorine, it is preferable to set it as about 600 ppm.

Moreover, it is preferable that content of Fe, Al, Si, S in titanium dioxide particle is 0.01 weight% or less, respectively. When each content of Fe, Si, Al, and S exceeds 0.01 weight%, it does not only make a difference in the mixing ratio of a titanium dioxide and a barium source, but may have a big influence on dielectric properties. Although there is no restriction | limiting in particular in a lower limit, From a viewpoint of a manufacturing cost, 0.0001 weight% or more is preferable.

In addition, it is preferable that the particle size distribution of the titanium dioxide particles be uniform. In the present invention, the effect of making the particle size of barium titanate uniform while maintaining the state of good particle size distribution of titanium dioxide has an important meaning, so that the more uniform the particle size distribution of the raw material, the more prominent effect can be expected. Specifically, the particle size distribution of titanium dioxide as a raw material is preferably represented by a ratio of ((D90-D10) / D50), preferably 0.5 to 2.0, more preferably 1.5 or less, and particularly preferably 1.0 or less. For example, it is known that in the titanium dioxide particles obtained by the vapor phase method using titanium tetrachloride as a raw material, it is possible to produce that the value of (D90-D10) / D50 becomes 1.0 with fine particles having a specific surface area of 30 m 2 / g.

In addition, D10 diameter, D50 diameter, and D90 diameter mean the particle diameter of the cumulative 10%, 50%, and 90% of the cumulative particle size distribution from the particulate side, respectively, and are evaluated using the laser diffraction scattering method.

Barium carbonate is preferable as the barium compound particles of the raw material. Barium carbonate particles are not particularly limited, and known barium carbonate particles are used. However, in order to promote mixed dispersion and solid phase reaction and to obtain fine barium titanate particles, it is preferable to use raw material particles having a relatively small particle size. Therefore, the BET specific surface area of the barium compound particle used as a raw material is 10 m <2> / g or more, Preferably it is 10-40 m <2> / g, More preferably, it is 20-40 m <2> / g.

By using the above-mentioned specific titanium dioxide and barium carbonate particles as raw material particles, solid phase reaction is promoted. Therefore, the heat treatment temperature can be reduced and the heat treatment time can be shortened, thereby reducing the energy cost. Further, by using the above-described raw materials and subjecting the following first and second heat treatment steps, variations in particle growth during heat treatment are suppressed, whereby barium titanate particles having a small particle size and uniform particle properties are obtained. In addition, since the obtained barium titanate fine particles grow by continuation of heat treatment, it is also possible to easily obtain high crystalline barium titanate particles having a desired particle size by appropriately setting the second heat treatment time.

In addition, there is no problem in particular if the ratio of the barium carbonate particles and the titanium dioxide particles in the mixed powder is near the stoichiometric composition capable of producing barium titanate. Therefore, Ba / Ti (molar ratio) in mixed powder should just be 0.990-1.10. When Ba / Ti exceeds 1.010, unreacted barium carbonate may remain, and when less than 0.990, abnormality containing Ti may be produced.

The manufacturing method of mixed powder is not specifically limited, What is necessary is just to employ | adopt a conventional method, such as a wet method using a ball mill. The obtained mixed powder is dried and then heat treated to obtain barium titanate particles. However, as disclosed in Non-Patent Document 1, it is necessary to mix under mixed dispersion conditions in which the aggregation of titanium dioxide particles is sufficiently released to make the composition of barium and titanium uniform.

The heat treatment of the mixed powder in the present invention includes at least the following first heat treatment step and second heat treatment step.

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. Subsequently, the titanium dioxide particles having the barium titanate phase formed thereon and the unreacted mixed powder are heat-treated at 800 to 1000 ° C. in the second heat treatment step to obtain barium titanate particles. In the first heat treatment step and the second heat treatment step, the powder may be heat treated while being in the form of granules, may be subjected to a disintegration treatment, or may be formed into a pellet by pressure molding. In addition, before the 1st heat processing process, you may perform the binder removal process (heat processing before and after 250 degreeC-450 degreeC) of pressure shaping | molding, and heat processing around 250 degreeC-500 degreeC which removes organic components, such as a dispersing material at the time of mixed dispersion, and You may perform a process. The heat treatment step of removing these organic components is different from the first heat treatment step and does not affect the effect of the present invention.

The heat treatment temperature in the first heat treatment step is various depending on the heat treatment atmosphere and the like, but is lower than the heat treatment temperature in the second heat treatment step, and the barium titanate phase is formed on the surface of the titanium dioxide particles by the reaction of the titanium dioxide particles and the barium compound. That's enough.

The heat treatment time of the first heat treatment step is 15% by weight or more, preferably 20 to 75% by weight of the mixed powder, and even more preferably 25 to 55% by weight of barium titanate, and is averaged on the surface of the titanium dioxide particles. What is necessary is just enough time to produce the barium titanate phase of 3 nm or more in thickness, Preferably it is 4-10 nm, More preferably, 4-7 nm. The barium titanate phase on the surface of the titanium dioxide particles has a continuous thin layer, and is preferably 2 to 3 nm or more even in a thin portion. It is also preferable that at least three quarters of the titanium dioxide particles have a barium titanate phase on such a surface.

If the production rate of barium titanate in the first heat treatment step is less than 15% by weight or the average thickness of the barium titanate phase is less than 3 nm, the ratio of barium titanate phase on the surface of the titanium dioxide particles becomes insufficient, resulting in the barium titanate phase. The shielding effect on the surface of titanium particle falls. As a result, when titanium dioxide particles contact, titanium dioxide particles may sinter and amorphous particle growth may lead to deterioration of particle size distribution of barium titanate particles as a dielectric powder and deterioration of crystallinity.

Particles of titanium dioxide particles are formed when the heat treatment step is performed without uniformly generating the barium titanate phase on the surface, for example, the production rate of barium titanate is 70% by weight or more, or when the average thickness of the barium titanate phase is too thick. Growth and necking are likely to occur at creation. In addition, since Ba ions are in a state in which the titanium ions are unevenly diffused into titanium dioxide, high crystallinity is hardly obtained and uniformity in the powder of Ba / Ti composition is deteriorated.

Between the first heat treatment step and the second heat treatment step, an intermediate heat treatment step of advancing the reaction at 700 to 800 ° C. may be put, and a step of sufficiently advancing the reaction may be added. However, since the effect of the present invention is to form a continuous layer of barium titanate on the surface of the titanium dioxide particles in the first heat treatment step, for example, the first heat treatment step is 600 ° C., the intermediate heat treatment step is 750 ° C., and the second heat treatment is performed. It is also possible to make a process 95O degreeC.

Further, in the first heat treatment step, preferably at least 75% of the titanium dioxide particles in the total number of titanium dioxide particles, more preferably at least 80%, particularly preferably at 90%, averaged on the surface of the titanium dioxide particles. A barium titanate phase continuous at a thickness of 4 nm or more is produced.

The amount of barium titanate produced and the average thickness of the barium titanate phase can be controlled by changing the heat treatment temperature and the heat treatment time. The treatment time and temperature can be controlled by appropriately setting the amount of the mixed powder during the heat treatment, the volume of the furnace, and the like. For example, by increasing the heat treatment temperature or lengthening the heat treatment time, the amount of barium titanate produced and the average thickness of the barium titanate phase tend to increase. However, if the heat treatment temperature is too high, the grains grow before the barium compound particles or titanium dioxide particles which are the raw materials react, and there is a limit to miniaturizing the barium titanate particles.

For this reason, when performing a 1st heat processing process in the pressure of 1x10 <^3> Pa or more and 1.0133x10 <^5> Pa or less using a normal baking furnace, Preferably it is 575-650 degreeC, More preferably, it is 580-640 degreeC, Especially preferably, it carries out at 590-630 degreeC. Here, a normal firing furnace means the furnace which bakes mixed powder in a stationary state like a batch furnace, for example. An elevated temperature may be performed from room temperature, and the said elevated temperature operation may be performed after preheating a mixed powder. The heat treatment time in this case is a time sufficient to produce a predetermined thickness and a predetermined amount of barium titanate on the surface of the titanium dioxide particles, and in general, the holding time at the heat treatment temperature is 0.5 to 6 hours, preferably 1 to 4 hours. . If the heat treatment temperature is too low or the heat treatment time is too short, the predetermined barium titanate phase may not be produced.

In the temperature increase process reaching the heat treatment temperature, the temperature increase rate is preferably about 1.5 to 20 ℃ / min. The atmosphere in the temperature raising process is not particularly limited, and may be an atmospheric atmosphere, or may be a gas atmosphere such as nitrogen, or reduced pressure or vacuum.

In addition, you may perform a 1st heat processing process in the baking furnace which flow-calculates powder. In this case, the heat treatment is preferably performed at 600 to 700 ° C, more preferably at 620 to 680 ° C, and particularly preferably at 625 to 650 ° C in an air atmosphere. Here, the kiln which flow-calculates powder is a rotary kiln, for example. The rotary kiln is an inclined heating tube having a mechanism that rotates about a central axis of the heating tube. The mixed powder injected from the upper part of a heating tube is heated up in the process of moving downward inside a tube. Therefore, by controlling the temperature of the heating tube and the passage speed of the mixed powder, it is possible to appropriately control the attained temperature and the temperature increase rate of the mixed powder. The holding time at the heat treatment temperature in this case is 0.1 to 4 hours, preferably 0.2 to 2 hours.

In the first heat treatment step, the CO ₂ gas concentration in the atmosphere is preferably controlled to 15 mol% or less, even more preferably 0 to 10 mol%, particularly preferably 0 to 5 mol%.

The CO ₂ gas may be calculated by adjusting the gas to be substituted so as to be 15 mol% or less, calculated from the maximum amount of time generated by the reaction of the mixed powder and the flow rate for replacing the atmosphere in the furnace of the heat treatment. Further, in the first heat treatment step of 600 ° C to 650 ° C, when the concentration of CO ₂ gas is increased, the produced barium titanate becomes 10% by weight or less of the mixed powder, so that the concentration of CO ₂ gas in the atmosphere is indirectly derived from the amount of barium titanate produced. It is also possible to estimate. In the first heat treatment step, the concentration of CO ₂ gas in the atmosphere is preferably set to be lower than or equal to the constant, but in the second heat treatment step, the concentration of CO ₂ gas is not affected.

Although a 2nd heat processing process may be performed immediately after a 1st heat processing process, you may interpose a temperature-fall process between a 1st heat processing process and a 2nd heat processing process. Specifically, after the first heat treatment step, the obtained product may be cooled to 550 ° C. or lower, for example, about room temperature, and then a second heat treatment step may be performed. Between the first heat treatment step and the second heat treatment step, by lowering the temperature to stop the formation of the surface barium titanate phase, the reaction of only the titanium dioxide surface can be distinguished. Accordingly, the diffusion of Ba ions into titanium dioxide is preferable because the variation in composition due to the continuous reaction in the first heat treatment step and the reaction in the second heat treatment step can be reduced. In addition, since the barium titanate phase on the surface of the titanium dioxide in the first heat treatment step is not easy to be completely continuous in all the particles, it is possible to stop the reaction at the contacted part such as the necking once by lowering the temperature below 550 ° C. It is preferable in the sense of making it good. Moreover, since it is also possible to divide the baking furnace which performs a 1st heat treatment process, and the baking furnace which performs a 2nd heat treatment process, and freedom of process design becomes high, it is preferable.

The first heat treatment step may be performed at 450 to 600 ° C., preferably 475 to 550 ° C., and more preferably 500 to 540 ° C. under a reduced pressure of atmospheric pressure or lower, for example, at a pressure of about 1 × 10 ³ Pa or less. have. In this case, the holding time at the heat treatment temperature is 0.5 to 6 hours, preferably 1 to 4 hours.

Under atmospheric pressure, for example, under a reduced pressure of 10 Pa, the temperature at which the barium titanate phase is formed on the titanium dioxide surface is lowered by about 50 ° C. to 80 ° C. than in atmospheric pressure. Therefore, it becomes easy to suppress grain growth of titanium dioxide particles. However, in the case of performing the first heat treatment step under reduced pressure, since it is necessary to continuously intake carbon dioxide generated in the reaction process, a large amount of equipment is required. In addition, since the carbon dioxide gas of the barium carbonate escapes to become barium oxide (BaO), staining occurs in reactivity, or the influence of titanium oxide (TiOx) that is missing due to oxygen defects on the titanium dioxide surface is not easy to control.

By going through the above first heat treatment step, at least 15% by weight of the mixed powder becomes barium titanate, thereby producing a barium titanate phase having an average thickness of 3 nm or more on the surface of the titanium dioxide particles.

The formation of the predetermined barium titanate phase in the first heat treatment step can be confirmed by powder X-ray diffraction analysis and transmission electron microscope analysis of the product in the first heat treatment step. Therefore, in carrying out the production method of the present invention, the step of confirming the product in the first heat treatment step by powder X-ray diffraction analysis and transmission electron microscope analysis after the first heat treatment step and before moving to the second heat treatment step It is preferable to include.

Subsequently, a second heat treatment step is performed following the first heat treatment step. The heat processing temperature in a 2nd heat processing process is 800-1000 degreeC, Preferably it is 850-950 degreeC, More preferably, it is 900-950 degreeC. In the present invention, since the second heat treatment step is performed after the barium titanate phase is formed on the surface of the titanium dioxide particles by the first heat treatment step as described above, the tetragonality is good even at a low temperature of 950 ° C. or lower. Fine particles of barium titanate having high crystallinity and uniform particle shape are obtained. Further, the heat treatment time is a time sufficient to substantially complete the solid phase reaction of the barium carbonate particles and the titanium dioxide particles, and in general, the holding time at the heat treatment temperature is 0.5 to 4 hours, preferably 0.5 to 2 hours. The atmosphere during the heat treatment is not particularly limited, and may be an atmospheric atmosphere, or may be a gas atmosphere such as nitrogen, or reduced pressure or vacuum. If the heat treatment temperature is too low or the heat treatment time is too short, homogeneous barium titanate particles may not be obtained.

In the temperature increase process reaching the heat treatment temperature, the temperature increase rate is preferably about 1.5 to 20 ℃ / min. The atmosphere in the temperature raising process is not particularly limited, and may be an atmospheric atmosphere, or may be a gas atmosphere such as nitrogen, or reduced pressure or vacuum.

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

By the second heat treatment step, barium ion species diffuse through the barium titanate phase formed on the surface of the titanium dioxide particles in the first heat treatment step, and barium titanate particles having a small particle size are obtained in the initial stage of the heat treatment. These fine barium titanate particles grow particles by continuing heat treatment. Therefore, according to this invention, barium titanate particle | grains of a desired particle size can be obtained simply by setting the heat processing time in a 2nd heat processing process suitably. In particular, according to the present invention, since barium titanate particles having a uniform particle shape can be obtained, growth of abnormal particles is suppressed even when grain growth is performed. After the heat treatment, the temperature was lowered to obtain barium titanate particles. The temperature-fall rate at this time is not specifically limited, What is necessary is just about 3-100 degreeC / min from a viewpoint of safety | security etc.

According to the present invention, grain growth during the production of barium titanate is suppressed. Particularly, fine particles of barium titanate having good tetragonality, high crystallinity and uniform particle shape are obtained in the initial stage of heat treatment.

C / a, which is the ratio of the c-axis to the a-axis, which is an index of tetragonality, is determined by X-ray diffraction analysis, preferably 1.008 or more, and even more preferably 1.009 or more.

In addition, the crystallinity of barium titanate particle | grains can be evaluated by the half value width of the peak of the diffraction line of the (111) plane, for example in an X-ray diffraction chart. The narrower the half value width, the higher the crystallinity.

In addition, the crystallinity of the barium titanate particles in the X-ray diffraction chart is (200) with respect to the intensity (Ib) at the midpoint between the peak point angle of the (002) plane diffraction plane and the peak point angle of the (200) plane diffraction line. It can also evaluate by ratio (I ₍₂₀₀₎ / Ib) (henceforth "K value") of the peak intensity I _{(200) of a} plane diffraction line. The higher the ratio (I ₍₂₀₀₎ / Ib), the higher the crystallinity. As the dielectric powder material, the K value is preferably 4 or more.

In addition, particle shape can be evaluated by obtaining a particle size by X-ray diffraction analysis or a scanning electron microscope, and calculating the deviation of a particle size. The variation of the particle diameter can be confirmed, for example, from the standard deviation of the average particle diameter and the particle diameter. In addition, the variation of the particle size can be confirmed from the particle size distribution ((D80-D20) / D50) or ((D90-D10) / D50). Moreover, the particle shape can also be confirmed from the specific surface area by BET method.

The barium titanate particles obtained by the present invention are used as a common material added to a raw material for producing dielectric ceramics and a paste for forming an electrode layer after being pulverized as necessary. Various well-known methods can be employ | adopted without particular restriction in manufacture of dielectric ceramics. For example, the subcomponent used for manufacture of dielectric ceramics can be suitably selected according to the dielectric characteristic to target. Moreover, what is necessary is just to follow suitably a well-known method also about manufacture of a paste, a green sheet, formation of an electrode layer, and sintering of a green body.

As mentioned above, although the example which manufactures barium titanate as a dielectric particle was demonstrated and demonstrated about this invention, the manufacturing method of this invention is a manufacturing method of various dielectric particles which have the process of heat-processing the mixed powder containing a titanium dioxide particle and a barium compound particle. Applicable For example, when (Ba, Sr) TiO ₃ , (Ba, Ca) TiO ₃ , (Ba, Sr) (Ti, Zr) O ₃ , (Ba, Ca) (Ti, Zr) O _3, and the like are synthesized In the solid phase reaction, when a compound serving as an Sr source, a Ca source, or a Zr source is added or after synthesizing barium titanate, a compound serving as an Sr source, a Ca source, and a Zr source is further added to perform heat treatment (firing). do.

<Example>

Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples.

The titanium dioxide raw material was prepared from two types of titanium dioxide particles having good particle size distribution in the titanium dioxide particles obtained by a gas phase method using titanium tetrachloride as a raw material. The titanium dioxide raw material is not particularly limited, but if the specific surface area is 20 m 2 / g or more and a raw material having a good distribution is not used, no significant effect of the present invention can be seen. Two types of titanium dioxide particles shown in Table 1 were used as starting materials. Two types of raw materials were selected to confirm that the effects of the present invention do not depend on the raw materials.

Specific surface area [㎡ / g] Impurity chlorine Other impurity concentration Rutile rate [%] Particle Size Distribution (D90-D10) / D50 TiO ₂ (A) 31.2 <600 ppm <100 ppm 13.9 1.36 TiO ₂ (B) 33.3 <600 ppm <100 ppm 9.1 1.04

The physical properties of the titanium dioxide particles were evaluated as follows.

(Specific surface area)

The specific surface area of the titanium dioxide particle which is a raw material was calculated | required by the BET method. Specifically, using a NOVA2200 (high speed specific surface area meter), it measured on the conditions of 15 minutes hold | maintenance at 1 g of powder amount, nitrogen gas, 1 point method, and degassing condition 300 degreeC.

(Residual Chlorine Content)

10 mg of titanium dioxide particles used as a raw material were steam distilled at 1100 ° C., and the decomposition product was collected in 5 ml of 0.09% hydrogen peroxide to quantify the amount of chlorine by ion chromatography.

(Other impurity concentration)

The amount of impurities other than chlorine was evaluated by the plasma emission spectrometry.

(Rutylation rate)

Rutile rate was calculated | required by the X-ray-diffraction analysis of the titanium dioxide particle used as a raw material. Specifically, using a fully automatic multi-purpose X-ray diffractometer D8 ADVANCE manufactured by BRUKER AXS, measured at Cu-Kα, 40 kV, 40 mA, 2θ: 20 to 120 deg, one-dimensional high-speed detector LynxEye, diverging slit 0.5 deg, scattering Slit 0.5 deg was used. In addition, scanning was performed at scan: 0.01-0.02 deg, scan speed: 0.3-0.8 s / div. Rietvelt analysis software (Topas (BRUKER AXS)) was used for the analysis.

(Particle size distribution)

The particle diameter of titanium dioxide as a raw material was evaluated using a laser diffraction scattering method. The fine particle side of a cumulative particle size distribution was used for the laser diffraction particle size distribution meter using MT3000 (Nikkiso Co., Ltd. microtrack particle size distribution meter), and the ultrasonic dispersion by dispersing 0.4 wt% of the dispersant in the pure water solution. The particle size of 10% cumulative, 50% cumulative, and 90% cumulative was calculated from.

In addition, barium carbonate particles having a BET specific surface area of 30 m 2 / g were used as the barium compound as a starting material. Specific surface area was measured similarly to the above. The barium carbonate particles are not necessarily limited to a large specific surface area, but a raw material of 30 m 2 / g was selected in order to increase the uniformity of the mixed dispersion.

(1st to 3rd Example)

[Preparation of mixed powder]

A barium carbonate particle having a specific surface area of 30 m 2 / g and titanium dioxide particles (TiO ₂ (A)) were weighed so that the Ba / Ti ratio was 0.997, and a ball having a capacity of 50 liters using a zirconia (ZrO ₂ ) medium having a diameter of 2 mm was used. After wet mixing with a mill for 72 hours, it was dried by spray drying to obtain a mixed powder. The wet mixing was carried out under the condition that the slurry concentration was 40% by weight, and 0.5% by weight of the polycarbonate dispersant was added. Since titanium dioxide particles are microparticles | fine-particles with a large specific surface area, it is necessary to fully mix raw materials.

[First Heat Treatment Step]

The mixed powder is heated up from the room temperature to the first heat treatment temperature (T ₀ = 60O ° C.) shown in Table 2 at an elevated temperature of 3.3 ° C./min (200 ° C./hour) in the atmospheric atmosphere in an atmospheric pressure by an electric furnace (batch furnace). It was. Then, it kept at heat processing temperature for 2 hours, and it cooled down at 3.3 degree-C / min (200 degree-C / hour). An example in which TiO ₂ (A) is used as the titanium dioxide raw material, and the first heat treatment temperature T ₀ is 600 ° C. and a holding time of 2 hours is referred to as Example 1A. Also referred to as the Example 1B was used for TiO ₂ (B). In the case where the first heat treatment was performed in a batch furnace, 100 g to 250 g of mixed powder was filled into a container made of alumina, and the heat treatment was performed under conditions in which atmospheric flow was performed so that the concentration of CO ₂ gas generated at the time of reaction was 15 mol% or less. .

Particle X-ray diffraction analysis and transmission electron microscopy analysis of the product in the first heat treatment step were performed, and the barium titanate production amount and the average thickness of the barium titanate phase on the titanium dioxide particle surface were measured. The measurement was performed on condition of the following.

(Particle X-ray diffraction analysis)

It measured on the conditions similar to the case of the titanium dioxide particle mentioned above. The result was analyzed using Rietveld analysis software (Topas (manufactured by BRUKER AXS)) to calculate the weight concentration of barium titanate.

(Transmission electron microscope analysis-TEM analysis)

Using a transmission electron microscope (HD-2000, manufactured by Hitachi), a TEM image was obtained at a magnification of 20 to 600,000 times and an acceleration voltage of 200.0 kV, and composition mapping was performed by EDS (energy dispersive X-ray spectroscopy device). The peak of titanium dioxide and the peak of barium titanate were removed, and the barium titanate phase on the surface of the titanium dioxide particles was identified. The average thickness of the barium titanate phase on the surface of the titanium dioxide was calculated from 600,000 times the images of the STEM phase and the Z contrast phase. In addition, in calculating the ratio of the titanium dioxide particles in which the barium titanate phase having an average thickness of 4 nm or more was formed on the surface among all the titanium dioxide particles, 50 or more titanium dioxide particles (cross-sectional shape can be observed in the field of view of 6 images at a magnification of 200,000 times). Counts). Here, the titanium dioxide particle in which the barium titanate phase with an average thickness of 4 nm or more was formed on the surface is coat | covered continuously in the particle cross section. With continuous coating, the barium titanate phase having a thickness of 3 nm or more in the Z contrast phase was in a state in which 90% or more of the cross-section outer periphery was continuous.

Table 2 shows the results of Example 1B using TiO ₂ (B) as the titanium dioxide particles.

In addition, the result of having performed TEM observation by the said method is shown to FIG. 1A-1D. In FIG. 1A, it is a TEM image which observed the barium titanate phase of the surface at 600,000 times. FIG. 1D is a Z contrast image and can be observed as bright partial contrast from the presence of Ba ions, which are heavy elements on the barium titanate on the surface. From this result, it can be confirmed that the barium titanate phase on the surface is continuous and has a thin layered structure. 1B and 1C are EDS (energy dispersive X-ray spectroscopy) mapping images of Ti-K rays and Ba-L rays. In the mapping, the thickness and continuity of the layer cannot be clearly confirmed due to the decomposition ability, but Ba ions are selectively observed around the titanium dioxide particles. The BaTiO ₃ coated particle ratio represents the ratio of the number of particles in which 90% or more of the outer peripheral portion of the titanium dioxide particle cross section is continuously covered with 3 nm or more of barium titanate phase in the total number of titanium dioxide particles. Also BaTiO ₃ is the production rate, the percentage yield on a wt% of BaTiO ₃ is generated for the mixed powder from the analysis of the powder X-ray diffraction.

1st heat treatment process BaTiO ₃ production rate BaTiO ₃ Cloth Particle Ratio T ₀ [℃] Time [h] [weight%] [%] 2B Comparative Example 450 2 0 0 3B Comparative Example 550 2 6 11 Example 1B 600 2 33 89 Example 2B 650 2 50 88

Except for changing the heat treatment temperature of the first heat treatment step to 650 ° C., the same operations as those of the first embodiment B were performed. Example 2B and the heat treatment temperature of the first heat treatment step were 700 ° C. are referred to as Example 3B. . The TEM analysis results are also shown in Table 2.

(1st to 3rd comparative example)

The first comparative example is performed without performing the first heat treatment step and performing the same operation as in the first embodiment except for the above. Titanium dioxide as a raw material is referred to as Comparative Example 1A in the case of TiO ₂ (A), and Comparative Example 1B in the case of TiO ₂ (B). Although the 1st heat processing process is not implemented in the 1st comparative example, since the maximum temperature of the spray-drying drying condition after wet grinding | pulverization is 250 degreeC, in the table | surface and drawing, it was enumerated as what processed the heat processing temperature at 250 degreeC for convenience.

The second comparative example is carried out in the same manner as in the first comparative example except that the heat treatment for removing the organic component of the mixed powder is performed at 450 ° C without performing the first heat treatment step, and the holding time is 2 hours. Also in the 2nd comparative example, it was enumerated as what was heat-processed at 450 degreeC for comparison in a figure and a table similarly.

The same operation as that of the first embodiment was performed with the heat treatment temperature of the first heat treatment step being 550 ° C., referred to as a third comparative example. The TEM analysis results are also shown in Table 2.

In the results shown in Table 2, in the first heat treatment temperature of 550 ℃ Although the barium titanate is produced 6% by weight, a BaTiO ₃ coating, the proportion of particles is 10% or so. In Example 1B and Example 2B, it was confirmed that the coverage ratio was 85% or more. In Example 1B, when the titanium dioxide particles coated relatively uniformly are representative particles, the average thickness of the barium titanate continuous layer is about 4 to 5 nm. 3 to 3.5 nm in the thin portion and 5 to 7 nm in the thick portion. In Example 2B, although the coverage is the same, the representative particle | grains which are uniform in coating show that the thickness is 7-10 nm, but there are many variations in thickness, and the small titanium dioxide particle in distribution distributes barium titanate to the inside.

(4th to 6th embodiment)

The mixed powder was prepared in the same manner as in Example 1B.

[First Heat Treatment Step]

The rotary kiln (reduced by RK furnace) was subjected to a heat treatment of the mixed powder for 0.3 hour at a first heat treatment temperature of 600 ° C. in an air atmosphere. 0.3 hour of processing time made the average residence time of a powder into the heat retention part of a rotary kiln as processing time. The titanium dioxide which is a raw material is TiO ₂ (B), and the first heat treatment step was performed with RK at 600 ° C. for 0.3 hour to be referred to as Example 4B. Example 4B except that the heat treatment temperature of the first heat treatment step was changed to 650 ° C., except that the heat treatment temperature of the first heat treatment process was changed to 700 ° C., except that the same operation as in Example 4B was performed. The same operations as those in Example 6 are referred to as Example 6B.

A rotary kiln (RK furnace) with fluidity in the mixed powder is carried out as an example of a fluidized kiln in a batch furnace (reduced as B furnace) in which heat treatment is performed while the mixed powder is stopped.

The production rates of barium titanate calculated from powder X-ray diffraction in the first to sixth examples and the first to third comparative examples are shown in FIGS. 2 and 3.

2 shows that the heat treatment temperature of the first annealing process to 575 ℃, 625 ℃, 800 ℃ , Fig. 3, were also shown with a result of a T ₀ is 0 to 12 hours for the holding time of the 650 ℃.

From the results of FIG. 2, significant differences in TiO ₂ raw materials A and B were not. At 575 ° C to 625 ° C, the reaction is almost stable at 30 to 40% by weight. In the first heat treatment temperature region, as shown in the TEM results, a thin barium titanate phase of 3 nm or more is continuously coated on the titanium dioxide surface. When the heat treatment temperature of the first heat treatment step is 700 ° C. to 80 ° C., the barium titanate reaction is promoted, and at least 75% by weight is a barium titanate phase. However, since the specific surface area of titanium dioxide is 30 ㎡ / g or more, it is considered that the temperature in the reaction is also conducted at the same time, i.e., grain growth of the titanium dioxide with a specific surface area of TiO ₂ sharply decreases. Moreover, even if the rutile rate of the raw material is 30% or less, since the transition from the anatase structure to the rutile structure is performed at 700 ° C or higher, the rutile rate of the raw material cannot be sufficiently reflected. For this reason, it can be said that 575 degreeC-650 degreeC of 1st heat processing temperature in atmospheric pressure and in atmospheric atmosphere is preferable. However, in this temperature range, the reaction is not stable unless the CO ₂ gas concentration in the furnace atmosphere is 15 mol% or less. For instance, by design of barium titanate where the CO ₂ is also subjected to a first heat treatment at 625 ℃ from 50 mol% or more atmosphere, generation becomes not more than 5% by weight. When the amount of the mixed powder is, for example, 1 kg or more, the influence of CO ₂ generated in the reaction cannot be ignored. When the amount of the mixed powder is large, the influence of the CO ₂ gas may be reduced by setting the pressure to 1 × 10 ³ Pa or more and 1.0133 × 10 ⁵ Pa or less not only by atmospheric replacement but also by exhaust gas by intake or the like.

From the result of FIG. 2, since the reaction time is short as 0.3 hours in the RK which is a fluidized-fired baking of the powder, the production rate of barium titanate is higher than that maintained in the batch furnace (to B) in which the powder is stopped. This tends to be small. However, in the RK furnace, compared with B furnace, the temperature raising and lowering processes are rapid, corresponding to a temperature raising rate of 50 ° C./min or more. Therefore, since it is hard to be affected by the variation of the particle growth of the raw material during the temperature rising process, and the powder flows, there is also a great influence of the temperature unevenness due to the heat conduction inside the powder and the local CO ₂ gas generated in the reaction. It is expected that the width can be reduced.

In addition, from the result of FIG. 3, when the holding time is 10 minutes (the temperature rise and the temperature fall in common at 3.3 ° C / min), the production of barium titanate is 14% by weight, and the first heat treatment step is not sufficient. The production rate here also includes the reaction in the temperature raising or lowering process. Moreover, the reaction tends to saturate at the holding time of 2 hours, and the reaction is slowly progressing at the holding time of 6 hours and 12 hours. When the holding time is short, the effect in the first heat treatment step of the present invention is not seen. Moreover, it is preferable to set retention time suitably according to the quantity of mixed powder and the temperature distribution of a furnace.

Fig. 4 shows the results obtained by approximating the specific surface areas of the raw materials with respect to the thickness of the barium titanate phase on the surface and the production rate of barium titanate of 5, 20, 30 and 50 m 2 / g.

This estimation assumes the following and ideally assumes that a barium titanate phase is formed on the surface, and is estimated by calculation.

Assuming that the reaction of the barium titanate on the surface was ideally uniform, and that the ideal titanium dioxide particles were perfectly spherical and uniform in particle size, the production rate of barium titanate was calculated in weight percent based on the thickness of the surface reaction layer.

On the other hand, since the particle growth of titanium dioxide particles by heat treatment and the like are not taken into account, the barium titanate production rate by the treatment at the first heat treatment temperature is not directly reflected.

In Fig. 4, when titanium dioxide powder having a specific surface area of 30 m 2 / g is used as a raw material, the layer thickness of the surface is estimated to be 3 nm when the barium titanate production rate is 15% by weight or more. Although it is difficult to realize the ideal state completely from the actual powder, it is considered that in the first embodiment, the barium titanate phase on the surface is 4 to 5 nm, and the barium titanate production rate is 30% by weight, which is very close to the ideal state. This result is considered to theoretically support the TEM result. Thus, in Embodiment 1B, it was found that the present invention can be realized.

Second Heat Treatment Process

The second heat treatment step was performed on the powders that passed through the first heat treatment steps of the first to sixth examples and the first to third comparative examples. After the first heat treatment step, the temperature was once lowered to room temperature, the powder was divided, and the temperature in the second heat treatment step in the batch furnace (to B) was performed under conditions of 900 to 1000 ° C. and holding time for 2 to 12 hours. In a 2nd heat processing process, it is performed in atmospheric | air atmosphere in atmospheric pressure, it is set as temperature rising rate 3.3 degree-C / min (200 degree-C / hour), temperature-fall rate 3.3 degree-C / min (200 degreeC / hour), and 5-50 g of powder are made from alumina The container was filled and heat-treated. Table 3 and Table 4 show typical results.

The first heat treatment is embodiment 1A, which is referred to as Examples 1A-1 to 1A-4, and similarly to Embodiments 1B-1 to 1B-6, Examples 2B-1 to 2B-3, and Example 3B. -1 to 3B-3 Examples, 1A-1 to 1A-3 Comparative Examples, 1B-1 to 1B-3 Comparative Examples, 2B-1 Comparative Examples, 3B-1 to 3B-3 Comparative Examples, Examples 4B-1 to 4B-8, Examples 5B-1 to 5B-5, and Examples 6B-1 to 6B-5. First comparison, the second comparative example, the temperature T ₀ is as above, and with 250 ℃, 450 ℃. Although this is not actually the first heat treatment step, it corresponds to the heat treatment at an arbitrary temperature, and therefore the values are conveniently described in the tables and drawings. The powder flowability in Table 4 was marked as "not present" for the first heat treatment in B furnace and "having" for the first heat treatment in RK furnace.

The obtained barium titanate particles were subjected to X-ray diffraction analysis to determine c / a values as indices of tetragonality and ratio (I ₍₂₀₀₎ / Ib) values as indices of crystallinity (hereinafter referred to as "K value"). And half-value widths of the peaks of the (111) plane refractive line were determined. In calculating the K value and the half width of the (111) diffraction line, the contribution of the Cu-Kα2 line was removed so that only the background and the Cu-Kα1 were removed.

On the other hand, K value of the peak intensity (I ₍₂₀₀₎ ) of the (200) plane diffraction line with respect to the intensity (Ib) at the midpoint between the peak point angle of the (002) plane diffraction line and the peak point angle of the (200) plane diffraction line. Although defined by the ratio (I ₍₂₀₀₎ / Ib), when it is difficult to distinguish the diffraction lines from the X-ray diffraction results, K values are described as follows for convenience.

If the diffraction line of the (200) plane and the diffraction line of the (002) plane are not clear, the K value is set to 1.5. If the c / a value is 1.008 or less, it is difficult to distinguish between the tetragonal and cubic crystals. It was described as.

For the barium titanate particles obtained in Examples 1B-2, 3B-2, 1B-1 Comparative, and 3B-2 Comparative Example, the K value, that is, the ratio (I ₍₂₀₀₎ / Ib) is calculated. The X-ray diffraction result on which it is based is shown in FIG. In comparison with the case where the second heat treatment temperature is 925 ° C, it can be seen that in the examples shown by the solid lines, the K value is remarkably improved compared to the comparative examples shown by the broken lines. This difference cannot be known only by comparing the c / a values.

As known from Patent Literature 1, the K value is an index showing the crystallinity in the case of using a chip capacitor. Therefore, in barium titanate, not only the c / a ratio, which is an index of tetragonality, but also the grain size is fine and uniform, and the K value needs to be large.

In addition, in the present invention, by forming a continuous barium titanate phase on the surface in the first heat treatment step, not only the second heat treatment temperature is lowered, but also the effect of aging grain growth of barium titanate by a long second heat treatment can be expected. 9 and 12, a very high K value can be realized. Although the K value becomes the highest value in the fourth embodiment, this is considered to be an effect due to the uniform and ideally reacting of the first heat treatment. Therefore, it turns out that RK is preferable as a means of performing a 1st heat processing.

In addition, in order to evaluate the particle shape, the particle size was obtained by Rietveld analysis of the X-ray diffraction analysis ray. The particle size obtained from the X-ray diffraction is referred to as particle size (XRD) in order to distinguish it from the particle size obtained from SEM or specific surface area. In addition, the surface area was similarly measured.

X-ray diffraction analysis and specific surface area measurement were performed in the same manner as above. The results are shown in Table 3 and Table 4.

The relationship between the second heat treatment temperature T ₁ and the K value is shown in FIG. 6, the relationship between the second heat treatment temperature T ₁ and the c / a value is shown in FIG. 7, and the relationship between the K value and the particle diameter is shown in FIG. 8. It was. 6 and 7 only show that the holding time at the second heat treatment temperature T ₁ is 2 hours for comparison. FIG. 8 also shows Examples 1B-6 in which the holding time of the first example, the third example, and the third comparative example is 2 hours, and the holding time is 12 hours.

9 shows the relationship between the K value of the barium titanate particles and the first heat treatment temperature T ₀ at the second heat treatment temperature T ₁ at 925 ° C. FIG. 10 shows a relationship between the c / a value of the barium titanate particles and the first heat treatment temperature T _{0 at} the second heat treatment temperature T ₁ at 925 ° C.

Second heat-treatment temperature (T ₁₎ is set forth in and of the barium titanate particles K value of from 950 ℃, the first 11 the relationship between the heat treatment temperature (T _0). 12 shows the relationship between the second heat treatment temperature (T ₁ ) and the K value for the barium titanate particles obtained in Comparative Examples 1B and 4B to 6B.

13 shows the relationship between the second heat treatment temperature (T ₁ ) and the c / a value for the barium titanate particles obtained in Comparative Examples 1B and Examples 4B to 6B.

From the results of Table 3, Table 4, Fig. 7, and Fig. 13, it can be seen from the examples of the present invention that the c / a value is 1.008 or more, or 1.009 or more, indicating very high tetragonality. In addition to the c / a value, the first embodiment of the present invention showed a high K value. As a result of the K value with respect to the particle size XRD of FIG. 8, it can be seen that in the first embodiment, the K value at the same particle size is improved. In addition, it can be seen that the second heat treatment step results in higher crystallinity even at 900 to 950 ° C., and that barium titanate having good characteristics can be obtained even at a low second heat treatment temperature.

9-11 is a figure which shows the characteristic of the barium titanate obtained by the 2nd heat processing process, making the 1st heat processing temperature the horizontal axis. In FIG. 9, K value and c / a value are the most favorable when 1st heat processing temperature is about 600 degreeC. Although only the K value is high, it is a high value even at 700 ° C and 800 ° C, but it is not preferable in the sense of particle uniformity and granulation because it is inferior in the K value with respect to the particle diameter as shown in FIG. 8 and the variation in the particle diameter is also increased. In the thinning of the chip capacitor, it is necessary to have fine particles, high K value and uniform particle size, and the dielectric powder obtained in the present invention can satisfy both of them.

In addition, scanning electron micrographs of barium titanate particles obtained in Examples 1B-3, 1B-3, 3B-3, 4B-3 and 6B-2 were obtained. Photographs were taken at magnifications of 20,000 to 50,000 times. Average particle size, standard deviation of particle size, and particle size distribution ((D80-D20) / D50), ((D90-D10) in the case of circular approximation using commercially available image analysis software, for 250 or more particles arbitrarily selected from the obtained SEM images. ) / D50) was calculated. Moreover, the average particle diameter was also computed from the specific surface area by BET method.

The average particle diameter was calculated from the BET specific surface area according to the following equation.

BET average particle size = 6 (theoretical density / specific surface area) x 1000

The theoretical density was 5.7 g / cm 3.

The results are shown in Table 5.

The particle size distribution is greatly improved in Examples 1B and 4B with respect to Comparative Examples 1B having a specific surface area of about 3 m 2 / g. This indicates that the particle size becomes uniform in the particles at the first heat treatment temperature of about 600 ° C. Since titanium dioxide which is a raw material transfers to a rutile structure at around 700 ° C and there is a large decrease in specific surface area in titanium dioxide alone at 700 ° C or more, the first heat treatment at atmospheric pressure is preferably about 575 to 650 ° C. In Non-Patent Document 1, the particle size distribution is presented as an index of M value, that is, 1 / (log (D80) -log (D20)). The larger the M value, the better the distribution. For reference, when the M value is used as an index, the M value is 5.2 in the first comparative example, which is equivalent to the M value 5.0 in the non-patent literature. The M value is 6.3 in the first example and the M value 6.8 in the fourth example. It can be seen that the improvement. Therefore, the dielectric powder obtained by the present invention has a high c / a or K value, so that crystallinity is very good and particles are very uniform.

(Evaluation of Dielectric Properties of Barium Titanate)

In order to evaluate the dielectric properties of barium titanate, a sample was prepared as follows. To barium titanate particles obtained in Examples (1B-1, 1A-2, 1B-2, 3B-2, 4B-2, 6B-1) and Comparative Example (1B-3) of the present invention, PVA (poly) 10 weight% of vinyl alcohol resin) was added and pressure-molded, and the disk-shaped sample of diameter 12.5mm and thickness about 0.6mm was obtained. Next, as a binder removal process of the obtained disc shaped sample, heat processing in air was performed at 400 degreeC, holding time for 4 hours. Then, heat treatment was performed under the condition that the firing temperature T ₂ was 1250 ° C. Atmosphere: In air | atmosphere, holding time: It was set as the conditions of the temperature increase rate of 3.3 degree-C / min for 2 hours.

In-Ga was applied to both surfaces of the obtained dielectric property evaluation samples to form an electrode. The electrode was 6 mm in diameter.

For each obtained sample, the relative dielectric constant (εr), ferroelectric transition temperature (T _C ) and dielectric loss tanδ were measured by the method described below.

With respect to the capacitor sample, a signal of frequency 1 kHz and input signal level (measurement voltage) 1 Vrms was inputted at a digital LCR meter (HP 4284A) at -55 ° C to 140 ° C in a room temperature of 20 ° C and a temperature bath, and the electrostatic capacitance C and dielectric loss tan δ were measured. The relative dielectric constant epsilon r (unitless) was calculated based on the thickness of the dielectric sample, the effective electrode area, and the electrostatic capacitance C obtained as a result of the measurement. The ferroelectric transition temperature (Curie temperature T _C ) was obtained from the peak temperature of the relative dielectric constant. The results are shown in Table 6.

In addition, the temperature dependence of the dielectric constant epsilon r and the dielectric loss tanδ was investigated for the dielectric property evaluation samples obtained using the barium titanate particles of Examples 1B-1, 1B-2, and 1B-3 Comparative Example. . The results are shown in FIGS. 14 and 15, respectively. The shift of the Curie temperature T _C and the abnormality of the dielectric loss tan δ are not seen, and the relative dielectric constant ε r is dramatically improved. This is considered to be attributable not only to the high c / a but also to the K value of the uniform and fine particle barium titanate obtained by the effect of the present invention.

It is evident that the barium titanate obtained by the present invention has sufficient characteristics as the dielectric material. This means that even the fine particles exhibit a high dielectric constant because of their high K value and uniform particle size. Therefore, the present invention suppresses the growth of the abnormal particles and obtains dielectric particles of fine particles having high tetragonality, thereby enabling new thinning of the multilayer ceramic capacitor.

1A is a transmission microscope image (600,000 times TEM image) of the powder after the first heat treatment step.

1B is an EDS mapping of the Ti-K line of the transmission microscope of the powder after the first heat treatment process.

FIG. 1C is an EDS mapping of Ba-L lines of the transmission microscope of the powder after the first heat treatment process. FIG.

1D is a STEM-Z contrast image in a transmission microscope image (200,000 times) of the powder after the first heat treatment step.

FIG. 2 is a diagram showing the relationship between the treatment temperature (T ₀ ) and the barium titanate production rate (production rate) in the first heat treatment step.

3 is a diagram showing a relationship between a holding time and a barium titanate production rate in a first heat treatment step (650 ° C.).

4 is a graph showing the relationship between the surface barium titanate thickness and the production rate of barium titanate.

FIG. 5 shows a diffraction line 200 as a basis for calculating Examples 1B-2, 3B-2, 1B-1 Comparative Example, 3B-2 Comparative Example, and ratio (I ₍₂₀₀₎ / Ib). ) And (002) show the results of X-ray diffraction.

6 is a diagram illustrating a relationship between the second heat treatment temperature T ₁ and the K value.

7 is a diagram illustrating a relationship between the second heat treatment temperature T ₁ and a c / a value.

8 is a diagram illustrating a relationship between the K value and the particle size XRD.

9 is a diagram showing a relationship between the K value of the barium titanate particles and the first heat treatment temperature T ₀ at the second heat treatment temperature T ₁ at 925 ° C. FIG.

10 is a view showing the relationship between the second heat-treating temperature (T ₁₎ the c / a value of the barium titanate particles at 925 ℃ and the first heat-treatment temperature (T _0).

11 is a view showing the relationship between the K value and the first heat-treatment temperature (T ₀₎ of the barium titanate particles in the second heat treatment temperature (T ₁₎ is 950 ℃.

12 is a view showing the relationship between the value in Comparative Example 1B, the 4B to 6B claim carried out on the barium titanate particles obtained in the example, the second heat treatment temperature (T ₁₎ and K.

13 is a view showing the relationship of the comparative example 1B, the 4B to 6B claim carried out on the barium titanate particles obtained in the example, the second heat treatment temperature (T ₁₎ and c / a values.

Fig. 14 is a diagram showing the temperature dependence of the relative dielectric constant? R for samples for evaluating dielectric properties obtained using the barium titanate particles of Examples 1B-1, 1B-2, and 1B-3 Comparative Example.

Fig. 15 is a diagram showing the temperature dependence of the dielectric loss tan δ for samples for evaluating dielectric properties obtained using the barium titanate particles of Examples 1B-1, 1B-2, and 1B-3 Comparative Example.

Claims (11)

Preparing a titanium dioxide particle having a rutileization rate of 30% or less and a BET specific surface area of 20 m 2 / g or more, Preparing a barium carbonate particle having a BET specific surface area of 10 m 2 / g or more, Preparing a mixed powder by mixing titanium dioxide particles and barium carbonate particles; A first heat treatment process of heat treating the mixed powder to form a barium titanate phase on the surface of the titanium dioxide particles; A second heat treatment step of performing a heat treatment at 800 to 1000 ° C. after the first heat treatment step, The heat treatment temperature in the first heat treatment step is lower than the heat treatment temperature in the second heat treatment step, and at least 15% by weight of the mixed powder after the first heat treatment step becomes barium titanate, and the barium titanate having an average thickness of 3 nm or more on the surface of the titanium dioxide particles. A method of making a dielectric particle that is allowed to react for a time sufficient to produce a phase. The method of claim 1, In the first heat treatment step, at least 75% of the total titanium dioxide particles, a step of continuously generating a barium titanate phase having an average thickness of 4 nm or more on the surface of the titanium dioxide particles, wherein at least 20% by weight of the mixed powder contains barium titanate. Method for producing a dielectric particle. The method according to claim 1 or 2, The heat treatment temperature of a 2nd heat treatment process is 850-950 degreeC, and the manufacturing method of the dielectric particle whose c / a value of the produced barium titanate particle is 1.008 or more. The method according to any one of claims 1 to 3, The heat treatment temperature of the 2nd heat treatment process is 850-950 degreeC, and the produced barium titanate particle is X-ray intensity in the midpoint of the peak point of (200) plane and (002) plane in the powder X-ray diffraction of X-ray CuK (alpha) ray. The manufacturing method of the dielectric particle whose ratio (I ₍₂₀₀₎ / Ib) of diffraction line intensity I ₍₂₀₀₎ of (Ib) and (200) plane is four or more. The method of claim 1, The first heat treatment step is performed at 575 to 650 ° C. in an air atmosphere at a pressure of 1 × 10 ³ Pa or more and 1.0133 × 10 ⁵ Pa or less, and 25% by weight or more and 55% by weight or less of the dielectric powder becomes barium titanate. Method of preparation. The method of claim 1, The first heat treatment step is performed at 600 to 700 ° C. in an air atmosphere at a pressure of 1 × 10 ³ Pa or more and 1.0133 × 10 ⁵ Pa or less in a calcining furnace for flow-firing the powder, and at least 20% by weight to 75% by weight in the mixed powder. A method for producing a dielectric particle, which will be barium titanate as follows. The method according to claim 5 or 6, In the first heat treatment step, the production method of the dielectric particles to control the CO ₂ gas concentration in the atmosphere to 15 mol% or less. The method according to claim 5 or 6, A method for producing a dielectric particle comprising a step of cooling to 550 ° C. or less after the first heat treatment step, and then performing a second heat treatment step. The method of claim 1, A method for producing a dielectric particle, wherein the first heat treatment step is performed at 450 to 600 ° C. under a pressure of 1 × 10 ³ Pa or less. The method of claim 1, A method for producing a dielectric particle comprising a step of evaluating the weight concentration of barium titanate phase by confirming the progress of the first heat treatment step by performing powder X-ray diffraction analysis on the product in the first heat treatment step. The method of claim 1, A method for producing a dielectric particle, comprising the step of observing a product in a first heat treatment step by transmission electron microscopy to confirm the barium titanate phase on the surface of the titanium dioxide particles, and to confirm the progress of the first heat treatment step.

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