KR102581034B1 - Method for producing barium titanate powder - Google Patents

Abstract

[Problem to be solved] To provide a method for producing perovskite-type barium titanate powder that is industrially advantageous and has fine and high tetragonality.
[Solution] Perovskite-type barium titanate powder is characterized by having a firing process to obtain perovskite-type barium titanate powder by firing the firing raw material at 600 to 1200°C while supplying superheated water vapor to the firing atmosphere. Manufacturing method.

Description

Method for producing barium titanate powder {METHOD FOR PRODUCING BARIUM TITANATE POWDER}

The present invention relates to a method for producing perovskite-type barium titanate powder, and relates to a method for producing perovskite-type barium titanate powder useful as a raw material for functional ceramics such as piezoelectric materials, optoelectronic materials, dielectrics, semiconductors, and sensors. will be.

Perovskite-type barium titanate powder has conventionally been used as a raw material for functional ceramics such as piezoelectric materials and multilayer ceramic capacitors. However, in recent years, multilayer ceramic capacitors have been required to increase the number of layers or to have a high dielectric constant in order to achieve high capacity, and for this reason, perovskite-type barium titanate powder, which is a raw material, is required to have fine and high tetragonality.

One method for producing perovskite-type barium titanate powder is a method of calcining a complex organic acid salt containing Ba atoms and Ti atoms. For example, a representative example is the oxalate method, in which a solution containing barium chloride and titanium chloride is brought into contact with an aqueous oxalic acid solution to react to obtain barium titanyl oxalate, and then the barium titanyl oxalate is calcined and treated with deoxalic acid. Complex organic acid salt methods such as the oxalate method have the advantage of producing high-quality products with fewer impurities derived from raw materials compared to the solid-phase method described later, and making it easier to obtain barium titanate with a uniform composition.

For example, in Patent Document 1 below, fine barium titanyl oxalate (BaTiO(C ₂ O ₄ )·H ₂ obtained by mixing a water-soluble barium salt, a water-soluble titanium salt, and an aqueous solution of oxalic acid simultaneously and pulverizing the gel with strong stirring in a short period of time. A method of calcining the crystals of O) at 700 to 900° C. has been proposed.

Additionally, Patent Documents 2 and 3 below propose a method of subjecting barium titanyl oxalate to wet grinding to obtain fine barium titanyl oxalate, and then calcining the obtained barium titanyl oxalate.

In addition, in Patent Document 4 below, a mixed aqueous solution of barium chloride aqueous solution and titanium chloride aqueous solution is added to an oxalic acid aqueous solution to precipitate barium titanate oxalate, then aged, washed, filtered, and dried to produce barium titanate oxalate. ; Preparing fine barium titanate powder by first calcining the prepared barium titanate oxalate and then pulverizing it; and secondary calcination of the fine barium titanate powder, followed by secondary pulverization.

Additionally, in Patent Document 5 below, there is a method for producing barium titanate powder in which a solid reactant is obtained by contacting an aqueous titanium compound solution with an aqueous barium compound solution, and then the solid reactant is heat-treated while being brought into contact with water vapor. The titanium acid compound and the barium compound are An oxalate method has been proposed.

Additionally, in Patent Document 6 below, there is a method for producing perovskite-type barium titanate powder having fine and high tetragonality by calcining a complex organic acid salt containing Ba atoms and Ti atoms in the presence of humidified air in a kiln. It is proposed.

Additionally, as another method for producing perovskite-type barium titanate powder, the so-called solid phase method is known, in which the mixture obtained by mixing barium carbonate and titanium dioxide is calcined. This solid-phase method has the advantage that barium titanate can be obtained in a simple process at a low cost compared to complex organic acid salt methods such as the oxalate method.

A method of increasing the tetragonality of perovskite-type barium titanate obtained by a solid-phase method is thought to be to increase the firing temperature when producing perovskite-type barium titanate by firing a mixture containing barium carbonate and titanium dioxide. However, if the firing temperature is raised, particle growth or condensation between particles occurs, making it difficult to refine perovskite-type barium titanate.

In this regard, for example, in Patent Document 7 below, a method of producing fine-grained perovskite-type barium titanate with a high c/a ratio is described by calcining a mixture containing barium carbonate and titanium dioxide in steam or the like. there is.

Additionally, Patent Document 8 below proposes a method of producing fine barium titanate by calcining a raw material containing Ba and Ti in a calcining atmosphere containing heated air containing water vapor.

In addition, Patent Document 9 below proposes a method of producing perovskite-type barium titanate powder having fine and high tetragonality by calcining a mixed powder containing barium carbonate and titanium dioxide in the presence of humidified air in a kiln. It is done.

Japanese Patent Publication No. 61-146710 Japanese Patent Publication No. 2004-123431 Japanese Patent Publication No. 2002-53320 Japanese Patent Publication No. 2003-212543 Japanese Patent Publication No. 2000-344519 Japanese Patent Publication No. 2009-209002 Japanese Patent Publication No. 2005-314153 Japanese Patent Publication No. 2012-116728 Japanese Patent Publication No. 2009-209001

As in the above prior art, various methods for producing perovskite-type barium titanate powder using complex organic acid salts, including the oxalate method using oxalate, are being examined, which is an industrially more advantageous method, and the complex organic acid salt method is As perovskite-type barium titanate powder obtained by , a method for producing perovskite-type barium titanate powder having fine and high tetragonality was desired.

Also, in the case of the solid-phase method, various methods of producing perovskite-type barium titanate powder by the solid-phase method, like the above-described prior art, are being examined. This is an industrially more advantageous method, and the perovskite obtained by the solid-phase method is As a skyte-type barium titanate powder, a method for producing fine perovskite-type barium titanate powder with high tetragonality has been desired.

Therefore, the object of the present invention is to provide an industrially advantageous method for producing perovskite-type barium titanate powder by calcining a complex organic acid salt having a Ba atom and a Ti atom, and to provide a fine and highly tetragonal method. The object is to provide a method for producing louvskite-type barium titanate powder. Another object of the present invention is to provide a method for producing perovskite-type barium titanate powder having fine and high tetragonality, which is an industrially advantageous solid-phase method.

The present inventors have conducted extensive research in consideration of the above-mentioned circumstances and as a result, when calcining a complex organic acid salt containing Ba atoms and Ti atoms in the complex organic acid salt method, or in the solid phase method, it is possible to obtain a product containing barium carbonate and titanium dioxide. When firing the raw material mixture, if a large amount of carbon dioxide gas is present in the firing atmosphere, barium carbonate is generated on the surface or inside the perovskite-type barium titanate powder, so the ratio of the c-axis to the a-axis, which is an indicator of tetragonality ( As c/a) is lowered, perovskite-type barium titanate powder with low ferroelectric properties is produced. Additionally, by reducing the carbon dioxide gas concentration in the atmosphere during firing, fine and highly tetragonal crystals are formed even at the same firing temperature. It is possible to produce a perovskite-type barium titanate powder having a. Furthermore, when firing is performed with a large amount of superheated water vapor present in the atmosphere, carbon dioxide gas is more effectively absorbed into the superheated water vapor, and this causes carbon dioxide in the atmosphere during firing. It was found that by reducing the gas concentration, a perovskite-type barium titanate powder that is fine and has high tetragonality even at the same firing temperature can be obtained, leading to the completion of the present invention.

That is, the present invention (1) has a firing process for obtaining perovskite-type barium titanate powder by firing a firing raw material containing a Ba source and a Ti source at 600 to 1200°C while supplying superheated water vapor to the firing atmosphere. A method for producing perovskite-type barium titanate powder is provided.

Furthermore, the present invention (2) provides the method for producing perovskite-type barium titanate powder of (1), wherein the firing raw material is a complex organic acid salt having Ba atoms and Ti atoms.

In addition, the present invention (3) provides a method for producing the perovskite-type barium titanate powder of (2), wherein the complex organic acid salt is a carboxylic acid salt.

In addition, the present invention (4) provides a method for producing the perovskite-type barium titanate powder of (2), wherein the complex organic acid salt is oxalate.

Additionally, the present invention (5) provides the method for producing perovskite-type barium titanate powder of (1), wherein the fired raw material is a raw material mixture containing barium carbonate and titanium dioxide.

In addition, the present invention (6) provides a method for producing the perovskite-type barium titanate powder of (5), wherein the BET specific surface area of the barium carbonate is 10 m 2 /g or more.

In addition, the present invention (7) provides the method for producing perovskite-type barium titanate of (5) or (6), wherein the BET specific surface area of the titanium dioxide is 5 m 2 /g or more.

In addition, the present invention (8) provides a method for producing the perovskite-type barium titanate powder of any one of (1) to (7), characterized in that superheated water vapor of 200 to 1200 ° C. is supplied to the firing atmosphere. will be.

According to the present invention, it is an industrially advantageous method, and it is possible to produce perovskite-type barium titanate powder having fine and high tetragonality. And the perovskite-type barium titanate powder produced by the method for producing perovskite-type barium titanate powder of the present invention is useful as a raw material for functional ceramics for electronic components such as piezoelectric materials, optoelectronic materials, dielectrics, semiconductors, and sensors. do.

Figure 1 is a schematic cross-sectional view showing a firing furnace for carrying out an example of the method for producing perovskite-type barium titanate powder of the present invention.

The method for producing perovskite-type barium titanate powder of the present invention is to sinter raw materials containing a Ba source and a Ti source while supplying superheated steam to a sintering atmosphere, preferably at a temperature of 200 to 1200°C. A method for producing perovskite-type barium titanate powder, characterized in that it has a firing process for obtaining perovskite-type barium titanate powder by firing at 600 to 1200°C.

And the method for producing the perovskite-type barium titanate powder of the first form of the present invention is a sintering process according to the method for producing the perovskite-type barium titanate powder of the present invention, wherein Ba atoms and Ti are used as sintering raw materials. It is a form that uses a complex organic acid salt with atoms. That is, the method for producing perovskite-type barium titanate powder of the first form of the present invention is to sinter a complex organic acid salt having a Ba atom and a Ti atom at 600 to 1200° C. while supplying superheated water vapor to the sintering atmosphere. A method for producing perovskite-type barium titanate powder, characterized by having a sintering process (1) for obtaining the perovskite-type barium titanate powder.

A method for producing perovskite-type barium titanate powder of the first form of the present invention will be described with reference to FIG. 1. Figure 1 is a schematic diagram showing a firing furnace for carrying out an example of the method for producing perovskite-type barium titanate powder of the present invention, and is a cross-sectional view.

In an example using the firing furnace 1 shown in FIG. 1, first, an alumina vessel containing a firing raw material (complex organic acid salt having a Ba atom and a Ti atom) 5 is placed in the firing furnace 1 covered with an alumina fiber board. Place it and cover it with the cover (2). Next, the inside of the kiln 1 is preheated. Next, while supplying superheated steam 11 from the superheated steam supply pipe 7 into the kiln 1, the temperature inside the kiln 1 is raised to a predetermined sintering temperature, and after reaching the predetermined sintering temperature, the sintering furnace 1 Firing is performed by maintaining the temperature while supplying superheated steam 11 inside. And when the firing raw material (composite organic acid salt having Ba and Ti atoms) is fired, barium titanate is produced through thermal decomposition and carbon dioxide gas derived from the organic acid is generated. The generated carbon dioxide gas is absorbed into the surrounding superheated water vapor and becomes superheated water vapor 12 containing carbon dioxide gas. Therefore, the superheated water vapor 12 containing carbon dioxide gas is discharged from the exhaust pipe 4. That is, in the embodiment using the firing furnace 1 shown in FIG. 1, firing is performed while supplying superheated steam 11 to the atmosphere and discharging superheated steam 12 containing carbon dioxide gas from the atmosphere.

At this time, since superheated water vapor 11 is continuously supplied into the firing furnace 1, the atmosphere to which the firing raw material (complex organic acid salt having Ba atoms and Ti atoms) 5 is exposed is an atmosphere in which a large amount of superheated water vapor exists. do. In the embodiment using the firing furnace 1 shown in FIG. 1, the inside of the firing furnace 1 is not sealed and firing is performed in an open system, so there is some air in the firing atmosphere, and superheated water vapor 11 is present in the firing atmosphere. By continuously supplying , the amount of air in the firing atmosphere can be greatly reduced. Additionally, a complete superheated steam atmosphere can be created by controlling the supply amount of superheated steam. In other words, by performing firing while supplying superheated water vapor to the firing atmosphere, the firing atmosphere of the firing raw material (composite organic acid salt having Ba atoms and Ti atoms) is set to a superheated water vapor atmosphere with a very small amount of air, or a completely superheated water vapor atmosphere. Firing can be performed.

Furthermore, if carbon dioxide gas generated by firing exists around the produced barium titanate powder, it adversely affects the tetragonality. However, in the embodiment using the firing furnace 1 shown in FIG. 1, a large amount of superheated water vapor is present in the firing atmosphere. Because it exists as carbon dioxide gas, it is absorbed into superheated water vapor. Therefore, in the embodiment using the firing furnace 1 shown in FIG. 1, adverse effects due to carbon dioxide gas can be prevented. In addition, in the embodiment using the firing furnace 1 shown in FIG. 1, there is very little air in the firing atmosphere, so side reactions caused by carbon dioxide can be prevented.

The method for producing perovskite-type barium titanate powder of the first form of the present invention is to sinter a complex organic acid salt having a Ba atom and a Ti atom at 600 to 1200° C. while supplying superheated water vapor to the sintering atmosphere to produce perovskite-type barium titanate powder. A method for producing perovskite-type barium titanate powder, characterized by having a sintering step (1) to obtain a perovskite-type barium titanate powder.

That is, the calcination process (1) according to the method for producing perovskite-type barium titanate powder of the first form of the present invention involves calcination of a complex organic acid salt having Ba atoms and Ti atoms to powder perovskite-type barium titanate powder. This is the process of obtaining.

The composite organic acid salt having a Ba atom and a Ti atom (hereinafter also referred to as Ba-Ti composite organic acid salt) according to the firing process (1) is not particularly limited as long as it can form a double salt of Ba and Ti, examples For example, carboxylic acid salts such as formate, oxalate, acetate, propionate, succinate, malate, tartrate, citrate, and lactate, or formic acid, oxalic acid, acetic acid, propionate, succinic acid, malic acid, tartaric acid, and citric acid. and complex salts having two or more types of carboxylic acids such as lactic acid (see International Publication No. WO2008/102785). Specifically, barium titanyl oxalate, barium titanyl citrate, barium titanyl succinate, etc. are mentioned. Among these, oxalate and citrate are preferable as Ba-Ti complex organic acid salts, and oxalate, which has an atomic ratio of Ba/Ti near 1, is particularly preferable because it is easy to manufacture and has low manufacturing costs.

The molar ratio of Ba to Ti (Ba/Ti) in atomic terms in the Ba-Ti composite organic acid salt is 0.99 to 1.01, preferably 0.995 to 1.005. If the molar ratio of Ba to Ti (Ba/Ti) is less than 0.99, it becomes titanium rich, and perovskite-type barium titanate with high tetragonality cannot be obtained. On the other hand, if it exceeds 1.01, it becomes barium rich, and tetragonality is not obtained. High perovskite barium titanate is not obtained.

Barium titanate obtained by performing the firing step (1) is a perovskite-type complex oxide in which the A-site element is Ba and the B-site element is Ti. The barium titanate obtained by performing the firing step (1) may be perovskite-type barium titanate in which the A-site element is only Ba and the B-site element is only Ti, or some of the Ba atoms of the A-site element may be Substituted with either Ca or Sr or both Ca and Sr; Part of the Ti atom of the B-site element is substituted with Zr; or Part of the Ba atom of the A-site element is substituted with either Ca or Sr. Both Ca and Sr may be substituted, and a portion of the Ti atoms of the B site element may be substituted with Zr.

In the method for producing perovskite-type barium titanate of the first form of the present invention, a perovskite in which some of the Ba atoms of the A site elements are replaced with Ca or Sr, or some of the Ti atoms of the B site elements are replaced with Zr In order to obtain barium titanate in the barium titanate form, the Ba-Ti composite organic acid salt may have Ca atoms or Sr atoms as partial replacement atoms for Ba atoms, and may also have Zr atoms as partial replacement atoms for Ti atoms. When a part of Ba atom is replaced with either Ca or Sr or both Ca and Sr, the content of Ca atom or Sr atom in the Ba-Ti composite organic acid salt is not particularly limited, but in atomic terms, the Ca atom relative to Ba atom is not particularly limited. The content such that the total ratio of atoms and Sr atoms is less than 50 mol% is preferable. When some of the Ti atoms are replaced with Zr, the content of the compound having Zr atoms in the Ba-Ti composite organic acid salt is not particularly limited, but the content is such that the ratio of Zr atoms to Ti atoms in atomic terms is less than 50 mol%. This is desirable. Among the Ba-Ti composite organic acid salts, the molar ratio of the sum of Ti atoms and Zr atoms as B-site elements to the sum of Ba atoms, Ca atoms, and Sr atoms as A-site elements in atomic terms is 0.99 to 1.01, preferably. is from 0.995 to 1.005.

The average particle diameter of the Ba-Ti composite organic acid salt is preferably 200 μm or less, particularly preferably 100 μm or less. When the average particle diameter of the Ba-Ti composite organic acid salt is within the above range, it becomes easy to obtain fine perovskite-type barium titanyl titanate with high tetragonality. In addition, in the present invention, the average particle diameter is determined by scanning electron microscope (SEM) observation, and represents the average value of 1000 samples randomly extracted from the SEM images of scanning electron microscope (SEM) observation.

The method for producing the Ba-Ti complex organic acid salt is not particularly limited, and for example, it can be obtained by a known method. When the Ba-Ti complex organic acid salt is an oxalate, for example, an aqueous solution containing titanium chloride and barium chloride is brought into contact with an aqueous oxalic acid solution to precipitate the oxalate, aging is performed as necessary, and then, by a conventional method. A complex oxalate of Ba and Ti can be obtained by separating solid and liquid, recovering it, and performing washing, drying, grinding, etc. as necessary. In addition, as a method for producing Ba-Ti composite oxalate, Japanese Patent Application Laid-Open No. 2006-321722, Japanese Patent Application Laid-Open No. 2006-321723, Japanese Patent Application Laid-Open No. 2006-348026, and Japanese Patent Application Laid-open No. 2004-123431 Methods described in, etc. may be mentioned.

In addition, when the Ba-Ti complex organic acid salt is citrate, for example, a solution of barium chloride is added to a citric acid solution of titanium to precipitate citrate, aging is performed as necessary, and then solid-liquid separation is performed by a conventional method. By recovering, washing, drying, grinding, etc. as necessary, a composite citrate of Ba and Ti can be obtained. Additionally, examples of the method for producing Ba-Ti composite citrate include methods described in U.S. Patent No. 3,231,328, etc.

In addition, when the Ba-Ti complex organic acid salt is a complex salt of a carboxylic acid having both oxalic acid and lactic acid, for example, a solution containing a titanium component, a barium component, and a lactic acid component and a solution containing an oxalic acid component are mixed with alcohol. By contacting and reacting in a solvent, a complex salt of oxalic acid and lactic acid containing Ba and Ti can be obtained (for example, International Publication No. WO2008/102785).

After the Ba-Ti composite organic acid salt is prepared by the method exemplified above, the Ba-Ti composite organic acid salt can be pulverized for the purpose of controlling the particle diameter. A wet method is preferable as the grinding method, and an example is a method of grinding a slurry containing a Ba-Ti complex organic acid salt using a wet grinding device. Wet grinding devices include ball mills and bead mills. Additionally, solvents used in the wet method include, for example, water, methanol, ethanol, propanol, butanol, toluene, xylene, acetone, methylene chloride, ethyl acetate, dimethylformamide, and diethyl ether. Among these, organic solvents such as methanol, ethanol, propanol, butanol, toluene, xylene, acetone, methylene chloride, ethyl acetate, dimethylformamide, and diethyl ether, and those with low elution of Ba and Ti are highly crystalline. This is preferable because perovskite-type barium titanate powder can be obtained. Additionally, after grinding by a wet method, the slurry can be dried using a spray dryer.

The higher the purity of the Ba-Ti complex organic acid salt, the more preferable it is in order to obtain high-purity perovskite-type barium titanate powder.

And in the firing process (1), the Ba-Ti complex organic acid salt is fired. The firing temperature in the firing process (1) is 600 to 1200°C, preferably 700 to 1000°C. If the sintering temperature is below the above range, the solid phase reaction to change into perovskite-type barium titanate does not occur and it tends to remain unreacted. On the other hand, if it exceeds the above range, the produced perovskite-type barium titanate grows into particles. Because it causes a fine product, no fine product is obtained. The firing time in the firing process (1) is 4 hours or more, and is preferably 6 to 30 hours. In addition, in the firing process (1), after firing at 600 to 1200°C, preferably at 700 to 1000°C, the fired product is pulverized, granulated if desired, and then heated at 600 to 1200°C, preferably at 700 to 700°C. Firing may be carried out at 1000°C, and in order to make the powder properties homogeneous, the once-baked product may be pulverized and fired again may be repeated.

The firing furnace used in the firing process (1) includes a batch or continuous electric furnace or a gas furnace, and examples thereof include a roller hearth kiln, rotary kiln, pusher furnace, etc.

In the firing process (1), the Ba-Ti complex organic acid salt is fired at 600 to 1200°C, preferably 700 to 1000°C, while supplying superheated water vapor to the firing atmosphere and removing carbon dioxide and the like generated by the reaction from the firing atmosphere. This is done while discharging superheated water vapor containing carbon dioxide gas.

Superheated steam refers to a colorless and transparent H ₂ O gas obtained by further heating saturated steam at 100°C while maintaining normal pressure. Since superheated water vapor maintains the saturated state of water in the air at high temperatures, firing is performed while supplying superheated water vapor to the firing atmosphere, thereby effectively absorbing carbon dioxide gas generated during the production of barium titanate into the superheated water vapor and maintaining the firing temperature. The reaction can proceed without lowering . Additionally, since most of what exists in the firing atmosphere becomes superheated water vapor, side reactions caused by the presence of carbon dioxide in the air can be suppressed.

Since superheated steam is obtained by further heating saturated steam at 100°C while maintaining atmospheric pressure, the method of firing while supplying superheated steam to the firing atmosphere allows the reaction to be carried out under atmospheric pressure, and there is no need to carry out the reaction in a firing furnace with internal pressure.

In the firing process (1), the temperature of the superheated water vapor supplied to the firing atmosphere is preferably 200 to 1200°C, particularly preferably 300 to 1000°C. If the temperature of the superheated steam is less than the above range, it is difficult for the firing temperature to decrease, and if it exceeds the above range, a decrease in the firing temperature can be prevented, but the energy for generating the superheated steam increases, so the manufacturing cost increases.

Methods for generating superheated water vapor include heating saturated water vapor obtained by heating water to 100°C or higher directly or indirectly with fuel such as oil or gas, or heating it with heating means such as infrared rays, electromagnetic waves, or microwaves. there is. As means for generating such superheated steam, for example, the UPSS series of Tokuden Co., Ltd., the IHSS series of Fuji Denki Co., Ltd., the superheated steam generator of Nihon Tennetsu Co., Ltd., and the superheated steam generator of Shinnetsu Kogyo Co., Ltd. Processing devices, etc. can be mentioned.

The supply amount of superheated water vapor to the firing atmosphere is appropriately selected, but is preferably 5 L/min or more per 1 kg of Ba-Ti complex organic acid salt, more preferably 10 to 200 L/min per kg of Ba-Ti complex organic acid salt, especially Preferably, it is 15 to 100 L/min per 1 kg of Ba-Ti complex organic acid salt. When the supply amount of superheated water vapor to the firing atmosphere is within the above range, carbon dioxide gas generated within the kiln during the reaction can be efficiently absorbed and the temperature inside the furnace can be prevented from lowering due to superheated water vapor. In addition, it is the time to introduce superheated steam into the kiln, and introducing superheated water vapor into the kiln at least before perovskite-type barium titanate is generated by the reaction of the Ba-Ti complex organic acid salt effectively removes carbon dioxide gas generated during the reaction process. This is desirable because it can absorb and suppress the occurrence of adverse effects caused by carbon dioxide gas.

After performing the firing step (1), if necessary, the fired perovskite-type barium titanate powder can be washed with an acid solution, washed with water, dried, pulverized, classified, etc. to make a product. The drying method may be a normal method and is not particularly limited, but when wet grinding treatment is performed, for example, a method using a spray dryer can be applied.

The perovskite-type barium titanate powder obtained by carrying out the method for producing the perovskite-type barium titanate powder of the first form of the present invention has high tetragonality, and the ratio of the c-axis to the a-axis (c/ a) is preferably 1.004 or more, particularly preferably 1.006 to 1.010. The average particle diameter of the perovskite-type barium titanate powder obtained by performing the method for producing the perovskite-type barium titanate powder of the first form of the present invention is preferably the average particle diameter determined by electron microscope observation. It is 0.5 μm or less, particularly preferably 0.05 to 0.3 μm, and the BET specific surface area is preferably 2 m 2 /g or more, particularly preferably 3 to 20 m 2 /g. The perovskite-type barium titanate powder obtained by carrying out the method for producing the perovskite-type barium titanate powder of the first form of the present invention is of extremely high purity, and is used in electronic components such as piezoelectric materials, optoelectronic materials, dielectrics, semiconductors, and sensors. It is useful as a raw material for functional ceramics.

In addition, in the method for producing perovskite-type barium titanate powder of the first form of the present invention, when producing the Ba-Ti complex organic acid salt, Sc, Y, La, Ce, Pr, Nd, Pm, Rare earth elements such as Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Li, Bi, Zn, Mn, Al, Si, Sr, Co, V, Nb, Ni, Cr, B, A subcomponent element-containing compound containing at least one element selected from Fe and Mg is mixed with the reaction raw material to obtain a Ba-Ti complex organic acid salt containing these accessory elements, and the obtained Ba-Ti complex organic acid salt is used as a calcination raw material. It is fired in the sintering process, or rare earth elements such as Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. are added to the Ba-Ti complex organic acid salt. Obtained by mixing secondary element-containing compounds containing at least one element selected from the elements Li, Bi, Zn, Mn, Al, Si, Sr, Co, V, Nb, Ni, Cr, B, Fe and Mg. By calcining the mixture in a calcining process, perovskite-type barium titanate containing oxides of minor elements can be obtained.

The type and mixing amount of the compounds containing these accessory elements are arbitrarily selected according to the dielectric properties required for the barium titanate powder for production purposes. The specific addition amount of the compound containing the secondary element is 0.1 to 5 parts by mass in terms of atoms in the compound containing the secondary element, per 100 parts by mass of the perovskite-type barium titanate powder. Additionally, the compound containing the accessory element may be either an inorganic substance or an organic substance. Examples include oxides, hydroxides, chlorides, nitrates, oxalates, carboxylates, and alkoxides containing the above-mentioned accessory elements. When the subcomponent element-containing compound is a compound containing Si element, silica sol or sodium silicate, etc. are also used.

In addition, the method for producing perovskite-type barium titanate powder of the second form of the present invention includes barium carbonate and dioxide as firing raw materials in the firing process according to the method for producing perovskite-type barium titanate powder of the present invention. This type uses a mixture of raw materials containing titanium. That is, the method for producing perovskite-type barium titanate powder of the second form of the present invention is to sinter a raw material mixture containing barium carbonate and titanium dioxide at 600 to 1200° C. while supplying superheated water vapor to the sintering atmosphere. A method for producing perovskite-type barium titanate powder, characterized by having a sintering process (2) to obtain the perovskite-type barium titanate powder.

A method for producing perovskite-type barium titanate powder of the second form of the present invention will be described with reference to FIG. 1.

In an example using the firing furnace 1 shown in FIG. 1, first, an alumina container containing a firing raw material (a raw material mixture containing barium carbonate and titanium dioxide) 5 is placed in the firing furnace 1 covered with an alumina fiber board. Place it and cover it with the cover (2). Next, the inside of the kiln 1 is preheated. Next, while supplying superheated steam 11 from the superheated steam supply pipe 7 into the kiln 1, the temperature inside the kiln 1 is raised to a predetermined sintering temperature, and after reaching the predetermined sintering temperature, the sintering furnace 1 Firing is performed by maintaining the temperature while supplying superheated steam 11 inside. Then, when the firing raw material (raw material mixture containing barium carbonate and titanium dioxide) 5 is fired, the barium carbonate and titanium dioxide react to produce barium titanate powder and carbon dioxide gas is generated. The generated carbon dioxide gas is absorbed into the surrounding superheated water vapor and becomes superheated water vapor 12 containing carbon dioxide gas. Therefore, the superheated water vapor 12 containing carbon dioxide gas is discharged from the exhaust pipe 4. That is, in the embodiment using the firing furnace 1 shown in FIG. 1, firing is performed while supplying superheated steam 11 to the atmosphere and discharging superheated steam 12 containing carbon dioxide gas from the atmosphere.

At this time, since superheated water vapor 11 is continuously supplied into the firing furnace 1, the atmosphere to which the firing raw material (raw material mixture containing barium carbonate and titanium dioxide) 5 is exposed is an atmosphere in which a large amount of superheated water vapor exists. do. In the example of the form shown in FIG. 1, the inside of the firing furnace 1 is not sealed and firing is performed in an open system, so there is some air in the atmosphere. By continuously supplying superheated water vapor 11 to the atmosphere, the atmosphere is The amount of air can be greatly reduced. Additionally, a complete superheated steam atmosphere can be created by controlling the supply amount of superheated steam. In other words, by performing firing while supplying superheated water vapor to the atmosphere, the firing atmosphere of the firing raw material (raw material mixture containing barium carbonate and titanium dioxide) is fired in a superheated water vapor atmosphere with a very small amount of air, or a completely superheated water vapor atmosphere. can be done.

Furthermore, if carbon dioxide gas generated by firing exists around the produced barium titanate powder, it adversely affects the tetragonality. However, in the embodiment using the firing furnace 1 shown in FIG. 1, a large amount of superheated water vapor is present in the atmosphere. Because of its presence, carbon dioxide gas is absorbed into the superheated water vapor. Therefore, in the embodiment using the firing furnace 1 shown in FIG. 1, adverse effects due to carbon dioxide gas can be prevented. In addition, in the embodiment using the firing furnace 1 shown in FIG. 1, there is very little air in the atmosphere, so side reactions caused by carbon dioxide can be prevented.

That is, the method for producing perovskite-type barium titanate powder of the second form of the present invention is to sinter a raw material mixture containing barium carbonate and titanium dioxide at 600 to 1200° C. while supplying superheated water vapor to the sintering atmosphere. A method for producing perovskite-type barium titanate powder, characterized by having a sintering process to obtain the perovskite-type barium titanate powder.

The firing process (2) according to the method for producing perovskite-type barium titanate powder of the second form of the present invention is to obtain perovskite-type barium titanate powder by firing a raw material mixture containing barium carbonate and titanium dioxide. It's fair.

The barium carbonate used in the firing process (2) is not particularly limited as long as it is industrially available. The BET specific surface area of barium carbonate is preferably 10 m2/g or more, particularly preferably 30 to 50 m2/g, from the viewpoint of obtaining fine, highly tetragonal perovskite barium titanate. The average particle diameter of barium carbonate determined by scanning electron microscope (SEM) observation is preferably 0.1 μm or less, and preferably 0.03 to 0.05, since fine perovskite-type barium titanate with high tetragonality can be obtained. It is ㎛.

In addition, in the present invention, the average particle diameter is determined by scanning electron microscope (SEM) observation, and represents the average value of 1000 samples randomly extracted from the SEM images of scanning electron microscope (SEM) observation.

Titanium dioxide according to the firing process (2) is not particularly limited as long as it is industrially available. The BET specific surface area of titanium dioxide is preferably 5 m 2 /g or more, particularly preferably 8 to 50 m 2 /g, from the viewpoint of obtaining fine and highly tetragonal perovskite barium titanate. The average particle diameter of titanium dioxide determined by scanning electron microscope (SEM) observation is preferably 0.1 μm or less, and particularly preferably 0.03 to 0.05 μm.

The higher the purity of barium carbonate and titanium dioxide, the more preferable it is in order to obtain high-purity perovskite-type barium titanate powder. The particle shape of barium carbonate and titanium dioxide is not particularly limited and may be needle-shaped, spherical, granular, or irregularly shaped.

The raw material mixture containing barium carbonate and titanium dioxide, which becomes the firing raw material in the firing process (2), is obtained by mixing barium carbonate, titanium dioxide, and other raw materials used as necessary, and the more uniformly the raw materials are mixed, the more preferable. do. The mixing ratio of barium carbonate and titanium dioxide is such that the molar ratio of Ba to Ti (Ba/Ti) in atomic terms is 0.99 to 1.01, preferably 0.995 to 1.005. If the molar ratio of Ba to Ti (Ba/Ti) is less than 0.99, it becomes titanium rich, and perovskite-type barium titanate with high tetragonality cannot be obtained. On the other hand, if it exceeds 1.01, it becomes barium rich, and tetragonality is not obtained. High perovskite barium titanate is not obtained.

Barium titanate obtained by performing the firing step (2) is a perovskite-type complex oxide in which the A-site element is Ba and the B-site element is Ti. The barium titanate obtained by performing the firing process may be perovskite-type barium titanate in which the A-site element is only Ba and the B-site element is only Ti, or some of the Ba atoms of the A-site element may be Ca or Sr. one or both of Ca and Sr, a portion of the Ti atom of the B site element is substituted with Zr, or a portion of the Ba atom of the A site element is substituted with either Ca or Sr, or Ca and Sr. Both sides may be substituted, and part of the Ti atom of the B site element may be substituted with Zr.

In the method for producing perovskite-type barium titanate of the second form of the present invention, a perovskite in which part of the Ba atom of the A site element is replaced with Ca or Sr, or part of the Ti atom of the B site element is replaced with Zr In order to obtain barium titanate in the barium titanate form, a compound having a Ca atom, a compound having a Sr atom, or a compound having a Zr atom can be contained together with barium carbonate and titanium oxide in the raw material mixture. When a part of Ba atom is replaced with either Ca or Sr, or both Ca and Sr, the content of the compound having a Ca atom or the compound having a Sr atom in the raw material mixture is not particularly limited, but in atomic terms, it is The content is preferably such that the total ratio of Ca atoms and Sr atoms to each other is less than 50 mol%. When replacing part of Ti atoms with Zr, the content of the compound having Zr atoms in the raw material mixture is not particularly limited, but the content is preferably such that the ratio of Zr atoms to Ti atoms in atomic terms is less than 50 mol%. The mixing ratio of barium carbonate, a compound having a Ca atom, a compound having a Sr atom, and a compound having titanium oxide and a Zr atom is B relative to the sum of Ba atoms, Ca atoms, and Sr atoms, which are A site elements in atomic terms. The mixing ratio is such that the total molar ratio of Ti atoms and Zr atoms serving as site elements is 0.99 to 1.01, preferably 0.995 to 1.005. In addition, compounds having Ca atoms, compounds having Sr atoms, and compounds having Zr atoms include carbonates, oxides, and organic acid salts of these atoms, and physical properties are not particularly limited, but from the viewpoint of dispersibility in the raw material mixture. A fine one is preferable.

The method of mixing barium carbonate and titanium dioxide includes using a mechanical means with a strong shear force by a wet or dry method so that barium carbonate, titanium dioxide, and other raw materials used as necessary are uniformly mixed in the above ratio. You can.

The wet method is performed using devices such as ball mills, bead mills, disper mills, homogenizers, vibrating mills, sand grind mills, attritors, and powerful stirrers. Additionally, the dry method is performed using devices such as a high-speed mixer, super mixer, turbo sphere mixer, Henschel mixer, Nauta mixer, and ribbon blender. Among these, in the present invention, preparing the raw material mixture by a wet method is preferable because a uniform raw material mixture is obtained and a dielectric with a high dielectric constant is obtained.

Solvents used in the wet method include, for example, water, methanol, ethanol, propanol, butanol, toluene, xylene, acetone, methylene chloride, ethyl acetate, dimethylformamide, and diethyl ether. Among these, alcohols such as methanol, ethanol, propanol, and butanol are preferable because they produce a dielectric ceramic with a small change in composition and a high dielectric constant.

When mixing by a wet method, a dispersant can be added to the slurry containing various raw materials as needed for the purpose of improving dispersibility. After mixing by the wet method, the slurry can be dried using a spray dryer, if desired.

In addition, mixing by these wet or dry methods is not limited to the method using the mechanical means illustrated. Additionally, a device capable of simultaneously mixing and pulverizing, such as a jet mill, can be used to mix the raw materials while also adjusting the particle size of the raw material mixture.

Then, in the firing process (2), the raw material mixture containing barium carbonate and titanium dioxide is fired. The firing temperature in the firing process (2) is 600 to 1200°C, preferably 700 to 1000°C. If the sintering temperature is below the above range, the solid phase reaction to change into perovskite-type barium titanate does not occur and it tends to remain unreacted. On the other hand, if it exceeds the above range, the produced perovskite-type barium titanate grows into particles. Because it causes a fine product, no fine product is obtained. The firing time in the firing process (2) is 4 hours or more, and is preferably 6 to 30 hours. In addition, in the firing process (2), after firing at 600 to 1200°C, preferably 700 to 1000°C, the fired product is pulverized, granulated if desired, and then fired at 600 to 1200°C, preferably 700 to 1000°C. may be further performed, and in order to make the powder properties homogeneous, the once-fired powder may be pulverized and re-fired may be repeated.

The firing furnace used in the firing process (2) includes a batch or continuous electric furnace or a gas furnace, and examples thereof include a roller hearth kiln, a rotary kiln, and a pusher furnace.

In the calcination process (2), the raw material mixture containing barium carbonate and titanium dioxide is calcinated at 600 to 1200°C, preferably 700 to 1000°C, while supplying superheated water vapor to the calcination atmosphere and further reacting from the calcination atmosphere. This is done while discharging the superheated water vapor containing carbon dioxide generated by the process.

Superheated steam refers to a colorless and transparent H ₂ O gas obtained by further heating saturated steam at 100°C while maintaining normal pressure. Since superheated water vapor maintains the saturated state of water in the air at high temperatures, firing is performed while supplying superheated water vapor to the firing atmosphere, thereby effectively absorbing carbon dioxide gas generated during the production of barium titanate into the superheated water vapor and maintaining the firing temperature. The reaction can proceed without lowering . Additionally, since most of what exists in the firing atmosphere becomes superheated water vapor, side reactions caused by the presence of carbon dioxide in the air can be suppressed.

Since superheated steam is obtained by further heating saturated steam at 100°C while maintaining atmospheric pressure, the method of firing while supplying superheated steam to the firing atmosphere allows the reaction to be carried out under atmospheric pressure and does not need to be carried out in a firing furnace with internal pressure.

In the firing process (2), the temperature of the superheated water vapor supplied to the firing atmosphere is preferably 200 to 1200°C, particularly preferably 300 to 1000°C. If the temperature of the superheated steam is less than the above range, it is difficult for the firing temperature to decrease, and if it exceeds the above range, a decrease in the firing temperature can be prevented, but the energy for generating the superheated steam increases, so the manufacturing cost increases.

Methods for generating superheated water vapor include heating saturated water vapor obtained by heating water to 100°C or higher directly or indirectly with fuel such as oil or gas, or heating it with heating means such as infrared rays, electromagnetic waves, or microwaves. there is. As means for generating such superheated steam, for example, the UPSS series of Tokuden Co., Ltd., the IHSS series of Fuji Denki Co., Ltd., the superheated steam generator of Nihon Tennetsu Co., Ltd., and the superheated steam generator of Shinnetsu Kogyo Co., Ltd. Processing devices, etc. can be mentioned.

The amount of superheated water vapor supplied to the firing atmosphere is appropriately selected, but is preferably 5 L/min or more per 1 kg of raw material mixture, more preferably 10 to 200 L/min per 1 kg of raw material mixture, and particularly preferably 1 kg of raw material mixture. 15 to 100 L/min. When the amount of superheated water vapor supplied to the firing atmosphere is within the above range, carbon dioxide gas generated within the kiln during the solid phase reaction can be efficiently absorbed and the temperature inside the furnace can be prevented from lowering due to overheated water vapor. In addition, it is the time to introduce superheated water vapor into the kiln, and introducing superheated water vapor into the kiln at least before perovskite-type barium titanate is produced by the solid-phase reaction of barium carbonate and titanium dioxide is to avoid carbon dioxide gas generated during the reaction. It is desirable because it can effectively absorb and suppress the occurrence of adverse effects caused by carbon dioxide gas.

After performing the firing step (2), if necessary, the fired perovskite-type barium titanate powder can be washed with an acid solution, washed with water, dried, pulverized, classified, etc. to make a product. The drying method may be a normal method and is not particularly limited, but when wet grinding treatment is performed, for example, a method using a spray dryer can be applied.

The perovskite-type barium titanate powder obtained by carrying out the method for producing the perovskite-type barium titanate powder of the second form of the present invention has high tetragonality, and the ratio of the c-axis to the a-axis (c/ a) is preferably 1.005 or more, particularly preferably 1.0055 to 1.010. The average particle diameter of the perovskite-type barium titanate powder obtained by performing the method for producing the perovskite-type barium titanate powder of the second form of the present invention is preferably the average particle diameter determined by electron microscope observation. It is 0.5 μm or less, particularly preferably 0.05 to 0.2 μm, and the BET specific surface area is preferably 2 m 2 /g or more, particularly preferably 3 to 20 m 2 /g. The perovskite-type barium titanate powder obtained by performing the method for producing the perovskite-type barium titanate powder of the second form of the present invention is of extremely high purity, and is used in electronic components such as piezoelectric materials, optoelectronic materials, dielectrics, semiconductors, and sensors. It is useful as a raw material for functional ceramics.

In addition, in the method for producing perovskite-type barium titanate powder of the second form of the present invention, when mixing barium carbonate and titanium dioxide, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, if necessary. Rare earth elements such as , Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Li, Bi, Zn, Mn, Al, Si, Sr, Co, V, Nb, Ni, Cr, B, Fe and a secondary element-containing compound containing at least one element selected from Mg to obtain a raw material mixture, and the resulting raw material mixture is calcined in a sintering process, or a raw material mixture containing barium carbonate and titanium dioxide is obtained, The resulting raw material mixture contains rare earth elements such as Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Li, Bi, Zn, Mn, By firing in a firing process a mixture obtained by mixing a compound containing sub-component elements containing at least one element selected from Al, Si, Sr, Co, V, Nb, Ni, Cr, B, Fe and Mg, the sub-component elements Perovskite-type barium titanate containing the oxide can be obtained.

The type and mixing amount of the compounds containing these accessory elements are arbitrarily selected in accordance with the dielectric properties required for the barium titanate powder for production purposes. The specific addition amount of the compound containing the secondary element is 0.1 to 5 parts by mass in terms of atoms in the compound containing the secondary element, based on 100 parts by mass of the perovskite-type barium titanate powder. Additionally, the compound containing the accessory element may be either an inorganic substance or an organic substance. Examples include oxides, hydroxides, chlorides, nitrates, oxalates, carboxylates, and alkoxides containing the above-mentioned accessory elements. When the subcomponent element-containing compound is a compound containing Si element, silica sol, sodium silicate, etc. are also used.

As described above, the method for producing the perovskite-type barium titanate powder of the present invention, for example, the method for producing the perovskite-type barium titanate powder of the first form of the present invention and the method of producing the perovskite-type barium titanate powder of the second form of the present invention. In the method for producing barium titanate powder of the perovskite type, perovskite barium titanate powder is obtained. The perovskite-type barium titanate powder obtained by the method for producing perovskite-type barium titanate powder of the present invention is used as a raw material for manufacturing multilayer capacitors. For example, first, the perovskite-type barium titanate powder obtained by the method for producing perovskite-type barium titanate powder of the present invention is mixed with conventionally known mixing agents such as additives, organic binders, plasticizers, and dispersants. It is dispersed into a slurry, and the solid material in the resulting slurry is molded to obtain a ceramic sheet. Next, a conductive paste for forming internal electrodes is printed on one side of the ceramic sheet, and after drying, a plurality of ceramic sheets are stacked and then pressed in the thickness direction to form a laminate. Additionally, this laminate is heat treated, subjected to debonding agent treatment, and fired to obtain a fired body. Thereafter, a multilayer capacitor can be obtained by applying In-Ga paste, Ni paste, Ag paste, nickel alloy paste, copper paste, copper alloy paste, etc. to this fired body and baking.

In addition, the perovskite-type barium titanate powder obtained by the method for producing perovskite-type barium titanate powder of the present invention can be mixed with a resin such as an epoxy resin, polyester resin, or polyimide resin to form a resin sheet. , resin films, adhesives, etc., can be appropriately used for materials such as printed wiring boards and multilayer printed wiring boards. In addition, the perovskite-type barium titanate powder is used as a dielectric material for EL devices, a co-material for suppressing the difference in shrinkage between the internal electrode and the dielectric layer, a base material for an electrode ceramic circuit board or a glass ceramic circuit board, and materials around the circuit. It is appropriately used as a raw material, a catalyst used in reactions such as exhaust gas removal or chemical synthesis, and a surface modifier for printing toner that provides antistatic or cleaning effects.

[Example]

Hereinafter, the present invention will be described in detail through examples, but the present invention is not limited to these.

In addition, in the examples, the average particle diameter was determined as the average value obtained from scanning electron microscopy (SEM) for 1000 randomly selected samples. In addition, the Ba/Ti molar ratio was calculated based on the value obtained from fluorescence X-ray analysis.

<Complex organic acid salt method>

<Preparation of barium titanyl oxalate>

A mixed solution was prepared by dissolving 600 g (2.456 mole) of barium chloride dihydrate and 444 g (2.342 mole) of titanium tetrachloride in 4,100 ml of water, and this was referred to as solution A. Next, 620 g of oxalic acid was dissolved in 1500 ml of hot water at 70°C to prepare an oxalic acid aqueous solution, which was referred to as solution B. Liquid B was added to liquid A over 120 minutes with stirring while maintaining the temperature at 70°C, and the mixture was further aged at 70°C with stirring for 1 hour. After cooling, barium titanyl oxalate was recovered by filtration. Next, the recovered barium titanyl oxalate was repulped three times with 4.5 L of distilled water and washed. Subsequently, it was dried at 105°C and ground to obtain 1000 g of barium titanyl oxalate (BaTiO(C ₂ O ₄ )·4H ₂ O). The average particle diameter of the obtained barium titanyl oxalate was 25 μm, and the molar ratio of Ba/Ti was 1.00.

(Examples 1 to 3)

In a calcination furnace including an electric batch furnace shown in FIG. 1, 50 g of the barium titanyl oxalate sample was heated to the temperature shown in Table 1 at a temperature increase rate of 2.5°C/min under air to start calcination. At the start of firing, superheated steam heated to the temperature shown in Table 1 was introduced into the kiln at a rate of 4 L/min, and firing was performed for 6 hours. After completion of firing, it was cooled and pulverized to obtain barium titanate powder.

(Comparative Examples 1 to 3)

As in Example 1, 50 g of a sample of barium titanyl oxalate was heated to the temperature shown in Table 1 at a temperature increase rate of 2.5/min in an electric batch furnace and fired for 6 hours. The firing was carried out under normal atmosphere without introducing superheated water vapor into the firing furnace. After completion of firing, it was cooled and pulverized to obtain barium titanate powder.

(Comparative Examples 4 to 6)

As in Example 1, 50 g of a sample of barium titanyl oxalate was heated to the temperature shown in Table 1 at a temperature increase rate of 2.5°C/min in an electric batch furnace and calcined for 6 hours. Additionally, at the start of firing, firing was performed while introducing humidified air (dew point 21°C) humidified by passing through water heated to 30°C into the kiln at a rate of 4 L/min. After completion of firing, it was cooled and pulverized to obtain barium titanate powder.

<Evaluation of physical properties of barium titanate samples>

For the barium titanate samples obtained in Examples 1 to 3 and Comparative Examples 1 to 6, the average particle diameter, BET specific surface area, and the ratio of the c axis to the a axis (c/a), which is an indicator of tetragonality, were measured. The results are shown in Table 2. Additionally, the ratio of the c-axis and a-axis was obtained by X-ray diffraction.

<Law of honor>

<Barium carbonate sample>

Commercially available barium carbonate with a purity of 99.5 mass%, a BET specific surface area of 30 m2/g, and an average particle diameter of 0.05 μm was used.

<Titanium dioxide sample>

Commercially available titanium dioxide with a purity of 99.5 mass%, a BET specific surface area of 30 m2/g, and an average particle diameter of 0.05 μm was used.

<Superheated water vapor>

Superheated water vapor was generated using UPSS-W20 manufactured by Tokuden Co., Ltd.

(Examples 4 to 6)

The barium carbonate sample and the titanium dioxide sample were mixed for 6 hours using a ball mill (bead diameter; 1 mm zirconia beads, solvent: water) as a wet mixer so that the molar ratio of Ba/Ti was 1.00, and then mixed at 1.00. Dry powder was obtained by drying at ℃ for 2 hours.

In a calcination furnace including an electric batch furnace shown in FIG. 1, 50 g of the dry powder was heated to the temperature shown in Table 1 at a temperature increase rate of 2.5°C/min under air to start calcination. At the start of firing, superheated steam heated to the temperature shown in Table 3 was introduced into the kiln at a rate of 4 L/min, and firing was performed for 6 hours. After completion of firing, it was cooled and pulverized to obtain barium titanate powder.

(Comparative Examples 7 to 9)

Dry powder was prepared in the same manner as in Example 4, and 50 g of the dry powder was heated to the temperature shown in Table 3 at a temperature increase rate of 2.5°C/min in an electric batch furnace and calcined for 6 hours. The firing was carried out under normal atmosphere without introducing superheated water vapor into the firing furnace. After completion of firing, it was cooled and pulverized to obtain barium titanate powder.

(Comparative Examples 10 to 12)

Dry powder was prepared in the same manner as in Example 4, and 50 g of the dry powder was heated to the temperature shown in Table 3 at a temperature increase rate of 2.5°C/min in an electric batch furnace and calcined for 6 hours. Additionally, at the start of firing, firing was performed while introducing humidified air (dew point 21°C) humidified by passing through water heated to 30°C into the kiln at a rate of 4 L/min. After completion of firing, it was cooled and pulverized to obtain barium titanate powder.

<Evaluation of physical properties of barium titanate samples>

For the barium titanate samples obtained in Examples 4 to 6 and Comparative Examples 7 to 12, the average particle diameter, BET specific surface area, and the ratio of the c axis to the a axis (c/a), which is an indicator of tetragonality, were measured. The results are shown in Table 4. Additionally, the ratio of the c-axis and a-axis was obtained by X-ray diffraction.

From Tables 2 and 4, barium titanate obtained by firing by introducing superheated water vapor has the same firing temperature and compared to that obtained by firing without introducing superheated water vapor, the c-axis and a-axis, which are indicators of tetragonality, are It can be seen that the ratio (c/a) is high and the tetragonality is excellent.

Since the present invention can produce perovskite-type barium titanate powder having fine and high tetragonality, the produced perovskite-type barium titanate powder is particularly used in electronics such as piezoelectric materials, optoelectronic materials, dielectrics, semiconductors, and sensors. It can be used as a raw material for functional ceramics for parts.

1: Calciner
2: cover
4: exhaust pipe
5: Plastic raw materials
7: Superheated steam supply pipe
11: Superheated water vapor
12: Superheated water vapor containing carbon dioxide

Claims (8)

It has a sintering process to obtain perovskite-type barium titanate powder by sintering raw materials containing a Ba source and a Ti source at 600 to 1200°C while supplying superheated water vapor at 200 to 1200°C to the sintering atmosphere, and the perovskite A method for producing perovskite-type barium titanate powder, characterized in that the ratio (c/a) of the c-axis and a-axis of the skyte-type barium titanate powder is 1.004 to 1.010. The method for producing perovskite-type barium titanate powder according to claim 1, wherein the fired raw material is a complex organic acid salt having a Ba atom and a Ti atom. The method for producing perovskite-type barium titanate powder according to claim 2, wherein the complex organic acid salt is a carboxylic acid salt. The method for producing perovskite-type barium titanate powder according to claim 2, wherein the complex organic acid salt is oxalate. The method for producing perovskite-type barium titanate powder according to claim 1, wherein the fired raw material is a raw material mixture containing barium carbonate and titanium dioxide. The method for producing perovskite-type barium titanate powder according to claim 5, wherein the BET specific surface area of the barium carbonate is 10 m2/g or more. The method for producing perovskite-type barium titanate powder according to claim 5 or 6, wherein the BET specific surface area of the titanium dioxide is 5 m2/g or more. delete

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