JP4671618B2 - Calcium titanate and method for producing the same - Google Patents

Description

The present invention relates to calcium titanate used for electronic materials such as dielectric materials, piezoelectric materials, pyroelectric materials, multilayer ceramic capacitors, and the like, and a method for producing the same.
Specifically, the present invention relates to a calcium titanate powder having a single crystal, a small particle size, excellent dispersibility, and excellent electrical characteristics, and a method for producing the same.

  Titanium-based composite oxides having a perovskite crystal structure are widely used as electronic materials because they exhibit excellent electrical properties such as dielectric properties, pyroelectricity, and piezoelectricity. In recent years, electronic components have been improved in performance, size, and weight, so that titanium composite oxides are desired to be highly dispersed, highly crystallized, and fine particles.

  Here, calcium titanate having a perovskite crystal structure is often used as a temperature-compensating ceramic capacitor material as one of titanium-based composite oxides. Further, it is also used as an additive for suppressing a rapid change in dielectric constant at the Curie point of a barium titanate high dielectric constant capacitor.

Therefore, as with other titanium-based composite oxides, titanium-based materials used in electronic materials where the development of calcium titanate with a small particle size, excellent dispersibility, high crystallinity, and excellent electrical properties is desired. As a method for producing composite oxide particles, a solid phase method, an oxalic acid method, a hydrothermal synthesis method, an alcoside method, and the like are generally known, and improvements in these synthesis methods are actively performed.

  However, the solid-phase method is low in production cost, but the generated titanium-based composite oxide particles have a large particle size, and thus need to be pulverized. When the pulverization is performed, the particle size distribution becomes wide and the crystal structure is distorted, resulting in a problem that the electrical characteristics are deteriorated.

  On the other hand, the oxalate method has an advantage that smaller particles can be obtained than the solid phase method, but carbonic acid derived from oxalic acid remains and the electrical characteristics are lowered.

  In addition, the hydrothermal synthesis method synthesizes particles under high-temperature and high-pressure conditions, so that there is a problem that dedicated equipment is required and the cost increases.

  In the alkoxide method, finer titanium-based composite oxides can be obtained than in the hydrothermal synthesis method. However, since hydroxyl groups resulting from the water taken into the particles remain, there are many crystal defects, resulting in improved electrical characteristics. It is difficult to obtain an excellent titanium-based composite oxide. In addition, the alkoxide method has a drawback that a carbonate group remains.

  For example, if the technique disclosed in Patent Document 1 or Patent Document 2 is used, fine particles with few submicron particles can be obtained at a relatively low cost. However, ultra-fine particles (0.01 μm or less) and agglomerated particles are further reduced, providing particles with excellent dispersibility, high crystallinity, and excellent electrical characteristics, and reducing the size, weight and performance of electronic components. It is desirable to respond.

  Patent Document 3 and Patent Document 4 disclose a method for producing spherical calcium titanate. However, it is desirable to provide calcium titanate that is even more crystalline and has excellent electrical properties.

International Publication No. 00/35811 Pamphlet International Publication No. 03/004416 Pamphlet JP 59-45927 JP-A-5-178617

  An object of the present invention is to provide calcium titanate having few ultrafine particles and agglomerated particles, sharp particle size distribution, excellent dispersibility, particularly high crystallinity and excellent electrical characteristics, and a method for producing the same. is there.

As a result of earnestly examining the above-mentioned problems, the present inventors have mixed and reacted a calcium salt having a solubility equal to or higher than the saturation solubility in an alkaline solution in which a basic compound is present. The inventors have found that calcium titanate powder having characteristics can be obtained, and completed the present invention.
The present invention has the following configuration.

[1] A calcium titanate powder having a perovskite crystal structure and having a square column or a shape similar to a square column.
[2] The calcium titanate powder according to 1 above, which is a single crystal.
[3] The calcium titanate powder according to 1 or 2 above, wherein the ratio of the long side to the short side of the calcium titanate crystal is 1.1 to 6.
[4] The calcium titanate powder according to any one of 1 to 3, wherein a long side extends to a unit cell (010) plane.
[5] The titanic acid according to any one of 1 to 4 above, wherein the D2 / D1 value is 1 or more and 3 or less, where D1 is an average primary particle size and D2 is an average secondary particle size. Calcium powder.
[6] Any one of 1 to 5 above, wherein in the particle size distribution of the secondary particles, the D3 / D2 value is 0.1 or more and 0.9 or less when the particle size from the minimum particle size to 10% is D3. The calcium titanate powder according to item.
[7] In the particle size distribution of the secondary particles, the D4 / D2 value is 1.1 or more and 10 or less when the particle size from the minimum particle size to 90% is D4. The calcium titanate powder described.
[8] The calcium titanate powder according to any one of 1 to 7 above, wherein the content of calcium carbonate is 3% by mass or less.
[9] The calcium titanate powder according to any one of 1 to 8 above, wherein the specific surface area is 1 to 10 m ² / g.
[10] The calcium titanate powder according to any one of 1 to 9 above, wherein when calcined at any temperature in the range of 900 ° C. to 1200 ° C., the amount of decrease in specific surface area is 8 m ² / g or less. .
[11] The method for producing a calcium titanate powder as described in any one of 1 to 10 above, wherein a titanium oxide sol and a calcium salt having a saturation solubility or higher are charged and reacted in an alkaline aqueous solution containing a basic compound.
[12] The method for producing calcium titanate as described in 11 above, wherein a calcium salt having a weight of 10 to 10000 mass times is added and reacted with respect to the saturated solubility of an alkaline solution in which a basic compound is present.
[13] The method for producing calcium titanate as described in 11 or 12 above, wherein the calcium salt is a hydroxide.
[14] The method for producing calcium titanate according to any one of the above 11 to 13, comprising a step of reacting by controlling the CO ₂ equivalent concentration of the carbonate group in the reaction solution to 500 ppm or less.
[15] The method for producing calcium titanate according to the above 11 to 14, comprising a step of boiling at 100 ° C. or higher for 4 hours or longer.
[16] Titanium according to any one of the above 11 to 15, which includes a step of removing impurities as a gas by evaporation and / or thermal decomposition under atmospheric pressure or reduced pressure in a temperature range of room temperature to firing temperature. Method for producing calcium acid.
[17] The method for producing calcium titanate according to any one of 11 to 16, wherein the titanium oxide sol is obtained by hydrolyzing a titanium compound in an acidic solution.
[18] The method for producing calcium titanate according to any one of the above 11 to 17, wherein the titanium oxide sol contains a brookite crystal.
[19] The method for producing calcium titanate according to any one of the above 11 to 18, wherein the basic compound is a substance that becomes a gas by evaporation, sublimation, and / or thermal decomposition under atmospheric pressure or reduced pressure. .
[20] The method for producing calcium titanate according to any one of the above 11 to 19, wherein the basic compound is an organic base.
[21] The method for producing calcium titanate according to any one of the above 11 to 20, wherein the basic compound is tetramethylammonium hydroxide.
[22] A dielectric material comprising the calcium titanate powder according to any one of 1 to 10 above.
[23] A paste containing the calcium titanate powder according to any one of 1 to 10 above.
[24] A slurry containing the calcium titanate powder according to any one of 1 to 10 above.
[25] A thin film-like formed product comprising the calcium titanate powder according to any one of 1 to 10 above.
[26] A dielectric ceramic comprising the calcium titanate powder according to any one of 1 to 10 above.
[27] A pyroelectric ceramic containing the calcium titanate powder according to any one of 1 to 10 above.
[28] A piezoelectric ceramic containing the calcium titanate powder according to any one of 1 to 10 above.
[29] A capacitor comprising the dielectric ceramic according to [26].
[30] An electronic device comprising at least one selected from the group consisting of the thin film-like product according to 25 to 29, a porcelain and a capacitor.
[31] A sensor comprising one or more of the thin film-like formed products or porcelains according to 25 to 28 above.
[32] A dielectric film using the calcium titanate powder described in any one of 1 to 10 above.
[33] A capacitor using the dielectric film as described in 32 above.

  The calcium titanate particles of the present invention have high crystallinity, fine powder, and little aggregation. Therefore, dielectric ceramics, pyroelectric ceramics, piezoelectric ceramics, and the like obtained from the above become electronic materials having excellent characteristics. Furthermore, by using these for electronic devices, electronic devices can be reduced in size, weight and performance. Can be realized.

Hereinafter, the present invention will be described in detail.
The calcium titanate of the present invention has a perovskite crystal structure, has a shape similar to a square column or a square column, is a single crystal, has few ultrafine particles and agglomerated particles, has a sharp particle size distribution, and is highly dispersible. It has the feature of being excellent.

The calcium titanate of the present invention is a compound having a perovskite crystal structure represented by the general formula ABO ₃ , and refers to CaTiO _{3 in} which A is Ca and B is Ti. The crystal structure can be known by X-ray diffraction measurement.

  The shape of the calcium titanate of the present invention can be known by magnifying observation with a scanning electron microscope. The calcium titanate powder of the present invention having a perovskite crystal structure and having a square column or a similar shape to a square column is a columnar hexahedral shape, its bottom surface is nearly square, and its side surface is nearly rectangular. It has a shape. Each surface intersects at a substantially right angle, but at least one corner may be slightly rounded or missing. The number of particles whose surfaces intersect at right angles is 80% or more of the whole powder, preferably 90% or more, and more preferably 95% or more. When the corner is slightly bordered and rounded, the radius of curvature is 10 μm or more.

  Most of the calcium titanate particles of the present invention observed with a scanning electron microscope had a short side length of 0.2 μm to 0.6 μm and a long side length of 0.2 μm to 1.2 μm. However, the ratio of such particles is 80% or more, preferably 85% or more, more preferably 90% or more.

  Further, the ratio of the long side to the short side can be obtained by measuring the maximum long side and the minimum short side for each calcium titanate particle. In the calcium titanate production method of the present invention, the ratio of the long side to the short side is obtained. 1.1-6 square pillars can be manufactured stably. It is preferable that the ratio of the long side to the short side of the calcium titanate crystal is larger in the longitudinal direction of the perovskite structure that expresses electrical characteristics.

  The fact that the calcium titanate of the present invention is a single crystal and the long side of the calcium titanate extends to the unit cell (010) plane can be known by analysis of an electron diffraction pattern with a transmission electron microscope. .

  A single crystal means that the crystallinity is extremely high. The long side extends in the direction of the unit lattice (010) plane because it grows in the longitudinal direction of the perovskite structure that exhibits electrical characteristics. Therefore, the electrical characteristics such as dielectric properties, piezoelectricity, pyroelectricity are very excellent.

The specific surface area of the calcium titanate of the present invention is in the range of ^{1 to} 10 m ² / g, preferably 1 to 8 m ² / g, more preferably 1 to 6 m ² / g. The specific surface area is measured by the BET method. In order to reduce the size of the electronic material, it is necessary to use particles having a specific surface area of 1 m ² / g or more. However, if the specific surface area exceeds 100 m ² / g, the particles tend to aggregate and Handling becomes difficult.

  The calcium titanate of the present invention is a particle having fine particles, a sharp particle size distribution and excellent dispersibility with little aggregation.

Here, the average particle diameter D1 of the primary particles can be obtained from the formula (I) by converting the specific surface area obtained by the BET method into a spherical shape.
D1 = 6 / ρS (I)
(Wherein ρ is the true specific gravity of the particle and S is the specific surface area of the particle.)

  The secondary particle diameter of the aggregated particles is measured with a particle size distribution meter by dispersing calcium titanate in a solvent. In general, a particle size distribution meter suitable for the particle size distribution range to be measured is selected. The secondary particle diameter of the calcium titanate of the present invention can be measured with high accuracy by a centrifugal sedimentation method, a microtrack method or the like. By this method, the particle size distribution of the secondary particles is measured on a weight basis, and an average particle size D2, a minimum 10% particle size D3, and a 90% particle size D4 are obtained. The particle diameter obtained here is a spherical equivalent diameter.

  The D2 / D1 ratio between the average particle diameter D1 of the primary particles and the average particle diameter D2 of the secondary particles is theoretically 1 if both measured particles are spherical. This indicates that the higher the D2 / D1 ratio, the more the primary particles are aggregated and the dispersibility is worsened. The D2 / D1 ratio of the calcium titanate of the present invention is 1 to 3, preferably 1 to 2.7, more preferably 1 to 2.5.

  From the particle size distribution D3 / D2 ratio and D4 / D2 ratio of the calcium titanate of the present invention, the particle size distribution of the secondary particles can be known. As each value approaches 1, the particle size distribution of secondary particles becomes sharper, which is preferable.

  The D3 / D2 value in the present invention is 0.1 or more and 0.9 or less, preferably 0.15 or more and 0.7 or less, more preferably 0.2 or more and 0.5 or less. The D4 / D2 value is 1.1 or more and 10 or less, preferably 1.2 or more and 8 or less, and more preferably 1.4 or more and 5 or less.

The calcium carbonate contained in the calcium titanate of the present invention is 0 to 3% by mass, preferably 0 to 2% by mass, and more preferably 0 to 1% by mass. The amount of calcium carbonate contained in calcium titanate can be known by measuring an infrared absorption spectrum. Specifically, the peak area intensity of standard calcium carbonate near 880 cm ⁻¹ can be obtained by comparing the peak area intensity of the calcium titanate of the present invention.

In addition, the calcium titanate of the present invention has the characteristics that it is difficult for grains to grow in the firing step and the specific surface area is difficult to decrease. In general, fine-grained titanium-based composite oxides tend to grow in the firing step, and thus the specific surface area tends to decrease significantly. However, the calcium titanate of the present invention does not show such a tendency. For example, when the calcium titanate powder of the present invention is fired at 900 to 1200 ° C., the specific surface area decrease is 8 m ² / g or less, preferably 5 m ² / g or less, more preferably 2 m ² / g or less. It is.

  Next, the manufacturing method of this invention is demonstrated. In the method for producing calcium titanate according to the present invention, calcium titanate is produced by reacting a titanium oxide sol with a calcium salt having a saturation solubility or higher in an alkaline solution containing a basic compound.

The reaction can be carried out with heating and stirring, which is the most industrial. Carbonate groups in the reaction solution (including carbon dioxide species such as CO ₂ , H ₂ CO ₃ , HCO ₃ ⁻ , and CO ₃ ²⁻ ) react with calcium hydroxide to produce stable calcium carbonate. Calcium carbonate does not react with titanium oxide and remains as an impurity in calcium titanate. Therefore, high-concentration calcium titanate is stably produced by controlling the concentration of carbonic acid groups in the reaction solution (CO ₂ equivalent value, hereinafter the same unless otherwise specified).

The CO ₂ equivalent concentration of the carbonate group in the reaction solution is 500 ppm by mass or less, preferably 0 to 200 ppm by mass, more preferably 0 to 100 ppm by mass.

  In order to reduce the concentration of carbonate groups in the reaction solution, it is preferable to decarboxylate the water before dissolving the basic compound by heat treatment immediately before dissolution. Moreover, since the reaction solution is alkaline, it easily absorbs carbon dioxide in the air. Therefore, it is preferable to carry out the reaction while sealing or blowing an inert gas so that the reaction solution does not come into contact with air.

  In order to increase crystallinity, it is preferable to raise the reaction temperature as much as possible. When the reaction temperature is increased, a hydrothermal reaction from 100 ° C. to the critical temperature of the solution is possible. For this purpose, a high-pressure facility such as an autoclave is required. Therefore, it is preferable to boil at 100 ° C. or higher at normal pressure and maintain the temperature. Further, mechanical stirring is preferable because the raw materials are mixed. The reaction time is 3 hours or more, preferably 4 hours or more, more preferably 6 hours or more.

  In general, impurities remain not only when the crystallinity of calcium titanate is lowered, but also when used as an electronic material, such as when the porcelain is used, the characteristics of dielectric materials, piezoelectric materials, etc. are reduced. Adversely affects electrical characteristics.

  Here, the impurities refer to all compounds other than calcium titanate, and include components such as trace amounts of metal ions and anions.

  In order to remove the impurity ions, there are various methods such as electrodialysis, ion exchange, water washing, acid washing, and treatment with a permeable membrane after completion of the reaction. However, in these methods, the calcium contained in the calcium titanate at the same time as the impurity ions may be ionized and partially dissolved in the slurry, which makes it difficult to obtain a desired composition ratio. Defects occur and the crystallinity decreases.

  Therefore, it is necessary to select a raw material with few impurities, to prevent mixing of impurities in the reaction and firing. In addition, it is preferable to remove impurities as a gas by evaporation, sublimation, and / or thermal decomposition under atmospheric pressure or reduced pressure in a temperature range of room temperature to firing temperature.

  Firing is generally performed to improve the crystallinity of the titanium-based composite oxide. On the other hand, impurities can be removed as a gas by evaporation, sublimation, and / or thermal decomposition. Impurities that can be removed by this method include organic amines having a low carbon number, organic bases such as ammonia salt hydroxides, and trace amounts of organic substances and carbonates as impurities contained in the raw material. Usually, baking is performed at 350-1200 degreeC. There is no restriction | limiting in particular in a baking atmosphere, Usually, it carries out in air | atmosphere or pressure reduction.

  In addition, it is preferable to perform baking after solid-liquid separation of the slurry from the viewpoint of reducing thermal energy and improving crystallinity during baking. Solid-liquid separation includes the steps of particle settling, concentration, filtration, and / or drying and crushing. Impurities that dissolve in the liquid can be removed by sedimentation, concentration, and filtration. Here, an aggregating agent or a dispersing agent may be used to change the sedimentation rate or the filtration rate. The flocculant or dispersant is preferably one that can be removed as a gas by evaporation, sublimation, and / or thermal decomposition.

  The drying step is a step of evaporating water, but depending on the type of basic compound or impurities, some or all of the impurities can be removed by evaporation, sublimation and / or thermal decomposition. For drying, methods such as reduced-pressure drying, hot-air drying, and freeze-drying are used. Drying is usually performed at room temperature to 350 ° C. for 1 to 24 hours. The drying atmosphere is not particularly limited, but is usually performed in the air, in an inert gas, or under reduced pressure. Then, you may crush by an appropriate method.

  In the present invention, the calcium salt must be added to an alkaline solution containing at least a basic compound at a saturation solubility or higher. Although the reaction mechanism is not clear, at the initial stage of the reaction, the dissolved calcium salt reacts with the titanium oxide sol to produce ultrafine calcium titanate, and then the undissolved calcium salt gradually dissolves and reacts with the titanium oxide sol. Thus, it is considered that while the new calcium titanate is produced, it grows on the calcium titanate produced in the initial stage.

  Therefore, it is considered that not only the number of ultrafine particles is small, but also the particle size distribution is narrow and the particle size is suitable for downsizing of electronic components. Also, because the solubility of calcium salts is very small, the newly produced calcium titanate particles become very small in size very slowly and change to a stable shape before growth, resembling a square pillar. It is considered that single crystal particles having different shapes can be obtained.

  The amount of calcium salt input is not particularly limited as long as it is equal to or higher than the saturation solubility. However, if the amount input into the alkaline aqueous solution is small, ultrafine calcium titanate is likely to be mixed, and calcium titanate having a sharp particle size distribution is obtained. I can't. Therefore, it is preferable to increase the concentration of the calcium salt. However, if the amount of the salt added to the alkaline aqueous solution is too large, the calcium salt cannot be uniformly mixed in the alkaline aqueous solution or the solution viscosity is high.

  Accordingly, it is preferable to add a calcium salt having a weight of 10 to 10,000 times the saturated solubility of the alkaline aqueous solution.

  The calcium salt used in the present invention is not particularly limited as long as it is hardly soluble in an alkaline aqueous solution, and hydroxides, nitrates, sulfates, halides, and salts with organic substances such as carboxylic acids and alcohols can also be used. Moreover, these may be used individually by 1 type, and it is also possible to mix and use 2 or more types of compounds by arbitrary ratios.

  Among these, a hydroxide is preferable as the calcium salt. This is because calcium hydroxide is hardly soluble in water and is further hardly soluble in an alkaline aqueous solution. Moreover, it is because it has the advantage that the anion in calcium hydroxide is easily removed as a gas.

  In addition, what forms a stable chelate salt with calcium, such as ethylenediaminetetraacetic acid, is not preferable because saturation solubility becomes high and calcium titanate cannot be produced.

  The production of the calcium titanate of the present invention requires an alkaline solution in which a basic compound is present. The higher the alkalinity, the higher the poor solubility of the calcium salt, which is preferable. The pH of the solution is preferably 13 or more, particularly preferably 14 or more. The upper limit of the amount of basic compound used is the saturated solubility of the basic compound in water.

  The basic compound used in the present invention is not particularly limited, but is preferably a substance that becomes a gas by evaporation, sublimation, and / or thermal decomposition under atmospheric pressure or reduced pressure. For example, organic bases such as ammonia, organic amines having a high carbon solubility and a low carbon number, and hydroxides of ammonium salts can be used.

  Among them, ammonium salt hydroxide is preferable because it dissolves in water and acts as a strong base with a high degree of detachment and does not volatilize during the reaction.

  Industrially known as the hydroxide of ammonium salt are choline, tetramethylammonium hydroxide (TMAH) and the like, which are available at low cost. In particular, tetramethylammonium hydroxide is used in the electronics industry, and is not only available as a product with few metal ions as impurities, but is also suitable because it can be removed as a gas for thermal decomposition at 135 ° C to 140 ° C. is there.

  Also, the calcium titanate of the present invention can be produced using an inorganic compound such as lithium hydroxide, sodium hydroxide or potassium hydroxide.

  These may be used alone or in a mixture of two or more compounds at an arbitrary ratio.

  It is difficult to separate and remove the calcium titanate, unreacted calcium salt and titanium oxide sol of the present invention after the reaction. Therefore, the titanium oxide sol is blended so that the ratio of calcium to titanium in the calcium titanate becomes a predetermined ratio when the reaction is completed.

  Although there is no restriction | limiting in particular as a titanium oxide sol used for this invention, The titanium oxide sol containing a brookite type crystal is preferable. Alternatively, a titanium oxide sol obtained by hydrolyzing a titanium salt in an acidic solution is preferable.

  As long as it contains brookite-type crystals, it may contain brookite-type titanium oxide alone, or rutile-type or anatase-type titanium oxide. When the rutile type or anatase type titanium oxide is included, the ratio of the brookite type titanium oxide in the titanium oxide is not particularly limited, but is usually 1 to 100% by mass, preferably 10 to 100% by mass, more preferably Is 50 to 100% by mass. This is because the crystalline particles are more easily formed into single particles than the amorphous particles, so that the dispersibility of the titanium oxide particles in the solvent is improved.

  In particular, blue kite type titanium oxide is excellent in dispersibility in a solvent. The reason for this is not clear, but it is assumed that the zeta potential at pH 2 of the blue kite type is higher than the zeta potential of the rutile type and the anatase type.

  A method for producing titanium oxide particles containing brookite-type crystals includes a production method for obtaining titanium oxide particles containing brookite-type crystals by heat-treating anatase-type titanium oxide particles, titanium tetrachloride, titanium trichloride, titanium alkoxide, There is a production method in a liquid phase obtained as a titanium oxide sol in which titanium oxide particles are dispersed by neutralizing or hydrolyzing a solution of a titanium compound such as titanium sulfate.

  As a method of producing titanium oxide particles containing brookite crystals, there is a method of obtaining titanium oxide sol by hydrolyzing a titanium salt in an acidic solution because the particles have a small particle size and excellent dispersibility. preferable. For example, titanium tetrachloride is added to hot water of 75 to 100 ° C., and the titanium tetrachloride is hydrolyzed while controlling the chlorine ion concentration at a temperature of 75 ° C. or higher and lower than the boiling point of the solution to obtain blue as a titanium oxide sol. A method of obtaining titanium oxide particles containing kite-type crystals (Japanese Patent Laid-Open No. 11-43327), or the addition of titanium tetrachloride to hot water at 75 to 100 ° C., and the presence of one or both of nitrate ions and phosphate ions Below, titanium tetrachloride is hydrolyzed while controlling the total concentration of chlorine ions, nitrate ions and phosphate ions at a temperature of 75 ° C. or higher and lower than the boiling point of the solution to obtain a blue kite type crystal as a titanium oxide sol. A method of obtaining titanium oxide particles contained therein (International Publication No. 99/58451 pamphlet) is preferred.

  When a titanium oxide sol obtained by hydrolyzing a titanium salt in an acidic solution is used, the crystal form of titanium oxide is not limited and is not limited to a brookite type. Hydrolysis of titanium salts such as titanium tetrachloride and titanium sulfate in acidic solutions suppresses the reaction rate compared to neutral or alkaline solutions, so the particle size is reduced to a single particle and oxidized with excellent dispersibility. A titanium sol is obtained. In addition, since anions such as chlorine ions and sulfate ions are not easily taken into the generated titanium oxide particles, mixing of the anions into the particles of calcium titanate particles can be reduced.

  On the other hand, when the hydrolysis is carried out in a neutral or alkaline solution, the reaction rate increases and many nuclei are generated in the initial stage. Therefore, it becomes a titanium oxide sol having a small particle size but poor dispersibility, and the particles are aggregated in a bowl shape. When calcium titanate particles are produced using such a titanium oxide sol as a raw material, the obtained particles have poor dispersibility even if the particle size is small. In addition, anions are likely to be mixed inside the titanium oxide particles, and it becomes difficult to remove these anions in the subsequent steps.

  The method for obtaining a titanium oxide sol by hydrolyzing a titanium salt in an acidic solution is not particularly limited as long as the solution is kept acidic, but in a reactor equipped with a reflux condenser using titanium tetrachloride as a raw material. The method of suppressing the escape of chlorine generated at that time and keeping the solution acidic (JP-A-11-43327) is preferred.

  Moreover, it is preferable that the density | concentration in the acidic solution of a titanium salt is 0.01-5 mol / L. This is because when the concentration exceeds 5 mol / L, the hydrolysis reaction rate increases, and a titanium oxide sol having a large particle size and poor dispersibility is obtained. When the concentration is less than 0.01 mol / L, the resulting titanium oxide is obtained. This is because the concentration decreases and the productivity deteriorates.

  There is no particular limitation on the method of adding the titanium oxide sol, but in order to obtain calcium titanate having excellent dispersibility by suppressing aggregation of the titanium oxide sol, a calcium salt having a saturation solubility or higher is added to an alkaline solution containing a basic compound. It is preferable to add little by little to the heated and stirred reaction liquid. Examples of the method of adding the titanium oxide sol in small amounts include a method of dropping using a pump or the like, and a method of injecting into the liquid.

Calcium titanate produced in this way has a small particle size, excellent dispersibility, high crystallinity, and excellent electrical characteristics, and is suitable for dielectric ceramics, pyroelectric ceramics, and piezoelectric ceramics. Molded.
These porcelain and thin film-like products are used for capacitor materials, sensors, and the like.

  In addition, the calcium titanate powder of the present invention is mixed with a single product or other dielectric material (for example, a titanium-based composite oxide such as barium titanate), water, an existing inorganic binder, an existing organic binder. It is also possible to use a slurry or paste with one or more solvents selected from the group consisting of:

  The electrical properties of the calcium titanate powder of the present invention are obtained by adding various additives such as a sintering aid to the particles and forming into a disk shape, or adding various additives to a slurry, paste, etc. containing this powder. After being molded into a thin film or the like under appropriate conditions, it can be evaluated using an impedance analyzer or the like.

  A film having a high dielectric constant can be obtained by dispersing the filler containing the calcium titanate powder of the present invention into at least one selected from the group consisting of a thermosetting resin and a thermoplastic resin.

  When a filler other than the calcium titanate powder of the present invention is included, it is possible to use one or more selected from the group consisting of alumina, titania, zirconia, tantalum oxide, and the like.

  Thermosetting resins and thermoplastic resins are not particularly limited, and commonly used resins can be used. Examples of thermosetting resins include epoxy resins, polyimide resins, polyamide resins, and bistriazine resins. Is preferred. As the thermoplastic resin, for example, polyolefin resin, styrene resin, polyamide and the like are suitable.

  In order to uniformly disperse the filler containing the calcium titanate powder of the present invention into at least one of a thermosetting resin and / or a thermoplastic resin, the filler is dispersed in advance in a solvent or a mixture of the resin composition and the solvent. It is desirable to obtain a slurry.

  A method for obtaining a slurry by dispersing the filler in a solvent or a mixture of the resin composition and the solvent is not particularly limited, but it is preferable to include a wet crushing step.

  The solvent is not particularly limited, and any commonly used coupling agent can be used. For example, methyl ethyl ketone, toluene, ethyl acetate, methanol, ethanol, N, N-dimethylformamide, N, N-dimethyl Acetamide, N-methylpyrrolidone and methyl cellosolve can be used alone or in admixture of two or more.

  In order to obtain a slurry in which the filler is dispersed in a solvent or a mixture of the resin composition and the solvent, it is desirable to add a coupling agent. The coupling agent is not particularly limited, and examples thereof include silane coupling agents, titanate coupling agents, and aluminate coupling agents. Since the hydrophilic group of the coupling agent reacts with the active hydrogen on the surface of the filler containing the calcium titanate powder of the present invention and is coated on the surface, the dispersibility in the solvent is improved. The selection of the hydrophobic group of the coupling agent can increase the compatibility with the resin. For example, when an epoxy resin is used as the resin, a silane coupling agent having any one of monoamino, diamino, cationic styryl, epoxy, mercapto, anilino, ureido and the like as one of functional groups, phosphite, amino, A titanate coupling agent having any one of diamino, epoxy, mercapto and the like as one of functional groups is suitable. When using a polyimide resin as the resin, a silane coupling agent having one of monoamino, diamino, anilino, etc. as one of the functional groups, or a titanate system having any of monoamino, diamino, etc. as one of the functional groups Coupling agents are preferred. Among these, one can be used alone, or two or more can be mixed and used.

  The blending amount of the coupling material is not particularly limited as long as a part or all of the calcium titanate powder of the present invention is coated, but if it is large, it may remain unreacted and adversely affect it, and is too small. And the coupling effect may be lowered. Therefore, it is preferable to select a blending amount capable of uniformly dispersing the filler according to the particle diameter and specific surface area of the filler containing the calcium titanate powder of the present invention and the type of coupling agent. A blending amount of about 0.05 to 20% by weight of the filler containing powder is desirable.

  In order to complete the reaction between the hydrophilic group of the coupling agent and the active hydrogen on the surface of the filler containing the calcium titanate powder of the present invention, it is desirable to include a heat treatment step after forming the slurry. Although there is no restriction | limiting in particular in heating temperature and time, It is preferable to heat-process at 100-150 degreeC for 1 hour to 3 hours. In addition, when the boiling point of the solvent is 100 ° C. or lower, the heating temperature is preferably lower than the boiling point of the solvent, and the heating time is increased accordingly.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not limited at all by these examples.

Example 1:
Titanium tetrachloride (manufactured by Sumitomo Titanium Co., Ltd .: purity 99.9%) An aqueous solution with a concentration of 0.25 mol / L was introduced into a reactor equipped with a reflux condenser to suppress the escape of chlorine ions and keep it acidic. Heated to near boiling point. The titanium tetrachloride was hydrolyzed by maintaining the temperature for 60 minutes to obtain a titanium oxide sol. The obtained titanium oxide sol was dried at 110 ° C., and the crystal form was examined with an X-ray diffractometer (RAD-B rotor flex) manufactured by Rigaku Corporation. As a result, it was found to be blue kite type titanium oxide.

  29.6 g of calcium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd .: purity 99.9%) and the sol were removed with an electrodialyzer until the chlorine content reached 500 ppm, and then the titanium oxide concentration obtained by precipitation concentration was 15 mass. % Sol 213 g, tetramethylammonium hydroxide 20 mass% aqueous solution (Seikem Showa Co., Ltd., carbonate group concentration 60 ppm or less) was added 456 g, and a small amount of nitrogen was allowed to flow in a reactor equipped with a reflux condenser. While heating until boiling. Boiling was maintained for 6 hours with stirring. Heating was stopped while stirring, and after air cooling to 50 ° C. or lower, the cake obtained by vacuum filtration was dried at 300 ° C. for 5 hours to obtain a dry powder. The ratio of the actual yield to the theoretical yield calculated from the amount of titanium oxide and calcium hydroxide used in the reaction was 99.9% by mass.

As a result of examining the X-ray diffraction of this powder with an X-ray diffractometer (RAD-B rotor flex) manufactured by Rigaku Corporation, it was found that the obtained powder was perovskite calcium titanate. The X-ray diffraction spectrum at that time is shown in FIG. The specific surface area of the obtained particles determined by the BET method was 4.7 m ² / g. The obtained powder had a shape resembling a square pillar as shown in a scanning electron micrograph of FIG.

  When observed with a transmission electron microscope, the obtained calcium titanate particles were single crystals. Furthermore, when the imaging result of the electron beam was analyzed, it was found that the long side of the square columnar particles extended in the (010) direction.

The average particle diameter D1 of the primary particles calculated from the formula (I) was 0.32 μm.
This powder was dispersed in water in which 0.03% of Poise 532A (manufactured by Kao Corporation) was dissolved as a dispersant. Using a Shimadzu centrifugal sedimentation device particle size distribution analyzer (SA-CP4L type), the conditions were set so that the particle size distribution in the range of 30 μm maximum and 0.03 μm minimum could be measured on a weight basis. The particle size distribution of the particles was measured.

  The average particle diameter D2 is 0.71 μm, the particle diameter D3 having a distribution of 10% from the minimum particle diameter is 0.34 μm, the particle diameter D4 from the minimum particle diameter of 90% is 1.10 μm, and D2 / D1 = 2.2. D3 / D2 = 0.48 and D4 / D2 = 1.55.

About 6 mg of this powder and about 900 mg of KBr were pulverized and mixed, and then about 800 mg was pressed into a tablet. Similarly, standard calcium carbonate (Wako Pure Chemical Industries, Ltd., purity 99.99%) was pressed into a tablet shape. The infrared absorption spectrum was measured with FTS6000 manufactured by Bio-Rad. The peak intensity of standard calcium carbonate near 880 cm ⁻¹ was compared with the peak area intensity of the calcium titanate of the present invention. The amount of calcium carbonate contained in this powder was 0.5% by mass.

Example 2:
In the same manner as in Example 1, perovskite calcium titanate powder was obtained. The powder was fired by holding at 950 ° C. for 2 hours.
When examined in the same manner as in Example 1, the obtained powder had a specific surface area of 3.6 m ² / g and was found to be perovskite calcium titanate. An X-ray diffraction spectrum is shown in FIG. The amount of decrease in specific surface area due to firing was 1.1 m ² / g. The obtained powder had a shape resembling a square pillar as shown in a scanning electron micrograph of FIG. Further, the obtained powder was observed with a transmission electron microscope (H-9000UHR, manufactured by Hitachi, Ltd.), and limited-field electron diffraction was performed under an acceleration voltage of 300 kV. The results are shown in FIG. The obtained particles were single crystals, and as a result of analysis, it was found that the long side direction was the (010) plane and the short side direction was the (101) plane.
When the particle size distribution was measured in the same manner as in Example 1, D1 was 0.42 μm, D2 was 1.12 μm, D3 was 0.28 μm, D4 was 5.56 μm, D2 / D1 = 2.7, D3 / D2 = 0.25 and D4 / D2 = 4.96.

Example 3:
Calcium titanate was synthesized in the same manner as in Example 1 except that 45 and 6 g of a tetramethylammonium hydroxide 20 mass% aqueous solution (manufactured by Seychem Showa Co., Ltd.) was diluted by adding 410.4 g of pure water. The ratio of the actual yield to the theoretical yield was 99.7% by mass.
When examined in the same manner as in Example 1, the obtained powder had a specific surface area of 5.7 m ² / g and was found to be perovskite calcium titanate. It was found that the shape was similar to a square pillar shape. Moreover, it was a single crystal and it turned out that the long side of a square columnar particle is extended in the (010) direction.
When the particle size distribution was measured in the same manner as in Example 1, D1 was 0.26 μm, D2 was 0.72 μm, D3 was 0.30 μm, D4 was 1.75 μm, and D2 / D1 = 2.8, D3. /D2=0.42 and D4 / D2 = 2.43.

Example 4:
Calcium titanate was synthesized in the same manner as in Example 1 except that a commercially available anatase type titanium oxide sol (ST-02 manufactured by Ishihara Sangyo Co., Ltd.) was used instead of the blue kite type titanium oxide sol synthesized in Example 1. . The ratio of the actual yield to the theoretical yield was 99.9% by mass.
When examined in the same manner as in Example 1, the obtained powder had a specific surface area of 3.9 m ² / g and was found to be perovskite calcium titanate. It was found that the shape was similar to a square pillar shape. Moreover, it was a single crystal and it turned out that the long side of a square columnar particle is extended in the (010) direction.
When the particle size distribution was measured in the same manner as in Example 1, D1 was 0.38 μm, D2 was 0.69 μm, D3 was 0.17 μm, D4 was 1.08 μm, and D2 / D1 = 1.8, D3. /D2=0.25 and D4 / D2 = 1.57.

Example 5:
Calcium titanate was synthesized in the same manner as in Example 1 except that the calcium hydroxide was changed to 0.296 g. The ratio of the actual yield to the theoretical yield was 99.9% by mass. When examined in the same manner as in Example 1, it was found that the obtained powder was perovskite calcium titanate.
When examined in the same manner as in Example 1, the obtained powder had a specific surface area of 4.8 m ² / g and was found to be perovskite calcium titanate. It was found that the shape was similar to a square pillar shape. Moreover, it was a single crystal and it turned out that the long side of a square columnar particle is extended in the (010) direction.
When the particle size distribution was measured in the same manner as in Example 1, D1 was 0.31 μm, D2 was 0.65 μm, D3 was 0.23 μm, D4 was 1.21 μm, and D2 / D1 = 2.1 and D3. /D2=0.35 and D4 / D2 = 1.86.

Example 6:
Calcium titanate was synthesized in the same manner as in Example 1 except that 58.8 g of calcium chloride dihydrate (manufactured by Wako Pure Chemical Industries, Ltd .: purity 99.9%) was used instead of calcium hydroxide. The cake obtained by vacuum filtration was repeatedly washed with water and filtered to adjust the Cl concentration to 100 ppm. Thereafter, the cake obtained by vacuum filtration was dried at 300 ° C. for 5 hours to obtain a dry powder. The ratio of the actual yield to the theoretical yield calculated from the amount of titanium oxide and calcium hydroxide used in the reaction was 99.9% by mass.
When examined in the same manner as in Example 1, the obtained powder had a specific surface area of 4.6 m ² / g and was found to be perovskite calcium titanate. It was found that the shape was similar to a square pillar shape. Moreover, it was a single crystal and it turned out that the long side of a square columnar particle is extended in the (010) direction.
When the particle size distribution was measured in the same manner as in Example 1, D1 was 0.33 μm, D2 was 0.75 μm, D3 was 0.22 μm, D4 was 1.36 μm, and D2 / D1 = 2.3 and D3. /D2=0.29 and D4 / D2 = 1.81.

Example 7:
Calcium titanate was synthesized in the same manner as in Example 1 except that KOH (special grade manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of TMAH. The cake obtained by vacuum filtration was repeatedly washed with water and filtered to adjust the K concentration to 100 ppm. Thereafter, the cake obtained by vacuum filtration was dried at 300 ° C. for 5 hours to obtain a dry powder. The ratio of the actual yield to the theoretical yield calculated from the amount of titanium oxide and calcium hydroxide used in the reaction was 99.3% by mass.
When examined in the same manner as in Example 1, the obtained powder had a specific surface area of 4.4 m ² / g and was found to be perovskite calcium titanate. It was found that the shape was similar to a square pillar shape. Moreover, it was a single crystal and it turned out that the long side of a square columnar particle is extended in the (010) direction.
When the particle size distribution was measured in the same manner as in Example 1, D1 was 0.34 μm, D2 was 0.74 μm, D3 was 0.23 μm, D4 was 1.30 μm, and D2 / D1 = 2.2 and D3. /D2=0.31 and D4 / D2 = 1.76.

Comparative Example 1:
Calcium titanate was prepared in the same manner as in Example 1, except that a 20% by mass aqueous solution of tetramethylammonium hydroxide (Sechem Chem Showa, carbonate concentration of 60 ppm or less) was left in the atmosphere to adjust the concentration of carbonate groups to 6000 ppm. Was synthesized. The ratio of the actual yield to the theoretical yield was 99.9% by mass.
When examined in the same manner as in Example 1, it was found that 6% by mass of calcium carbonate was mixed in the obtained powder. The BET specific surface area was 7.2 m ² / g.
When the particle size distribution was measured in the same manner as in Example 1, D1 was 0.20 μm, D2 was 0.80 μm, D3 was 0.20 μm, D4 was 2.10 μm, and D2 / D1 = 4.0, D3. /D2=0.25 and D4 / D2 = 2.63.

Comparative Example 2:
Calcium titanate was synthesized in the same manner as in Example 1 except that calcium hydroxide was changed to 0.0185 g. The ratio of the actual yield to the theoretical yield was 99.9% by mass.
When examined in the same manner as in Example 1, it was found that the obtained powder was perovskite calcium titanate. The specific surface area of the obtained particles was 23 m ² / g, and it was found that the particles were mostly spherical fine particles.
When the particle size distribution was measured in the same manner as in Example 1, D1 was 0.065 μm, D2 was 0.6 μm, D3 was 0.04 μm, D4 was 11.0 μm, and D2 / D1 = 9.2, D3. /D2=0.06 and D4 / D2 = 18.3.

Comparative Example 3:
Calcium titanate was synthesized by the same operation as in Example 1 using 368 g of pure water instead of adding TMAH. The pH at this time was 7.1. The ratio of the actual yield to the theoretical yield was 99.6% by mass. When examined in the same manner as in Example 1, the obtained powder was found to contain a large amount of calcium hydroxide and titanium oxide in perovskite calcium titanate.

Comparative Example 4:
Calcium titanate was synthesized in the same manner as in Example 1 except that 73 g of ethylenediaminetetraacetic acid was added and calcium hydroxide was dissolved and reacted. The obtained dry powder was held at 900 ° C. for 2 hours to decompose ethylenediaminetetraacetic acid. When examined in the same manner as in Example 1, almost no calcium perovskite calcium titanate was obtained.

Comparative Example 5:
Calcium titanate was synthesized in the same manner as in Example 1 except that the reaction time was 1 hour. The ratio of the actual yield to the theoretical yield was 99.5% by mass. The BET specific surface area of the obtained powder was 27.1 m ² / g. In the X-ray diffraction spectrum, although only a few peaks of raw material titanium oxide and calcium hydroxide were observed, it was found that most were perovskite type calcium titanate.
Most of the particle shapes observed with a scanning electron microscope were spherical fine particles, and there were few tetragonal fine particles.
The particle size distribution was measured in the same manner as in Example 1. As a result, D1 was 0.06 μm, D2 was 0.64 μm, D3 was 0.05 μm, D4 was 11.5 μm, and D2 / D1 = 10.6, D3. /D2=0.08 and D4 / D2 = 18.0.

4 is an X-ray diffraction spectrum diagram of the calcium titanate powder obtained in Example 1. FIG. 2 is a scanning electron micrograph of the calcium titanate powder obtained in Example 1. FIG. 4 is an X-ray diffraction spectrum diagram of the calcium titanate powder obtained in Example 2. FIG. 4 is a scanning electron micrograph of the calcium titanate powder obtained in Example 2. FIG. The transmission electron micrograph and electron diffraction diagram of the calcium titanate powder obtained in Example 2.

Claims (32)

It has a perovskite crystal structure with a D2 / D1 value of 1 or more and 3 or less, where D1 is an average primary particle size and D2 is an average particle size of secondary particles, and a square column or a square column-like shape. calcium titanate powder having. In the particle size distribution of the secondary particles, when the average particle size of the secondary particles is D2, and the particle size of 10% from the minimum particle size is D3, the D3 / D2 value is 0.1 or more and 0.9 or less. The calcium titanate powder according to claim 1, which has a perovskite crystal structure and has a square pillar or a square pillar-like shape. In the particle size distribution of the secondary particles, a perovskite crystal having a D4 / D2 value of 1.1 or more and 10 or less when the average particle size of the secondary particles is D2 and the particle size from the minimum particle size to 90% is D4. The calcium titanate powder according to claim 1 or 2, which has a structure and has a square pillar or a square pillar-like shape. The calcium titanate powder according to any one of claims 1 to 3, which has a perovskite crystal structure with a calcium carbonate content of 3% by mass or less and has a square column or a shape similar to a square column. The calcium titanate powder according to any one of claims 1 to 4, which has a perovskite crystal structure having a specific surface area of 1 to 10 m ² / g and has a square column or a shape similar to a square column. When fired at any temperature in the range of 1200 ° C. from 900 ° C., decrease in the specific surface area is less than 8m ² / g, having a perovskite crystal structure, wherein having a square pillar or square pillar shape similar Item 6. The calcium titanate powder according to any one of Items 1 to 5 .
The calcium titanate powder according to any one of claims 1 to 6, which is a single crystal. The calcium titanate powder according to any one of claims 1 to 7, wherein the ratio of the long side to the short side of the calcium titanate crystal is 1.1 to 6. The calcium titanate powder according to any one of claims 1 to 8, wherein a long side extends to a unit cell (010) plane. The method for producing a calcium titanate powder according to any one of claims 1 to 9 , wherein a titanium oxide sol and a calcium salt having a saturation solubility or higher are introduced into an alkaline aqueous solution containing a basic compound and reacted. The method for producing a calcium titanate powder according to claim 10 , wherein a calcium salt having a weight of 10 mass times or more and 10000 mass times or less is added and reacted with respect to an alkaline solution saturated solubility in which a basic compound is present. The method for producing a calcium titanate powder according to claim 10 or 11 , wherein the calcium salt is a hydroxide. Method of manufacturing a calcium titanate powder according to any one of claims 10 to 12 comprising the step of reacting the CO ₂ concentration in terms of carbonate groups in the reaction solution was controlled to 500ppm or less. The method for producing calcium titanate powder according to any one of claims 10 to 13, comprising a step of boiling at 100 ° C or more for 4 hours or more. The calcium titanate according to any one of claims 10 to 14 , comprising a step of removing impurities as a gas by evaporation and / or thermal decomposition under atmospheric pressure or reduced pressure in a temperature range of room temperature to firing temperature. Powder manufacturing method. The method for producing a calcium titanate powder according to any one of claims 10 to 15 , wherein the titanium oxide sol is obtained by hydrolyzing a titanium compound in an acidic solution. The method for producing a calcium titanate powder according to any one of claims 10 to 16 , wherein the titanium oxide sol contains a brookite crystal. The method for producing a calcium titanate powder according to any one of claims 10 to 17 , wherein the basic compound is a substance that becomes a gas by evaporation, sublimation, and / or thermal decomposition under atmospheric pressure or reduced pressure. The method for producing a calcium titanate powder according to any one of claims 10 to 18 , wherein the basic compound is an organic base. The method for producing a calcium titanate powder according to any one of claims 10 to 19 , wherein the basic compound is tetramethylammonium hydroxide. A dielectric material comprising the calcium titanate powder according to any one of claims 1 to 9 . A paste comprising the calcium titanate powder according to any one of claims 1 to 9 . A slurry containing the calcium titanate powder according to any one of claims 1 to 9 . A thin film-like formation containing the calcium titanate powder according to any one of claims 1 to 9 . A dielectric ceramic comprising the calcium titanate powder according to any one of claims 1 to 9 . A pyroelectric ceramic containing the calcium titanate powder according to any one of claims 1 to 9 . A piezoelectric ceramic comprising the calcium titanate powder according to any one of claims 1 to 9 . A capacitor comprising the dielectric ceramic according to claim 25 . 29. An electronic device comprising at least one selected from the group consisting of the thin film-like product according to claim 24, 28 , 28, and 28 , and a capacitor. Sensor comprising one or more film-like formations or porcelain according to claim 24 or 27. A dielectric film using the calcium titanate powder according to any one of claims 1 to 9 . A capacitor using the dielectric film according to claim 31 .