KR20230075395A - Method for producing microparticles of strontium titanate - Google Patents

Abstract

Provided is a method for producing fine strontium titanate particles capable of producing fine strontium titanate particles with excellent dispersibility under simple conditions.
A reaction step of reacting an organic titanic acid ester with a strontium compound in the presence of hydrazine or a hydrazide compound under conditions of a pH of 12 or higher, a reaction temperature of 150°C or higher and 250°C or lower, and a reaction time of 0.5 hour or higher and 2 hours or lower, A method for producing fine particles of strontium titanate wherein the molar ratio of the hydrazine or hydrazide compound to the organic titanate ester (hydrazine or hydrazide compound/organic titanate ester) is 10 to 75.

Description

Method for producing microparticles of strontium titanate

The present invention relates to a method for producing fine particles of strontium titanate.

Since strontium titanate (SrTiO ₃ ) has dielectric properties, thermoelectric properties, photocatalytic performance, and high refractive index, it is expected to be developed for various uses as a functional material.

For example, Patent Document 1 discloses that strontium titanate having an average particle diameter of 50 nm or less, an average aspect ratio of 1.0 to 1.2, and a refractive index of 1.8 to 2.6 has a high refractive index. Further, Patent Literature 1 discloses that when strontium titanate is used as a component imparting high refractive index, high dispersibility without aggregation in the coating film is required.

Further, as a method for producing strontium titanate, for example, Patent Document 2 discloses a method for producing strontium titanate by heating ammonium titanium peroxolactate and strontium hydroxide in a constant temperature bath at 200°C for 24 hours in the presence of oleic acid and hydrazine. has been

However, since the method described in Patent Document 2 takes too much time in the production of strontium titanate, a method that can be produced more simply has been desired.

[Patent Document 1] International Publication No. 2011/004750 [Patent Document 2] Japanese Unexamined Patent Publication No. 2011-068500

An object of the present invention is to provide a method for producing fine strontium titanate particles capable of producing fine strontium titanate particles having excellent dispersibility under simple conditions.

The present inventors have intensively studied the method for producing fine particles of strontium titanate. As a result, by reacting an organic titanate ester with a strontium compound containing a specific amount of hydrazine or a hydrazide compound under predetermined conditions (temperature and reaction time), a shorter reaction than before was obtained. It was found that fine particles of strontium titanate with excellent dispersibility could be prepared over time.

The present invention is a method for reacting an organic titanic acid ester with a strontium compound in the presence of hydrazine or a hydrazide compound under the conditions of a pH of 12 or more, a reaction temperature of 150 ° C or more and 250 ° C or less, and a reaction time of 0.5 hour or more and 2 hours or less. A method for producing fine strontium titanate particles having a reaction step and having a molar ratio (hydrazine or hydrazide compound/organic titanate ester) of the hydrazine or hydrazide compound to the organic titanate ester of 10 to 75.

The method for producing fine strontium titanate particles of the present invention includes a mixing step of mixing an organic titanate ester with hydrazine or a hydrazide compound in a solvent to obtain a mixed solution, an adjustment step of adjusting the pH of the mixed solution to 12 or higher, and the above reaction step. desirable.

In the method for producing strontium titanate of the present invention, it is preferable to carry out the reaction step in the presence of a polyhydric alcohol. The polyhydric alcohol is preferably ethylene glycol.

Also, the organic titanic acid ester is preferably titanium lactate.

The strontium compound is preferably at least one selected from strontium acetate and strontium formate.

Moreover, it is preferable to perform the said reaction process in the presence of an aminosilane compound.

Also, the aminosilane compound is preferably 3-aminopropyltriethoxysilane.

The method for producing fine strontium titanate particles of the present invention can produce fine strontium titanate particles with excellent dispersibility under simple conditions.

The present invention is a method for reacting an organic titanic acid ester with a strontium compound in the presence of hydrazine or a hydrazide compound under the conditions of a pH of 12 or more, a reaction temperature of 150 ° C or more and 250 ° C or less, and a reaction time of 0.5 hour or more and 2 hours or less. A method for producing fine strontium titanate particles having a reaction step and having a molar ratio (hydrazine or hydrazide compound/organic titanate ester) of the hydrazine or hydrazide compound to the organic titanate ester of 10 to 75.

First, various materials used in the method for producing fine strontium titanate particles according to the present invention will be described.

(organic titanic acid ester)

Examples of the organic titanic acid ester include tetraethyl titanate, tetraisopropyl titanate, tetra-normal butyl titanate, butyl titanate dimer, tetra(2-ethylhexyl) titanate, and polymers thereof, and titanium acetyl titanate. Titanium chelate compounds, such as nate, polytitanium acetyl acetonate, titanium octyl glycinate, titanium lactate, titanium lactate ethyl ester, titanium triethanol aminate, and phosphate ester titanium complex, etc. are mentioned.

Especially, titanium lactate is preferable from a hydrophilic viewpoint.

(hydrazine or hydrazide compound)

Examples of the hydrazide compound include 1-monomethylhydrazine, 1,1-dimethylhydrazine, 1-ethyl-2-methylhydrazine, adipic acid dihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, and succinic acid dihydrazide. hydrazide, glutaric acid dihydrazide, isophthalic acid dihydrazide, sebacic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, itaconic acid dihydrazide and the like.

Among them, hydrazine is preferable because it is relatively easy to handle and has an excellent effect of controlling the shape of the resulting strontium titanate fine particles.

The state of hydrogenation may be sufficient as the said hydrazine or hydrazide compound.

As the content of the hydrazine or hydrazide compound, the molar ratio (hydrazine or hydrazide compound/organic titanate ester) to the organic titanate is 10 to 75, preferably 30 to 65.

The shape of the obtained strontium titanate fine particles can be controlled by setting the above range.

(strontium compound)

As the strontium compound, the nitrate strontium, hydroxide strontium, carbonate strontium, peroxide strontium, formate strontium, acetic acid strontium, lactic acid strontium, oxalate strontium, strontium chloride, fluoride strontium Acid strontium, iodic acid strontium, and hydrophilic acid strontium, etc. can be heard You may use these as a hydrate.

Among them, from the viewpoint of hydrophilicity, at least one selected from strontium acetate and strontium formate is preferred, and strontium acetate is more preferred.

As the content of the strontium compound, it is preferable that the molar ratio (strontium compound/organic titanate ester) to the organic titanate ester is 1.0 or more.

The progress of crystallization can be appropriately controlled by setting it as the said range.

Further, from the viewpoint of reducing the raw material cost, the molar ratio (strontium compound/organic titanic acid ester) is more preferably 2.0 or less.

(menstruum)

It is preferable to use ion-exchanged water as a solvent used in the method for producing fine strontium titanate particles of the present invention.

In addition, it is preferable that the solvent contains a polyhydric alcohol.

Examples of the polyhydric alcohol include divalent divalent alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, butanediol, pentanediol, hexanediol, heptanediol, nonanediol, decanediol, and neopentyl glycol. and trihydric or higher polyhydric alcohols such as alcohol, glycerin, trimethylolpropane, and pentaerythritol.

Among them, at least one selected from ethylene glycol, propylene glycol, diethylene glycol, and 1,3-propanediol is preferable from the viewpoint of adjusting the particle diameter of the resulting strontium titanate fine particles and maintaining the dispersibility in the reaction system appropriately. , ethylene glycol is more preferred.

The content of the polyhydric alcohol is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, still more preferably 7 to 12% by mass, based on the total amount of the solvent.

(pH adjusting agent)

In the method for producing fine strontium titanate particles of the present invention, it is preferable to adjust the pH using a pH adjuster.

Lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide etc. are mentioned as said pH adjuster.

Especially, potassium hydroxide is preferable from a solubility viewpoint to the said solvent.

When adjusting the pH, the pH is set to 12 or higher from the viewpoint of controlling the reaction rate and the shape of the resulting strontium titanate fine particles.

As for pH, it is preferable that it is 12.5 or more, it is more preferable that it is 13 or more, and it is still more preferable that it is 13.5 or more.

Content of the said pH adjuster is not limited, What is necessary is just to add suitably according to the target pH.

(Aminosilane compound)

It is preferable to perform the said reaction process in the presence of an aminosilane compound.

By carrying out the above reaction step in the presence of an aminosilane compound, the average particle diameter of the resulting strontium titanate fine particles can be further reduced, and dispersibility can be imparted more favorably.

Examples of aminosilane compounds include 3-aminopropyltrimethoxysilane, 3-aminopropylethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3- Aminopropyl trimethoxysilane, N-phenyl-3-aminopropyl trimethoxysilane, etc. are mentioned.

Among them, 3-aminopropyl triethoxysilane is preferred.

The content of the aminosilane compound is preferably 0.003 to 0.025, more preferably 0.004 to 0.019, and still more preferably 0.007 to 0.015 in terms of the molar ratio (aminosilane compound/hydrazine or hydrazide compound) relative to the hydrazine or hydrazide compound. desirable.

(etc)

In the method for producing fine strontium titanate particles of the present invention, an amphiphilic compound may not be added.

In the conventional method for producing fine particles of strontium titanate, the reaction is conducted in the presence of an amphiphilic compound to highly control the size and shape of the particles to impart dispersibility to the particles.

On the other hand, in the method for producing fine strontium titanate particles, when the amphiphilic compound is added, it is non-uniformly dispersed in the system, resulting in an increase in average particle diameter of the obtained fine strontium titanate particles.

Examples of the amphiphilic compound include propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, and ligno acid. Saturated fatty acids such as seric acid, α-linolenic acid, stearidonic acid, eicosapentaenoic acid, docosahexaenoic acid, linoleic acid, γ-linolenic acid, dihomo-γ-linolenic acid, arachidonic acid, oleic acid, elaidic acid, and unsaturated fatty acids such as erucic acid and nervonic acid.

(Manufacturing method)

The method for producing fine strontium titanate particles of the present invention comprises a reaction step of reacting an organic titanate ester with a strontium compound under the conditions of a pH of 12 or more, a reaction temperature of 150°C or more and 250°C or less, and a reaction time of 0.5 hour or more and 2 hours or less. have

The method for producing fine strontium titanate particles of the present invention includes, for example, a mixing step of mixing an organic titanate ester and a hydrazine or hydrazide compound in a solvent to obtain a mixed solution, an adjustment step of adjusting the pH of the mixed solution to 12 or higher, and the above reaction step. It is desirable to have

The mixing step is a step of adding an organic titanic acid ester and a hydrazine or hydrazide compound in a solvent.

It is presumed that hydrazine is coordinated to the organic titanic acid ester by the above mixing step.

The method of adding various materials in the mixing step is not particularly limited, and addition, stirring, or the like may be performed by known methods.

In the said manufacturing process, pH is adjusted. In this way, the reaction rate and the shape of the resulting strontium titanate fine particles can be suitably controlled.

In addition, it is considered that the increase in the average particle diameter of the organic titanate ester coordinated with hydrazine can be controlled by the above mixing step, and the average particle diameter of the resulting fine strontium titanate particles can be controlled within an appropriate range.

Moreover, it is preferable to adjust pH using the said pH adjuster.

Moreover, when adding the said aminosilane compound, it is preferable to add in the said adjustment process together with the said pH adjuster.

Crystal growth of strontium titanate fine particles is accelerated when a large amount of water is present, while aggregation is promoted when the hydrophobicity of the solvent increases because the surface of the strontium titanate fine particles is hydrophilic.

On the other hand, since the polyhydric alcohol is hydrophilic and has an effect of inhibiting crystal growth, it is preferable to add it in the preparation step.

The method of adding various materials in the preparation step is not particularly limited, and addition, stirring, or the like may be performed by a known method.

In the reaction step, the organic titanic acid ester and the strontium compound are reacted under the conditions of a pH of 12 or more, a reaction temperature of 150°C or more and 250°C or less, and a reaction time of 0.5 hour or more and 2 hours or less.

The said reaction temperature is 150 degreeC or more and 250 degreeC or less.

If the reaction temperature is less than 150°C, the reaction does not proceed and desired strontium titanate fine particles cannot be obtained, while if it exceeds 250°C, the reaction efficiency decreases and the obtained strontium titanate fine particles become large and dispersibility decreases.

The reaction temperature is preferably 180 to 250°C, more preferably 200 to 240°C.

The said reaction time is 0.5 hour or more and 2 hours or less.

If the reaction time is less than 0.5 hours, the reaction does not proceed and target strontium titanate fine particles cannot be obtained, while if it exceeds 2 hours, the reaction efficiency decreases and the resulting strontium titanate particles increase in size and dispersibility decreases.

The reaction time is preferably 1 to 2 hours.

The pressure at the time of reacting may be, for example, about 2 to 5 MPa, and it is not necessary to apply a pressure exceeding 10 MPa.

It does not specifically limit as a method of performing the said reaction process, Any method which satisfies the said conditions is good.

For example, a pressure reaction vessel or the like can be used.

(fine particles of strontium titanate)

The strontium titanate fine particles obtained by the method for producing fine strontium titanate particles of the present invention have the following properties.

The strontium titanate fine particles preferably have a spherical particle shape.

Here, the spherical shape includes not only a true sphere but also an ellipsoidal shape, a cylindrical shape, a rod shape (a shape in which the corner of a cylinder is rounded), and the like.

Specifically, it means that the circularity of the fine particles of strontium titanate is 0.900 to 1.000.

In addition, the shape of the strontium titanate fine particles can be confirmed by observing, for example, with a transmission electron microscope ("JEM-1011" manufactured by JEOL Co., Ltd.) at an observation magnification of 300,000 times.

In addition, the circularity of the strontium titanate fine particles can be calculated as circularity = 4πS/L ² when S is the area of the fine particles and the circumferential length is L in the image taken with a transmission electron microscope.

In addition, the said circularity is an average value excluding those which have a specific shape clearly different from the said spherical shape among the microparticles|fine-particles which appear in the image taken by the transmission electron microscope.

The strontium titanate fine particles preferably have an average particle diameter of 10 nm to 30 nm, more preferably 14 nm to 25 nm.

By having such an average particle diameter, it can be set as having excellent dispersibility.

In addition, the above-mentioned average particle diameter was measured by dissolving strontium titanate fine particles in methanol to obtain a dispersion, putting the obtained dispersion into a measuring cell, and using a laser diffraction/scattering type particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., “Microtrac MT3300EXII”). It means average particle diameter (D50).

The strontium titanate fine particles have excellent dispersibility.

Here, the dispersibility refers to dissolving 50 mg of strontium titanate microparticles in 50 mL of methanol to obtain a dispersion, putting the obtained dispersion into a screw tube bottle, placing black paper on the back side, and visually checking the state of the dispersion to see if it causes cloudiness or not. can judge When cloudiness does not occur, it can be evaluated as having excellent dispersibility, and can be suitably applied, for example, to a high refractive index material.

Preferably, the strontium titanate fine particles have good crystallinity.

In addition, the crystallinity of the strontium titanate fine particles is the same [particle diameter ratio (particle diameter observed with a transmission electron microscope / calculated with an X-ray diffraction device)] If the crystallite diameter) is 0.9 to 1.0], the crystallinity is judged to be good, and if it is small or no crystals are confirmed, it is judged to be poor.

It is preferable that the content of hydrazine or a hydrazide compound in the strontium titanate fine particles is 0.1 mass% to 60 mass% based on the strontium titanate fine particles.

Dispersibility becomes good in such a content.

Example

The present invention will be described in more detail by way of examples below, but the present invention is not limited only to these examples. In addition, "%" means "mass %", and "part" means "mass part" unless otherwise indicated.

Materials used in Examples and Comparative Examples are as follows.

(organic titanic acid ester)

Titanium lactate (Orgatics TC-310, ingredient concentration 44wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.)

Phosphate ester titanium complex (Orgatics TC-1040, ingredient concentration 75wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.)

(hydrazine or hydrazide compound)

Hydrogenated hydrazine (manufactured by Nippon Carbide Industrial Co., Ltd.)

(strontium compound)

Strontium acetate 0.5 hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

Strontium formate dihydrate

(menstruum)

Ethylene glycol

propylene glycol

Purified water (ion-exchanged water)

(pH adjusting agent)

potassium hydroxide

(Aminosilane compound)

3-Aminopropyltriethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.)

(Example 1)

To 0.584 g of titanium lactate (Orgatix TC-310, ingredient concentration: 44 wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.), 3 g of purified water and 3.0 g of hydrogenated hydrazine (manufactured by Nippon Carbide Industrial Co., Ltd.) were added to obtain a yellow transparent solution.

Subsequently, a solution prepared from 0.48 g of potassium hydroxide, 0.432 g of ethylene glycol, and 5.088 g of purified water was added to the yellow transparent solution to obtain a cloudy solution.

Thereafter, 0.429 g of strontium acetate 0.5 hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the obtained cloudy solution, and stirred at room temperature for 30 minutes to obtain a transparent solution. The obtained transparent solution was placed in a pressure reaction vessel and reacted at 230°C for 1 hour. The pressure was about 2.8 MPa.

The solution containing the reactants was subjected to centrifugal separation treatment (model name: SIGMA 3-30KS, conditions: 15000 rpm, 5 minutes) to settle the fine particles, thereby performing separation and purification from unreacted substances. Separation and purification were completed by preparing a redispersion solution of the fine particles in purified water, centrifuging, and repeating the operation of sedimenting the fine particles three times.

The obtained fine particles were collected and observed with an X-ray diffractometer ("MiniFlex600-C" manufactured by Rigaku Corporation), and it was confirmed that they were fine particles of strontium titanate.

(Examples 2 to 8, Comparative Examples 1 to 6)

Strontium titanate fine particles were produced in the same manner as in Example, except that the blending amount of various materials and reaction conditions were changed as shown in Table 1.

Also in Examples 5 and 6, 3-aminopropyl triethoxysilane was added along with a pH adjuster (potassium hydroxide).

The obtained fine particles were collected and observed with an X-ray diffractometer ("MiniFlex600-C" manufactured by Rigaku Co., Ltd.). In Examples 2 to 8 and Comparative Example 4, it was confirmed that they were fine particles of strontium titanate.

On the other hand, in Comparative Examples 1 to 3, 5 and 6, the reaction did not proceed and strontium titanate was not obtained.

<Evaluation method>

(particle shape)

The strontium titanate microparticles obtained in Examples and Comparative Examples were recovered and observed at an observation magnification of 300,000 times with a transmission electron microscope (“JEM-1011” manufactured by JEOL Co., Ltd.) to confirm the particle shape.

The circularity of the confirmed microparticles|fine-particles was 0.900-1.000, and it was evaluated as spherical.

(crystalline)

The microparticles obtained in Examples and Comparative Examples were observed with a transmission electron microscope ("JEM-1011" manufactured by JEOL Corporation) and an X-ray diffractometer ("MiniFlex600-C" manufactured by Rigaku Corporation), and evaluated according to the following criteria.

○: The ratio of the crystallite diameter calculated with an X-ray diffractometer and the particle diameter observed with a transmission electron microscope is 0.9 to 1.0

△: The ratio of the crystallite diameter calculated with an X-ray diffractometer and the particle diameter observed with a transmission electron microscope is less than 0.9

×: no crystals were formed

(average particle size)

50 mg of the microparticles obtained in Examples and Comparative Examples was dissolved in 50 mL of methanol to obtain a dispersion.

The resulting dispersion was placed in a measuring cell, and the average particle diameter (D50) was measured with a laser diffraction/scattering type particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., "Microtrac MT3300EXII").

(dispersity)

50 mg of strontium titanate microparticles obtained in Examples and Comparative Examples was dissolved in 50 mL of methanol to obtain a dispersion.

The obtained dispersion was placed in a screw tube bottle, a black paper was placed on the back, the state of the dispersion was visually confirmed, and the following criteria were evaluated.

○: The obtained dispersion liquid was a transparent solution.

x: The obtained dispersion liquid was a cloudy solution.

It was confirmed that the strontium titanate fine particles obtained in the examples had a spherical particle shape, an average particle diameter of 14 nm to 30 nm, and excellent crystallinity and dispersibility.

In particular, in Examples 5 and 6 in which 3-aminopropyltriethoxysilane was added, fine strontium titanate particles having a small average particle diameter and excellent dispersibility were obtained.

Further, in Example 7 using the phosphate ester titanium complex and Example 8 using propylene glycol as the solvent, the transparency of the dispersion was slightly lower than that of the other Examples, and the dispersibility was slightly lower than that of the other Examples.

On the other hand, in Comparative Examples 1 to 3, 5 and 6, the reaction did not proceed and fine strontium titanate particles could not be obtained.

In addition, the microparticles obtained by Comparative Examples 1 to 3 that did not contain hydrazine or a hydrazide compound or the amount of addition was not within a predetermined range had a large average particle diameter and poor dispersibility (the dispersion was cloudy).

In addition, the strontium titanate fine particles obtained in Comparative Example 4 in which the reaction temperature was outside the predetermined range had insufficient crystallinity.

Further, the fine particles obtained in Comparative Example 5 in which the reaction time was too long had a large average particle diameter and poor dispersibility (the dispersion was cloudy).

Further, in Comparative Example 6 in which the reaction time was long and the pH was low, the reaction did not proceed and fine particles were not obtained.

The strontium titanate fine particles of the present invention are, for example, high refractive index agents, thermoelectric conversion materials, photocatalysts, ion conductive materials, ferroelectric materials, magnetic materials, catalytic materials, oxygen electrode materials, piezoelectric materials, pyroelectric materials, nonlinear optical materials, fillers, etc. It is useful in that fine particles of strontium titanate that can be used as a functional material can be obtained.

Claims (8)

In the presence of hydrazine or a hydrazide compound, the pH is 12 or more, the reaction temperature is 150 ° C. or more and 250 ° C. or less, and the reaction time is 0.5 hour or more and 2 hours or less.
It has a reaction step of reacting an organic titanic acid ester with a strontium compound,
A method for producing fine particles of strontium titanate wherein the molar ratio of the hydrazine or hydrazide compound to the organic titanate ester (hydrazine or hydrazide compound/organic titanate ester) is 10 to 75. The method for producing fine strontium titanate particles according to claim 1, comprising a mixing step of mixing an organic titanate ester and hydrazine or a hydrazide compound in a solvent to obtain a mixture solution, an adjustment step of adjusting the pH of the mixture solution to 12 or higher, and the reaction step. . The method for producing fine strontium titanate particles according to claim 1 or 2, wherein the reaction step is performed in the presence of a polyhydric alcohol. The method of claim 3, wherein the polyhydric alcohol is ethylene glycol. The method for producing fine strontium titanate particles according to any one of claims 1 to 4, wherein the organic titanate ester is titanium lactate. The method for producing fine strontium titanate particles according to any one of claims 1 to 5, wherein the strontium compound is at least one selected from strontium acetate and strontium formate. The method for producing fine strontium titanate particles according to any one of claims 1 to 6, wherein the reaction step is performed in the presence of an aminosilane compound. The method of claim 7, wherein the aminosilane compound is 3-aminopropyltriethoxysilane.