JP2022058092A - Method for producing strontium titanate fine particles - Google Patents

Abstract

To provide a method for producing strontium titanate fine particles capable of producing strontium titanate fine particles excellent in dispersibility under simple conditions.SOLUTION: A method for producing strontium titanate fine particles comprises a reaction step of reacting an organic titanate ester with a strontium compound in the presence of a hydrazine or a hydrazide compound under conditions of a pH of 12 or greater, a reaction temperature of 150°C or higher and 250°C or lower, and a reaction time of 0.5 hours or longer and 2 hours or shorter, in which a molar ratio of the hydrazine or hydrazide compound to the organic titanate ester (hydrazine or hydrazide compound/organic titanate ester) is 10 to 75.SELECTED DRAWING: None

Description

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

Since strontium titanate (SrTiO ₃ ) has dielectric properties, thermoelectric properties, photocatalytic activity, high refractive index properties, etc., it is expected to be used in various applications as a functional material.

For example, in Patent Document 1, strontium titanate having an average particle size 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. Is disclosed. Further, Patent Document 1 discloses that when strontium titanate is used as a component that imparts high refractive index property, high dispersibility that does not aggregate in the coating film is required.

Further, as a method for producing strontium titanate, for example, in Patent Document 2, titanium peroxoammonium lactate and strontium hydroxide are heat-treated in a constant temperature bath at 200 ° C. for 24 hours in the presence of oleic acid and hydrazine. A method for producing strontium titanate is disclosed.
However, in the method described in Patent Document 2, it takes too much time to produce strontium titanate, so that a method that can be produced more easily has been required.

International Publication No. 2011/004750 Japanese Unexamined Patent Publication No. 2011-068500

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

The present inventors have diligently studied a method for producing strontium titanate fine particles, and found that a specific amount of hydrazine or hydrazide compound is contained, and the organic titanium acid ester is reacted with the strontium compound under predetermined conditions (temperature and reaction time). As a result, it has been found that strontium titanate fine particles having excellent dispersibility can be produced in a shorter reaction time than before.

The present invention presents the organic titanium acid ester and the 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 hours or more and 2 hours or less in the presence of hydrazine or a hydrazide compound. It is a method for producing strontium titanate fine particles having a reaction step of reacting with and having a molar ratio of the hydrazine or hydrazide compound to the organic titanium acid ester (hydrazine or hydrazide compound / organic titanium acid ester) of 10 to 75. ..
The method for producing strontium titanate fine particles of the present invention is a mixing step of mixing an organic titanium acid ester and a hydrazine or a hydrazide compound in a solvent to obtain a mixed solution, and an adjusting step of adjusting the pH of the mixed solution to 12 or more. , And it is preferable to have the above reaction step.
In the method for producing strontium titanate of the present invention, it is preferable to carry out the above reaction step in the presence of a polyhydric alcohol. The polyhydric alcohol is preferably ethylene glycol.
Further, the organic titanium acid ester is preferably titanium lactate.
Further, the strontium compound is preferably at least one selected from strontium acetate and strontium formate.
Further, it is preferable to carry out the above reaction step in the presence of the aminosilane compound.
The aminosilane compound is preferably 3-aminopropyltriethoxysilane.

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

The present invention presents the organic titanium acid ester and the 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 hours or more and 2 hours or less in the presence of a hydrazine or a hydrazide compound. It is a method for producing strontium titanate fine particles having a reaction step of reacting with and having a molar ratio of the hydrazine or hydrazide compound to the organic titanium acid ester (hydrazine or hydrazide compound / organic titanium acid ester) of 10 to 75. ..
First, various materials used in the method for producing strontium titanate fine particles of the present invention will be described.

(Organic titanium acid ester)
Examples of the organic titanium acid ester include tetraethyl titanate, tetraisopropyl titanate, tetranormal butyl titanate, butyl titanate dimer, tetra (2-ethylhexyl) titanate, and polymers thereof, titanium acetyl titanate, and polytitanium acetylacetonate. , Titanium octylglycinate, titanium lactate, titanium lactate ethyl ester, titanium triethanolaminate, titanium phosphate ester titanium complex and other titanium chelate compounds and the like.
Of these, titanium lactate is preferable from the viewpoint of hydrophilicity.

(Hydrazine or hydrazide compound)
Examples of the hydrazide compound include 1-monomethyl hydrazine, 1,1-dimethyl hydrazine, 1-ethyl-2-methyl hydrazine, adipic acid dihydrazide, dihydrazide oxalic acid, dihydrazide malonate, dihydrazide succinate, dihydrazide glutarate, and isophthalate. Examples thereof include acid dihydrazide, sebasic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, andaconic acid dihydrazide.
Of these, hydrazine is preferable because it is relatively easy to handle and has an excellent effect of controlling the shape of the obtained strontium titanate fine particles.
The hydrazine or hydrazide compound may be hydrogenated.

As for the content of the hydrazine or the hydrazide compound, the molar ratio (hydrazine or hydrazide compound / organic titanium acid ester) to the organic titanium acid ester is preferably 10 to 75, preferably 30 to 65.
Within the above range, the shape of the obtained strontium titanate fine particles can be controlled.

(Strontium compound)
Examples of the strontium compound include strontium nitrate, strontium hydroxide, strontium carbonate, strontium peroxide, strontium formate, strontium acetate, strontium lactate, strontium oxalate, strontium chloride, strontium fluoride, strontium iodide, strontium bromide, and chloric acid. Examples thereof include strontium, strontium iodate, and strontium perchlorate. These may be used as hydrates.
Among them, at least one selected from strontium acetate and strontium formate is preferable, and strontium acetate is more preferable, from the viewpoint of hydrophilicity.

As for the content of the strontium compound, the molar ratio (strontium compound / organic titanium acid ester) to the organic titanium acid ester is preferably 1.0 or more.
Within the above range, the progress of crystallization can be suitably controlled.
Further, from the viewpoint of reducing raw material costs, the molar ratio (strontium compound / organic titanium acid ester) is more preferably 2.0 or less.

(solvent)
Ion-exchanged water is preferably used as the solvent used in the method for producing strontium titanate fine particles of the present invention.
Moreover, it is preferable that the solvent contains a polyhydric alcohol.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, butanediol, pentanediol, hexanediol, heptanediol, nonanediol, decanediol, and neopentyl glycol. Examples thereof include dihydric alcohols and trihydric or higher polyhydric alcohols such as glycerin, trimethylolpropane, and pentaerythritol.
Among them, at least one selected from ethylene glycol, propylene glycol, diethylene glycol, and 1,3-propanediol from the viewpoint of adjusting the particle size of the obtained strontium titanate fine particles and maintaining suitable dispersibility in the reaction system. Is preferable, and ethylene glycol is more preferable.

The content of the polyhydric alcohol is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, and even more preferably 7 to 12% by mass with respect to the total amount of the solvent. ..

(PH regulator)
In the method for producing strontium titanate fine particles of the present invention, it is preferable to adjust the pH using a pH adjuster.
Examples of the pH adjuster include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide and the like.
Of these, potassium hydroxide is preferable from the viewpoint of solubility in the above solvent.

When adjusting the pH, the pH is set to 12 or more from the viewpoint of controlling the reaction rate and the shape of the obtained strontium titanate fine particles.
The pH is preferably 12.5 or higher, more preferably 13 or higher, and even more preferably 13.5 or higher.
The content of the pH adjuster is not limited and may be appropriately added according to the target pH.

(Aminosilane compound)
The reaction step is preferably carried out in the presence of the aminosilane compound.
By performing the above reaction step in the presence of the aminosilane compound, the average particle size of the obtained strontium titanate fine particles can be further reduced, and the dispersibility can be more preferably imparted.

Examples of the aminosilane compound include 3-aminopropyltrimethoxysilane, 3-aminopropylethoxysilane, N-2- (aminoethyl) -3-aminopropylmethyldimethoxysilane, and N-2- (aminoethyl) -3-aminopropyl. Examples thereof include trimethoxysilane and N-phenyl-3-aminopropyltrimethoxysilane.
Of these, 3-aminopropyltriethoxysilane is preferable.

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

(others)
In the method for producing strontium titanate fine particles of the present invention, it is not necessary to add an amphipathic compound.
In the conventional method for producing strontium titanate fine particles, the particle size and shape are highly controlled by advancing the reaction in the presence of an amphipathic compound, and the dispersibility of the particles is imparted.
On the other hand, in the method for producing strontium titanate fine particles of the present invention, when the above amphoteric compound is added, the particles are dispersed non-uniformly in the system, and as a result, the average particle size of the obtained strontium titanate fine particles is large. turn into.
Examples of the amphoteric compound include saturation of propionic acid, butyric acid, valeric acid, caproic acid, capric acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, linolenic acid and the like. Non-fatty acids, α-linolenic acid, stearidonic acid, eicosapentaenoic acid, docosahexaenoic acid, linolenic acid, γ-linolenic acid, dihomo-γ-linolenic acid, arachidonic acid, oleic acid, ellaic acid, erucic acid, nervonic acid, etc. Saturated fatty acids and the like can be mentioned.

(Production method)
The method for producing strontium titanate fine particles of the present invention comprises an organic strontium ester and a strontium compound under the conditions of a pH of 12 or more, a reaction temperature of 150 ° C. or higher and 250 ° C. or lower, and a reaction time of 0.5 hours or more and 2 hours or less. It has a reaction step of reacting with.
The method for producing strontium titanate fine particles of the present invention is, for example, a mixing step of mixing an organic titanium acid ester and a hydrazine or a hydrazide compound in a solvent to obtain a mixed solution, and adjusting the pH of the mixed solution to 12 or more. It is preferable to have an adjustment step and the above reaction step.

The mixing step is a step of adding an organic titanium acid ester and a hydrazine or a hydrazide compound to the solvent.
It is presumed that hydrazine is coordinated to the organic titanium acid ester by the above mixing step.
In the above mixing step, the method of adding various materials is not particularly limited, and addition, stirring and the like may be performed by a well-known method.

In the above preparation step, the pH is adjusted. Thereby, the reaction rate and the shape of the obtained strontium titanate fine particles can be suitably controlled.
Further, it is considered that the increase in the average particle size of the organic titanium acid ester coordinated with hydrazine can be controlled by the above mixing step, and as a result, the average particle size of the obtained strontium titanate fine particles can be controlled in a suitable range.
The pH is preferably adjusted using the above pH adjuster.
When the aminosilane compound is added, it is preferable to add it together with the pH adjusting agent in the adjusting step.

Crystal growth of strontium titanate fine particles becomes faster in the presence of a large amount of water, while when the hydrophobicity of the solvent becomes high, the surface of the strontium titanate fine particles is hydrophilic and promotes aggregation.
On the other hand, since the polyhydric alcohol has an effect of suppressing crystal growth while being hydrophilic, it is preferable to add it in the preparation step.
In the above preparation step, the method of adding various materials is not particularly limited, and addition, stirring and the like may be performed by a well-known method.

In the above reaction step, the organic titanic acid ester is reacted with the 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 hours or more and 2 hours or less.

The reaction temperature is 150 ° C. or higher and 250 ° C. or lower.
If the reaction temperature is less than 150 ° C., the reaction does not proceed and the desired strontium titanate fine particles cannot be obtained. If the reaction temperature exceeds 250 ° C., the reaction efficiency decreases and the obtained strontium titanate fine particles become large. And the dispersibility is reduced.
The reaction temperature is preferably 180 to 250 ° C, more preferably 200 to 240 ° C.

The reaction time is 0.5 hours or more and 2 hours or less.
If the reaction time is less than 0.5 hours, the reaction does not proceed and the desired strontium titanate fine particles cannot be obtained. If the reaction time exceeds 2 hours, the reaction efficiency is lowered and the obtained strontium titanate fine particles are obtained. Increases and the dispersibility decreases.
The reaction time is preferably 1 to 2 hours.

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

The method for carrying out the above reaction step is not particularly limited, and any method that satisfies the above conditions may be used.
For example, a pressure reaction vessel or the like can be used.

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

The strontium titanate fine particles preferably have a spherical particle shape.
Here, the spherical shape means not only a true sphere but also an elliptical shape, a cylinder shape, a bale shape (a shape in which the corners of the cylinder are rounded), and the like.
Specifically, it means that the circularity of the strontium titanate fine particles is 0.900 to 1.000.
The shape of the strontium titanate fine particles can be confirmed, for example, by observing with a transmission electron microscope (“JEM-1011” manufactured by JEOL Ltd.) at an observation magnification of 300,000 times.
Further, the circularity of the strontium titanate fine particles can be calculated by circularity = 4πS / L ² , where S is the area of the fine particles in the image taken by the transmission electron microscope and L is the peripheral length.
The circularity is an average value excluding those having a specific shape clearly different from the spherical shape among the fine particles appearing 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, and more preferably 14 nm to 25 nm.
By having such an average particle size, it is possible to have excellent dispersibility.
The average particle size is determined by dissolving strontium titanate fine particles in methanol to obtain a dispersion, then putting the obtained dispersion into a measuring cell, and using a laser diffraction / scattering particle size distribution measuring machine (manufactured by Nikkiso Co., Ltd.). , "Microtrack MT3300EXII") means the average particle size (D50).

The strontium titanate fine particles have excellent dispersibility.
Here, dispersibility means that 50 mg of strontium titanate fine particles are dissolved in 50 mL of methanol to obtain a dispersion, the obtained dispersion is placed in a screw tube bottle, and black paper is placed on the back surface to disperse the dispersion. When the state of the liquid is visually confirmed, it can be determined whether or not white turbidity occurs. When white turbidity does not occur, it can be evaluated as having excellent dispersibility, and can be suitably applied to, for example, a material having a high refractive index.

The strontium titanate fine particles preferably have good crystallinity.
The crystallinity of the strontium titanate fine particles is such that the crystallite size calculated by the X-ray diffractometer is the same as the particle size observed with the transmission electron microscope [the ratio of the particle size (with the transmission electron microscope). If the observed particle size / crystallite size calculated by the X-ray diffractometer) is 0.9 to 1.0], it is judged that the crystallinity is good, and if it is small or no crystal is confirmed, it is judged to be defective. ..

The strontium titanate fine particles preferably have a hydrazine or hydrazide compound content of 0.1% by mass to 60% by mass with respect to the strontium titanate fine particles.
With such a content, the dispersibility becomes good.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "part" means "part by mass".

The materials used in the examples and comparative examples are as follows.
(Organic titanium acid ester)
Titanium Lactate (Organic TC-310, component concentration 44 wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.)
Phosphoric acid ester titanium complex (Organic acid TC-1040, component concentration 75 wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.)
(Hydrazine or hydrazide compound)
Mizuka Hydrazine (manufactured by Nippon Carbide Industry Co., Ltd.)
(Strontium compound)
Strontium acetate 0.5 hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
Strontium formate dihydrate (solvent)
Ethylene glycol Propylene glycol purified water (ion-exchanged water)
(PH regulator)
Potassium hydroxide (aminosilane compound)
3-Aminopropyltriethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.)

(Example 1)
Add 3.0 g of purified water and 3.0 g of hydrated hydrazine (manufactured by Nippon Carbide Industries) to 0.584 g of titanium lactate (organic TC-310, component concentration 44 wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.) to make a yellow transparent solution. bottom.
Then, a solution prepared with 0.48 g of potassium hydroxide, 0.432 g of ethylene glycol, and 5.088 g of purified water was added to the above yellow transparent solution to obtain a cloudy solution.
Then, 0.429 g of strontium acetate 0.5 hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the obtained cloudy solution, and the mixture was 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.
Centrifugal separation treatment (model name SIGMA 3-30KS, condition 15000 rpm, 5 minutes) was performed on the solution containing the reaction product, and the fine particles were settled to separate and purify the unreacted product. Separation and purification was completed by repeating the operation of preparing a redispersion solution of the fine particles with purified water, centrifuging and precipitating the fine particles three times.
The obtained fine particles were collected and observed with an X-ray diffractometer (“MiniFlex600-C” manufactured by Rigaku Co., Ltd.). As a result, it was confirmed that the fine particles were strontium titanate.

(Examples 2 to 8, Comparative Examples 1 to 6)
Strontium titanate fine particles were produced in the same manner as in Examples except that the blending amounts of various materials and the reaction conditions were changed as shown in Table 1.
In Examples 5 and 6, 3-aminopropyltriethoxysilane was added together with the pH adjuster (potassium hydroxide).
The obtained fine particles were collected and observed with an X-ray diffractometer (“MiniFlex600-C” manufactured by Rigaku Co., Ltd.). As a result, they were fine particles of strontium titanate in Examples 2 to 8 and Comparative Example 4. It was confirmed.
On the other hand, in Comparative Examples 1 to 3, 5 and 6, the reaction did not proceed and strontium titanate fine particles could not be obtained.

<Evaluation method>
(Particle shape)
The fine particles obtained in Examples and Comparative Examples were collected and observed with a transmission electron microscope (“JEM-1011” manufactured by JEOL Ltd.) at an observation magnification of 300,000 times to confirm the particle shape.
The confirmed fine particles having a circularity of 0.900 to 1.000 were evaluated as spherical.

(crystalline)
The fine particles obtained in Examples and Comparative Examples were observed with a transmission electron microscope (“JEM-1011” manufactured by JEOL Ltd.) and an X-ray diffractometer (“MiniFlex600-C” manufactured by Rigaku Ltd.), and the following were observed. Evaluated by criteria.
〇: The ratio of the crystallite diameter calculated by the X-ray diffractometer to the particle diameter observed by the transmission electron microscope is 0.9 to 1.0.
Δ: The ratio of the crystallite diameter calculated by the X-ray diffractometer to the particle diameter observed by the transmission electron microscope is less than 0.9 ×: No crystals are formed.

(Average particle size)
50 mg of the fine particles obtained in Examples and Comparative Examples were dissolved in 50 mL of methanol to obtain a dispersion.
The obtained dispersion was placed in a measuring cell, and the average particle size (D50) was measured with a laser diffraction / scattering type particle size distribution measuring machine (“Microtrack MT3300EXII” manufactured by Nikkiso Co., Ltd.).

(Dispersity)
50 mg of the fine particles obtained in Examples and Comparative Examples were dissolved in 50 mL of methanol to obtain a dispersion.
The obtained dispersion was placed in a screw tube bottle, black paper was placed on the back surface, and the state of the dispersion was visually confirmed and evaluated according to the following criteria.
〇: The obtained dispersion was a transparent solution.
X: The obtained dispersion was a cloudy solution.

It was confirmed that the strontium titanate fine particles obtained in the examples had a spherical particle shape and an average particle diameter of 14 nm to 30 nm, and were excellent in crystallinity and dispersibility.
In particular, in Examples 5 and 6 to which 3-aminopropyltriethoxysilane was added, strontium titanate fine particles having a small average particle size and excellent dispersibility could be obtained.
In Example 7 using the phosphoric acid 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 was higher than that of the other examples. The result was that the dispersibility was slightly low.
On the other hand, in Comparative Examples 1 to 3, 5 and 6, the reaction did not proceed and strontium titanate fine particles could not be obtained.
Further, the fine particles obtained in Comparative Examples 1 to 3 which did not contain hydrazine or a hydrazide compound or whose addition amount was not in the predetermined range had a large average particle size and were inferior in dispersibility (the dispersion liquid became cloudy). Was).
Further, the strontium titanate fine particles obtained in Comparative Example 4 in which the reaction temperature was not in 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 size and were inferior in dispersibility (the dispersion liquid 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 could not be obtained.

The method for producing strontium titanate fine particles of the present invention is, for example, a high refractive index agent, a thermoelectric conversion material, a photocatalyst, an ionic conductive material, a dielectric material, a magnetic material, a catalyst material, an oxygen electrode material, a piezoelectric material, and a pyroelectricity. It is useful in that it is possible to obtain strontium titanate fine particles that can be used as functional materials such as materials, nonlinear optical materials, and fillers.

Claims (8)

In the presence of hydrazine or hydrazide compound, the conditions are such that 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 hours or more and 2 hours or less.
It has a reaction step of reacting an organic titanium acid ester with a strontium compound, and has a reaction step.
A method for producing strontium titanate fine particles, wherein the molar ratio of the hydrazine or the hydrazide compound to the organic titanium acid ester (hydrazine or hydrazide compound / organic titanium acid ester) is 10 to 75. The first aspect of the present invention has a mixing step of mixing an organic titanium acid ester and a hydrazine or a hydrazide compound in a solvent to obtain a mixed solution, an adjusting step of adjusting the pH of the mixed solution to 12 or more, and the reaction step. The method for producing strontium titanate fine particles according to the above method. The method for producing strontium titanate fine particles according to claim 1 or 2, wherein the reaction step is performed in the presence of a polyhydric alcohol. The method for producing strontium titanate fine particles according to claim 3, wherein the polyhydric alcohol is ethylene glycol. The method for producing strontium titanate fine particles according to any one of claims 1 to 4, wherein the organic titanium acid ester is titanium lactate. The method for producing strontium titanate fine 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 strontium titanate fine particles according to any one of claims 1 to 6, wherein the reaction step is carried out in the presence of an aminosilane compound. The method for producing strontium titanate fine particles according to claim 7, wherein the aminosilane compound is 3-aminopropyltriethoxysilane.