WO2015122180A4

WO2015122180A4 - Manufacturing method for strontium titanate fine particles

Info

Publication number: WO2015122180A4
Application number: PCT/JP2015/000617
Authority: WO
Inventors: 佐々木　勉; 田中　淳; 鈴木　真之; 阿尻　雅文
Original assignee: 富士フイルム株式会社; 国立大学法人東北大学
Priority date: 2014-02-14
Filing date: 2015-02-10
Publication date: 2015-10-01
Also published as: WO2015122180A1; JP2015151303A; JP6065286B2

Abstract

[Problem] To manufacture perovskite-phase strontium titanate fine particles in low alkali conditions. [Solution] Strontium titanate fine particles are manufactured by performing the following steps: step A1, in which an Sr-containing aqueous solution and a Ti-containing aqueous solution are prepared; step B1, in which the Sr-containing aqueous solution and the Ti-containing aqueous solution are mixed to prepare a mixed solution; step C1, in which a basic substance is added to the mixed solution to adjust the pH of the mixed solution so as to be greater than 10, and a reaction solution is prepared; and step D1 in which the reaction solution is subjected to a hydrothermal reaction at a temperature of at least 250℃, or a sub-critical or super-critical reaction. If the pH of the reaction solution to be prepared in step C1 is taken as X, and the reaction temperature of the reaction solution in step D1 is taken as Y, X and Y satisfy Y>-100X+1400, and X≥10, and Y≥250.

Description

Method for producing strontium titanate fine particles

The present invention relates to a method for producing strontium titanate particles suitable as a mother catalyst for dielectric materials and photocatalysts.

Strontium titanate is one of the materials having many excellent physical properties such as dielectric properties, thermoelectric properties, and high refractive index as an optical material. In addition, from the viewpoint of energy and environmental problems in recent years, strontium titanate (SrTiO ₃ ) particles formed by supporting a metal such as platinum on the surface as a co-catalyst is one of those being developed as a hydrogen generation photocatalyst. Can be mentioned.

From the high stability under light irradiation and the strength of photoreduction power, SrTiO ₃ is expected to be a photocatalyst that enables hydrogen production using only sunlight. In such a hydrogen generation photocatalyst, the strontium titanate particles serving as a mother catalyst are required to have optimum particle size and shape and high crystallinity in order to be able to support the cocatalyst with a larger surface area. There is.

There are solid phase method, flux method, sol-gel method, hydrothermal synthesis method etc. in the manufacturing method of strontium titanate particles, but hydrothermal synthesis method is a method which can synthesize fine particles of submicron or less It has been known.

Patent Documents 1 to 10 describe a method of producing titanium oxide particles or fine powder by hydrothermal synthesis.

Patent Documents

8, 9 and 10 disclose methods of producing titanate oxide particles by subcritical or supercritical synthesis.

As described in Patent Documents 1 to 10, in order to synthesize titanic acid oxide particles or fine powder with good crystallinity by hydrothermal or subcritical, supercritical synthesis, the pH is as strong as more than 13.5. It is necessary to carry out under alkaline conditions. Some of these documents do not mention pH conditions, and some documents mention that they can be produced under lower alkaline conditions, but any of them can be produced as far as production is reported in the examples. The pH is manufactured through strongly alkaline conditions of more than 13.5. In particular, synthesis of strontium titanate particles has only been reported as an example of preparation under conditions of pH 14 or higher.

For example, Patent Document 6 discloses, as a method for producing a single phase titanium-containing perovskite oxide at low temperature and pressure, a method of hydrothermally synthesizing in an aqueous solution of an alkali metal hydroxide of 10 molar concentration or more. It is done. Although Patent Document 4 states that it is preferable to use an aqueous solution of barium hydroxide having a pH of 7 to 10 in the third step, the third step is a re-hydrothermal treatment, and the second step for performing hydrothermal synthesis is As described in Example 1, it is carried out under strongly alkaline conditions of pH 13.5 or more. In patent document 7, it implements by two-step heating, and the process is complicated. In addition, it is stated that it is desirable that pH> 10 for mixed solution, but there is no description of clear pH at the time of synthesis, and it is presumed that it is strongly alkaline because there is much ammonia water introduced. .

Japanese Examined Patent Publication 3-39016 Japanese Examined Patent Publication No. 6-649 Japanese Examined Patent Publication No. 2-46531 Patent No. 3838523 gazette Unexamined-Japanese-Patent No. 6-322587 Japanese Patent Application Publication No. 2007-31176 Tokuhei 8-32559 Patent No. 3663408 Patent No. 4593124 Japanese Patent Application Publication No. 2003-261329

In order to perform hydrothermal synthesis, subcritical synthesis, or supercritical synthesis under strongly alkaline conditions such as exceeding pH 13.5, alkali resistance in the reaction vessel is essential. As a reaction container having alkali resistance, ones made of Teflon (registered trademark) or those made of Hastelloy (registered trademark) are known, however, those made of Teflon (registered trademark) have limited heat resistance, so the reaction temperature is There is a limit and there is a problem that the product made of Hastelloy (registered trademark) is very expensive, resulting in high equipment cost. From the viewpoints of heat resistance and equipment cost, it is preferable that a reaction container made of SUS etc., which is excellent in heat resistance, is highly versatile and inexpensive, can be used as a reaction container, and for that purpose It is preferable to be able to manufacture on conditions.

The present invention has been made in view of the above circumstances, and an object thereof is to produce perovskite-type strontium titanate fine particles under low alkaline conditions.

The first production method of the strontium titanate fine particles of the present invention is
Preparing a Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Preparing the mixed solution by mixing the prepared Sr-containing aqueous solution with the Ti-containing aqueous solution, B1;
Preparing a reaction solution by adding a basic substance to the mixed solution to adjust the pH to prepare a reaction solution;
The reaction liquid has a hydrothermal reaction or a subcritical reaction or a supercritical reaction at a temperature of 250 ° C. or higher, and a step D1. In the first production method, when the pH of the reaction solution prepared in step C1 is X and the reaction temperature of the reaction solution in step D1 is Y, X and Y satisfy Y> -100X + 1400, and X ≧ 10. And YY250 is satisfied.

As used herein, "reacting the reaction solution" means reacting one or more components contained in the reaction solution.

Further, in the present specification, the term "fine particles" shall mean those having a size of less than 10 μm in average particle size, preferably nanoparticles. The nanoparticles may generally refer to those having an average particle size of 200 nm or less, preferably 200 nm or less. In some cases, the nanoparticles may be of a size with an average particle size of 100 nm or less, and in other cases with a size of 50 nm or less. Also preferably, the nanoparticles are of a size whose average particle size is 20 nm or less, and in other cases whose average particle size is 10 nm or less or 5 nm or less You may Also, in a preferred case, the particle size of the nanoparticles is preferably uniform, but in some cases, it may be preferable to mix particles having different particle sizes at a certain ratio.

The average particle size can be measured by a method known in the art, and can be measured by, for example, an electron microscope (TEM, SEM), an adsorption method, a light scattering method, X-ray small angle scattering (SAXS) or the like. In electron microscopy, when the particle size distribution is wide, it is necessary to pay attention to whether or not the particles within the field of view represent all particles.

In the present specification, water above the critical point of water (temperature 374 ° C., pressure 22 MPa) is supercritical water, and water at a temperature near 350 ° C. near critical point is subcritical water The reaction in supercritical water is a supercritical reaction, and the reaction in subcritical water is a subcritical reaction.

In the first production method, X, which is the pH of the reaction solution prepared in step C1, preferably satisfies X ≧ 11, more preferably 11 ≦ X ≦ 13.5, and 11 ≦ X. It is further preferable to satisfy ≦ 12.

In the present invention, in the case of producing strontium titanate fine particles under a low alkaline condition having a pH closer to neutrality, the second method for producing a strontium titanate fine particle of the present invention shown below can be applied.

The second production method of the strontium titanate fine particles of the present invention comprises a step A2 of preparing an Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Step B2 of mixing the prepared Sr-containing aqueous solution with the Ti-containing aqueous solution to prepare a mixed solution in which the molar ratio Sr / Ti of the contained Sr component and Ti component is more than 1.0.
A basic substance is added to the mixed solution to adjust the pH of the mixed solution to prepare a reaction solution C2.
The reaction liquid has a hydrothermal reaction or a subcritical reaction or a supercritical reaction at a temperature of 250 ° C. or higher. In the second production method, when the pH of the reaction solution prepared in step C2 is X and the reaction temperature of the reaction solution in step D2 is Y, X and Y satisfy YY−500 × + 5150, and X ≧ 9. And YY250 is satisfied.

In the second production method, X, which is the pH of the reaction solution prepared in step C2, preferably satisfies 9 ≦ X ≦ 13.5, and more preferably 9 ≦ X ≦ 12.
In step B2, it is preferable to mix the Sr-containing aqueous solution and the Ti-containing aqueous solution so that the molar ratio Sr / Ti of the Sr component and the Ti component contained in the mixed solution is 1.3 or more.

In the first production method and the second production method, the Ti-containing aqueous solution used in the step of preparing the mixed solution (step B1 and step B2) preferably does not contain TiO ₂ as a main component of the Ti component. .
In the present specification, the "main component" means a component having a content of 50% by mass or more.

In the steps of preparing the Sr-containing aqueous solution and the Ti-containing aqueous solution (steps A1 and A2), it is preferable that the Sr-containing aqueous solution be prepared by dissolving strontium acetate or hydroxide or nitrate in water, The Ti-containing aqueous solution is preferably a titanium tetrachloride aqueous solution.

In the step of preparing the reaction liquid by adjusting the pH of the mixed solution (Step C1, Step C2), a reaction liquid containing Ti (OH) ₄ and / or HTiO ₃ ^- ion as a main component of Ti component is prepared Is preferred. Moreover, as a basic aqueous solution used for adjustment of pH, sodium hydroxide aqueous solution or potassium hydroxide aqueous solution is preferable. In addition, in the step of adjusting the pH of the mixed solution to prepare a reaction solution, it is preferable to grind solids generated during the adjustment of pH.

According to the present invention, perovskite-type strontium titanate fine particles can be produced by a hydrothermal reaction, a subcritical reaction or a supercritical reaction under a condition of alkali lower than neutrality. Moreover, highly crystalline strontium titanate fine particles can be produced by using a Ti-containing aqueous solution to be mixed with a Sr-containing aqueous solution that does not contain TiO ₂ as a main component of the Ti component.

Flow chart of the method for producing strontium titanate fine particles of the present invention The figure which shows the availability of manufacture of the perovskite type strontium titanate microparticles | fine-particles in pH condition of Example 1 (1st manufacturing method) and the comparative example 1, and the temperature condition of hydrothermal reaction. The figure which shows the availability of manufacture of the perovskite type strontium titanate microparticles | fine-particles in pH condition of Example 2 (2nd manufacturing method) and the comparative example 2, and the temperature condition of hydrothermal reaction. The figure which shows the XRD spectrum of the strontium titanate microparticles | fine-particles obtained by supercritical reaction in Example 1 (1st manufacturing method) The figure which shows the XRD spectrum of strontium titanate microparticles | fine-particles obtained by adjusting pH of the reaction liquid to 12 in Example 1 (1st manufacturing method), a subcritical reaction, and a supercritical reaction. The figure which shows the XRD spectrum of strontium titanate microparticles | fine-particles obtained by adjusting pH of the reaction liquid to 11 in Example 1 (1st manufacturing method), a subcritical reaction, and a supercritical reaction. The figure which shows the XRD spectrum of the strontium titanate microparticles | fine-particles obtained by supercritical reaction in Example 2 (2nd manufacturing method) The figure which shows the XRD spectrum of the strontium titanate microparticles | fine-particles obtained by adjusting pH of the reaction liquid to 11 in Example 2 (2nd manufacturing method), or a hydrothermal reaction or a supercritical reaction. The figure which shows the XRD spectrum of the strontium titanate microparticles | fine-particles obtained by adjusting pH of the reaction liquid to 11.5 in Example 2 (2nd manufacturing method), or a hydrothermal reaction or a supercritical reaction. The figure which shows the XRD spectrum of the strontium titanate microparticles | fine-particles obtained by adjusting pH of the reaction liquid to 9 in Example 2 (2nd manufacturing method), or a hydrothermal method or a supercritical reaction.

"Production method of strontium titanate fine particles"
With reference to the drawings, a method of manufacturing strontium titanate particles according to an embodiment of the present invention will be described. FIG. 1 shows a flow diagram of the method for producing strontium titanate fine particles of the present embodiment.

As described above, in order to synthesize fine particles or fine powder of perovskite-type titanium oxide with good crystallinity by hydrothermal reaction, subcritical reaction, or supercritical reaction, a strong alkaline condition having a pH of more than 13.5. It is considered to be technical common sense to carry out. As described in Patent Document 10, in the synthesis of a perovskite-type titanium oxide by a hydrothermal reaction, titanium dioxide is used as an intermediate product, so the reaction solution is used as a strongly alkaline condition to increase the solubility of titanium dioxide to perform the reaction. Nonpolar Perovskite by setting the temperature so that titanium dioxide is hard to precipitate in it and raising the temperature rapidly in that state to make it a subcritical reaction or supercritical reaction near the critical point where water becomes a nonpolar gas state The barium titanate fine particles having a high degree of crystallinity not containing crystal water or hydroxyl groups can be relatively low temperature and short time by remarkably increasing the formation rate of the crystalline titanium oxide and greatly reducing the concentration of dissolved ions. And it is possible to manufacture efficiently.

In the synthesis of strontium titanate fine particles by a hydrothermal reaction, a subcritical reaction, or a supercritical reaction, the present inventors proceed with the synthesis by suppressing the precipitation of titanium dioxide as an intermediate product without using strong alkaline conditions. We made a keen study on the method.

The inventors focused on the instability of the Ti-containing aqueous solution and focused on the potential-pH diagram of Ti. According to the potential-pH diagram of Ti, at room temperature (25 ° C.), Ti is not in the ion dissociation state but in the hydrate of titanium dioxide (TiO ₂ · H ₂ O) in a weak acid to a weak alkaline environment of less than pH 12. Due to its stability, it is considered that, at room temperature, conversion to titanium dioxide hydrate starts shortly after preparation of the Ti-containing aqueous solution when in a weak acid to a weak alkaline environment of less than pH 12.
On the other hand, in an alkaline environment at a pH of 12 or more, Ti is considered to be in the form of Ti hydroxide (Ti (OH) ₄ ) or HTiO ₃ ⁻ from the potential-pH diagram. Therefore, in a strong alkaline environment, it is considered that the aqueous solution state can be maintained without precipitation of titanium dioxide.

The inventor infers that the factor for obtaining a perovskite oxide with good crystallinity in a strong alkaline environment is in the state of Ti in water under a strong alkaline environment, and as a reaction site for hydrothermal synthesis, By using a reaction liquid in which Ti in the liquid maintains Ti (OH) ₄ or HTiO ₃ ^- ion state, it is considered that not only in a strongly alkaline environment, but also a perovskite oxide with good crystallinity can be produced.

In addition, after preparing the Ti-containing aqueous solution, the present inventors start to change to titanium dioxide hydrate due to temporal changes such as ultraviolet light and temperature conditions after the Ti ion in the aqueous solution, and then white crystals of titanium dioxide start to precipitate. Have confirmed that. Then, the crystal structure of titanium dioxide formed at this stage is mainly rutile type, and once crystals of rutile type nonuniform and large in particle diameter are precipitated, production of strontium titanate fine particles with uniform crystallinity is good. Confirmed that it was difficult.

As a result, if the skeleton formation or precipitation of large size titanium dioxide can be minimized at the stage of mixing the strontium-containing aqueous solution and the titanium-containing aqueous solution, good crystallinity can be obtained without using strong alkaline conditions. It suggests that strontium titanate can be produced.

The inventors of the present invention have been able to obtain titanium dioxide having a large size in the mixed solution by mixing the Ti-containing aqueous solution with the Sr-containing aqueous solution while maintaining the state immediately after preparation under the condition that the pH of the reaction solution to be hydrothermally reacted is 11 or more. It has been found that skeletal formation or precipitation can be substantially suppressed, and strontium titanate having high crystallinity can be synthesized by a subsequent hydrothermal reaction, subcritical reaction, or supercritical reaction (see Example 1 below).

Further, in order to set the condition of pH 10 or more to less than 12 close to neutrality, where the stability of the hydrate of titanium dioxide is high, the inventor kept the state immediately after preparation of the Ti-containing aqueous solution with the Sr-containing aqueous solution. In addition to mixing, it has been found that it is necessary to cause a supercritical reaction in a Sr-rich state in which the amount of Sr in the reaction liquid is larger than the number of moles of the amount of Ti. Under Sr-rich conditions, strontium titanate fine particles can be synthesized by hydrothermal, subcritical, and supercritical reactions even in a pH range of 12 or more.

In the supercritical reaction beyond the critical point, the ions are destabilized because the water is in a nonpolar gas state, and the equilibrium of the metal salt aqueous solution is from the ion dissociation state to the hydroxide side and further to the oxide side. Shift very fast. In addition, in the presence of Ti ions, Sr is presumed to be more stable than strontium hydroxide and hydroxide, and it is possible to rapidly make a hydrothermal reaction by forming an Sr-rich environment in the reaction liquid. In this case, fine crystalline strontium titanate fine particles with less heterophase can be produced (see Examples below).

That is, according to the first method for producing strontium titanate fine particles of the present invention,
Preparing a Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Preparing the mixed solution by mixing the prepared Sr-containing aqueous solution with the Ti-containing aqueous solution, B1;
Preparing a reaction solution by adding a basic substance to the mixed solution to adjust the pH to prepare a reaction solution;
The reaction liquid has a hydrothermal reaction or a subcritical reaction or a supercritical reaction at a temperature of 250 ° C. or higher, and a step D1. In the first production method, when the pH of the reaction solution prepared in step C1 is X and the reaction temperature of the reaction solution in step D1 is Y, X and Y satisfy Y> -100X + 1400, and X ≧ 10. And YY250 is satisfied.

The second method for producing strontium titanate fine particles of the present invention comprises a step A2 of preparing an Sr-containing aqueous solution and a Ti-containing aqueous solution, and
Step B2 of mixing the prepared Sr-containing aqueous solution with the Ti-containing aqueous solution to prepare a mixed solution in which the molar ratio Sr / Ti of the contained Sr component and Ti component is more than 1.0.
A basic substance is added to the mixed solution to adjust the pH of the mixed solution to prepare a reaction solution C2.
The reaction liquid has a hydrothermal reaction or a subcritical reaction or a supercritical reaction at a temperature of 250 ° C. or higher. In the second production method, when the pH of the reaction solution prepared in step C2 is X and the reaction temperature of the reaction solution in step D2 is Y, X and Y satisfy YY−500 × + 5150, and X ≧ 9. And YY250 is satisfied.

Each step will be described below with reference to FIG.

<Step (A1, A2)>
Both step A1 and step A2 are steps for preparing an Sr-containing aqueous solution and a Ti-containing aqueous solution, respectively.
The aqueous solution containing Sr is not particularly limited, but hydroxides of Sr, oxides, chlorides, fluorides, halides such as iodide, inorganic salts such as nitrates, carbonates, sulfates, acetates, oxalic acid A salt, an organic acid salt such as a lactic acid salt, etc. may be dissolved in water, and an acetate, a hydroxide or a nitrate may be dissolved in water.

The method for preparing the Sr-containing aqueous solution is not particularly limited, and any known method depending on the substance can be adopted as appropriate.

The aqueous solution containing Ti is not particularly limited, but hydroxides of Ti, oxides, chlorides, fluorides, halides such as iodide, inorganic salts such as nitrates, carbonates, sulfates, acetates, oxalic acid A salt, an organic acid salt such as lactic acid salt and the like dissolved in water may be mentioned, and titanium tetrachloride which is a chloride is preferable.
The method for preparing the Ti-containing aqueous solution is not particularly limited, and any known method depending on the substance can be appropriately adopted.

Further, although the details will be described in the description of the next step, since it is preferable to use an aqueous solution in which the state immediately after preparation is maintained in the next step, the Ti-containing aqueous solution does not carry out the next step B1 or B2 immediately after preparation. Immediately after preparation, in order to maintain the condition immediately after preparation, store the product in a light-shielded, refrigerated or frozen state.

<Step (B1, B2)>
Steps B1 and B2 are both steps of mixing the Sr-containing aqueous solution and the Ti-containing aqueous solution prepared in steps A1 and A2. The Ti-containing aqueous solution to be mixed with the Sr-containing aqueous solution in the step B1 or the step B2 preferably does not contain TiO ₂ as a main component of the Ti component.

As described above, the Ti-containing aqueous solution is considered to cause a change to the hydrate of titanium dioxide soon after preparation under conditions other than a strong alkaline environment of pH 12 or more at room temperature. Under other conditions of temperature and pH, the presence or absence and the rate of the change are considered to be different, so under the conditions where it is difficult to change titanium dioxide into hydrate, the mixed solution of the next step is not necessarily immediately after preparation. Although it is not necessary to carry out the preparation, if the mixed solution of the next step is prepared immediately after the preparation of the Ti-containing aqueous solution, the temperature condition and the pH condition can be achieved by carrying out the later steps. Regardless, it is possible to form strontium titanate particles with low crystallinity.
Therefore, it is preferable to carry out step B1 or B2 using the Ti-containing aqueous solution immediately after preparation of the Ti-containing aqueous solution or otherwise using the Ti-containing aqueous solution stored in a light-shielded refrigerated state or frozen immediately after preparation.

In step B1 of the first production method, the Ti-containing aqueous solution and the Sr-containing aqueous solution are used so that the molar ratio Sr / Ti of Sr component and Ti component in the mixed solution can be 1 which can form a normal stoichiometric composition. (There is no problem even if it deviates from 1 within the range in which the perovskite type can be formed in technical common sense).

As described above, in the formation of the perovskite type under lower alkaline conditions in the hydrothermal reaction, subcritical reaction, and supercritical reaction, the molar ratio Sr / Ti in the mixed solution is usually Sr / Ti in the mixed solution. The stoichiometric composition needs to be larger than 1 and preferably 1.3 or more, and more preferably 1.3 or more and 1.7 or less. Therefore, in step B2 of the second production method, the Ti-containing aqueous solution and the Sr-containing aqueous solution may be mixed so that the molar ratio Sr / Ti of the Sr component and the Ti component in the mixed solution is more than one.

In the steps B1 and B2, from the viewpoint of minimizing the formation of precipitates in the mixed solution during the preparation of the mixed solution, it is preferable to thoroughly stir during the steps B1 and B2. Moreover, it is more preferable to implement stirring until immediately before the next step C1 or C2 is performed.

<Step (C1, C2), Step (D1, D2)>
In steps C1 and C2, a basic substance is added to the mixed solution prepared in steps B1 and B2, and the pH of the mixed solution is adjusted to be the conditions for performing the next step D1 or D2 to prepare a reaction liquid It is a process.
Steps D1 and D2 are steps of synthesizing strontium titanate fine particles by performing a hydrothermal reaction or a subcritical or supercritical reaction using the reaction solution prepared in steps C1 and C2.

As the pH of the mixed solution in steps C1 and C2 is higher in the reaction temperature of the next step, steps D1 and D2, it becomes easy to be able to produce perovskite-type strontium titanate fine particles even under low alkaline conditions.

FIG. 2 plots the data of Examples and Comparative Examples described later, with the pH of the mixed solution adjusted in Step C1 as the abscissa and the reaction temperature of Step D1 as the ordinate.
Moreover, FIG. 3 plots pH of the mixed solution adjusted in step C2 as the abscissa and the reaction temperature of step D2 as the ordinate, and plots data of Examples and Comparative Examples described later.

As shown in FIG. 2, in the case of Sr / Ti = 1 (first production method) in the mixed solution, within the region divided by the long broken line in FIG. 2 (not including Y = −100 × + 1400), That is, when the pH of the reaction solution prepared in step C1 is X (horizontal axis) and the reaction temperature of the reaction solution in step D1 is Y (vertical axis), X and Y satisfy Y> -100X + 1400, and In the region satisfying X ≧ 10 and Y ≧ 250, strontium titanate fine particles having a perovskite structure can be produced.

It is shown in FIG. 2 that X, which is the pH of the mixed solution, is preferably 11 or more, and more preferably 12 or more.

In addition, as shown in FIG. 3, in the case of Sr / Ti> 1 (second production method) in the mixed solution, it is prepared in the region divided by the long broken line in FIG. 3, that is, in step C2. Assuming that the pH of the reaction solution is X (horizontal axis) and the reaction temperature of the reaction solution in step D2 is Y (vertical axis), X and Y are Y ≧ −500 × + 1400 and X ≧ 9 and Y 且つIn the region satisfying 250, strontium titanate fine particles having a perovskite structure can be produced.

It is shown in FIG. 3 that X, which is the pH of the mixed solution, preferably satisfies 9 ≦ X ≦ 13.5, and more preferably 9 ≦ X ≦ 12.

In the second production method, the pH of the hydrate of titanium dioxide hydrate is lower than that of low alkali by the hydrothermal reaction, subcritical reaction or supercritical reaction of the reaction liquid in Sr-rich conditions. Under the conditions, strontium titanate fine particles with good crystallinity can be produced. In the second production method, in the synthesis under low alkaline conditions of pH 9 or more and 12 or less, the supercritical reaction is most effective.

As described above, in the first and second manufacturing methods, the steps C1 and C2 and the steps D1 and D2 are performed as the X value and the Y value in the regions shown in FIGS. 2 and 3, respectively. A reaction liquid containing Ti (OH) ₄ and / or HTiO ₃ ⁻ ion as a main component of Ti component is prepared in C 1 or step C 2, and perovskite type strontium titanate fine particles are synthesized in step D 1 or D 2 be able to.

The basic aqueous solution used in the steps C1 and C2 is not particularly limited, but an ionization degree of 0.8 or more is desirable, and it is preferable to use a strong base near one. As such a basic aqueous solution, a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is preferably exemplified.

The dropwise addition of the basic aqueous solution is preferably carefully added drop by drop. There is no problem in producing such precipitates, but if the variation in the size of the precipitates is large or if the precipitates themselves are large in units of milli units or more even if the variation is small, the crystallinity is good at the end of the next step It is presumed that the yield of strontium titanate is likely to be low. Therefore, when a precipitate is produced, it is preferable to carry out stirring or grinding so as to be as fine as possible. The means for stirring or pulverizing is not particularly limited, and may be carried out manually using a stirring rod or the like, or may be dispersed by a stirrer or ultrasonic treatment.

In the steps D1 and D2, the reaction time can be appropriately set according to the temperature condition and the pH condition, and further whether or not it is a supercritical reaction. In addition, under the conditions of 250 ° C. or higher, hydrothermal synthesis is usually synthesis under pressure.
As described above, strontium titanate fine particles can be obtained.

According to the first production method and the second production method, it is possible to produce strontium titanate fine particles of good crystallinity by hydrothermal reaction, subcritical reaction, or supercritical reaction under low alkali conditions. . Moreover, highly crystalline strontium titanate fine particles can be produced by using a Ti-containing aqueous solution to be mixed with a Sr-containing aqueous solution that does not contain TiO ₂ as a main component of the Ti component.

"Design changes"
The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the scope of the present invention.

Example 1
First, a required amount of purified water was collected as an Sr-containing aqueous solution, and weighed with strontium nitrate to prepare a strontium nitrate aqueous solution. Moreover, titanium tetrachloride aqueous solution was prepared as Ti containing aqueous solution. Ampoule-like TiCl ₄ is slowly added dropwise to purified water. At that time, it is carried out with stirring and cooling, and immediately after adjustment to the designated concentration, it is shielded from light and stored refrigerated. As a solvent water, purified water was used unless otherwise stated.
The aqueous solution of titanium tetrachloride was shielded from light, and immediately after preparation, it was stored in a refrigerator to maintain the state immediately after preparation, and then mixed with an aqueous solution of strontium nitrate to obtain a mixed solution. At the time of mixing, the molar ratio Sr / Ti of the Sr component to the Ti component in the mixed solution was mixed so as to be 1.

Next, the mixed solution was stored in a beaker, and the aqueous solution of potassium hydroxide was dropped into the mixed solution one by one to adjust the pH of the mixed solution. Immediately after the addition of the aqueous potassium hydroxide solution, a gel-like white precipitate was produced, and the pH of the mixed solution was 7, 10, 11, 1.5, 12, 13.5 while stirring and grinding the precipitate. The respective reaction solutions were prepared.

The reaction solution of each pH thus obtained was subjected to a hydrothermal reaction, a subcritical reaction or a supercritical reaction in the range of 200 ° C. to 400 ° C. to carry out synthesis of strontium titanate fine particles. The reaction conditions are shown in Table 1.
According to each temperature, the reaction solution is put into a designated volume of Hastelloy (registered trademark) container (made by AKICO) having an inner volume of about 5 cm ³ , and it is sealed in a stainless steel pressure container. The reaction was carried out for 10 minutes under the temperature conditions described in Table 1 and a pressure of 30 MPa, and then quenched.

About the evaluation result of crystallinity of the obtained strontium titanate microparticles | fine-particles, it shows in Table 1 and FIG. The evaluation of crystallinity was evaluated by a powder X-ray diffraction measurement (XRD) apparatus (RINT 2000 manufactured by RIGAKU).
In Table 1 and FIG. 2, the evaluation results of crystallinity are shown by symbols. In Table 1 and FIG. 2, .circle-solid. Indicates the perovskite phase, .tangle-solidup. Indicates the perovskite phase but the heterophase / amorphous is mixed, and x indicates the heterophase or amorphous.

Representative XRD spectra are shown in FIGS. FIG. 4 compares the XRD spectra of the strontium titanate fine particles obtained at four pHs in the case of the supercritical reaction, and FIG. 5 shows the temperatures of 300 ° C. and 350 ° C. at the pH 12 (subcritical) 6) compares the XRD spectra of the strontium titanate fine particles obtained at 400 ° C. (supercritical), FIG. 6 shows the result at 300 ° C., 350 ° C. (subcritical) and 400 ° C. (supercritical) when pH 11 is used The XRD spectrum of the obtained strontium titanate fine particles is compared. FIG. 4 also shows the XRD spectrum of the strontium titanate fine particles synthesized at pH 7 for comparison.

FIG. 4 shows that a perovskite phase is obtained at pH 12 and 13.5 under supercritical conditions. In addition, although mixing of a different phase is slightly confirmed at pH 11, it is considered that fine particles having a main perovskite phase are obtained as compared with the XRD spectrum at pH 7 in which the different phase is the main.

In FIG. 5, it is confirmed that the perovskite phase is obtained at 300 ° C., 350 ° C. (subcritical) and 400 ° C. (supercritical) under conditions of pH 12. In FIG. 6, it is confirmed that the perovskite phase is obtained at 400 ° C. (supercritical) and 350 ° C. (subcritical) under the condition of pH 11, but it becomes amorphous at 300 ° C. (subcritical).

(Example 2)
A mixed solution was prepared in the same manner as Example 1, except that the molar ratio Sr / Ti of Sr component to Ti component in the mixed solution was set to 1.3 or more.
Next, the pH of the mixed solution was adjusted in the same manner as in Example 1. Immediately after the addition of the aqueous potassium hydroxide solution, a gel-like white precipitate was produced, and the pH of the mixed solution was 7, 9, 10, 11, 11.5, 12, 13 while stirring and crushing the precipitate. .5 were prepared respectively.

The reaction solution of each pH thus obtained is subjected to a hydrothermal reaction, a subcritical reaction or a supercritical reaction in the range of 250 ° C. to 400 ° C. to obtain strontium titanate fine particles in the same manner as in Example 1. The synthesis was performed. The reaction conditions are shown in Table 2.

The evaluation results of the crystallinity of the strontium titanate fine particles obtained in the synthesis are shown in Table 2 and FIG. About the display of the evaluation result of Table 2 and FIG. 3, it is the same as that of Example 1. FIG.

Representative XRD spectra are shown in FIGS. 7-10. FIG. 7 compares the XRD spectra of the strontium titanate fine particles obtained at two pHs in the case of the supercritical reaction, and FIG. 8 shows a temperature of 300 ° C. and 350 ° C. in the case of pH 11 (subcritical) And XRD spectra of strontium titanate fine particles obtained at 400 ° C. (supercritical). In addition, in FIG. 7, when it synthesize | combined as pH 7, the XRD spectrum of the comparative example from which the perovskite phase was not obtained is also shown collectively as Sr / Ti = 1.7.

In FIG. 7, under supercritical conditions, a perovskite phase is obtained at pH = 11 by setting Sr / Ti = 1.3, and a different phase is obtained at pH = 9 by setting Sr / Ti = 1.5. It has been shown that strontium titanate having a perovskite phase is obtained. In addition, it is confirmed that anatase-type titanium dioxide is easily formed at pH 7 as compared with the XRD spectrum at pH 7.

In FIG. 8, it is confirmed that the perovskite phase is obtained at 300 ° C., 350 ° C. (subcritical), and 400 ° C. (supercritical) under conditions of pH 11. FIG. 8 also shows the XRD when Sr / Ti = 1 under the supercritical condition of 400 ° C. At a pH of 11, when the supercritical reaction is carried out without Sr-rich, different phases such as Ti ₃ O ₅ and KTi ₈ O _16.5 are confirmed.

FIG. 9 is an XRD of strontium titanate fine particles synthesized by hydrothermal reaction at Sr / Ti = 1.3, pH = 11.5, 250 ° C. FIG. 10 shows Sr / Ti = 1.3, pH = It is a XRD spectrum of strontium titanate microparticles | fine-particles synthesize | combined by making it hydrothermally react at 9,350 degreeC and 400 degreeC. FIGS. 9 and 10 show that strontium titanate fine particles in the perovskite phase are obtained.

In addition, although the Example of this specification was described as Example 1 and Example 2, it is a comparative example about what the perovskite phase in Table 1 is not obtained.

The method for producing strontium titanate fine particles according to the present invention can be suitably applied to the production of strontium titanate fine particles suitable as a photocatalyst or a functional material for electronic parts such as a piezoelectric or dielectric.

Claims

Preparing a Sr-containing aqueous solution and a Ti-containing aqueous solution respectively;
Preparing a mixed solution by mixing the Sr-containing aqueous solution and the Ti-containing aqueous solution;
Preparing a reaction solution by adding a basic substance to the mixed solution to adjust the pH of the mixed solution;
The reaction liquid is subjected to a hydrothermal reaction or a subcritical reaction or a supercritical reaction at a temperature of 250 ° C. or higher,
The pH of the reaction solution prepared in the step C1 is X,
When the synthesis temperature of the reaction solution in the step D1 is Y,
A method for producing strontium titanate fine particles, wherein the X and the Y satisfy Y> -100X + 1400, XX10, and Y ≧ 250.
The method for producing strontium titanate particles according to claim 1, wherein the X further satisfies X1111.
The method for producing strontium titanate particles according to claim 2, wherein said X further satisfies 11 ≦ X ≦ 13.5.
The method for producing strontium titanate fine particles according to claim 3, wherein the X further satisfies 11 ≦ X ≦ 12.
Step A2 of preparing an Sr-containing aqueous solution and a Ti-containing aqueous solution,
Step B2 of mixing the Sr-containing aqueous solution with the Ti-containing aqueous solution to prepare a mixed solution in which the molar ratio Sr / Ti of the contained Sr component to the Ti component is more than 1.0.
Preparing a reaction solution by adding a basic substance to the mixed solution to adjust the pH of the mixed solution;
And B. a step D2 of subjecting the reaction solution to a hydrothermal reaction, a subcritical reaction or a supercritical reaction at a temperature of 250 ° C. or higher,
Let the pH of the reaction solution prepared in the step C2 be X,
When the synthesis temperature of the reaction solution in the step D2 is Y,
A method for producing strontium titanate fine particles, wherein the X and the Y satisfy Y500−500 × + 5150, X ≧ 9, and Y ≧ 250.
The method for producing strontium titanate fine particles according to claim 5, wherein the X further satisfies 9 ≦ X ≦ 13.5.
The method for producing strontium titanate fine particles according to claim 5, wherein the X further satisfies 9 ≦ X ≦ 12.
In the step B2, the Sr-containing aqueous solution and the Ti-containing aqueous solution are mixed such that the molar ratio Sr / Ti of the Sr component and the Ti component contained in the mixed solution is 1.3 or more. The method for producing strontium titanate fine particles according to any one of the above items 1 to 7.
The method for producing strontium titanate fine particles according to any one of claims 1 to 8, wherein the Ti-containing aqueous solution not containing TiO 2 as a main component of Ti component is used in the step B1 or the step B2.
In the step A1 or the step A2,
The method for producing strontium titanate fine particles according to any one of claims 1 to 9, wherein the Sr-containing aqueous solution is obtained by dissolving strontium acetate or hydroxide or nitrate in water.
In the step C1 or the step C2,
The method for producing strontium titanate fine particles according to any one of claims 1 to 10, wherein a reaction liquid comprising Ti (OH) 4 and / or HTiO 3 - ion as a main component of Ti component is prepared.
The method for producing strontium titanate fine particles according to any one of claims 1 to 11, wherein a titanium tetrachloride aqueous solution is prepared as the Ti-containing aqueous solution in the step A1 or the step A2.
The method for producing strontium titanate fine particles according to any one of claims 1 to 12, wherein in the step C1 or the step C2, the basic aqueous solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution.
The method for producing strontium titanate fine particles according to any one of claims 1 to 13, wherein solid matter generated during the preparation is crushed in the step C1 or the step C2.