JP6257243B2 - Rare earth titanate powder, method for producing the same, and dispersion containing the same - Google Patents

Description

  The present invention relates to a rare earth titanate powder and a method for producing the same.

  Up to now, a dispersion liquid in which a powder composed of an inorganic oxide having a high refractive index is dispersed in a dispersion medium, which is used to form thin films and resin moldings that form the surfaces of various substrates, A technique for obtaining a thin film or a molded body having a refractive index is known.

One of the inorganic oxides having such a high refractive index is rare earth titanate. For example, Patent Document 1 describes a method for producing lanthanum titanate particles that obtain lanthanum titanate particles represented by LaTiO ₃ by hydrothermally treating lanthanum hydroxide particles and titanium oxide particles under specific conditions. Has been. In this document, it is possible to produce LaTiO ₃ particles that are fine and have a high refractive index by using the production method described above, and that a dispersion liquid in which LaTiO ₃ particles are dispersed in a dispersion medium is used to form an optical material. Have been described.

JP 2012-184136 A

  In order to obtain a high refractive index and highly transparent thin film or resin molding useful for optical materials using a dispersion of an inorganic oxide having a high refractive index, an inorganic oxide that is a dispersoid is used in the dispersion. It is necessary to be in a sufficiently fine state. However, since the lanthanum titanate particles obtained by the production method described in Patent Document 1 are difficult to be crushed, when dispersed in a dispersion medium using a pulverizer, the lanthanum titanate particles are not easily formed into fine particles, and are dispersed in the dispersion medium. The nature is not enough.

Further, the lanthanum titanate particles produced by the method described in Patent Document 1 are represented by LaTiO ₃ as described above. Lanthanum titanate has a perovskite crystal structure represented by LaTiO ₃ and a pyrochlore crystal structure represented by Ln ₂ Ti ₂ O ₇ (wherein Ln represents a rare earth element). Things are known. In this document, La ₂ Ti ₂ O ₇ is manufactured as a comparative example. In paragraph [0028] of the same document relating to the comparative example, “the produced fine particles are La ₂ Ti ₂ O ₇ particles, and the LaTiO ₃ particles 100 produced by the production method according to this embodiment are constituent elements. It was described that the ratio, that is, the composition ratio was different. ”As is apparent from this description, La ₂ Ti ₂ O ₇ is an impurity that is not preferable to be generated in this document.

  The subject of this invention is providing the rare earth titanate powder which can eliminate the various fault which the prior art mentioned above has.

The inventors of the present invention surprisingly have a rare earth titanate represented by Ln ₂ Ti ₂ O ₇ which is regarded as an impurity in Patent Document 1, and a powder that satisfies a specific condition regarding particle disintegration, It has been found that a rare earth titanate is sufficiently finely divided in a dispersion medium and a highly dispersed dispersion liquid can be easily obtained.

That is, the present invention is a powder comprising a rare earth titanate represented by Ln ₂ Ti ₂ O ₇ (wherein Ln represents a rare earth element),
After ultrasonic irradiation under the conditions of 22.5 kHz, 30 W, and 3 minutes, the value of the volume cumulative particle diameter D _99.99 of the cumulative volume 99.99 vol% by the laser diffraction scattering particle size distribution measurement method is the value before ultrasonic irradiation. The present invention provides a rare earth titanate powder having a D _99.99 value of 0.85 or less.

  Further, the present invention is a method for producing the rare earth titanate powder, wherein an aqueous solution containing one or two or more rare earth element sources and a titanium source and an aqueous solution containing an acid or an alkali are added simultaneously. The present invention provides a method for producing a rare earth titanate powder including a step of forming a rare earth titanate precursor.

  The present invention also provides a dispersion obtained by wet-grinding a slurry obtained by mixing the rare earth titanate powder and a dispersion medium, wherein the dispersion medium is water or water and a water-soluble organic solvent. A dispersion liquid which is a mixed solvent is provided.

  When the dispersion liquid is prepared using the rare earth titanate powder of the present invention, it is possible to obtain a dispersion liquid in which the rare earth titanate is sufficiently finely dispersed and highly dispersed in the dispersion medium.

Hereinafter, the present invention will be described based on preferred embodiments thereof. The rare earth titanate powder of the present invention is a rare earth titanate represented by Ln ₂ Ti ₂ O ₇ (Ln represents at least one rare earth element. Hereinafter, the term “Ln” is used in this sense). It is an aggregate of particles consisting of In the following description, the term “rare earth titanate powder” refers to the powder itself, which is an aggregate of particles made of rare earth titanate, and the individual particles constituting the powder, depending on the context. There is. The rare earth titanate represented by Ln ₂ Ti ₂ O ₇ is generally a material having a high refractive index. Therefore, the rare earth titanate powder of the present invention is suitable as a raw material for producing an optical material such as an optical lens.

The rare earth element in the rare earth titanate represented by Ln ₂ Ti ₂ O ₇ includes Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, There are Yb and Lu. Among these, it is selected from Y, La, Eu, Gd, Yb, and Lu because it has a particularly high refractive index of titanate and is a white powder that becomes colorless and transparent by forming nanoparticles without coloring. It is preferable to use rare earth elements.

The rare earth titanate used in the present invention may be crystalline or amorphous (amorphous). When crystalline, the rare earth titanate represented by Ln ₂ Ti ₂ O ₇ (hereinafter, also simply referred to as Ln ₂ Ti ₂ O ₇ ) used in the present invention has a pyrochlore structure. On the other hand, since lanthanum titanate represented by LaTiO ₃ described in Patent Document 1 described above has a perovskite structure, its crystal structure is different from that of Ln ₂ Ti ₂ O ₇ used in the present invention. It is. Ln ₂ Ti ₂ O ₇ having a pyrochlore structure has higher structural stability than LnTiO ₃ having a perovskite structure.

As described above, the LnTiO ₃ powder of Patent Document 1 is difficult to be crushed, but the rare earth titanate powder of the present invention (hereinafter also referred to as Ln ₂ Ti ₂ O ₇ powder) is dissolved by the action of external force. It is easy to be crushed. As a result of the study by the present inventors, as a measure of the ease of crushing, volume cumulative particles at a cumulative volume of 99.99% by volume by a laser diffraction scattering type particle size distribution measurement method before and after ultrasonic irradiation under specific conditions. It has been found that the degree of change of the diameter D _99.99 is important. Specifically, the value of D _99.99 after irradiation with ultrasonic waves to Ln ₂ Ti ₂ O ₇ powder under conditions to be described later, tends to be crushed smaller than the value of the ultrasonic irradiation before D _99.99. From this point of view, the present inventors diligently examined. As a result, the value of D _99.99 after irradiating the Ln ₂ Ti ₂ O ₇ powder with ultrasonic waves under the conditions described later is higher than the value of D _99.99 before ultrasonic irradiation. It has been found that when it is 0.85 or less, it is easy to wet-grind the Ln ₂ Ti ₂ O ₇ powder in a dispersion medium. Ln ₂ Ti ₂ O ₇ powder in which the ratio of D _99.99 before and after ultrasonic irradiation is outside this range cannot easily obtain a dispersion in which fine particles of Ln ₂ Ti ₂ O ₇ are highly dispersed by wet grinding. The reason is as follows. The Ln ₂ Ti ₂ O ₇ powder having a D _99.99 ratio of more than 0.85 has a strong aggregation between primary particles and is difficult to be crushed by ordinary wet pulverization. Therefore, when such a powder has a large particle size, even if wet pulverization is performed on the powder, it is difficult to form a fine particle and is difficult to disperse in a dispersion medium. If the particle size is small, it tends to aggregate in a dry state, so that it is difficult to disperse in the dispersion medium. On the other hand, since the Ln ₂ Ti ₂ O ₇ powder of the present invention in which the ratio of D _99.99 before and after the ultrasonic irradiation is within the above range is easily pulverized by wet pulverization, aggregation is prevented before wet pulverization. Therefore, the particle size can be increased to some extent. In addition, the fine particles that are easily crushed during the wet pulverization and are newly generated by the pulverization are fine particles, and thus are highly dispersible in the dispersion medium. In order to further enhance the effect of the Ln ₂ Ti ₂ O ₇ powder of the present invention, the value of D _99.99 after ultrasonic irradiation is 0.80 or less with respect to the value of D _99.99 before ultrasonic irradiation. It is preferable that it is, and it is more preferable that it is 0.75 or less. Further, the ratio of D _99.99 after the ultrasonic wave irradiation to D _99.99 before the ultrasonic wave irradiation is preferably close to 0, but if the ratio is as small as 0.4, particularly about 0.5, the intended aspect of the present invention is achieved. The purpose of is achieved. The Ln ₂ Ti ₂ O ₇ powder of the present invention having such characteristics can be produced by, for example, a method described later.

The volume cumulative particle size D _99.99 measured by the laser diffraction / scattering particle size distribution measurement method can be measured by LA920 manufactured by Horiba, Ltd. The ultrasonic irradiation conditions described above are 22.5 kHz, 30 W, and 3 minutes. The ultrasonic irradiation is performed by an ultrasonic apparatus attached to the circulation system of the laser diffraction / scattering particle size distribution measuring apparatus.

In the present invention, the reason why D _99.99 is expressed instead of the volume cumulative particle diameter D ₁₀₀ at a cumulative volume of 100 vol% by the laser diffraction / scattering particle size distribution measurement method is that D _{100 is} an accurate measurement due to the specifications of the measuring instrument. This is because of the difficulty.

In order to make the Ln ₂ Ti ₂ O ₇ powder of the present invention sufficiently fine and highly dispersible in the dispersion medium, in addition to the ease of crushing of the Ln ₂ Ti ₂ O ₇ powder, the particles The diameter is also important. From this viewpoint, the Ln ₂ Ti ₂ O ₇ powder of the present invention preferably has a D _99.99 in a specific range before ultrasonic irradiation. Specifically, it is preferable to set D _99.99 to 2 μm or more and 150 μm or less. When D _99.99 before ultrasonic irradiation is 150 μm or less, it becomes easier to obtain a dispersion in which fine particles are highly dispersed by simple pulverization. There is no particular limitation on the lower limit of D _99.99 before ultrasonic irradiation, and it is preferable that it is smaller. However, if D _99.99 is reduced to about 2 μm, a raw material powder that can sufficiently increase the transparency of the dispersion liquid is obtained. . From these viewpoints, D _99.99 is more preferably 12 μm or more and 150 μm or less, and further preferably 20 μm or more and 150 μm or less.

In order to make the Ln ₂ Ti ₂ O ₇ powder of the present invention sufficiently fine and more highly dispersible in the dispersion medium, D _99.99 after the ultrasonic irradiation is 1 μm or more and 125 μm. Or less, more preferably 10 μm or more and 125 μm or less.

The Ln ₂ Ti ₂ O ₇ powder of the present invention preferably has a BET specific surface area of 35 m ² / g or more and 120 m ² / g or less. By using Ln ₂ Ti ₂ O ₇ salt particles having a BET specific surface area within this range, even if the particles are fine particles, the particles can be easily and stably dispersed in a dispersion medium. In this _respect, BET specific surface area of Ln 2 _Ti 2 _{O 7} powder, more preferably at most 35m ² / g or more 110m ² / g, and still more preferably 35m ² / g or more 100m ² / g or less .

  In the present invention, the BET specific surface area is measured using powder before ultrasonic irradiation. For example, “Micromeritics Flowsorb II2300” manufactured by Shimadzu Corporation is used as a BET specific surface area measuring device, and JIS R 1626 “fine ceramic powder” is used. According to “(3.5) One-point method” in “6.2 Flow method” of “Specific surface area measurement method by gas adsorption BET method”. As a gas used for the measurement, a nitrogen-helium mixed gas containing 30% by volume of nitrogen as an adsorption gas and 70% by volume of helium as a carrier gas is used.

As the shape of the Ln ₂ Ti ₂ O ₇ powder of the present invention, for example, a spherical shape, a polyhedral shape, a needle shape or the like can be adopted. In particular, when the rare earth titanate particles are spherical, when an optical lens is produced from a dispersion containing the particles, birefringence is less likely to occur in the optical lens.

Next, a description will be given of a preferred manufacturing process of _Ln 2 _Ti 2 _{O 7} powder of the present invention. The Ln ₂ Ti ₂ O ₇ powder generates a rare earth titanate precursor by mixing an aqueous solution containing one or more rare earth element sources and a titanium source with an aqueous solution containing an acid or an alkali. The precursor is obtained by firing.

  In an aqueous solution containing a rare earth element source and a titanium source, the concentration of the rare earth element source in the aqueous solution is 0.01 to 1 mol / liter, particularly 0.03 to 1 mol / liter, particularly preferably 0. It is preferable to use one of 05 to 0.5 mol / liter.

  In the aqueous solution containing the rare earth element source and the titanium source, the concentration of the titanium source in the aqueous solution is 0.01 to 1 mol / liter, particularly 0.03 to 1 mol / liter, especially 0.05 to 5 in terms of titanium. It is preferable to set it as 0.5 mol / liter.

In order to prepare an aqueous solution containing a rare earth element source and a titanium source, for example, an acidic aqueous solution such as hydrochloric acid is prepared, and a rare earth oxide (for example, Ln ₂ O ₃ or the like) which is one of the rare earth element sources is added thereto. And titanium tetrachloride which is one of the titanium sources may be added.

The ratio of the rare earth element source to the titanium source in the aqueous solution containing the rare earth element source and the titanium source is 0.6 to 1.8, particularly 0.75 to 1.5, especially in terms of the molar ratio of titanium / rare earth element. it is preferable from the viewpoint of efficiently _Ln 2 _Ti 2 _{O 7} is obtained is 0.95 to 1.1.

  In the aqueous solution containing the acid or alkali, examples of the acid include mineral acids such as hydrochloric acid, nitric acid, and sulfuric acid, and carboxylic acids such as acetic acid and propionic acid. Examples of the alkali include ammonia, ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate, ethylamine, propylamine, sodium hydroxide, potassium hydroxide, and the like. Sodium hydroxide, potassium hydroxide, ammonia Is preferably used.

  In this production method, an aqueous solution containing a rare earth element source and a titanium source and an aqueous solution containing an acid or an alkali are mixed and added at the same time. As a result of the study by the present inventors, it was found that by performing this operation, a rare earth titanate powder that can be easily crushed by the action of an external force can be obtained. On the other hand, when both are not added at the same time, the resulting powder is not easily crushed by the action of external force.

  In this production method, simultaneous addition means that one liquid and the other liquid are simultaneously added and mixed in one container. However, it is not necessary that the addition start timing and / or the addition completion timing of one liquid and the other liquid completely coincide with each other. Inevitably, a deviation occurs in the addition start timing and / or the completion timing of addition. Therefore, the operation of adding the other liquid to one liquid stored in the container is not a simultaneous addition.

  In the case where an aqueous solution containing a rare earth element source and a titanium source and an aqueous solution containing an acid or alkali are added simultaneously, it is preferable to add both of them simultaneously under high shear conditions. The simultaneous addition under high shear conditions has the advantage that a rare earth titanate powder that can be easily crushed by the action of external force can be obtained more easily.

  In order to simultaneously add an aqueous solution containing a rare earth element source and a titanium source and an aqueous solution containing an acid or an alkali under high shear conditions, for example, various homogenizers or a high-pressure wet jet mill can be used. In particular, it is preferable to add both aqueous solutions simultaneously in a homogenizer because rare earth titanate powder that can be easily crushed by the action of external force is more easily obtained. The rotation speed of the homogenizer is preferably 1000 to 20000 rpm, more preferably 5000 to 20000 rpm. Moreover, it is preferable that pH of the slurry obtained by mixing the aqueous solution containing a rare earth element source and a titanium source and the aqueous solution containing an acid or an alkali is 5-12, and it is more preferable that it is 7-11.

  As described above, a slurry containing a rare earth titanate precursor as a precipitation product is obtained. The slurry is subjected to solid-liquid separation according to a conventional method, and then the obtained precursor is washed with water once or a plurality of times. Washing with water is preferably performed until the electrical conductivity of the liquid reaches, for example, 2000 μS / cm or less.

The obtained precursor is baked. Firing can be performed in an oxygen-containing atmosphere such as in the air. In this case, the firing condition is preferably a firing temperature of 600 to 1000 ° C., more preferably 650 to 850 ° C. By adopting this temperature range, it is possible to easily obtain a powder of Ln ₂ Ti ₂ O ₇ in which the degree of change of D _99.99 due to ultrasonic treatment is the target range. If the firing temperature is excessively high, sintering proceeds and the particles tend not to be crushed. The firing time is preferably 1 to 24 hours, more preferably 1 to 12 hours, provided that the firing temperature is within this range. By this firing, the Ln ₂ Ti ₂ O ₇ powder of the present invention is obtained.

The Ln ₂ Ti ₂ O ₇ powder of the present invention obtained as described above may be used in a dry state as it is, or may be used in the state of a dispersion liquid dispersed in a dispersion medium. In particular, the Ln ₂ Ti ₂ O ₇ powder of the present invention in which the degree of change of D _99.99 due to ultrasonic treatment is in the range as described above is easy to be crushed by the action of external force. By performing wet pulverization with a media mill described later, it is easy to obtain a dispersion in which the Ln ₂ Ti ₂ O ₇ powder is sufficiently fine and highly dispersed. Therefore, _as Ln ₂ Ti ₂ O ₇ is a dispersoid in the dispersion can be dispersed at a high concentration without causing precipitation. In particular, Ln ₂ Ti ₂ O ₇ powder in which the value of D _99.99 is in the above-described range has good dispersibility in the dispersion medium. As described above, the dispersion in which the Ln ₂ Ti ₂ O ₇ powder of the present invention is dispersed at a high concentration is desired even when the number of times of coating is reduced, for example, when an optical lens is manufactured by coating the dispersion. This is advantageous in that a thin film having a thickness can be formed.

The dispersion may contain one kind of rare earth titanate, or may contain two or more kinds as required. In any case, since this dispersion liquid contains Ln ₂ Ti ₂ O ₇ powder, which is a material having a high refractive index, the dispersion liquid containing such a material can be used for an optical material such as an optical lens. It is suitable as a raw material for manufacturing.

The dispersion may further include a metal oxide powder having a high refractive index in addition to the Ln ₂ Ti ₂ O ₇ powder. Examples of such metal oxides include Mg, Ca, Ti, Zn, Zr, Ta, Nb, Ga, Ge, Sn, In, Hf, Y, and lanthanoids (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and other metal oxides. These metal oxides can be used alone or in combination of two or more. These metal oxides can be used in an amount of about 0.1 to 50% by mass with respect to the entire particles as solids contained in the dispersion. However, it is desirable that the dispersion does not contain solid components other than the Ln ₂ Ti ₂ O ₇ powder, regardless of the type of the dispersion medium.

  As a dispersion medium of the dispersion liquid, water or a mixed solvent of water and a water-soluble organic solvent can be used.

  As the water-soluble organic solvent, for example, a solvent compatible with water such as monoalcohol, polyhydric alcohol, ketone, ester, amine, thiol, and pyrrolidone can be used. These water-soluble organic solvents can be used singly or in combination of two or more.

  In order to increase the stability of the dispersion, it is preferable to add an appropriate pH adjusting agent or / and a dispersing agent. Examples of the dispersant in this case include mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, and carboxylic acids such as acetic acid and phthalic acid, tetramethylammonium hydroxide, aqueous ammonia, tetraethylammonium hydroxide, tetrabutylammonium hydroxide and the like. Tetraalkylammonium hydroxide, isopropylamine, isopropanolamine, isobutylamine, ethylenediamine, diisopropylamine, diisobutylamine, diisopropylethylamine, diethanolamine, diethylamine, diethylenetriamine, diphenylamine, dimethylamine, triethanolamine, triethylamine, trioctylamine, tri-n -Butylamine, tripropylamine, trimethylamine, t-butylamine, propylene di Min, monoethanolamine, monoethylamine, include phosphates, such as nitrogen-containing compounds as well as sodium hexametaphosphate, such as monomethylamine. These dispersing agents can be used individually by 1 type or in combination of 2 or more types.

  The dispersion can be produced, for example, by mixing a rare earth titanate powder and a dispersion medium to form a slurry, and performing wet pulverization using a media mill such as a bead mill. Examples of the beads to be used include zirconia beads and alumina beads. In this case, the rare earth titanate powder can be easily brought close to a monodispersed state by adding various pH adjusting agents and / or dispersing agents to the slurry and performing a pulverization operation.

After the wet pulverization, the liquid and beads are separated, and the coarse particles are removed by a membrane filter to obtain a dispersion liquid in which the Ln ₂ Ti ₂ O ₇ powder of the present invention is highly dispersed in the dispersion medium.

The dispersion obtained in this way is high due to the high refractive index of Ln ₂ Ti ₂ O ₇ contained therein and the fact that Ln ₂ Ti ₂ O ₇ is dispersed in a sufficiently fine state in the dispersion medium. Utilizing transparency, it can be used for various optical materials and electronic materials. For example, it can be used for optical system parts such as lenses, antireflection films, infrared transmission films and the like. Specifically, a thin film having high transparency and a high refractive index is formed by applying the dispersion liquid on the surface of various substrates such as transparent substrates and lenses to form a coating film and drying the coating film. Can be formed. The dried thin film may be fired as necessary under an inert atmosphere, an oxidizing atmosphere such as air, or a weakly reducing atmosphere (for example, a hydrogen-containing atmosphere having an explosion limit concentration or less). This thin film is useful for further increasing the refractive index of the lens or as a thin lens itself. Further, the dispersion is also suitably used as a raw material for a resin lens in which Ln ₂ Ti ₂ O ₇ powder contained therein is dispersed in a resin.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
1) Production of lutetium titanate precursor Lu ₂ O ₃ (manufactured by Japan Yttrium Co.), TiCl ₄ solution (manufactured by Wako Pure Chemical Industries, CAS. No 7550-45-0), 35% hydrochloric acid (Wako Pure Chemical Industries, Ltd.) Manufactured), sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.) and pure water, liquid A (composition containing a rare earth element source and titanium source) and liquid B (acid or alkali) having the composition shown in Table 1 below. Aqueous solution) was prepared. Next, liquid A and liquid B are each stirred at room temperature, and liquid A and liquid B are respectively sent to a homogenizer which is a high shear mixing device at 10 mL / min and 40 mL / min with a liquid feed pump, and simultaneously into the homogenizer. The slurry was added and mixed to obtain a lutetium titanate precursor slurry. The rotation speed of the homogenizer was set to 20000 rpm. Moreover, pH of the obtained slurry was 8.0. The obtained slurry was subjected to repulp washing with pure water until the supernatant has a conductivity of 100 μS / cm or less, and then filtered. The filtered cake was dried at 120 ° C. for 6 hours to obtain a lutetium titanate precursor powder.

2) Production of lutetium titanate powder The lutetium titanate precursor powder obtained in 1) was calcined at 750 ° C. for 3 hours in the air in a calcining furnace. Was subjected to XRD measurement of the obtained baked powder was confirmed to be titanate lutetium crystalline represented by Lu ₂ Ti ₂ O _7. The resulting titanate lutetium powder was measured by the method described above a BET specific surface area before D _99.99 and ultrasonic irradiation before and after ultrasonic irradiation. These results are shown in Table 2.

3) Production of aqueous dispersion 3 g of lutetium titanate powder obtained in 2) and 27 g of 1% sodium hexametaphosphate aqueous solution were placed in a 50 ml resin container. Further, 100 g of zirconia beads having a diameter of 0.1 mmΦ was added, the container was sealed, and wet pulverized with a paint shaker (manufactured by Asada Tekko) for 3 hours. Finally, the pulverized slurry was passed through a 0.2 μm membrane filter to remove coarse particles, thereby obtaining a target aqueous dispersion of lutetium titanate. The particle size distribution of titanium lutetium particles in the dispersion was measured as follows. The results are shown in Table 3.
<Measurement of particle size distribution of dispersion>
The dispersion is weighed about 1 cc, and a volume cumulative particle size D ₅₀ having a cumulative volume of 50% by volume and a volume cumulative particle size D ₉₉ having a cumulative volume of 99% by volume are measured using a particle size distribution measuring device (Specetas Co., Ltd., Zetasizer). It was measured.

[Example 2]
1) Production of gadolinium titanate precursor Gd ₂ O ₃ (manufactured by Japan Yttrium Co.) was used instead of Lu ₂ O ₃ , and the composition of the liquid A was as shown in Table 1, and was the same as in Example 1. A gadolinium titanate precursor powder was obtained.

2) Production of gadolinium titanate powder The gadolinium titanate precursor powder obtained in 1) was calcined at 750 ° C. for 3 hours in the air in a calcining furnace. XRD measurement of the obtained fired powder confirmed that although the diffraction peak of the crystal structure represented by Ga ₂ Ti ₂ O ₇ was slightly observed, it was amorphous gadolinium titanate as a whole. did. About the obtained gadolinium titanate powder, _D99.99 before and behind ultrasonic irradiation and the BET specific surface area before ultrasonic irradiation were measured by the method mentioned above. These results are shown in Table 2.

3) Production of aqueous dispersion An aqueous dispersion was produced in the same manner as in Example 1 except that the gadolinium titanate powder obtained in 2) above was used instead of the lutetium titanate powder, and the resulting dispersion was obtained. The particle size distribution of the liquid was measured. Table 3 shows the measurement results of the particle size distribution.

Example 3
1) Production of lanthanum titanate precursor La ₂ O ₃ (manufactured by Japan Yttrium Co.) was used instead of Lu ₂ O ₃ and the composition of the liquid A was as shown in Table 1, and was the same as in Example 1. A lanthanum titanate precursor powder was obtained.

2) Production of lanthanum titanate powder The lanthanum titanate precursor powder obtained in 1) was calcined in a firing furnace in the air at 750 ° C for 3 hours. Was subjected to XRD measurement of the obtained baked powder was confirmed to be lanthanum titanate crystalline represented by La ₂ Ti ₂ O _7. About the obtained lanthanum titanate powder, D _99.99 before and after ultrasonic waves and the BET specific surface area before ultrasonic irradiation were measured by the method described above. These results are shown in Table 2.

3) Production of aqueous dispersion An aqueous dispersion was produced in the same manner as in Example 1 except that the lanthanum titanate powder obtained in 2) above was used instead of the lutetium titanate powder, and the resulting dispersion was obtained. The particle size distribution of the liquid was measured. Table 3 shows the measurement results of the particle size distribution.

Example 4
1) Production of yttrium titanate precursor Y ₂ O ₃ (manufactured by Japan Yttrium Co.) was used instead of Lu ₂ O ₃ , and the composition of the liquid A was as shown in Table 1, as in Example 1. The yttrium titanate precursor powder was obtained.

2) Production of yttrium titanate powder The yttrium titanate precursor powder obtained in 1) was calcined at 750 ° C. for 3 hours in the atmosphere in a calcining furnace. Was subjected to XRD measurement of the obtained baked powder was confirmed to be titanate yttrium crystalline represented by Y ₂ Ti ₂ O _7. About the obtained yttrium titanate powder, D _99.99 before and after ultrasonic irradiation and the BET specific surface area before ultrasonic irradiation were measured by the method mentioned above. These results are shown in Table 2.

3) Production of aqueous dispersion An aqueous dispersion was produced in the same manner as in Example 1 except that the yttrium titanate powder obtained in 2) above was used instead of the lutetium titanate powder, and the resulting dispersion was obtained. The particle size distribution was measured. Table 3 shows the measurement results of the particle size distribution.

The following Comparative Examples 1 to 4 are examples in which an aqueous solution containing a rare earth source and a titanium source and an aqueous solution containing an acid or an alkali were not added simultaneously in the synthesis of the rare earth titanate.
[Comparative Example 1]
1) Manufacture of lutetium titanate precursor Liquid A and liquid B were prepared with the compositions shown in Table 1 below. Next, the liquid A (pH = 1.0 or less) was stirred at room temperature, and the liquid B was fed into the liquid A at 10 ml / min with a liquid feed pump to obtain a slurry of a lutetium titanate precursor. The resulting slurry had a pH of 7.8. The obtained slurry was filtered after repulp washing with pure water until the conductivity of the supernatant was 100 μS / cm or less. The filtered cake was dried at 120 ° C. for 6 hours to obtain a lutetium titanate precursor powder.

2) Production of lutetium titanate powder The lutetium titanate precursor powder obtained in 1) was calcined at 750 ° C. for 3 hours in the air in a calcining furnace. Was subjected to XRD measurement of the obtained baked powder was confirmed to be titanate lutetium crystalline represented by Lu ₂ Ti ₂ O _7. The resulting titanate lutetium powder was measured by the method described above a BET specific surface area before D _99.99 and ultrasonic irradiation before and after ultrasonic irradiation. These results are shown in Table 2.

3) Manufacture of aqueous dispersion The manufacture by the same method as 3) of Example 1 was tried, but a dispersion liquid was not obtained because lutetium titanate powder precipitated. The particle size distribution could not be measured because precipitation was observed.

[Comparative Example 2]
1) Production of gadolinium titanate precursor Gd ₂ O ₃ (manufactured by Japan Yttrium Co.) was used instead of Lu ₂ O ₃ and the composition of the liquid A was as shown in Table 1, and was the same as in Comparative Example 1. A gadolinium titanate precursor powder was obtained.

2) Production of gadolinium titanate powder The gadolinium titanate precursor powder obtained in 1) was calcined at 750 ° C. for 3 hours in the air in a calcining furnace. XRD measurement of the obtained fired powder confirmed that although the diffraction peak of the crystal structure represented by Ga ₂ Ti ₂ O ₇ was slightly observed, it was amorphous gadolinium titanate as a whole. did. About the obtained gadolinium titanate powder, _D99.99 before and behind ultrasonic irradiation and the BET specific surface area before ultrasonic irradiation were measured by the method mentioned above. These results are shown in Table 2.

3) Manufacture of aqueous dispersion The manufacture by the same method as 3) of Example 1 was tried, but the dispersion liquid was not obtained because the gadolinium titanate powder precipitated. The particle size distribution could not be measured because precipitation was observed.

[Comparative Example 3]
1) Production of lanthanum titanate precursor La ₂ O ₃ (manufactured by Japan Yttrium Co.) was used instead of Lu ₂ O ₃ , and the composition of the liquid A was as shown in Table 1, as in Comparative Example 1. The lanthanum titanate precursor powder was obtained.

2) Production of lanthanum titanate powder The lanthanum titanate precursor powder obtained in 1) was calcined in the atmosphere at 750 ° C. for 3 hours in a firing furnace. Was subjected to XRD measurement of the obtained baked powder was confirmed to be lanthanum titanate crystalline represented by La ₂ Ti ₂ O _7. About the obtained lanthanum titanate powder, D _99.99 before and after ultrasonic irradiation and the BET specific surface area before ultrasonic irradiation were measured by the method described above. These results are shown in Table 2.

3) Manufacture of aqueous dispersion The manufacture by the same method as 3) of Example 1 was attempted, but a dispersion was not obtained because lanthanum titanate powder precipitated. The particle size distribution could not be measured because precipitation was observed.

[Comparative Example 4]
1) Manufacture of yttrium titanate precursor Y ₂ O ₃ (manufactured by Japan Yttrium Co.) was used instead of Lu ₂ O ₃ and the composition of the liquid A was as shown in Table 1, and was the same as in Comparative Example 1. A yttrium titanate precursor powder was obtained.

2) Production of yttrium titanate powder The yttrium titanate precursor powder obtained in 1) was calcined at 750 ° C. for 3 hours in the atmosphere in a calcining furnace. Was subjected to XRD measurement of the obtained baked powder was confirmed to be titanate yttrium crystalline represented by Y ₂ Ti ₂ O _7. About the obtained yttrium titanate powder, D _99.99 before and after ultrasonic irradiation and the BET specific surface area before ultrasonic irradiation were measured by the method mentioned above. These results are shown in Table 2.

3) Manufacture of aqueous dispersion The manufacture by the same method as 3) of Example 1 was attempted, but a dispersion was not obtained because yttrium titanate powder precipitated. The particle size distribution could not be measured because precipitation was observed.

As it is apparent from the results shown in Table 3, the dispersion prepared from rare earth titanate powder used in each example, made from the values of the D ₅₀ and D _99, rare earth titanates sufficiently fine nanoparticle You can see that Further, the dispersion prepared from rare earth titanate powder used in each _example, since the value of the ratio _D 99 _{/ D 50} of the _{D 99} for _{D 50} is about 4-7, rare earth titanates It can be seen that it is highly dispersed in the dispersion medium.

Claims (6)

A powder comprising a rare earth titanate represented by Ln ₂ Ti ₂ O ₇ (wherein Ln represents a rare earth element),
The powder is a powder before being irradiated with an ultrasonic wave, and after being irradiated with an ultrasonic wave under conditions of 22.5 kHz, 30 W and 3 minutes, a cumulative volume of 99.99 volumes by a laser diffraction scattering type particle size distribution measuring method. % Rare earth titanate powder having a volume cumulative particle diameter D _99.99 of 0.85 or less with respect to the value of D _99.99 before ultrasonic irradiation. The rare earth titanate powder according to claim 1, wherein D _99.99 before ultrasonic irradiation is 2 µm or more and 150 µm or less. The rare earth titanate powder according to claim 1 or 2, wherein the BET specific surface area is 35 m ² / g or more and 120 m ² / g or less. A method for producing the rare earth titanate powder according to any one of claims 1 to 3,
A rare earth titanate powder comprising a step of simultaneously adding an aqueous solution containing one or more rare earth element sources and a titanium source and an aqueous solution containing an acid or an alkali to form a precursor of the rare earth titanate. Production method.   The method for producing a rare earth titanate powder according to claim 4, wherein an aqueous solution containing one or two or more rare earth element sources and a titanium source and an aqueous solution containing an acid or an alkali are simultaneously added to a homogenizer. A dispersion containing the rare earth titanate powder according to any one of claims 1 to 3.