Titanium oxide particles and method for producing the same

Abstract

The present invention provides: titanium oxide particles which exhibits excellent uniformity and excellent dispersibility, while containing less coarse particles; a method for producing the titanium oxide particles; and a slurry, a dispersion, a composition and a dielectric starting material, each of which contains the titanium oxide particles. With respect to the titanium oxide particles according to the present invention, the D90(LD) / D50(LD) of the titanium oxide particles as determined by a laser diffraction / scattering method is more than 1.0 but not more than 2.0; and the concentration (on a number basis) of coarse particles relative to D50 (SEM) of primary particles as determined by the observation with a field-emission scanning electronic microscope is 20 ppm or less, the coarse particles having a size more than 16 times the D50 (SEM). During the production of the titanium oxide particles, when a starting material gas and an oxidizing gas are introduced into a reaction tube so as to be reacted with each other, the inner wall of the reaction tube is provided with a blow-off opening for a purge medium and the blow-off angle of the purge medium and the blow-off rate (B) of the purge medium from the inner wall of the reaction tube are set so that the purge medium whirls along the inner wall of the reaction tube.

Description

[Technical Field]

[0001] The present invention relates to titanium oxide particles, a method for producing the same, and a slurry, dispersion, composition, and dielectric material containing the titanium oxide particles. [Background technology]

[0002] Titanium oxide has an extremely wide range of industrial applications, including cosmetics, UV screening materials, and additives for silicone rubber, and in recent years has been used in a wide variety of applications, including photocatalysts, solar cells, dielectric materials, and electrode materials for Li-ion batteries. Note that although "titanium oxide" is listed as titanium dioxide in the Japanese Industrial Standards (JIS), titanium oxide is widely used as the generic name, so in this specification titanium dioxide (TiO2) will be abbreviated to titanium oxide.

[0003] Recently, titanium oxide has been attracting attention as a raw material for high-performance dielectrics, such as BaTiO3, which can be obtained by the following reaction under heating: BaCO3+TiO2→BaTiO3+CO2 The above reaction is a solid-state reaction, during which BaCO3 first decomposes at high temperatures to produce BaO, which then diffuses into TiO2 particles and dissolves to form BaTiO3. Therefore, the size of BaTiO3 particles is governed by the size of TiO2 particles. In recent years, as multilayer ceramic capacitors have become smaller, thinner dielectric layers have become a key challenge, making finer and more uniform BaTiO3 particles essential. Furthermore, the presence of BaTiO3 particles larger than the dielectric layer thickness can cause short circuits within multilayer ceramic capacitors, leading to device failure. Therefore, finer and more uniform TiO2 particles, the raw material for BaTiO3, are necessary, and it is preferable to avoid coarse TiO2 particles. Similarly, for other applications, finer and more uniform titanium oxide particles are required, and the absence of coarse particles is also desirable.

[0004] Methods for producing titanium oxide are roughly divided into a liquid phase method in which titanium tetrachloride or titanium sulfate is hydrolyzed, and a gas phase method in which titanium tetrachloride is reacted with oxygen or water vapor at high temperatures.

[0005] The liquid-phase method has the advantage of being able to produce titanium oxide under relatively mild conditions and easily obtaining fine primary particles. However, because titanium oxide is obtained in the form of a sol or slurry, its applications are limited when used in this state. The sol or slurry must be dried before it can be used as titanium oxide particles, and after drying, they generally undergo severe agglomeration. Such severely agglomerated titanium oxide particles have the problem of having a non-uniform particle size distribution. Another problem is that the titanium oxide particles obtained by drying have poor dispersibility when dispersed in a solvent. Poor dispersibility means that when raw materials are mixed to produce the above-mentioned BaTiO3, the titanium oxide particles are not sufficiently mixed with other raw materials, resulting in uneven distribution of raw material components and uneven growth during the reaction, resulting in quality variations.

[0006] On the other hand, with the gas phase method, the primary particle size of the titanium oxide produced can be adjusted by adjusting production conditions such as temperature. Furthermore, since the gas phase method does not use a solvent, titanium oxide is obtained as a powder, and the problems mentioned with the liquid phase method are less likely to occur. Furthermore, the gas phase method has the advantage that the reaction is carried out at a relatively higher temperature than the liquid phase method, resulting in titanium oxide with high crystallinity.

[0007] However, because the gas-phase method involves a reaction at a higher temperature than the liquid-phase method, if the titanium oxide particles are exposed to a large amount of heat, for example, if the temperature is too high or the residence time of the titanium oxide particles is too long in the reaction tube or in the cooling tube after the introduction of a cooling medium, excessive sintering of the titanium oxide particles occurs, making it difficult to obtain titanium oxide fine particles and resulting in a non-uniform particle size distribution. If the temperature of the reaction zone is lowered too much to avoid sintering of the titanium oxide particles, titanium oxide nucleation does not occur sufficiently, making it difficult to obtain fine particles or only titanium oxide with low crystallinity is obtained. On the other hand, immediate cooling of the reaction gas with a cooling medium can suppress sintering of the titanium oxide particles and result in the production of fine titanium oxide particles. If cooling is not performed immediately or if there are uneven cooling, uneven sintering of the particles occurs, making it difficult to obtain uniform titanium oxide fine particles.

[0008] Patent Document 1 describes a method for producing titanium oxide particles, characterized by reacting a titanium halide gas with an oxidizing gas under specific conditions, with the aim of obtaining uniform titanium oxide particles by a gas phase method.

[0009] Furthermore, Patent Document 2 describes a method for producing titanium oxide particles, characterized in that the method involves reacting TiCl4 vapor with an oxidizing agent and introducing the oxidizing agent into a reaction tube in a laminar flow, thereby suppressing the formation of scale on the reaction tube and producing a small number of metal oxide particles with a diameter greater than 100 nm, with the aim of obtaining uniform titanium oxide particles free of coarse particles by a gas phase method. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-265094 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-28017 Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, titanium oxide particles with excellent uniformity and dispersibility are desired, and compared to titanium oxide particles obtained by liquid phase methods, the gas phase method has the advantage of providing superior uniformity and dispersibility. Therefore, the present inventors have investigated the production of titanium oxide particles based on the gas phase method to produce titanium oxide particles with even greater uniformity and dispersibility. However, it has been found that even if titanium oxide fine particles with excellent uniformity and dispersibility are produced by the gas phase method, the titanium oxide particles may become significantly coarse, and the inclusion of coarse particles in the titanium oxide fine particles is unavoidable.

[0012] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide titanium oxide microparticles that are excellent in uniformity and dispersibility when produced by a gas phase method and contain few coarse particles, a method for producing the same, and to provide a slurry, dispersion, composition, and dielectric raw material that contain the titanium oxide microparticles. [Means for solving the problem]

[0013] The present inventors have conducted extensive research in light of the above-mentioned problems. As a result, they have found that in Patent Document 1, no measures are taken to prevent adhesion of titanium oxide to the reaction tube wall, and that titanium oxide powder adheres to the reaction tube wall, resulting in the formation of coarse particles due to sintering caused by the adhesion and retention of titanium oxide powder on the reaction tube wall; that in Patent Document 2, the Reynolds number of the oxidant gas must be reduced, resulting in problems in productivity and quality, such as poor raw material mixability, low conversion, and a tendency for particle size to become non-uniform; and that in the process of producing titanium oxide particles by reacting a gas containing titanium tetrachloride and an inert gas with a gas containing an oxidizing gas in a reaction tube, the gas containing titanium tetrachloride and the gas containing an oxidizing gas are each introduced into the reaction tube and reacted, and then a purge medium is introduced along the tube wall under specific conditions, thereby suppressing the adhesion of powder to the tube wall and enabling the production of titanium oxide particles that are uniform, preferably excellent in dispersibility, and contain fewer coarse particles, and have thereby completed the present invention.

[0014] The present invention provides at least the following aspects, but is not limited to these. (Aspect 1) Titanium oxide particles in which the D90(LD) / D50(LD) ratio measured by laser diffraction / scattering analysis is greater than 1.0 and less than 2.0, and the concentration (by number) of coarse particles exceeding 16 times the D50(SEM) of primary particles observed with a field emission scanning electron microscope is 20 ppm or less. (Aspect 2) The titanium oxide particles according to Aspect 1, wherein the D90(SEM) / D50(SEM) of the primary particles of the titanium oxide particles observed with a field emission scanning electron microscope is greater than 1.0 and not greater than 2.0. (Aspect 3) 3. The titanium oxide particles according to claim 1, wherein the ratio of [D90(SEM)-D10(SEM)] / D50(SEM) of primary particles of the titanium oxide particles observed with a field emission scanning electron microscope is 0.82 or less. (Aspect 4) The titanium oxide particles according to any one of Aspects 1 to 3, wherein D99(SEM) / D50(SEM) of the primary particles of the titanium oxide particles observed with a field emission scanning electron microscope is greater than 1.0 and not greater than 2.0. (Aspect 5) The titanium oxide particles according to any one of Aspects 1 to 4, wherein the titanium oxide particles have a D90(DLS) / D50(DLS) ratio measured by dynamic light scattering of more than 1.0 and not more than 2.0. (Aspect 6) Titanium oxide particles according to any one of aspects 1 to 5, having a D90(DLS) / D90(SEM) ratio, which is the ratio of D90(DLS) of primary particles of titanium oxide particles measured by dynamic light scattering to D90(SEM) of titanium oxide particles observed with a field emission scanning electron microscope, of 2.2 or less. (Aspect 7) 7. The titanium oxide particles according to any one of Aspects 1 to 6, wherein the titanium oxide particles have a D90 (LD) of 3000 nm or less as measured by laser diffraction / scattering analysis. (Aspect 8) The titanium oxide particles according to any one of aspects 1 to 7, wherein the D90 (DLS) of the titanium oxide particles measured by dynamic light scattering and the D90 (SEM) of the primary particles of the titanium oxide particles observed with a field emission scanning electron microscope are 200 nm or less, and the D50 (SEM) is 10 to 150 nm. (Aspect 9) The titanium oxide particles according to any one of aspects 1 to 8, having an anatase content of 70% or more. (Aspect 10) BET specific surface area is 5 to 200 m 2 / g. (Aspect 11) 11. The titanium oxide particles according to any one of aspects 1 to 10, wherein the Cl content of the titanium oxide particles measured by silver nitrate potentiometric titration is 0.2% or less. (Aspect 12) 12. The titanium oxide particles according to any one of aspects 1 to 11, wherein the contents of Na, Al, S, Fe, Ni, Cr, Nb, and Zr are each 10 ppm by mass or less, and the contents of Si and C are each 500 ppm by mass or less. (Aspect 13) 1. A method for producing titanium oxide particles, comprising: introducing a raw material gas containing titanium tetrachloride and an inert gas into a reaction tube; reacting the raw material gas with an oxidizing gas containing at least one of oxygen gas and water vapor and the inert gas; and cooling the reacted raw material gas to produce titanium oxide particles; providing a purge medium outlet on the inner wall of the reaction tube; introducing the purge medium in a swirling manner along the inner wall of the reaction tube; and providing a purge medium blowing angle α of the purge medium from the inner wall of the reaction tube with respect to a line connecting the purge medium outlet and the central axis of the reaction tube, projected onto a cross section of the reaction tube perpendicular to the axis of the reaction tube, of 50° or more; and providing a blowing flow rate (B) of the purge medium of 35 m / s or more. (Aspect 14) Aspect 14. The method for producing titanium oxide particles according to aspect 13, wherein a purge medium blowing angle β from an inner wall of the reaction tube relative to the axial direction of the reaction tube is 60° or more, with a side of the reaction gas flowing forward being defined as 0°, in a plane projected onto a vertical cross section of the reaction tube including the axis of the reaction tube. (Aspect 15) Aspect 13. The method for producing titanium oxide particles according to aspect 14, wherein the purging medium is introduced so that the ratio B / A is 0.5 or more, where A is the flow rate of the reaction gas formed from the raw material gas and the oxidizing gas in the reaction tube, and B is the blowing flow rate of the purging medium. (Aspect 16) A slurry comprising the titanium oxide particles according to any one of aspects 1 to 12. (Aspect 17) A dispersion comprising the titanium oxide particles according to any one of aspects 1 to 12. (Aspect 18) A composition comprising the titanium oxide particles according to any one of aspects 1 to 12. (Aspect 19) A dielectric material comprising the titanium oxide particles according to any one of aspects 1 to 12. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide titanium oxide particles that are uniform, more preferably excellent in dispersibility, and have few coarse particles, a method for producing the same, and a slurry, dispersion, composition, and dielectric raw material containing the titanium oxide. [Brief explanation of the drawings]

[0016] [Figure 1] 1(a) and 1(b) are micrographs of titanium oxide particles of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating a preferred example of the first step in the method for producing titanium oxide particles of the present invention. [Figure 3] FIG. 3 is a schematic cross-sectional view illustrating a preferred example of the first step in the method for producing titanium oxide particles of the present invention. [Figure 4] FIG. 4 is a schematic vertical cross-sectional view illustrating a preferred example of the first step in the method for producing titanium oxide particles of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The numerical values ​​of various measurements in this specification are defined taking into account significant figures unless otherwise specified or unless a different meaning is suggested from the context. For example, 0 ppm means less than 0.5 ppm.

[0018] In this specification, D10, D50, D90, and D99 in D10(SEM), D50(SEM), D90(SEM), D99(SEM), D50(LD), D90(LD), D50(DLS), and D90(DLS) refer to the particle sizes (particle diameters) at which the integrated totals of the reference amounts from the smallest particle sizes in each integrated particle size distribution are 10%, 50%, 90%, and 99%, respectively, of the total integrated value, based on number, volume, mass, number of moles, etc., where SEM represents measurement by field emission scanning electron microscope, LD represents laser diffraction / scattering analysis, and DLS represents measurement by dynamic light scattering.

[0019] In the field of fine particles such as that of the present invention, it is desirable to comprehensively assess the uniformity and dispersibility of titanium oxide particles by performing SEM observation, laser diffraction / scattering analysis measurement, and dynamic light scattering measurement, as described below.

[0020] [Titanium oxide particles] The titanium oxide particles according to one embodiment of the present invention are characterized in that the D90(LD) / D50(LD) of the titanium oxide particles measured by laser diffraction / scattering analysis is greater than 1.0 and not greater than 2.0, and the concentration (by number) of coarse particles exceeding 16 times the D50(SEM) is not greater than 20 ppm. These titanium oxide particles have excellent uniformity and dispersibility, and can be suitably produced by the titanium oxide particle production method described below.

[0021] When the D90(LD) / D50(LD) ratio of titanium oxide particles measured by laser diffraction / scattering analysis is more than 1.0 and not more than 2.0, the particle size of the titanium oxide particles is highly uniform, and is preferably not more than 1.8, more preferably not more than 1.6, and most preferably not more than 1.5. When it is not more than 2.0, the particle size distribution is uniform, which is preferable. It can also be not less than 1.1. When the concentration of coarse particles exceeding 16 times D50 (SEM) is 20 ppm or less, the titanium oxide particles have a low coarse particle content. Titanium oxide particles with a uniform particle size and a low coarse particle content meet the quality and uniformity required of titanium oxide particles, making them excellent and useful in a wide range of applications, including cosmetics, UV screening materials, additives for silicone rubber, photocatalysts, solar cells, dielectric materials, and electrode materials for Li-ion batteries.

[0022] D50 (LD), D90 (LD) by laser diffraction / scattering method Titanium oxide particles generally form secondary particles formed by aggregation of primary particles. The particle sizes D50 and D90 of titanium oxide particles in an aggregated state (aggregates of primary and secondary particles) are measured using a laser diffraction particle size analyzer (herein, the above D50 and D90 are referred to as D50(LD) and D90(LD), respectively). According to "Ultrafine Particle Handbook" edited by Shinroku Saito, Fuji Techno System, p. 93 (1990), particle size distribution measurement methods include sedimentation, microscopy, laser diffraction / scattering analysis (light scattering), and direct counting. However, the sedimentation and direct counting methods are limited to measurable particle sizes of several hundred nanometers or more, making them unsuitable for measuring the particle size distribution of particles with diameters of 100 nm or less. Furthermore, microscopy is also subject to fluctuations in measured values ​​depending on the sampling and pretreatment of the target sample, making it unsuitable as a measurement method. In contrast, laser diffraction / scattering analysis (light scattering) can measure particle sizes in the range of several nm to several μm, making it suitable for measuring fine particles. Details of the procedure for measuring particle size distribution using laser diffraction / scattering analysis (light scattering) will be explained in the Examples.

[0023] The D50(LD) of the titanium oxide particles in one embodiment of the present invention is preferably 1000 nm or less, more preferably 500 nm or less. D50(LD) corresponds to the effective diameter (aggregation diameter) when dissolved in a solvent, and the smaller the value, the better the dispersibility.

[0024] Furthermore, a small D90(LD) value indicates that the titanium oxide particles have weak cohesion and good dispersibility in the solvent. The D90(LD) of the titanium oxide particles in one embodiment of the present invention is preferably 3000 nm or less, more preferably 2000 nm or less, even more preferably 1000 nm or less, and still more preferably 600 nm or less.

[0025] D10 (SEM), D50 (SEM), D90 (SEM), D99 (SEM) of primary particles of titanium dioxide particles by field emission scanning electron microscope In one embodiment of the present invention, the D90(SEM) / D50(SEM) ratio of primary particles of titanium oxide particles observed with a field emission scanning electron microscope is preferably greater than 1.0 and not greater than 2.0. When the D90(SEM) / D50(SEM) ratio is greater than 1.0 and not greater than 2.0, the titanium oxide particles can be slurried and dispersed with excellent particle size uniformity. From the same perspective, the D90(SEM) / D50(SEM) ratio is preferably greater than 1.2, more preferably 1.3 or greater, 1.4 or greater, and even more preferably 1.5 or greater. Details of the measurement procedure will be described in the Examples.

[0026] In one embodiment of the present invention, when the titanium oxide particles are observed with a field-emission scanning electron microscope, if the D99(SEM) / D50(SEM) value of the primary particles is small, the primary particle size distribution is determined to be uniform. The D99(SEM) / D50(SEM) value of the titanium oxide particles may be greater than 1.0 and not greater than 2.0, preferably not greater than 1.9, more preferably not greater than 1.8, and most preferably not greater than 1.7. A ratio of 2.0 or less is preferred because the particle size distribution is uniform. Alternatively, the ratio may be 1.1 or greater.

[0027] As described above, D90(SEM) / D50(SEM) is used as an index of uniformity of particle size distribution for particles larger than D50(SEM). However, [D90(SEM)-D10(SEM)] / D50(SEM) is sometimes used as an index of uniformity of the entire particle size distribution, including particles smaller than D50(SEM) to larger particles, and this is also applicable to the present disclosure. A smaller value indicates a more uniform particle size distribution. In one embodiment of the present invention, [D90(SEM)-D10(SEM)] / D50(SEM) is preferably 0.82 or less, more preferably 0.80 or less. Furthermore, [D90(SEM)-D10(SEM)] / D50(SEM) may be 0.75 or less, or 0.71 or less.

[0028] The titanium oxide particles according to one embodiment of the present invention preferably have a D50 (SEM) of 10 to 100 nm, more preferably 10 to 50 nm, and even more preferably 10 to 30 nm. Such titanium oxide particles are suitable for applications requiring submicron particle sizes, such as photocatalysis, solar cells, and dielectrics.

[0029] Furthermore, if the D90(SEM) value is small, the number of particles larger than D90(SEM) is limited, so the D90(SEM) of the titanium oxide particles in one embodiment of the present invention is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less.

[0030] Dynamic light scattering (D50(DLS) and D90(DLS) The titanium oxide particles to be measured are crushed, and the D50 and D90 of the titanium oxide particles are measured by dynamic light scattering (herein, the D50 and D90 are referred to as D50(DLS) and D90(DLS), respectively). D50(DLS) and D90(DLS) are measured using a dynamic light scattering particle size analyzer. Here, crushing refers to a process that separates secondary particles without destroying primary particles, and is different from a grinding process in which primary particles are destroyed. The particle size distribution of the crushed particles is an index of the crushability and dispersibility of the secondary particles, but also reflects the bonding state between primary particles and the ease of disintegration of aggregated particles.

[0031] The crushing process may be performed using a method similar to that used for pulverization (particularly ball milling), but the size and weight of the balls and the processing time are adjusted to separate secondary particles without destroying primary particles. D50 (DLS) and D90 (DLS) measurements using dynamic light scattering were performed by adding 300 ml of pure water to 100 g of titanium oxide particles and adding 5% polycarboxylic acid-type polymer dispersant (100% ammonium salt of acrylic acid polymer) per titanium oxide weight to form a slurry. This slurry was then placed in a 1 L ball mill container (polypropylene, dimensions φ92 mm × 198 mm), and 1.2 kg of 0.5 mm diameter zirconia balls (Nikkato YTZ balls) were added. The container was then placed on the ball mill stand and rotated at 7 rpm for 72 hours to obtain the crushed titanium oxide slurry. The particle size distribution (volume-integrated particle size distribution) of the resulting titanium oxide slurry was measured using a dynamic light scattering particle size distribution analyzer. The particle size distribution analyzer, such as the ELS-Z manufactured by Otsuka Electronics, may be used. If pulverization occurs during the crushing process, the primary particle size of titanium oxide in the slurry will be reduced by the pulverization, and the BET specific surface area (m 2 / g) increases, and the titanium oxide powder obtained by drying the slurry after the crushing treatment at 100°C or less is measured using a BET specific surface area analyzer to obtain a titanium oxide powder. This can be confirmed by comparing the BET specific surface area obtained with the BET specific surface area of ​​the titanium oxide powder before the crushing treatment and finding that there is no significant difference. Here, a significant difference means that the difference in the BET specific surface area of ​​the titanium oxide powder before and after the crushing treatment exceeds the range of variation deviation during measurement. As the BET specific surface area analyzer, for example, a specific surface area analyzer (Macsorb) manufactured by Mountech may be used. Details of the measurement procedure will be explained in the Examples.

[0032] Since a small D90(DLS) / D50(DLS) value indicates that the titanium oxide particles have a uniform particle size distribution, the D90(DLS) / D50(DLS) of the titanium oxide particles in one embodiment of the present invention is preferably greater than 1.0 and not greater than 2.0, more preferably not greater than 1.8, even more preferably not greater than 1.7, and most preferably not greater than 1.6. A ratio of 2.0 or less is preferable because the particle size distribution is uniform. Alternatively, the ratio may be 1.1 or greater.

[0033] If the D90(DLS) value is small, it can be determined that the titanium oxide particles have weak cohesion and good disintegration properties. Therefore, the D90(DLS) of the titanium oxide particles in one embodiment of the present invention is preferably 500 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and most preferably 100 nm.

[0034] In one embodiment of the present invention, both the D90(DLS) and D90(SEM) values ​​are preferably 200 nm or less, more preferably 100 nm or less. In one embodiment of the present invention, the D90(DLS) / D90(SEM) value is preferably 2.2 or less, and may be 1.1 or more and 2.0 or less. A value of 2.2 or less indicates a high proportion of easily loosened secondary particles, making short circuits less likely to occur when used as a dielectric in a multilayer ceramic capacitor. The D90(DLS) / D90(SEM) value is more preferably 2.1 or less, and even more preferably 2.0 or less.

[0035] The D50 (DLS) of the titanium oxide particles in one embodiment of the present invention is preferably 10 to 150 nm, more preferably 10 to 100 nm, and even more preferably 10 to 65 nm. The smaller the D50 (DLS), the better the tendency for the particles to be dispersed in an affinity solvent.

[0036] Titanium dioxide coarse particle concentration The coarse particles in the titanium oxide particles are defined by the size of the primary particles measured by a field emission scanning electron microscope (SEM), and the content of the coarse titanium oxide particles is also measured by a field emission scanning electron microscope. Details of the measurement procedure are described in the Examples.

[0037] Coarse primary particles and agglomerated particles (secondary particles) should be distinguished by their appearance; for example, coarse particles have the appearance shown in the center of Figure 1(a). Particles composed of fine primary particles, as shown in Figure 1(b), are considered agglomerated particles and are not counted as coarse particles. If it is difficult to distinguish between coarse particles and agglomerated particles, it is advisable to increase the observation magnification to a level where discrimination is easier.

[0038] In this specification, coarse particles of titanium oxide refer to particles whose primary particle diameter measured by the above-mentioned measurement method exceeds 16 times D50 (SEM). Titanium oxide particles in one embodiment of the present invention are titanium oxide particles having a particle concentration (by number) exceeding 16 times D50 (SEM) of 20 ppm or less, more preferably 10 ppm or less, and even more preferably 5 ppm or less.

[0039] The dielectric thickness of the most advanced multilayer ceramic capacitors is said to be less than 1 μm, and it is desirable that the titanium oxide in one embodiment contain as few particles above a specific size as possible. Generally, dielectric layers within multilayer ceramic capacitors that contain coarse particles tend to have lower insulation resistance than dielectric layers that do not contain coarse particles, making them more susceptible to breakdowns (short circuits) due to poor insulation. This low concentration of coarse particles above a specific size can be a desirable characteristic for various applications of titanium oxide.

[0040] Anatase content As described in Patent Document 1, anatase type titanium oxide is preferred for photoelectrochemical activity. In one embodiment of the present invention, the anatase content (molar basis) of titanium oxide is preferably 70% or more, more preferably 75% or more, and even more preferably 95% or more. A content of 70% or more is preferred because it ensures sufficient photoelectrochemical activity. Here, the anatase content refers to the content of anatase type crystals in titanium oxide.

[0041] ·BET specific surface area The BET specific surface area (m 2 / g) is 5 to 200 m from the viewpoint of obtaining titanium oxide particles with excellent uniformity and dispersibility. 2 / g is preferable, and 10 to 150m 2 / g, more preferably 20 to 100m 2 / g. The BET specific surface area is 5m 2 / g or more, fine particles can be obtained, which is preferable. 2 If it is smaller than / g, it is preferable because a suitable BET specific surface area can be obtained.

[0042] Chlorine (Cl) content In one embodiment of the present invention, the Cl (chlorine atom) concentration of titanium oxide particles is preferably 0.20% by mass or less, as this minimizes problems in downstream processes when the titanium oxide particles are used as a raw material. For example, using titanium oxide particles with a Cl concentration exceeding 0.20% by mass as a raw material for BaTiO3 or other materials can cause flux during firing. Molten flux tends to localize, resulting in increased aggregation in the localized areas and inconsistent quality compared to other areas. Furthermore, particle aggregation can cause crystal growth in the BaTiO3 particles, resulting in abnormal particles and degrading the dielectric properties of BaTiO3. From this perspective, the Cl content in the titanium oxide particles is more preferably 0.15% by mass or less, and even more preferably 0.10% by mass or less.

[0043] Other impurity content In one embodiment of the present invention, the titanium oxide particles preferably contain 50 ppm by mass or less of Na, Al, S, Fe, Ni, Cr, Nb, and Zr, and more preferably 10 ppm by mass or less. The titanium oxide particles also preferably contain 500 ppm by mass or less of Si and C, and more preferably 100 ppm by mass or less. Such low impurity content reduces problems in downstream processes when the titanium oxide is used as a raw material. For example, when a dielectric is obtained using the titanium oxide particles as a raw material, the presence of impurities is prevented from deteriorating the dielectric properties. Furthermore, when the titanium oxide particles are used in photocatalysts or solar cells, a decrease in transparency due to coloration caused by Fe is prevented or suppressed, and a decrease in photocatalytic or solar cell function due to lattice defects caused by Al, S, etc. is prevented or suppressed.

[0044] The titanium oxide particles of the present disclosure preferably have a titanium oxide content of 99.0% by mass or more, more preferably 99.9% by mass or more, which increases the purity and reduces the influence of impurities such as those described above.

[0045] [Slurry, dispersion, composition and dielectric raw material] The slurry, dispersion, composition, and dielectric raw material according to one embodiment of the present invention contain the titanium oxide particles. A slurry is a mixture of particles in a liquid, often referring to a highly viscous (thick) fluid. A dispersion generally refers to a mixture of solid particles dispersed in a liquid, including low-concentration mixtures. A composition refers to a composition composed of multiple components. A dielectric raw material refers to a raw material for producing a dielectric. The slurry, dispersion, composition, and dielectric raw material according to one embodiment are suitable for photocatalytic applications, solar cell applications, and dielectric applications. Other uses of slurries, dispersions, and compositions containing titanium oxide particles are well known. Known methods can be used to produce slurries, dispersions, compositions, and dielectric raw materials using the titanium oxide particles of the present disclosure. The slurry, dispersion, composition, and dielectric raw material according to one embodiment of the present invention do not contain coarse particles, thereby enabling the uniformity and quality of the final product to be excellent. In particular, the absence of coarse particles prevents short circuits and contributes to improved quality when thinning the dielectric of multilayer ceramic capacitors. In the case of a multilayer ceramic capacitor, for example, it is desirable to minimize the number of coarse particles of 0.7 μm or more, and even 0.5 μm or more.

[0046] [Method of manufacturing titanium oxide particles] A method for producing titanium oxide particles according to one embodiment of the present invention will be described. In one embodiment of the present invention, a production method for titanium oxide particles is produced by introducing a raw material gas (G1) containing titanium tetrachloride and an inert gas and an oxidizing gas (G2) containing at least one of oxygen gas and water vapor and an inert gas into a reaction tube, reacting them, and then cooling them, characterized in that a purge medium outlet is provided on the inner wall of the reaction tube, the purge medium is introduced so as to swirl along the inner wall of the reaction tube, the blowing angle α of the purge medium from the inner wall of the reaction tube to a line connecting the purge medium outlet and the central axis of the reaction tube is 50° or more in a plane projected onto a cross section of the reaction tube perpendicular to the axis of the reaction tube, and the blowing flow rate (B) of the purge medium is 35 m / s or more.

[0047] By setting the blowing angle α of the purging medium from the inner wall of the reaction tube to 50° or more and the blowing flow rate (B) of the purging medium to 35 m / s or more, the purging medium can be introduced into the reaction tube while swirling along the wall of the reaction tube, which promotes the formation of a purging medium layer near the wall of the reaction tube, prevents titanium oxide powder from adhering to and remaining on the wall surface of the tube, and suppresses sintering of titanium oxide.

[0048] The method for producing particulate titanium oxide according to one embodiment of the present invention will be described in more detail below. (Source gas G1) The raw material gas G1 contains titanium tetrachloride and an inert gas. From an economical viewpoint, the supply rate of titanium tetrachloride is preferably 100 mol / hr or more, more preferably 200 mol / hr or more. From the viewpoint of suppressing sintered grain growth due to reaction heat, the supply rate is preferably 5000 mol / hr or less, more preferably 3000 mol / hr or less, and even more preferably 2000 mol / hr or less. In the raw material gas G1, the content of the inert gas per 1 mol of titanium tetrachloride is preferably 0.01 mol or more, more preferably 0.1 mol or more, and even more preferably 1 mol or more, from the viewpoint of suppressing the particle size of the resulting titanium oxide particles. Furthermore, from the viewpoint of promoting the reaction, the content is preferably 50 mol or less, more preferably 10 mol or less, and even more preferably 5 mol or less. Examples of the inert gas include nitrogen gas, helium gas, and argon gas. From an economical viewpoint, nitrogen gas is preferred. G1 is preferably heated (preheated) to 600°C or higher but lower than 1,200°C before being introduced into the reaction tube, more preferably 700°C or higher but lower than 1,200°C, and even more preferably 800°C or higher but lower than 1,200°C.

[0049] (Oxidizing gas G2) The oxidizing gas G2 contains at least one of oxygen gas and water vapor, and an inert gas. The total amount of the oxidizing gas and water vapor in the oxidizing gas G2 is preferably 2 to 150 mol, more preferably 2 to 50 mol, and even more preferably 2 to 15 mol, per mol of titanium tetrachloride in the raw material gas G1. Increasing the amount of oxidizing gas G2 increases the number of nuclei generated, making it easier to obtain ultrafine particles, and shortens the high-temperature residence time, improving the uniformity of the primary particle size. If the amount of oxidizing gas G2 exceeds 150 mol, productivity deteriorates. On the other hand, if the amount of at least one of the oxidizing gas and water vapor per mol of titanium tetrachloride is less than 2 mol, titanium oxide with many oxygen defects will be obtained, resulting in coloration. The ratio of at least one of the oxygen gas and water vapor in the oxidizing gas G2 containing an inert gas is preferably 80 to 99.5 mol%, more preferably 90 to 99.5 mol%. G2 is preferably heated (preheated) to 600°C or higher but lower than 1,200°C before being introduced into the reaction tube. The inert gas is preferably the same as that described in the section on source gas G1, and more preferably the same inert gas as that in source gas G1.

[0050] (Reaction tube) To ensure uniform flow of the raw material gas, oxidizing gas, purge medium, and reaction gas, the reaction tube may be horizontal, but a vertical reaction tube with a circular cross section is preferred. Preheated raw material gas and oxidizing gas are introduced downward from the top of the heated reaction tube through their respective supply pipes, and a purge medium is introduced from the side of the reaction tube in a direction along the reaction tube wall, allowing the purge medium to rotate along the reaction tube wall. The direction of introduction of the purge medium relative to the reaction tube is preferably such that the angle α mentioned above is 50° or greater, and the angle β described below is 60° or greater. The raw material gas, oxidizing gas, and the reaction gas mixture thereof flow downward through the reaction tube. The reaction gas is cooled by introducing a cooling medium or the like to terminate the reaction. The cooling gas introduction angle may be perpendicular to the flow of the reaction gas and toward the center of the circular cross section of the reaction tube, but this angle is not necessarily required. After cooling, the titanium oxide particles and remaining gas are discharged to the outside at the bottom of the reaction tube. The reaction gas may contain titanium oxide as a reaction product.

[0051] The raw material gas G1 and the oxidizing gas G2 are introduced into the reaction tube from its inlet (end face side) in the axial direction of the reaction tube. The ratio (S1 / S2) of the cross-sectional area (S1) of the reaction tube inlet (end face or cross section of the reaction tube) to the sum (S2) of the cross-sectional area of ​​the inlet tubes for the raw material gas G1 and the oxidizing gas G2 is preferably 1 or more and 7.0 or less. By setting the ratio within this range, the temperature in the reaction zone and the high-temperature zone time can be made more uniform. Here, the cross-sectional area (S1) of the reaction tube inlet is the cross-sectional area including the cross-sectional area (S2) of the outlet tubes for the raw material gas G1 and the oxidizing gas G2. The ratio (S1 / S2) is more preferably 1 or more and 2.5 or less, 1 or more and 2.0 or less, or 1 or more and 1.5 or less. The raw material gas G1 and the oxidizing gas G2 supplied from the inlet tubes are mixed and reacted in the reaction tube. To achieve uniform growth of titanium oxide particles, it is preferable to make the temperature in the reaction zone and the high-temperature zone time more uniform. When the source gas G1 and the oxidizing gas G2 are introduced from the end face side of the reaction tube, it is unthinkable that the cross-sectional area (S1) of the reaction tube is smaller than the sum of the cross-sectional areas of the source gas introduction tubes (S2) (S1 / S2<1). If the S1 / S2 ratio exceeds 2.5, the influence of diffusion in the direction perpendicular to the gas flow becomes large, which may result in non-uniform primary particle diameters. It is preferable, but not limited to, that the source gas G1 and the oxidizing gas G2 are introduced into the reaction tube in the gas flow direction within the reaction tube. Conventionally, it was thought that it was difficult to achieve a uniform primary particle diameter when the S1 / S2 ratio exceeded 2.5. However, according to this embodiment, titanium oxide particles with few coarse particles can be produced even under conditions where the S1 / S2 ratio exceeds 2.5 by adjusting the angle of the purge medium, etc.

[0052] (Reaction temperature and reaction time) The temperature in the reaction zone into which the raw material gas G1 and the oxidizing gas G2 are introduced is preferably 800°C or higher and lower than 1,200°C, more preferably 800°C or higher and lower than 1,100°C. A temperature of 800°C or higher in the reaction zone is preferable because the reaction proceeds sufficiently, resulting in a uniform particle size distribution of the titanium oxide particles and high crystallinity. By increasing the reaction zone temperature, the reaction is completed simultaneously with mixing, uniform nucleation is promoted, and the reaction zone can be made smaller. On the other hand, a temperature in the reaction tube of less than 1,200°C is preferable because particle growth proceeds moderately and fine particles are obtained.

[0053] The residence time of both the raw material gas G1 and the oxidizing gas G2 in the reaction zone at a high temperature of 800°C or higher but lower than 1,200°C is preferably 0.1 seconds or less, more preferably 0.03 seconds or less, and even more preferably 0.02 seconds or less. A temperature of 0.1 seconds or less is preferable because excessive particle growth does not occur. If the reaction gas is not cooled and the residence time in the high temperature zone is long, the titanium oxide particles may grow and sintering of the particles may progress.

[0054] The raw material gas G1 and oxidizing gas G2 to be introduced into the reaction tube are preferably heated (preheated) in advance to preferably from 600° C. to less than 1,200° C., more preferably from 800° C. to less than 1,200° C., and even more preferably from 800° C. to less than 1,100° C. This allows for more precise control of the temperatures of the raw material gas G1 and oxidizing gas G2 during the reaction, the reaction time, and the particle size distribution of the titanium oxide particles to be produced.

[0055] Furthermore, if there is a temperature range exceeding 500°C in the cooling zone following the reaction zone of the reaction tube, sintering of particles may occur. Therefore, the residence time in the zone of 500°C or higher is preferably 1 second or less, more preferably 0.5 seconds or less, and even more preferably 0.3 seconds or less. If it is 1 second or less, excessive particle growth does not occur, which is preferable.

[0056] (Flow rates and flow velocities of raw material gas, oxidizing gas, and reactant gas) The flow rates of the raw material gas and the oxidizing gas can be calculated from the introduction rate (flow rate) from the inlet of the reaction tube and the cross-sectional area of ​​the reaction tube. The flow rate (m 3 The flow rate (A) (m / s) of the reaction gas flow in the reaction tube can be calculated from the flow rate (m / s) of the reaction gas flow after the reaction of the raw material gas G1 and the oxidizing gas G2, assuming that the raw material gas and the oxidizing gas react immediately. 3 / s) and the cross-sectional area of ​​the reaction tube (m 2 ) can also be calculated from

[0057] The flow velocity (A) (m / s) of the reaction gas flow is preferably 1 m / s or more, more preferably 10 m / s or more, and even more preferably 20 m / s or more. If the flow velocity is less than 1 m / s, the residence time of the reaction gas flow becomes long, which may promote over-sintering and coarsening of the titanium oxide.

[0058] ( purge medium) As the purging medium, methods of introducing gases such as air, nitrogen gas, or carbon monoxide, or methods of spraying water, etc., are also suitably employed. The purging medium is preferably at a temperature of 0°C to 100°C, more preferably 10°C to 90°C. It is also preferable that the temperature does not exceed the temperature of the cooling medium described below. A temperature within this range does not adversely affect the cooling effect of the cooling medium.

[0059] (Purge method) If the generated titanium oxide particles adhere to and remain on the inner wall of the reaction tube, they will coarsen due to sintered grain growth. If these particles detach and become mixed in, this can cause a non-uniform particle size distribution. Therefore, by providing a purge medium outlet on the inner wall or upper part of the reaction tube and introducing the purge medium while swirling it along the reaction tube wall, the formation of a purge medium layer near the reaction tube wall is promoted, preventing the titanium oxide particles from adhering to and remaining on the tube wall surface, thereby suppressing the sintering of the titanium oxide particles. Introducing the purge medium continuously or intermittently is expected to be effective in preventing the adhesion of titanium oxide. It is also preferable to provide multiple purge holes. The shape of the purge medium outlet can be a single hole or a slit.

[0060] ( Purge medium blowout conditions (direction, flow rate, etc.) The present invention is characterized in that a purging medium outlet is provided on the inner wall of the reaction tube, and the purging medium is introduced so as to swirl along the inner wall of the reaction tube. By swirling the purging medium near the inner wall of the reaction tube, it is expected that adhesion of titanium oxide particles to the wall surface of the reaction tube can be prevented.

[0061] If the direction in which the purge medium is blown out is not close to the inner wall of the reaction tube relative to the reaction gas flow, the swirling flow will not be maintained, and the effective effect of preventing the deposition of titanium oxide on the reaction tube wall surface will not be expected.

[0062] In the present invention, the blowing direction of the purge medium is such that the angle α (see FIG. 3 ) of the purge medium (axial direction of the purge medium outlet) relative to the line connecting the purge medium outlet and the central axis of the reaction tube is 50° or more in a plane projected onto the cross section of the reaction tube perpendicular to the flow direction of the reaction gas (axial direction of the reaction tube). Here, the angle α is the angle at which the outlet is set relative to the reaction tube in the plane projected onto the cross section of the reaction tube, and corresponds to the angle at which the purge medium is blown out from the outlet. Since the purge medium merges with the reaction gas flow after being blown out from the outlet, the flow direction within the cross section of the reaction tube may change, but the angle α is determined by the setting direction of the purge medium outlet. By setting the angle α to 50° or more, the purge medium can be rotated close to the inner wall of the reaction tube, which preferably prevents titanium oxide from adhering to the wall surface of the reaction tube. The angle α is preferably 60° or more. The angle α is generally less than 90°.

[0063] In addition, in the projection plane of the vertical cross section of the reaction tube including the axial direction of the reaction tube (the flow direction of the reaction gas), the direction in which the purge medium is blown into the reaction tube may be perpendicular to the axial line of the reaction tube (the flow direction of the reaction gas) (horizontal direction in the case of a vertical reaction tube). Although the blowing direction perpendicular to the axial line of the reaction tube (horizontal direction in the case of a vertical reaction tube) is preferred, the blowing direction may be inclined from the blowing direction perpendicular to the axial line of the reaction tube toward the flow direction of the reaction gas. Although blowing in the direction opposite to the flow direction of the reaction gas is not impossible, a backflow of the reaction gas may occur. In the projection plane of the vertical cross section of the reaction tube, the blowing angle β of the purge medium with respect to the axial direction of the reaction tube (see FIG. 4) is preferably 60° or more (an inclination angle of 30° or less with respect to the cross section of the reaction tube), with the side of the axial direction of the reaction tube in the flow direction of the reaction gas being 0°, more preferably 70° or more, and may further be 80° or more. In addition, the blowing angle β is particularly preferably 90° or less. Such an angle is preferable because it is possible to achieve an excellent effect of preventing titanium oxide from adhering to the wall surface of the reaction tube.

[0064] The location of the outlet for the purging medium for the reaction tube may be one, preferably two or more, more preferably three or more, or even four or more, locations in the cross-section of the reaction tube, as long as the purging medium can rotate along the inner wall of the reaction tube. Generally, the number of outlets per circumference of the cross-section of the reaction tube may be smaller as the angle α increases and as the flow rate of the purging medium increases. The locations of the outlets for the purging medium may be one, preferably two or more, or even three or more locations in the axial direction of the reaction tube, as projected onto the longitudinal cross-section of the reaction tube. The outlets for the purging medium are preferably located at multiple locations within one or more of the same cross-sections in the axial direction, as projected onto the longitudinal cross-section of the reaction tube. However, the outlets may be arranged spirally on the inner wall of the reaction tube, and do not necessarily have to be located at multiple locations within the same cross-section.

[0065] The outlet for the purge medium may be installed in the reaction zone from the vicinity of the raw material gas inlet to just before the cooling zone, and preferably further in the cooling zone, so that a swirling flow of the purge medium is formed along the inner wall of the reaction tube in these zones.

[0066] The blowing flow velocity (B) of the purge medium is 35 m / s or more, preferably 50 m / s or more, and more preferably 60 m / s or more, in order to prevent the produced titanium oxide particles from adhering to the reaction tube wall. If it is 35 m / s or more, the swirl on the tube wall surface will be sufficient, and a better effect of preventing titanium oxide from adhering to the tube wall surface can be expected. Here, the blowing flow velocity (B) of the purge medium is determined by the purge gas flow rate (m 3 / s) divided by the cross-sectional area of ​​the outlet (unit: m / s).

[0067] When the flow rate (A) of the reaction gas formed from the raw material gas and the oxidizing gas in the reaction tube is A and the blowing flow rate (B) of the purge medium is B, the ratio B / A is preferably 0.5 or more, more preferably 1.0 or more, even more preferably 3.0 or more, and most preferably 5.0 or more. If the blowing flow rate (B) of the purge medium blown in the swirling direction is less than 0.5 relative to the flow rate (A) of the reaction gas, which is a vertical flow, a sufficient vector in the swirling direction cannot be obtained, making it difficult for the purge medium to swirl and obtaining uniform particles.

[0068] ( cooling medium) As the cooling medium, a method of introducing a gas such as air, nitrogen gas, or carbon monoxide, or a method of spraying water, etc., can also be suitably adopted. The cooling medium is preferably at a temperature of 0°C to 100°C, more preferably 10°C to 90°C. A temperature within this range provides a high cooling effect.

[0069] Coolant blowout conditions (direction, flow rate, etc.) In the present invention, a cooling medium outlet is provided on the inner wall of the reaction tube, and the cooling medium is blown out and mixed with the reaction gas, thereby cooling the reaction gas.

[0070] If the direction in which the cooling medium is blown out is not close to the center of the reaction tube relative to the reaction gas flow, the gases will not mix and a sufficient cooling effect cannot be expected.

[0071] In the present invention, the cooling medium is blown out at an angle γ (see FIG. 3 ) of 0° or more and less than 50° relative to a line connecting the cooling medium outlet and the central axis of the reaction tube, as projected onto the cross section of the reaction tube perpendicular to the flow direction of the reaction gas (the axial direction of the reaction tube). Here, the angle γ is the angle at which the outlet is set relative to the reaction tube in the projection plane onto the cross section of the reaction tube, and coincides with the angle at which the cooling medium is blown out from the outlet. Since the cooling medium merges with the reaction gas flow after being blown out from the outlet, the flow direction within the cross section of the reaction tube may change, but the angle γ is determined by the setting direction of the cooling medium outlet. By setting the angle γ to 0° or more and less than 50°, the cooling medium can flow near the center of the reaction tube, where it is thoroughly mixed with the reaction gas, thereby achieving a favorable cooling effect. The angle γ is preferably less than 30°.

[0072] In addition, in a projection plane of the reaction tube onto a vertical cross section including the axial direction of the reaction tube (flow direction of the reaction gas), the direction in which the cooling medium is blown into the reaction tube may be perpendicular to the axis of the reaction tube (flow direction of the reaction gas) (horizontal direction in the case of a vertical reaction tube). This blowing direction perpendicular to the axis of the reaction tube (horizontal direction in the case of a vertical reaction tube) is preferred, but the blowing direction may be inclined from the blowing direction perpendicular to the axis of the reaction tube toward the flow direction of the reaction gas. Although it is not impossible to blow in the direction opposite to the flow direction of the reaction gas, it is not desirable because a backflow of the reaction gas may occur. In a projection plane of the reaction tube onto a vertical cross section, cooling medium The angle δ (see FIG. 4) at which the gas is blown out is, for example, preferably 60° or more (an inclination angle of 30° or less with respect to the cross section of the reaction tube), with the side of the reaction gas flow direction in the axial direction of the reaction tube being 0°, more preferably 70° or more, and may be further 80° or more. In particular, the blowing angle δ is preferably 90° or less. Such an angle is preferred because it provides an excellent cooling effect.

[0073] The region from the raw material gas inlet to the cooling medium outlet in the reaction tube is called the reaction region, and the region from the cooling medium outlet to the outlet side is called the cooling region. When there are multiple cooling medium outlets, the region from the raw material gas inlet to the first cooling medium outlet in the reaction tube is called the reaction region, and the region from the first cooling medium outlet to the outlet side is called the cooling region.

[0074] The cooling medium outlets may be installed at one or two or more locations in the cross section of the reaction tube as long as the cooling medium is mixed with the reaction gas. The cooling medium outlets may be installed at one location, preferably two or more locations, or even three or more locations in the axial direction of the reaction tube in the projected cross section of the reaction tube. The cooling medium outlets are preferably installed at multiple locations within one or more identical cross sections in the axial direction in the projected cross section of the reaction tube.

[0075] Schematic diagram showing the purging method 2 to 4 are schematic diagrams showing preferred embodiments of the first step (reaction step). FIG. 2 is a longitudinal cross-sectional view of the reaction tube 1 (a longitudinal cross-sectional view including the axis of the reaction tube). First, a raw material gas G1 and an oxidizing gas G2 are introduced into the reaction tube 1. It is preferable to preheat the reaction zone 1' so that the temperature in the reaction zone 1' after the introduction of the raw material gas G1 and the oxidizing gas G2 into the reaction tube 1 is within a predetermined temperature range. The reaction gas (based on the raw material gas G1 and the oxidizing gas G2) is retained in the reaction tube 1 for a predetermined time. A purge medium outlet 5 is provided on the wall of the reaction tube 1, and a purge medium is introduced continuously or intermittently. A cooling medium is then blown out from the cooling medium outlet 3 to rapidly cool the reaction gas containing the raw material gas and the oxidizing gas. The reaction product, crude titanium oxide particles, are then discharged from the cooling zone 2 together with the cooling medium. This allows for the efficient production of crude titanium oxide particles. The resulting crude titanium oxide particles are sent to the second step (dechlorination step).

[0076] 3 is a cross-sectional view (a cross-sectional view perpendicular to the axis of the reaction tube) of the reaction tube 1 as viewed from above (the side where the raw material gas G1 and the oxidizing gas G2 are introduced), and arrows indicate the purge medium P introduced from the purge medium outlet 5 of the reaction tube 1 and the cooling medium Q introduced from the cooling medium outlet 3. The blowing angle of the purge medium is α, and the blowing angle of the cooling medium is γ.

[0077] 4 is a longitudinal cross-sectional view of the reaction tube 1 as seen from the side (a longitudinal cross-sectional view including the axis of the reaction tube), in which arrows indicate the purging medium P introduced from the purging medium outlet 5 of the reaction tube 1 and the cooling medium Q introduced from the cooling medium outlet 3. The blowing angle of the purging medium is β, and the blowing angle of the cooling medium is δ.

[0078] The swirling flow of the purge medium swirls near the wall of the reaction tube under specific conditions, titanium This can effectively prevent particles from adhering to the pipe wall, remaining there, and growing. It is also preferable to form a swirling flow of the purge medium not only in the reaction zone but also in the cooling zone.

[0079] As described above, the reactor is typically vertical, with the source gas G1, oxidizing gas G2, and reactant gas R flowing from top to bottom, but if the reactor is of a different type, the method for determining the swirl angle described above will be modified accordingly. The introduction direction of the purge medium P does not need to be the same as above, but the swirl angle β of the purge medium P relative to the flow of the reactant gas R should be the same as above.

[0080] (Dechlorination treatment) The crude titanium oxide produced as described above is preferably subjected to a dechlorination treatment. Dechlorination of titanium oxide by heating is preferably carried out by heating the titanium oxide particles to a temperature of 200°C to 550°C while contacting them with steam so that the mass ratio of water to titanium oxide (= mass of steam / mass of titanium oxide; the same applies below) is 0.01 or greater. More preferably, the mass ratio of water to titanium oxide is 0.04 or greater, and the heating temperature is 250°C to 450°C. Heating temperatures above 550°C promote sintering of the titanium oxide particles, resulting in non-uniform primary particle diameters. Heating temperatures below 200°C drastically reduce the efficiency of dechlorination. To achieve dechlorination while suppressing particle growth, it is preferable to also control the mass ratio of water to titanium oxide. A mass ratio of water to titanium oxide of 0.01 or greater is effective in suppressing particle growth, and is preferably 0.01 to 1, more preferably 0.05 to 2, and even more preferably 0.2 to 1.8.

[0081] The water vapor to be contacted with titanium oxide is preferably mixed with a gas, such as air, that efficiently transfers chlorine separated from titanium oxide out of the system. When air is used, the water vapor content in the air is preferably 0.1% by volume or more, more preferably 5% by volume or more, and particularly preferably 10% by volume or more and 80% by volume or less. The water vapor-containing air is preferably heated to a temperature of 200°C to 1,000°C, more preferably 450°C to 850°C.

[0082] In the dechlorination of titanium oxide, reducing the pressure inside the vessel used for dechlorination is also an effective method for transferring the chlorine removed from the titanium oxide to the outside of the system. The degree of reduced pressure inside the vessel is preferably 0.5 kPa or more, and more preferably 0.5 kPa to 3.5 kPa. The degree of reduced pressure here refers to the pressure difference between the pressure inside the reduced pressure vessel and atmospheric pressure.

[0083] The titanium oxide particles according to this embodiment contain almost no chlorine inside the particles, and most of the chlorine is on the particle surface, which can be removed by washing with water, etc. Therefore, it is possible to reduce the chlorine content by a wet method. Examples of wet dechlorination methods include suspending the titanium oxide particles in pure water and separating the chlorine that has migrated to the liquid phase outside the system using an ultrafiltration membrane, a reverse osmosis membrane, a filter press, etc.

[0084] Anatase content In the reaction of titanium oxide, the higher the temperature in the reaction process, the lower the anatase content and the more likely it is that rutile transition will occur, but the anatase content can be adjusted by adjusting the amount of heat received by the titanium oxide by introducing a cooling medium after the reaction. Also, if the temperature in the reaction process is too low, the reaction will not be completed, leading to a decrease in the crystallinity of the resulting titanium oxide.

[0085] ·Impurity concentration The fewer impurities contained in the raw material titanium tetrachloride, the fewer impurities there will be in the titanium oxide, so it is preferable to use high-purity titanium tetrachloride with few impurities.

[0086] ·BET specific surface area In the reaction of titanium oxide, the higher the temperature during the reaction process, the more easily titanium oxide particles sinter, resulting in a decrease in BET specific surface area. Methods for improving the BET specific surface area include suppressing sintering by introducing a diluent gas into the reaction site or by cooling. [Example]

[0087] Examples and comparative examples will be specifically described below, but the present invention is not limited to these in any way.

[0088] The physical properties of the titanium oxide particles were measured as follows. (1) Anatase content The content of anatase crystals in titanium oxide particles (anatase content) was measured by powder X-ray diffraction. Specifically, X-ray diffraction measurements were performed on dried titanium oxide particles using a PANalytical X'pertPRO measuring instrument, a copper target, and Cu-Kα radiation at a tube voltage of 45 kV, a tube current of 40 mA, a measurement range of 2θ = 10 to 80 deg, a sampling width of 0.0167 deg, and a scanning speed of 0.0192 deg / s. The peak heights of the maximum peaks corresponding to anatase crystals (Ha), brookite crystals (Hb), and rutile crystals (Hr) were determined, and the content of anatase crystals in titanium oxide particles (anatase content) was calculated using the following formula: Anatase content (%) = {Ha / (Ha+Hb+Hr)} x 100

[0089] (2) BET specific surface area BET specific surface area of ​​titanium oxide particles (m 2 / g) was measured using a Mountec specific surface area measuring device (Macsorb). Nitrogen was used as the measurement gas.

[0090] (3) Chlorine (Cl) content The Cl content in the titanium oxide particles was measured by silver nitrate potentiometric titration. That is, the titanium oxide particles were weighed. Next, a silver nitrate solution was added dropwise to the solution of the titanium oxide particles, and the potential difference was measured to determine the mass of chlorine atoms in the solution, and the chlorine content (mass%) was calculated.

[0091] (4) D10 (SEM), D50 (SEM), D90 (SEM), D99 (SEM) of primary particles of titanium oxide particles by scanning electron microscope 1 g of sample was placed in 100 ml of ethanol and ultrasonically irradiated (30 W, 5 min). Approximately 0.05 g of the dispersion was dispensed using a Pasteur pipette and dropped onto aluminum foil. After air-drying in a laboratory atmosphere, the aluminum foil was fixed to a SEM sample stage and analyzed using a field-emission scanning electron microscope (Hitachi High-Tech Fielding S-5500). The SEM measurement conditions were an accelerating voltage of 2.0 kV. Images were taken so that 200–300 primary particles were counted per field of view. The primary particle diameter (circle-equivalent diameter, specifically, Heywood diameter) of each of the approximately 200–300 particles in the image was calculated using image analysis software. The image analysis software used was Particle Analysis Ver. 3 (Sumitomo Metal Technology Co., Ltd.) or Mac-View Ver. 3 (Mountec Co., Ltd.). The same procedure was repeated for other fields of view of the same sample until the total number of particles used to calculate the primary particle size exceeded 1,000. In the obtained cumulative particle size distribution based on number, the particle sizes D10(SEM), D50(SEM), D90(SEM), and D99(SEM) were calculated when the cumulative total values ​​of the reference amounts from the smaller particle sizes were 10%, 50%, 90%, and 99%, respectively, of the total cumulative value.

[0092] (5) D50 (LD) of titanium dioxide particles by laser diffraction and scattering method 、 D90(LD) A 100 ml tall beaker was charged with 0.05 g of titanium oxide particles, 50 ml of pure water, and 100 μl of 10% by mass sodium hexametaphosphate aqueous solution to prepare a slurry. The slurry in the tall beaker was stirred using an 8 mm diameter Teflon rod while being irradiated with ultrasound (50 kHz, 100 W) for 3 minutes. Stirring was only performed for 1 minute after the start of ultrasonic irradiation. The ultrasonic bath was box-shaped with internal dimensions of 230 mm × 200 mm × 152 mm, and the water volume was 450 ml. The tall beaker was positioned near the center of the ultrasonic bath during ultrasonic irradiation. The slurry was subjected to measurement of particle size distribution (volume-integrated particle size distribution) using a Microtrac laser diffraction particle size distribution analyzer (Microtrac MT3300EXII). D50 (LD) and D90 (LD) were calculated.

[0093] (6) D50 of crushed titanium dioxide particles by dynamic light scattering (DLS)、 D90(DLS) 300 ml of pure water was added to 100 g of titanium oxide particles, and 5% polycarboxylic acid per titanium oxide weight was added as a dispersant to prepare a slurry. This was placed in a ball mill container, and 1.2 kg of zirconia balls 0.5 mm in diameter were added. The container was then placed on the base of the ball mill and rotated at 7 rpm for 72 hours to obtain a crushed titanium oxide slurry. The volumetric particle size distribution was measured using a dynamic light scattering particle size distribution analyzer (ELS-Z, manufactured by Otsuka Electronics).

[0094] (7) Coarse particle concentration Using a field-emission scanning electron microscope, images were taken with a primary particle count of, for example, 8,000–12,000 particles per field of view. The presence or absence of large particles above a specific size (e.g., 0.20 μm or larger, 0.30 μm or larger) taking into account D50 (SEM) was confirmed using the particle measurement tool in the image analysis software. If particles above a specific size were present, their primary particle diameter (circular equivalent diameter, specifically, Heywood diameter) was determined using the image analysis software. The same procedure was repeated for other fields of the same sample, until a field corresponding to at least 1 million particles was observed. The coarse particle content (particle concentration) was determined by dividing the number of coarse particles above the specific size listed in Table 2 by the total number of particles observed. The total number of particles observed was calculated from the number of primary particles per field of view and the number of fields of view observed.

[0095] (8) Other impurity content The method for measuring impurities is as follows. Fe: Atomic absorption spectrometry (Hitachi High-Technologies Z-2300 atomic absorption spectrophotometer) Al, Si: X-ray fluorescence analysis (XRF) (Rigaku Simultex 10) C, S: High-frequency induction furnace combustion and infrared absorption method Na, Ni, Cr, Nb, Zr: Inductively coupled plasma-mass spectrometry

[0096] Example 1 <1st process> Using a vertical reactor tube with a circular cross section, 1053 mol / hr of gaseous titanium tetrachloride (titanium tetrachloride purity ≥ 99.99 mass%) was diluted with 223 mol / hr of nitrogen gas to obtain diluted titanium tetrachloride gas (G1). The diluted titanium tetrachloride gas (G1) was preheated to 950°C and mixed with 982 mol / hr of oxygen and 1786 molNm 3 An oxidizing gas (G2) obtained by mixing 22 mol / hr of nitrogen gas with 22 mol / hr of steam was preheated to 870°C, and these gases (G1 and G2) were introduced into the top of a reactor in which the ratio (S1 / S2) of the cross-sectional area of ​​the reaction tube (S1) to the sum (S2) of the cross-sectional areas of the inlet tubes for the titanium tetrachloride-containing gas (G1) and the oxidizing gas (G2) was 6.7. Purge air and cooling air were introduced into the reaction tube from the side so that the high-temperature residence time at 800°C or higher but lower than 1,200°C was 0.05 seconds, and crude titanium oxide particles were collected at the bottom of the reaction tube using a polytetrafluoroethylene bag filter. Other conditions are also shown in Table 1. The flow rate of the reaction gas flow (m / s) was determined by the cross-sectional area (m 2 ) and the flow rate of the reaction gas flow after the raw material gas and the oxidizing gas react (m 3 / s).

[0097] <Second process> The obtained crude titanium oxide particles were passed through a cylindrical rotary heating furnace and dechlorinated at a steam to crude titanium oxide mass ratio of 0.06 (mass of steam / mass of crude titanium oxide particles) at a heating temperature of 450°C to obtain titanium oxide particles, and various physical properties were measured. The measurement results are shown in Table 2.

[0098] Examples 2 to 5 The first step was carried out under various conditions. The conditions are shown in Table 1. The second step was carried out in the same manner as in Example 1. The measurement results are shown in Table 2.

[0099] Comparative Example 1 Except for the purge medium blowing angle α, the first and second steps were carried out in the same manner as in Example 1. The measurement results are shown in Table 2.

[0100] Comparative Example 2 Except for the blowout flow velocity (B) of the purge medium, the first step and the second step were carried out in the same manner as in Example 2. The measurement results are shown in Table 2.

[0101] Comparative Example 3 The first and second steps were carried out in the same manner as in Example 4, except for the preheating temperature of the raw material gas G1, the flow rate of the oxidizing gas G2, and the blowout flow rate (B) of the purge medium. The measurement results are shown in Table 2.

[0102] Comparative Example 4 (liquid phase method) An aqueous solution of titanium tetrachloride with a concentration of 0.5 mol / L was heated to reflux at 100°C for 3 hours for hydrolysis, yielding ultrafine titanium oxide sol. The resulting titanium oxide sol was washed repeatedly with pure water and then dried in a hot air circulation dryer at 120°C for 12 hours. Various physical properties of the resulting titanium oxide particles were measured. The results are shown in Table 2.

[0103] [Table 1]

[0104] [Table 2]

[0105] [Table 3]

[0106] Referring to Tables 1 to 3, although no clear difference is observed in the particle size distribution shown in Table 2 between the vapor-phase process titanium oxide particles in Examples 1 to 5 and Comparative Examples 1 to 3, the particle concentration exceeding 16 times D50 (SEM) is low in Examples 1 to 5, which suggests that the introduction of a purging medium onto the reaction tube wall at a specific angle or greater is effective in reducing coarse particles. Furthermore, although no coarse particles exceeding a specific size were observed in the liquid-phase process titanium oxide particles of Comparative Example 4, their large D50 (LD) and D90 (LD) suggest that their dispersibility in the dispersion medium is low.

[0107] Thus, the present invention provides titanium oxide particles produced by a vapor phase method, which have fewer coarse particles and are more uniform and dispersible than conventional titanium oxide particles having a comparable BET specific surface area, and a method for producing the same. The titanium oxide particles of the present invention are suitable for photocatalytic applications, solar cell applications, dielectric applications, etc., and, as a powder, do not require a crushing process or can be produced with extremely light equipment, making them of great practical value industrially. [Industrial Applicability]

[0108] The titanium oxide particles of the present invention are suitable for photocatalytic applications, solar cell applications, dielectric applications, etc., and as a powder, they do not require a crushing process or can be produced with extremely light equipment, making them of great practical value industrially. [Explanation of symbols]

[0109] 1 reaction tube 1' reaction region 2 Cooling area 3 Coolant outlet 4 Reaction tube center 5 Purge medium outlet G1 raw gas G2 Oxidizing gas P Purging medium Q Cooling medium R Reaction gas flow direction α Purge medium blowing angle (in a plane perpendicular to the reaction gas flow direction) β Purge medium blowing angle (in the plane including the reaction gas flow direction) γ Coolant blowing angle (in a plane perpendicular to the reaction gas flow direction) δ Coolant blow-out angle (within the plane including the reaction gas flow direction)

Claims

1. The titanium oxide particles have a D90(LD) / D50(LD) ratio of more than 1.0 and not more than 2.0 as measured by laser diffraction / scattering analysis, and the concentration (by number) of coarse particles having a primary particle diameter exceeding 16 times the D50(SEM) of primary particles observed for 1 million or more particles with a field emission scanning electron microscope is 20 ppm or less, D90(LD) is 3000 nm or less, D50(LD) is 1000 nm or less, and the BET specific surface area (m ２ / g) is 5 to 200 m ２ / g of titanium oxide particles.

2. 2. The titanium oxide particles according to claim 1, wherein the D90(SEM) / D50(SEM) ratio of the primary particles of the titanium oxide particles observed with a field emission scanning electron microscope is greater than 1.0 and not greater than 2.

0.

3. 3. The titanium oxide particles according to claim 1, wherein the ratio of [D90(SEM)-D10(SEM)] / D50(SEM) of primary particles of the titanium oxide particles observed with a field emission scanning electron microscope is 0.82 or less.

4. 3. The titanium oxide particles according to claim 1, wherein the D99(SEM) / D50(SEM) ratio of the primary particles of the titanium oxide particles observed with a field emission scanning electron microscope is greater than 1.0 and not greater than 2.

0.

5. 3. The titanium oxide particles according to claim 1, wherein the D90(DLS) / D50(DLS) ratio of the titanium oxide particles measured by dynamic light scattering is greater than 1.0 and not greater than 2.

0.

6. 3. The titanium oxide particles according to claim 1, wherein D90(DLS) / D90(SEM), which is the ratio of D90(DLS) of the titanium oxide particles measured by dynamic light scattering to D90(SEM) of the primary particles of the titanium oxide particles observed with a field emission scanning electron microscope, is 2.2 or less.

7. 3. The titanium oxide particles according to claim 1, wherein the D90 (DLS) of the titanium oxide particles measured by dynamic light scattering and the D90 (SEM) of the primary particles of the titanium oxide particles observed with a field emission scanning electron microscope are 200 nm or less, and the D50 (SEM) is 10 to 150 nm.

8. 3. The titanium oxide particles according to claim 1, having an anatase content of 70% or more.

9. 3. The titanium oxide particles according to claim 1, wherein the Cl content of the titanium oxide particles measured by silver nitrate potentiometric titration is 0.2% by mass or less.

10. 3. The titanium oxide particles according to claim 1, wherein the contents of Na, Al, S, Fe, Ni, Cr, Nb, and Zr are each 10 ppm by mass or less, and the contents of Si and C are each 500 ppm by mass or less.

11. A slurry comprising the titanium oxide particles according to claim 1 or 2.

12. A dispersion comprising the titanium oxide particles according to claim 1 or 2.

13. A composition comprising the titanium oxide particles according to claim 1 or 2.

14. A dielectric material comprising the titanium oxide particles according to claim 1 or 2.

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