Titanium oxide particles and method for producing the same

Abstract

To provide titanium oxide particles and a method for producing the same, the titanium oxide particles having a high anatase content, reduced coarse particles, and superior uniformity and dispersibility.SOLUTION: A method for producing titanium oxide particles is provided, comprising: a reaction step in which 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 as well as an inert gas, are introduced into a reaction tube to generate a reaction gas; and a cooling step in which the reaction gas is cooled by introducing a cooling gas, thereby yielding titanium oxide particles, in which the ratio FG1T / FG1, which is the flow rate (FG1T) of titanium tetrachloride in G1 to the flow rate (FG1) of G1 in the reaction step, is 0.01 or more and less than 0.4, and the ratio of a TiO2 mass (kg) after introduction of the cooling gas in the cooling step to a total gas volume (m3), (TiO2 mass) / (total gas volume), is more than 0 and 0.07 kg / m3 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to titanium dioxide particles and a method for producing the same. [Background technology]

[0002] Titanium dioxide has an extremely wide range of industrial applications, including cosmetics, UV shielding materials, and additives to silicone rubber. In recent years, its uses have expanded to include photocatalysts, solar cells, dielectric materials, and electrode materials for lithium-ion batteries. Although the Japanese Industrial Standards (JIS) refer to it as titanium dioxide, the general term titanium dioxide (TiO2) is widely used, so in this disclosure, titanium dioxide (TiO2) will be abbreviated as titanium dioxide.

[0003] Recently, titanium dioxide has attracted particular attention as a raw material for high-performance dielectrics, such as BaTiO3. BaTiO3 is obtained by the following reaction under heating. BaCO3 + TiO2 → BaTiO3 + CO2

[0004] The above reaction is a solid-phase reaction in which BaCO3 first decomposes at high temperature to produce BaO, and then BaO diffuses and dissolves in the TiO2 particles to become BaTiO3. Therefore, the size of the BaTiO3 particles is governed by the size of the TiO2 particles. In recent years, with the miniaturization of multilayer ceramic capacitors, thinning the dielectric layer has become a challenge, and for this purpose, the fineness and homogenization of BaTiO3 particles are essential. Furthermore, if BaTiO3 particles larger than the dielectric layer thickness are present, a short circuit will occur within the multilayer ceramic capacitor, leading to equipment failure. Therefore, the fineness and homogenization of TiO2, the raw material for BaTiO3, are necessary, and it is preferable that coarse TiO2 particles are not included. Similarly, in other applications, the fineness and homogenization of titanium oxide particles are required, and it is preferable that coarse particles are not included.

[0005] There are two main methods for producing titanium dioxide: the liquid-phase method, which involves hydrolyzing titanium tetrachloride or titanium sulfate, and the gas-phase method, which involves reacting titanium tetrachloride with oxygen or water vapor at high temperatures.

[0006] The liquid-phase method has the advantage of producing titanium dioxide under relatively mild conditions and easily obtaining fine primary particles. However, since the titanium dioxide is obtained in the form of a sol or slurry, its applications are limited when used in this state. To use the sol or slurry as titanium dioxide particles, it needs to be dried, and after drying, aggregation generally becomes severe. Such severely aggregated titanium dioxide particles have the problem of having an uneven particle size distribution. In addition, when the dried titanium dioxide particles are dispersed in a solvent, they have poor dispersibility. Poor dispersibility means that when mixing the raw materials for the production of BaTiO3, the titanium dioxide particles and other raw materials do not mix sufficiently, resulting in uneven distribution of raw material components, causing uneven growth during the reaction, and leading to variations in quality.

[0007] On the other hand, with the gas-phase method, the primary particle size of the titanium dioxide produced can be adjusted by controlling manufacturing conditions such as temperature. Furthermore, since the gas-phase method does not use a solvent, the titanium dioxide is obtained as a powder, and the problems associated with the liquid-phase method are less likely to occur. Additionally, because the gas-phase method involves a relatively higher reaction temperature than the liquid-phase method, the resulting titanium dioxide has the advantage of higher crystallinity.

[0008] However, in the gas phase method, the reaction takes place at a higher temperature than in the liquid phase method. Therefore, if the temperature in the reaction tube or the cooling tube after the introduction of the cooling gas is too high, or if the residence time of the titanium oxide particles is too long, the titanium oxide particles will receive a large amount of heat. This can lead to excessive sintering of the titanium oxide particles, making it difficult to obtain fine titanium oxide particles and resulting in an uneven particle size distribution. If the temperature of the reaction zone is lowered too much to avoid sintering of titanium oxide particles, nucleation of titanium oxide will not occur sufficiently, making it difficult to obtain fine particles or only titanium oxide with low crystallinity can be obtained. On the other hand, by immediately cooling the reaction gas with a cooling gas, sintering of titanium oxide particles can be suppressed, and fine titanium oxide particles can be obtained. If cooling is not performed immediately or is uneven, uneven sintering of particles occurs, making it difficult to obtain uniform titanium oxide fine particles.

[0009] Patent Document 1 describes a method for obtaining uniform titanium oxide particles by a gas-phase method using titanium halogen gas and an oxidizing gas. and A method for producing titanium dioxide particles, characterized by reacting them under specific conditions, is described.

[0010] Furthermore, Patent Document 2 describes a method for producing titanium oxide particles, characterized by reacting TiCl4 vapor with hydrogen and oxygen, with the aim of obtaining uniform titanium oxide particles without coarse particles by a gas-phase method, and having a small amount of metal oxide particles with a diameter larger than 45 μm. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] International Publication No. 2022 / 244620 [Patent Document 2] Patent No. 4445972 specification [Overview of the project] [Problems that the invention aims to solve]

[0012] As described above, titanium oxide particles with excellent uniformity and dispersibility are desired, and the gas-phase method offers the advantage of superior uniformity and dispersibility compared to titanium oxide particles obtained by the liquid-phase method.

[0013] According to Patent Document 1, titanium oxide particles with fewer coarse particles can be produced. In Patent Document 1, the amount of coarse particles exceeding 16 times the D50 is quantified using a scanning electron microscope. However, this quantification method involves capturing and evaluating images with 8,000 to 12,000 primary particles per field of view, so coarse particles at the tens of micrometers level could not be evaluated. Furthermore, because particle size is determined by image analysis, the amount of particles coarsened by aggregation (secondary particles) could not be evaluated.

[0014] Patent document 2 describes a method for synthesizing titanium oxide particles with a low proportion of coarse particles having a particle size of several tens of micrometers. However, it uses a mixed gas of hydrogen and oxygen as the oxidizing gas, and because the combustion of hydrogen and the oxidation of TiCl4 occur simultaneously, the reaction temperature tends to be high and the anatase content tends to be low.

[0015] This disclosure provides titanium dioxide particles with a high anatase content, few coarse particles, and excellent uniformity and dispersibility, as well as a method for producing the same. [Means for solving the problem]

[0016] The present inventors have found that the above problems can be solved by setting the flow rate ratio of the gases in the reaction step and the total amount of gas relative to the mass of TiO2 in the cooling step within a predetermined range in a method for producing titanium oxide particles, which includes reacting a raw material gas containing titanium tetrachloride and an inert gas with an oxidizing gas containing at least one of oxygen gas and water vapor and an inert gas, and cooling the reaction gas with a cooling gas, and have completed the present invention.

[0017] This disclosure includes the following aspects: [Aspect 1] A reaction step of 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 to generate a reaction gas, A cooling step of introducing a cooling gas to cool the reaction gas to obtain titanium oxide particles A method for producing titanium oxide particles, comprising: In the reaction step, the ratio F G1T , G1 of the flow rate (F G1T ) of titanium tetrachloride in G1 to the flow rate (F G1T ) of G1 is 0.01 or more and less than 0.4, and the ratio (TiO2 mass) / (total gas amount) of the TiO2 mass (kg) after introducing the cooling gas to the total gas amount (m 3 ) in the cooling step is more than 0 and 0.07 kg / m 3 or less. A method for producing titanium oxide particles. [Aspect 2] The method for producing titanium oxide particles according to Aspect 1, wherein the ratio of the flow rate (F G1T ) of titanium tetrachloride / (the flow rate (F G2W ) of water vapor + the flow rate (F G2O ) of oxygen gas) is 0.01 or more and less than 0.3. [Aspect 3] The method for producing titanium oxide particles according to Aspect 1 or 2, wherein the ratio of the amount of the cooling gas / the total gas amount in the cooling step is 0.3 or more and 0.6 or less. [[ID=3,3]] [Aspect 4] The method for producing titanium oxide particles according to any one of Aspects 1 to 3, wherein the ratio of the flow rate (F G1 ) of G1 to the flow rate (F G2 ) of G2 is 0.3 or more and 1.2 or less. [Aspect 5] A purge medium outlet is provided on the inner wall or upper part of the reaction tube. In the cross section of the reaction tube perpendicular to the central axis of the reaction tube, with respect to the line connecting the purge medium outlet and the central axis of the reaction tube, the blowout angle α of the purge medium is 45 ° or more, and the blowout flow rate of the purge medium is 35 m / s or more. The method for producing titanium oxide particles according to any one of Aspects 1 to 4.​​ [Aspect 6] A method for producing titanium oxide particles according to any one of embodiments 1 to 5, wherein the ratio (S1 / S2) of the sum of the cross-sectional areas (S1) at the inlet of the reaction tube and the cross-sectional areas (S2) at the outlet of the introduction tube for the raw material gas (G1) and the oxidizing gas (G2) is 1.0 or more and 10.0 or less. [Aspect 7] BET specific surface area 40m 2 / g super 120m 2 Titanium dioxide particles having a concentration of 13 ppm or less of anatase, an anatase content of 94% or more, and when placed in water at 25°C, pH 7, and subjected to ultrasonic dispersion by water sieving at an ultrasonic intensity of 55 W and 38 kHz for 5 minutes, the residue concentration that did not pass through a sieve with a mesh size of 45 μm is 13 ppm or less. [Aspect 8] Titanium oxide particles according to embodiment 7, wherein the Cl content of the titanium oxide particles measured by silver nitrate potentiometric titration is 0.20% by mass or less. [Aspect 9] Titanium oxide particles according to embodiment 7 or 8, wherein the content of Na, Al, S, Fe, Ni, Cr, Nb, and Zr is 50 ppm by mass or less each, and the content of Si and C is 500 ppm by mass or less each. [Aspect 10] A slurry containing titanium dioxide particles according to any one of embodiments 7 to 9. [Aspect 11] A dispersion containing titanium dioxide particles according to any one of embodiments 7 to 9. [Aspect 12] A composition comprising titanium dioxide particles according to any one of embodiments 7 to 9. [Aspect 13] A dielectric material containing titanium oxide particles according to any one of embodiments 7 to 9. [Effects of the Invention]

[0018] According to this disclosure, it is possible to provide titanium oxide particles with a high anatase content, few coarse particles, and excellent uniformity and dispersibility, as well as a method for producing the same. The titanium oxide particles of this disclosure can be suitably used as slurries, dispersions, compositions, and dielectric raw materials. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic diagram showing the blowing angles of the cooling gas and purging medium in a cross-section of a reaction tube in a method for producing titanium oxide particles according to one embodiment. [Figure 2] This is a schematic diagram showing the blowing angles of the cooling gas and purge medium in a longitudinal cross-section of a reaction tube in a method for producing titanium oxide particles according to one embodiment. [Modes for carrying out the invention]

[0020] The embodiments of the present invention will be described below, but please understand that the present invention is not limited to these forms and can be applied in various ways within its spirit and scope.

[0021] In this disclosure, when "~" is used to indicate a numerical range, the numbers at both ends are the upper and lower limits, respectively, and are included in the numerical range. If multiple upper or lower limits are listed, a numerical range can be created from all combinations of upper and lower limits. Similarly, if multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining upper and lower limits from those ranges.

[0022] Unless otherwise specified or indicated by the surrounding context, the numerical values ​​of the various measurements in this disclosure are defined with regard to significant figures. For example, 0 ppm means less than 0.5 ppm.

[0023] [Titanium dioxide particles] In one embodiment, the titanium oxide particles have a BET specific surface area of ​​40 m². 2 / g super 120m 2Titanium dioxide particles with a concentration of 13 ppm or less per gram, an anatase content of 94% or more, and a residue concentration of 13 ppm or less when sieved by ultrasonic dispersion using 55 W ultrasonic intensity, 38 kHz for 5 minutes in water at 25°C, pH 7, and not passing through a sieve with a mesh size of 45 μm.

[0024] (BET specific surface area) In one embodiment, the BET specific surface area of ​​titanium oxide particles is 40m due to its excellent uniformity and dispersibility. 2 / g super 120m 2 The BET specific surface area is 40m². 2 If the value exceeds 1 / g, it is suitable as a raw material for electronic materials. From a similar viewpoint, the BET specific surface area is 50m². 2 Preferably 1 / g or more, 90m 2 A value of 120 m² or more is more preferable. 2 If the value is less than / g, it exhibits excellent dispersibility. The BET specific surface area is 100m². 2 Preferably less than / g, 95m 2 It is more preferable that the BET specific surface area is less than or equal to / g. In this disclosure, the BET specific surface area is measured by the method described in the examples.

[0025] (Anatase content) In one embodiment, the anatase content (on a molar basis) of the titanium dioxide particles is 94% or more, preferably 95% or more. A high photoelectrochemical activity is exhibited when the anatase content is 94% or more. The upper limit of the anatase content is not particularly limited, but it can be, for example, 100% or less, 99% or less, or 98% or less. In this disclosure, the anatase content refers to the content of anatase-type crystals in the titanium dioxide particles and is measured by the method described in the examples.

[0026] (Residue concentration) In one embodiment, when titanium dioxide particles are placed in water at 25°C and pH 7, and subjected to ultrasonic dispersion by water sieving at an ultrasonic intensity of 55W and 38kHz for 5 minutes, the residue concentration that did not pass through a sieve with a mesh size of 45μm is 13ppm or less. If the residue concentration is 13ppm or less, there are few coarse particles, and the uniformity and dispersibility are excellent. From a similar viewpoint, the residue concentration is preferably 10ppm or less, and more preferably 7ppm or less. The lower limit of the residue concentration is not particularly limited, but it can be 0.1ppm or more, 0.2ppm or more, or 1ppm or more. In this disclosure, the residue concentration is determined by the method described in the examples. Titanium dioxide particles with few coarse particles have high uniformity and can meet the high quality requirements for titanium dioxide particles, and are therefore particularly useful in a wide range of applications such as cosmetics, UV shielding materials, additives to silicone rubber, photocatalysts, solar cells, dielectric raw materials, and electrode material raw materials for Li-ion batteries.

[0027] (Tap density) The tap density of titanium dioxide particles is 0.01 g / cm³. 3 More than 0.50g / cm 3 The following is preferable: Tap density of 0.01 g / cm³ 3 A density of 0.05 g / cm³ or higher is advantageous in terms of transportation costs, etc. From a similar perspective, a tap density of 0.05 g / cm³ is desirable. 3 The above is more preferable, 0.1 g / cm³ 3 The above is even more preferable. Tap density is 0.50 g / cm³. 3 The following conditions result in superior dispersibility in water. From a similar perspective, the tap density is 0.45 g / cm³. 3 The following is more preferable: 0.40 g / cm³ 3 The following is even more preferable. In this disclosure, the tap density is measured by the method described in the examples.

[0028] (pH) When titanium dioxide particles are dispersed in water, the pH is preferably between 1.0 and 5.0. Within this pH range, the particles remain stable in water and maintain their dispersion easily. Similarly, a pH between 2.0 and 4.5 is more preferable, and between 3.5 and 4.3 is even more preferable.

[0029] (Chlorine (Cl) content) The chlorine (Cl) content of titanium oxide particles is preferably 0.20% by mass or less. If the Cl content is 0.20% by mass or less, problems are less likely to occur in subsequent processes when titanium oxide particles are used as a raw material. For example, if titanium oxide particles with a Cl content exceeding 0.20% by mass are used as a raw material for BaTiO3, flux may be generated during firing. Molten flux tends to localize, and aggregation increases in the localized areas, which may cause variations in quality between different parts of the particle. Also, if particles aggregate, the crystals of the BaTiO3 particles may grow, resulting in abnormal particles, which may reduce the dielectric properties of BaTiO3. From this viewpoint, the Cl content of titanium oxide particles is more preferably 0.15% by mass or less, and even more preferably 0.10% by mass or less. The lower limit of the Cl content of titanium oxide particles is not particularly limited, but it can be 0.01% by mass or more, 0.02% by mass or more, or 0.05% by mass or more. In this disclosure, the Cl content is measured using the method described in the examples with silver nitrate potentiometric titration.

[0030] (Content of other impurities) The content of Na, Al, S, Fe, Ni, Cr, Nb, and Zr in the titanium oxide particles is preferably 50 ppm by mass or less, and more preferably 10 ppm by mass or less. Furthermore, the content of Si and C in the titanium oxide particles is preferably 500 ppm by mass or less, and more preferably 100 ppm by mass or less. Using titanium oxide particles with such low impurity levels as a raw material reduces the likelihood of problems in subsequent processes. For example, when obtaining a dielectric material using titanium oxide particles as a raw material, the deterioration of dielectric properties due to the presence of impurities is suppressed. Also, when these titanium oxide particles are used in photocatalysts or solar cells, the deterioration of transparency due to coloration by Fe is prevented or suppressed, and the deterioration of function as a photocatalyst or solar cell due to lattice defects caused by Al, S, etc., is also prevented or suppressed. In this disclosure, the content of other impurities is measured by the method described in the examples.

[0031] [Slurries, dispersions, compositions, and dielectric materials] The slurry, dispersion, composition, and dielectric raw material in one embodiment include the aforementioned titanium oxide particles. A slurry is a mixture in which particles are mixed in a liquid, but it often refers to a highly viscous fluid. A dispersion is a broad and general term for a mixture in which solid particles are dispersed in a liquid, and includes low concentrations. A composition refers to a composition consisting of multiple components. A dielectric raw material refers to a raw material for manufacturing a dielectric. The slurry, dispersion, composition, and dielectric raw material of one embodiment are suitable for photocatalytic applications, solar cell applications, dielectric applications, etc. Other applications of the slurry, dispersion, and composition containing titanium oxide particles are known. Known methods can be used to manufacture the slurry, dispersion, composition, and dielectric raw material using the titanium oxide particles of this disclosure. Because the slurry, dispersion, composition, and dielectric raw material containing titanium oxide particles of one embodiment do not contain coarse particles, the uniformity and quality of the final product can be improved. In particular, in the thinning of dielectrics in multilayer ceramic capacitors, the absence of coarse particles prevents short circuits and contributes to quality improvement.

[0032] [Method for producing titanium dioxide particles] A method for producing titanium oxide particles according to one embodiment includes a reaction step of 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 to generate a reaction gas, and a cooling step of introducing a cooling gas to cool the reaction gas and obtain titanium oxide particles, wherein the flow rate of G1 in the reaction step is (F G1 Flow rate of titanium tetrachloride in G1 relative to (F G1T ) ratio F G1T / F G1 The ratio is 0.01 or more and less than 0.4, and the mass of TiO2 (kg) and the total amount of gas (m³) after the introduction of the cooling gas in the cooling process are... 3 The ratio (TiO2 mass) / (total gas volume) is greater than 0 and is 0.07 kg / m³. 3 The following applies:

[0033] (Reaction tube) The reaction tube may be a horizontal type, but a vertical type is preferred because it makes it easier to ensure a uniform flow of various gases, and a reaction tube with a circular cross-section is preferred. In the case of a circular vertical reaction tube, preheated raw material gas (G1) and oxidizing gas (G2) are introduced from the upper end of the heated reaction tube through their respective supply pipes toward the bottom of the reaction tube to generate the reaction gas. This process is called the reaction process. A cooling gas outlet is provided on the inner wall of the reaction tube, and the cooling gas is blown out from there and mixed with the reaction gas to cool it. This process is called the cooling process.

[0034] The area from the raw material gas inlet to the cooling gas outlet in the reaction tube is called the reaction region, and the area from the cooling gas outlet to the outlet is called the cooling region. If there are multiple cooling gas outlets, the area from the raw material gas inlet to the first cooling gas outlet in the reaction tube is called the reaction region, and the area from the first cooling gas outlet to the outlet is called the cooling region.

[0035] 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 also contain titanium oxide, which is a reaction product.

[0036] The raw material gas (G1) and the oxidizing gas (G2) are introduced from the inlet (end face side) of the reaction tube 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 of the cross-sectional areas (S2) of the introduction tube outlets for the raw material gas (G1) and the oxidizing gas (G2) is preferably 1.0 or more and 10.0 or less. By keeping it within this range, the temperature or high-temperature zone time in the reaction region can be made more uniform. In this disclosure, the cross-sectional area (S1) of the reaction tube inlet is the cross-sectional area including the cross-sectional area (S2) of the introduction tube outlets for the raw material gas (G1) and the oxidizing gas (G2). The ratio (S1 / S2) is more preferably 1.2 or more and 7.0 or less, and even more preferably 1.5 or more and 2.5 or less. The raw material gas (G1) and the oxidizing gas (G2) are preferably introduced in the direction of gas flow within the reaction tube.

[0037] The temperature of the reaction region into which the raw material gas (G1) and oxidizing gas (G2) are introduced is preferably 800°C or higher and less than 1,200°C, more preferably 800°C or higher and less than 1,100°C. If the temperature of the reaction region is 800°C or higher, the reaction proceeds sufficiently, the particle size distribution of titanium oxide particles becomes uniform, and crystallinity can be increased. By raising the temperature of the reaction region, the reaction is completed simultaneously with mixing, uniform nucleation is promoted, and the reaction zone can be made smaller. On the other hand, if the temperature of the reaction region is less than 1,200°C, particle growth proceeds moderately, but aggregation is less likely to occur, so coarse particles are less likely to be generated. In addition, by keeping the temperature of the reaction region below 1,200°C, the anatase content can be increased.

[0038] (Raw material gas (G1)) The raw material gas (G1) contains titanium tetrachloride (G1T) and an inert gas (G1I). The titanium tetrachloride in the raw material gas is in gaseous form.

[0039] Flow rate of raw material gas (F G1 ) is 1.0 Nm 3 Preferably, it is 1.0 Nm or more. 3 / hr That's all. This shortens the residence time of the raw material gas (G1) in the reaction region, making oversintering and coarsening of titanium oxide less likely. From a similar perspective, F G1 8.0 Nm 3 More preferably 15.0 Nm 3 / hr or more is even more preferable. F G1 The upper limit can be set appropriately according to manufacturing conditions such as the size of the reaction tube and the temperature of the reaction region, and is not particularly limited, but for example, 100 Nm 3 / hr or less, 50Nm 3 / hr or less, or 40Nm 3 It can be set to / hr or less.

[0040] Flow rate of titanium tetrachloride (F G1T ) is 1.0 Nm from the perspective of increasing the yield per hour. 3 It is preferable that the value be 2.0 Nm² or more, and the current is 2.0 Nm². 3More preferably 3.0 Nm 3 A value of 1 / hr or more is even more preferable. From the viewpoint of suppressing sintering grain growth due to reaction heat, F G1T Preferably 50.0 Nm 3 / hr or less, more preferably 40.0 Nm 3 Less than / hr, more preferably 30.0 Nm 3 It is less than / hr.

[0041] Examples of inert gases include nitrogen gas, helium gas, and argon gas, with nitrogen gas being preferred from an economic standpoint.

[0042] Flow rate of raw material gas (F G1 ) Titanium tetrachloride in G1 n flow rate (F G1T ) Ratio F G1T / F G1 It is between 0.01 and less than 0.4. G1T / F G1 Make it 0.01 or greater. And the opposite This can promote a response. From a similar perspective, F G1T / F G1 F is preferably 0.05 or higher, and more preferably 0.10 or higher. G1T / F G1 By setting F to less than 0.4, it becomes easier to keep the particle size of the resulting titanium oxide particles small. From a similar viewpoint, G1T / F G1 A value of 0.38 or less is preferred, and a value of 0.35 or less is more preferred.

[0043] The raw material gas (G1) is preferably introduced into the reaction tube at a temperature of 600°C or higher but less than 1,200°C, more preferably 700°C or higher but less than 1,200°C, and even more preferably 800°C or higher but less than 1,200°C.

[0044] (Oxidizing gas (G2)) The oxidizing gas (G2) contains at least one of oxygen gas (G2O) and water vapor (G2W), and an inert gas (G2I).

[0045] Flow rate of oxidizing gas (FG2 ) is preferably 1.0 Nm 3 / hr or more. With 1.0 Nm 3 / hr That's all. , the residence time in the reaction region of the oxidizing gas (G2) becomes short, and over-sintering and coarsening of the titanium oxide particles are less likely to occur. From the same viewpoint, F G2 is more preferably 15.0 Nm 3 / hr or more, and even more preferably 30.0 Nm 3 / hr or more. The upper limit of F G2 can be appropriately set according to production conditions such as the size of the reaction tube and the temperature of the reaction region and is not particularly limited. For example, it can be 100 Nm 3 / hr or less, 80 Nm 3 / hr or less, or 60 Nm 3 / hr or less.

[0046] The flow rate ratio ((F G2W +F G2O ) / F G2 ) of at least one of oxygen gas and water vapor in the oxidizing gas (G2) is preferably 0.8 to 0.999, more preferably 0.9 to 0.998, and even more preferably 0.99 to 0.997.

[0047] The ratio F G1T ) of the flow rate of titanium tetrachloride and to the total of the flow rate of water vapor (F G2W ) and and the flow rate of oxygen gas (F G2O ) is preferably 0.01 or more and less than 0.3. F G1T / (F G2W +F G2O ) being 0.01 or more can increase the yield. From the same viewpoint, F G1T / (F G2W +F G2O ) is more preferably 0.05 or more, and even more preferably 0.08 or more. F G1T / (F G2W +F G2O ) G1T / (F G2W +F G2O) is less than 0.3, which not only increases the nucleation number of titanium oxide particles and makes it easier to obtain ultrafine particles, but also makes it easier to suppress the generation of colored titanium oxide with fewer oxygen defects. From the same perspective, F G1T / (F G2W +F G2O ) is more preferably 0.25 or less, and even more preferably 0.20 or less.

[0048] The ratio F G1 ) and of the flow rate (F G2 ) of raw material gas to the flow rate (F G1 ) of oxidizing gas, i.e., F G2 / F G1 / F G2 , is preferably 0.3 or more and 1.2 or less. When F G1 / F G2 is 0.3 or more, the mixing of raw material gas (G1) and oxidizing gas (G2) is promoted, and titanium oxide with a low specific surface area can be obtained. From the same perspective, F G1 / F G2 is more preferably 0.40 or more, and even more preferably 0.45 or more. When F G1 / F G2 is 1.2 or less, not only does the nucleation number of titanium oxide particles increase and it becomes easier to obtain ultrafine particles, but also the high-temperature residence time is shortened, so the uniformity of the primary particle size can be improved. From the same perspective, F G1 / F G2 is more preferably 1.0 or less, and even more preferably 0.90 or less.

[0049] The oxidizing gas (G2) is preferably introduced into the reaction tube at 600 °C or higher and lower than 1,200 °C.

[0050] Examples of the inert gas include nitrogen gas, helium gas, argon gas, etc., and nitrogen gas is preferred from an economic perspective. It is preferable that the inert gas in the oxidizing gas (G2) is the same chemical species as the inert gas in the raw material gas (G1).

[0051] (Cooling gas) In one embodiment, a blowout port for the cooling gas is provided on the inner wall of the reaction tube, and the reaction gas is cooled by blowing out the cooling gas and mixing it with the reaction gas.

[0052] As a cooling gas, for example, air, nitrogen gas, or carbon monoxide can be used. From the viewpoint of enhancing the cooling effect, the temperature of the cooling gas is preferably 0°C to 100°C, and more preferably 10°C to 90°C. Spray water can also be used in combination with the cooling gas.

[0053] The blowing angle γ of the cooling gas Q (see Figure 1) is defined as the angle at which the cooling gas Q is blown out (the angle of the blowing port 3 of the cooling gas Q with respect to the direction of the central axis 4) of the reaction tube 1, with the line connecting the blowing port 3 of the cooling gas Q and the central axis 4 of the reaction tube 1 being defined as 0° in a cross-section perpendicular to the central axis 4 of the reaction tube 1. A value of 0° or more and less than 50° is preferred. By having an angle γ of 0° or more and less than 50°, the cooling gas can be directed towards the center of the reaction tube, allowing for sufficient mixing with the reaction gas and obtaining a high cooling effect. From a similar viewpoint, an angle γ of 0° or more and 30° or less is more preferred.

[0054] The blowing angle δ of the cooling gas Q (see Figure 2) is preferably 60° or more, more preferably 70° or more, and even more preferably 80° or more, when the direction of flow of the reaction gas in the direction of the central axis of the reaction tube 1 is defined as 0° in a longitudinal cross-section including the central axis of the reaction tube 1 (flow direction of the reaction gas G1). The blowing angle δ of the cooling gas Q is preferably 90° or less. By setting the blowing angle δ of the cooling gas Q to such an angle, a high cooling effect can be obtained.

[0055] From the viewpoint of promoting mixing of the cooling gas and the reaction gas, there should be one or more cooling gas outlets, preferably two or more. Similarly, in the same cross-section of the reaction tube, there may be one, two or more cooling gas outlets. In the same longitudinal section of the reaction tube, there may be one, two or more cooling gas outlets along the central axis of the reaction tube.

[0056] (Purge media) A purging medium outlet may be provided on the inner wall or top of the reaction tube, and the purging medium may be introduced through this outlet. By flowing the purging medium in a swirling motion along the inner wall of the reaction tube, the adhesion of titanium oxide particles to the inner wall of the reaction tube can be prevented. Examples of purging medium outlet shapes include single holes and slits.

[0057] If the generated titanium oxide particles adhere to and accumulate on the inner wall of the reaction tube, they will coarseen due to sintering grain growth. If these coarseened particles detach from the inner wall and mix with the titanium oxide particles obtained as a product, it can cause a non-uniform particle size distribution. By introducing a purging medium, the adhesion and accumulation of titanium oxide particles on the inner wall of the reaction tube can be prevented. The purging medium can be introduced continuously or intermittently.

[0058] A gas or liquid can be used as the purging medium. Examples of purging mediums include air, nitrogen gas, carbon monoxide, and spray water. The temperature of the purging medium is preferably 0°C to 100°C, and more preferably 10°C to 90°C. It is preferable that the temperature of the purging medium does not exceed the temperature of the cooling gas. This enhances the cooling effect of the cooling gas.

[0059] The discharge angle α of the purge medium P (see Figure 1) is defined as the angle at which the purge medium P is discharged (the angle of the discharge port 5 of the purge medium P with respect to the direction of the central axis 4) in a cross-section perpendicular to the central axis 4 of the reaction tube 1 (the direction of flow of the reaction gas), with the line connecting the discharge port 5 of the purge medium P and the central axis 4 of the reaction tube 1 being defined as 0°. A value of 45° or greater is preferred. An angle α of 45° or greater allows the purge medium to swirl near the inner wall of the reaction tube, effectively preventing titanium oxide from adhering to the inner wall of the reaction tube. From a similar viewpoint, an angle α of 50° or greater is preferred. An angle α of less than 90° is also preferred.

[0060] The blowing angle β of the purging medium P (see Figure 2) is preferably 60° or more, more preferably 70° or more, and even more preferably 80° or more, when the direction of flow of the reaction gas in the direction of the central axis of the reaction tube 1 is defined as 0° in a longitudinal cross-section including the central axis of the reaction tube 1 (flow direction of the reaction gas G1). The blowing angle β of the purging medium P is preferably 90° or less. By setting the blowing angle β of the purging medium P to such an angle, the adhesion of titanium dioxide to the inner wall of the reaction tube can be effectively prevented.

[0061] From the viewpoint of preventing titanium oxide particles from adhering to the inner wall of the reaction tube, it is preferable to have one or more outlets for the purge medium, and more preferably two or more. From a similar viewpoint, it is preferable to have one or more outlets for the purge medium in the same cross-section of the reaction tube, and more preferably two or more. In general, the number of outlets per circumference of the cross-section of the reaction tube can be reduced as the angle α is large or as the flow velocity of the purge medium is large. In the same longitudinal cross-section of the reaction tube, there may be one, two or more outlets for the purge medium along the central axis of the reaction tube. The outlets for the purge medium may be arranged spirally on the inner wall of the reaction tube. The outlets for the purge medium are installed in the reaction region, and preferably also in the cooling region. It is preferable that a swirling flow of the purge medium is formed along the inner wall of the reaction tube in both the reaction region and the cooling region.

[0062] The discharge velocity of the purge medium is preferably 35 m / s or more, more preferably 50 m / s or more, and even more preferably 55 m / s or more, from the viewpoint of effectively preventing the generated titanium oxide particles from adhering to the inner wall of the reaction tube. In this disclosure, the discharge velocity of the purge medium is the flow rate of the purge medium (m 3 / s) is the cross-sectional area (m²) of the outlet of the purging medium. 2 It is defined as the result of dividing by (m / s).

[0063] (Titanium dioxide mass / Total gas volume) In one embodiment of the cooling process, the mass of titanium oxide (kg) and the total amount of gas (m³) after the introduction of the cooling gas. 3The ratio (TiO2 mass) / (total gas volume) is greater than 0 and 0.07 kg / m³ 3 The following applies. The mass of titanium oxide is calculated assuming that all of the introduced titanium tetrachloride is converted into titanium oxide, i.e., it is defined as introduced titanium tetrachloride mass (kg) × 79.87 / 189.71. The total amount of gas = amount of gas remaining after the reaction × temperature correction (based on the temperature of the reaction region) + amount of purge medium introduced + amount of cooling gas introduced, and the amount of gas remaining after the reaction = amount of gas produced (Cl component) + amount of residual oxidizing gas + amount of inert gas. (TiO2 mass) / (total amount of gas) is 0.07 kg / m³ 3 If the ratio is below the specified level, the reaction gas becomes dilute, making condensation less likely to occur during the cooling process and reducing the amount of coarse particles generated. From a similar perspective, (TiO2 mass) / (total gas volume) should be 0.06 kg / m³. 3 The following is preferable: 0.05 kg / m 3 The following are more preferable: From the viewpoint of obtaining titanium oxide, (TiO2 mass) / (total gas amount) should be greater than 0, and from the viewpoint of increasing the yield per unit time, it should be 0.01 kg / m³. 3 The above is preferable, and 0.02 kg / m 3 The above is more preferable, 0.05 kg / m 3 The above is even more preferable.

[0064] (Cooling gas volume / Total gas volume) Cooling gas volume (m³) in one embodiment 3 ) / Total gas volume (m³ 3 The ratio of ) is preferably 0.3 to 0.6. When the above ratio is 0.3 or higher, sufficient cooling is achieved and coarse particles are less likely to be generated. From a similar viewpoint, the above ratio is preferably 0.33 or higher, and more preferably 0.35 or higher. When the above ratio is 0.6 or lower, the backflow of excess cooling gas into the reaction region is suppressed, and the reaction can proceed smoothly. From a similar viewpoint, the above ratio is preferably 0.50 or lower, and more preferably 0.45 or lower.

[0065] (Dechlorination process) The manufactured titanium oxide particles are preferably subjected to a dechlorination process. Dechlorination of the titanium oxide particles by heating is preferably carried out by heating the titanium oxide particles at a temperature of 200°C to 550°C, preferably 250°C to 450°C, while contacting the titanium oxide particles with water vapor, so that the mass ratio of water to titanium oxide particles (mass of water vapor / mass of titanium oxide particles) is 0.01 or more, preferably 0.04 or more. By setting the temperature to 550°C or lower, sintering of the titanium oxide particles can be suppressed and the primary particle size can be made uniform. By setting the temperature to 200°C or higher, the efficiency of dechlorination can be increased. If the mass ratio of water to titanium oxide particles is 0.01 or higher, particle growth can be effectively suppressed. The mass ratio of water to titanium oxide particles is preferably 0.01 to 3, more preferably 0.05 to 2, and even more preferably 0.2 to 1.8.

[0066] It is preferable to use water vapor mixed with a gas that efficiently moves chlorine separated from titanium oxide particles out of the system, such as air. When using air, it is preferable that the water vapor is contained in the air at a concentration of 0.1% by volume or more, more preferably 5% by volume or more, and even more preferably 10% by volume or more and 80% by volume or less. It is preferable to heat the air containing water vapor to a temperature of 200°C to 1,000°C, more preferably 450°C to 850°C.

[0067] One method for moving chlorine removed from titanium oxide particles out of the system is to reduce the pressure inside the container used for dechlorination. The degree of pressure reduction inside the container is preferably 0.5 kPa or higher, and more preferably 0.5 kPa or higher and 3.5 kPa or lower. In this disclosure, the degree of pressure reduction is the pressure difference between the pressure inside the reduced-pressure container and atmospheric pressure.

[0068] The titanium dioxide particles of this disclosure contain almost no chlorine inside the particles, with the majority of the chlorine existing on the particle surface. Therefore, it is possible to reduce the chlorine content through a wet process, such as by washing with water. Examples of wet methods include suspending the titanium dioxide particles in pure water and separating the chlorine that has migrated to the liquid phase from the system using an ultrafiltration membrane, reverse osmosis membrane, filter press, etc. [Examples]

[0069] The following describes specific examples and comparative examples, but the present invention is not limited to these.

[0070] The method for measuring the physical properties of titanium dioxide particles is as follows:

[0071] (1) BET specific surface area In accordance with JIS R 1626:1996, a fully automated BET specific surface area analyzer ("Macsorb(trademark) HM model-1208", manufactured by Mountec Co., Ltd.) was used. As a pretreatment, the sample was heated to 180°C and nitrogen gas was flowed through it for 20 minutes. The BET specific surface area was measured using the BET 3-point method with nitrogen gas as the adsorbate. The applicable range for the BET method was P / P0 = 0.00 to 0.95.

[0072] (2) Anatase content The anatase content in titanium dioxide particles was measured by powder X-ray diffraction. Specifically, dried titanium dioxide particles were subjected to X-ray diffraction measurements using PANalytical's "X'pertPRO" as the measuring instrument, with a copper target and Cu-Kα1 radiation, under the following conditions: tube voltage 45kV, tube current 40mA, measurement range 2θ = 10~80deg, sampling width 0.0167deg, and scanning speed 0.0192deg / s. The peak height of the maximum peak corresponding to the anatase crystal (Ha), the peak height of the maximum peak corresponding to the brookite crystal (Hb), and the peak height of the maximum peak corresponding to the rutile crystal (Hr) were determined, and the anatase content in the titanium dioxide particles was calculated using the following formula. Anatase content (%) = {Ha / (Ha+Hb+Hr)} × 100

[0073] (3) Residue (coarse particles) concentration A 300g sample was showered with water at a pressure of 300±20kPa on a mesh with a mesh opening of 45μm until it became clear. Then, it was placed in pure water at 25℃ and pH 7, and sieved using ultrasonic dispersion with a tabletop ultrasonic cleaner (Sonocleaner, manufactured by Kaijo Co., Ltd.) at an ultrasonic intensity of 55W and 38kHz for 5 minutes. The residue concentration was defined as the mass of the residue remaining on the sieve divided by the total amount of sample.

[0074] (4) Tap density Place titanium dioxide particles in a cup and tap for 3 minutes. Transfer to a 100 mL container and calculate the tap density (g / cm³) from the mass of titanium dioxide particles in the container. 3 ) was calculated.

[0075] (5) pH A 10% suspension of titanium dioxide particles was prepared in accordance with JIS K 5101-17-2:2004, and the pH of the suspension was measured. The suspension was prepared using water as the dispersion medium and without the use of a wetting agent.

[0076] (6) Chlorine (Cl) content The chlorine content in titanium dioxide particles was measured by silver nitrate potentiometric titration. Specifically, 0.5 g of titanium dioxide particles were weighed. Then, a silver nitrate solution (concentration 0.02 mol) was added dropwise to the solution of these titanium dioxide particles, and the mass of chlorine atoms in the solution was determined by measuring the potential difference, thereby calculating the chlorine content (mass %).

[0077] (7) Content of other impurities The measurement methods for each impurity are as follows. Fe: Atomic absorption spectrometry (Hitachi High-Tech Corporation Z-2300 atomic absorption spectrophotometer) Al, Si: X-ray fluorescence analysis (XRF) (Simultex 10, manufactured by Rigaku Denki Kogyo Co., Ltd.) C, S: High-frequency induction furnace combustion and infrared absorption method Na, Ni, Cr, Nb, Zr: Inductively coupled plasma-mass spectrometry

[0078] Example 1 <1st process> Using a vertical reaction tube with a circular cross-section, a raw material gas (G1) consisting of titanium tetrachloride (titanium tetrachloride purity of 99.99% by mass or higher) and nitrogen gas is heated to 950°C, with a flow rate of 28.7 Nm³. 3 At a rate of / hr, an oxidizing gas (G2) consisting of oxygen, water vapor, and nitrogen gas is heated to 900°C, with a flow rate of 45.8 Nm³. 3 At a rate of / hr, reaction gases were generated by introducing them from the top of the reaction tube. The purging medium (nitrogen gas) was introduced from the inner wall of the reaction tube in the reaction region. In the cooling region, the cooling gas (air) was introduced at a rate of TiO2 mass (kg) / total gas volume (m³) per hour. 3 ) is 0.07 kg / m 3 The mixture was introduced in this manner to obtain titanium dioxide particle raw material. Subsequently, the titanium dioxide particle raw material was collected at the bottom of the reaction tube using a polytetrafluoroethylene bag filter. The manufacturing conditions, including other conditions, are shown in Table 1.

[0079] <Second process> The obtained titanium dioxide particle raw material was passed through a cylindrical rotary heating furnace, and dechlorinated at a temperature of 450°C with a mass ratio of water vapor mixed with air to the titanium dioxide raw material (mass of water vapor / mass of titanium dioxide particle raw material) of 0.06 to obtain titanium dioxide particles. Various physical properties of the obtained titanium dioxide particles were measured. The results of the physical property evaluation are shown in Table 2.

[0080] Examples 2-3, Comparative Examples 1-6 The first step was carried out in the same manner as in Example 1, except that the conditions for the raw material gas (G1), oxidizing gas (G2), cooling gas, purging medium, and total gas amount in the first step were changed, and titanium oxide particle raw materials were obtained. The conditions are shown in Table 1. The second step was carried out in the same manner as in Example 1, and titanium oxide particles were obtained. The results of the physical property evaluation are shown in Table 2. Comparative Example 5 was manufactured according to the method of Example 5 in Patent Document 1 (International Publication No. 2022 / 244620), and Comparative Example 6 was manufactured according to the method of Example 3 in Patent Document 1 (International Publication No. 2022 / 244620).

[0081] Comparative Example 7 Titanium oxide particles were manufactured according to the method of Example A1 in the specification of Japanese Patent No. 4445972. The results of the physical property evaluation are shown in Table 2.

[0082] Comparative Example 8 Titanium oxide particles were manufactured according to the method of Example A6 in the specification of Japanese Patent No. 4445972. The results of the physical property evaluation are shown in Table 2.

[0083] Comparative Example 9 Titanium oxide particles were manufactured according to the method of Example A7 in the specification of Japanese Patent No. 4445972. The results of the physical property evaluation are shown in Table 2.

[0084] [Table 1]

[0085] [Table 2]

[0086] As shown in Table 2, in Examples 1 to 3, titanium dioxide particles were obtained with a BET specific surface area within the predetermined range, a high anatase content, and a low residue concentration. In Comparative Examples 1 to 5, F G1T / F G1 The BET specific surface area was small because it was greater than 0.4. Also, TiO2 mass (kg) / total gas volume (m³) 3 ) is 0.08 kg / m 3 Therefore, a large amount of coarse particles were generated and the residue concentration was high. In Comparative Example 6, TiO2 mass (kg) / total gas volume (m³) 3 ) is 0.08 kg / m 3 Therefore, a large amount of coarse particles were generated, resulting in a high residue concentration.

[0087] In Comparative Examples 7-9, a mixture of hydrogen and oxygen was used as the oxidizing gas. Because hydrogen combustion and TiCl4 oxidation occurred simultaneously, the reaction temperature was high and the anatase content was low.

[0088] According to this disclosure, titanium oxide particles with fewer coarse particles and a higher anatase content compared to conventional titanium oxide particles having a similar BET specific surface area, and methods for producing these particles are provided. [Industrial applicability]

[0089] The titanium oxide particles of this disclosure are suitable for photocatalytic applications, solar cell applications, dielectric applications, etc., and since they can be manufactured using equipment that does not require or requires only minimal crushing processes, they have very significant practical industrial value. [Explanation of symbols]

[0090] 1 reaction tube 3 Cooling gas outlet 4. Center of the reaction tube 5. Purge media outlet G1 raw material gas G2 Oxidizing gas P purging media Q Cooling gas α The blowing angle of the purging medium (in a plane perpendicular to the flow direction of the reaction gas) β The blowing angle of the purging medium (in-plane, including the flow direction of the reaction gas) γ Cooling gas outlet angle (in a plane perpendicular to the flow direction of the reaction gas) δ Cooling gas outlet angle (in-plane, including the flow direction of the reaction gas)

Claims

1. A reaction step in which 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 are introduced into a reaction tube to generate a reaction gas, A cooling step to obtain titanium oxide particles by introducing a cooling gas and cooling the reaction gas, A method for producing titanium dioxide particles, comprising: The flow rate of G1 in the reaction step (F Ｇ１ Flow rate of titanium tetrachloride in G1 relative to (F Ｇ１Ｔ ) ratio F Ｇ１Ｔ / F Ｇ１ The TiO after the introduction of the cooling gas in the cooling process is 0.01 or more and less than 0.

4. ２ Mass (kg) and total gas volume (m³) ３ ) ratio (TiO ２ (Mass) / (Total gas volume) is greater than 0 and equals 0.07 kg / m³ ３ The method for producing titanium dioxide particles is as follows:

2. The flow rate (F Ｇ１Ｔ ) of the titanium tetrachloride / (the flow rate (F Ｇ２Ｗ ) of the water vapor + the flow rate (F Ｇ２Ｏ )) of the oxygen gas) is 0.01 or more and less than 0.

3. The method for producing titanium oxide particles according to claim 1.

3. A method for producing titanium oxide particles according to claim 1 or 2, wherein the ratio of the amount of cooling gas to the total amount of gas in the cooling step is 0.3 or more and 0.6 or less.

4. Flow rate of G1 (F Ｇ１ ) / G2 flow rate (F Ｇ２ A method for producing titanium oxide particles according to claim 1 or 2, wherein the ratio is 0.3 or more and 1.2 or less.

5. A method for producing titanium oxide particles according to claim 1 or 2, wherein a purging medium outlet is provided on the inner wall or upper part of the reaction tube, and in a cross-section of the reaction tube perpendicular to the central axis of the reaction tube, the purging angle α of the purging medium is 45° or more with respect to a line connecting the purging medium outlet and the central axis of the reaction tube, and the purging flow velocity of the purging medium is 35 m / s or more.

6. A method for producing titanium oxide particles according to claim 1 or 2, wherein the ratio (S1 / S2) of the sum of the cross-sectional areas (S1) at the inlet of the reaction tube and the cross-sectional areas (S2) at the outlets of the introduction tubes for the raw material gas (G1) and the oxidizing gas (G2) is 1.0 or more and 10.0 or less.

7. BET specific surface area is 40 m² ２ / g over 120m ２ Titanium dioxide particles having a concentration of 94% or more anatase, and when placed in water at 25°C and pH 7, and subjected to ultrasonic dispersion by water sieving at an ultrasonic intensity of 55W and 38kHz for 5 minutes, the concentration of residue that did not pass through a sieve with a mesh size of 45μm is 13 ppm or less.

8. Titanium oxide particles according to claim 7, wherein the Cl content of the titanium oxide particles, as measured by silver nitrate potentiometric titration, is 0.20% by mass or less.

9. Titanium oxide particles according to claim 7 or 8, wherein the content of Na, Al, S, Fe, Ni, Cr, Nb, and Zr is 50 ppm by mass or less each, and the content of Si and C is 500 ppm by mass or less each.

10. A slurry containing titanium oxide particles according to claim 7 or 8.

11. A dispersion comprising titanium oxide particles according to claim 7 or 8.

12. A composition comprising titanium dioxide particles according to claim 7 or 8.

13. A dielectric material comprising titanium oxide particles according to claim 7 or 8.

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