Titanium oxide particles and method for producing same

Abstract

The invention discloses titanium oxide particles and a method for producing the same. Provided are: titanium oxide particles having a high anatase content, a small amount of coarse particles, and excellent uniformity and dispersibility; and a method for producing the titanium oxide particles. The method for producing titanium oxide particles includes: a reaction step for introducing a raw material gas G1 containing titanium tetrachloride and an inert gas and an oxidizing gas G2 containing at least one gas selected from oxygen and water vapor and the inert gas into a reaction tube to generate a reaction gas; and a cooling step for cooling the reaction gas by introducing a cooling gas to obtain titanium oxide particles, the ratio FG1T / FG1 of the flow rate FG1T of titanium tetrachloride in G1 in the reaction step to the flow rate FG1 of G1 being 0.4 or more and less than 1.0. The ratio of TiO2 mass / total gas amount, which is the ratio of TiO2 mass in kg to total gas amount in m3 after introduction of the cooling gas in the cooling step, is greater than 0 kg / m < 3 > and 0.21 kg / m < 3 > or less.

Description

Technical Field

[0001] The present disclosure relates to titanium oxide particles and methods for producing the same. Background Art

[0002] Titanium oxide has a wide range of industrial applications, including cosmetics, ultraviolet shielding materials, and additives to silicone rubber. In recent years, it has been used in photocatalysts, solar cells, dielectric materials, and raw materials for electrodes for Li-ion batteries. In addition, the so-called "titanium oxide" is recorded as titanium dioxide in the Japanese Industrial Standards (JIS), but titanium oxide is widely used as a general name, so in this disclosure, titanium dioxide (TiO2) is simply referred to as titanium oxide.

[0003] Recently, titanium oxide has attracted attention as a raw material for high-performance dielectric materials, such as BaTiO 3 . BaTiO 3 is obtained by the following reaction under heating.

[0004] BaCO3+TiO2→BaTiO3+CO2

[0005] The above reaction is a solid phase reaction. It is generally believed that at this time, BaCO3 is first decomposed at high temperature to generate BaO, and BaO diffuses and solid-dissolves in TiO2 particles to become BaTiO3. Therefore, the size of BaTiO3 particles is dominated by the size of TiO2 particles. In recent years, along with the miniaturization of multilayer ceramic capacitors, the thinning of dielectric layers has become a problem. For this reason, the micronization and homogenization of BaTiO3 particles have become indispensable. In addition, if there are BaTiO3 particles larger than the thickness of the dielectric layer, a short circuit will occur in the multilayer ceramic capacitor, leading to equipment failure. Therefore, it is necessary to micronize and homogenize TiO2, which is the raw material of BaTiO3, and it is preferred not to contain coarse TiO2 particles. Micronization and homogenization of titanium oxide particles are also required in other uses. In addition, it is better not to contain coarse particles.

[0006] Methods for producing titanium oxide can be 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 a high temperature.

[0007] The liquid phase method has the advantages of being able to manufacture titanium oxide under relatively mild conditions and easily obtain fine primary particles, but since titanium oxide is obtained in the form of a sol or slurry, when used in this state, there is a problem of limited use. In order to use the sol or slurry as titanium oxide particles, it is necessary to dry it, and after drying, it generally aggregates violently. In this way, the titanium oxide particles that aggregate violently have the problem of uneven particle size distribution. In addition, there is also the problem of poor dispersibility when the titanium oxide particles obtained by drying are dispersed in a solvent. If the dispersibility is poor, when the raw materials are mixed for the generation of the above-mentioned BaTiO3, the titanium oxide particles and other raw materials are not fully mixed, the raw material components are uneven, and uneven growth is caused during the reaction, resulting in quality deviations, etc.

[0008] On the other hand, if the gas phase method is used, the primary particle size of the generated titanium oxide can be adjusted by adjusting the manufacturing conditions such as temperature. In addition, in the gas phase method, no solvent is used, so the titanium oxide is obtained as a powder, and the problems listed in the liquid phase method are less likely to occur. Moreover, in the gas phase method, the reaction is carried out at a relatively high temperature compared to the liquid phase method, so the obtained titanium oxide has the advantage of high crystallinity.

[0009] However, in the gas phase method, due to reacting at a temperature higher than that of the liquid phase method, when the temperature in the cooling tube after the reaction tube or the introduction of the cooling gas is too high or the residence time of the titanium oxide particles is too long, the titanium oxide particles are sintered excessively, and it is difficult to obtain the microparticles of titanium oxide, and the particle size distribution also becomes inhomogeneous. If the temperature of the reaction zone is too low in order to avoid the sintering of titanium oxide each other, the nucleus generation of titanium oxide is not fully carried out, and it is difficult to obtain microparticles or can only obtain titanium oxide with low crystallinity. On the other hand, by adopting the cooling gas to cool the reaction gas immediately, the sintering of titanium oxide each other can be suppressed, and the titanium oxide of microparticles can be obtained. In the case of not cooling immediately and the cooling being uneven, the sintering of particles each other is produced inhomogeneously, and it is difficult to obtain uniform titanium oxide microparticles.

[0010] Patent Document 1 describes a method for producing titanium oxide particles for the purpose of obtaining uniform titanium oxide particles by a gas phase method. The method is characterized in that a titanium halide gas and an oxidizing gas are reacted under specific conditions.

[0011] In addition, Patent Document 2 describes a method for producing titanium oxide particles for the purpose of obtaining uniform titanium oxide particles without coarse particles by a gas phase method, wherein TiCl4 vapor is reacted with hydrogen and oxygen, and there are few metal oxide particles having a diameter greater than 45 μm.

[0012] Prior Art Literature

[0013] Patent Literature

[0014] Patent Document 1: International Publication No. 2022 / 244620

[0015] Patent Document 2: Japanese Patent No. 4445972 Summary of the invention

[0016] As described above, it is desired to obtain titanium oxide particles having excellent uniformity and dispersibility. However, when a vapor phase method is used, titanium oxide particles having excellent uniformity and dispersibility are obtained compared with titanium oxide particles obtained by a liquid phase method.

[0017] According to Patent Document 1, titanium oxide particles with few coarse particles can be manufactured. In Patent Document 1, the amount of coarse particles exceeding 16 times D50 is quantified using a scanning electron microscope, and in this quantitative method, an image is taken so that the number of primary particles per field of view becomes 8000 to 12000 and evaluated, so coarse particles of the order of tens of μm cannot be evaluated. In addition, since the size of the particles is determined by image analysis, the amount of particles that have been coarsened due to agglomeration (secondary particles) cannot be evaluated.

[0018] Patent Document 2 mentions a method for synthesizing titanium oxide particles with a particle size of tens of μm and few coarse particles. However, since a mixed gas of hydrogen and oxygen is used as an oxidizing gas and hydrogen combustion and TiCl4 oxidation are performed simultaneously, there is a tendency for the reaction temperature to be high and the anatase content to be low.

[0019] The present disclosure provides titanium oxide particles having a high anatase content, a small number of coarse particles, and excellent uniformity and dispersibility, and a method for producing the same.

[0020] The present inventors have discovered that in a method for producing titanium oxide particles comprising reacting a raw material gas containing titanium tetrachloride and an inert gas with an oxidizing gas containing at least one gas selected from oxygen and water vapor and the inert gas, and cooling the reaction gas with a cooling gas, the above-mentioned problems can be solved by controlling the gas flow ratio in the reaction step and the ratio of the mass of TiO2 to the total gas amount in the cooling step to be within a prescribed range, thereby completing the present invention.

[0021] The present disclosure includes the following aspects.

[0022] [Scheme 1] A method for producing titanium oxide particles, comprising:

[0023] A reaction step of introducing a raw material gas (G1) and an oxidizing gas (G2) into a reaction tube to generate a reaction gas, wherein the raw material gas (G1) contains titanium tetrachloride and an inert gas, and the oxidizing gas (G2) contains at least one gas selected from oxygen and water vapor and the inert gas; and

[0024] a cooling step of cooling the reaction gas by introducing a cooling gas to obtain the titanium oxide particles;

[0025] The flow rate (F) of titanium tetrachloride in G1 in the reaction step G1T ) relative to the flow rate of G1 (F G1 ) G1T / F G1 is greater than 0.4 and less than 1.0, the mass (kg) of TiO2 after the cooling gas is introduced in the cooling step and the total gas volume (m 3 ) ratio, i.e., TiO2 mass / total gas volume, exceeds 0 kg / m 3 And at 0.21kg / m 3 the following.

[0026] [Scheme 2] The method for producing titanium oxide particles according to Scheme 1,

[0027] The flow rate (F G1T ) / (the flow rate of the water vapor (F G2W )+the flow rate of the oxygen (F G2O )) is greater than or equal to 0.3 and less than or equal to 0.6.

[0028] [Scheme 3] The method for producing titanium oxide particles according to scheme 1 or 2,

[0029] The ratio of the amount of the cooling gas to the total amount of gas in the cooling step is 0.3 or more and 0.6 or less.

[0030] [Scheme 4] The method for producing titanium oxide particles according to any one of schemes 1 to 3,

[0031] The flow rate of G1 (F G1 ) / G2 flow (F G2 ) is greater than or equal to 0.3 and less than or equal to 1.2.

[0032] [Scheme 5] The method for producing titanium oxide particles according to any one of schemes 1 to 4,

[0033] A blowing outlet for a purge medium is provided on the inner wall or the upper part of the reaction tube. In a cross section of the reaction tube perpendicular to the central axis of the reaction tube, a blowing angle α of the purge medium relative to a line connecting the blowing outlet for the purge medium and the central axis of the reaction tube is greater than 45°, and a blowing flow rate of the purge medium is greater than 35 m / s.

[0034] [Scheme 6] The method for producing titanium oxide particles according to any one of schemes 1 to 5,

[0035] The ratio (S1 / S2) of the cross-sectional area (S1) of the inlet of the reaction tube to the sum (S2) of the cross-sectional areas of the outlets of the introduction tubes for the raw gas (G1) and the oxidizing gas (G2) is greater than or equal to 1.0 and less than or equal to 10.0.

[0036] [Scheme 7] A titanium oxide particle having a BET specific surface area of ​​15 to 40 m 2 / g, the rutile content is more than 70%, and when it is placed in water at 25°C and pH 7 and water-sieved by ultrasonic dispersion at an ultrasonic intensity of 55W and 38kHz for 5 minutes, the concentration of residues that do not pass through the sieve with a mesh size of 45μm is less than 100ppm.

[0037] [Scheme 8] The titanium oxide particles according to scheme 7,

[0038] The Cl content of the titanium oxide particles measured by silver nitrate potentiometric titration was 0.20 mass % or less.

[0039] [Scheme 9] The titanium oxide particles according to scheme 7 or 8,

[0040] The contents of Na, Al, S, Fe, Ni, Cr, Nb and Zr are each 50 mass ppm or less, and the contents of Si and C are each 500 mass ppm or less.

[0041] [Structure 10] A slurry comprising the titanium oxide particles according to any one of Structures 7 to 9.

[0042] [Scheme 11] A dispersion comprising the titanium oxide particles according to any one of schemes 7 to 9.

[0043] [Scheme 12] A composition comprising the titanium oxide particles according to any one of schemes 7 to 9.

[0044] [Scheme 13] A dielectric raw material comprising the titanium oxide particles according to any one of schemes 7 to 9.

[0045] According to the present disclosure, titanium oxide particles having a high anatase content, few coarse particles, excellent uniformity and dispersibility, and a method for producing the same can be provided. The titanium oxide particles disclosed in the present disclosure can be used very suitably as slurry, dispersion, composition, and dielectric raw material. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram showing the blowing angles of the cooling gas and the purge medium in the cross section of the reaction tube in the method for producing titanium oxide particles according to one embodiment.

[0047] Figure 2 This is a schematic diagram showing the blowing angles of the cooling gas and the purge medium in the vertical section of the reaction tube in the method for producing titanium oxide particles according to one embodiment.

[0048] Description of Reference Numerals

[0049] 1 reaction tube

[0050] 3Cooling gas outlet

[0051] 4 reaction tube center

[0052] 5. Blowing medium outlet

[0053] G1 Raw Gas

[0054] G2 Oxidizing Gas

[0055] Purge medium

[0056] QCooling Gas

[0057] α Blowing angle of the purge medium (in the plane perpendicular to the flow direction of the reaction gas)

[0058] β Blowing angle of the purge medium (within the plane including the flow direction of the reaction gas)

[0059] Gamma cooling gas blowing angle (in the plane perpendicular to the flow direction of the reaction gas)

[0060] δ Cooling gas blowing angle (within the plane including the flow direction of the reaction gas) DETAILED DESCRIPTION

[0061] Hereinafter, embodiments of the present invention will be described, but it should be understood that the present invention is not limited to these embodiments and can be variously applied within the spirit and scope of the present invention.

[0062] In the present disclosure, when "~" is used in relation to a numerical range, the values ​​at both ends are the upper limit and the lower limit, respectively, and are included in the numerical range. When multiple upper limits or lower limits are recorded, the numerical range can be constructed based on all combinations of the upper limits and the lower limits. Similarly, when multiple numerical ranges are recorded, another numerical range can be constructed by selecting upper limits and lower limits from those numerical ranges and combining them.

[0063] The numerical values ​​of various measured values ​​in the present disclosure are defined with consideration of significant figures unless otherwise specified and unless the context does not suggest a different meaning. For example, 0 ppm means less than 0.5 ppm.

[0064] [Titanium oxide particles]

[0065] The titanium oxide particles in one embodiment have a BET specific surface area of ​​15 to 40 m 2 / g, the rutile content is more than 70%, and when it is placed in water at 25°C and pH 7 and water-sieved by ultrasonic dispersion at an ultrasonic intensity of 55W and 38kHz for 5 minutes, the concentration of residues that do not pass through the sieve with a mesh size of 45μm is less than 100ppm.

[0066] (BET specific surface area)

[0067] The BET specific surface area of ​​the titanium oxide particles in one embodiment is 15 to 40 m2 from the viewpoint of excellent uniformity and dispersibility. 2 / g. If the BET specific surface area is 15m 2 / g or more, it is very suitable as a raw material for electronic materials. From the same point of view, the BET specific surface area is preferably 17m 2 / g or more, more preferably 20m 2 / g or more. If the BET specific surface area is 40m 2 / g or less, the dispersibility is excellent. The BET specific surface area is preferably 35m 2 / g or less, more preferably 30m 2 In the present disclosure, the BET specific surface area is measured by the method described in the Examples.

[0068] (Anatase content)

[0069] The anatase content (molar basis) of the titanium oxide particles in one embodiment is 70% or more, preferably 75% or more. If the anatase content is 70% or more, high photoelectrochemical activity can be exerted. The upper limit of the anatase content is not particularly limited, but can be set to, for example, 100% or less, 99% or less, or 98% or less. In the present disclosure, the anatase content means the content of anatase-type crystals in the titanium oxide particles, which is measured by the method described in the examples.

[0070] (Residue concentration)

[0071] When the titanium oxide particles in one embodiment are placed in water at 25°C and a pH value of 7 and water screened, the residue concentration that does not pass through the sieve with a mesh size of 45 μm is less than 100 ppm, and the water screening is performed by ultrasonic dispersion at an ultrasonic intensity of 55W and 38kHz for 5 minutes. If the residue concentration is less than 100 ppm, there are fewer coarse particles, and the uniformity and dispersibility are excellent. From the same point of view, the residue concentration is preferably less than 80 ppm, and more preferably less than 50 ppm. The lower limit of the residue concentration is not particularly limited, but can be set to more than 1 ppm, more than 2 ppm, or more than 5 ppm. In the present disclosure, the residue concentration is determined by the method described in the embodiment. Titanium oxide particles with fewer coarse particles have high uniformity and can meet the high quality required for titanium oxide particles. Therefore, they are particularly useful in a wide range of uses such as cosmetics, ultraviolet shielding materials, additives to silicone rubber, photocatalysts, solar cells, dielectric raw materials, and electrode materials for Li-ion batteries.

[0072] (Tap density)

[0073] The tap density of the titanium oxide particles is preferably 0.20 g / cm 3 Above and 0.50g / cm 3 Below. If the tap density is 0.20g / cm 3 If the tap density is higher than 0.25 g / cm, the density is high, which is advantageous in terms of transportation cost, etc. From the same viewpoint, the tap density is more preferably 0.25 g / cm 3 More preferably, 0.30 g / cm 3 If the tap density is 0.50g / cm 3 From the same viewpoint, the tap density is more preferably 0.45 g / cm 3 Below, more preferably 0.40 g / cm 3 In the present disclosure, the tap density is measured by the method described in the Examples.

[0074] (pH value)

[0075] The pH value when the titanium oxide particles are dispersed in water is preferably 1.0 or more and 5.0 or less. If the pH value is within the above range, the particles are stable in water and are easily maintained in a dispersed state. From the same viewpoint, the pH value is more preferably 2.0 or more and 4.0 or less, and further preferably 2.5 or more and 3.0 or less. In the present disclosure, the pH value when the titanium oxide particles are dispersed in water is measured by the method described in the examples.

[0076] (Chlorine (Cl) content)

[0077] The Cl (chlorine atom) content of the titanium oxide particles is preferably 0.20% by mass or less. If the Cl content is 0.20% by mass or less, it is difficult to cause problems in the subsequent process when the titanium oxide particles are used as raw materials. For example, when titanium oxide particles with a Cl content exceeding 0.20% by mass are used as raw materials such as BaTiO3, flux may be produced during sintering. The molten flux is easy to exist locally, and the agglomeration becomes more in the part where it exists locally, and sometimes there is a deviation in quality between other parts. In addition, if the particles agglomerate, the crystals of the BaTiO3 particles grow and become abnormal particles, sometimes reducing the dielectric properties of BaTiO3. From this viewpoint, the Cl content of the titanium oxide particles is more preferably 0.18% by mass or less, and further preferably 0.16% by mass or less. The lower limit of the Cl content of the titanium oxide particles is not particularly limited, but can be set to 0.01% by mass or more, 0.02% by mass or more, or 0.05% by mass or more. In the present disclosure, the Cl content is measured using a silver nitrate potentiometric titration method using the method described in the Examples.

[0078] (Content of other impurities)

[0079] The content of Na, Al, S, Fe, Ni, Cr, Nb and Zr in the titanium oxide particles is preferably less than 50 mass ppm, more preferably less than 10 mass ppm. In addition, the content of Si and C in the titanium oxide particles is preferably less than 500 mass ppm, more preferably less than 100 mass ppm. In the case of using such titanium oxide particles with few impurities as raw materials, it is difficult to cause problems in the subsequent process. For example, when a dielectric is obtained by using titanium oxide particles as a raw material, the reduction of dielectric properties caused by the presence of impurities can be suppressed. In addition, when the titanium oxide particles are used for photocatalysts or solar cells, the reduction of transparency caused by the coloring of Fe can be prevented or suppressed, and the reduction of the function as a photocatalyst or solar cell caused by lattice defects caused by Al, S, etc. can also be prevented or suppressed. In the present disclosure, the content of other impurities is determined by the method described in the embodiments.

[0080] [Slurry, dispersion, composition and dielectric raw material]

[0081] The slurry, dispersion, composition and dielectric raw material in one embodiment contain the aforementioned titanium oxide particles. Slurry is a mixture of particles mixed in a liquid, but mostly refers to a highly viscous fluid. Dispersion generally refers to a mixture of solid particles dispersed in a liquid, including a low concentration of the mixture. Composition refers to a composition composed of multiple components. Dielectric raw material refers to a raw material for manufacturing dielectrics. The slurry, dispersion, composition and dielectric raw material of one embodiment are very suitable for photocatalyst applications, solar cell applications, dielectric applications, etc. Other uses of slurries, dispersions and compositions containing titanium oxide particles are well known. As a method for manufacturing slurries, dispersions, compositions and dielectric raw materials using the titanium oxide particles disclosed in the present invention, known methods can be used. The slurry, dispersion, composition and dielectric raw material containing the titanium oxide particles of one embodiment do not contain coarse particles, so the uniformity and quality of the final product can be improved. Especially in the thin filmization of the dielectric of the multilayer ceramic capacitor, the absence of coarse particles can prevent short circuits and help improve quality.

[0082] [Method for producing titanium oxide particles]

[0083] A method for producing titanium oxide particles according to one embodiment includes:

[0084] A reaction step of introducing a raw material gas (G1) and an oxidizing gas (G2) into a reaction tube to generate a reaction gas, wherein the raw material gas (G1) contains titanium tetrachloride and an inert gas, and the oxidizing gas (G2) contains at least one gas selected from oxygen and water vapor and the inert gas; and

[0085] A cooling step of cooling the titanium oxide particles by introducing a cooling gas to cool the reaction gas.

[0086] The flow rate (F) of titanium tetrachloride in G1 in the reaction step G1T ) relative to the flow rate of G1 (F G1 ) G1T / F G1 is greater than 0.4 and less than 1.0, the mass (kg) of TiO2 after the cooling gas is introduced in the cooling process and the total gas volume (m 3 ) ratio, i.e., TiO2 mass / total gas volume, exceeds 0 kg / m 3 And at 0.21kg / m 3 the following.

[0087] (Reaction tube)

[0088] The reaction tube may be a horizontal reaction tube, but it is preferably a vertical reaction tube, preferably a reaction tube with a circular cross section, in order to easily make the flow of various gases uniform. In the case of a circular vertical reaction tube, the preheated raw material gas (G1) and the oxidizing gas (G2) are introduced from the upper end of the heated reaction tube toward the bottom of the reaction tube through their respective supply pipes to generate the reaction gas. This process is called a reaction process. The reaction gas is cooled by providing a blowing port for cooling gas on the inner wall of the reaction tube and blowing out the cooling gas therefrom to mix with the reaction gas. This process is called a cooling process.

[0089] The region from the raw gas inlet to the cooling gas outlet in the reaction tube is called the reaction region, and the region closer to the exhaust port than the cooling gas outlet is called the cooling region. In the case of multiple cooling gas outlets, the region from the raw gas inlet to the first cooling gas outlet in the reaction tube is called the reaction region, and the region closer to the exhaust port than the first cooling gas outlet is called the cooling region.

[0090] The cooled titanium oxide particles and the remaining gas are exhausted to the outside at the lower part of the reaction tube. In addition, the reaction gas may contain titanium oxide as a reaction product.

[0091] The raw material gas (G1) and the oxidizing gas (G2) are introduced from the inlet (end face side) of the reaction tube along 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 outlets of the introduction pipes for the raw material gas (G1) and the oxidizing gas (G2) is preferably 1.0 or more and 10.0 or less. By setting it to this range, the temperature of the reaction area or the time in the high temperature zone can be made close to uniform. In the present disclosure, the cross-sectional area (S1) of the reaction tube inlet is the cross-sectional area of ​​the cross-sectional area (S2) of the outlet of the introduction pipe including the raw material gas (G1) and the oxidizing gas (G2). The ratio (S1 / S2) is more preferably 1.5 or more and 7.0 or less, further preferably 3.0 or more and 7.0 or less, and particularly preferably 6.0 or more and 7.0 or less. It is preferred that the raw material gas (G1) and the oxidizing gas (G2) are introduced along the gas flow direction in the reaction tube, respectively.

[0092] The temperature of the reaction zone into which the raw material gas (G1) and the oxidizing gas (G2) are introduced is preferably 800°C or more and less than 1200°C, more preferably 800°C or more and less than 1100°C. If the temperature of the reaction zone is above 800°C, the reaction proceeds sufficiently, the particle size distribution of the titanium oxide particles becomes uniform, and the crystallinity can be improved. By increasing the temperature of the reaction zone, the reaction can be completed while mixing, uniform nuclei are generated, and the reaction zone is reduced. On the other hand, if the temperature of the reaction zone is lower than 1200°C, the particle growth proceeds moderately, and agglomeration is difficult to occur, so it is difficult to produce coarse particles. In addition, by making the temperature of the reaction zone lower than 1200°C, the anatase content can be increased.

[0093] (Raw material gas (G1))

[0094] The raw material gas (G1) contains titanium tetrachloride (G1T) and an inert gas (G1I). The titanium tetrachloride in the raw material gas is in a gaseous state.

[0095] The flow rate of raw gas (F G1 ) is preferably 1.0 Nm 3 / hr (standard cubic meters per hour) or more. Passing is 1.0Nm 3 / hr or more, the residence time of the raw material gas (G1) in the reaction zone becomes shorter, and it is difficult for the titanium oxide to be over-sintered and coarsened. From the same point of view, F G1 More preferably 8.0 Nm 3 / hr or more, more preferably 15.0Nm 3 / hr or more. G1 The upper limit of can be appropriately set according to the manufacturing conditions such as the size of the reaction tube and the temperature of the reaction region, and is not particularly limited, but can be set to 100 Nm, for example. 3 / hr or less, 50Nm 3 / hr or less, or 40Nm 3 / hr or less.

[0096] The flow rate of titanium tetrachloride (F G1T ), from the viewpoint of increasing the yield per unit time, preferably 1.0 Nm 3 / hr or more, more preferably 8.0Nm 3 / hr or more, more preferably 15.0Nm 3 / hr or more. From the perspective of suppressing the growth of sintered particles due to reaction heat, F G1T Preferably 50.0Nm 3 / hr or less, more preferably 40.0Nm 3 / hr or less, more preferably 30.0Nm 3 / hr or less.

[0097] Examples of the inert gas include nitrogen, helium, and argon. From the viewpoint of economic efficiency, nitrogen is preferred.

[0098] The flow rate of titanium tetrachloride in G1 (F G1T ) relative to the flow rate of raw gas (F G1 ) G1T / F G1 is 0.4 or more and less than 1.0. G1T / F G1 When F is 0.4 or more, the reaction can be promoted and titanium oxide particles having a low specific surface area can be obtained. G1T / F G1 It is preferably 0.45 or more, and more preferably 0.47 or more. G1T / F G1 When F is less than 1.0, the generation of coarse particles due to sintering of the obtained titanium oxide particles can be suppressed. G1T / F G1 It is preferably 0.99 or less.

[0099] The raw material gas (G1) is introduced into the reaction tube at a temperature of preferably 600°C or higher and lower than 1200°C, more preferably 700°C or higher and lower than 1200°C, and further preferably 800°C or higher and lower than 1200°C.

[0100] (Oxidizing gas (G2))

[0101] The oxidizing gas (G2) contains at least one gas of oxygen (G2O) and water vapor (G2W) and an inert gas (G2I).

[0102] Oxidizing gas flow rate (F G2 ) is preferably 1.0 Nm 3 / hr or more. Passing 1.0Nm 3 / hr or more, the residence time of the oxidizing gas (G2) in the reaction zone becomes shorter, and it is difficult for the titanium oxide particles to be over-sintered and coarsened. G2 More preferably 15.0 Nm 3 / hr or more, more preferably 30.0Nm 3 / hr or more. G2 The upper limit of can be appropriately set according to the manufacturing conditions such as the size of the reaction tube and the temperature of the reaction region, and is not particularly limited, but can be set to 100 Nm, for example. 3 / hr or less, 80Nm 3 / hr or less, or 60Nm 3 / hr or less.

[0103] The total flow rate ratio of oxygen and water vapor in the oxidizing gas (G2) (F G2W +F G2O ) / F G2 ) is preferably 0.8 to 0.999, more preferably 0.9 to 0.998, and further preferably 0.99 to 0.997.

[0104] The flow rate of titanium tetrachloride (F G1T ) and the flow rate of water vapor (F G2W ) and oxygen flow rate (F G2O ) G1T / (F G2W +F G2O ) is preferably 0.3 or more and 0.6 or less. G1T / (F G2W +F G2O ) is 0.3 or more, the yield can be increased. From the same point of view, F G1T / (F G2W +F G2O ) is more preferably 0.40 or more, and even more preferably 0.45 or more. G1T / (F G2W +F G2O ) is 0.6 or less, the number of nuclei generated in the titanium oxide particles increases, and ultrafine particles are easily obtained. In addition, it is easy to reduce oxygen defects and suppress the generation of colored titanium oxide. From the same point of view, F G1T / (F G2W +F G2O ) is more preferably less than 0.55, and further preferably less than 0.50.

[0105] The flow rate of raw gas (F G1 ) and the flow rate of oxidizing gas (F G2 ) G1 / F G2 It is preferably 0.3 or more and 1.2 or less. G1 / F G2 When F is 0.3 or more, the mixing of the raw material gas (G1) and the oxidizing gas (G2) can be promoted, and titanium oxide with a low specific surface area can be obtained. G1 / F G2 It is more preferably 0.40 or more, and even more preferably 0.45 or more. G1 / F G2 When F is 1.20 or less, the number of nuclei generated in the titanium oxide particles increases, ultrafine particles are easily obtained, and the high-temperature residence time is shortened, thereby improving the uniformity of the primary particle size. G1 / FG2 It is more preferably 0.55 or less, and even more preferably 0.50 or less.

[0106] The oxidizing gas (G2) is preferably introduced into the reaction tube at a temperature of 600°C or higher and lower than 1200°C.

[0107] Examples of the inert gas include nitrogen, helium, and argon. Nitrogen is preferred from the viewpoint of economic efficiency. The inert gas in the oxidizing gas (G2) is preferably the same chemical species as the inert gas in the raw material gas (G1).

[0108] (Cooling gas)

[0109] In one embodiment, a cooling gas blowing port is provided on the inner wall of the reaction tube, and the cooling gas is blown out to mix with the reaction gas, thereby cooling the reaction gas.

[0110] As the cooling gas, for example, air, nitrogen, or carbon monoxide can be used. From the viewpoint of improving the cooling effect, the temperature of the cooling gas is preferably 0° C. to 100° C., more preferably 10° C. to 90° C. The cooling gas can also be used together with spray water.

[0111] The blowing angle γ of the cooling gas Q (refer to Figure 1 ) is defined as: in a cross section perpendicular to the central axis 4 of the reaction tube 1 (the flow direction of the reaction gas), the angle at which the cooling gas Q is blown out (the angle of the cooling gas Q outlet 3 relative to the line connecting the outlet 3 and the central axis 4 of the reaction tube 1) when the line connecting the outlet 3 and the central axis 4 of the reaction tube 1 is set to 0°, preferably 0° or more and less than 50°. By making the angle γ 0° or more and less than 50°, the cooling gas can flow to the vicinity of the center of the reaction tube, and can be fully mixed with the reaction gas to obtain a high cooling effect. From the same point of view, the angle γ is more preferably 0° or more and 30° or less.

[0112] The blowing angle δ of the cooling gas Q (refer to Figure 2 ), when the direction of the reaction gas flow in the direction of the central axis of the reaction tube 1 is set to 0° in the longitudinal section including the central axis of the reaction tube 1 (the flow direction of the reaction gas), it is preferably 60° or more, more preferably 70° or more, and further preferably 80° or more. 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.

[0113] From the viewpoint of promoting mixing of the cooling gas and the reaction gas, the number of the cooling gas outlets is one or more, preferably two or more. From the same viewpoint, the number of the cooling gas outlets may be one, two or more in the same cross section of the reaction tube. The number of the cooling gas outlets may be one, two or more in the same longitudinal section of the reaction tube along the central axis of the reaction tube.

[0114] (Purge medium)

[0115] A purge medium outlet may be provided on the inner wall or upper portion of the reaction tube, and the purge medium may be introduced. The purge medium is caused to flow while swirling along the inner wall of the reaction tube, thereby preventing titanium oxide particles from adhering to the inner wall of the reaction tube. Examples of the shape of the purge medium outlet include a single hole and a slit.

[0116] When the generated titanium oxide particles adhere to and remain on the inner wall of the reaction tube, they will grow coarse due to sintering. If the coarsened particles detach from the inner wall and mix into the titanium oxide particles obtained as a product, it will cause the particle size distribution to be non-uniform. By introducing a purge medium, it is possible to prevent the titanium oxide particles from adhering to and remaining on the inner wall of the reaction tube. The purge medium can be introduced continuously or intermittently.

[0117] As the purge medium, a gas or a liquid can be used. Examples of the purge medium include gases such as air, nitrogen, carbon monoxide, and sprayed water. The temperature of the purge medium is preferably 0°C to 100°C, more preferably 10°C to 90°C. The temperature of the purge medium is preferably not higher than the temperature of the cooling gas. This can improve the cooling effect of the cooling gas.

[0118] The blowing angle α of the purge medium P (refer to Figure 1 ) is defined as: in a cross section perpendicular to the central axis 4 of the reaction tube 1 (the flow direction of the reaction gas), the angle at which the purge medium P is blown out (the angle of the purge medium P outlet 5 relative to the line connecting the purge medium P outlet 5 and the central axis 4 of the reaction tube 1) is preferably 45° or more. When the angle α is 45° or more, the purge medium can be swirled near the inner wall of the reaction tube, and the attachment of titanium oxide to the inner wall of the reaction tube can be effectively prevented. From the same point of view, the angle α is preferably 50° or more. The angle α is less than 90°.

[0119] The blowing angle β of the purge medium P (refer to Figure 2), when the direction of the reaction gas flow in the direction of the central axis of the reaction tube 1 is set to 0° in the longitudinal section including the central axis of the reaction tube 1 (the flow direction of the reaction gas), it is preferably 60° or more, more preferably 70° or more, and further preferably 80° or more. The blowing angle β of the purge medium P is preferably 90° or less. By setting the blowing angle β of the purge medium P to such an angle, it is possible to effectively prevent titanium oxide from adhering to the inner wall of the reaction tube.

[0120] From the viewpoint of preventing titanium oxide particles from adhering to the inner wall of the reaction tube, the blowing outlet of the purge medium is preferably at least one, and more preferably at least two. From the same viewpoint, the blowing outlet of the purge medium is preferably at least one, and more preferably at least two, in the same cross section of the reaction tube. Generally, the larger the angle α, or the greater the flow rate of the purge medium, the fewer the number of blowing outlets per week on the periphery of the cross section of the reaction tube. The blowing outlet of the purge medium may be at one, or at two or more, along the central axis direction of the reaction tube in the same longitudinal section of the reaction tube. The blowing outlet of the purge medium may be arranged in a spiral shape on the inner wall of the reaction tube. The blowing outlet of the purge medium is arranged in the reaction zone, and preferably is further arranged in the cooling zone. It is preferred to form a swirling flow of the purge medium along the inner wall of the reaction tube in both the reaction zone and the cooling zone.

[0121] The blowing velocity of the purge medium is preferably 35 m / s or more, more preferably 50 m / s or more, and further 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. The upper limit of the blowing velocity of the purge medium is not particularly limited, but can be set to, for example, 100 m / s or less, 75 m / s or less, or 65 m / s or less. In the present disclosure, the blowing velocity of the purge medium is defined as: the flow rate (m 3 / s) divided by the cross-sectional area of ​​the purge medium outlet (m 2 ) and obtain the value (m / s).

[0122] (Titanium oxide mass / total gas volume)

[0123] The mass (kg) of titanium oxide after the introduction of cooling gas and the total gas volume (m 3 ) ratio, i.e., TiO2 mass / total gas volume, exceeds 0 kg / m 3 And at 0.21kg / m 3The following is the mass of titanium oxide, which is calculated by assuming that all the titanium tetrachloride introduced is converted into titanium oxide, i.e., it is defined as the mass of titanium tetrachloride introduced (kg) × 79.87 / 189.71. The total gas volume = the amount of gas remaining after the reaction × the temperature correction coefficient (based on the temperature of the reaction area) + the amount of purge medium introduced + the amount of cooling gas introduced. The amount of gas remaining after the reaction = the amount of gas generated (Cl component) + the amount of residual oxidizing gas + the amount of inactive gas. If the mass of TiO2 / total gas volume is 0.21kg / m 3 From the same point of view, the TiO2 mass / total gas volume is preferably 0.18 kg / m 3 Below, more preferably 0.15kg / m 3 From the perspective of obtaining titanium oxide, the mass of TiO2 / total gas volume exceeds 0 kg / m 3 , preferably 0.10kg / m 3 above.

[0124] (Cooling gas volume / total gas volume)

[0125] The amount of cooling gas in one embodiment (m 3 ) / total gas volume (m 3 ) is preferably 0.3 or more and 0.6 or less. If the above ratio is 0.3 or more, cooling is fully performed and it is difficult to produce coarse particles. From the same viewpoint, the above ratio is preferably 0.40 or more, more preferably 0.45 or more. If the above ratio is 0.6 or less, it is possible to suppress the excessive cooling gas from flowing back to the reaction zone and allow the reaction to proceed smoothly. From the same viewpoint, the above ratio is preferably 0.58 or less, more preferably 0.56 or less.

[0126] (Dechlorination process)

[0127] The titanium oxide particles produced are preferably dechlorinated in the dechlorination process. The dechlorination of the titanium oxide particles by heating is preferably carried out by bringing water vapor into contact with the titanium oxide particles in such a manner 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, while heating to a temperature of 200°C or more and 550°C or less, preferably 250°C or more and 450°C or less. By setting the temperature to 550°C or less, the sintering of the titanium oxide particles can be suppressed and the primary particle size can be uniformed. By setting the temperature to 200°C or more, the efficiency of dechlorination can be improved. If the mass ratio of water to titanium oxide particles is 0.01 or more, particle growth can be effectively suppressed. The mass ratio of water to titanium oxide particles is preferably 0.01 or more and 3 or less, more preferably 0.05 or more and 2 or less, and further preferably 0.2 or more and 1.8 or less.

[0128] The water vapor is preferably mixed with a gas, such as air, that has the function of efficiently moving the chlorine separated from the titanium oxide particles to the outside of the system. When air is used, the water vapor is preferably contained in the air in an amount of 0.1% by volume or more, more preferably 5% by volume or more, and further preferably 10% by volume or more and 80% by volume or less. The air containing the water vapor is preferably preheated to a temperature of 200° C. or more and 1000° C. or less, and more preferably 450° C. or more and 850° C. or less.

[0129] As a method for moving the chlorine removed from the titanium oxide particles to the outside of the system, a method of reducing the pressure inside the container used for dechlorination can also be cited. The degree of reduced pressure inside the container is preferably 0.5 kPa or more, more preferably 0.5 kPa or more and 3.5 kPa or less. In the present disclosure, the degree of reduced pressure is the pressure difference between the pressure inside the reduced pressure container and the atmospheric pressure.

[0130] The titanium oxide particles disclosed herein have almost no chlorine inside the particles, and the chlorine on the particle surface accounts for most of the chlorine, so it can also be removed by wet low chlorination, such as by washing with water. As a wet method, for example, there is a method in which the titanium oxide particles are suspended in pure water, and the chlorine transferred to the liquid phase is separated to the outside of the system by an ultrafiltration membrane, a reverse osmosis membrane, a filter press, etc.

[0131] Example

[0132] Hereinafter, although an Example and a comparative example are demonstrated concretely, this invention is not limited to these at all.

[0133] The physical properties of the titanium oxide particles were measured as follows.

[0134] (1) BET specific surface area

[0135] According to JIS R 1626:1996, a fully automatic BET specific surface area measuring device ("Macsorb (trademark) HMmodel-1208", manufactured by Macsorb Co., Ltd.) was used. The BET specific surface area was measured by the BET three-point method using nitrogen as the adsorbent for the sample heated to 180°C and flowed with nitrogen for 20 minutes as a pretreatment. The application range of the BET method is set to P / P0 = 0.00 to 0.95.

[0136] (2) Anatase content

[0137] The content of anatase crystals in titanium oxide particles (anatase content) was measured by powder X-ray diffraction. Specifically, for dried titanium oxide particles, "X'pertPRO" manufactured by PANalytical was used as a measuring device, a copper target was used, and Cu-Kα1 rays were used. X-ray diffraction measurement was performed under the conditions of tube voltage 45kV, tube current 40mA, measurement range 2θ=10~80deg (degrees), sampling width 0.0167deg, and scanning speed 0.0192deg / s. The peak height (Ha) of the maximum peak corresponding to the anatase crystal, the peak height (Hb) of the maximum peak corresponding to the brookite crystal, and the peak height (Hr) of the maximum peak corresponding to the rutile crystal were obtained, and the content of anatase crystals in the titanium oxide particles (anatase content) was obtained by the following calculation formula.

[0138] Anatase content (%) = {Ha / (Ha+Hb+Hr)}×100

[0139] (3) Residue (coarse particles) concentration

[0140] 300 g of the sample was rinsed on a mesh sieve with a mesh size of 45 μm at a water pressure of 300 ± 20 kPa until it became transparent. Then, it was placed in pure water at 25°C and pH 7, and water-sieved using a desktop ultrasonic cleaner (sonar cleaner, manufactured by Kaijiyo Co., Ltd.), and the value obtained by dividing the mass of the residue remaining on the sieve by the total amount of the sample was taken as the residue concentration. The water sieve was performed by ultrasonic dispersion at an ultrasonic intensity of 55 W and 38 kHz for 5 minutes.

[0141] (4) Tap density

[0142] Titanium oxide particles were placed in a measuring cup and tapped for 3 minutes to measure the volume. The particles were transferred to a 100 mL container and the tap density (g / cm2) was calculated from the mass of the titanium oxide particles in the container. 3 ).

[0143] (5) pH value

[0144] A suspension of titanium oxide particles having a content of 10% by mass 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 a dispersion medium and without using a wetting agent.

[0145] (6) Chlorine (Cl) content

[0146] The Cl content in the titanium oxide particles was determined by the silver nitrate potentiometric titration method. Specifically, 0.5 g of titanium oxide particles were weighed. Then, a silver nitrate solution (concentration 0.02 mol / L) was added dropwise to the solution of the titanium oxide particles, and the potential difference was measured. The mass of chlorine atoms in the solution was obtained, and the chlorine content (mass %) was calculated.

[0147] (7) Content of other impurities

[0148] The measurement methods of each impurity are shown below.

[0149] Fe: Atomic absorption method (Z-2300 atomic absorption spectrophotometer manufactured by Hitachi High-Tech Co., Ltd.)

[0150] Al, Si: X-ray fluorescence analysis (XRF) (Symartex 10 manufactured by Rigaku Corporation)

[0151] C, S: High frequency induction furnace combustion-infrared absorption method

[0152] Na, Ni, Cr, Nb, Zr: Inductively Coupled Plasma Mass Spectrometry

[0153] Example 1

[0154] <1st step>

[0155] A vertical reaction tube with a circular cross section was used. A raw material gas (G1) consisting of titanium tetrachloride (the purity of titanium tetrachloride was 99.99 mass % or more) and nitrogen was heated to 965°C. An oxidizing gas (G2) consisting of oxygen, water vapor and nitrogen was heated to 900°C. The raw material gas (G1) was heated at a flow rate of 26.2 Nm 3 / hr, oxidizing gas (G2) at a flow rate of 55.4Nm 3 / hr are introduced from the top of the reaction tube to generate the reaction gas. The purge medium (nitrogen) is introduced from the inner wall of the reaction tube in the reaction zone. In the cooling zone, the cooling gas (air) is introduced at a rate of TiO2 mass (kg) / total gas volume (m 3 ) becomes 0.19kg / m 3 The titanium oxide particle raw material was introduced in a manner to obtain the titanium oxide particle raw material. Then, the titanium oxide particle raw material was captured at the lower part of the reaction tube using a polytetrafluoroethylene bag filter. The production conditions including other conditions are shown in Table 1.

[0156] <Step 2>

[0157] The obtained titanium oxide particle raw material was introduced into a cylindrical rotary heating furnace, and dechlorinated at a mass ratio of water vapor mixed with air to the titanium oxide raw material (mass of water vapor / mass of titanium oxide particle raw material) of 0.06 and a temperature of 450° C. to obtain titanium oxide particles. Various physical properties of the obtained titanium oxide particles were measured. The physical property evaluation results are shown in Table 2.

[0158] Examples 2 to 4, Comparative Examples 1, 2, 4 to 6

[0159] Except for changing the conditions of the raw material gas (G1), oxidizing gas (G2), cooling gas, purge medium and total gas amount in the first step, the first step was carried out in the same manner as in Example 1 to obtain a raw material of titanium oxide particles. The conditions are shown in Table 1. The second step was carried out in the same manner as in Example 1 to obtain titanium oxide particles. The results of physical property evaluation are shown in Table 2. Comparative Example 1 was manufactured according to the method of Example 5 of Patent Document 1 (International Publication No. 2022 / 244620), and Comparative Example 2 was manufactured according to the method of Example 3 of Patent Document 1 (International Publication No. 2022 / 244620).

[0160] Comparative Example 3

[0161] Titanium oxide particles were produced according to the method of Example A4 in Japanese Patent No. 4445972. Table 2 shows the results of physical property evaluation.

[0162]

[0163]

[0164] As shown in Table 2, in Examples 1 to 4, titanium oxide particles with a BET specific surface area within the specified range, a high anatase content, and a low residue concentration were obtained. In Comparative Example 1, due to the ratio of TiO2 mass (kg) / total gas volume (m 3 ) more than 0.21kg / m 3 Therefore, more coarse particles are generated and the residue concentration is high. G1T / F G1 It is less than 0.4, which is relatively low, so the BET specific surface area is high.

[0165] In Comparative Example 3, since a mixed gas of hydrogen and oxygen was used as the oxidizing gas and combustion of hydrogen and oxidation of TiCl 4 were performed simultaneously, the reaction temperature became high and the anatase content was low.

[0166] According to the present disclosure, it is possible to provide titanium oxide particles having fewer coarse particles and a higher anatase content than conventional titanium oxide particles having an equivalent BET specific surface area, and a method for producing the same.

[0167] Industrial Applicability

[0168] The titanium oxide particles disclosed in the present invention are very suitable for use in photocatalyst applications, solar cell applications, dielectric applications, etc., and do not require a pulverization process or can be implemented using very little equipment, so they have very great practical value in industry.

Claims

1. A method for producing titanium oxide particles, comprising: A reaction step of introducing a raw material gas G1 and an oxidizing gas G2 into a reaction tube to generate a reaction gas, wherein the raw material gas G1 contains titanium tetrachloride and an inert gas, and the oxidizing gas G2 contains at least one gas selected from oxygen and water vapor and the inert gas; and a cooling step of cooling the reaction gas by introducing a cooling gas to obtain the titanium oxide particles; The flow rate F of titanium tetrachloride in G1 in the reaction step G1T Flow F relative to G1 G1 Ratio F G1T / F G1 is greater than 0.4 and less than 1.0, and the mass of TiO2 in kg after the cooling gas is introduced in the cooling step is greater than the mass of TiO2 in m 3 The ratio of the total gas volume, i.e., the mass of TiO2 / total gas volume, exceeds 0 kg / m 3 And at 0.21kg / m 3 the following.

2. The method for producing titanium oxide particles according to claim 1, The flow rate F of the titanium tetrachloride G1T / (the flow rate of the water vapor F G2W + The oxygen flow rate F G2O ) is greater than or equal to 0.3 and less than or equal to 0.

6.

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

4. The method for producing titanium oxide particles according to claim 1 or 2, G1 flow F G1 / G2 flow rate F G2 It is 0.3 or more and 1.2 or less.

5. The method for producing titanium oxide particles according to claim 1 or 2, A blowing outlet for a purge medium is provided on the inner wall or the upper part of the reaction tube. In a cross section of the reaction tube perpendicular to the central axis of the reaction tube, a blowing angle α of the purge medium relative to a line connecting the blowing outlet for the purge medium and the central axis of the reaction tube is greater than 45°, and a blowing flow rate of the purge medium is greater than 35 m / s.

6. The method for producing titanium oxide particles according to claim 1 or 2, A ratio S1 / S2 of a cross-sectional area S1 of the inlet of the reaction tube to a sum S2 of cross-sectional areas of outlets of the introduction tubes for the source gas G1 and the oxidizing gas G2 is greater than or equal to 1.0 and less than or equal to 10.

0.

7. A titanium oxide particle having a BET specific surface area of ​​15 to 40 m 2 / g, the rutile content is more than 70%, and when it is placed in water at 25°C and pH 7 and water-sieved by ultrasonic dispersion at an ultrasonic intensity of 55W and 38kHz for 5 minutes, the concentration of residues that do not pass through the sieve with a mesh size of 45μm is less than 100ppm.

8. The titanium oxide particles according to claim 7, The Cl content of the titanium oxide particles measured by a silver nitrate potentiometric titration method was 0.20 mass % or less.

9. The titanium oxide particles according to claim 7 or 8, The contents of Na, Al, S, Fe, Ni, Cr, Nb and Zr are each 50 mass ppm or less, and the contents of Si and C are each 500 mass ppm or less. 10 . A slurry comprising the titanium oxide particles according to claim 7 or 8 .

11. A dispersion comprising the titanium oxide particles according to claim 7 or 8. 12 . A composition comprising the titanium oxide particles according to claim 7 . 13 . A dielectric material comprising the titanium oxide particles according to claim 7 or 8 .

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