Titanium oxide powder and method for producing same

Abstract

The purpose of the present invention is to provide: an anatase type titanium oxide powder which has a high specific surface area and high dispersibility; and a method for producing same.　Provided is a titanium oxide powder which has a BET specific surface area, as measured using a nitrogen adsorption method, of 300 m2 / g-480 m2 / g, has an anatase crystal phase content, as measured using XRD measurements, of 90% or more, and has a spin-spin relaxation time T2, as measured by pulsed NMR using a 5 mass% suspension produced using ion exchanged water, of 46-103 ms.

Description

Titanium oxide powder and its manufacturing method

[0001] The present invention relates to a titanium oxide powder and a method for producing the same.

[0002] Titanium(IV) oxide (TiO ２ Titanium dioxide (IV) is a chemically stable material and is widely used industrially as a white pigment. Titanium dioxide (IV) reacts with barium carbonate to produce barium titanate. Barium titanate is known to be used as a material for multilayer ceramic capacitors, a component of smartphones and other devices. Titanium dioxide can have three main crystalline structures: anatase, brookite, and rutile. Anatase titanium dioxide, in particular, has a higher surface hydroxyl group content than other crystalline phases, resulting in high hydrophilicity and dispersibility. Furthermore, because anatase titanium dioxide has a high surface hydroxyl group content, it is highly reactive with other metal elements, making it highly sought after as a raw material for dielectric and battery materials. In recent years, there has been a demand for fine anatase titanium dioxide with a high specific surface area to achieve higher functionality in these applications.

[0003] On the other hand, as the particles become finer, the surface free energy increases, which makes the particles more likely to aggregate and deteriorates dispersibility. In order to suppress the aggregation of particles, a manufacturing method has been reported in which the particle surfaces are modified with a modifying agent such as a silane agent, and the particles are dispersed and stabilized in a dispersion liquid containing an amine agent, as in Patent Document 1.

[0004] Generally, nanoparticles are mixed with an aqueous solvent or an alcohol solvent, and therefore, a method for increasing the affinity with the solvent by increasing the hydrophilicity of the particle surface is used. One method for increasing the hydrophilicity of the particle surface is to modify the particle surface with a polymer containing silicon or the like, as described in Patent Documents 2 and 3.

[0005] JP 2008-247712 A JP 2015-212355 A JP 2010-95392 A

[0006] However, while the manufacturing method of Patent Document 1 can produce a dispersion of nanoparticles, it is difficult to control the concentration during manufacturing and storage in the form of a dispersion. Therefore, the dispersion obtained by the manufacturing method disclosed in Patent Document 1 is not suitable for producing titanium oxide for electronic device applications such as dielectric materials and battery materials, which require strict composition control. Furthermore, the silicon and phosphorus contained in the dispersant significantly affect key properties of materials for electronic devices, such as the dielectric constant and conductivity, making them unsuitable as electronic device materials. Furthermore, the titanium oxides described in Patent Documents 2 and 3 also contain large amounts of silicon, making them unsuitable as electronic device materials.

[0007] For these reasons, when used as an electronic device material, there is a demand for highly dispersible ultrafine particles of anatase titanium dioxide in a dry powder form that can be uniformly mixed with other raw materials after carefully calculating the composition. Furthermore, to prevent the properties of electronic device materials from deteriorating, it is also required that the fine particles of anatase titanium dioxide do not contain semimetallic elements such as silicon and phosphorus, metallic elements such as sodium and magnesium, or polymeric organic acid chains such as polyols.

[0008] An object of the present invention is to provide an anatase-type titanium oxide powder having a large specific surface area and high dispersibility, and a method for producing the same.

[0009] The inventors have discovered that by synthesizing anatase titanium oxide through the hydrolysis of titanium tetrachloride in the presence of a dispersant such as urea, an ammonium compound, an inorganic acid, or an organic acid, and then drying the synthesized titanium oxide in an atmosphere with an initial relative humidity of 70 to 100%, it is possible to suppress dense aggregation of particles and particle growth, and by obtaining a dry powder without deactivating the hydroxyl groups on the particle surfaces, it is possible to obtain anatase titanium oxide powder with a large specific surface area, high affinity with solvents, and high dispersibility.The configurations of the present invention that achieve the above objects are as follows.

[0010] (1) The titanium oxide powder according to one embodiment of the present invention has a BET specific surface area of ​​300 m2 measured using a nitrogen adsorption method. ２ / g or more 480m ２ / g or less, the anatase content of the crystalline phase measured by XRD measurement is 90% or more, and the spin-spin relaxation time T2 of a 5 wt % suspension prepared using ion-exchanged water, measured by pulse NMR, is 46 ms or more and 103 ms or less.

[0011] (2) In the titanium oxide powder of (1) above, the carbon content may be 0.5 mass % or less.

[0012] (3) In the titanium oxide powder of (1) or (2) above, the chlorine content may be 0.1% by mass or less, the silicon content may be 0.1% by mass or less, and the sulfur content may be 0.1% by mass or less.

[0013] (4) In the titanium oxide powder of any one of (1) to (3) above, the diffraction angle 2θ of the diffraction peak at 24.5° to 26.0° may be 1.10° to 2.00° in terms of half-width.

[0014] (5) The titanium oxide powder of any one of (1) to (4) above may have a zeta potential of −63 mV or more and −40 mV or less.

[0015] (6) A method for producing a titanium oxide powder according to one embodiment of the present invention includes a synthesis step of mixing an aqueous solution containing urea with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 so that the urea / Ti (molar ratio) is 0.001 or more and 0.058 or less to precipitate titanium oxide, and a drying step of drying the obtained titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to powder it.

[0016] (7) A method for producing a titanium oxide powder according to one embodiment of the present invention includes a synthesis step of mixing an aqueous solution containing an ammonium compound with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 so that the ammonium compound / Ti (molar ratio) is 0.001 or more and 0.029 or less to precipitate titanium oxide, and a drying step of drying the obtained titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to powder it.

[0017] (8) In the method for producing titanium oxide powder according to (6) or (7) above, the aqueous solution containing at least one of urea and an ammonium compound may have a pH of less than 12.0.

[0018] (9) A method for producing a titanium oxide powder according to one embodiment of the present invention includes a synthesis step of mixing an aqueous solution containing an inorganic acid with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 so that the inorganic acid / Ti (molar ratio) is 0.001 or more and 0.030 or less to precipitate titanium oxide, and a drying step of drying the obtained titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to powder it.

[0019] (10) A method for producing a titanium oxide powder according to one embodiment of the present invention includes a synthesis step of mixing an aqueous solution containing an organic acid with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 so that the acidic functional groups of the organic acid / Ti (molar ratio) is 0.001 or more and 0.037 or less to precipitate titanium oxide, and a drying step of drying the obtained titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to powder it.

[0020] (11) In the method for producing titanium oxide powder according to (10) above, the organic acid may be an α-hydroxycarboxylic acid.

[0021] (12) In the method for producing titanium oxide powder according to (10) or (11) above, the molecular weight of the organic acid or inorganic acid in the aqueous solution may be 300 or less.

[0022] (14) The method for producing titanium oxide powder according to any one of (6) to (13) above may further include a purification step of purifying titanium oxide using one or more of an ultrafiltration membrane, a reverse osmosis membrane, an ion exchange resin, and an electrodialysis membrane.

[0023] According to the present invention, it is possible to provide an anatase-type titanium oxide powder having a large specific surface area and high dispersibility, and a method for producing the same.

[0024] An example of an embodiment of the present invention will be described below, but the present invention is not limited to the following example.

[0025] In this embodiment, "titanium oxide" refers to titanium oxide (IV) (TiO) unless otherwise specified. ２ The "Ti concentration" refers to the concentration obtained by dividing (the amount of Ti atoms taking into consideration all titanium-atom-containing components that constitute titanium compounds, titanium-containing ions, complexes, etc.) by (the volume of the solution containing Ti).

[0026] <1. Titanium oxide powder> The titanium oxide powder according to one embodiment of the present invention has a BET specific surface area of ​​300 m2 measured using a nitrogen adsorption method. ２ / g or more 480m ２ / g or less, the anatase content of the crystalline phase measured by XRD measurement is 90% or more, and the spin-spin relaxation time T2 measured by pulsed NMR (Nuclear Magnetic Resonance) of a 5% by mass suspension prepared using ion-exchanged water is 46 ms or more and 103 ms or less.

[0027] (BET specific surface area) As described above, the BET specific surface area of ​​the titanium oxide powder according to one embodiment of the present invention is 300 m ２ / g or more. ２ / g or more, when titanium oxide is reacted with other substances, an ultrafine particle material such as a 0201 size multilayer ceramic capacitor material can be obtained. From the same viewpoint, in order to obtain an ultrafine particle material with a finer particle size, the BET specific surface area of ​​the titanium oxide powder is 350 m ２ / g or more is preferable, and 380m ２ / g or more is more preferable.

[0028] As described above, the BET specific surface area of ​​the titanium oxide powder of one embodiment of the present invention is 480 m ２ / g or less. ２ / g or less, abnormal grain growth of titanium oxide can be suppressed even when reacted with barium carbonate at high temperatures, and the particle size distribution of the resulting barium titanate material is made uniform. From the same viewpoint, in order to obtain a material with a more uniform particle size distribution, the BET specific surface area of ​​the titanium oxide powder is 430 m ２ / g or less is preferable, and 400m ２ / g or less is more preferable.

[0029] (Anatase content) In the titanium oxide powder of this embodiment, the content of the anatase phase in the crystalline phase measured using XRD measurement is 90% or more. When titanium oxide is reacted with other substances, a high content of the anatase phase in the titanium oxide powder is advantageous because it increases reactivity. From the same viewpoint, the content of the anatase phase is more preferably 95% or more, and even more preferably 99% or more.

[0030] (Spin-Spin Relaxation Time) Unlike high-resolution NMR, pulse NMR does not provide chemical shift information, but instead is a technique that can rapidly measure the relaxation times (spin-lattice relaxation time T1 and spin-spin relaxation time T2) of 1H nuclei, which are closely related to molecular mobility. The use of pulse NMR has rapidly spread in recent years, and measurement methods in pulse NMR include the Hahn echo method, the solid echo method, the CPMG method, and 90° pulse NMR, any of which can be suitably used. In the present invention, the spin-spin relaxation time T2 means the spin-spin relaxation time T2 of 1H nuclei measured by the CPMG method.

[0031] In the titanium oxide of this embodiment, the spin-spin relaxation time T2 of 1H nuclei measured by the CPMG method of pulsed NMR while the titanium oxide is dispersed in water is thought to be a characteristic related to the state of water molecules bound to the titanium oxide surface. Specifically, the shorter the spin-spin relaxation time T2, the more water molecules are bound to the titanium oxide surface (due to a thicker hydration layer), which is thought to improve the dispersibility of the titanium oxide and facilitate improved filtration performance.

[0032] In one embodiment of the present invention, the titanium oxide powder has a spin-spin relaxation time T2 of 46 ms or more and 103 ms or less, measured by the CPMG method of pulsed NMR for a 5% by weight suspension prepared using ion-exchanged water. If the spin-spin relaxation time T2 of the suspension is 46 ms or more, when the titanium oxide powder is reslurried to form a dispersion to obtain barium titanate, it will not become over-dispersed, and the viscosity will be kept appropriately low, resulting in excellent fluidity, which is advantageous when reacting with other substances. From the same perspective, the spin-spin relaxation time T2 is preferably 60 ms or more, and more preferably 70 ms or more. If the spin-spin relaxation time T2 is 103 ms or less, it is believed that a large number of water molecules are bound to the titanium oxide surface (due to a thick hydration layer), resulting in excellent dispersibility. From the same perspective, the spin-spin relaxation time T2 is preferably 90 ms or less, and more preferably 80 ms or less.

[0033] (Elemental Analysis) When the titanium oxide powder according to this embodiment is used as a raw material for a dielectric material, the presence of Cl (chlorine), Fe (iron), Al (aluminum), Si (silicon), and S (sulfur) is thought to cause a decrease in the dielectric constant. Therefore, the chlorine content, aluminum content, silicon content, and sulfur content of the titanium oxide powder according to this embodiment are each preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less. There are no particular restrictions on the lower limit, but from the viewpoint of the cost of the production method, 0.0001% by mass or more is preferred.

[0034] In order to suppress the deposition of by-products derived from C (carbon), the carbon content of titanium oxide according to one embodiment of the present invention is preferably 0.50% by mass or less, more preferably 0.30% by mass or less, and even more preferably 0.10% by mass or less. There is no particular restriction on the lower limit, but from the viewpoint of the cost of the production method, 0.001% by mass or more is preferred.

[0035] (Full Width at Half Maximum of Diffraction Peak in Crystalline X-Ray Diffraction Measurement) The full width at half maximum (FWHM) of the diffraction peak appearing in the diffraction angle 2θ range of 24.5° to 26.0° obtained by X-ray diffraction (XRD) measurement of the titanium oxide powder of this embodiment is preferably 1.10° or more. In this case, the smaller the FMHM of the titanium oxide powder, the higher the crystallinity, and this is preferable. However, in order to make the FMHM very small, the reaction is carried out at a high temperature, which tends to cause aggregation of the titanium oxide powder and reduce the BET specific surface area. Therefore, from the viewpoint of obtaining a titanium oxide powder that is not significantly aggregated, it is desirable to set the FMHM to a certain value or more, and 1.10° or more is preferable. From the same viewpoint, the FWHM is more preferably 1.30° or more, and even more preferably 1.50° or more.

[0036] The FWHM is preferably 2.00° or less. This is because the better the crystallinity of titanium oxide, the better the crystallinity of products produced using titanium oxide. From the same perspective, the FWHM is more preferably 1.90° or less, and even more preferably 1.80° or less.

[0037] By virtue of the above-described configuration, the titanium oxide powder according to one embodiment of the present invention has a zeta potential of -63 mV or more and -40 mV or less. That is, the absolute value of the zeta potential of the titanium oxide powder according to this embodiment is 40 mV or more and 63 mV or less. As such, the titanium oxide powder according to one embodiment of the present invention has a high zeta voltage, which increases dispersibility, and because the zeta potential is not excessive, it is possible to prevent over-dispersion when attempting to produce barium titanate, which would result in excessive viscosity of the dispersion and poor flow.

[0038] 2. Titanium oxide powder manufacturing method 1> A method for manufacturing titanium oxide powder according to the above embodiment will be described below. The titanium oxide powder manufacturing method according to one aspect of the present invention includes a synthesis step and a drying treatment step. The synthesis step is a step of mixing an aqueous solution containing any one selected from the group consisting of urea, an ammonia compound, an organic acid, and an inorganic acid with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 to precipitate titanium oxide. In the synthesis step, (i) when an aqueous solution containing urea is used, mixing is performed so that the urea / Ti (molar ratio) is 0.001 or more and 0.058 or less, (ii) when an aqueous solution containing an ammonia compound is used, mixing is performed so that the urea / Ti (molar ratio) is 0.001 or more and 0.029 or less, (iii) when an aqueous solution containing an inorganic acid is used, mixing is performed so that the inorganic acid / Ti (molar ratio) is 0.001 or more and 0.030 or less, and (iv) when an aqueous solution containing an organic acid is used, mixing is performed so that the acidic functional group of the organic acid / Ti (molar ratio) is 0.001 or more and 0.037 or less. In the drying step, the obtained titanium oxide is dried and powdered in an atmosphere with an initial relative humidity of 70 to 100%.

[0039] First, as Production Method 1, a method for producing titanium oxide powder using urea as an additive to a titanium tetrachloride aqueous solution will be described.

[0040] The method for producing titanium oxide powder according to this embodiment includes a synthesis step of mixing an aqueous solution containing urea with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 so that the molar ratio (urea [mol] / Ti [mol]) is 0.001 or more and 0.058 or less to precipitate titanium oxide, and a drying step of drying the obtained titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to powder it.

[0041] <2-1. Synthesis Step> As described above, first, an aqueous solution containing urea and an aqueous solution containing titanium tetrachloride are mixed to obtain an aqueous solution. Hereinafter, the aqueous solution obtained by mixing may be referred to as a mixed solution. In the synthesis step, hydrolysis of titanium tetrachloride proceeds. The aqueous solution containing titanium tetrachloride has a pH value of less than 3. This is to allow the hydrolysis reaction to proceed preferentially. Furthermore, the aqueous solution containing titanium tetrachloride preferably has a pH of 2 or less, even more preferably a pH of 1 or less, and may, for example, be 0.1 or more.

[0042] Urea acts as a reaction inhibitor. Adding urea moderates the generation of titanium oxide particles, suppressing the phase transition to the rutile phase and inhibiting aggregation.

[0043] The pH of the aqueous solution containing urea is preferably less than 12.0. At a pH of less than 12.0, the hydrolysis reaction occurs quickly, making it difficult to generate heterogeneous phases including the brookite phase, and titanium oxide gradually precipitates and is easily dispersed. From the same perspective, the pH is more preferably 11.5 or less, and even more preferably 11.0 or less. Furthermore, it is preferable that the pH is greater than 10, i.e., the pH is greater than 10. This is because the rate of the hydrolysis reaction is sufficiently suppressed and the phase transition of the stable phase to the rutile phase is suppressed.

[0044] The Ti atom concentration in the aqueous solution (mixed solution) obtained by mixing an aqueous solution containing urea and an aqueous solution containing titanium tetrachloride is preferably 0.01 mol / L or more. This is to allow the hydrolysis reaction to proceed preferentially. From the same viewpoint, it is more preferably 0.03 mol / L or more, and even more preferably 0.05 mol / L or more. The Ti atom concentration in the mixed solution is preferably 1.00 mol / L or less. This is to prevent the precipitation of the rutile phase, which is a stable phase, by suppressing the Ti concentration. From the same viewpoint, it is more preferably 0.50 mol / L or less, and even more preferably 0.20 mol / L or less.

[0045] Regarding the content of urea in the mixed solution, the ratio of the amount of urea to the amount of Ti in the mixed solution (urea [mol] / Ti [mol]) is 0.001 or more. This is to sufficiently slow down the rate of the hydrolysis reaction and suppress the phase transition from the stable phase to the rutile phase. From the viewpoint of further suppressing the phase transition to the rutile phase, the ratio (urea [mol] / Ti [mol]) is preferably 0.013 or more, more preferably 0.030 or more. The ratio (urea [mol] / Ti [mol]) is 0.058 or less, preferably 0.050 or less. This is to prevent excessive suppression of the hydrolysis reaction.

[0046] The mixed solution is preferably heated to precipitate titanium oxide. From the viewpoint of productivity, it is preferable to heat the mixed solution at a high temperature increase rate. On the other hand, in order to suppress the precipitation of amorphous titanium oxide and improve crystallinity, it is preferable to suppress the rapid progress of the reaction and to suppress the temperature increase rate so as to allow sufficient crystal growth. Therefore, the mixed solution is preferably heated to the target temperature, i.e., the synthesis temperature, at a temperature increase rate of 0.1°C / min to 1.5°C / min, more preferably 0.3°C / min to 1.0°C / min, and even more preferably 0.6°C / min to 1.0°C / min.

[0047] The synthesis temperature is preferably 50°C or higher, and more preferably 60°C or higher, in order to allow the hydrolysis reaction to proceed predominantly. The synthesis temperature is preferably 100°C or lower, in order to suppress the phase transition from the stable phase to the rutile phase.

[0048] The time for which the mixed solution is held at the synthesis temperature can be set arbitrarily, and the temperature may be lowered without holding, or may be held for a predetermined time. The time for which the mixed solution is held at the synthesis temperature is preferably 15 minutes or more from the viewpoint of allowing the reaction to proceed sufficiently. After the reaction is completed, it is preferable to allow the mixture to cool to room temperature.

[0049] <2-2. Purification Step> The method for producing titanium oxide powder according to one embodiment of the present invention preferably includes a purification step of purifying titanium oxide. The purification step uses, for example, one or more of an ultrafiltration membrane, a reverse osmosis membrane, an ion exchange resin, and an electrodialysis membrane. The method for producing titanium oxide powder according to one embodiment of the present invention further includes a purification step, which makes it possible to remove Cl (chlorine), S (sulfur), Si (silicon), Fe (iron), Al (aluminum), and the like from the slurry containing titanium oxide obtained in the synthesis step. The purification step is carried out after the synthesis step. Since the purification step is carried out in a state in which titanium oxide is dispersed in a liquid, it is desirable to carry out the purification step before the drying treatment step.

[0050] <2-3. Dehydration Step> The method for producing titanium oxide powder according to one embodiment of the present invention may further include a dehydration step in which the slurry is dehydrated using a filter press or the like to obtain a solid content. The dehydration step is carried out, for example, after the synthesis step and before the drying step. When the method for producing titanium oxide powder includes a purification step, the dehydration step is carried out after the purification step. Dehydration allows the drying step to be carried out efficiently.

[0051] <2-4. Drying Treatment Step> A method for producing titanium oxide powder according to one embodiment of the present invention includes a drying treatment step (drying step) in which the obtained titanium oxide is dried and powdered in an atmosphere with an initial relative humidity of 70 to 100%. The initial relative humidity is the relative humidity at the start of the drying treatment step. The drying atmosphere may be air or an inert gas atmosphere.

[0052] Titanium oxide may be dried in the form of a slurry dispersed or dissolved in water, or may be dried after being dehydrated using a filter press or the like.

[0053] In the drying treatment step, in order to remove moisture while suppressing the deactivation of hydroxyl groups on the titanium oxide surface, drying is carried out in an atmosphere with an initial relative humidity of 70% or more and 100% or less. From the same perspective, a humidity of 75% or more is preferred, a humidity of 80% or more is more preferred, and a humidity of 90% or more is even more preferred. Furthermore, the initial relative humidity in the drying treatment step may be 99% or less, or 97% or less. To promote drying, it is preferable to dry in an atmosphere with an initial relative humidity of 70% or more for a certain period of time, and then perform a drying treatment in the atmosphere after a certain period of time has passed. The treatment of maintaining an initial relative humidity of 70% or more is also called an aging treatment. The aging treatment time is preferably 3 to 48 hours, more preferably 5 to 30 hours.

[0054] In the drying step, the obtained sample is dried until the moisture content reaches 2% by mass to 15% by mass, for example, to obtain a titanium oxide solid content. The obtained oxide solid content is pulverized in a mortar or the like to obtain titanium oxide powder.

[0055] 3. Titanium Oxide Powder Manufacturing Method 2 Next, manufacturing method 2 will be described, which is a method for manufacturing titanium oxide powder using an ammonium compound as an additive to an aqueous titanium tetrachloride solution.

[0056] A titanium oxide powder production method (production method 2), which is another aspect of production method 1 according to one embodiment of the present invention, includes a synthesis step of mixing an aqueous solution containing an ammonium compound with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 so that the molar ratio (ammonium compound [mol] / Ti [mol]) is 0.001 or more and 0.029 or less to precipitate titanium oxide, and a drying step of drying the resulting titanium oxide to powder in an atmosphere with an initial relative humidity of 70 to 100%. The initial relative humidity in the drying step is preferably 70% or more. The titanium oxide powder production method of this aspect differs from the titanium oxide powder production method of the above aspect (production method 1) in the conditions for the synthesis step. In the titanium oxide powder production method of this aspect, the steps other than the synthesis step can be the same as those in the titanium oxide powder production method of the above aspect. That is, in production method 2, one or both of a purification step and a dehydration step can be performed between the synthesis step and the drying step. Furthermore, the preferred conditions for the purification step, dehydration step, and drying step can be the same as those in production method 1. In the following, the conditions of the synthesis step of the titanium powder production method of this embodiment that differ from Production Method 1 will be described.

[0057] Ammonium compounds act as reaction inhibitors. Addition of these compounds moderates the generation of titanium oxide particles, inhibiting the phase transition to the rutile phase and suppressing aggregation. Preferred ammonium compounds are ammonia, ammonium chloride, and ammonium carbonate, with ammonium carbonate being particularly preferred. Ammonium carbonate is easy to adjust to the desired pH, allowing titanium oxide powder to be produced under ideal conditions.

[0058] Regarding the content of the ammonium compound in an aqueous solution (mixture) obtained by mixing an aqueous solution containing an ammonium compound with an aqueous solution containing titanium tetrachloride and having a pH of less than 3, the ratio of the amount of substance of the ammonium compound to the amount of substance of Ti in the mixture (ammonium compound [mol] / Ti [mol]) is preferably 0.001 or more. This is to sufficiently slow down the rate of the hydrolysis reaction and suppress the phase transition from the stable phase to the rutile phase. From the viewpoint of further suppressing the phase transition to the rutile phase, the ratio of the amount of substance is more preferably 0.005 or more, and even more preferably 0.013 or more. The ratio of the amount of substance (ammonium compound [mol] / Ti [mol]) is preferably 0.029 or less. This is to prevent excessive suppression of the hydrolysis reaction. From the same viewpoint, it is more preferably 0.020 or less.

[0059] 4. Titanium Oxide Powder Manufacturing Method 3 Next, manufacturing method 3 of titanium oxide powder using an aqueous solution containing an inorganic acid as an additive to an aqueous titanium tetrachloride solution will be described.

[0060] A method for producing titanium oxide powder according to one embodiment of the present invention, which is different from Production Methods 1 and 2, includes a synthesis step in which an aqueous solution containing an inorganic acid is mixed with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 so that the molar ratio (inorganic acid [mol] / Ti [mol]) is 0.001 or more and 0.030 or less to precipitate titanium oxide, and a drying step in which the resulting titanium oxide is dried and powdered in an atmosphere with an initial relative humidity of 70 to 100%. The initial relative humidity in the drying step is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. The titanium oxide powder production method of this embodiment differs from the titanium oxide powder production method of the above embodiment (Production Method 1) in the conditions for the synthesis step. In the titanium oxide powder production method of this embodiment, the steps other than the synthesis step can be the same as those in the titanium oxide powder production method of the above embodiment. That is, in Production Method 3, either or both of a purification step and a dehydration step may be performed between the synthesis step and the drying step. In addition, the preferred conditions for the purification step, dehydration step, and drying step can be the same as those for Production Method 1. Hereinafter, the conditions for the synthesis step in the method for producing titanium oxide powder of this embodiment, which differ from those in Production Method 1, will be described.

[0061] <4-1. Synthesis Step> The aqueous solution containing titanium tetrachloride has a pH of less than 3. This is to allow the hydrolysis reaction to proceed preferentially. The pH is more preferably 2 or less, and even more preferably 1 or less.

[0062] The inorganic acid adheres to the generated titanium oxide particles to stabilize the surface and acts as a phase transition inhibitor that inhibits the phase transition from the anatase phase to the rutile phase. The inorganic acid modifies the titanium oxide surface. It also has the effect of inhibiting the aggregation of particles. The inorganic acid is preferably a strong inorganic acid, and sulfuric acid (molecular weight 98.08) is preferred from the viewpoint of inhibiting the phase transition to the rutile phase.

[0063] The molecular weight of the inorganic acid is preferably 300 or less. When an inorganic acid with an excessively high molecular weight is added, the inorganic acid molecules are too long relative to the precipitated titanium oxide, making it difficult to uniformly modify the titanium oxide surface, and the particles may not be sufficiently dispersed. In such cases, there is a risk that the particles may aggregate together, causing a phase transition to the rutile phase to proceed from the aggregated surfaces. By setting the molecular weight of the inorganic acid to 300 or less, the inorganic acid can uniformly modify the titanium oxide surface, thereby improving the dispersibility of the particles. From the same perspective, the molecular weight of the inorganic acid is preferably 250 or less, more preferably 200 or less. Furthermore, the molecular weight of the inorganic acid is, for example, 30 or more.

[0064] The Ti concentration in the mixed solution obtained by mixing an aqueous solution containing an inorganic acid with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 is preferably 0.01 mol / L or more. This is to allow the hydrolysis reaction to proceed preferentially. From the same viewpoint, the Ti concentration is more preferably 0.05 mol / L or more, and even more preferably 0.30 mol / L or more.

[0065] The Ti concentration in the mixed solution is preferably 2.00 mol / L or less to suppress the phase transition to the rutile phase. From the same viewpoint, the Ti concentration is more preferably 1.50 mol / L or less, and even more preferably 1.00 mol / L or less.

[0066] Regarding the content of the acidic compound in a mixed solution of an aqueous solution containing an inorganic acid and an aqueous solution containing titanium tetrachloride and having a pH of less than 3, the ratio of the amount of substance of the inorganic acid to the amount of substance of titanium (inorganic acid [mol] / Ti [mol]) (molar ratio) is 0.001 or more and 0.037 or less. This is to suppress the phase transition from the anatase phase to the rutile phase. From the same viewpoint, it is more preferable that it is 0.010 or more, and even more preferable that it is 0.015 or more. The ratio of the amount of substance (inorganic acid [mol] / Ti [mol]) is preferably 0.030 or less. This is because adding a large excess of inorganic acid is likely to inhibit the reaction.

[0067] 5. Titanium Oxide Powder Manufacturing Method 4 Next, manufacturing method 4 of titanium oxide powder using an aqueous solution containing an organic acid as an additive to an aqueous titanium tetrachloride solution will be described.

[0068] The method for producing titanium oxide powder of this embodiment differs from the method for producing titanium oxide powder of the above embodiment (production method 1) in the conditions for the synthesis step. In the method for producing titanium oxide powder of this embodiment, the steps other than the synthesis step can be the same as those in the method for producing titanium oxide powder of the above embodiment. That is, in production method 3, one or both of the purification step and the dehydration treatment step may be performed between the synthesis step and the drying treatment step. Furthermore, the preferred conditions for the purification step, dehydration step, and drying treatment step can also be the same as those in production method 1. Below, the conditions for the synthesis step of the method for producing titanium oxide powder of this embodiment that differ from those in production method 1 will be described.

[0069] Another method for producing titanium oxide powder according to one embodiment of the present invention, different from Production Methods 1 to 3, includes a synthesis step of mixing an aqueous solution containing an organic acid with an aqueous solution containing titanium tetrachloride and having a pH of less than 3 so that the molar ratio (acidic functional groups [mol] of the organic acid / Ti [mol]) is 0.001 or more and 0.037 or less to precipitate titanium oxide, and a drying step of drying the resulting titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to powder it. The initial relative humidity in the drying step is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more.

[0070] <5-1. Synthesis Step> The aqueous solution containing titanium tetrachloride has a pH of less than 3. This is to allow the hydrolysis reaction to proceed preferentially. The pH is more preferably 2 or less, and even more preferably 1 or less.

[0071] The organic acid adheres to the titanium oxide particles to stabilize their surface and acts as a phase transition inhibitor, inhibiting the phase transition from anatase to rutile. It also inhibits particle aggregation. The organic acid is preferably an α-hydroxycarboxylic acid, with malic acid (molecular weight 134.09) and citric acid (192.12) being more preferred from the viewpoint of inhibiting the phase transition to rutile.

[0072] For the same reasons as for inorganic acids, the molecular weight of the organic acid is preferably 300 or less. That is, when an organic acid with an excessively high molecular weight is added, the molecules of the acidic compound are too long relative to the precipitated titanium oxide particles, making it difficult to uniformly modify the titanium oxide surface, and the particles may not be sufficiently dispersed. In such cases, the particles may aggregate together, and the phase transition to the rutile phase may proceed starting from the aggregated surfaces. By setting the molecular weight of the organic acid to 300 or less, the organic acid can uniformly modify the titanium oxide surface, thereby improving the dispersibility of the particles. From the same perspective, the molecular weight of the acidic compound is preferably 250 or less, and more preferably 200 or less. Furthermore, the molecular weight of the organic acid is, for example, 30 or more, and preferably 40 or more.

[0073] The Ti concentration in the mixed solution of an organic acid-containing aqueous solution and a titanium tetrachloride-containing aqueous solution having a pH of less than 3 is preferably 0.01 mol / L or more. This is to allow the hydrolysis reaction to proceed preferentially. From the same viewpoint, 0.05 mol / L or more is more preferable, and 0.30 mol / L or more is even more preferable. The Ti concentration is preferably 2.00 mol / L or less. This is to suppress the phase transition to the rutile phase. From the same viewpoint, 1.50 mol / L or less is more preferable, and 1.00 mol / L or less is even more preferable.

[0074] Regarding the content of the acidic functional groups of the organic acid in a mixed solution of an organic acid and an aqueous solution containing titanium tetrachloride and having a pH of less than 3, the ratio of the amount of substance of the acidic functional groups of the organic acid to the amount of substance of Ti in the mixed solution (acidic functional groups of the organic acid [mol] / Ti [mol]) (molar ratio) is preferably 0.001 or more and 0.037 or less. This is to suppress the phase transition from the anatase phase to the rutile phase. From the same viewpoint, it is more preferably 0.010 or more, and even more preferably 0.015 or more. The ratio of the amount of substance (amount of substance of the acidic functional groups of the organic acid [mol] / Ti [mol]) is preferably 0.037 or less. This is because adding an excessive amount of organic acid is likely to inhibit the reaction. From the same viewpoint, it is more preferably 0.030 or less.

[0075] Here, the amount of substance of the acidic functional groups of the organic acids in the mixed solution represents the sum of the amounts of substance of the acidic functional groups of the organic acids contained in the mixed solution. For example, if the only organic acid contained in the mixed solution is 1 mol of citric acid, the amount of substance of the acidic functional groups of the organic acids in the mixed solution is 3 mol because citric acid has three acidic functional groups.

[0076] According to the above embodiment, anatase-type titanium oxide is synthesized through hydrolysis of titanium tetrachloride in the presence of a dispersant such as urea, an ammonium compound, an inorganic acid, or an organic acid, and the synthesized titanium oxide is then dried in an atmosphere with an initial relative humidity of 70 to 100%, thereby preventing dense aggregation of particles and particle growth and obtaining a dry powder without deactivating the hydroxyl groups on the particle surfaces, thereby providing anatase-type titanium oxide powder with a large specific surface area, high affinity with solvents, and high dispersibility.

[0077] Examples and comparative examples of the present invention will be described below, but they do not limit the technical scope of the present invention.

[0078] Example 1 A urea solution adjusted to pH 11 with aqueous ammonia was added to a titanium tetrachloride aqueous solution (pH: 0.8) with a Ti concentration of 15% by mass (titanium tetrachloride concentration of 59% by mass) maintained at 20°C. This resulted in a mixed solution with a Ti molar concentration of 0.096 mol / L and a (mol of urea / mol of Ti) ratio of 0.026. The liquid temperature was maintained at 20°C throughout this preparation process. The mixed solution was then transferred to a glass reactor. While stirring the mixed solution at 60 rpm using a stirrer, the temperature was increased to 60°C at a rate of 0.4°C / min using an external heater and maintained at this temperature for 30 minutes. The reaction solution was then allowed to cool to room temperature (25°C) to obtain a slurry. The cooled slurry was neutralized with aqueous ammonia, filtered and recovered using an ultrafiltration membrane (Microza UF (registered trademark) manufactured by Asahi Kasei Corporation), and washed with ion-exchange water. The washed slurry was dehydrated using a filter press to a solid content of 30% by mass. The titanium oxide solid obtained by dehydration was placed in a container set to an air atmosphere and an initial relative humidity of 80% and aged for 24 hours, and then dried in the air until the moisture content reached 10% by mass, yielding a titanium oxide solid. This solid was pulverized in a mortar to obtain a titanium oxide powder.

[0079] Example 2 A titanium oxide powder was obtained under the same conditions as in Example 1, except that the molar concentration of Ti in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of urea [mol] / amount of Ti [mol]) was 0.042.

[0080] Example 3 A titanium oxide powder was obtained under the same conditions as in Example 1, except that the molar concentration of Ti in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of urea [mol] / amount of Ti [mol]) was 0.053.

[0081] Example 4: An aqueous ammonium carbonate solution adjusted to pH = 11 was added to an aqueous titanium tetrachloride solution (pH: 0.8) with a Ti concentration of 15% by mass (titanium tetrachloride concentration of 59% by mass) maintained at 20°C. This resulted in a mixed solution with a Ti molar concentration of 0.096 mol / L and a (amount of substance [mol] of ammonium compound / amount of substance [mol] of Ti) of 0.010. The liquid temperature was constantly maintained at 20°C during this preparation process. The mixed solution was then transferred to a glass reactor. While stirring the mixed solution at 60 rpm using a stirrer, the temperature was raised to 60°C at a heating rate of 0.4°C / min using an external heater and maintained at this temperature for 30 minutes. The reaction solution was then allowed to cool to room temperature (25°C) to obtain a slurry. The cooled slurry was then neutralized with aqueous ammonia, filtered and recovered using an ultrafiltration membrane (Microza UF (registered trademark) manufactured by Asahi Kasei Corporation), and washed with ion-exchanged water. The washed slurry was dehydrated using a filter press to a solid content of 30% by mass. The titanium oxide solid obtained by dehydration was placed in a container in an air atmosphere with an initial relative humidity of 80% and aged for 24 hours, and then dried in the air until the moisture content reached 10% by mass, yielding a titanium oxide solid. This solid was pulverized in a mortar to obtain a titanium oxide powder.

[0082] Example 5 A titanium oxide powder was obtained under the same conditions as in Example 4, except that the molar concentration of Ti in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of substance of ammonium compound [mol] / amount of substance of Ti [mol]) was 0.016.

[0083] Example 6 Aqueous sulfuric acid solution was added to a titanium tetrachloride aqueous solution (pH: 0.7) with a Ti concentration of 15% by mass (titanium tetrachloride concentration of 59% by mass) maintained at 20°C, to obtain a mixed solution prepared so that the Ti molar concentration was 0.074 mol / L and the (mol amount of inorganic acid [mol] / mol amount of Ti [mol]) was 0.026. The liquid temperature was constantly maintained at 20°C during this preparation process. The mixed solution was then transferred to a glass reactor. While stirring the mixed solution at 60 rpm using a stirrer, the temperature was raised to 80°C at a heating rate of 0.2°C / min using an external heater and maintained for 30 minutes. The reaction solution was then allowed to cool to room temperature (25°C) to obtain a slurry. The cooled slurry was then neutralized with aqueous ammonia, filtered and recovered using an ultrafiltration membrane (Microza UF (registered trademark) manufactured by Asahi Kasei Corporation), and washed with ion-exchanged water. The washed slurry was then dehydrated using a filter press to a solid content of 30% by mass. The titanium oxide solid obtained by dehydration was then placed in a container in an air atmosphere with an initial relative humidity of 80%, aged for 24 hours, and then dried in the air until the moisture content reached 10% by mass, yielding a titanium oxide solid. This solid was then pulverized in a mortar to obtain a titanium oxide powder.

[0084] Example 7 A titanium oxide powder was obtained under the same conditions as in Example 6, except that the Ti molar concentration in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of substance of inorganic acid [mol] / amount of substance of Ti [mol]) was 0.027.

[0085] Example 8 A titanium oxide powder was obtained under the same conditions as in Example 6, except that the Ti molar concentration in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of substance of inorganic acid [mol] / amount of substance of Ti [mol]) was 0.029.

[0086] Example 9 A titanium oxide powder was obtained in the same manner as in Example 6, except that in the preparation step, an aqueous citric acid solution was used instead of sulfuric acid, the mixed solution was prepared so that the Ti molar concentration was 0.074 mol / L and the (amount of substance [mol] of acidic functional group of organic acid / amount of substance [mol] of Ti) was 0.022, and the initial relative humidity of the container used when drying the titanium oxide solid obtained by dehydration to obtain a titanium oxide solid content was changed to 95%.

[0087] Example 10 A titanium oxide powder was obtained under the same conditions as in Example 9, except that the molar concentration of Ti in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of substance [mol] of acidic functional group of organic acid / amount of substance [mol] of Ti) was 0.034.

[0088] Example 11 A titanium oxide powder was obtained in the same manner as in Example 9, except that in the preparation step, malic acid was used instead of citric acid, and the mixed solution was prepared so that the Ti molar concentration was 0.074 mol / L and the (amount of substance [mol] of acidic functional group of organic acid / amount of substance [mol] of Ti) was 0.026.

[0089] Example 12 A titanium oxide powder was obtained under the same conditions as in Example 11, except that the molar concentration of Ti in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of substance [mol] of acidic functional group of organic acid / amount of substance [mol] of Ti) was 0.036.

[0090] Comparative Example 1 A titanium oxide powder was obtained in the same manner as in Example 1, except that in the preparation step, no urea aqueous solution was used, and an aqueous titanium tetrachloride solution (Ti molar concentration 0.096 mol / L) with a Ti concentration of 15% by mass (titanium tetrachloride concentration 59% by mass) was used instead of the mixed solution.

[0091] Comparative Example 2 A titanium oxide powder was obtained under the same conditions as in Example 1, except that the molar concentration of Ti in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of urea [mol] / amount of Ti [mol]) was 0.063.

[0092] Comparative Example 3 A titanium oxide powder was obtained under the same conditions as in Example 4, except that the titanium tetrachloride aqueous solution used for mixing was changed to one with a pH of 0.9, and the conditions for the adjustment step were changed so that (amount of substance [mol] of ammonium compound / amount of substance [mol] of Ti) was 0.033 without changing the molar concentration of Ti in the mixed solution.

[0093] Comparative Example 4: Titanium oxide powder was obtained in the same manner as in Example 6, except that in the preparation step, a titanium tetrachloride aqueous solution (Ti molar concentration 0.074 mol / L) with a Ti concentration of 15% by mass (titanium tetrachloride concentration 59%) was used instead of the mixed solution, instead of using an aqueous urea solution, and that the initial relative humidity of the container when the titanium oxide solid obtained by dehydration was wet-dried to obtain a titanium oxide solid content was changed to 80%. Comparative Example 5: Titanium oxide powder was obtained under the same conditions as in Example 6, except that the initial relative humidity of the container when the titanium oxide solid obtained by dehydration was dried to obtain a titanium oxide solid content was changed to 0%. That is, in Comparative Example 5, the titanium oxide solid obtained by dehydration was dry-dried. Comparative Example 6: Titanium oxide powder was obtained under the same conditions as in Example 6, except that the initial relative humidity of the container when the titanium oxide solid obtained by dehydration was wet-dried to obtain a titanium oxide solid content was changed to 30%.

[0094] Comparative Example 7 A titanium oxide powder was obtained under the same conditions as in Example 6, except that the conditions of the adjustment step were changed so that the molar concentration of Ti in the mixed solution was not changed and the ratio (amount of substance of inorganic acid [mol] / amount of substance of Ti [mol]) was 0.031, and the initial relative humidity of the container used when wet-drying the titanium oxide solid obtained by dehydration to obtain the titanium oxide solid content was changed to 80%.

[0095] Comparative Example 8 A titanium oxide powder was obtained in the same manner as in Example 9, except that in the preparation step, the citric acid aqueous solution was not used, and an aqueous titanium tetrachloride solution (Ti molar concentration 0.096 mol / L) with a Ti concentration of 15 mass % (titanium tetrachloride concentration 59%) was used instead of the mixed solution.

[0096] Comparative Example 9 The titanium oxide solid obtained by dehydration was dried to obtain titanium oxide powder under the same conditions as in Example 9, except that the initial relative humidity of the container when obtaining the titanium oxide solid content was changed to 0%.

[0097] Comparative Example 10 The titanium oxide solid obtained by dehydration was dried to obtain titanium oxide powder under the same conditions as in Example 9, except that the initial relative humidity of the container when obtaining the titanium oxide solid content was changed to 30%.

[0098] Comparative Example 11 Titanium oxide powder was obtained under the same conditions as in Example 9, except that the molar concentration of Ti in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of substance [mol] of acidic functional group of organic acid / amount of substance [mol] of Ti) was 0.038. Comparative Example 12 Titanium oxide powder was obtained under the same conditions as in Example 11, except that the titanium oxide solid obtained by dehydration was dried and the initial relative humidity of the container when obtaining the titanium oxide solid content was changed to 0%. Comparative Example 13 Titanium oxide powder was obtained under the same conditions as in Example 11, except that the titanium oxide solid obtained by dehydration was dried and the initial relative humidity of the container when obtaining the titanium oxide solid content was changed to 30%.

[0099] Comparative Example 14 A titanium oxide powder was obtained under the same conditions as in Example 11, except that the molar concentration of Ti in the mixed solution was not changed and the conditions of the adjustment step were changed so that (amount of substance [mol] of acidic functional group of organic acid / amount of substance [mol] of Ti) was 0.045.

[0100] The conditions for producing the titanium oxide powders in Examples 1 to 12 and Comparative Examples 1 to 14 are summarized in Table 1. In Table 1, in Comparative Examples where the additive type is indicated by "-", no additive was used, and an aqueous titanium tetrachloride solution was used instead of the mixed solution. For ease of explanation, Comparative Example 1, which contains the same experimental data, is listed in multiple places. The same applies to Comparative Example 7.

[0101]

[0102] The titanium oxide powders of Examples 1 to 12 and Comparative Examples 1 to 14 were evaluated by the following evaluation methods.

[0103] <BET specific surface area> The specific surface area of ​​the titanium oxide powder was calculated from the nitrogen adsorption / desorption curve by the BET method in accordance with JIS Z8830:2013. To measure the specific surface area by the BET method (BET specific surface area), a sample was pretreated by heating to 180°C and passing nitrogen gas through it for 20 minutes, and the sample was measured using a QUADRASORV evo manufactured by Quantachrome. The applicable range of the BET method is P / P ０ = 0.00 to 0.95.

[0104] <Anatase Content, Rutile Content> Powder X-ray diffraction measurement was performed on the titanium oxide powder, and the anatase content was calculated from the peak intensity (Ia) corresponding to the anatase crystalline phase, the peak intensity (Ib) corresponding to the brookite crystalline phase, and the peak intensity (Ir) corresponding to the rutile crystalline phase. The anatase content (anatase rate) of the crystalline phase of the titanium oxide powder was calculated using the following formula: Anatase Content [%] = {Ia / (Ia + Ib + Ir)} × 100. The rutile content (rutile rate) of the crystalline phase of the titanium oxide powder was also calculated using the following formula. Rutile content [%] = {Ir / (Ia + Ib + Ir)} x 100 Powder X-ray diffraction measurements were performed using a Rigaku SmartLab SE with a copper target and Cu-Kα1 radiation under the following conditions: tube voltage 45 kV, tube current 40 mA, measurement range 2θ = 20 to 35 [deg], sampling width 0.0167 [deg], and scan rate 0.0192 [deg / s]. Ia: Intensity of the peak (2θ = 24.5° to 26.0°) corresponding to the anatase crystal phase; Ir: Intensity of the peak (2θ = 26.6° to 28.1°) corresponding to the rutile crystal phase; Ib: Intensity of the peak (2θ = 30.8° to 32.3°) corresponding to the brookite crystal phase.

[0105] <Frequency Width at Half Maximum of Diffraction Peak in Crystalline X-ray Diffraction Measurement> For titanium oxide powder, a SmartLab SE manufactured by Rigaku Corporation was used, and Cu-Kα1 radiation from a copper target was used under the conditions of a tube voltage of 45 kV, a tube current of 40 mA, a measurement range of 2θ = 24.5 to 26.0 [deg], a sampling width of 0.0167 [deg], and a scanning speed of 0.0192 [deg / s], and the FWHM of the main peak of the anatase phase near 2θ = 25° was analyzed.

[0106] In the analysis, the background was measured using only the glass cell, and the diffraction intensity of the sample was corrected by subtracting the background diffraction intensity from the diffraction intensity measured using the sample containing titanium oxide and the glass cell.

[0107] <Spin-Spin Relaxation Time> A 5% by mass titanium oxide slurry was prepared using ion-exchanged water. This slurry was filled into a disposable NMR sample tube, AS1NMR, manufactured by AS ONE Corporation. Immediately after filling the sample tube with the slurry, pulsed NMR measurement was performed using an Acorn Area manufactured by XiGo Nanotools. The spin-spin relaxation time T2 of the titanium oxide powder was measured by pulsed NMR measurement. The measurement was performed under the following conditions: measurement frequency: 13.1 MHz, measurement nucleus: after a single pulse irradiation at 90°, a 180° pulse was irradiated at 0.5 ms intervals, and this scan was repeated four times. Measurement method: CPMG pulse sequence method, sample amount: 0.5 ml, temperature: 23°C, Specific Surface Relaxivity (Ka): 0.0075 g / m ２ / ms

[0108] <Elemental analysis> The Ti, Cl, Si, Al, and Fe in the raw material were measured using an atomic absorption spectrometer Z-2300 manufactured by Hitachi, Ltd., after mixing the sample with an aqueous hydrogen fluoride solution and completely dissolving it using a microwave sample pretreatment device ETHOS EASY manufactured by Milestone General Co., Ltd. The Ti, Cl, Si, Al, and Fe contents in the finished titanium oxide powder were also measured using the same device after mixing the sample with an aqueous hydrogen fluoride solution and completely dissolving it in the solution. The C (carbon) and S (sulfur) in the titanium oxide powder were measured using a carbon-sulfur analyzer CS744 (manufactured by LECO Corporation).

[0109] <Moisture Content Measurement> Using an MX50 heat-drying moisture meter manufactured by A&D, 2 g of titanium oxide powder was heated to 200°C and then heated with infrared rays at 120°C until the weight change was 0.01% by mass or less, and the moisture content of the titanium oxide powder was measured.

[0110] <Zeta Potential Measurement> A slurry containing 0.1% by mass of titanium oxide was prepared using ion-exchanged water. The zeta potential of this slurry was measured using an ELZ-2000 manufactured by Otsuka Electronics Co., Ltd. after filling it into a sapphire cell.

[0111]

[0112] Table 2 summarizes the physical properties of the titanium oxide powders of Examples 1 to 12 and Comparative Examples 1 to 14. In the content ratios in Table 2, the symbol "<" is used in some places, indicating that the value is less than the value following the "<". For example, the Fe content of Comparative Example 1 is less than 0.002% by mass. As shown in Table 2, the titanium oxide powders of Examples 1 to 12 have absolute zeta potentials of 42 to 63 mV. Titanium oxides within this range have good dispersibility, are not overdispersed, and do not cause poor flow, making them suitable for synthesizing dielectric materials and battery materials. On the other hand, the titanium oxide powders of Comparative Examples 1 to 6 and 8 to 13 have absolute zeta potentials of 39 mV or less. It is known that a small absolute zeta potential results in poor dispersibility and particles that are prone to aggregation, and these titanium oxides have poor dispersibility. The titanium oxide powders of Comparative Examples 7 and 14 have absolute zeta potentials of 66 mV or more. It is known that if the absolute value of the zeta potential is too large, the dispersion will be over-dispersed and the viscosity of the dispersion will increase too much, causing poor flow, and therefore such titanium oxides are unsuitable for use in synthesizing, for example, barium titanate.

[0113] Furthermore, when the spin-spin relaxation times T2 of Examples 1 to 12 and Comparative Examples 1 to 14 were compared, the spin-spin relaxation times were 42 to 99 ms in Examples 1 to 14, confirming that titanium oxide powders were produced that did not become over-dispersed when reslurried to form a dispersion.

[0114] By comparing the above Examples and Comparative Examples, it was confirmed that the present invention can provide an anatase type titanium oxide powder having a large specific surface area and high dispersibility.

Claims

1. The BET specific surface area measured using the nitrogen adsorption method is 300 m ２ / g or more and 480 m ２ / g or less, the anatase content of the crystal phase measured using XRD measurement is 90% or more, and the spin-spin relaxation time T2 measured by pulse NMR of a 5 mass% suspension prepared using ion-exchanged water is 46 ms or more and 103 ms or less of titanium oxide powder.

2. The titanium oxide powder according to claim 1, having a carbon content of 0.5% by mass or less.

3. The titanium oxide powder according to claim 1 or 2, having a chlorine content of 0.1% by mass or less, a silicon content of 0.1% by mass or less, and a sulfur content of 0.1% by mass or less.

4. The titanium oxide powder according to claim 1 or 2, wherein the half-value width of the diffraction peak at a diffraction angle 2θ of 24.5° to 26.0° is 1.10° to 2.00°.

5. The titanium oxide powder according to claim 1 or 2, having a zeta potential of -63 mV or more and -40 mV or less.

6. A method for producing titanium oxide powder, comprising a synthesis step of mixing an aqueous solution containing urea and an aqueous solution containing titanium tetrachloride with a pH of less than 3 so that the urea / Ti (molar ratio) is 0.001 or more and 0.058 or less to precipitate titanium oxide, and a heat treatment step of drying the obtained titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to form a powder.

7. A method for producing titanium oxide powder, comprising a synthesis step of mixing an aqueous solution containing an ammonium compound and an aqueous solution containing titanium tetrachloride with a pH of less than 3 so that the ammonium compound / Ti (molar ratio) is 0.001 or more and 0.029 or less to precipitate titanium oxide, and a drying treatment step of drying the obtained titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to form a powder.

8. The method for producing titanium oxide powder according to claim 6 or 7, wherein the aqueous solution containing at least one of urea or an ammonium compound has a pH < 12.

0.

9. A method for producing titanium oxide powder, comprising a synthesis step of mixing an aqueous solution containing an inorganic acid and an aqueous solution containing titanium tetrachloride with a pH of less than 3 so that the inorganic acid / Ti (molar ratio) is 0.001 or more and 0.030 or less to precipitate titanium oxide, and a drying treatment step of drying the obtained titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to form a powder.

10. A method for producing titanium oxide powder, comprising a synthesis step of mixing an aqueous solution containing an organic acid and an aqueous solution containing titanium tetrachloride with a pH of less than 3 so that the acidic functional group of the organic acid / Ti (molar ratio) is 0.001 or more and 0.037 or less to precipitate titanium oxide, and a drying treatment step of drying the obtained titanium oxide in an atmosphere with an initial relative humidity of 70 to 100% to form a powder.

11. The method for producing titanium oxide powder according to claim 10, wherein the organic acid is an α-hydroxycarboxylic acid.

12. The method for producing titanium oxide powder according to any one of claims 9 to 11, wherein the molecular weight of the organic acid or inorganic acid in the aqueous solution is 300 or less.

13. The method for producing titanium oxide powder according to any one of claims 9 to 11, further comprising a purification step of purifying titanium oxide using any one or more of an ultrafiltration membrane, a reverse osmosis membrane, an ion exchange resin, and an electrodialysis membrane.

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