Cerium oxide particle production method

Abstract

The present application provides a method for producing cerium oxide particles having an average particle diameter within the range of 1-100 nm, the method involving a step for mixing at least a first fluid and a second fluid to precipitate cerium oxide particles, wherein the method is characterized in that one of the first fluid and the second fluid is a cerium oxide raw material liquid at least including trivalent metal ions and / or tetravalent metal ions, the trivalent metal ions and / or tetravalent metal ions include trivalent cerium ions and / or tetravalent cerium ions, the other one of the first fluid and the second fluid is a cerium oxide precipitation solution at least including a basic substance, and the molar ratio between the trivalent metal ions and the tetravalent metal ions is set so as to achieve said average particle diameter. According to this production method, cerium oxide particles with a controlled average particle diameter can be stably supplied in a simple manner using a method suitable for large-scale production without requiring complex chemical reaction or heat treatment.

Description

Method for producing cerium oxide particles

[0001] The present invention relates to a method for producing cerium oxide particles, more particularly to a method for producing cerium oxide particles having a controlled average particle size, a method for producing a dispersion of cerium oxide particles, and a method for controlling the average particle size of cerium oxide particles within the range of 1 nm to 100 nm.

[0002] Cerium oxide is CeO ２ It is an oxide represented by the formula (IV) and has long been widely used as a CMP (Chemical Mechanical Polishing) slurry for polishing glass and semiconductors. Its physical properties include ultraviolet absorption and high oxygen storage and release capabilities. Due to its unique properties, its use has recently expanded beyond abrasives to include new applications such as ultraviolet absorbers in cosmetics, high-refractive-index materials, solid electrolytes for fuel cells, and catalyst supports for decomposing automobile exhaust gases.

[0003] When synthesizing particles of various metal oxides, including cerium oxide, particle size is typically controlled by varying the concentration of the metal oxide raw materials in the system, reaction temperature, reaction time, etc. Increasing the raw material concentration, reaction temperature, or reaction time tends to increase particle size. However, because it is difficult to control the amount of nuclei generated and nuclei growth, particle size variation often occurs, leading to particle growth and coarsening. Therefore, to suppress particle growth and aggregation, additives such as polymers and surfactants are typically added as surface protection or surface treatment agents to produce nanoparticles with particle sizes of submicron or less. The smaller the target particle size, the more additives are required, which poses the problem of increased additive concentration when preparing dispersions or coatings.

[0004] Patent Document 1 describes cerium oxide nanoparticles characterized by being surface-treated with a hydroxyl-free carboxylic acid and a hydroxyl-containing carboxylic acid. These cerium oxide nanoparticles have excellent dispersibility in a wide range of solvents and monomers. It is presumed that the hydroxyl-free carboxylic acid and the hydroxyl-containing carboxylic acid also function as inhibitors of aggregation and crystal growth. According to Table 1, the coating amount of the cerium oxide nanoparticles produced in the examples was high at 20-30%, and the crystallite diameters were all 3-4 nm, with no particle size control.

[0005] Patent Document 2 describes a method for producing oxide particles, which involves mixing a first fluid and a second fluid between opposing, relatively rotating processing surfaces that can approach and separate from each other, and discharging the mixed fluid containing precipitated oxide particles from between the processing surfaces. The method controls the crystallinity of the oxide particles discharged from between the processing surfaces by changing at least one parameter selected from the group consisting of the temperature of the first fluid introduced between the processing surfaces, the temperature of the second fluid introduced between the processing surfaces, and the temperature at the time of mixing the first and second fluids. In each of the examples, cerium oxide particles of 20 nm or less are produced without using a surface protective agent or a surface treatment agent. However, the average particle size is not controlled.

[0006] Patent Document 3 describes a method for producing a sol in which metal oxide fine particles such as cerium oxide having an average particle size in the range of 5 to 150 nm are dispersed. This production method provides a metal oxide sol having a uniform particle size distribution and excellent stability. In the examples, only a tetravalent cerium salt is used as the raw material for cerium oxide, and there is no mention of a method for controlling the particle size of the metal oxide by changing the valence.

[0007] Non-Patent Document 1 describes a method for producing cerium oxide particles by dissolving a metal salt of cerium in polyethylene glycol and heat-treating the resulting solution. It also mentions that the use of polyethylene glycol with a molecular weight of 1,000 or more results in nearly spherical cerium oxide particles, and that the particle size can be controlled by adding ethylene glycol and varying the amount of ethylene glycol added. However, the particles obtained are 40 nm to 0.66 μm in size, which is too large for transparent ultraviolet absorbers that transmit visible light or for catalytic applications, limiting their use.

[0008] JP 2018-145057 A, WO 2017 / 010557 A, JP 2006-182604 A

[0009] Naofumi Kamikawa, "Development of an environmentally friendly manufacturing method for monodispersed spherical cerium oxide nanoparticles for UV screening agents," Cosmetology, vol. 12, 2004, pp. 40-44

[0010] Cerium oxide particles have a wide range of applications, and in order to meet recent demands for higher functionality and performance, it has been necessary to precisely control the average particle size of cerium oxide. However, as described above, it has been difficult to satisfactorily meet these demands using conventional techniques. In view of the above, an object of the present invention is to provide a method for producing cerium oxide particles that does not require complex chemical reactions or heat treatments and that can easily and stably produce cerium oxide particles with a controlled average particle size using a method suitable for mass production.

[0011] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors discovered that the average particle size can be controlled by changing the molar ratio of trivalent cerium ions to tetravalent cerium ions, and that cerium oxide particles having a controlled average particle size can be continuously and stably obtained, thereby completing the present invention.

[0012] [1] A method for producing cerium oxide particles having an average particle size within the range of 1 nm to 100 nm, comprising a step of mixing at least a first fluid and a second fluid to precipitate cerium oxide particles, wherein one of the first fluid and the second fluid is a cerium oxide raw material solution containing at least trivalent metal ions and / or tetravalent metal ions, trivalent cerium ions and / or tetravalent cerium ions are contained in the trivalent metal ions and / or tetravalent metal ions, and the other of the first fluid and the second fluid is a cerium oxide precipitating solution containing at least a basic substance, and the molar ratio of the trivalent metal ions and the tetravalent metal ions is set to obtain the average particle size.

[0013] [2] The method according to [1], wherein the trivalent cerium ions are supplied from a cerium salt selected from cerium (III) nitrate, cerium (III) chloride, cerium (III) acetate, cerium (III) carbonate, cerium (III) sulfate, cerium (III) oxalate, cerium (III) citrate, and ammonium cerium (III) nitrate, and / or the tetravalent cerium ions are supplied from a cerium salt selected from ammonium cerium (IV) nitrate, cerium (IV) sulfate, and ammonium cerium (IV) sulfate.

[0014] [3] The method according to [1] or [2], wherein the ratio d / D of the average crystallite diameter (d) of the cerium oxide particles obtained by X-ray diffraction measurement to the average particle diameter (D) of the cerium oxide particles is 0.50 or more. [4] The method according to any one of [1] to [3], wherein the cerium oxide particles contain an element other than cerium and oxygen, and the element other than cerium and oxygen is at least one selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Si, Ti, V, Cr, Mn, Fe, Co, Mo, Y, Zr, In, Sn, and Hf. [5] A manufacturing method according to any one of [1] to [4], wherein at least two fluids to be treated, including the cerium oxide raw material liquid and the cerium oxide deposition solution, are continuously introduced between processing surfaces disposed opposite to each other and rotating relatively so as to be approachable and separable from each other; the at least two fluids to be treated are mixed between the processing surfaces disposed opposite to each other and rotating relatively so as to be approachable and separable from each other, thereby precipitating cerium oxide particles; and the mixed fluid containing the precipitated cerium oxide particles is discharged from between the processing surfaces to continuously produce cerium oxide particles.

[0015] [6] The manufacturing method according to [5], wherein one of the cerium oxide raw material solution and the cerium oxide precipitating solution passes between the processing surfaces while forming a thin film fluid, and the other of the cerium oxide raw material solution and the cerium oxide precipitating solution passes through another introduction path independent of the flow path introduced between the processing surfaces and is introduced between the processing surfaces from an opening formed in at least one of the processing surfaces, and the cerium oxide raw material solution and the cerium oxide precipitating solution are mixed between the processing surfaces.

[0016] [7] A method for producing surface-modified cerium oxide particles, comprising the steps of producing cerium oxide particles by the production method according to any one of [1] to [6], and modifying the surface state of the particles by stirring the produced cerium oxide particles in an acidic aqueous solution. [8] The production method according to [7], wherein the acidic aqueous solution contains a carboxylic acid. [9] A method for producing a dispersion of cerium oxide particles, comprising the steps of producing cerium oxide particles by the production method according to any one of [1] to [8], and dispersing the produced cerium oxide particles in a dispersion medium containing at least one of a solvent, a dispersant, and a resin.

[0017]

[10] A method for controlling the average particle size of cerium oxide particles within a range of 1 nm to 100 nm, comprising a step of mixing at least a first fluid and a second fluid to precipitate cerium oxide particles, wherein one of the first fluid and the second fluid is a cerium oxide raw material solution containing at least trivalent metal ions and / or tetravalent metal ions, trivalent cerium ions and / or tetravalent cerium ions are contained in the trivalent metal ions and / or tetravalent metal ions, and the other of the first fluid and the second fluid is a cerium oxide precipitation solution containing at least a basic substance, and wherein the molar ratio of the trivalent metal ions and the tetravalent metal ions is changed.

[0018]

[11] The method according to

[10] , wherein the average particle size of the cerium oxide particles is increased by increasing the molar ratio of the trivalent metal ions to the total metal ions consisting of the trivalent metal ions and the tetravalent metal ions, or the average particle size of the cerium oxide particles is decreased by decreasing the molar ratio.

[0019] The production method of the present invention does not require complex chemical reactions or heat treatments, and makes it possible to simply and stably produce cerium oxide particles with a controlled average particle size in a manner suitable for mass production.

[0020] 1 is a schematic cross-sectional view of a fluid treatment device according to an embodiment of the present invention; FIG. 2 is a schematic plan view of a first treatment surface of the fluid treatment device shown in FIG. 1; ３＋1 is a graph showing the relationship between the molar ratio [%] of cerium oxide particles and the average particle size. 2 is a TEM photograph of cerium oxide particles obtained in Example 1 of the present invention. 3 is a schematic plan view of an apparatus used in Example 32 of the present invention. 4 is a TEM photograph of cerium oxide particles obtained in Example 34 of the present invention.

[0021] The following describes one embodiment of the present invention. 1. Method for Producing Cerium Oxide Particles The method for producing cerium oxide particles of the present invention is a method for producing cerium oxide particles having an average particle size within a range of 1 nm to 100 nm, and includes a step of mixing at least a first fluid and a second fluid to precipitate cerium oxide particles, wherein one of the first fluid and the second fluid is a cerium oxide source solution containing at least trivalent metal ions and / or tetravalent metal ions, the trivalent metal ions and / or tetravalent cerium ions being contained in the trivalent metal ions and / or tetravalent metal ions, and the other of the first fluid and the second fluid is a cerium oxide precipitation solution containing at least a basic substance, and the molar ratio of the trivalent metal ions and the tetravalent metal ions is set to obtain the average particle size.

[0022] (Preparation of Cerium Oxide Particle Raw Material and Cerium Oxide Raw Material Solution) The cerium oxide particle raw material used in the production method of the present invention is not particularly limited as long as it can supply trivalent cerium ions or tetravalent cerium ions in the solution, and examples thereof include cerium simple substance, hydroxides, salts, etc., and preferably cerium salts. These cerium oxide particle raw materials may be used alone or in combination.

[0023] Examples of the cerium oxide particle raw material that supplies trivalent cerium ions include trivalent cerium salts, such as cerium(III) nitrate, cerium(III) chloride, cerium(III) acetate, cerium(III) carbonate, cerium(III) sulfate, cerium(III) oxalate, cerium(III) citrate, ammonium cerium(III) nitrate, cerium(III) hydroxide, etc. From the viewpoint of solubility in the solvent used to prepare the cerium oxide raw material solution, cerium(III) nitrate, cerium(III) chloride, etc. are preferred.

[0024] Examples of the cerium oxide particle raw material that supplies tetravalent cerium ions include tetravalent cerium salts, such as ammonium cerium (IV) nitrate, cerium (IV) sulfate, ammonium cerium (IV) sulfate, cerium (IV) hydroxide, etc. From the viewpoint of solubility in the solvent used to prepare the cerium oxide raw material solution, ammonium cerium (IV) nitrate is preferred.

[0025] It is possible to replace some or all of the trivalent cerium ions with ions of other elements, and / or to replace some or all of the tetravalent cerium ions with ions of other elements. When replacing with ions of other elements, it is possible to form a solid solution or composite with elements other than cerium and oxygen in the cerium oxide particles. The elements other than cerium and oxygen are not particularly limited, but it is preferable that the elements other than cerium be at least one selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Si, Ti, V, Cr, Mn, Fe, Co, Mo, Y, Zr, In, Sn, and Hf, which can stably assume trivalent and / or tetravalent ionic states in solution. A specific method for dissolving or compounding the other element can be achieved by mixing, dissolving, or molecularly dispersing a compound containing an element other than cerium and oxygen in a cerium oxide raw material solution, and then mixing the resulting mixture between the processing surfaces to precipitate the other element other than cerium and oxygen together with the cerium oxide particles. The compound containing an element other than cerium and oxygen is not particularly limited, but examples thereof include simple substances, hydroxides, salts, etc. of these elements.

[0026] When elements other than cerium and oxygen are contained in the cerium oxide particles, the content of the other metal ions relative to the total metal ions in the raw materials in the cerium oxide raw material liquid is, for example, 0 to 50 mol %, preferably 0.1 to 40 mol %, and more preferably 0.2 to 30 mol %.

[0027] Alternatively, a cerium oxide raw material solution can be prepared by adding an oxidizing agent or a reducing agent to trivalent cerium ions and / or tetravalent cerium ions to oxidize or reduce the cerium ions. That is, by adding a required amount of an oxidizing agent to a solution in which trivalent cerium ions have been dissolved, some of the trivalent cerium ions can be oxidized and converted to tetravalent cerium ions. By adding a required amount of a reducing agent to a solution in which tetravalent cerium ions have been dissolved, some of the tetravalent cerium ions can be reduced and converted to trivalent cerium ions.

[0028] In the production method of the present invention, the cerium oxide raw material solution can be prepared by mixing at least the cerium oxide particle raw material in a solvent to dissolve or molecularly disperse the cerium oxide particle raw material.

[0029] (Preparation of Basic Substance and Cerium Oxide Precipitation Solution) Examples of basic substances used in the production method of the present invention include metal hydroxides such as alkali metal hydroxides (e.g., sodium hydroxide, potassium hydroxide, etc.), quaternary ammonium hydroxides such as tetramethylammonium hydroxide, benzyltrimethylammonium hydroxide, etc., metal alkoxides such as alkali metal alkoxides (e.g., sodium methoxide, sodium isopropoxide, etc.), ammonia, and amines such as triethylamine, diethylaminoethanol, and diethylamine. Urea, which generates a basic substance upon reaction, can also be used. To improve the crystallinity of the produced cerium oxide, it is preferable to use alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, ammonia, etc. as the basic substance. In the present invention, the cerium oxide deposition solution can be prepared by dissolving or molecularly dispersing at least the basic substance in a solvent by mixing it.

[0030] (Solvent) The solvent is not particularly limited as long as it can dissolve or molecularly disperse the cerium oxide particle raw material and the basic substance, and examples thereof include water, organic solvents, and mixtures thereof. Examples of water include tap water, ion-exchanged water, pure water, ultrapure water, and RO water. Examples of organic solvents include alcohol solvents such as ethanol, ethylene glycol, and glycerin; ketone solvents such as acetone and 2-butanone; ether solvents such as diethyl ether and tetrahydrofuran; aromatic solvents such as toluene and xylene; amine solvents such as triethylamine and ethylenediamine; amide solvents such as N,N-dimethylformamide; aliphatic hydrocarbon solvents such as hexane and liquid paraffin; nitrile solvents such as acetonitrile; sulfoxide solvents such as dimethyl sulfoxide; halogenated solvents such as dichloromethane; ester solvents such as ethyl acetate and ethylene glycol monoethyl ether acetate; carboxylic acid solvents such as acetic acid and propionic acid; aprotic polar solvents such as carbon disulfide and N-methyl-2-pyrrolidone; ionic liquids; and sulfonic acid compounds. Each solvent may be used alone or in combination. From the viewpoint of the solubility of the cerium oxide particle raw material and the basic substance, it is preferable to prepare the cerium oxide raw material solution and the cerium oxide deposition solvent using water or a mixed solvent of water and an alcohol solvent.

[0031] Additives such as oxidizing agents or reducing agents for changing the valence of cerium ions in the cerium oxide raw material solution, acidic or basic substances or their salts for adjusting the pH or ion concentration, surface protective agents for preventing particle aggregation, surfactants, dispersants, etc., may be added to the solvent as needed. Examples of acidic substances include inorganic acids such as aqua regia, hydrochloric acid, nitric acid, fuming nitric acid, sulfuric acid, and fuming sulfuric acid, and organic acids such as formic acid, acetic acid, chloroacetic acid, dichloroacetic acid, oxalic acid, trifluoroacetic acid, and trichloroacetic acid. Surface protective agents, surfactants, and dispersants include various commonly used commercial products, products, and newly synthesized products. Examples include dispersants such as anionic surfactants, cationic surfactants, nonionic surfactants, and various polymers. These may be used alone or in combination. The surface protective agents, surfactants, and dispersants may be contained in either or both of the cerium oxide raw material solution and the cerium oxide deposition solvent.

[0032] (Preparation Apparatus) In the production method of the present invention, the apparatus for preparing the cerium oxide raw material solution or the cerium oxide deposition solvent is preferably an apparatus that achieves homogeneous mixing by applying shear force to the fluid, such as an apparatus that rotates stirrers of various shapes, such as rod-shaped, plate-shaped, or propeller-shaped, in a tank, or an apparatus equipped with a screen that rotates relative to the stirrers. A preferred example of a rotary disperser is the stirrer disclosed in Japanese Patent No. 5,147,091.

[0033] The rotary disperser may be a batch type or a continuous type. In the case of a continuous type device, the fluid may be continuously supplied to and discharged from a stirring tank, or a continuous mixer may be used without using a stirring tank, and the stirring energy can be appropriately controlled using a known stirrer or stirring means. The stirring energy is described in detail in JP-A-4-114725 filed by the applicant of the present application. The stirring method in the present invention is not particularly limited, and can be carried out using various shear type, friction type, high-pressure jet type, ultrasonic type stirrers, dissolvers, emulsifiers, dispersers, homogenizers, etc. Examples of such emulsifiers include continuous emulsifiers such as Ultra Turrax (manufactured by IKA), Polytron (manufactured by Kinematica), TK Homomixer (manufactured by Primix), Ebara Milder (manufactured by Ebara Corporation), TK Homomic Lineflow (manufactured by Primix), Colloid Mill (manufactured by Kobe Steel Pantech), Slasher (manufactured by Nippon Coke Engineering Co., Ltd.), Trigonal Wet Mill (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.), Cavitron (manufactured by Eurotech), and Fine Flow Mill (manufactured by Pacific Machinery Works), as well as batch or continuous dual-use emulsifiers such as Clearmix (manufactured by M Technique), Clearmix Dissolver (manufactured by M Technique), and Filmix (manufactured by Primix). In particular, it is desirable to prepare the cerium oxide raw material solution or cerium oxide precipitation solution using a stirrer equipped with rotating stirring blades, particularly the Clearmix (manufactured by M Technique) or Clearmix Dissolver (manufactured by M Technique).

[0034] In the production method of the present invention, the cerium oxide raw material solution and the cerium oxide deposition solution can be mixed by a known method, such as a batch method in which the mixture is carried out in a beaker or a tank, or a continuous method in which the reaction is carried out in a tubular reactor or a microreactor. Among these, it is preferable to use a fluid treatment device similar to that described in JP 2011-189348 A shown in FIG. 1 .

[0035] The fluid treatment device shown in FIG. 1 will be described in detail. In FIGS. 1 and 2, R indicates the direction of rotation. The fluid treatment device comprises two opposing processing members, first and second, 10 and 20, and the first processing member 10 rotates. The opposing surfaces of the processing members 10 and 20 serve as processing surfaces. The first processing member 10 comprises a first processing surface 1, and the second processing member 20 comprises a second processing surface 2. The processing surfaces 1 and 2 are connected to flow paths d1 and d2 for the first and second fluids to be treated, respectively, and form part of a sealed flow path for the fluids to be treated. The gap between the processing surfaces 1 and 2 is usually adjusted to a very small gap of 1 mm or less, for example, approximately 0.1 μm to 50 μm. As a result, the fluid to be treated passing between the processing surfaces 1 and 2 is forced into a thin film fluid by the processing surfaces 1 and 2.

[0036] Using a fluid processing device, fluid processing is performed between the processing surfaces 1 and 2, reacting first and second fluids to be processed and precipitating cerium oxide particles. More specifically, the device includes a first holder 11 for holding the first processing member 10, a second holder 21 for holding the second processing member 20, a surface-approaching pressure imparting mechanism 43, a rotation drive mechanism (not shown), a first introduction part d1, a second introduction part d2, and fluid pressure imparting mechanisms p1 and p2. Compressors or other pumps can be used for the fluid pressure imparting mechanisms p1 and p2. The first introduction part d1 and the second introduction part d2 each include a thermometer and a pressure gauge, which can measure the introduction pressure of the first and second fluids to be processed and their temperatures under the introduction pressure.

[0037] The first processing member 10 and the second processing member 20 are ring-shaped disks. The materials for the first and second processing members 10, 20 can be metal, carbon, ceramic, sintered metal, wear-resistant steel, sapphire, or other metals that have been hardened, or those that have been lined, coated, or plated with hard materials. In the above embodiment, the first and second processing surfaces 1, 2 of both processing members 10, 20 facing each other are mirror-polished, and the arithmetic mean roughness is 0.01 to 1.0 μm.

[0038] The second holder 21 is fixed to the apparatus, and the first holder 11 attached to the rotation shaft 50 of the rotation drive mechanism also fixed to the apparatus rotates, causing the first processing member 10 supported by this first holder 11 to rotate relative to the second processing member 20. Of course, the second processing member 20 may be rotated, or both may be rotated. In the manufacturing method of the present invention, the rotation speed may be, for example, 350 to 5000 rpm.

[0039] The second processing member 20 approaches and moves away from the first processing member 10 in the direction of the rotation axis 50, and a portion of the second processing member 20 opposite the processing surface 2 side is accommodated in a accommodating portion 41 provided in the second holder 21 so as to be able to protrude and retract. However, conversely, the first processing member 10 may approach and move away from the second processing member 20, or both processing members 10, 20 may approach and move away from each other. The accommodating portion 41 is a recess that accommodates the portion of the second processing member 20 opposite the processing surface 2 side, and is a groove formed in an annular shape. This accommodating portion 41 accommodates the second processing member 20 with sufficient clearance to allow the portion of the second processing member 20 opposite the processing surface 2 side to protrude and retract.

[0040] The surface-approaching pressure imparting mechanism is a mechanism for generating a force (hereinafter referred to as surface-approaching pressure) that pushes the first processing surface 1 of the first processing member 10 and the second processing surface 2 of the second processing member 20 in a direction toward each other. The balance between this surface-approaching pressure and a force (hereinafter referred to as a separating force) that separates the processing surfaces 1 and 2 due to the fluid pressure of the cerium oxide raw material solution and the cerium oxide deposition solution generates a thin film fluid having a minute film thickness on the order of nanometers or micrometers while maintaining a predetermined minute gap between the processing surfaces 1 and 2. In the above embodiment, the surface-approaching pressure imparting mechanism applies the surface-approaching pressure by biasing the second processing member 20 toward the first processing member 10 using a spring 43 provided in the second holder 21.

[0041] Furthermore, the pressure of a fluid such as air for back pressure can be applied in addition to the spring 43. The sum of all these pressures is the aforementioned contact pressure, which is balanced with the separating force due to the fluid pressure of the cerium oxide raw material solution and the cerium oxide deposition solution. As an example of adjusting the contact pressure, if the fluid pressure between the processing surfaces 1 and 2 is set higher than standard atmospheric pressure, the boiling point of the fluid increases with the increase in fluid pressure between the processing surfaces 1 and 2, making it possible to raise the reaction temperature above the boiling point of the fluid at standard atmospheric pressure. The contact pressure that balances the increase in fluid pressure is also set high. For example, the pressure of the fluid for back pressure can be set to 0.005 to 0.500 MPaG, preferably 0.050 to 0.400 MPaG, more preferably 0.100 to 0.350 MPaG, and the pressure of the spring 43 can be set to 0.007 to 0.300 MPa, preferably 0.010 to 0.20 MPa.

[0042] The first fluid to be treated pressurized by the fluid pressure imparting mechanism p1 is introduced from the first introduction part d1 into the space inside both processing members 10, 20. On the other hand, the second fluid to be treated pressurized by the fluid pressure imparting mechanism p2 is introduced from the second introduction part d2 through a passage provided inside the second processing member 20 and from an opening d20 formed on the second processing surface into the space inside both processing members 10, 20. At the opening d20, the first fluid to be treated and the second fluid to be treated join and mix.

[0043] At this time, the mixed fluid to be treated becomes a thin film fluid forced by both processing surfaces 1 and 2 which maintain the minute gap, and tries to move to the outside of both annular processing surfaces 1 and 2. Because the first processing member 10 is rotating, the mixed fluid to be treated does not move linearly from the inside to the outside of both annular processing surfaces 1 and 2, but a resultant vector of a movement vector in the radial direction of the annulus and a movement vector in the circumferential direction acts on the fluid to be treated, causing it to move in a substantially spiral shape from the inside to the outside.

[0044] As shown in FIG. 2 , groove-shaped recesses 13 extending radially from the center of the first processing member 10 to the outside may be formed on the first processing surface 1. The planar shape of the recesses 13 may be a curved or spiral shape extending on the first processing surface 1, or (not shown) a straight outward extension, an L-shaped or other bent or curved shape, continuous, discontinuous, or branched. The recesses 13 may also be formed on the second processing surface 2, or on both the first and second processing surfaces 1 and 2. Forming such recesses 13 can produce a micropump effect, enabling the fluid to be treated to be transported between the first and second processing surfaces 1 and 2.

[0045] It is desirable that the base end of the recess 13 reaches the inner periphery of the first processing member 10. The tip of the recess 13 extends toward the outer periphery of the first processing surface 1, and its depth gradually decreases from the base end toward the tip. A flat surface 16 without a recess 13 is provided between the tip of the recess 13 and the outer periphery of the first processing surface 1.

[0046] The opening d20 is preferably provided at a position facing the flat surface of the first processing surface 1. In particular, it is preferable to provide the opening d20 at a position facing the flat surface 16 downstream of the point where the flow direction of the first fluid to be treated when introduced by the micropump effect is changed to the flow direction of a spiral laminar flow formed between the processing surfaces 1 and 2. This makes it possible to mix multiple fluids to be treated and precipitate fine particles under laminar flow conditions.

[0047] It is preferable that the second introduction part d2 has directional properties. For example, the introduction direction from the opening d20 of the second processing surface 2 may be inclined at a predetermined elevation angle with respect to the second processing surface 2, or the introduction direction from the opening d20 of the second processing surface 2 may have directional properties in a plane along the second processing surface 2, and the introduction direction of the second fluid may be an outward direction away from the center in the radial direction of the processing surface and a forward direction in the rotational direction of the fluid between the rotating processing surfaces. In this way, by making the flow of the first treated fluid at the opening d20 a laminar flow and by making the second introduction part d2 directional, the second treated fluid can be introduced between the processing surfaces 1 and 2 while suppressing turbulence in the flow of the first treated fluid.

[0048] The mixed fluid to be treated that has been discharged to the outside of both processing members 10, 20 is collected as a discharged liquid in a beaker b via a vessel v. In an embodiment of the present invention, as will be described later, the discharged liquid contains cerium oxide particles.

[0049] In the example shown in Figure 1, the number of types of fluid to be treated and the number of flow paths therefor are two, but they may be three or more. Furthermore, the shape, size, and number of the introduction openings provided in each processing section are not particularly limited and may be modified as appropriate. For example, as shown in Figure 1, the shape of the opening d20 may be a concentric ring shape surrounding the central opening of the processing surface 2, which is a ring-shaped disk, and the ring-shaped openings may be continuous or discontinuous. Furthermore, an introduction opening may be provided immediately before or further upstream of the first and second processing surfaces 1 and 2.

[0050] When cerium oxide particles are produced using the fluid treatment apparatus, for example, a cerium oxide raw material solution is introduced as a first fluid to be treated through the first introduction part d1, a cerium oxide deposition solvent is introduced as a second fluid to be treated through the second introduction part d20, and the two fluids are mixed between the processing surfaces 1 and 2 to precipitate cerium oxide particles. The mixed fluid from which the cerium oxide particles have been precipitated between the processing surfaces 1 and 2 is discharged outside the processing members 10 and 20 and collected in a beaker b as a discharged liquid via a vessel v.

[0051] In the present invention, it is sufficient that the fluid treatment can be performed between the processing surfaces 1 and 2, and the second fluid to be treated may be introduced through the first introduction part d1 and the first fluid to be treated may be introduced through the second introduction part d2. For example, the terms "first" and "second" for each fluid merely have the meaning of identifying the nth fluid among multiple fluids, and as mentioned above, there may also be three or more fluids.

[0052] (Molar Ratio of Trivalent Metal Ions to Total Metal Ions in the Cerium Oxide Raw Material Solution and Average Particle Size) The average particle size of the cerium oxide particles produced by the production method of the present invention can be controlled by changing the molar ratio of trivalent metal ions to the total metal ions, including trivalent and tetravalent metal ions, in the cerium oxide raw material solution. Specifically, for example, the molar ratio of trivalent metal ions to the total metal ions: ([Ce ３＋ ]+[M ３＋ ]) / ([Ce ３＋ ]+[Ce ４＋ ]+[M ３＋ ]+[M ４＋ ]) (wherein M is another element)) can be increased to increase the average particle size. By decreasing the molar ratio, the average particle size can be decreased. One of the reasons for the change in average particle size is thought to be due to differences in ionic radius and lattice energy. Generally, the larger the valence of an ion, the smaller the ionic radius and the larger the lattice energy. Similarly, in the case of cerium ions, trivalent cerium ions Ce ３＋ Tetravalent cerium ion Ce ４＋has a smaller ionic radius and a larger lattice energy. Lattice energy is the cohesive energy when atoms, molecules, or ions that make up the crystal lattice change from a gaseous state to a solid crystal, and the larger the lattice energy, the more stable the ions are in the solid state. When the cerium oxide raw material solution is mixed with the cerium oxide deposition solution, the cerium ions react with the hydroxide ions to precipitate cerium hydroxide, and then a dehydration reaction occurs to form cerium oxide. When cerium hydroxide precipitates, cerium (IV) hydroxide has a larger lattice energy than cerium (III) hydroxide, so it is more likely to coagulate from the solvated state, i.e., the tetravalent cerium ions Ce ４＋ According to nucleation theory, the more nuclei are generated, the less material is available for particle growth, resulting in a smaller average particle size.

[0053] Specifically, in the manufacturing method of the present invention, the raw metal ions were prepared using cerium (III) nitrate hexahydrate as the trivalent metal ion and diammonium cerium (IV) nitrate as the tetravalent metal ion, with the total metal concentration (cerium ion concentration) adjusted to 46 mM, and the reaction was carried out in a neutral pH range of approximately pH 7 after mixing with a basic substance. As shown in Figure 3, when the molar ratio of trivalent cerium ions to all metal ions was changed to 50%, the average particle size could be reduced by approximately half compared to the average particle size when the molar ratio of trivalent cerium ions to all metal ions was 100%. The rate of change in average particle size with respect to the molar ratio of trivalent cerium ions was not constant. The rate of change was small when the molar ratio of trivalent cerium ions was 0% to 15% and 25% to 85%, and large when the molar ratio of trivalent cerium ions was 15% to 25% and 85% to 100%. When the molar ratio of trivalent cerium ions is 0%, 25%, and 100%, the average particle size is approximately linear with respect to the molar ratio.

[0054] The average particle size varies depending on the concentrations of the cerium oxide raw material solution and the cerium oxide deposition solution; the higher the concentration, the larger the average particle size, and the lower the concentration, the smaller the average particle size. The average particle size also varies depending on the reaction temperature and the counter ions of the metal ions. However, the molar ratio of trivalent metal ions to all metal ions and the change in average particle size tend to be similar. Therefore, in the production method of the present invention, cerium oxide particles with a desired average particle size can be obtained by converting the molar ratio of trivalent metal ions that results in a desired particle size based on the average particle sizes when the molar ratio of trivalent metal ions is 0% and 100%.

[0055] (pH) In the production method of the present invention, when the pH of the mixed fluid obtained by mixing at least the first fluid and the second fluid is in the range of 3.5 to 8.5, substantially spherical particles are obtained. When the pH exceeds 8.5, rod-shaped particles are obtained, and when the pH exceeds 9.5, crystallinity decreases. When the pH is below 7.0, hydroxide ions are insufficient, so the lower the pH, the lower the yield, and the smaller the average particle size becomes, seemingly similar to when the metal ion concentration of the raw material in the cerium oxide raw material solution is reduced. When the pH is below 5.0, substantially spherical particles are obtained, but in addition to the reduced yield, crystallinity also decreases, and when the pH is below 3.5, almost no precipitation is observed. When it is necessary to increase the yield and obtain highly crystalline particles, the pH of the mixed fluid is preferably 5.0 to 9.5, and more preferably 6.0 to 9.0. When the pH exceeds 8.5, the average particle size and aspect ratio (the ratio of the short side to the long side of the particles) of the obtained rod-shaped particles can be controlled by the molar ratio of trivalent metal ions to all metal ions in the raw material in the cerium oxide raw material solution. In this case, unlike the case of spherical particles, the rate of change is small when the molar ratio of trivalent metal ions to all metal ions is 0 to 50%, but the average particle size changes quadratically when the molar ratio of trivalent metal ions to all metal ions is 50 to 100%. The pH can be controlled by controlling the concentrations of the cerium oxide particle raw material, basic substance, acidic substance, etc. contained in the cerium oxide raw material solution and the cerium oxide deposition solution, and the introduction flow rates of the cerium oxide raw material solution and the cerium oxide deposition solvent.

[0056] (Washing of Particles) The cerium oxide particles produced by the production method of the present invention can be washed as needed. There are no particular limitations on the washing method, and various known methods such as decantation, centrifugation, and filtration can be used. As the washing solvent, any solvent capable of dissolving the inorganic salt by-product can be used, and examples thereof include pure water and ion-exchanged water.

[0057] The particle size of the cerium oxide produced by the production method of the present invention has a primary particle size of 1 to 100 nm, and the particle size can be precisely controlled to within a few nanometers. Furthermore, the ratio d / D of the average crystallite size (d) calculated from XRD measurement results to the average particle size (D) obtained by particle size distribution measurement, transmission electron microscope observation (TEM observation), scanning electron microscope observation (SEM observation), or scanning transmission electron microscope observation (STEM observation) is preferably 0.50 to 1.00, more preferably 0.70 to 1.00. A dispersion of the cerium oxide particles produced by the production method of the present invention in a solvent has few aggregates, and a transparent dispersion can be obtained.

[0058] In the production method of the present invention, it is preferable that at least one selected from the group consisting of the temperature of the first fluid, the temperature of the second fluid, and the temperature of a mixed fluid obtained by mixing the first fluid and the second fluid is 100° C. or higher. This at least one temperature is more preferably 110 to 250° C., and even more preferably 120 to 200° C. By setting the temperature to 100° C. or higher, the crystallinity of the cerium oxide particles is increased, and the ratio d / D is improved.

[0059] (Acid Treatment) The cerium oxide particles obtained by the production method of the present invention can be further subjected to a stirring treatment in an acidic aqueous solution to modify the surface condition of the particles. The stirring treatment can be carried out using the above-mentioned preparation apparatus. The acid contained in the acidic aqueous solution is preferably a carboxylic acid, and more preferably a C acid such as acetic acid. １ ~C ５A low-molecular-weight carboxylic acid such as the above is preferred. The concentration of the acid in the acidic aqueous solution is preferably 5 to 50% by mass, more preferably 10 to 30% by mass. The treatment temperature is preferably 20°C or higher but 95°C or lower, more preferably 20°C or higher but 80°C or lower. The treatment time is preferably 5 to 48 hours, more preferably 10 to 24 hours. The acid treatment bonds the carboxylic acid to the surface of the cerium oxide particles, which modifies the surface condition, breaks down agglomerations, and improves dispersibility in a solvent.

[0060] The production method of the present invention makes it possible to easily and stably produce cerium oxide particles having a controlled particle size.

[0061] 2. Method for Producing a Dispersion of Cerium Oxide Particles The method for producing a dispersion of cerium oxide particles of the present invention includes the steps of producing cerium oxide particles by the method for producing cerium oxide particles of the present invention, and dispersing the produced cerium oxide particles in a dispersion medium containing at least one of a solvent, a dispersant, and a resin.

[0062] The cerium oxide particles produced by the method for producing cerium oxide particles of the present invention can be dispersed in various solvents. Prior to dispersion in a solvent, acid treatment may be performed followed by acid removal and / or solvent substitution. Acid removal and / or solvent substitution can be achieved by various known methods, such as decantation, centrifugation, filtration, and evaporation. A dispersion can be prepared by adding a solvent, dispersant, resin, etc. to the resulting cerium oxide particles. Because the acid treatment breaks down particle agglomerates, the particles can be dispersed in many solvents without a dispersant, and if a dispersant is used, the amount used can be significantly reduced.

[0063] 3. Method for Controlling the Average Particle Size of Cerium Oxide Particles The method for controlling the average particle size of cerium oxide particles of the present invention is a method for controlling the average particle size of cerium oxide particles to within a range of 1 nm to 100 nm, comprising a step of mixing at least a first fluid and a second fluid to precipitate cerium oxide particles, wherein one of the first fluid and the second fluid is a cerium oxide raw material solution containing at least trivalent metal ions and / or tetravalent metal ions, trivalent cerium ions and / or tetravalent cerium ions are contained in the trivalent metal ions and / or tetravalent metal ions, and the other of the first fluid and the second fluid is a cerium oxide precipitation solution containing at least a basic substance, and the method is characterized in that the molar ratio of the trivalent metal ions and the tetravalent metal ions is changed.

[0064] The molar ratio of the trivalent metal ions to the total metal ions consisting of the trivalent metal ions and the tetravalent metal ions: ([Ce ３＋ ]+[M ３＋ ]) / ([Ce ３＋ ]+[Ce ４＋ ]+[M ３＋ ]+[M ４＋ ]) (wherein M is another element)), the average particle size of the cerium oxide particles can be increased. The average particle size of the cerium oxide particles can be decreased by decreasing the molar ratio. The control method of the present invention is as described above in the method for producing cerium oxide particles of the present invention.

[0065] The present invention will be described below using examples, but the present invention is not limited to these examples. In the following examples 1 to 37, liquid A refers to the first treated fluid introduced from the first introduction part d1 of the apparatus shown in Figure 1, and liquid B refers to the second treated fluid introduced from the second introduction part d2 of the apparatus.

[0066] Example 1 A cerium oxide raw material solution and a cerium oxide precipitation solution were each prepared using a Clearmix (product name: CLM-0.8S, manufactured by M Technique), a high-speed rotary dispersion and emulsification device. Specifically, a cerium oxide particle raw material and pure water were mixed based on the formulation of the cerium raw material solution shown in Example 1 of Table 1, and the mixture was homogeneously mixed by stirring using the Clearmix at a rotor speed of 20,000 rpm at a preparation temperature of 50°C for 30 minutes to dissolve the cerium oxide particle raw material in the pure water, thereby preparing a cerium oxide raw material solution. A basic substance and pure water were mixed based on the formulation of the cerium oxide precipitation solution shown in Example 1 of Table 1, and the mixture was homogeneously mixed by stirring using the Clearmix at a rotor speed of 15,000 rpm at a preparation temperature of 45°C for 30 minutes to prepare a cerium oxide precipitation solution.

[0067] In Tables 1 to 6, Ce(NO ３ ) ３ ・6H ２ O is cerium(III) nitrate hexahydrate, CeCl ３ ・7H ２ O is cerium(III) chloride heptahydrate, Ce(CH ３ COO) ３ ・H ２ O is cerium(III) acetate monohydrate, Ce(NH ４ ) ２ (NO ３ ) ６ is diammonium cerium(IV) nitrate, ZrO(NO ３ ) ２ ・2H ２ O is zirconium oxynitrate dihydrate, H ２ O ２ is hydrogen peroxide, TMAH is tetramethylammonium hydroxide, NH ３ represents ammonia, and NaOH represents sodium hydroxide. Ce(NO ３ ) ３ ・6H ２ O is a special grade reagent manufactured by Wako Pure Chemical Industries, Ltd., CeCl ３ ・7H ２ O is a high-purity reagent manufactured by Kanto Chemical Co., Ltd., Ce(CH ３ COO) ３ ・H ２ O is a high-purity reagent manufactured by Kanto Chemical Co., Ltd., Ce(NH４ ) ２ (NO ３ ) ６ is a special grade reagent manufactured by Kishida Chemical, ZrO(NO ３ ) ２ ・2H ２ O is a special grade reagent manufactured by Kishida Chemical Co., Ltd., H ２ O ２ is a special grade reagent (H) manufactured by Kanto Chemical ２ O ２ 30.0% to 35.5% of TMAH), TMAH is a precision analytical reagent manufactured by Kanto Chemical (contains 25 wt% of TMAH) NH ３ is a special grade reagent (NH ３ The amount of hydrogen peroxide and ammonia listed in the recipe is not the content of the components, but the amount of each reagent used.

[0068] Next, the prepared cerium oxide raw material solution and the cerium oxide deposition solvent were mixed in the fluid treatment device shown in Figure 1 under the treatment conditions shown in Table 1. Specifically, the cerium oxide raw material solution was introduced as the first fluid to be treated (liquid A) between the processing surfaces through the first inlet d1 of the fluid treatment device shown in Figure 1. While the processing unit 10 was operating at a rotation speed of 2250 rpm, the cerium oxide deposition solvent was introduced as the second fluid to be treated (liquid B) between the processing surfaces 1 and 2 through the second inlet d2 of the fluid treatment device shown in Figure 1, and mixed in a thin film fluid. Cerium oxide particles were precipitated between the processing surfaces 1 and 2, and a discharge liquid containing the cerium oxide particles was discharged from between the processing surfaces 1 and 2 of the fluid treatment device. The discharge liquid containing the cerium oxide particles was recovered in a beaker b via a vessel v.

[0069] The introduction temperatures (liquid delivery temperatures) of liquid A and liquid B were measured using a thermometer installed in the sealed introduction path (first introduction part d1 and second introduction part d2) connecting between the processing surfaces 1 and 2. The introduction temperature of liquid A shown in Table 1 is the actual temperature of liquid A in the first introduction part d1, and the introduction temperature of liquid B is the actual temperature of liquid B in the second introduction part d2.

[0070] A HORIBA Model D-51 pH meter was used for the pH measurements. Before introducing the first and second fluids to be treated into the fluid treatment device, the pH of the fluids to be treated and the temperature at the time of pH measurement were measured. In addition, since it is difficult to measure the pH of the mixed fluid immediately after mixing the cerium oxide raw material solution and the cerium oxide deposition solution, the pH of the cerium oxide particle dispersion discharged from the device and recovered in beaker b was measured at room temperature.

[0071] A dry powder and a wet cake sample were prepared from the discharged liquid containing cerium oxide particles collected in beaker b. The preparation methods were performed according to known methods. Specifically, the discharged liquid containing cerium oxide particles was collected by centrifugation, the cerium oxide particles were allowed to settle, and the supernatant was removed. The cerium oxide particles were then washed by repeating washing with pure water (pH 6.34, conductivity 0.86 μS / cm) and settling twice. A portion of the resulting wet cake of cerium oxide particles was dried to prepare a dry powder. The other portion was used as the wet cake sample.

[0072] (Preparation of Sample for TEM Observation) A portion of the wet cake sample of cerium oxide particles after the washing treatment obtained in Example 1 was dispersed in methanol. The obtained diluted solution was dropped onto a grid with a support film and dried to prepare a sample for TEM observation.

[0073] (Transmission Electron Microscope) A transmission electron microscope, JEM-2100 (manufactured by JEOL) was used for transmission electron microscope (TEM) observation. The observation conditions were an acceleration voltage of 200 kV and an observation magnification of 10,000 to 800,000. Under the conditions shown in Tables 1 and 3 to 7 where approximately spherical particles were observed, the listed average particle diameter (D) is the average value of primary particle diameters, and under the conditions shown in Table 2 where rod-shaped particles were observed, the long side particle diameter (A) is the length of the long side of the rod-shaped particles, and the short side particle diameter (B) is the average value of the lengths of the short sides of the rod-shaped particles, and the average values ​​are shown as the results of measuring the particle diameters of 100 particles by TEM observation.

[0074] (X-ray Diffraction Measurement) For X-ray diffraction (XRD) measurement, an EMPYREAN powder X-ray diffractometer (manufactured by Malvern Panalytical) was used. The measurement conditions were: measurement range: 10 to 100 [°2 Theta] Cu anticathode, tube voltage: 45 kV, tube current: 40 mA, scan rate: 0.3° / min. XRD measurement was performed using the dried powder of cerium oxide particles obtained in the examples, and the crystallite diameter was calculated using the obtained peak near 28.5° according to the Scherrer equation using the measurement results of a silicon polycrystalline plate, and this was taken as the average crystallite diameter (d).

[0075] (Examples 2 to 11) In Examples 2 to 11, similarly to Example 1, the cerium oxide deposition solution and cerium oxide raw material solution were mixed according to the respective formulations and treatment conditions shown in Table 1, and particles were precipitated between the treatment surfaces 1 and 2. Dry powder and wet cake samples were prepared from the discharged liquid containing cerium oxide particles that was discharged from the fluid treatment device and recovered in beaker b via vessel v, and TEM observation and XRD measurement were carried out in the same manner as in Example 1. Conditions not shown in Table 1 were the same as in Example 1.

[0076] The measurement results of Examples 1 to 11 are shown in Table 1. A TEM photograph of the cerium oxide particles obtained in Example 1 is shown in FIG.

[0077]

[0078] As shown in Table 1 and Fig. 4, the average particle size of cerium oxide particles could be controlled to be large by increasing the molar ratio of trivalent metal ions to all metal ions in the raw materials in the cerium oxide raw material solution, and to be small by decreasing this molar ratio.

[0079] XRD measurements showed that the cerium oxide particles obtained in Examples 1 to 8 and 11 had d / D ratios of 0.95 to 1.00. The particles shown in Figure 4 exhibited crystal lattice fringes (atomic arrangements in a crystal), and were therefore determined to be single crystals. Examples 1, 9, and 11 were run under substantially the same reaction conditions, but the introduction temperatures of Liquid A and Liquid B were varied. As the reaction temperature increased, the average particle size (D), crystallite size (d), and d / D increased. In Example 9, the introduction temperatures of Liquid A and Liquid B were 77°C and 68°C, respectively, which were less than 100°C, but the d / D was a low 0.64. In Examples 9 and 10, the introduction temperatures of Liquid A and Liquid B were less than 100°C, and the d / D was less than 0.9. However, by increasing the molar ratio of trivalent metal ions to the total metal ions in the raw material in the cerium oxide raw material solution, the average particle size of the cerium oxide particles could be increased, and particle size control was possible even under conditions of low crystallinity.

[0080] Examples 12 to 15 Compared to Examples 1 to 8, Examples 12 to 15 are examples in which precipitation was carried out using a strongly alkaline discharge solution with a pH of 10 or higher. As in Example 1, the cerium oxide raw material solution and cerium oxide deposition solution were mixed according to the formulations and treatment conditions shown in Table 2, and particles were precipitated between processing surfaces 1 and 2. Dry powder and wet cake samples were prepared from the discharge solution containing cerium oxide particles that was discharged from the fluid treatment device and recovered in beaker b via vessel v, and TEM observation and XRD measurement were carried out in the same manner as in Example 1. Conditions not shown in Table 2 were the same as in Example 1. The measurement results of Examples 12 to 15 are shown in Table 2.

[0081]

[0082] When the discharge liquid was strongly alkaline with a pH of 10 or more, the particles were rod-shaped. However, as in Example 1, the average particle size of the cerium oxide particles could be controlled to be larger by increasing the molar ratio of trivalent metal ions to all metal ions in the raw material in the cerium oxide raw material liquid.

[0083] Examples 16 to 23 Examples 16 to 23 are examples in which the cerium oxide particle raw material liquid and the cerium oxide deposition solution were changed compared to Examples 1 to 8. The cerium oxide raw material liquid and the cerium oxide deposition solution were mixed according to the formulations and processing conditions shown in Table 3, and particles were deposited between processing surfaces 1 and 2. Dry powder and wet cake samples were prepared from the discharged liquid containing cerium oxide particles that was discharged from the fluid processing device and recovered in beaker b via vessel v, and TEM observation and XRD measurement were performed in the same manner as in Example 1. Conditions not shown in Table 3 were the same as in Example 1. The measurement results of Examples 16 to 23 are shown in Table 3.

[0084]

[0085] Even when the cerium oxide particle raw material was changed, the average particle size of the cerium oxide particles could be controlled to be large by increasing the molar ratio of trivalent metal ions to all metal ions in the raw materials in the cerium oxide raw material liquid, as in Examples 1 to 8.

[0086] Examples 24 to 26 In Examples 24 to 26, the concentrations of the components contained in the cerium oxide raw material solution and the cerium oxide deposition solution were increased compared to Examples 1 to 8. As in Example 1, the cerium oxide raw material solution and the cerium oxide deposition solution were mixed according to the formulations and treatment conditions shown in Table 4, and particles were precipitated between the treatment surfaces 1 and 2. A discharged solution containing cerium oxide particles was discharged from the fluid treatment device and recovered in beaker b via vessel v. Dry powder and wet cake samples were prepared from the discharged solution, and TEM observation and XRD measurement were performed in the same manner as in Example 1. Conditions not shown in Table 4 were the same as in Example 1. The measurement results of Examples 24 to 26 are shown in Table 4.

[0087]

[0088] Even when the concentrations of the components contained in the cerium oxide raw material solution and the cerium oxide deposition solution were increased, the average particle size of the cerium oxide particles could be controlled to be larger by increasing the molar ratio of trivalent metal ions to all metal ions in the raw materials in the cerium oxide raw material solution, as in Examples 1 to 8.

[0089] Examples 27 to 31 Examples 27 to 31 are examples in which liquid A and liquid B are interchanged compared to Examples 1 to 8. Liquid A was used as a cerium oxide deposition solution, and liquid B was used as a cerium oxide raw material solution. The cerium oxide deposition solution and cerium oxide raw material solution were mixed according to the formulations and processing conditions shown in Table 5, and particles were precipitated between processing surfaces 1 and 2. A discharged liquid containing cerium oxide particles was discharged from the fluid processing device and recovered in beaker b via vessel v. Dry powder and wet cake samples were prepared from the discharged liquid, and TEM observation and XRD measurement were performed in the same manner as in Example 1. Conditions not shown in Table 5 were the same as in Example 1. The measurement results of Examples 27 to 31 are shown in Table 5.

[0090]

[0091] Even when the solutions A and B were interchanged, the average particle size of the cerium oxide particles could be controlled to be large by increasing the molar ratio of trivalent metal ions to all metal ions in the raw materials in the cerium oxide raw material solution, as in Examples 1 to 8.

[0092] Examples 32 to 33 are examples in which an apparatus having the schematic plan view shown in Fig. 5 was used. As in Example 1, a cerium oxide raw material liquid and a cerium oxide precipitation solution were each prepared based on the formulations shown in Table 6. The prepared cerium oxide raw material liquid was placed in tank c and pumped by a pump (MF25, manufactured by Hanatsuka Seisakusho) into a dispersing vessel d equipped with a disperser (Clearmix, high-speed rotary dispersing and emulsifying device, product name: CLM-0.8S, manufactured by M Technique). The dispersing vessel was filled, and the overflow was returned to tank c, thereby circulating the cerium oxide raw material liquid.

[0093] A heat medium was introduced into the jacket attached to the dispersion vessel d, and the temperature inside the vessel was heated to 120°C. The rotor rotation speed was then set to 20,000 rpm (circumferential speed: 31.4 m / s), and the disperser was started. Next, the prepared cerium oxide deposition solution was sent to the dispersion vessel d from an inlet provided separately from the circulation line, and the mixture was mixed under the treatment conditions shown in Table 6 to carry out a reaction. After completion of the reaction, the treatment solution was cooled and the pH was measured. The particles were washed in the same manner as in Example 1, and dried powder and wet cake samples were prepared, followed by TEM observation and XRD measurement.

[0094] Example 34 As in Example 1, a cerium oxide raw material solution and a cerium oxide precipitation solution were prepared based on the formulations shown in Table 6. The prepared cerium oxide raw material solution and cerium oxide precipitation solution were added to a tank with stirring, the tank was sealed, and a reaction was carried out under the conditions shown in Table 6. After completion of the reaction, the treated solution was cooled and the pH was measured. As in Example 1, the particles were washed, and dried powder and wet cake samples were prepared, followed by TEM observation and XRD measurement. The measurement results for Examples 32 to 34 are shown in Table 6. A TEM photograph of the cerium oxide particles obtained in Example 34 is shown in FIG. 6.

[0095]

[0096] Even when the apparatus having the schematic plan view shown in FIG. 5 was used, the average particle size of cerium oxide particles could be controlled to be large by increasing the molar ratio of trivalent metal ions to all metal ions in the raw material in the cerium oxide raw material solution, as in Examples 1 to 8.

[0097] (Preparation of Dispersion) (Example 35) 255 g of purified water and 45 g of acetic acid were added to 20 g of the cerium oxide particle wet cake obtained in Example 1. The acetic acid was a special-grade reagent manufactured by Kanto Chemical. The pH was 2.57, and the mixture was stirred for 12 hours using a Clearmix rotor at 5,000 rpm. The color of the treated solution was cloudy before treatment, but changed to a transparent orange solution after treatment. To remove the acetic acid, the particles were washed. Particle washing can be performed using known methods, but specifically, the following procedure was used. Acetic acid was removed and the mixture was concentrated using the apparatus described in Patent 6,151,469, using an ultrafiltration membrane as the filtration membrane. The pH after washing was 6.03. 200 g of a pale yellow, transparent aqueous dispersion was obtained, and the cerium oxide concentration was 10% by mass.

[0098] Example 36 100 g of ethanol (99.5%, Kishida Chemical Co., Ltd.) was added to 30 g of the transparent dispersion of cerium oxide obtained in Example 35, and the solvent was distilled off using an evaporator. After the solvent was distilled off until the remaining amount was 10 g, ethanol was further added and the solvent was distilled off, and this process was repeated three times to obtain 10 g of a transparent ethanol dispersion.

[0099] Example 37 50 g of 1-methoxy-2-propanol (special grade, manufactured by Kanto Chemical Co., Ltd., hereinafter referred to as PGME) and 0.03 g of Plysurf A215C as a dispersant were added to 10 g of the transparent ethanol dispersion of cerium oxide obtained in Example 36, and the mixture was stirred. To remove the ethanol and concentrate the mixture, the solvent was distilled off using an evaporator. After distilling off the solvent until the remaining amount was 10 g, PGME was further added and the solvent was distilled off, and this process was repeated three times to obtain 10 g of a transparent PGME dispersion.

[0100] Comparative Example 1: 40 g of ethanol (99.5%, Kishida Chemical Co., Ltd.) was added to 6 g of the cerium oxide particle wet cake obtained in Example 1, and the mixture was stirred. The color of the treated liquid remained cloudy even after the treatment. The mixture was recovered by centrifugation, the cerium oxide particles were allowed to settle, and the supernatant was removed. 40 g of ethanol was then added, and the water was removed by repeating this process twice by centrifugation to allow settling and remove the supernatant, yielding an ethanol wet cake of cerium oxide particles. The resulting ethanol wet cake was added to ethanol and subjected to a dispersion treatment, but the dispersion did not become transparent.

[0101] Comparative Example 2: 51 g of ethanol (99.5%, Kishida Chemical Co., Ltd.) and 9 g of acetic acid were added to 6 g of the cerium oxide particle wet cake obtained in Example 1, and the mixture was stirred. The color of the treated liquid remained cloudy even after the treatment. As in Comparative Example 1, water and acetic acid were removed by centrifugation, and the resulting ethanol wet cake was added to ethanol and subjected to a dispersion treatment, but the dispersion did not become transparent.

[0102] Comparative Example 3: 51 g of pure water and 9 g of citric acid were added to 6 g of the wet cake of cerium oxide particles obtained in Example 1, and the mixture was stirred. The citric acid used was a special grade reagent manufactured by Kanto Chemical Co., Ltd. The color of the treatment liquid remained cloudy even after treatment.

[0103] As can be seen from the examples, the production method of the present invention makes it possible to easily produce cerium oxide particles with a controlled average particle size, and also to produce a dispersion of cerium oxide particles.

[0104] The production method of the present invention does not require complex chemical reactions or heat treatments, and makes it possible to simply and stably produce cerium oxide particles with a controlled average particle size in a manner suitable for mass production.

[0105] 1 First processing surface 2 Second processing surface 10 First processing member 11 First holder 20 Second processing member 21 Second holder d1 First introduction part d2 Second introduction part d20 Opening

Claims

1. A method for producing cerium oxide particles having an average particle size in the range of 1 nm to 100 nm, comprising the steps of: The method includes a step of mixing at least a first fluid and a second fluid to precipitate cerium oxide particles, one of the first fluid and the second fluid is a cerium oxide raw material solution containing at least trivalent metal ions and / or tetravalent metal ions; Trivalent cerium ions and / or tetravalent cerium ions are included in the trivalent metal ions and / or tetravalent metal ions, the other of the first fluid and the second fluid is a cerium oxide deposition solution containing at least a basic substance; A production method, characterized in that the molar ratio of the trivalent metal ions and the tetravalent metal ions is set so as to obtain the above-mentioned average particle diameter.

2. the trivalent cerium ions are provided from a cerium salt selected from cerium (III) nitrate, cerium (III) chloride, cerium (III) acetate, cerium (III) carbonate, cerium (III) sulfate, cerium (III) oxalate, cerium (III) citrate, and ammonium cerium (III) nitrate; and / or 2. The method of claim 1, wherein the tetravalent cerium ions are provided from a cerium salt selected from ammonium cerium (IV) nitrate, cerium (IV) sulfate, and ammonium cerium (IV) sulfate.

3. 2. The method according to claim 1, wherein the ratio d / D of the average crystallite diameter (d) of the cerium oxide particles obtained by X-ray diffraction measurement to the average particle diameter (D) of the cerium oxide particles is 0.50 or more.

4. the cerium oxide particles contain elements other than cerium and oxygen, 2. The manufacturing method according to claim 1, wherein the other element is at least one selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Si, Ti, V, Cr, Mn, Fe, Co, Mo, Y, Zr, In, Sn, and Hf.

5. continuously introducing at least two fluids to be treated, including the cerium oxide raw material solution and the cerium oxide deposition solution, between processing surfaces disposed opposite to each other and rotating relatively so as to be approachable and separable from each other; mixing the at least two fluids to be treated between processing surfaces that are disposed opposite to each other and rotate relatively toward and away from each other, thereby precipitating cerium oxide particles; 2. The method according to claim 1, wherein the mixed fluid containing the precipitated cerium oxide particles is discharged from between the processing surfaces to continuously produce cerium oxide particles.

6. one of the cerium oxide raw material solution and the cerium oxide deposition solution passes between the processing surfaces while forming a thin film fluid; the other of the cerium oxide raw material solution and the cerium oxide deposition solution is introduced into the space between the processing surfaces through another introduction path independent of the flow path introduced into the space between the processing surfaces, and from an opening formed in at least one of the processing surfaces; The method according to claim 5 , wherein the cerium oxide raw material solution and the cerium oxide deposition solution are mixed between the processing surfaces.

7. A step of producing cerium oxide particles by the method according to any one of claims 1 to 6; and A method for producing surface-modified cerium oxide particles, comprising the step of modifying the surface state of the produced cerium oxide particles by subjecting the produced cerium oxide particles to a stirring treatment in an acidic aqueous solution.

8. The method according to claim 7 , wherein the acidic aqueous solution contains a carboxylic acid.

9. A step of producing cerium oxide particles by the method according to any one of claims 1 to 6; and A method for producing a dispersion of cerium oxide particles, comprising a step of dispersing the produced cerium oxide particles in a dispersion medium containing at least one of a solvent, a dispersant, and a resin.

10. A method for controlling the average particle size of cerium oxide particles within a range of 1 nm to 100 nm, comprising the steps of: The method includes a step of mixing at least a first fluid and a second fluid to precipitate cerium oxide particles, one of the first fluid and the second fluid is a cerium oxide raw material solution containing at least trivalent metal ions and / or tetravalent metal ions; Trivalent cerium ions and / or tetravalent cerium ions are included in the trivalent metal ions and / or tetravalent metal ions, the other of the first fluid and the second fluid is a cerium oxide deposition solution containing at least a basic substance; A method for controlling the particle size of cerium oxide particles, comprising changing the molar ratio of the trivalent metal ions and the tetravalent metal ions.

11. The method according to claim 10, wherein the average particle size of the cerium oxide particles is increased by increasing the molar ratio of the trivalent metal ions to the total metal ions consisting of the trivalent metal ions and the tetravalent metal ions, or the average particle size of the cerium oxide particles is decreased by decreasing the molar ratio.

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