Barium titanate particles and method for producing the same

Abstract

The disclosed method for manufacturing barium titanate particles includes: step (i), preparing titanium hydroxide by simultaneously neutralizing an aqueous solution of titanium halide and an alkaline substance under specified conditions; step (ii), preparing a slurry of the aforementioned titanium hydroxide; step (iii), preparing a titanium compound by adding specified amounts of inorganic acid and organic acid to the aforementioned slurry and maintaining the slurry at a temperature in the range of 40–90°C; and step (iv), synthesizing barium titanate particles by hydrothermal synthesis using raw materials containing the aforementioned titanium compound. The titanium compound contains amorphous titanium hydroxide and anatase titanium dioxide. The specific surface area of ​​the titanium compound is 250 m² / s. 2 / g or more.

Description

Technical Field

[0001] This disclosure relates to barium titanate particles and methods for their manufacture. Background Technology

[0002] Barium titanate particles are used as dielectric materials in various fields. For example, they are used as materials in multilayer ceramic capacitors (MLCCs). Various manufacturing methods for barium titanate particles have been proposed. Furthermore, various proposals have been made regarding titanium oxide and titanium hydroxide, which are used as raw materials for barium titanate particles.

[0003] Claim 1 of Patent Document 1 (Japanese Patent Application Publication No. 8-208228) describes: "A method for manufacturing an amorphous titanium dioxide sol, comprising the following steps: (a) a step in which an aqueous solution of a water-soluble titanium salt having a concentration of 0.5 to 10% by weight (based on TiO2) is maintained at 40 to 75°C, and a water-soluble base is added to the aqueous solution of the titanium salt at a rate of 0.033 to 2 equivalents per minute relative to 1 equivalent of the anions contained in the titanium salt, thereby forming an aqueous slurry of precipitated titanium hydroxide having a pH of 4.5 to 6.5; (b) a step in which the aqueous slurry of precipitated titanium hydroxide obtained from step (a) is..." The impurities and water contained therein are removed, thereby recovering the precipitated titanium hydroxide; and in step (c), an aqueous medium, the precipitated titanium hydroxide obtained in step (b) and a water-soluble acid in a ratio of 0.05 to 0.50 equivalents relative to 1 mole of the precipitated titanium hydroxide are mixed to form a reaction mixture containing the precipitated titanium hydroxide at a concentration of 1 to 45% by weight based on TiO2. Then, while maintaining the temperature of the reaction mixture at freezing point to boiling point, the precipitated titanium hydroxide in the reaction mixture is reacted with the water-soluble acid until an aqueous sol containing amorphous titanium oxide with a particle size of 20 to 300 nm at a concentration of 1 to 45% by weight based on TiO2 is formed.

[0004] Claim 1 of Patent Document 2 (Japanese Patent Application Publication No. 2014-133688) describes: "A titanium dioxide solution, characterized in that it is a weakly acidic to neutral colorless and transparent liquid obtained by heating titanium hydroxide, which is generated by hydrolyzing a titanium compound with bicarbonate, and ammonium citrate in an aqueous solvent."

[0005] Claim 1 of Patent Document 3 (Japanese Patent Application Publication No. 2015-224147) describes: "A method for manufacturing barium titanate, characterized in that titanium dioxide TiO2 sol and barium hydroxide aqueous solution Ba(OH)2 are used as starting materials, and a hydrothermal reaction is carried out in a flow-through reactor using supercritical water."

[0006] Claim 2 of Patent Document 4 (Japanese Patent Application Publication No. 2019-085282) discloses "a method for manufacturing titanium hydroxide, comprising: Step A involves simultaneously neutralizing an aqueous solution of titanium halide with an alkaline substance at a pH of 4.8–5.2 and a temperature of 40–55°C to obtain a BET specific surface area of ​​300 m². 2 Titanium hydroxide with a density of 20 Å or more per g and a crystal grain size of 20 Å or more; Step B involves washing the titanium hydroxide with water, dispersing it in water to obtain a slurry containing the titanium hydroxide, and then heating the slurry to 80-90°C in the presence of inorganic and organic acids within a pH range of 1.0-3.0, followed by water washing to disperse the titanium hydroxide in the water, thus obtaining a slurry containing the titanium hydroxide. Step C involves adding (a) 1.0–5.0% by weight of a phosphorus compound or 2.0–5.0% by weight of a silicon compound, or (b) a total of 1.0–5.0% by weight or less of a phosphorus compound and a silicon compound, relative to the above-mentioned titanium hydroxide in the form of titanium oxide (TiO2), to the slurry to obtain a mixed slurry. The mixed slurry is then washed with water and dried.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 8-208228 Patent Document 2: Japanese Patent Application Publication No. 2014-133688 Patent Document 3: Japanese Patent Application Publication No. 2015-224147 Patent Document 4: Japanese Patent Application Publication No. 2019-085282 Summary of the Invention

[0008] The problem the invention aims to solve With the miniaturization and high performance of electronic devices, high-performance properties are required for barium titanate, which is used as a raw material. Under such circumstances, one of the objectives of this disclosure is to provide barium titanate particles with high crystallinity, small particle size distribution deviation, a specified average particle size, and low impurity concentration, as well as a method for manufacturing the same.

[0009] The means to solve the problem One aspect of this disclosure is a method for manufacturing barium titanate particles, comprising the following steps: Step (i) involves simultaneously neutralizing an aqueous solution of titanium halide and an alkaline substance under conditions ranging from pH 4.5 to 5.5 and a temperature ranging from 35 to 45°C to prepare titanium hydroxide. Step (ii) involves preparing a slurry of titanium hydroxide by washing the titanium hydroxide with water and then dispersing it in water. Step (iii) involves adding 1 to 20 parts by mass of an inorganic acid and 1 to 20 parts by mass of an organic acid (equivalent to 100 parts by mass of titanium dioxide, as described above) to the slurry, and then maintaining the slurry at a temperature in the range of 40 to 90°C to prepare a titanium compound; and Step (iv) involves the synthesis of barium titanate particles using a hydrothermal synthesis of a raw material containing the aforementioned titanium compound. The above titanium compounds contain amorphous titanium hydroxide and anatase titanium dioxide; The specific surface area of ​​the above titanium compound is 250 m². 2 / g or more.

[0010] Another aspect of this disclosure relates to barium titanate particles having a lattice constant ratio c / a of 1.0095 or higher. By mass ratio, the content of Si is less than 10 ppm, the content of P is less than 10 ppm, the content of Na is less than 10 ppm, the content of Cl is less than 15 ppm, and the content of S is less than 10 ppm. The dispersion index Di, calculated from the image obtained by scanning electron microscopy using the following formula, is below 700. Dispersion index Di = 100 × (maximum particle size) / (minimum particle size) The average particle size is above 50nm and below 200nm.

[0011] Invention Effects According to this disclosure, barium titanate particles with high crystallinity, small deviation in particle size distribution, a specified average particle size, and low impurity concentration can be obtained.

[0012] The novel features of the invention are set forth in the appended claims, but the composition and content of the invention, together with other objects and features of the invention, will be more clearly understood by referring to the following detailed description of the accompanying drawings. Attached Figure Description

[0013] Figure 1 SEM image showing an example of a particle produced by the manufacturing method of this disclosure.

[0014] Figure 2 This is an SEM image of an example of particles produced using the manufacturing method of the comparative example. Detailed Implementation

[0015] The following examples illustrate embodiments of this disclosure, but this disclosure is not limited to the examples described below. Although specific numerical values ​​and materials are illustrated in the following description, other numerical values ​​and materials are also applicable as long as the effects of this disclosure are achieved. In this specification, the phrase "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can also be expressed as "numerical value A or higher and numerical value B or lower." In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties and conditions are illustrated, any combination of either the illustrated lower limit or the illustrated upper limit is permissible, provided the lower limit does not exceed the upper limit. In the following description, when examples of constituent elements or methods are listed, unless otherwise specified, only one of the listed examples may be used, or multiple examples may be used concurrently. In this specification, the term "particle" may sometimes be replaced with "powder."

[0016] (Manufacturing method of barium titanate particles) Hereinafter, the manufacturing method of this embodiment will sometimes be referred to as "manufacturing method (M)". Manufacturing method (M) is a method for manufacturing barium titanate particles.

[0017] The manufacturing method (M) sequentially includes steps (i), (ii), (iii), and (iv). According to the manufacturing method (M), as shown in the examples, barium titanate particles (barium titanate powder) with high crystallinity, small particle size distribution deviation, a specified average particle size, and low impurity concentration can be obtained. The steps of the manufacturing method (M) are described below.

[0018] (Process (i)) Step (i) is a process for preparing titanium hydroxide by simultaneously neutralizing an aqueous solution of titanium halide with an alkaline substance under conditions ranging from pH 4.5 to 5.5 and temperature 35 to 45°C. The pH and temperature are the pH and temperature of the reaction solution generated by mixing the aqueous solution of titanium halide with the alkaline substance during simultaneous neutralization. Titanium hydroxide is prepared while maintaining the pH and temperature of the reaction solution within the aforementioned ranges. In step (i), titanium dioxide (e.g., anatase titanium dioxide) is typically not formed.

[0019] The pH of the reaction solution is above 4.5, or above 5.0 or higher. The pH of the reaction solution is below 5.5, or below 5.0 or lower than 5.0. The temperature of the reaction solution is above 35℃, or above 40℃ or higher. The temperature of the reaction solution is below 45℃, or below 40℃ or lower than 40℃.

[0020] The reaction solution is preferably prepared by mixing the total amount of the aqueous titanium halide solution and the total amount of the alkaline substance, and then maintaining it at a temperature in the range of 35–45°C for at least 10 hours (e.g., at least 15 hours). There is no particular upper limit to the time the reaction solution is maintained at the temperature in the range of 35–45°C, but it can be up to 40 hours. The reaction solution is preferably maintained at the specified temperature while being stirred.

[0021] In this specification, "simultaneous neutralization of an aqueous solution of titanium halide with an alkaline substance" means simultaneously adding an aqueous solution of titanium halide and an alkaline substance into a container (a reaction solution holding container) and mixing them therein. At this time, the alkaline substance can also be added to the container in its aqueous solution state. By performing simultaneous neutralization, the pH of the reaction solution can be easily maintained within a specified range. The result is the acquisition of the desired barium titanate particles.

[0022] The aqueous solution of titanium halide and the alkaline substance (an aqueous solution of the alkaline substance) can also be slowly added to the container while maintaining their respective proportions. In an example of simultaneous neutralization, water is added to the container beforehand, and then the aqueous solution of titanium halide and the aqueous solution of the alkaline substance are slowly added to the container in a prescribed ratio. The ratio of the aqueous solution of titanium halide to the aqueous solution of the alkaline substance can be selected based on the concentration of these aqueous solutions, ensuring that the pH of the reaction solution falls within the aforementioned range.

[0023] Neutralization achieved by pre-preparing an aqueous solution of titanium halide in a container and then adding an alkaline substance (or an aqueous solution of an alkaline substance) is not simultaneous neutralization. Similarly, neutralization achieved by pre-preparing an aqueous solution of an alkaline substance in a container and then adding an aqueous solution of titanium halide is not simultaneous neutralization. These methods, which involve non-simultaneous neutralization, make it difficult to maintain a constant pH in the reaction solution.

[0024] Examples of titanium halides include titanium tetrachloride. Examples of alkaline substances include alkali metal hydroxides (sodium hydroxide, potassium hydroxide, etc.). However, other substances may also be used.

[0025] The temperature of the reaction solution can be controlled by adjusting the water temperature inside the container, the temperature of the aqueous solution added to the container, and the ambient temperature (temperature around the container) of the process (i).

[0026] (Process (ii)) Step (ii) is a step of preparing a titanium hydroxide slurry by washing titanium hydroxide with water and then dispersing it in water. The water used for washing titanium hydroxide and dispersing titanium hydroxide is preferably water with few impurities, but ion-exchanged water or RO water (water permeated through a reverse osmosis membrane) can also be used.

[0027] In step (ii), the washing of titanium hydroxide is preferably carried out until the conductivity of the water used for washing (e.g., filtrate) becomes less than 1 mS / cm (e.g., less than 0.1 mS / cm). By washing in this way, barium titanate particles with particularly low impurity concentration can be obtained.

[0028] (Process (iii)) Step (iii) involves adding 1 to 20 parts by mass of an inorganic acid and 1 to 20 parts by mass of an organic acid (equivalent to 100 parts by mass of titanium dioxide relative to titanium hydroxide in the slurry) to the slurry, and then maintaining the slurry at a temperature ranging from 40 to 90°C, thereby preparing a titanium compound. The titanium compound prepared in step (iii) is sometimes referred to as "titanium compound (TC)" below. Titanium compound (TC) contains amorphous titanium hydroxide and anatase titanium dioxide. The specific surface area of ​​titanium compound (TC) is 250 m². 2 / g or more. Specific surface area can be determined by the BET method. Specifically, it can be determined by the method described in the examples.

[0029] By adding an inorganic acid to the slurry in step (iii), the impurity concentration of the manufactured titanium compound (TC) and the impurity concentration of the barium titanate particles manufactured using the titanium compound (TC) can be reduced. Furthermore, by adding an inorganic acid to the slurry in step (iii), the half-width W of the peak of the titanium compound (TC) in the X-ray diffraction spectrum in the range of 2θ = 20° to 30° can be reduced. By adding an organic acid to the slurry in step (iii), the specific surface area of ​​the manufactured titanium compound (TC) can be increased, and the lattice constant ratio c / a of the barium titanate particles manufactured using the titanium compound (TC) can be increased. Furthermore, by adding both inorganic and organic acids to the slurry in step (iii), the dispersity index Di (described later) can be reduced. Additionally, the lattice constant ratio c / a is an indicator of tetragonal crystallinity; a larger lattice constant ratio c / a indicates higher tetragonal crystallinity.

[0030] Examples of inorganic acids include nitric acid (HNO3), hydrogen chloride (HCl), and sulfuric acid (H2SO4). Nitric acid is a preferred example of an inorganic acid. Inorganic acids can also be added to the slurry in aqueous solution form. Inorganic acids may also contain phosphorus compounds (e.g., phosphoric acid). However, from the viewpoint of reducing impurities, inorganic acids preferably do not contain phosphoric acid.

[0031] Examples of organic acids include organic carboxylic acids. Specifically, examples of organic acids include citric acid, acetic acid, tartaric acid, glycine, glutamic acid, malonic acid, maleic acid, trimellitic anhydride, succinic acid, malic acid, glycolic acid, alanine, fumaric acid, oxalic acid, glutaric acid, and formic acid. Citric acid is a preferred example of an organic acid. Organic acids can also be added to the slurry in aqueous solution form.

[0032] In step (iii), the amount of inorganic acid added relative to 100 parts by mass of titanium dioxide (converted from titanium hydroxide in the above slurry) can be in the range of 1 to 20 parts by mass, or it can be in the range of 3 to 20 parts by mass, 6 to 20 parts by mass, 9 to 20 parts by mass, 10 to 20 parts by mass, or 12 to 20 parts by mass. Within these ranges, as long as the lower limit does not exceed the upper limit, the upper limit can also be 15 parts by mass, 12 parts by mass, 10 parts by mass, 9 parts by mass, or 6 parts by mass.

[0033] In step (iii), the amount of organic acid added relative to 100 parts by mass of titanium dioxide (converted from titanium hydroxide in the above slurry) can be in the range of 1 to 20 parts by mass, or it can be in the range of 3 to 20 parts by mass, 5 to 20 parts by mass, 6 to 20 parts by mass, 9 to 20 parts by mass, or 12 to 20 parts by mass. Within these ranges, as long as the lower limit does not exceed the upper limit, the upper limit can also be 15 parts by mass, 12 parts by mass, 9 parts by mass, 6 parts by mass, or 5 parts by mass.

[0034] The temperature of the slurry after adding acid is maintained in the range of 40–90°C, or it can be in the range of 60–90°C, 70–90°C, or 85–90°C. In any of these ranges, as long as the lower limit does not exceed the upper limit, the upper limit can also be 85°C, 70°C, or 60°C, or it can be less than 80°C.

[0035] In step (iii), it is preferable to add the aforementioned inorganic acid and organic acid to a slurry with a temperature in the range of 40 to 90°C. The temperature of the slurry can be controlled by the temperature of the slurry before adding the acid, the temperature of the aqueous solution of the added acid, and the temperature around the slurry. The temperature of the slurry before adding the acid can also be within the range exemplified for maintaining the temperature of the slurry after adding the acid.

[0036] Step (iii) can be performed by adding inorganic and organic acids to the slurry and then maintaining the slurry at a temperature in the range of 40–90°C for a specified holding time. The preferred holding time varies depending on the slurry temperature, but can be more than 1 hour, more than 5 hours, or less than 10 hours. The slurry is preferably maintained at the specified temperature while being stirred.

[0037] Generally, the amount of hydrated water in titanium hydroxide obtained by neutralizing titanium halide in water with an alkaline substance is not fixed. Therefore, it is inappropriate to use the mass of such titanium hydroxide as a basis for determining the amount of acid to be added to the titanium hydroxide. Therefore, the amount of acid added in step (iii) is set as a quantity based on the mass of titanium hydroxide in the slurry obtained in step (ii) converted to titanium dioxide. The mass of titanium hydroxide in the slurry obtained in step (ii) converted to titanium dioxide is determined by heating titanium hydroxide to convert it into titanium dioxide. Specifically, it is determined by the method described in the examples.

[0038] The specific surface area of ​​titanium compounds (TC) can also be 250 m². 2 / g or more, 251m 2 / g or more, 276m 2 / g or more or 300m 2 / g or more. The specific surface area of ​​titanium compounds (TC) can also be 350m². 2 / g or less or 307m 2 / g or less.

[0039] In titanium compounds (TC), the mass ratio Va of amorphous titanium hydroxide to Vc of anatase titanium dioxide (Vc / Vc) can be 0.6 or higher, 0.7 or higher, 1.0 or higher, or 1.2 or higher, or 18 or lower, 9.7 or lower, or 6.1 or lower. By making the Va / Vc ratio 0.6 or higher, the target barium titanate particles are easily obtained. The Va / Vc ratio can be increased, for example, by increasing the amount of organic acid added, decreasing the amount of inorganic acid added, lowering the holding temperature of the slurry after adding acid, or shortening the holding time.

[0040] In the manufacturing method (M), a water washing step (a) is preferably performed after step (iii) and before step (iv) to wash the titanium compound (TC) with water. Water with low impurity levels is preferably used for washing; ion-exchanged water or RO water (water permeated through a reverse osmosis membrane) may also be used. In the water washing step (a), the washing of the titanium compound (TC) is preferably continued until the conductivity of the water used for washing (e.g., filtrate) becomes 150 μS / cm or less (e.g., 50 μS / cm or less). By performing water washing in this way, barium titanate particles with particularly low impurity concentrations can be obtained.

[0041] (Process (iv)) Step (iv) is a step of synthesizing barium titanate particles by hydrothermal synthesis using a raw material containing a titanium compound (TC). The raw material for hydrothermal synthesis includes a titanium source and a barium source. The titanium source uses a titanium compound (TC). Examples of barium sources include barium compounds, such as barium hydroxide.

[0042] The titanium compound (titanium hydroxide) obtained from step (ii) is preferably used as a raw material for hydrothermal synthesis in step (iv) without the addition of at least one compound selected from the group consisting of phosphorus compounds and silicon compounds. This yields barium titanate particles with low impurity concentration. For example, it is preferable that at least one compound selected from the group consisting of phosphorus compounds and silicon compounds is not added when acid is added to the slurry in step (iii). Typically, in step (iii), only acid or an aqueous solution of acid is added to the slurry. Furthermore, typically, the titanium compound (TC) prepared in step (iii) does not react or mix with other compounds, and is used as a raw material for hydrothermal synthesis in step (iv). For example, the titanium compound (TC) prepared in step (iii) is preferably used as a raw material in step (iv) without the addition of at least one compound selected from the group consisting of phosphorus compounds and silicon compounds. Examples of phosphorus compounds include phosphoric acid. Examples of silicon compounds include silicon dioxide (e.g., silica sol).

[0043] Since the synthesis of barium titanate using hydrothermal synthesis has been carried out in the past, it can also be carried out under known conditions. In one example of hydrothermal synthesis, a titanium compound (TC) and a barium compound are reacted in an aqueous liquid (e.g., water) at a pressure of 0.2 MPa or higher and a temperature of 120°C or higher. The reaction pressure can also be 0.2 MPa or higher, 0.7 Pa or higher, 1.5 MPa or lower, or 1.3 MPa or lower. The reaction temperature can also be 120°C or higher, 165°C or higher, 198°C or lower, or 191°C or lower. The reaction time can also be 18 hours or higher, 55 hours or higher, 200 hours or lower, or 65 hours or lower. In step (iv), a slurry containing only titanium compound (TC) and barium compound as raw materials for barium titanate particles can also be used for hydrothermal synthesis. A preferred example of the slurry used for hydrothermal synthesis in step (iv) is that it does not contain silicon compounds, phosphorus compounds, sodium compounds, chlorine compounds, sulfur compounds, or their solutions.

[0044] Barium titanate was synthesized via hydrothermal synthesis in step (iv). The barium titanate synthesized via the above steps has the specified physical properties as shown in the examples.

[0045] (Barium titanate particles) Hereinafter, the barium titanate particles of this embodiment will sometimes be referred to as "barium titanate particles (P)" or "particles (P)". The barium titanate particles (P) have the following characteristics (1) to (4).

[0046] (1) The lattice constant ratio c / a is above 1.0095.

[0047] (2) By mass ratio, the content of Si is less than 10 ppm, the content of P is less than 10 ppm, the content of Na is less than 10 ppm, the content of Cl is less than 15 ppm, and the content of S is less than 10 ppm.

[0048] (3) The dispersion index Di calculated by the following formula based on the image of the scanning electron microscope is below 700.

[0049] Dispersion index Di = 100 × (maximum particle size Dmax) / (minimum particle size Dmin) (4) The average particle size Dav is above 50nm and below 200nm.

[0050] Barium titanate particles (P) can be manufactured by manufacturing method (M). The matters described with respect to manufacturing method (M) also apply to particles (P).

[0051] Barium titanate particles (P) contain a tetragonal crystal structure. Regarding the above characteristic (1), the so-called lattice constant ratio c / a is the ratio obtained by dividing the c-axis length c of a unit lattice of the barium titanate crystal by the a-axis length a of a unit lattice. The lattice constant ratio c / a can be determined by X-ray diffraction. Specifically, it can be determined by the method described in the examples. The lattice constant ratio c / a can also be 1.0096 or more or 1.0097 or more. The lattice constant ratio c / a can also be 1.0110 or less (e.g., 1.0098 or less).

[0052] The preferred concentration of impurities in barium titanate particles (P) is as follows: The Cl content in the particles (P) may also be less than 11 ppm, less than 8 ppm, or less than 6 ppm. The P, Na, and S contents in the barium titanate particles (P) may also be less than 10 ppm. Their contents (ppm) are mass ratios. The contents of the above elements in the barium titanate particles (P) can be determined by the methods described in the examples.

[0053] Regarding the aforementioned characteristic (3), the dispersion index Di can also be below 550, below 500, or below 480. The dispersion index Di is above 1. The smaller the dispersion index Di, the smaller the deviation in particle (P) size and the fewer outliers.

[0054] Regarding the above-mentioned feature (4), the average particle size Dav of barium titanate particles (P) can be above 100 nm, above 120 nm or above 121 nm, or below 150 nm, below 141 nm or below 140 nm.

[0055] The coefficient of variation (CV) relating to the particle size of barium titanate (P) is expressed by the following formula. In the following formula, ρ is the standard deviation of the particle size (P), and Dav is the average particle size (P).

[0056] CV(%) = 100 × ρ / Dav The coefficient of variation (CV) for barium titanate particles (P) can also be below 25.0% or 20.0%. The closer the coefficient of variation (CV) is to zero, the smaller the deviation in particle size (P). Therefore, a low coefficient of variation (CV) is preferred.

[0057] The average value Av(Ci) of the sphericity Ci of barium titanate particles (P) can also be 0.95 or higher, 0.96 or higher, or 0.97 or higher. The sphericity Ci is calculated using the following formula. In the formula, S is the area of ​​the particle, and L is the perimeter of the particle. S and L can be determined from images obtained using a scanning electron microscope. In the case of a perfect circle, the sphericity Ci is 1.

[0058] Circularity Ci = 4πS / L 2 In this specification, the particle size is the spherical equivalent diameter. The average particle size Dav, standard deviation ρ of the particle size, maximum particle size Dmax, minimum particle size Dmin, average sphericity Ci Av(Ci), and dispersity index Di of the particles (P) are determined by analyzing images taken using a scanning electron microscope. The number of particles used in the analysis is in the range of 400 to 800. Specifically, the above evaluation values ​​can be obtained by the methods described in the examples.

[0059] This disclosure provides a titanium compound (TC) and a method (Mt) for manufacturing the titanium compound (TC). The manufacturing method (Mt) includes the above-described steps (i), (ii), and (iii). The manufacturing method (Mt) may further include the above-described water washing step (a) after step (iii). The manufacturing method (Mt) may also include a water washing step (a) and a drying step of drying the water-washed titanium compound (TC) after step (iii). Steps (i) to (iii) and the water washing step (a) have been described above, so repeated descriptions are omitted. The drying step is not particularly limited, and a general drying step may be used.

[0060] Titanium compound (TC) is manufactured by a manufacturing method (Mt). Titanium compound (TC) possesses the characteristics described above. Titanium compound (TC) is preferably used as a raw material for the synthesis (especially hydrothermal synthesis) of barium titanate particles.

[0061] Example The present disclosure is further described in detail below through embodiments, but the present disclosure is not limited to the following embodiments. In these embodiments, barium titanate particles are prepared under different conditions. The various preparation conditions are described below.

[0062] (The creation of particle A1) Particle A1, which is a barium titanate particle, is prepared according to the following procedure.

[0063] (1) Process 1 First, pure water was prepared in a reaction vessel. Then, titanium tetrachloride and sodium hydroxide were simultaneously neutralized by adding an aqueous solution of titanium tetrachloride and an aqueous solution of sodium hydroxide to the pure water in the reaction vessel. The titanium tetrachloride aqueous solution used was an aqueous solution with a concentration of 44 g / L, converted from titanium dioxide. The concentration of titanium dioxide was determined from the formula weights of titanium tetrachloride (189.7) and titanium dioxide (79.9). At this time, the aqueous solution of titanium halide and the aqueous solution of sodium hydroxide were simultaneously neutralized under conditions of pH 4.5–5.5 and temperature 35–45°C. Specifically, the reaction solution obtained by adding the aqueous solution of titanium halide and the aqueous solution of sodium hydroxide to the pure water was stirred and maintained for 4 hours at a temperature of 35–45°C and pH 4.5–5.5. A slurry of titanium hydroxide was obtained by utilizing this simultaneous neutralization reaction. Then, the obtained titanium hydroxide slurry was stirred for 4 hours while maintaining it at 40°C.

[0064] (2) Process 2 The resulting titanium hydroxide slurry is then filtered and washed with water. Washing continues until the conductivity of the resulting water (filtrate) reaches 1 mS / cm. This process yields a titanium hydroxide filter cake. The resulting titanium hydroxide filter cake is then dispersed in pure water to obtain a slurry with a titanium dioxide concentration of 50 g / L.

[0065] The titanium dioxide equivalent mass of titanium hydroxide is determined using the following procedure. First, a portion of the titanium hydroxide from the slurry obtained in step 2 is taken as a sample and filtered to obtain a titanium hydroxide filter cake. Then, the titanium hydroxide filter cake is heated to 1000°C, converting it into titanium dioxide. By measuring the mass of this titanium dioxide, the titanium dioxide equivalent mass of the titanium hydroxide in the slurry is determined.

[0066] (3) Process 3 Nitric acid and citric acid are added to the slurry obtained from step 2. At this point, 10.0 parts by mass of nitric acid and 5.0 parts by mass of citric acid are added relative to 100 parts by mass of titanium dioxide (equivalent to titanium hydroxide). After adding nitric acid and citric acid to the slurry, it is heated to 85°C and stirred for 5 hours. The resulting slurry is cooled to room temperature and then filtered and washed with water. Washing continues until the conductivity of the washed water (filtrate) reaches 150 μS / cm. This process yields a filter cake of titanium compound.

[0067] (4) Process 4 177 ml of pure water and 330 g of barium hydroxide octahydrate were added to a reaction vessel (capacity: 5 L). The liquid in the vessel was then heated to 100 °C, thereby dissolving the barium hydroxide octahydrate in the water to prepare a barium hydroxide aqueous solution.

[0068] The filter cake of the titanium compound obtained in step 3 was then dispersed in pure water to prepare a slurry of the titanium compound. This slurry was heated to 100°C. The slurry (temperature: 100°C) was then mixed with the above-mentioned barium hydroxide aqueous solution (temperature: 100°C). This process was repeated to obtain a slurry of the barium titanate precursor (concentration: 0.74 g / L converted to BaTiO3). The Ba / Ti molar ratio at the point when the addition of the titanium compound slurry to the barium hydroxide aqueous solution was complete was 2.0.

[0069] The slurry of the above-mentioned barium titanate precursor was added to a container in an autoclave and reacted at 190°C for 65 hours to carry out the hydrothermal synthesis of barium titanate particles. The reaction product in the autoclave was then cooled to room temperature. The resulting reaction product was filtered, washed with water, and dried at 95°C. This process yielded barium titanate particles (particles A1).

[0070] (Particles A2~A11, C1~C2) As shown in Table 1, the amount of acid added in step 3 above is changed. Otherwise, particles A2 to A11 and C1 to C2 (barium titanate particles) are produced by the same method and conditions as the production of particles A1.

[0071] (Particles A12~A14) In step 3, as shown in Table 1, the temperature of the slurry is changed after adding acid and heating. Otherwise, particles A12 to A14 (barium titanate particles) are produced using the same method and conditions as particles A1. The stirring time after adding acid and heating is set to 5 hours, the same as in step 3 for particles A1. Furthermore, steps 1, 2, 3, and 4 in the production of particles A1 to A14 correspond to steps (i), (ii), (iii), and (iv) above, respectively.

[0072] (Particle C3) Prepare particles C3 as barium titanate particles according to the following procedure.

[0073] (1) Process 1 First, pure water is prepared in the reaction vessel. Then, an aqueous solution of titanium tetrachloride and an aqueous solution of sodium hydroxide are simultaneously added to the pure water in the reaction vessel, thereby neutralizing the titanium tetrachloride and sodium hydroxide simultaneously. The titanium tetrachloride aqueous solution used is an aqueous solution with a concentration of 44 g / L, converted from titanium dioxide. At this time, the aqueous solution of titanium halide and the aqueous solution of sodium hydroxide are simultaneously neutralized under conditions of pH range 2.0 to 3.0 and temperature range 45 to 55°C. Specifically, the reaction solution obtained by adding the aqueous solution of titanium halide and the aqueous solution of sodium hydroxide to the pure water is stirred and maintained for 4 hours at a temperature of pH range 2.0 to 3.0 and 45 to 55°C. By utilizing this simultaneous neutralization reaction, a slurry containing titanium hydroxide is obtained. Then, the obtained titanium hydroxide-containing slurry is stirred while maintaining it at 60°C for 4 hours.

[0074] (2) Process 2 The resulting titanium hydroxide-containing slurry was then filtered and washed with water to obtain a filter cake of titanium compounds. Washing continued until the conductivity of the resulting water (filtrate) reached 150 μS / cm. This process was repeated to obtain a filter cake containing titanium hydroxide.

[0075] Then, without performing step 3 above, the titanium hydroxide-containing compound obtained in step 2 is used as the titanium compound in step 4. Otherwise, hydrothermal synthesis and subsequent steps are performed according to the methods and conditions described in step 4 above. This process yields particles C3.

[0076] (C4 particles) Except for the different preparation method of the titanium compound slurry in step 4, particles C4 are prepared using the same method and conditions as particles A1. Specifically, the filter cake of the titanium compound obtained in step 3 is dispersed in pure water, and 2.0 parts by mass of monoammonium phosphate (NH4H2PO4) converted to P2O5 are added to 100 parts by mass relative to the mass of titanium dioxide in titanium hydroxide. The titanium compound slurry is prepared in this manner. That is, in the preparation of particles C4, the titanium compound with added phosphorus is used as the raw material in the hydrothermal synthesis of step 4. Here, the mass converted to P2O5 is determined using the formula weight of monoammonium phosphate and the formula weight of P2O5.

[0077] (Particle C5) Except for the different preparation method of the titanium compound slurry in step 4, particles C5 are prepared using the same method and conditions as particles A1. Specifically, the filter cake of the titanium compound obtained in step 3 is dispersed in pure water, and 2.0 parts by mass of spherical silica (silica sol, manufactured by Sakai Chemical Industry Co., Ltd.) is added to 100 parts by mass relative to the titanium dioxide mass of titanium hydroxide. The titanium compound slurry is prepared in this way. That is, in the preparation of particles C5, the titanium compound with added silicon compound is used as the raw material in the hydrothermal synthesis of step 4.

[0078] (Particle C6) Except for the different preparation method of the titanium compound slurry in step 4, particles C6 are prepared using the same method and conditions as particles A1. Specifically, the filter cake of the titanium compound obtained in step 3 is dispersed in pure water, and 2.0 parts by mass of monoammonium phosphate (NH4H2PO4) and 2.0 parts by mass of spherical silica (silica sol, manufactured by Sakai Chemical Industry Co., Ltd.) are added, equivalent to 100 parts by mass of titanium dioxide (equivalent to titanium hydroxide). The titanium compound slurry is prepared in this manner. That is, in the preparation of particles C6, a titanium compound with added phosphorus and silicon compounds is used as the raw material in the hydrothermal synthesis of step 4.

[0079] (evaluate) The titanium compounds used in the synthesis of barium titanate particles and the barium titanate particles were evaluated using the following methods. Additionally, regarding the titanium compounds used in the synthesis of particle C3, the titanium hydroxide-containing material obtained in step 2 was evaluated.

[0080] (Specific surface area) Specific surface area was determined using the BET method. Specifically, the specific surface area of ​​particles was determined using the BET one-point method with a continuous flow surface area measuring device manufactured by Mounttech Corporation (with an environmental countermeasures unit added to the Macsorb HM-1201).

[0081] (Average particle size Dav, roundness Ci, coefficient of variation CV, dispersity index Di) The average particle size Dav, roundness Ci, coefficient of variation CV, and dispersion index Di are determined by acquiring particle images using a scanning electron microscope and then processing those images. Specifically, they are determined using the following procedure.

[0082] First, SEM images of the particles (magnification: 50,000x) were obtained using a scanning electron microscope (SU8020, Hitachi High-Technologies Co., Ltd.). Then, image-resolution particle size distribution measurement software (Mac-View) was used to analyze the particles present in the SEM images, thereby calculating the average particle size, the arithmetic mean of the roundness Ci (calculated from the particle area S and the particle perimeter L) Av(Ci), the maximum particle size Dmax, the minimum particle size Dmin, and the coefficient of variation CV. Furthermore, the particle size of each particle was calculated as the equivalent diameter of a circle. The average particle size was obtained by arithmetically averaging the particle sizes (equivalent diameters of all particles). The maximum particle size Dmax is the largest particle size among the analyzed particles. The minimum particle size Dmin is the smallest particle size among the analyzed particles. The dispersity index Di was calculated from the maximum particle size Dmax and the minimum particle size Dmin. The number of analyzed particles ranged from 400 to 800.

[0083] (Lattice constant ratio c / a, ratio Va / Vc, half-width W of the specified peak for titanium compounds (TC)) The lattice constants of the particles, the ratios c / a and Va / Vc, and the half-width W of the peaks of titanium compounds (TC) in the range of 2θ = 20° to 30° were determined by X-ray diffraction analysis. Specifically, they were determined using the following method.

[0084] The particles of the target sample were placed in an X-ray diffraction apparatus, and XRD profiles were measured in the range of 2θ = 20° to 120°. A BRUKER D8 ADVANCE X-ray diffraction apparatus was used. The obtained XRD profiles were processed using dedicated software (TOPAS BBQ), and peak fitting and Rietveld analysis were performed. Through this analysis, the ratio of the mass Va of tetragonal titanium hydroxide to the mass Vc of anatase titanium dioxide (Va / Vc) was determined, along with the half-width W of the peak for titanium compounds (TC) in the range of 2θ = 20° to 30°.

[0085] (Content of Si, P, and Na) The content of Si, P and Na in the particles was determined by standard curve method using a multi-element sequential ICP emission spectrophotometer (PS3520DDII, Hitachi High-TechScience Co., Ltd.).

[0086] (Content of Cl and S) The content of Cl and S in the particles was determined by standard curve method using a combustion apparatus (AQF-2100H, Mitsubishi Chemical Analytech) and a Thermo Scientific Dionex ion chromatograph (Thermo Fisher Scientific).

[0087] Table 1 shows some of the conditions for steps 3 and 4 in the production of each particle. The “Amount Added” in Table 1 is the amount in 100 parts by mass relative to titanium dioxide in titanium hydroxide. The “Heating Temperature” in Table 1 is the heating temperature in step 3. Note that step 3 was not performed in the production of particle C3.

[0088] Table 2 shows the evaluation results of the titanium compound obtained in step 3. However, for particle C3, Table 2 shows the evaluation results of the titanium hydroxide-containing particles obtained in step 2.

[0089] Table 3 shows the lattice constant c / a and the relevant evaluation results of impurities of the barium titanate particles obtained by hydrothermal synthesis in step 4.

[0090] Table 4 shows other evaluation results for the barium titanate particles obtained from the hydrothermal synthesis in step 4. In Table 4, the number of resolved particles indicates the number of particles used for analysis during image resolution.

[0091] Particles A1 to A14 are barium titanate particles (P) manufactured using the manufacturing method (M) of this disclosure. On the other hand, particles C1 to C6 are comparative example barium titanate particles manufactured using the manufacturing method of the comparative examples. Figure 1 The image shown is a partial example of a SEM image of particle A1 (barium titanate particle). Furthermore, in Figure 2 The image shown is a portion of an example SEM image of particle C3 (barium titanate particles). Figure 1 and Figure 2 As shown, particle A1 has a smaller deviation in particle size and a more consistent shape compared to particle C3.

[0092] As shown in Tables 3 and 4, barium titanate particles with high crystallinity (tetragonal crystallinity), small deviation in particle size distribution, a specified average particle size, and low impurity concentration can be obtained according to manufacturing method (M).

[0093] Industrial availability This invention can be applied to barium titanate particles and their manufacturing methods.

[0094] While the present invention has been described with respect to preferred embodiments, such disclosure is not intended to be limiting. Those skilled in the art to which this invention pertains will naturally recognize various variations and modifications upon reading the foregoing disclosure. Therefore, the appended claims should be interpreted as encompassing all modifications and changes that do not depart from the true spirit and scope of the invention.

Claims

1. A method for manufacturing barium titanate particles, comprising the following steps: Step (i) involves simultaneously neutralizing an aqueous solution of titanium halide and an alkaline substance under conditions ranging from pH 4.5 to 5.5 and temperature 35 to 45°C to prepare titanium hydroxide. Step (ii) involves preparing a slurry of titanium hydroxide by washing the titanium hydroxide with water and then dispersing it in water. Step (iii) involves adding 1 to 20 parts by mass of an inorganic acid and 1 to 20 parts by mass of an organic acid (equivalent to 100 parts by mass of titanium dioxide in relation to the titanium hydroxide) to the slurry, and then maintaining the slurry at a temperature in the range of 40 to 90°C to prepare a titanium compound; and Step (iv) involves the synthesis of barium titanate particles using a hydrothermal synthesis of a raw material containing the titanium compound. The titanium compound contains amorphous titanium hydroxide and anatase titanium dioxide; The specific surface area of ​​the titanium compound is 250 m². 2 / g or more.

2. The manufacturing method according to claim 1, wherein, In the titanium compound, the mass ratio Va of amorphous titanium hydroxide to Vc of anatase titanium dioxide is 0.6 or higher.

3. The production method according to claim 1 or 2, wherein The titanium halide is titanium tetrachloride.

4. A barium titanate particle having a lattice constant ratio c / a of 1.0095 or higher. By mass ratio, the content of Si is less than 10 ppm, the content of P is less than 10 ppm, the content of Na is less than 10 ppm, the content of Cl is less than 15 ppm, and the content of S is less than 10 ppm. The dispersion index Di, calculated from the image obtained by scanning electron microscopy using the following formula, is below 700. Dispersion index Di = 100 × (maximum particle size) / (minimum particle size) The average particle size is above 50nm and below 200nm.

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