Barium titanate particles and method for producing the same

Abstract

The disclosed method for producing barium titanate particles includes the steps of: (i) preparing titanium hydroxide by simultaneously neutralizing an aqueous solution of titanium halide and an alkaline substance under predetermined conditions; (ii) preparing a slurry of the titanium hydroxide; (iii) preparing a titanium compound by adding predetermined amounts of inorganic and organic acids to the slurry and then maintaining the slurry at a temperature in the range of 40 to 90°C; and (iv) synthesizing barium titanate particles by hydrothermal synthesis using raw materials 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 m. 2 / g or more.

Description

[Technical Field]

[0001] The present disclosure relates to barium titanate particles and methods for making the same. [Background technology]

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

[0003] Claim 1 of Patent Document 1 (JP 8-208228 A) describes a process comprising: "(a) a step of forming an aqueous slurry of precipitated titanium hydroxide having a pH of 4.5 to 6.5 by adding a water-soluble alkali to an aqueous solution of a water-soluble titanium salt having a concentration of 0.5 to 10% by weight as TiO2 at a temperature of 40 to 75°C at a rate of 0.033 to 2 equivalents of alkali per equivalent of acid radical contained in the titanium salt at a rate of 1 minute; and (b) a step of recovering precipitated titanium hydroxide by removing impurities and water contained in the aqueous slurry of precipitated titanium hydroxide obtained in (a)." and (c) step of mixing an aqueous medium with the precipitated titanium hydroxide obtained in step (b) and a water-soluble acid in an amount of 0.05 to 0.50 equivalents per mole of the precipitated titanium hydroxide to form a reaction mixture containing the precipitated titanium hydroxide at a concentration of 1 to 45% by weight in terms of TiO2, and then, while maintaining the temperature of the reaction mixture at a temperature between the freezing point and the boiling point, reacting the precipitated titanium hydroxide in this reaction mixture with the water-soluble acid until an aqueous sol is formed containing amorphous titanium oxide having a particle size of 20 to 300 nm at a concentration of 1 to 45% by weight in terms of TiO2.

[0004] Claim 1 of Patent Document 2 (JP 2014-133688 A) describes "a titanium dioxide solution characterized by being a weakly acidic to neutral, colorless, transparent liquid obtained by heat-treating titanium hydroxide produced by hydrolyzing a titanium compound with hydrogen carbonate and ammonium citrate in an aqueous solvent."

[0005] Claim 1 of Patent Document 3 (JP 2015-224147 A) describes a "method for producing barium titanate, characterized by using titanium dioxide TiO2 sol and an aqueous barium hydroxide solution Ba(OH)2 as starting materials and carrying out a hydrothermal reaction using supercritical water in a flow reactor."

[0006] Claim 2 of Patent Document 4 (JP 2019-085282 A) states, "A titanium halide aqueous solution and an alkaline substance are simultaneously neutralized under conditions of pH 4.8 to 5.2 and a temperature of 40 to 55°C to produce a titanium dioxide powder having a BET specific surface area of 300 m². 2 A step A of obtaining titanium hydroxide having a crystallite diameter of 20 Å or more and a step B of washing the titanium hydroxide with water and dispersing it in water to obtain a slurry containing the titanium hydroxide, and then heating the slurry to a temperature of 80 to 90°C in the presence of an inorganic acid and an organic acid at a pH of 1.0 to 3.0, followed by washing with water, and dispersing the titanium hydroxide thus treated in water to obtain a slurry containing the titanium hydroxide; This slurry was converted to titanium oxide (TiO2) based on the titanium hydroxide. (a) 1.0 to 5.0% by weight of a phosphorus compound or 2.0 to 5.0% by weight of a silicon compound, or (b) a step C of adding a phosphorus compound and a silicon compound in a total amount of 1.0 to 5.0% by weight or less, washing the resulting mixed slurry with water, and drying it; "A method for producing titanium hydroxide, comprising: [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-208228 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-133688 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-224147 [Patent Document 4] Japanese Patent Application Publication No. 2019-085282 Summary of the Invention [Problem to be solved by the invention]

[0008] Currently, with the miniaturization and high performance of electronic devices, high properties are also required for barium titanate, which is the raw material for electronic devices. In this situation, one of the objects of the present disclosure is to provide barium titanate particles with high crystallinity, small variation in particle size distribution, a predetermined average particle size, and a low impurity concentration, and a method for producing the same. [Means for solving the problem]

[0009] One aspect of the present disclosure is a method for producing barium titanate particles, comprising: (i) a step of preparing titanium hydroxide by simultaneously neutralizing an aqueous solution of titanium halide and an alkaline substance at a pH in the range of 4.5 to 5.5 and a temperature in the range of 35 to 45°C; (ii) preparing a slurry of the titanium hydroxide by washing the titanium hydroxide with water and then dispersing the titanium hydroxide in water; a step (iii) of adding 1 to 20 parts by mass of an inorganic acid and 1 to 20 parts by mass of an organic acid to the slurry relative to 100 parts by mass of the titanium hydroxide converted into titanium dioxide, and then maintaining the slurry at a temperature in the range of 40 to 90°C to prepare a titanium compound; and (iv) a step of synthesizing barium titanate particles by hydrothermal synthesis using 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 m 2The present invention relates to a method for producing barium titanate particles having a viscosity of 1 / g or more.

[0010] Another aspect of the present disclosure is a barium titanate particle comprising: The lattice constant ratio c / a is 1.0095 or more, The Si content is 10 ppm or less, the P content is 10 ppm or less, the Na content is 10 ppm or less, the Cl content is 15 ppm or less, and the S content is 10 ppm or less, by mass ratio; The dispersibility index Di calculated based on a scanning electron microscope image using the following formula is 700 or less, Dispersity index Di=100×(maximum particle size) / (minimum particle size) The present invention relates to barium titanate particles having an average particle size of 50 nm or more and 200 nm or less. [Effects of the Invention]

[0011] According to the present disclosure, barium titanate particles having high crystallinity, small variation in particle size distribution, a predetermined average particle size, and a low impurity concentration can be obtained. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows an SEM image of an example of a particle produced by the production method according to the present disclosure. [Figure 2] FIG. 2 shows an SEM image of an example of a particle produced by the comparative manufacturing method. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be used as examples. However, other numerical values and other materials may be used as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be interpreted as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits of numerical values related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified. In this specification, the term "particle" may be interpreted as "powder."

[0014] (Method of manufacturing barium titanate particles) The production method according to this embodiment may be hereinafter referred to as “production method (M).” Production method (M) is a method for producing barium titanate particles.

[0015] The manufacturing method (M) includes steps (i), (ii), (iii), and (iv) in this order. According to the manufacturing method (M), as shown in the examples, barium titanate particles (barium titanate powder) having high crystallinity, small particle size distribution variation, a predetermined average particle size, and a low impurity concentration can be obtained. Each step of the manufacturing method (M) is described below.

[0016] (Step (i)) Step (i) is a step of preparing titanium hydroxide by simultaneously neutralizing an aqueous solution of titanium halide with an alkaline substance at a pH in the range of 4.5 to 5.5 and a temperature in the range of 35 to 45°C. The pH and temperature refer to the pH and temperature of the reaction solution produced by mixing the aqueous solution of titanium halide with the alkaline substance during simultaneous neutralization. Titanium hydroxide is prepared while the pH and temperature of the reaction solution are maintained within the above ranges. In step (i), titanium dioxide (e.g., anatase titanium dioxide) is not usually produced.

[0017] The pH of the reaction solution may be 4.5 or higher, 5.0 or higher, or greater than 5.0. The pH of the reaction solution may be 5.5 or lower, 5.0 or lower, or less than 5.0. The temperature of the reaction solution may be 35°C or higher, 40°C or higher, or greater than 40°C. The temperature of the reaction solution may be 45°C or lower, 40°C or lower, or less than 40°C.

[0018] After mixing the entire amount of the titanium halide aqueous solution with the entire amount of the alkaline substance, the reaction solution is preferably maintained at a temperature in the range of 35 to 45°C for 10 hours or more (for example, 15 hours or more). There is no particular upper limit to the time for maintaining the reaction solution at a temperature in the range of 35 to 45°C, but it may be 40 hours or less. The reaction solution is preferably maintained at a predetermined temperature while stirring.

[0019] In this specification, "simultaneous neutralization of an aqueous solution of titanium halide and an alkaline substance" means that the aqueous solution of titanium halide and the alkaline substance are simultaneously introduced into a container (a reaction solution holding container) and mixed in the container. In this case, the alkaline substance may be introduced into the container in the form of an aqueous solution. By carrying out simultaneous neutralization, the pH of the reaction solution can be easily maintained within a predetermined range. As a result, the desired barium titanate particles can be obtained.

[0020] The titanium halide aqueous solution and the alkaline substance (aqueous solution of the alkaline substance) may be gradually added to the container while maintaining the same ratio. In one example of simultaneous neutralization, water is placed in a container beforehand, and then the titanium halide aqueous solution and the alkaline substance aqueous solution are gradually added to the container at a predetermined ratio. The ratio of the titanium halide aqueous solution and the alkaline substance aqueous solution may be selected according to the concentrations of these aqueous solutions so that the pH of the reaction solution is within the above range.

[0021] Neutralization carried out by placing an aqueous solution of titanium halide in a container beforehand and then adding an alkaline substance (or an aqueous solution of an alkaline substance) to it is not simultaneous neutralization. Similarly, neutralization carried out by placing an aqueous solution of an alkaline substance in a container beforehand and then adding an aqueous solution of titanium halide to it is not simultaneous neutralization. With these methods that are not simultaneous neutralization, it is difficult to maintain a constant pH in the reaction solution.

[0022] Examples of titanium halides include titanium tetrachloride, etc. Examples of alkaline substances include alkali metal hydroxides (sodium hydroxide, potassium hydroxide, etc.), etc. However, substances other than these may also be used.

[0023] The temperature of the reaction solution can be controlled by controlling the temperature of the water in the vessel, the temperature of the aqueous solution introduced into the vessel, and the ambient temperature (temperature around the vessel) in which step (i) is carried out.

[0024] (Step (ii)) In step (ii), titanium hydroxide is washed with water and then dispersed in water to prepare a titanium hydroxide slurry. Water with a low impurity content is preferably used for washing titanium hydroxide and for dispersing titanium hydroxide, and ion-exchanged water or RO water (water that has passed through a reverse osmosis membrane) may also be used.

[0025] In step (ii), the titanium hydroxide is preferably washed with water until the conductivity of the water used for washing (e.g., the filtrate) becomes 1 mS / cm or less (e.g., 0.1 mS / cm or less). By washing with water in this manner, barium titanate particles with a particularly low impurity concentration can be obtained.

[0026] (Step (iii)) Step (iii) is a step of preparing a titanium compound by adding 1 to 20 parts by mass of an inorganic acid and 1 to 20 parts by mass of an organic acid to the slurry, relative to 100 parts by mass of titanium hydroxide in the slurry, calculated as titanium dioxide, and then maintaining the slurry at a temperature in the range of 40 to 90°C. The titanium compound prepared in step (iii) may be referred to as "titanium compound (TC)" below. The titanium compound (TC) contains amorphous titanium hydroxide and anatase titanium dioxide. The specific surface area of the titanium compound (TC) is 250 m 2 The specific surface area can be determined by the BET method. Specifically, it can be determined by the method described in the Examples.

[0027] Adding an inorganic acid to the slurry in step (iii) can reduce the impurity concentration of the titanium compound (TC) produced and the impurity concentration of barium titanate particles produced using the titanium compound (TC). Furthermore, adding an inorganic acid to the slurry in step (iii) can reduce the half-width W of the peak in the 2θ range of 20° to 30° in the X-ray diffraction spectrum of the titanium compound (TC). Adding an organic acid to the slurry in step (iii) can increase the specific surface area of the titanium compound (TC) produced and the lattice constant ratio c / a of the barium titanate particles produced using the titanium compound (TC). Furthermore, adding an inorganic acid and an organic acid to the slurry in step (iii) can reduce the dispersity index Di, which will be described later. The lattice constant ratio c / a is an index of tetragonality, and a larger lattice constant ratio c / a indicates a higher tetragonality.

[0028] Examples of inorganic acids include nitric acid (HNO), hydrogen chloride (HCl), and sulfuric acid (HSO). A preferred example of the inorganic acid is nitric acid. The inorganic acid may be added to the slurry in the form of an aqueous solution. The inorganic acid may contain a phosphorus compound (e.g., phosphoric acid). However, in order to reduce impurities, it is preferable that the inorganic acid does not contain phosphoric acid.

[0029] 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. A preferred example of an organic acid is citric acid. The organic acid may be added to the slurry in the form of an aqueous solution.

[0030] In step (iii), the amount of inorganic acid added per 100 parts by mass of titanium hydroxide in the slurry, calculated as titanium dioxide, is in the range of 1 to 20 parts by mass, and may 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, the upper limit may be 15 parts by mass, 12 parts by mass, 10 parts by mass, 9 parts by mass, or 6 parts by mass, as long as the lower limit is not equal to or greater than the upper limit.

[0031] In step (iii), the amount of organic acid added per 100 parts by mass of titanium hydroxide in the slurry, calculated as titanium dioxide, is in the range of 1 to 20 parts by mass, and may 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, the upper limit may be 15 parts by mass, 12 parts by mass, 9 parts by mass, 6 parts by mass, or 5 parts by mass, as long as the lower limit is not equal to or greater than the upper limit.

[0032] The temperature at which the slurry is maintained after the addition of the acid is in the range of 40 to 90° C., and may be in the range of 60 to 90° C., 70 to 90° C., or 85 to 90° C. In any of these ranges, the upper limit may be 85° C., 70° C., or 60° C., or may be less than 80° C., as long as the lower limit is not equal to or greater than the upper limit.

[0033] In step (iii), the inorganic acid and organic acid are preferably added to a slurry having 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 the acid is added, the temperature of the aqueous solution of the acid to be added, the ambient temperature of the slurry, etc. The temperature of the slurry before the acid is added may be within the range exemplified for the temperature at which the slurry is maintained after the acid is added.

[0034] Step (iii) can be carried out by adding an inorganic acid and an organic acid to a slurry, and then maintaining the slurry at a temperature in the range of 40 to 90°C for a predetermined period of time. The preferable maintenance period varies depending on the temperature of the slurry, but may be 1 hour or more, 5 hours or more, or 10 hours or less. The slurry is preferably maintained at the predetermined temperature while being stirred.

[0035] Generally, titanium hydroxide obtained by neutralizing titanium halide with an alkaline substance in water has an indefinite amount of water of hydration, etc. Therefore, it is not appropriate to determine the amount of acid to be added to titanium hydroxide based on the mass of such titanium hydroxide. Therefore, the amount of acid added in step (iii) is based on the mass of titanium hydroxide in the slurry obtained in step (ii) when converted to titanium dioxide. The mass of titanium hydroxide in the slurry obtained in step (ii) converted to titanium dioxide can be determined by heating titanium hydroxide to convert it to titanium dioxide. Specifically, it can be determined by the method described in the Examples.

[0036] The specific surface area of titanium compounds (TC) is 250m 2 / g or more, and 251m 2 / g or more, 276m2 / g or more, or 300m 2 The specific surface area of the titanium compound (TC) may be 350 m / g or more. 2 / g or less, or 307m 2 / g or less.

[0037] In the titanium compound (TC), the ratio Va / Vc of the mass Va of amorphous titanium hydroxide to the mass Vc of anatase titanium dioxide may be 0.6 or more, 0.7 or more, 1.0 or more, or 1.2 or more, and may be 18 or less, 9.7 or less, or 6.1 or less. By setting the ratio Va / Vc to 0.6 or more, the desired barium titanate particles are more easily obtained. The ratio Va / Vc can be increased, for example, by increasing the amount of organic acid added, reducing the amount of inorganic acid added, lowering the temperature at which the slurry is maintained after acid addition, or shortening the maintenance time.

[0038] The manufacturing method (M) preferably includes a water-washing step (a) of washing the titanium compound (TC) with water after step (iii) and before step (iv). The water used for washing is preferably water with low impurities, and ion-exchanged water or RO water (water passed through a reverse osmosis membrane) may be used. In the water-washing step (a), the titanium compound (TC) is preferably washed with water until the conductivity of the water used for washing (e.g., filtrate) reaches 150 μS / cm or less (e.g., 50 μS / cm or less). By washing in this manner, barium titanate particles with a particularly low impurity concentration can be obtained.

[0039] (Step (iv)) Step (iv) is a step of synthesizing barium titanate particles by hydrothermal synthesis using raw materials containing a titanium compound (TC). The raw materials for hydrothermal synthesis include a titanium source and a barium source. The titanium source is a titanium compound (TC). Examples of barium sources include barium compounds, such as barium hydroxide.

[0040] The titanium compound (titanium hydroxide) obtained in 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 allows for the production of barium titanate particles with a low impurity concentration. For example, when adding an acid to the slurry in step (iii), it is preferable not to add at least one compound selected from the group consisting of phosphorus compounds and silicon compounds. Typically, in step (iii), only an acid or an aqueous solution of an acid is added to the slurry. Also, typically, the titanium compound (TC) prepared in step (iii) is used as a raw material for hydrothermal synthesis in step (iv) without reacting or mixing with other compounds. For example, the titanium compound (TC) prepared in step (iii) is preferably used as the 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).

[0041] Since the synthesis of barium titanate by hydrothermal synthesis has been performed in the past, it may be performed 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 more and a temperature of 120°C or more. The pressure during the reaction may be 0.2 MPa or more or 0.7 Pa or more, and 1.5 MPa or less or 1.3 MPa or less. The temperature during the reaction may be 120°C or more or 165°C or more, and 198°C or less or 191°C or less. The reaction time may be 18 hours or more or 55 hours or more, and 200 hours or less or 65 hours or less. In step (iv), hydrothermal synthesis may be performed using a slurry containing only a titanium compound (TC) and a barium compound as raw materials for barium titanate particles. A preferred example of the slurry used for the hydrothermal synthesis in step (iv) does not contain silicon compounds, phosphorus compounds, sodium compounds, chlorine compounds, sulfur compounds, or their dissolved products.

[0042] Barium titanate is synthesized by the hydrothermal synthesis in step (iv). The barium titanate synthesized by the above steps has predetermined physical properties, as shown in the examples.

[0043] (barium titanate particles) The barium titanate particles according to this embodiment may be referred to hereinafter as "barium titanate particles (P)" or "particles (P)." The barium titanate particles (P) have the following characteristics (1) to (4). (1) The lattice constant ratio c / a is 1.0095 or more. (2) By mass ratio, the Si content is 10 ppm or less, the P content is 10 ppm or less, the Na content is 10 ppm or less, the Cl content is 15 ppm or less, and the S content is 10 ppm or less. (3) The dispersibility index Di calculated based on a scanning electron microscope image using the following formula is 700 or less. Dispersity index Di=100×(maximum particle size Dmax) / (minimum particle size Dmin) (4) The average particle size Dav is 50 nm or more and 200 nm or less.

[0044] The barium titanate particles (P) can be produced by the production method (M). The matters explained about the production method (M) can be applied to the particles (P). The matters explained about the particles (P) may also be applied to the production method (M).

[0045] The barium titanate particles (P) have a tetragonal crystal structure. Regarding the above characteristic (1), the lattice constant ratio c / a is the ratio of the length c of the c-axis of a unit lattice of the barium titanate crystal divided by the length a of the a-axis of the 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 may be 1.0096 or more, or 1.0097 or more. The lattice constant ratio c / a may be 1.0110 or less (e.g., 1.0098 or less).

[0046] The barium titanate particles (P) preferably have a low impurity concentration. The particles (P) may have a Cl content of 11 ppm or less, 8 ppm or less, or 6 ppm or less. The barium titanate particles (P) may have a P content, a Na content, and a S content of less than 10 ppm. These 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.

[0047] Regarding the above characteristic (3), the dispersity index Di may be 550 or less, 500 or less, or 480 or less. The dispersity index Di is 1 or more. The smaller the dispersity index Di, the smaller the particle size variation of the particles (P) and the fewer outliers there are.

[0048] Regarding the above characteristic (4), the average particle size Dav of the barium titanate particles (P) may be 100 nm or more, 120 nm or more, or 121 nm or more, and may be 150 nm or less, 141 nm or less, or 140 nm or less.

[0049] The coefficient of variation (CV) of the particle size of the barium titanate particles (P) is expressed by the following formula: In the following formula, ρ is the standard deviation of the particle size of the particles (P), and Dav is the average particle size of the particles (P). CV(%)=100×ρ / Dav

[0050] The coefficient of variation (CV) of the barium titanate particles (P) may be 25.0% or less, or 20.0% or less. The closer the coefficient of variation (CV) is to zero, the smaller the particle size variation of the particles (P). Therefore, a low coefficient of variation (CV) is preferable.

[0051] The average value Av(Ci) of the circularity Ci of the barium titanate particles (P) may be 0.95 or more, 0.96 or more, or 0.97 or more. The circularity Ci is calculated by the following formula: In the following formula, S is the area of the particle, and L is the perimeter of the particle. S and L are measured from an image taken with a scanning electron microscope. For a perfect circle, the circularity Ci is 1. Circularity Ci=4πS / L 2

[0052] In this specification, the particle diameter is the equivalent circle diameter. The average particle diameter Dav, standard deviation ρ of particle diameter, maximum particle diameter Dmax, minimum particle diameter Dmin, average value Av(Ci) of circularity Ci, and dispersity index Di of particles (P) are determined by analyzing images taken with a scanning electron microscope. The number of particles used for analysis is in the range of 400 to 800. Specifically, the above evaluation values can be determined by the method described in the examples.

[0053] The present disclosure provides a titanium compound (TC) and a method (Mt) for producing the titanium compound (TC). The production method (Mt) includes the above-described steps (i), (ii), and (iii). The production method (Mt) may further include the above-described water-washing step (a) after step (iii). The production method (Mt) may also include the water-washing step (a) and a drying step for 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 redundant explanations will be omitted. The drying step is not particularly limited, and a general drying step may be used.

[0054] The titanium compound (TC) is produced by the production method (Mt). The titanium compound (TC) has the above-mentioned characteristics. The titanium compound (TC) is preferably used as a raw material for the synthesis (particularly hydrothermal synthesis) of barium titanate particles. [Example]

[0055] The present disclosure will be described in more detail below with reference to examples, but is not limited to the following examples. In these examples, barium titanate particles were prepared under different conditions. Each preparation condition is described below.

[0056] (Preparation of Particle A1) Particles A1, which are barium titanate particles, were prepared by the following procedure.

[0057] (1) Process 1 First, pure water was placed in a reaction vessel. Next, a titanium tetrachloride aqueous solution and a sodium hydroxide aqueous solution were simultaneously added to the pure water in the reaction vessel to simultaneously neutralize the titanium tetrachloride and sodium hydroxide. The titanium tetrachloride aqueous solution had a titanium dioxide equivalent concentration of 44 g / L. The titanium dioxide equivalent concentration was calculated from the formula weight of titanium tetrachloride (189.7) and the formula weight of titanium dioxide (79.9). The titanium halide aqueous solution and the sodium hydroxide aqueous solution were simultaneously neutralized under conditions of a pH range of 4.5 to 5.5 and a temperature range of 35 to 45°C. Specifically, the reaction solution obtained by adding the titanium halide aqueous solution and the sodium hydroxide aqueous solution to pure water was maintained with stirring for 4 hours at a pH range of 4.5 to 5.5 and a temperature range of 35 to 45°C. This simultaneous neutralization reaction produced a titanium hydroxide slurry. Thereafter, the resulting titanium hydroxide slurry was stirred for 4 hours while being maintained at 40°C.

[0058] (2) Process 2 Next, the obtained titanium hydroxide slurry was filtered and washed with water. Washing was continued until the conductivity of the water (filtrate) after washing reached 1 mS / cm. In this way, a titanium hydroxide cake was obtained. The obtained titanium hydroxide cake was dispersed in pure water to obtain a slurry with a concentration of 50 g / L in terms of titanium dioxide.

[0059] The mass of titanium hydroxide in terms of titanium dioxide was determined by the following procedure. First, a portion of the titanium hydroxide in the slurry obtained in step 2 was collected as a sample, and the sample was filtered to obtain a titanium hydroxide cake. Next, the titanium hydroxide cake was heated to 1000°C to convert it into titanium dioxide. The mass of the titanium dioxide was measured to determine the mass of titanium hydroxide in the slurry in terms of titanium dioxide.

[0060] (3) Process 3 Nitric acid and citric acid were added to the slurry obtained in step 2. At this time, 10.0 parts by mass of nitric acid and 5.0 parts by mass of citric acid were added per 100 parts by mass of titanium hydroxide converted to titanium dioxide. After adding nitric acid and citric acid to the slurry in this manner, the slurry was heated to 85°C and stirred for 5 hours. The obtained slurry was cooled to room temperature, filtered, and washed with water. The washing was continued until the conductivity of the water (filtrate) after washing reached 150 μS / cm. In this way, a titanium compound cake was obtained.

[0061] (4) Process 4 177 ml of pure water and 330 g of barium hydroxide octahydrate were placed in a reaction vessel (volume: 5 L). Next, the liquid in the vessel was heated to 100°C, dissolving the barium hydroxide octahydrate in the water to prepare an aqueous barium hydroxide solution.

[0062] Next, the titanium compound cake obtained in step 3 was dispersed in pure water to prepare a titanium compound slurry. The slurry was heated to 100°C. This slurry (temperature: 100°C) was mixed with the above-mentioned barium hydroxide aqueous solution (temperature: 100°C). In this way, a barium titanate precursor slurry (concentration: 0.74 g / L in terms of BaTiO3) was obtained. The Ba / Ti molar ratio was 2.0 when the titanium compound slurry was completely added to the barium hydroxide aqueous solution.

[0063] The barium titanate precursor slurry was placed in an autoclave and reacted at 190°C for 65 hours to hydrothermally synthesize barium titanate particles. The reaction product in the autoclave was then allowed to cool to room temperature. The resulting reaction product was filtered and washed with water, and then dried at 95°C. In this way, barium titanate particles (particles A1) were obtained.

[0064] (Particles A2~A11, C1~C2) Particles A2 to A11 and C1 to C2 (barium titanate particles) were produced using the same method and conditions as for producing particles A1, except that the amount of acid added in step 3 above was changed as shown in Table 1.

[0065] (Particles A12~A14) Particles A12 to A14 (barium titanate particles) were produced by the same method and under the same conditions as those used to produce particles A1, except that in step 3, the temperature at which the slurry was heated after adding the acid to the slurry was changed as shown in Table 1. The stirring time after adding the acid and heating was 5 hours, the same as in step 3 for particles A1. Steps 1, 2, 3, and 4 in the production of particles A1 to A14 correspond to the above-mentioned steps (i), (ii), (iii), and (iv), respectively.

[0066] (particle C3) Particles C3, which are barium titanate particles, were prepared by the following procedure.

[0067] (1) Process 1 First, pure water was placed in a reaction vessel. Next, a titanium tetrachloride aqueous solution and a sodium hydroxide aqueous solution were simultaneously added to the pure water in the reaction vessel to simultaneously neutralize the titanium tetrachloride and sodium hydroxide. The titanium tetrachloride aqueous solution had a titanium dioxide equivalent concentration of 44 g / L. The titanium halide aqueous solution and the sodium hydroxide aqueous solution were simultaneously neutralized under conditions of a pH range of 2.0 to 3.0 and a temperature range of 45 to 55°C. Specifically, the reaction solution obtained by adding the titanium halide aqueous solution and the sodium hydroxide aqueous solution to pure water was maintained with stirring for 4 hours at a pH range of 2.0 to 3.0 and a temperature range of 45 to 55°C. This simultaneous neutralization reaction produced a slurry of hydrous titanium oxide. The resulting slurry was then stirred for 4 hours while maintained at 60°C.

[0068] (2) Process 2 The resulting slurry of hydrous titanium oxide was then filtered and washed with water to obtain a cake of titanium compound. The washing was continued until the conductivity of the water (filtrate) after washing reached 150 μS / cm. In this way, a cake of hydrous titanium oxide was obtained.

[0069] Next, hydrothermal synthesis and subsequent steps were carried out by the method and conditions described in step 4 above, except that step 3 was not carried out and the hydrous titanium oxide obtained in step 2 was used as the titanium compound in step 4. In this way, particles C3 were obtained.

[0070] (particle C4) Particles C4 were produced by the same method and under the same conditions as those for producing particles A1, except for the preparation method of the titanium compound slurry in step 4. Specifically, the titanium compound cake obtained in step 3 was dispersed in pure water, and 2.0 parts by mass of monoammonium phosphate (NH4H2PO4) calculated as P2O5 was added per 100 parts by mass of titanium hydroxide calculated as titanium dioxide. In this manner, a titanium compound slurry was prepared. That is, in the production of particles C4, the titanium compound to which a phosphorus compound had been added was used as a raw material for the hydrothermal synthesis in step 4. Here, the mass calculated as P2O5 was calculated using the formula weight of monoammonium phosphate and the formula weight of P2O5.

[0071] (Particle C5) Particles C5 were produced by the same method and under the same conditions as those for producing particles A1, except that the method for preparing the titanium compound slurry in step 4 was different. Specifically, the titanium compound cake obtained in step 3 was dispersed in pure water, and 2.0 parts by mass of spherical silica (silica sol, manufactured by Sakai Chemical Industry Co., Ltd.) was added per 100 parts by mass of titanium hydroxide converted to titanium dioxide. In this manner, a titanium compound slurry was prepared. That is, in the production of particles C5, the titanium compound to which the silicon compound had been added was used as a raw material in the hydrothermal synthesis in step 4.

[0072] (particle C6) Particles C6 were produced by the same method and under the same conditions as those for producing particles A1, except for the preparation method of the titanium compound slurry in step 4. Specifically, the titanium compound cake obtained in step 3 was 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.) were added per 100 parts by mass of titanium hydroxide in terms of titanium dioxide, in terms of P2O5. In this manner, a titanium compound slurry was prepared. That is, in the production of particles C6, the titanium compound to which a phosphorus compound and a silicon compound had been added was used as a raw material for the hydrothermal synthesis in step 4.

[0073] (evaluation) The titanium compound used in the synthesis of barium titanate particles and the barium titanate particles were evaluated by the following methods. Note that the titanium compound used in the synthesis of particles C3 was the hydrous titanium oxide obtained in step 2.

[0074] (specific surface area) The specific surface area was determined by the BET method. Specifically, the specific surface area of the particles was measured by the BET single-point method using a continuous flow surface area measurement device (Macsorb HM-1201 with an environmental protection unit) manufactured by Mountech Co., Ltd.

[0075] (average particle size Dav, circularity Ci, coefficient of variation CV, dispersity index Di) The average particle size Dav, circularity Ci, coefficient of variation CV, and dispersity index Di were determined by photographing the particles with a scanning electron microscope, obtaining particle images, and processing the images. Specifically, they were determined by the following procedure.

[0076] First, a scanning electron microscope (SU8020, Hitachi High-Technologies Corporation) was used to obtain SEM images (magnification: 50,000 times) of the particles. The particles in the SEM images were then analyzed using image analysis particle size distribution measurement software (Mac-View) to determine the average particle size, the average (arithmetic mean) Av(Ci) of the circularity Ci (calculated from the particle area S and the particle perimeter L), the maximum particle size Dmax, the minimum particle size Dmin, and the coefficient of variation CV. The particle size of each particle was calculated as the equivalent circle diameter. The average particle size was determined by arithmetically averaging the particle diameters (equivalent circle diameters) of each particle. 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 particles analyzed ranged from 400 to 800.

[0077] (lattice constant ratio c / a, ratio Va / Vc, half-width W of a given peak of titanium compound (TC)) The particle lattice constant ratio c / a, the ratio Va / Vc, and the half-value width W of the peak of the titanium compound (TC) in the range of 2θ = 20° to 30° were determined by analyzing the particles using X-ray diffraction. Specifically, they were determined by the following method.

[0078] The particles to be measured were placed in an X-ray diffractometer, and the XRD profile was measured in the 2θ range of 20° to 120°. A BRUKER D8 ADVANCE X-ray diffractometer was used. The obtained XRD profile was processed using dedicated software (TOPAS BBQ) to perform peak fitting and Rietveld analysis. This analysis determined the tetragonality (lattice constant ratio c / a), the ratio Va / Vc of the mass of amorphous titanium hydroxide Va to the mass of anatase titanium dioxide Vc, and the half-width W of the titanium compound (TC) peak in the 2θ range of 20° to 30°.

[0079] (Si, P, Na content) The contents of Si, P, and Na in the particles were measured by the calibration curve method using a multi-element sequential ICP emission spectrometer (PS3520DDII, Hitachi High-Tech Science Corporation).

[0080] (Cl, S content) The Cl and S contents in the particles were measured by the calibration curve method using a combustion apparatus (AQF-2100H, Mitsubishi Chemical Analytech Co., Ltd.) and a Thermo Scientific Dionex ion chromatograph (Thermo Fisher Scientific Co., Ltd.).

[0081] Some of the conditions for steps 3 and 4 when each particle was produced are shown in Table 1. The "addition amount" in Table 1 is the amount per 100 parts by mass of titanium hydroxide converted to titanium dioxide. 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.

[0082] [Table 1]

[0083] The evaluation results of the titanium compound obtained in step 3 are shown in Table 2. However, for particles C3, the evaluation results of the hydrous titanium oxide particles obtained in step 2 are shown in Table 2.

[0084] [Table 2]

[0085] Table 3 shows the evaluation results for the lattice constant c / a and impurities of the barium titanate particles obtained by the hydrothermal synthesis in step 4.

[0086] [Table 3]

[0087] Other evaluation results of the barium titanate particles obtained by hydrothermal synthesis in step 4 are shown in Table 4. In Table 4, the number of analyzed particles indicates the number of particles used in the image analysis.

[0088] [Table 4]

[0089] Particles A1 to A14 are barium titanate particles (P) produced by the production method (M) according to the present disclosure. Meanwhile, particles C1 to C6 are comparative barium titanate particles produced by a comparative production method. FIG. 1 shows a portion of an example SEM image of particles A1 (barium titanate particles). FIG. 2 shows a portion of an example SEM image of particles C3 (barium titanate particles). As shown in FIGS. 1 and 2, particles A1 had smaller particle size variation and more uniform shape than particles C3.

[0090] As shown in Tables 3 and 4, according to production method (M), barium titanate particles having high crystallinity (tetragonal crystallinity), small variation in particle size distribution, a predetermined average particle size, and a low impurity concentration can be obtained. [Industrial Applicability]

[0091] INDUSTRIAL APPLICABILITY The present invention can be used for barium titanate particles and a method for producing the same. While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

Claims

1. A method for producing barium titanate particles, comprising: (i) preparing titanium hydroxide by simultaneously neutralizing an aqueous solution of titanium halide and an alkaline substance at a pH in the range of 4.5 to 5.5 and a temperature in the range of 35 to 45°C; (ii) preparing a slurry of the titanium hydroxide by washing the titanium hydroxide with water and then dispersing the titanium hydroxide in water; (iii) a step of preparing a titanium compound by adding 1 to 20 parts by mass of an inorganic acid and 1 to 20 parts by mass of an organic acid to the slurry relative to 100 parts by mass of the titanium hydroxide in terms of titanium dioxide, and then maintaining the slurry at a temperature in the range of 40 to 90°C; a water washing step (a) of washing the titanium compound with water; and (iv) synthesizing barium titanate particles by hydrothermal synthesis using the water-washed 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 m ２ / g or more.

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

3. 3. The method according to claim 1, wherein the titanium halide is titanium tetrachloride.

4. The inorganic acid does not contain a phosphorus compound, The method according to claim 1 or 2, wherein the organic acid is an organic carboxylic acid.

5. The inorganic acid is at least one selected from the group consisting of nitric acid, hydrogen chloride, and sulfuric acid, The method according to claim 1 or 2, wherein the organic acid is an organic carboxylic acid.

6. Barium titanate particles, The lattice constant ratio c / a is 1.0095 or more, The Si content is 10 ppm or less, the P content is 10 ppm or less, the Na content is 10 ppm or less, the Cl content is 15 ppm or less, and the S content is 10 ppm or less, by mass ratio; The dispersibility index Di calculated based on a scanning electron microscope image by the following formula is 700 or less, Dispersity index Di=100×(maximum particle size) / (minimum particle size) Barium titanate particles having an average particle size of 50 nm or more and 200 nm or less.

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