Barium titanate particles and method for producing same

Abstract

Disclosed is a method for producing barium titanate particles, the method including: a step (i) for preparing titanium hydroxide by simultaneously neutralizing an aqueous solution of titanium halide and an alkaline substance under specific conditions; a step (ii) for preparing a slurry of the titanium hydroxide; a step (iii) for preparing a titanium compound by adding a predetermined amount of an inorganic acid and a predetermined amount of an organic acid to the slurry and subsequently holding the resulting slurry at a temperature within the range of 40-90°C; and a step (iv) for synthesizing barium titanate particles by means of hydrothermal synthesis using a starting material that contains the titanium compound. The titanium compound contains amorphous titanium hydroxide and anatase-type titanium dioxide. The specific surface area of the titanium compound is 250 m2 / g or more.

Description

Barium titanate particles and method for producing the same

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

[0002] Barium titanate particles are used as a dielectric material in various fields. 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 raw materials for barium titanate particles.

[0003] Claim 1 of Patent Document 1 (JP-A-8-208228) states, "TiO ２ The present invention includes a step (a) of forming an aqueous slurry of precipitated titanium hydroxide having a pH of 4.5 to 6.5 by adding a water-soluble alkali in an amount of 0.033 to 2 equivalents per equivalent of the acid radical contained in the titanium salt to the aqueous solution of the titanium salt at a rate of 1 minute while maintaining the aqueous solution of the water-soluble titanium salt having a concentration of 0.5 to 10% by weight as calculated at 40 to 75°C; a step (b) of recovering precipitated titanium hydroxide by removing impurities and water contained therein from the aqueous slurry of precipitated titanium hydroxide obtained in the step (a); and a step (c) of recovering precipitated titanium hydroxide by mixing an aqueous medium with the precipitated titanium hydroxide obtained in the step (b) and a water-soluble acid in an amount of 0.05 to 0.50 equivalents per mole of the precipitated titanium hydroxide. ２ A reaction mixture containing 1 to 45% by weight of TiO 3 is formed, and while maintaining the temperature of the reaction mixture at a temperature between freezing and boiling, amorphous titanium oxide having a particle size of 20 to 300 nm is added in the form of TiO 3 . ２ and (c) reacting the precipitated titanium hydroxide in the reaction mixture with a water-soluble acid until an aqueous sol containing titanium hydroxide at a concentration of 1 to 45% by weight is formed."

[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, which is produced by hydrolyzing a titanium compound with hydrogencarbonate, and ammonium citrate in an aqueous solvent."

[0005] Claim 1 of Patent Document 3 (JP 2015-224147 A) states, "Titanium dioxide TiO ２ Sol and aqueous barium hydroxide solution Ba(OH) ２ and a method for producing barium titanate, which is characterized by carrying out a hydrothermal reaction using supercritical water in a flow reactor with the above starting materials.

[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, and a titanium halide having a BET specific surface area of ​​300 m 2 / g or more and a crystallite diameter of 20 Å or more; step A of washing the titanium hydroxide and then 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 and then washing it with water, and dispersing the treated titanium hydroxide in water to obtain a slurry containing the titanium hydroxide; and step C of adding to the slurry (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 phosphorus compound and a silicon compound in a total amount of 1.0 to 5.0% by weight or less, calculated as titanium oxide (TiO2) relative to the titanium hydroxide, and then washing the resulting mixed slurry with water and drying.

[0007] Japanese Patent Laid-Open No. 8-208228 Japanese Patent Laid-Open No. 2014-133688 Japanese Patent Laid-Open No. 2015-224147 Japanese Patent Laid-Open No. 2019-085282

[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 that have 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.

[0009] One aspect of the present disclosure is a method for producing barium titanate particles, comprising: step (i) of preparing titanium hydroxide by simultaneously neutralizing an aqueous solution of titanium halide and an alkaline substance under conditions of a pH in the range of 4.5 to 5.5 and a temperature in the range of 35 to 45°C; step (ii) of preparing a slurry of the titanium hydroxide by washing the titanium hydroxide with water and then dispersing it in water; step (iii) 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 per 100 parts by mass of the titanium hydroxide converted to titanium dioxide to the slurry, and then maintaining the slurry at a temperature in the range of 40 to 90°C; and step (iv) of synthesizing barium titanate particles by hydrothermal synthesis using raw materials containing the titanium compound, wherein the titanium compound contains amorphous titanium hydroxide and anatase titanium dioxide, and the specific surface area of ​​the titanium compound is 250 m ２ / g or more.

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

[0011] According to the present disclosure, barium titanate particles having high crystallinity, narrow particle size distribution variation, 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.

[0012] Fig. 1 shows an SEM image of an example of a particle produced by the production method according to the present disclosure, and Fig. 2 shows an SEM image of an example of a particle produced by a comparative production method.

[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 for Producing Barium Titanate Particles) The production method according to this embodiment may be hereinafter referred to as “production method (M).” The 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 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. The pH and temperature refer to the pH and temperature of the reaction solution produced by mixing the aqueous solution of titanium halide and the alkaline substance during the 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 (for example, 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 being stirred.

[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 in advance, 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 the 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 of 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 atmospheric temperature (temperature around the vessel) in which step (i) is carried out.

[0024] (Step (ii)) Step (ii) is a step of preparing a titanium hydroxide slurry by washing titanium hydroxide with water and then dispersing it in water. It is preferable to use water with few impurities as the water for washing titanium hydroxide and the water 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) reaches 1 mS / cm or less (e.g., 0.1 mS / cm or less). By washing with water in this manner, barium titanate particles having 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 the 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)" hereinafter. Titanium compound (TC) contains amorphous titanium hydroxide and anatase titanium dioxide. The specific surface area of ​​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 = 20 ° to 30 ° range 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, described below. 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 ３ ), hydrogen chloride (HCl), and sulfuric acid (H ２ SO ４ ) and the like. 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 terms of reducing 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 held 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 the inorganic acid and the organic acid to the slurry, and then holding the slurry at a temperature in the range of 40 to 90°C for a predetermined holding time. The preferable holding time 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 held 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. 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 the titanium hydroxide to convert it to titanium dioxide. Specifically, this can be determined by the method described in the Examples.

[0036] The specific surface area of ​​titanium compound (TC) is 250 m ２ / g or more, and 251m ２ / g or more, 276m ２ / 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 holding temperature of the slurry after adding the acid, or shortening the holding 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 performing water 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 the barium source 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 results in 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 conventionally performed, 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) under a pressure of 0.2 MPa or more and at 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 dissolved compounds thereof.

[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) Hereinafter, the barium titanate particles according to this embodiment may be referred to as "barium titanate particles (P)" or "particles (P)." The barium titanate particles (P) have the following characteristics (1) to (4): (1) a lattice constant ratio c / a of 1.0095 or more; (2) a mass ratio of Si content of 10 ppm or less, P content of 10 ppm or less, Na content of 10 ppm or less, Cl content of 15 ppm or less, and S content of 10 ppm or less; (3) a dispersity index Di calculated based on an image obtained by a scanning electron microscope using the following formula is 700 or less: dispersity index Di = 100 × (maximum particle diameter Dmax) / (minimum particle diameter Dmin); (4) an average particle diameter Dav of 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 described for the production method (M) can be applied to the particles (P). The matters described for 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 feature (1), the lattice constant ratio c / a is the ratio of the length c of the c-axis of the 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] In the barium titanate particles (P), the concentration of impurities is preferably low. In the particles (P), the Cl content may be 11 ppm or less, 8 ppm or less, or 6 ppm or less. In the barium titanate particles (P), the P content, Na content, and S content may be 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 method 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 equal to or greater than 1. 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 feature (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 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. In the case of 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) after step (iii) and a drying step for drying the water-washed titanium compound (TC). 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.

[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 Particles A1) Particles A1, which are barium titanate particles, were prepared by the following procedure.

[0057] (1) Step 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, thereby simultaneously neutralizing 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 in the range of 4.5 to 5.5 and a temperature in the 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 for 4 hours with stirring at a pH in the range of 4.5 to 5.5 and a temperature in the 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) Step 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) Step 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 manner, a cake of titanium compound was obtained.

[0061] (4) Step 4: 177 ml of pure water and 330 g of barium hydroxide octahydrate were placed in a reaction vessel (volume: 5 L). The liquid in the vessel was then heated to 100°C to dissolve the barium hydroxide octahydrate in the water, thereby preparing 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 barium hydroxide aqueous solution (temperature: 100°C). In this way, a barium titanate precursor slurry (concentration: BaTiO ３ At the time when the addition of the titanium compound slurry to the aqueous barium hydroxide solution was completed, the Ba / Ti molar ratio was 2.0.

[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 manner, barium titanate particles (particles A1) were obtained.

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

[0065] (Particles A12 to 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 the acid was added to the slurry was changed as shown in Table 1. The stirring time after the addition of the acid and heating was 5 hours, the same as in step 3 for particles A1. Note that 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] (Particles C3) Particles C3, which are barium titanate particles, were prepared by the following procedure.

[0067] (1) Step 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, thereby simultaneously neutralizing 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 of hydrous titanium oxide was then stirred for 4 hours while maintained at 60°C.

[0068] (2) Step 2 Next, the obtained slurry of hydrous titanium oxide was 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] (Particles C4) Particles C4 were produced by the same method and under the same conditions as those for producing particles A1, except for the method for preparing the titanium compound slurry in step 4. Specifically, the titanium compound cake obtained in step 3 was dispersed in pure water, and P ２ O ５ 2.0 parts by mass of monoammonium phosphate (NH ４ H ２ P.O. ４ In this way, a slurry of the titanium compound was prepared. That is, in the production of particles C4, the titanium compound to which the phosphorus compound was added was used as a raw material in the hydrothermal synthesis in step 4. Here, P ２ O ５ The converted mass is the formula weight of monoammonium phosphate and P ２ O ５ The formula weight was calculated using the formula:

[0071] (Particles C5) Particles C5 were produced by the same method and under the same conditions as those for producing particles A1, except for the method for preparing 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 spherical silica (silica sol, manufactured by Sakai Chemical Industry Co., Ltd.) 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 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] (Particles C6) Particles C6 were produced by the same method and under the same conditions as those for producing particles A1, except for the method for preparing the titanium compound slurry in step 4. Specifically, the titanium compound cake obtained in step 3 was dispersed in pure water, and P ２ O ５ 2.0 parts by mass of monoammonium phosphate (NH ４ H ２ P.O. ４), and 2.0 parts by mass of spherical silica (silica sol, manufactured by Sakai Chemical Industry Co., Ltd.) were added. In this manner, a titanium compound slurry was prepared. That is, in the production of particles C6, the titanium compound to which the phosphorus compound and the silicon compound had been added was used as a raw material in the hydrothermal synthesis of step 4.

[0073] (Evaluation) The titanium compound used in the synthesis of the 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 measuring device (Macsorb HM-1201 with an environmental protection unit added) 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 particles with a scanning electron microscope to obtain images of the particles 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 an SEM image (magnification: 50,000 times) of the particles. Next, the particles present in the SEM image were analyzed using image analysis particle size distribution measurement software (Mac-View) to determine the average particle size, the average value (arithmetic mean value) 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 circle-equivalent diameter. The average particle size was determined by arithmetically averaging the particle sizes (circle-equivalent diameters) of each particle. The maximum particle size Dmax is the largest particle size among the particle sizes analyzed. The minimum particle size Dmin is the smallest particle size among the particle sizes analyzed. The dispersity index Di was calculated from the maximum particle size Dmax and the minimum particle size Dmin. The number of particles analyzed was in the range of 400 to 800.

[0077] (Lattice constant ratio c / a, ratio Va / Vc, and half-value width W of a predetermined peak of titanium compound (TC)) The lattice constant ratio c / a, ratio Va / Vc, and half-value width W of a peak of titanium compound (TC) in the range of 2θ=20° to 30° of the particles were determined by analyzing the particles by 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 an 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 peak of the titanium compound (TC) in the 2θ range of 20° to 30°.

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

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

[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 into 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]

[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]

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

[0086]

[0087] Other evaluation results of the barium titanate particles obtained by the 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]

[0089] Particles A1 to A14 are barium titanate particles (P) produced by the production method (M) according to the present disclosure. On the other hand, 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 manufacturing 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.

[0091] The present invention is applicable to barium titanate particles and methods for producing the same. While the present invention has been described with reference to presently preferred embodiments, such disclosure should not be interpreted as limiting. Various modifications and variations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims should be construed to cover all modifications and variations that do not depart from the true spirit and scope of the present 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 under conditions of a pH range of 4.5 to 5.5 and a temperature range of 35 to 45°C; (ii) preparing a slurry of the titanium hydroxide by washing the titanium hydroxide with water and dispersing it in water; (iii) 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 in an amount of 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; and (iv) synthesizing barium titanate particles by hydrothermal synthesis using raw materials containing the titanium compound, wherein the titanium compound contains amorphous titanium hydroxide and anatase titanium dioxide, and the specific surface area of ​​the titanium compound is 250 m or more. ２ / g or more.

2. The method according to claim 1, wherein in said 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. The method according to claim 1 or 2, wherein the titanium halide is titanium tetrachloride.

4. Barium titanate particles having a lattice constant ratio c / a of 1.0095 or more, a mass ratio of Si being 10 ppm or less, P being 10 ppm or less, Na being 10 ppm or less, Cl being 15 ppm or less, and S being 10 ppm or less, a dispersion index Di calculated based on an image taken with a scanning electron microscope using the following formula: Dispersion index Di = 100 x (maximum particle size) / (minimum particle size) is 700 or less, and an average particle size of 50 nm or more and 200 nm or less.

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