CN118164751A - Barium calcium titanate powder, and preparation method and application thereof - Google Patents

Abstract

The present invention relates to the technical field of capacitor materials, and in particular to a calcium barium titanate powder, a preparation method and application thereof. The calcium barium titanate powder has a chemical formula shown in formula (I); under the condition of 25±3°C, the unit cell volume V of the calcium barium titanate powder is measured by XRD to satisfy formula (1). In the calcium barium titanate powder provided by the present invention, calcium is uniformly doped and there are no impurities such as calcium titanate, calcium hydroxide, and calcium carbonate. Compared with the prior art, the advantage of the present invention is that all calcium can be dissolved into the calcium barium titanate, and only the minimum amount of necessary calcium is required, so the performance is better than the current technology. Because all the calcium replaces the calcium with a larger atomic radius, compared with the current technology under the condition of the same amount of calcium added, the unit cell volume becomes smaller and the crystal plane spacing becomes narrower.

Description

Barium calcium titanate powder, preparation method and application thereof

Technical Field

The present invention relates to the technical field of capacitor materials, and in particular to calcium barium titanate powder, a preparation method and application thereof.

Background technique

At present, barium titanate is used as the main material of the dielectric layer in MLCC capacitors. The defect of this material is that it is not resistant to reduction. MLCC consists of a dielectric layer, an inner electrode, and an outer electrode. The electrode material is a nickel electrode. In order to ensure that the nickel electrode is not oxidized when the manufacturer is firing the MLCC, it must be fired in a reducing atmosphere. However, when the ceramic powder based on barium titanate is fired at high temperature in a reducing atmosphere to form MLCC, the oxygen atoms on the lattice are easily lost and converted into oxygen to escape, forming oxygen vacancies, which leads to reduced reliability.

Calcium barium titanate powder is a new type of perovskite dielectric ceramic nanopowder, used as the main material of the dielectric layer in MLCC capacitors. Doping calcium in barium titanate can effectively improve the anti-reduction ability. The introduction of calcium can change the chemical energy of thermal transformation and inhibit the generation of oxygen vacancies, which can effectively improve the anti-reduction ability and improve the problem that BT powder may be reduced.

Currently, the methods for preparing barium titanate disclosed include solid phase sintering method, oxalic acid precipitation method, metal alkoxide method, hydrothermal method, and normal pressure hydrothermal method using titanium compound and barium compound to carry out synthesis reaction in strong alkaline solution. Calcium barium titanate is a product obtained by adding calcium source for doping during the preparation of barium titanate.

The problem of solid phase firing method in preparing barium titanate is that after mixing and dispersing barium carbonate, titanium dioxide and the like as raw materials, the product is prepared by high temperature firing. Although the manufacturing cost is low, due to high temperature firing, large difference in particle size between titanium source and barium source raw materials, it is difficult to prepare products with small particle size and good particle size distribution by solid phase firing method. When preparing barium calcium titanate, in addition to barium carbonate and titanium dioxide raw materials, calcium carbonate is added as raw material, and barium calcium titanate is prepared by uniform mixing or sand grinding and firing. For example, the patent with publication number CN 114105190 A (Patent 1) discloses a barium calcium titanate nanocrystalline medium material and a preparation method thereof, wherein titanium dioxide, barium carbonate and calcium carbonate are mixed in a stoichiometric ratio, water and a dispersant are added to obtain a slurry, and the slurry is dried, sieved and calcined to obtain barium calcium titanate powder. Its shortcomings are: ① The solid phase sintering method requires a relatively high temperature to sinter barium calcium titanate, so it is impossible to obtain a small-particle barium calcium titanate product; ② Due to the different primary particle sizes of titanium dioxide, barium carbonate and calcium carbonate raw materials, the particle sizes of barium carbonate and calcium carbonate are significantly higher than that of titanium dioxide. It is difficult to evenly mix the three raw materials during the sand grinding process, resulting in difficulty in homogenizing the powder composition after calcination, thereby affecting the powder performance; ③ During the sintering process of barium calcium titanate, the grain growth temperatures of each component are different, and some components grow preferentially, affecting the uniformity of the synthetic components. Patent No. CN 100373508C (Patent 2) discloses a method for manufacturing raw material powder for dielectric ceramics, dielectric ceramics and multilayer ceramic capacitors, and points out that "even if the micronized barium carbonate powder and titanium dioxide powder are uniformly dispersed, the barium carbonate particles are easy to grow in the calcination process of synthesizing barium titanate from the barium carbonate powder and titanium dioxide. Therefore, the barium carbonate particles have grown before the titanium dioxide reacts, which makes it difficult to react uniformly with the titanium dioxide." Therefore, in the methods described in the above-mentioned Patents 1 and 2, it is difficult to prepare fine-grained, uniformly calcium-doped barium calcium titanate powder, which is mainly limited by the process characteristics of the high-temperature solid phase method.

The oxalic acid precipitation method uses titanium source, barium source and calcium source to synthesize oxalate precipitation in an oxalic acid environment, and then removes carbonate through high-temperature calcination to obtain barium calcium titanate powder. The problem with this method is that the carbonate in oxalate will exist as an impurity, which increases the impurity content of barium carbonate. In addition, a large number of hydroxyl defects are introduced during the synthesis process, which causes holes to form on the surface and inside of the powder, affecting the electrical properties of the product.

The metal alkoxide method is to mix alcohol solutions of barium source, titanium source and calcium source, hydrolyze and react to precipitate at a specific temperature to synthesize barium calcium titanate powder, and then sinter at a high temperature to obtain a tetragonal barium calcium titanate powder. For example, the patent with the publication number CN1338430A (Patent 3) discloses a barium titanate microparticle powder, a calcium-modified barium titanate microparticle powder and a method for manufacturing the same, using barium hydroxide aqueous solution, an alcohol solution of alkoxy titanium, an alcohol solution of calcium nitrate, etc. as raw materials, pre-mixing the alcohol solution of alkoxy titanium and the alcohol solution of calcium nitrate, and then mixing them with the barium hydroxide solution in a certain ratio to synthesize barium calcium titanate, and heat treating at a temperature of 950 to 1100°C to obtain barium calcium titanate. The advantage of this method is that it can prepare barium calcium titanate powder with a small particle size, ranging from 0.145 to 0.250 μm, but the disadvantage is that when the alcohol solution of alkoxy titanium, the alcohol solution of calcium nitrate, and the barium hydroxide solution are mixed and reacted, calcium titanate is also generated at the same time as barium calcium titanate. Calcium titanate exists in the form of impurities, affecting the electrical properties of the product. In addition, the generated calcium titanate impurities occupy a part of calcium. In order to make barium calcium titanate have the required reduction resistance, more calcium than the required doping amount has to be added, but this leads to a decrease in the dielectric constant.

The atmospheric pressure hydrothermal method for synthesizing calcium barium titanate using titanium source, barium source and calcium source under alkaline conditions generally uses the hydrolysis product of titanium compound, water-soluble barium source and calcium source to synthesize powder under alkaline environment, and sintering at high temperature to prepare calcium barium titanate. For example, the patent with publication number CN100575263C (Patent 4) discloses a calcium barium titanate, a method for manufacturing the same and a capacitor, wherein barium titanate is synthesized by adding barium hydroxide and titanium dioxide to an alkaline solution containing alkaline compounds with a pH of 10 or higher and reacting the solution to synthesize barium titanate, and then calcium hydroxide is added to react to synthesize calcium barium titanate. This method can prepare calcium barium titanate with small particle size and relatively uniform calcium doping. In this method, the calcium source is doped after the synthesis of barium titanate. The doped calcium enters the barium titanate lattice structure to form barium calcium titanate. When the ratio of the sum of the molar amounts of calcium and barium to the molar amount of titanium reaches 1.0000, it is difficult for the remaining calcium to enter the barium calcium titanate lattice to replace the barium. They are more likely to exist on the surface of barium calcium titanate in the form of calcium hydroxide or oxide. Although this part of calcium can be detected during component detection, it loses its due role, and during long-term storage, it gradually reacts with carbon dioxide in the air to form calcium carbonate, which becomes an impurity in barium calcium titanate and affects the electrical properties.

As we all know, the purpose of doping calcium in barium titanate is to improve the reduction resistance, but the more calcium is added, the disadvantage of lowering the dielectric constant will appear. The calcium added in the previous synthesis technology cannot be completely dissolved in the barium calcium titanate, and part of the calcium exists on the surface of the barium calcium titanate in the form of calcium hydroxide, calcium carbonate, and calcium titanate. Therefore, in order to obtain sufficient reduction resistance, it is necessary to add more than the required amount of calcium. In comparison, the advantage of the present invention is that all the calcium can be dissolved into the barium calcium titanate, and only the minimum amount of necessary calcium is added, so the performance is better than the current technology. Because all the calcium replaces the calcium with a larger atomic radius, compared with the current technology under the condition of the same amount of calcium added, the unit cell volume becomes smaller and the crystal plane spacing becomes narrower.

Summary of the invention

In view of this, the technical problem to be solved by the present invention is to provide a barium calcium titanate powder, a preparation method and application thereof. In the barium calcium titanate powder provided by the present invention, calcium is uniformly doped and there are no impurities such as calcium titanate, calcium hydroxide, and calcium carbonate.

The present invention provides a barium calcium titanate powder having a chemical formula (I):

Ba _x+z Ca _y TiO ₃ (I);

In formula (I), y is the molar content of Ca, which is 0<y≤0.15, and 0.98≤x+y+z≤1.015;

At 25±3°C, the unit cell volume V of the calcium barium titanate powder measured by XRD satisfies the formula (1):

V≤64.3-6.6×y (1);

In formula (1), 0<y≤0.15.

Preferably, the barium calcium titanate powder has a (110) crystal plane FWHM ≤ 0.40°, and a (111) crystal plane FWHM ≤ 0.30°.

The present invention also provides a method for preparing the barium calcium titanate powder as described above, comprising the following steps:

A) mixing a portion of the barium source with a strong alkaline solution, heating the obtained mixed solution, and then mixing it with a titanium source solution to react to obtain a product solution containing barium titanate represented by formula (II);

Ba _x TiO ₃ formula (Ⅱ);

In formula (II), 0.85≤x<1.00;

B) mixing the product solution containing barium titanate represented by formula (II) with a calcium source, and reacting to obtain a barium calcium titanate process product represented by formula (III):

Ba _x Ca _y TiO ₃ formula (III);

In formula (III), 0<y≤0.15, 0.85<x+y≤1.00;

C) reacting the barium calcium titanate process product represented by formula (III) with the remaining barium source to obtain the barium calcium titanate precursor represented by formula (I);

Ba _x+z Ca _y TiO ₃ formula (Ⅰ);

In formula (I), 0<y≤0.15, z>0, 0.98≤x+y+z≤1.015.

Preferably, after step C), the method further comprises:

D) calcining the barium calcium titanate precursor represented by formula (I) to obtain barium calcium titanate powder having the chemical formula represented by formula (I).

Preferably, the barium source includes at least one of barium hydroxide octahydrate, barium hydroxide monohydrate, anhydrous barium hydroxide, barium chloride, barium chlorate, barium acetate, barium nitrate and barium oxide.

Preferably, in step A), the pH value of the strong alkaline solution is ≥12;

The strong base includes lithium hydroxide, sodium hydroxide, potassium hydroxide or a quaternary ammonium base.

Preferably, in step A), the titanium source comprises at least one of titanium tetrachloride solution, titanium hydroxide suspension, hydrated titanium dioxide suspension, titanium oxychloride and titanium dioxide suspension;

The specific surface area of the powder of the titanium dioxide suspension after drying is 50 to 200 m ² /g, and the primary particle size is 8 to 30 nm;

In the titanium dioxide suspension, the crystal form requirements of titanium dioxide include: the mass content of rutile is ≤20%, and the rest is at least one of anatase and brookite.

Preferably, the calcium source includes at least one of calcium hydroxide powder, calcium chloride powder and calcium oxide powder.

The present invention also provides a dielectric material, wherein the raw material for preparing the dielectric material comprises the barium calcium titanate powder described above or the barium calcium titanate powder prepared by the preparation method described above.

The present invention also provides a ceramic capacitor, wherein the raw material for preparing the ceramic capacitor includes the barium calcium titanate powder described above or the barium calcium titanate powder prepared by the preparation method described above.

The present invention also provides a slurry, wherein the raw materials for preparing the slurry include the barium calcium titanate powder described above or the barium calcium titanate powder prepared by the preparation method described above.

The present invention also provides an original sheet, wherein the raw materials for preparing the original sheet include the barium calcium titanate powder described above or the barium calcium titanate powder prepared by the preparation method described above.

The present invention provides a barium calcium titanate powder having a chemical formula (I):

Ba _x+z Ca _y TiO ₃ (I);

In formula (I), y is the molar content of Ca, which is 0<y≤0.15, and 0.98≤x+y+z≤1.015;

At 25±3°C, the unit cell volume V of the calcium barium titanate powder measured by XRD satisfies the formula (1):

V≤64.3-6.6×y (1);

In formula (1), 0<y≤0.15.

The calcium doping in the barium calcium titanate powder provided by the present invention is uniform, and there are no impurities such as calcium titanate, calcium hydroxide, and calcium carbonate. Compared with the prior art, the advantage of the present invention is that all calcium can be dissolved into the barium calcium titanate, and only the minimum amount of necessary calcium is added, so the performance is better than the current technology. Because all calcium replaces calcium with a larger atomic radius, compared with the current technology under the condition of the same amount of calcium added, the unit cell volume becomes smaller and the crystal plane spacing becomes narrower.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an XRD diagram of a barium calcium titanate precursor prepared in Example 1 of the present invention;

FIG2 is a TEM-EDS element mapping diagram of the barium calcium titanate precursor prepared in Example 1 of the present invention;

FIG3 is an XRD diagram of barium calcium titanate powder 1-1 in Example 1;

FIG4 is a TEM-EDS element mapping diagram of barium calcium titanate powder 1-1 in Example 1;

FIG5 is a SEM image of barium calcium titanate powder 1-1 in Example 1;

FIG6 is an XRD diagram of the barium calcium titanate precursor of Comparative Example 1;

FIG7 is an XRD diagram of the barium calcium titanate precursor of Comparative Example 3;

FIG8 is an XRD pattern of the barium calcium titanate precursor of Comparative Example 4;

FIG. 9 is an XRD diagram of the barium calcium titanate precursor of Comparative Example 5.

Detailed ways

The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Barium titanate-based ferroelectrics will undergo phase transition at temperatures below 130°C, which is close to room temperature. Therefore, the lattice constant will fluctuate greatly at room temperature. Therefore, the unit cell volume V, which is an important condition of the present invention, needs to be measured at a certain temperature range.

The present invention provides a barium calcium titanate powder having a chemical formula (I):

Ba _x+z Ca _y TiO ₃ (I);

In formula (I), y is the doping concentration of Ca, that is, the molar ratio of the element, which is 0<y≤0.15, and 0.98≤x+y+z≤1.015;

Under the condition of 25±3°C, the unit cell volume V of the calcium barium titanate powder measured by XRD satisfies the formula (1):

V≤64.3-6.6×y (1);

In formula (1), y is the doping concentration of Ca, that is, the molar ratio of the element, 0<y≤0.15; the unit of V is angstrom3.

In certain embodiments of the present invention, in formula (I), z>0.

In certain embodiments of the present invention, x=0.9445, y=0.0503, z=0.0112, x+y+z=1.0055; in certain embodiments of the present invention, x=0.9464, y=0.0504, z=0.0082, x+y+z=1.0050; in certain embodiments of the present invention, x+z=0.9948, y=0.0103; in certain embodiments of the present invention, x+z=0.9754, y=0.0300; in certain embodiments of the present invention, x+z=0.9549, y=0.0503; in certain embodiments of the present invention, x+z=0.9048, y=0.1004; in certain embodiments of the present invention, x+z=0.8550, y=0.1509.

In certain embodiments of the present invention, V=63.59 Angstroms3, 63.96 Angstroms3, 63.95 Angstroms3, 64.22 Angstroms3, 64.07 Angstroms3, 63.61 Angstroms3, or 63.29 Angstroms3.

In certain embodiments of the present invention, the (110) crystal plane FWHM of the barium calcium titanate powder is ≤0.40°, and the (111) crystal plane FWHM is ≤0.30°. In certain embodiments, the (110) crystal plane FWHM of the barium calcium titanate powder is 0.300°, 0.267°, 0.260°, 0.235°, 0.247°, 0.324°, or 0.379°; the (111) crystal plane FWHM is 0.245°, 0.201°, 0.198°, 0.192°, 0.193°, 0.2°, 0.254°, or 0.289°.

In some embodiments of the present invention, the particle size of the barium calcium titanate powder is 50-250 nm.

The present invention also provides a method for preparing the barium calcium titanate powder as described above, comprising the following steps:

A) mixing a portion of the barium source with a strong alkaline solution, heating the obtained mixed solution, and then mixing it with a titanium source solution to react to obtain a product solution containing barium titanate represented by formula (II);

Ba _x TiO ₃ formula (Ⅱ);

In formula (II), 0.85≤x<1.00;

B) mixing the product solution containing barium titanate represented by formula (II) with a calcium source, and reacting to obtain a barium calcium titanate process product represented by formula (III):

Ba _x Ca _y TiO ₃ formula (III);

In formula (III), 0<y≤0.15, 0.85<x+y≤1.00;

C) reacting the barium calcium titanate process product represented by formula (III) with the remaining barium source to obtain the barium calcium titanate precursor represented by formula (I);

Ba _x+z Ca _y TiO ₃ formula (Ⅰ);

In formula (I), 0<y≤0.15, z>0, 0.98≤x+y+z≤1.015.

In step A):

Mixing a portion of the barium source with a strong alkali solution, heating the obtained mixed solution, and then mixing it with a titanium source solution to react to obtain a product solution containing barium titanate represented by formula (II);

Ba _x TiO ₃ formula (Ⅱ);

In formula (II), 0.85≤x<1.00; preferably, 0.90≤x<1.00.

In certain embodiments of the present invention, the barium source includes at least one of barium hydroxide octahydrate, barium hydroxide monohydrate, anhydrous barium hydroxide, barium chloride, barium chlorate, barium acetate, barium nitrate and barium oxide.

In certain embodiments of the present invention, the strong alkali solution is a soluble alkaline catalyst, and the pH value of the strong alkali solution is ≥12, preferably ≥13, and specifically, may be 14. The strong alkali includes lithium hydroxide, sodium hydroxide, potassium hydroxide or quaternary ammonium base.

In some embodiments of the present invention, before mixing part of the barium source with the strong alkali solution, the method further comprises:

The strong base solution is heated to ≥80°C and kept warm for ≥10 min. In certain embodiments of the present invention, the strong base is heated to 80-90°C, specifically, 88°C or 90°C.

In some embodiments of the present invention, mixing a portion of the barium source with the strong alkaline solution includes: dissolving a portion of the barium source in the strong alkaline solution.

In certain embodiments of the present invention, a barium source is mixed with a strong alkaline solution, and the resulting mixed solution is heated to a reaction temperature.

In certain embodiments of the present invention, the titanium source includes at least one of titanium tetrachloride solution, titanium hydroxide suspension, hydrated titanium dioxide suspension, titanium dichloride and titanium dioxide suspension. In certain embodiments, the titanium source is a titanium dioxide suspension. The specific surface area of the powder of the titanium dioxide suspension after drying is 50-200m ² /g, specifically, 150m ² /g, 146m ² /g; the primary particle size is 8-30nm, specifically, 10nm. In the titanium dioxide suspension, the crystal form requirements of titanium dioxide include: the mass content of rutile ≤ 20%, specifically, 9.2%, 7.82%; the rest is at least one of anatase and brookite. In certain embodiments, the crystal form of the titanium dioxide powder includes: rutile with a mass content of 9.2%, brookite with a mass content of 62.83%, and anatase with a mass content of 27.97%. In certain embodiments, the crystal forms of the titanium dioxide powder include: 7.82% by mass of rutile, 66.84% by mass of brookite, and 25.34% by mass of anatase.

In certain embodiments of the present invention, the method for preparing the titanium dioxide suspension comprises:

Titanium dioxide suspension is obtained by hydrolyzing titanium tetrachloride solution.

In certain embodiments of the present invention, the concentration of the titanium tetrachloride solution is 0.4 mol/L. The temperature of the hydrolysis is 104°C.

Specifically, after the hydrolysis, the method further includes cooling to room temperature, removing impurities, and concentrating to obtain a titanium dioxide suspension. The cooling rate is 2°C/min. The impurity removal method can be anion exchange resin, electrodialysis, high-purity water cleaning, etc.; specifically, anion exchange resin is used for impurity removal, and the dosage ratio of the anion exchange resin to the cooled solution is 1403g:1L. When the pH value of the solution is 3.6, the impurity removal is stopped. The concentration can be carried out by a hollow fiber membrane concentration system, a ceramic membrane concentration system, a centrifugal system, etc. The mass concentration of the titanium dioxide suspension is 15.68%.

In certain embodiments of the present invention, the method for preparing the titanium dioxide suspension comprises:

Titanium dioxide powder is dispersed in water to prepare a titanium dioxide suspension.

Specifically, the method comprises: mixing titanium dioxide powder, water and a dispersant, and then performing sand milling to disperse the obtained liquid to obtain a titanium dioxide dispersion, namely, a titanium dioxide suspension, wherein the titanium dioxide suspension is uniform and stable.

In certain embodiments of the present invention, the solid content of the mixed liquid is 8wt% to 28wt%, and the content of the dispersant in the liquid is 1wt% to 3wt%. Specifically, the solid content of the mixed liquid is 20wt%, and the content of the dispersant in the liquid is 2wt%.

The specific surface area of the titanium dioxide powder is 50 to 200 m ² /g, specifically, 150 m ² /g; the primary particle size of the titanium dioxide powder is 8 to 30 nm, specifically, 10 nm.

The crystal form requirements of the titanium dioxide powder include: the mass content of rutile is ≤ 20%, specifically, it can be 9.2%; the rest is at least one of anatase and brookite. In some embodiments, the crystal form of the titanium dioxide powder includes: rutile with a mass content of 9.2%, brookite with a mass content of 62.83%, and anatase with a mass content of 27.97%.

In certain embodiments of the present invention, the dispersant includes at least one of sodium hexametaphosphate, ammonium hexametaphosphate, sodium polybenzoate and polycarboxylate ammonium salt dispersants.

In certain embodiments of the present invention, the reaction temperature is 90-110° C., the pressure is normal pressure, and the reaction time is 1-2 h. In certain embodiments, the reaction temperature is 105° C., and the reaction time is 1.5 h.

In step B):

The product solution containing barium titanate represented by formula (II) is mixed with a calcium source and reacted to obtain a barium calcium titanate process product represented by formula (III):

Ba _x Ca _y TiO ₃ formula (III);

In formula (III), 0<y≤0.15, 0.85<x+y≤1.00.

In some embodiments of the present invention, x=0.9445, y=0.0500, x+y=0.9945. In some embodiments of the present invention, x=0.9464, y=0.0500, x+y=0.9964.

In certain embodiments of the present invention, the calcium source includes at least one of calcium hydroxide powder, calcium chloride powder and calcium oxide powder.

In certain embodiments of the present invention, the reaction temperature is 90-110° C., the pressure is normal pressure, and the reaction time is 4-12 hours. In certain embodiments, the reaction temperature is 105° C., and the reaction time is 8 hours.

In certain embodiments of the present invention, after the reaction, the process further comprises: sampling and testing to obtain the element molar ratios of Ba/Ti and Ca/Ti, and then obtaining the barium calcium titanate process product represented by formula (III).

In step C):

The barium calcium titanate process product represented by formula (III) is reacted with the remaining barium source to obtain the barium calcium titanate precursor represented by formula (I);

Ba _x+z Ca _y TiO ₃ formula (Ⅰ);

In formula (I), 0<y≤0.15, z>0, 0.98≤x+y+z≤1.015.

In some embodiments of the present invention, x = 0.9445, y = 0.0503, z = 0.0112, x + y + z = 1.0055. In some embodiments of the present invention, x = 0.9464, y = 0.0504, z = 0.0082, x + y + z = 1.0050.

In certain embodiments of the present invention, the reaction temperature is 90-110° C., the pressure is normal pressure, and the reaction time is 1-2 hours. In certain embodiments, the reaction temperature is 105° C., and the reaction time is 1 hour.

In certain embodiments of the present invention, after the reaction is completed, the process further comprises: allowing the slurry to settle after the reaction, washing, filtering and drying to obtain a barium calcium titanate precursor represented by formula (I).

The detergent used for the cleaning includes alcohol substances, such as ethanol or ethylene glycol, to remove alkaline substances, impurities, etc. in the reaction process, and further obtain high-purity barium calcium titanate powder. The mass ratio of the detergent to the precipitate is 1.5 to 6:1; specifically, it can be 5:1.

The filtering and drying methods can be plate and frame filter pressing + drying; centrifugal filtration + drying; flash drying; spray drying; three-in-one equipment for cleaning, filtering and drying, etc.

In some embodiments of the present invention, the drying temperature is 150-300°C, specifically, 200°C.

In certain embodiments of the present invention, after drying, the process further comprises: crushing through a 100-mesh sieve.

In certain embodiments of the present invention, after the reaction, the process further comprises: sampling and testing to obtain the element molar ratios of Ba/Ti and Ca/Ti, thereby obtaining the barium calcium titanate precursor represented by formula (I).

In certain embodiments of the present invention, after step C), the method further comprises:

D) calcining the barium calcium titanate precursor represented by formula (I) to obtain barium calcium titanate powder having the chemical formula represented by formula (I).

In step D):

The barium calcium titanate precursor represented by the formula (I) is sintered to obtain a barium calcium titanate powder having the chemical formula represented by the formula (I).

Specifically, the barium calcium titanate precursor represented by formula (I) is heated to a sintering temperature and sintered to obtain barium calcium titanate powder having the chemical formula represented by formula (I).

In certain embodiments of the present invention, the heating rate is 8 to 12°C/min, specifically, 10°C/min; the sintering temperature is 600 to 1200°C, specifically, 960°C or 1010°C; the sintering time is 1.5 to 2.5h, specifically, 2h.

The present invention has no particular limitation on the sources of the raw materials used above, and they can be generally commercially available.

The invention provides a novel preparation method of barium calcium titanate powder. The prepared barium calcium titanate powder is uniformly doped with calcium and free of impurities such as calcium titanate, calcium hydroxide and calcium carbonate.

The present invention also provides a dielectric material, wherein the raw material for preparing the dielectric material comprises the barium calcium titanate powder described above or the barium calcium titanate powder prepared by the preparation method described above.

The present invention also provides a ceramic capacitor, wherein the raw material for preparing the ceramic capacitor includes the barium calcium titanate powder described above or the barium calcium titanate powder prepared by the preparation method described above.

The present invention also provides a slurry, wherein the raw materials for preparing the slurry include the barium calcium titanate powder described above or the barium calcium titanate powder prepared by the preparation method described above.

The present invention also provides an original sheet, wherein the raw materials for preparing the original sheet include the barium calcium titanate powder described above or the barium calcium titanate powder prepared by the preparation method described above.

In order to further illustrate the present invention, a calcium barium titanate powder, a preparation method and an application thereof provided by the present invention are described in detail below in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

Embodiment 1:

Titanium dioxide powder (mass content of rutile is 9.2%) with a specific surface area of 150 ^m2 /g and a primary particle size of 10 nm was mixed with water and a polycarboxylate ammonium salt dispersant to obtain a slurry with a solid content of 20wt% and a dispersant content of 2wt%. Sand milling was performed and the solid content of the powder during sand milling was designed to be 20wt% and the dispersant content was 2wt%. After sand milling, a uniform and stable titanium dioxide suspension was obtained. The specific surface area and crystal form of the titanium dioxide powder in the titanium dioxide suspension were detected and shown in Table 1:

Table 1 Detection results of titanium dioxide powder in titanium dioxide suspension in Example 1

Specific surface area [m ² /g] Brookite [wt%] Anatase [wt%] Rutile [wt%] 150 62.83 27.97 9.20

1.5 L of 2 mol/L sodium hydroxide solution (pH value is 14) was prepared, and the electric heating mantle was heated to 88° C. and kept warm for 10 min. 445.3 g of barium hydroxide octahydrate powder was added and stirred for dissolution for 10 min. Then, the obtained mixed solution was heated to 105° C., and 584.7 g of the titanium dioxide suspension was added. The mixture was reacted at normal pressure and 105° C. for 1.5 h. After the reaction, a product solution of barium titanate (wherein x=0.9445) represented by formula (II) was obtained. 5.83 g of calcium hydroxide powder was added, and the mixture was reacted at normal pressure and 105° C. for 8 h. The sampling and detection results showed that Ba/Ti=0.9445 and Ca/Ti=0.0500, and a barium calcium titanate process suspension represented by the formula Ba _0.9445 Ca _0.0500 TiO ₃ (wherein x=0.9445 and y=0.0500) was obtained.

The remaining barium hydroxide octahydrate, weighing 4.7 g, was added. After adding the materials, the reaction was continued at normal pressure and 105°C for 1 hour to complete the reaction. After settling, the supernatant was poured out, and after washing with ethanol 5 times the mass of barium calcium titanate, it was filtered into a powder cake, dried at 200°C, and crushed through a 100-mesh sieve to obtain a powder. The composition test results showed that Ba/Ti=0.9552, Ca/Ti=0.0503, that is, a barium calcium titanate precursor represented by the formula Ba _0.9552 Ca _0.0503 TiO ₃ (wherein x=0.9445, y=0.0503, z=0.0112) was obtained. In this precursor, z>0, x+y+z=1.0055, which meets the requirements of formula (I).

FIG1 is an XRD diagram of the barium calcium titanate precursor prepared in Example 1 of the present invention. As shown in FIG1 , the sample only contains barium calcium titanate without impurities such as calcium titanate, calcium hydroxide or calcium carbonate. FIG2 is a TEM-EDS element mapping diagram of the barium calcium titanate precursor prepared in Example 1 of the present invention. It can be judged from FIG2 that the calcium doping is uniform.

The obtained precursor was heat treated: the heating rate was 10°C/min, and the heat treatment was performed at 960°C for 2h to obtain barium calcium titanate powder 1-1; the heating rate was 10°C/min, and the heat treatment was performed at 1010°C for 2h to obtain barium calcium titanate powder 1-2.

The test results shown in Table 2 were obtained through X-ray fluorescence spectroscopy analysis, specific surface area detector, X-ray diffractometer and other tests:

Table 2 Test results of calcium barium titanate powder obtained in Example 1

In Table 2, D (specific surface area) is a particle size value calculated by assuming that the barium calcium titanate particles are spheres.

FIG3 is an XRD graph of the barium calcium titanate powder 1-1 in Example 1. As shown in FIG3 , the sample contains only barium calcium titanate without impurities such as calcium titanate, calcium hydroxide or calcium carbonate. FIG4 is a TEM-EDS element mapping graph of the barium calcium titanate powder 1-1 in Example 1. It can be judged from FIG4 that the calcium doping is uniform. FIG5 is a SEM graph of the barium calcium titanate powder 1-1 in Example 1. It can be seen from FIG5 that the particle size distribution of the barium calcium titanate powder prepared by the present invention is relatively uniform.

Embodiment 2:

5L of 0.4mol/L titanium tetrachloride solution was taken and poured into a four-necked flat-bottomed flask, heated to 104°C, and hydrolyzed at 104°C for 60min, then cooled to room temperature at a rate of 2°C/min, and the obtained solution was decontaminated with an anion exchange resin, the amount ratio of the anion exchange resin to the solution was 1403g:1L, and when the pH value of the solution was 3.6, the decontamination was stopped, and then the hollow fiber membrane was used for concentration to obtain a titanium dioxide suspension with a mass concentration of 15.68%. The specific surface area and crystal form of the titanium dioxide were detected and shown in Table 3:

Table 3 Specific surface area and crystal form test results of titanium dioxide in Example 2

Specific surface area [m ² /g] Brookite [wt%] Anatase [wt%] Rutile [wt%] 146 66.84 25.34 7.82

1.5 L of 2 mol/L sodium hydroxide solution (pH value is 14) was prepared, and the electric heating mantle was heated to 90° C. and kept warm for 10 min. 445.3 g of barium hydroxide octahydrate powder was added and stirred for dissolution for 10 min. Then, the obtained mixed solution was heated to 105° C., and 745.8 g of the titanium dioxide suspension was added. The mixture was reacted at normal pressure and 105° C. for 1.5 h. After the reaction was completed, a product solution of barium titanate (wherein x=0.9464) represented by formula (II) was obtained. Then, 5.83 g of calcium hydroxide powder was added, and the reaction was continued for 8 h. The sampling and detection results showed that Ba/Ti=0.9464 and Ca/Ti=0.0500, and a barium calcium titanate process suspension represented by the formula Ba _0.9464 Ca _0.0500 TiO ₃ (wherein x=0.9464 and y=0.0500) was obtained.

The remaining barium hydroxide octahydrate, weighing 4.7g, was added. After adding the materials, the reaction was continued at normal pressure and 105°C for 1h to complete the reaction. After standing and settling, the supernatant was poured out, and after washing with ethanol 5 times the mass of barium calcium titanate, it was filtered into a powder cake, dried at 200°C, and crushed through a 100-mesh sieve to obtain a powder. The component test results showed that Ba/Ti=0.9546, Ca/Ti=0.0504, that is, a barium calcium titanate precursor represented by the formula Ba _0.9546 Ca _0.0504 TiO ₃ (wherein x=0.9464, y=0.0504, z=0.0082) was obtained. In the precursor, z>0, x+y+z=1.0050, which met the requirements of formula (I). The sample was measured by an X-ray diffractometer to contain only barium calcium titanate, without impurities such as calcium titanate, calcium hydroxide or calcium carbonate; the calcium doping was determined to be uniform by TEM-EDS element mapping.

The obtained precursor was heat treated at a heating rate of 10°C/min and a temperature of 1010°C for 2h to obtain the barium calcium titanate powder of Example 2.

The test results shown in Table 4 were obtained through X-ray fluorescence spectroscopy analysis, specific surface area detector, X-ray diffractometer and other tests:

Table 4 Test results of calcium barium titanate powder obtained in Example 2

In Table 4, D (specific surface area) is a particle size value calculated by assuming that the barium calcium titanate particles are spheres.

The samples of Example 2 were subjected to X-ray diffraction detection and TEM-EDS element mapping detection. The X-ray diffraction spectrum showed that both samples contained only barium calcium titanate, without impurities such as calcium titanate, calcium hydroxide or calcium carbonate. The TEM-EDS element mapping detection results showed that the calcium doping in both samples was uniform.

Embodiment 3:

According to the same synthesis method as in Example 2, calcium barium titanate precursors 3-1, 3-2, 3-3, 3-4, and 3-5 with different calcium doping concentrations were synthesized, and the corresponding y values were 1.0%, 3.0%, 5.0%, 10.0%, and 15.0%, respectively. Each precursor was then heat-treated at a heating rate of 10°C/min, a heat treatment temperature of 1000°C, and a heat treatment time of 2h to obtain calcium barium titanate powders 3-1, 3-2, 3-3, 3-4, and 3-5.

The test results shown in Table 5 were obtained through X-ray fluorescence spectroscopy analysis, specific surface area detector, X-ray diffractometer and other tests:

Table 5 Test results of calcium barium titanate powder obtained in Example 3

In Table 5, D (specific surface area) is a particle size value calculated by assuming that the barium calcium titanate particles are spheres.

X-ray diffraction detection and TEM-EDS element mapping detection were performed on the five samples in Example 3. The X-ray diffraction spectrum showed that the five samples only contained barium calcium titanate, without impurities such as calcium titanate, calcium hydroxide or calcium carbonate. The TEM-EDS element mapping detection results showed that the Ca doping in the five samples was uniform.

Comparative Example 1:

Take _5L of 1.2mol/L TiCl4 solution, pour it into a four-necked flat-bottom flask, heat it to 104℃, and hydrolyze it at 104℃ for 60min, then cool it to room temperature at a rate of 2℃/min, remove impurities from the obtained solution using anion exchange resin, the amount ratio of the anion exchange resin to the solution is 4210g:1L, when the pH value of the solution is 3.5, stop removing impurities, and then use a hollow fiber membrane to concentrate to obtain a titanium dioxide suspension with a mass concentration of 15.02%. The specific surface area and crystal form of titanium dioxide are shown in Table 6:

Table 6 Specific surface area and crystal form test results of titanium dioxide in comparative example 1

Specific surface area [m ² /g] Brookite [wt%] Anatase [wt%] Rutile [wt%] 93 53.24 20.45 26.31

Then, barium calcium titanate was synthesized according to the same steps as in Example 2 to obtain a barium calcium titanate precursor represented by Ba _0.9560 Ca _0.0503 TiO ₃ (wherein x=0.9451, y=0.0503, z=0.0109), which meets the requirements of formula (I).

FIG6 is an XRD diagram of the barium calcium titanate precursor of Comparative Example 1. As shown in FIG6 , in addition to containing barium calcium titanate, characteristic peaks of calcium titanate appear near 33° and 47.5° at 2θ, indicating that calcium titanate impurities are generated in this sample.

Comparative Example 2:

A titanium dioxide suspension was prepared using the method in Example 2 to obtain a titanium dioxide suspension with a mass concentration of 15.3%, and then calcium barium titanate was synthesized. Different from Example 2, in step A), all the barium source was added to synthesize barium titanate, and in step B), a calcium source was added to react to obtain a calcium barium titanate precursor represented by the formula Ba _0.9562 Ca _0.0504 TiO ₃ (wherein x=0.9562, y=0.0504, z=0). Since all the barium source was added to the synthesis in step A), step C was eliminated. The calcium barium titanate precursor was tested, and the X-ray diffraction spectrum showed that the sample contained only calcium barium titanate, and no impurities such as calcium titanate, calcium hydroxide or calcium carbonate.

The precursor obtained in Comparative Example 2 was heat treated in the same manner as in Example 2. The test results shown in Table 7 were obtained by X-ray fluorescence spectrometry, specific surface area detector, X-ray diffractometer, etc.:

Table 7 Test results of calcium barium titanate powder obtained in Comparative Example 2

In Table 7, D (specific surface area) is a particle size value calculated by assuming that the barium calcium titanate particles are spheres.

The unit cell volume V=64.03 Å3, which is higher than that of the sample in Example 2 and does not meet the unit cell volume requirement of claim 2, indicating that part of the calcium in the barium titanate prepared by the feeding method did not enter the barium titanate lattice. Although this part of calcium can be detected during component detection, when it is prepared into MLCC components, this part of calcium will not have the ability to improve the reduction resistance, but it reduces the dielectric constant.

Comparative Example 3

A titanium dioxide suspension was prepared using the method in Example 2 to obtain a titanium dioxide suspension with a mass concentration of 15.3%, and then barium calcium titanate was synthesized. Different from Example 2, in step A), the barium source and the calcium source were added simultaneously to synthesize barium calcium titanate, and steps B) and C) were omitted. After synthesis, a barium calcium titanate precursor represented by the formula Ba _0.9557 Ca _0.0502 TiO ₃ (wherein x=0.9557, y=0.0502, z=0) was obtained.

FIG7 is an XRD diagram of the barium calcium titanate precursor of Comparative Example 3. As shown in FIG7 , in addition to the characteristic peaks of barium calcium titanate, it also contains characteristic peaks of calcium titanate impurities, indicating that when the barium source and the calcium source are simultaneously fed and synthesized, while synthesizing barium calcium titanate, the calcium source also reacts with titanium dioxide to generate calcium titanate impurities.

Comparative Example 4

A titanium dioxide suspension was prepared using the method in Example 2 to obtain a titanium dioxide suspension with a mass concentration of 16.5%, and then calcium barium titanate was synthesized. Unlike Example 2, the molar concentration of the sodium hydroxide solution is lower. When preparing the sodium hydroxide solution, a pH meter was used to monitor the pH value so that the pH of the prepared sodium hydroxide solution was 10.9, and then the synthesis was carried out. After the synthesis, it was confirmed by detection that Ba/Ti=0.9549, Ca/Ti=0.0503, and a calcium barium titanate precursor represented by the formula Ba _0.9549 Ca _0.0503 TiO ₃ was obtained. Figure 8 is an XRD diagram of the calcium barium titanate precursor of Comparative Example 4. As shown in Figure 8, in addition to the characteristic peaks of calcium barium titanate, it also contains characteristic peaks of impurities such as calcium titanate and barium carbonate.

Comparative Example 5

A titanium dioxide suspension was prepared using the method in Example 2 to obtain a titanium dioxide suspension with a mass concentration of 16.5%, and then calcium barium titanate was synthesized. Unlike Example 2, the calcium doping concentration was increased in Comparative Example 5. By increasing the amount of calcium source fed, the calcium doping concentration reached 20%, and a calcium barium titanate precursor represented by the formula Ba _0.8045 Ca _0.2012 TiO ₃ was obtained. Figure 9 is an XRD diagram of the calcium barium titanate precursor of Comparative Example 5. As shown in Figure 9, in addition to the characteristic peaks of calcium barium titanate, it also contains impurity peaks of calcium hydroxide, indicating that the amount of calcium source fed has exceeded the solid solubility limit at this time, and the excess portion remains in the solution in the form of calcium hydroxide.

The description of the above embodiments is only used to help understand the method of the present invention and its core idea. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims (12)

1. A barium calcium titanate powder having the chemical formula (I): Ba _x+z Ca _y TiO ₃ (I); In formula (I), y is the molar content of Ca, which is 0<y≤0.15, and 0.98≤x+y+z≤1.015; At 25±3°C, the unit cell volume V of the calcium barium titanate powder measured by XRD satisfies the formula (1): V≤64.3-6.6×y (1); In formula (1), 0<y≤0.15. 2. The barium calcium titanate powder according to claim 1, characterized in that the (110) crystal plane FWHM of the barium calcium titanate powder is ≤0.40°, and the (111) crystal plane FWHM is ≤0.30°. 3. The method for preparing the barium calcium titanate powder according to claim 1 or 2, comprising the following steps: A) mixing a portion of the barium source with a strong alkaline solution, heating the obtained mixed solution, and then mixing it with a titanium source solution to react to obtain a product solution containing barium titanate represented by formula (II); Ba _x TiO ₃ formula (Ⅱ); In formula (II), 0.85≤x<1.00; B) mixing the product solution containing barium titanate represented by formula (II) with a calcium source, and reacting to obtain a barium calcium titanate process product represented by formula (III): Ba _x Ca _y TiO ₃ formula (III); In formula (III), 0<y≤0.15, 0.85<x+y≤1.00; C) reacting the barium calcium titanate process product represented by formula (III) with the remaining barium source to obtain the barium calcium titanate precursor represented by formula (I); Ba _x+z Ca _y TiO ₃ formula (Ⅰ); In formula (I), 0<y≤0.15, z>0, 0.98≤x+y+z≤1.015. 4. The preparation method according to claim 3, characterized in that after step C), it further comprises: D) calcining the barium calcium titanate precursor represented by formula (I) to obtain barium calcium titanate powder having the chemical formula represented by formula (I). 5. The preparation method according to claim 3, characterized in that the barium source comprises at least one of barium hydroxide octahydrate, barium hydroxide monohydrate, anhydrous barium hydroxide, barium chloride, barium chlorate, barium acetate, barium nitrate and barium oxide. 6. The preparation method according to claim 3, characterized in that, in step A), the pH value of the strong alkaline solution is ≥ 12; The strong base includes lithium hydroxide, sodium hydroxide, potassium hydroxide or a quaternary ammonium base. 7. The preparation method according to claim 3, characterized in that in step A), the titanium source comprises at least one of titanium tetrachloride solution, titanium hydroxide suspension, hydrated titanium dioxide suspension, titanium oxychloride and titanium dioxide suspension; The specific surface area of the powder of the titanium dioxide suspension after drying is 50 to 200 m ² /g, and the primary particle size is 8 to 30 nm; In the titanium dioxide suspension, the crystal form requirements of titanium dioxide include: the mass content of rutile is ≤20%, and the rest is at least one of anatase and brookite. 8. The preparation method according to claim 3, characterized in that the calcium source comprises at least one of calcium hydroxide powder, calcium chloride powder and calcium oxide powder. 9. A dielectric material, characterized in that the raw material for preparing the dielectric material comprises the barium calcium titanate powder according to any one of claims 1 to 2 or the barium calcium titanate powder prepared by the preparation method according to any one of claims 3 to 8. 10. A ceramic capacitor, characterized in that the raw material for preparing the ceramic capacitor comprises the barium calcium titanate powder according to any one of claims 1 to 2 or the barium calcium titanate powder prepared by the preparation method according to any one of claims 3 to 8. 11. A slurry, characterized in that the raw materials for preparing the slurry include the barium calcium titanate powder according to any one of claims 1 to 2 or the barium calcium titanate powder prepared by the preparation method according to any one of claims 3 to 8. 12. A raw sheet, characterized in that the raw material for preparing the raw sheet comprises the barium calcium titanate powder described in any one of claims 1 to 2 or the barium calcium titanate powder prepared by the preparation method described in any one of claims 3 to 8.