Fine-grained barium titanate ceramic dielectric material coated with bismuth borosilicate glass and its preparation method

Abstract

This invention relates to a fine-grained barium titanate ceramic dielectric material coated with bismuth borosilicate glass and its preparation method. A bismuth borosilicate glass sol is prepared using a sol-gel method, wherein the bismuth borosilicate glass is a Bi₂O₃-B₂O₃-SiO₂ glass. BaTiO₃ powder is dispersed in the bismuth borosilicate glass sol to obtain bismuth borosilicate glass sol-coated BaTiO₃ powder. The bismuth borosilicate glass-coated BaTiO₃ powder is calcined to obtain fine-grained barium titanate ceramic powder coated with bismuth borosilicate glass. The fine-grained barium titanate ceramic powder coated with bismuth borosilicate glass is granulated and shaped to obtain a barium titanate ceramic green body. Heating further yields a fine-grained barium titanate dielectric ceramic, which is the fine-grained barium titanate ceramic dielectric material coated with bismuth borosilicate glass. Compared with the prior art, the present invention prepares glass-coated BaTiO3 powder to form a core-shell structure powder by sol-gel method. This core-shell structure powder of glass-coated BaTiO3 powder is used for the preparation of fine-grained barium titanate ceramics and can be widely used in the field of electronic materials applications.

Description

Technical Field

[0001] This invention relates to the field of sol-gel glass preparation technology, and in particular to a fine-grained barium titanate ceramic dielectric material coated with bismuth borosilicate glass and its preparation method. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are electronic components widely used in surface-mount circuits. They are typically made by stacking ceramic dielectric films with printed internal electrodes in a staggered manner, sintering at high temperatures, and then sealing external electrodes at both ends of the chip. BaTiO3, with its high polarization value, is an ideal energy storage capacitor and is often used as the ceramic dielectric in MLCCs. Currently, the main development trends of MLCCs are miniaturization, increased capacitance, lead-free technology, and specialization. Miniaturization and increased capacitance require MLCC devices to have a high number of dielectric layers and a low dielectric layer thickness. Due to its extremely high surface activity, small-particle-size BaTiO3 is prone to overgrowth. Therefore, reducing the sintering temperature is also a necessary condition for the development of MLCC devices. Bi2O3-B2O3-SiO2 glass, as a low-melting-point glass powder, can be used as a sintering aid for BaTiO3 ceramics to lower the ceramic sintering temperature.

[0003] When BaTiO3 powder is mixed and sintered with glass powder, glass powder with a similar particle size to BaTiO3 powder is usually selected to ensure better uniform mixing and prevent pores caused by glass liquefaction after sintering. However, it is difficult to obtain glass powder that matches nano-BaTiO3 powder by melt ball milling. The method of coating BaTiO3 powder with sol-gel glass not only achieves more uniform mixing of glass and BaTiO3 powder and increases the contact area between the glass and BaTiO3 powder after liquefaction, thus further promoting sintering, but also the coating layer is generally several to tens of nanometers in size, with almost no large pores after liquefaction. Currently reported methods utilize Bi2O3-B2O3-SiO2 glass-coated BaTiO3 powder to prepare fine-grained barium titanate ceramics at a relatively low temperature of 900℃. The way (Werner) Arthur Fink, Ernst Bohn, "Controlled growth of monodisperse silica spheres in the micron size range," *Journal of Colloid and Interface Science*, Volume 26, Issue 1, 1968, Pages 62-69, used 27 vol% Bi₂O₃-B₂O₃-SiO₂ glass deposited on the surface of BaTiO₃ powder. This coating method, using precipitation under alkaline conditions, cannot precisely control the composition and content of the coating glass. Summary of the Invention

[0004] The existing method of preparing fine-grained barium titanate ceramics by deposition under alkaline conditions followed by centrifugation suffers from the problem of not being able to precisely control the composition and content of the coating glass. This invention provides a bismuth borosilicate glass-coated fine-grained barium titanate ceramic dielectric material and its preparation method. This invention prepares glass-coated BaTiO3 powder to form a core-shell structure powder using the sol-gel method. This core-shell structure powder of glass-coated BaTiO3 powder is widely applicable in the preparation of fine-grained barium titanate ceramics and can be widely used in electronic materials applications.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] This invention provides a method for preparing fine-grained barium titanate ceramic powder coated with bismuth borosilicate glass, comprising the following steps:

[0007] S1. Prepare bismuth borosilicate glass sol using the sol-gel method, wherein the bismuth borosilicate glass is Bi2O3-B2O3-SiO2 glass;

[0008] S2. Disperse BaTiO3 powder in bismuth borosilicate glass sol to obtain BaTiO3 powder coated with bismuth borosilicate glass sol;

[0009] S3. After calcination, the BaTiO3 powder coated with bismuth borosilicate glass sol was used to obtain fine-grained barium titanate ceramic powder coated with bismuth borosilicate glass.

[0010] In one embodiment of the present invention, the method for preparing bismuth borosilicate glass sol using the sol-gel method in step S1 is specifically as follows:

[0011] The silicon-containing precursor and the boron-containing precursor were added to a mixed solution of water and ethanol for hydrolysis to obtain solution one.

[0012] When bismuth salts are added to acids or organic solvents, solution two is obtained.

[0013] Dissolve solutions one and two separately by stirring at 50–70°C until they become transparent;

[0014] After mixing solutions one and two, stir continuously at 50–70°C for 1–3 hours to obtain a bismuth borosilicate glass sol solution.

[0015] In one embodiment of the present invention, the silicon-containing precursor is a silicon-containing organic precursor selected from tetraethyl orthosilicate;

[0016] In one embodiment of the present invention, the boron-containing precursor includes a boron-containing organic precursor or a boron-containing inorganic precursor, wherein the boron-containing precursor is selected from one or a combination of boric acid, triethyl borate or tributyl borate;

[0017] In one embodiment of the present invention, the bismuth salt includes an organic bismuth salt or an inorganic bismuth salt, and is selected from one or a combination of several of bismuth nitrate pentahydrate or bismuth acetate;

[0018] In one embodiment of the present invention, the acid is selected from nitric acid or acetic acid, and the organic solvent is selected from one or more of ethylene glycol or glycerol.

[0019] In one embodiment of the present invention, the molar ratio of the silicon-containing precursor, the boron-containing precursor, and the bismuth salt is in the range of silicon-containing precursor: boron-containing precursor: bismuth salt = 5-35%: 5-35%: 30-70%; more preferably 10-35%: 5-35%: 30-65%; the mass of the mixed solution of water and ethanol is 5-15 times that of the silicon-containing precursor and the boron-containing precursor, and the ratio of water to ethanol is 2:1 to 1:3; the mass of the acid or organic solvent is 2-8 times that of the bismuth salt.

[0020] The bismuth borosilicate glass sol solution is a transparent bismuth borosilicate glass sol solution.

[0021] In one embodiment of the present invention, in step S2, the particle size of the BaTiO3 powder is 50-800 nanometers.

[0022] In one embodiment of the present invention, in step S2, the method of dispersing BaTiO3 powder in bismuth borosilicate glass sol to obtain BaTiO3 powder coated with bismuth borosilicate glass sol is as follows: the BaTiO3 powder is ultrasonically dispersed in ethanol or water, and then a certain amount of bismuth borosilicate glass sol solution prepared in step S1 is added dropwise. The solvent is removed by continuous stirring and heating under an air atmosphere to obtain BaTiO3 powder coated with bismuth borosilicate glass sol.

[0023] In one embodiment of the present invention, the mass of barium titanate is 7-49 times the mass of bismuth borosilicate glass contained in the bismuth borosilicate glass sol solution.

[0024] In one embodiment of the present invention, in step S3, the calcination conditions are: calcination at 300-500°C for 2-4 hours in an air atmosphere. The purpose of calcination is to remove residual solvents and precursor decomposition products in the gel, including water, ethanol, acetic acid, glycerol, ethylene glycol and nitrogen oxides, and to completely densify the bismuth borosilicate gel to form a glassy substance.

[0025] In one embodiment of the present invention, in step S3, after calcination and cooling, the bismuth borosilicate glass-coated fine-grained barium titanate ceramic powder obtained contains 2 to 12 wt% of the bismuth borosilicate glass-coated barium titanate powder.

[0026] The present invention further provides fine-grained barium titanate ceramic powder coated with bismuth borosilicate glass prepared by the above method.

[0027] The present invention further provides a method for preparing a fine-grained barium titanate ceramic dielectric material coated with bismuth borosilicate glass. The fine-grained barium titanate ceramic powder coated with bismuth borosilicate glass prepared by the above method is granulated and shaped to obtain a barium titanate ceramic green body. The green body is heated to 400-600℃ and held at that temperature for 1-3 hours, then heated to 1000-1250℃ and held at that temperature for 1-3 hours to obtain a fine-grained barium titanate dielectric ceramic, which is the fine-grained barium titanate ceramic dielectric material coated with bismuth borosilicate glass.

[0028] In one embodiment of the present invention, the method for obtaining barium titanate ceramic green body by granulation and molding of fine-grained barium titanate ceramic powder coated with bismuth borosilicate glass is as follows: fine-grained barium titanate ceramic powder coated with bismuth borosilicate glass and organic binder are mixed and granulated, wherein the mass ratio of fine-grained barium titanate ceramic powder coated with bismuth borosilicate glass is 90% to 97%, and the mass ratio of organic binder is 3% to 10%, wherein the organic binder is selected from one or more of polyacrylate, ethyl cellulose, polyvinyl alcohol or polyurethane.

[0029] The present invention further provides a fine-grained barium titanate ceramic dielectric material coated with bismuth borosilicate glass prepared by the above preparation method.

[0030] The fine-grained barium titanate dielectric ceramic prepared by this invention involves sintering barium titanate powder coated with bismuth borosilicate glass to form a core-shell structure. The shell structure formed by the bismuth borosilicate glass inhibits the mutual contact growth of the barium titanate powder itself, resulting in almost no grain growth after sintering. The ceramic grain size can be determined using a scanning electron microscope, the dielectric properties of the barium titanate ceramic can be measured using a broadband dielectric impedance spectroscopy, and the density and porosity of the sintered ceramic can be measured using an electronic hydrometer.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] Compared to the traditional method of mechanically mixing glass powder obtained by ball milling and BaTiO3 powder, this invention uses a sol-gel method to coat BaTiO3 powder, obtaining a core-shell structured powder. This results in more uniform contact between the glass phase and the BaTiO3 powder during melting, and the Bi content in the glass phase is higher. 3+ It reacts more uniformly with the surface of BaTiO3 powder, forming core-shell structured BaTiO3 grains, and inhibiting abnormal grain growth during sintering. Compared to The core-shell structured powder prepared by this method uses a sol-gel crosslinking method under acidic conditions to transform into a gel-adhesive powder and remove all solvents, thereby achieving controllability of the glass coating components and content, and improving the operability and repeatability of the process.

[0033] Unlike existing technologies that involve deposition under alkaline conditions followed by centrifugation, this invention utilizes acidic conditions to further crosslink the sol, transforming it into a gel that adheres to the powder surface. Heating removes all solvents, resulting in bismuth borosilicate glass-coated barium titanate powder with controllable glass composition and content. This invention is applicable to coating barium titanate powders of various sizes, with coating contents ranging from 2-12 wt%. It achieves complete grain size control after sintering and densification of barium titanate ceramics, allowing for the preparation of barium titanate ceramic samples with controllable grain size by controlling the initial barium titanate powder particle size. Attached Figure Description

[0034] Figure 1 Scanning electron microscope image of untreated barium titanate nanoparticles;

[0035] Figure 2 Transmission electron microscope image and selected electron diffraction pattern of 5% bismuth borosilicate glass coated with 95% nano-barium titanate powder.

[0036] Figure 3 Scanning electron microscope image of fine-grained barium titanate ceramic obtained by sintering 95% by mass barium nanoparticles coated with 5% by mass bismuth borosilicate glass at 1000℃.

[0037] Figure 4 Scanning electron microscope image of fine-grained barium titanate ceramic obtained by sintering 95% by mass submicron barium titanate powder coated with 5% by mass bismuth borosilicate glass at 1100℃. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0039] Example 1:

[0040] This embodiment provides a method for preparing bismuth borosilicate glass-coated barium titanate powder and its fine-grained dielectric ceramic.

[0041] 1.04 g of tetraethyl orthosilicate and 0.62 g of boric acid were added to a mixed solution of ethanol and water and hydrolyzed at 70 °C until transparent and clear. 14.60 g of bismuth nitrate pentahydrate was added to an acetic acid solution and heated and stirred at 70 °C until clear. The two precursor solutions were mixed uniformly and stirred continuously at 70 °C for 6 hours to obtain a transparent and clear bismuth borosilicate glass sol. 47.5 g of barium titanate powder with a particle size <100 nm was added... Figure 1 The bismuth borosilicate glass was ultrasonically dispersed in water, and a glass sol containing 2.5g of calcined bismuth borosilicate glass was added dropwise. The mixture was stirred continuously in air and heated at 70°C to remove the solvent, yielding bismuth borosilicate gel-coated nano-BaTiO3 powder. The gel-coated barium titanate powder was then calcined at 400°C for 4 hours in air to obtain bismuth borosilicate glass-coated nano-barium titanate powder. Figure 2 ),Depend on Figure 2 It can be seen that there is a distinct coating layer of about 10 nm without lattice fringes at the edge of the barium titanate powder. The electron diffraction pattern shows that there are obvious amorphous diffraction rings. This coating layer is an amorphous bismuth borosilicate glass coating layer.

[0042] The above-mentioned bismuth borosilicate glass-coated barium titanate powder and 5 wt% polyacrylol were mixed and granulated to obtain a ceramic green body. This green body was then placed in a muffle furnace and heated to 600℃ for 3 hours, followed by heating to 1000℃ and holding for 2 hours to obtain fine-grained barium titanate ceramic. Figure 3 As shown, by Figure 3 It can be seen that the nano-BaTiO3 powder hardly grows at all, because the presence of the bismuth borosilicate glass coating layer inhibits the mutual contact growth of the nano-BaTiO3 powder.

[0043] Example 2:

[0044] This embodiment provides a method for preparing bismuth borosilicate glass-coated barium titanate powder and its fine-grained dielectric ceramic.

[0045] The specific preparation method is the same as in Example 1, except that the nano-barium titanate powder used in Example 1 is replaced with submicron barium titanate powder with D50 = 200nm, resulting in bismuth borosilicate glass-coated submicron barium titanate powder. The second-stage sintering temperature of the ceramic is changed to 1100℃, similarly yielding fine-grained barium titanate ceramic, such as... Figure 4 As shown, by Figure 4 It can be seen that the ceramic grain size remains similar to that of the initial powder, and the grains do not grow with increasing temperature.

[0046] Example 3:

[0047] This embodiment provides a method for preparing bismuth borosilicate glass-coated barium titanate powder and its fine-grained dielectric ceramic.

[0048] The specific preparation method is the same as in Example 1, except that the mass of barium titanate powder in Example 1 is changed to 48g, and the content of the added glass sol is changed to contain 2g of bismuth borosilicate glass after calcination.

[0049] Example 4:

[0050] This embodiment provides a method for preparing bismuth borosilicate glass-coated barium titanate powder and its fine-grained dielectric ceramic.

[0051] 1.30 g of tetraethyl orthosilicate and 0.77 g of boric acid were added to a mixed solution of ethanol and water and heated at 60 °C until hydrolyzed to a clear, transparent state. 12.10 g of bismuth nitrate pentahydrate was added to an ethylene glycol solution and heated and stirred at 60 °C until clear. The two precursor solutions were uniformly mixed and stirred continuously at 60 °C for 6 hours to obtain a clear, transparent bismuth borosilicate glass sol. 47.5 g of barium titanate powder with a particle size <100 nm was ultrasonically dispersed in alcohol and added dropwise to a glass sol containing 2.5 g of bismuth borosilicate glass after calcination. The mixture was stirred continuously in air and heated at 150 °C to remove the solvent, yielding bismuth borosilicate gel-coated nano-BaTiO3 powder. The gel-coated barium titanate powder was calcined at 400 °C for 2 hours in air to obtain bismuth borosilicate glass-coated nano-barium titanate powder.

[0052] The above-mentioned bismuth borosilicate glass-coated barium titanate powder and 5 wt% polyacrylol were mixed and granulated to obtain a ceramic green body. The green body was placed in a muffle furnace and heated to 600℃ and held for 3 hours, and then heated to 1000℃ and held for 2 hours to obtain fine-grained barium titanate ceramic.

[0053] Comparative Example 1:

[0054] Barium titanate powder with a particle size of less than 100 nm was mixed with 5 wt% polyacrylol and granulated to obtain a ceramic green body. The green body was placed in a muffle furnace and heated to 600 °C for 3 h, then heated to 1000 °C for 2 h to obtain barium titanate ceramic.

[0055] Comparative Example 2:

[0056] The specific preparation method is the same as that of Comparative Example 1, except that the nano barium titanate powder used in Comparative Example 1 is changed to submicron barium titanate powder with D50 = 200nm, and the sintering temperature of the second stage of ceramic is changed to 1100℃, and barium titanate ceramic is obtained in the same way.

[0057] The grain size, dielectric properties, and density of the barium titanate ceramics in Examples 1-5 and Comparative Examples 1-2 are shown in Table 1. The comparison shows that, compared with the uncoated barium titanate ceramics, the coated barium titanate ceramics exhibited almost no growth of BaTiO3 grains after sintering, achieving finer grains, and the dielectric loss was significantly reduced.

[0058] Table 1. Grain size, dielectric properties, and density of barium titanate ceramics in Examples 1-5 and Comparative Examples 1-2.

[0059]

[0060]

[0061] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A process for the preparation of bismuth borosilicate glass-coated barium titanate ceramic powder, characterized in that, The method comprises the following steps: S1, preparing a bismuth borosilicate glass sol by a sol-gel method, wherein the bismuth borosilicate glass is a Bi2O3-B2O3-SiO2 glass; S2, dispersing BaTiO3 powder in the bismuth borosilicate glass sol to obtain BaTiO3 powder coated with the bismuth borosilicate glass sol; S3, calcining the BaTiO3 powder coated with the bismuth borosilicate glass sol to obtain fine-grained barium titanate ceramic powder coated with the bismuth borosilicate glass; In step S1, the method for preparing the bismuth borosilicate glass sol by the sol-gel method is as follows: adding a silicon-containing precursor and a boron-containing precursor into a mixed solution of water and ethanol to hydrolyze and obtain solution one, adding a bismuth salt into an acid to obtain solution two, stirring and dissolving solution one and solution two at 50-70 ℃ until transparent, mixing solution one and solution two and continuously stirring at 50-70 ℃ for 1-3 h to obtain a bismuth borosilicate glass sol solution; the silicon-containing precursor is selected from tetraethyl orthosilicate; the boron-containing precursor is selected from one or a combination of boric acid, triethyl borate or tributyl borate; the bismuth salt is selected from one or a combination of bismuth nitrate pentahydrate or bismuth acetate; the acid is selected from nitric acid or acetic acid; in step S3, the calcination condition is as follows: calcining at 300-500 ℃ for 2-4 h in an air atmosphere; in step S3, after calcination and cooling, the fine-grained barium titanate ceramic powder coated with the bismuth borosilicate glass contains 2-12 wt% of the bismuth borosilicate glass in the fine-grained barium titanate ceramic powder coated with the bismuth borosilicate glass.

2. A process for the preparation of a bismuth borosilicate glass coated barium titanate ceramic powder as claimed in claim 1, wherein, The molar ratio of the silicon-containing precursor, the boron-containing precursor and the bismuth salt ranges from 10-35%:5-35%:30-65%; the mass of the mixed solution of water and ethanol is 5-15 times that of the silicon-containing precursor and the boron-containing precursor, and the ratio of water to ethanol is 2:1-1:3; the mass of the acid is 2-8 times that of the bismuth salt.

3. The method of claim 1, wherein the bismuth borosilicate glass-coated barium titanate ceramic powder is characterized by: In step S2, the particle size of the BaTiO3 powder is 50-800 nm; In step S2, the method for dispersing the BaTiO3 powder in the bismuth borosilicate glass sol to obtain the BaTiO3 powder coated with the bismuth borosilicate glass sol is as follows: ultrasonic dispersing the BaTiO3 powder in ethanol or water, then dropping a certain amount of the bismuth borosilicate glass sol solution prepared in step S1, continuously stirring and heating to remove the solvent in an air atmosphere, and obtaining the BaTiO3 powder coated with the bismuth borosilicate glass sol; The mass of the barium titanate is 7-49 times that of the bismuth borosilicate glass in the bismuth borosilicate glass sol solution.

4. Fine-grained barium titanate ceramic powder coated with the bismuth borosilicate glass prepared by the method according to any one of claims 1-3.

5. A method of making a bismuth borosilicate glass-clad barium fine-grained titanate ceramic dielectric material, characterized by, The fine-grained barium titanate ceramic powder coated with the bismuth borosilicate glass according to claim 4 is granulated and molded to obtain a barium titanate ceramic green body, heated to 400-600 ℃, kept at the temperature for 1-3 h, then heated to 1000-1250 ℃, kept at the temperature for 1-3 h, to obtain fine-grained barium titanate dielectric ceramic, i.e. fine-grained barium titanate ceramic dielectric material coated with the bismuth borosilicate glass.

6. A process for the preparation of a bismuth borosilicate glass-clad barium fine-grained titanate ceramic dielectric material according to claim 5, characterized in that, Mixing and granulating bismuth borosilicate glass-coated barium titanate ceramic powder and organic binder, wherein the mass ratio of bismuth borosilicate glass-coated barium titanate ceramic powder is 90% to 97%, and the mass ratio of organic binder is 3 to 10%, and the organic binder is selected from one or more of polyacrylate, ethyl cellulose, polyvinyl alcohol or polyurethane.

7. Bismuth borosilicate glass-coated barium titanate ceramic dielectric material prepared based on the method of claim 5 or 6.

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