A solid phase preparation method for ultrafine barium titanate powder

Abstract

The present invention relates to a solid-phase method for preparing ultrafine barium titanate powder. The method comprises: preparing porous anatase and rutile mixed-crystal titanium dioxide microspheres, wherein the ratio of the anatase phase to the rutile phase in the porous titanium dioxide microspheres is 15% to 30%: 70% to 85%, and the particle size is less than 50 nm; pulverizing the BaO raw material using a high-energy ball mill at a rotation speed of 1100 to 1200 rpm for 6 to 10 hours; and achieving a particle size ratio of the titanium dioxide microspheres to the pulverized BaO of 0.5 to 1.2. The present invention improves the uniformity of the overall sintering process by selecting a specific particle size ratio of the porous anatase and rutile mixed-crystal titanium dioxide microspheres to the raw material, and using the mixed-crystal porous titanium dioxide microspheres in conjunction with a two-stage microwave sintering process, thereby obtaining an ultrafine barium titanate powder with higher particle size uniformity, better dispersibility, and finer size.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic material preparation, and in particular to a solid-phase preparation method of ultrafine barium titanate powder and a product thereof. Background Art

[0002] Barium titanate, a typical perovskite ferroelectric ceramic material, is widely used in multilayer ceramic capacitors (MLCCs), sensors, memory and other fields due to its excellent dielectric, ferroelectric and piezoelectric properties.

[0003] Currently, the main methods for preparing barium titanate powder include solid-phase, liquid-phase (such as hydrothermal and sol-gel), and vapor-phase methods. The solid-phase method has become the mainstream industry practice due to its simplicity and low cost. However, its core challenge lies in uneven mixing of the raw materials. The traditional solid-phase method involves mechanically mixing barium titanate with titanium dioxide. Titanium dioxide typically has a single crystal form (such as anatase or rutile). This variability in crystal form leads to inconsistent reactivity and the formation of agglomerated particles with uneven particle size during sintering. Furthermore, the high sintering temperature results in coarse grains. Solid-phase reactions rely on high-temperature diffusion, which can easily lead to excessive growth. Furthermore, the dense structure of titanium dioxide limits the reaction interface, making it difficult to obtain an ultrafine powder. The preparation of porous barium titanate presents even greater technical challenges, and research on its preparation is relatively limited. The preparation of porous barium titanate powders also suffers from uneven particle size, small specific surface area, uncontrollable particle size, and insufficient fineness. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a solid-phase preparation method for ultrafine barium titanate powder.

[0005] The present invention relates to a solid-phase preparation method for ultrafine barium titanate powder, the method comprising the following steps: (1) preparing porous anatase and rutile mixed crystal titanium dioxide microspheres, wherein the ratio of anatase phase to rutile phase in the porous titanium dioxide microspheres is 15% to 30%: 70% to 85%, and the particle size is less than 50 nm.

[0006] (2) The BaO raw material was crushed using a high-energy ball mill at a speed of 1100-1200 rpm for 6-10 hours. The particle size of the BaO after crushing was less than 100 nm, and the ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the crushed BaO particle size was 0.5-1.2.

[0007] (3) The crushed BaO and the porous anatase and rutile mixed crystal titanium dioxide microspheres prepared in step (1) are dissolved in deionized water, stirred and subjected to ultrasonic oscillation treatment to uniformly mix the raw materials, and then fully dehydrated and dried in a drying oven at 50-150°C to obtain a dry mixed powder.

[0008] (4) The mixed powder of step (3) is placed in a microwave reactor and heated with microwaves at 1.0-2.0 GHz for 10-25 min. The microwave frequency is then increased to 2.3-2.7 GHz and the heating is continued for 15-30 min to obtain porous ultrafine barium titanate powder.

[0009] Preferably, the porous anatase and rutile mixed crystal titanium dioxide microspheres in step (1) are porous anatase and rutile mixed crystal titanium dioxide microspheres prepared by a template method.

[0010] Preferably, in step (2), the high-energy ball mill uses two types of mixed beads with different particle sizes, including 0.7 mm and 1.1 mm mixed beads.

[0011] Preferably, in step (2), the particle size ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the crushed BaO is 0.6-1.

[0012] Preferably, the ultrasonic oscillation treatment in step (3) is carried out in the range of 10 kHz to 50 kHz for 0.2 to 1 hour.

[0013] Preferably, the dehydration and drying time in step (3) is 0.5-5 h, and the moisture content of the mixed powder is lower than 0.1 wt%.

[0014] Preferably, in step (4), the microwave frequency is increased to 2.3-2.4 GHz and heating is continued for 20-25 minutes.

[0015] The present invention also relates to an ultrafine barium titanate powder, which is prepared by any one of the above preparation methods.

[0016] The beneficial effect of the present invention is that by selecting specific porous anatase and rutile mixed crystal titanium dioxide microspheres and controlling the ratio of the anatase phase to the rutile phase therein, the reaction in the subsequent sintering process is more controllable, the particle uniformity of barium titanate prepared by microwave solid phase sintering is improved, and the size is smaller.

[0017] By using high-energy ball milling to pulverize BaO, the mechanical and chemical activation processes initiated during the high-energy ball milling process promote the activity of the subsequent sintering reaction, thereby reducing the high-temperature sintering reaction temperature to a certain extent. The use of mixing beads in the high-energy ball milling process not only ensures uniform pulverization of the BaO raw material, but also provides a good dispersion effect, facilitating uniform mixing and sintering synthesis with titanium dioxide.

[0018] When porous anatase and rutile mixed crystal titanium dioxide microspheres are mixed with BaO powder, ultrasonic oscillation is used to fully disperse the two raw materials and greatly shorten the mixing time of the two raw materials, thereby improving production efficiency.

[0019] Compared with the traditional solid-phase synthesis method, the sintering of the present invention adopts a two-stage sintering process, which makes full use of the different reaction characteristics of anatase and rutile in the raw materials of porous anatase and rutile mixed crystal titanium dioxide microspheres, and combines with the sintering process to make full use of the characteristics of high microwave heating rate and high reactivity, so that part of the rutile phase preferentially reacts to form tetragonal crystals under rapid microwave heating at a relatively low temperature, and provides a favorable diffusion channel for the second stage sintering of the anatase phase-based reaction. Compared with the traditional sintering process, the use of mixed crystal porous titanium dioxide microspheres with a two-stage microwave sintering process improves the synthesis uniformity of the overall sintering process, and obtains a higher particle size uniformity, good dispersibility, and a smaller size of ultrafine barium titanate powder. The porous ultrafine barium titanate powder prepared by the present invention has an average particle size of less than 170nm, a D99 / D50 range of less than 1.27, a uniform particle size distribution, fine particles, and high purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 The present invention discloses a flow chart of a solid-phase preparation method for ultrafine barium titanate powder. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] The existing preparation of porous barium titanate powder has the following technical problems: uneven particle size, small specific surface area, uncontrollable particle size, and insufficient fineness. Figure 1 As shown, a solid phase method for preparing ultrafine barium titanate powder according to an embodiment of the present invention comprises the following steps: (1) preparing porous anatase and rutile mixed crystal titanium dioxide microspheres, wherein the ratio of anatase phase to rutile phase in the porous titanium dioxide microspheres is 15% to 30%: 70% to 85%, and the particle size is less than 50 nm.

[0024] (2) The BaO raw material was crushed using a high-energy ball mill at a speed of 1100-1200 rpm for 6-10 hours. The particle size of the BaO after crushing was less than 100 nm, and the ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the crushed BaO particle size was 0.5-1.2.

[0025] (3) The crushed BaO and the porous anatase and rutile mixed crystal titanium dioxide microspheres prepared in step (1) are dissolved in deionized water, stirred and subjected to ultrasonic oscillation treatment to uniformly mix the raw materials, and then fully dehydrated and dried in a drying oven at 50-150°C to obtain a dry mixed powder.

[0026] (4) The mixed powder of step (3) is placed in a microwave reactor and heated with microwaves at 1.0-2.0 GHz for 10-25 min. The microwave frequency is then increased to 2.3-2.7 GHz and the heating is continued for 15-30 min to obtain porous ultrafine barium titanate powder.

[0027] In one embodiment, the porous anatase and rutile mixed crystal titanium dioxide microspheres in step (1) are porous anatase and rutile mixed crystal titanium dioxide microspheres prepared by a template method.

[0028] The template method is a conventional method for preparing porous titanium dioxide. For example, porous titanium dioxide microspheres can be hydrothermally synthesized using dodecylamine as a template and inorganic titanium salt as a precursor. The desired titanium dioxide microspheres can be obtained by controlling the calcination temperature between 700-1100°C.

[0029] The porous titanium dioxide microspheres used in the present invention have a ratio of anatase phase to rutile phase of 15% to 30%:70% to 85%, and the particle size of the microspheres is less than 50 nm. By selecting the porous anatase and rutile mixed crystal titanium dioxide microspheres in this specific ratio, the density of titanium dioxide in the anatase phase is lower than that of titanium dioxide in the rutile structure, so the sintering synthesis temperature can be reduced. The rutile phase can be synthesized into tetragonal crystals at a lower temperature, making the reaction in the subsequent sintering synthesis process more controllable, improving the particle uniformity of barium titanate prepared by solid-phase sintering, and making the particle size smaller.

[0030] In one embodiment, in step (2), the ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the crushed BaO particle size is 0.6-1.

[0031] The appropriate particle size ratio of porous anatase and rutile mixed crystal titanium dioxide microspheres to crushed BaO has a significant influence on the microwave sintering reaction activity and grain growth. This may be because different particle size ratios affect the contact interface between different particles, thereby affecting the formation and grain growth of barium titanate, thereby affecting the particle size and uniformity of barium titanate. When the particle size ratio of porous anatase and rutile mixed crystal titanium dioxide microspheres to crushed BaO is 0.5-1.2, the particle size uniformity of barium titanate is better, and the particle size ratio is more preferably 0.6-1.

[0032] In one embodiment, the high-energy ball mill in step (2) uses two types of mixed beads with different particle sizes, including 0.7 mm and 1.1 mm mixed beads.

[0033] By using a high-energy ball mill to pulverize BaO, the mechanical and chemical activation processes initiated during the milling process promote the activity of the subsequent sintering reaction, thereby reducing the reaction conditions for microwave sintering to a certain extent. The use of mixed beads, including 0.7mm and 1.1mm, during the high-energy ball milling process ensures uniform pulverization of the BaO raw material while also providing good dispersion, facilitating uniform mixing and sintering with titanium dioxide.

[0034] In one embodiment, the ultrasonic oscillation treatment in step (3) is performed in the range of 10 kHz to 50 kHz for 0.2 to 1 hour. When the porous anatase and rutile mixed crystal titanium dioxide microspheres are mixed with BaO powder, ultrasonic oscillation can fully disperse the two raw materials and greatly shorten the mixing time, thereby improving production efficiency.

[0035] In one embodiment, the dehydration and drying time in step (3) is 0.5 to 5 hours, and the moisture content of the mixed powder is less than 0.1w%.

[0036] In one embodiment, in step (4), the microwave frequency is increased to 2.3-2.4 GHz and heating is continued for 20-25 minutes.

[0037] Compared with the traditional solid-phase synthesis method, the sintering of the present invention adopts a two-stage microwave sintering process, which fully utilizes the different reaction characteristics of anatase and rutile in the raw material of porous anatase and rutile mixed crystal titanium dioxide microspheres, and fully utilizes the characteristics of microwave high heating rate and high reactivity. In the first stage, microwave heating is carried out with a frequency of 1.0-2.0 GHz for 10-25 minutes. Through rapid heating and sintering, part of the rutile phase preferentially reacts to form tetragonal crystals at a relatively low temperature, and provides a favorable diffusion channel for the second stage sintering reaction dominated by the anatase phase. In the second stage, the microwave frequency is increased to 2.3-2.7 GHz and heating is continued for 15-30 minutes. At a higher temperature, the remaining BaO and titanium dioxide can react quickly and completely, reducing the sintering temperature and improving the sintering efficiency compared to traditional sintering. The use of mixed crystal porous titanium dioxide microspheres in combination with the two-stage microwave sintering process improves the synthesis uniformity of the overall sintering process, and obtains ultrafine barium titanate powder with higher particle size uniformity, good dispersibility, and finer size.

[0038] The present invention also relates to an ultrafine barium titanate powder, which is prepared by any one of the above preparation methods.

[0039] Example 1: (1) Using dodecylamine as a template and inorganic titanium salt as a precursor, porous titanium dioxide microspheres were hydrothermally synthesized by a template method. The ratio of anatase phase to rutile phase in the titanium dioxide microspheres was 15%:85%, and the particle size was 50 nm.

[0040] (2) The BaO raw material was crushed using a high-energy ball mill at a speed of 1120 rpm for 9 hours; the high-energy ball mill used two mixed beads with different particle sizes, including 0.7 mm and 1.1 mm mixed beads; the average particle size of BaO after high-energy ball milling was 70 nm.

[0041] (3) The crushed BaO and the porous anatase and rutile mixed crystal titanium dioxide microspheres prepared in step (1) were dissolved in deionized water, stirred and subjected to ultrasonic oscillation treatment in the range of 20 kHz for 0.5 h to uniformly mix the raw materials, and then fully dehydrated and dried in a drying oven at 100°C for 0.5 h to obtain a dry mixed powder with a moisture content of less than 0.1 w%.

[0042] (4) The mixed powder of step (3) was placed in a microwave reactor and heated with microwaves at 2.0 GHz for 15 min. The microwave frequency was then increased to 2.7 GHz and the heating was continued for 15 min to obtain porous ultrafine barium titanate powder.

[0043] Example 2: (1) Using dodecylamine as a template and inorganic titanium salt as a precursor, porous titanium dioxide microspheres were hydrothermally synthesized by a template method. The ratio of anatase phase to rutile phase in the titanium dioxide microspheres was 20%:80%, and the particle size was 40 nm.

[0044] (2) The BaO raw material was crushed using a high-energy ball mill at a speed of 1130 rpm for 7 hours; the high-energy ball mill used two mixed beads with different particle sizes, including 0.7 mm and 1.1 mm mixed beads; the average particle size of BaO after high-energy ball milling was 80 nm.

[0045] (3) The crushed BaO and the porous anatase and rutile mixed crystal titanium dioxide microspheres prepared in step (1) were dissolved in deionized water, stirred and subjected to ultrasonic oscillation treatment in the range of 10 kHz for 0.6 h to uniformly mix the raw materials, and then fully dehydrated and dried in a drying oven at 90°C for 1 h to obtain a dry mixed powder with a moisture content of less than 0.1 w%.

[0046] (4) The mixed powder of step (3) was placed in a microwave reactor and heated with microwaves at 1.5 GHz for 15 min. The microwave frequency was then increased to 2.5 GHz and the heating was continued for 20 min to obtain porous ultrafine barium titanate powder.

[0047] Example 3: (1) Using dodecylamine as a template and inorganic titanium salt as a precursor, porous titanium dioxide microspheres were hydrothermally synthesized by a template method. The ratio of anatase phase to rutile phase in the titanium dioxide microspheres was 30%:70%, and the particle size was 40 nm.

[0048] (2) The BaO raw material was crushed using a high-energy ball mill at a speed of 1180 rpm for 9 hours; the high-energy ball mill used two mixed beads with different particle sizes, including 0.7 mm and 1.1 mm mixed beads; the average particle size of BaO after high-energy ball milling was 34 nm.

[0049] (3) The crushed BaO and the porous anatase and rutile mixed crystal titanium dioxide microspheres prepared in step (1) were dissolved in deionized water, stirred and subjected to ultrasonic oscillation treatment in the range of 40 kHz for 1 h to uniformly mix the raw materials, and then fully dehydrated and dried in a drying oven at 80°C for 2 h to obtain a dry mixed powder with a moisture content of less than 0.1 w%.

[0050] (4) The mixed powder of step (3) was placed in a microwave reactor and heated with microwaves at 1.0 GHz for 25 min. The microwave frequency was then increased to 2.3 GHz and the heating was continued for 30 min to obtain porous ultrafine barium titanate powder.

[0051] Example 4: (1) Using dodecylamine as a template and inorganic titanium salt as a precursor, porous titanium dioxide microspheres were hydrothermally synthesized by a template method. The ratio of anatase phase to rutile phase in the titanium dioxide microspheres was 25%:75%, and the particle size was 40 nm.

[0052] (2) The BaO raw material was crushed using a high-energy ball mill at a speed of 1170 rpm for 8 hours; the high-energy ball mill used two mixed beads with different particle sizes, including 0.7 mm and 1.1 mm mixed beads; the average particle size of BaO after high-energy ball milling was 40 nm.

[0053] (3) The crushed BaO and the porous anatase and rutile mixed crystal titanium dioxide microspheres prepared in step (1) were dissolved in deionized water, stirred and subjected to ultrasonic oscillation treatment in the range of 50 kHz for 0.2 h to uniformly mix the raw materials, and then fully dehydrated and dried in a drying oven at 80°C for 5 h to obtain a dry mixed powder with a moisture content of less than 0.1 w%.

[0054] (4) The mixed powder of step (3) was placed in a microwave reactor and heated with microwaves at 1.0 GHz for 25 min. The microwave frequency was then increased to 2.4 GHz and the heating was continued for 20 min to obtain porous ultrafine barium titanate powder.

[0055] Comparative Example 1: The preparation method of barium titanate powder in Comparative Example 1 is different from that in Example 1 only in that: in step (1), the ratio of anatase phase to rutile phase in the titanium dioxide microspheres is 10%:90%, and the particle size is 100 nm.

[0056] The particle size ratio of porous anatase and rutile mixed crystal titanium dioxide microspheres to crushed BaO is 1.43.

[0057] Comparative Example 2: The preparation method of barium titanate powder in Comparative Example 2 differs from that in Example 1 only in that, in step (2), the high-energy ball milling was performed at 900 rpm for 9 hours, resulting in an average particle size of 150 nm for the BaO powder after high-energy ball milling. The particle size ratio of the porous anatase and rutile mixed-crystal titanium dioxide microspheres to the crushed BaO was 0.33.

[0058] Comparative Example 3: The preparation method of barium titanate powder in Comparative Example 3 is different from that in Example 1 only in that: in step (4), heating treatment is carried out with microwaves at 1.0 GHz for 7 minutes, and then the microwave frequency is increased to 2.4 GHz and heating is continued for 20 minutes to obtain porous ultrafine barium titanate powder.

[0059] Comparative Example 4: The preparation method of barium titanate powder in Comparative Example 4 is different from that in Example 1 only in that: in step (4), heating treatment is carried out with 1.0 GHz microwaves for 25 minutes, and then the microwave frequency is increased to 2.2 GHz and heating is continued for 10 minutes to obtain porous ultrafine barium titanate powder.

[0060] The porous ultrafine barium titanate powders prepared in Examples 1-4 and Comparative Examples 1-4 were tested. The average grain size was measured using a scanning electron microscope and an image analysis program. The particle size distribution curve width was calculated using Minitable software, expressed as D99 / D50. D50 refers to the particle size equivalent to 10% of the total volume when the particle size is accumulated from the small particles, and D99 refers to the particle size equivalent to 99% of the total volume when the particle size is accumulated from the small particles. The results are shown in Table 1.

[0061] Table 1: Performance data of porous ultrafine barium titanate powders prepared in Examples 1-4 and Comparative Examples 1-4

[0062] As shown in Table 1, the porous ultrafine barium titanate powder prepared by the present invention has an average particle size of 117 nm to 170 nm, a D99 / D50 ratio of 1.12 to 1.27, and a uniform particle size distribution, fine particles, and high purity. By varying the crystal form of the porous titanium dioxide microspheres, the ratio of the porous anatase / rutile mixed crystal titanium dioxide microspheres to the crushed BaO particle size, and the microwave sintering conditions, the uniformity of the obtained barium titanate particle size distribution deteriorated, and the powder particle size increased, which also had a certain impact on the sintering purity.

[0063] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A solid phase method for preparing ultrafine barium titanate powder, characterized in that: The following steps are involved: (1) preparing porous anatase and rutile mixed crystal titanium dioxide microspheres, wherein the ratio of anatase phase to rutile phase in the porous titanium dioxide microspheres is 20%-30%:70%-80%, and the particle size is less than 50 nm; (2) The BaO raw material is crushed using a high-energy ball mill at a speed of 1100-1200 rpm for 6-10 hours, and the BaO particle size after crushing is less than 100 nm, and the ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the crushed BaO particle size is 0.5-1.2; (3) dissolving the crushed BaO and the porous anatase and rutile mixed crystal titanium dioxide microspheres prepared in step (1) in deionized water, stirring and ultrasonically oscillating the raw materials to uniformly mix the raw materials, and then fully dehydrating and drying in a drying oven at 50-150°C to obtain a dry mixed powder; (4) placing the mixed powder of step (3) into a microwave reactor, heating it with microwaves at 1.0-2.0 GHz for 10-25 min, then increasing the microwave frequency to 2.3-2.7 GHz and continuing heating for 15-30 min to obtain porous ultrafine barium titanate powder; In step (2), the high-energy ball mill uses two types of mixed beads with different particle sizes, including 0.7 mm and 1.1 mm mixed beads.

2. The solid phase method for preparing ultrafine barium titanate powder according to claim 1, characterized in that: The porous anatase and rutile mixed crystal titanium dioxide microspheres in step (1) are porous anatase and rutile mixed crystal titanium dioxide microspheres prepared by a template method.

3. The solid phase method for preparing ultrafine barium titanate powder according to claim 1, characterized in that: In step (2), the ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the crushed BaO particle size is 0.6-1.

4. The solid phase method for preparing ultrafine barium titanate powder according to claim 1, characterized in that: In step (3), the ultrasonic oscillation treatment is carried out in the range of 10 kHz to 50 kHz for 0.2 to 1 hour.

5. The solid phase method for preparing ultrafine barium titanate powder according to claim 1, characterized in that: The dehydration and drying time in step (3) is 0.5 to 5 hours, and the moisture content of the mixed powder is less than 0.1 wt%.

6. The solid phase method for preparing ultrafine barium titanate powder according to claim 1, characterized in that: In step (4), the microwave frequency is increased to 2.3-2.4 GHz and heating is continued for 20-25 minutes.

7. An ultrafine barium titanate powder, characterized in that: The powder is prepared by the preparation method according to any one of claims 1 to 6.

Images