Solid-phase preparation method of superfine barium titanate powder

Abstract

The invention relates to a solid-phase preparation method of superfine barium titanate powder. The method comprises the steps that porous anatase and rutile mixed crystal type titanium dioxide microspheres are prepared, the proportion of an anatase phase to a rutile phase in the porous titanium dioxide microspheres is (15%-30%): (70%-85%), and the particle size is 50 nm or below; the BaO raw material is subjected to high-energy ball milling for 6-10 h by using a high-energy ball mill at the rotating speed of 1100-1200 rpm for crushing; the particle size ratio of the titanium dioxide microspheres to the crushed BaO is 0.5-1.2. By selecting the specific particle size ratio of the porous anatase and rutile mixed crystal type titanium dioxide microspheres to the raw materials and using the mixed crystal porous titanium dioxide microspheres to be matched with a two-stage microwave sintering process, the synthesis uniformity of the whole sintering process is improved, and the porous titanium dioxide microspheres with higher particle size uniformity, good dispersity and good stability are obtained. The size of the superfine barium titanate powder is smaller.

Description

Technical Field

[0001] The 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, as a typical perovskite ferroelectric ceramic material, is widely used in multilayer ceramic capacitors (MLCC), sensors, memory and other fields due to its excellent dielectric, ferroelectric and piezoelectric properties.

[0003] At present, the preparation methods of barium titanate powder mainly include solid phase method, liquid phase method (such as hydrothermal method, sol-gel method) and gas phase method. Among them, the solid phase method has become the mainstream of the industry due to its simple process and low cost, but its core problem is that the raw materials are not mixed evenly. The traditional solid phase method uses mechanical mixing of barium titanate and titanium dioxide. Titanium dioxide is mostly a single crystal form (such as anatase or rutile). The difference in crystal form leads to inconsistent reaction activity, and agglomerated particles with uneven particle size are easily formed during the sintering process. In addition, the sintering temperature is high and the grains are coarse: the solid phase reaction depends on high temperature diffusion, which easily leads to excessive growth, and the dense structure of titanium dioxide limits the reaction interface, making it difficult to obtain ultrafine powder. The preparation of porous barium titanate has greater technical difficulty. There is relatively little research on the preparation of porous barium titanate in the prior art. The preparation of porous barium titanate powder also has technical problems such as uneven particle size, small specific surface area, uncontrollable particle size, and insufficient fineness. Summary of the invention

[0004] In view of 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 of 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%-30%:70%-85%, and the particle size is less than 50 nm.

[0006] (2) The BaO raw material is crushed by a high-energy ball mill at a rotation speed of 1100-1200 rpm for 6-10 hours, and the particle size of the BaO after crushing is less than 100 nm, and the ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the BaO particle size after crushing is 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 kinds of mixed beads with different particle sizes, including mixed beads of 0.7 mm and 1.1 mm.

[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 h.

[0013] Preferably, the dehydration and drying time in step (3) is 0.5-5 h, and the moisture content of the mixed powder is less 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 min-25 min.

[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 crush BaO, the mechanical and chemical activation process initiated during the high-energy ball milling process is used to promote the activity of the subsequent sintering reaction and reduce the high-temperature reaction temperature of sintering to a certain extent. The use of mixing beads in the high-energy ball milling process can ensure that the BaO raw material is evenly crushed while also having a good dispersion effect, which is convenient for 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 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, making 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 combining with the sintering process, making full use of the characteristics of high microwave heating rate and high reactivity, so that part of the rutile phase reacts preferentially to form tetragonal crystals at a relatively low temperature under microwave rapid heating, and provides a favorable diffusion channel for the reaction dominated by the second stage sintering anatase phase. Compared with the traditional sintering process, the use of mixed crystal porous titanium dioxide microspheres in combination 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 drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 The present invention is a schematic flow chart of a solid phase preparation method of ultrafine barium titanate powder disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. 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.

[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%-30%:70%-85%, and the particle size is less than 50 nm.

[0024] (2) The BaO raw material is crushed by a high-energy ball mill at a rotation speed of 1100-1200 rpm for 6-10 hours, and the particle size of the BaO after crushing is less than 100 nm, and the ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the BaO particle size after crushing is 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, dodecylamine can be used as a template agent and inorganic titanium salt can be used as a precursor to hydrothermally synthesize porous titanium dioxide microspheres. The desired titanium dioxide microspheres can be obtained by controlling the calcination temperature between 700-1100°C.

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

[0030] In one embodiment, 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.

[0031] The appropriate particle size ratio of porous anatase and rutile mixed crystal titanium dioxide microspheres to crushed BaO has a great influence on the microwave sintering reaction activity and grain growth. This may be because different particle size ratios will 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, in step (2), the high energy ball mill uses two kinds of mixed beads with different particle sizes, including 0.7 mm and 1.1 mm mixed beads.

[0033] By using high-energy ball milling to crush BaO, the mechanical and chemical activation process triggered by the high-energy ball milling process promotes the activity of the subsequent sintering reaction, and to a certain extent reduces the reaction conditions of microwave sintering. The use of mixed beads containing 0.7mm and 1.1mm in the high-energy ball milling process can ensure that the BaO raw material is evenly crushed, and also has a good dispersion effect, which is convenient for uniform mixing and sintering synthesis with titanium dioxide.

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

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

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

[0037] Compared with the traditional solid phase synthesis method, the sintering of the present invention adopts a two-stage microwave sintering process, making full use of the different reaction characteristics of anatase and rutile in the porous anatase and rutile mixed crystal titanium dioxide microsphere raw material, and making full use of the high heating rate and high reactivity of microwaves. In the first stage, the microwave of 1.0~2.0GHz is used for heating treatment for 10~25min. Through rapid heating and sintering, part of the rutile phase reacts preferentially to form tetragonal crystals at a relatively low temperature, and provides a favorable diffusion channel for the reaction dominated by the anatase phase in the second stage. In the second stage, the microwave frequency is increased to 2.3~2.7GHz and continued to heat for 15min-30min. At a higher temperature, the remaining BaO and titanium dioxide can react quickly and completely, and the sintering temperature is reduced compared with traditional sintering, and the sintering efficiency is improved. The use of mixed crystal porous titanium dioxide microspheres in combination with a 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 agent 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 rotation 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) are 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 agent 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 rotation 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) are 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 1.5 GHz microwaves 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 agent 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 rotation 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) are 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 1.0 GHz microwave 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 using 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 rotation 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) are 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 the crushed BaO is 1.43.

[0057] Comparative Example 2: The preparation method of barium titanate powder in Comparative Example 2 is different from that in Example 1 only in that: in step (2), the high-energy ball mill is used for pulverization at a speed of 900 rpm for 9 hours, and the average particle size of BaO after high-energy ball milling is 150 nm. The ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the pulverized BaO particle size is 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 1.0GH microwave for 7 minutes, and then the microwave frequency is increased to 2.4GHz 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, and the average grain size was measured using a scanning electron microscope and an image analysis program. The width of the particle size distribution curve was statistically calculated using minitable software, and expressed as D99 / D50, where D50 refers to the particle size equivalent to 10% of the total volume when the particle size is accumulated from small particles, and D99 refers to the particle size equivalent to 99% of the total volume when the volume is accumulated from 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] It can be found from Table 1 that the porous ultrafine barium titanate powder prepared by the present invention has an average particle size of 117nm-170nm, a D99 / D50 range of 1.12-1.27, a uniform particle size distribution, fine particles, and high purity. After changing the crystal form of porous titanium dioxide microspheres, the particle size ratio of porous anatase and rutile mixed crystal titanium dioxide microspheres to crushed BaO, and microwave sintering conditions, the uniformity of the obtained barium titanate particle size distribution becomes worse, the powder particle size also increases, and the sintering purity is also affected to a certain extent.

[0063] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 15%-30%:70%-85%, and the particle size is less than 50 nm; (2) using a high-energy ball mill to grind the BaO raw material at a speed of 1100-1200 rpm for 6-10 hours, and the BaO particle size after grinding is less than 100 nm, and the ratio of the porous anatase and rutile mixed crystal titanium dioxide microspheres to the BaO particle size after grinding is 0.5-1.2; (3) grinding the BaO raw material into a powder; aO and the porous anatase and rutile mixed crystal titanium dioxide microspheres of 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; (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, and then the microwave frequency is increased to 2.3-2.7 GHz and heating is continued for 15-30 min to obtain a porous ultrafine barium titanate powder.

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 high energy ball mill uses two kinds of mixed beads with different particle sizes, including 0.7 mm and 1.1 mm mixed beads.

4. The solid phase method for preparing ultrafine barium titanate powder according to claim 1, characterized in that: 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.

5. 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 h.

6. 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%.

7. 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.

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

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