A tetragonal barium titanate powder and its hydrothermal synthesis process and obtained product

Abstract

The present invention provides a tetragonal barium titanate powder, its hydrothermal synthesis process and the obtained product, belonging to the technical field of preparation of electronic ceramic powders. The tetragonal barium titanate powder provided by the present invention utilizes a titanium dioxide colloid to participate in the atmospheric pressure hydrothermal synthesis reaction of cubic barium titanate seeds. By regulating the distribution of the solid particle sizes D10, D50, D90 of the titanium dioxide colloid and the range of the diameter distance, the one-step hydrothermal synthesis of the tetragonal barium titanate powder is achieved. Moreover, the prepared tetragonal barium titanate powder has uniform particle size, good dispersibility, a specific surface area of 7.5 - 9.5 m<supgt;2< / supgt> / g, a particle diameter of 80 - 110 nm, and an axial ratio maintained above 1.0085.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic ceramic powder preparation, and in particular relates to a tetragonal barium titanate powder and a hydrothermal synthesis process thereof and the obtained product. Background Art

[0002] Multilayer ceramic capacitors (MLCC) are widely used in mobile phones, computers, LED TVs, aerospace energy storage devices, tanks and other equipment due to their small size, large capacity, fast charge and discharge rate, high power density, DC isolation, and stable current. With the update of products, performance requirements are getting higher and higher. Since the 5G era, the high functionality and lightweight of electronic products have promoted the development of MLCC towards miniaturization, thinness, and high capacity. To achieve high capacity of MLCC, there are two main aspects: one is to select raw material powders with high dielectric constants; the other is to increase the number of layers of MLCC. Therefore, the dispersibility, particle uniformity and high tetragonality of submicron barium titanate have attracted attention from all parties.

[0003] The currently known methods for synthesizing barium titanate powder are mainly hydrothermal method, hydrolysis method, solid phase synthesis, oxalate method and citric acid method. For the liquid phase method, submicron barium titanate powder below 200nm can be synthesized, but lattice defects will be introduced during the synthesis process, resulting in a large number of hydroxyl defects and barium vacancies in the crystal, making the barium titanate present a cubic phase structure, which cannot meet the requirements of high dielectric powder. In the traditional solid phase reaction method, the raw material titanium oxide itself has agglomeration, and when mixed with barium carbonate, it is necessary to deagglomerate the titanium oxide itself and mix it with barium carbonate, which makes it difficult to obtain a homogeneous mixture under certain mixing conditions; solid phase barium titanate also has problems such as large particles, uneven distribution, and serious agglomeration, making it difficult to obtain submicron barium titanate powder. Summary of the invention

[0004] The invention provides a tetragonal barium titanate powder and a hydrothermal synthesis process and the resulting product. The process aims to prepare submicron tetragonal barium titanate powder with good sphericity, uniform particle size and good dispersibility by changing the titanium source raw material mode in view of the shortcomings of the existing one-step hydrothermal process.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a tetragonal barium titanate powder, which utilizes titanium dioxide colloid to participate in the normal pressure hydrothermal synthesis reaction of cubic barium titanate seeds, and realizes the one-step hydrothermal synthesis of tetragonal barium titanate powder by regulating the distribution of solid particle sizes D10, D50, and D90 of titanium dioxide colloid and the range of diameter distance.

[0006] Preferably, the particle size D10 of the solid particles is 40-85 nm, D50 is 100-140 nm, D90 is 760-810 nm, and the diameter distance is between 5 and 7. The calculation formula of the diameter distance is (D90-D10) / D50.

[0007] Preferably, the specific surface area of ​​the obtained tetragonal barium titanate powder is 7.5-9.5 m 2 / g, the particle size is 80-110nm, and the axial ratio is maintained above 1.0085.

[0008] Preferably, the obtained tetragonal barium titanate powder is sintered into porcelain at 1350°C using a rolled film punching disc, and both sides of the disc are polished to obtain a measurement sample with a thickness of 1 mm. At a test frequency of 1 kHz, the dielectric constant is 2710-2760 and the loss is 0.0040-0.0045.

[0009] The present invention also provides a method for preparing tetragonal barium titanate powder according to any of the above technical solutions, wherein a titanium source is hydrolyzed to form a precursor, nano-titanium dioxide colloid is formed by hydrothermal and concentration, the nano-titanium dioxide colloid is mixed with a barium source under normal pressure to form cubic barium titanate seeds, and finally tetragonal barium titanate powder is prepared at high temperature.

[0010] Preferably, the preparation steps of nano titanium dioxide colloid are as follows:

[0011] Add a certain amount of pure water to the reactor, add the alkali raw material and the titanium source under stirring, then add pure water to 80% of the reactor, keep the pH between 8-9, and continue stirring to obtain the precursor;

[0012] Add pure water to the obtained precursor, mix well and transfer to the reactor, add pure water to make the filling degree 80%, keep warm in the reactor at 120-150℃ for 280-310min, keep stirring during the heating stage, turn off stirring during the insulation stage, keep stirring during the cooling stage, and unload when the temperature is below 80℃;

[0013] The obtained slurry is washed with a ceramic membrane, and its solid content is concentrated to 7%-15% to obtain a titanium dioxide colloid with a stable solution system.

[0014] In the above scheme, the preparation temperature and reaction time of nano-titanium dioxide colloid are crucial. When the reaction temperature and time are lower than a specific range, the prepared titanium dioxide colloid particles are smaller, and the final barium titanate particles have more hydroxyl groups and barium vacancies inside, causing the crystal to exhibit a cubic phase at room temperature; when the reaction temperature and time are too high, the titanium dioxide colloid particles are larger, and the final barium titanate particles cannot maintain a spherical shape, and some particles will grow abnormally. In addition, in terms of operation, since chloride ions have a greater impact on the subsequent preparation of barium titanate, it is necessary to perform pressure filtration to remove chlorine when using a titanium source with chloride ions.

[0015] Preferably, the heating rate is 4°C / min, the cooling rate is 7-12°C / min, and the stirring rate is 630-800rpm.

[0016] Preferably, the titanium source is selected from titanium tetrachloride and tetrabutyl titanate, the barium source is at least one of barium hydroxide and barium acetate, and the alkali raw material is selected from at least one of ammonia water, potassium hydroxide and sodium hydroxide.

[0017] Preferably, the method of forming cubic barium titanate seeds by mixing nano titanium dioxide colloid with a barium source under normal pressure specifically includes:

[0018] Add barium source and pure water to the reaction vessel and place in a water bath at 72-90°C to ensure that the solution pH is > 13;

[0019] Titanium dioxide colloid is weighed into another reaction container according to the stoichiometric ratio of barium to titanium of 2.5-4, and placed in a water bath at 72-90°C with magnetic stirring;

[0020] The titanium source and the barium source are mixed together and placed in a water bath at 72-90° C., magnetic stirring is turned on, and cubic barium titanate seed crystals are synthesized under normal pressure.

[0021] In the above scheme, the barium source is a barium solution dissolved at 90°C. If it is directly added to the block, the size of the seed crystals will be uneven, resulting in a wide distribution of barium titanate particles synthesized later. In addition, for the above process, the barium-titanium ratio is crucial. When the barium-titanium ratio is 2.5-4, the prepared barium titanate particles are uniform, with fewer hydroxyl groups and barium vacancies inside, making it appear as a tetragonal phase at room temperature. When the barium-titanium ratio, reaction temperature and time are too high, the particle shape cannot remain spherical, and some particles will grow abnormally.

[0022] Preferably, the high temperature preparation of tetragonal barium titanate powder specifically includes:

[0023] The obtained cubic phase barium titanate seed mixed solution was transferred to a reaction kettle and placed in an oven at 200-240°C for 34-38 hours;

[0024] After the reaction is completed, the inner tank of the reactor is placed in 60-70°C warm water for heating, the white precipitate is collected and washed with pure water, and the remaining slurry is dried to obtain a tetragonal barium titanate powder with high dispersibility, uniform particle size and high axial ratio.

[0025] The present invention also provides a multilayer ceramic capacitor, which is prepared by using the tetragonal barium titanate powder described in any one of the above claims.

[0026] Compared with the prior art, the advantages and positive effects of the present invention are:

[0027] 1. The present invention provides a tetragonal barium titanate powder, which is prepared by changing the titanium source raw material, that is, forming a precursor by hydrolyzing the titanium source, and forming a nano-titanium dioxide colloid by hydrothermal and concentration. Specifically, the nano-titanium dioxide colloid is prepared by regulating the distribution of the solid particle size D10, D50, and D90 of the titanium dioxide colloid and the range of the diameter, and the tetragonal barium titanate powder is synthesized by one-step hydrothermal synthesis.

[0028] 2. The nano titanium dioxide colloid prepared by the process of the present invention can still maintain a state of sedimentation equilibrium after being diluted with pure water and is evenly distributed in the solution. The titanium dioxide has a stable structure at low temperatures, and the skeleton of Ti and O atoms is loosely arranged inside, which is convenient for barium ions to enter at room temperature, which is beneficial to reducing internal defects. Under the influence of high temperature, the diffusion rate of barium ions is accelerated, and the alkali ions in the solution can eliminate the hydroxyl groups on the crystals, so tetragonal barium titanate can be prepared, and the powder particles have uniform particle size, good dispersibility, and a specific surface area of ​​7.5-9.5m 2 / g, the particle size is 80-110nm, and the axial ratio is maintained above 1.0085. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the XRD diffraction pattern of titanium dioxide obtained in Example 1 of the present invention;

[0030] Figure 2 is a scanning electron microscope image of titanium dioxide obtained in Example 1 of the present invention;

[0031] Figure 3 is the XRD diffraction pattern of cubic barium titanate obtained in Example 1 of the present invention;

[0032] Figure 4 is the XRD diffraction pattern of tetragonal barium titanate obtained in Examples 1, 2, 3, 4, and 5 of the present invention;

[0033] Figure 5 This is a scanning electron microscope image of the tetragonal barium titanate powder obtained in Example 1 of the present invention;

[0034] Figure 6 This is a scanning electron microscope image of the tetragonal barium titanate powder obtained in Example 2 of the present invention;

[0035] Figure 7 This is a scanning electron microscope image of the tetragonal barium titanate powder obtained in Example 3 of the present invention;

[0036] Figure 8 This is a scanning electron microscope image of the tetragonal barium titanate powder obtained in Example 4 of the present invention;

[0037] Fig. 9 This is a scanning electron microscope image of the tetragonal barium titanate powder obtained in Example 5 of the present invention;

[0038] Fig.10 is the XRD diffraction pattern of barium titanate obtained in Comparative Examples 1, 2, 3, and 4 of the present invention;

[0039] Fig.11 This is a scanning electron microscope image of the barium titanate powder obtained in Comparative Example 1 of the present invention;

[0040] Fig.12 This is a scanning electron microscope image of the barium titanate powder obtained in Comparative Example 2 of the present invention;

[0041] Fig.13 This is a scanning electron microscope image of the barium titanate powder obtained in Comparative Example 3 of the present invention;

[0042] Fig.14 This is a scanning electron microscope image of the barium titanate powder obtained in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0044] Example 1

[0045] 1) Add 22 kg of pure water to a clean 100 L reactor, then add 4.5 kg of ammonia water (17.031%), start stirring, then add 4 kg of titanium tetrachloride (45.1061%), stir for 5 min, and finally add 50 kg of pure water, continue stirring for 10 min, and keep the pH between 8-9;

[0046] 2) washing and filtering the hydrolyzed precursor twice to remove internal chloride ions;

[0047] 3) Take 7.5kg of filter cake and put it in a 20L white barrel, add 4.5kg of pure water for pulping, and stir for 30 minutes; transfer the mixed slurry to a 10L reactor, add pure water appropriately to make it 80% full, keep it in a 140℃ reactor for 290 minutes, and heat it up at a rate of 4℃ / min. Keep stirring all the time, turn off stirring during the heat preservation process, keep stirring during the cooling process, and discharge it when it is below 80℃;

[0048] 4) The obtained slurry is washed with a ceramic membrane, and the amount of pure water used for washing is 70 kg, and the solid content thereof is concentrated to 13.63%, and a titanium dioxide colloid having a stable solution system is obtained. The test results are as follows: Figure 1 , Figure 2 , as shown in Table 1.

[0049] 5) Take 362.7g Ba(OH)2·8H2O (purity 98%) and 240g pure water in a 1L beaker and dissolve in a 90℃ water bath;

[0050] 6) According to the barium-titanium ratio of 3, weigh 220.1g of titanium oxide colloid (solid content 13.63%) into a beaker, place it in a 90℃ water bath, and turn on magnetic stirring for 10 minutes;

[0051] 7) The titanium source and barium source prepared above were mixed together and placed in a 90°C water bath, and magnetic stirring was turned on for 30 minutes. The cubic barium titanate seed crystals were synthesized under normal pressure, such as Figure 3 As shown;

[0052] 8) The barium titanate seed solution obtained in 7) was transferred to a 1L reactor, and the filling degree was adjusted to 80% with pure water;

[0053] 9) Place the reactor in an oven at 200°C and keep warm for 36 hours;

[0054] 10) After the reaction is completed, heat the reactor in warm water at 60-70°C, remove the supernatant and pour it into a waste liquid bucket, collect the white precipitate and wash it with 40L of pure water;

[0055] 11) The remaining slurry was dried at 120°C to obtain a specific surface area of ​​8.18 m 2 / g, particle size of about 80nm, barium-titanium ratio = 1.0032, c / a = 1.0091, and uniform tetragonal barium titanate powder, such as Figure 4 , Figure 5 As shown; a wafer made of rolled film is used and sintered into porcelain at high temperature. After polishing the upper and lower surfaces of the wafer, a screen-printed silver electrode is used. The sample thickness is measured with a micrometer, and the wafer capacitance and loss are tested with an LCR resistance meter. According to the formula εr=Cd / ε0A, the dielectric constant is calculated to be 2750 and the loss is 0.0042.

[0056] Example 2

[0057] 1) Add 22 kg of pure water to a clean 100 L reactor, add 0.375 kg of potassium hydroxide (98%), start stirring, then add 5.8484 kg of tetrabutyl titanate (55.351%), stir for 5 min, and finally add 53 kg of pure water and continue stirring for 10 min;

[0058] 2) Take 8L of the slurry in 1) and put it into a 10L reactor. Add pure water to make the filling degree 80%. Keep it in the reactor at 150℃ for 310min. The heating rate is 4℃ / min. Stir it all the time. Turn off the stirring during the insulation process. Keep stirring during the cooling process. Unload the material when the temperature is below 80℃.

[0059] 3) The obtained slurry was washed with a ceramic membrane using 70 kg of pure water, and the solid content was concentrated to 9.4% to obtain a titanium dioxide colloid with a stable solution system. The test results are shown in Table 1.

[0060] 4) Take 290.7g of barium acetate (purity 99%) and 240g of pure water in a 1L beaker and place it in a 90℃ water bath to dissolve;

[0061] 5) Add 64.5 g potassium hydroxide (purity 98%) to 4);

[0062] 6) According to the barium-titanium ratio of 3, weigh 319.2 g of titanium oxide colloid (solid content 9.4%) into a beaker, place it in a 90°C water bath, and turn on magnetic stirring for 10 minutes;

[0063] 7) The titanium source and barium source prepared above were mixed together and placed in a 90° C. water bath, and magnetic stirring was turned on for 30 minutes to synthesize cubic barium titanate seed crystals under normal pressure;

[0064] 8) The barium titanate seed solution obtained in 7) was transferred to a 1L reactor, and the filling degree was adjusted to 80% with pure water;

[0065] 9) Place the reactor in an oven at 200°C and keep warm for 38 hours;

[0066] 10) After the reaction is completed, heat the reactor in warm water at 60-70°C, remove the supernatant and pour it into a waste liquid bucket, collect the white precipitate and wash it with 40L of pure water;

[0067] 11) The remaining slurry was dried at 120°C to obtain a specific surface area of ​​8.643 m 2 / g, particle size of about 85nm, barium-titanium ratio = 1.0024, c / a = 1.0088, and uniform tetragonal barium titanate powder, such as Figure 4 , Figure 6 As shown; a wafer made of rolled film is used and sintered into porcelain at high temperature. After polishing the upper and lower surfaces of the wafer, a screen-printed silver electrode is used. A micrometer is used to measure the sample thickness. An LCR resistance meter is used to test the wafer capacitance and loss. According to the formula εr=Cd / ε0A, the dielectric constant is calculated to be 2720 and the loss is 0.0041.

[0068] Example 3

[0069] 1) Add 22 kg of pure water to a clean 100 L reactor, add 4.5 kg of ammonia water (17.031%), start stirring, then add 4 kg of titanium tetrachloride (45.1061%), stir for 5 min, and finally add 50 kg of pure water, continue stirring for 10 min, and keep the pH between 8-9;

[0070] 2) washing and filtering the hydrolyzed precursor twice to remove internal chloride ions;

[0071] 3) Take 7.5kg of filter cake and put it in a 20L white barrel, add 4.5kg of pure water for pulping, and stir for 30 minutes; transfer the mixed slurry to a 10L reactor, add pure water appropriately to make it 80% full, keep it in a 120℃ reactor for 310 minutes, and heat it up at a rate of 4℃ / min. Keep stirring all the time, turn off stirring during the heat preservation process, keep stirring during the cooling process, and discharge it when it is below 80℃;

[0072] 4) The obtained slurry was washed with a ceramic membrane using 70 kg of pure water, and the solid content was concentrated to 9.4% to obtain a titanium dioxide colloid with a stable solution system. The test results are shown in Table 1.

[0073] 5) Take 387.7g of barium acetate (purity 99%) and 300g of pure water in a 1L beaker and place it in a 90℃ water bath to dissolve;

[0074] 6) Add 61.4 g of sodium hydroxide (purity 98%) to the solution in 5);

[0075] 7) According to the barium-titanium ratio of 4, weigh 319.2 g of titanium oxide colloid (solid content 9.4%) into a beaker, place it in a 90°C water bath, and turn on magnetic stirring for 10 minutes;

[0076] 8) The titanium source and barium source prepared above were mixed together and placed in a 90° C. water bath, and magnetic stirring was turned on for 30 minutes to synthesize cubic barium titanate seed crystals under normal pressure;

[0077] 9) The barium titanate seed mixed solution obtained in 8) was transferred to a 1L reactor, and the filling degree was adjusted to 80% with pure water;

[0078] 10) Place the reactor in an oven at 240°C and keep warm for 36 hours;

[0079] 11) After the reaction is completed, heat the reactor in warm water at 60-70°C, remove the supernatant and pour it into a waste liquid bucket, collect the white precipitate and wash it with 40L of pure water;

[0080] 12) The remaining slurry was dried at 120°C to obtain a specific surface area of ​​7.683 m 2 / g, a particle size of about 110nm, a barium-titanium ratio of 1.0087, and a c / a of 1.0094, such as Figure 4 , Figure 7 As shown; a wafer made of rolled film is used and sintered into porcelain at high temperature. After polishing the upper and lower surfaces of the wafer, a screen-printed silver electrode is used. A micrometer is used to measure the sample thickness. An LCR resistance meter is used to test the wafer capacitance and loss. According to the formula εr=Cd / ε0A, the dielectric constant is calculated to be 2710 and the loss is 0.0043.

[0081] Example 4

[0082] 1) Add 22 kg of pure water to a clean 100 L reactor, add 0.375 kg of sodium hydroxide (98%), start stirring, then add 4 kg of titanium tetrachloride (45.1061%), stir for 5 min, and finally add 50 kg of pure water, continue stirring for 10 min, and keep the pH between 8-9;

[0083] 2) washing and filtering the hydrolyzed precursor twice to remove internal chloride ions;

[0084] 3) Take 7.5kg of filter cake and put it in a 20L white barrel, add 4.5kg of pure water for pulping, and stir for 30 minutes; transfer the mixed slurry to a 10L reactor, add pure water appropriately to make it 80% full, keep it in a 150℃ reactor for 280 minutes, with a heating rate of 4℃ / min, keep stirring all the time, turn off stirring during the insulation process, keep stirring during the cooling process, and unload when the temperature is below 80℃;

[0085] 4) The obtained slurry was washed with a ceramic membrane using 70 kg of pure water, and the solid content was concentrated to 9.4% to obtain a titanium dioxide colloid with a stable solution system. The test results are shown in Table 1.

[0086] 5) Take 302.3g Ba(OH)2·8H2O (purity 98%) and 200g pure water in a 1L beaker and dissolve in a 90℃ water bath;

[0087] 6) With a barium-titanium ratio of 2.5, weigh 319.2 g of titanium oxide colloid (solid content 9.4%) into a beaker, place it in a 90°C water bath, and start magnetic stirring for 10 min;

[0088] 7) The titanium source and barium source prepared above were mixed together and placed in a 90° C. water bath, and magnetic stirring was turned on for 30 minutes to synthesize cubic barium titanate seed crystals under normal pressure;

[0089] 8) The barium titanate seed solution obtained in 7) was transferred to a 1L reactor, and the filling degree was adjusted to 80% with pure water;

[0090] 9) Place the reactor in an oven at 240°C and keep warm for 38 hours;

[0091] 10) After the reaction is completed, heat the reactor in warm water at 60-70°C, remove the supernatant and pour it into a waste liquid bucket, collect the white precipitate and wash it with 40L of pure water;

[0092] 11) The remaining slurry was dried at 120°C to obtain a specific surface area of ​​9.346 m 2 / g, a particle size of about 100nm, a barium-titanium ratio of 0.9839, and a c / a of 1.0086, such as Figure 4 , Figure 8 As shown; a wafer made of rolled film is used and sintered into porcelain at high temperature. After polishing the upper and lower surfaces of the wafer, a screen-printed silver electrode is used. A micrometer is used to measure the sample thickness. An LCR resistance meter is used to test the wafer capacitance and loss. According to the formula εr=Cd / ε0A, the dielectric constant is calculated to be 2730 and the loss is 0.0045.

[0093] Example 5

[0094] 1) Add 22 kg of pure water to a clean 100 L reactor, add 4.5 kg of ammonia water (17.031%), start stirring, then add 4 kg of titanium tetrachloride (45.1061%), stir for 5 min, and finally add 50 kg of pure water, continue stirring for 10 min, and keep the pH between 8-9;

[0095] 2) washing and filtering the hydrolyzed precursor twice to remove internal chloride ions;

[0096] 3) Take 7.5kg of filter cake and put it in a 20L white barrel, add 4.5kg of pure water for pulping, and stir for 30 minutes; transfer the mixed slurry to a 10L reactor, add pure water appropriately to make it 80% full, keep it in a 130℃ reactor for 300 minutes, and heat it up at a rate of 4℃ / min. Keep stirring all the time, turn off stirring during the insulation process, keep stirring during the cooling process, and discharge it when it is below 80℃;

[0097] 4) The obtained slurry was washed with a ceramic membrane using 70 kg of pure water, and the solid content was concentrated to 13.63% to obtain a titanium dioxide colloid with a stable solution system. The test results are shown in Table 1.

[0098] 5) Take 362.7g Ba(OH)2·8H2O (purity 98%) and 240g pure water in a 1L beaker and dissolve in a 90℃ water bath;

[0099] 6) According to the barium-titanium ratio of 3, weigh 319.2 g of titanium oxide colloid (solid content 9.4%) into a beaker, place it in a 90°C water bath, and turn on magnetic stirring for 10 minutes;

[0100] 7) The titanium source and barium source prepared above were mixed together and placed in a 90° C. water bath, and magnetic stirring was turned on for 30 minutes to synthesize cubic barium titanate seed crystals under normal pressure;

[0101] 8) The barium titanate seed solution obtained in 7) was transferred to a 1L reactor, and the filling degree was adjusted to 80% with pure water;

[0102] 9) Place the reactor in an oven at 200°C and keep warm for 34 hours;

[0103] 10) After the reaction is completed, heat the reactor in warm water at 60-70°C, remove the supernatant and pour it into a waste liquid bucket, collect the white precipitate and wash it with 40L of pure water;

[0104] 11) The remaining slurry was dried at 120°C to obtain a specific surface area of ​​9.186 m 2 / g, a particle size of about 100nm, a barium-titanium ratio of 1.0047, and a c / a of 1.0087, such as Figure 4 , Fig. 9 As shown; a wafer made of rolled film is used and sintered into porcelain at high temperature. After polishing the upper and lower surfaces of the wafer, a screen-printed silver electrode is used. The sample thickness is measured with a micrometer, and the wafer capacitance and loss are tested with an LCR resistance meter. According to the formula εr=Cd / ε0A, the dielectric constant is calculated to be 2760 and the loss is 0.0040.

[0105] Table 1 shows the particle size distribution and diameter distance parameters of titanium oxide colloid used in Examples 1, 2, 3, 4, and 5

[0106] experiment D10 / nm D50 / nm D90 / nm Diameter Example 1 61 113 758 6.2 Example 2 83 104 764 6.5 Example 3 42 135 769 5.4 Example 4 71 109 807 6.8 Example 5 54 128 797 5.8

[0107] From the data in Table 1, it can be seen that titanium dioxide particles with a diameter distance of 5.4-6.8 can play an important role in the subsequent synthesis of barium titanate seeds. The diameter distance represents the width of the particle distribution. Narrow particle size distribution and smaller particle size make it easier for titanium dioxide to form barium titanate particles of uniform size at room temperature, and the subsequent growth of barium titanate particles themselves maintains a good sphericity.

[0108] Comparative Example 1

[0109] 1) Add 22 kg of pure water to a clean 100 L reactor, add 4.5 kg of ammonia water (17.031%), start stirring, then add 4 kg of titanium tetrachloride (45.1061%), stir for 5 min, and finally add 50 kg of pure water, continue stirring for 10 min, and keep the pH between 8-9;

[0110] 2) washing and filtering the hydrolyzed precursor twice to remove internal chloride ions;

[0111] 3) Take 7.5kg of filter cake and put it in a 20L white barrel, add 4.5kg of pure water for pulping, and stir for 30 minutes; transfer the mixed slurry to a 10L reactor, add pure water appropriately to make it 80% full, keep it in a 100℃ reactor for 290 minutes, and heat it up at a rate of 4℃ / min. Keep stirring all the time, turn off stirring during the heat preservation process, keep stirring during the cooling process, and discharge it when it is below 80℃;

[0112] 4) The obtained slurry was washed with a ceramic membrane using 70 kg of pure water, and the solid content was concentrated to 9.4% to obtain a titanium dioxide colloid with a stable solution system. The test results are shown in Table 2.

[0113] 5) Take 387.7g of barium acetate (purity 99%) and 300g of pure water in a 1L beaker and place it in a 90℃ water bath to dissolve;

[0114] 6) Add 61.4 g of sodium hydroxide (purity 98%) to the solution in 5);

[0115] 7) According to the barium-titanium ratio of 4, weigh 319.2 g of titanium oxide colloid (solid content 9.4%) into a beaker, place it in a 90°C water bath, and turn on magnetic stirring for 10 minutes;

[0116] 8) The titanium source and barium source prepared above were mixed together and placed in a 90° C. water bath, and magnetic stirring was turned on for 30 minutes to synthesize cubic barium titanate seed crystals under normal pressure;

[0117] 9) The barium titanate seed mixed solution obtained in 8) was transferred to a 1L reactor, and the filling degree was adjusted to 80% with pure water;

[0118] 10) Place the reactor in an oven at 240°C and keep warm for 36 hours;

[0119] 11) After the reaction is completed, heat the reactor in warm water at 60-70°C, remove the supernatant and pour it into a waste liquid bucket, collect the white precipitate and wash it with 40L of pure water;

[0120] 12) The remaining slurry was dried at 120°C to obtain a specific surface area of ​​8.596 m 2 / g, a cubic phase barium titanate powder with a particle size of about 83nm, a barium-titanium ratio of 1.0087, and c / a of 1.0000, such as Fig.10 , Fig.11 As shown; a wafer made of rolled film is used and sintered into porcelain at high temperature. After polishing the upper and lower surfaces of the wafer, a screen-printed silver electrode is used. A micrometer is used to measure the sample thickness. An LCR resistance meter is used to test the wafer capacitance and loss. According to the formula εr=Cd / ε0A, the dielectric constant is calculated to be 710 and the loss is 0.0450.

[0121] Comparative Example 2

[0122] 1) Add 22 kg of pure water to a clean 100 L reactor, add 4.5 kg of ammonia water (17.031%), start stirring, then add 4 kg of titanium tetrachloride (45.1061%), stir for 5 min, and finally add 50 kg of pure water, continue stirring for 10 min, and keep the pH between 8-9;

[0123] 2) washing and filtering the hydrolyzed precursor twice to remove internal chloride ions;

[0124] 3) Take 7.5kg of filter cake and put it in a 20L white barrel, add 4.5kg of pure water for pulping, and stir for 30 minutes; transfer the mixed slurry to a 10L reactor, add pure water appropriately to make it 80% full, keep it in a 170℃ reactor for 280 minutes, and heat it up at a rate of 4℃ / min. Keep stirring all the time, turn off stirring during the insulation process, keep stirring during the cooling process, and discharge the material when it is below 80℃;

[0125] 4) The obtained slurry was washed with a ceramic membrane using 70 kg of pure water, and the solid content was concentrated to 9.4% to obtain a titanium dioxide colloid with a stable solution system. The test results are shown in Table 2.

[0126] 5) Take 362.7g Ba(OH)2·8H2O (purity 98%) and 300g pure water in a 1L beaker and dissolve in a 90℃ water bath;

[0127] 6) According to the barium-titanium ratio of 4, weigh 319.2 g of titanium oxide colloid (solid content 9.4%) into a beaker, place it in a 90°C water bath, and turn on magnetic stirring for 10 minutes;

[0128] 7) The titanium source and barium source prepared above were mixed together and placed in a 90° C. water bath, and magnetic stirring was turned on for 30 minutes to synthesize cubic barium titanate seed crystals under normal pressure;

[0129] 8) The barium titanate seed solution obtained in 7) was transferred to a 1L reactor, and the filling degree was adjusted to 80% with pure water;

[0130] 9) Place the reactor in an oven at 240°C and keep warm for 37 hours;

[0131] 10) After the reaction is completed, heat the reactor in warm water at 60-70°C, remove the supernatant and pour it into a waste liquid bucket, collect the white precipitate and wash it with 40L of pure water;

[0132] 11) The remaining slurry was dried at 120°C to obtain a specific surface area of ​​6.673 m 2 / g, average particle size of about 125nm, barium-titanium ratio = 1.0052, c / a = 1.0075, tetragonal barium titanate powder, such as Fig.10 , Fig.12 As shown in the figure, when the preparation temperature of titanium oxide exceeds the standard, the local titanium oxide particles grow abnormally, and finally the barium titanate cannot be a regular sphere; the discs of rolled film punching are used and sintered into porcelain at high temperature. After the upper and lower surfaces of the discs are polished, the silver electrodes are screen-printed and the sample thickness is measured with a micrometer. The capacitance and loss of the disc are tested with an LCR resistance meter. According to the formula εr=Cd / ε0A, the dielectric constant is calculated to be 1730 and the loss is 0.0130.

[0133] Comparative Example 3

[0134] 1) Take 362.7g Ba(OH)2·8H2O (purity 98%) and 240g pure water in a 1L beaker and dissolve in a 90℃ water bath;

[0135] 2) drying and grinding the titanium oxide colloid in Example 1;

[0136] 3) According to the barium-titanium ratio of 3, take 2) 30.3g titanium oxide powder in a beaker, add water and stir, and place it in a 90℃ water bath, and turn on magnetic stirring for 10 minutes;

[0137] 4) The titanium source and barium source prepared above were mixed together and placed in a 90° C. water bath, and magnetic stirring was turned on for 30 minutes to synthesize cubic barium titanate seed crystals under normal pressure;

[0138] 5) The barium titanate seed solution obtained in 4) was transferred to a 1L reactor, and the filling degree was adjusted to 80% with pure water;

[0139] 6) Place the reactor in an oven at 210°C and keep warm for 34 hours;

[0140] 7) After the reaction is completed, heat the reactor in warm water at 60-70°C, remove the supernatant and pour it into a waste liquid bucket, collect the white precipitate and wash it with 40L of pure water;

[0141] 8) The remaining slurry was dried at 120°C to obtain a specific surface area of ​​4.145 m 2 / g, average particle size of about 210nm, barium titanium ratio = 1.0301, c / a = 1.0071, tetragonal barium titanate powder; the results show that after drying and grinding, titanium oxide will form more agglomerates, resulting in greater differences in the size of barium titanate particles in the later stage, such as Fig.10 , Fig.13 As shown; a wafer made of rolled film is used and sintered into porcelain at high temperature. After polishing the upper and lower surfaces of the wafer, a screen-printed silver electrode is used. A micrometer is used to measure the sample thickness. An LCR resistance meter is used to test the wafer capacitance and loss. According to the formula εr=Cd / ε0A, the dielectric constant is calculated to be 1880 and the loss is 0.0160.

[0142] Comparative Example 4

[0143] 1) Take 362.7g Ba(OH)2·8H2O (purity 98%) and 240g pure water in a 1L beaker and dissolve in a 90℃ water bath;

[0144] 2) According to the barium-titanium ratio of 3, weigh 264.7g of tetrabutyl titanate in a beaker, add water and stir evenly, and place it in a 90℃ water bath, turn on the magnetic stirring for 10 minutes;

[0145] 3) The titanium source and barium source prepared above were mixed together and placed in a 90° C. water bath, and magnetic stirring was turned on for 30 minutes to synthesize cubic barium titanate seed crystals under normal pressure;

[0146] 4) The barium titanate seed solution obtained in 3) was transferred to a 1L reactor, and the filling degree was adjusted to 80% with pure water;

[0147] 5) Place the reactor in an oven at 200°C and keep warm for 34 hours;

[0148] 6) After the reaction is completed, heat the reactor in warm water at 60-70°C, remove the supernatant and pour it into a waste liquid bucket, collect the white precipitate and wash it with 40L of pure water;

[0149] 7) The remaining slurry was dried at 120°C to obtain a specific surface area of ​​7.145 m 2 / g, particle size of about 95nm, barium-titanium ratio = 1.0024, c / a = 1.0000 cubic phase barium titanate powder; the results show that direct use of tetrabutyl titanate hydrolysis to obtain titanium dioxide precursor to prepare barium titanate cannot form a tetragonal phase, such as Fig.10 , Fig.14 As shown; a wafer made of rolled film is used and sintered into porcelain at high temperature. After polishing the upper and lower surfaces of the wafer, a screen-printed silver electrode is used. A micrometer is used to measure the sample thickness. An LCR resistance meter is used to test the wafer capacitance and loss. According to the formula εr=Cd / ε0A, the dielectric constant is calculated to be 640 and the loss is 0.0410.

[0150] Table 2 is the particle size distribution and diameter distance parameters of titanium oxide colloid used in Examples 1, 2, 3, and 4

[0151] experiment D10 / nm D50 / nm D90 / nm Diameter Comparative Example 1 40 120 600 4.7 Comparative Example 2 120 200 900 3.9 Comparative Example 3 1543 4281 11394 2.3 Comparative Example 4 2185 6147 15455 2.16

[0152] It can be seen from the data in Table 2 that when the preparation temperature of titanium dioxide is too high or too low, the diameter distance of the titanium oxide colloid particles is not between 5.4 and 6.8, so it is impossible to prepare tetragonal barium titanate with good sphericity and uniform particles; and after the titanium oxide colloid is dried, its particles become larger and a stable colloidal state cannot be formed in the solution, which ultimately leads to the growth of multiple barium titanate particles together; after the titanium source is hydrolyzed, titanium dioxide will not be formed, but titanic acid or metatitanic acid, and it is also difficult to form a tetragonal phase.

Claims

1. A method for preparing tetragonal barium titanate powder, characterized in that: A precursor is formed by hydrolyzing a titanium source, and a nano-titanium dioxide colloid is formed by hydrothermal and concentration. The nano-titanium dioxide colloid is mixed with a barium source under normal pressure to form a cubic barium titanate seed crystal, and finally a tetragonal barium titanate powder is prepared at high temperature. The solid particle size D10 of the titanium dioxide colloid is 40-85 nm, D50 is 100-140 nm, D90 is 760-810 nm, and the diameter distance is between 5 and 7. The calculation formula of the diameter distance is (D90-D10) / D50.

2. The preparation method according to claim 1, characterized in that: The preparation steps of nano titanium dioxide colloid are as follows: Add a certain amount of pure water to the reactor, add the alkali raw material and the titanium source under stirring, then add pure water to 80% of the reactor, keep the pH between 8-9, and continue stirring to obtain the precursor; Add pure water to the obtained precursor, mix well and transfer to the reactor, add pure water to make the filling degree 80%, keep warm in the reactor at 120-150℃ for 280-310 min, keep stirring during the heating stage, turn off stirring during the insulation stage, keep stirring during the cooling stage, and unload when the temperature is below 80℃; The obtained slurry is washed with a ceramic membrane, and its solid content is concentrated to 7%-15% to obtain a titanium dioxide colloid with a stable solution system.

3. The preparation method according to claim 2, characterized in that: The heating rate was 4°C / min, the cooling rate was 7-12°C / min, and the stirring rate was 630-800 rpm.

4. The preparation method according to claim 2, characterized in that: The titanium source is selected from titanium tetrachloride and tetrabutyl titanate, the barium source is at least one of barium hydroxide and barium acetate, and the alkali raw material is selected from at least one of ammonia water, potassium hydroxide and sodium hydroxide.

5. The preparation method according to claim 1, characterized in that: The method of forming cubic barium titanate seed crystals by mixing nano titanium dioxide colloid with a barium source under normal pressure specifically includes: Add barium source and pure water to the reaction vessel and place in a water bath at 72-90°C to ensure that the solution pH is > 13; Titanium dioxide colloid is weighed into another reaction container according to the stoichiometric ratio of barium to titanium of 2.5-4, and placed in a water bath at 72-90°C with magnetic stirring; The titanium source and the barium source are mixed together and placed in a water bath at 72-90° C., magnetic stirring is turned on, and cubic barium titanate seed crystals are synthesized under normal pressure.

6. The preparation method according to claim 1, characterized in that: The high temperature preparation of tetragonal barium titanate powder specifically includes: The obtained cubic phase barium titanate seed mixed solution was transferred to a reaction kettle and placed in an oven at 200-240°C for 34-38 hours; After the reaction is completed, the inner tank of the reactor is placed in 60-70°C warm water for heating, the white precipitate is collected and washed with pure water, and the remaining slurry is dried to obtain a tetragonal barium titanate powder with high dispersibility, uniform particle size and high axial ratio.

7. The preparation method according to claim 1, characterized in that: The specific surface area of ​​the obtained tetragonal barium titanate powder is 7.5-9.5 m 2 / g, particle size is 80-110nm, and axial ratio is maintained above 1.0085.

8. The preparation method according to claim 7, characterized in that: The obtained tetragonal barium titanate powder was sintered into porcelain at 1350°C using a rolled film punched disc, and both sides of the disc were polished to obtain a measurement sample with a thickness of 1 mm. At a test frequency of 1 kHz, its dielectric constant was 2710-2760 and the loss was 0.0040-0.0045.

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