Preparation method of flaky barium titanate template powder with uniform size and high length-diameter ratio

Abstract

The invention discloses a preparation method of flaky barium titanate template powder with uniform size and high length-diameter ratio. A three-step molten salt method is adopted, meanwhile, the proportion of nitric acid is controlled in the later period, cavities and small particles with non-uniform particle sizes generated on a template in the preparation process of the barium titanate flaky powder are effectively removed, the obtained barium titanate powder is in a regular flaky shape, no second phase is generated, the size of the flaky powder is about 5-7 micrometers, and the size of the flaky powder is about 5-7 micrometers. According to the present invention, the sheet-shaped BT template has characteristics of uniform thickness and uniform size, and the surface of the sheet-shaped BT template is smooth and regular, such that the sheet-shaped BT template can be used as the template to prepare the high-performance piezoelectric texture ceramic, and can be widely used in the high-tech fields such as ultrasonic transducers, ceramic filters, surface acoustic wave devices, electro-optical devices, and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric materials, and particularly to a preparation method of a sheet-like barium titanate material with uniform size and high aspect ratio. Background Art

[0002] Piezoelectric materials are an important part of information functional materials, which can realize the mutual conversion of electrical energy and mechanical energy, and are widely used in the fields of information and aerospace. They are one of the important electronic materials for the development of contemporary science and technology. Among the piezoelectric materials currently in use, lead-based materials dominate, such as: lead bismuth zirconate titanate, lead lanthanum zirconate titanate, lead lanthanum titanate zirconate. However, lead oxide in lead-based ceramics is highly toxic, and in addition, it has high volatility during the sintering process. Therefore, lead-based ceramics will cause serious harm to humans and the ecological environment during production, use, and post-disposal processes. Therefore, developing high-performance, new environmentally friendly lead-free ferroelectric materials is a research topic of great practical significance. So far, the systems of lead-free piezoelectric ceramics that can be considered mainly include: barium titanate (BT), potassium sodium niobate (KNN), sodium bismuth titanate (BNT), and bismuth ferrite (BF), etc.

[0003] The electrical properties of piezoelectric single crystals are significantly superior to those of piezoelectric ceramics. However, piezoelectric single crystal materials have a series of problems such as small size, difficult processing, and high cost, which limit the application range of piezoelectric single crystals. The preparation process of piezoelectric ceramics is simple, the cost is low, the limitations in terms of size and shape are small, and the grain orientation in the ceramics is randomly distributed, and the influence of crystal axis orientation disappears. Therefore, its performance is far lower than that of single crystal materials. Many research results show that by "texturing" or "grain orientation", the originally randomly oriented ceramic grains can be oriented and grown, so as to obtain high-performance piezoelectric ceramic materials with performance close to that of single crystals. The commonly used template grain growth (TGG) technology is to select a suitable low-dimensional template material, and then arrange the template in the matrix in a directional manner according to its characteristic morphology and crystal orientation. Finally, at high temperature, the matrix grains grow epitaxially on the template to form textured ceramics. Therefore, factors such as the type of template material, the morphological structure and size of the template particles are one of the key factors affecting the electrical properties of the final textured ceramics.

[0004] Among them, barium titanate (BaTiO3) is a typical lead-free ferroelectric ceramic material, belonging to the perovskite-type polycrystalline structure, which can be represented by ABO3. The A site is the Ba element, and the B site is the Ti element, with good ferroelectric polarization response. Due to its stable chemical properties and high piezoelectric coefficient, it becomes an ideal textured ceramic template material required for experiments. Among them, the high-temperature molten salt method is the most commonly used chemical method for preparing flaky oxide templates. This method uses molten salt as the mass transfer for the reaction between oxides. Under this mass transfer condition, ions have a high diffusion rate, and the chemical reaction can be completed in a short time. Among them, the three-step molten salt method prepares Bi4Ti3O 12 (BIT) and BaBi4Ti4O 15 (BBT) as precursors and then obtains smooth-surfaced, regular-structured, and pure-phase BaTiO3 (BT) flakes through ion exchange. Nevertheless, during multiple ion exchange processes, small-sized fragments are likely to be generated, resulting in a large size gap in the prepared BT template powder. In addition, during the process of nitric acid cleaning of the by-product Bi2O3, the nitric acid concentration and cleaning time will also affect the morphology of the BT template. For example, corrosion pores appear on the BT flaky template. To address the above problems, in this work, the three-step synthesis method is still used to prepare flaky barium titanate templates, and by adjusting the nitric acid concentration, cleaning time, cleaning temperature and other means, flaky barium titanate two-dimensional templates with regular morphology, uniform size, and high aspect ratio are prepared. Summary of the Invention

[0005] Aiming at the problems of uneven size distribution and different template morphologies of the barium titanate flaky two-dimensional template prepared by the three-step molten salt method. The present invention provides a method for preparing a flaky barium titanate two-dimensional material with regular morphology, uniform size, and high aspect ratio, providing the necessary template raw materials for the preparation of related textured ceramics.

[0006] The technical solution of the present invention is as follows: A method for preparing a flaky barium titanate template powder with uniform size and high aspect ratio, including:

[0007] (1) Sinter Bi4Ti3O 12 with TiO2, BaCO3 and the auxiliary reaction salt KCl-BaCl2·2H2O at high temperature for a period of time, wash, filter by suction, and dry to obtain BaBi4Ti4O 15 flaky precursors;

[0008] (2) Mix BaCO3 with the BaBi4Ti4O 15 flaky precursors and the auxiliary salt KCl, mix them evenly, and carry out a molten salt reaction at high temperature to obtain BaTiO3 powder;

[0009] (3) It is washed multiple times with 1 mol / L HNO₃ to remove the by-product Bi₂O₃, and a barium titanate template powder with uniform size and high aspect ratio in the form of flakes is obtained.

[0010] Further, Bi₄Ti₃O 12 is obtained by mixing Bi₂O₃, TiO₂ and the molten salt system NaCl-KCl, carrying out a high-temperature molten salt reaction at 1050 °C for 2 h, washing, and then performing suction filtration.

[0011] Further, in step (1), Bi₄Ti₃O 12 is reacted with TiO₂, BaCO₃ and the auxiliary reaction salt KCl-BaCl₂·2H₂O at 1080 °C for 2 h to obtain.

[0012] Further, in step (2), the molten salt reaction temperature is 950 °C and the reaction time is 3 h.

[0013] Further, in step (2), BaCO₃, the barium bismuth titanate 15 flake-shaped precursor and the auxiliary salt KCl are placed in absolute ethanol and mixed evenly.

[0014] Further, in step (3), it is washed multiple times with 1 mol / L HNO₃, and the entire washing process lasts for 30 h.

[0015] Compared with the prior art, the advantages of the present invention are as follows: The present invention provides a barium titanate two-dimensional flake powder with smooth, complete, uniform size and no second phase in its microstructure, as well as a preparation method, which can meet the requirements of an important two-dimensional template material for the preparation of textured ceramics. It solves the problems that during the multi-step topological replacement process for preparing barium titanate two-dimensional powder by the molten salt method, the fragments generated lead to non-uniform size distribution of the prepared barium titanate two-dimensional powder, and the problem that the microstructure of the flake-shaped barium titanate is irregular due to improper pickling conditions when removing the by-product Bi₂O₃. By adjusting parameters such as the synthesis temperature of the precursor in the early stage and the concentration of the acid and the pickling time during the later pickling process, a barium titanate two-dimensional flake powder with uniform size distribution, complete microstructure and no second phase is prepared, which can meet the requirements of the relevant fields for the preparation and application of piezoelectric textured ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the size uniformity, microstructure of the barium titanate flake two-dimensional powder prepared by the present invention and its ability to meet the requirements of the template for the preparation of textured ceramics, it is shown and described herein in the form of drawings:

[0017] Figure 1 Scanning electron microscope pictures of the BT two-dimensional flake powder after being treated with nitric acid of different concentrations in the present invention; (a) 3 mol / L HNO₃; (b) 1 mol / L HNO₃.

[0018] Figure 2 Scanning electron microscope images of barium titanate two-dimensional flake powders after being washed with 1 mol / L nitric acid for different times in the present invention; (a) is for 10 h; (b) is for 30 h.

[0019] Figure 3 XRD diffraction pattern of the obtained BT two-dimensional flake powder in the present invention. Detailed implementation manners

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0021] The molecular general formula of the barium titanate two-dimensional flake powder is: BaTiO3

[0022] The raw materials used are all analytical pure raw materials: titanium dioxide (TiO2, 99.8%), bismuth oxide (Bi2O3, 99.9%), barium carbonate (BaCO3, 99.95%). The salts used for the auxiliary reaction in the high-temperature molten salt are: sodium chloride (NaCl, 99%), potassium chloride (KCl, 99%), barium chloride dihydrate (BaCl2·2H2O).

[0023] The experiment mainly includes the synthesis of the precursors Bi4Ti3O 12 and BaBi4Ti4O 15 and the synthesis of the barium titanate two-dimensional flake powder.

[0024] (1) Synthesis of the precursor Bi4Ti3O 12 Synthesis of the precursor powder:

[0025] 2Bi2O3 + 3TiO2 → Bi4Ti3O 12

[0026] Weigh about 10 g of the raw materials Bi2O3 and TiO2 per can according to the above formula ratio, add the NaCl-KCl mixed salt, use anhydrous ethanol as the medium, ball-mill and mix at 300 rpm for 12 h, and then dry the slurry at 90 °C. The mixed powder is placed in a covered alumina crucible and subjected to a high-temperature molten salt reaction at different temperatures for 2 h. The obtained powder is ultrasonically cleaned with hot deionized water to remove NaCl and KCl, and dried after the supernatant is titrated with an AgNO3 solution without precipitation to obtain flaky Bi4Ti3O 12 microcrystals. Table 1 shows the different temperatures for the high-temperature molten salt synthesis of the Bi4Ti3O 12 precursor.

[0027] Table 1

[0028] Temperature 950℃，1000℃，1050℃

[0029] (2) Synthesis of the precursor BaBi4Ti4O 15 Synthesis of the precursor:

[0030] Bi4Ti3O 12 +TiO2+BaCO3 → BaBi4Ti4O 15 +CO2

[0031] According to the above formula, weigh BaCO3, TiO2, and flaky Bi4Ti3O according to the raw material ratio 12 and KCl - BaCl2·2H2O, use absolute ethanol as the medium, stir magnetically to mix evenly, dry at 90 °C, place the mixed powder in a covered alumina crucible, and carry out a high-temperature molten salt reaction at 1080 °C for 2 h. After the product is ultrasonically cleaned with hot deionized water multiple times to remove chloride salts and excess reactants, until there is no precipitate when titrated with AgNO3 solution in the supernatant, filter by suction, and dry to finally obtain BaBi4Ti4O 15 microcrystals.

[0032] (3) Preparation of BT template

[0033] BaBi4Ti4O 15 +3BaCO3 → 4BaTiO3+2Bi2O3+3CO2

[0034] According to the above formula, weigh BaBi4Ti4O 15 , BaCO3, and KCl, add absolute ethanol, stir magnetically to mix evenly, dissolve all the salts into a paste and coat it on the surface of the powder, and dry at 90 °C. Place the mixed powder in a covered alumina crucible and carry out a high-temperature molten salt reaction at 950 °C for 3 h. The obtained dark brown product is washed several times with hot deionized water.

[0035] Washing to remove the by-product Bi2O3: Wash the synthesized powder with dilute nitric acid of different concentrations to remove the by-product Bi2O3 generated during the high-temperature molten salt reaction. The pickling conditions for the synthesized barium titanate are shown in Table 2 below:

[0036] Table 2

[0037] Concentration of nitric acid 3mol / L, 2mol / L, 1mol / L Pickling time 10h, 20h, 30h

[0038] Characterize the crystal structure, micro-morphology, etc. of the barium titanate two-dimensional flaky powder obtained under different synthesis conditions and pickling conditions. The optimized synthesis conditions for preparing barium titanate two-dimensional flaky powder with uniform size are: the synthesis temperatures of flaky bismuth titanate precursor, flaky barium bismuth titanate precursor, and flaky barium titanate are 1050 °C, 1080 °C, and 950 °C respectively. The optimized pickling condition for the synthesized powder is: use 1 mol / L dilute nitric acid and pickle for 30 h. The micro-morphology of the barium titanate two-dimensional flaky powder is evaluated by scanning electron microscopy (SEM) as Figure 1 and 2 shown. Figure 1The results show that using low-concentration nitric acid is beneficial to keeping the surface of the synthesized barium titanate flaky particles smooth and intact. As Figure 2 shown, after long-term cleaning with dilute nitric acid, the fragments in the BT powder can be effectively removed, and a two-dimensional flaky template with uniform size can be obtained. The crystal structure of the finally obtained BT two-dimensional flaky template is characterized by XRD as Figure 3 shown. As shown by the above results, the prepared barium titanate powder presents regular thin flakes, without the formation of a second phase. The size of the flaky powder is about 5-7 microns, and the thickness is about 0.5 microns, with uniform size. And the surface of the flaky BT template is smooth and regular.

[0039] In summary, by using the traditional three-step molten salt method combined with long-term cleaning with sufficiently dilute nitric acid in the later stage, the important problems of uneven size distribution and different template morphologies of the prepared barium titanate flaky two-dimensional template can be fully solved. By exploring the synthesis temperature of the Bi4Ti3O 12 precursor, the optimal conditions for synthesizing barium titanate by the three-step molten salt method are found, and the quality of the barium titanate flaky powder is improved. In addition, by exploring the optimal pickling conditions of the final barium titanate, the size uniformity and micro-morphology of the flaky powder can be effectively improved. The prepared barium titanate two-dimensional flaky powder has no second phase, with a smooth, regular morphology, uniform size, and a high aspect ratio, meeting the requirements of the flaky template for the preparation of piezoelectric textured ceramics and the needs of other related application fields.

Claims

1. A preparation method of a sheet-like barium titanate template powder with uniform size and high aspect ratio, characterized in that, Including: (1) Sinter Bi4Ti3O 12 with TiO2, BaCO3 and the auxiliary reaction salt KCl - BaCl2·2H2O at high temperature for a period of time, wash, filter by suction, and obtain the BaBi4Ti4O 15 flake - shaped precursor after drying; (2) Mix BaCO3 with the flaky precursor of BaBi4Ti4O 15 and the auxiliary salt KCl. After mixing evenly, conduct a molten salt reaction at high temperature to obtain BaTiO3 powder; (3) Repeatedly wash with 1 mol / L HNO3 to remove the by-product Bi2O3 and obtain a barium titanate template powder with uniform size and high aspect ratio in the form of flakes.

2. The method according to claim 1, wherein Bi4Ti3O 12 It is obtained by mixing Bi2O3, TiO2 and the molten salt system NaCl-KCl, carrying out a high-temperature molten salt reaction at 1050 °C for 2 h, washing, and then performing suction filtration.

3. The method according to claim 1, characterized in that, In step (1), Bi4Ti3O 12 is obtained by reacting with TiO2, BaCO3 and the auxiliary reaction salt KCl-BaCl2·2H2O at 1080 °C for 2 h.

4. The method according to claim 1, wherein In step (2), the molten salt reaction temperature is 950 °C and the reaction time is 3 h.

5. The method according to claim 1, wherein In step (2), BaCO3, the BaBi4Ti4O 15 flake-shaped precursor, and the auxiliary salt KCl are placed in absolute ethanol and mixed evenly.

6. The method according to claim 1, characterized in that, In step (3), repeatedly wash with 1 mol / L HNO3, and the entire washing process lasts for 30 h.

Images