CN102093045B - Barium titanate and barium ferrite composite powder with nucleus shell structure and preparation method thereof - Google Patents

Abstract

The invention discloses a core-shell structure barium titanate-barium ferrite composite powder material and a preparation method thereof. The material is a ferroelectric and ferromagnetic multifunctional composite powder material with a core-shell structure. The core is ferroelectric powder material barium titanate, and the outer core is a ferromagnetic shell layer with controllable thickness composed of barium ferrite. , The shell thickness is adjustable in the range of 10-100nm. The preparation method of the material is a uniform co-precipitation heterogeneous coating method. The co-precipitation process uses urea as a precipitant without any surface modification on the barium titanate. The shell coats the core completely, and there is no independent shell in the product. Layer particles exist, the cost is low, the operation is simple, the equipment is simple, the application is wide, and it is suitable for large-scale production.

Description

A core-shell structure barium titanate-barium ferrite composite powder material and its preparation method

technical field

The invention relates to a ferroelectric-ferromagnetic multifunctional composite powder material with a core-shell structure and a preparation method thereof, more particularly, a barium titanate-barium ferrite composite powder material with a core-shell structure and its The preparation method belongs to the field of novel multifunctional composite powder materials.

Background technique

Multifunctional composite powder materials are currently a hot research field. This kind of materials integrates various physical and chemical functions such as magnetism, electricity, light, heat, and catalysis. Significance.

Ferroelectric-ferromagnetic multifunctional powder is a kind of powder material with both ferroelectric and ferromagnetic properties. The product effect caused by the coupling between ferroelectric and ferromagnetic phases makes it widely used in microwave, High-voltage transmission line measurement, wide-band detection, magnetic field sensors and converters, micro-nano device control and other fields have great application potential, and thus have attracted widespread attention from all over the world.

There are few single-phase materials with both ferroelectric and ferromagnetic properties in nature, mainly bismuth-based perovskites, rare earth manganites, and fangfenite, and their magnetoelectric properties only exist at low temperatures. The magnetoelectric coupling coefficient is very low. Although the magnetoelectric coupling coefficient and operating temperature of single-phase ferroelectric-ferromagnetic materials can be improved by element doping and atomic substitution, the results are still far from large-scale practical applications.

Therefore, using the idea of material compounding, compounding mature ferroelectrics and ferromagnets in a certain way has become an important way to prepare ferroelectric-ferromagnetic powder materials. For example, Yao Xi et al. physically mixed ferroelectric powder and ferromagnetic powder to obtain a composite powder material with both ferroelectric and ferromagnetic properties. (Yao Xi.Ferroelectric and ferromagneticmicrocrystalline glass ceramics.Ferroelectrics, 2001, 261(1):3), Xie Shuhong prepared a ferroelectric-ferromagnetic composite fiber material (CN101274844A) by sol-gel electrospinning.

In the current ferroelectric-ferromagnetic composite materials, people often use spinel ferrite (AB ₂ O ₄ ), and barium ferrite has higher saturation magnetization and magnetocrystalline anisotropy, which can It can easily overcome the snoek limitation and play a role in high-frequency electromagnetic environments. It plays a very important role in the fields of microwave absorbing materials, vertical recording materials and microwave and millimeter wave device materials. If it is combined with a ferroelectric phase, it is expected to go further Expand the application range of ferroelectric-ferromagnetic materials, and have a more profound impact on the fields of magnetoelectric mutual control and energy conversion.

From simple physical mixing to micro-nano-scale mixing realized by sol-gel method, the uniformity of mixing of ferroelectric and ferromagnetic phases has been qualitatively improved. However, the problem of component segregation of the powder in the subsequent application field cannot be solved only by physical mixing; at the same time, due to the weak interaction between the two phases, it is impossible to fully utilize the new phase generated by the coupling effect between the magnetoelectric phases. Physicochemical properties. For this reason, it is urgent to develop new composite methods.

The core-shell structure has the advantages of high stability, shape, size, composition and structure controllability, etc., which can realize sufficient and effective coupling of different components at the micro-nano scale, and can be artificially designed and controllable to meet many specific requirements. Therefore, it is considered to be an ideal structural form for preparing ferroelectric-ferromagnetic multifunctional composite powder materials. V.Corral-Flores adopts the core-shell structure, which significantly improves the magnetoelectric coefficient of the magnetoelectric composite (V.Corral-Flores, Enhanced magnetoelectric effect in core-shell particulate composites, Journal of applied physics, 99, 2006); CAFVaz et al. adopted core-shell structure Fe ₃ O ₄ /BaTiO ₃ (CAFVaz, J.Hoffman, A.-B.Posadas, CHAhn, Magnetic anisotropy modulation of magnetite in Fe ₃ O ₄ /BaTiO3(100) epitaxial structures, Applied physics letters, 94, 2009) realized the adjustable magnetic anisotropy. ChaoWang et al. coated a layer of BaTiO ₃ on the surface of BaFe ₁₂ O ₁₉ powder, and realized the manipulation of the dielectric properties of the powder through the interaction between the core (BaFe ₁₂ O ₁₉ ) and the shell (BaTiO ₃ ) (ChaoWang , Xijiang Han, Ping Xu, Xiaohong Wang, Xueai Li, Hongtao Zhao, Magnetic and dielectric properties of barium titanate-coated barium ferrite, Journal of Alloys and Compounds, 476, 2009).

At present, the preparation methods of core-shell powder mainly include sol-gel method (Chinese patent 200410041128.9, Chinese patent 200710171827.9, Chinese patent 200710100330.8, Chinese patent 200710040489.5), emulsion polymerization (Chinese patent 200510087784.7, Chinese patent 01105317.8, Chinese patent 200610125136.0), chemical reduction method (Chinese patent 200510028257.9, Chinese patent 200510049662.9), solvothermal method (Chinese patent 200710164855.8), layer-by-layer self-assembly method (Chinese patent 200810123880.6, Chinese patent 200410018588.X), magnetron sputtering method (Chinese patent 200610015536.6), etc.

However, the above-mentioned methods all have different disadvantages in themselves. For example: the sol-gel method has the disadvantage of high cost due to its expensive metal alkoxide; the emulsion polymerization method, chemical reduction method and layer-by-layer self-assembly method involve the modification of the surface of the core material, so the preparation process is more complicated ; while the solvothermal method and the magnetron sputtering method have higher requirements on the equipment.

The precipitation method has the advantages of low cost and simple operation. The preparation of powder ceramic powder materials by precipitation method has achieved industrial production. In recent years, the use of precipitation to prepare core-shell particles has attracted people's attention. Tang Fangqiong used the deposition method to coat the semiconductor ZnO and TiO ₂ on the surface of SiO ₂ , and prepared a core-shell composite powder material with special physical properties ( CN1296917A); Chen Heguo etc. coated tin oxide (CN101613078A) on the surface of _SiO2 by precipitation method; Yang Dean et al. prepared core-shell strontium/calcium hydroxyapatite nanopowder by co-precipitation method (CN101428777); Xu Sailong et al. In-situ growth of hydrotalcite on the surface of sulfonated polystyrene microspheres by chemical precipitation (CN101274769A); Chen Jianding et al prepared manganese ferrite on the surface of polystyrene microspheres by precipitation method (CN101086911); Liu Zhengping and others Fe ₃ O ₄ was prepared on the surface of polystyrene spheres by co-deposition method, and magnetic microspheres with core-shell structure (CN1718619A) were obtained.

In many examples of preparing core-shell particles by chemical precipitation, strong base precipitants such as NaOH and KOH are often used, which makes it difficult to control the supersaturation of the solution. The precipitation coating process is accompanied by a large number of homogeneous nucleation processes, resulting in core-shell particles. There are often a large number of independent shell particles mixed in the body, the purity of the product is limited, and the difficulty of separation is also increased. Although the purity of the product can be improved by surface treatment of coated particles, most of the organic coupling agents used in surface treatment are expensive, which increases the cost; in addition, the additional surface treatment process undoubtedly makes the operation more cumbersome .

Therefore, it is of great significance for the basic theory and application research of ferroelectric and ferromagnetic core-shell particles to develop a co-precipitation preparation process with low cost, simple operation and suitable for large-scale production.

Contents of the invention

The object of the present invention is to provide a barium titanate-barium ferrite composite powder and a preparation method thereof for homogeneous coprecipitation and heterogeneous coating. The material is a ferroelectric and ferromagnetic multifunctional composite powder material with a core-shell structure. The core is ferroelectric powder material barium titanate, and the outer core is a ferromagnetic shell with controllable thickness composed of barium ferrite. And the shell thickness can be adjusted in the range of 10-100nm. The co-precipitation process uses urea as a precipitant. The preparation process has the following advantages: no surface modification of barium titanate is required, the thickness of barium ferrite (ferromagnetic shell) is controllable, the shell is completely coated on the core, and there is no The existence of independent shell particles has the advantages of low cost, simple operation, simple equipment, wide application and suitable for large-scale production.

Technical scheme of the present invention is as follows:

The ferroelectric and ferromagnetic multifunctional composite powder material of the present invention is a powder material with a core-shell structure, the core of which is barium titanate, and the outside of the core is a ferromagnetic shell composed of barium ferrite. The particle size of the barium titanate powder is in the range of 0.05-2 μm.

The present invention adopts uniform co-precipitation heterogeneous coating technology to prepare multifunctional powder materials with core-shell structure. The preparation method is to use urea precipitant to decompose under certain temperature conditions to produce OH ^- and CO ₃ ^2- , and slowly increase the pH of the solution value, gradually increasing the supersaturation, causing the precipitation reaction of metal ions in the solution. By adjusting the experimental conditions such as the concentration of metal ions in the solution, the concentration of urea, and the reaction temperature, the metal precipitates are controlled to nucleate and grow in the form of heterogeneous nucleation on the surface of the ferroelectric powder, thereby realizing the barium ferrite precursor Coating the barium titanate powder to obtain the ferroelectric ferromagnetic core-shell particle precursor (hereinafter referred to as the precursor); The coating is transformed into barium ferrite, thereby obtaining a multifunctional composite barium titanate-barium ferrite composite powder material (hereinafter referred to as the core-shell material).

The preparation process of the present invention comprises the following steps:

(1) Cleaning and degreasing of barium titanate powder: put a certain volume of barium titanate powder in deionized water, ultrasonically treat it for 10 to 30 minutes, and then filter and collect the cleaned barium titanate; The cleaned barium titanate is placed in absolute ethanol, ultrasonically treated for 10-40 minutes, and then collected by filtration; the barium titanate after the above-mentioned cleaning and degreasing process is placed in a vacuum drying oven at 50-80°C. dry to obtain the product for use;

(2) Reaction solution configuration: Dissolve the metal salt in deionized water at a certain concentration ratio according to the stoichiometric ratio, and add an appropriate amount of precipitant and surfactant into the solution after complete dissolution. Wherein the molar ratio of the total amount of metal ions to urea is 1:20 to 200, and the surfactant concentration is 0.05 to 0.8 wt %;

Wherein, the metal salt in the reaction solution is ferric nitrate and barium nitrate, and its molar concentration is configured according to the stoichiometric ratio of the shell to be coated. The total molar concentration of metal ions in the reaction solution is 0.0001-0.08mol/L, preferably 0.001 ～0.01; In the reaction solution, the precipitation agent is urea, and the molar concentration in the reaction solution is 0.08～2.5mol/L, preferably 0.4～2.0mol/L; The surfactant is polyvinylpyrrolidone, sodium dodecylsulfonate, One or both of sodium dodecylbenzenesulfonate and polyvinyl alcohol, the concentration of the surfactant in the reaction solution is defined according to the mass percentage of the added coated barium titanate powder, and its concentration is 0.05 -0.8 wt%, preferably 0.1-0.3 wt%.

(3) Precursor preparation: Add an appropriate amount of barium titanate after cleaning and degreasing into the reaction solution obtained in step (2), and after ultrasonic treatment for 30-60 minutes at room temperature, place the reaction solution in a closed container , and then keep warm at 60-120°C for 1-48h under stirring condition.

Wherein, the concentration of barium titanate ferroelectric powder is 0.1-10g/L, preferably 1-5g/L;

(4) Aging: After step (3) is completed, the reaction device is naturally cooled at room temperature and left to stand for 1-24 hours.

(5) Collection of precursors: After step (4) is completed, the obtained product is centrifuged at 6000rpm, and after removing the supernatant, add ultrapure water to redisperse, then centrifuge, first use deionized water, and then Repeat the above process three times with absolute ethanol, put the precursor after cleaning and separation into a vacuum drying oven, and dry at 50-80° C. for 12 hours.

(6) Preparation of barium titanate-barium ferrite composite powder: put the precursor prepared in step (5) into a muffle furnace, and calcinate at 600-1100°C for 0.5-8h to obtain titanium with a core-shell structure Barium acid-barium ferrite composite powder material.

In step (1) of the present invention, the barium titanate powder used can be prepared by mechanical ball milling, sol-gel method, co-precipitation method, and hydrothermal method. See 1. Hu MZC, Payzant EA, Rawn CJ, Miller GA, "Homogeneous (co) precipitation of inorganic salts for synthesis of monodispersed barium titanate particles", Journal of Materials Science 35(2000) 2927-2936; 2. Burtrand Lee, Jianping Zhang, "Preparation, structure evolution and dielectric properties of BaTiO ₃ thin films and powders by anaqueous sol-gel process", Thin Solid Films 388(2001) 107-113; 3. Chinese patent CN1275117; 4. Zhang Jianguang, Zhang Mingfu, Han Jiecai , He Xiaodong, Du Shanyi, "The crystallization process of nano-barium titanate prepared by high-energy ball milling", Piezoelectricity and Acousto-Optics, 200123(5).

The advantage of the present invention is that: the barium titanate-barium ferrite composite powder prepared by the present invention is a ferroelectric and ferromagnetic multifunctional composite powder with a core-shell structure, and its ferroelectric and ferromagnetic properties can be conveniently within a certain range Controlled, the powder has a strong magnetoelectric coupling coefficient. The deposition process uses urea as the precipitating agent. The prepared composite material is completely coated, the product is single, and there is no separate shell particle. Modification, the preparation method is simple, no large-scale equipment and instruments are required, and it is suitable for large-scale production.

Description of drawings

Fig. 1 is the TEM (a is the precursor, b is the core-shell particle) of the precursor and the core-shell particle prepared for embodiment 1;

Fig. 2 is the XRD spectrogram (a barium titanate, b precursor, c core-shell particle) of barium titanate, precursor and core-shell particle prepared for embodiment 1;

FIG. 3 is a hysteresis loop of the core-shell particles prepared in Example 1. FIG.

Detailed ways

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

Example 1

Weigh an appropriate amount of Fe(NO ₃ ) ₃ 9H ₂ O, Ba(NO ₃ ) ₂ and urea and dissolve them in deionized water so that the molar concentrations of the three are 0.006mol/L, 0.0005mol/L and 0.8mol/L, respectively, and weigh Take 0.5 g of barium titanate powder that has been cleaned and degreased, and add it to 200 ml of the above reaction solution, and at the same time add 3 wt % polyvinylpyrrolidone as a dispersant. After the above solution was ultrasonically treated for 30 minutes, it was placed in an airtight container and reacted under stirring conditions. The reaction temperature was 100°C and the reaction time was 12 hours; Add ultrapure water to the supernatant to redisperse, then centrifuge, repeat the above process three times with deionized water first, and then with absolute ethanol, and put the coated precursor after cleaning and separation into a vacuum drying oven at 80°C Put the dried coated precursor into a muffle furnace and calcined at 1100°C for 2 hours to obtain the core-shell of barium ferrite (BaFe ₁₂ O ₉ ) coated barium titanate (BaTiO ₃ ) Structural ferroelectric ferromagnetic composite powder material. The average thickness of its barium ferrite cladding layer is 12nm. The TEM photos, XRD and hysteresis loops of the precursor and core-shell particles under this condition are shown in Figure 1, Figure 2 and Figure 3, respectively.

Example 2

Weigh an appropriate amount of Fe(NO ₃ ) ₃ 9H ₂ O, Ba(NO ₃ ) ₂ and urea and dissolve them in deionized water so that the molar concentrations of the three are 0.006mol/L, 0.0005mol/L and 0.8mol/L, respectively, and weigh Take 0.1 g of barium titanate powder that has been cleaned and degreased, and add it to 200 ml of the above reaction solution, and at the same time add 3 wt % polyvinylpyrrolidone as a dispersant. After the above solution was ultrasonically treated for 30 minutes, it was placed in an airtight container and reacted under stirring conditions. The reaction temperature was 100°C and the reaction time was 12 hours; Add ultrapure water to the supernatant to redisperse, then centrifuge, repeat the above process three times with deionized water first, and then with absolute ethanol, and put the coated precursor after cleaning and separation into a vacuum drying oven at 80°C Put the dried coated precursor into a muffle furnace and calcined at 1100°C for 2 hours to obtain the core-shell of barium ferrite (BaFe ₁₂ O ₉ ) coated barium titanate (BaTiO ₃ ) Structural ferroelectric ferromagnetic composite powder material. The average thickness of its barium ferrite cladding layer is 23nm.

Example 3

Weigh an appropriate amount of Fe(NO ₃ ) ₃ 9H ₂ O, Ba(NO ₃ ) ₂ and urea and dissolve them in deionized water so that the molar concentrations of the three are 0.024mol/L, 0.002mol/L and 0.8mol/L, respectively, and weigh Take 0.5 g of barium titanate powder that has been cleaned and degreased, and add it to 200 ml of the above reaction solution, and at the same time add 3 wt % polyvinylpyrrolidone as a dispersant. After the above solution was ultrasonically treated for 30 minutes, it was placed in an airtight container and reacted under stirring conditions. The reaction temperature was 90°C and the reaction time was 24 hours; Add ultrapure water to the supernatant to redisperse, then centrifuge, repeat the above process three times with deionized water first, and then with absolute ethanol, and put the coated precursor after cleaning and separation into a vacuum drying oven at 80°C Put the dried coating precursor into a muffle furnace and calcined at 800°C for 2 hours to obtain the core-shell of barium ferrite (BaFe ₁₂ O ₉ ) coated barium titanate (BaTiO ₃ ) Structural ferroelectric ferromagnetic composite powder material.

Claims (4)

1. nucleocapsid structure barium titanate-barium ferrite composite powder material, it is characterized in that, this material is the ferroelectric-ferromagnetic multifunctional composite powder body material with nucleocapsid structure, and its nuclear is ferroelectric powder material barium titanate, and nuclear is outer to be the controlled ferromegnetism shell of thickness that consists of with barium ferrite.

2. the preparation method of nucleocapsid structure barium titanate as claimed in claim 1-barium ferrite composite powder material is characterized in that concrete steps are as follows:

(1) the cleaning oil removing of barium carbonate powder: the certain volume barium carbonate powder is placed deionized water, and supersound process 10～30 minutes will be cleaned afterwards barium titanate later and be filtered collection; To place dehydrated alcohol through washed with de-ionized water barium titanate later, supersound process 10～40 minutes is filtered it afterwards and is collected; To place vacuum drying oven to dry in 50～80 ℃ of conditions through the barium titanate after the above-mentioned cleaning oil removing process, it be stand-by to obtain product;

(2) reaction soln preparation: according to stoichiometric ratio metal-salt is dissolved in the deionized water in the finite concentration ratio, in solution, adds until completely dissolved an amount of precipitation agent urea and tensio-active agent;

(3) precursor preparation: get an amount of barium titanate that cleans after the oil removing through step (1) and join in the reaction soln that is obtained by step (2), supersound process is after 30～60 minutes under the room temperature condition, reaction soln is placed encloses container, under agitation condition, be incubated 1～48h in 60～120 ℃ again;

(4) ageing: after step (3) is complete, with reaction unit naturally cooling at ambient temperature, and leave standstill 1～24h;

(5) collect precursor: after step (4) is complete, with the centrifugation under the 6000rpm condition of resulting product, remove and add again ultrapure water after the supernatant liquor and again disperse, centrifugal again, use first deionized water, use again dehydrated alcohol, repeat said process three times, the precursor that cleans after separating is put into vacuum drying oven, at 50～80 ℃ of dry 12h;

(6) preparation barium titanate-barium ferrite composite granule: the precursor that step (5) makes is put into retort furnace, at 600～1100 ℃ of calcining 0.5～8h, obtain having the barium titanate of nucleocapsid structure-barium ferrite composite powder material.

3. the preparation method of nucleocapsid structure barium titanate as claimed in claim 2-barium ferrite composite powder material, it is characterized in that the described metal-salt of step (2) is iron nitrate, nitrate of baryta, the stoichiometric ratio of barium and iron is configured in the barium ferrite shell that its volumetric molar concentration coats as required, and the metal ion total mol concentration is 0.0001～0.08mol/L in the reaction soln; Precipitation agent is urea in the reaction soln, and the volumetric molar concentration in reaction soln is 0.08～2.5mol/L; Tensio-active agent is one or both in polyvinylpyrrolidone, sodium laurylsulfonate, Sodium dodecylbenzene sulfonate, the polyvinyl alcohol, the concentration of tensio-active agent is according to its mass percent definition that is wrapped by ferroelectric powder that accounts for adding in the reaction soln, and its concentration is 0.05～0.8wt%.

4. the preparation method of nucleocapsid structure barium titanate as claimed in claim 2-barium ferrite composite powder material is characterized in that the adding concentration of the described barium titanate ferroelectric powder of step (3) is 0.1～10g/L.

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