CN117228734A - Chemical coprecipitation preparation method of 18H hexaferrite - Google Patents

Abstract

The invention discloses a chemical coprecipitation preparation method of 18H hexagonal ferrite. First, the chemical coprecipitation method is used to precipitate divalent Ba ²⁺ , Co ²⁺ , Zn ²⁺ and trivalent Fe ³⁺ to form a metal salt. Hydroxide or carbonate is precipitated, and then the obtained precursor precipitate powder is mixed with rutile phase nano-titanium dioxide powder according to a specific ratio. Finally, after high-temperature calcination, the divalent Ba ²⁺ , Co ²⁺ , Zn ²⁺ , and trivalent Fe ³⁺ ions in the precursor are combined with the tetravalent Ti ions in the rutile phase nanotitanium dioxide to form a stable polyphase. Crystal 18H hexagonal ferrite. This method overcomes the problem that Ti(OH) ₄ precipitation is difficult to stably exist in an alkaline environment. It has the advantages of simple process, easy control of ingredients and high purity of the product. It provides a basis for the development of high-performance miniaturized antenna magnetoelectric materials that meet the requirements of the sub-6 GHz frequency band. Provides new ways.

Description

A chemical coprecipitation preparation method of 18H hexagonal ferrite

Technical field

The invention belongs to the technical field of material preparation and relates to a method for preparing ferrite materials, specifically a method for preparing chemical co-precipitation of 18H hexagonal ferrite.

Background technique

With the rapid development of 5G technology, communication equipment is constantly developing towards high frequency and miniaturization. As an important medium for transmitting signals in communication equipment, antennas are constantly evolving towards miniaturization and integration. Miniaturized antenna magnetoelectric materials that simultaneously have high magnetic permeability, matched dielectric constant and low loss in the sub-6 GHz frequency band have received great attention from academia and industry. Three important indicators to evaluate the performance of miniaturized antenna magnetoelectric materials are the performance factor PF at a specific frequency (defined as: magnetic quality factor Q , the highest operating frequency f ₀ corresponding to Q ≥ 10.0 and the real part of the magnetic permeability product of the three), characteristic impedance and miniaturization factor/> (/> is the real part of the complex dielectric constant). First, the higher the operating frequency and PF value, the more potential the material has for high-frequency and low-loss applications. Second, the closer the real part of the magnetic permeability is to the real part of the dielectric constant, the better the impedance matching performance. Third, miniaturization factor/> The higher it is, the better it is to reduce the size of the antenna. Traditional spinel ferrite is subject to low magnetocrystalline anisotropy, the operating frequency is usually lower than 1.0 GHz, and the PF value is low. Planar hexagonal ferrite benefits from large out-of-plane anisotropy, and its operating frequency can exceed 1.0 GHz, which can increase the PF value. Although the magnetoelectric properties of the above-mentioned ferrites can be controlled by substituting metal cations or doping sintering aids, the operating frequency of these ferrites is almost difficult to reach 5.0 GHz, and the PF value is difficult to reach 70.0 GHz. It is difficult to Meet the needs of miniaturized antennas in the sub-6 GHz frequency band.

ROSavage and A.Tauber et al. reported a unique crystal phase, named 18H hexagonal ferrite, with a stoichiometric ratio of M ₅ Me ₂ Ti ₃ Fe ₁₂ O ₃₁ (M= Ba ²⁺ , Sr ²⁺ or Any combination of them, Me=Mg ²⁺ , Zn ²⁺ , Cu ²⁺ , Co ^{2 +} or any combination thereof). The unit cell of this ferrite has an 18-layer close-packed structure, which can be regarded as a three-layer hexagonal barium titanate structure nested within the T block in the Y-shaped ferrite structure. QF Li and YJChen et al. used solid-state reaction method to synthesize Ba ₅ Mg _2-x Zn _x Ti ₃ Fe ₁₂ O ₃₁ (0≤x≤1.25) polycrystalline Mg-Zn 18H ferrite, which is the highest work on this material. The frequency is 4.0GHz, the real part of the magnetic permeability is 1.7, the magnetic quality factor is 10.0, and the PF value reaches 68.0 GHz. The PF has been significantly improved compared with traditional planar hexagonal ferrite. However, the solid-state reaction method used in the above studies requires secondary ball milling and secondary sintering of the initial raw materials, and the preparation process is relatively cumbersome. The chemical co-precipitation method is an important method for preparing high-quality ferrite powder. It has the advantages of easy control of the composition, difficulty in mixing impurity ions, and only one sintering. However, the preparation of 18H hexagonal ferrite by chemical co-precipitation method has not yet been reported.

Contents of the invention

The purpose of the present invention is to disclose a chemical co-precipitation preparation method of 18H hexagonal ferrite to fill the gaps in the existing technology and has the advantages of simple process, easy control of ingredients and high product purity.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A chemical co-precipitation preparation method of 18H hexagonal ferrite, taking the synthesis of CoZn 18H hexagonal ferrite as an example, the molecular formula is Ba ₅ Co _2-x Zn _x Ti ₃ Fe ₁₂ O ₃₁ (x=0, 0.2, 0.4, 0.6, 0.8, 1.0), including the following steps:

1) First, weigh BaCl ₂ ·2H ₂ O, CoCl ₂ ·6H ₂ O, FeCl ₃ ·6H ₂ O and ZnCl ₂ and dissolve them in molar ratio 5: (1~2): 12: (0~1). Ionized water to form a mixed salt solution; then weigh NaOH and Na ₂ CO ₃ to form an alkaline aqueous solution at a molar ratio of 7:1. After the alkaline aqueous solution heats up to 90°C, pour the mixed salt solution into the alkaline aqueous solution at one time Stir the reaction, quickly add tetraethylene glycol to the mixed system during the reaction, react for 1 to 2 hours, stir and cool to room temperature, wash repeatedly with deionized water and absolute ethanol until neutral, centrifuge to remove the precipitate, and place at 60°C After drying in the environment for 24 hours, take it out and grind it to powder to obtain the precursor powder; among them, the molar ratio of BaCl ₂ ·2H ₂ O and NaOH in the mixed system is 1:8, and the molar ratio of tetraethylene glycol in the mixed system is 1:8. The volume fraction is 5%~7%;

(2) Take the rutile phase nano-titanium dioxide powder and put it into the precursor powder, stir and mix evenly. The amount of rutile phase nano-titanium dioxide powder added is 8% to 12% of the mass of the precursor powder;

3) Place the uniformly mixed rutile phase nano-titanium dioxide powder and precursor powder in a muffle furnace, keep it at a temperature of 1150~1250°C for 4~6 hours at a heating rate of 1~3°C/min, and then cool to room temperature with the furnace. , that is, CoZn 18H hexagonal ferrite is obtained.

Generally speaking, alkaline precipitants (such as sodium hydroxide and anhydrous sodium carbonate) can be used to co-precipitate the required metal cations to form divalent or trivalent hydroxide or carbonate precipitates. However, 18H hexagonal ferrite contains tetravalent Ti ions. In order to precipitate tetravalent Ti ions, it is necessary to use a water-soluble tetravalent Ti salt to react with an alkaline precipitant to form Ti(OH) ₄ precipitation. However, Ti(OH) ₄ is an amphoteric hydroxide and can be dissolved in a hot concentrated alkali environment, which makes it difficult for Ti(OH) ₄ precipitation to exist stably in the alkaline environment of the co-precipitation reaction. Therefore, the present invention first uses a chemical co-precipitation method to precipitate divalent Ba ²⁺ , Co ²⁺ , Zn ²⁺ and trivalent Fe ³⁺ to form hydroxides and carbonates of metal salts, and then precipitate them according to a specific ratio. Mix the precursor powder obtained in the first step with the rutile phase nano titanium dioxide powder. Finally, after high-temperature calcination, the Ba ²⁺ , Co ²⁺ , Zn ²⁺ , and Fe ³⁺ ions in the precursor are combined with the tetravalent Ti ions in the rutile phase nano-titanium dioxide to form a stable 18H hexagonal ferrite. Polycrystalline phase.

In summary, the present invention overcomes the problem that Ti(OH) ₄ precipitation is difficult to stably exist in an alkaline environment, successfully prepares CoZn 18H hexagonal ferrite, and provides a method for preparing this type of 18H hexagonal ferrite through chemical coprecipitation. new method of body. This preparation method has the advantages of simple process, easy composition control and high product purity, and provides a new way to develop high-performance miniaturized antenna magnetoelectric materials that meet the sub-6 GHz frequency band.

Description of drawings

Figure 1 is a schematic diagram of the entire process of synthesis and sample preparation of CoZn 18H hexagonal ferrite of the present invention.

Figure 2 is the X-ray diffraction pattern of the CoZn 18H hexagonal ferrite ring sample of the present invention under different substitution amounts of Zn ions.

Figure 3 is a cross-sectional SEM image of the CoZn 18H hexagonal ferrite ring sample of the present invention under different substitution amounts of Zn ions.

Figure 4 is a static magnetic property diagram of the CoZn 18H hexagonal ferrite ring sample of the present invention under different substitution amounts of Zn ions.

Figure 5 is a graph showing the relationship between the real part of the complex dielectric constant and the frequency of the CoZn 18H hexagonal ferrite disc sample of the present invention under different substitution amounts of Zn ions.

Figure 6 is a diagram showing the relationship between the complex magnetic permeability and frequency of the CoZn 18H hexagonal ferrite ring sample of the present invention under different substitution amounts of Zn ions, in which: (a) real part, (b) imaginary part.

Detailed ways

The present invention will be further explained below in conjunction with specific embodiments.

Example

Referring to Figure 1, taking the synthesis of CoZn 18H hexagonal ferrite as an example, the molecular formula is Ba ₅ Co _2-x Zn _x Ti ₃ Fe ₁₂ O ₃₁ (x=0,0.2, 0.4, 0.6, 0.8, 1.0). The specific steps are as follows :

1. Precursor powder preparation

Using a stirring rod, stir 25.64 g (0.105 mol) BaCl ₂ ∙2H ₂ O, 5.00 g (0.021 mol) ~ 9.99g (0.042 mol) CoCl ₂ ∙6H ₂ O, 68.22 g (0.252 mol) FeCl ₃ ∙6H ₂ O, 0g~2.87 g (0.021 mol) ZnCl ₂ is evenly mixed and dissolved in a 500 mL beaker filled with 400 mL deionized water at a rotation speed of 600 r/min to form a mixed salt solution; use a stirring rod to stir 33.65g (0.841 mol) NaOH and 12.49 g (0.118 mol) Na ₂ CO ₃ were evenly dissolved in a 2 L beaker filled with 400 mL deionized water, and the beaker was placed in a 90°C water bath for heating; wait until the temperature of the above alkaline solution reaches After reaching 90°C, pour the mixed salt solution into the 2 L beaker of the reaction vessel containing the alkaline solution at once, and the rotation speed is 600 r/min. The reaction begins, and then add 50 mL of tetraethylene glycol to the 2 L beaker. , tetraethylene glycol is used as a surfactant, which is beneficial to the formation of ferrite particles; the reaction lasts for 2 h, after which the reactor is taken out of the water bath and stirred at room temperature until cooled to room temperature; then, deionization is performed using Wash the precipitate repeatedly with water and absolute ethanol, and centrifuge at 6000r/min for 1 minute to separate the precipitate and supernatant until the pH of the supernatant reaches 7.0. Place the washed precipitate at 60°C. Dry in an oven for 24 hours; finally, grind the dried precipitate into powder to obtain precursor powder.

2. Mixing

Weigh 15.0 g of dry and ground precursor powder and 1.46 g of rutile phase nano-titanium dioxide (40 nm) powder, put them into the mixing tank of a three-dimensional mixer, and mix for 8 h to make the two powders evenly mixed.

3. Granulation

Weigh 1.6 g of the mixed powder obtained in step 2 and mix with 0.18 g of polyvinyl alcohol aqueous solution (8 wt%). Use an agate mortar for granulation. The grinding time is 5 min. The sample appears as plate-shaped particles and is collected.

4. Pressure ring

Weigh 0.25 g of the granulated particles obtained in step 3, pour it into a mold with an outer diameter of 7.5 mm and an inner diameter of 3 mm, and press it for 4 minutes under an axial pressure of 1270 MPa.

5. Press disc

Weigh 5.0 g of the mixed powder obtained in step 2 and 0.56 g of polyvinyl alcohol aqueous solution (8 wt%), and prepare a dielectric property measurement sample using the method for preparing ferrite dielectric property measurement samples given in the invention patent CN115745590B .

6. Sintering

The ring-shaped and disc-shaped samples obtained in steps 4 and 5 were placed in a box-type muffle furnace and kept at 1200°C for 5 h with a heating rate of 1.5°C/min. The samples were naturally cooled to room temperature in the furnace.

7. Laser cutting

Because the inner and outer diameters of the ring-shaped 18 H hexagonal ferrite samples will shrink after sintering. In order to meet the subsequent measurement needs of complex magnetic permeability, we used a laser cutting machine to cut the inner diameter of the sintered ring-shaped sample until the inner diameter of the sample reached 3.0 mm.

Steps 3, 4, 5, and 7 are necessary steps for preparing samples for measuring dielectric and complex magnetic permeability characteristics, and are not steps for the synthesis of CoZn 18H hexagonal ferrite.

Structure Characterization

First, X-ray diffraction was performed on the CoZn 18H hexagonal ferrite ring samples with different Zn ion substitution amounts mentioned above, and the results are shown in Figure 2. As can be seen from Figure 2, the X-ray diffraction peak positions of the CoZn 18H hexagonal ferrite ring samples under different Zn ion substitution amounts are consistent with the theoretical diffraction peak positions, proving that all samples do not contain impurity phases.

Secondly, cross-sectional scanning electron microscopy analysis was performed on the CoZn 18H hexagonal ferrite ring sample with different Zn ion substitution amounts mentioned above, and the results are shown in Figure 3. As can be seen from Figure 3, the particle size of most sample particles is between 1.8 μm and 9.8 μm, and the particles have a typical hexagonal shape.

In summary, it can be seen that the chemical co-precipitation method of the present invention can successfully prepare CoZn 18H hexagonal ferrite with higher purity.

Performance evaluation

Figure 4 is a line chart of static magnetic properties of CoZn 18H hexagonal ferrite ring samples under different Zn ion substitution amounts. It can be seen from Figure 4 that as the substitution amount of Zn ions increases, the super-exchange effect in CoZn 18H hexagonal ferrite will change, thereby changing the saturation magnetization. The specific mechanism of action requires subsequent measurement and analysis of CoZn 18H hexagonal ferrite. The neutron diffraction spectrum of the oxygen body determines its magnetic structure. At the same time, as the substitution amount of Zn ions increases, the anisotropy constant of the sample gradually decreases. Since the intrinsic coercive force is proportional to the anisotropy constant, the coercive force of the sample gradually decreases.

Figure 5 shows the relationship between the real part of the complex dielectric constant of the CoZn 18H hexagonal ferrite disc sample as a function of frequency under different substitution amounts of Zn ions. As can be seen from Figure 5, the real part of the complex dielectric constant of all samples is between 9.8 and 15.5, and almost does not change with frequency. It has good frequency stability and helps to obtain a higher miniaturization factor.

Figure 6 is a graph showing the variation of the complex permeability with frequency of the CoZn 18H hexagonal ferrite ring sample under different substitution amounts of Zn ions, in which (a) the real part; (b) the imaginary part. It can be seen from Figure 6 that as the substitution amount of Zn ions increases, the real part of the corresponding complex permeability at 0.1 GHz gradually increases, and the natural resonance frequency corresponding to the maximum value of the imaginary part of the complex permeability gradually moves to low frequency. According to magnetic theory, for polycrystalline planar hexagonal ferrite with grain orientation in any direction, its natural resonance frequency is proportional to the product of the out-of-plane anisotropic field H _θ and the in-plane anisotropic field H _φ . H _θ and H _φ are proportional to the anisotropy constants ( K ₁ +2 K ₂ ) and | K ₃ |, respectively. This shows that as the Zn ion content increases, the anisotropy constant ( K ₁ +2 K ₂ ) and | K ₃ | gradually decrease, and H _θ and H _φ decrease, causing the natural resonance frequency to gradually move to low frequency. In addition, since the magnetic susceptibility contributed by the magnetic moment rotation is inversely proportional to both H _θ and H _φ , as the Zn ion content increases, the real part of the complex magnetic permeability at 0.1 GHz gradually increases.

In addition, in order to more intuitively judge whether CoZn 18H hexagonal ferrite with different Zn ion substitution amounts meets the application requirements of miniaturized antenna magnetoelectric materials, the main performance parameters of CoZn 18H hexagonal ferrite with different Zn ion substitution amounts were measured. , the results are shown in Table 1 below.

Table 1 Main performance parameters of CoZn 18H hexagonal ferrite under different Zn ion substitution amounts

It can be seen from Table 1 that when x=0, the CoZn 18H hexagonal ferrite sample has the highest operating frequency and PF value, reaching 4.97 GHz and 68.6 GHz respectively, and the miniaturization factor reaches 4.07.

The above results show that the CoZn 18H hexagonal ferrite synthesized by the chemical co-precipitation method of the present invention has excellent magnetoelectric material properties for miniaturized antennas and has potential application in the sub-6 GHz frequency band.

Claims (3)

1. Taking a synthetic CoZn18H hexaferrite as an example, the chemical coprecipitation preparation method of the 18H hexaferrite has the following molecular formula: ba (Ba) ₅ Co _2-x Zn _x Ti ₃ Fe ₁₂ O ₃₁ (x=0, 0.2, 0.4, 0.6, 0.8, 1.0), comprising the steps of:

1) Firstly, the molar ratio is 5: (1-2): 12: (0-1) weighing BaCl ₂ ·2H ₂ O、CoCl ₂ ·6H ₂ O、FeCl ₃ ·6H ₂ O and ZnCl ₂ Co-dissolving in deionized water to form a mixed salt solution; then, the molar ratio is 7:1 weighing NaOH and Na ₂ CO ₃ Preparing an alkaline aqueous solution, after the alkaline aqueous solution is heated to 90 ℃, pouring the mixed salt solution into the alkaline aqueous solution for stirring reaction at one time, rapidly adding tetraethylene glycol into the mixed system during the reaction, stirring and cooling to room temperature after the reaction is carried out for 1-2 hours, repeatedly washing to neutrality by using deionized water and absolute ethyl alcohol, centrifuging to obtain precipitate, drying for 24 h at 60 ℃, taking out, and grinding to powder, thus obtaining the productObtaining precursor powder;

(2) Placing rutile phase nano titanium dioxide powder into precursor powder, and uniformly stirring and mixing, wherein the addition amount of the rutile phase nano titanium dioxide powder is 8% -12% of the mass of the precursor powder;

3) And placing the uniformly mixed rutile phase nano titanium dioxide powder and precursor powder into a muffle furnace, preserving heat for 4-6 hours at 1150-1250 ℃ at a heating rate of 1-3 ℃/min, and then cooling to room temperature along with the furnace to obtain the CoZn18H hexaferrite.

2. The method for preparing 18H hexaferrite by chemical coprecipitation according to claim 1, wherein in step 1), baCl ₂ ·2H ₂ The mol ratio of O to NaOH in the mixed system is 1:8.

3. the chemical coprecipitation preparation method of 18H hexaferrite according to claim 1, wherein in the step 1), the volume fraction of tetraethylene glycol in a mixed system is 5% -7%.