CN115745590B - Preparation method of nano ferrite dielectric property measurement sample - Google Patents

Abstract

The invention discloses a preparation method of a nano ferrite dielectric property measurement sample, which utilizes an adhesive to carry out multiple adhesive granulation on nano precursor powder, so that static friction force among nano precursor particles can be effectively reduced, flowability among particles is improved, and thus the sample is easier to press and form, and cracking phenomenon is avoided; meanwhile, the nano precursor particles can be uniformly distributed by sieving after each gluing and granulating, and uneven pressing stress distribution caused by uneven particle size distribution is avoided, so that cracking phenomenon in the sample pressing and forming process is avoided, and a supporting effect is achieved for accurately measuring the dielectric characteristics of the nano ferrite.

Description

Preparation method of nano ferrite dielectric property measurement sample

Technical Field

The invention relates to a preparation method of a nano ferrite sample, in particular to a preparation method of a nano ferrite dielectric property measurement sample, and belongs to the technical field of material molding.

Background

With the rapid development of 5G communication technology, there is a great demand for integrated radio frequency antennas. Magneto-electric materials play an important role in the field of miniaturized antennas. On the one hand, the higher magneto-electric material miniaturization factor (n= (mu 'epsilon') ^1/2 ) The physical size of the antenna can be effectively reduced. On the other hand, in order for the antenna to obtain good impedance matching characteristics, the characteristic impedance of the magneto-electric material needs to be as close as possible to the free space impedance, i.e., μ '≡ε'. The magnetic conductivity of the magnetoelectric material is continuously improved, so that the larger n value is obtained, and good impedance matching characteristics are realized. In addition, in order to reduce the weakening of the antenna performance by material loss, the magneto-electric material also needs to have a lower dielectric loss (tan delta _ε ) And magnetic loss tangent (tan delta) _μ ) Values. Studies have shown that refinement of the material particle size effectively suppresses domain wall movement, significantly reducing the magnetic loss tangent (Qifan Li, yajie Chen, qifan Li, lezhong Li, kun Qian, vincent g, harris, suppressed domain wall damping in planar BaM hexaferrites forminiaturization of microwave devices, j. The nano NiZnCo ferrite has become a potential miniaturized antenna magneto-electric material due to the small particle size approximate to a single domain and the higher ferromagnetic resonance frequency. In previous studies, researchers have passed through chemical coprecipitationSuccessfully preparing Ni by a precipitation method and a sintering process _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ The nano ferrite ring sample was measured for high frequency electromagnetic parameters of the sample using a vector network analyzer (j. -l.mattei, e.le Guen, a. Chemalier, dense and half-Dense NiZnCo ferrite ceramics: their respective relevancefor antenna downsizing, according to their dielectric and magneticproperties at microwave frequencies, j. Appl. Phys.117 (2015) 084904.). However, since the ferrite sample is calcined and then subjected to size shrinkage, the sample cannot completely fill the coaxial test fixture, an air gap exists between the fixture and the annular sample, and the dielectric constant measurement result is often lower than the true value, which seriously affects the accuracy and reliability of dielectric characteristic measurement. To solve the problems, we prepared disc-shaped Ni based on the prior study _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ The method can effectively avoid the influence of an air gap between the coaxial test clamp and the sample on measurement in the process of measuring the dielectric property of the annular sample by using the vector network analyzer, and obtain a more accurate dielectric constant measurement result. However, ni obtained by the coprecipitation method _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ The precursor powder is nano particles, the specific surface area of the particles is large, the static friction force among the particles is large in the compression molding process, and the fluidity is poor, so that the sample cracking phenomenon easily occurs in the traditional molding method when the wafer-shaped sample is compressed.

Disclosure of Invention

The invention aims to provide a preparation method of a nano ferrite dielectric property measurement sample, which aims to solve the problem that a nano ferrite substrate sample is easy to crack in the forming process.

1. Dielectric property measurement sample preparation

1. Preparation and refinement of nano precursor powder

Setting the total concentration of metal cationsThe metal salts were weighed at 2.0 mol/L and all metal salts were uniformly dissolved in 300 mL deionized water, with the atomic ratio of Ni to Zn to Co to Fe being 0.5 to 0.3 to 0.2 to 1.98, respectively. The weighed NaOH pellets were uniformly dissolved in 350 mL deionized water and the NaOH solution was placed in a water bath at 90 ℃ for water bath heating. After the temperature of the NaOH solution reached 90 ℃, the mixed metal salt solution was poured into the NaOH solution and stirring was continued for 40min. In the reaction process, a preservative film needs to be covered on the reaction container to prevent the solution from evaporating. Subsequently, the reaction solution was taken out of the water bath, left to stand at room temperature and stirred for another 1 hour. Subsequently, the reacted suspension was centrifuged at 6000 rpm for a plurality of times by using a high-speed centrifuge, and washed with deionized water for a plurality of times until the pH of the supernatant was 7.0. Next, the separated precipitate was placed in an oven at 60℃and dried for 24 hours. Finally, grinding and crushing the obtained dry product to obtain Ni _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ Precursor powder.

Ni obtained by chemical coprecipitation reaction using planetary ball mill _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ And (5) carrying out refinement treatment on the precursor powder. The specific ball milling conditions are as follows: the solvent is absolute ethyl alcohol, zirconia ball milling beads with the diameter of 5mm and an agate ball milling tank with the volume ratio of the ball milling beads to precursor powder in each ball milling tank being 20:1, the ball milling time is 370min, and the ball milling rotating speed is 350 revolutions per minute. The ball-milled powder was then separated by a centrifuge and dried in an oven at 60℃for 24 hours. Finally, grinding and crushing the obtained product to obtain refined Ni _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ Precursor powder.

2. Nano precursor powder forming

(1) Weighing a plurality of ball-milled and refined Ni _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ The mass ratio of the precursor powder to the adhesive is 12-14: 1, mixing and grinding for 4-6 min to obtain primary mixed particles;

(2) Sieving the primary mixed particles obtained in the step (1) in sequence, and selecting intermediate layer particles with 20-80 meshes for later use;

(3) Weighing the bottom layer fine particles smaller than 80 meshes in the step (2), and mixing the bottom layer fine particles with an adhesive according to a mass ratio of 12-14: 1, mixing and grinding for 4-6 min to obtain secondary mixed particles;

(4) Repeating the step (2), sequentially sieving the secondary mixed particles obtained in the step (3), and continuously selecting intermediate layer particles with 20-80 meshes for later use;

(5) Weighing the bottom layer fine particles smaller than 80 meshes in the step (4), and mixing the bottom layer fine particles with an adhesive according to a mass ratio of 12-14: 1, mixing and grinding for 4-6 min to obtain tertiary mixed particles;

(6) Uniformly mixing the intermediate layer particles obtained in the step (2), the intermediate layer particles obtained in the step (4) and the tertiary mixed particles obtained in the step (5) to obtain quaternary mixed particles;

(7) And (3) placing the four-time mixed particles obtained in the step (6) in a die, and taking out and drying the four-time mixed particles after compression molding to obtain a nano precursor molded sample.

In the preparation process, the adhesive is a polyvinyl alcohol aqueous solution with the mass concentration of 7% -9%.

3. Sintering of nano precursor forming sample

And (3) placing the nano precursor molding sample in a muffle furnace, sintering 9 h at 900 ℃, wherein the heating rate is 0.5 ℃/min, and naturally cooling to room temperature along with the furnace after sintering is completed, so as to obtain the dielectric property measurement sample.

2. Dielectric property measurement sample characterization

The invention uses the nano precursor molding sample before sintering to characterize the molding effect of the dielectric property measurement sample.

1. Nanometer precursor molding sample prepared by traditional method

Weighing refined Ni _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ 1.67g of precursor powder, 0.13g of an 8wt% aqueous solution of polyvinyl alcohol (PVA) was weighed and ground in an agate mortarGrinding for 5min to obtain mixed particles; then pouring the obtained mixed particles into a die with the inner diameter of 15mm, and pressing for 30min under 1270MPa by using a powder tablet press to obtain a wafer-shaped sample; then, the wafer-shaped sample was taken out, and the pressed wafer-shaped sample was put into an oven at 60℃and dried for 30 minutes, and then taken out, and the result is shown in FIG. 1 a.

2. The nano precursor molded sample prepared by the method of the invention

Weighing refined Ni according to the same proportion _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ Granulating precursor powder and 8wt% polyvinyl alcohol (PVA) aqueous solution by adopting the method, finally pouring 1.8g of four-time mixed particles into a die with the inner diameter of 15mm, and pressing for 30min under 1270MPa by using a powder tablet press to obtain a wafer-shaped sample; then, the wafer-shaped sample was taken out, and the pressed wafer-shaped sample was put into an oven at 60℃and dried for 30 minutes, and then taken out, and the result is shown in FIG. 1 b.

As can be seen from a comparison of FIG. 1a and FIG. 1b, under the same conditions, due to Ni _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ Precursor body

The powder is nano particles, the specific surface area of the particles is large, the static friction force between the particles is large, the fluidity of the particles is poor, and the sample is severely cracked in the compression molding process (shown in figure 1 a). The sample preparation method effectively improves the fluidity among particles, obtains a wafer-shaped sample with a flat surface (shown in a figure 1 b), and effectively avoids the occurrence of sample cracking.

3. Evaluation of dielectric Property measurement sample Performance

1. Good process stability

Weighing 4.0 and g of ball-milled nano precursor powder and 0.3g of PVA aqueous solution (PVA mass concentration is 8 wt%) and grinding for 5min in an agate mortar to obtain primary mixed particles; placing a 20-target standard screen on the upper layer, placing an 80-target standard screen on the bottom layer, sequentially sieving the primary mixed particles, and selecting middle layer particles for standby; weighing the first sieved bottom layer particles, and calculating the mass of the required PVA aqueous solution (PVA mass concentration is 8 wt%) according to the bottom layer particles accounting for 93wt% in the mixed system; mixing the first-sieved bottom layer particles with a required PVA aqueous solution, and grinding for 5min in an agate mortar to obtain secondary mixed particles; placing a 20-target standard screen on the upper layer, placing an 80-target standard screen on the bottom layer, sequentially sieving the mixed particles, and selecting intermediate layer particles for standby; weighing bottom layer particles remained after the second sieving, calculating the content of the required PVA aqueous solution (PVA mass concentration is 8 wt%) according to the particle proportion of 93.0. 93.0 wt%, mixing the bottom layer particles remained after the second sieving with the required PVA aqueous solution, and grinding for 5min in an agate mortar to obtain three-time mixed particles; and mixing the tertiary mixed particles with the intermediate layer particles obtained after the first sieving and the intermediate layer particles obtained after the second sieving to obtain quaternary mixed particles.

Repeating the above operation to obtain multiple groups of four-time mixed particles, weighing 1.8g of four-time mixed particles, respectively, namely a sample 1, a sample 2, a sample 3 and a sample 4, pouring the four groups of sample particles into a die with the diameter of 15.0mm, pressing for 30min under 1270MPa by using a powder tablet press, taking out a disc-shaped sample, and then putting the pressed disc-shaped sample into a 60 ℃ oven, drying for 30min and then taking out.

And (3) placing the four groups of wafer-shaped samples in a muffle furnace, sintering the wafer-shaped samples at the temperature of 900 ℃ for 9 h, wherein the heating rate is 0.5 ℃/min, and naturally cooling the wafer-shaped samples to room temperature along with the furnace after the sintering is completed, and taking out the wafer-shaped samples to obtain the dielectric constant measurement samples. Sample shrinkage is shown in table 1:

TABLE 1 dimensional parameters before and after sintering of disk samples among different samples and shrinkage

Therefore, the wafer-shaped nano precursor formed sample prepared by the method has the dimensional shrinkage phenomena of different degrees after being sintered, and the shrinkage rate is stabilized at about 6%, so that the dielectric constant test sample prepared by the method has good repeatability, good stability and small influence on dielectric characteristic test data of the sample.

2. The dielectric constant measurement data has good accuracy

The dielectric characteristics of the wafer-shaped sample prepared by the invention are measured by using an impedance analyzer (model: keysight E4991B) and a dielectric constant measuring clamp (model: keysight 16453A), and the measuring frequency band is 100-1000MHz. The dielectric properties of the existing ring samples were measured using a vector network analyzer (model: agilent PNA-X N5247A), measuring frequency bands of 100-1000MHz.

(1) Dielectric constant measurement of the wafer-like sample of the present invention

Dielectric properties were measured by taking the above sintered samples 1, 2, 3 and 4, and the results are shown in fig. 3a and 3 b.

(2) Dielectric constant measurement of existing annular samples

Weighing 0.2g of the four-time mixed particles, pouring the four-time mixed particles into a die with the outer diameter of 7.0 mm and the inner diameter of 3.04 mm, and pressing the four-time mixed particles for 4min under the pressure of 1270MPa in unit area by using a powder tablet press to obtain an annular sample; then placing the pressed annular sample into a baking oven at 60 ℃, drying for 30min, and taking out; then placing the annular sample in a muffle furnace, sintering 9 h at 900 ℃ at a heating rate of 0.5 ℃/min, naturally cooling to room temperature along with the furnace after sintering is completed, and taking out to obtain an annular dielectric constant measurement sample;

the dielectric characteristics were measured by taking the above-mentioned annular dielectric constant measurement sample, and the results are shown in fig. 2a and 2 b.

Referring to fig. 2 and 3, at 700 MHz, the dielectric characteristic measurement results of the wafer-shaped sample were taken and compared with the measurement results of the ring-shaped sample, as shown in table 2;

TABLE 2 comparison of dielectric Property measurements of disk samples with annular sample measurements at 700 MHz

As can be seen from table 2, the dielectric properties of the wafer-shaped and ring-shaped samples prepared under the same process conditions were greatly different. This is because there is a dimensional shrinkage phenomenon before and after ferrite sintering, so that when measuring the dielectric properties of the annular sample, a large air gap exists between the coaxial measuring jig and the annular sample, so that the measurement result of the real part of the dielectric constant is lower than the true value, the measurement result of the dielectric loss tangent is higher than the true value, for example, the measurement result of the real part of the dielectric constant of the annular sample is lower than the disk-shaped sample, and the measurement result of the dielectric loss tangent is higher than the disk-shaped sample.

In summary, the invention has the following advantages:

1. the adhesive is added into the nano precursor powder for multiple gluing and granulating, so that the static friction force among nano precursor particles can be effectively reduced, and the fluidity among particles is improved, so that a sample is easier to press and form, and the cracking phenomenon is avoided. Meanwhile, the nano precursor particles can be uniformly distributed by sieving after each gluing and granulating, so that uneven pressing stress distribution caused by uneven particle size distribution is avoided, and the cracking phenomenon in the sample pressing and forming process is avoided;

2. the nano ferrite forming method provided by the invention can effectively improve the fluidity among nano precursor particles, solves the problem of sample cracking in the compression forming process, and plays a supporting role in accurately measuring the dielectric characteristics of the nano ferrite.

Drawings

FIG. 1a is a graphical representation of a pre-sintering nano-precursor sample obtained by conventional methods;

FIG. 1b is a sample schematic of a pre-sintering nano-precursor obtained by the method of the present invention;

FIG. 2a is a graph showing the relationship between the real part of the permittivity of a ring sample after sintering and the frequency change measured by using a vector network analyzer in the prior art;

FIG. 2b is a graph showing the dielectric loss tangent of a ring sample after sintering as a function of frequency using a vector network analyzer in the prior art;

FIG. 3a is a graph showing the relationship between the real part of the dielectric constant of a wafer-shaped sample after sintering and the frequency by using an impedance analyzer in the embodiment of the invention;

FIG. 3b is a graph showing the dielectric loss tangent of a wafer-shaped sample after sintering as a function of frequency using an impedance analyzer in an embodiment of the present invention.

Detailed Description

The invention is further illustrated by the following examples.

Examples

1. Preparation of nano precursor powder

Weighing NiCl ₂ ∙6H ₂ O（0.12 mol）：27.85 g，CoCl ₂ ∙6H ₂ O（0.05 mol）：11.13 g， FeCl ₃ ∙6H ₂ O（0.46 mol）：125.63 g，ZnCl ₂ (0.07 mol): 9.56g were placed in a beaker, 300 mL deionized water was added to the beaker and stirring was continued for 40 minutes using an electric stirrer. Solid NaOH 78.0 g (1.95 mol) was weighed into another beaker, 350. 350 mL deionized water was added, the beaker containing NaOH solution was placed in a water bath at 90 ℃ and stirring was continued using an electric stirrer until complete dissolution. Then, the uniformly dissolved mixed salt solution was poured into NaOH solution, and the reaction was continued for 40min. Next, the beaker containing the reactant was removed from the water bath, placed in a room temperature environment, and stirred continuously using an electric stirrer for 1h. Then, the reacted suspension was centrifuged several times at 6000 rpm using a high-speed centrifuge, and washed several times with deionized water until the pH of the supernatant was 7.0. Next, the separated precipitate was placed in an oven at 60℃and dried for 24 hours. Finally, grinding and crushing the obtained dry product to obtain Ni _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ Nano precursor powder.

2. Nanometer precursor powder refinement

Multiple 100mL agate ball milling tanks were taken, and 40.0g and 2.0. 2.0gNi of zirconia ball milling beads with a diameter of 5mm were weighed _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ The nano precursor powder is poured into an agate ball milling tank, and absolute ethyl alcohol is filled into the ball milling tank. Ball milling with planetary ball mill for 370min at speed of 350 r ∈And (5) min. The ball-milled powder was then separated using a high-speed centrifuge and dried in an oven at 60 ℃ for 24 hours. Finally, grinding and crushing the obtained product to obtain refined Ni _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ Nano precursor powder.

3. Shaping of nano precursor sample

Weighing 4.0. 4.0 g of ball-milled Ni _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ The nano precursor powder and 0.3g PVA water solution (PVA mass concentration is 8 wt%) are ground for 5min in an agate mortar to obtain primary mixed particles; placing a 20-target standard screen on the upper layer, placing an 80-target standard screen on the bottom layer, sequentially sieving the primary mixed particles, and selecting middle layer particles for standby; weighing the first sieved bottom layer particles, and calculating the mass of the required PVA aqueous solution (PVA mass concentration is 8 wt%) according to the bottom layer particles accounting for 93wt% in the mixed system; mixing the first-sieved bottom layer particles with a required PVA aqueous solution, and grinding for 5min in an agate mortar to obtain secondary mixed particles; placing a 20-target standard screen on the upper layer, placing an 80-target standard screen on the bottom layer, sequentially sieving the mixed particles, and selecting intermediate layer particles for standby; weighing bottom layer particles remained after the second sieving, calculating the content of the required PVA aqueous solution (PVA mass concentration is 8 wt%) according to the particle proportion of 93.0. 93.0 wt%, mixing the bottom layer particles remained after the second sieving with the required PVA aqueous solution, and grinding for 5min in an agate mortar to obtain three-time mixed particles; and mixing the tertiary mixed particles with the intermediate layer particles obtained after the first sieving and the intermediate layer particles obtained after the second sieving to obtain quaternary mixed particles.

Weighing 1.8g of four-time mixed particles, pouring into a die with the diameter of 15.0 and mm, pressing for 30min under 1270MPa by using a powder tablet press, taking out a wafer-shaped sample, putting the pressed wafer-shaped sample into a baking oven at 60 ℃, drying for 30min, and taking out; the shaping effect is shown in fig. 1 b.

4. Dielectric constant measurement sample preparation

And (3) placing the wafer-shaped sample in a muffle furnace, sintering 9 h at 900 ℃, wherein the heating rate is 0.5 ℃/min, and naturally cooling to room temperature along with the furnace after sintering is completed, and taking out to obtain the dielectric constant measurement sample.

5. Dielectric constant measurement

Four sets of circular sheets of Ni prepared in this example were measured using an impedance analyzer (model: keysight E4991B) and a dielectric constant measurement jig (model: keysight 16453 a) _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ The dielectric properties of the nano ferrite sample are shown in fig. 3a and 3 b.

Claims (1)

1. The preparation method of the nano ferrite dielectric property measurement sample is characterized by comprising the following steps of:

(1) Weighing a plurality of ball-milled and refined nano precursor powders and an adhesive according to the mass ratio of 12-14: 1, mixing and grinding for 4-6 min to obtain primary mixed particles; the nano precursor powder is Ni _0.5 Zn _0.3 Co _0.2 Fe _1.98 O _4-δ The nanometer precursor, the said adhesive is polyvinyl alcohol aqueous solution with 7-9% of mass concentration;

(2) Sieving the primary mixed particles obtained in the step (1) in sequence, and selecting intermediate layer particles with 20-80 meshes for later use;

(3) Weighing the bottom layer fine particles smaller than 80 meshes in the step (2), and mixing the bottom layer fine particles with an adhesive according to a mass ratio of 12-14: 1, mixing and grinding for 4-6 min to obtain secondary mixed particles;

(4) Repeating the step (2), sequentially sieving the secondary mixed particles obtained in the step (3), and continuously selecting intermediate layer particles with 20-80 meshes for later use;

(5) Weighing the bottom layer fine particles smaller than 80 meshes in the step (4), and mixing the bottom layer fine particles with an adhesive according to a mass ratio of 12-14: 1, mixing and grinding for 4-6 min to obtain tertiary mixed particles;

(6) Uniformly mixing the intermediate layer particles obtained in the step (2), the intermediate layer particles obtained in the step (4) and the tertiary mixed particles obtained in the step (5) to obtain quaternary mixed particles;

(7) And (3) placing the four-time mixed particles obtained in the step (6) in a die, and taking out and drying the four-time mixed particles after compression molding to obtain the nano precursor sample.

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