阅读说明：本技术 一种片状羰基铁粉及其制备方法 (Flaky carbonyl iron powder and preparation method thereof ) 是由 陈小雨 郭洪波 李树索 罗光谱 龙正茂 宫声凯 于 2021-09-08 设计创作，主要内容包括：一种片状羰基铁粉及其制备方法,该制备方法包括以下步骤：混合球形羰基铁粉、磨球和溶剂,在惰性气氛下进行湿法球磨,过滤得到含粉料浆；冻结所述含粉料浆,在负压环境下升华含粉料浆中的溶剂,得到所述片状羰基铁粉。本发明制备得到的片状羰基铁粉为破碎片状,相对传统制备方法中直接球磨或进一步经气流粉碎获得的片状铁粉,表面呈现凹凸不平的形貌,有效地提升了吸波的表面积,显著地提高了片状铁粉的吸波性能,同时,本发明从根源上解决了湿法球磨在干燥过程存在的团聚现象,进而能够实现超过80％的片状羰基铁粉产率,且生产过程不涉及污染环境的物质且无粉尘等排放物,生产成本更低,非常适合大规模工业化生产。(A flaky carbonyl iron powder and a preparation method thereof are disclosed, wherein the preparation method comprises the following steps: mixing spherical carbonyl iron powder, grinding balls and a solvent, carrying out wet ball milling in an inert atmosphere, and filtering to obtain powder-containing slurry; freezing the powder-containing slurry, and sublimating the solvent in the powder-containing slurry under a negative pressure environment to obtain the flaky carbonyl iron powder. Compared with the flaky iron powder obtained by direct ball milling or further air flow crushing in the traditional preparation method, the flaky carbonyl iron powder prepared by the invention has the advantages that the surface is uneven, the wave-absorbing surface area is effectively improved, the wave-absorbing performance of the flaky iron powder is obviously improved, meanwhile, the agglomeration phenomenon existing in the drying process of wet ball milling is fundamentally solved, the yield of the flaky carbonyl iron powder exceeding 80% can be further realized, the production process does not relate to substances polluting the environment, and no emissions such as dust and the like exist, the production cost is lower, and the flaky carbonyl iron powder is very suitable for large-scale industrial production.)

1. A preparation method of flaky carbonyl iron powder is characterized by comprising the following steps:

mixing spherical carbonyl iron powder, grinding balls and a solvent, carrying out wet ball milling in an inert atmosphere, and filtering to obtain powder-containing slurry;

freezing the powder-containing slurry, and sublimating the solvent in the powder-containing slurry under a negative pressure environment to obtain the flaky carbonyl iron powder.

2. The method for preparing a flaky carbonyl iron powder according to claim 1, wherein the grinding balls comprise a first grinding ball, a second grinding ball and a third grinding ball, wherein the ratio of the particle sizes of the first grinding ball, the second grinding ball and the third grinding ball is 6: 3: 1.

3. the method for preparing flaky carbonyl iron powder according to claim 2, wherein the mass ratio of the first grinding ball to the second grinding ball to the third grinding ball is 3: 4: 3.

4. the method for preparing flaky carbonyl iron powder according to any one of claims 1 to 3, wherein the mass ratio of the grinding balls to the spherical carbonyl iron powder is 7-10: 1.

5. the preparation method of flaky carbonyl iron powder according to claim 4, wherein a ball milling aid is added during wet ball milling, and the ball milling aid comprises at least one of a dispersant, a grinding aid and a surface modifier, wherein the dispersant is added in an amount of 0.2-0.5% by mass of the spherical carbonyl iron powder, the grinding aid is added in an amount of 0.3-0.6% by mass of the spherical carbonyl iron powder, and the surface modifier is added in an amount of 0.1-0.5% by mass of the spherical carbonyl iron powder.

6. The method of claim 1, wherein the solvent is at least one of t-butanol, dimethyl sulfoxide, ethylene glycol, diethylene glycol, 1, 3-propanediol, and cyclohexane.

7. The method for preparing flaky carbonyl iron powder according to claim 6, wherein the solvent comprises, by mass, 60 to 80 parts of cyclohexane, 5 to 10 parts of ethylene glycol, and 5 to 10 parts of dimethyl sulfoxide.

8. The method for preparing flaky carbonyl iron powder according to claim 6 or 7, wherein the mass ratio of the solvent to the spherical carbonyl iron powder is 2-2.5: 1.

9. a flaky carbonyl iron powder prepared by the preparation method of any one of claims 1 to 8, wherein the longest length of the flaky carbonyl iron powder is 10 to 15 μm, the length-thickness ratio is 30 to 105, and the average grain size is less than 10 nm.

10. The flaky carbonyl iron powder of claim 9, wherein the reflection loss of the carbonyl iron powder in the 9-18 GHz band is not more than-5 dB.

Technical Field

The invention relates to the field of wave-absorbing materials, in particular to flaky carbonyl iron powder and a preparation method thereof.

Background

The wave-absorbing material is mainly applied to the fields of stealth, microwave absorption, electronic shielding and the like, and the incident electromagnetic waves are dissipated in the material in a heat energy mode through magnetic loss, dielectric loss, interference cancellation and the like, so that the absorption or attenuation of the electromagnetic waves is realized. The magnetic loss type material is the most efficient and widely applied wave-absorbing material, and the indexes for evaluating the wave-absorbing performance of the material are mainly relative dielectric constant, magnetic permeability and reflection loss R calculated by the relative dielectric constant and the magnetic permeability_L。

Among various wave-absorbing materials, carbonyl iron powder has quite excellent dielectric property and magnetic property, so that the carbonyl iron powder becomes one of the most widely used wave-absorbing materials all over the world. At present, the traditional spherical carbonyl iron powder is processed into flaky carbonyl iron powder, so that the wave absorbing performance of the carbonyl iron powder is improved, and the method can be put into formal large-scale production and is particularly important.

In the prior art, the production method of flaky carbonyl iron powder mainly comprises the steps of grinding by ball milling or high-energy ball milling, then screening to obtain the flaky carbonyl iron powder, and crushing the flaky carbonyl iron powder by a few gas dispersion methods or plasma dispersion methods to obtain the flaky carbonyl iron powder. The preparation raw material of the flaky carbonyl iron powder is superfine spherical carbonyl iron powder, and the superfine powder belongs to inflammable substances, so the ball milling method can only adopt wet milling, and solvents are ethanol, 200# aviation gasoline and the like. The solvent is required to be dried after the powder is ground, at the moment, the flaky powder is bound to have agglomeration phenomena in different degrees, only a small amount of micron powder can be obtained after mechanical grinding and screening, and the obtaining rate is extremely low. Thus, the conventional ball milling method or the high-energy ball milling method is only suitable for laboratory use, and does not have the possibility of mass production.

The gas dispersion method or the plasma dispersion method is to crush and break the agglomerated powder obtained by wet ball milling in an inert gas environment by high-speed airflow so as to prevent the powder from agglomerating and obtain the superfine flaky carbonyl iron powder. For example, patent CN105702409A discloses a preparation method of a flake carbonyl iron powder microwave absorbent, which is to filter ball-milled spherical micron carbonyl iron powder, collect the solid, vacuum-dry the solid, and then perform jet milling under the protection of nitrogen gas to obtain monodisperse flake carbonyl iron powder. Although the method is theoretically practicable, the method has high energy consumption, powder loss is generated in the ball milling and gas dispersion processes, the gas dispersion equipment discharges the powder in the powder production process, and corresponding dust removal equipment is required to meet the requirement, so that the problems of high investment and high cost are encountered in industrial production.

Disclosure of Invention

The invention aims to provide a preparation method of flaky carbonyl iron powder, which adopts a freeze-drying process to cool and freeze slurry obtained by wet ball milling and then vacuumize the slurry, so that a solvent is sublimated in a vacuum environment, and solvent-free powder is obtained.

The invention is realized by the following technical scheme:

a flaky carbonyl iron powder and a preparation method thereof comprise the following steps:

mixing spherical carbonyl iron powder, grinding balls and a solvent, carrying out wet ball milling in an inert atmosphere, and filtering to obtain powder-containing slurry;

freezing the powder-containing slurry, and sublimating the solvent in the powder-containing slurry under a negative pressure environment to obtain the flaky carbonyl iron powder.

In the technical scheme, the method comprises two links of wet ball milling and freeze drying. Specifically, firstly, uniformly mixing raw materials of spherical carbonyl iron powder, a grinding ball and a solvent suitable for freeze drying according to a certain proportion, then carrying out ball milling, extruding the spherical carbonyl iron powder into flaky carbonyl iron powder by utilizing high-speed rotary extrusion of the grinding ball, and filtering powder-containing slurry by utilizing a screen after ball milling. In the technical scheme, the wet ball milling is carried out in an inert atmosphere to prevent active oxides from being generated on the surface of iron powder in the ball milling process, and the inert atmosphere is preferably a nitrogen or argon atmosphere.

And then, pouring the slurry into a container of freeze drying equipment, such as a cold trap, cooling until the slurry is completely frozen, then quickly transferring the frozen slurry into a vacuum chamber, starting a mechanical pump to pump vacuum until the vacuum degree is less than a preset value, stopping pumping, keeping the vacuum degree, drying the slurry in a negative pressure environment, and sublimating the solvent in the drying process to obtain the solvent-free flaky iron powder. And finally, taking out the dried flaky carbonyl iron powder to detect whether the solvent residue and the particle size of the flaky iron powder are qualified.

In one or more embodiments, the ball milling speed is 400 to 550r/min, and the ball milling time is 12 to 24 hours. After ball milling, powder-containing slurry is obtained by filtering with a 100-mesh screen.

In one or more embodiments, the temperature in the freeze drying cold trap is between-40 ℃ and-32 ℃, preferably the freezing temperature is-38 ℃ and the freezing time is 3-5 hours, so as to completely freeze the powder-containing slurry.

In one or more embodiments, the vacuum chamber is operated at a vacuum of less than 100Pa and for a drying time of 16-24 hours to sublimate all of the solvent in the powder-containing slurry.

The flaky carbonyl iron powder prepared by the method is in a broken flaky shape, and compared with the flaky iron powder obtained by direct ball milling or further airflow crushing in the traditional preparation method, the surface of the flaky carbonyl iron powder is uneven, so that the wave-absorbing surface area is effectively improved, and the wave-absorbing performance of the flaky iron powder is remarkably improved; in addition, the preparation method radically solves the agglomeration phenomenon existing in the drying process of wet ball milling, and further can realize the yield of the flaky carbonyl iron powder which is more than 80% and is far less than 20% in the traditional preparation method, and the production process does not involve substances which pollute the environment, does not contain emissions such as dust and the like, has lower production cost, and is very suitable for large-scale industrial production.

As a preferred embodiment of the grinding ball in the present invention, the grinding ball comprises a first grinding ball, a second grinding ball and a third grinding ball, wherein the ratio of the particle diameters of the first grinding ball, the second grinding ball and the third grinding ball is 6: 3: 1. in the technical scheme, the grinding balls are mixed grinding balls which are graded according to a certain proportion by adopting grinding balls with three sizes, namely large, medium and small sizes. In some embodiments, the first grinding ball has a diameter of 6mm, the second grinding ball has a diameter of 3mm, and the third grinding ball has a diameter of 1 mm. Through setting up mixed ball-milling, can improve ball-milling efficiency effectively, promote the homogenization of ball-milling result, further improve the superficial area of inhaling of slice carbonyl iron powder, simultaneously, mixed ball-milling still helps reducing the reunion degree of ball-milling in-process material, improves the productivity of slice iron powder. In one or more embodiments, the grinding balls are zirconia grinding balls.

Further, the mass ratio of the first grinding ball to the second grinding ball to the third grinding ball is 3: 4: 3. in the technical scheme, the proportion of the first grinding balls with the diameter of 6mm is 30%, the proportion of the second grinding balls with the diameter of 3mm is 40%, and the proportion of the third grinding balls with the diameter of 1mm is 30%.

Further, the mass ratio of the grinding balls to the spherical carbonyl iron powder is 7-10: 1.

further, during ball milling, a ball milling auxiliary agent is added into a mixture of the raw materials, the solvent and the grinding balls, wherein the ball milling auxiliary agent comprises at least one of a dispersing agent, a grinding aid and a surface modifier, the addition amount of the dispersing agent is 0.2-0.5% of the mass of the spherical carbonyl iron powder, the addition amount of the grinding aid is 0.3-0.6% of the mass of the spherical carbonyl iron powder, and the addition amount of the surface modifier is 0.1-0.5% of the mass of the spherical carbonyl iron powder. The ball milling auxiliary agent can improve the surface polarity of the materials, improve the ball milling efficiency, further reduce the agglomeration degree of the materials in the ball milling process and improve the yield of carbonyl iron powder.

In some examples, the ball milling aid employs a dispersant, a grinding aid, and a surface modifier simultaneously. In one or more embodiments, the dispersant is polyvinylpyrrolidone or methylcellulose, and is added in an amount of 0.5% by mass of the material. In one or more embodiments, the grinding aid is zinc stearate and is added in an amount of 0.2% by mass of the material. In one or more embodiments, the surface modifier is a silane coupling agent KH560, added in an amount of 0.5% by mass of the material.

In the technical scheme, the solvent is an organic solvent so as to prevent active oxygen contained in water from corroding carbonyl iron powder in the high-speed ball milling process. Specifically, the solvent is at least one of tert-butyl alcohol, dimethyl sulfoxide, ethylene glycol, diethylene glycol, 1, 3-propylene glycol and cyclohexane.

Further, as a preferable embodiment of the solvent in the present invention, the solvent includes, by mass, 60 to 80 parts of cyclohexane, 5 to 10 parts of ethylene glycol, and 5 to 10 parts of dimethyl sulfoxide. In the technical scheme, the polarity, melting point and safety of the solvent are considered according to the proportion of the solvent. Firstly, as for the polarity of the solvent, the smaller the polarity of the solvent is, the better the surface of the abrasive can be wetted, the air on the surface of the abrasive is removed, the grinding efficiency is improved, and the agglomeration of the abrasive is reduced; conversely, the degree of abrasive agglomeration increases. In the case of ethylene glycol, the polarity is about 7.9, so that when the ethylene glycol is used alone, a lot of powder agglomeration can still be generated in the ball milling process, and the uniformity of the powder particle size is reduced and the cost is wasted. Secondly, the melting point of a solvent, such as t-butanol, although only about 3.9 polar, is relatively high and solidifies after a drop in ambient temperature, and thus cannot be used alone. Finally, benzene, although better than ethylene glycol or t-butanol in both polarity and melting point, is more toxic and not suitable for industrial production from the viewpoint of safety. In the technical scheme, the solvent ratio designed by the technical scheme not only has lower polarity and melting point, but also is safe, so that the safety of the preparation method of the freeze-dried flaky carbonyl iron powder in large-scale production is effectively enhanced, the production cost is reduced, and the production efficiency is improved.

Further, the addition amount of the solvent is not too large so as to avoid increasing the treatment difficulty and energy consumption of a subsequent drying process, the addition amount of the solvent is not too small so as to cause poor slurry fluidity, two points are considered comprehensively, and in actual operation, the mass ratio of the solvent to the spherical carbonyl iron powder is 2-2.5: 1.

another object of the present invention is to provide a flaky carbonyl iron powder prepared by the above preparation method, wherein the surface of the flaky carbonyl iron powder has an uneven morphology, such that the wave-absorbing surface area is significantly increased compared to the conventional flaky carbonyl iron powder, and the flaky carbonyl iron powder has a smaller size and stronger wave-absorbing property compared to the iron powder prepared by the conventional preparation method.

The longest length of the flaky carbonyl iron powder prepared by any one of the preparation methods is 10-15 mu m, the length-thickness ratio is 30-105, and the average grain size is less than 10 nm. By the preparation method, the reflection loss of the flaky carbonyl iron powder is much higher than that of the spherical carbonyl iron powder. The maximum reflection loss is-5.5 dB (15.2GHz), the reflection loss of the flaky carbonyl iron powder is not more than-5 dB within the range of 9-18 GHz, and the reflection loss of the spherical carbonyl iron powder is close to-5 dB when the frequency band reaches 18 GHz. Therefore, the wave absorbing performance of the prepared flaky carbonyl iron powder is greatly improved, and the application space of the flaky carbonyl iron powder is greatly expanded.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. the flaky carbonyl iron powder prepared by the invention is in a broken flaky shape, and compared with the flaky iron powder obtained by direct ball milling or further airflow crushing in the traditional preparation method, the surface of the flaky carbonyl iron powder is uneven, so that the wave-absorbing surface area is effectively improved, and the wave-absorbing performance of the flaky iron powder is remarkably improved;

2. the invention radically solves the agglomeration phenomenon in the drying process of wet ball milling, and further can realize the yield of the flaky carbonyl iron powder which is more than 80 percent and is far more than the yield of less than 20 percent in the traditional preparation method, and the production process does not involve substances which pollute the environment and does not have emissions such as dust and the like, has lower production cost and is very suitable for large-scale industrial production;

3. the mixed grinding ball can effectively improve the ball milling efficiency, promote the homogenization of ball milling products, further improve the wave-absorbing surface area of the flaky carbonyl iron powder, and meanwhile, the mixed grinding ball is also beneficial to reducing the agglomeration degree of materials in the ball milling process and improving the yield of the flaky iron powder;

4. the mixed solvent disclosed by the invention not only has lower polarity and melting point, but also is safe, so that the safety of the preparation method of the freeze-dried flaky carbonyl iron powder in large-scale production is effectively enhanced, the production cost is reduced, and the production efficiency is improved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

fig. 1 is a flow chart of a method for preparing flaky carbonyl iron powder in an embodiment of the invention;

fig. 2 is a scanning electron microscope image of carbonyl iron powder of an embodiment of the present invention and a comparative example, wherein fig. 2(a) is a spherical carbonyl iron powder, i.e., a raw material, at a magnification of 5000 times, fig. 2(b) is a flake carbonyl iron powder prepared in example 2 at a magnification of 2000 times, fig. 2(c) is a flake carbonyl iron powder prepared in example 3 at a magnification of 2000 times, and fig. 2(d) is a flake carbonyl iron powder prepared in a comparative example at a magnification of 2000 times;

FIG. 3 is a graph showing a comparison of reflection loss between flaky carbonyl iron powder and raw material prepared in examples and comparative examples of the present invention;

FIG. 4 is a graph showing a comparison of complex permeability of the raw material and the embodiment of the present invention, wherein FIG. 4(a) shows a real part of complex permeability and FIG. 4(b) shows an imaginary part of complex permeability;

FIG. 5 is a graph showing a comparison of complex dielectric constants of the raw materials and the embodiment of the present invention, in which FIG. 5(a) shows a real part of the complex dielectric constant and FIG. 5(b) shows an imaginary part of the complex dielectric constant.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.

All of the starting materials of the present invention, without particular limitation as to their source, are commercially available or can be prepared according to conventional methods well known to those skilled in the art.

All the raw materials of the invention are not particularly limited in purity, and the invention preferably adopts the purity requirements of analytical purity or carbonyl iron powder preparation fields.

All the raw materials, the marks and the acronyms thereof belong to the conventional marks and the acronyms in the field, each mark and acronym is clear and definite in the field of related application, and the raw materials can be purchased from the market or prepared by the conventional method by the technical staff in the field according to the marks, the acronyms and the corresponding application.

Example 1:

the preparation method of the flaky carbonyl iron powder shown in figure 1 comprises the following steps:

mixing spherical carbonyl iron powder, grinding balls and a solvent, carrying out wet ball milling in an inert atmosphere, and filtering to obtain powder-containing slurry;

specifically, uniformly mixing spherical carbonyl iron powder, a solvent and grinding balls according to a certain proportion, and then carrying out ball milling in an inert atmosphere, wherein the ball milling speed is preferably 400-550 r/min, the ball milling time is 12-24 hours, and filtering powder-containing slurry by using a 100-mesh screen after ball milling;

freezing the powder-containing slurry, and sublimating a solvent in the powder-containing slurry under a negative pressure environment to obtain the flaky carbonyl iron powder;

pouring the slurry containing the powder into a freeze-drying cold trap, opening a temperature switch to start cooling, setting the temperature in the freeze-drying cold trap to be about-38 ℃, freezing for 4 hours, taking the material out of the cold trap after the slurry is completely frozen, transferring the material into a vacuum chamber of equipment, and ensuring that the transfer speed is as high as possible to prevent the material from being thawed and dissolved. And (3) after the mixture is placed into a vacuum chamber, opening a mechanical pump of the equipment to pump vacuum, stopping until the vacuum degree of the chamber is less than 100Pa, then keeping the vacuum degree of the chamber of the equipment, and drying for 16-24 hours until the solvent is completely sublimated.

In one or more embodiments, the zirconia grinding ball is a mixed grinding ball graded in three sizes, namely, large, medium and small, according to a certain proportion, and the specific proportion is as follows: the proportion of the first grinding balls with the diameter of 6mm is 30%, the proportion of the second grinding balls with the diameter of 3mm is 40%, and the proportion of the third grinding balls with the diameter of 1mm is 30%, so that the ball milling efficiency can be greatly improved, and the homogenization of ball milling products is promoted. Preferably, the mass ratio of the grinding balls to the materials, namely the ball-material ratio is 7-10: 1.

in some embodiments, a ball milling aid is added during wet ball milling, and the ball milling aid includes at least one of a dispersant, a grinding aid and a surface modifier, wherein the addition amount of the dispersant is 0.2-0.5% of the mass of the spherical carbonyl iron powder, the addition amount of the grinding aid is 0.3-0.6% of the mass of the spherical carbonyl iron powder, and the addition amount of the surface modifier is 0.1-0.5% of the mass of the spherical carbonyl iron powder.

In some embodiments, the solvent comprises, by mass, 60-80 parts of cyclohexane, 5-10 parts of ethylene glycol, and 5-10 parts of dimethyl sulfoxide. The solvent ratio not only has lower polarity and melting point, but also is safe, effectively enhances the safety of the preparation method of the sheet carbonyl iron powder by adopting freeze drying in large-scale production, reduces the production cost and improves the production efficiency. Preferably, the mass ratio of the solvent to the spherical carbonyl iron powder is 2-2.5: 1.

examples 2 to 5: preparation of flaky carbonyl iron powder

Example 2:

uniformly mixing 500g of spherical carbonyl iron powder, 5000g of mixed zirconia grinding balls and 1200g of mixed solvent, wherein the mixture ratio of the mixed zirconia grinding balls is that a first grinding ball with the diameter of 6mm accounts for 30%, a second grinding ball with the diameter of 3mm accounts for 40%, and a third grinding ball with the diameter of 1mm accounts for 30%; the mixture ratio of the mixed solvent comprises 60 parts of cyclohexane, 7 parts of ethylene glycol and 8 parts of dimethyl sulfoxide by mass; after mixing, carrying out wet ball milling under the argon atmosphere, wherein the ball milling speed is 450r/min, the ball milling time is 8 hours, and filtering powder-containing slurry by using a 100-mesh screen after ball milling; after wet ball milling, the slurry was put into a freeze dryer and frozen for 5 hours, and the yield of flaky carbonyl iron powder obtained after drying for 16 hours was 86.47%, and the scanning electron microscope photograph thereof is shown in fig. 2 (b).

Example 3:

uniformly mixing 500g of spherical carbonyl iron powder, 5000g of mixed zirconia grinding balls and 1000g of mixed solvent, wherein the mixture ratio of the mixed zirconia grinding balls is that a first grinding ball with the diameter of 6mm accounts for 30%, a second grinding ball with the diameter of 3mm accounts for 40%, and a third grinding ball with the diameter of 1mm accounts for 30%; the mixture ratio of the mixed solvent comprises 70 parts of cyclohexane, 10 parts of ethylene glycol and 5 parts of dimethyl sulfoxide by mass; after mixing, carrying out wet ball milling under the argon atmosphere, wherein the ball milling speed is 460r/min, the ball milling time is 24 hours, and filtering powder-containing slurry by using a 100-mesh screen after ball milling; after wet ball milling, the slurry is put into a freeze dryer to be frozen for 5 hours, and the yield of the flaky carbonyl iron powder obtained after drying for 20 hours is 94.73%, and the scanning electron microscope picture is shown in fig. 2 (c).

Example 4:

uniformly mixing 500g of spherical carbonyl iron powder, 3500g of mixed zirconia grinding balls and 1200g of mixed solvent, wherein the mixture ratio of the mixed zirconia grinding balls is that a first grinding ball with the diameter of 6mm accounts for 30%, a second grinding ball with the diameter of 3mm accounts for 40%, and a third grinding ball with the diameter of 1mm accounts for 30%; the mixture ratio of the mixed solvent comprises 60 parts of cyclohexane, 7 parts of ethylene glycol and 8 parts of dimethyl sulfoxide by mass; after mixing, carrying out wet ball milling under the argon atmosphere, wherein the ball milling speed is 450r/min, the ball milling time is 8 hours, and filtering powder-containing slurry by using a 100-mesh screen after ball milling; and (3) after wet ball milling, putting the slurry into a freeze dryer, freezing for 5 hours, and drying for 16 hours to obtain the flaky carbonyl iron powder with the yield of 81.22%.

Example 5:

uniformly mixing 500g of spherical carbonyl iron powder, 3500g of mixed zirconia grinding balls and 1000g of mixed solvent, wherein the mixture ratio of the mixed zirconia grinding balls is that a first grinding ball with the diameter of 6mm accounts for 30%, a second grinding ball with the diameter of 3mm accounts for 40%, and a third grinding ball with the diameter of 1mm accounts for 30%; the mixture ratio of the mixed solvent comprises 70 parts of cyclohexane, 10 parts of ethylene glycol and 5 parts of dimethyl sulfoxide by mass; after mixing, carrying out wet ball milling under the argon atmosphere, wherein the ball milling speed is 460r/min, the ball milling time is 24 hours, and filtering powder-containing slurry by using a 100-mesh screen after ball milling; and (3) after wet ball milling, putting the slurry into a freeze dryer, freezing for 5 hours, and drying for 20 hours to obtain the flaky carbonyl iron powder with the yield of 83.18%.

Comparative example:

uniformly mixing 500g of spherical carbonyl iron powder, 5000g of zirconia grinding balls and 1000g of solvent, carrying out wet ball milling in an argon atmosphere, wherein the ball milling speed is 460r/min, the ball milling time is 24 hours, and the yield of the flaky carbonyl iron powder obtained by mechanical grinding and screening after ball milling is 15.34%. The scanning electron microscope image is shown in FIG. 2 (d).

Therefore, the preparation method of the invention solves the agglomeration phenomenon existing in the drying process of wet ball milling, and simultaneously, the yield of the flaky carbonyl iron powder which is as high as 94.73 percent can be realized by combining the mixed solvent and the mixed milling ball, which is far more than that of the traditional preparation method.

FIG. 3 shows the comparison of the reflection loss of examples 2 to 5, the comparative example and the spherical carbonyl iron powder, and as shown in the figure, the sample is pressed into a coaxial ring sample of 0.4mm and then tested, and the reflection loss performance of example 3 is the best, and the reflection loss R is within the frequency band of 9 to 18GHz_LThe band width is as high as 9GHz, the maximum reflection loss is close to-5.5 dB, and similarly, the reflection loss of the embodiments 2, 4 and 5 is lower than that of the spherical carbonyl iron powder and the comparative example in a wider frequency band, which shows that the preparation method provided by the invention can obviously improve the wave absorbing performance of the flaky iron powder. In comparison, the comparative examples have reflection losses in the 7-18 GHz bandThe wave absorbing performance is much worse than that of the raw materials.

Fig. 4 shows the comparison of the complex magnetic permeability performance tests of examples 2 and 3 with the raw material spherical carbonyl iron powder, and as shown in the figure, the real part of the complex magnetic permeability of example 3 in the low frequency band is larger than that of the spherical carbonyl iron powder and is about 2 times larger than that of the spherical carbonyl iron powder. The real part of complex permeability of example 3 is slightly smaller than that of spherical carbonyl iron powder as the frequency increases. In example 3, the imaginary part of the complex permeability shows a trend of increasing and then decreasing in a 2-18 GHz test frequency band, and is always larger than the imaginary part of the complex permeability of the spherical carbonyl iron powder. This means that in the frequency band of 2-18 GHz, the magnetic performance of the flaky carbonyl iron powder prepared in example 3 is greatly superior to that of the traditional spherical carbonyl iron powder, the magnetic loss is larger than that of the latter, and the wave-absorbing performance is stronger.

Fig. 5 shows the comparison of the complex dielectric constant performance tests of examples 2 and 3 with the raw material spherical carbonyl iron powder, as shown in the figure, the real part and the imaginary part of the complex dielectric constant of the flaky carbonyl iron powder prepared in example 3 are both obviously larger than those of the spherical carbonyl iron powder and the flaky iron powder prepared in example 2, and the real part of the complex dielectric constant of the sample in example 3 is almost 3 times larger than that of the spherical carbonyl iron powder in the frequency band of 2-18 GHz, wherein the content of the flaky carbonyl iron powder is increased. The imaginary part of the complex dielectric constant of example 3 is seen as more peaks, indicating polarization at multiple frequencies. The carbonyl iron powder complex dielectric property is obviously enhanced, which means that the dielectric loss of the material in a low frequency band can be obviously improved, thereby enhancing the wave absorbing capability.

In conclusion, the flaky carbonyl iron powder prepared by the method is in a broken flaky shape, and compared with the flaky iron powder obtained by direct ball milling or further air flow crushing in the traditional preparation method, the surface of the flaky carbonyl iron powder is in an uneven shape, so that the wave-absorbing surface area is effectively improved, and the wave-absorbing performance of the flaky iron powder is remarkably improved; in addition, the preparation method radically solves the agglomeration phenomenon existing in the drying process of wet ball milling, and further can realize the yield of the flaky carbonyl iron powder which is more than 80% and is far less than 20% in the traditional preparation method, and the production process does not involve substances which pollute the environment, does not contain emissions such as dust and the like, has lower production cost, and is very suitable for large-scale industrial production.

As used herein, "first," "second," "third," etc. (e.g., first grinding ball, second grinding ball, third grinding ball, etc.) merely distinguish the respective components for clarity of description and are not intended to limit any order or to emphasize importance, etc.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.