CN115087338A - Electromagnetic loss material with uniform electromagnetism and impedance matching and preparation method thereof - Google Patents
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- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
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Abstract
The invention discloses an electromagnetic uniform and impedance matching electromagnetic loss material and a preparation method thereof, belonging to the field of resin-based electromagnetic loss composite materials.A carbonyl iron powder, resin and gas-phase silica are weighed and mixed uniformly at room temperature to obtain electromagnetic slurry; carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry; and placing the defoamed electromagnetic slurry into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetism and impedance matching. The electromagnetic loss material obtained by the invention has uniform upper and lower properties, low dielectric constant and good wave-absorbing property.
Description
Technical Field
The invention relates to an electromagnetic loss material with uniform electromagnetism and impedance matching and a preparation method thereof, belonging to the field of resin-based electromagnetic loss composite materials.
Background
With the development and need of electromagnetic stealth technology in the aerospace field and the increasing severity of problems of electromagnetic interference and electromagnetic pollution in daily life, microwave absorbing materials gradually become a research hotspot in the field of functional materials. The existing wave-absorbing materials can be classified into a resistance loss type, a dielectric loss type and a magnetic loss type according to a wave-absorbing mechanism. The magnetic loss type wave-absorbing material becomes a research hotspot at present due to the excellent wave-absorbing performance of the material. Carbonyl iron powder is the most common absorbent for preparing magnetic loss type wave-absorbing materials, has both magnetic loss performance and dielectric loss performance, and has the advantages of good wave-absorbing effect, wide absorption frequency band and the like.
Although carbonyl iron powder has good electromagnetic loss performance, the carbonyl iron powder is easy to settle in the forming process of low-viscosity electromagnetic slurry due to high density in the process of preparing the resin-based electromagnetic loss material, so that the upper and lower performance of the electromagnetic loss material is uneven; in the process of mixing the high-viscosity electromagnetic slurry, the powder is easy to agglomerate due to the existence of a large amount of free hydroxyl on the surface of the powder, so that the dielectric constant of the material is high, impedance mismatch is caused, and the wave-absorbing performance of the material is influenced.
Patent CN106497313A discloses a high temperature resistant wave-absorbing coating and its application, which has two places relating to silicon dioxide, the first place is carbonyl iron powder, the outer surface is coated with a silicon dioxide film, the silicon dioxide film is formed mainly by organic silicon source (ethyl orthosilicate, etc.), and is deposited on the surface of carbonyl iron powder through chemical hydrolysis reaction to form a compact silicon dioxide film (not gas phase silicon dioxide); the second place uses gas phase silicon dioxide as a rheological agent, which is mainly used for regulating and controlling the rheological viscosity of the coating and preventing the coating from flowing after being sprayed into a film layer. Patent CN107286647A discloses a wave-absorbing prepreg preparation method and a wave-absorbing prepreg, and patent CN108976986A discloses a high-solid-content graphene wave-absorbing coating and a preparation method thereof, wherein the electromagnetic slurry is mainly used for preparing a thin-layer wave-absorbing adhesive film and a wave-absorbing coating, and fumed silica is only used as an anti-settling agent, so that the particle size of the used powder is not determined, and the thixotropic agent has a single effect. Patent CN110283373A discloses a thermoplastic magnetic composite material and a preparation method thereof, wherein silicon dioxide used as an organic silicon source (silane coupling agent, ethyl orthosilicate, etc.) is deposited on the surface of carbonyl iron powder through a chemical hydrolysis reaction to form a dense silicon dioxide film (not gas phase silicon dioxide). Patent CN110760187A discloses a carbonyl iron composite W-band radar wave-absorbing silica gel patch, and the gas-phase silica used in the patent has the functions of improving the mechanical strength of the wave-absorbing silica gel patch, resisting high and low temperature and resisting flame. Patent CN112409653A discloses a wave absorbing agent, a preparation method and an application thereof, the patent mainly utilizes nano silica particles to modify the absorbing agent by a mechanical ball milling method, and silica is coated on the edge and/or surface of flaky carbonyl iron powder by a chemical reaction, so as to obtain the wave absorbing agent with good processing performance and impedance matching performance, and the silica needs to be hydroxylated in advance. None of the above patents can obtain an electromagnetic loss material having uniform upper and lower properties, a low dielectric constant, and good wave absorption properties.
Disclosure of Invention
The invention aims to provide an electromagnetic loss material with uniform electromagnetism and impedance matching and a preparation method thereof, and the obtained electromagnetic loss material has uniform upper and lower properties, low dielectric constant and good wave-absorbing property.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for preparing an electromagnetic loss material with uniform electromagnetism and impedance matching comprises the following steps:
weighing carbonyl iron powder, resin and gas-phase silica, and uniformly mixing at room temperature to obtain electromagnetic slurry;
carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
and placing the defoamed electromagnetic slurry into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetism and impedance matching.
Preferably, the fumed silica has a particle size of 50 to 200 nm.
Preferably, the addition ratio of the fumed silica is 0.3-1% of the total weight of carbonyl iron powder and resin, and the mass ratio of the carbonyl iron powder to the resin is (85-91): (9-15).
Preferably, the carbonyl iron powder, the resin and the fumed silica are placed in a vertical kneader for mixing for 1-2 h.
Preferably, the electromagnetic slurry is placed in a planetary vacuum defoaming machine for secondary mixing homogenization and defoaming treatment.
Preferably, the rotation speed of the vacuum defoaming machine is 400-600r/min, and the time is 120-300 s.
Preferably, the curing conditions of the curing molding are firstly heat preservation at 190 ℃ for 2-3 hours at 170-.
An electromagnetic loss material with uniform electromagnetism and impedance matching is prepared by the method.
The electromagnetic loss material prepared by the invention is a rigid resin-based electromagnetic loss material, whether low-viscosity or high-viscosity electromagnetic paste, and the viscosity is reduced due to the heating of the resin in the curing process, wherein the doped carbonyl iron powder with higher specific gravity is easy to settle to cause the deterioration of the uniformity of the material and the increase of the dielectric property caused by the agglomeration of the absorbent. Therefore, the method takes the fumed silica as a regulator, and uniformly mixes the fumed silica, carbonyl iron powder and resin through a vertical kneader and a planetary vacuum defoaming machine. The fumed silica is a superfine nano powder material, and in the high-temperature hydrolysis condensation process, partial silicon hydroxyl groups remain on the surface, so that the surface polarity is stronger, the activity is higher, a stable three-dimensional network structure can be formed among silica particles, and the performances of sedimentation prevention, thickening, toughening and the like are achieved; meanwhile, the surface silicon hydroxyl can form hydrogen bonds with the carbonyl iron powder surface hydroxyl to form a dielectric matching layer, so that the split dispersion is facilitated, the agglomeration is reduced, and the dielectric constant is reduced. The mechanism of fumed silica action is shown in FIGS. 2A-2C. In addition, the inventor considers that the regulation and control effects of different particle sizes and dosage aiming at different viscosity systems are different, and the uniformity and the dielectric property of the prepared material are improved by designing the particle size and the addition amount of the fumed silica. The inventor of the invention determines through a great deal of research that the particle size is less than 50nm, the gas-phase silicon dioxide is easy to agglomerate and is difficult to disperse uniformly; the particle size is larger than 200nm, the particle size is too large, the effective coating of micron or submicron iron powder cannot be realized, and the dielectric regulation and control performance is poor, so that the particle size is determined to be within the range of 50-200 nm. The inventor determines that the optimal proportion is the adding proportion of the fumed silica when the adding proportion of the fumed silica is 0.3-1% of the total weight of the carbonyl iron powder and the resin, and the effective coating of the carbonyl iron powder and the formation of the anti-sedimentation three-dimensional network cannot be realized if the adding amount of the fumed silica is too small; on the other hand, if the amount is too large, the viscosity of the slurry tends to increase, and defoaming and molding are difficult. In addition, the inventor determines through research that the curing and forming are divided into two heating stages, the curing degree can be effectively controlled, the curing heat is slowly released, and production safety accidents caused by implosion caused by too fast curing are avoided. The invention can directly and effectively regulate and control the performance of the prepared material, and the method is simple.
Drawings
FIG. 1 is a flow chart of a method for making an electromagnetically uniform and impedance matched electromagnetically lossy material in accordance with the present invention.
FIGS. 2A-2C are schematic diagrams of the mechanism of action of fumed silica;
fig. 3A-3B are schematic diagrams of electromagnetic lossy material uniformity test sampling locations.
Detailed Description
In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.
The following are 6 examples and 2 comparative examples, wherein the examples prepare the electromagnetic loss material by using the preparation method provided by the present invention, the comparative examples prepare the electromagnetic loss material by using the existing method, and the properties of the prepared electromagnetic loss material are tested and compared.
Example 1
A preparation method of an electromagnetic loss material with uniform electromagnetism and impedance matching is disclosed, the flow is shown in figure 1, and the specific steps are as follows:
the method comprises the following steps: 850g of carbonyl iron powder, 150g of epoxy resin and 3g of fumed silica with the particle size of 50nm are weighed and placed in a vertical kneader;
step two: kneading and stirring for 1h at room temperature by adopting a vertical kneader, and uniformly mixing the three raw materials;
step three: placing the mixed electromagnetic slurry obtained in the second step into a planetary vacuum defoaming machine, operating for 300s at 400r/min, and carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
step four: and (4) placing the electromagnetic slurry obtained by the reaction in the step three into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetic parameters and good impedance matching.
The electromagnetic loss material prepared in the embodiment is added into an S-waveband waveguide sample according to a standard machine, sampling is carried out according to the uniformity test sampling position of the electromagnetic loss material shown in figures 3A-3B, and the electromagnetic parameters are measured by a vector grid analyzer to obtain complex dielectric constants epsilon ', epsilon' and magnetic conductivities mu 'and mu'.
Example 2
A method for preparing an electromagnetic loss material with uniform electromagnetism and impedance matching comprises the following specific steps:
the method comprises the following steps: weighing 910g of carbonyl iron powder, 90g of epoxy resin and 3g of fumed silica with the particle size of 50nm, and placing the materials in a vertical kneader;
step two: kneading and stirring for 1h at room temperature by adopting a vertical kneader, and uniformly mixing the three raw materials;
step three: placing the mixed electromagnetic slurry obtained in the second step into a planetary vacuum defoaming machine, operating for 300s at 400r/min, and carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
step four: and (4) placing the electromagnetic slurry obtained by the reaction in the step three into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetic parameters and good impedance matching.
The electromagnetic loss material prepared in the embodiment is added into an S-waveband waveguide sample according to a standard machine, and the electromagnetic parameters of the sample are measured by a vector grid analyzer to obtain complex dielectric constants epsilon ', epsilon' and magnetic conductivities mu 'and mu'.
Example 3
A preparation method of an electromagnetic loss material with uniform electromagnetism and impedance matching comprises the following specific steps:
the method comprises the following steps: 850g of carbonyl iron powder, 150g of epoxy resin and 3g of fumed silica with the particle size of 200nm are weighed and placed in a vertical kneader;
step two: kneading and stirring for 1h at room temperature by adopting a vertical kneader, and uniformly mixing the three raw materials;
step three: placing the mixed electromagnetic slurry obtained in the second step into a planetary vacuum defoaming machine, operating for 300s at 400r/min, and carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
step four: and (4) placing the electromagnetic slurry obtained by the reaction in the step three into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetic parameters and good impedance matching.
The electromagnetic loss material prepared in the embodiment is added into an S-waveband waveguide sample according to a standard machine, and the electromagnetic parameters of the sample are measured by a vector grid analyzer to obtain complex dielectric constants epsilon ', epsilon' and magnetic conductivities mu 'and mu'.
Example 4
A preparation method of an electromagnetic loss material with uniform electromagnetism and impedance matching comprises the following specific steps:
the method comprises the following steps: 850g of carbonyl iron powder, 150g of epoxy resin and 10g of fumed silica with the particle size of 50nm are weighed and placed in a vertical kneader;
step two: kneading and stirring for 1h at room temperature by adopting a vertical kneader, and uniformly mixing the three raw materials;
step three: placing the mixed electromagnetic slurry obtained in the second step into a planetary vacuum defoaming machine, operating for 300s at 400r/min, and carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
step four: and (4) placing the electromagnetic slurry obtained by the reaction in the step three into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetic parameters and good impedance matching.
The electromagnetic loss material prepared in the embodiment is added into an S-waveband waveguide sample according to a standard machine, and the electromagnetic parameters of the sample are measured by a vector grid analyzer to obtain complex dielectric constants epsilon ', epsilon' and magnetic conductivities mu 'and mu'.
Example 5
A preparation method of an electromagnetic loss material with uniform electromagnetism and impedance matching comprises the following specific steps:
the method comprises the following steps: 850g of carbonyl iron powder, 150g of epoxy resin and 3g of fumed silica with the particle size of 50nm are weighed and placed in a vertical kneader;
step two: kneading and stirring for 2 hours at room temperature by adopting a vertical kneader, and uniformly mixing the three raw materials;
step three: placing the mixed electromagnetic slurry obtained in the second step into a planetary vacuum defoaming machine, operating for 300s at 400r/min, and carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
step four: and (4) placing the electromagnetic slurry obtained by the reaction in the step three into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetic parameters and good impedance matching.
The electromagnetic loss material prepared in the embodiment is added into an S-waveband waveguide sample according to a standard machine, and the electromagnetic parameters of the sample are measured by a vector grid analyzer to obtain complex dielectric constants epsilon ', epsilon' and magnetic conductivities mu 'and mu'.
Example 6
A preparation method of an electromagnetic loss material with uniform electromagnetism and impedance matching comprises the following specific steps:
the method comprises the following steps: 850g of carbonyl iron powder, 150g of epoxy resin and 3g of fumed silica with the particle size of 50nm are weighed and placed in a vertical kneader;
step two: kneading and stirring for 1h at room temperature by adopting a vertical kneader, and uniformly mixing the three raw materials;
step three: placing the mixed electromagnetic slurry obtained in the second step into a planetary vacuum defoaming machine, operating for 120s at 600r/min, and carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
step four: and (4) placing the electromagnetic slurry obtained by the reaction in the step three into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetic parameters and good impedance matching.
The electromagnetic loss material prepared in the embodiment is added into an S-waveband waveguide sample according to a standard machine, and the electromagnetic parameters of the sample are measured by a vector grid analyzer to obtain complex dielectric constants epsilon ', epsilon' and magnetic conductivities mu 'and mu'.
Comparative example 1
A preparation method of an electromagnetic loss material with uniform electromagnetism and impedance matching comprises the following specific steps:
the method comprises the following steps: 850g of carbonyl iron powder and 150g of epoxy resin are weighed and placed in a vertical kneader;
step two: kneading and stirring for 1h at room temperature by adopting a vertical kneader, and uniformly mixing the three raw materials;
step three: placing the mixed electromagnetic slurry obtained in the second step into a planetary vacuum defoaming machine, operating for 300s at 400r/min, and carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
step four: and (4) placing the electromagnetic slurry obtained by the reaction in the step three into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetic parameters and good impedance matching.
Comparative example 2
A preparation method of an electromagnetic loss material with uniform electromagnetism and impedance matching comprises the following specific steps:
the method comprises the following steps: weighing 910g of carbonyl iron powder and 90g of epoxy resin, and placing in a vertical kneader;
step two: kneading and stirring for 1h at room temperature by adopting a vertical kneader, and uniformly mixing the three raw materials;
step three: placing the mixed electromagnetic slurry obtained in the second step into a planetary vacuum defoaming machine, operating for 300s at 400r/min, and carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
step four: and (4) placing the electromagnetic slurry obtained by the reaction in the step three into a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetic parameters and good impedance matching.
The wave-absorbing material prepared by the embodiment is added into an S-waveband waveguide sample according to a standard machine, and the electromagnetic parameters of the sample are measured by a vector grid analyzer to obtain complex dielectric constants epsilon ', epsilon' and magnetic conductivities mu 'and mu'.
The following table 1 describes complex dielectric constants epsilon ', epsilon ' and magnetic conductivities mu ' and mu ' obtained by testing the electromagnetic loss materials prepared in the above examples and comparative examples, as well as wave impedances and dispersion coefficients and other data, wherein epsilon ', epsilon ", mu ' and mu ' are main parameters for characterizing the wave-absorbing material, and the wave impedances are root-mean-square of real parts of the magnetic conductivities and the dielectric constants of the material. The coefficient of variation is equal to the ratio of the standard deviation to the mean, with smaller coefficients of variation indicating better material uniformity.
TABLE 1 homogeneity and impedance value comparison of materials before and after fumed silica addition
The impedance matching characteristic is particularly important for the electromagnetic loss material, because even if the electromagnetic loss characteristic is stronger, if the impedance matching characteristic is not satisfied, the incident electromagnetic wave is reflected on the surface of the material and cannot enter the material, so that the wave absorbing effect cannot be achieved. The method for realizing impedance matching characteristic is to create special boundary condition to make incident electromagnetic wave not be reflected on the surface of material and enter the interior of material as much as possible. The simplest condition is that electromagnetic waves are vertically incident to the surface of a material from a free space, for a single-layer wave-absorbing material, when a beam of sinusoidal plane waves vertically irradiates the surface of the single-layer wave-absorbing material connected with a load, incidence and reflection phenomena can occur at an interface, and the reflection coefficient R can be expressed as: r ═ Z 0 -Z)/(Z 0 +Z)，Z 0 The wave impedance of air (377 Ω) and Z are the wave impedance of the medium. From this theory, it is necessary to minimize the reflected electromagnetic wave by making the reflection coefficient R zero, that is, maintaining the wave impedance of the electromagnetic loss material and the wave impedance of air in as wide a frequency range as possibleApproximately equal. In other words, the smaller the value of the reflection coefficient and the smaller the dispersion coefficient, the better the performance of the electromagnetic loss material produced. As can be seen from table 1, the data of comparative example 1 shows that the material has a relatively obvious sedimentation behavior without adding fumed silica, and the dielectric constant is relatively low due to the sedimentation of carbonyl iron powder and the low content of the absorbent in the upper layer of the material, and the dielectric constants on the upper left and the upper right are about 17; the lower layer of the material has high absorbent content and high dielectric constant, and the dielectric constants of the left lower layer and the right lower layer are about 24. The dispersion coefficients of the real part and the imaginary part of the dielectric are obviously larger than those of the embodiment columns, which shows that the method of the invention is more excellent. Comparative example 1 the average reflection coefficient was less than that of examples 1-4, but the dispersion was large and did not effectively reflect the overall material properties. The lateral reflectance and dispersion coefficient of comparative example 2 are high, and the properties of the prepared material are far inferior to those of examples 1 to 6.
The material prepared in example 6 has the best overall performance, because the adopted fumed silica has the particle size of 50nm, agglomeration caused by too small particle size is avoided, and uniform dispersion is difficult; and the particle size is too large, so that the effective coating of the iron powder of the micron or submicron ironing machine cannot be realized. The addition amount is 3g, namely the addition proportion is 0.3 percent of the total weight of the carbonyl iron powder and the resin, so that the effective coating and the anti-sedimentation of the carbonyl iron powder are realized; has little influence on the viscosity of the system. According to the early test, the vertical kneading machine has high efficiency, and the homogenization of the slurry can be realized after stirring for 1 hour. The defoaming treatment rotating speed is 600r/min, the running time is 120s, the slurry can be quickly kneaded and extruded at a high rotating speed, the defoaming work is completed in a short time, and meanwhile, the short-time running time avoids the overheating of the slurry, the viscosity of the system is reduced again, the absorbent is settled, and the integral uniformity is influenced. In conclusion, example 6 works best.
Although the present invention has been described with reference to the above embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (8)
1. A preparation method of an electromagnetic loss material with uniform electromagnetism and impedance matching is characterized by comprising the following steps:
weighing carbonyl iron powder, resin and gas-phase silica, and uniformly mixing at room temperature to obtain electromagnetic slurry;
carrying out secondary mixing homogenization and defoaming treatment on the electromagnetic slurry;
and placing the defoamed electromagnetic slurry in a forming die for curing and forming to obtain the electromagnetic loss material with uniform electromagnetism and impedance matching.
2. The method of claim 1, wherein the fumed silica has a particle size of 50 to 200 nm.
3. The method of claim 1, wherein the fumed silica is added in a proportion of 0.3% to 1% by weight of carbonyl iron powder to resin, and the mass ratio of carbonyl iron powder to resin is (85-91): (9-15).
4. The method of claim 1, wherein the carbonyl iron powder, the resin and the fumed silica are placed in a vertical kneader and mixed for 1-2 hours.
5. The method according to claim 1, wherein the electromagnetic slurry is placed in a planetary vacuum defoaming machine for secondary mixing homogenization and defoaming treatment.
6. The method as claimed in claim 5, wherein the rotation speed of the vacuum defoaming machine is 400-600r/min and the time is 120-300 s.
7. The method of claim 1, wherein the curing conditions for the curing molding are 180 ℃ for 2 hours, and then 200 ℃ for 1 hour.
8. An electromagnetically uniform and impedance-matched electromagnetically lossy material, prepared by the method of any one of claims 1 to 7.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210686186.5A CN115087338A (en) | 2022-06-16 | 2022-06-16 | Electromagnetic loss material with uniform electromagnetism and impedance matching and preparation method thereof |
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