NZSP wave-absorbing coating with three-dimensional periodic structure and preparation method of NZSP wave-absorbing coating

Abstract

The invention relates to the technical field of coatings for absorbing electromagnetic waves, and discloses a preparation method of an NZSP wave-absorbing coating with a three-dimensional periodic structure, and the preparation method comprises the following steps: step 1, obtaining NZSP spherical powder; step 2, spraying NZSP spherical powder on the substrate to obtain a first coating; 3, determining the shape of the periodic unit; the plurality of periodic units are arranged into a periodic structure according to a regular space array; step 4, performing laser sintering on the NZSP spherical powder spread on the first coating; 5, laying powder layer by layer, and carrying out accumulative sintering until a preset height is reached, so as to obtain a second coating; and 6, forming the NZSP wave-absorbing coating with a three-dimensional periodic structure by the first coating and the second coating. The first coating and the second coating are manufactured on the basis of the NZSP spherical powder, and the method has outstanding advantages in weight reduction application; the absorption bandwidth of the NZSP wave-absorbing coating is expanded through the macroscopic design of the periodic structure, the wave-absorbing performance is improved, and the NZSP wave-absorbing coating is suitable for the field of aerospace.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic wave absorbing coatings, and particularly relates to a NZSP absorbing coating with a three-dimensional periodic structure and a preparation method thereof. Background Art

[0002] NZSP refers to NASICON-type Na3Zr2Si2PO 12 , NZSP ceramics, as a highly regarded ceramic material, exhibit a series of unique and valuable properties. In terms of wave absorption performance, they can effectively absorb electromagnetic waves of specific frequencies; and they are structurally stable at high temperatures and are not prone to chemical reactions with oxygen, moisture, etc. in the air; and they can resist a certain degree of acid-base corrosion, which makes them potentially applicable in a variety of complex environments. The theoretical density of NZSP ceramics is 3.24 g·cm -3 , compared with other wave-absorbing materials, NZSP ceramics have an extremely low density. This low-density characteristic has brought a major breakthrough in the field of wave-absorbing materials, enabling the effective reduction of the weight of wave-absorbing materials, which is extremely beneficial to the lightweight design and manufacturing of related equipment. In addition, NZSP ceramics also have significant advantages in terms of raw material acquisition and preparation process. Their raw materials are extremely abundant and widely exist in nature, which provides a solid material basis for large-scale production. And the preparation process is relatively easy and does not require complex and expensive equipment and technologies, greatly reducing production costs and improving production efficiency.

[0003] However, the practical application and transformation of NZSP ceramics are not smooth sailing, and there are some problems that need to be solved urgently. Due to the low thermal conductivity of NZSP powder, it is difficult to completely melt in a rapid plasma jet, and it impacts the substrate in a semi-molten state and solidifies, forming a relatively loose coating. Therefore, the wave absorption performance of the obtained wave-absorbing coating is relatively low and cannot meet some application scenarios with high requirements for wave absorption performance. In the field of wave-absorbing materials, the following common methods are used to expand the absorption bandwidth of NZSP ceramics: composite doping, constructing a multi-layer structure, nanostructuring, and designing a macroscopic structure. Component design has a limited range of performance regulation and it is difficult to further expand the absorption bandwidth, and improvement is needed through the design of the macroscopic structure. Therefore, a NZSP wave-absorbing coating that improves wave absorption performance through macroscopic structure design is required. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an NZSP absorbing coating with a three-dimensional periodic structure and a preparation method thereof aiming at the deficiencies in the above-mentioned prior art. The structure is simple and reasonable. The first coating and the second coating are made based on NZSP spherical powder, which has outstanding advantages in weight reduction applications and is suitable for the aerospace field. The absorption bandwidth of the NZSP absorbing coating is expanded through the macroscopic design of the periodic structure, the absorbing performance is improved, and electromagnetic interference is reduced. The periodic structure of the second coating is prepared by selective laser sintering, which has a high degree of design freedom.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows: In the first aspect, the present invention provides a preparation method of an NZSP absorbing coating with a three-dimensional periodic structure, which is characterized by including the following steps: Step 1: Obtain NZSP spherical powder; Step 2: Spray NZSP spherical powder on a substrate to obtain a first coating; Step 3: Determine the shape of the periodic unit; determine the optimized geometric parameters of the periodic unit, and the geometric parameters at least include the maximum length, the maximum width, and the preset height; several periodic units are arranged in a regular space array to form a periodic structure; Step 4: Spread NZSP spherical powder on the first coating; use laser sintering to sinter the NZSP spherical powder spread on the first coating, and the cross-sectional shape of the sintering area is the same as the cross-section of the periodic structure; Step 5: Repeat Step 4, layer by layer spreading powder and cumulative sintering until the height of the periodic unit reaches the preset height, complete the laser sintering, and obtain a second coating; Step 6: The first coating and the second coating together constitute an NZSP absorbing coating with a three-dimensional periodic structure.

[0006] The above-mentioned preparation method of an NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: the periodic unit is a rectangular loop, and the rectangular loop includes: a first rectangular patch, a third rectangular patch having the same structure as the first rectangular patch and symmetrically distributed about the X axis; a second rectangular patch, a fourth rectangular patch having the same structure as the second rectangular patch and symmetrically distributed about the Y axis; the X axis and the Y axis are perpendicular to each other; the minimum width between the first rectangular patch and the third rectangular patch is not less than the length of the second rectangular patch; the minimum length between the second rectangular patch and the fourth rectangular patch is not less than the length of the first rectangular patch.

[0007] The above-mentioned preparation method of an NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: the regular space array means that the periodic units are distributed in rows and columns, the periodic units in each row are evenly distributed, and the periodic units in each column are evenly distributed.

[0008] The preparation method of the above NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: in step three, the specific steps for determining the optimized geometric parameters of the periodic unit are as follows: Step 301: Define the geometric parameters of the periodic unit and arrange the periodic unit into a periodic structure according to a regular space array; Step 302: Define the objective function, select the geometric parameters of the periodic unit as the optimization variables, use the genetic algorithm as the optimization method, adjust the optimization variables, and calculate the value of the objective function; Step 303: Use the combination of geometric parameters that minimizes the value of the objective function as the optimized geometric parameters of the periodic unit.

[0009] The preparation method of the above NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: the objective function includes a reflection loss integral term and a bandwidth function term.

[0010] The preparation method of the above NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: an absorber is mixed in the NZSP spherical powder in step one.

[0011] The preparation method of the above NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: the absorber is one of SiC, TiN, SrTiO3, and ITO.

[0012] The preparation method of the above NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: the specific method for obtaining the NZSP spherical powder is as follows: Step 101: Mix the sodium source, zirconium source, silicon source, and phosphorus source and load them into a ball milling tank; Step 102: Add ethanol to the ball milling tank and perform wet ball milling. After the ball milling is completed, take out and dry to obtain the reactant powder; Step 103: Calcinate the reactant powder at 1180 - 1220 °C for 5 - 7 h. After the calcination is completed, cool and grind to obtain the NZSP coarsely ground particles; Step 104: Introduce the NZSP coarsely ground particles into the ball milling tank, add distilled water, and perform wet ball milling. After the ball milling is completed, obtain a mixed solution; Step 105: Add an antifoaming agent and a binder to the mixed solution, then add it to a spray granulator, stir and granulate to obtain the NZSP spherical powder.

[0013] The preparation method of the above NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: in step two, when spraying the NZSP spherical powder on the substrate, supersonic plasma spraying is used.

[0014] In a second aspect, the present invention provides an NZSP absorbing coating with a three-dimensional periodic structure, characterized in that: the first coating and the second coating together constitute an NZSP absorbing coating with a three-dimensional periodic structure, which is prepared by the preparation method of any one of the above.

[0015] The present invention has the following advantages compared with the prior art: 1. The structure of the present invention is simple, reasonably designed, and convenient to implement and use.

[0016] 2. The present invention makes the first coating and the second coating based on NZSP spherical powder. Since the density of NZSP is relatively low, the weight is significantly reduced, and it has outstanding advantages in weight reduction applications. At the same time, it has excellent absorbing performance and high-temperature stability, and is suitable for the aerospace field.

[0017] 3. The present invention expands the absorption bandwidth of the NZSP absorbing coating through the macroscopic design of the periodic structure. The periodic structure can generate multiple resonance modes, which can cover multiple frequency ranges, achieve broadband absorption, further improve the absorbing performance, and reduce electromagnetic interference, and the use effect is good.

[0018] 4. The present invention uses selective laser sintering to prepare the periodic structure of the second coating. The laser beam controlled by a computer selectively sinters the NZSP spherical powder, which has a design freedom; layer-by-layer melting can prepare a relatively complex three-dimensional periodic structure; only the NZSP spherical powder in a specific area is scanned and sintered, and the unsintered NZSP spherical powder can be used as a support and recycled.

[0019] In summary, the structure of the present invention is simple, reasonably designed, makes the first coating and the second coating based on NZSP spherical powder, has outstanding advantages in weight reduction applications, and is suitable for the aerospace field; expands the absorption bandwidth of the NZSP absorbing coating through the macroscopic design of the periodic structure, improves the absorbing performance, reduces electromagnetic interference, and uses selective laser sintering to prepare the periodic structure of the second coating, which has a design freedom.

[0020] Next, through the drawings and embodiments, the technical solutions of the present invention will be further described in detail. Description of the Drawings

[0021] Figure 1 It is a flowchart of the method of the present invention.

[0022] Figure 2 It is a flowchart of the method for obtaining NZSP spherical powder of the present invention.

[0023] Figure 3 It is a schematic structural diagram of the NZSP absorbing coating with a three-dimensional periodic structure of the present invention.

[0024] Figure 4 It is a schematic structural diagram of the rectangle of the present invention.

[0025] Figure 5 Schematic diagram of the geometric parameters of the rectangle of the present invention.

[0026] Figure 6 Reflection loss spectrum diagram of the NZSP absorbing coating with aperiodic structure.

[0027] Figure 7 Reflection loss bandwidth characteristic diagram of the NZSP absorbing coating with three-dimensional periodic structure.

[0028] Figure 8 Response of the reflectivity of the NZSP absorbing coating with periodic structure in the second embodiment of the present invention to the incident angle of electromagnetic waves in the TE polarization mode.

[0029] Figure 9 Response of the reflectivity of the NZSP absorbing coating with periodic structure in the second embodiment of the present invention to the incident angle of electromagnetic waves in the TM polarization mode.

[0030] Description of reference numerals: 10 - Second coating; 11 - First coating; 101 - First rectangular patch; 102 - Second rectangular patch; 103 - Third rectangular patch; 104 - Fourth rectangular patch. Detailed implementation manners

[0031] The method of the present invention will be further described in detail below with reference to the accompanying drawings and the embodiments of the present invention.

[0032] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0033] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the present application. As used herein, unless otherwise clearly specified in the context, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0034] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of this application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of this application described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0035] For ease of description, spatial relative terms such as "above", "on top of", "on the upper surface", "above" etc. can be used here to describe the spatial positional relationship of a device or feature shown in the figure with other devices or features. It should be understood that spatial relative terms are intended to include different orientations in use or operation in addition to the orientation described in the figure for the device. For example, if the device in the figure is inverted, the device described as "above other devices or structures" or "on top of other devices or structures" will then be positioned "below other devices or structures" or "beneath other devices or structures". Thus, the exemplary term "above" can include both the orientations of "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and corresponding interpretations are made for the spatial relative descriptions used here.

[0036] Embodiment 1

[0037] As Figure 1 shown, a preparation method of an NZSP absorbing coating with a three-dimensional periodic structure according to the present invention includes the following steps: Step 1, obtain NZSP spherical powder.

[0038] As Figure 2 shown, in a possible embodiment, the specific method for obtaining NZSP spherical powder is: Step 101, mix the sodium source, zirconium source, silicon source and phosphorus source and load them into a ball milling tank.

[0039] In a possible embodiment, both the sodium source and the phosphorus source are Na3PO 12 ·12H2O, the zirconium source is ZrO2, the silicon source is SiO2, and the molar ratio of Na3PO 12 ·12H2O, ZrO2 and SiO2 is 1.15:1.8:2.

[0040] Step 102: Add ethanol into the ball milling tank and perform wet ball milling for 12 - 24 h. After the ball milling is completed, take out and dry to obtain the reactant powder; Step 103: Calcinate the reactant powder at 1180 - 1220 °C for 5 - 7 h. After the calcination is completed, cool and grind to obtain the roughly ground NZSP particles; Step 104: Introduce the roughly ground NZSP particles into the ball milling tank, add distilled water, and perform wet ball milling for 12 - 16 h. After the ball milling is completed, obtain the mixed solution; Step 105: Add an antifoaming agent and a binder to the mixed solution, and then add it to a spray granulator, stir and granulate to obtain the spherical NZSP powder. In actual use, PVA solution is used as the binder.

[0041] The inlet air temperature of the spray granulator is 290 - 310 °C, the air temperature in the chamber is 130 - 150 °C, the outlet air temperature is 100 - 120 °C, the nozzle rotation speed is 28000 - 30000 r / min, the feeding rate is 110 - 120 g / min, and the atomizing air flow rate is 20 - 22 m 3 / h.

[0042] NZSP is selected as the absorbing coating material because, on the one hand, NZSP has a relatively low density, enabling the prepared absorbing coating to effectively reduce the overall load in application scenarios, especially in fields with strict weight requirements such as aerospace. On the other hand, the thermal expansion coefficient of NZSP is highly matched with common metal materials. This good match ensures that the NZSP absorbing coating and the metal substrate can always maintain a stable bonding state under different temperature environments, significantly improving the durability and reliability of the coating. Third, NZSP itself has a certain degree of absorbing ability and does not require modification or compounding to obtain the absorbing performance, which has a positive impact on the direct improvement of the absorbing performance.

[0043] Step Two: Spray the spherical NZSP powder on the substrate to obtain the first coating 11.

[0044] First, sandblast the substrate, and then spray the spherical NZSP powder on the substrate. The spraying is carried out by supersonic plasma spraying. The parameter settings of the supersonic plasma spraying are as follows: voltage is 120 - 130 V, current is 360 - 380 A, argon gas flow rate is 65 - 70 L / min, hydrogen gas flow rate is 15 - 20 L / min, powder feeding rate is 30 - 35 g / min, spraying distance is 90 - 100 mm, and the coating thickness is 1.8 - 2.4 mm. It should be noted that the substrate can be workpieces such as the air intake duct of an aircraft engine, engine fan, radome, combustion chamber, wing, and tail wing that are prone to reflecting radar waves.

[0045] Supersonic plasma spraying can endow the NZSP spherical powder with extremely high speed and temperature, making the NZSP spherical powder melt more fully, making the first coating 11 denser, ensuring good wave absorption performance; at the same time, significantly improving the bonding strength between the NZSP spherical powder and the substrate surface, making the first coating 11 bond more firmly and durably with the substrate; supersonic plasma spraying has a high deposition efficiency and can quickly form a coating on the substrate surface, thereby preparing a first coating 11 with good uniformity and thickness meeting the requirements, meeting the needs of different substrates for wave-absorbing coatings.

[0046] Step 3: Determine the shape of the periodic unit; determine the optimized geometric parameters of the periodic unit, where the geometric parameters at least include the maximum length, the maximum width, and the preset height; several periodic units are arranged into a periodic structure according to a regular spatial array.

[0047] Such as Figure 3 、 Figure 4 and Figure 5 As shown, in a possible embodiment, the periodic unit is a rectangular loop, and the rectangular loop includes: a first rectangular patch 101, a third rectangular patch 103 that has the same structure as the first rectangular patch 101 and is symmetrically distributed about the X axis; a second rectangular patch 102, a fourth rectangular patch 104 that has the same structure as the second rectangular patch 102 and is symmetrically distributed about the Y axis; the X axis and the Y axis are perpendicular to each other; the minimum width between the first rectangular patch 101 and the third rectangular patch 103 is not less than the length of the second rectangular patch 102; the minimum length between the second rectangular patch 102 and the fourth rectangular patch 104 is not less than the length of the first rectangular patch 101.

[0048] Such as Figure 5 As shown, the more specific linear constraint conditions for the geometric parameters of the rectangular loop are: , where C1 represents the maximum width of the rectangular loop, that is, the maximum width between the first rectangular patch 101 and the third rectangular patch 103; C2 represents the maximum length of the rectangular loop, that is, the maximum length between the second rectangular patch 102 and the fourth rectangular patch 104; D2 represents the length of the outer rectangle of the second rectangular patch 102, D1 represents the width of the second rectangular patch 102, d2 represents the length of the first rectangular patch 101, d1 represents the thickness of the first rectangular patch 101, t x represents the distance between the second rectangular patch 102 and the fourth rectangular patch 104, and t y represents the distance between the first rectangular patch 101 and the third rectangular patch 103. It should be noted that the thicknesses of the first rectangular patch 101, the second rectangular patch 102, the third rectangular patch 104, and the fourth rectangular patch 104 are all the same.

[0049] The periodic unit can also be rectangular, circular, triangular, or cross-shaped. However, in comparison, the rectangular shape has the advantages of being easy to design and control, having good polarization characteristics, and being convenient for preparation and processing. Moreover, the rectangular pattern is also convenient for integration with other materials or structures to form a composite absorbing material, further improving the absorbing performance.

[0050] After determining the shape of the periodic unit, the next step is to determine the optimized geometric parameters of the periodic unit. The specific steps are as follows: Step 301: Define the geometric parameters of the periodic unit and arrange the periodic units in a regular spatial array to form a periodic structure. In a possible embodiment, the regular spatial array means that the periodic units are distributed in rows and columns, and the periodic units in each row are evenly distributed, and the periodic units in each column are evenly distributed. By changing the unit, geometric parameters, spatial array arrangement method, and material parameters of the periodic unit, etc., the performance of the absorbing material can be conveniently adjusted to meet different application requirements.

[0051] For example, in the HFSS software, define the shape and geometric parameters of the rectangle, copy the periodic unit of the rectangle, and arrange it into a periodic array according to a 10x10 array, with equal row spacing and column spacing.

[0052] Then set the master-slave boundary and Floquet excitation port, input the material name, such as NZSP, define the coating material properties and periodic structure material properties, that is, import the electromagnetic parameters of the material measured by the network analyzer, and set the corresponding frequency range in the frequency sweep setting, for example, 8.2~12.4 GHz, and the frequency change step is the same as the frequency change step output by the vector network analyzer, which is 0.021 GHz.

[0053] Step 302: Define the objective function, select the geometric parameters of the periodic unit as the optimization variables, adopt the genetic algorithm as the optimization method, adjust the optimization variables, and calculate the value of the objective function. In actual use, the objective function includes a reflection loss integral term and a bandwidth function term. The objective function , where represents the reflection loss in the frequency range; represents the proportionality coefficient of the reflection loss in the total performance; represents the proportionality coefficient of the bandwidth in the total performance, where is negative; represents the bandwidth function; , represents the dielectric constant of the absorbing material, The electromagnetic parameters represent the absorbing material, h represents the thickness of the absorbing material, and parameters such as C and D are the shape parameters of the periodic structure. C = (C1, C2), D = (D1, D2), C1 represents the maximum width of the rectangular loop, C2 represents the maximum length of the rectangular loop, D2 represents the length of the outer rectangle of the rectangular loop, and D1 represents the width of the outer rectangle of the rectangular loop. Among them represents the functional relationship between RL and ε, μ, h, C, D which can be determined by electromagnetic theory modeling or experimental data fitting.

[0054] Select the geometric parameters of the periodic structure as the optimization variables, adjust the optimization variables, and set the range of the variables, such as the length ranging from 2 mm to 5 mm. Then, adopt the genetic algorithm as the optimization method. The genetic algorithm selects the uniform crossover mode, and sets the individual crossover probability to 90% and the single-point crossover probability to 50%; the number of initial individuals, the number of individuals in the mating pool, the number of offspring individuals, and the number of individuals in the next generation are all 30; the roulette wheel selection is enabled; the optimization stop condition is to stop evolving after 500 generations; the range of h variation is from 0.5 mm to 2.2 mm, the range of t variation is from 0.01 mm to 1 mm, and the range of variation of the remaining geometric parameters is from 0.5 mm to 30.0 mm.

[0055] Step 303: Use the combination of geometric parameters that minimizes the value of the objective function as the optimized geometric parameters of the periodic unit. In actual use, by adjusting the geometric parameters of the periodic structure, the reflection loss integral term is minimized and the bandwidth function term is maximized. is negative to achieve the objective function to be minimized, and make the objective function The geometric parameters that minimize it have the optimal wave absorption performance, and determine the combination of these geometric parameters as the optimized geometric parameters of the periodic structure.

[0056] Arrange the periodic units with determined shapes and optimized geometric parameters into a periodic structure according to the regular space array.

[0057] Step Four: Spread NZSP spherical powder on the first coating; use laser sintering to sinter the NZSP spherical powder spread on the first coating 11, and the cross-sectional shape of the sintering area is consistent with the cross-section of the periodic structure.

[0058] In a possible embodiment, the NZSP spherical powder is evenly spread on the surface of the first coating 11 to form a thin layer with a thickness of 0.05 - 0.1 mm; a laser beam is used to selectively melt the NZSP spherical powder so that the cross-sectional shape of the sintered area is consistent with the cross-section of the periodic structure. For example, a path is generated by slicing the CAD model, and the galvanometer system controls the laser beam to scan and sinter according to a preset trajectory. The non-scanned and sintered part remains in powder state, and the solidified NZSP spherical powder after scanning and sintering binds to the first coating 11, so that the cross-sectional shape of the sintered area is consistent with the cross-section of the periodic structure.

[0059] Repeat step four, layer by layer powder spreading and cumulative sintering until the height of the periodic unit reaches the preset height, completing the laser sintering to obtain the second coating 10.

[0060] In a possible embodiment, by adjusting the powder thickness of each layer, the accuracy of the periodic structure can be precisely controlled. After each layer of NZSP spherical powder is sintered, the next layer of NZSP spherical powder is spread. Each newly sintered powder layer firmly binds to the lower layer, improving the stability of the periodic structure; layer by layer powder spreading and sintering can construct complex shapes, with design freedom; and it reduces thermal stress, makes the heat distribution uniform, and avoids local overheating caused by sintering a large amount of powder at one time, thereby improving the quality and performance of the periodic structure.

[0061] In a possible embodiment, during laser sintering, the laser power is 100 - 120 W, the laser scanning speed is 200 - 300 mm / s, and the laser spot diameter is 0.1 - 0.2 mm.

[0062] Selective laser sintering, as an additive manufacturing technology, does not require a mold. It selectively sinters NZSP spherical powder through a computer-controlled laser beam, with design freedom; layer by layer melting can prepare relatively complex three-dimensional periodic structures; only the NZSP spherical powder in a specific area is scanned and sintered, and the unsintered NZSP spherical powder can be used as a support and recycled, with good practical effects.

[0063] The first coating 11 and the second coating 10 together constitute an NZSP wave-absorbing coating with a three-dimensional periodic structure.

[0064] This application expands the absorption bandwidth of the NZSP wave-absorbing coating through the macroscopic design of the periodic structure. The periodic structure can generate multiple resonance modes, covering multiple frequency ranges to achieve broadband absorption, with better wave-absorbing performance, which can reduce the reflection and scattering of the electromagnetic signals of the aircraft itself by the workpiece that is prone to reflecting radar waves, and reduce electromagnetic interference; both the coating and the periodic structure have good high-temperature stability, ensuring the normal operation of the electronic equipment on the aircraft and improving the reliability and stability of the avionics system; and the preparation difficulty of the periodic structure is low, the process is relatively mature, and the periodic structure can be precisely fabricated on a large-area substrate, with a simple process and being conducive to mass production.

[0065] In this application, the NZSP absorbing coating with a three-dimensional periodic structure significantly reduces the weight due to its light and thin characteristics. At the same time, it has excellent absorbing performance and high-temperature stability, and has outstanding advantages in weight reduction applications. It is suitable for the aerospace field, such as the air intake of engines, engine fans, radomes, combustion chambers, wings, tail fins and other parts.

[0066] Example Two

[0067] Different from Example One, in this example, an absorber is mixed in the NZSP spherical powder.

[0068] In actual use, the powder of the absorber and the NZSP spherical powder in Step One are mixed, then ball-milled, and then spray granulated to form NZSP mixed powder. The NZSP mixed powder is sprayed on the substrate to obtain the first coating 11 mixed with the absorber; by using the method of selective laser sintering, the NZSP mixed powder is sintered on the first coating 11 to prepare the second coating 10, forming an NZSP absorbing coating with a three-dimensional periodic structure.

[0069] In a possible embodiment, the absorbers of the first coating 11 and the second coating 10 are the same. Using the same absorber can ensure the mutual matching of the absorbing performance and the high-temperature resistance performance, so as to work better in cooperation. In addition, using the same absorber can make the first coating 11 and the second coating 10 better combined at the microscopic level to form a stable structure.

[0070] Adding absorber powder to the NZSP spherical powder can avoid the problems of too thick NZSP coating and weak interlayer bonding force. The absorber can be selected from one or several of SiC, TiN, SrTiO3 and ITO. Taking SiC as an example, adding SiC powder to the NZSP spherical powder, SiC has unique electromagnetic characteristics and can act synergistically with NZSP to enhance the loss of electromagnetic waves. Compared with the case without adding SiC, when the same absorbing performance is achieved after adding, the required thickness of the NZSP coating is effectively reduced. In addition, the SiC powder can be adsorbed on the surface of the NZSP spherical powder, which helps to strengthen the interaction between the powder particles between layers. Moreover, the SiC powder can promote the NZSP spherical powder to form a more uniform and dense microstructure during sintering, reduce the interlayer pores and defects, and significantly improve the interlayer bonding force.

[0071] Example Three

[0072] An NZSP absorbing coating with a three-dimensional periodic structure of the present invention, the first coating 11 and the second coating 10 together constitute an NZSP absorbing coating with a three-dimensional periodic structure, and the preparation process is as follows: Step One: Obtain NZSP spherical powder.

[0073] Step 101: Obtain NZSP spherical powder based on sodium source, zirconium source, silicon source and phosphorus source.

[0074] Both the sodium source and the phosphorus source use Na3PO 12 ·12H2O, the zirconium source uses ZrO2, the silicon source uses SiO2, and the molar ratio of Na3PO 12 ·12H2O, ZrO2 and SiO2 is 1.15:1.8:2. Mix Na3PO 12 ·12H2O, ZrO2 and SiO2 and load them into a ball milling jar; Step 102: Add ethanol into the ball milling jar and perform wet ball milling for 12 - 24 h. After the ball milling is completed, take out and dry to obtain the reactant powder; Step 103: Calcinate the reactant powder at 1180 - 1220 °C for 5 - 7 h. After the calcination is completed, cool and grind to obtain the roughly ground NZSP particles; Step 104: Introduce the roughly ground NZSP particles into the ball milling jar, add distilled water, and perform wet ball milling for 12 - 16 h. After the ball milling is completed, obtain a mixed solution; Step 105: Add an antifoaming agent and a binder to the mixed solution, then add it to a spray granulator, stir and granulate to obtain NZSP spherical powder.

[0075] The binder uses a PVA solution. The inlet air temperature of the spray granulator is 290 - 310 °C, the air temperature inside the chamber is 130 - 150 °C, the outlet air temperature is 100 - 120 °C, the nozzle rotation speed is 28000 - 30000 r / min, the feeding rate is 110 - 120 g / min, and the atomizing air flow rate is 20 - 22 m 3 / h.

[0076] Step Two: Spray the NZSP spherical powder on the substrate to obtain the first coating 11.

[0077] First, perform sandblasting on the substrate, and then spray the NZSP spherical powder on the substrate. The spraying uses supersonic plasma spraying. The parameter settings of the supersonic plasma spraying are as follows: the voltage is 120 - 130 V, the current is 360 - 380 A, the argon gas flow rate is 65 - 70 L / min, the hydrogen gas flow rate is 15 - 20 L / min, the powder feeding rate is 30 - 35 g / min, the spraying distance is 90 - 100 mm, and the coating thickness is 1.8 - 2.4 mm. It should be noted that the substrate can be workpieces such as the air intake duct of an aircraft engine, the engine fan, the radome, the combustion chamber, the wing, and the tail wing that are prone to reflecting radar waves.

[0078] Step 3. Determine the shape of the periodic unit; determine the optimized geometric parameters of the periodic unit, where the geometric parameters at least include the maximum length, the maximum width, and the preset height; arrange a number of periodic units in a regular spatial array to form a periodic structure.

[0079] In a possible embodiment, the periodic unit is a rectangular loop, and the rectangular loop includes: a first rectangular patch 101, and a third rectangular patch 103 that has the same structure as the first rectangular patch 101 and is symmetrically distributed about the X axis; a second rectangular patch 102, and a fourth rectangular patch 104 that has the same structure as the second rectangular patch 102 and is symmetrically distributed about the Y axis; the X axis and the Y axis are perpendicular to each other; the minimum width between the first rectangular patch 101 and the third rectangular patch 103 is not less than the length of the second rectangular patch 102; the minimum length between the second rectangular patch 102 and the fourth rectangular patch 104 is not less than the length of the first rectangular patch 101.

[0080] Then arrange the periodic units in a preset regular spatial array. In a possible embodiment, the regular spatial array means that the periodic units are distributed in rows and columns, the periodic units in each row are evenly distributed, and the periodic units in each column are evenly distributed. For example, arrange them in a 10x10 array to form a periodic array, and the row spacing and the column spacing are equal.

[0081] Adjust the geometric parameters of the periodic structure to minimize the integral term of the reflection loss and maximize the bandwidth function term, so that the combination of geometric parameters that minimizes the value of the objective function is used as the optimized geometric parameters of the periodic unit. The geometric parameters at least include the maximum length, the maximum width, and the preset height. In this embodiment, the rectangular loop is used as the optimized geometric parameters of the periodic unit, as shown in Table 1: Table 1 Optimized geometric parameter table of the rectangular loop as the periodic unit

[0082] After obtaining the optimized geometric parameters, start to fabricate the second coating 10 on the basis of the first coating 11, specifically: Step 4. Spread NZSP spherical powder on the first coating; use laser sintering to sinter the NZSP spherical powder spread on the first coating, and the cross-sectional shape of the sintering area is consistent with the cross-section of the periodic structure; In a possible embodiment, spread the NZSP spherical powder evenly on the surface of the first coating to form a thin layer, and the thickness of the thin layer is 0.05 - 0.1 mm; use a laser beam to selectively melt the NZSP spherical powder. For example, generate a path through CAD model slicing, and the galvanometer system controls the laser beam to scan and sinter according to a preset trajectory. The part that has not been scanned and sintered remains in powder state, and the sintered NZSP spherical powder solidifies and combines with the first coating, so that the cross-sectional shape of the sintering area is consistent with the cross-section of the periodic structure.

[0083] Repeat step 4, layer by layer powder spreading and cumulative sintering until the height of the periodic unit reaches the preset height, complete the laser sintering, and obtain the second coating 10.

[0084] The first coating 11 and the second coating 10 formed on the first coating 11 by laser sintering together constitute an NZSP absorbing coating with a three-dimensional periodic structure.

[0085] During laser sintering, the laser power is 100 - 120 W, the laser scanning speed is 200 - 300 mm / s, and the laser spot diameter is 0.1 - 0.2 mm.

[0086] Performance Test 1 Denote the NZSP absorbing coating without a periodic structure as sample 1, and denote the NZSP absorbing coating with a three-dimensional periodic structure in Example 3 as sample 2. Figure 6 is the reflection loss spectrum diagram of sample 1. It can be seen that the absorption bandwidth with RL < -10 dB is 2.69 GHz, and the bandwidth with RL < -15 dB is 0 GHz. Figure 7 is the reflection loss bandwidth characteristic diagram of sample 2. It can be seen that when RL < -15 dB, the bandwidth is 3.38 GHz. Compare the absorbing properties of sample 1 and sample 2 as shown in Table 2: Table 2 Comparison Table of Absorbing Properties

[0087] Compared with sample 1, sample 2 significantly improves the absorbing property, reduces the thickness, decreases the minimum reflectivity. Especially in terms of the absorption bandwidth, there is an obvious improvement. The absorption bandwidth with RL < -10 dB can cover the entire X-band, and the absorption bandwidth with RL < -15 dB is extended from 0 GHz to 3.38 GHz.

[0088] Performance Test 2 For the NZSP absorbing coating with a three-dimensional periodic structure prepared in Example 3, test the influence on the reflectivity under different polarization modes and different electromagnetic wave incident angles to evaluate the stability of the absorbing property of the absorbing coating and the absorbing effect under different conditions.

[0089] Figure 8 is the response of the NZSP absorbing coating with a three-dimensional periodic structure to the electromagnetic wave incident angle under the TE polarization mode. As Figure 8As shown, by changing the incident angle of the electromagnetic wave from 0° to different angles, the change in the reflectivity of the NZSP absorbing coating with a three-dimensional periodic structure is observed, so as to analyze the absorbing performance of the NZSP absorbing coating with a three-dimensional periodic structure at different incident angles. When the incident angle of the electromagnetic wave increases from 0° to 30°, the absorbing material exhibits relatively stable absorbing performance, and the reflectivity is lower than -10 dB throughout the X-band; when the incident angle of the electromagnetic wave is greater than 45°, the absorption bandwidth of the material gradually narrows, the intensity of the absorption peak gradually weakens, and the absorbing performance deteriorates.

[0090] Figure 9 This is the response of the reflectivity of the NZSP absorbing coating with a three-dimensional periodic structure to the incident angle of the electromagnetic wave in the TM polarization mode. As Figure 8 shown, when the incident angle of the electromagnetic wave is between 0 and 30°, the absorbing material exhibits relatively stable absorbing performance, and when the incident angle of the electromagnetic wave is greater than 45°, the absorbing performance deteriorates.

[0091] The results show that when the incident angle of the electromagnetic wave is between 0 and 30°, for electromagnetic waves with different polarization modes, the NZSP absorbing coating with a three-dimensional periodic structure can generate effective electromagnetic coupling and loss inside the structure, so as to achieve the absorption of electromagnetic waves in different polarization states and exhibit relatively stable absorbing performance.

[0092] The above are only embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent structural changes made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a NZSP absorbing coating having a three-dimensional periodic structure, characterized in that: The steps include: Step 1, obtaining NZSP spherical powder; Step 2: spraying NZSP spherical powder on the substrate to obtain a first coating (11); Step 3, determining the shape of the periodic unit; determining the optimized geometric parameters of the periodic unit, the geometric parameters at least including the maximum length, the maximum width and the preset height; a plurality of periodic units are arranged into a periodic structure according to a regular spatial array; Step 4: Spreading NZSP spherical powder on the first coating layer; using laser sintering to sinter the NZSP spherical powder spread on the first coating layer, the cross-sectional shape of the sintered area is consistent with the cross-sectional shape of the periodic structure; Step 5, repeating step 4, spreading powder layer by layer, and sintering cumulatively until the height of the periodic unit reaches a preset height, completing laser sintering, and obtaining a second coating (10); Step six: The first coating (11) and the second coating (10) together form a NZSP absorbing coating with a three-dimensional periodic structure.

2. The method for preparing a NZSP absorbing coating having a three-dimensional periodic structure according to claim 1, characterized in that: The periodic unit is a rectangular shape, which includes: A first rectangular patch (101), and a third rectangular patch (103) having the same structure as the first rectangular patch (101) and symmetrically distributed about the X-axis; A second rectangular patch (102), and a fourth rectangular patch (104) having the same structure as the second rectangular patch (102) and symmetrically distributed about the Y axis; The X-axis and the Y-axis are perpendicular to each other; The minimum width between the first rectangular patch (101) and the third rectangular patch (103) is not less than the length of the second rectangular patch (102); The minimum length between the second rectangular patch (102) and the fourth rectangular patch (104) is not less than the length of the first rectangular patch (101).

3. The method for preparing a NZSP absorbing coating having a three-dimensional periodic structure according to claim 1, characterized in that: A regular spatial array means that the periodic units are distributed in rows and columns, the periodic units in each row are evenly distributed, and the periodic units in each column are evenly distributed.

4. The method for preparing a NZSP absorbing coating having a three-dimensional periodic structure according to claim 1 or 2, characterized in that: In step 3, the specific steps for determining the optimized geometric parameters of the periodic unit are: Step 301, defining geometric parameters of periodic units, and arranging the periodic units into a periodic structure according to a regular spatial array; Step 302: define the objective function, select the geometric parameters of the periodic unit as optimization variables, use the genetic algorithm as the optimization method, adjust the optimization variables, and calculate the value of the objective function; Step 303: The geometric parameter combination that minimizes the value of the objective function is used as the optimized geometric parameter of the periodic unit.

5. The method for preparing a NZSP absorbing coating having a three-dimensional periodic structure according to claim 4, characterized in that: The objective function includes the reflection loss integral term and the bandwidth function term.

6. The method for preparing a NZSP absorbing coating having a three-dimensional periodic structure according to claim 1, characterized in that: The NZSP spherical powder in step 1 is mixed with an absorbent.

7. The method for preparing a NZSP absorbing coating having a three-dimensional periodic structure according to claim 6, characterized in that: The absorber is one of SiC, TiN, SrTiO3 and ITO.

8. The method for preparing a NZSP absorbing coating having a three-dimensional periodic structure according to claim 1, characterized in that: The specific method for obtaining NZSP spherical powder is: Step 101, mixing a sodium source, a zirconium source, a silicon source and a phosphorus source and putting them into a ball mill; Step 102, adding ethanol to a ball mill, wet ball milling, and after the ball milling is completed, taking out and drying to obtain a reactant powder; Step 103, calcining the reactant powder at 1180-1220° C. for 5-7 hours, cooling and grinding after calcination to obtain NZSP coarse ground particles; Step 104, the NZSP coarsely ground particles are introduced into a ball mill, distilled water is added, and wet ball milling is performed. After the ball milling is completed, a mixed solution is obtained; Step 105: Add a defoamer and a binder to the mixed solution, then add the mixed solution to a spray granulator, stir and granulate to obtain NZSP spherical powder.

9. The method for preparing a NZSP absorbing coating having a three-dimensional periodic structure according to claim 1, characterized in that: In step 2, when spraying the NZSP spherical powder on the substrate, supersonic plasma spraying is adopted.

10. A NZSP absorbing coating with a three-dimensional periodic structure, characterized in that: The first coating (11) and the second coating (10) together constitute a NZSP absorbing coating with a three-dimensional periodic structure, which is prepared by the preparation method according to any one of claims 1 to 9.

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