An NZSP absorbing coating with a three-dimensional periodic structure and a preparation method thereof

Abstract

The present invention relates to the technical field of coatings for absorbing electromagnetic waves, and discloses a method for preparing an NZSP absorbing coating having a three-dimensional periodic structure, comprising the following steps: Step 1: obtaining NZSP spherical powder; Step 2: spraying the NZSP spherical powder onto a substrate to obtain a first coating; Step 3: determining the shape of periodic units; arranging the periodic units into a periodic structure according to a regular spatial array; Step 4: laser sintering the NZSP spherical powder spread on the first coating; Step 5: applying the powder layer by layer and cumulatively sintering until a preset height is reached to obtain a second coating; Step 6: the first and second coatings constitute an NZSP absorbing coating having a three-dimensional periodic structure. The present invention utilizes NZSP spherical powder to produce the first and second coatings, and has outstanding advantages in weight reduction applications. The macroscopic design of the periodic structure expands the absorption bandwidth of the NZSP absorbing coating, improving its absorbing performance and making it suitable for the aerospace field.

Description

Technical Field

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

[0002] NZSP refers to NASICON type Na3Zr2Si2PO 12 As a highly anticipated ceramic material, NZSP ceramics exhibit a series of unique and valuable properties. In terms of wave absorption, they can effectively absorb electromagnetic waves of a specific frequency; their structure is stable at high temperatures and they are not easily chemically reacted with oxygen and moisture in the air; and they can resist a certain degree of acid and alkali corrosion, which makes them potentially applicable in a variety of complex environments. The theoretical density of NZSP ceramics is 3.24g·cm -3 Compared to other absorbing materials, NZSP ceramics have an extremely low density. This low-density characteristic has brought a major breakthrough in the field of absorbing materials, effectively reducing the weight of absorbing materials and greatly facilitating the lightweight design and manufacturing of related equipment. Furthermore, NZSP ceramics also have significant advantages in raw material acquisition and preparation processes. Their raw materials are extremely abundant and widely found in nature, providing a solid material foundation for large-scale production. Furthermore, the preparation process is relatively easy, requiring no complex and expensive equipment or technology, significantly reducing production costs and improving production efficiency.

[0003] However, the transformation of NZSP ceramics into practical applications has not been smooth sailing, and there are some urgent problems to be solved. Due to the low thermal conductivity of NZSP powder, it is difficult to completely melt in the fast plasma jet. Instead, it hits the substrate in a semi-molten form and solidifies, forming a relatively loose coating. Therefore, the resulting absorbing coating has relatively low absorbing performance and cannot meet some application scenarios with high requirements for absorbing performance. In the field of absorbing materials, the following common methods are used to expand the absorption bandwidth of NZSP ceramics: composite doping, constructing multilayer structures, nanostructuring, and designing macrostructures. Component design has a limited range of performance control, making it difficult to further expand the absorption bandwidth, and it needs to be improved through the design of macrostructures. Therefore, there is a need for an NZSP absorbing coating that improves absorbing performance through macrostructure design. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned prior art and provide a NZSP absorbing coating with a three-dimensional periodic structure and a preparation method. The coating has a simple structure and a reasonable design. The first and second coating layers are made from NZSP spherical powder, which has outstanding advantages in weight reduction applications and is suitable for the aerospace field. The macroscopic design of the periodic structure expands the absorption bandwidth of the NZSP absorbing coating, improves the absorbing performance, and reduces electromagnetic interference. The periodic structure of the second coating layer is prepared by laser selective sintering, which provides design freedom.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] In a first aspect, the present invention provides a method for preparing an NZSP absorbing coating having a three-dimensional periodic structure, characterized in that the method comprises the following steps:

[0007] Step 1: Obtain NZSP spherical powder;

[0008] Step 2: spraying NZSP spherical powder on the substrate to obtain a first coating;

[0009] Step 3: Determine the shape of the periodic unit; determine the optimized geometric parameters of the periodic unit, the geometric parameters including at least the maximum length, maximum width and preset height; arrange the periodic units into a periodic structure according to a regular spatial array;

[0010] Step 4: Spreading NZSP spherical powder on the first coating layer; Sintering the NZSP spherical powder spread on the first coating layer by laser, so that the cross-sectional shape of the sintered area is consistent with the cross-sectional shape of the periodic structure;

[0011] Step 5: Repeat step 4, spreading powder layer by layer, accumulating and sintering until the height of the periodic unit reaches the preset height, completing laser sintering to obtain the second coating;

[0012] Step 6: The first coating layer and the second coating layer together form a NZSP absorbing coating layer with a three-dimensional periodic structure.

[0013] The above-mentioned method for preparing an NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: the periodic unit is a rectangular shape, and the rectangular shape 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, and 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; and the minimum length between the second rectangular patch and the fourth rectangular patch is not less than the length of the first rectangular patch.

[0014] The above-mentioned method for preparing a NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: 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.

[0015] The above-mentioned method for preparing a NZSP absorbing coating having a three-dimensional periodic structure is characterized in that: in step 3, the specific steps of determining the optimized geometric parameters of the periodic unit are:

[0016] Step 301: define geometric parameters of periodic units and arrange the periodic units into a periodic structure according to a regular spatial array;

[0017] 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;

[0018] 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.

[0019] The above-mentioned method for preparing the 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.

[0020] The above-mentioned method for preparing the NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: the NZSP spherical powder in step 1 is mixed with an absorbent.

[0021] The above-mentioned method for preparing the NZSP absorbing coating with a three-dimensional periodic structure is characterized in that the absorber is one of SiC, TiN, SrTiO3 and ITO.

[0022] The above-mentioned method for preparing a NZSP absorbing coating with a three-dimensional periodic structure is characterized in that the specific method for obtaining NZSP spherical powder is:

[0023] Step 101: Mix a sodium source, a zirconium source, a silicon source, and a phosphorus source and put them into a ball mill;

[0024] Step 102: adding ethanol to a ball mill, and wet-milling the mixture. After the milling is completed, the mixture is taken out and dried to obtain a reactant powder;

[0025] Step 103: calcining the reactant powder at 1180-1220° C. for 5-7 hours, cooling and grinding the reactant powder to obtain NZSP coarse ground particles;

[0026] Step 104: The coarsely ground NZSP 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;

[0027] Step 105: Add a defoamer and a binder to the mixed solution, then add the solution to a spray granulator, stir and granulate to obtain NZSP spherical powder.

[0028] The above-mentioned method for preparing the NZSP absorbing coating with a three-dimensional periodic structure is characterized in that: in step 2, when spraying the NZSP spherical powder on the substrate, supersonic plasma spraying is adopted.

[0029] In a second aspect, the present invention provides a NZSP absorbing coating with a three-dimensional periodic structure, characterized in that: the first coating and the second coating together constitute the NZSP absorbing coating with a three-dimensional periodic structure, which is prepared by any of the above preparation methods.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. The present invention has a simple structure, reasonable design, and is easy to implement and operate.

[0032] 2. The present invention uses NZSP spherical powder to make the first coating and the second coating. Due to the low density of NZSP, the weight is significantly reduced, which has outstanding advantages in weight reduction applications. At the same time, it has excellent wave absorption performance and high-temperature stability, and is suitable for the aerospace field.

[0033] 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, cover multiple frequency ranges, achieve broadband absorption, further improve the absorbing performance, reduce electromagnetic interference, and have a good use effect.

[0034] 4. The present invention uses laser selective sintering to prepare the periodic structure of the second coating. The NZSP spherical powder is selectively sintered by a computer-controlled laser beam, which provides design freedom. Layer-by-layer melting can produce relatively complex three-dimensional periodic structures. Only specific areas of the NZSP spherical powder are scanned and sintered, and the unsintered NZSP spherical powder can be used as support and recycled.

[0035] In summary, the present invention has a simple structure and reasonable design. The first and second coatings are made from NZSP spherical powder, which has outstanding advantages in weight reduction applications and is suitable for the aerospace field. The macroscopic design of the periodic structure expands the absorption bandwidth of the NZSP absorbing coating, improves the absorbing performance, and reduces electromagnetic interference. The periodic structure of the second coating is prepared by laser selective sintering, which has design freedom.

[0036] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Flow chart of the method of the present invention.

[0038] Figure 2 This is a flow chart of the method for obtaining NZSP spherical powder according to the present invention.

[0039] Figure 3 Schematic diagram of the structure of the NZSP absorbing coating with a three-dimensional periodic structure of the present invention.

[0040] Figure 4 It is a schematic diagram of the rectangular structure of the present invention.

[0041] Figure 5 Schematic diagram of geometric parameters of the rectangular shape of the present invention.

[0042] Figure 6 This is the reflection loss spectrum of the NZSP absorbing coating with a non-periodic structure.

[0043] Figure 7 This is a graph showing the reflection loss bandwidth characteristics of the NZSP absorbing coating with a three-dimensional periodic structure.

[0044] Figure 8 Response of the NZSP absorbing coating with periodic structure to the reflectivity under TE polarization mode according to the incident angle of electromagnetic waves in the second embodiment of the present invention.

[0045] Figure 9 Response of the NZSP absorbing coating with periodic structure to the reflectivity under TM polarization mode according to the incident angle of electromagnetic waves in the second embodiment of the present invention.

[0046] Description of the accompanying drawings:

[0047] 10—second coating layer; 11—first coating layer; 101—first rectangular patch; 102—second rectangular patch; 103—third rectangular patch; 104—fourth rectangular patch. DETAILED DESCRIPTION

[0048] The method of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments of the present invention.

[0049] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0050] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, 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.

[0051] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0052] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0053] Example 1

[0054] like Figure 1 As shown, the method for preparing a NZSP absorbing coating having a three-dimensional periodic structure of the present invention comprises the following steps:

[0055] Step 1: Obtain NZSP spherical powder.

[0056] like Figure 2 As shown, in one possible embodiment, the specific method for obtaining NZSP spherical powder is:

[0057] Step 101: Mix a sodium source, a zirconium source, a silicon source, and a phosphorus source and put them into a ball mill.

[0058] In one possible embodiment, both the sodium source and the phosphorus source are Na3PO 12 12H2O, ZrO2 as zirconium source, SiO2 as silicon source, Na3PO 12The molar ratio of 12H2O, ZrO2, and SiO2 is 1.15:1.8:2.

[0059] Step 102: Add ethanol to a ball mill and wet-mill for 12-24 hours. After the ball milling is completed, remove the reactant and dry it to obtain a reactant powder;

[0060] Step 103: calcining the reactant powder at 1180-1220° C. for 5-7 hours, cooling and grinding the reactant powder to obtain NZSP coarse ground particles;

[0061] Step 104: The coarsely ground NZSP particles are introduced into a ball mill, distilled water is added, and wet ball milling is performed for 12-16 hours. After the ball milling is completed, a mixed solution is obtained;

[0062] Step 105: Add defoamer and binder to the mixed solution, then add it to a spray granulator, stir and granulate to obtain NZSP spherical powder. In actual use, the binder is a PVA solution.

[0063] The inlet air temperature of the spray granulator is 290-310℃, the air temperature in the cavity is 130-150℃, the outlet air temperature is 100-120℃, the nozzle rotation speed is 28000-30000r / min, the feed rate is 110-120g / min, and the atomizing air flow rate is 20-22m 3 / h.

[0064] NZSP was chosen as the absorbing coating material because, firstly, its low density allows the resulting absorbing coating to effectively reduce the overall load in applications, particularly those with strict weight requirements, such as aerospace. Secondly, NZSP's coefficient of thermal expansion is highly compatible with common metal materials. This excellent compatibility ensures a stable bond between the NZSP absorbing coating and the metal substrate under varying temperatures, significantly improving the coating's durability and reliability. Thirdly, NZSP inherently possesses a certain degree of absorbing capability, eliminating the need for modification or compounding to achieve absorbing properties, which directly impacts the improvement of absorbing performance.

[0065] Step 2: Spray NZSP spherical powder onto the substrate to obtain a first coating layer 11.

[0066] The substrate is first sandblasted and then sprayed with NZSP spherical powder using supersonic plasma spraying. The supersonic plasma spraying parameters are set as follows: voltage 120-130V, current 360-380A, argon flow rate 65-70L / min, hydrogen flow rate 15-20L / min, powder feed rate 30-35g / min, spray distance 90-100mm, and coating thickness 1.8-2.4mm. It should be noted that the substrate can be an aircraft engine inlet, engine fan, radome, combustion chamber, wing, tail, or other workpieces that are easily reflective of radar waves.

[0067] Supersonic plasma spraying enables the NZSP spherical powder to achieve extremely high speeds and temperatures, allowing it to melt more fully, making the first coating 11 denser and ensuring good absorbing performance. It also significantly improves the bonding strength between the NZSP spherical powder and the substrate surface, making the first coating 11 more firmly and lastingly bonded to 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 the required thickness, meeting the requirements of different substrates for absorbing coatings.

[0068] Step 3: Determine the shape of the periodic unit; determine the optimized geometric parameters of the periodic unit, which include at least a maximum length, a maximum width, and a preset height; and arrange several periodic units into a periodic structure according to a regular spatial array.

[0069] like Figure 3 、 Figure 4 and Figure 5 As shown, in a possible embodiment, the periodic unit is a rectangular shape, which includes: a first rectangular patch 101, 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; and 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.

[0070] like Figure 5 As shown, more specific linear constraints on the geometric parameters of the rectangle are: , where C1 represents the maximum width of the rectangle, that is, the maximum width between the first rectangular patch 101 and the third rectangular patch 103; C2 represents the maximum length of the rectangle, 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, and d1 represents the thickness of the first rectangular patch 101. x represents the distance between the second rectangular patch 102 and the fourth rectangular patch 104, 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.

[0071] Periodic units can also take the form of rectangles, circles, triangles, or crosses. However, the rectangular shape offers advantages over the conventional one: ease of design and control, good polarization properties, and ease of fabrication and processing. Furthermore, rectangular patterns can be easily integrated with other materials or structures to form composite absorbers, further enhancing their absorbing properties.

[0072] 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:

[0073] Step 301: Define the geometric parameters of the periodic units and arrange them into a periodic structure in a regular spatial array. In one embodiment, the regular spatial array means that the periodic units are arranged in rows and columns, with the periodic units evenly distributed across rows and columns. By varying the periodic unit units, geometric parameters, spatial array arrangement, and material parameters, the performance of the absorbing material can be easily adjusted to meet different application requirements.

[0074] For example, in HFSS software, define the shape and geometric parameters of the rectangular shape, copy the periodic units of the rectangular shape, and arrange them into a periodic array according to a 10x10 array with equal row spacing and column spacing.

[0075] Then set the master-slave boundaries and Floquet excitation ports, enter the material name, such as NZSP, define the coating material properties and periodic structure material properties, that is, import the material electromagnetic parameters measured by the network analyzer, and set the corresponding frequency range in the sweep setting, for example, 8.2~12.4GHz. The frequency change step size is consistent with the frequency change step size output by the vector network analyzer, which is 0.021GHz.

[0076] 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.

[0077] In actual use, the objective function includes the reflection loss integral term and the bandwidth function term. ,in Reflection loss exist Integration over frequency range; Represents the proportion of reflection loss to the total performance; Represents the ratio of bandwidth to total performance, where is negative; represents the bandwidth function; , represents the dielectric constant of the absorbing material, Represents the electromagnetic parameters of 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 shape, C2 represents the maximum length of the rectangular shape, D2 represents the length of the outer rectangle of the rectangular shape, and D1 represents the width of the outer rectangle of the rectangular shape. represents the functional relationship between RL and ε, μ, h, C, and D, It can be determined by electromagnetic theory modeling or experimental data fitting.

[0078] The geometric parameters of the periodic structure were selected as optimization variables, and the optimization variables were adjusted, with a range set, such as length from 2 mm to 5 mm. A genetic algorithm was then used as the optimization method, using a uniform crossover model. The probability of individual crossover was set to 90%, and the probability of single-point crossover was set to 50%. The number of individuals in the first generation, the number of individuals in the mating pool, the number of offspring individuals, and the number of individuals in the next generation were all set to 30. Roulette selection was enabled, and the optimization stopped at 500 generations. The range of h was set to 0.5 mm to 2.2 mm, the range of t was set to 0.01 mm to 1 mm, and the range of the remaining geometric parameters was set to 0.5 mm to 30.0 mm.

[0079] 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. 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, achieving the objective function Minimize the objective function The minimized geometric parameters have the best wave absorbing performance, and the combination of the geometric parameters is determined as the optimized geometric parameters of the periodic structure.

[0080] The periodic units with determined shapes and optimized geometric parameters are arranged into a periodic structure in a regular spatial array.

[0081] Step 4: Spread NZSP spherical powder on the first coating layer; and sinter the NZSP spherical powder spread on the first coating layer 11 by laser sintering, so that the cross-sectional shape of the sintered area is consistent with the cross-sectional shape of the periodic structure.

[0082] In one possible embodiment, 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 then used to selectively melt the NZSP spherical powder, so that the cross-sectional shape of the sintered region matches that of the periodic structure. For example, a path is generated by slicing a CAD model. A galvanometer system controls the laser beam to scan and sinter along a preset trajectory. The unsintered portion remains in a powdered state. The scanned and sintered NZSP spherical powder solidifies and bonds to the first coating 11, so that the cross-sectional shape of the sintered region matches that of the periodic structure.

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

[0084] In one possible embodiment, the accuracy of the periodic structure can be precisely controlled by adjusting the thickness of each powder layer. After each layer of NZSP spherical powder is sintered, the next layer of NZSP spherical powder is applied. Each newly sintered layer of powder firmly bonds with the layer below, enhancing the stability of the periodic structure. Layer-by-layer powder application and sintering allows for the construction of complex shapes, providing design freedom. It also reduces thermal stress, ensuring uniform heat distribution and avoiding localized overheating caused by sintering a large amount of powder at once, thereby improving the quality and performance of the periodic structure.

[0085] 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.

[0086] Selective laser sintering (SLS) is an additive manufacturing technology that eliminates the need for molds and selectively sinters NZSP spherical powders using a computer-controlled laser beam, offering design freedom. Layer-by-layer melting allows for the fabrication of complex three-dimensional periodic structures. By scanning and sintering only specific areas of NZSP spherical powder, the unsintered NZSP spherical powder can be used as support and recycled, resulting in excellent practical results.

[0087] The first coating layer 11 and the second coating layer 10 together constitute an NZSP absorbing coating having a three-dimensional periodic structure.

[0088] This application expands the absorption bandwidth of the NZSP absorbing coating through the macroscopic design of a periodic structure. The periodic structure can generate multiple resonance modes covering multiple frequency ranges, achieving broadband absorption and improving absorption performance. This can reduce the reflection and scattering of the aircraft's own electromagnetic signals by artifacts that easily reflect radar waves, thereby reducing electromagnetic interference. Both the coating and the periodic structure have excellent high-temperature stability, ensuring the normal operation of aircraft electronic equipment and improving the reliability and stability of avionics systems. The periodic structure is also easy to prepare, with a relatively mature process. It can be precisely fabricated on large substrates, with a simple process that facilitates mass production.

[0089] In this application, the NZSP absorbing coating with a three-dimensional periodic structure significantly reduces the weight due to its light and thin characteristics, while also having excellent absorbing performance and high-temperature stability. It has outstanding advantages in weight reduction applications and is suitable for the aerospace field, such as engine air intakes, engine fans, radomes, combustion chambers, wings, tail fins and other parts.

[0090] Example 2

[0091] Different from the first embodiment, in this embodiment, the NZSP spherical powder is mixed with an absorbent.

[0092] In actual use, the absorber powder is mixed with the NZSP spherical powder from step one, followed by ball milling and spray granulation to form the NZSP mixed powder. The NZSP mixed powder is sprayed onto a substrate to form a first coating 11 containing the absorber. Laser selective sintering is then used to sinter the NZSP mixed powder onto the first coating 11 to form a second coating 10, creating an NZSP absorbing coating with a three-dimensional periodic structure.

[0093] In one possible embodiment, the absorbent of the first coating 11 and the absorbent of the second coating 10 are the same. Using the same absorbent ensures that the microwave absorption performance and high-temperature resistance are matched, thereby improving synergy. Furthermore, using the same absorbent allows the first coating 11 and the second coating 10 to better bond at the microscopic level, forming a stable structure.

[0094] Adding absorber powder to NZSP spherical powder can avoid the problems of excessively thick NZSP coatings and weak interlayer bonding. The absorber can be one or more of SiC, TiN, SrTiO3, and ITO. Taking SiC as an example, adding SiC powder to NZSP spherical powder has unique electromagnetic properties that synergize with NZSP to enhance electromagnetic wave loss. Compared to the case without SiC, the required NZSP coating thickness is significantly reduced to achieve equivalent absorption performance. Furthermore, SiC powder can adsorb to the surface of the NZSP spherical powder, which helps strengthen the interaction between the layers and the powder particles between them. Furthermore, SiC powder can promote the formation of a more uniform and dense microstructure during sintering of the NZSP spherical powder, reducing interlayer porosity and defects and significantly improving interlayer bonding.

[0095] Example 3

[0096] The present invention provides an NZSP absorbing coating having a three-dimensional periodic structure. The first coating layer 11 and the second coating layer 10 together constitute the NZSP absorbing coating having a three-dimensional periodic structure. The preparation process is as follows:

[0097] Step 1: Obtain NZSP spherical powder.

[0098] Step 101: Obtain NZSP spherical powder based on a sodium source, a zirconium source, a silicon source, and a phosphorus source.

[0099] Both sodium and phosphorus sources are Na3PO 12 12H2O, ZrO2 as zirconium source, SiO2 as silicon source, Na3PO 12 The ratio of the amount of 12H2O, ZrO2 and SiO2 is 1.15:1.8:2. 12 12H2O, ZrO2 and SiO2 are mixed and placed in a ball mill;

[0100] Step 102: Add ethanol to a ball mill and wet-mill for 12-24 hours. After the ball milling is completed, remove the reactant and dry it to obtain a reactant powder;

[0101] Step 103: calcining the reactant powder at 1180-1220° C. for 5-7 hours, cooling and grinding the reactant powder to obtain NZSP coarse ground particles;

[0102] Step 104: The coarsely ground NZSP particles are introduced into a ball mill, distilled water is added, and wet ball milling is performed for 12-16 hours. After the ball milling is completed, a mixed solution is obtained;

[0103] Step 105: Add a defoamer and a binder to the mixed solution, then add the solution to a spray granulator, stir and granulate to obtain NZSP spherical powder.

[0104] The adhesive uses PVA solution. The inlet air temperature of the spray granulator is 290-310℃, the air temperature in the cavity is 130-150℃, the outlet air temperature is 100-120℃, the nozzle rotation speed is 28000-30000r / min, the feed rate is 110-120g / min, and the atomizing air flow rate is 20-22m 3 / h.

[0105] Step 2: Spray NZSP spherical powder onto the substrate to obtain a first coating layer 11.

[0106] The substrate is first sandblasted and then sprayed with NZSP spherical powder using supersonic plasma spraying. The supersonic plasma spraying parameters are set as follows: voltage 120-130V, current 360-380A, argon flow rate 65-70L / min, hydrogen flow rate 15-20L / min, powder feed rate 30-35g / min, spray distance 90-100mm, and coating thickness 1.8-2.4mm. It should be noted that the substrate can be an aircraft engine inlet, engine fan, radome, combustion chamber, wing, tail, or other workpieces that are easily reflective of radar waves.

[0107] Step 3: Determine the shape of the periodic unit; determine the optimized geometric parameters of the periodic unit, which include at least a maximum length, a maximum width, and a preset height; and arrange several periodic units into a periodic structure according to a regular spatial array.

[0108] In one possible embodiment, the periodic unit is a rectangular shape, which includes: a first rectangular patch 101, 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; and 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.

[0109] The periodic units are then arranged in a predetermined regular spatial array. In one possible embodiment, the regular spatial array means that the periodic units are arranged in rows and columns, with the periodic units in each row and each column being evenly distributed. For example, a 10x10 array is arranged to form a periodic array, with equal spacing between rows and columns.

[0110] The geometric parameters of the periodic structure are adjusted to minimize the integral term of the return loss and maximize the bandwidth function term. The geometric parameter combination that minimizes the value of the objective function is used as the optimized geometric parameters of the periodic unit. The geometric parameters include at least the maximum length, maximum width, and preset height. In this embodiment, a rectangular shape is used as the optimized geometric parameters of the periodic unit, as shown in Table 1:

[0111] Table 1 Optimized geometric parameters of the rectangular shape as a periodic unit

[0112]

[0113] After obtaining the optimized geometric parameters, the second coating 10 is prepared on the basis of the first coating 11, specifically:

[0114] Step 4: Spreading NZSP spherical powder on the first coating layer; Sintering the NZSP spherical powder spread on the first coating layer by laser, so that the cross-sectional shape of the sintered area is consistent with the cross-sectional shape of the periodic structure;

[0115] In one possible embodiment, NZSP spherical powder is evenly spread on the surface of the first coating 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. For example, a path is generated by slicing a CAD model, and a galvanometer system controls the laser beam to scan and sinter along a preset trajectory. The unscanned sintered portion remains in a powder state. The scanned and sintered NZSP spherical powder solidifies and combines with the first coating, so that the cross-sectional shape of the sintered area is consistent with the cross-sectional shape of the periodic structure.

[0116] Repeat step 4, apply powder layer by layer, and perform cumulative sintering until the height of the periodic unit reaches a preset height, complete laser sintering, and obtain the second coating 10.

[0117] The first coating layer 11 and the second coating layer 10 sintered on the first coating layer 11 by laser sintering together constitute an NZSP absorbing coating with a three-dimensional periodic structure.

[0118] During laser sintering, the laser power is 100-120W, the laser scanning speed is 200-300mm / s, and the laser spot diameter is 0.1-0.2mm.

[0119] Performance Test 1

[0120] The NZSP absorbing coating without a periodic structure is recorded as Sample 1, and the NZSP absorbing coating with a three-dimensional periodic structure in Example 3 is recorded as Sample 2. Figure 6 This is the reflection loss spectrum of sample 1. It can be seen that the absorption bandwidth is 2.69 GHz when RL < -10 dB, and the bandwidth is 0 GHz when RL < -15 dB. Figure 7The reflection loss bandwidth characteristic diagram of sample 2 shows that when RL < -15dB, the bandwidth is 3.38GHz. The absorption performance of samples 1 and 2 is compared, as shown in Table 2:

[0121] Table 2 Comparison of wave absorption performance

[0122]

[0123] Compared with sample 1, sample 2 has significantly improved the absorption performance, reduced the thickness, and reduced the minimum reflectivity, especially in the absorption bandwidth, with obvious improvements. It can cover the absorption bandwidth of RL<-10dB to the entire X-band, and expand the absorption bandwidth of RL<-15dB from 0GHz to 3.38GHz.

[0124] Performance Test 2

[0125] The NZSP absorbing coating with a three-dimensional periodic structure prepared in Example 3 was tested for its effect on reflectivity under different polarization modes and different electromagnetic wave incident angles to evaluate the stability of the absorbing performance of the absorbing coating and its absorbing effect under different conditions.

[0126] Figure 8 The response of the NZSP absorbing coating with a three-dimensional periodic structure to the reflectivity under the TE polarization mode is shown in Figure 2. Figure 8 As shown in the figure, by varying the incident angle of the electromagnetic wave from 0° to various angles, the reflectivity of the NZSP absorbing coating with a three-dimensional periodic structure was observed, thereby analyzing 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, with the reflectivity remaining below -10dB throughout the entire X-band. When the incident angle of the electromagnetic wave exceeds 45°, the material's absorption bandwidth gradually narrows, the absorption peak intensity gradually weakens, and the absorbing performance deteriorates.

[0127] Figure 9 The response of the NZSP absorbing coating with a three-dimensional periodic structure to the reflectivity under the TM polarization mode is shown in Figure 2. Figure 8 As shown in FIG, 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.

[0128] The results show that when the incident angle of the electromagnetic wave is between 0 and 30°, the NZSP absorbing coating with a three-dimensional periodic structure can generate effective electromagnetic coupling and loss within the structure for electromagnetic waves of different polarization modes, thereby achieving absorption of electromagnetic waves of different polarization states and exhibiting relatively stable absorbing performance.

[0129] The above description is merely an embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention shall still fall within the scope of protection 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: Obtain NZSP spherical powder; Step 2: spraying NZSP spherical powder on the substrate to obtain a first coating (11); Step 3: Determine the shape of the periodic unit; determine the optimized geometric parameters of the periodic unit, the geometric parameters including at least the maximum length, maximum width and preset height; arrange the periodic units into a periodic structure according to a regular spatial array; Step 4: Spreading NZSP spherical powder on the first coating layer; Sintering the NZSP spherical powder spread on the first coating layer by laser, so that the cross-sectional shape of the sintered area is consistent with the cross-sectional shape of the periodic structure; Step 5: Repeat step 4, spreading powder layer by layer, accumulating and sintering until the height of the periodic unit reaches a preset height, completing laser sintering to obtain a second coating (10); Step 6: The first coating (11) and the second coating (10) together form an 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 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: define geometric parameters of periodic units and arrange 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: Mix a sodium source, a zirconium source, a silicon source, and a phosphorus source and put them into a ball mill; Step 102: adding ethanol to a ball mill, and wet-milling the mixture. After the milling is completed, the mixture is taken out and dried to obtain a reactant powder; Step 103: calcining the reactant powder at 1180-1220° C. for 5-7 hours, cooling and grinding the reactant powder to obtain NZSP coarse ground particles; Step 104: The coarsely ground NZSP 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 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 NZSP spherical powder on the substrate, supersonic plasma spraying is adopted.

10. A NZSP absorbing coating having a three-dimensional periodic structure, characterized in that: The first coating (11) and the second coating (10) together constitute an 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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