Low-temperature porous nasicon stealth material and preparation method thereof

Abstract

The application provides a low-temperature porous NASICON stealth material and a preparation method thereof, and belongs to the technical field of porous ceramic materials. The method comprises the following steps: mixing Na3PO4.12H2O, SiO2 and ZrO2 weighed according to a stoichiometric ratio and 10wt%-50wt% excess Na3PO4.12H2O, ball milling, and drying to obtain a pre-preparation powder; performing three-step heat treatment on the pre-preparation powder, and sequentially keeping at 600 DEG C, 700 DEG C and 900 DEG C to obtain an intermediate powder; after secondary ball milling and drying of the intermediate powder, mixing the intermediate powder with a polyvinyl alcohol solution, and performing freeze drying to form a porous pre-preparation body; and finally sintering at 900 DEG C to obtain the material. The application successfully constructs a three-dimensional connected porous structure with uniform pores. The method is simple, and the prepared material has excellent thermal stability of the NASICON phase and the light weight, wave absorption characteristics of the porous structure, and is suitable for the field of high-temperature stealth.

Description

Technical Field

[0001] This invention relates to the field of porous ceramic materials technology, and more specifically, to a low-temperature porous NASICON stealth material and its preparation method. Background Technology

[0002] Radar stealth technology is one of the key technologies in modern defense equipment. Its core lies in using microwave absorbing materials to reduce the radar cross-section of a target. An ideal absorbing material must meet the requirements of being "thin, light, wide, and strong" (i.e., thin, lightweight, with a wide absorption bandwidth and strong absorption capacity), while also maintaining stable performance under harsh environments such as high temperature, high humidity, and corrosion. Therefore, developing new high-temperature resistant, lightweight, and efficient absorbing materials is of great significance.

[0003] Porous ceramic materials, due to their unique structure, have shown great potential in the field of stealth. The pores within the material can effectively regulate impedance matching, allowing radar waves to penetrate the material; simultaneously, the pore interfaces can cause multiple reflections and scattering of radar waves, thus converting electromagnetic energy into heat energy for dissipation. Furthermore, the porous structure also brings the advantage of lightweight design. Currently, the most studied porous stealth ceramics include Al2O3, Si3N4, and SiC. However, these materials still have limitations in some aspects, such as high sintering temperatures, insufficient toughness, or the need to improve chemical stability.

[0004] NASICON-type materials, a typical example of which is Na3Zr2Si2PO4 12 NZSP (Nephrite Solids Polymer), a fast sodium-ion conductor, has attracted attention due to its excellent thermal stability, chemical stability, and structural designability. Designing it as a porous structure holds promise for combining the microwave absorption mechanism of porous materials with the intrinsic high-temperature resistance and good stability of NASICON materials, making it a promising new high-temperature stealth material. However, the traditional solid-state sintering temperature of NASICON materials is typically high (usually above 1200℃), which not only consumes a lot of energy but also easily leads to excessive grain growth and reduced porosity at high temperatures, hindering the formation of an ideal porous microwave absorption structure. Therefore, developing a method to prepare NASICON stealth materials with a good porous structure at relatively low temperatures (e.g., around 900℃) has become a pressing technical problem in this field. Summary of the Invention

[0005] (a) Technical problems to be solved The technical problem to be solved by this invention is that the traditional solid-state sintering temperature of NASICON materials is usually high (usually above 1200°C), which not only consumes a lot of energy, but also easily leads to excessive grain growth and reduced porosity at high temperatures, which is not conducive to the formation of an ideal porous microwave absorbing structure.

[0006] (II) Technical Solution To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, this aspect provides a method for preparing a low-temperature porous NASICON stealth material, comprising the following steps: S1. Weigh the raw materials Na3PO4·12H2O, SiO2 and ZrO according to the stoichiometric ratio, mix them with excess Na3PO4·12H2O, and obtain the pre-made powder by ball milling and drying for the first time. S2. The pre-formed powder is subjected to multi-stage heat treatment: first, the temperature is raised to 600℃ and held, then the temperature is raised to 700℃ and held, and finally the temperature is raised to 900℃ and held to obtain intermediate powder. This step-by-step heat treatment is beneficial to the decomposition of sodium source, the generation and transformation of intermediate phase, and the initial development of grains, laying the foundation for final low-temperature sintering.

[0007] S3. The intermediate powder is ball-milled and dried a second time to further refine the particles and improve the activity, so as to obtain a secondary-treated powder with better dispersibility and higher activity. S4. The secondary processed powder is mixed with polyvinyl alcohol (PVA) solution at a mass ratio of 1:1 to 1:10, and then freeze-dried to form a porous preform. The vacuum degree of the freeze-drying is 1-10 Pa, and the processing time is 6-48 hours. During this process, the water in the PVA solution sublimates, leaving a three-dimensional network skeleton maintained by the PVA binder, thereby forming a precursor with a porous structure.

[0008] S5. The porous preform is sintered at 900°C to obtain the low-temperature porous NASICON stealth material. During the sintering process, the PVA binder is decomposed and removed, and a strong sintering neck is formed between the NASICON grains, ultimately resulting in a low-temperature porous NASICON stealth material with a stable porous structure.

[0009] Preferably, in step S1, the medium for the first ball milling is agate balls, the solvent is anhydrous ethanol, the ball milling speed is 100-900 r / min, and the ball milling time is 1-12 hours; the drying temperature is 50-70℃, and the drying time is 2-8 hours.

[0010] Preferably, in step S2, the specific process of the multi-stage heat treatment is as follows: heating to 600°C at a heating rate of 1-4°C / min and holding for 2-10 hours; then heating to 700°C at a heating rate of 1-4°C / min and holding for 2-10 hours; then heating to 900°C at a heating rate of 1-8°C / min and holding for 2 hours.

[0011] Preferably, the heating rates to 600℃, 600℃ to 700℃, and 700℃ to 900℃ are all 1℃ / min, and the holding time at 600℃ is 10 hours. The staged heating with a relatively slow heating rate and sufficient low-temperature holding are beneficial to the complete decomposition of phosphate and uniform reaction.

[0012] Preferably, in step S3, the medium for the second ball milling is agate balls, the solvent is anhydrous ethanol, the ball milling speed is 100-900 r / min, and the ball milling time is 3-24 hours; the drying temperature is 50-70℃, and the drying time is 2-8 hours.

[0013] Preferably, in step S3, the second ball milling speed is 300-500 r / min, and the milling time is 5 hours. Appropriate secondary ball milling can effectively break up the soft agglomerates generated after the first heat treatment, obtaining finer and more uniform powder, which is beneficial for the subsequent formation of a fine porous structure.

[0014] Preferably, in step S4, the mass percentage concentration of the polyvinyl alcohol solution is 5%.

[0015] Preferably, in step S1, the mass fraction of Na3PO4·12H2O ranges from 10wt% to 50wt%. The addition of excess sodium source can compensate for volatilization loss at high temperatures and act as a flux, effectively reducing the synthesis and sintering temperature of the material.

[0016] Preferably, in step S4, the mixing mass ratio of the secondary processed powder to the polyvinyl alcohol solution is 1:1:1 to 1:10, the vacuum degree of the freeze-drying is 1-10 Pa, and the processing time is 6-48 hours. These conditions are conducive to forming an ideal porous framework with uniform pore size and good pore connectivity.

[0017] Secondly, the present invention also provides a low-temperature porous NASICON stealth material prepared by the aforementioned method. The chemical composition of this material is mainly Na3Zr2Si2PO4. 12 Its microscopic feature lies in its three-dimensional interconnected porous structure formed through freeze-drying and low-temperature sintering. This structure endows the material with lightweight properties and a high specific surface area, and achieves effective absorption through multiple reflections and scattering of electromagnetic waves.

[0018] (III) Beneficial Effects The above-described technical solution of the present invention has at least the following advantages: 1. This invention introduces excess Na3PO4·12H2O as a volatile sodium source and flux, and combines it with an optimized three-step heat treatment process, so that the synthesis and densification sintering of the final NASICON phase can be completed at a relatively low temperature of 900℃. Compared with the traditional solid-state method (>1200℃), this significantly reduces energy consumption and suppresses abnormal grain growth.

[0019] 2. This invention innovatively uses PVA solution as a binder combined with freeze-drying technology. The porous template left by ice crystal sublimation during freeze-drying is preserved and solidified after low-temperature sintering, thereby preparing a three-dimensional porous network structure with uniform pore size, controllable distribution, and good connectivity. This structure is highly advantageous for achieving impedance matching and multiple reflection absorption of radar waves.

[0020] 3. The method provided by this invention uses conventional solid-phase ball milling and heat treatment equipment, combined with mature freeze-drying technology. The steps are clear, the parameters are controllable, and it is easy to achieve batch preparation, which has good prospects for industrial application.

[0021] 4. The porous NASICON material prepared by this invention inherits the excellent thermal and chemical stability of NASICON materials, making it suitable for stealth applications in harsh environments such as high temperature and corrosion. At the same time, the unique low-temperature porous preparation process avoids damage to the pore structure caused by high temperatures, enabling the material to maintain structural stability while achieving lightweight design. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a morphological diagram of the low-temperature porous NASICON stealth material provided in an embodiment of the present invention.

[0024] Figure 2 This is an XRD pattern of the low-temperature porous NASICON stealth material provided in an embodiment of the present invention. Detailed Implementation

[0025] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0026] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0027] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments: Example 1 (1) Prepare a 5wt% PVA solution.

[0029] (2) Weigh the raw materials Na3PO4·12H2O, SiO2 and ZrO2 according to the stoichiometric ratio.

[0030] (3) Add 10wt% Na3PO4·12H2O.

[0031] (4) Add the mixture from step (3) into a polytetrafluoroethylene ball milling jar, use agate balls as the milling medium, pour in a certain amount of anhydrous ethanol, and mill for 5 hours at a milling speed of 300 r / min.

[0032] (5) Dry the mixed slurry in step (4) at a temperature of 50°C for 8 hours to obtain pre-made powder.

[0033] (6) Place the pre-made powder from step (5) into a muffle furnace and heat it to 600°C at a rate of 1°C / min, and hold it for 10 hours.

[0034] (7) Continue heating the pre-made powder from step (6) to 700°C at a heating rate of 1°C / min and keep it at that temperature for 2-10 hours.

[0035] (8) The pre-made powder in step (7) is heated to 900°C at a rate of 1°C / min, kept at that temperature for 2 hours, and then cooled to room temperature before being taken out for use to obtain intermediate powder.

[0036] (9) The intermediate powder from step (8) is added to a polytetrafluoroethylene ball milling jar, agate balls are used as the ball milling medium, a certain amount of anhydrous ethanol is poured in, and the ball milling is carried out for 5 hours at a speed of 300 r / min.

[0037] (10) Dry the mixed slurry in step (9) at a temperature of 50°C for 8 hours to obtain a secondary processed powder with better dispersibility and higher activity.

[0038] (11) A certain amount of 5wt% PVA solution was measured and mixed with the secondary processed powder at a ratio of 1:10. The mixture was then placed in a freeze dryer for processing. The vacuum degree was 3Pa and the processing time was 48h to obtain a porous preform.

[0039] (12) The porous preform is placed in a muffle furnace and heated to 900°C at a rate of 1°C / min. It is held for 5 hours and then removed after cooling to room temperature to obtain low-temperature porous NASICON material.

[0040] The low-temperature porous NASICON material prepared in this embodiment was tested for microwave absorption. The minimum reflectivity value was -18dB, and the reflectivity of less than -5dB covered the entire X-band.

[0041] Example 2 (1) Prepare a 5wt% PVA solution.

[0042] (2) Weigh the raw materials Na3PO4·12H2O, SiO2 and ZrO2 according to the stoichiometric ratio.

[0043] (3) Add 50wt% Na3PO4·12H2O.

[0044] (4) Add the mixture from step (3) into a polytetrafluoroethylene ball milling jar, use agate balls as the milling medium, pour in a certain amount of anhydrous ethanol, and mill for 3 hours at a milling speed of 500 r / min.

[0045] (5) Dry the mixed slurry in step (4) at a temperature of 70°C for 3 hours to obtain pre-made powder.

[0046] (6) Mix 5wt% PVA solution with preformed powder at a ratio of 1:3, put it into a freeze dryer for processing, vacuum degree of 5 Pa, processing time of 48 h, to obtain porous preform.

[0047] (7) Place the porous preform into a muffle furnace and heat it to 600°C at a rate of 1°C / min, and hold it for 10 hours.

[0048] (8) Continue heating the porous preform from step (7) to 700°C at a heating rate of 1°C / min and hold for 2-10 hours.

[0049] (9) Continue heating the porous preform from step (8) to 900°C at a rate of 1°C / min, keep it at that temperature for 2 hours, and then take it out for use after cooling to room temperature to obtain low-temperature porous NASICON material.

[0050] The low-temperature porous NASICON material prepared in this embodiment was tested for microwave absorption. The minimum reflectivity value was -23dB, and the effective bandwidth of less than -5dB in the X-band reached 3.6GHz.

[0051] SEM analysis (corresponding) Figure 1 ):like Figure 1 As shown, the low-temperature porous NASICON material prepared in Example 1 exhibits a rich three-dimensional interconnected porous structure with pore size distribution mainly in the range of 1-10 micrometers, clear pore walls, and a robust structure.

[0052] XRD analysis (corresponding) Figure 2 ):like Figure 2 As shown, the diffraction pattern of the low-temperature porous NASICON material prepared in Example 1 is compared with that of Na3Zr2Si2PO4. 12 The standard spectra were in high agreement, and no obvious impurity phase peaks were detected, indicating that a high-purity NASICON crystal phase had been successfully synthesized at the final sintering temperature of 900℃.

[0053] The porous NASICON material prepared by the above-mentioned low-temperature process not only reduces energy consumption, but also the porous structure obtained is expected to endow the material with excellent lightweight properties and wave absorption performance, and has important application potential in the field of high-temperature stealth.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a low-temperature porous NASICON stealth material, characterized in that, Includes the following steps: S1. Weigh the raw materials Na3PO4·12H2O, SiO2 and ZrO2 according to the stoichiometric ratio, mix them with excess Na3PO4·12H2O, and obtain the pre-made powder by ball milling and drying for the first time; S2. The pre-made powder is subjected to multi-stage heat treatment: first, the temperature is raised to 600°C and held, then the temperature is raised to 700°C and held, and finally the temperature is raised to 900°C and held to obtain intermediate powder. S3. The intermediate powder is ball-milled a second time and dried to obtain a secondary processed powder. S4. The secondary processed powder is mixed with polyvinyl alcohol solution at a mass ratio of 1:1 to 1:10, and then freeze-dried to form a porous preform. The vacuum degree of the freeze-drying is 1-10 Pa, and the processing time is 6-48 hours. S5. The porous preform is sintered at 900°C to obtain the low-temperature porous NASICON stealth material.

2. The method for preparing the low-temperature porous NASICON stealth material as described in claim 1, characterized in that, In step S1, the medium for the first ball milling is agate balls, the solvent is anhydrous ethanol, the ball milling speed is 100-900 r / min, and the ball milling time is 1-12 hours; the drying temperature is 50-70℃, and the drying time is 2-8 hours.

3. The method for preparing the low-temperature porous NASICON stealth material as described in claim 1, characterized in that, In step S2, the specific process of the multi-stage heat treatment is as follows: the temperature is raised to 600°C at a heating rate of 1-4°C / min and held for 2-10 hours; then the temperature is raised to 700°C at a heating rate of 1-4°C / min and held for 2-10 hours; then the temperature is raised to 900°C at a heating rate of 1-8°C / min and held for 2 hours.

4. The method for preparing the low-temperature porous NASICON stealth material as described in claim 3, characterized in that, The heating rates to 600℃, 600℃ to 700℃, and 700℃ to 900℃ are all 1℃ / min, and the holding time at 600℃ is 10 hours.

5. The method for preparing the low-temperature porous NASICON stealth material as described in claim 1, characterized in that, In step S3, the medium for the second ball milling is agate balls, the solvent is anhydrous ethanol, the ball milling speed is 100-900 r / min, and the ball milling time is 3-24 hours; the drying temperature is 50-70℃, and the drying time is 2-8 hours.

6. The method for preparing the low-temperature porous NASICON stealth material as described in claim 5, characterized in that, In step S3, the rotation speed of the second ball mill is 300-500 r / min, and the ball milling time is 5 hours.

7. The method for preparing the low-temperature porous NASICON stealth material as described in claim 1, characterized in that, In step S4, the mass percentage concentration of the polyvinyl alcohol solution is 5%.

8. The method for preparing the low-temperature porous NASICON stealth material as described in claim 1, characterized in that, In step S1, the mass fraction of Na3PO4·12H2O ranges from 10wt% to 50wt%.

9. The method for preparing the low-temperature porous NASICON stealth material as described in claim 1, characterized in that, In step S4, the mixing mass ratio of the secondary processed powder to the polyvinyl alcohol solution is 1:1 to 1:10, the vacuum degree of the freeze drying is 1-10 Pa, and the processing time is 6-48 hours.

10. A low-temperature porous NASICON stealth material prepared by the preparation method of the low-temperature porous NASICON stealth material according to any one of claims 1 to 9.

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