A medium-temperature curing high-temperature resistant quartz fiber phosphate radome material, a preparation method thereof and an application thereof

Abstract

The application discloses a kind of medium-temperature curing high-temperature-resistant quartz fiber phosphate radome materials and preparation method and application, it is related to high-temperature-resistant material technical field, the radome material is phosphate as matrix, flaky nanometer hydroxyl silicon dioxide is solidifying agent, continuous quartz fiber is reinforced phase after silicon sol surface treatment, it is prepared at 80-120 ℃ medium-temperature curing.The solidifying agent is obtained by airflow crushing after hydrolysis of hydrophilic fumed silica at 80 ℃ with 20 wt% NaOH, washing to sodium ion <5 ppm, drying and 200-400 ℃ treatment;Quartz fiber is impregnated with acidic silica sol after desizing at 400 ℃, and transition layer of nanometer silicon dioxide is formed on the surface to improve interface and inhibit the corrosion of acidic matrix to fiber.Under optimal conditions (white carbon black A200, processing temperature 300 ℃) the dielectric constant of the obtained material is about 3.1, the dielectric loss is about 0.004, the bending strength at room temperature is 140 MPa, the bending strength at 1000 ℃ is 85 MPa, the service temperature is below 1000 ℃, and it can be used for high-speed aircraft high-temperature-resistant wave-transparent radome.

Description

Technical Field

[0001] This invention relates to the field of high-temperature resistant materials technology, specifically to a medium-temperature curing high-temperature resistant quartz fiber phosphate radome material, its preparation method, and its application. Background Technology

[0002] Radomes are critical protective structural components for the communication, telemetry, and guidance systems of high-speed aircraft, and their materials must meet both electromagnetic wave transmission and high-temperature mechanical requirements. Currently in service, high-temperature resistant ceramic radomes are mainly composed of various silica-based materials, with some systems incorporating small amounts of alumina or boron nitride to improve mechanical or dielectric properties.

[0003] In terms of manufacturing processes, existing silica-based radomes mainly rely on high-temperature methods such as hot-pressing sintering and reaction sintering, with molding temperatures typically exceeding 1200℃. This requires sophisticated equipment, has a long manufacturing cycle, and consumes a lot of energy. Phosphate systems are inexpensive and are considered one of the preferred matrix options for high-temperature resistant, wave-transparent radome materials. However, phosphate matrices corrode fibers, have high curing temperatures, and exhibit moisture absorption during long-term storage, which fails to meet usage requirements.

[0004] Existing high-temperature resistant wave-transparent radome materials and their fabrication processes can be found in patent application CN102769197A, "Wave-transparent Materials and Radomes and Antenna Systems," and in publications such as *Modern Technical Ceramics*, Vol. 39, No. 3, 2018. These materials use silica as a matrix (with some systems incorporating small amounts of alumina or boron nitride to improve mechanical or dielectric properties), relying on high-temperature routes such as hot-pressing sintering or reaction sintering. The forming temperature is typically >1200℃, resulting in common problems such as high equipment requirements, high energy consumption, and long production cycles. Phosphate matrices are considered one of the preferred matrix directions for high-temperature resistant wave-transparent radome materials due to their low cost, but there are currently no reports of their engineering feasibility. The reasons are as follows: Existing phosphate-based high-temperature transparent radome materials have three prominent defects: First, the phosphate matrix is ​​acidic, which corrodes quartz fibers and damages the reinforcing phase during preparation and service; second, conventional silica is chemically inert and requires very high temperatures to undergo a curing reaction with phosphate, resulting in high curing temperatures and high energy consumption; third, this type of curing reaction is prone to reversible reactions during long-term storage, manifesting as material moisture absorption and performance degradation.

[0005] Therefore, there is an urgent need to develop a high-temperature transparent radome material for high-speed aircraft that can inhibit fiber corrosion, reduce curing temperature, and suppress moisture absorption. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material, its preparation method, and its application.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material, characterized by comprising the following steps: S1. Hydrophilic fumed silica is used as raw material. After alkaline activation and hydrolysis, it is washed to remove sodium, dried, treated at high temperature of 200–400℃, and pulverized to obtain flake-like nano-hydroxy silica. S2. Quartz fibers are treated at 350-450℃ to remove the sizing agent, washed, and then immersed in acidic silica sol and dried at room temperature to form a nano-silica transition layer on the fiber surface. S3. A mixed slurry is formed using phosphate as the matrix and the flake-like nano-hydroxy silica from step S1 as the curing agent. Then, the quartz fiber surface-treated with acidic silica sol from step S2 is used as the reinforcing phase and laid up with the mixed slurry (such as hand lay-up). The mixture is cured at 0.05–0.2 MPa and 80–120°C to obtain a medium-temperature curing high-temperature resistant quartz fiber phosphate radome material.

[0008] As a further preferred embodiment of the present invention, the specific surface area of ​​the hydrophilic fumed silica is 150–380 m² / g. For example, silica grades A150, A200, A300, and A380 correspond to specific surface areas of approximately 150, 200, 300, and 380 m² / g, respectively. By selecting different grades of fumed silica (specific surface area 150–380 m² / g) and different treatment temperatures (200–400℃), the hydroxyl density and lamellar morphology of the resulting curing agent can be systematically controlled, thereby obtaining a series of curing agents with varying curing rates and cured product properties. This curing agent allows phosphates to be cured at 80–120℃. More preferably, the specific surface area of ​​the hydrophilic fumed silica is 200–300 m² / g, and the high-temperature treatment temperature is 250–350℃.

[0009] As a further preferred technical solution of the present invention, step S1 includes the following steps in sequence: (1) adding hydrophilic fumed silica to a sodium hydroxide aqueous solution with a concentration of 15–25 wt% and hydrolyzing it at 70–90℃ for 0.5–2 h; (2) filtering and washing with deionized water until the sodium ion content of the filtrate is <5 ppm; (3) drying at 90–110℃ for 1–3 h and then treating it at 200–400℃ for 1–3 h; (4) obtaining flake-like nano-hydroxy silica by air jet pulverization.

[0010] As a further preferred embodiment of the present invention, the acidic silica sol is prepared by reacting silica with nitric acid. Furthermore, the pH of the acidic sol gel is 2–4.

[0011] As a further preferred technical solution of the present invention, the pressure applied during curing is 0.05–0.2 MPa, and more preferably 0.1 MPa; the higher the pressure, the denser the product, but it should not be too high to avoid crushing the fibers.

[0012] As a further preferred embodiment of the present invention, the amount of curing agent added to the matrix is ​​5–20 wt%, more preferably 10 wt%; and / or, the mass ratio of the quartz fiber after acidic silica sol surface treatment to the mixed slurry is 0.8:1–1.2:1, more preferably 1:1.

[0013] According to a second aspect of the present invention, the present invention also provides a medium-temperature curing high-temperature resistant quartz fiber phosphate radome material, which is prepared by the preparation method of the first aspect described above.

[0014] As a further preferred technical solution of the present invention, the radome material has a working temperature below 1000℃, a dielectric constant of ≤3.2 at room temperature, a dielectric loss of ≤0.005, a bending strength of ≥108 MPa at room temperature, and a bending strength of ≥56 MPa at 1000℃.

[0015] According to a third aspect of the present invention, the present invention also provides an application of a medium-temperature curing high-temperature resistant quartz fiber phosphate radome material as a high-temperature resistant wave-transparent radome for aircraft.

[0016] The medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material of the present invention relies on the synergistic design of the curing agent, matrix, and reinforcing phase to achieve medium-temperature curing, fiber corrosion resistance, and storage durability. The specific mechanism is as follows: (i) Inhibiting fiber corrosion: Continuous quartz fibers are surface treated with silica sol to form a nano-silica inorganic transition layer on the fiber surface, which isolates the acidic phosphate matrix from the quartz fiber, inhibits the corrosion of the fiber by phosphate and improves the interfacial bonding.

[0017] (ii) Lowering the curing temperature: Conventional silica is highly inert and requires high temperature to react with phosphate; the flake-like, nanoscale silica with certain hydroxyl groups on the surface of the present invention is used as a curing agent - the surface hydroxyl groups provide the reactivity, and the nanoscale and flake morphology endow it with high specific surface area and high reactivity, so that the crosslinking point density is high when it reacts with phosphate, thus curing can be completed at a medium temperature of 80-120℃.

[0018] (III) Moisture Absorption Suppression: Ordinary curing systems are prone to reversible reactions and moisture absorption during long-term storage; the high cross-linking density curing product formed by the flake-like nano-hydroxyl silica and phosphate of this invention is less prone to reversible reactions, thus significantly suppressing moisture absorption and improving storage stability. Thus, the curing agent, matrix, and reinforcing phase work synergistically to achieve a medium-temperature curing, high-temperature resistant, low dielectric loss, and storage-resistant radome material.

[0019] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) Preparation process: The flake-like nano-hydroxyl silica curing agent can cure the phosphate matrix at a medium temperature of 80–120℃. It is made by hand lay-up and pressure molding, which is simple, requires low equipment and has low energy consumption. It overcomes the shortcomings of existing silica-based antenna covers that rely on hot pressing / reaction sintering at temperatures above 1200℃. The curing agent can cure phosphate and the curing is irreversible and resistant to storage, which is not available in conventional silica.

[0020] (2) Material properties: The dielectric constant of the obtained material is about 3.1, the dielectric loss is about 0.004, the bending strength at room temperature reaches 140 MPa, the bending strength at 600–1000℃ decreases gradually, and it still maintains 56–85 MPa at 1000℃, without any sharp decay.

[0021] (3) Antenna radome application: It has both excellent wave transmission / dielectric properties and high temperature mechanical properties; the raw materials (phosphate, silicon dioxide) are low in cost, which is more economical than oxide ceramic radomes and the high-cost process of "quartz fiber weaving + repeated impregnation with silica sol", and is suitable for the molding of large-size irregular radomes. Attached Figure Description

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 This is a SEM image of the flake-like nano-hydroxy silica prepared in Example 1.

[0024] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0026] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0027] Example 1 The medium-temperature curing, high-temperature resistant quartz fiber phosphate radome provided in this embodiment is prepared by the following method: (a) Preparation of curing agent (flake-like nano-hydroxyl silica): 100 g of hydrophilic fumed silica (A200, specific surface area approximately 200 m² / g) was added to 500 mL of a 20 wt% sodium hydroxide aqueous solution and hydrolyzed at 80℃ for 1 h; after filtration, the solution was repeatedly washed with deionized water until the sodium ion content in the filtrate was below 5 ppm; then dried at 100℃ for 2 h, followed by high-temperature treatment at 300℃ for 2 h; the solution was then air-jet pulverized and sieved to obtain the following: Figure 1 The image shows a flake-like nano-hydroxyl silica curing agent.

[0028] (b) Preparation of acidic silica sol: An acidic sol gel was prepared by reacting silica with nitric acid, wherein the silica content was about 10 wt% and the pH was adjusted to about 3 with dilute nitric acid.

[0029] (c) Surface treatment of quartz fiber: The continuous quartz fiber is heat-treated at 400°C for 1 h to remove the sizing agent, washed with deionized water, and then immersed in the above-mentioned acidic silica sol and air-dried at room temperature to form a nano-silica transition layer on the fiber surface.

[0030] (d) Ingredients and molding: The curing agent (accounting for 10% of the phosphate matrix by mass) is mixed evenly with the phosphate matrix, and then the treated quartz fiber is hand-laid at a mass ratio of 1:1. The mixture is then cured under pressure of 0.1 MPa and heat-preserved at 120℃ for 3 h. The radome is obtained by demolding.

[0031] Example 2 (changing the grade of silica to A380): The only difference from Example 1 is that the grade of silica is changed to A380; all other conditions are the same as in Example 1. Compared to silica A200, A380 has a higher specific surface area and enhanced curing activity.

[0032] Example 3 (Changing the processing temperature to 200°C): The only difference from Example 1 is that the high-temperature treatment in the preparation of the curing agent is at 200°C; all other conditions are the same as in Example 1. Compared to the high-temperature treatment at 300°C, the relatively low-temperature treatment results in a higher hydroxyl content.

[0033] Example 4 (Changing the processing temperature to 400°C): The only difference from Example 1 is that the high-temperature treatment in the preparation of the curing agent is at 400°C; all other conditions are the same as in Example 1. Compared to the 400°C high-temperature treatment, the relatively high-temperature treatment causes some hydroxyl groups to be removed, resulting in a decrease in curing activity.

[0034] Comparative Example 1 (without alkali activation treatment): The only difference from Example 1 is that the original fumed silica A200 was directly air-jet pulverized and used as a curing agent, omitting the steps of NaOH hydrolysis, water washing, and high-temperature treatment. The other conditions are the same as in Example 1.

[0035] Comparative Example 2 (without quartz fiber silica sol surface treatment): The only difference from Example 1 is that the continuous quartz fibers are only heat-treated at 400°C and washed with water, without being impregnated with acidic silica sol. All other conditions are the same as in Example 1.

[0036] Comparative Example 3 (insufficient rinsing, high sodium ion residue): The only difference from Example 1 is that the washing of the curing agent was stopped when the sodium ion content of the filtrate was about 200 ppm, while the other conditions were the same as in Example 1.

[0037] Comparative Example 4 (Spherical Silica Curing Agent): The flake-shaped nano-hydroxyl silica used as the curing agent in the "Ingredient Preparation and Molding" step of Example 1 was replaced with an equal mass of spherical nano-silica (particle size approximately 80 nm), with all other conditions remaining the same as in Example 1. Because the spherical particles have more gaps between them and poor coverage density when stacked, the resulting radome material has a dielectric constant of 3.20, a dielectric loss of 0.006, and bending strengths of 75 MPa at room temperature, 60 MPa at 600°C, 45 MPa at 800°C, and 32 MPa at 1000°C. All these properties are significantly lower than those of Example 1.

[0038] Comparative Example 5 (Rod-shaped silica curing agent): The flake-shaped nano-hydroxyl silica used as curing agent in the "Ingredient Preparation and Molding" step of Example 1 was replaced with an equal mass of rod-shaped nano-silica (approximately 40 nm in diameter and 200 nm in length), with all other conditions remaining the same as in Example 1. Because the dense layering effect of the rod-shaped particles is between that of flakes and spheres, the resulting material has a dielectric constant of 3.15, a dielectric loss of 0.005, and bending strengths of 105 MPa at room temperature, 88 MPa at 600℃, 70 MPa at 800℃, and 55 MPa at 1000℃, indicating moderate performance.

[0039] Comparative Example 6 (Unhydroxylated silica curing agent): The curing agent used in the "Ingredient Preparation and Molding" step of Example 1 was replaced with unhydroxylated silica (i.e., the NaOH alkaline activation and hydrolysis process step was omitted), and the other conditions were the same as in Example 1. Due to the lack of sufficient reactive hydroxyl groups on the surface, the phosphate could not be fully cured at 80–120°C, resulting in incomplete curing of the sample and failure to obtain effective mechanical and dielectric property data.

[0040] The dielectric and mechanical properties of Examples 1-4 and Comparative Examples 1-3 are summarized in the table below.

[0041] As can be seen from the data in Examples 1 to 4, by selecting different grades of fumed silica and different processing temperatures, the material properties can be adjusted within the range of flexural strength from 108 to 140 MPa and dielectric constant from 3.05 to 3.12 at room temperature. Example 1 (A200, processed at 300℃) is the formulation with the best overall performance. The flexural strength of the materials in each example decreases gradually in the range of 600℃ to 1000℃, and still maintains 56 to 85 MPa at 1000℃, without a sharp decline.

[0042] Comparative Example 1 shows that the original fumed silica without alkali activation treatment does not have the ability to cure phosphate at medium temperature. The sample could not be cured at 120°C, which proves the necessity of the curing agent preparation process.

[0043] Comparative Example 2 shows that after omitting the silica sol surface treatment with quartz fibers, the room temperature flexural strength decreased from 140 MPa to 95 MPa (a decrease of 32%), and the 1000℃ flexural strength decreased from 85 MPa to 52 MPa (a decrease of 39%), indicating that silica sol surface treatment is crucial for interfacial bonding.

[0044] Comparative Example 3 shows that when insufficient water washing leads to high sodium ion residue, although the mechanical properties are only slightly affected (132 MPa), the dielectric constant increases to 3.98 and the dielectric loss increases to 0.022, which seriously degrades the wave transmission performance, proving the necessity of the water washing sodium removal process.

[0045] Comparative Examples 4–6 show that the scaly morphology (layer-by-layer, large specific surface area, and good sealing) and surface hydroxylation (providing reactivity and increasing crosslinking density) together determine the medium-temperature curing ability of the curing agent and the performance of the product; neither can be omitted. Figure 1 The image shows an SEM image of the hydroxyl silica curing agent prepared in Example 1, confirming that it has a scaly morphology.

[0046] In summary, this invention achieves medium-temperature curing of the phosphate matrix at 80 to 120°C using a self-made hydroxyl silica curing agent. The material properties can be adjusted within a certain range by selecting different grades of fumed silica and different processing temperatures. Under optimal conditions, the resulting quartz fiber phosphate radome material has a dielectric constant of approximately 3.1, a dielectric loss of approximately 0.004, a room-temperature flexural strength of 140 MPa, and an operating temperature below 1000°C.

[0047] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing a medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material, characterized in that, Includes the following steps: S1. Hydrophilic fumed silica with a specific surface area of ​​150–380 m² / g is used as raw material. After alkaline activation and hydrolysis, it is washed to remove sodium, dried, treated at a high temperature of 200–400℃, and pulverized to obtain flake-like nano-hydroxy silica. S2. Quartz fibers are treated at 350-450℃ to remove the sizing agent, washed, and then immersed in acidic silica sol and dried at room temperature to form a nano-silica transition layer on the fiber surface. S3. A mixed slurry is formed using phosphate as the matrix and the flake-like nano-hydroxy silica from step S1 as the curing agent. Then, the quartz fiber surface-treated with acidic silica sol from step S2 is used as the reinforcing phase and layered with the mixed slurry. The mixture is cured at 0.05–0.2 MPa and 80–120 °C to obtain a medium-temperature curing high-temperature resistant quartz fiber phosphate radome material.

2. The preparation method of the medium-temperature curing high-temperature resistant quartz fiber phosphate radome material according to claim 1, characterized in that, The specific surface area of ​​the hydrophilic fumed silica is 200–300 m² / g; and / or the temperature of the high-temperature treatment is 250–350 °C.

3. The preparation method of the medium-temperature curing high-temperature resistant quartz fiber phosphate radome material according to claim 1, characterized in that, Step S1 specifically includes the following steps performed sequentially: (1) Add hydrophilic fumed silica to a 15–25 wt% sodium hydroxide aqueous solution and hydrolyze at 70–90℃ for 0.5–2 h; (2) After filtration, wash with deionized water until the sodium ion content in the filtrate is <5 ppm; (3) Dry at 90–110℃ for 1–3 h and then treat at 200–400℃ for 1–3 h; (4) Flake-shaped nano-hydroxy silica is obtained by air jet pulverization.

4. The method for preparing the medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material according to claim 1, characterized in that, The acidic silica sol is prepared by reacting silicon dioxide with nitric acid.

5. The method for preparing the medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material according to claim 1, characterized in that, The pH of the acidic silica sol is 2–4.

6. The method for preparing the medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material according to claim 1, characterized in that, The curing pressure is 0.1 MPa and the temperature is 120℃.

7. The method for preparing the medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material according to claim 1, characterized in that, The curing agent is added to the matrix in an amount of 5–20 wt%; and / or the mass ratio of the quartz fiber surface-treated with acidic silica sol to the mixed slurry is 0.8:1–1.2:

1.

8. A medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. The medium-temperature curing, high-temperature resistant quartz fiber phosphate radome material according to claim 8, characterized in that, The radome material has a working temperature below 1000℃, a dielectric constant of ≤3.2 at room temperature, a dielectric loss of ≤0.005, a bending strength of ≥108 MPa at room temperature, and a bending strength of ≥56 MPa at 1000℃.

10. The medium-temperature curing high-temperature resistant quartz fiber phosphate radome material prepared by the preparation method according to any one of claims 1-7, or the medium-temperature curing high-temperature resistant quartz fiber phosphate radome material according to claim 8 or 9, is used as a high-temperature resistant wave-transparent radome for aircraft.

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