Lightweight close-packed hollow-sphere silica thermal insulation material and preparation method and application thereof

Abstract

The application discloses light-weight dense-silica hollow sphere heat-insulating material and a preparation method and application thereof, and belongs to the technical field of novel heat-insulating materials.The application uses a special SiO2 hollow sphere structure, uses inorganic adhesive to bond, and makes the SiO2 hollow spheres tightly combine in a sintering process, thereby significantly improving the volume of air in the material, solving the problem of strong hygroscopicity caused by the fibrous aerogel material in the prior art, and being simple in the preparation steps, cheap and easy to obtain in raw materials, and being conducive to realizing large-scale production and being applicable to the field of aviation.

Description

Technical Field

[0001] This invention belongs to the field of novel thermal insulation materials technology, and particularly relates to a lightweight, densely packed silica hollow sphere thermal insulation material, its preparation method, and its application. Background Technology

[0002] When an aircraft flies at high speeds, the intense friction between its fuselage and the air can cause surface temperatures to reach thousands of degrees Celsius. Meanwhile, the electronic and electrical equipment inside the aircraft must operate at temperatures not exceeding 85°C. This significant temperature difference places higher demands on the design and verification of the aircraft's thermal protection system. With the continuous increase in the flight speed of hypersonic vehicles, existing thermal protection structural design principles and insulation materials are no longer sufficient to meet the requirements for reusable design. Thermal protection technology has become a technological bottleneck hindering the development of hypersonic vehicles. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a lightweight, close-packed silica (SiO2) hollow sphere thermal insulation material, its preparation method, and its applications. This invention utilizes a specially designed SiO2 hollow spherical structure, bonded together with an inorganic binder, to achieve a tight bond between the SiO2 hollow spheres during sintering, significantly increasing the air volume within the material. Traditional aerogel materials are prepared by mixing fibers and fillers, resulting in numerous continuous pores, strong water absorption, and fiber collapse. Water absorption damages the structure, severely impacting the material's thermal insulation performance. This invention uses hollow SiO2 micron-sized spheres as the basic framework, connected by an inorganic binder. Through a heat treatment process, it transforms into a stable inorganic structure, allowing moisture to pass through the gaps between the spheres, thus unaffected by hygroscopicity. Therefore, it solves the problem of strong hygroscopicity caused by the use of fibrous aerogel materials in existing technologies; moreover, the preparation steps are simple, the raw materials are inexpensive and readily available, facilitating large-scale production.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] To achieve the above objectives, the present invention provides a method for preparing a lightweight, close-packed SiO2 hollow sphere thermal insulation material, comprising the following steps:

[0006] S1. Rinse the SiO2 hollow spheres with water until the pH is neutral (pH=7), then dry; rinsing removes surface impurities from the SiO2 hollow spheres.

[0007] S2. Lay out a single layer of SiO2 hollow spheres treated in S1, spray with an inorganic binder, and repeat the above laying method to obtain a multi-layer densely packed SiO2 hollow sphere structure.

[0008] S3. The multi-layer densely packed SiO2 hollow sphere structure is dehydrated to obtain a lightweight densely packed SiO2 hollow sphere thermal insulation material blank; the inorganic binder is dried to remove moisture, so that the inorganic binder is cured in situ to initially stabilize the blank structure.

[0009] S4. The lightweight close-packed SiO2 hollow sphere insulation material blank is sintered to obtain the lightweight close-packed SiO2 hollow sphere insulation material. To enhance the stability of the blank, sintering is used to transform the inorganic binder and SiO2 hollow spheres into an ordered crystalline structure. Combined with the grain boundary diffusion mechanism, the point-to-point connection structure of the spheres-binder-spheres is more stable and unaffected by hygroscopicity.

[0010] This invention removes surface impurities from SiO2 hollow spheres by rinsing, then lays the treated SiO2 hollow spheres in a single layer in a mold, sprays an inorganic binder to form bonding sites between the SiO2 hollow sphere particles, and repeats the above laying method multiple times to obtain a multi-layer densely packed SiO2 hollow sphere structure to ensure that the SiO2 hollow spheres can be tightly connected and have plasticity, meeting the material shape requirements of different fields; then the obtained densely packed structure is dehydrated and dried to remove moisture from the material, and finally sintered to obtain a multi-layer densely packed SiO2 hollow sphere structure thermal insulation material.

[0011] Furthermore, in S1, the SiO2 hollow spheres are prepared as follows: using hydrogen-containing silicone oil as raw material, adding acid solution and emulsifier during stirring, and curing at high temperature to form SiO2 hollow spheres.

[0012] Further, in S1, the acid solution is an acetic acid solution with a concentration of 20 wt%. In this invention, cross-linking and curing are carried out by adding an acid solution. The mass ratio of the acid solution to the hydrogen-containing silicone oil should be controlled. Excessive acidity will cause flash coagulation, which is not conducive to the formation of spheres. Preferably, the mass ratio of the hydrogen-containing silicone oil to the acetic acid solution is 1:5.

[0013] The emulsifiers include alkylphenol polyoxyethylene ethers, dibenzylphenol polyoxyethylene ethers, alkylphenol polyoxyethylene ethers, or fatty alcohol polyoxyethylene ethers. All of these emulsifiers are lipophilic emulsifiers with a low HLB value, which can increase the contact angle between the hydrogen-containing silicone oil and the aqueous solution, facilitating cross-linking into spheres under acidic stirring conditions.

[0014] Furthermore, in S1, the drying temperature is 20–180°C, and the drying time is 2–10 h, preferably 80–100°C and 2–4 h.

[0015] Further, in S1, the high-temperature curing temperature is 500–1500°C, preferably 850–1100°C, and more preferably 900°C. If the curing temperature is too low, the material's crystal phase transformation will be incomplete, and the final blank will undergo another phase transformation at high temperatures, affecting its structural stability at high temperatures; if the curing temperature is too high, SiO2 will be unable to maintain a stable structure and will deform and decompose.

[0016] Furthermore, when rinsing the SiO2 hollow spheres with deionized water, an immersion filtration method should be chosen to prevent the SiO2 hollow spheres from being damaged by violent shaking.

[0017] Furthermore, in S2, the inorganic binder includes a sodium silicate solution or an aluminum phosphate solution. Such inorganic binders can bond the interface contact points of the SiO2 hollow spheres in the initial stage of spraying, and form Si-Al-O and P-Al-O systems in situ during the heating and oxidation process, thus stabilizing the material structure.

[0018] Furthermore, in S2, the concentrations of the sodium silicate solution and the aluminum phosphate solution are both 5wt% to 60wt%.

[0019] Furthermore, the inorganic binder is sprayed onto each layer of SiO2 hollow spheres 2 to 20 times;

[0020] The SiO2 hollow spheres are repeated 15 to 30 times. Insufficient inorganic binder application hinders the formation of a point-to-point connection between the spheres and the binder, resulting in an unstable basic framework for the hollow SiO2 micron-sized spheres. Excessive inorganic binder application increases the material's thermal conductivity, leading to poorer thermal performance. Too few repetitions result in incomplete material formation, while too many repetitions increase the material thickness, occupying space in spacecraft and causing difficulties in laying other materials.

[0021] Furthermore, in S2, a single layer of SiO2 hollow spheres with a thickness of 0.5 mm is laid out, and a sodium silicate solution with a concentration of 20 wt% is sprayed four times.

[0022] Furthermore, in S3, the multilayer densely packed SiO2 hollow sphere structure is dehydrated by drying, and the drying method is freeze drying or oven heating drying.

[0023] Furthermore, in S4, the sintering temperature is 400–800°C, preferably 500°C. If the sintering temperature is too low, organic impurities introduced during material preparation cannot be removed; if the sintering temperature is too high, the aluminum dihydrogen phosphate binder may decompose.

[0024] Sintering at 500℃ can remove organic impurities while having little impact on inorganic binders.

[0025] This invention uses hydrogen-containing silicone oil as a raw material, crosslinks it with an acid solution, emulsifies it into spheres using an emulsifier, and cures it at high temperature to form hollow SiO2 spherical shells (i.e., hollow SiO2 spheres). A single layer of hollow SiO2 spheres is laid flat in a mold, and a silicate or phosphate inorganic binder, such as sodium silicate solution or aluminum phosphate solution, is sprayed onto the spheres to form bonding sites between the SiO2 sphere particles. This laying process is repeated multiple times to obtain a multi-layered, densely packed SiO2 hollow sphere structure. The resulting densely packed structure is then dehydrated, dried, and sintered to obtain a lightweight, densely packed SiO2 hollow sphere thermal insulation material. The abundant hollow structures between the internal and external SiO2 spheres effectively hinder heat dissipation, providing thermal insulation and lightweight properties. The lightweight, densely packed SiO2 hollow sphere thermal insulation material of this invention exhibits excellent overall thermal insulation performance and a long service life in practical applications.

[0026] The present invention also provides a lightweight close-packed SiO2 hollow sphere thermal insulation material prepared by the above preparation method.

[0027] This invention also provides the application of the lightweight, closely packed SiO2 hollow sphere thermal insulation material in the aerospace field. For example, the lightweight, closely packed SiO2 hollow sphere thermal insulation material of this invention can be used to manufacture aircraft; it can be used to manufacture rocket fairing shell materials, improving their thermal insulation performance and ensuring that the internal structure of the rocket is not damaged.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] The lightweight, closely packed SiO2 hollow sphere thermal insulation material of this invention features abundant hollow structures within the SiO2 hollow spheres, effectively hindering heat dissipation and providing both thermal insulation and weight reduction. This lightweight, closely packed SiO2 hollow sphere thermal insulation material offers high stability, strong controllability, lightweight construction, excellent thermal insulation performance, long service life, and readily available and inexpensive raw materials, facilitating large-scale production. Compared to patent application CN 106608630 A, this invention incorporates an emulsifier and utilizes mechanical stirring, resulting in better sphericity and uniform dispersion of the hydrogen-containing silicone oil. Furthermore, an inorganic binder-based molding process yields a thermal insulation material applicable to the aerospace field, improving upon the hygroscopicity issues faced by traditional aerogel materials through structural design.

[0030] The lightweight, close-packed SiO2 hollow sphere thermal insulation material prepared according to the method of this invention can be used as a rocket fairing shell material in the aerospace field, improving existing bottleneck problems. The SiO2 hollow spheres of this invention, with a diameter of approximately 10 μm, have an outer shell of only 100 nm and an entirely hollow internal structure. Therefore, under ideal conditions, their thermal conductivity can be infinitely close to that of air, while possessing ultra-low density to achieve lightweight characteristics. Furthermore, the spherical structure exhibits extremely high fluidity, laying the foundation for the preparation of specific structures. In addition, SiO2 has extremely high thermal and chemical stability, with a melting point above 1700℃ and a boiling point above 2200℃. It is resistant to rain and acid corrosion and has extremely high compatibility with the thermal insulation systems required for hypersonic vehicles. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0032] Figure 1 This is a SEM image of the lightweight close-packed SiO2 hollow sphere thermal insulation material obtained in Example 1 of the present invention;

[0033] Figure 2 The image shown is a SEM image of the thermal insulation material obtained in Comparative Example 1 of this invention. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] All raw materials used in this invention were purchased. For example, the hydrogen-containing silicone oil in the embodiments was purchased from Xingchi Chemical Co., Ltd., model XC202; the alkylphenol polyoxyethylene ether was purchased from Maclean's reagent, CAS number 9002-93-1; the dibenzylphenol polyoxyethylene ether was purchased from Maclean's reagent, CAS number 68310-58-7; the alkylphenol polyoxyethylene ether was purchased from Maclean's reagent, CAS number 9002-93-1; and the fatty alcohol polyoxyethylene ether was purchased from Maclean's reagent, CAS number 52292-17-8.

[0040] The technical solution of the present invention will be further illustrated by the following embodiments.

[0041] Example 1

[0042] This embodiment provides a method for preparing a lightweight, close-packed SiO2 hollow sphere thermal insulation material:

[0043] S1. Using hydrogen-containing silicone oil (purchased from Xingchi Chemical Co., Ltd., model XC202, the same below) as raw material, add acetic acid solution with a concentration of 20wt% for crosslinking, the mass ratio of hydrogen-containing silicone oil to acetic acid solution is 1:5, add alkylphenol polyoxyethylene ether to emulsify into spheres, and cure at a high temperature of 900℃ to form hollow SiO2 spheres (i.e., SiO2 hollow spheres).

[0044] S2, Pretreatment of SiO2 hollow spheres: Use deionized water to rinse the SiO2 hollow spheres. When rinsing, choose the soaking and filtering method to prevent the SiO2 hollow spheres from being damaged by violent shaking until the pH=7. Then put them in an oven and dry them at 80℃ for 4 hours before taking them out for use.

[0045] S3. Place the SiO2 hollow spheres treated in S2 in a single layer in the mold, spray a 20wt% sodium silicate solution 10 times to form bonding sites between the SiO2 hollow sphere particles, and repeat the above laying method 30 times to obtain a multi-layer close-packed SiO2 hollow sphere structure (close-packed structure).

[0046] S4. Freeze-dry the close-packed structure obtained in S3 to obtain a rough blank of lightweight close-packed SiO2 hollow sphere thermal insulation material. Take out the rough blank of lightweight close-packed SiO2 hollow sphere thermal insulation material from the mold.

[0047] S5. Place the lightweight, densely packed SiO2 hollow sphere insulation material blank into a muffle furnace and sinter it at a heating rate of 5℃ / min to 500℃ to obtain the lightweight, densely packed SiO2 hollow sphere insulation material.

[0048] Example 2

[0049] This embodiment provides a method for preparing a lightweight, close-packed SiO2 hollow sphere thermal insulation material:

[0050] S1. Using hydrogen-containing silicone oil as raw material, a 20wt% acetic acid solution is added for crosslinking. The mass ratio of hydrogen-containing silicone oil to acetic acid solution is 1:5. Fatty alcohol polyoxyethylene ether is added to emulsify into spheres, which are then cured into SiO2 hollow spheres at a high temperature of 900℃.

[0051] S2, Pretreatment of SiO2 hollow spheres: Use deionized water to rinse the SiO2 hollow spheres. When rinsing, choose the soaking and filtering method to prevent the SiO2 hollow spheres from being damaged by violent shaking until the pH=7 is reached. Then put them in an oven and dry them at 90℃ for 3 hours before taking them out for use.

[0052] S3. The SiO2 hollow spheres treated in S2 are laid in a single layer in the mold, and a sodium silicate solution with a concentration of 25wt% is sprayed 10 times to form bonding sites between the SiO2 hollow sphere particles. The above laying method is repeated 30 times to obtain a multi-layer densely packed SiO2 hollow sphere structure.

[0053] S4. Freeze-dry the close-packed structure obtained in S3 to obtain a rough blank of lightweight close-packed SiO2 hollow sphere thermal insulation material. Take out the rough blank of lightweight close-packed SiO2 hollow sphere thermal insulation material from the mold.

[0054] S5. Place the lightweight, densely packed SiO2 hollow sphere insulation material blank into a tube furnace and sinter it at a heating rate of 6℃ / min to 550℃ to obtain the lightweight, densely packed SiO2 hollow sphere insulation material.

[0055] Example 3

[0056] This embodiment provides a method for preparing a lightweight, close-packed SiO2 hollow sphere thermal insulation material:

[0057] S1. Using hydrogen-containing silicone oil as raw material, crosslinking is achieved by adding a 20wt% acetic acid solution. The mass ratio of hydrogen-containing silicone oil to acetic acid solution is 1:5. Dibenzylphenol polyoxyethylene ether is used to emulsify the mixture into spheres, which are then cured into SiO2 hollow spheres at a high temperature of 900℃.

[0058] S2, Pretreatment of SiO2 hollow spheres: Use deionized water to rinse the SiO2 hollow spheres. When rinsing, choose the soaking and filtering method to prevent the SiO2 hollow spheres from being damaged by violent shaking until the pH=7. Then put them in an oven and dry them at 100℃ for 2 hours before taking them out for use.

[0059] S3. The hollow spheres treated in S2 are laid in a single layer in the mold, and a 20wt% aluminum phosphate solution is sprayed 6 times to form bonding sites between the hollow sphere particles. The above laying method is repeated 30 times to obtain a multi-layer densely packed SiO2 hollow sphere structure.

[0060] S4. Freeze-dry the close-packed structure obtained in S2 to obtain a rough blank of lightweight close-packed SiO2 hollow sphere thermal insulation material. Take out the rough blank of lightweight close-packed SiO2 hollow sphere thermal insulation material from the mold.

[0061] S5. Place the lightweight, densely packed SiO2 hollow sphere insulation material blank into a tube furnace and sinter it at a heating rate of 7℃ / min to 600℃ to obtain the lightweight, densely packed SiO2 hollow sphere insulation material.

[0062] Example 4

[0063] This embodiment provides a method for preparing a lightweight, close-packed SiO2 hollow sphere thermal insulation material:

[0064] S1. Using hydrogen-containing silicone oil as raw material, adding 20wt% acetic acid solution for crosslinking, the mass ratio of hydrogen-containing silicone oil to acetic acid solution is 1:5, using dibenzylphenol polyoxyethylene ether to emulsify into spheres, and curing at 850℃ to form SiO2 hollow spheres.

[0065] S2, Pretreatment of SiO2 hollow spheres: Use deionized water to rinse the SiO2 hollow spheres. When rinsing, choose the soaking and filtering method to prevent the SiO2 hollow spheres from being damaged by violent shaking until the pH=7. Then put them in an oven and dry them at 80℃ for 4 hours before taking them out for use.

[0066] S3. Place the SiO2 hollow spheres treated in S2 in a single layer in the mold, spray a 20wt% sodium silicate solution 10 times to form bonding sites between the SiO2 hollow sphere particles, and repeat the above laying method 20 times to obtain a multi-layer densely packed SiO2 hollow sphere structure.

[0067] S4. The densely packed structure obtained in S3 is heated and dried in an oven to obtain a rough blank of lightweight densely packed SiO2 hollow sphere thermal insulation material. The rough blank of lightweight densely packed SiO2 hollow sphere thermal insulation material is taken out from the mold.

[0068] S5. Place the lightweight, densely packed SiO2 hollow sphere insulation material blank into a tube furnace and sinter it at a heating rate of 5℃ / min to 500℃ to obtain the lightweight, densely packed SiO2 hollow sphere insulation material.

[0069] Example 5

[0070] This embodiment provides a method for preparing a lightweight, close-packed SiO2 hollow sphere thermal insulation material:

[0071] S1. Using hydrogen-containing silicone oil as raw material, crosslinking is achieved by adding 20wt% acetic acid solution. The mass ratio of hydrogen-containing silicone oil to acetic acid solution is 1:5. Dibenzylphenol polyoxyethylene ether is used to emulsify the spheres, which are then cured into SiO2 hollow spheres at a high temperature of 1100℃.

[0072] S2, Pretreatment of SiO2 hollow spheres: Use deionized water to rinse the SiO2 hollow spheres. When rinsing, choose the soaking and filtering method to prevent the SiO2 hollow spheres from being damaged by violent shaking until the pH=7 is reached. Then put them in an oven and dry them at 90℃ for 3 hours before taking them out for use.

[0073] S3. The SiO2 hollow spheres treated in S2 are laid in a single layer in the mold, and a sodium silicate solution with a concentration of 25wt% is sprayed 8 times to form bonding sites between the SiO2 hollow sphere particles. The above laying method is repeated 30 times to obtain a multi-layer densely packed SiO2 hollow sphere structure.

[0074] S4. The densely packed structure obtained in S3 is heated and dried in an oven to obtain a rough blank of lightweight densely packed SiO2 hollow sphere thermal insulation material. The rough blank of lightweight densely packed SiO2 hollow sphere thermal insulation material is taken out from the mold.

[0075] S5. Place the lightweight, densely packed SiO2 hollow sphere insulation material blank into a tube furnace and sinter it at a heating rate of 6℃ / min to 550℃ to obtain the lightweight, densely packed SiO2 hollow sphere insulation material.

[0076] Example 6

[0077] This embodiment provides a method for preparing a lightweight, close-packed SiO2 hollow sphere thermal insulation material:

[0078] S1. Using hydrogen-containing silicone oil as raw material, 20wt% acetic acid solution is added for crosslinking. The mass ratio of hydrogen-containing silicone oil to acetic acid solution is 1:5. Alkylphenol polyoxyethylene ether is used to emulsify into spheres, which are then cured at 1000℃ to form hollow SiO2 spherical shells.

[0079] S2, Pretreatment of SiO2 hollow spheres: Use deionized water to rinse the SiO2 hollow spheres. When rinsing, choose the soaking and filtering method to prevent the SiO2 hollow spheres from being damaged by violent shaking until the pH=7. Then put them in an oven and dry them at 100℃ for 2 hours before taking them out for use.

[0080] S3. Place the SiO2 hollow spheres treated in S2 in a single layer in the mold, spray a sodium silicate solution with a concentration of 40wt% 10 times to form bonding sites between the SiO2 hollow sphere particles, and repeat the above laying method 25 times to obtain a multi-layer densely packed SiO2 hollow sphere structure.

[0081] S4. The densely packed structure obtained in S3 is heated and dried in an oven to obtain a rough blank of lightweight densely packed SiO2 hollow sphere thermal insulation material. The rough blank of lightweight densely packed SiO2 hollow sphere thermal insulation material is taken out from the mold.

[0082] S5. Place the lightweight, densely packed SiO2 hollow sphere insulation material blank into a tube furnace and sinter it at a heating rate of 7℃ / min to 600℃ to obtain the lightweight, densely packed SiO2 hollow sphere insulation material.

[0083] Example 7

[0084] This embodiment provides a method for preparing a lightweight, close-packed SiO2 hollow sphere thermal insulation material:

[0085] S1. Using hydrogen-containing silicone oil as raw material, a 20wt% acetic acid solution is added for crosslinking. The mass ratio of hydrogen-containing silicone oil to acetic acid solution is 1:5. Alkylphenol polyoxyethylene ether is added to emulsify into spheres, which are then cured into SiO2 hollow spheres at a high temperature of 1500℃.

[0086] S2, Pretreatment of SiO2 hollow spheres: Use deionized water to rinse the SiO2 hollow spheres. When rinsing, choose the soaking and filtering method to prevent the SiO2 hollow spheres from being damaged by violent shaking until the pH=7 is reached. Then put them in an oven and dry them at 180℃ for 2 hours before taking them out for use.

[0087] S3. Place the SiO2 hollow spheres treated in S2 in a single layer in a mold, and spray with an aluminum phosphate solution with a concentration of 20wt% 20 times to form bonding sites between the SiO2 hollow sphere particles. Repeat the above laying method 30 times to obtain a multi-layer close-packed SiO2 hollow sphere structure (close-packed structure).

[0088] S4. Freeze-dry the close-packed structure obtained in S3 to obtain a rough blank of lightweight close-packed SiO2 hollow sphere thermal insulation material. Take out the rough blank of lightweight close-packed SiO2 hollow sphere thermal insulation material from the mold.

[0089] S5. Place the lightweight, densely packed SiO2 hollow sphere insulation material blank into a tube furnace and sinter it at a heating rate of 5℃ / min to 800℃ to obtain the lightweight, densely packed SiO2 hollow sphere insulation material.

[0090] Comparative Example 1

[0091] The preparation method of the comparative thermal insulation material is the same as that of Example 1, except that S3 is: SiO2 hollow spheres treated in S2 are laid in a single layer in a mold, and a sodium silicate solution with a concentration of 70wt% is sprayed 10 times to form bonding sites between the SiO2 hollow sphere particles. The above laying method is repeated 30 times to obtain a multi-layer densely packed SiO2 hollow sphere structure.

[0092] In this comparative example, due to the high concentration of sodium silicate (i.e., high sodium silicate content), sodium silicate accounts for a large proportion in the material, resulting in an increase in the heat transfer medium of the material, a decrease in the proportion of SiO2 hollow spheres, and an increase in thermal conductivity.

[0093] Comparative Example 2

[0094] The preparation method of the comparative thermal insulation material is the same as that of Example 1, except that S3 is: SiO2 hollow spheres treated in S2 are laid in a single layer in a mold, and a sodium silicate solution with a concentration of 3wt% is sprayed 10 times to form bonding sites between the SiO2 hollow sphere particles. The above laying method is repeated 30 times to obtain a multi-layer densely packed SiO2 hollow sphere structure.

[0095] In this comparative example, due to the low concentration of sodium silicate (i.e., low sodium silicate content), the proportion of sodium silicate in the material is small, resulting in a looser connection between the hollow spheres. The material structure is easily deformed and broken under pressure.

[0096] Comparative Example 3

[0097] The preparation method of the thermal insulation material in this comparative example is the same as that in Example 1, except that S5 is: the lightweight close-packed SiO2 hollow sphere thermal insulation material blank is placed in a tube furnace and heated to 1200°C at a heating rate of 5°C / min for sintering to obtain the thermal insulation material.

[0098] In this comparative example, the sintering temperature was too high, which caused the inorganic products to crystallize, thus increasing thermal conductivity and density.

[0099] Comparative Example 4

[0100] The preparation method of the thermal insulation material in this comparative example is the same as that in Example 1, except that S5 is: the lightweight close-packed SiO2 hollow sphere thermal insulation material blank is placed in a tube furnace and heated to 350°C at a heating rate of 5°C / min for sintering to obtain the thermal insulation material.

[0101] In this comparative example, the sintering temperature was too low, resulting in low bonding strength between powder particles and easy deformation of the material structure under pressure.

[0102] Comparative Example 5

[0103] The preparation method of the comparative thermal insulation material is the same as that of Example 1, except that S1 is: using hydrogen-containing silicone oil as raw material, adding acetic acid solution with a concentration of 70wt% for crosslinking, emulsifying into spheres using alkylphenol polyoxyethylene ether, and curing into SiO2 hollow spheres at a high temperature of 900℃.

[0104] In this comparative example, the acid solution used for crosslinking was too concentrated, causing flash condensation, which was not conducive to the formation of spheres and resulted in unstable material structure.

[0105] Comparative Example 6

[0106] The preparation method of the comparative thermal insulation material is the same as that of Example 1, except that S1 is: using hydrogen-containing silicone oil as raw material, adding acetic acid solution with a concentration of 3wt% for crosslinking, emulsifying into spheres using alkylphenol polyoxyethylene ether, and curing into SiO2 hollow spheres at a high temperature of 900℃.

[0107] In this comparative example, the acid solution used for crosslinking had too low a concentration, resulting in a weak acidic environment that was not conducive to the formation of spheres and made the material structure unstable.

[0108] Comparative Example 7

[0109] The preparation method of the comparative thermal insulation material is the same as that of Example 1, except that S1 is: using hydrogen-containing silicone oil as raw material, adding acetic acid solution with a concentration of 20wt% for crosslinking, emulsifying into spheres using alkylphenol polyoxyethylene ether, and curing into SiO2 hollow spheres at a high temperature of 450℃.

[0110] In this comparative example, the hollow sphere in S1 was cured at too low a temperature, resulting in insufficient curing of the material, which was not conducive to the formation of the sphere and made the material structure unstable.

[0111] Comparative Example 8

[0112] The preparation method of the comparative thermal insulation material is the same as that of Example 1, except that S1 is: using hydrogen-containing silicone oil as raw material, adding acetic acid solution with a concentration of 20wt% for crosslinking, emulsifying into spheres using alkylphenol polyoxyethylene ether, and curing into SiO2 hollow spheres at a high temperature of 1700℃.

[0113] In this comparative example, the high-temperature curing temperature of the hollow spheres in S1 was too high, resulting in excessively thick walls of the SiO2 hollow spheres and reduced internal air content, which affected the thermal insulation performance of the material.

[0114] Figure 1The image shows a SEM image of the lightweight, densely packed SiO2 hollow sphere thermal insulation material obtained in Example 1 of this invention. It can be seen that the spherical structure is tightly arranged and there is a small amount of sodium silicate connecting the SiO2 hollow spheres, which ensures the material has a low thermal conductivity.

[0115] Figure 2 The SEM image of the thermal insulation material obtained in Comparative Example 1 of this invention shows that excessive spraying of sodium silicate solution leads to a loose arrangement of spherical structures, and excessive sodium silicate content leads to an increase in the thermal conductivity of the material, which is detrimental to the thermal insulation performance of the fairing.

[0116] Density was determined using Archimedes' displacement method. The first step involved measuring the sample's mass (M0) in its dry state, also known as dry weight. The second step involved placing the sample in a beaker filled with deionized water and evacuating it in a vacuum drying oven until the water filled all the internal pores and no air bubbles appeared on the surface. The sample was then removed from the water, wiped dry, and weighed again to obtain its wet weight, denoted as M1. The third step involved weighing the sample in deionized water to obtain its buoyant weight, recorded as M2. The actual density (ρ) of the sample was then calculated using a formula.

[0117]

[0118] Thermal conductivity was measured using the DRPL-II geotechnical thermal conductivity tester. The instrument employs a method where a stable hot surface temperature is applied to one side of the sample, and heat is transferred through the sample to the cold surface (room temperature). The thermal conductivity and thermal resistance are calculated by measuring the transferred heat flow. The instrument references the standards GB / T10295-2008 (Determination of Steady-State Thermal Resistance and Related Properties of Insulation Materials by Heat Flow Meter Method) and ASTM C518-04 Test Method for Determining Steady-State Heat Flux and Heat Transfer Characteristics by Heat Flow Meter Method.

[0119] Main technical parameters:

[0120] 1. Thermal conductivity range: 0.001~100W / mk, with an accuracy better than 3%.

[0121] 2. Hot surface temperature: room temperature to 99.99℃, measured by a high-precision digital display meter with 0.2-level accuracy and 0.01℃ resolution.

[0122] 3. Cold surface temperature: Room temperature, measured using a high-precision digital display meter with 0.2-level accuracy and 0.01℃ resolution.

[0123] 4. Hot surface temperature control: room temperature to 99.99℃, using a high-precision programmable digital display temperature meter with 0.2-level accuracy and 0.01℃ resolution, flat plate heater, and bidirectional thyristor control.

[0124] 5. Cold noodles are cooled by forced water.

[0125] 6. Computer-automated testing is used.

[0126] 7. A WPY heat flow meter was used, with a heat flow parameter of 23.26 W / m. 2 .mV.

[0127] 8. Heat transfer area of ​​hot and cold plates: 150×150 (mm).

[0128] 9. Adjustable spacing between hot and cold plates: 0~160 (mm).

[0129] The thermal conductivity and average density of the insulation materials prepared in Examples 1-7 and Comparative Examples 1-8 are shown in Table 1.

[0130] Table 1. Performance comparison of lightweight close-packed SiO2 prepared in Examples 1-7 and Comparative Examples 1-8

[0131] Thermal conductivity / W / m K <![CDATA[Average density / g·cm -3 > Example 1 0.021 0.13 Example 2 0.023 0.14 Example 3 0.022 0.13 Example 4 0.020 0.13 Example 5 0.024 0.15 Example 6 0.026 0.16 Example 7 0.032 0.18 Comparative Example 1 0.038 0.16 Comparative Example 2 0.031 0.15 Comparative Example 3 0.036 0.15 Comparative Example 4 0.024 0.13 Comparative Example 5 0.042 0.20 Comparative Example 6 0.041 0.18 Comparative Example 7 0.052 0.22 Comparative Example 8 0.028 0.16

[0132] In Example 7, the excessively high curing temperature of the spheres led to an increase in wall thickness and even deformation of the formed structure, resulting in increased density and improved thermal conductivity. In Comparative Example 2, the sodium silicate content was low, but the degree of powder extrusion and fragmentation increased, causing the average density of SiO2 not to decrease. As shown in Table 1, compared with Comparative Examples 1-8, the lightweight, densely packed SiO2 hollow sphere thermal insulation material prepared using the method of this invention exhibits lower density and excellent thermal insulation performance.

[0133] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a lightweight, close-packed silica hollow sphere thermal insulation material, characterized in that, Includes the following steps: S1. Rinse the silica hollow spheres with water until the pH is neutral, then dry. S2. Lay out a single layer of silica hollow spheres treated in S1, spray with inorganic binder, and repeat the above laying method to obtain a multi-layer densely packed silica hollow sphere structure. S3. Dehydrate the multilayer densely packed silica hollow sphere structure to obtain a rough blank of lightweight densely packed silica hollow sphere thermal insulation material; S4. The rough blank of the lightweight close-packed silica hollow sphere thermal insulation material is sintered to obtain the lightweight close-packed silica hollow sphere thermal insulation material; In S1, the preparation method of the silica hollow spheres is as follows: using hydrogen-containing silicone oil as raw material, adding acid solution and emulsifier, and curing at high temperature of 500~1500℃ to form silica hollow spheres; In S1, the acid solution is an acetic acid solution; the emulsifier includes alkylphenol polyoxyethylene ether, dibenzylphenol polyoxyethylene ether, alkylphenol polyoxyethylene ether, or fatty alcohol polyoxyethylene ether. In S1, during the preparation of silica hollow spheres, the mass ratio of hydrogen-containing silicone oil to acetic acid solution is 1:

5.

2. The method for preparing the lightweight close-packed silica hollow sphere thermal insulation material according to claim 1, characterized in that, In S2, the inorganic binder includes sodium silicate solution or aluminum phosphate solution.

3. The method for preparing the lightweight close-packed silica hollow sphere thermal insulation material according to claim 2, characterized in that, In S2, the concentrations of the sodium silicate solution and the aluminum phosphate solution are both 5 wt% to 60 wt%.

4. The method for preparing the lightweight close-packed silica hollow sphere thermal insulation material according to claim 1, characterized in that, Each layer of flat-laid silica hollow spheres is sprayed with inorganic binder 2 to 20 times; The silica hollow spheres are repeated 15 to 30 times.

5. A lightweight, close-packed silica hollow sphere thermal insulation material, characterized in that, It is prepared according to any one of claims 1 to 4.

6. The application of the lightweight close-packed silica hollow sphere thermal insulation material according to claim 5 in the aerospace field.

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