Layered freeze-thaw-resistant thermal insulation material and preparation method thereof

Abstract

The invention relates to a preparation method of a layered freeze-thaw-resistant thermal insulation material, and aims to solve the problems that a traditional thermal insulation material in a high-humidity freeze-thaw environment is prone to increase in heat conductivity coefficient and deterioration in mechanical property, an inner-outer double-layer composite structure is designed, an inner-layer dry blend comprises aluminum silicate ceramic fibers, sodium borate and silicon dioxide aerogel, and an outer-layer dry blend comprises aluminum silicate ceramic fibers, sodium borate and silicon dioxide aerogel. The outer-layer dry blend comprises rock wool and silicon dioxide aerogel; phenolic resin is applied to the surface of the outer layer through a directional spraying technology, silica sol is coated on the surface of the inner layer, partitioned high-temperature curing is carried out after rolling preforming is carried out, and a metal fiber layer is bonded to the surface of the outermost layer of the layered blank blanket after partitioned curing is completed. The prepared layered composite material has low thermal conductivity, high breaking strength and high compressive strength, the gradient functional layer structure of the layered composite material can effectively block moisture permeation, stable heat preservation and mechanical properties are kept in repeated freezing and thawing cycles, and the layered composite material is suitable for building heat preservation engineering in a high-humidity freezing and thawing environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal insulation materials, in particular to a layered anti-freezing and anti-thawing thermal insulation material and a preparation method thereof, and in particular to a high-strength and low-thermal-conductivity composite thermal insulation material prepared by using recycled aluminum silicate ceramic fibers and rock wool through a specific layered structure and process. BACKGROUND

[0002] In the current industrial production and construction field operation process, a large amount of waste thermal insulation materials such as rock wool and aluminum silicate ceramic fibers are generated every year. If these materials are randomly stacked or landfilled, not only a large amount of land resources are occupied, but also the fibers contained therein are easy to drift, causing air and soil pollution and affecting the ecological environment and human health. On the other hand, the production of traditional new thermal insulation materials still heavily relies on mineral exploitation and high-temperature smelting, consuming a large amount of primary resources and energy, resulting in high costs, and it is difficult to balance economic benefits and environmental sustainability.

[0003] The currently widely used traditional thermal insulation materials such as rock wool and aluminum silicate ceramic fibers can still maintain certain thermal insulation performance at room temperature or low temperature, basically meeting the general thermal insulation requirements. However, as the use temperature increases, especially in the industrial scene of steam pipes, heat pipes and other high-temperature and high-humidity environments with frequent freezing-thawing cycle fluctuations, conventional thermal insulation materials are not only subject to high-temperature performance degradation, but also prone to thermal insulation layer cracking, delamination or surface pulverization, resulting in failure of the thermal insulation system and a substantial increase in maintenance costs.

[0004] Therefore, it has become an urgent need to develop a new type of thermal insulation material that can comprehensively utilize industrial solid waste while having low thermal conductivity, high bending and compressive strength, and excellent hydrophobic performance to cope with high-humidity freezing-thawing cycle environments. SUMMARY

[0005] The present application aims to solve the problem of the increase in thermal conductivity and the deterioration of mechanical properties of traditional thermal insulation materials caused by water intrusion in high-humidity freezing-thawing cycle environments. A functional layered design is adopted, and an inner layer dry mixture containing recycled aluminum silicate ceramic fibers, sodium borate and silica aerogel particles, and an outer layer dry mixture containing recycled rock wool and silica aerogel particles are prepared respectively. The inner layer dry mixture and the outer layer dry mixture are laid in turn to form a layered mat, and then a silicasol is applied to the inner layer of the layered mat and a phenolic resin is applied to the outer layer of the layered mat by directional spraying technology. Finally, the material is preformed by rolling and cured in different zones. The obtained material has excellent properties of low thermal conductivity, high hydrophobicity and high bending strength, and can effectively resist structural damage caused by freezing-thawing cycles. The technical scheme provided by the present application is as follows: On the one hand, the present application provides a preparation method of a layered anti-freezing and anti-thawing thermal insulation material, comprising the following steps: (1) Dry mixing and cotton laying forming: respectively preparing inner layer dry mixture and outer layer dry mixture, then laying the inner layer dry mixture and the outer layer dry mixture in turn to form a layered blank; wherein the inner layer dry mixture comprises aluminum silicate ceramic fiber, 3 wt%-8 wt% of sodium borate based on the total weight of the inner layer dry mixture, and 3 wt%-5 wt% of silica aerogel particles based on the total weight of the inner layer dry mixture; the outer layer dry mixture comprises rock wool, and 5 wt%-8 wt% of silica aerogel particles based on the total weight of the outer layer dry mixture; (2) Directional spraying of binder: first, spraying phenolic resin from top to bottom on the outer layer of the layered blank, the addition amount of the phenolic resin being 3 wt%-5 wt% of the total weight of the outer layer dry mixture; then, spraying silica sol from bottom to top on the inner layer of the layered blank, the addition amount of the silica sol being 10 wt%-15 wt% of the total weight of the inner layer dry mixture, and the addition amount of the silica sol being based on its solid content; (3) Preforming: roll preforming the layered blank after directional spraying of the binder; (4) Zonal curing: sequentially passing the preformed layered blank through a first curing zone and a second curing zone for zonal curing; wherein the temperature of the first curing zone is 200℃-250℃, and the temperature of the second curing zone is 800℃-900℃; (5) Bonding metal fiber layer: bonding a metal fiber layer on the outermost surface of the layered blank after zonal curing.

[0006] Optionally, before step (1), it further comprises raw material pretreatment: Crushing and impurity removing the aluminum silicate ceramic fiber and the rock wool respectively to obtain fiber particles; Heat treating the hydrophobic silica aerogel particles to change the surface from hydrophobic to hydrophilic.

[0007] Optionally, the crushing is sequentially coarse crushing and fine crushing, and finally the fiber particles with a particle size of 1 mm-3 mm are obtained; the impurity removing is a combined process of magnetic separation and air flow separation.

[0008] Optionally, after the heat treatment, it further comprises surface chemical modification of the silica aerogel particles using a coupling agent; the coupling agent is selected from one of aminosilane, epoxy silane or methacryloyloxy silane.

[0009] Optionally, the temperature of the heat treatment is 400℃-450℃.

[0010] Optionally, before step (3), it further comprises a pre-drying step: pre-drying the layered blank at 80℃-100℃.

[0011] Optionally, in step (4), the curing time of the layered blank in the first curing zone is 2-5 min, and the curing time of the layered blank in the second curing zone is 3-8 min.

[0012] Optionally, in step (4), the layered blank is conveyed through the first curing zone and the second curing zone in sequence by a high-temperature-resistant conveying belt.

[0013] Optionally, after step (4), a post-processing step is further included, that is, the cured layered blank is cooled to room temperature and cut into a predetermined size.

[0014] In another aspect, the application further provides a layered anti-freeze-thaw thermal insulation material prepared by the above-mentioned preparation method.

[0015] By adopting the technical scheme, the layered anti-freeze-thaw thermal insulation material and the preparation method thereof have the following beneficial effects: 1. The application realizes efficient thermal resistance management through the functional design of the inner and outer layers and the gradient distribution of silica aerogel particles. The inner layer uses aluminum silicate ceramic fiber as the matrix, combines sodium borate and silica aerogel particles, and forms a high-temperature thermal insulation layer to ensure thermal stability under high-temperature working conditions. The outer layer uses rock wool as the matrix and combines a high content of silica aerogel particles to build a moisture-proof and low-temperature thermal resistance barrier. The two layers of materials form a continuous thermal resistance layer through the gradient distribution of aerogel, and can still maintain stable thermal insulation performance in a humid environment.

[0016] 2. The innovative zoned curing process of the application realizes the optimized construction of the material structure. The first curing zone is cured by phenolic resin to make the material have good initial strength and toughness. The high-temperature treatment of the second curing zone converts the silica sol into a stable silicon-oxygen network structure to realize inorganic ceramic reinforcement. Through the zoned curing process of "low-temperature organic curing + high-temperature inorganic ceramicization", the material meets the requirements of bending and compressive strength under high temperature and effectively resists the ice expansion stress generated by freeze-thaw cycles.

[0017] 3. The application adopts the design concept of functional layering to prepare a composite blank composed of an inner layer and an outer layer. The inner layer improves the moisture resistance and high-temperature stability of the material by sodium borate modification. The outer layer fully utilizes the natural hydrophobic property of rock wool and combines a high content of silica aerogel particles to form an efficient moisture-proof and thermal insulation barrier, so that the hydrophobic rate of the material is more than 95%. This multi-level protection design ensures that the material maintains stable thermal insulation performance and structural integrity in a high-humidity and freeze-thaw cycle environment for a long time, prolonging the service life.

[0018] 4. The method realizes high-value recycling of waste aluminum silicate ceramic fiber and rock wool, converts industrial solid waste into high-performance thermal insulation products, reduces raw material cost, reduces environmental burden, and conforms to the concept of green manufacturing and circular economy development. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced in the following. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0020] Figure 1 A cross-sectional schematic diagram of the layered anti-freezing and thawing thermal insulation material provided by the embodiments of the present application is shown in FIG. 1. Figure 2 A schematic diagram of the layered anti-freezing and thawing thermal insulation material provided by the embodiments of the present application is shown in FIG. 2. Figure One Figure 3 A schematic diagram of the layered anti-freezing and thawing thermal insulation material provided by the embodiments of the present application is shown in FIG. 3. Figure Two . DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the scope of protection of the present application.

[0022] ​​The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. In the description of the invention, it should be understood that the terms "upper," "lower," "top," "bottom," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to 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 invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein.

[0023] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0024] The inventors discovered that under conditions of frequent freeze-thaw cycles, the performance degradation of traditional insulation materials is a complex problem resulting from the combined effects of physical and chemical processes. The root cause lies in the following: First, moisture penetrates and dynamically replaces the static air layer within the material's pores. Since the thermal conductivity of water (~0.6 W / m·K) is tens of times greater than that of still air (~0.026 W / m·K),... The thermal conductivity (W / m·K) causes a sharp increase in the overall equivalent thermal conductivity of the material, leading to a decline in system energy efficiency primarily due to conductive heat loss. Secondly, and more critically, and often overlooked, is the microscopic mechanical damage caused by the water-ice phase transition during freeze-thaw cycles. When water freezes, it undergoes approximately 9% volume expansion, applying vertical tensile stress to the pore walls. If the material's flexural strength is insufficient, this directly induces the initiation and propagation of microcracks, which, after cyclical accumulation, evolve into macroscopic cracks, delamination, and even pulverization. Simultaneously, the compressive stress generated by the phase transition continuously tests the compressive strength and fatigue resistance of the material's framework, easily leading to irreversible collapse of the pore structure and an increase in porosity. This not only further degrades the thermal insulation performance but also creates conditions for internal air convection, thus enhancing the convective heat transfer effect and forming a vicious cycle of synergistic deterioration of both thermal and structural performance. Traditional homogeneous materials, due to limitations in composition and structure, cannot simultaneously address the triple challenges of high thermal insulation, hydrophobicity and impermeability, and high mechanical strength.

[0025] Based on the above findings, this invention provides a method for preparing a layered freeze-thaw resistant thermal insulation material. In the prepared structure: a functionally differentiated "inner solid and outer protective" double-layer composite system is constructed. The inner layer uses high-temperature resistant aluminum silicate ceramic fiber as the matrix, combined with sodium borate and silica aerogel particles, to form a structural thermal insulation layer responsible for high-temperature thermal insulation and mechanical support. The outer layer uses hydrophobic rock wool as the matrix, combined with a high content of silica aerogel particles, to form a moisture-proof and heat-insulating barrier layer that prevents moisture intrusion. The gradient distribution of silica aerogel particles between the two layers forms a continuous and efficient thermal resistance layer. More importantly, the "low-temperature curing-high-temperature sintering" partitioned curing process precisely matches the chemical and physical properties of the inner and outer layers: the low-temperature stage causes the outer phenolic resin to cross-link, cure, and solidify; the subsequent high-temperature stage causes the inner borate layer to melt, forming "glass weld points" and co-constructing a robust ceramic network with nano-SiO2 particles. Simultaneously, after the outer phenolic resin undergoes sacrificial carbonization, it can still maintain its shape and hydrophobic function thanks to the rock wool fibers and carbon skeleton, thus achieving an organic combination of the excellent properties of the two layers at the microscopic level. This enables the material to maintain excellent comprehensive performance—low thermal conductivity, high hydrophobicity, and high flexural and compressive strength—even under harsh freeze-thaw conditions, solving the key technical challenge of rapid degradation of thermal performance and microstructural damage caused by moisture intrusion, phase transformation stress, and the resulting enhanced convection effect.

[0026] Specifically, the following steps are included: Raw material pretreatment: First, the recycled waste aluminosilicate ceramic fibers and rock wool are sorted and sorted, and then crushed and impurity removed in sequence. First, the materials are coarsely crushed into blocky materials with a particle size of 5-10 cm by a jaw crusher, and then finely crushed by an impact crusher to finally obtain uniform fiber particles with a particle size of 1-3 mm, laying the foundation for subsequent mixing processes. The impurity removal process adopts a combination of magnetic separation and air separation. First, the magnetic separator removes metal impurities (such as iron wires and nails left over from construction), and then the air separation separates light impurities such as dust and plastic fragments based on density differences, thereby ensuring the purity of the recycled fibers. In addition, the silica aerogel particles are pretreated by heating the hydrophobic silica aerogel particles in air to 400~450°C and holding them at that temperature for a period of time (e.g., 2h) to decompose the hydrophobic groups on their surface and restore them to hydrophilic silanol groups (-Si-OH). Subsequently, the surface is chemically modified using coupling agents such as aminosilanes (e.g., KH-550), epoxysilanes (e.g., KH-560), or methacryloyloxysilanes (e.g., KH-570), so that the siloxane end bonds to the silanol groups on the aerogel surface, while the active functional groups (amino, epoxy, etc.) at the other end provide chemical crosslinking sites for subsequent bonding with organic resin binders. This greatly enhances the chemical bonding between the silica aerogel particles and the organic binders, rather than simple physical adsorption, thus improving the bonding strength.

[0027] Dry mixing and lining molding: Prepare inner dry mix and outer dry mix separately, and then lay the inner dry mix and outer dry mix in sequence to form a layered blanket.

[0028] The inner dry mix includes aluminosilicate ceramic fibers, sodium borate accounting for 3 wt% to 8 wt% of the total weight of the inner dry mix, and silica aerogel particles accounting for 3 wt% to 5 wt% of the total weight of the inner dry mix. This layer, serving as the main structure near the heat source, uses aluminosilicate ceramic fiber as the primary material. While possessing excellent high-temperature resistance, it is more prone to water absorption than rock wool. Therefore, a small amount of sodium borate (such as sodium tetraborate decahydrate, chemical formula Na2B4O7·10H2O, commonly known as "borax") is added to enhance its moisture resistance. Sodium borate strengthens the silicate network's moisture resistance by reducing the ion diffusion rate, effectively reducing the overall water absorption rate of the aluminosilicate ceramic fiber. Simultaneously, at high temperatures, it forms a uniform, continuous, and sufficiently strong glassy phase, firmly bonding the fibers, improving structural strength, and enhancing moisture resistance. The optimal amount of sodium borate is controlled within the range of 3 wt% to 8 wt%. If it is below 3 wt%, the bonding phase is insufficient, resulting in fewer and discontinuous "welding points" between fibers, low fiber network bonding strength, and a loose structure. If it exceeds 8 wt%, the moisture absorption rate is also reduced. Excessive glass phase (wt%) can encapsulate the fibers, making them brittle and prone to vitrification and significant shrinkage at high temperatures, leading to a sharp decline in the material's high-temperature performance. Furthermore, due to the high operating temperature of the inner layer, 3wt%–5wt% silica aerogel particles are added. Appropriate amounts of silica aerogel particles can further improve thermal insulation performance while ensuring high-temperature stability and unobstructed pores. However, excessive silica aerogel particles can further weaken the integrity of the cured ceramic body, making it more prone to pulverization at high temperatures. Additionally, the ceramic fibers themselves are relatively fine, forming small pores; excessive filling can completely block the pores, hindering the release of internal moisture during furnace shutdown and increasing the risk.

[0029] The outer dry-mix layer comprises rock wool and 5 wt% to 8 wt% silica aerogel by weight. As the core functional layer for moisture and frost protection, this layer uses naturally hydrophobic rock wool as the matrix, incorporating a high proportion (5 wt% to 8 wt%) of silica aerogel particles to construct a highly efficient thermal insulation and moisture barrier. The outer layer requires extremely low thermal conductivity and extremely high hydrophobicity; appropriately increasing the silica aerogel particle content enhances its ability to block heat flow and resist liquid water penetration. Since the outer layer does not directly withstand high temperatures, its high-temperature strength requirements are slightly lower than those of the inner layer, thus allowing for greater space to accommodate functional fillers. Simultaneously, the coarser rock wool fibers and larger pore structure enable it to accommodate more silica aerogel particles without completely blocking the pore channels. The subsequently sprayed phenolic resin, during the low-temperature curing stage, can fully coat and fix the silica aerogel particles, maintaining the material's permeability while imparting excellent initial strength and shape stability to the outer layer, achieving synergistic optimization of moisture resistance, thermal insulation, and mechanical properties.

[0030] Directional application of adhesive: The layered raw blanket passes sequentially through two functionally independent spraying zones via a conveyor belt. First, the outer layer is sprayed: an array of nozzles arranged above atomizes and sprays phenolic resin of a specific viscosity from top to bottom. The amount added is precisely controlled at 3 wt%-5 wt% of the total weight of the outer layer dry mix. This optimal ratio fully utilizes the excellent film-forming properties of phenolic resin, effectively encapsulating and fixing silica aerogel particles to prevent detachment and pulverization, while avoiding decreased material permeability or increased volatiles at high temperatures due to excessive resin. By precisely controlling the spraying pressure and flow rate, it is ensured that the resin only wets and partially penetrates the outer layer of the rock wool, without penetrating into the inner layer. The layered blank then enters the inner coating zone, where the conveyor belt is replaced with a perforated plate or fine mesh belt structure. A nozzle array below sprays silica sol upwards, with the addition amount controlled at 10 wt%-15 wt% of the total weight of the inner dry mix, based on solid content. Under the combined force of spraying and capillary action, the silica sol preferentially wets and penetrates the inner layer of the aluminosilicate ceramic fibers. Its dosage ensures thorough encapsulation of the aerogel particles while precisely controlling the silica network structure after sintering. Increasing the dosage improves the degree of ceramicization and high-temperature strength, but also correspondingly increases the material's hardness and brittleness; therefore, strict control of the addition amount is necessary. The entire spraying process utilizes gravity to naturally inhibit excessive upward penetration of the silica sol, ensuring precise layering and positioning of the two functionally differentiated binders along the blank's thickness.

[0031] Pre-drying: The sprayed layered preform is placed in a hot air environment at 80℃~100℃ for drying. Before entering the high-temperature curing oven, the outer phenolic resin and the inner silica sol are preliminarily shaped, effectively reducing the fluidity of the binder during subsequent transportation and processing, thereby inhibiting interface mixing caused by mutual migration of the two binders, and providing a stable and clearly defined structural foundation for subsequent step curing.

[0032] Preforming: The pre-dried layered blanket is pre-formed by roll forming. Mechanical roll forming tightly integrates the inner and outer layers, eliminates gaps between layers, enhances the overall structural density and interface bonding strength, and ensures that the layered blanket maintains structural integrity during subsequent conveying and high-temperature curing, thus avoiding layer separation.

[0033] Zoned Curing: The pre-formed layered blank is sequentially conveyed to the first curing zone and the second curing zone via a high-temperature resistant conveyor belt (such as a metal mesh belt). The temperature in the first curing zone is controlled at 200℃~250℃ (e.g., 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃), and the curing time is 2~5min (e.g., 2min, 3min, 4min, or 5min). This temperature condition promotes the full cross-linking of the outer phenolic resin, forming a three-dimensional network structure, thereby establishing stable mechanical properties and geometry of the outer layer. At the same time, this temperature is much lower than the melting point of the inner sodium borate (approximately 740℃) and the sintering temperature of the silica sol. The inner layer only undergoes moisture evaporation and physical drying, and its fiber network remains in an unsintered "green" state. It relies on the fiber interweaving formed by the cotton-laying process to maintain a tight bond with the outer layer, preserving the structural basis for the subsequent ceramic sintering in the high-temperature zone. In the second curing zone, the temperature is 800℃~900℃ (the specific setting within this range needs to be determined experimentally based on the amount of sodium borate added and the sintering strength requirements), and the curing time is 3~8 minutes (e.g., 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, or 8 minutes). This high-temperature environment causes the inner layer of sodium borate to melt and form a glassy liquid phase, effectively wetting the surface of the aluminosilicate ceramic fibers and silica aerogel particles, and forming "glass weld points" at the fiber intersections. At the same time, the nano-SiO2 particles in the silica sol undergo high-temperature sintering, synergistically constructing a ceramicized porous structure, so that the inner layer forms a strong solid with high-temperature strength after cooling. Meanwhile, the cured phenolic resin of the outer layer decomposes and carbonizes at this temperature, and the resulting carbon skeleton and inorganic residues can still maintain the macroscopic shape of the outer layer and continue to fix the silica aerogel particles. Since the rock wool fibers themselves can withstand temperatures above 600℃, they will not melt when passing through this area for a short time. Finally, the outer layer maintains its structural integrity after the organic binder is burned off, and the overall rigidity is further improved.

[0034] Bonded Metal Fiber Layer: After zoned curing, a metal fiber layer (e.g., an aluminum fiber layer) is bonded to the outermost surface of the layered blanket, thus encapsulating the insulation material. This metal fiber layer effectively improves the infrared reflectivity of the material surface, enhancing its thermal insulation performance. Simultaneously, this structure is suitable for protecting special parts of pipes and equipment (such as top-mounted components, drainage components, and areas where metal protective plates cannot be installed), broadening the material's application range.

[0035] Post-processing: The layered blank blanket that has completed partition curing is transported to the cooling section, where it is cooled to room temperature by natural cooling or forced air cooling. Then, it is precisely processed into boards or blankets of predetermined sizes using cutting equipment, and finally, the finished layered anti-freeze-thaw insulation material that meets the design specifications is obtained.

[0036] Please see Figures 1 to 3This invention also provides a layered freeze-thaw resistant insulation material, which is prepared by the method described in any of the foregoing embodiments. The material comprises a composite preform consisting of an inner layer and an outer layer, and a metal fiber layer bonded to the outermost surface of the composite preform. This material exhibits excellent overall performance and is particularly suitable for harsh working conditions involving high humidity and frequent freeze-thaw cycles.

[0037] Example 1 A method for preparing a layered freeze-thaw resistant thermal insulation material: Alumina silicate ceramic fibers and rock wool are sequentially subjected to coarse and fine crushing to obtain fiber particles with a particle size of 2 mm. Impurities are removed using a combination of magnetic separation and airflow separation. Simultaneously, hydrophobic silica aerogel particles are heat-treated at 430℃ for 2 h to change their surface from hydrophobic to hydrophilic, and their surface is chemically modified using an aminosilane coupling agent (KH-550). Subsequently, an inner layer dry mix (1000 g, containing 910 g alumina silicate ceramic fibers, 50 g sodium borate (5.0 wt% of the total inner layer weight), and 40 g modified silica aerogel particles (4.0 wt% of the total inner layer weight)) and an outer layer dry mix (1000 g, containing 930 g rock wool and 70 g modified silica aerogel particles (7.0 wt% of the total outer layer weight)) are prepared. The above dry mixture is laid out in sequence to form a layered blank. 40 g of silica sol (4.0 wt% of the total weight of the inner layer by solid content) is sprayed onto the inner layer from bottom to top. 150 g of phenolic resin (15.0 wt% of the total weight of the outer layer) is sprayed onto the outer layer from top to bottom. After pre-drying at 90°C for 5 min, it is pre-formed by roller pressing. The pre-formed layered blank is then fed into the first curing zone at 220°C for 3 min and the second curing zone at 850°C for 5 min via a high-temperature resistant conveyor belt. After the zone curing is completed, an aluminum fiber layer is bonded to the outermost surface of the layered blank. Finally, it is cooled to room temperature and cut into predetermined sizes to obtain the finished layered anti-freeze-thaw insulation material.

[0038] Example 2 The preparation method is the same as in Example 1, except that the surface of the silica aerogel particles is not chemically modified.

[0039] Example 3 The preparation method is the same as in Example 1, except that the heat treatment temperature of the silica aerogel particles is controlled at 320°C in the raw material pretreatment step.

[0040] Example 4 The preparation method is the same as in Example 1, except that no pre-drying step is performed, and the adhesive is directly pre-formed by roll pressing after directional spraying.

[0041] Example 5 The preparation method is the same as in Example 1, except that the pre-drying temperature is 300°C.

[0042] Example 6 Referring to the preparation method of Example 1, the difference is that in the partition curing step, the curing time of the first curing zone is adjusted to 1.5 min and the curing time of the second curing zone is adjusted to 2.5 min.

[0043] Comparative Example 1 The preparation method is the same as in Example 1, except that the amount of sodium borate added to the inner dry mix is ​​10 g (accounting for 1.0 wt% of the total weight of the inner dry mix).

[0044] Comparative Example 2 The preparation method is the same as in Example 1, except that the amount of sodium borate added to the inner dry mix is ​​100 g (accounting for 10.0 wt% of the total weight of the inner dry mix).

[0045] Comparative Example 3 The preparation method is the same as in Example 1, except that the amount of modified silica aerogel particles added to the inner dry mix is ​​70 g (accounting for 7.0 wt% of the total weight of the inner dry mix).

[0046] Comparative Example 4 The preparation method is the same as in Example 1, except that the amount of modified silica aerogel particles added to the outer dry mix is ​​40 g (accounting for 4.0 wt% of the total weight of the outer dry mix).

[0047] Comparative Example 5 The preparation method is the same as in Example 1, except that the amount of phenolic resin added is 80 g (accounting for 8.0 wt% of the total weight of the outer dry mix).

[0048] Comparative Example 6 The preparation method is the same as in Example 1, except that the amount of silica sol added is 180 g (the amount of solid added accounts for 18.0 wt% of the total weight of the inner dry mix).

[0049] Comparative Example 7 The preparation method is the same as in Example 1, except that it is directly cured at 400°C for 10 min.

[0050] Comparative Example 8 Referring to the preparation method of Example 1, the difference is that the layered structure preparation is not carried out. The inner dry mix and the outer dry mix are mixed evenly and then laid out in one go to form a single-layer blank. The adhesive spraying process is adjusted to spray 40 g of phenolic resin on the single-layer blank from top to bottom and 150 g of silica sol from bottom to top.

[0051] Test case Systematic performance tests were conducted on the layered freeze-thaw resistant insulation materials prepared in Examples 1-6 and Comparative Examples 1-8, specifically including thermal conductivity, hydrophobicity, tensile strength, flexural strength, compressive strength, and durability. Thermal conductivity was measured using the steady-state heat flow method under a standard environment of 25°C and 50%RH, characterizing the material's ability to prevent heat transfer; a lower value indicates better insulation performance. Hydrophobicity was assessed by measuring the contact angle between the material surface and water using a contact angle meter; a contact angle greater than 90° indicates good hydrophobicity. Tensile strength was tested according to GB / T 1040 standard using a tensile testing machine at a rate of 5 mm / min, reflecting the material's resistance to tensile failure. Flexural strength was measured using the three-point bending method with a span of 30 mm and a loading rate of 1 mm / min, determining the material's resistance to bending fracture and reflecting its resistance to bending failure. Compressive strength was tested according to GB / T 13480 standard using a universal testing machine to test the compressive properties of specimens with dimensions of 100 mm × 100 mm × 50 mm. During testing, a compressive load was applied at a constant rate of 1 mm / min until the specimen showed significant deformation or failure. The maximum compressive load was recorded, and the compressive strength was calculated. This index directly reflects the material's ability to resist external pressure loads and is a key mechanical parameter for evaluating the structural integrity of insulation materials during pipe wrapping construction and long-term service. Durability was assessed through freeze-thaw cycle performance testing, involving 50 freeze-thaw cycles at temperatures ranging from ~20℃ to 5℃. The rate of change in thermal conductivity after each cycle was measured to reflect the stability of the insulation performance. The retention rates of flexural strength and compressive strength were measured to evaluate the durability of mechanical properties. The appearance integrity was observed, checking for cracks, delamination, and powdering to determine structural stability. The characterization results are shown in Tables 1 and 2.

[0052] Table 1 Test Results of Basic Performance Parameters

[0053] Table 2 Durability Test Results

[0054] Comprehensive analysis of the test data shows that Example 1 exhibits the best overall performance, with a room temperature thermal conductivity of 0.028 W / (m·K), a hydrophobicity of 98%, a flexural strength of 0.45 MPa, a compressive strength of 0.38 MPa, and a strength retention rate exceeding 92% after 50 freeze-thaw cycles, maintaining a good appearance, fully verifying the ideal match between the formulation system and process parameters. Example 2, due to the lack of chemical modification of the aerogel, resulted in weakened interfacial bonding, causing the thermal conductivity to rise to 0.029 W / (m·K); Example 3, due to insufficient heat treatment temperature, caused the hydrophobicity to drop to 92%; Example 4, due to the lack of pre-drying, resulted in weak interlayer bonding, leading to edge cracking after freeze-thaw cycles; Example 5, due to excessively high pre-drying temperature introducing internal stress, reduced the flexural strength retention rate to 75%; Example 6, due to insufficient curing time, resulted in overall material strength deterioration and delamination. Comparative Example 1, due to insufficient sodium borate content in the inner layer, resulted in too few "glass weld points" formed at high temperatures, leading to a loose material structure and a flexural strength of only 0.20 MPa. Severe cracking and delamination occurred after freeze-thaw cycles. Comparative Example 2, due to excessive sodium borate, experienced significant embrittlement due to the excess glass phase, causing a sharp drop in flexural strength to 0.15 MPa. Simultaneously, high-temperature shrinkage led to structural deterioration, increasing the thermal conductivity to 0.040 W / (m·K). Comparative Example 3, after adding excessive silica aerogel to the inner layer, achieved the lowest thermal conductivity (0.026 W / (m·K)). However, severe pore blockage significantly weakened the overall integrity of the ceramic body, drastically reducing the compressive strength to 0.22 MPa. During freeze-thaw cycles, internal moisture could not be effectively expelled, resulting in internal pulverization and a loose structure. Comparative Example 4, due to insufficient outer aerogel, significantly weakened its moisture-proof and heat-insulating barrier function, increasing the thermal conductivity to 0.034 W / (m·K). Localized damage to the outer layer occurred after freeze-thaw cycles. Comparative Example 5 used insufficient phenolic resin in the outer layer, failing to adequately encapsulate and fix the aerogel particles, leading to particle detachment and a decrease in tensile strength to 0.09 MPa. Surface cracking occurred after freeze-thaw cycles. Comparative Example 6, due to excessive silica sol in the inner layer, resulted in an overly hard and brittle material. Although it achieved the highest initial flexural strength (0.48 MPa), macroscopic cracks appeared under freeze-thaw cycle stress. Particularly noteworthy is Comparative Example 7, which employed a single medium-temperature curing process, causing the material to simultaneously lose both high-temperature ceramic strength and low-temperature organic bonding, resulting in the worst overall performance and a thermal conductivity as high as 0.045 W / (m·K). Severe pulverization and structural collapse occurred after freeze-thaw cycles. Comparative Example 8, by eliminating the layered structure, exhibited overall cracking and delamination after freeze-thaw cycles, fully demonstrating the core role of functional gradient design and zoned curing processes in improving the material's freeze-thaw durability. These comparative results further verify the importance of the optimized design of the component ratios and process parameters in this invention for achieving comprehensive material performance improvement.

[0055] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing a layered freeze-thaw resistant thermal insulation material, characterized by, The method comprises the following steps: (1) Dry mixing and cotton laying forming: preparing inner layer dry mixture and outer layer dry mixture respectively, then laying the inner layer dry mixture and the outer layer dry mixture in sequence to form a layered blank; wherein the inner layer dry mixture comprises aluminum silicate ceramic fiber, 3 wt%-8 wt% of sodium borate based on the total weight of the inner layer dry mixture, and 3 wt%-5 wt% of silica aerogel particles based on the total weight of the inner layer dry mixture; the outer layer dry mixture comprises rock wool, and 5 wt%-8 wt% of silica aerogel particles based on the total weight of the outer layer dry mixture; (2) Directional spraying of binder: first, spraying phenolic resin from top to bottom on the outer layer of the layered blank, the addition amount of the phenolic resin being 3 wt%-5 wt% of the total weight of the outer layer dry mixture; then, spraying silica sol from bottom to top on the inner layer of the layered blank, the addition amount of the silica sol being 10 wt%-15 wt% of the total weight of the inner layer dry mixture, and the addition amount of the silica sol being based on the solid content thereof; (3) Preforming: roll preforming the layered blank after directional spraying of the binder; (4) Zoning curing: sequentially passing the preformed layered blank through a first curing zone and a second curing zone for zoning curing; wherein the temperature of the first curing zone is 200℃-250℃, and the temperature of the second curing zone is 800℃-900℃; (5) Bonding metal fiber layer: bonding a metal fiber layer on the outermost surface of the layered blank after zoning curing.

2. The production method according to claim 1, characterized by, Before step (1), the method further comprises raw material pretreatment: crushing and impurity removal of the aluminum silicate ceramic fiber and the rock wool respectively to obtain fiber particles; heat treating the hydrophobic silica aerogel particles to change the surface thereof from hydrophobic to hydrophilic.

3. The production method according to claim 2, characterized by, The crushing is performed in sequence of coarse crushing and fine crushing to finally obtain fiber particles with a particle size of 1 mm-3 mm; the impurity removal is performed by a combined process of magnetic separation and airflow separation.

4. The production method according to claim 2, characterized by, After the heat treatment, the method further comprises surface chemical modification of the silica aerogel particles using a coupling agent; the coupling agent is selected from one of aminosilane, epoxysilane or methacryloyloxy silane.

5. The production method according to claim 2 or 4, characterized by, The temperature of the heat treatment is 400℃-450℃.

6. The method of claim 1, wherein, Before step (3), the method further comprises a pre-drying step: pre-drying the layered blank at 80℃-100℃.

7. The production method according to claim 1, characterized by, In step (4), the curing time of the layered blank in the first curing zone is 2 min-5 min, and the curing time of the layered blank in the second curing zone is 3 min-8 min.

8. The method of claim 1, wherein, In step (4), the layered blank is conveyed through the first curing zone and the second curing zone by a high-temperature-resistant conveyor belt.

9. The method of claim 1, wherein, After step (4), the method further comprises a post-treatment step: cooling the cured layered blank to room temperature and cutting it into a predetermined size.

10. A layered freeze-thaw resistant insulation material, characterized by, The method is prepared by any one of claims 1-9.

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