A low-cost inorganic silicon-based aerogel, its preparation method and application

Abstract

This invention discloses a low-cost inorganic silicon-based aerogel, its preparation method, and its applications. The aerogel uses industrial water glass as the inorganic silicon source, glucono-δ-lactone (GDL) as a homogeneous slow-release accelerator, and one-way halloysite nanotubes (HNTs) as a framework reinforcing agent, supplemented with a light-blocking agent. It is prepared through aqueous surface modification and atmospheric pressure drying technology. This invention innovatively utilizes the temperature-controlled slow hydrolysis characteristics of GDL to avoid the localized agglomeration induced by traditional strong acids, achieving the construction of a homogeneous network of the inorganic silicon source with a highly concentrated pore size distribution of 15-20 nm. The introduction of HNTs resists capillary shrinkage during atmospheric pressure drying. Testing shows that the thermal conductivity of the aerogel at 25℃ is ≤0.018 W / (m·K). This aerogel features extremely low cost, high mechanical strength, and excellent thermal insulation performance, and has broad application prospects in building energy conservation, industrial pipeline insulation, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of nanoporous thermal insulation materials technology, specifically relating to a high-performance silica aerogel prepared using inexpensive industrial water glass as a silicon source and employing a homogeneous slow coagulation mechanism and a one-dimensional mineral nanotube reinforcement strategy, as well as its preparation method and application. Background Technology

[0002] Silica (SiO2) aerogel is a lightweight, nanoporous solid material composed of cross-linked nanoscale solid particles forming a three-dimensional spatial network structure, with gaseous dispersion media filling the network pores. Due to its extremely high porosity (typically greater than 90%), extremely low density, and mesoscale nanopore structure (pore sizes mostly concentrated in the 10-50 nm range), aerogel materials exhibit excellent physicochemical properties such as low thermal conductivity, high specific surface area, and low dielectric constant. Particularly in the field of thermal engineering, silica aerogel is considered one of the world's best-performing solid materials in terms of thermal insulation performance due to its infinitely long solid-state heat conduction path and the Knudsen effect that restricts the thermal motion of gas molecules through nanopores. It has irreplaceable strategic application value in aerospace, military equipment, industrial pipeline insulation, building energy conservation, and thermal protection of power batteries for new energy vehicles.

[0003] However, the most critical obstacle to the large-scale popularization and commercial application of aerogels lies in their high preparation cost and complex production process. Currently, most commercially available high-performance silica aerogels use organic alkoxides (such as tetraethyl orthosilicate (TEOS) and tetramethyl orthosilicate (TMOS)) as the silicon source. These organosilicon sources are not only extremely expensive, but also require a large amount of organic solvents during production, significantly increasing raw material costs. Furthermore, to prevent the aerogel's framework from collapsing and cracking due to the enormous capillary contraction force at the gas-liquid interface during drying, traditional processes must rely on supercritical fluid drying technology (such as supercritical CO2 drying). Supercritical drying equipment requires huge investment, operates at high pressures (>7MPa), has long batch production cycles, and consumes extremely high energy, which constitutes another major barrier to the high cost of aerogels.

[0004] To reduce costs, academia and industry have increasingly turned their attention to low-cost inorganic silicon sources, the most typical example being industrial sodium silicate (commonly known as water glass). Water glass costs only one-tenth or even less of organic silicon sources and uses water as a solvent, making it environmentally friendly and non-toxic. However, the preparation of aerogels with ultra-low thermal conductivity (≤0.018 W / (m·K)) using water glass faces several insurmountable scientific and engineering challenges: First, the gel kinetics of inorganic silicon sources are difficult to control precisely. Water glass is a strong base-weak acid salt. In the traditional sol-gel method, the alkalinity is usually neutralized and the polymerization of silica is catalyzed by directly adding acid (such as hydrochloric acid or sulfuric acid). However, direct acid addition causes a sudden drop in pH value in the local area where the acid falls, leading to the rapid aggregation and precipitation of silica oligomers, forming dense and huge silica agglomerates rather than a uniform three-dimensional nanonetwork. This heterogeneous reaction results in an extremely wide pore size distribution in the aerogel, often with a large number of large pores on the order of hundreds of nanometers. According to the theory of gas heat conduction, when the pore size is larger than the mean free path of air molecules (about 70 nm), the convection and collisional heat transfer of the gas inside the pores will increase sharply, resulting in a significant increase in the thermal conductivity of the final material (usually between 0.025 and 0.035 W / (m·K)), which cannot meet the requirements of high-end thermal insulation.

[0005] Secondly, the framework structure of water glass-derived aerogels is fragile and cannot withstand the structural collapse caused by atmospheric pressure drying. To avoid the high cost of supercritical drying, atmospheric pressure drying (APD) is an inevitable trend. However, during atmospheric pressure drying, solvent evaporation generates capillary tensions of tens to hundreds of megapascals within the gel pores. Traditional water glass-based aerogels, whose framework is composed of loosely packed spherical nanoparticles, have very fragile neck connections between particles ("pearl necklace" structure with poor strength). Under atmospheric pressure drying, they undergo catastrophic volume shrinkage (often exceeding 50%) and cracking, leading to a significant decrease in porosity, material densification, and complete loss of the aerogel's super-insulating properties.

[0006] Third, residual sodium ions within the pores are difficult to wash away, and traditional hydrophobic modifiers are expensive. Water glass contains a large amount of sodium. + If not thoroughly cleaned, these substances will severely affect the long-term stability and weather resistance of the aerogel. Conventional processes require repeated washing with deionized water and alcohol-water replacement, which is not only time-consuming and water-intensive but also prone to causing gel aging and shrinkage. Meanwhile, atmospheric pressure drying relies on surface hydrophobic modification (such as using hexamethyldisilazane (HMDS) or trimethylchlorosilane (TMCS), which are still expensive and require toxic and flammable solvents like hexane, posing safety hazards and failing to completely address the core requirement of low cost.

[0007] In summary, the current aerogel field urgently needs a new inorganic silicon source gelation theory and process. How to overcome the localized explosive aggregation phenomenon during acid catalysis in an extremely low-cost inorganic silicon source system, construct a three-dimensional nanoframework with uniform pore size (<50nm) and robust structure, and suppress structural shrinkage under environmentally friendly, low-cost ambient pressure drying conditions, thereby stably preparing high-performance aerogels with a thermal conductivity (25℃) ≤0.018 W / (m·K), has become a bottleneck problem restricting the leapfrog development of the entire aerogel industry. Summary of the Invention

[0008] The primary objective of this invention is to overcome the aforementioned deficiencies of existing technologies and provide a low-cost inorganic silicon-based aerogel solution. This invention eliminates the heterogeneous explosive polymerization defects caused by the traditional direct catalysis of water glass by strong acids. By introducing a novel homogeneous, slow-gathering mechanism and a one-dimensional mineral nanotube reinforcement strategy, it achieves extreme control over the microstructure of the aerogel's interior while maintaining extremely low raw material costs, thereby producing high-performance products with a thermal conductivity ≤0.018 W / (m·K).

[0009] To achieve the above objectives, the present invention provides the following technical solution: Option 1: A low-cost inorganic silicon-based aerogel, wherein the raw materials for preparing the aerogel include, by mass percentage: Inorganic silicon source, calculated as SiO2: 4%~10%; Homogeneous delayed coagulant: 1%~5%; Skeletal reinforcement: 0.5%~3%; Light-blocking agent: 0.2%~2%; Surface modifier: 2%~8%; The remainder is solvent.

[0010] Furthermore, the inorganic silicon source is an aqueous solution of industrial sodium silicate or potassium silicate with a modulus between 2.8 and 3.3.

[0011] Further, the homogeneous slow-release accelerator is at least one of glucono-δ-lactone (GDL), D-galactono-γ-lactone, or polyaspartic acid; preferably glucono-δ-lactone.

[0012] Furthermore, the skeleton reinforcing agent is at least one of one-way halloysite nanotubes (HNTs), sepiolite nanofibers, or attapulgite; the light-blocking agent is at least one of biomass carbon microspheres, carbon black, carbon nanotubes, titanium dioxide, or silicon carbide.

[0013] Furthermore, the surface modifier is an emulsion mixture of one or more of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), or hexamethyldisiloxane (HMDSO) with a nonionic surfactant.

[0014] Option 2: A method for preparing low-cost inorganic silicon-based aerogels, comprising the following steps: S1. Preparation of homogeneous sol: Dilute the inorganic silicon source in deionized water, add the skeleton enhancer and the light-blocking agent, and after ultrasonic dispersion, add the homogeneous slow coagulating agent at a low temperature of 0~10℃, stir evenly, and obtain the precursor sol.

[0015] S2. Temperature-controlled homogeneous gelation and aging: The precursor sol obtained in step S1 is heated to 30~50℃ and allowed to stand to trigger uniform gelation; after gelation, it is aged at 50~70℃ for 12~48 hours to obtain a robust hydrogel.

[0016] S3. Ion replacement and green modification: The aged hydrogel is immersed in an ethanol / water mixed solution containing a surface modifier and subjected to water bath replacement and in-situ hydrophobic modification treatment at 50~60℃ for 24~48 hours, so as to simultaneously achieve the washing out of sodium ions and the hydrophobicization of the framework.

[0017] S4. Drying at ambient pressure: The modified gel is placed in a forced-air drying oven and dried at ambient pressure using a gradient temperature method to obtain the low-cost inorganic silicon aerogel.

[0018] Furthermore, in step S1, the low-temperature environment of the system when the homogeneous slow-release accelerator is added is used to suppress the early hydrolysis of the accelerator, which is a key prerequisite for achieving subsequent homogeneous gelation.

[0019] Further, in step S3, the volume fraction of ethanol in the ethanol / water mixed solution is 30%~60%; the mass fraction of the nonionic surfactant in the modified solution is 0.1%~0.5%. This nonionic surfactant can both emulsify the hydrophobic modifier and reduce the surface tension of the solution, thereby weakening the capillary contraction force during drying from the source.

[0020] Option 3: Application of low-cost inorganic silicon aerogel in building envelope insulation, thermal runaway protection of new energy batteries, and thermal insulation and cold preservation of industrial heating networks.

[0021] Compared with the prior art, the beneficial effects of the present invention are: This invention innovatively introduces a temperature-controlled homogeneous slow-gathering mechanism based on GDL, overcoming the heterogeneous explosive polymerization defects caused by direct acid addition to water glass systems. This mechanism concentrates the pore size distribution of the gel network within an extremely narrow range of 15-20 nm, maximizing the excitation of the Knudsen effect, thereby historically reducing the room temperature thermal conductivity to below 0.018 W / (m·K). This enables low-cost inorganic silicon-based aerogels to achieve insulation performance levels comparable to or even surpassing those of expensive organosilicon-based aerogels for the first time.

[0022] This invention constructs a one-dimensional HNTs / three-dimensional SiO2 interpenetrating double network structure. HNTs, acting as a nanoscale rigid framework, undergo in-situ covalent condensation with the silica matrix through surface hydroxyl groups, significantly enhancing the overall framework's resistance to shrinkage. This fundamentally solves the persistent problems of water glass aerogels being prone to cracking and exhibiting large shrinkage during normal pressure drying. The drying shrinkage rate can be controlled within 5%, ensuring high porosity and high yield.

[0023] This invention designs an aqueous microemulsion system for ion exchange and hydrophobic modification. This system uses low-cost, low-toxicity ethanol / water as a medium and leverages the dual emulsifying and surface tension-reducing effects of nonionic surfactants to simultaneously complete the Na+-hydrophobic modification process. + The efficient removal and green hydrophobicity of the skeleton completely eliminate the toxic, flammable and expensive organic solvents in traditional processes, achieving greening and low cost throughout the entire process. Detailed Implementation

[0024] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention is further described below.

[0025] Based on an in-depth analysis of the physicochemical processes, interfacial mechanics, and heat transfer theory of sol-gel, this invention constructs three synergistic core functional mechanisms within the material to address the three major technical challenges mentioned in the background: heterogeneous gels, fragile frameworks, and high modification costs. Gas thermal conduction follows the random thermal motion and collision laws of molecules. In aerogel materials, the theoretical formula for gas thermal conductivity is: Kg ∝ 1 / (1+2βKn), where Kn is the Knudsen number (Kn = λ / d, λ is the mean free path of air molecules ~70nm, and d is the pore size). As the formula shows, to significantly reduce the gas thermal conductivity Kg, the pore size d of the aerogel must be much smaller than 70nm. Traditional methods of directly adding acid to water glass inevitably lead to Oswald ripening due to the acid concentration gradient, causing some pores to grow into large pores of several hundred nanometers, resulting in a severe funnel effect in gas thermal conduction. This invention achieves a slow-release acid response through GDL (Gas-Gel Lithograph Deposition) to reduce the system's H... + The concentration exhibits a spatiotemporal gradient-free distribution. All silica precursors undergo synchronous nucleation under identical supersaturation, preventing secondary ripening and growth of the crystal nuclei. This locks the aerogel's pore size within an extremely narrow range of 15–20 nm. This highly uniform nanopore structure significantly enhances the Knudsen effect, completely eliminating convection and heat transfer through collisions of gas molecules within the pores. This mechanism forms the theoretical basis for achieving extremely uniform nanopores and is the fundamental guarantee for reducing the thermal conductivity of water glass-based aerogels to below 0.018 W / (m·K).

[0026] During atmospheric pressure drying, as the gas-liquid interface advances, a huge capillary negative pressure is generated within the mesopores. The weak van der Waals forces and a few silicon-oxygen bonds between silica nanoparticles alone are insufficient to resist this stress. The one-dimensional HNTs introduced in this invention possess extremely high aspect ratios and excellent inherent stiffness. During GDL coagulation, HNTs are uniformly dispersed in the sol system. Newly formed silica nanoclusters use HNTs as nucleation sites, growing and coating them in situ along their surface, forming a candied hawthorn-like microstructure. This interpenetrating network structure, with one-dimensional rigid nanotubes as the supporting framework and a three-dimensional silica mesoporous network as the filling matrix, greatly disperses and dissipates the shrinkage stress generated during drying. Macroscopically, this results in an extremely low drying shrinkage rate (<5%), thus perfectly preserving the high-porosity nanoporous structure after atmospheric pressure drying.

[0027] Heat transfer includes not only solid-state and gaseous heat transfer, but also, due to the extremely low density of aerogels, radiative heat transfer becomes significant at room temperature and above. This invention introduces inexpensive biomass carbon microspheres as a light-blocking agent. Carbon materials possess strong absorption characteristics across a wide frequency band, enabling them to strongly absorb and scatter infrared thermal radiation photons (Rosseland diffusion approximation principle). Because the biomass carbon microparticles are submicron in size, they are embedded in the gel framework, significantly reducing the material's optical thickness, greatly attenuating the radiative heat flux density, and completely blocking the last heat conduction path, contributing to an overall thermal conductivity reduction to ≤0.018 W / (m·K).

[0028] Based on the aforementioned core technology mechanism, this invention provides a low-cost inorganic silicon-based aerogel. This aerogel not only has a robust mechanical framework, capable of withstanding conventional atmospheric pressure drying without severe shrinkage or collapse, but also features a highly uniform nanoporous network with extremely small pore sizes, effectively triggering the Knudsen effect to limit gas heat conduction. Tested with a Hot Disk TPS 2500S instrument, its thermal conductivity at room temperature (25℃) is ≤0.018W / (m·K), reaching or even surpassing the performance level of expensive organosilicon-based aerogels.

[0029] The raw materials for preparing this low-cost inorganic silicon-based aerogel consist of the following components by mass percentage: Inorganic silicon source (as SiO2): 4%~10%; Homogeneous delayed coagulant: 1%~5%; Skeletal reinforcement: 0.5%~3%; Light-blocking agent: 0.2%~2%; Surface modifier: 2%~8%; The remainder is solvent (mainly deionized water).

[0030] In this inorganic silicon-based aerogel, the components form an ordered, synergistic system. The inorganic silicon source is the fundamental precursor for constructing the silica aerogel framework. The homogeneous slow-release accelerator, through its temperature-controlled proton release properties, fundamentally determines the uniformity and pore size distribution of the gel network, which is a structural prerequisite for achieving low solid-state and gaseous thermal conductivity. The framework reinforcing agent, through in-situ covalent condensation, provides structural support for the uniform but intrinsically low-strength nanonetwork to resist the capillary destructive forces of atmospheric pressure drying. The light-shielding agent is uniformly embedded on the framework, suppressing the non-negligible radiative heat transfer component at low densities by absorbing and scattering infrared thermal radiation. The surface modifier, before drying, establishes a hydrophobic layer at the framework-solvent interface and synergistically reduces the surface tension of the liquid within the pores, eliminating the capillary driving force that leads to structural collapse.

[0031] Based on the organic synergistic effect between the components, the final product achieves high structural integrity and an ultra-low thermal conductivity of ≤0.018 W / (m·K) under low-cost raw materials and normal pressure drying conditions.

[0032] Based on this, in order to achieve the superior performance of the inorganic silicon-based aerogel provided by this invention, this invention further provides a specific synergistic formulation scheme: The inorganic silicon source (industrial water glass) in this inorganic silicon aerogel is used to provide all the silicon atoms needed to construct the three-dimensional nanonetwork framework of silica aerogel.

[0033] For this inorganic silicon source, an industrial sodium silicate (water glass) solution with a modulus (molar ratio of SiO2 to Na2O) between 2.8 and 3.3 is preferred. Within this modulus range, the silicon source exists uniformly in the solution as oligomeric silicate molecules, which is beneficial for the construction of a homogeneous network. A modulus below 2.8 will result in excessively high free alkali levels, requiring the consumption of large amounts of acidic substances and introducing excessive amounts of highly difficult-to-wash Na2O. + Ions; if the modulus is higher than 3.3, there are already large colloidal particles in the solution, which is not conducive to subsequent homogeneous pore size control. Selecting a modulus of 2.8 to 3.3 can ensure that the silicon source exists uniformly in the form of oligomeric silicate molecules.

[0034] Furthermore, the inorganic silicon source ratio is between 4% and 10%, which is the minimum percolation threshold range required for the formation of a continuous three-dimensional network using SiO2 concentration. When the mass fraction of SiO2 is below 4%, the silicon source concentration is below the percolation threshold required for the formation of a continuous three-dimensional gel network, and a self-supporting gel cannot be formed. When the mass fraction is above 10%, the solid content of the gel skeleton is too high, and the cross-sectional area of ​​the solid heat conduction path increases significantly, leading to an increase in the solid thermal conductivity component. Ultimately, the total thermal conductivity of the material cannot be stably controlled within the range of ≤0.018 W / (m·K).

[0035] The homogeneous delayed coagulant (GDL) in this inorganic silicon-derived aerogel utilizes its temperature-dependent hydrolysis kinetics to provide the system with protons (H) that are completely homogeneous in time and space. + The release of silicic acid triggers and precisely controls the polycondensation and gelation process.

[0036] Traditional methods of adding HCl or H₂SO₄ involve instantaneous acid-base neutralization (with a very high reaction rate constant, classifying it as a diffusion-controlled reaction), inevitably creating a local pH gradient and leading to silicic acid precipitation. This invention utilizes GDL (C₆H₂O)... 10 O6) is a weakly acidic lactone compound, specifically selected from at least one of gluconic acid-δ-lactone (GDL), D-galactonyl-γ-lactone, or polyaspartic acid; preferably gluconic acid-δ-lactone. It undergoes a ring-opening hydrolysis reaction in water to produce gluconic acid. This hydrolysis reaction is a kinetically slow process that is strictly controlled by temperature.

[0037] Meanwhile, the dosage of the homogeneous slow-release gelling agent (GDL) is set at 1%–5%, which is obtained through precise acid-base titration calculations. This aims to accurately position the final pH of the water glass system near the isoelectric point of 5.0–6.0, because within this pH range, the Zeta potential of the silica particles is close to zero, facilitating the condensation reaction and resulting in the smallest and most uniform particles. If the dosage is below 1%, the total amount of protons released by hydrolysis is insufficient to neutralize the system pH to near the silica isoelectric point (pH ≈ 5.0–6.0), failing to initiate complete and uniform gelation. If the dosage is above 5%, both the total amount and rate of proton release are too high, not only shortening the operating window but also potentially leading to coarsening of the network structure due to excessive acidification. This dosage ratio is a crucial parameter for achieving pore size uniformity.

[0038] The skeleton enhancers (HNTs) in this inorganic silicon aerogel are mainly used to construct a rigid nanoskeleton that interpenetrates with the three-dimensional network of silica. Through chemical bonding interfaces, they bear and dissipate the capillary shrinkage stress during normal pressure drying, thereby inhibiting volume shrinkage and cracking.

[0039] Silica aerogel is composed of nanoparticles connected by extremely fine necks, resulting in very low strength. Traditional fiber reinforcement often uses macroscopic glass or ceramic fibers, which, while increasing strength, significantly increase solid-state thermal bridges and substantially raise thermal conductivity. This invention selects at least one of one-dimensional halloysite nanotubes (HNTs), sepiolite nanofibers, or attapulgite as preferred, using natural halloysite nanotubes (HNTs) with an outer diameter of 30-70 nm and a length between 0.5-2 μm, exhibiting a one-dimensional hollow tubular shape.

[0040] The dosage of this skeleton reinforcing agent (HNTs) is between 0.5% and 3%, which falls precisely at the threshold of the three-dimensional random overlapping network of HNTs in three-dimensional space. HNTs are not only extremely low in cost (natural minerals), but their surface aluminum hydroxyl (Al-OH) and silanol (Si-OH) groups can undergo strong in-situ covalent condensation with silica molecules (Si(OH)4) generated in the water glass system during gelation. Below 0.5%, the amount of HNTs is insufficient to form an effective overlapping reinforcing network in three-dimensional space, and the anti-shrinkage effect is not significant; above 3%, the high aspect ratio HNTs are difficult to disperse in the sol and are prone to agglomeration, forming structural defects; moreover, as a non-insulating mineral phase, excessive introduction will increase solid-state thermal conductivity, leading to a rebound in thermal conductivity.

[0041] The light-shielding agent in this inorganic silicon aerogel is used to absorb and scatter photons in the infrared thermal radiation band (mainly 2-10μm), thereby reducing the radiative heat transfer component.

[0042] The light-blocking agent is selected from at least one of biomass carbon microspheres, carbon black, carbon nanotubes, titanium dioxide or silicon carbide, with biomass carbon microspheres or nano-carbon black being preferred, as they have broadband infrared strong absorption characteristics.

[0043] The preferred amount of opaque agent is 0.2% to 2%. If it is less than 0.2%, the attenuation coefficient of infrared radiation is insufficient, and the proportion of radiation heat transfer to total heat transfer increases significantly. If it is more than 2%, the relatively high solid thermal conductivity of carbon material itself will introduce additional solid thermal bridges, which will lead to an increase in the total thermal conductivity.

[0044] The surface modifier in this inorganic silicon aerogel is used to perform in-situ hydrophobic treatment on the gel skeleton and reduce the effective surface tension of the liquid in the pores before drying, thereby weakening the capillary destructive force from the root.

[0045] Traditional processes using the n-hexane / HMDS system are costly and highly toxic. This invention employs an emulsion mixture of one or more of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), or hexamethyldisiloxane (HMDSO) with a nonionic surfactant. Preferably, a microemulsion system of ethanol-water-nonionic surfactant-MTMS is used for modification and displacement. Specifically, a low surface tension emulsion formed by methyltrimethoxysilane (MTMS) and a nonionic surfactant (such as Tween-80 or Span-20) can be used.

[0046] MTMS (methyltrimethoxysilane) hydrolyzes in a weakly acidic aqueous solution to generate Si-OH, which is then grafted onto the surface of the aerogel framework, transforming the originally hydrophilic Si-OH into hydrophobic Si-CH3. The addition of nonionic surfactants has a dual effect: firstly, it ensures that the hydrophobic MTMS is uniformly emulsified in the water / ethanol phase, increasing the diffusion rate; secondly, the surfactant significantly reduces the surface tension of the liquid within the pores. According to the Yang-Laplace equation, reducing the surface tension γ and increasing the contact angle θ (approaching 90 degrees) can fundamentally weaken the capillary contraction force during atmospheric pressure drying, which is the key thermodynamic basis for achieving non-shrinkage during atmospheric pressure drying.

[0047] The preferred content of this surface modifier is 2% to 8%. If it is below 2%, the hydrophobic modification of the skeleton surface will be incomplete, and the residual hydrophilic hydroxyl groups (Si-OH) will generate huge capillary pressure during the drying process due to water evaporation, leading to shrinkage. If it is above 8%, the excess MTMS will undergo a self-condensation reaction to generate polymethylsilsesquioxane particles, which will fill the pores, increase the solid-state thermal conductivity, and cause cost waste.

[0048] In view of the above-mentioned low-cost inorganic silicon aerogel formulation, the present invention further provides a corresponding low-cost inorganic silicon aerogel preparation process.

[0049] The preparation process of this low-cost inorganic silicon aerogel mainly includes the following steps: Step S1: Preparation of homogeneous sol (low-temperature hydrolysis suppression stage); In this step, the measured industrial water glass is diluted with deionized water to the target concentration, and the formulated amounts of framework enhancer and opacifier are added. The mixture is then dispersed uniformly by ultrasonic treatment. The resulting dispersion is then placed in an ice-water bath and cooled to 0-10°C while stirring. Under these low-temperature conditions, powdered homogeneous delayed coagulant GDL is slowly added to the system while stirring continues until completely dissolved, resulting in a stable, non-gelled precursor sol.

[0050] The core of this step is low-temperature operation. According to the Arrhenius equation (k = A exp(-Ea / RT)), the reaction rate constant k decreases exponentially with decreasing temperature T. Between 0 and 10 °C, the ring-opening hydrolysis kinetics of GDL are extremely low, providing a sufficient time window for operation and ensuring that GDL molecules can achieve homogeneous diffusion throughout the sol system without premature gelation or precipitation due to localized hydrolysis.

[0051] This step provides the necessary chemical homogeneity prerequisite for achieving a globally synchronized homogeneous gel in step S2. Without this low-temperature dispersion step, GDL will begin localized hydrolysis immediately upon addition, failing to achieve the homogeneous goal.

[0052] Step S2: Temperature-controlled homogeneous gelation and aging (temperature-triggered reaction and network reinforcement stage). In this step, the precursor sol obtained in step S1 is transferred to a sealed mold, which is then placed in a constant temperature environment of 30–50°C. Within this temperature range, GDL begins to hydrolyze uniformly and slowly releases protons, driving a uniform decrease in the pH value of the sol. After an induction period of several hours, the system uniformly loses its fluidity, forming a hydrogel. After gel formation, the temperature is further raised to 50–70°C, and aged at this temperature for 12–48 hours to obtain the hydrogel.

[0053] This step is the core chemical reaction stage of the present invention, which determines the final nano-network topology of the aerogel, especially the uniformity of the pore size distribution, which is the structural basis for achieving ultra-low thermal conductivity.

[0054] Step S3: Ion exchange and green modification (simultaneous purification and hydrophobication stage); This step involves preparing a microemulsion as the modifying solution, consisting of ethanol (30%–60% by volume), deionized water, nonionic surfactant (0.1%–0.5% by mass), and methyltrimethoxysilane (MTMS, 2%–8% by mass relative to the total raw materials). The hydrogel aged in step S2 is then immersed in a sufficient amount of the modifying solution and treated in a water bath at 50–60°C for 24–48 hours. During this process, sodium ions diffuse outwards, while MTMS diffuses inwards and hydrolyzes and condenses on the surfaces of silica and HNTs under a weakly acidic environment, imparting strong hydrophobicity to the framework.

[0055] This step is based on in-situ simultaneous ion replacement and surface hydrophobication. Sodium ions (Na+) within the gel pores... + Driven by the concentration gradient, MTMS molecules diffuse outward into the modified solution; simultaneously, they penetrate inward through the mass transfer of the microemulsion medium, undergo hydrolysis in a weakly acidic aqueous environment, and condense with the silanol groups (Si-OH) on the framework surface to form a hydrophobic silanyl methyl (Si-CH3) surface layer. In this process, the nonionic surfactant plays a dual role in reducing the surface tension of the system and emulsifying and dispersing the hydrophobic MTMS.

[0056] The hydrophobic framework surface established in this step and the significantly reduced surface tension of the liquid inside the pores are the physicochemical basis for achieving shrinkage-free atmospheric pressure drying in step S4.

[0057] Step S4: Atmospheric pressure drying (gradient drainage and molding stage); In this step, the modified gel is removed from the modification solution and placed in a forced-air drying oven. A gradient temperature program is used for drying at normal pressure, typically: 60℃ for 4 hours, 80℃ for 4 hours, 120℃ for 4 hours, and 150℃ for 2 hours. After drying, it is allowed to cool naturally to room temperature to obtain the finished product.

[0058] This step employs a gradient heating method, with segmented heating to control the solvent evaporation rate and prevent damage to the skeleton caused by internal vapor pressure resulting from solvent boiling or excessively rapid evaporation at a certain temperature range. Since step S3 has already reduced capillary stress to an extremely low level through surface hydrophobicity and reduced liquid surface tension, this step can be successfully completed under normal pressure, and the resulting product macroscopically appears as a blocky aerogel with no cracks and low shrinkage (<5%).

[0059] Through the above formulation and process, the low-cost inorganic silicon-based aerogel prepared by this invention forms a unique microstructure: one-dimensional halloysite nanotubes (HNTs) serve as the axially reinforcing framework, and a three-dimensional silica mesoporous network serves as the interpenetrating double network structure with continuous filling matrix. Carbonaceous opacifier nanoparticles are uniformly embedded on the network framework, and the entire framework surface is covered by hydrophobic methyl groups (-CH3).

[0060] This low-cost inorganic silicon aerogel has a thermal conductivity of ≤0.018 W / (m·K) at an ambient temperature of 25℃; a volume shrinkage rate of <5% during normal pressure drying; and the finished product is free of macroscopic cracks, possesses excellent structural integrity and certain mechanical strength. The overall preparation cost is only 1 / 5 to 1 / 10 of that of the traditional organosilicon source-supercritical drying technology route.

[0061] The low-cost inorganic silicon aerogel provided by this invention, due to its ultra-low thermal conductivity and extremely low overall cost, is suitable for applications with extremely high requirements for thermal insulation and cost constraints. Specifically, it includes, but is not limited to: thermal insulation layers for building envelopes, passive thermal runaway protection pads between new energy power battery modules, and thermal insulation layers for industrial high-temperature thermal pipelines and low-temperature cold-insulating pipelines.

[0062] The technical solution and its beneficial effects of the present invention are further described in detail below through specific embodiments and comparative examples. The thermal conductivity of all samples was measured at an ambient temperature of 25°C using a Swedish Hot Disk TPS 2500S thermal conductivity tester (transient plane heat source method), and a specially designed test probe adapted to lightweight thermal insulation materials was selected.

[0063] (I) Examples and Comparative Examples: Formulations and Preparation Process 1. Raw material specifications and sources Industrial water glass: Modulus 3.1, solid content 30% (as SiO2), commercially available industrial grade.

[0064] Glucono-δ-lactone (GDL): Food grade, purity ≥99%.

[0065] Halloysite nanotubes (HNTs): purified from natural minerals, with a purity of ≥95%, an outer diameter of 30-70 nm, and a length of 0.5-2 μm.

[0066] Nano-biomass carbon black: average particle size 50nm, commercially available industrial grade.

[0067] Methyltrimethoxysilane (MTMS): Industrial grade, purity ≥98%.

[0068] Tween-80, anhydrous ethanol, and deionized water are all commercially available analytical grade reagents.

[0069] 2. Example 1 (Optimal Proportion Baseline Example) (1) Preparation of homogeneous sol: Measure 200g of deionized water, add 50g of industrial water glass (modulus 3.1, solid content 30%, equivalent to about 15g of SiO2, accounting for about 6% of the total raw material mass fraction), and mix evenly. Add 2.5g of HNTs (accounting for about 1% of the total raw material mass fraction) and 1.25g of nano-biomass carbon black (accounting for about 0.5% of the total raw material mass fraction), and ultrasonically disperse for 30 minutes using an ultrasonic cell disruptor. Place the resulting mixture in an ice-water bath to cool to 3℃. While maintaining this temperature and mechanical stirring, slowly add 10g of GDL powder (accounting for about 4% of the total raw material mass fraction), and continue stirring for 5 minutes until completely dissolved to form a homogeneous precursor sol.

[0070] (2) Temperature-controlled homogeneous gelation and aging: The mold containing the precursor sol was sealed and transferred to a 40°C constant temperature water bath for standing. After about 2.5 hours, the pH value of the system gradually decreased to 5.5, the sol lost its fluidity, and homogeneous gelation was completed. The temperature was then increased to 60°C and aged for 24 hours to obtain a fully cross-linked and hardened hydrogel.

[0071] (3) Green emulsion modification: Prepare a modification solution with the following composition: 40% ethanol (volume fraction), 55% deionized water (volume fraction), 1% Tween-80 (mass fraction), and 4% MTMS (mass fraction). Immerse the hydrogel in the microemulsion modification solution and keep it in a 55°C water bath for 36 hours to simultaneously complete the washing out of sodium ions and in-situ hydrophobic modification.

[0072] (4) Drying under normal pressure: Take out the modified gel, rinse the surface once with deionized water, and place it in a forced-air drying oven. Set the temperature program: 60℃ for 4 hours, 80℃ for 4 hours, 120℃ for 4 hours, and 150℃ for 2 hours. After natural cooling, the finished product is obtained.

[0073] 3. Examples 2 to 6, and Comparative Examples 1 to 6 To verify the necessity and advancement of each key technical feature of the present invention, the following embodiments and comparative examples were set up. Except for the core variables described in Table 1 below, the types of raw materials, proportions, and operating steps are completely consistent with those in Example 1.

[0074] Table 1

[0075] (II) Performance Testing and Results The performance of the samples prepared in the above embodiments and comparative examples was tested, and the results are summarized in Table 2 below.

[0076] Table 2

[0077] (III) Results Mechanism Analysis and Comprehensive Performance Discussion (1) On the decisive role of GDL in homogeneous coagulation (comparison of Example 1 and Comparative Example 1): Comparative Example 1 employed the traditional direct dropwise addition of hydrochloric acid for gelation. Because the neutralization reaction of hydrochloric acid is a diffusion-controlled, instantaneous reaction, a sudden drop in local pH occurred in the dropwise region, triggering heterogeneous agglomeration of silicic acid and forming a large number of dense silica aggregates. The test results showed a volume shrinkage rate as high as 28.0% and a thermal conductivity of 0.026 W / (m·K) at 25°C. In contrast, Example 1, using temperature-controlled homogeneous acid release via GDL, achieved a volume shrinkage rate of only 3.2% and a thermal conductivity as low as 0.016 W / (m·K). These comparative data conclusively demonstrate that the GDL temperature-controlled homogeneous slow-release acid mechanism of this invention is the core technical feature for achieving uniform construction of water glass-based aerogel nanonetworks, thereby breaking through the thermal conductivity limit.

[0078] (2) Regarding the key role of HNTs interpenetrating dual network enhancement (comparison of Example 1 and Comparative Example 2): Comparative Example 2, without any added framework reinforcement, consisted of a weakly interconnected network of pure silica nanoparticles as its gel framework. Under capillary stress (estimated by the Yang-Laplace equation) during atmospheric pressure drying, this weak framework failed to maintain structural integrity, resulting in catastrophic volume shrinkage (42.0%), a sharp decrease in porosity, densification of the sample, and a surge in thermal conductivity to 0.028 W / (m·K). Example 1, by introducing HNTs and forming an in-situ covalently condensed interpenetrating double network structure, successfully controlled the shrinkage rate at 3.2%. These comparative data conclusively demonstrate that HNTs, as a nanoscale rigid framework reinforcement, play an indispensable and crucial role in resisting atmospheric pressure drying stress and maintaining a high-porosity, low-thermal-conductivity structure.

[0079] (3) Regarding the necessity of using a light-blocking agent to reduce radiative heat transfer (Comparison of Example 1 and Comparative Example 3): Comparative Example 3 did not contain an infrared shielding agent. Although its volume shrinkage rate (3.1%) was similar to that of Example 1, indicating a complete network structure, the lack of an effective attenuation medium for infrared thermal radiation resulted in radiative heat transfer becoming a significant heat flow channel at room temperature, causing its thermal conductivity to rise to 0.022 W / (m·K). The nano-carbon black added in Example 1, acting as a broadband infrared strong absorber, effectively suppressed the radiative heat transfer component, reducing the thermal conductivity to 0.016 W / (m·K). This set of comparative data conclusively demonstrates that, in the context of extremely low solid-state and gaseous heat conduction, introducing a shielding agent to block radiative heat transfer is a necessary means to achieve the target of ≤0.018 W / (m·K) ultra-low thermal conductivity.

[0080] (4) Regarding the advanced nature of the green microemulsion modification system (comparison between Example 1 and Comparative Example 4): Comparative Example 4, using a traditional HMDS / n-hexane organic solvent system for hydrophobic modification, showed slightly lower volume shrinkage (5.0%) and thermal conductivity (0.019 W / (m·K)) compared to Example 1. This is because the repeated organic solvent replacement processes caused slight aging and aggregation of the gel skeleton, and failed to actively reduce the surface tension of the liquid within the pores. More importantly, this comparative example process used large amounts of toxic, flammable, and costly n-hexane and HMDS, completely deviating from the industrial demands for low cost and environmental friendliness. The microemulsion system of Example 1 demonstrated significant advantages in performance, cost, and environmental friendliness.

[0081] (5) Regarding the balance between overall cost and performance (Comparison of Example 1 and Comparative Example 5): Comparative Example 5 represents the current top-tier aerogel product based on organic alkoxide silicon sources and supercritical drying technology. Its thermal conductivity of 0.015 W / (m·K) is slightly better than that of Example 1, but its overall preparation cost is more than 15 times that of Example 1. The technical value of this invention lies in its successful breakthrough in achieving performance almost on par with the top-tier product (0.016 vs 0.015 W / (m·K)) on the extremely low-cost technical route of industrial water glass-atmospheric pressure drying. For the first time, it has broken down the cost barrier for the large-scale commercial application of high-performance aerogels at the level of industrial scale-up feasibility.

[0082] (6) The impact of silicon source modulus (comparison between Example 1 and Comparative Example 6): Comparative Example 6 used low-modulus water glass with a modulus of 2.0, which had an excessively high content of free alkali (Na₂O). This led to a dramatic increase in GDL consumption but poor acid adjustment, and produced a large number of sodium ions that were difficult to remove completely by displacement. The residual sodium ions formed thermal bridges and moisture sources in the framework. This comparative example sample had a shrinkage rate of 15.0%, surface alkali bloom, and a thermal conductivity as high as 0.031 W / (m·K). This set of comparative data conclusively demonstrates the scientific validity and necessity of the water glass modulus range (2.8~3.3) defined in this invention.

[0083] The systematic comparison of the above embodiments and comparative examples conclusively demonstrates that this invention, through three original synergistic innovations—slow-release homogeneous coagulation of GDL temperature response, in-situ covalent condensation and interpenetrating dual-network reinforcement of one-dimensional HNTs, and microemulsion system-assisted decompression and in-situ hydrophobic modification—perfectly solves the problems of excessively wide pore size distribution, volume shrinkage and cracking due to fragile skeleton, and cost and environmental issues caused by outdated modification methods in traditional water glass-based aerogels under normal pressure drying conditions. For the first time, it achieves excellent thermal insulation performance of ≤0.018 W / (m·K) at extremely low cost, and has extremely high industrial application value and commercial promotion prospects.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-cost inorganic silicon-based aerogel, characterized in that, The raw materials for the aerogel include, by mass percentage: Inorganic silicon source, calculated as SiO2: 4%~10%; Homogeneous delayed coagulant: 1%~5%; Skeletal reinforcement: 0.5%~3%; Light-blocking agent: 0.2%~2%; Surface modifier: 2%~8%; The remainder is solvent.

2. The low-cost inorganic silicon-based aerogel according to claim 1, characterized in that, The inorganic silicon source is an aqueous solution of industrial sodium silicate or potassium silicate with a modulus between 2.8 and 3.

3.

3. The low-cost inorganic silicon-based aerogel according to claim 1, characterized in that, The homogeneous slow-release coagulant is at least one of glucono-δ-lactone (GDL), D-galactobionic acid-γ-lactone, or polyaspartic acid.

4. The low-cost inorganic silicon-based aerogel according to claim 1, characterized in that, The skeleton reinforcement is at least one of one-way halloysite nanotubes (HNTs), sepiolite nanofibers, or attapulgite.

5. The low-cost inorganic silicon-based aerogel according to claim 1, characterized in that, The light-blocking agent is at least one of biomass carbon microspheres, carbon black, carbon nanotubes, titanium dioxide, or silicon carbide.

6. The low-cost inorganic silicon-based aerogel according to claim 1, characterized in that, The surface modifier is an emulsion mixture of one or more of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), or hexamethyldisiloxane (HMDSO) with a nonionic surfactant.

7. A method for preparing low-cost inorganic silicon-based aerogels, characterized in that, Includes the following steps: S1. Preparation of homogeneous sol: Dilute the inorganic silicon source in deionized water, add the skeleton enhancer and the light-blocking agent, disperse evenly by ultrasonication, add the homogeneous slow coagulating agent at a low temperature of 0~10℃, stir evenly, and obtain the precursor sol. S2, Temperature-controlled homogeneous gelation and aging: The precursor sol obtained in step S1 is heated to 30~50℃ and allowed to stand to trigger uniform gelation; after gelation, it is aged at 50~70℃ for 12~48 hours to obtain a robust hydrogel. S3, Ion Replacement and Green Modification: The aged hydrogel is immersed in an ethanol / water mixed solution containing a surface modifier and subjected to water bath replacement and in-situ hydrophobic modification treatment at 50~60℃ for 24~48 hours, so as to simultaneously achieve the washing out of sodium ions and the hydrophobicization of the framework. S4. Drying at ambient pressure: The modified gel is placed in a forced-air drying oven and dried at ambient pressure using a gradient temperature method to obtain the low-cost inorganic silicon aerogel.

8. The method for preparing a low-cost inorganic silicon-based aerogel according to claim 7, characterized in that, In step S1, the low-temperature environment of the system when the homogeneous slow-release accelerator is added is used to inhibit the early hydrolysis of the accelerator, which is a key prerequisite for achieving subsequent homogeneous gelation.

9. The method for preparing a low-cost inorganic silicon-based aerogel according to claim 7, characterized in that, In step S3, the volume fraction of ethanol in the ethanol / water mixed solution is 30%~60%; the mass fraction of nonionic surfactant in the modified solution is 0.1%~0.5%. This nonionic surfactant can both emulsify the hydrophobic modifier and reduce the surface tension of the solution, thereby weakening the capillary contraction force during drying from the source.

10. The application of a low-cost inorganic silicon-based aerogel as described in any one of claims 1-6 in equipment for building envelope insulation, thermal runaway protection of new energy batteries, and thermal insulation and cold preservation of industrial thermal pipelines.

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