Fly ash-based high-infrared-reflecting double thermal insulation energy-saving coating and preparation method thereof

Abstract

The present application belongs to the field of solid waste resource utilization and functional coating, taking the solid waste fly ash of coal-fired power plant as raw material, through directional crystallization and high-efficiency separation technology, high-purity flaky alpha-Al2O3 and nano-porous silica aerogel are prepared, realizing high-value utilization of aluminum-silicon double resources and in-situ removal of hematite impurities. The core technology highlights the synergistic innovation of compound functional fillers: flaky alumina can efficiently reflect solar near-infrared radiation, silica aerogel can block heat conduction and convection due to its extremely low intrinsic thermal conductivity, and a double heat insulation mechanism of active reflection and passive blocking is constructed, which significantly improves the heat insulation performance compared with single coating. The coating is suitable for building exterior walls, industrial storage tanks and other scenes, while realizing solid waste emission reduction, it can greatly reduce energy consumption, has environmental protection benefit and energy saving value, and has outstanding technological innovation and industrialization prospect.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and functional coating technology, specifically to a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating and its preparation method. Background Technology

[0002] With the increasing severity of energy shortages and environmental pollution, building energy conservation and industrial energy conservation technologies have received widespread attention. Thermal insulation coatings, as an economical and effective technical means, are widely used in building exteriors, industrial plants, petrochemical storage tanks, and other fields to reduce external heat transfer and lower internal cooling energy consumption. Traditional thermal insulation coatings mostly employ a single insulation mechanism. One type is reflective thermal insulation coatings, which mainly achieve insulation by adding functional fillers such as titanium dioxide to reflect sunlight (especially visible and near-infrared light), but their blocking effect on long-wave infrared heat radiation is limited. Another type is barrier thermal insulation coatings, which rely on adding fillers with low thermal conductivity, such as ceramic microspheres, to slow down heat conduction, but their reflectivity against solar radiation is usually weak. Existing technologies have attempted to simply combine reflective and barrier materials, but often due to improper material selection or unreasonable proportions, the synergistic effect is poor. For example, commonly used reflective fillers such as titanium dioxide do not have optimal reflectivity in the near-infrared band; while some barrier fillers have high density, are prone to sedimentation, or have poor compatibility with resins, affecting the film-forming properties and durability of the coating. Therefore, developing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating that can efficiently coordinate the dual mechanisms of "reflection" and "blocking" and its preparation method has important practical application value. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating with excellent heat insulation performance, good durability and easy construction, as well as its preparation method. This coating achieves efficient synergy between "reflection" and "blocking" by carefully selecting functional fillers and optimizing their compounding ratio. To achieve the above objectives, the present invention provides the following technical solution: A fly ash-based high infrared reflectance dual heat insulation and energy-saving coating comprises the following components by mass percentage: 20%-40% silicone-acrylic emulsion, 30%-55% functional filler, 3%-15% additives, and the balance being deionized water; the functional filler comprises micron-sized flake alumina and silica aerogel powder, wherein the mass ratio of the micron-sized flake alumina to the silica aerogel powder is 1-4:1.

[0004] As a further description of the above scheme, the aspect ratio of the micron-sized sheet-like alumina is 8~15.

[0005] As a further description of the above scheme, the additives include polyacrylate dispersants, silicone wetting agents, silicone emulsion defoamers, polyether-modified polysiloxane leveling agents, and propylene glycol methyl ether.

[0006] A method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating as described above includes the following steps: 1) Preparation of flake alumina: Solid waste fly ash is pretreated by alkaline washing to enhance the activity of internal silicon and aluminum components. The pretreated fly ash is ground and mixed with ammonium fluoride, and then calcined under vacuum to complete the solid-phase reaction. After cooling to room temperature, the resulting solid is mixed with ethanol in a certain proportion, and after ultrasonic stirring and drying, micron-sized flake alumina is obtained. 2) Preparation of nano-silica from desilication solution: The fluorine-containing gas generated by high-temperature calcination in step 1) is passed into water for absorption. The resulting absorption solution is the desilication solution. Ammonia water is then added to adjust the pH value, followed by low-temperature stirring, filtration, heating and concentration, and freeze drying to finally obtain nano-silica. 3) Preparation of silica aerogel: The nano silica, template agent and co-solvent obtained in step 2) are added to the solvent, stirred evenly, heated, allowed to stand, filtered and dried to obtain silica aerogel; 4) Coating preparation: Mix 50% of deionized water, 60% of polyacrylate dispersant, and 60% of silicone wetting agent with the micron-sized flake alumina obtained in step 1), and disperse at high speed in a water bath to obtain slurry A; mix 50% of deionized water, 40% of silicone wetting agent, and 50% of silica aerogel powder obtained in step 3), and stir at low speed in a water bath to obtain slurry B; after adding silicone acrylic emulsion to the paint mixing tank, add slurry A, slurry B, silicone emulsion defoamer, polyether-modified polysiloxane leveling agent, and propylene glycol methyl ether in sequence under low speed stirring, stir until uniform, filter and discharge to obtain the double heat insulation and energy-saving coating.

[0007] As a further description of the above scheme, the alkaline washing pretreatment process in step 1) uses a NaOH solution with a concentration of 2~8 mol / L, the liquid-to-solid ratio of fly ash to NaOH solution is 2~6 mL / g, and a homogeneous reactor is used for heating. The heating temperature is 60~120℃, the holding time is 100~200 min, and the rotation speed is 50~200 r / min. The ultrasonic stirring power is 300~500 W, and the ultrasonic stirring time is 20~40 min. The heating rate of the vacuum calcination is 5~10℃ / min, the calcination temperature is 1000~1300℃, the holding time is 30~180 min, and the nitrogen flow rate is 100~200 mL / min. The resulting micron-sized sheet-like alumina has a polygonal structure, and the length of the longest diagonal of the polygonal structure is 2~10 μm.

[0008] As a further description of the above scheme, the ammonia concentration in step 2) is 5~15wt%, the pH value of the precipitation reaction is controlled at 7~11; the heating and stirring reaction temperature is 50~90℃, the heating and stirring reaction time is 0.5~2h, and the stirring speed is 30~300r / min; 100~300ml of deionized water is added during filtration, and the filtration time is 10~40min; the heating temperature is 40~80℃, the stirring speed is set to 50~150rpm, and the solution is freeze-dried and recovered at -10~5℃ after evaporation.

[0009] As a further description of the above scheme, in step 3), the template agent is chitosan and sodium alginate, the co-solvent is potassium hydroxide, and the solvent is anhydrous ethanol and water. The mass ratio of nano-silica to potassium hydroxide is 1:0.1~0.5; the mass ratio of nano-silica:chitosan:sodium alginate is 1:0.001~0.01:0.001~0.01; the volume ratio of anhydrous ethanol to water is 0.5~2:1; the mass ratio of solvent to nano-silica is 1:0.05~0.3; the temperature of the solvothermal synthesis reaction is 80~170℃; the reaction time is 0.5~8h; the stirring speed is 30~300r / min; the reaction is allowed to stand at room temperature for 10d~15d; and the filtration time is 60min.

[0010] As a further description of the above scheme, in step 4), a water bath mixing pot is used for high-speed dispersion, with a stirring speed of 500~1500 r / min, a time of 20~60 min, and a temperature between 20~45℃; a water bath mixing pot is used for low-speed stirring, with a stirring speed of 50~400 r / min, a time of 10~50 min, and a temperature of 20℃.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Dual Insulation, Synergistic Efficiency: This invention synergistically combines high-infrared-reflective sheet-like alumina with ultra-low thermal conductivity nanomaterials, enabling the coating to simultaneously possess the dual functions of "near-infrared reflection" and "heat blocking." Test data shows that the near-infrared reflectance of this embodiment can reach a maximum of 0.90, while the thermal conductivity is as low as 0.061 W / m·K. Under this dual effect, the lower surface temperature of the coating is reduced by up to 22°C compared to Comparative Example 1, demonstrating a significantly superior insulation effect compared to single-function coatings. This innovatively solves the problem of insufficient efficiency in traditional coatings with a single insulation mechanism.

[0012] 2. Superior Performance: The coating of this invention exhibits excellent solar reflectance and low thermal conductivity. The highest solar reflectance (TSR) of the embodiments can reach 0.91, and the highest near-infrared reflectance can reach 0.90, which can effectively reflect the near-infrared band, which accounts for the largest proportion of heat in sunlight; at the same time, the thermal conductivity of the coating is only 0.061~0.074 W / m·K, which is much lower than 0.20 W / m·K of Comparative Example 1.

[0013] 3. High Durability: The lamellar alumina not only provides high infrared reflectivity, but also significantly improves the coating's wear resistance and weather resistance due to its high hardness and excellent chemical stability. This synergistic design of "function + protection" enables the coating to maintain stable performance in long-term outdoor or complex industrial environments, solving the problem of traditional heat insulation coatings struggling to balance functionality and durability.

[0014] 4. Wide range of applications: The coating preparation process of this invention is simple, and through the synergistic design of the components, large-scale production can be achieved without complex equipment. This coating is suitable for summer cooling of building roofs and exterior walls, as well as surface insulation of industrial equipment, ships, and vehicles, possessing strong adaptability to various scenarios and industrialization potential.

[0015] 5. Synergistic closed-loop of raw material pretreatment and functional filler preparation: Alkali washing pretreatment enhances the activity of fly ash silica and alumina, laying the foundation for subsequent directional crystallization of flaky alumina; Fluorine-containing gas is generated simultaneously during the calcination process and is directly used as raw material for desiliconization liquid to prepare nano-silica, realizing a resource closed loop of "pretreatment-alumina preparation-silica recovery", maximizing the utilization rate of solid waste and reducing raw material loss compared with traditional step-by-step preparation.

[0016] 6. Synergistic unity of process parameters and environmental benefits: Water is used as the main solvent throughout the process, combined with low-temperature freeze drying (-10~5℃) and vacuum calcination to reduce volatile organic compound emissions; parameters of each step (such as alkali washing concentration and calcination temperature) are precisely matched to avoid energy waste caused by excessive reaction, and the energy consumption of the coating preparation process is reduced by more than 25% compared with traditional processes, taking into account both industrial feasibility and environmental protection requirements. Attached Figure Description

[0017] Figure 1 This is a scanning electron microscope (SEM) image of the fly ash-based high infrared reflectance dual heat insulation and energy-saving coating of the present invention. Figure 2 This is a TEM image of nano-silica. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] A fly ash-based high infrared reflectance dual heat insulation and energy-saving coating comprises the following components by mass percentage: 20%-40% silicone-acrylic emulsion, 30%-55% functional filler, 3%-15% additives, and the balance being deionized water; the functional filler comprises micron-sized flake alumina and silica aerogel powder, wherein the mass ratio of the micron-sized flake alumina to the silica aerogel powder is 1-4:1.

[0020] The aspect ratio of the micron-sized sheet-like alumina of the present invention is 8~15.

[0021] The additives of this invention include polyacrylate dispersants, organosilicon wetting agents, organosilicon emulsion defoamers, polyether-modified polysiloxane leveling agents, and propylene glycol methyl ether.

[0022] This application synergistically combines high-infrared-reflective sheet-like alumina with ultra-low thermal conductivity nanomaterials, enabling the coating to possess both "near-infrared reflection" and "heat insulation" functions. Test data shows that the near-infrared reflectance of this embodiment can reach a maximum of 0.90, while the thermal conductivity is as low as 0.061 W / m·K. Under this dual effect, the lower surface temperature of the coating is reduced by up to 22°C compared to Comparative Example 1, demonstrating a significantly better heat insulation effect than single-function coatings. This innovatively solves the problem of insufficient efficiency in traditional coatings with a single heat insulation mechanism.

[0023] The silicone-acrylic emulsion of the present invention is a film-forming resin, and the deionized water is a solvent.

[0024] The additives of this invention include dispersants, wetting agents, defoamers, leveling agents, and film-forming aids. The polyacrylate dispersant is a dispersant; the organosilicon wetting agent is a wetting agent; the organosilicon emulsion-type defoamer is a defoamer; the polyether-modified polysiloxane leveling agent is a leveling agent; and the propylene glycol methyl ether is a film-forming aid. The coating of this application exhibits excellent solar reflectance and low thermal conductivity. The highest solar reflectance (TSR) of the embodiments can reach 0.91, and the highest near-infrared reflectance can reach 0.90, effectively reflecting the near-infrared band, which accounts for the largest proportion of heat in sunlight. Simultaneously, the thermal conductivity of the coating is only 0.061~0.074 W / m·K, far lower than the 0.20 W / m·K of Comparative Example 1. Furthermore, the lamellar alumina not only provides high infrared reflectance but also significantly improves the wear resistance and weather resistance of the coating due to its high hardness and excellent chemical stability. This synergistic design of "function + protection" enables the coating to maintain stable performance in long-term outdoor or complex industrial environments, solving the problem that traditional heat insulation coatings cannot balance function and durability.

[0025] Micron-sized sheet-like alumina, as an infrared reflective filler, has the function of efficiently reflecting solar near-infrared radiation, while silica aerogel powder, as a barrier filler, has the function of blocking heat conduction and convection.

[0026] A method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating as described above includes the following steps: 1) Preparation of flake alumina: Solid waste fly ash is pretreated by alkaline washing to enhance the activity of internal silicon and aluminum components. The pretreated fly ash is ground and mixed with ammonium fluoride, and then calcined under vacuum to complete the solid-phase reaction. After cooling to room temperature, the resulting solid is mixed with ethanol in a certain proportion, and after ultrasonic stirring and drying, micron-sized flake alumina is obtained. 2) Preparation of nano-silica from desilication solution: The fluorine-containing gas generated by high-temperature calcination in step 1) is passed into water for absorption. The resulting absorption solution is the desilication solution. Ammonia water is then added to adjust the pH value, followed by low-temperature stirring, filtration, heating and concentration, and freeze drying to finally obtain nano-silica. 3) Preparation of silica aerogel: The nano silica, template agent and co-solvent obtained in step 2) are added to the solvent, stirred evenly, heated, allowed to stand, filtered and dried to obtain silica aerogel; 4) Coating preparation: Mix 50% of deionized water, 60% of polyacrylate dispersant, and 60% of silicone wetting agent with the micron-sized flake alumina obtained in step 1), and disperse at high speed in a water bath to obtain slurry A; mix 50% of deionized water, 40% of silicone wetting agent, and 50% of silica aerogel powder obtained in step 3), and stir at low speed in a water bath to obtain slurry B; after adding silicone acrylic emulsion to the paint mixing tank, add slurry A, slurry B, silicone emulsion defoamer, polyether-modified polysiloxane leveling agent, and propylene glycol methyl ether in sequence under low speed stirring, stir until uniform, filter and discharge to obtain the double heat insulation and energy-saving coating. The synergistic closed loop of raw material pretreatment and functional filler preparation in this application: alkaline washing pretreatment enhances the activity of fly ash silica-alumina, laying the foundation for subsequent directional crystallization of sheet alumina; fluorine-containing gas is generated simultaneously during the calcination process, which is directly used as raw material for desilication liquid to prepare nano-silica, realizing a resource closed loop of "pretreatment-alumina preparation-silica recovery", maximizing the utilization rate of solid waste, and reducing raw material loss compared with traditional step-by-step preparation.

[0027] In step 1) of this invention, the alkaline washing pretreatment process uses a NaOH solution with a concentration of 2-8 mol / L, and the liquid-to-solid ratio of fly ash to NaOH solution is 2-6 mL / g. Heating is performed in a homogeneous reactor at a temperature of 60-120℃, a holding time of 100-200 min, and a rotation speed of 50-200 r / min. Ultrasonic stirring power is 300-500 W, and ultrasonic stirring time is 20-40 min. The vacuum calcination process involves a heating rate of 5-10℃ / min, a calcination temperature of 1000-1300℃, a holding time of 30-180 min, and a nitrogen flow rate of 100-200 mL / min. The resulting micron-sized sheet-like alumina has a polygonal structure, with the longest diagonal of the polygonal structure being 2-10 μm.

[0028] In step 2) of this invention, the ammonia concentration is 5-15 wt%, the pH value of the precipitation reaction is controlled at 7-11, the heating and stirring reaction temperature is 50-90℃, the heating and stirring reaction time is 0.5-2h, and the stirring speed is 30-300 r / min; 100-300 ml of deionized water is added during filtration, and the filtration time is 10-40 min; the heating temperature is 40-80℃, the stirring speed is set at 50-150 rpm, and the solution is freeze-dried and recovered at -10-5℃ after evaporation.

[0029] In step 3) of this invention, the template agent is chitosan and sodium alginate, the co-solvent is potassium hydroxide, and the solvent is anhydrous ethanol and water. The mass ratio of nano-silica to potassium hydroxide is 1:0.1~0.5; the mass ratio of nano-silica:chitosan:sodium alginate is 1:0.001~0.01:0.001~0.01; the volume ratio of anhydrous ethanol to water is 0.5~2:1; the mass ratio of solvent to nano-silica is 1:0.05~0.3; the temperature of the solvothermal synthesis reaction is 80~170℃; the reaction time is 0.5~8h; the stirring speed is 30~300r / min; the reaction is allowed to stand at room temperature for 10d~15d; and the filtration time is 60min.

[0030] In step 4) of this invention, a water bath is used for high-speed dispersion, with a stirring speed of 500-1500 r / min, a stirring time of 20-60 min, and a temperature between 20-45°C; a water bath is used for low-speed stirring, with a stirring speed of 50-400 r / min, a stirring time of 10-50 min, and a temperature of 20°C. The low-speed stirring operations for preparing the barrier filler slurry B, and the low-speed stirring operations for mixing slurry A with slurry B, silicone-acrylic emulsion, and remaining additives, are all carried out using a water bath, with a stirring speed of 50-400 r / min, a stirring time of 10-50 min, and a system temperature controlled at 20°C.

[0031] Example 1 A method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating utilizes aluminum and silicon elements in fly ash, a solid waste from coal-fired power plants, to convert them into alumina and nano-silica, respectively, achieving efficient separation and utilization of both aluminum and silicon resources. The method includes preparing sheet-like alumina, preparing nano-silica with a desilication solution, preparing silica aerogel, and coating preparation. The specific steps are as follows: 1) Preparation of flake alumina: Solid waste fly ash is pretreated with an alkaline wash using a 5 mol / L NaOH solution. The liquid-to-solid ratio of fly ash to NaOH solution is 4 mL / g. Heating is performed in a homogeneous reactor at 90℃ for 150 min at a rotation speed of 150 r / min to enhance the activity of the internal silicon-aluminum components. The pretreated fly ash is then ground and mixed with ammonium fluoride, followed by vacuum calcination to complete the solid-phase reaction. The heating rate during vacuum calcination is 7℃ / min, and the calcination temperature is 12℃. The temperature was 00℃, the holding time was 110 min, and the nitrogen flow rate was 150 mL / min. The role of nitrogen was twofold: firstly, to create an inert atmosphere to prevent the material from being oxidized during calcination and to ensure the smooth progress of the solid-phase reaction; secondly, to carry away the fluorine-containing gas produced during calcination, facilitating the subsequent resource recovery of the fluorine-containing tail gas. After cooling to room temperature, the obtained solid was mixed with ethanol in a certain proportion and ultrasonically stirred at a power of 400 W for 30 min. After drying, the morphology of the generated alumina could be observed through SEM images, such as... Figure 1 As shown, the obtained alumina has a regular sheet-like structure with a length in the micrometer range and high purity, which lays the foundation for the subsequent preparation of high-quality sol.

[0032] 2) Preparation of nano-silica from desilication solution: The fluorine-containing gas generated during high-temperature calcination in step 1) is absorbed by water, and the resulting absorbent is the desilication solution. Ammonia water is then added to adjust the pH value, with an ammonia concentration of 8 wt%, and the pH value of the precipitation reaction is controlled at 9. The heating and stirring reaction temperature is 70℃, the heating and stirring reaction time is 1 hour, and the stirring speed is 200 r / min. During vacuum filtration, 200 ml of deionized water is added, and the filtration time is 30 min. Heating and concentration are performed using a DF-101SS heat-collecting magnetic stirrer at a heating temperature of 60℃ and a stirring speed of 90 rpm / min. After the solution evaporates, it is freeze-dried at -10~5℃ to recover the nano-silica. Figure 2 This is a TEM image of nano-silica. The product is nano-sized amorphous silica with high activity, suitable for constructing aerogel networks.

[0033] 3) Preparation of silica aerogel: The nano-silica obtained in step 2) was added to a solvent along with a template agent and a co-solvent. Chitosan and sodium alginate were used as template agents, potassium hydroxide as a co-solvent, and anhydrous ethanol and water as solvents. The mass ratio of nano-silica to potassium hydroxide was 1:0.3; the mass ratio of nano-silica to chitosan to sodium alginate was 1:0.005:0.005; the volume ratio of anhydrous ethanol to water was 1.25:1; and the mass ratio of anhydrous ethanol + water to nano-silica was 1:0.15. The solvothermal synthesis reaction was carried out at 120℃ for 4 hours, with a stirring speed of 120 r / min. After standing at room temperature for 12 days, the mixture was filtered and dried to obtain silica aerogel. A fly ash-based high infrared reflectance dual heat insulation and energy-saving coating has the following formula by mass percentage: Silicone-acrylic emulsion: 40% Flake-shaped alumina (aspect ratio of 8): 44% Silica aerogel powder: 11% Dispersant: 0.7% Wetting agent: 0.2% Defoamer: 0.3% Leveling agent: 0.3% Film-forming aid: 1.5% Deionized water: Balance (2%) Preparation method: Mix 50% deionized water, 0.7% dispersant, 60% wetting agent by mass, and 44% flake alumina in the total formula, and disperse in a water bath at 1500 r / min and 25°C for 30 minutes to obtain slurry A.

[0034] Mix the remaining 50% of deionized water, 40% of the total wetting agent mass, and 11% of silica aerogel powder in a water bath at 400 r / min and 20°C for 15 minutes to avoid damaging its structure, and obtain slurry B.

[0035] Add 40% silicone-acrylic emulsion to the paint mixing tank, and add slurry A, slurry B, 0.3% defoamer, 0.3% leveling agent and 1.5% film-forming aid in sequence while stirring at low speed (300 r / min). Stir at 20℃ for 20 minutes until uniform, and then filter and discharge.

[0036] Example 2 A method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating utilizes aluminum and silicon elements in fly ash, a solid waste from coal-fired power plants, to convert them into alumina and nano-silica, respectively, achieving efficient separation and utilization of both aluminum and silicon resources. The method includes preparing sheet-like alumina, preparing nano-silica with a desilication solution, preparing silica aerogel, and coating preparation. The specific steps are as follows: 1) Preparation of flake alumina: Solid waste fly ash was pretreated with an alkaline washing solution. The alkaline washing pretreatment process used a 2 mol / L NaOH solution, with a liquid-to-solid ratio of fly ash to NaOH solution of 6 mL / g. Heating was performed in a homogeneous reactor at 120℃ for 100 min at a rotation speed of 50 r / min to enhance the activity of the internal silicon-aluminum components. The pretreated fly ash was then ground and mixed with ammonium fluoride, followed by vacuum calcination to complete the solid-phase reaction. The vacuum calcination heating rate was 5℃ / min, the calcination temperature was 1300℃, the holding time was 180 min, and the nitrogen flow rate was 20. 0 mL / min, nitrogen gas serves two purposes: firstly, it creates an inert atmosphere to prevent the material from being oxidized during calcination, ensuring the smooth progress of the solid-phase reaction; secondly, it can carry the fluorine-containing gas generated during calcination, facilitating the subsequent resource recovery of the fluorine-containing tail gas. After cooling to room temperature, the obtained solid is mixed with ethanol in a certain proportion and ultrasonically stirred at a power of 500 W for 40 min. After drying, the morphology of the generated alumina can be observed through SEM images, as shown in the figure. The obtained alumina has a regular sheet-like structure with a length in the micrometer range and high purity, laying the foundation for the subsequent preparation of high-quality sol.

[0037] 2) Preparation of nano-silica from desilication solution: The fluorine-containing gas generated during high-temperature calcination in step 1) is absorbed by water, and the resulting absorbent is the desilication solution. Ammonia water is then added to adjust the pH value, with an ammonia concentration of 15 wt%, and the pH value of the precipitation reaction is controlled at 11. The heating and stirring reaction temperature is 90℃, the heating and stirring reaction time is 2 hours, and the stirring speed is 300 r / min. During filtration, 100 ml of deionized water is added, and the filtration time is 15 minutes. Heating and concentration are performed using a DF-101SS heat-collecting magnetic stirrer at 40℃ and a stirring speed of 50 rpm. After the solution evaporates, it is freeze-dried at -10~5℃ to recover the nano-silica. Figure 2 This is a TEM image of nano-silica. The product is nano-sized amorphous silica with high activity, suitable for constructing aerogel networks.

[0038] 3) Preparation of silica aerogel: The nano-silica obtained in step 2) was added to a solvent along with a template agent and a co-solvent. Chitosan and sodium alginate were used as template agents, potassium hydroxide as a co-solvent, and anhydrous ethanol and water as solvents. The mass ratio of nano-silica to potassium hydroxide was 1:0.1; the mass ratio of nano-silica to chitosan to sodium alginate was 1:0.001:0.01; the volume ratio of anhydrous ethanol to water was 2:1; and the mass ratio of anhydrous ethanol + water to nano-silica was 1:0.3. The solvothermal synthesis reaction was carried out at a temperature of 170℃ for 0.5 h, with a stirring speed of 30 r / min. The mixture was allowed to stand at room temperature for 15 days, filtered, and dried to obtain silica aerogel. A fly ash-based high infrared reflectance dual heat insulation and energy-saving coating has the following formula by weight percentage: Silicone-acrylic emulsion: 30% Flake-shaped alumina (aspect ratio 10): 30% Silica aerogel powder: 12% Dispersant: 1.2% Wetting agent: 0.8% Defoamer: 0.8% Leveling agent: 1.7% Film-forming aid: 4.5% Deionized water: Balance (19%) Preparation method: Mix 50% deionized water, 1.2% dispersant, 60% wetting agent by mass, and 30% flake alumina in the total formula, and disperse in a water bath at 500 r / min and 45°C for 35 minutes to obtain slurry A.

[0039] Mix the remaining 50% of deionized water, 40% of the total wetting agent mass, and 12% of silica aerogel powder in a water bath at 50 r / min and 20°C for 50 minutes to avoid damaging its structure, and obtain slurry B.

[0040] Add 30% silicone-acrylic emulsion to the paint mixing tank, and add slurry A, slurry B, 0.8% defoamer, 1.7% leveling agent and 4.5% film-forming aid in sequence under low speed stirring (300 r / min). Stir at 20℃ for 20 minutes until uniform, and then filter and discharge.

[0041] Example 3

[0042] A method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating utilizes aluminum and silicon elements in fly ash, a solid waste from coal-fired power plants, to convert them into alumina and nano-silica, respectively, achieving efficient separation and utilization of both aluminum and silicon resources. The method includes preparing sheet-like alumina, preparing nano-silica with a desilication solution, preparing silica aerogel, and coating preparation. The specific steps are as follows: 1) Preparation of flake alumina: Solid waste fly ash was pretreated with an alkali wash using an 8 mol / L NaOH solution. The liquid-to-solid ratio of fly ash to NaOH solution was 2 mL / g. Heating was performed in a homogeneous reactor at 60℃ for 200 min at a rotation speed of 200 r / min to enhance the activity of the internal silicon-aluminum components. The pretreated fly ash was then ground and mixed with ammonium fluoride, followed by vacuum calcination to complete the solid-phase reaction. The vacuum calcination heating rate was 10℃ / min, the calcination temperature was 1000℃, the holding time was 30 min, and the nitrogen flow rate was 10 m / min. 0 mL / min, nitrogen gas serves two purposes: firstly, it creates an inert atmosphere to prevent the material from being oxidized during calcination, ensuring the smooth progress of the solid-phase reaction; secondly, it can carry the fluorine-containing gas generated during calcination, facilitating the subsequent resource recovery of fluorine-containing tail gas. After cooling to room temperature, the obtained solid is mixed with ethanol in a certain proportion and ultrasonically stirred at a power of 300 W for 20 min. After drying, the morphology of the generated alumina can be observed through SEM images, as shown in the figure. The obtained alumina has a regular sheet-like structure with a length in the micrometer range and high purity, laying the foundation for the subsequent preparation of high-quality sol.

[0043] 2) Preparation of nano-silica from desilication solution: The fluorine-containing gas generated during high-temperature calcination in step 1) is absorbed by water, and the resulting absorbent is the desilication solution. Ammonia water is then added to adjust the pH value, with an ammonia concentration of 5 wt%, and the pH value for the precipitation reaction is controlled at 7. The heating and stirring reaction temperature is 50℃, the heating and stirring reaction time is 0.5 h, and the stirring speed is 250 r / min. During filtration, 300 ml of deionized water is added, and the filtration time is 40 min. Heating and concentration are performed using a DF-101SS heat-collecting magnetic stirrer at a heating temperature of 80℃ and a stirring speed of 150 rpm / min. After the solution evaporates, it is freeze-dried at -10~5℃ to recover the nano-silica. Figure 2 This is a TEM image of nano-silica. The product is nano-sized amorphous silica with high activity, suitable for constructing aerogel networks.

[0044] 3) Preparation of silica aerogel: The nano silica obtained in step 2) was added to a solvent along with a template agent and a co-solvent. Chitosan and sodium alginate were used as template agents, potassium hydroxide as a co-solvent, and anhydrous ethanol and water as solvents. The mass ratio of nano silica to potassium hydroxide was 1:0.5; the mass ratio of nano silica to chitosan to sodium alginate was 1:0.01:0.001; the volume ratio of anhydrous ethanol to water was 0.5:1; and the mass ratio of anhydrous ethanol + water to nano silica was 1:0.05. The solvothermal synthesis reaction was carried out at a temperature of 80℃ for 8 hours, with a stirring speed of 300 r / min. After standing at room temperature for 10 days, the mixture was filtered and dried to obtain silica aerogel. A fly ash-based high infrared reflectance dual heat insulation and energy-saving coating has the following formula by weight percentage: Silicone-acrylic emulsion: 20% Flake-shaped alumina (aspect ratio 15): 15% Silica aerogel powder: 15% Dispersant: 1.5% Wetting agent: 1.4% Defoamer: 1.2% Leveling agent: 1.9% Film-forming aid: 9% Deionized water: Balance (35%) Preparation method: Mix 50% deionized water, 1.5% dispersant, 60% wetting agent by mass, and 15% flake alumina in the total formula, and disperse in a water bath at 1000 r / min and 35°C for 25 minutes to obtain slurry A.

[0045] Mix the remaining 50% of deionized water, 40% of the total wetting agent mass, and 15% of silica aerogel powder in a water bath at 200 rpm and 20°C for 35 minutes to avoid damaging its structure, and obtain slurry B.

[0046] Add 20% silicone-acrylic emulsion to the paint mixing tank, and add slurry A, slurry B, 1.2% defoamer, 1.9% leveling agent and 9% film-forming aid in sequence while stirring at low speed (350 r / min). Stir at 20℃ for 20 minutes until uniform, and then filter and discharge.

[0047] Comparative Example 1: Pure silicone-acrylic emulsion coating without any functional fillers. Effect test To verify the practical application effect of the fly ash-based high infrared reflectance dual heat insulation and energy-saving coating of the present invention, a comparative test experiment was set up. The specific test conditions, results, and performance advantages are analyzed as follows: The coatings prepared in Examples 1, 2, 3, and the comparative example were uniformly applied to a cement asbestos board. After drying into a film, the temperature was tested using a solar reflectivity meter and a thermal conductivity meter. Under the same solar radiation, the temperature of the substrate under the coating was measured, as shown in Table 1. Comparative Example 1 0.15 0.10 0.20 benchmark Example 1 0.89 0.88 0.067 20°C Example 2 0.86 0.85 0.061 22°C Example 3 0.91 0.90 0.074 18°C Table 1 As can be clearly seen from the test data in Table 1, the coating performance of Examples 1-3 of the present invention is comprehensively superior to that of Comparative Example 1, specifically as follows: Significantly improved reflectivity: Comparative Example 1 has a solar reflectivity of only 0.15 and a near-infrared reflectivity of only 0.10, which cannot effectively reflect heat from solar radiation; while Examples 1-3 all have solar reflectivity of over 0.86, with Example 3 reaching as high as 0.91, and the near-infrared reflectivity is also stable above 0.85, with Example 3 reaching 0.90, which means that the coating can reflect more than 85% of near-infrared light, achieving the core design goal of active reflection.

[0048] The thermal conductivity is significantly reduced: the thermal conductivity of Comparative Example 1 is 0.20 W / m·K, and heat can easily penetrate the coating through conduction; while the thermal conductivity of Examples 1-3 is controlled between 0.061 and 0.074 W / m·K, with Example 2 having the lowest thermal conductivity of only 0.061 W / m·K, which is much lower than that of the Comparative Example, demonstrating the excellent effect of silica aerogel in passively blocking heat conduction and convection.

[0049] Outstanding heat insulation and cooling effect: Under the same solar radiation conditions, the substrate temperature of Examples 1-3 was reduced by 20℃, 22℃ and 18℃ respectively compared with Comparative Example 1. Among them, Example 2 had the best cooling effect, reaching 22℃. This fully demonstrates that the dual heat insulation mechanism of active reflection and passive blocking is highly efficient and can reduce heat intake and block heat transfer from the source, which is significantly better than the traditional single mechanism coating.

[0050] Meanwhile, the process parameters and environmental benefits of this invention are synergistically unified: water is used as the main solvent throughout the process, combined with low-temperature freeze drying (-10-5℃), vacuum calcination and other processes to reduce the emission of volatile organic compounds; the parameters of each step (such as alkali washing concentration and calcination temperature) are precisely matched to avoid energy waste caused by excessive reaction, and finally the energy consumption of the coating preparation process is reduced by more than 25% compared with the traditional process, taking into account both industrial feasibility and environmental protection requirements.

[0051] The coating preparation process described in this application is simple, and through the synergistic design of components, large-scale production can be achieved without complex equipment. This coating is suitable for summer cooling of building roofs and exterior walls, as well as surface insulation of industrial equipment, ships, and vehicles, demonstrating strong adaptability and industrialization potential.

[0052] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0053] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A fly ash-based high infrared reflectance dual heat insulation and energy-saving coating, characterized in that, The product comprises the following components by mass percentage: 20%-40% silicone-acrylic emulsion, 30%-55% functional filler, 3%-15% additives, and the balance being deionized water; the functional filler comprises micron-sized flake alumina and silica aerogel powder, wherein the mass ratio of the micron-sized flake alumina to the silica aerogel powder is 1-4:

1.

2. The fly ash-based high infrared reflectance dual heat insulation and energy-saving coating according to claim 1, characterized in that, The micron-sized sheet-like alumina has a diameter-to-thickness ratio of 8 to 15.

3. The fly ash-based high infrared reflectance dual heat insulation and energy-saving coating according to claim 1, characterized in that, The additives include polyacrylate dispersants, silicone wetting agents, silicone emulsion defoamers, polyether-modified polysiloxane leveling agents, and propylene glycol methyl ether.

4. A method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating as described in any one of claims 1-3, characterized in that, Includes the following steps: 1) Preparation of flake alumina: Solid waste fly ash is pretreated by alkaline washing to enhance the activity of internal silicon and aluminum components. The pretreated fly ash is ground and mixed with ammonium fluoride, and then calcined under vacuum to complete the solid-phase reaction. After cooling to room temperature, the resulting solid is mixed with ethanol in a certain proportion, and after ultrasonic stirring and drying, micron-sized flake alumina is obtained. 2) Preparation of nano-silica from desilication solution: The fluorine-containing gas generated by high-temperature calcination in step 1) is passed into water for absorption. The resulting absorption solution is the desilication solution. Ammonia water is then added to adjust the pH value, followed by low-temperature stirring, filtration, heating and concentration, and freeze drying to finally obtain nano-silica. 3) Preparation of silica aerogel: The nano silica, template agent and co-solvent obtained in step 2) are added to the solvent, stirred evenly, heated, allowed to stand, filtered and dried to obtain silica aerogel; 4) Coating preparation: Mix 50% of deionized water, 60% of polyacrylate dispersant, and 60% of silicone wetting agent with the micron-sized flake alumina obtained in step 1), and disperse at high speed in a water bath to obtain slurry A; mix 50% of deionized water, 40% of silicone wetting agent, and 50% of silica aerogel powder obtained in step 3), and stir at low speed in a water bath to obtain slurry B; after adding silicone acrylic emulsion to the paint mixing tank, add slurry A, slurry B, silicone emulsion defoamer, polyether-modified polysiloxane leveling agent, and propylene glycol methyl ether in sequence under low speed stirring, stir until uniform, filter and discharge to obtain the double heat insulation and energy-saving coating.

5. The method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating according to claim 4, characterized in that, The alkaline washing pretreatment process in step 1) involves using a NaOH solution with a concentration of 2-8 mol / L, a liquid-to-solid ratio of fly ash to NaOH solution of 2-6 mL / g, and heating in a homogeneous reactor at a temperature of 60-120℃ for 100-200 min at a rotation speed of 50-200 r / min. Ultrasonic stirring is performed at a power of 300-500 W for 20-40 min. Vacuum calcination is carried out at a heating rate of 5-10℃ / min, a calcination temperature of 1000-1300℃, a holding time of 30-180 min, and a nitrogen flow rate of 100-200 mL / min. The resulting micron-sized sheet-like alumina has a polygonal structure, with the longest diagonal of the polygonal structure measuring 2-10 μm.

6. The method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating according to claim 4, characterized in that, In step 2), the ammonia concentration is 5-15 wt%, the pH value of the precipitation reaction is controlled at 7-11, the heating and stirring reaction temperature is 50-90℃, the heating and stirring reaction time is 0.5-2h, and the stirring speed is 30-300r / min. When filtering, 100-300ml of deionized water is added, and the filtration time is 10-40min. The heating temperature is 40-80℃, the stirring speed is set to 50-150rpm, and after the solution evaporates, it is freeze-dried and recovered at -10-5℃.

7. The method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating according to claim 4, characterized in that, In step 3), the template agent is chitosan and sodium alginate, the co-solvent is potassium hydroxide, and the solvent is anhydrous ethanol and water. The mass ratio of nano-silica to potassium hydroxide is 1:0.1~0.5; the mass ratio of nano-silica:chitosan:sodium alginate is 1:0.001~0.01:0.001~0.01; the volume ratio of anhydrous ethanol to water is 0.5~2:1; the mass ratio of solvent to nano-silica is 1:0.05~0.

3. The temperature of the solvothermal synthesis reaction is 80~170℃, the reaction time is 0.5~8h, the stirring speed is 30~300r / min, the reaction is allowed to stand at room temperature for 10d~15d, and the filtration time is 60min.

8. The method for preparing a fly ash-based high infrared reflectance dual heat insulation and energy-saving coating according to claim 4, characterized in that, In step 4), a water bath is used for high-speed dispersion, with a stirring speed of 500~1500 r / min, a time of 20~60 min, and a temperature between 20~45℃; a water bath is used for low-speed stirring, with a stirring speed of 50~400 r / min, a time of 10~50 min, and a temperature of 20℃.

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