Highly insulating and low thermal conductive coated sand and method for preparing the same

Abstract

The application discloses high-thermal-insulation low-thermal-conductivity coated sand and a preparation method thereof. The method comprises the following steps: firstly, drying raw sand and then performing surface activation treatment on the raw sand by using 3-aminopropyl triethoxysilane to obtain activated raw sand; secondly, dispersing hollow silica nanoparticles in a weak alkaline aqueous solution, forming a polydopamine coating layer under the action of dopamine, and then introducing sheet-shaped hexagonal boron nitride nanosheets to prepare hollow silica / hexagonal boron nitride composite thermal-insulation particles; thirdly, preparing the composite thermal-insulation particles into a dispersion slurry and depositing the dispersion slurry on the surface of the activated raw sand to form a composite thermal-insulation intermediate layer; and finally, adding thermoplastic phenolic resin, a curing agent and a lubricant to perform coating to obtain the high-thermal-insulation low-thermal-conductivity coated sand. The coated sand prepared by the application comprises, from inside to outside, a raw sand base layer, an active interface layer, a composite thermal-insulation intermediate layer and a resin coating layer.

Description

Technical Field

[0001] This invention relates to the field of coated sand technology, and in particular to a high-insulation, low-thermal-conductivity coated sand and its preparation method. Background Technology

[0002] Coated sand is a type of molding sand widely used in the foundry industry. It typically uses raw sand as aggregate and thermoplastic phenolic resin as the main coating and binding component. Through heating and mixing, the resin coats the surface of the sand grains, resulting in better flowability, moldability, and core strength. Current coated sand technology mainly focuses on improving room temperature strength, hot strength, flowability, collapsibility, and reducing gas generation. Relatively mature technical systems have been established in areas such as raw sand selection, resin system modification, curing agent ratio, and additives. In recent years, with the development of high-temperature alloy castings, complex thin-walled castings, and precision casting processes, higher requirements have been placed on the thermal insulation performance and low thermal conductivity of coated sand under high-temperature conditions. To reduce the rapid heat transfer from molten metal into the molding sand, slow down local sintering and thermal damage, and improve the surface quality of castings, existing technologies have begun to explore the introduction of low thermal conductivity fillers such as ceramic powder, hollow microspheres, nano-silica, and nitride materials into coated sand, or to improve the thermal insulation capacity of coated sand by changing the coating thickness, optimizing the resin system, and improving the surface condition of sand particles.

[0003] However, existing technologies mainly focus on the direct blending or simple surface adhesion of low thermal conductivity fillers, and generally suffer from the following shortcomings: Nanofillers, especially sheet-like or granular inorganic nanomaterials, are prone to agglomeration, making it difficult to distribute uniformly and stably on the sand surface, resulting in unstable insulation performance; the interfacial bonding between low thermal conductivity fillers and the original sand surface and resin coating layer is insufficient, making them prone to detachment during heating, coating, transportation, and use, affecting both insulation performance and the integrity of the coating layer; existing solutions mostly focus on single fillers or single modification methods, with insufficient research on how to construct a multi-interface synergistic insulation structure that can simultaneously achieve stable adhesion, inhibit agglomeration, and block heat conduction. There is a lack of a preparation method that combines original sand surface activation, construction of nanocomposite insulation particles, and synergistic regulation of the coating layer interface. Therefore, there is an urgent need to provide a method for preparing high-insulation, low-thermal-conductivity coated sand to solve the problems of poor dispersibility of insulation fillers, weak interfacial bonding, insufficient insulation layer stability, and limited reduction in thermal conductivity in existing coated sand. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a high-insulation, low-thermal-conductivity coated sand and its preparation method. First, the surface of the original sand is activated and modified. Then, a hollow silica / hexagonal boron nitride nanocomposite thermal insulation interlayer bridged by dopamine is constructed. Finally, a resin coating layer is formed on its outer side. This method utilizes the thermal resistance of the hollow structure, the heat-insulating effect of the sheet layer, and the synergistic effect of multi-interface scattering to block the heat conduction path. This reduces the thermal conductivity of the coated sand, improves its thermal insulation performance, and enhances the bonding stability between the nano-insulating phase, the sand particles, and the resin layer.

[0005] This invention can be achieved through the following technical solutions: A method for preparing a high-insulation, low-thermal-conductivity coated sand includes the following steps: S1. After removing dust from the raw sand, dry it at 105-140℃ for 1-3 h to make the moisture content of the raw sand not higher than 0.05wt% to obtain dried raw sand. Then add an alcohol-water solution containing 3-aminopropyltriethoxysilane to the dried raw sand and perform surface modification treatment at 25-50℃ for 20-90 min. After washing and drying, activated raw sand is obtained. S2. Hollow silica nanoparticles are dispersed in a weakly alkaline aqueous solution with pH 8.0-9.5. Dopamine is added, and self-polymerization deposition is carried out at 20-40℃ for 1-6 h to form a polydopamine coating layer on the surface of the hollow silica particles. Then, plate-shaped hexagonal boron nitride nanosheets are added and the dispersion reaction continues, so that the plate-shaped hexagonal boron nitride is loaded on the surface of the hollow silica nanoparticles under the action of the polydopamine coating layer, resulting in hollow silica / hexagonal boron nitride composite heat insulation particles. The composite heat insulation particles are then prepared into a dispersion slurry with water as the dispersion medium and a solid content of 2-15 wt%. The slurry is sprayed onto the surface of activated original sand at an addition amount of 0.3-3.0 wt% relative to the original sand. The composite particles are uniformly deposited on the surface of activated original sand under stirring at 150-700 rpm. Then, the slurry is dried at 60-120℃ for 15-120 min to obtain pre-coated sand with a composite heat insulation intermediate layer on the surface. S3. Heat the pre-coated sand to 120-165℃, add thermoplastic phenolic resin and mix for 20-120 s, so that the thermoplastic phenolic resin melts and coats the outside of the composite heat insulation intermediate layer. Then add hexamethylenetetramine curing agent and lubricant and continue mixing for 20-180 s. Cool to 20-40℃ to obtain high heat insulation and low thermal conductivity coated sand.

[0006] Preferably, the raw sand is one of quartz sand, alumina sand, or ceramsite sand, with a particle size of 50-100 mesh.

[0007] Preferably, the amount of 3-aminopropyltriethoxysilane used is 0.1-1.5 wt% of the original sand mass, and the volume ratio of alcohol to water in the alcohol-water solution is (60-95):(5-40).

[0008] Preferably, the hollow silica nanoparticles have an average particle size of 80-300 nm and a shell thickness of 15-50 nm; the sheet-like hexagonal boron nitride nanosheets have a sheet diameter of 0.2-2 μm and a thickness of 10-80 nm.

[0009] Preferably, the mass ratio of the hollow silica nanoparticles to the sheet-like hexagonal boron nitride nanosheets is 100:(10-80), and the amount of dopamine used is 1-15% of the mass of the hollow silica nanoparticles.

[0010] Preferably, the amount of thermoplastic phenolic resin added is 1.5-4.5 wt% of the original sand mass, the amount of hexamethylenetetramine curing agent added is 8-18 wt% of the resin mass, and the amount of lubricant added is 0.05-0.5 wt% of the original sand mass. The lubricant is one or two of calcium stearate and zinc stearate.

[0011] A high-insulation, low-thermal-conductivity coated sand, wherein the surface of a single particle of the coated sand consists of, from the inside out, an original sand matrix layer, an amino-containing active interface layer, a hollow silica / hexagonal boron nitride composite heat insulation intermediate layer, and a resin coating layer, wherein the composite heat insulation intermediate layer is continuously attached to the surface of the original sand and is embedded and fixed by the resin coating layer.

[0012] The beneficial effects of this invention are: This invention first activates and modifies the surface of raw sand, then uses dopamine bridging to construct hollow silica / hexagonal boron nitride composite insulating particles, which are preferentially deposited on the surface of the raw sand to form a composite insulating intermediate layer. Finally, a resin coating layer is formed on the outer side, thus establishing a multi-interface synergistic insulating structure that differs from existing simple mixing or single-adhesion methods. This technical route not only improves the adhesion stability of the composite insulating particles on the surface of the raw sand and inhibits the agglomeration and detachment of nanofillers, but also allows the thermal resistance of the hollow structure, the heat-insulating effect of the lamellar structure, and the interfacial scattering effect to be synergistically utilized, significantly extending the heat conduction path and reducing the overall thermal conductivity of the coated sand. The resulting coated sand exhibits superior insulating performance and lower back-fired surface temperature rise, while maintaining good room-temperature flexural strength and relatively stable gas generation. This indicates that the invention achieves low thermal conductivity and high insulating performance while also considering the integrity of the coating layer and the stability of use, effectively meeting the requirements for insulating performance, interfacial firmness, and comprehensive performance of coated sand under high-temperature casting conditions. Attached Figure Description

[0013] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 For the thermal insulation properties of coated sand; Figure 2The thermal conductivity, room temperature flexural strength, and gas generation of the coated sand are considered. Detailed Implementation

[0014] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0015] Example 1: A method for preparing a high-insulation, low-thermal-conductivity coated sand, comprising the following steps: S1. Take 1000 g of quartz sand with a particle size of 50 mesh, remove dust, place it in an oven, and dry it at 105℃ for 1 h to ensure that the moisture content of the raw sand is not higher than 0.05 wt%, thus obtaining dried raw sand; weigh 1 g of 3-aminopropyltriethoxysilane and add it to an alcohol-water mixture with a volume ratio of 60:40 to prepare a surface modification solution; spray the surface modification solution onto the surface of the dried raw sand, modify it at 25℃ for 90 min, then wash and dry it to obtain activated raw sand; S2. Take 2.7 g of hollow silica nanoparticles with an average particle size of 80 nm and a shell thickness of 15 nm, disperse them in a weakly alkaline aqueous solution with pH 8.0, add 0.03 g of dopamine, and perform self-polymerization deposition at 20℃ for 6 h to form a polydopamine coating layer on the surface of the hollow silica particles. Then add 0.27 g of sheet-like hexagonal boron nitride nanosheets with a sheet diameter of 0.2 μm and a thickness of 10 nm, and continue the dispersion reaction to load the sheet-like hexagonal boron nitride onto the surface of the hollow silica nanoparticles under the action of the polydopamine coating layer, thus obtaining hollow silica / hexagonal boron nitride composite thermal insulation particles. Then, prepare a dispersion slurry with water as the dispersion medium and a solid content of 2 wt%. Since the amount added relative to the original sand is 0.3 wt%, the total amount of composite thermal insulation particles added is 3 g, and the total mass of the dispersion slurry is 150 g, of which the amount of water is 147 g. g, the dispersion slurry is sprayed onto the surface of the activated raw sand, and the composite particles are uniformly deposited on the surface of the activated raw sand under stirring at 150 rpm. Then, it is dried at 60℃ for 120 min to obtain pre-coated sand with a composite heat insulation intermediate layer formed on the surface. S3. Heat the pre-coated sand to 120°C, add 15 g of thermoplastic phenolic resin, mix for 20 s, so that the thermoplastic phenolic resin melts and coats the outside of the composite heat insulation intermediate layer, then add 1.2 g of hexamethylenetetramine curing agent and 0.5 g of zinc stearate, continue mixing for 20 s, cool to 20°C, and obtain high heat insulation and low thermal conductivity coated sand.

[0016] Example 2: A method for preparing a high-insulation, low-thermal-conductivity coated sand, comprising the following steps: S1. Take 1000 g of quartz sand with a particle size of 70 mesh, remove dust, place it in an oven, and dry it at 120℃ for 2 h to make the moisture content of the raw sand no more than 0.05 wt%, thus obtaining dried raw sand; weigh 8 g of 3-aminopropyltriethoxysilane and add it to an alcohol-water mixture with a volume ratio of 80:20 to prepare a surface modification solution; spray the surface modification solution onto the surface of the dried raw sand, modify it at 35℃ for 60 min, then wash and dry it to obtain activated raw sand; S2. Take 11 g of hollow silica nanoparticles with an average particle size of 200 nm and a shell thickness of 30 nm, disperse them in a weakly alkaline aqueous solution with pH 8.5, add 0.88 g of dopamine, and perform self-polymerization deposition at 30℃ for 4 h to form a polydopamine coating layer on the surface of the hollow silica particles. Then add 5 g of sheet-like hexagonal boron nitride nanosheets with a sheet diameter of 1 μm and a thickness of 40 nm, and continue the dispersion reaction to load the sheet-like hexagonal boron nitride onto the surface of the hollow silica nanoparticles under the action of the polydopamine coating layer, thus obtaining hollow silica / hexagonal boron nitride composite thermal insulation particles. Then prepare a dispersion slurry with water as the dispersion medium and a solid content of 8 wt%. Since the amount added relative to the original sand is 1.5 wt%, the total amount of composite thermal insulation particles added is 15 g, and the total mass of the dispersion slurry is 188 g, of which the amount of water is 150 g. g, the dispersion slurry is sprayed onto the surface of the activated raw sand, and the composite particles are uniformly deposited on the surface of the activated raw sand under stirring at 400 rpm. Then, it is dried at 90℃ for 60 min to obtain pre-coated sand with a composite heat insulation intermediate layer formed on the surface. S3. Heat the pre-coated sand to 140°C, add 30 g of thermoplastic phenolic resin, mix for 60 s, so that the thermoplastic phenolic resin melts and coats the outside of the composite heat insulation intermediate layer, then add 3.6 g of hexamethylenetetramine curing agent and 30 g of zinc stearate, continue mixing for 100 s, cool to 30°C, and obtain high heat insulation and low thermal conductivity coated sand.

[0017] Example 3: A method for preparing a high-insulation, low-thermal-conductivity coated sand, comprising the following steps: S1. Take 1000 g of quartz sand with a particle size of 100 mesh, remove dust, place it in an oven, and dry it at 140℃ for 1 h to make the moisture content of the raw sand no more than 0.05 wt%, thus obtaining dried raw sand; weigh 15 g of 3-aminopropyltriethoxysilane, add it to an alcohol-water mixture with a volume ratio of 95:5 to prepare a surface modification solution; spray the surface modification solution onto the surface of the dried raw sand, modify it at 50℃ for 20 min, then wash and dry it to obtain activated raw sand; S2. Take 15.38 g of hollow silica nanoparticles with an average particle size of 300 nm and a shell thickness of 50 nm, disperse them in a weakly alkaline aqueous solution with pH 9.5, add 2.31 g of dopamine, and perform self-polymerization deposition at 40℃ for 1 h to form a polydopamine coating layer on the surface of the hollow silica particles. Then add 12.31 g of sheet-like hexagonal boron nitride nanosheets with a sheet diameter of 2 μm and a thickness of 80 nm, and continue the dispersion reaction to load the sheet-like hexagonal boron nitride onto the surface of the hollow silica nanoparticles under the action of the polydopamine coating layer, thus obtaining hollow silica / hexagonal boron nitride composite thermal insulation particles. Then prepare a dispersion slurry with water as the dispersion medium and a solid content of 15 wt%. Since the amount added relative to the original sand is 3.0 wt%, the total amount of composite thermal insulation particles added is 30 g, and the total mass of the dispersion slurry is 200 g, of which the amount of water is 170 g. g, the dispersion slurry is sprayed onto the surface of the activated raw sand, and the composite particles are uniformly deposited on the surface of the activated raw sand under stirring at 700 rpm. Then, it is dried at 120℃ for 15 min to obtain pre-coated sand with a composite heat insulation intermediate layer formed on the surface. S3. Heat the pre-coated sand to 165°C, add 45 g of thermoplastic phenolic resin, mix for 120 s to melt and coat the outside of the composite heat insulation intermediate layer with the thermoplastic phenolic resin, then add 8.1 g of hexamethylenetetramine curing agent and 5 g of zinc stearate, continue mixing for 180 s, and cool to 40°C to obtain high heat insulation and low thermal conductivity coated sand.

[0018] Comparative Example 1: The difference between this comparative example and Example 1 is that the original sand was not subjected to silane activation treatment.

[0019] A method for preparing a high-insulation, low-thermal-conductivity coated sand includes the following steps: S1. Take 1000 g of quartz sand with a particle size of 50 mesh, remove dust and place it in an oven, dry it at 105℃ for 1 h, so that the moisture content of the original sand is not higher than 0.05 wt%, and obtain dry original sand, which is then not modified by silane coupling agent. S2. Take 2.7 g of hollow silica nanoparticles with an average particle size of 80 nm and a shell thickness of 15 nm, disperse them in a weakly alkaline aqueous solution with pH 8.0, add 0.03 g of dopamine, and perform self-polymerization deposition at 20℃ for 6 h to form a polydopamine coating layer on the surface of the hollow silica particles. Then add 0.27 g of sheet-like hexagonal boron nitride nanosheets with a sheet diameter of 0.2 μm and a thickness of 10 nm, and continue the dispersion reaction to load the sheet-like hexagonal boron nitride onto the surface of the hollow silica nanoparticles under the action of the polydopamine coating layer, thus obtaining hollow silica / hexagonal boron nitride composite thermal insulation particles. Then, prepare a dispersion slurry with water as the dispersion medium and a solid content of 2 wt%. Since the amount added relative to the original sand is 0.3 wt%, the total amount of composite thermal insulation particles added is 3 g, and the total mass of the dispersion slurry is 150 g, of which the amount of water is 147 g. g, the dispersion slurry is sprayed onto the surface of the unactivated original sand, and the composite particles are uniformly deposited on the surface of the unactivated original sand under stirring at 150 rpm. Then, it is dried at 60℃ for 120 min to obtain pre-coated sand with a composite heat insulation intermediate layer formed on the surface. S3. Heat the pre-coated sand to 120°C, add 15 g of thermoplastic phenolic resin, mix for 20 s to melt and coat the outside of the composite heat insulation intermediate layer with the thermoplastic phenolic resin, then add 1.2 g of hexamethylenetetramine curing agent and 0.5 g of zinc stearate, continue mixing for 20 s, cool to 20°C, and obtain the coated sand.

[0020] Comparative Example 2: The difference between this comparative example and Example 1 is that dopamine bridging was not used to construct the composite thermal insulation particles.

[0021] A method for preparing a high-insulation, low-thermal-conductivity coated sand includes the following steps: S1. Take 1000 g of quartz sand with a particle size of 50 mesh, remove dust, place it in an oven, and dry it at 105℃ for 1 h to ensure that the moisture content of the raw sand is not higher than 0.05 wt%, thus obtaining dried raw sand; weigh 1 g of 3-aminopropyltriethoxysilane and add it to an alcohol-water mixture with a volume ratio of 60:40 to prepare a surface modification solution; spray the surface modification solution onto the surface of the dried raw sand, modify it at 25℃ for 90 min, then wash and dry it to obtain activated raw sand; S2. Take 2.7 g of hollow silica nanoparticles with an average particle size of 80 nm and a shell thickness of 15 nm, and directly disperse them in a weakly alkaline aqueous solution with pH 8.0; then add 0.27 g of sheet-like hexagonal boron nitride nanosheets with a sheet diameter of 0.2 μm and a thickness of 10 nm, and mix the two by mechanical stirring only to obtain a mixed heat-insulating particle slurry; then prepare it into an aqueous dispersion slurry with a solid content of 2 wt%, and spray it onto the surface of activated original sand at an addition amount of 0.3 wt% relative to the original sand, stir and deposit at 150 rpm, and dry at 60℃ for 120 min to obtain pre-coated sand; S3. Heat the pre-coated sand to 120°C, add 15 g of thermoplastic phenolic resin, mix for 20 s to melt and coat the outside of the composite heat insulation intermediate layer with the thermoplastic phenolic resin, then add 1.2 g of hexamethylenetetramine curing agent and 0.5 g of zinc stearate, continue mixing for 20 s, cool to 20°C, and obtain the coated sand.

[0022] Comparative Example 3: The difference between this comparative example and Example 1 is that the composite heat insulation particles are directly blended with resin and coated.

[0023] A method for preparing a high-insulation, low-thermal-conductivity coated sand includes the following steps: S1. Take 1000 g of quartz sand with a particle size of 50 mesh, remove dust, place it in an oven, and dry it at 105℃ for 1 h to ensure that the moisture content of the raw sand is not higher than 0.05 wt%, thus obtaining dried raw sand; weigh 1 g of 3-aminopropyltriethoxysilane and add it to an alcohol-water mixture with a volume ratio of 60:40 to prepare a surface modification solution; spray the surface modification solution onto the surface of the dried raw sand, modify it at 25℃ for 90 min, then wash and dry it to obtain activated raw sand; S2. Take 2.7 g of hollow silica nanoparticles with an average particle size of 80 nm and a shell thickness of 15 nm, disperse them in a weakly alkaline aqueous solution with pH 8.0, add 0.03 g of dopamine, and carry out self-polymerization deposition at 20℃ for 6 h to form a polydopamine coating layer on the surface of the hollow silica particles. Then add 0.27 g of sheet-like hexagonal boron nitride nanosheets with a sheet diameter of 0.2 μm and a thickness of 10 nm, and continue the dispersion reaction to load the sheet-like hexagonal boron nitride onto the surface of the hollow silica nanoparticles under the action of the polydopamine coating layer, and obtain hollow silica / hexagonal boron nitride composite heat insulation particles. S3. Heat the activated raw sand to 120°C, add 15 g of thermoplastic phenolic resin and 3 g of composite heat insulation particles, then add 1.2 g of hexamethylenetetramine curing agent and 0.5 g of zinc stearate, continue mixing for 20 s, cool to 20°C, and obtain coated sand.

[0024] Performance testing 1 Thermal conductivity The determination was carried out in accordance with the GB / T 10294-2008 standard.

[0025] 2 Thermal insulation performance The determination was carried out in accordance with the JB / T 13037-2017 standard.

[0026] 3. Room temperature flexural strength The determination was carried out in accordance with the GB / T 2684-2025 standard.

[0027] 4. Gas output The determination was carried out in accordance with the GB / T 2684-2025 standard.

[0028] Table 1 Performance test results of coated sand

[0029] As shown in Table 1, the coated sand prepared in Examples 1-3 all exhibited low thermal conductivity, low unexposed surface temperature, high thermal insulation temperature difference, and good room temperature flexural strength. Specifically, with the increased surface activation of the original sand, the increased loading of hollow silica / hexagonal boron nitride composite insulating particles, and the optimized construction conditions of the composite insulating intermediate layer in Examples 1 to 3, the thermal conductivity of the coated sand gradually decreased from 0.298 W / (m·K) to 0.219 W / (m·K), the unexposed surface temperature decreased from 437℃ to 366℃, the thermal insulation temperature difference increased from 263℃ to 334℃, and the room temperature flexural strength increased from 3.42 MPa to 3.71 MPa. The fact that the gas emission only increased slightly and remained within an acceptable range at MPa indicates that the present invention, by first constructing an amino-containing active interface layer on the surface of the original sand, then using dopamine to bridge and form hollow silica / hexagonal boron nitride composite thermal insulation particles, and forming a stable composite thermal insulation intermediate layer between the original sand and the resin coating, can effectively leverage the synergistic effect of hollow structure thermal resistance, sheet thermal resistance effect and multi-interface scattering, significantly blocking the heat conduction path, and maintaining good mechanical properties while improving thermal insulation performance and reducing thermal conductivity.

[0030] Compared with Example 1, the overall performance of Comparative Examples 1-3 was significantly worse. Comparative Example 1 did not undergo silane activation treatment on the raw sand, resulting in insufficient interfacial bonding between the composite insulating particles and the raw sand surface, and weak adhesion of the insulating interlayer. Consequently, it had the highest thermal conductivity, the highest unexposed surface temperature, and the lowest room-temperature flexural strength. Comparative Example 2 did not use dopamine bridging to construct the composite insulating particles; it only used a simple physical mixture of hollow silica and hexagonal boron nitride, which easily caused particle agglomeration and uneven distribution, making it difficult to form a stable and effective insulating structure. Its thermal conductivity and insulating performance were inferior to the Example. Comparative Example 3 did not construct a composite insulating interlayer on the surface of the raw sand; instead, it directly blended and coated the sand with resin. This made it difficult for the insulating particles to be oriented and evenly distributed at the raw sand / resin interface, failing to form a continuous and stable multi-interface discontinuous thermal conduction path. Therefore, its insulating effect and mechanical properties were lower than those of the Example.

[0031] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-insulation, low-thermal-conductivity coated sand, characterized in that, Includes the following steps: S1. After removing dust from the raw sand, dry it at 105-140℃ for 1-3 h to make the moisture content of the raw sand not higher than 0.05 wt% to obtain dried raw sand. Then add an alcohol-water solution containing 3-aminopropyltriethoxysilane to the dried raw sand and perform surface modification treatment at 25-50℃ for 20-90 min. After washing and drying, activated raw sand is obtained. S2. Hollow silica nanoparticles are dispersed in a weakly alkaline aqueous solution with pH 8.0-9.

5. Dopamine is added, and self-polymerization deposition is carried out at 20-40℃ for 1-6 h to form a polydopamine coating layer on the surface of the hollow silica particles. Then, sheet-like hexagonal boron nitride nanosheets are added and the dispersion reaction continues, so that the sheet-like hexagonal boron nitride is loaded on the surface of the hollow silica nanoparticles under the action of the polydopamine coating layer, resulting in hollow silica / hexagonal boron nitride composite heat insulation particles. The composite heat insulation particles are then prepared into a dispersion slurry with water as the dispersion medium and a solid content of 2-15 wt%. The slurry is sprayed onto the surface of activated original sand at an addition amount of 0.3-3.0 wt% relative to the original sand. The composite particles are uniformly deposited on the surface of activated original sand under stirring at 150-700 rpm. Then, the slurry is dried at 60-120℃ for 15-120 min to obtain pre-coated sand with a composite heat insulation intermediate layer on the surface. S3. Heat the pre-coated sand to 120-165℃, add thermoplastic phenolic resin and mix for 20-120 seconds to melt and coat the outside of the composite heat insulation intermediate layer. Then add hexamethylenetetramine curing agent and lubricant and continue mixing for 20-180 seconds. Cool to 20-40℃ to obtain high heat insulation and low thermal conductivity coated sand.

2. The method for preparing high-insulation, low-thermal-conductivity coated sand according to claim 1, characterized in that, The raw sand is one of quartz sand, pearl sand, or ceramsite sand, with a particle size of 50-100 mesh.

3. The method for preparing high-insulation, low-thermal-conductivity coated sand according to claim 1, characterized in that, The amount of 3-aminopropyltriethoxysilane used is 0.1-1.5 wt% of the original sand mass, and the volume ratio of alcohol to water in the alcohol-water solution is (60-95):(5-40).

4. The method for preparing high-insulation, low-thermal-conductivity coated sand according to claim 1, characterized in that, The hollow silica nanoparticles have an average particle size of 80-300 nm and a shell thickness of 15-50 nm; the sheet-like hexagonal boron nitride nanosheets have a sheet diameter of 0.2-2 μm and a thickness of 10-80 nm.

5. The method for preparing high-insulation, low-thermal-conductivity coated sand according to claim 1, characterized in that, The mass ratio of hollow silica nanoparticles to sheet-like hexagonal boron nitride nanosheets is 100:(10-80), and the amount of dopamine used is 1-15% of the mass of the hollow silica nanoparticles.

6. The method for preparing high-insulation, low-thermal-conductivity coated sand according to claim 1, characterized in that, The amount of thermoplastic phenolic resin added is 1.5-4.5 wt% of the original sand mass, the amount of hexamethylenetetramine curing agent added is 8-18 wt% of the resin mass, and the amount of lubricant added is 0.05-0.5 wt% of the original sand mass. The lubricant is one or two of calcium stearate and zinc stearate.

7. A high-insulation, low-thermal-conductivity coated sand prepared by the preparation method according to any one of claims 1-6, characterized in that, The surface of each coated sand particle consists of, from the inside out, the original sand matrix layer, the amino-containing active interface layer, the hollow silica / hexagonal boron nitride composite thermal insulation intermediate layer, and the resin coating layer. The composite thermal insulation intermediate layer is continuously attached to the surface of the original sand and is embedded and fixed by the resin coating layer.

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