Low-thermal-conductivity spray coating and preparation method thereof

Abstract

The invention relates to a low-thermal-conductivity spray coating, which is prepared by adding alkaline silica sol, an aluminum dihydrogen phosphate aqueous solution with the mass concentration of 33%, hydroxypropyl cellulose, hexagonal boron nitride, aluminum silicate powder, methylallyl alcohol polyoxyethylene ether, silicon resin polyether emulsion, poloxamer 188 and deionized water into non-metal mineral modified silicon dioxide aerogel and hollow ceramic microbeads which serve as main materials. According to the invention, non-metallic minerals such as modified silicon dioxide aerogel and hollow ceramic microbeads are used as main materials, and the Zeta potential of the spray coating is effectively regulated and stabilized at-35 to-45 mV through the cooperative and synergistic effect of all the components, so that the physical and chemical properties of slurry are improved, and the problems of agglomeration, sedimentation and the like caused by non-uniform charge distribution in the slurry are effectively inhibited; the prepared coating has excellent low thermal conductivity, excellent mechanical properties and high bonding strength with a matrix, the thermal conductivity of the prepared coating can be as low as 0.022 W / m.K, the bonding strength with the matrix can reach 17 MPa, and the use temperature can reach 1400 DEG C.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation coating technology, specifically to a low thermal conductivity spray coating and its preparation method. Background Technology

[0002] With the increasing demands for thermal insulation of high-temperature equipment in aerospace, energy and chemical industries, traditional thermal insulation materials (such as ceramic fiber felt and calcium silicate board) have revealed problems such as weak interfacial bonding (≤1.5MPa) and poor construction adaptability (only applicable to flat substrates), complex construction, and susceptibility to moisture and aging. Therefore, coating products are needed to achieve "lightweight and integrated" thermal insulation and reduce heat loss.

[0003] Low thermal conductivity coatings, also known as heat insulation coatings or thermal insulation coatings, currently have three generations of technology: The first generation (1980-2000) uses zirconium oxide (YSZ) as the main component, forming a porous structure through atmospheric plasma spraying (APS), reducing the thermal conductivity to 1.1-1.3 W / (m²). . K), for the first time, achieved "coating" insulation for high-temperature equipment, but there is a risk of phase transformation cracking; the second-generation technology (2000-2020) introduced rare earth doping and prepared columnar crystal structures through electron beam physical vapor deposition (EB-PVD), reducing the thermal conductivity to 0.8-1.0 W / (m). . However, the production cost of the first generation of technology (K) is too high, hindering its widespread adoption. The third generation technology (2020-present) employs a nanocomposite system combined with high-velocity vapor deposition (HVOF) to achieve a thermal conductivity of 0.05-0.12 W / (m²). . K) Breakthrough. However, nanoparticles have high surface energy and are prone to forming agglomerates during mixing, resulting in uneven thermal insulation performance inside the coating and local thermal conductivity fluctuations of ±15%. Although low thermal conductivity coatings have achieved industrial application, it is difficult to balance low thermal conductivity with mechanical properties (adhesion, impact resistance) and workability (viscosity, curing speed). For example, although high filler content reduces thermal conductivity, it easily leads to coating agglomeration and cracking. The agglomeration problem of nanoparticles in the third-generation technology further exacerbates this contradiction. Although the third-generation nanocomposite coatings have been extended to medium and high temperature scenarios, their long-term temperature stability is insufficient. At high temperatures above 400℃ or in humid environments (relative humidity >85%), the interface between nanoparticles and the matrix is ​​prone to chemical reactions (such as the hydrolysis reaction between nano silica and resin), leading to interface separation, which cannot meet the "high temperature + vibration resistance" requirements of aerospace, high-end equipment and other fields. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a low thermal conductivity spray coating. This spray coating simultaneously achieves low thermal conductivity and high mechanical properties, improving the thermal insulation uniformity of the coating and its bonding strength with the substrate.

[0005] Another objective of this invention is to provide a method for preparing a low thermal conductivity spray coating. This method effectively solves the problem of nanoparticle agglomeration in the spray coating, improves the dispersion uniformity of the coating, and thus enhances the thermal insulation uniformity and long-term temperature resistance stability of the coating.

[0006] The objective of this invention is achieved through the following technical solution: A low thermal conductivity spray coating is characterized by being composed of non-metallic mineral modified silica aerogel and hollow ceramic microspheres as the main materials, and adding alkaline silica sol, 33% aluminum dihydrogen phosphate aqueous solution, hydroxypropyl cellulose, hexagonal boron nitride, aluminum silicate powder, methyl allyl alcohol polyoxyethylene ether, silicone resin polyether emulsion, poloxamer 188 and deionized water.

[0007] Furthermore, by weight, the components of the low thermal conductivity spray coating are: 35-40 parts modified silica aerogel, 25-28 parts hollow ceramic microspheres, 10-13 parts alkaline silica sol, 8-10 parts of 33% aluminum dihydrogen phosphate aqueous solution, 4-6 parts hydroxypropyl cellulose, 3-6 parts hexagonal boron nitride, 5-7 parts aluminum silicate powder, 2-4 parts methyl allyl alcohol polyoxyethylene ether, 1-2 parts silicone resin polyether emulsion, 2-3 parts poloxamer 188, and 20-25 parts deionized water.

[0008] Furthermore, the modified silica aerogel is prepared by immersing the silica aerogel in a 1% (w / w) ethanol solution of silane coupling agent KH550, drying it, and then calcining it.

[0009] Furthermore, the calcination temperature is 600~650℃, and the calcination time is 2~3h.

[0010] Furthermore, the slurry is prepared by taking the prescribed amount of deionized water, adding poloxamer 188, stirring evenly, letting it stand for 6-8 hours, then heating to 45-50°C, adding hydroxypropyl cellulose while stirring at 50-60 rpm until it is completely dissolved, cooling, adding alkaline silica sol, aluminum dihydrogen phosphate aqueous solution, and methyl allyl alcohol polyoxyethylene ether, stirring at 2000-3000 rpm for 10-15 minutes, then adding modified silica aerogel, hollow ceramic microspheres, and hexagonal boron nitride in sequence, continuing to stir for 5-8 minutes, then reducing the speed to 600-800 rpm, adding aluminum silicate powder, stirring for 3-5 minutes, finally adding silicone resin polyether emulsion, continuing to stir for 2-3 minutes, and letting it stand for 30-60 minutes.

[0011] A method for preparing a low thermal conductivity spray coating, characterized by comprising the following steps: (a) Aerogel modification The silica aerogel was immersed in an ethanol solution of silane coupling agent KH550 for 6-8 hours, dried, calcined, and then removed and cooled for later use. (II) Slurry preparation Take deionized water, add poloxamer 188, stir and disperse evenly, heat to 45~50℃, add hydroxypropyl cellulose, cool to room temperature, add alkaline silica sol, 33% aluminum dihydrogen phosphate aqueous solution, and methacrylic acid polyoxyethylene ether, mix evenly, then add modified silica aerogel, hollow ceramic microspheres, hexagonal boron nitride, and aluminum silicate powder in sequence, and finally add silicone resin polyether emulsion. Stir for 2~3 minutes at a speed of 600~800 rpm, stop stirring, and let stand for 30~60 minutes to obtain the spray coating.

[0012] Furthermore, the calcination temperature is 600~650℃, and the calcination time is 2~3h.

[0013] Furthermore, by weight, the following components are present: 35-40 parts modified silica aerogel, 25-28 parts hollow ceramic microspheres, 10-13 parts alkaline silica sol, 8-10 parts of 33% aluminum dihydrogen phosphate aqueous solution, 4-6 parts hydroxypropyl cellulose, 3-6 parts hexagonal boron nitride, 5-7 parts aluminum silicate powder, 2-4 parts methyl allyl alcohol polyoxyethylene ether, 1-2 parts silicone resin polyether emulsion, 2-3 parts poloxamer 188, and 20-25 parts deionized water.

[0014] Non-metallic mineral-modified silica aerogel and hollow ceramic microspheres are used as the main heat insulation components. The hollow ceramic microspheres improve the strength of the spray coating. Alkaline silica sol and aluminum dihydrogen phosphate are used as binders, and hydroxypropyl cellulose is used as a thickener to prevent sedimentation or delamination of the spray coating. Hexagonal boron nitride is used as a toughening agent, and silicone polyether emulsion is used as a defoamer. This invention uses a biphase bonding system, which broadens the temperature resistance of the coating and improves the structural stability of the coating.

[0015] Further addition of aluminum silicate powder allows HPC to form a continuous structure, providing flexibility and adhesion. The aluminum silicate powder fills the pores of the continuous HPC structure, making the coating structure denser and reducing defects. The hydroxyl groups on the surface of the aluminum silicate powder interact with the hydroxypropyl groups of HPC, enhancing the bonding force between the particles and the matrix.

[0016] A method for preparing a low thermal conductivity spray coating, characterized by comprising the following steps: (a) Aerogel modification The silica aerogel was soaked in a 1% (w / w) ethanol solution of silane coupling agent KH550 for 6-8 hours, then removed and dried at 55-60℃. It was then placed in a muffle furnace at 600-650℃ and calcined for 2-3 hours. After removing and cooling, it was ready for use. (II) Slurry preparation Take 20-25 parts by weight of deionized water, add 2-3 parts of poloxamer 188, stir and disperse evenly, let stand for 6-8 hours, then heat to 45-50℃, and add 4-6 parts of hydroxypropyl cellulose while stirring at 50-60 rpm. Continue stirring until completely dissolved, stop stirring, cool to room temperature, transfer to a shear mixer, add 10-13 parts of alkaline silica sol, 8-10 parts of 33% aluminum dihydrogen phosphate aqueous solution, and 2-4 parts of methyl allyl alcohol polyoxyethylene ether. Turn on the shear mixer and set the speed to 2000-3000 rpm, disperse for 1 hour. Add 0-15 min, then add 35-40 parts of modified silica aerogel, 25-28 parts of hollow ceramic microspheres, and 3-6 parts of hexagonal boron nitride in sequence. Control the temperature at 25-35℃ and continue stirring at 2000-3000 rpm for 5-8 min. Then reduce the speed to 600-800 rpm and add 5-7 parts of aluminum silicate powder (passed through 1250 mesh). Continue stirring for 3-5 min. Finally, add 1-2 parts of silicone polyether emulsion and stir for another 2-3 min at 600-800 rpm. Stop stirring and let stand for 30-60 min to obtain the final product.

[0017] A method for preparing a heat-insulating coating, characterized by comprising the following steps: (a) Aerogel modification The silica aerogel was immersed in a 1% (w / w) ethanol solution of silane coupling agent KH550 for 6-8 hours, then removed, dried at 55-60℃, and then calcined at 600-650℃ for 2-3 hours. After calcination, it was removed, cooled, and ready for use. (II) Slurry preparation Take deionized water, add poloxamer 188, stir to disperse evenly, and let stand for 6-8 hours. Then heat to 45-50℃, and add hydroxypropyl cellulose while stirring at 50-60 rpm. Continue stirring until completely dissolved, stop stirring, and let cool to room temperature. Transfer to a shear mixer, add alkaline silica sol, a 33% aluminum dihydrogen phosphate aqueous solution, and methacrylic acid polyoxyethylene ether. Turn on the shear mixer and set the speed to 2000-3000 rpm, dispersing for 10-15 minutes. Then add modified silica aerogel, hollow ceramic microspheres, and hexagonal boron nitride in sequence, controlling the temperature at 25-35℃ and maintaining the speed at 2000-3000 rpm, continuing to stir for 5-8 minutes. Then reduce the speed to 600-800 rpm, add aluminum silicate powder (passed through 1250 mesh), continue stirring for 3-5 minutes, and finally add silicone polyether emulsion. Stir for another 2-3 minutes at a speed of 600-800 rpm, stop stirring, and let stand for 30-60 minutes to obtain the spray coating. By weight, the coating consists of 35-40 parts modified silica aerogel, 25-28 parts hollow ceramic microspheres, 10-13 parts alkaline silica sol, 8-10 parts of 33% aluminum dihydrogen phosphate aqueous solution, 4-6 parts hydroxypropyl cellulose, 3-6 parts hexagonal boron nitride, 5-7 parts aluminum silicate powder, 2-4 parts methyl allyl alcohol polyoxyethylene ether, 1-2 parts silicone polyether emulsion, 2-3 parts poloxamer 188, and 20-25 parts deionized water. (iii) Spraying After the substrate is sandblasted, ultrasonically cleaned, and dried, it is heated to 80-90℃ at a heating rate of 5-10℃ / min and kept at that temperature. A dual-channel spray gun is used, with the main channel pressure at 0.6-0.7MPa and the auxiliary channel pressure at 0.3-0.4MPa. The spray paint prepared in step (II) is sprayed, with the spray gun held at a height of 30-35cm above the substrate, a lateral movement speed of 0.8-1.2m / s, an overlap rate of 30%-40%, and a slurry output of 300-400mL / min. The spraying is repeated multiple times. After each layer is sprayed, the surface is immediately tested with a hygrometer (RH should be <15%). A dehumidifier is used to maintain the ambient humidity below 40%. If necessary, a hot air gun (60-80℃) is used to assist drying. The thickness of each layer is ≤1mm, and the final total thickness is 3-5mm. (iv) Segmented curing The sprayed intermediate product is baked at 140~150℃ for 2~3 hours, then heated to 600~650℃ at a rate of 5~8℃ / min and held for 1~2 hours, then heated to 1000~1100℃ at a rate of 5~8℃ / min and held for 30~60 minutes, then cooled naturally to room temperature and removed to obtain the final product.

[0018] The core of thermal shock resistance is the material's ability to resist cracking and peeling under repeated thermal shocks (rapid temperature rises and falls), which depends on the combined effects of thermal stress control, structural stability, and mechanical toughness. Modified silica aerogel is used as a core material for thermal insulation, but its nanoporous structure leads to insufficient mechanical strength, making it prone to skeletal cracking due to thermal mismatch stress during thermal cycling. Thermal expansion mismatch between hollow ceramic microspheres and organic or metal matrices can also lead to interfacial delamination. In addition, the density difference between the two and insufficient rheological properties of the slurry can easily cause sedimentation and delamination after spraying.

[0019] The addition of hexagonal boron nitride and aluminum silicate powder in this invention effectively mitigates differences in thermal expansion. The layered crystal structure of hexagonal boron nitride acts as a buffer against thermal shock, and its excellent internal thermal conductivity effectively and uniformly transfers the localized high temperature generated by thermal shock to the entire coating, preventing localized overheating. Its good lubricity reduces the frictional stress between aerogel particles, preventing particles from falling off during thermal shock. The ultrafine aluminum silicate powder fills the gaps between the hexagonal boron nitride particles, reducing porosity stress concentration and mitigating cracks generated during alternating hot and cold periods. The hexagonal boron nitride prevents localized overheating, and the extremely low thermal conductivity of aluminum silicate prevents the sacrifice of thermal insulation due to excessive thermal conductivity.

[0020] During the preparation of the spray coating, due to the instability of the Zeta potential, the particles are prone to agglomeration, sedimentation, and stratification. The spray coating has high viscosity, poor coating performance, and is difficult to spray. The prepared coating has poor uniformity, serious performance degradation, poor coating density, and low adhesion to the substrate. In this invention, alkaline silica sol serves as the charged framework to provide initial charge. The charge intensity is adjusted by neutralization with aluminum dihydrogen phosphate cations. Methyl allyl alcohol polyoxyethylene ether, possessing both hydrophilic and hydrophobic properties, adsorbs onto the particle surface through hydrophobic interactions. Its hydrophilic segments form steric hindrance, hindering particle aggregation. Combined with the nonionic properties of poloxamer 188, it can adsorb onto any particle surface, forming physical isolation, effectively reducing aggregation and inhibiting sedimentation and stratification. Through this aggregation-inhibiting effect, methyl allyl alcohol polyoxyethylene ether strengthens the "charge repulsion" effect of the double layer through charge interactions, while poloxamer 188 synergistically balances the charge distribution of each particle, enhancing double-layer stability and homogenizing charge distribution, reducing instability caused by local charge differences. The Zeta potential of the system is precisely controlled within -35 to -45 mV, avoiding both particle aggregation (insufficient charge) and abnormal viscosity (excessive charge), ensuring the dispersion stability and coating performance of the spray coating. Furthermore, in this system, Al... 3+ It forms coordination bonds with the edge hydroxyl groups of hexagonal boron nitride, which improves the dispersibility and interfacial bonding of hexagonal boron nitride at high temperatures.

[0021] The present invention has the following technical effects: In this invention, non-metallic mineral modified silica aerogel and hollow ceramic microspheres are used as the main heat insulation components. Through the synergistic effect of each component, the zeta potential of the spray coating is effectively controlled and stabilized at -35~-45mV, which improves the physicochemical properties of the slurry and effectively inhibits problems such as agglomeration and sedimentation caused by uneven charge distribution in the slurry. The prepared coating has excellent low thermal conductivity, excellent mechanical properties, and high bonding strength with the substrate. The thermal conductivity of the prepared coating can be as low as 0.022W / m·K, the bonding strength with the substrate can reach 17MPa, and the operating temperature can reach 1400℃. Attached Figure Description

[0022] Figure 1 The effect of different components on the zeta potential of spray coating.

[0023] Figure 2 Scanning electron microscope image of the low thermal conductivity coating prepared in Example 2 of this invention.

[0024] Figure 3 Scanning electron microscope image of the coating prepared in Comparative Example 1.

[0025] Figure 4 Scanning electron microscope image of the coating prepared in Comparative Example 2. Detailed Implementation

[0026] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0027] The methyl allyl alcohol polyoxyethylene ether used in this invention has the CAS number 31497-33-3 and the silicone resin polyether emulsion model is FM-550.

[0028] Example 1 A method for preparing a low thermal conductivity spray coating includes the following steps: (a) Aerogel modification The silica aerogel was immersed in a 1% (w / w) ethanol solution of silane coupling agent KH550 for 7 hours, then removed, dried at 55°C, and then calcined in a muffle furnace at 620°C for 2.5 hours. After calcination, it was removed, cooled, and ready for use. (II) Slurry preparation Take 24 parts by weight of deionized water, add 2.5 parts of poloxamer 188, stir to disperse evenly, let stand for 7 hours, then heat to 48°C, add 5 parts of hydroxypropyl cellulose while stirring at 55 rpm, continue stirring until completely dissolved, stop stirring, cool to room temperature, transfer to a shear mixer, add 12 parts of alkaline silica sol, 9 parts of 33% aluminum dihydrogen phosphate aqueous solution, and 3 parts of methyl allyl alcohol polyoxyethylene ether, turn on the shear mixer and set the speed to 2500 rpm. Disperse for 12 minutes, then add 38 parts of modified silica aerogel, 26 parts of hollow ceramic microspheres, and 4 parts of hexagonal boron nitride in sequence. Control the temperature at 30℃ and continue stirring at 2500 rpm for 6 minutes. Then reduce the speed to 700 rpm and add 6 parts of aluminum silicate powder (passed through 1250 mesh). Continue stirring for 5 minutes. Finally, add 1.5 parts of silicone polyether emulsion FM-550 and stir for another 3 minutes at 700 rpm. Stop stirring and let stand for 40 minutes to obtain the final product.

[0029] A low absolute value of the Zeta potential indicates insufficient surface charge density of the particles. The electrostatic repulsion between particles cannot overcome van der Waals forces, ultimately disrupting the dispersion stability of the slurry and leading to problems such as agglomeration and sedimentation. The presence of agglomerates reduces the slurry's fluidity, resulting in poor continuity during spraying, decreased spray uniformity and density, and reduced adhesion to the substrate and coating stability. Conversely, a high absolute value of the Zeta potential indicates strong electrostatic repulsion, leading to abnormal rheological properties of the slurry. Excessive negative charge on the particle surface creates "charge repulsion" with the substrate, significantly reducing the interfacial adhesion between the coating and the substrate.

[0030] In the preparation process, modified silica and hollow ceramic microspheres were used as the main functional components, and alkaline silica sol was used as the binder. Even with the addition of hydroxypropyl cellulose to inhibit sedimentation, the absolute value of the zeta potential of the prepared spray coating was significantly too high, the slurry rheology was poor, and due to the poor uniformity of charge distribution, obvious agglomeration and sedimentation stratification still occurred. Therefore, we further added aluminum dihydrogen phosphate, methyl allyl alcohol polyoxyethylene ether, and poloxamer 188 sequentially for adjustment. The effect of each component on the zeta potential of the spray coating was tested. Based on the formulation of Example 1 above, the spray coating prepared without the addition of aluminum dihydrogen phosphate, methyl allyl alcohol polyoxyethylene ether, and poloxamer 188 was designated as D1, the spray coating with the addition of aluminum dihydrogen phosphate was designated as D2, and the spray coating with the addition of methyl allyl alcohol polyoxyethylene ether was designated as D3. The zeta potentials were compared with those of Example 1, and the results are as follows. Figure 1As shown, the Zeta potential in group D1 reached -72.1mV. After further adding aluminum dihydrogen phosphate, its Zeta potential was significantly reduced to -31.8mV. In group D3, the Zeta potential was further fine-tuned to -42.2mV by adding methyl allyl alcohol polyoxyethylene ether. Poloxamer 188 itself does not carry a charge, but through its surface-active properties, it homogenizes the charge distribution. Together with aluminum dihydrogen phosphate and methyl allyl alcohol polyoxyethylene ether, it adjusts and balances the overall negative charge uniformity, stabilizing the Zeta potential of the spray coating at -35~-45mV. This potential range is the equilibrium range of low thermal conductivity coating slurry. Within this range, the surface charge density of the slurry particles is moderate. The electrostatic repulsion force can effectively counteract van der Waals attraction, avoid agglomeration, sedimentation and stratification, and ensure long-term stable dispersion of the slurry. At the same time, it will not cause abnormal viscosity due to excessive repulsion force, thus taking into account the flowability requirements of the coating process.

[0031] Comparative Example 1 Compared to Example 1, Tween 20 was used instead of Poloxamer 188 in the spray coating formulation, while the rest of the formulation steps were the same.

[0032] Comparative Example 2 Compared with Example 1, no aluminum silicate powder was added to the spray coating formulation, and the remaining steps were the same as in Example 1.

[0033] Comparative Example 3 Compared with Example 1, zirconium phosphate was used instead of aluminum dihydrogen phosphate as a high-temperature binder in the spray coating formulation, and the remaining steps were the same as in Example 1.

[0034] The spray coating prepared in Comparative Example 3 exhibited significant agglomeration and sedimentation. The Zeta potential of the spray coating prepared in Comparative Example 3 was tested to be -54.7 mV. During subsequent spray coating preparation, the slurry continuity was poor, the uniformity of the prepared coating was unsatisfactory, and its density was significantly lower than that of Example 1.

[0035] Example 2 A method for preparing a heat-insulating coating includes the following steps: Prepare the spray coating according to the same steps as in steps (i) and (ii) of Example 1; (iii) Spraying After sandblasting, ultrasonic cleaning, and drying, the stainless steel substrate was heated to 85°C at a heating rate of 10°C / min and held at that temperature. A dual-channel spray gun was used, with a main channel pressure of 0.65 MPa and an auxiliary channel pressure of 0.35 MPa. The coating material prepared in Example 1 was sprayed, with the spray gun maintained at a height of 30 cm above the substrate, a lateral movement speed of 1 m / s, an overlap rate of 35%, and a slurry output of 350 mL / min. The coating was repeated multiple times. After each layer was sprayed, the surface was immediately tested with a hygrometer (RH should be <15%). A dehumidifier was used to maintain the ambient humidity below 40%. The thickness of each layer was ≤1 mm, and the final total thickness was 3.5 mm. (iv) Segmented curing The sprayed intermediate product is baked at 145℃ for 2.5 hours, then heated to 620℃ at a rate of 6℃ / min and held for 1.5 hours, then heated to 1050℃ at a rate of 6℃ / min and held for 40 minutes, and then cooled to room temperature naturally. The product is then ready.

[0036] The coating prepared in this embodiment is as follows: Figure 2 As shown, the coating is dense and uniform.

[0037] The spray coatings prepared in Comparative Examples 1-3 were used to prepare coatings according to the process in Example 2, wherein the coatings prepared in Comparative Examples 2 and 3 were respectively as follows: Figure 3 and Figure 4 As shown, compared with Example 1, the coating structure is rough and the density is reduced. In Comparative Example 2, obvious unevenness also appeared in the coating.

[0038] High temperature resistance test: The coating prepared in this embodiment has excellent high temperature resistance and can withstand working environments with temperatures above 800°C for a long time. It also showed no peeling after more than 30 seconds of oxyacetylene flame test. Thermal conductivity test: The thermal conductivity of the coating was tested according to the hot wire method in GB / T 10294. Bond strength test: The bond strength between the coating and the substrate was tested according to the tensile method of ASTM C633 standard; Compressive strength: Tested according to standard GB / T 1964-1996, and the test results are shown in Table 1.

[0039] Table 1:

[0040] Thermal shock resistance test: The substrate for the sprayed coating was heated to 1200℃, then quickly removed and water-quenched at room temperature. This cycle was repeated. In addition to observing the integrity of the coating structure, the changes in the thermal conductivity and mechanical properties of the coating were further observed after testing. During the cycle, the coating was observed for cracking, peeling, bulging, etc. When cracking, peeling, bulging, etc. first appeared, the performance changes of the sample were tested. The results are shown in Table 2.

[0041] Table 2:

[0042] In the thermal shock resistance test, after 42 cycles in Example 1, microcracks appeared at the coating edge, and the coating completely failed after 59 cycles. In Comparative Example 1, the coating surface bulged after 29 cycles and completely failed after 44 cycles. In Comparative Examples 2 and 3, microcracks appeared at the coating edge after 20 and 22 cycles, respectively, and the coating completely failed after 35 and 36 cycles. The thermal conductivity, mechanical properties, and adhesion to the substrate of each comparative example were significantly lower than those of Example 1.

[0043] Example 3 A method for preparing a low thermal conductivity spray coating includes the following steps: (a) Aerogel modification The silica aerogel was soaked in a 1% (w / w) ethanol solution of silane coupling agent KH550 for 6 hours, then removed and dried at 60°C. It was then placed in a muffle furnace at 650°C and calcined for 2 hours. After being removed and cooled, it was ready for use. (II) Slurry preparation Take 20 parts by weight of deionized water, add 2 parts of poloxamer 188, stir to disperse evenly, let stand for 6 hours, then heat to 45°C, add 4 parts of hydroxypropyl cellulose while stirring at 50 rpm, continue stirring until completely dissolved, stop stirring, cool to room temperature, transfer to a shear mixer, add 10 parts of alkaline silica sol, 8 parts of 33% aluminum dihydrogen phosphate aqueous solution, and 2 parts of methyl allyl alcohol polyoxyethylene ether, turn on the shear mixer and set the speed to 2000 rpm. Disperse for 15 minutes, then add 35 parts of modified silica aerogel, 25 parts of hollow ceramic microspheres, and 3 parts of hexagonal boron nitride in sequence. Control the temperature at 25℃ and continue stirring at 2000 rpm for 8 minutes. Then reduce the speed to 600 rpm and add 5 parts of aluminum silicate powder (passed through 1250 mesh). Continue stirring for 3 minutes. Finally, add 1 part of silicone polyether emulsion FM-550 and stir for another 3 minutes at 600 rpm. Stop stirring and let stand for 30 minutes to obtain the final product.

[0044] Example 4 A method for preparing a heat-insulating coating includes the following steps: Prepare the spray coating according to the same steps as in steps (i) and (ii) of Example 2; (iii) Spraying After the substrate is sandblasted, ultrasonically cleaned, and dried, it is heated to 80°C at a heating rate of 10°C / min and kept at that temperature. A dual-channel spray gun is used, with a main channel pressure of 0.6MPa and an auxiliary channel pressure of 0.3MPa. The coating material prepared in Example 2 is sprayed, with the spray gun held at a height of 35cm above the substrate, a lateral movement speed of 1.2m / s, an overlap rate of 30%, and a slurry output of 300mL / min. The coating is sprayed repeatedly. After each layer is sprayed, the surface is immediately tested with a hygrometer (RH should be <15%). A dehumidifier is used to maintain the ambient humidity below 40%. If necessary, a hot air gun (60°C) is used to assist drying. The thickness of each layer is ≤1mm, and the final total thickness is 4.2mm. (iv) Segmented curing The sprayed intermediate product is baked at 140℃ for 3 hours, then heated to 650℃ at a rate of 5℃ / min and held for 1 hour, then heated to 1100℃ at a rate of 5℃ / min and held for 30 minutes, and then cooled naturally to room temperature. The product is then ready.

[0045] The low thermal conductivity coating prepared in this embodiment has a thermal conductivity of 0.022 W / m·K, a bonding strength with the substrate of 17.1 MPa, and a thermal shock resistance of 40 cycles.

[0046] Example 5 A method for preparing a low thermal conductivity spray coating and a thermal insulation coating includes the following steps: (a) Aerogel modification The silica aerogel was soaked in a 1% (w / w) ethanol solution of silane coupling agent KH550 for 8 hours, then removed and dried at 55°C. It was then placed in a muffle furnace at 600°C and calcined for 3 hours. After being removed and cooled, it was ready for use. (II) Slurry preparation Take 25 parts by weight of deionized water, add 3 parts of poloxamer 188, stir to disperse evenly, let stand for 8 hours, then heat to 50°C, add 6 parts of hydroxypropyl cellulose while stirring at 60 rpm, continue stirring until completely dissolved, stop stirring, cool to room temperature, transfer to a shear mixer, add 13 parts of alkaline silica sol, 10 parts of 33% aluminum dihydrogen phosphate aqueous solution, and 4 parts of methyl allyl alcohol polyoxyethylene ether, turn on the shear mixer, set the speed to 3000 rpm, and continue stirring. Disperse for 10 minutes, then add 40 parts of modified silica aerogel, 28 parts of hollow ceramic microspheres, and 3-6 parts of hexagonal boron nitride in sequence. Control the temperature at 35℃ and continue stirring at 3000 rpm for 5 minutes. Then reduce the speed to 800 rpm and add 7 parts of aluminum silicate powder (passed through 1250 mesh). Continue stirring for 5 minutes. Finally, add 2 parts of silicone polyether emulsion FM-550 and stir for another 2 minutes at 800 rpm. Stop stirring and let stand for 60 minutes to obtain the final product. (iii) Spraying After the substrate is sandblasted, ultrasonically cleaned and dried, it is heated to 90°C at a heating rate of 5°C / min and kept at that temperature. The coating material prepared in step (II) is then sprayed using a dual-channel spray gun (main channel pressure 0.7MPa, auxiliary channel pressure 0.4MPa). The spray gun is kept 30cm above the substrate, the lateral movement speed is 0.8m / s, the overlap rate is ~40%, the slurry output is 400mL / min, and the coating is repeated multiple times. After each layer is sprayed, the surface is immediately tested with a hygrometer (RH should be <15%). The ambient humidity is maintained below 40% using a dehumidifier. If necessary, a hot air gun (80°C) is used to assist drying. The thickness of each layer is ≤1mm, and the final total thickness is 4.7mm. (iv) Segmented curing The sprayed intermediate product is baked at 150℃ for 2 hours, then heated to 600℃ at a rate of 8℃ / min and held for 2 hours, then heated to 1000℃ at a rate of 8℃ / min and held for 60 minutes, and then cooled naturally to room temperature. The product is then obtained.

[0047] The low thermal conductivity coating prepared in this embodiment has a thermal conductivity of 0.023 W / m·K, a bonding strength with the substrate of 17.2 MPa, and a thermal shock resistance of 41 cycles.

Claims

1. A low thermal conductivity spray coating, characterized in that: It is composed of non-metallic mineral modified silica aerogel and hollow ceramic microspheres as the main materials, and added alkaline silica sol, 33% aluminum dihydrogen phosphate aqueous solution, hydroxypropyl cellulose, hexagonal boron nitride, aluminum silicate powder, methyl allyl alcohol polyoxyethylene ether, silicone resin polyether emulsion, poloxamer 188 and deionized water.

2. The low thermal conductivity spray coating as described in claim 1, characterized in that: By weight, the components of the low thermal conductivity spray coating are: 35-40 parts modified silica aerogel, 25-28 parts hollow ceramic microspheres, 10-13 parts alkaline silica sol, 8-10 parts of 33% aluminum dihydrogen phosphate aqueous solution, 4-6 parts hydroxypropyl cellulose, 3-6 parts hexagonal boron nitride, 5-7 parts aluminum silicate powder, 2-4 parts methyl allyl alcohol polyoxyethylene ether, 1-2 parts silicone resin polyether emulsion, 2-3 parts poloxamer 188, and 20-25 parts deionized water.

3. A low thermal conductivity spray coating as described in claim 1 or 2, characterized in that: The modified silica aerogel is prepared by immersing the silica aerogel in a 1% (w / w) ethanol solution of silane coupling agent KH550, drying it, and then calcining it.

4. A low thermal conductivity spray coating as described in any one of claims 1-3, characterized in that: The slurry is prepared by taking the prescribed amount of deionized water, adding poloxamer 188, stirring evenly, and letting it stand for 6-8 hours. Then, the temperature is raised to 45-50°C, and hydroxypropyl cellulose is added under stirring at 50-60 rpm until it is completely dissolved. After cooling, alkaline silica sol, aluminum dihydrogen phosphate aqueous solution, and methyl allyl alcohol polyoxyethylene ether are added. The mixture is stirred at 2000-3000 rpm for 10-15 minutes. Then, modified silica aerogel, hollow ceramic microspheres, and hexagonal boron nitride are added in sequence, and stirring is continued for 5-8 minutes. The stirring speed is then reduced to 600-800 rpm, aluminum silicate powder is added, and stirring is carried out for 3-5 minutes. Finally, silicone resin polyether emulsion is added, and stirring is continued for 2-3 minutes. The mixture is then allowed to stand for 30-60 minutes.

5. A method for preparing a low thermal conductivity spray coating, characterized in that, Includes the following steps: (a) Aerogel modification The silica aerogel was immersed in an ethanol solution of silane coupling agent KH550 for 6-8 hours, dried, calcined, and then removed and cooled for later use. (II) Slurry preparation Take deionized water, add poloxamer 188, stir and disperse evenly, heat to 45~50℃, add hydroxypropyl cellulose, cool to room temperature, add alkaline silica sol, 33% aluminum dihydrogen phosphate aqueous solution, and methacrylic acid polyoxyethylene ether, mix evenly, then add modified silica aerogel, hollow ceramic microspheres, hexagonal boron nitride, and aluminum silicate powder in sequence, and finally add silicone resin polyether emulsion. Stir for 2~3 minutes at a speed of 600~800 rpm, stop stirring, and let stand for 30~60 minutes to obtain the spray coating.

6. The method for preparing a low thermal conductivity spray coating as described in claim 5, characterized in that: The calcination temperature is 600~650℃, and the calcination time is 2~3h.

7. The method for preparing a low thermal conductivity spray coating as described in claim 5 or 6, characterized in that: By weight, the following components are present: 35-40 parts modified silica aerogel, 25-28 parts hollow ceramic microspheres, 10-13 parts alkaline silica sol, 8-10 parts 33% aluminum dihydrogen phosphate aqueous solution, 4-6 parts hydroxypropyl cellulose, 3-6 parts hexagonal boron nitride, 5-7 parts aluminum silicate powder, 2-4 parts methyl allyl alcohol polyoxyethylene ether, 1-2 parts silicone resin polyether emulsion, 2-3 parts poloxamer 188, and 20-25 parts deionized water.

8. A method for preparing a low thermal conductivity spray coating, characterized in that, Includes the following steps: (a) Aerogel modification The silica aerogel was soaked in a 1% (w / w) ethanol solution of silane coupling agent KH550 for 6-8 hours, then removed and dried at 55-60℃. It was then placed in a muffle furnace at 600-650℃ and calcined for 2-3 hours. After removing and cooling, it was ready for use. (II) Slurry preparation Take 20-25 parts by weight of deionized water, add 2-3 parts of poloxamer 188, stir to disperse evenly, let stand for 6-8 hours, then heat to 45-50℃, add 4-6 parts of hydroxypropyl cellulose while stirring at 50-60 rpm, continue stirring until completely dissolved, stop stirring, cool to room temperature, transfer to a shear mixer, add 10-13 parts of alkaline silica sol, 8-10 parts of 33% aluminum dihydrogen phosphate aqueous solution, and 2-4 parts of methyl allyl alcohol polyoxyethylene ether, turn on the shear mixer and set the speed to 2000-3000 rpm. Disperse for 10-15 minutes, then add 35-40 parts of modified silica aerogel, 25-28 parts of hollow ceramic microspheres, and 3-6 parts of hexagonal boron nitride in sequence. Control the temperature at 25-35℃ and continue stirring at 2000-3000 rpm for 5-8 minutes. Then reduce the speed to 600-800 rpm and add 5-7 parts of aluminum silicate powder. Continue stirring for 3-5 minutes. Finally, add 1-2 parts of silicone polyether emulsion and stir for another 2-3 minutes at 600-800 rpm. Stop stirring and let stand for 30-60 minutes to obtain the final product.

9. A method for preparing a heat-insulating coating, characterized in that, Includes the following steps: (a) Aerogel modification The silica aerogel was immersed in a 1% (w / w) ethanol solution of silane coupling agent KH550 for 6-8 hours, then removed, dried at 55-60℃, and then calcined at 600-650℃ for 2-3 hours. After calcination, it was removed, cooled, and ready for use. (II) Slurry preparation Take deionized water, add poloxamer 188, stir to disperse evenly, and let stand for 6-8 hours. Then heat to 45-50℃, and add hydroxypropyl cellulose while stirring at 50-60 rpm. Continue stirring until completely dissolved, stop stirring, and let cool to room temperature. Transfer to a shear mixer, add alkaline silica sol, a 33% aluminum dihydrogen phosphate aqueous solution, and methacrylic acid polyoxyethylene ether. Turn on the shear mixer and set the speed to 2000-3000 rpm, dispersing for 10-15 minutes. Then add modified silica aerogel, hollow ceramic microspheres, and hexagonal boron nitride in sequence, controlling the temperature at 25-35℃ and maintaining the speed at 2000-3000 rpm, continuing to stir for 5-8 minutes. Then reduce the speed to 600-800 rpm, add aluminum silicate powder (passed through 1250 mesh), continue stirring for 3-5 minutes, and finally add silicone polyether emulsion. Stir for another 2-3 minutes at a speed of 600-800 rpm, stop stirring, and let stand for 30-60 minutes to obtain the spray coating. By weight, the coating consists of 35-40 parts modified silica aerogel, 25-28 parts hollow ceramic microspheres, 10-13 parts alkaline silica sol, 8-10 parts of 33% aluminum dihydrogen phosphate aqueous solution, 4-6 parts hydroxypropyl cellulose, 3-6 parts hexagonal boron nitride, 5-7 parts aluminum silicate powder, 2-4 parts methyl allyl alcohol polyoxyethylene ether, 1-2 parts silicone polyether emulsion, 2-3 parts poloxamer 188, and 20-25 parts deionized water. (iii) Spraying After the substrate is sandblasted, ultrasonically cleaned, and dried, it is heated to 80-90℃ at a heating rate of 5-10℃ / min and kept at that temperature. A dual-channel spray gun is used, with the main channel pressure at 0.6-0.7MPa and the auxiliary channel pressure at 0.3-0.4MPa. The spray paint prepared in step (II) is sprayed, with the spray gun held at a height of 30-35cm above the substrate, a lateral movement speed of 0.8-1.2m / s, an overlap rate of 30%-40%, and a slurry output of 300-400mL / min. The spraying is repeated multiple times. After each layer is sprayed, the surface is immediately tested with a hygrometer (RH should be <15%). A dehumidifier is used to maintain the ambient humidity below 40%. If necessary, a hot air gun (60-80℃) is used to assist drying. The thickness of each layer is ≤1mm, and the final total thickness is 3-5mm. (iv) Segmented curing The sprayed intermediate product is baked at 140~150℃ for 2~3 hours, then heated to 600~650℃ at 5~8℃ / min and held for 1~2 hours, then heated to 1000~1100℃ at 5~8℃ / min and held for 30~60 minutes, then cooled naturally to room temperature and removed.

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