High-thermal-conductivity high-temperature solar photothermal conversion coating as well as preparation method and application thereof

Abstract

The invention relates to a high-thermal-conductivity high-temperature solar photothermal conversion coating and a preparation method and application thereof, and belongs to the technical field of new energy materials. According to the method, a high-thermal-conductivity Sr or Ca-doped LaCoO3 oxide material is used as a main component of the coating, and double-layer spraying preparation of a body layer and a surface layer is adopted. Compared with a traditional spinel oxide-based coating, the coating prepared through the method has the advantages that the heat conductivity is remarkably higher, meanwhile, the high light absorption rate (higher than 95%) and the low emissivity (lower than 0.65) are achieved, surface heat radiation and heat convection loss are remarkably reduced under the high-temperature working condition, and therefore the photo-thermal conversion efficiency is improved. The photo-thermal conversion efficiency of the coating is remarkably higher than that of a commercial product PyroMark2500, and the preparation method is simple, low in cost and capable of achieving large-scale production.

Description

Technical Field

[0001] This invention relates to a high thermal conductivity high-temperature solar photothermal conversion coating, its preparation method and application, belonging to the field of new energy materials technology. Background Technology

[0002] Concentrated solar power (CSP) is a highly efficient renewable energy technology that converts focused sunlight into heat energy through photothermal conversion materials. This heat energy can then be used for power generation, thermocatalysis, metal smelting, or stored in a thermal storage medium. Thanks to the high efficiency and low cost of thermal energy storage, CSP technology can complement photovoltaic and wind power generation, effectively mitigating the intermittency and volatility of power generation and improving the stability of power output. Tower-type CSP systems have the highest concentration ratio (over 1000 times) and operating temperature (over 700 °C), achieving the highest theoretical CSP efficiency (over 35%). The power generation efficiency of a tower-type CSP plant includes collector efficiency (light to heat) and heat engine efficiency (heat to electricity). Heat engine efficiency is positively correlated with the hot-end temperature, but high temperatures increase heat convection and radiation losses on the collector surface, thus limiting the light-to-heat efficiency. Currently, commonly used oxide-based high-temperature solar collector photothermal coating materials are represented by commercial material Pyromark2500, which is based on spinel light-absorbing materials (Cu-Fe-Mn-O, Cu-Cr-Mn-O, etc.) and silicone grease. These coatings have excellent light absorption and high-temperature stability. However, due to the low thermal conductivity of these spinel materials themselves, the overall thermal conductivity of these coatings is low, which means that the heat energy generated by surface light absorption cannot be quickly dissipated, resulting in excessively high surface temperature and significant heat radiation and heat convection losses. To improve the thermal conductivity of coatings, a common strategy is to add high thermal conductivity fillers. However, this method has several drawbacks: 1. Commonly used high thermal conductivity metal additives such as Al or Cu are prone to oxidation and failure under tower-type photothermal conditions. High thermal conductivity ceramic materials such as SiC and BN require very small particle sizes as additives and are easily completely oxidized in high-temperature air environments. 2. Additives typically do not possess light absorption properties, which reduces the light absorption performance of the coating. 3. Additives create more heterogeneous interfaces, resulting in greater interfacial thermal resistance than homogeneous interfaces. Furthermore, interfacial mismatch reduces high-temperature stability and thermal shock resistance. 4. Using additives increases the complexity of coating preparation processes, making precise control of dispersion difficult. Based on these drawbacks, a more suitable approach is to use coating materials that integrate light absorption and thermal conductivity. Summary of the Invention

[0003] The purpose of this invention is to solve the problem of reduced photothermal efficiency due to surface heat radiation and heat convection loss of coatings under high-temperature operating conditions by using high thermal conductivity materials, and to provide a high-temperature solar photothermal coating with high photothermal conversion efficiency and its preparation method.

[0004] This invention uses Sr or Ca-doped LaCoO3 oxide materials with high thermal conductivity as the main component of the coating. These oxide materials have significantly higher thermal conductivity than spinel materials and possess good full-spectrum solar energy absorption performance. The coating's light-absorbing structure employs a double-layer design. The lower bulk layer uses large-particle oxide materials with high thermal conductivity, providing basic light absorption. The upper surface layer's spray slurry incorporates silicone grease, which thermally decomposes to form a network of small-particle silicon oxide particles, acting as an anti-reflective agent. Simultaneously, the decomposition of organic matter during heat treatment generates gases, naturally forming a porous structure within the coating, further enhancing its light absorption.

[0005] The technical solution of the present invention:

[0006] A high thermal conductivity, high-temperature solar thermal conversion coating comprises, from bottom to top, an alloy substrate, a coating body layer, and a surface layer; both the coating body layer and the surface layer comprise La oxide. 1-x Sr x CoO3, x = 0.1~0.3, or, La 1- x Ca x CoO3, x = 0.1~0.5.

[0007] Furthermore, the alloy substrate is stainless steel or a nickel-based alloy; the coating body layer and the surface layer also include silicon oxide formed by the thermal decomposition of silicone grease.

[0008] Furthermore, the oxide material used in the body layer of the coating has a large particle size, while the oxide material used in the surface layer has a small particle size.

[0009] Furthermore, the high-temperature solar thermal conversion coating exhibits a solar spectral absorptivity greater than 95% and an emissivity less than 0.650; at the operating temperature, the thermal conductivity of the high-temperature solar thermal conversion coating is higher than... Its photothermal efficiency is higher than that of the Pyromark2500 coating sprayed on the same substrate.

[0010] A method for preparing a high thermal conductivity, high-temperature solar thermal conversion coating involves spraying a coating body layer and a surface layer onto an alloy substrate. The preparation steps include oxide powder preparation, slurry preparation, spraying, and post-treatment.

[0011] Furthermore, the preparation methods of the oxide powders used in the coating body layer and the surface layer correspond to Method 1 and Method 2, respectively:

[0012] Method 1: According to the stoichiometric ratio of metal cations, grind and mix La2O3, Co3O4 and SrCO3 powder, or La2O3, Co3O4 and CaCO3 powder, and compress them into tablets. Place them in a muffle furnace and calcine at 1100~1200°C for 2~10 hours. Then, allow them to cool naturally and grind and crush the tablet material to obtain black, light-absorbing oxide powder.

[0013] Method 2: The steps are as follows:

[0014] (1) Prepare aqueous solution A according to the stoichiometric ratio of metal cations: including La(NO3)3, Co(NO3)2 and Sr(NO3)2, or La(NO3)3, Co(NO3)2 and Ca(NO3)2, wherein the concentration of Co ions is 20~100 mM;

[0015] (2) Prepare an oxalic acid aqueous solution B with the same volume as aqueous solution A, the concentration of oxalic acid being 3 times the concentration of Co ions in step (1), add sodium hydroxide solution, and adjust the pH to 4.0~4.5;

[0016] (3) Slowly add the solution obtained in step (2) to the aqueous solution A under stirring to form oxalate precipitate; continue stirring until the precipitation is complete, then centrifuge the precipitate and wash it several times to remove residual sodium ions;

[0017] (4) After drying and grinding the oxalate precipitate evenly, place it in a muffle furnace and calcine it at 850~900 °C for 2~10 hours to completely decompose it. Then, let it cool naturally to obtain a black oxide powder that can absorb light.

[0018] In both of the above methods, when using SrCO3 or Sr(NO3)2, the amount added should be in the molar ratio La:Sr:Co = 1-x:x:1, where x = 0.1~0.3; when using CaCO3 or Ca(NO3)2, the amount added should be in the molar ratio La:Ca:Co = 1-x:x:1, where x = 0.1~0.5.

[0019] Furthermore, the slurry comprises two types, prepared by methods as follows:

[0020] Slurry 1: Add 1-3% by mass of polyvinyl butyral (PVB) and 2-10% by mass of oxide powder for preparing the coating body layer to isobutanol solvent, and ball mill for more than 3 hours to mix evenly.

[0021] Slurry 2: Add 2-5% by volume of silicone grease (RSN-0805 or a similar imitation) and 2-10% by mass of oxide powder for preparing the surface layer to xylene solvent, and ball mill for more than 3 hours to mix evenly.

[0022] Furthermore, the spraying process is carried out using a spray gun with an air pressure of 40-50 psi. First, the metal substrate is fixed on a hot table at 100-150°C, and slurry 1 is sprayed on. Immediately after the surface is sprayed, slurry 2 is sprayed on. The volume ratio of the two slurries is 2-3:1.

[0023] Furthermore, the post-processing steps are as follows: after spraying, the coating is first dried and aged in room temperature air for more than 24 hours, then heated in a muffle furnace at a rate of 5~10°C / min to 120°C for 2 hours, 250°C for 2 hours, 540°C for 1 hour, and finally heated to the target working temperature of 550~850°C for 2~10 hours, and then cooled naturally.

[0024] The coating obtained by the above method is applied to high-temperature solar thermal conversion. The coating surface absorbs sunlight at the operating temperature and converts it into heat energy, which is then transferred to the metal substrate surface for output.

[0025] The beneficial effects of the present invention are as follows: The coating prepared by the present invention has high thermal conductivity, high light absorption and low emissivity, which can efficiently capture sunlight and convert it into heat energy and conduct it out efficiently. The photothermal conversion efficiency is significantly higher than that of the commercial product Pyromark2500. Moreover, the preparation method is simple, low cost and can be scaled up. Attached Figure Description

[0026] Figure 1 It is large-particle La 0.8 Sr 0.2 CoO3 and La 0.6 Ca 0.4 Comparison of thermal conductivity of CoO3 powder tablets and several typical spinel materials;

[0027] Figure 2 This is a schematic diagram of a double-layer coating spraying preparation method, and a double-layer La 0.8 Sr 0.2 Photo of CoO3 coating;

[0028] Figure 3 It is a double-layer La 0.8 Sr 0.2 CoO3 (LSCO) and La 0.6 Ca 0.4 The absorption spectrum of the CoO3 (LCCO) coating is compared with that of the Pyromark2500 (Py2500) coating prepared by spraying on the same substrate and the Pyromark2500 (Py2500 (Torres, 2024) coating reported in the literature, as well as the AM1.5G solar spectral energy distribution.

[0029] Table 1 compares the photothermal efficiency and surface temperature of the coatings prepared in Examples 1 and 2 (denoted as LSCO and LCCO, respectively, where #1 and #2 are samples prepared twice with the same coating) under laboratory conditions with that of the Pyromark2500 coating (where #1 and #2 are also samples prepared twice with the same coating).

[0030] Figure 4 The absorption spectra of the coating prepared in Example 1 before and after heat treatment in air atmosphere at 850 and 1000 °C for 200 hours are shown.

[0031] Figure 5 The large-particle La prepared in Example 1 0.8 Sr 0.2 Thermogravimetric (TG) and differential thermal analysis (DTA) curves of CoO3 powder in air atmosphere, from room temperature to 900°C;

[0032] Figure 6 Two particle sizes of La prepared in Comparative Example 1 0.8 Sr 0.2 Comparison of thermal conductivity of CoO3 powder tablets;

[0033] Figure 7 Comparative Example 1: La containing two particle sizes 0.8 Sr 0.2 Absorption spectrum of CoO3 coating and double-layer La 0.8 Sr 0.2 A comparison of CoO3 coatings and the solar spectral energy distribution of AM1.5G. Detailed Implementation

[0034] The following describes the implementation methods and effects of the present invention in detail with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited to the contents described in the following embodiments.

[0035] Example 1

[0036] Preparation of large-particle La 0.8 Sr 0.2 CoO3 (chemical abbreviation LSCO) powder was prepared as follows: La₂O₃, Co₃O₄, and SrCO₃ powders were weighed according to the stoichiometric ratio of metal cations La:Sr:Co = 0.8:0.2:1. The powders were ground and mixed evenly, then compressed into tablets. The tablets were placed in a muffle furnace and calcined at 1100 °C for 2 hours, then allowed to cool naturally. The compressed material was then ground and crushed to obtain black La₂O₃ powder. 0.8 Sr 0.2 CoO3 powder; the powder particle size is approximately 1~2 μm.

[0037] like Figure 1 As shown, the prepared large-particle La0.8 Sr 0.2 The thermal conductivity of CoO3 powder tablets measured at temperatures of 300–800 °C and above is greater than [value missing]. It is significantly higher than spinel materials such as CuCr2O4, CuFeMnO4, and CuCrMnO4.

[0038] Preparation of small-particle La 0.8 Sr 0.2 CoO3 (chemical formula abbreviation LSCO) powder, the method is as follows: (1) Prepare aqueous solution A according to the stoichiometric ratio of metal cations La:Sr:Co = 0.8:0.2:1: including La(NO3)3, Co(NO3)2 and Sr(NO3)2, wherein the concentration of Co ions is 50 mM; (2) Prepare an oxalic acid aqueous solution B with the same volume as solution A, the concentration of which is 150 mM, add sodium hydroxide solution, and adjust the pH to around 4.2; (3) Slowly add the solution obtained in step (2) to solution A under stirring to form oxalate precipitate; continue stirring until the precipitation is complete, then centrifuge the precipitate and wash it several times to remove residual sodium ions; (4) After drying and grinding the oxalate precipitate evenly, put it into a muffle furnace and calcine it at 850 °C for 2 hours to completely decompose it, and then cool it naturally to obtain black La. 0.8 Sr 0.2 CoO3 powder; the powder particle size is approximately 100~500 nm.

[0039] Two types of spray coating slurries were prepared. Slurry 1: 0.16 g of polyvinyl butyral (PVB) and 0.5 g of large-particle La were added to 10 mL of isobutanol solvent. 0.8 Sr 0.2 CoO3 powder was ball-milled for 3 hours until homogeneous; Slurry 2: 0.15 mL of silicone grease (RSN-0805) and 0.25 g of small-particle La were added to 5 mL of xylene solvent. 0.8 Sr 0.2 CoO3 powder was ball-milled for 3 hours to mix evenly.

[0040] A coating was prepared by spraying onto a 316 stainless steel disc substrate with a diameter of 30 mm, as follows: Figure 2As shown: The metal substrate is fixed on a hot table at 120 °C. Using a spray gun with an air pressure of approximately 40-50 psi, 10 mL of slurry 1 is first sprayed onto the surface. Immediately after spraying, 5 mL of slurry 2 is sprayed onto the surface. After spraying, the substrate is first dried and aged in room temperature air for at least 24 hours. Then, in a muffle furnace, the temperature is sequentially increased at a rate of 10 °C / min to 120 °C for 2 hours, 250 °C for 2 hours, 540 °C for 1 hour, and finally increased to 600 °C for 2 hours. After that, the substrate is allowed to cool naturally to obtain the final photothermal coating.

[0041] like Figure 3 As shown, the coating obtained in this embodiment ( Figure 3 LSCO (in this context) exhibits high absorptivity across the solar spectrum, with a solar spectral absorptivity of 95.88%, which is higher than that of Pyromark 2500 (prepared by spraying on the same substrate). Figure 3 The Py2500 in the literature (95.53%) and the Pyromark2500 reported in the literature ( Figure 3 The absorbance of Py2500 (Torres, 2024) was 95.67%. The emissivity of the coating was measured to be 0.639, which was significantly lower than that of Pyromark2500 (0.752) prepared by spraying on the same substrate.

[0042] Table 1

[0043]

[0044] As shown in Table 1, the coating obtained in this embodiment is in Incident light intensity With the convective heat transfer coefficient set at a constant coating output temperature of 21 °C and an ambient temperature of 300 K, the surface temperature was measured to be 294.3–314.0 °C, and the photothermal efficiency was 89.61–90.07%. The surface temperature was significantly lower than that of Pyromark2500 prepared by spraying on the same substrate (358.3–382.0 °C), while the efficiency was significantly higher than that of Pyromark2500 prepared by spraying on the same substrate (86.23–87.35%).

[0045] like Figure 4 As shown, the solar spectral absorptivity of the newly prepared coating is 95.88%; after heat treatment in air at 850 °C for 200 hours, the absorptivity is 95.63%, which is only slightly lower than that of the newly prepared coating; after heat treatment in air at 1000 °C for 200 hours, the absorptivity is 94.12%, which still maintains a high value, indicating the high-temperature stability and durability of the coating.

[0046] like Figure 5The image shows large-particle La used in the preparation of the coating body layer. 0.8 Sr 0.2 Thermogravimetric (TG) and differential thermal analysis (DTA) curves of CoO3 powder in air atmosphere. During the heating process from room temperature to 900 °C, the mass change of the powder was within 0.5%, and there was no significant DTA peak, indicating the high-temperature stability of the material. Further heating showed a small mass decrease and a small DTA endothermic peak, but during the cooling process, a reversible mass recovery occurred, indicating the thermal cycling stability of the material.

[0047] Example 2

[0048] Preparation of large-particle La 0.6 Ca 0.4 CoO3 (chemical abbreviation: LCCO) powder was prepared as follows: La₂O₃, Co₃O₄, and CaCO₃ powders were weighed according to the stoichiometric ratio of metal cations La:Sr:Co = 0.6:0.4:1. The powders were ground and mixed evenly, then compressed into tablets. The tablets were placed in a muffle furnace and calcined at 1100 °C for 2 hours, then allowed to cool naturally. The compressed material was then ground and crushed to obtain black La₂O₃ powder. 0.6 Ca 0.4 CoO3 powder; the powder particle size is approximately 1.5 μm.

[0049] like Figure 1 As shown, the prepared large-particle La 0.6 Ca 0.4 The thermal conductivity of CoO3 powder tablets measured was greater than [value missing] in the temperature range of room temperature to 800 °C. It is significantly higher than spinel materials such as CuCr2O4, CuFeMnO4, and CuCrMnO4.

[0050] Preparation of small-particle La 0.6 Ca 0.4 CoO3 (chemical formula abbreviation is LCCO) powder, the method is as follows: (1) According to the stoichiometric ratio of metal cations La:Sr:Co = 0.6:0.4:1, prepare aqueous solution A: including La(NO3)3, Co(NO3)2 and Ca(NO3)2, wherein the concentration of Co ions is 50 mM; (2) Prepare an oxalic acid aqueous solution B with the same volume as solution A, the concentration is 150 mM, add sodium hydroxide solution, and adjust the pH to around 4.2; (3) Slowly add the solution obtained in step (2) to solution A under stirring to form oxalate precipitate; continue stirring until the precipitation is complete, centrifuge the precipitate and wash it several times to remove residual sodium ions; (4) After drying and grinding the oxalate precipitate evenly, put it into a muffle furnace and calcine it at 850 °C for 2 hours to make it completely thermally decomposed, and then cool it naturally to obtain black La. 0.6 Ca0.4 CoO3 powder; the powder particle size is approximately 200 nm.

[0051] Two types of spray coating slurries were prepared. Slurry 1: 0.16 g of polyvinyl butyral (PVB) and 0.5 g of large-particle La were added to 10 mL of isobutanol solvent. 0.6 Ca 0.4 CoO3 powder was ball-milled for 3 hours until homogeneous; Slurry 2: 0.15 mL of silicone grease (RSN-0805) and 0.25 g of small-particle La were added to 5 mL of xylene solvent. 0.6 Ca 0.4 CoO3 powder was ball-milled for 3 hours to mix evenly.

[0052] A coating was prepared by spraying onto a 316 stainless steel disc substrate with a diameter of 30 mm, as follows: Figure 2 As shown: The metal substrate is fixed on a hot table at 120 °C. Using a spray gun with an air pressure of approximately 40-50 psi, 10 mL of slurry 1 is first sprayed onto the surface. Immediately after spraying, 5 mL of slurry 2 is sprayed onto the surface. After spraying, the substrate is first dried and aged in room temperature air for at least 24 hours. Then, in a muffle furnace, the temperature is sequentially increased at a rate of 10 °C / min to 120 °C for 2 hours, 250 °C for 2 hours, 540 °C for 1 hour, and finally increased to 600 °C for 2 hours. After that, the substrate is allowed to cool naturally to obtain the final photothermal coating.

[0053] like Figure 3 As shown, the coating obtained in this embodiment ( Figure 3 The LCCO in the image exhibits high absorptivity across the solar spectrum, with a solar spectral absorptivity of 95.07%, which is close to that of Pyromark 2500 prepared by spraying on the same substrate. Figure 3 The emissivity of the coating was 0.648, significantly lower than that of Pyromark2500 (0.752) prepared by spraying on the same substrate.

[0054] As shown in Table 1, the coating obtained in this embodiment is in Incident light intensity With the convective heat transfer coefficient, a fixed coating output temperature of 21 °C, and an ambient temperature of 300 K, the surface temperature was measured to be 311.3–315.7 °C, and the photothermal efficiency was 88.77–88.81%. The surface temperature was significantly lower than that of Pyromark2500 (358.3–382.0 °C), while the efficiency was significantly higher than that of Pyromark2500 (86.23–87.35%).

[0055] Comparative Example 1

[0056] Preparation of large and small La particles 0.8 Sr 0.2 CoO3 powder, the specific method is the same as in Example 1.

[0057] like Figure 6 As shown, the prepared large-particle La 0.8 Sr 0.2 The thermal conductivity of CoO3 powder tablets measured at temperatures of 300–800 °C and above is greater than [value missing]. ,; while small La particles 0.8 Sr 0.2 The thermal conductivity of CoO3 powder tablets measured was within the range of the entire test temperature. The concentration of La2+ is approximately 100 μL, significantly lower than that of large particle samples. This demonstrates that the concentration of La2+ in large particles is significantly lower than that in large particle samples. 0.8 Sr 0.2 CoO3 powder has a significant advantage in thermal conductivity compared to small particles.

[0058] Two types of spray coating slurries were prepared and applied to a 316 stainless steel disc substrate with a diameter of 30 mm to create a coating. The specific method is described in Example 1. The difference lies in the use of slurry 1 (large particle La). 0.8 Sr 0.2 CoO3 powder + PVB) and slurry 2 (small particle La) 0.8 Sr 0.2 Single-layer coating samples were prepared using CoO3 powder and silicone grease.

[0059] like Figure 7 As shown, large La particles 0.8 Sr 0.2 The solar spectral absorbance of the single-layer coating prepared by the CoO3 powder + PVB method is 93.56%, which is lower than that of small-particle La. 0.8 Sr 0.2 The single-layer coating prepared by the CoO3 powder + silicone grease method has an absorption rate of 95.24%, which is lower than the 95.88% absorption rate of the double-layer coating. This demonstrates that the surface layer of small particles has a certain light absorption advantage compared to the bulk layer of large particles, and the double-layer coating has a higher light absorption rate than the single-layer coating.

Claims

1. A high-temperature solar thermal conversion coating with high thermal conductivity, characterized in that: It includes, from bottom to top, an alloy substrate, a coating body layer, and a surface layer; both the coating body layer and the surface layer include La oxide. 1-x Sr x CoO3, x = 0.1~0.3, or, La 1-x Ca x CoO3, x = 0.1~0.

5.

2. The coating according to claim 1, characterized in that: The alloy substrate is stainless steel or a nickel-based alloy; the coating body layer and the surface layer also include silicon oxide formed by the thermal decomposition of silicone grease.

3. The coating according to claim 1, characterized in that: The oxide material used in the body layer of the coating has a large particle size, while the oxide material used in the surface layer has a small particle size.

4. The coating according to claim 1, characterized in that: The high-temperature solar thermal conversion coating exhibits a solar spectral absorptivity greater than 95% and an emissivity less than 0.650; at the operating temperature, the thermal conductivity of the high-temperature solar thermal conversion coating is higher than... Its photothermal efficiency is higher than that of the Pyromark2500 coating sprayed on the same substrate.

5. A method for preparing a high thermal conductivity high-temperature solar thermal conversion coating according to any one of claims 1-4, characterized in that: The coating body layer and surface layer are applied to the alloy substrate using a spraying method; the preparation steps include oxide powder preparation, slurry preparation, spraying, and post-treatment.

6. The preparation method according to claim 5, characterized in that: The preparation methods of the oxide powder used in the coating body layer and the surface layer correspond to the following methods 1 and 2, respectively: Method 1: According to the stoichiometric ratio of metal cations, grind and mix La2O3, Co3O4 and SrCO3 powder, or La2O3, Co3O4 and CaCO3 powder, and compress them into tablets. Place them in a muffle furnace and calcine at 1100~1200°C for 2~10 hours. Then, allow them to cool naturally and grind and crush the tablet material to obtain black, light-absorbing oxide powder. Method 2: The steps are as follows: (1) Prepare aqueous solution A according to the stoichiometric ratio of metal cations: including La(NO3)3, Co(NO3)2 and Sr(NO3)2, or La(NO3)3, Co(NO3)2 and Ca(NO3)2, wherein the concentration of Co ions is 20~100 mM; (2) Prepare an oxalic acid aqueous solution B with the same volume as aqueous solution A, the concentration of oxalic acid being 3 times the concentration of Co ions in step (1), add sodium hydroxide solution, and adjust the pH to 4.0~4.5; (3) The solution obtained in step (2) is slowly added to the aqueous solution A under stirring to form oxalate precipitate; Continue stirring until precipitation is complete, then centrifuge the precipitate and wash it several times to remove residual sodium ions. (4) After drying and grinding the oxalate precipitate evenly, put it into a muffle furnace and calcine it at 850~900°C for 2~10 hours to completely decompose it. Then let it cool naturally to obtain a black oxide powder that can absorb light. In both of the above methods, when using SrCO3 or Sr(NO3)2, the amount added should be in the molar ratio La:Sr:Co = 1-x:x:1, where x = 0.1~0.3; when using CaCO3 or Ca(NO3)2, the amount added should be in the molar ratio La:Ca:Co = 1-x:x:1, where x = 0.1~0.

5.

7. The preparation method according to claim 5, characterized in that: The slurry comprises two types, and the preparation methods are as follows: Slurry 1: Add 1-3% by mass of polyvinyl butyral and 2-10% by mass of oxide powder for preparing the coating body layer to isobutanol solvent, and ball mill for more than 3 hours to mix evenly; Slurry 2: Add 2-5% by volume of silicone grease and 2-10% by mass of oxide powder for preparing the surface layer to xylene solvent, and ball mill for more than 3 hours to mix evenly.

8. The preparation method according to claim 5, characterized in that: The spraying process uses a spray gun with an air pressure of 40-50 psi. First, the metal substrate is fixed on a hot table at 100-150°C, and slurry 1 is sprayed. Immediately after the surface is sprayed, slurry 2 is sprayed. The volume ratio of the two slurries is 2-3:

1.

9. The preparation method according to claim 5, characterized in that: The post-treatment process steps are as follows: After spraying, the coating is first dried and aged in room temperature air for more than 24 hours. Then, in a muffle furnace, the temperature is raised sequentially at a rate of 5~10°C / min to 120°C and held for 2 hours, 250°C and held for 2 hours, 540°C and held for 1 hour, and finally raised to the target working temperature of 550~850°C and held for 2~10 hours, and then cooled naturally.

10. The application of a high thermal conductivity high-temperature solar thermal conversion coating according to any one of claims 1-4, or a coating obtained by the preparation method according to any one of claims 5-9, characterized in that, It is used in high-temperature solar thermal conversion. The coating surface absorbs sunlight at the operating temperature and converts it into heat energy, which is then transferred to the metal substrate surface for output.

Images