Aerogel heat-absorbing body coating applied to solar heat collector

Abstract

The invention discloses an aerogel heat absorbing body coating applied to a solar heat collector. The heat absorbing body coating is of a multi-layer composite structure and sequentially comprises a core heat absorbing layer and a packaging protection layer from inside to outside. The core heat absorption layer is a composite coating formed by dispersing titanium nitride nanoparticles in a silicon dioxide aerogel matrix. Sunlight absorption is enhanced through the titanium nitride nanoparticles, the thermal emissivity is reduced through the aerogel matrix, and the photothermal conversion efficiency is remarkably improved; and the aluminum oxide packaging layer effectively blocks water and oxygen erosion, so that the coating is stable in performance and excellent in aging resistance in a high-temperature and high-humidity environment, and the service life is remarkably prolonged.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solar heat utilization, and in particular relates to an aerogel heat-absorbing coating applied to a solar heat collector. BACKGROUND

[0002] The performance of the solar heat collector, which is the core component of the solar heat utilization technology, mainly depends on the light-heat conversion efficiency and durability of the heat-absorbing coating. At present, the widely used heat-absorbing coating mainly includes traditional black chrome / black nickel coating, selective absorption film and new carbon-based material coating, etc., but these materials all have certain technical limitations. Although the black chrome and black nickel coating has a mature process, its solar absorptivity can generally only reach 0.90-0.93, and the infrared emissivity is as high as 0.10-0.15 at a working temperature of 80℃, resulting in significant heat loss during medium and high temperature operation, and the system heat collection efficiency is difficult to further improve. The selective absorption film has improved optical performance, with an absorptivity of more than 0.94 and an emissivity of less than 0.08, but its moisture and heat aging resistance is poor, and problems such as oxidation and film peeling easily occur when it is exposed to a high temperature and high humidity environment for a long time, and the actual service life is usually less than 10 years, which cannot meet the requirements of long-term operation.

[0003] In recent years, some researches have tried to use new high-absorption materials such as carbon nanotubes to improve the solar light capture capability, and the absorptivity can reach more than 0.95, however, the surface roughness of this kind of material is large, which results in a sharp increase in thermal emissivity, and thus increases the radiant heat loss. In addition, the raw material cost of carbon nanotubes is high, and the process is complex, which also limits its large-scale application.

[0004] In addition to the deficiencies in optical performance and weather resistance, the stability of the existing coating materials under high temperature working conditions also faces severe challenges. With the expansion of solar photothermal systems to medium and high temperature application fields (such as industrial heat energy, composite energy systems), the traditional coating is prone to performance degradation, cracking and even peeling in an environment above 150℃, which seriously restricts the system operation efficiency and service life.

[0005] Therefore, in order to solve the above problems, the present application provides an aerogel heat-absorbing coating applied to a solar heat collector. SUMMARY

[0006] The present application aims to overcome the defects of the prior art and provides an aerogel heat-absorbing coating applied to a solar heat collector.

[0007] The purpose of the present application can be achieved by the following technical solutions: An aerogel heat-absorbing coating applied to a solar heat collector is a multi-layer composite structure, which comprises a core heat-absorbing layer and an encapsulation protective layer from inside to outside; the core heat-absorbing layer is a composite coating formed by dispersing titanium nitride nanoparticles in a silica aerogel matrix.

[0008] More preferably, the particle size of the titanium nitride nanoparticles in the core heat-absorbing layer is 10-80 nm, and the mass ratio of the titanium nitride nanoparticles in the silica aerogel matrix is 3-20%.

[0009] More preferably, the encapsulation protective layer is an alumina aerogel layer with a thickness of 50-100 nm.

[0010] A preparation method of an aerogel heat-absorbing coating applied to a solar heat collector, comprising the following steps: S1: mixing a silicon source precursor, ethanol, deionized water and a catalyst to form a uniform silica sol; slowly adding titanium nitride nanoparticles into the silica sol and continuously stirring to form a composite sol; S2: cleaning, polishing and chemically pretreating the metal heat-absorbing substrate, then coating the composite sol on the surface and standing until complete gelation to obtain a wet gel film; S3: immersing the substrate with the wet gel film into ethanol at 40-60℃ for aging for 24 h, then immersing into a hexamethyldisilazane ethanol solution for reaction, after the reaction, washing and normal pressure drying to obtain a core heat-absorbing layer; S4: using atomic layer deposition technology to deposit an alumina aerogel film on the surface of the core heat-absorbing layer with trimethylaluminum and water as precursors to obtain an encapsulation protective layer.

[0011] More preferably, the preparation raw materials of the silica sol include the following components: 10-12 parts of a silicon source precursor, 20-30 parts of ethanol, 5-10 parts of deionized water and 0.1-0.2 parts of a catalyst by weight.

[0012] More preferably, the silicon source precursor is tetramethyl orthosilicate, and the catalyst is hydrochloric acid.

[0013] More preferably, in step S3, the procedure of the normal pressure drying is: slowly drying at 40-60℃ for 12-24 h, and then gradually heating to 80-120℃ for 4-8 h.

[0014] More preferably, in step S3, the process parameters of the reaction are: a temperature of 40-60℃ and a time of 10-12 h; and the concentration of the hexamethyldisilazane ethanol solution is 15 wt%.

[0015] More preferably, the temperature of the atomic layer deposition is 80-150℃.

[0016] The beneficial effects of the present application are: Firstly, the application utilizes the localized surface plasmon resonance effect of specific nanoparticles to significantly enhance the absorption capacity of the coating to the visible light-near infrared band in the solar spectrum; meanwhile, with the aid of the unique low refractive index characteristics of the aerogel material, the heat radiation performance of the coating in the infrared band is effectively inhibited, thereby realizing the ideal matching of the solar light absorption rate and the infrared emission rate in principle, and greatly reducing the radiant heat loss during the operation of the collector.

[0017] Secondly, the application constructs a dense inorganic encapsulation layer on the surface of the high-porosity aerogel heat-absorbing layer, and the coating can effectively block the invasion of corrosive media such as external water vapor and oxygen, thereby fundamentally preventing the degradation reactions such as oxidation and hydrolysis of the heat-absorbing functional material. This structural design enables the coating to remain stable in performance under harsh environments such as high temperature and high humidity, thereby significantly prolonging the service life.

[0018] Thirdly, the three-dimensional nanometer network structure of the aerogel in the application not only provides excellent thermal stability, enabling it to withstand higher operating temperatures, but also improves the bonding strength of the coating and the substrate, thereby avoiding problems such as cracking and peeling at high temperatures, and ensuring the long-term reliability of the coating. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the application will be clearly and completely described below in combination with the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the application.

[0020] Embodiment one: a preparation method of an aerogel heat-absorbing coating applied to a solar collector, comprising the following steps: S1: mixing 10 parts of methyl orthosilicate, 20 parts of ethanol, 5 parts of deionized water and 0.1 parts of hydrochloric acid to form a uniform silica sol by stirring; slowly adding titanium nitride nanoparticles into the above silica sol and continuously stirring to form a composite sol (the mass ratio of titanium nitride nanoparticles in the silica aerogel matrix is 3%); S2: cleaning, polishing and chemically pretreating the metal heat-absorbing body substrate, then coating the composite sol on the surface and standing until complete gelation to obtain a wet gel film; S3: immersing the substrate with the wet gel film into ethanol at 40°C for aging for 24 hours, then immersing it into a hexamethyldisilazane ethanol solution at 40°C for reaction for 10 hours, after the reaction, washing, slowly drying at 40°C for 12 hours, and then gradually increasing the temperature to 80°C for drying for 4 hours to obtain a core heat-absorbing layer; S4: Using atomic layer deposition technology, taking trimethylaluminum and water as precursors, depositing an aluminum oxide aerogel film on the surface of the core heat-absorbing layer at 80°C to obtain a packaging protective layer (thickness of 50 nm).

[0021] Example Two: A preparation method of an aerogel heat-absorbing coating applied to a solar heat collector, comprising the following steps: S1: Mix 12 parts of methyl orthosilicate, 30 parts of ethanol, 10 parts of deionized water, and 0.2 parts of hydrochloric acid to form a uniform silica sol; slowly add titanium nitride nanoparticles to the above silica sol and continuously stir to form a composite sol (the mass percentage of titanium nitride nanoparticles in the silica aerogel matrix is 20%); S2: Clean, polish, and chemically pretreat the metal heat-absorbing substrate, then coat the composite sol on the surface and let it stand until complete gelation to obtain a wet gel film; S3: Soak the substrate with the wet gel film in ethanol at 60°C for 24 hours, then soak it in a hexamethyldisilazane ethanol solution at 60°C for 12 hours. After the reaction is complete, wash and slowly dry at 60°C for 24 hours, then gradually increase the temperature to 120°C and dry for 8 hours to obtain a core heat-absorbing layer; S4: Using atomic layer deposition technology, taking trimethylaluminum and water as precursors, depositing an aluminum oxide aerogel film on the surface of the core heat-absorbing layer at 150°C to obtain a packaging protective layer (thickness of 100 nm).

[0022] Example Three: A preparation method of an aerogel heat-absorbing coating applied to a solar heat collector, comprising the following steps: S1: Mix 11 parts of methyl orthosilicate, 25 parts of ethanol, 7.5 parts of deionized water, and 0.15 parts of hydrochloric acid to form a uniform silica sol; slowly add titanium nitride nanoparticles to the above silica sol and continuously stir to form a composite sol (the mass percentage of titanium nitride nanoparticles in the silica aerogel matrix is 11.5%); S2: Clean, polish, and chemically pretreat the metal heat-absorbing substrate, then coat the composite sol on the surface and let it stand until complete gelation to obtain a wet gel film; S3: Soak the substrate with the wet gel film in ethanol at 50°C for 24 hours, then soak it in a hexamethyldisilazane ethanol solution at 50°C for 11 hours. After the reaction is complete, wash and slowly dry at 50°C for 18 hours, then gradually increase the temperature to 100°C and dry for 6 hours to obtain a core heat-absorbing layer; S4: Using atomic layer deposition technology, taking trimethylaluminum and water as precursors, depositing an aluminum oxide aerogel film on the surface of the core heat-absorbing layer at 115°C to obtain a packaging protective layer (thickness of 75 nm).

[0023] Comparative Example 1: no titanium nitride nanoparticles introduced into the core heat-absorbing layer.

[0024] Comparative Example 2: no encapsulation protective layer provided.

[0025] Test experiments: (1) The solar absorptance of the coating obtained in the examples and comparative examples was tested according to the standard ASTM E903; (2) The infrared emissivity of the coating obtained in the examples and comparative examples was tested according to the standard ASTM E408; (3) The coating obtained in the examples and comparative examples was placed in a muffle furnace, and was continuously heated at 200°C in an air atmosphere for 100h. The solar absorptance and infrared emissivity were measured before and after heating, and the performance decay rate was calculated; The data obtained are shown in the following table: Conclusion: The aerogel heat-absorbing coating provided by the present application exhibits excellent performance in terms of solar absorptance, infrared emissivity and high-temperature stability. The solar absorptance of Examples 1 to 3 is all higher than 0.96, and the infrared emissivity is all lower than 0.065, which is significantly better than Comparative Example 1 (without titanium nitride) and Comparative Example 2 (without encapsulation protective layer). After heating at 200°C for 100h, the performance decay rate of the examples is all lower than 2.5%, while the decay rates of Comparative Examples 1 and 2 are as high as 8.2%, 12.1% (absorptance) and 15.1%, 20.7% (emissivity), respectively, indicating that the present application effectively improves the photo-thermal performance and high-temperature aging resistance of the coating by introducing titanium nitride nanoparticles and an aluminum oxide encapsulation layer, and has good application prospects.

[0026] In the description of the specification, the description of the reference terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0027] The above is only an example and description of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace, as long as it does not deviate from the scope of the present application or exceed the scope defined by the present claims, which shall be within the protection scope of the present application.

Claims

1. An aerogel heat absorber coating applied to a solar collector, characterized by, The heat-absorbing coating is a multilayer composite structure, sequentially comprising a core heat-absorbing layer and an encapsulation protective layer from inside to outside; the core heat-absorbing layer is a composite coating formed by dispersing titanium nitride nanoparticles in a silica aerogel matrix.

2. An aerogel heat absorber coating for application to a solar collector according to claim 1, wherein, In the core heat-absorbing layer, the particle size of the titanium nitride nanoparticles is 10-80 nm, and the mass fraction of the titanium nitride nanoparticles in the silica aerogel matrix is 3-20%.

3. An aerogel heat absorber coating for application to a solar collector according to claim 1, wherein, The encapsulation protective layer is an alumina aerogel layer, and the thickness is 50-100 nm.

4. A method of making an aerogel heat absorber coating for a solar collector according to any one of claims 1-3, characterized in that, The method comprises the following steps: S1: mixing a silicon source precursor, ethanol, deionized water and a catalyst, stirring to form a uniform silica sol; slowly adding titanium nitride nanoparticles into the silica sol, continuously stirring to form a composite sol; S2: cleaning, polishing and chemically pretreating the metal heat-absorbing substrate, then coating the composite sol on the surface, and standing until complete gelation to obtain a wet gel film; S3: immersing the substrate with the wet gel film into ethanol at 40-60℃ for aging for 24 h, then immersing into a hexamethyldisilazane ethanol solution, reacting, washing after the reaction, and normal pressure drying to obtain the core heat-absorbing layer; S4: using atomic layer deposition technology, taking trimethylaluminum and water as precursors to deposit an alumina aerogel film on the surface of the core heat-absorbing layer to obtain the encapsulation protective layer.

5. The method of claim 4, wherein the aerogel heat absorber coating applied to a solar collector is prepared by the steps of: The preparation raw materials of the silica sol comprise the following components: 10-12 parts of a silicon source precursor, 20-30 parts of ethanol, 5-10 parts of deionized water and 0.1-0.2 parts of a catalyst by weight.

6. The method of claim 4, wherein the aerogel heat absorber coating applied to a solar collector is prepared by the steps of: The silicon source precursor is methyl orthosilicate, and the catalyst is hydrochloric acid.

7. The method of claim 4, wherein the aerogel heat absorber coating is applied to a solar collector. In step S3, the procedure of the normal pressure drying is: slowly drying at 40-60℃ for 12-24 h, and then gradually heating to 80-120℃ for drying for 4-8 h.

8. The method of claim 4, wherein the aerogel heat absorber coating applied to a solar collector is prepared by the steps of: In step S3, the process parameters of the reaction are: the temperature is 40-60℃, and the time is 10-12 h; the concentration of the hexamethyldisilazane ethanol solution is 15wt%.

9. The method of claim 4, wherein the aerogel heat absorber coating applied to a solar collector is prepared by the steps of: The temperature of the atomic layer deposition is 80-150℃.

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