CN109883073B - Quasi-optical microcavity structure solar spectrum selective absorption coating and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of material preparation, and provides a high temperature stable quasi-optical microcavity structure solar spectrum selective absorption coating and a preparation method thereof. The coating is composed of three parts from bottom to top: a metal infrared reflection layer, a quasi-optical microcavity absorber, and an optical antireflection layer. The coating material contains metal W, dielectrics Al ₂ O ₃ and SiO ₂ , and a substrate. It is a mechanically polished stainless steel 304, which is easy to prepare. Compared with the known coatings, it has the following advantages: (1) high solar absorption rate; (2) good high temperature stability; (3) easy adjustment of the spectral absorption range and easy industrial application.

Description

Quasi-optical microcavity structure solar spectrum selective absorption coating and preparation method thereof

technical field

The invention belongs to the technical field of material preparation, and provides a high temperature stable quasi-optical microcavity structure solar spectrum selective absorption coating and a preparation method thereof.

Background technique

For a long time, energy issues have been particularly important. As one of the alternative energy sources for traditional energy, solar energy has the advantages of cleanliness, no pollution, and large reserves. The most common solar energy utilization technologies can be roughly divided into two categories: photothermal and photovoltaics. Among them, photothermal technology has many advantages such as high energy utilization rate, low cost, and simple equipment. Solar thermal conversion technology absorbs and utilizes solar energy in the form of thermal energy and is widely used in solar water heaters, solar cooling systems and concentrated solar power generation systems (CSP). Photothermal technology of solar energy is not only another utilization method of solar energy technology, but also makes up for the inherent defects of photovoltaic power generation. It is suitable for the existing energy construction system and is an effective new energy application strategy. In the light-to-heat conversion system, one of the core parts is the solar selective absorption coating, which has a high absorption rate (α) of sunlight while maintaining the lowest thermal emissivity (ε) The light is absorbed and converted into heat energy for heating the liquid to form a high-temperature steam to drive the motor to generate electricity. The quality of its performance directly determines the excellent performance of the light-to-heat conversion system.

Solar selective absorption coating Solar selective absorption coating can be divided into the following six categories: 1) intrinsic absorption type coating; 2) multilayer film type absorption coating; 3) metal-semiconductor tandem type absorption coating; 4) Surface texture absorption coating; 5) Selective transmission and blackbody-like absorption coating; 6) Cermet type absorption coating. In recent years, due to the excellent properties of multilayer membrane-type selective absorption coatings and cermet-type selective absorption coatings, they have been more widely studied.

The main task of photothermal utilization of solar energy is to improve its photothermal conversion efficiency and thermal stability, and these two performance indicators are directly determined by the solar light absorption rate α, thermal emissivity ε and stability of the solar selective absorption coating. . Therefore, the research on solar thermal utilization technology mainly focuses on how to improve the solar absorption rate α, how to reduce the thermal emissivity ε and how to improve its high temperature stability.

At present, the main applications of solar thermal conversion technology include: solar water heaters, dryers, greenhouses and solar houses, solar cookers, heating and cooling, seawater desalination devices, solar thermal power generation devices and high-temperature solar furnaces. Among them, solar water heaters are the most widely used and rapidly industrialized fields of solar thermal utilization.

Solar photothermal conversion technology is mainly used in the field of medium and low temperature (<400 °C). Compared with the relatively mature low temperature absorption coating technology, the development of medium and high temperature selective absorption coatings faces greater challenges. After recycling, the optical performance becomes poor, and the light-to-heat conversion efficiency becomes low. To solve these problems, more in-depth and systematic research and analysis of materials, structures and fabrication processes are required.

For example, the reported patents CN102954611A, CN102653151A, CN102286720A, CN106167892A, CN103572233A, etc. have all studied the selective absorption coating of double-layer cermet structure. The disadvantage is that with the increase of temperature, the diffusion of metal atoms in the coating will affect the coating The optical properties of the layer are affected, resulting in a decrease in absorptivity and an increase in emissivity. That is, there are problems such as high temperature stability.

Therefore, how to improve the absorptivity of the absorbing coating, reduce the emissivity of the coating, and make the coating have good high temperature resistance and weather resistance is the consideration for the preparation of the selective absorbing coating.

The main problems of the existing technology include:

(1) The research is single, mainly focusing on multi-layer film type and cermet type absorbing coatings;

(2) Thermal stability needs to be improved;

(3) It is difficult to adjust the spectral selectivity.

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, the present invention provides a high temperature stable quasi-optical microcavity structure solar spectrum selective absorption coating and a preparation method thereof.

The invention provides a high temperature stable quasi-optical microcavity structure solar spectrum selective absorption coating, which can work stably in a high temperature environment. 5%, the photothermal conversion efficiency can reach ~95%, and the absorption spectrum is easy to control.

Specifically, the present invention is achieved through the following technical solutions:

A high-temperature stable quasi-optical microcavity structure solar spectrum selective absorption coating, comprising three parts: from bottom to top, a metal infrared reflection layer, a quasi-optical microcavity absorber, and an optical antireflection layer,

Among them, the quasi-optical microcavity absorber is composed of a cermet 1-metal-cermet 2 structure,

The metal is metal W, the cermet is W-SiO ₂ cermet, and the dielectrics of the optical antireflection layer are Al ₂ O ₃ and SiO ₂ .

Among them, metal W has a high melting point and a high reflectivity in the infrared region, and is suitable as a bottom infrared antireflection layer. Through a large number of experimental studies, it is found that the invention adopts the cermet-metal-cermet structure combined with the absorption of the cermet and the interaction between the film layers, which can absorb light in a wide range and has high solar light absorption. At the same time, the dielectric Al ₂ O ₃ and SiO ₂ layers are well matched with the optical constants of air, and the design of the antireflection layer on the top layer can reduce the reflection of light. Such material layer selection can further optimize solar light absorption.

As a preferred technical solution of the present invention, the present invention uses the optical constant of the single-layer film to perform fitting and optimization design through a large number of experiments, and obtains the thickness of the film layer structure: W infrared reflection layer is about 50-150nm, W-SiO ₂ metal The ceramic 1 is about 30-60nm, the intermediate metal W layer is about 3-15nm, the W- _SiO2 cermet ₂ is about 45-65nm, the _Al2O3 optical anti-reflection layer 1 is about 10-30nm, and the _SiO2 optical anti-reflection layer is about 10-30nm. The thickness of the reverse layer 2 is about 45-70 nm.

The selection of the thicknesses of the aforementioned material layers is optimized through a large number of experiments, and the absorption rates of other combinations without the aforementioned corresponding thicknesses cannot be improved.

As a preferred technical solution of the present invention, the volume ratio (W:SiO ₂ ) of the cermet components is 1:5 to 2:3.

The basis for the selection of the volume ratio of the aforementioned material components is mainly determined according to the optical constant of the single-layer film. The formed coating has good optical properties, and requires good optical constant matching between the film layers. Also, if the volume ratio of the components is not selected properly, the absorption will also be poor.

The present invention further provides a preparation method for preparing the aforesaid high temperature stable quasi-optical microcavity structure solar spectrum selective absorption coating, comprising:

Using mechanically polished stainless steel 304 as the substrate, the absorption coating is deposited from the bottom up by a high vacuum multi-target magnetron sputtering system, wherein the metal W is deposited by DC sputtering, and the power density is 2.00-2.50 (W cm ^-2 ), Al ₂ O ₃ and SiO ₂ were deposited by radio frequency sputtering with a power density of 3.00-4.00 (W cm ^-2 ), W-SiO ₂ cermets were deposited by direct current and radio frequency co-sputtering in sequence, The sputtering power densities are 0.50-1.00 (W cm ^-2 ) and 3.50-4.50 (W cm ^-2 ), respectively.

The selection of the process parameters of the aforementioned preparation method is mainly determined according to the deposition power used in the deposition of the monolayer film and the deposition rate of the corresponding material, combined with the optical constant of the monolayer film. Depending on the process parameters, the corresponding film structure and composition ratio will change accordingly. The rough steps of this work are to first deposit a single-layer film by selecting different process parameters (deposition power), and then determine the optimal process parameters by optical constants for film deposition.

As a preferred technical solution of the present invention, in the preparation method, the volume ratio (W:SiO ₂ ) of the cermet components is 1:5 to 2:3. The corresponding volume of W: _SiO2 was formed by the magnetron sputtering system, and the two targets were sputtered simultaneously.

As a kind of preferred technical scheme of the present invention, the concrete preparation process of described preparation method:

1) The mechanically polished stainless steel was scrubbed with acetone and anhydrous ethanol successively, and the substrate was fixed;

2) Vacuuming, the background vacuum is less than ~4×10 ^-4 Pa;

3) Carry out bias cleaning on the substrate, in an argon atmosphere, the air pressure is about 0.6-0.8Pa, and the cleaning time is 3-5min;

4) Start sputtering, in an argon environment, the pressure is about 0.3-0.5Pa, sputter the infrared metal W reflection layer, the QOM quasi-optical microcavity absorption layer, and the optical antireflection layer in turn;

5) After the deposition is completed, place it in a vacuum chamber for more than 20-25 minutes and take samples.

The selection of the process parameters of the aforementioned preparation method is mainly based on the optimal process parameters determined by the deposition power and the corresponding material deposition rate used in the deposition of the monolayer film, combined with the optical constant of the monolayer film.

The high temperature stable quasi-optical microcavity solar spectrum selective absorption coating provided by the present invention has the following advantages:

(1) The solar absorption rate is high, up to ~96%;

(2) Good high temperature stability, stable performance for 250h in a high temperature 600 ℃ vacuum environment has no tendency to deteriorate;

(3) The spectral absorption range is easy to adjust. Based on the selective absorption coating of the quasi-optical microcavity, it can be conveniently adjusted according to the proportion of metal components, the thickness of the cermet and the thickness of the intermediate metal layer.

Description of drawings

FIG. 1 is a schematic structural diagram and a reflection spectrum diagram of the W-SiO ₂ quasi-optical microcavity spectrum selective absorption coating of the present invention.

Specifically, Fig. 1(a) Schematic diagram of the structure of the high-temperature stable W-SiO quasi _- optical microcavity spectrally selective absorption coating, 1(b) reflection spectra of the absorption coating before and after annealing at 600 °C in a vacuum environment, 1(c) ) structure is SS(substrate)\W\W-SiO ₂ \Al ₂ O ₃ \SiO ₂ The reflection spectrum of sample S1, 1(d) is SS(substrate)\W-SiO ₂ \W\W-SiO ₂ Reflection spectrum of sample S2.

Detailed ways

The present invention will be described in further detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the invention are not limited thereto.

Example 1 QOM quasi-optical microcavity-based selective absorption coating

A high-temperature stable quasi-optical microcavity structure solar spectrum selective absorption coating, including three parts: from bottom to top, a metal infrared reflection layer, a quasi-optical microcavity absorber, and an optical antireflection layer, see 1(a) shown,

Among them, the quasi-optical microcavity absorber is composed of a cermet 1-metal-cermet 2 structure,

The metal is metal W, the cermet is W-SiO ₂ cermet, and the dielectrics of the optical antireflection layer are Al ₂ O ₃ and SiO ₂ .

Among them, the W infrared reflection layer is about 50-150nm, the W- _SiO2 cermet 1 is about 30-60nm, the intermediate metal W layer is about 3-15nm, the W- _SiO2 cermet 2 is about 45-65nm, and the _Al2 The thickness of the O ₃ optical anti-reflection layer 1 is about 10-30 nm, and the thickness of the SiO ₂ optical anti-reflection layer 2 is about 45-70 nm. The volume ratio of the cermet composition (W:SiO ₂ ) is about 1:3.

The preparation method includes: selecting mechanically polished stainless steel 304 as a substrate, and using a high-vacuum multi-target magnetron sputtering system to deposit the absorption coating, wherein the metal W adopts DC sputtering deposition, and the power density is 2.00-2.50 ( Wcm ^-2 ), Al ₂ O ₃ and SiO ₂ were sputtered by radio frequency with a power density of 3.00-4.00 (W cm ^-2 ), W-SiO ₂ cermet was deposited by co-sputtering of direct current and radio frequency, and its sputtering The power densities were 0.50-1.00 (W cm ^-2 ) and 3.50-4.50 (W cm ^-2 ), respectively.

Specific preparation process parameters:

The performance parameters of the used targets: the purity of each target is W (99.95%), SiO ₂ (99.99%) and Al ₂ O ₃ (99.99%). The sizes of W, SiO ₂ and Al ₂ O ₃ targets are Φ72.6mm×5mm, Φ50.8mm×4mm, Φ50.8mm×4mm, respectively. The dimensions of the stainless steel base are 20×20 mm ² .

Specific preparation process:

1) The mechanically polished stainless steel was scrubbed with acetone and anhydrous ethanol successively, and the substrate was fixed.

2) Evacuate, and the background vacuum is less than ~4×10 ^-4 Pa.

3) Carry out bias cleaning on the substrate, in an argon atmosphere, the air pressure is about 0.6-0.8Pa, and the cleaning time is 3-5min.

4) Start sputtering. In an argon atmosphere, the pressure is about 0.3-0.5Pa, and the infrared metal W reflection layer, the QOM quasi-optical microcavity absorption layer, and the optical antireflection layer are sequentially sputtered.

5) After the deposition is completed, place it in a vacuum chamber for more than 20-25 minutes and take samples.

Referring to the figure, Fig. 1(b) shows the reflection spectrum of the prepared coating, the solid line is the reflection spectrum of the deposited W-SiO quasi _- optical microcavity spectrally selective absorption coating without annealing measured before, The dotted curve is the reflectance spectrum measured after annealing at 600 °C for 250 h.

Comparative Example 1

S1 is the absorption coating of SS(substrate)\W\W _- SiO ₂ \Al ₂ O ₃ \SiO ₂ structure. The thickness of W infrared reflection layer is about 50-150nm, W- _SiO2 cermet _90-100nm , _Al2O3 optical anti-reflection layer 1 is about 12-17nm, _SiO2 optical anti-reflection layer 2 thickness is about 58 -62nm.

Comparative Example 2

S2 is the absorption coating of SS\W-SiO ₂ \W\W-SiO ₂ structure. Compared with the W-SiO ₂ quasi-optical microcavity spectral selective absorption coating, there is no top optical anti-reflection layer, and the thickness of each layer is Respectively: the W infrared reflection layer is about 100-150nm, the W- _SiO2 cermet 1 is about 30-60nm, the intermediate metal W layer is about 2-20nm, and the W- _SiO2 cermet 2 is about 40-65nm.

Among them, the S1 and S2 sample substrates are all mechanically polished stainless steel 304, and the sputtering deposition conditions are consistent with the QOM quasi-optical microcavity-based selective absorption coating.

And, referring to the figure, 1(c) is the reflection spectrum of SS\W\W-SiO ₂ \Al ₂ O ₃ \SiO ₂ sample S1, 1(d) is SS\W-SiO ₂ \W\W- Reflection spectrum of _SiO sample _S2 .

Embodiment 2 Performance testing comparison

Under the condition that only normal incidence is considered, the calculation formula of absorptivity can be simplified as:

Among them, λ is the wavelength; I is the standard solar spectrum (AM 1.5); R _λ is the emission spectrum of the corresponding wavelength. R _λ can be measured by UV-Vis-NIR spectrophotometer and Fourier transform infrared spectrometer. Similarly, under the condition of only normal incidence, the calculation formula of thermal emissivity can be simplified to the following formula:

where M _λ is the blackbody radiation intensity at the corresponding wavelength.

Then the light-to-heat conversion efficiency of the solar spectrum selective absorption coating was calculated according to the absorptivity α and the thermal emissivity ε. The photothermal conversion efficiency η _Thermal follows the following formula:

Among them, σ Stefan-Boltzmann constant; T coating surface temperature; C focusing multiple, its meaning is the ratio of the area irradiated by sunlight before and after focusing. If considering the use of Carnot heat engine to convert heat energy twice, the overall efficiency of the system follows the following formula:

Among them, η _Total is the total efficiency after the secondary conversion; T ₁ is the ambient temperature.

According to the above formula, the relevant performance calculation results of the high temperature stable W-SiO ₂ quasi-optical microcavity spectral selective absorption coating embodiment are shown in Table 1:

Table 1. Absorptivity, thermal emissivity, photothermal conversion efficiency and total system efficiency of W-SiO quasi _- optical microcavity spectrally selective absorption coatings under different annealing conditions

The quasi-optical microcavity selective absorption coating has an absorption of ∼0.96 and a thermal emissivity of ∼0.18 at 82 °C. It shows that the selective absorption coating has excellent absorption performance. At the same time, when working at a high temperature of 600 ° C and a 1000 times focusing environment, the photothermal conversion efficiency can reach ~0.95, and the total secondary conversion efficiency can reach about 0.65.

After the coating is annealed in the air at 600℃ for 250 hours, the change of the solar light absorption rate is very small (0.004), the working photothermal conversion efficiency can reach about 0.95 at the working temperature of 600℃, and the total secondary conversion efficiency can reach about 0.65. It shows that the spectral selective absorption coating of the quasi-optical microcavity structure prepared by the invention has the advantages of good high temperature stability and high solar light absorption rate.

It can be seen from the comparison of S1 that under the same conditions, the absorption of the QOM quasi-optical microcavity-based selective absorption coating is greater than that of the cermet-based selective absorption coating, up to 0.96. Compared with the S2 sample, in the presence of the optical anti-reflection layer, the reflection of sunlight will be reduced, which is beneficial to the absorption of sunlight by the coating.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (3)

1. a quasi-optical microcavity structure solar spectrum selective absorbing coating, is characterized in that, comprises three parts: from bottom to top, successively are metal infrared reflection layer, quasi-optical microcavity absorber, optical antireflection layer, Among them, the quasi-optical microcavity absorber is composed of a cermet 1-metal-cermet 2 structure, The metal is metal W, cermet 1 is W-SiO ₂ cermet 1, cermet 2 is W-SiO ₂ cermet 2, and the optical anti-reflection layer is Al ₂ O ₃ optical anti-reflection layer 1 and SiO ₂ optical Anti-reflection layer 2; Among them, the order from bottom to top is: the metal W infrared reflection layer is 50-150nm, the W- _SiO2 cermet 1 is 30-60nm, the middle metal W layer is 3-15nm, and the W- _SiO2 cermet 2 is 45- 65nm, the thickness of Al ₂ O ₃ optical anti-reflection layer 1 is 10-30 nm, and the thickness of SiO ₂ optical anti-reflection layer 2 is 45-70 nm; And, the volume ratio of the cermet composition W:SiO ₂ is 1:5 to 2:3. 2. a preparation method of a kind of quasi-optical microcavity structure solar spectrum selective absorption coating according to claim 1, is characterized in that, comprising: Using mechanically polished stainless steel 304 as the substrate, the absorption coating is deposited from the bottom up by a high vacuum multi-target magnetron sputtering system, wherein the metal W is deposited by DC sputtering, and the power density is 2.00-2.50 (W cm ^-2 ), Al ₂ O ₃ optical anti-reflection layer 1 and SiO ₂ optical anti-reflection layer 2 are RF sputtering, power density is 3.00-4.00 (W cm ^-2 ), W-SiO ₂ cermet The direct current and radio frequency co-sputtering depositions were successively used, and the sputtering power densities were 0.50-1.00 (W cm ^-2 ) and 3.50-4.50 (W cm ^-2 ), respectively. 3. preparation method according to claim 2, is characterized in that, described preparation method comprises: 1) The mechanically polished stainless steel was scrubbed with acetone and anhydrous ethanol successively, and the substrate was fixed; 2) Vacuuming, the background vacuum is less than 4×10 ^-4 Pa; 3) The substrate is subjected to bias cleaning, in an argon atmosphere, the air pressure is 0.6-0.8Pa, and the cleaning time is 3-5min; 4) Start sputtering, in an argon atmosphere, the air pressure is 0.3-0.5Pa, sputter the infrared metal W reflection layer, the quasi-optical microcavity absorber, and the optical antireflection layer in turn; 5) After the deposition is completed, place it in a vacuum chamber for 20-25 minutes and take a sample.

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