Simulation Design And Preparation Of W-Al₂O₃ Based Solar Absorption Coatings

Solar thermal power generation has received great attention in recent years due to its advantages of high energy conversion efficiency,stable power output,low energy consumption in production,no pollution during use,and continuous power generation through heat storage energy.Solar energy absorption coating is a key material for solar thermal power generation,and it is required to be able to absorb and convert solar radiation energy into heat energy efficiently in the visible-near infrared wave,and have high reflection（low heat emittance）in the infrared wave band to reduce heat energy as much as possible.loss.Since the solar energy absorption coating is composed of multiple layers of nano functional film,changes in the composition,structure,and thickness of each functional layer have a significant effect on the optical properties of the solar energy absorption coating.Based on computer simulation software,the design and optimization of solar absorption membrane system structure,and systematically studying the influence of factors such as composition,structure and optical thickness of each functional layer on its optical performance have important theoretical value and guiding significance for production practice.This project is based on the Matlab software platform and has independently developed a simulation program for the solar absorption coating.Taking the W-Al₂O₃ solar absorption coating as an example,the orthogonal experiment method was used to set the key factor affecting the structure of the film to six factors and five levels as L₂₅（5⁶）.Through software,simulates the reflection spectrum of the solar absorption coating in the wavelength range of 0.3to 25μm under different combinations,and calculates the absorptance and emittance of the corresponding film system.The results show that the strongest factor affecting the absorptance of the solar absorption coating is the thickness of d₁,which is the surface Al₂O₃ anti-reflection layer,and the strongest factor affecting the high-temperature 823 K emittance of the film is d₂,the thickness of the LMVF layer.Among the factors,the order of affecting the absorptance of the solar absorption coating is d₁>f₂>f₃=d₂>d₃>d₄,and the factors affecting the emittance of the solar absorptive coating is ranked as follows:d₂>f₂>f₃>d₃>d₁>d₄.Optimize the design by combining the combination with the highest absorptance and the lowest emittance in the orthogonal experiment table,and obtain a film structure with 50 nm Al₂O₃/40 nm W-Al₂O₃（f₂=0.2）/50 nm W-Al₂O₃（f₃=0.525）/120 nm W,the absorptance is 0.929,and the 823 K emittance is only 0.072.Based on the membrane structure,the influence on the optical properties of the solar absorption coating by continuous change of single factor was further studied using simulation software.It is found that with the increase of the antireflection layer thickness d₁,the cutoff wavelength of the reflectance spectrum of the solar energy absorption coating shifts to the right,the absorptance first increases and then decreases,and the emittance monotonously increases;as the thickness d₂ of the LMVF layer increases,The reflection spectrum of the absorption coating changes very sharply,the cutoff wavelength shifts to the right,the absorptance increases first and then decreases,and the emittance monotonously increases;with the increase of the fill factor f₂ of the LMVF layer,the reflection spectrum of the absorption coating is cut off.When the wavelength shifts to the left,the absorptance and the emittance of the absorption coating both increase first and then decrease.With the increase of the thickness d₃ of the HMVF layer,the cutoff wavelength of the absorption spectrum of the absorption coating does not shift significantly,and the absorptance of the absorption coating gradually increases.When the HMVF layer fill factor f₃ is increased,the cutoff wavelength of the absorption spectrum of the absorption coating slightly shifts to the left,and the absorptance and emittance of the absorption coating show a monotonous decrease.As the infrared reflection layer IR thickness d₄ increases,the change in the reflection spectrum is found to be very weak.When d₄ exceeds a certain value,the reflection spectral absorption coating is not changed significantly,and the emittance of the absorptance of the coating does not change substantially.In order to verify the validity and reliability of the above simulation results,the objective of this paper is to use the magnetron sputter coating equipment to prepare the corresponding W-Al₂O₃ solar absorption coating on the 321-mirror stainless steel substrate.Scanning electron microscope,atomic force microscope and X-ray diffractometer were used to analyze the microstructure and structure of the prepared solar absorption coating.The reflection spectrum of the preparation state solar absorption coating was measured by UV-Vis-NIR spectrophotometer and Fourier transform infrared spectrometer,and calculated to have an absorptance of 0.926 and a 823 K emittance of 0.116.The absorptance is basically in agreement with the simulation design result.The emittance is slightly higher than that of the analog design.The possible cause of the error is that the metal ions uniformly distributed in the ceramic matrix of high and low metal volumetric fraction layers are submicrolayer approximation in the process of preparation.In order to study the heat resistance of W-Al₂O₃ solar absorptive coating,the prepared W-Al₂O₃ solar absorptive coatings were annealed in a vacuum furnace at 580°C for 120 hours.The absorptance was 0.92 and the 823 K emittance was 0.072.The main reason for the decrease of the emission ratio of the solar absorption coating is that the average grain size of the W coating grows from 13 nm to 21 nm.