Study On The Preparation And Performance Of High-temperature Solar Selective Coatings Based On Double Ceramic Composite

Solar thermal power generation,as a clean renewable energy source,has the advantages of high energy conversion efficiency,low energy loss during production,clean and no pollution during use,continuous 24-hour power generation through heat storage.It can provide clean,stable and peak adjustable high-quality power to the power grid.It can replace conventional fossil energy with clean electricity,which has positive significance for protecting the ecological environment and achieving a harmonious society.Increasing the operating temperature of solar thermal power generation can increase its power generation efficiency and reduce the cost of electricity.However,the high temperature resistance of the solar energy absorbing film,which is the key material to realize the conversion of photothermal energy,is also put forward more stringent requirements.The research on the preparation technology of high-temperature and high-efficiency solar energy absorbing film has important and urgent practical significance for promoting the rapid development of high-temperature solar thermal power generation in China.In this thesis,ZrB₂ films and Al₂O₃ films were prepared by magnetron sputtering technology,and ZrB₂-A1₂O₃ composite solar absorbing films were prepared by co-sputtering technology.The composition,microstructure,morphology,electrical and optical properties of ZrB₂,Al₂O₃ and ZrB₂-Al₂O₃ composite solar absorbing films were characterized and analyzed by means of XPS,XRD,FESEM,four probe resistivity measurement system and UV-vis-NIR spectrophotometer.The effects of process conditions such as sputtering power,working pressure and other factors on the microstructure and properties of the films were studied.The effects of composition,structure and functional layers on optical absorption properties of ZrB₂-Al₂O₃ composite films were studied.Based on the MATLAB software simulation platform,the membrane structure of the ZrB₂-Al₂O₃ dual-phase ceramic composite solar absorbing films were programmed and designed.According to the optimal film system structure of the simulation design,ZrB₂-Al₂O₃ composite solar energy absorbing film was prepared.And its optical properties and high temperature thermal stability were studied.The research results show that the deposition rate of the film has a linearly increasing relationship with its power,and it has a trend of increasing and then decreasing with working pressure,no matter whether the Al₂O₃ films are deposited by RF power or the ZrB₂ films are deposited by DC power.The B/Zr atomic ratio in the fabricated ZrB₂ film is slightly higher than its stoichiometric ratio 2,while the composition of the Al₂O₃ film is basically close to its stoichiometric ratio.The ZrB₂ films deposited at low power sputtering?such as 100 W?or high working pressure?such as 1.2 Pa?is amorphous.As the sputtering power increases or the working pressure decreases,the film structure gradually changes from amorphous turn to nano-polycrystalline state,and the film growth is denser,the cross-section columnar structure features are more obvious,and the film's electrical conductivity is enhanced.However,the Al₂O₃ thin film made under different process conditions all have a dense amorphous structure.ZrB₂ and Al₂O₃ dual-target co-sputtering can be used to make amorphous ZrB₂-Al₂O₃ double ceramic composite films in a wide range of processes.The results of optical performance research show that the ZrB₂-Al₂O₃ double ceramic composite layer instead of the ZrB₂ absorbing layer can significantly broaden the absorption limit range,reduce the reflection of the film on incident sunlight,and improve the film's absorption of solar spectral energy.According to the simulation design results,the ZrB₂-Al₂O₃dual-phase ceramic composite solar absorbing films prepared on SUS321 mirror-surface stainless steel substrate has calculated an absorption ratio of 95.4%and an emission ratio of0.121at 550?,which is basically consistent with the computer simulation results.The composite films were subjected to vacuum heat treatment at 600?×400 h,and its absorption ratio and emission ratio at 550? were measured to become 95.2%and 0.126,respectively.The performance evaluation factor PC was about 0.003,which was far less than the threshold value of PC?0.05.It shows that the ZrB₂-Al₂O₃ double ceramic composite solar absorbing film designed and prepared in this paper has extremely high temperature resistance and should meet the requirements for high temperature solar thermal power generation at 550? or even 600?.