Preparation And Study On Multilayered Solar Selective Coatings Applied In Mid-high Temperature

As a clean and renewable energy,solar energy has huge reserves.At present,the utilization of solar energy needs the help of solar selective absorption coatings.The research on solar selective coatings that can be applied in medium-high temperature atmospheric environment still needs to be deepened.The purpose is to prepare coatings with excellent spectral selectivity and medium-high temperature stability.In consideration of the cost,process and practical properties,the Co-WC coating prepared by high-velocity oxy-fuel?HVOF?thermal spraying is used as the absorber layer on the bottom.The CuCoMnO_x spinel composite oxide prepared by sol-gel method is used as the secondary absorption layer,then,the CuCoMnO_x-SiO₂ composite sol is used as the transition layer connecting the absorption layer and the outer anti-reflection layer of SiO₂.This multilayer design combines the excellent medium-high temperature stability of the sprayed coatings and outstanding spectral selectivity of the sol-gel films to prepare high-performance selective absorbing coatings that can be stabilized in the medium-high temperature atmosphere.And the next,Ni was doped into CuCoMnO_x sol to further improve its spectral selectivity and thermal stability in order to improve the overall performance of the multilayer coatings again.The wetting angle between CuCoMnO_x sol and Co-WC sprayed coating is less than 10 degrees,that means the good bonding condition between the sol layer and sprayed coating.A further analysis shows that when the Co-WC layer is polished for10 minutes and the roughness is about 1.78?m,preparing CuCoMnO_x films on the Co-WC coating by spin-coating at the speed of 4000r/min can reach the best optical properties.Secondly,the interface between the transition sealing layer and the auxiliary absorption layer is obvious,and some crystal fusion can be observed locally.The element distribution shows gradient characteristics,showing a good transition of the overall multilayered coatings.With the coating of sol films,the pore defect and surface roughness of the Co-WC coating decrease continually,and the?/?of the coating increases from 0.821/0.434 to 0.914/0.291.When the multilayered structure coatings were insulated at 500?for 250 hours,there were minor cracks on the surface of the coatings.The degradation of optical properties showed gradient characteristics.The elements between the layers diffused.Benefiting from the protection of sol layers.The final?/?was 0.901/0.323,and the PC value was 0.0305,which met the experimental requirements.Subsequently,Ni doping was carried out on CuCoMnO_x layer.It was found that the doped Ni ions did not form compounds independently,but preferentially existed in the spinel lattice,which distorted the spinel lattice.The average grain size first decreased and then increased with the increase of doping amount.When the doping amount was 5%,the average grain size was 20.94 nm?±0.5 nm?.Doped films with best performance and uniform grain distribution could be obtained when the pulling rate was 40mm/min and annealed at 500?for 90min.The best?/?can reach0.943/0.180.When the CuCoMnO_x films were insulated for 120 hours at 550?,the degradation of CuCoMnO_x film is much more serious than that of Ni_0.05?CuCoMnO_x?_0.95.95 film.Co-WC/Ni_0.05?CuCoMnO_x?_0.95/Ni_0.05?CuCoMnO_x?_0.95-SiO₂/SiO₂ coatings were obtained by replacing the CuCoMnO_x film with Ni_0.05?CuCoMnO_x?_0.95 film,the?/?of the improved mutillayered coatings are0.927/0.270.The thermal stability of the coatings was also tested at 500?.After 250h heat preservation,the absorptivity and emissivity of the multilayered coatings are0.911/0.295 and the PC value is only 0.0255.The degradation rate of the coatings is much lower than that of the original multi-layer structure coatings.The comprehensive properties of the multilayered coatings have been further improved.the deterioration of optical properties met the experimental requirements.