Preparation And Research On Solar Energy Selective Absorbing Coating By Sol-gel Method

Energy is the basis of survival for people. In the development of the new source, solar energy has a unique advantage. The photothermal conversion is one of the principal agents of the utilization of solar energy and it is used for Solar Dynamic Power System. Solar energy selective absorbing coating is the core component of thermal power generation collector, the preparation of the solar energy selective absorbing coating has become an active subject in the field of solar thermal utilization. The purpose of the research about the coating is the study of its material choosing, structure designing, processing optimization and optical properties. However, there are some problems about the coatings which has been prepared, outstanding performance is in thermal stability and preparation. Some metals have the characteristics of solar energy selective absorbing, just like the W and Mo. Further more, the coatings made of these metals have a good thermal stability. Therefore, in order to promote the development of solar energy technology in China, the MoO2-NiO-Al2O3 coating and W-Al2O3 coating are prepared which is focus on exploring the new material system, esay process and thermal stability.This topic used the Sol-Gel method with uniform design, successful preparation of MoO2-NiO-Al2O3 coating and W-Al2O3 coating on the quartz basement. Properties of the coating were observed by TG-DSC tester, X-ray Diffraction, Scanning Electron Microscope, and spectrophotometer. In this paper, we explored the effects of the distribution ratio, the volume of the mixed sol, and the heating treating regime on the properties. We also studied the effects of the fill factor and Ni doping on the optical properties of the coating, and analysed the thermal stability of the coating.In the study of MoO2-NiO-AlaO3 coating, we analysed the effects of volume of the mixed sol and distribution ratio on the optical properties of the coating. The results show that: the mole fractions of MoO2 of various doped layers are 0.68,0.60 and 0.25, the volume of the mixed sol of three layers is 0.20ml,0.18ml and 0.22ml, while the antireflection is 0.26ml, coating has the best solar absorption properties, while the absorptivity can be up to 88.6%, the emissivity is 66.3%, the quality factor is 1.31. In the based on the study of MoO2- -NiO-Al2O3 coating, W was used in place of MoO2 and NiO to be a new coating of W-Al2O3. Then we analysed its properties that the effects of the distribution ratio and the volume of the mixed sol on W-Al2O3 coating. The results show that:he mole fractions of W of various doped layers are 0.95,0.43 and 0.18, the volume of the mixed sol of three layers is 0.20ml, 0.18ml,0.22ml and 0.08ml. While the antireflection is 0.26ml, coating has the best solar absorption properties, while the absorptivity can be up to91%, the emissivity is 79%, and the quality factor is 1.14. Compared to the W-Al2O3 coating, the optical properties of the MoO2--NiO-Al2O3 coating is better according to the quality factor.Based on the optimal analysis of MoO2-NiO-Al203 coating and W-Al2O3 coating, we made a study of these two kinds of coating. The research of MoO2-NiO-Al2O3 coating raised the best heating rate of sintering, by analyzing the effects of heat treatment on its micro-structure, micro-morphology and optical performance. The results show that:The optical properties of MoO2-NiO-Al2O3 coating are better than others, when heating rate keep a steady pace of 5℃/min. Then its quality factor is up to 1.32.In the research on W-Al2O3 coating, the influences of fill factor on the optical properties were investigated especially. And the changes of the optical performance were analysed on the basis of the original W-Al2O3 coating. The results show that:the influence of the mole fraction of W on the absorption of the coating varies with the solar spectrum band. The coating presents better optical performance in UV region (0.2um-0.8um), when lacking of the doping layer, which has the medium-sized fill factor. And the coating presents better optical performance in UV region (0.8um-2.5um), when lacking of the doping layer, which has the highest-sized fill factor. Compared with the original coating, the quality factor of Ni doping W-Al2O3 coating can be increased by 1%, when sputtering time is 10minIn order to explore thermal stability of MoO2-NiO-Al2O3 coating and W-Al2O3 coating, the properties change under the condition of 5 hours heating placed in the resistance furnace were studied. The results show that:The MoO2-NiO-Al2O3 coating gets a wonderful thermal stability under the heating temperature of 400 ℃, while the coating is of no rocks or peeling. And the W-Al2O3 coating is prone to oxidation when the heating temperature being over 500 ℃. This difference is caused by the difference between the structure and the composition of the two coatings.