Preparation And Properties Of Novel Solar Absorbing Coating

With the exhaustion of fossil fuels and the increasingly prominent environmental problems,the effective use of solar energy is becoming more and more important.As a clean environmental energy,solar energy has been widely used in various fields of life.Solar collector is the most widely used in the field of solar photothermal conversion,and its core element is the absorption plate with solar selective absorption coating.The solar selective absorption coating prepared by coating method has the characteristics of simple preparation process,low cost and certain commercial availability.It is usually composed of organic resin film forming agent and spectral selective powder filler.However,due to the influence of the film forming resin,its water resistance and high temperature resistance are poor,the thermal emissivity of the coating in the infrared region is high,and the preparation process and performance of the functional powder are urgently needed to improve.These problems limit the development of the coating solar absorption coating to a certain extent.Therefore,this paper explores the solar selective absorption coating from the two aspects of resin film forming agent and functional powder,successfully prepares the efficient and environmentally friendly solar selective absorption coating by coating method,and investigates its related properties.The main research contents are as follows:The first part:Preparation and properties of siloxane-terminated fluorinated polyurethane.Firstly,fluorinated dihydric alcohols（PFOH）were prepared by mercapto-ene click reaction between 1-mercaptoglycerol（MTG）and 2-（perfluorohexyl）ethyl methacrylate（PFOL）.Siloxane（TMSO）containing C-OH was prepared by hydrosilylation reaction between allyl hydroxyethyl ether（AYEL）and trimethoxysilane（TMS）.A series of siloxane-terminated fluorinated polyurethane（WFSi PU）were successfully prepared using isoporone diisocyanate（IPDI）,polycarbonate diol（PCDL）,2,2-dimethylpropionic acid（DMPA）,trimethylolpropane（TMP）,PFOH and TMSO as the main raw materials.The effects of PFOH and TMSO contents on the properties of waterborne polyurethane were studied.The results showed that with the introduction of PFOH and TMSO in the aqueous polyurethane system,the particle size of the emulsion gradually increased and the distribution became wider.The particle size of the emulsion increased from the initial 24 nm to 130.5 nm.The water contact Angle increased from 78.3°to 107.6°.Water absorption rate decreased from 16.67%to 3.51%;The introduction of TMSO has little effect on the transmittance of the film,while the introduction of PFOH can reduce the transparency of the film to a certain extent,but the film still maintains excellent transmittance.The mechanical properties and thermal stability of the film are improved to a certain extent.The water-based polyurethane film modified by fluorine silicon has good basic properties,water resistance,hardness and adhesion have been improved.Considering the light transmittance,thermal stability,hydrophobicity,storage stability and other factors of the coating,it is determined that when the PFOH addition amount is 8%,TMSO addition amount is 50%,the overall comprehensive performance of the coating film is the best,and meets the requirements of the resin base material for solar absorption coating.The second part:Preparation and properties of cerium composite Co Cu Mn O_xsolar selective absorption powder（Ce@Co Cu Mn O_x）and its corresponding coating.Using cerium nitrate hexahydrate,copper nitrate trihydrate,manganese chloride tetrahydrate,cobalt nitrate hexahydrate and sodium hydroxide as the main raw materials,Ce@Co Cu Mn O_xfunctional powder was prepared by co-precipitation and high-temperature sintering method.The silicoxane terminated fluorinated polyurethane prepared in part I was used as a film forming agent,and the solar selective absorption coating was prepared by spraying method.The effects of Ce content and calcination process on various properties of the sample were investigated.The results showed that:When the molar ratio of Ce,Co,Cu and Mn is1.5:2.5:1:1,the coating has the best absorption rate,α_sis 95.3%,and Ce@Co Cu Mn O_xmainly exists in the form of Co Cu Mn O_x,Co₃O₄and Ce O₂phases.With the increase of calcination temperature,the main morphology of the powder gradually changed from spherical block（450°C）to lamellar（850°C）,and the particle size gradually increased.When the calcination temperature was 450°C for 4h,the solar absorption coating prepared had the best selective absorption performance.At this time,the solar absorption rate of the coating was 95.9%.The emissivityε_Tis 23.8%,and the corresponding quality factor（α_s/ε_T）is 4.03.The third part:Preparation and properties of transition metal doped cu-based sulfide（Cu-M-S_x）solar absorption powders and corresponding coatings.Using ammonium molybdate tetrahydrate,copper nitrate trihydrate,ferric nitrate nine hydrate,manganese chloride tetrahydrate,cobalt chloride hexahydrate and thiourea as raw materials,four transition metal doped copper sulfide powders of Co,Fe,Mn and Mo were prepared by hydrothermal method.The powders were used as functional fillers to prepare selective solar absorption coatings.The influences of powder doping elements and doping amount,p H value of reaction system and calcination process on various properties of the prepared powder and corresponding coating were investigated.The results show that:The coating prepared by Cu-Mo-S_xpowder has the best performance,with an absorption rate of 96.03%and a band gap of 2.20 e V.In this case,the powder is a mixture of Cu S,Cu Mo₂S₃and Cu₂Mo₆S₈.When the doping amount of Mo element is 1.00 mol,the micromorphology of Cu-Mo-S_xfunctional powder is composed of dense and uniform spherical nanoparticles,and the pores between the particles are many and small,and the Cu-Mo-S_xfunctional powder has the best performance.When p H=2 in the reaction system,the coating has the best light absorption performance,the absorption rate can reach 96.90%,the powder is composed of double size micro/nano thin slices,the surface texture of the complex,formed an excellent optical trap.Calcination for 7 h at 280°C is the best calcination process.At this time,the selective absorption performance of the coating is excellent,the absorption rate and emissivity are 97.22%and 23.6%,respectively.The quality factor is 4.12.The temperature is finally stabilized at 84.2°C under the operation of the solar simulation device,which is better than the commercial coating（83.5°C）.It shows that Cu-Mo-S_xsolar absorption coating has certain practical value and market application prospect.