Preparation And Properties Of New Solar Absorbing Coating

With the rapid development of the world economy and the continuous consumption of non-renewable resources,the current energy structure needs to be adjusted and upgraded.As an excellent substitute for non-renewable resources,solar energy is a natural clean energy and has been applied in our daily life.The main device of solar energy utilization is solar collector,which core component is absorbent with selective absorption function.The solar absorbent coating prepared by coating method has the characteristics of easy synthesis,simple process and high performance as absorbent,and is mainly composed of functional powder and filler resin.However,the development of resin is restricted by volatile organic matter emission and the immature process of the preparation of functional powders.Based on this,this paper studies the synthesis scheme of a new type of coating for solar absorption coating,which can effectively use the solar energy and reduce the pollution to the environment.The main research contents are as follows:Firstly,synthesis of waterborne polyether/polyester two-component polyurethane.Castor oil-based polyester polyol（CSONOH）was prepared from castor oil,diethanolamine and itaconic acid as materials.Waterborne polyether/polyester two-omponent polyols were made from isoflone diisocyanate,polyether polyol,polycarbonate diol,or castor oil-based polyester polyol.Among them,depending on the polyester polyols can be divided into plant-based of two-component water-borne polyols and petroleum-based of two-component water-borne polyols,to explore the influence of different polyester content and types in polyols on the coating.The results show that the water resistance and high temperature resistance of the coating are decreased with the increase of polyester polyol content,but the mechanical properties such as tensile strength and pencil hardness are increased.When the proportion of polyester polyol was 25%,the coating combined with the higher water resistance,thermal stability and mechanical properties of polyether polyurethane had the best comprehensive properties.When the addition amount of CSONOH was 25%（WMPU-CSO-25%）,the coating’s transmittance was 87.6%,which was slightly improved compared with polyether polyurethane（T%=87.4%）,and better than that of PCDL（T%=86.3%）.The tensile strength of WMPU,WMPU-CSO-25%and WMPU-PCDL-25%is 0.89 MPa,3.5 MPa and 1.6 MPa,respectively.The thermal decomposition temperatures were 281.1℃,275.1℃and 281.4℃,respectively.The basic properties such as pencil hardness and adhesion of the plant-based modified polyurethane coating are better than that of the petroleum-based modified polyurethane coating.The synthetic coating is suitable for the application requirements of low temperature solar absorption coating,and the plant-based resin can replace the petroleum-based resin to a certain extent,which means high environmental protection value.Secondly,preparation of transition metal oxide absorbent powder by sol-gel combustion method.The ternary transition metal oxides were prepared from four metal nitrates of ferric nitrate,cobalt nitrate,copper nitrate and ferric nitrate.The Co Cu Mn O_x functional powders has the best optical absorption performance(α_sol=94.55%).When the ratio of the amount of combustion agent and nitric acid in the sol solution is 1.5:1,the xerogel combustion is the most sufficient.When the solution condition is alkaline,the functional powder synthesized has the largest specific surface area,and the specific surface area of the powder is 29.16 m²/g.In addition,when PEG-200 was used as alcohol additive,the average solar absorption rate（95.36%）of the sample was the highest,and the phase of the powder obtained by XRD and EDS analysis was Co Cu Mn O_1.92.When calcined at 600℃for 6 h,the coating has the best selective absorption property,the average solar absorption rate(α_sol)is 95.33%,and the emissivity（ε）is 21.34%.Thirdly,transition metal molybdenum-based sulfide（Me-Mo S_x）adsorption powders were prepared by hydrothermal method.Single metal doped molybdenum-based sulfides were prepared from ferric chloride,copper chloride,manganese chloride,cobalt chloride,ammonium molybdate and thiourea,respectively.The four functional powders all have excellent light absorption effect,but the absorption effect of Fe-Mo S_x is the best,which is 96.79%.When Fe content in the raw material is 1 mmol/L,the powder performance is the best.With the increase of the calcination temperature,the absorption rate of the powder increases first and then decreases.The optimal calcination process is determined at 150℃for 8 h.After two months,the absorption rate of the powder only decreases by 3%,indicating a certain storage stability,the spectral selectivity wasα_sol/ε=97.33%/29.58%.The solid content of Fe-Mo S_xpowder in the coating was simulated and analyzed with the commercial samples.The coating performance was the best when the solid content of Fe-Mo S_x powder was 30%,and the stable temperature（89.7℃）was higher than that of the commercial product（88.5℃）.On the whole,transition metal sulfide has a higher average solar absorption rate than composite transition metal oxides,and its preparation temperature is below 200℃,which reduces the production energy consumption,and has practical value.