| Inorganic nonmetallic crystal materials with high infrared radiation can be widely applied to heating and drying in industry. Doping is an effective way to improve the properties of the materials. The infrared radiation properties of the materials can be improved by doping. Currently, the researching of inorganic nonmetallic crystal materials with high infrared radiation based on MgO-Al2O3-SiO2system and CoFe2O4system is in the initial stage of development and it is rarely reported the application of high infrared radiance materials in the alkali liquor evaporation. Given that, Inorganic nonmetallic crystal materials with high infrared radiation were prepared in this paper. The effects of the preparation methods, the materials compositions and the crystal structure on the infrared radiation properties of the materials were studied and the applications of the materials in the alkali liquor evaporation were developed. In the study of the infrared radiance materials, MgO-Al2O3-SiO2system and CoFe2O4system were chosen as the basic materials respectively. In order to obtain the materials with high infrared emissivity, different dopants were added in the basic materials. The key factors which influencing the infrared radiation properties of the inorganic nonmetallic crystal materials were studied and the optimum conditions were selected in this paper.In the study of Ce4+doped MgO-Al2O3-SiO2system, the materials were prepared by solid-state reaction method and when the Ce4+content was0.08wt%, the sample had the highest infrared emissivity of0.92±0.01in8-14μmwaveband after sintering at1200℃for2h. In the system of CuFe2O4doped MgO-Al2O3-SiO2materials, the highest infrared emissivity of0.91±0.01in8-14μmwaveband was obtained after sintering at1150℃for2h with7.5%CuFe2O4were added. The infrared radiance materialsof Fe2O3/Co3O4co-doped MgO-Al2O3-SiO2system werealso prepared by solid-state reaction method. When the Fe2O3content was30wt%, the Co3O4content was20wt%, the sample had the highest infrared emissivity of0.92±0.01in8-14μmwaveband after sintering at1100℃for2h. High sintering temperature was demanded in the preparation of MgO-Ak2O3-SiO2system materials, which consuming a large number of energy. The highest infrared emissivity of the MgO-Al2O3-SiO2system materials was0.92±0.01, which should be further improved.RE3+(Ce、La、Y) doped cobalt ferrites were prepared by use of the sol-gel auto-combustion method. The sol-gel auto-combustion method was considered to be an energy-efficient way to synthesize the spinel ferrites (CoFe2-xRExO4).It reduced the sintering temperature by more than a half (from more than1000℃to600℃) compared to the traditional solid-state reaction method. Cobalt ferrite powdersvia the sol-gel method, where iron nitrate and cobalt nitrate were used as the original materials and citric acid as the chelating reagent. The pH value of the mixture was adjusted by adding a few drops of ammonia solution. The pH of the starting solution was5, the highest infrared emissivity (about0.91) of the CoFe2O4powders was achieved in the8～14μm waveband.In the RE(Ce, La, Y)-doped cobalt ferrites system, the RE3+content and the sintering temperature were the two crucial factors to influence on the infrared radiation properties of the CoFe2-xRExO4ferrites. In the Ce-doped cobalt ferrites materials, the second phase (CeO2) was inhibited when the Ce3+content (x) did not exceed0.05and the sintering temperature was lower than600℃.The highest infrared emissivity of0.92±0.01was reached from CoFe1.95Ceo.05O4with the treatment of sintering at600℃for2h. In the La-doped cobalt ferrites materials, the reaction between La3+and Fe3+could be effectively suppressed and the second phase (FeLaO3) was inhibited when the La3+content (x) did not exceed0.10and the sintering temperature was lower than600℃.The highest infrared emissivity of0.94±0.01was reached from CoFe1.90Lao.10O4with the treatment of sintering at600℃for2h. In the Y-doped cobalt ferrites materials, the second phase (FeYO3) was inhibited when the Y3+content (x) did not exceed0.20and the sintering temperature was lower than600℃.The highest infrared emissivity of0.95±0.01was reached from CoFe1.8oYo.20O4with the treatment of sintering at600℃for2h.In view of the application of high infrared radiance materials in the alkali liquor evaporation, vertical tube-type falling-film evaporator was designed in this paper and the infrared radiance materials were used as the infrared device in the evaporator. The infrared films were prepared from the infrared powders by using of the rolling method and PTFE was used as the binder. The main component of the vertical tube-type falling-film evaporator were vertical tube, liquor circulating system, heating system and temperature control system. The whole system was tested through experiment. The parameters were optimized, such as:operating temperature, alkali liquor flow, alkali liquor concentration and the adding proportion of PTFE. We also examined the application effect of RE-doped cobalt ferrites on the evaporation. The evaporation efficiency can be reached17%after running60min as the infrared film was prepared from CoFe1.80Y0.20O4ferrites, PTFE adding proportion was1:1.5, operating temperature was350℃, the alkali liquor flow was80L/h and the alkali liquor concentration was30g/L.A series of materials with high infrared emissivity were prepared in this paper and we tried to use this kind of materials in the vertical tube-type falling-film evaporator. The application research on alkali liquor evaporation has filled in gaps in the application of inorganic nonmetallic crystal materials with high infrared radiation in alkali liquor evaporation and realized the simulative study in the laboratory. This study has certain academic value and it will provide guidance to the practical engineering application and the further research. |
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