Preparation Of Co Doped TiO₂ And Their Infrared Emissivity And Thermochromic Properties

TiO₂ is an inexpensive,non-toxic,high low light absorbance in the ultraviolet region and high radiation dispersion in the near-infrared region,which has a wide range of areas such as organic pollutants degradation,photocatalysis and self-cleaning materials.With unique spectral reflectance in Visible and Infrared region,TiO₂ also has potential application prospects in aerospace aviation.In recent years,the research on TiO₂ mainly focuses on photocatalytic performance.However,the thermochromic and variable emissivity properties of TiO₂ fillers have not so far been reported.In this paper,the doped oxides Ti_1-xCo_xO were prepared by solid phase synthesis to form an impurity level inside the TiO₂ lattice to achieve the regulation of the TiO₂energy level,thereby improving its macroscopic properties.The doping concentration,calcination temperature,heat treatment time and atmosphere are considered as a single variable to analyze possible factors of the color change and emissivity of the powders,respectively.The main research results are as follows:（1）It is found that all Co doped TiO₂ powders are in good agreement with the tetragonal structured rutile TiO₂ phase.After doping suspension,all samples are green at room temperature.Besides,all the samples can change from green to ivory yellow with the increase of testing temperature from room temperature to 800℃.When cooled back to room temperature,all the samples return to original green color.Meanwhile,the infrared emissivity of the powders decreases firstly and then increases slowly,with a typical U-shaped feature.（2）The heat treatment process has important influence on the band gap,morphology and grain size of Ti_1-xCo_xO powders.The band gap of the doped powders decrease gradually with the increasing of doping concentration and annealing temperature.Therefore,the amount of color change and the amount of variable value in emissivity gradually increase.When the doping concentration is 7%and the heat treatment temperature is 1100℃,the powder has the best discoloration performance and variable values of emissivity.As the heat treatment time is extended,the band gap of TiO₂ is further narrowed,and the discoloration is more sensitive,but the emissivity changes slightly,so the optimal heat treatment time is 10h.The powder has better discoloration and variable emissivity performance when heat treated in air.Through research,the maximum color change of the powder is 8 and the maximum variable value of emissivity is 0.404.（3）The effects of heat treatment on the thermochromic and variable emissivity properties of Co-doped TiO₂ and ZnO-based powders are analyzed and compared.The results shows that the thermochromic and variable emissivity properties of Co doped ZnO are better than that of Co doped ZnO.However,TiO₂-based powders have lower infrared emissivity and are superior in low emissivity performance.