热分解法制备纳米WO_3的结构特征及其分散行为研究

以钨酸铵为原料,在350～600℃不同温度下,用热分解法制备了纳米WO3。用透射电子显微镜、X射线衍射与电子衍射并结合热分析法,研究了热分解温度对纳米WO3的粒径大小、形状、晶型的影响,发现钨酸铵在225～375℃吸热分解,在400℃时完全分解为简单六方结构WO3和简单单斜结构WO3两相混合物,简单六方结构WO3在404℃左右向简单单斜结构WO3转变,500℃与600℃热分解产物都是简单单斜结构WO3。WO3粒径随温度升高而增大,分解温度从400℃升至600℃时,WO3粒径从20nm增大到100nm左右。用表面活性剂对纳米WO3进行表面修饰,发现两性型十二烷基二甲基甜菜碱可提高纳米WO3在水溶液与甲苯中的分散稳定性,沉降速度降低50%。

Preparation of Nano-WO3 by Thermal Decomposition and Study of Its Grain Characteristics and Dispersion Behavior

Nano-WO3 was prepared by thermal decomposition of (NH4)2WO4 at different temperures of 350～600 ℃.TEM,XRD,ED and thermal analysis instruments of TG-DTG and DSC were used to study the effect of thermal decomposition process on the nano-WO3 characteristics,such as grain diameter and crystallographic form.It was found that (NH4)2WO4 decomposes to the mixed phases of hexagonal primitive and monoclinic primitive WO3 at 400 ℃,while the thermal decomposition products at 500 ℃ and 600 ℃ all exist in the single crystallographic form of monoclinic primitive WO3,resulting from that the hexagonal primitive WO3 transforms to monoclinic primitive WO3 nearly at 404 ℃.The grain size of the nano-WO3 prepared at different temperatures are all in the range of 20～100 nm.In order to improve the dispersion stability of the nano-WO3 in water/oil systems,cationic and zwitter-ionic surfactant were applied to the dispersion process.It was found that the nano-WO3 modified with zwitter-ionic surfactant of lauryl dimethyl betaine disperses very well in water and toluene through the sedimentation experiment,and its sedimentation vecolity decreases 50% against the unmodified.