Department of Mechanical Engineering, 2010 Black Engineering Building, Iowa State University, Ames, IA 50011, USA.
Nanotechnology. 2012 May 11;23(18):185701. doi: 10.1088/0957-4484/23/18/185701. Epub 2012 Apr 13.
Single anatase TiO₂ nanowire is synthesized using the electrospinning technique with the sol-gel method and is suspended over a pre-processed 100 µm-wide TEM grid for further characterization. The diameters of the nanowires fall in the range of 250-400 nm. The transient electrothermal (TET) method is adopted to acquire the voltage-time (U-t) profile of the Ir-coated nanowire under step Joule heating. The intrinsic thermal diffusivity of single anatase TiO₂ nanowires varies from 1.3 to 4.6 × 10⁻⁶ m² s⁻¹, and the thermal conductivity changes distinctly from 1.3 to 5.6 W m⁻¹ K⁻¹, much lower than the value of the bulk counterpart: 8.5 W m⁻¹ K⁻¹. The density and thermal conductivity increase significantly with the diameter, largely because at larger diameters less secondary porosity is left by decomposition of organic composites and their escape from the wire during calcination. The density of TiO₂ nanowires is found to be much lower than that of the bulk counterpart. This is supported by the SEM image of the secondary porous surface. High secondary porosity is observed for TiO₂ nanowires, ranging from 18% to 63%. This very high secondary porosity confirms that the decomposition of PVP content may distort the fibrous matrix and leave vacancies. In addition, the transition from amorphous to anatase phase could also create a porous state due to crystal particle aggregation.
采用静电纺丝技术和溶胶-凝胶法合成了单根锐钛矿 TiO₂ 纳米线，并将其悬浮在预处理的 100 µm 宽 TEM 网格上，以进行进一步的表征。纳米线的直径在 250-400nm 范围内。采用瞬态电热（TET）法在阶跃焦耳加热下获取 Ir 涂层纳米线的电压-时间（U-t）曲线。单根锐钛矿 TiO₂ 纳米线的本征热扩散系数在 1.3 到 4.6×10⁻⁶ m² s⁻¹ 之间变化，热导率从 1.3 到 5.6 W m⁻¹ K⁻¹ 明显变化，远低于体相的热导率：8.5 W m⁻¹ K⁻¹。密度和热导率随直径显著增加，主要是因为在较大直径下，有机复合材料的分解产生的二次孔隙较少，并且在煅烧过程中从纳米线中逸出。TiO₂ 纳米线的密度明显低于体相，这得到了二次多孔表面的 SEM 图像的支持。TiO₂ 纳米线的二次孔隙率很高，范围为 18%至 63%。这种非常高的二次孔隙率证实了 PVP 含量的分解可能会使纤维基质变形并产生空位。此外，由于颗粒聚集，非晶相向锐钛矿相的转变也可能导致多孔状态。
