四氧化三铁中空/螺旋纤维的制备及形成机理

Preparation and Formation Mechanism of Magnetite Hollow/Helical Fibers

以柠檬酸铁为原料,利用有机凝胶热分解法在低升温速率下热处理并还原制备了Fe3O4中空/螺旋纤维.通过TG/DTA,XRD和SEM对前驱体纤维热分解过程、产物物相和形貌进行了表征.结果表明,产物主要由80%的中空纤维和20%的螺旋纤维组成,其中中空纤维的直径为6μm左右,壁厚为500 nm.螺旋纤维的直径为6～10μm,螺旋纤维是由具有不同旋向的宽度为4～6μm的带状纤维卷曲而成,带状纤维的外表面壳层均匀密实,其厚度为600 nm左右,而内层疏松且不规则.Fe3O4中空/螺旋纤维是由晶粒尺寸为60 nm左右的纳米颗粒构成,并有少量的介孔.分析了中空纤维和螺旋纤维的形成机理,直径较小的前驱体纤维在热处理过程中内部凝胶向表层迁移收缩形成中空纤维;螺旋纤维是由直径较大的前驱体纤维在热处理过程中产生的强大的热应力导致纤维产生螺旋破裂形成的.

Hollow/helical magnetite fibers were prepared with ferric citrate as the original materials via the organic gel-thermal reduction method under a slow heating rate condition. The thermal decomposition process, structures and morphologies of organic gel-fiber precursors and fibers derived from heat treatment and reduction process were characterized by TG/DTA, XRD and SEM, respectively. The obtained fibers consisted of 80% of hollow fibers and 20% of helical fibers. The diameter of hollow fibers was about 5 μm, and the wall thickness was about 500 nm. The diameter of helical fibers was about 6--10 μm, whieh can be left- or right- handed. The helical structure resulted from coiled belt-like fibers with smooth and dense outer shell, and loose and irregular inner layer, its width and shell thickness were 4--6 p,m and 600 nm, respectively. The hollow/ helical fibers with a few pores on its surface were made up of fine crystalline partieles with a size of 60 nm. The formation mechanism of the hollow and helical fibers was proposed. During the heat treatment, the hollow fibers could be formed when the inner gel of the thinner precursor fibers was separated from the center and contracted to surface. However, the helical fibers could be generated when larger gel fibers were broken helically under thermal stress in the process of gel decomposing and contracting.