以镍为催化剂,通过控制碳源气体乙炔的流速,在1 013 K-1 053 K温度下,制备了纤维截面形状在生长过程中由扁平形变为圆形的螺旋炭纤维,同时螺旋直径也相应的由4.2 μm变化为6.0 μm,这种变截面螺旋炭纤维的发现,为微机械系统提供了一种新型弹簧.提出了变截面螺旋炭纤维的生长机理,认为催化剂颗粒的各向异性不仅影响螺旋炭纤维螺径的大小,还影响纤维的截面形状.随着生长过程中反应条件的改变,催化剂各向异性也发生改变,长方形催化剂既可以生长扁平形也可以生长圆形截面螺旋形炭纤维,但是立方形催化剂只能生长圆形截面螺旋形炭纤维.该机制的提出不仅有助于加深对双螺旋炭纤维生长本质的认识,还对指导螺旋形炭纤维的控制生长具有重要意义.
Carbon microcoils (CMCs) with a fiber cross-section changing from flat to circular along with a coil diameter changing from 4.2 to 6.0 μm, which may develop a novel spring for micromechanical systems, were obtained by controlling the acetylene flow rate using Ni catalyst at a temperature of 1 013-1 053 K. A growth model for these changes was proposed in which catalytic anisotropy is considered to be the possible factor changing the fiber cross-section shape of the CMCs. Owing to the change of catalytic anisotropy caused by reaction conditions, the same slender catalyst can produce both flat CMCs and circular CMCs depending on its relative orientation to the fiber axis. A cubic Ni catalyst can only produce a circular CMC, and can only change the coil diameter upon changing the reaction conditions. The model will give more insight into the formation of CMCs and provide information on the controlled synthesis of CMCs and carbon fibers.
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