Polygonization of Vapor-grown Carbon Fibers

Abstract

Vapor-grown carbon fiber (VGCF) is known to have an annual ring texture, and to be one of the most graphitizable carbons. A structural characteristic of VGCSs heat-treated at high temperatures is polygonal appearance. The present paper concetns a study of the polygonization process using a field emission gun type scanning electon microscope. VGCFs examind were prepared from a mixture of benzene and Linz-Donawitz converter gas floating catalytic seeds derived from ferrocene, cobalt acetylacetonate and thiophene. Heat treatments of VGCFs were made at the temperatures between 1900 and 3000°C for 30min. Effects of the heating time on polygonization were investigated at 2300, 2400 and 2500°C by changing it steparese as 5, 30 and 60 min. Surfaces and cross sections of these samples were observed with high fidelity modes. Polygonization of VGCF was found to initiate around 2400°C; the thinner the diameter the lower the heat treatment temperature at which polygonal from appears, It is inferred that the polygonization takes place first at the inside relatively close to hollow tube, and advances outward vertically to the tube axis.