Microstructure and Reaction Mechanism during Fluorination of Isotropic Pitch

Abstract

Isotropic pitch fluorides were prepared via the reaction of isotropic pitch with gas mixture containing F2 and N2 in a rotation nickel reactor. Isotropic pitch fluorides were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and elemental analysis. The results showed that the interlayer spacing of the resultant materials dramatically increase from 0.345 nm of the isotropic pitch to the range 0.643 nm to 0.798 nm. Further studies on the diversity of the functional groups indicated that the whole reaction process was composed of two steps, namely, diffusion of F2 inside the voids among isotropic pitch molecules on the surface of the particles and fluorination. The two processes interacted with each other and jointly determined the apparent speed of the reaction. The scanning electron microscopic micrographs showed that the larger bulk of isotropic pitch was gradually desquamated and became small particles, which can be attributed to the crack resulting from the volume expansion of the surface molecules of the isotropic pitch fluorides during the reaction. The final isotropic pitch fluorides were fine particles with diameters of less than 1 µm.