An EVS (electrochemical voltage spectroscopy) study for the comparison of graphitization behaviors of two petroleum needle cokes

Abstract

Electrochemical voltage spectroscopy (EVS) was utilized to compare the graphitization tendency of two needle cokes at 2000 to 3000°C. Of the two precursors, the NC-A-1000 has a higher density and lower impurity than NC-B-1000. The polarized optical microscopic pictures revealed that the NC-A-1000 has a flow-type texture whereas the NC-B-1000 a mixed (flow and mosaic) one, indicative of a better molecular ordering in the former. Both the X-ray and SEM (scanning electron microscopy) analysis on the resulting carbons indicated that the NC-A has a higher graphitizability, which likely stems from the higher molecular ordering (mesophase development) in the precursor states. The EVS study also supported the easier graphitization in the NC-A series, where it was found that the onset temperature for graphitization is lower in the NC-A series, and their EVS profiles look closer to those observed with natural graphites. The staging phenomenon involved in the resulting graphitized materials was analyzed by the EVS technique with a high potential resolution. Here, the intensity and location of the discharging EVS peaks was so sensitively affected by the degree of graphitization that it could be used as a probe for estimating the graphitizability. In particular, the peak labeled C in this report decreases in intensity with graphitization and the peak position steadily moves to the negative direction in the potential range of 0.16 to 0.25 V (versus Li/Li+).