Synthesis of Expanded Graphite Flakes by the Submerged Carbon Arc in Oleum

Abstract

Graphite layers expansion and exfoliation can be achieved in a couple of minutes by arcing graphite electrodes submerged in oleum (fuming sulphuric acid with 30% SO3). Not only do the electrodes submerged in oleum expand dramatically, but also a fine dispersion of graphite particles in oleum can be obtained. The method proposed is extremely effective and overcomes the conventional methods of graphite hydrogensulphate preparation, which require very long swelling times (hours) of graphite in concentrated sulphuric acid. The dispersion of graphite particles derived from arcing graphite electrodes in oleum has been studied in great detail with electronic absorption spectroscopy in the UV-VIS and in the NIR. Unfortunately, the workup adopted to remove the excess of oleum from the exfoliated graphite particles and from the swelled electrodes causes a partial restacking and clumping of the particles and a partial collapse of the swelled graphite electrodes. After the workup, the swelled anode and cathode material as well as the graphite dispersion were studied by thermogravimetric analysis as well as by scanning electron microscopy (SEM) and energy dispersive x-ray measurements (EDX). The presence of residual amounts of HSO4 − ions in all matrices has been quantitatively determined and compared with previous results reported in literature.