The influence of the composition of atmosphere on the mechanisms of degradation of graphite in planetary ball millers

Abstract

This study focuses on the degradation process of graphite in a planetary ball miller. It is shown that this degradation is only related to the milling mode. The sliding mode is very gentle toward the graphite structure whereas the shock milling mode leads to the quick degradation of the graphite structure producing poorly organized nanoparticles. Nevertheless, the milling mode is not determined by the ball miller rotation speed but by the ability of graphite to form a lubricating layer. The development of this lubricating layer in only possible in presence of oxygen which annihilates the reactive sites created during milling by forming oxygen groups. In this case, the sliding mode predominates. When the oxygen disappears or under inert atmosphere, the reactive sites stick to the ball surface, destroying the graphite lubricating layer and resulting in shock milling mode. This explains the link between the milling atmosphere and the graphite structure evolution in planetary ball millers. This also explains why the graphite structure evolution is far less sensitive toward environment in a vibratory ball miller in which the sliding milling mode is not possible.