Rod milling and thermal annealing of graphite: Passing the equilibrium barrier

Abstract

The change in graphitic carbon structure induced by mechanical milling has been monitored by Raman spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction. It is well known that progressive rod milling of graphite results in an increase in structural disorder. Here, it has been found that a milling time of around 80 h is crucial in producing maximum nanocrystallite formation and this affects the nature of the products formed before or after annealing. At about 80 h equilibrium forms and no further production of nanocrystallites is possible although if additional energy is added amorphous carbon begins to form. Annealing produces different nanographitic carbons depending on the milling conditions because the material may be milled to an equilibrium concentration of nanocrystallites or less, or with additional energy transformed further past equilibrium to new product. Linear morphological structures and trace amounts of carbon nanotubes were found on milling for 80 h and annealing, but concentric layers of carbons were observed in samples milled as long as 240 h.