Electrical discharge assisted mechanical milling in materials processing: formation of nano-structures in carbon and boron.

A novel device for ball milling, incorporating high voltage, low current electrical discharge was constructed and its application for material processing investigated. Recent results of investigations involving spark discharge milling of carbon and boron under various atmospheres and electrical conditions are presented and discussed. Samples including activated carbon, graphite, and crystalline boron powder were given electrical discharge milling treatment under Ar and N2 atmospheres. A range of nano-fragments was observed using transmission electron microscopy. Discharge milling of activated carbon in Ar, with small amounts of Fe powder, was found to promote the formation of multi-walled carbon nanotubes, while milling of the same activated carbon in nitrogen lead to the formation of carbon encapsulated iron nanoparticles. Experiment performed on graphite with Fe, discharge milled in Ar revealed the formation of both graphite nanoparticles and rolled-sheet graphite nanostructures. Milling of boron powder under a high voltage discharge was found to lead to the formation of fragmented particles of boron and unusual boron feather-like nanorods.