Magnetic packing of graphite encapsulated nickel nanoparticles

Graphite encapsulated metal nanoparticles (GEM) have a very special core-and-shell spherical structure (5-100 nm in diameter) The core is metal nanoparticle and the shell consists of several to over ten layers of graphitic sheets. Because the outer shell protects the inner metal nanoparticles, the materials remain stable in strong acid as well as at high temperature in an oxygen-free environment Nanoparticles are usually very difficult to compress: with the ferromagnetic metal core of NI-GEM, one would expect its compaction to be even more difficult. In this work, however, a new and simple magnetic packing method was developed, by which >90% dense Ni-GEM bulk can be produced without going through any of the conventional compaction procedures The as-made GEM powder will first be purified via an acid-bath to remove any poorly encapsulated Ni particles Then the GEM is dispersed in methanol, and subjected to a strong magnetic field After the entire amount of methanol has been evaporated, many small pieces of high-density bulk GEM material can be obtained. Preliminary results show there are several important factors which affect the final packing density of bulk Ni-GEM, the type of dispersant, the dispersant's evaporation rate and the magnetic field intensity. (C) 2009 Elsevier B V All rights reserved