Preliminary Study of Packing of Graphite Encapsulated Nickel Nanoparticles
Date Issued
2007
Date
2007
Author(s)
Tsai, Shao-Wei
DOI
zh-TW
Abstract
Graphite Encapsulated Metal (GEM) nanoparticles is a new spherical composite material with a diameter ranging between 5 and 100 nm. It has a core/shell structure, where the core is metal and the shell is graphite. Having the special structure and nanosizes, GEM has become an interesting research subject for the academic community.
Because they easily aggregate together, nanoparticles can’t compact very well in normal situation. Depends on various materials, it may need more than one thousand centigrade or several GPa to make a high density bulk. In this research, we accidentally find a simple way to make high density GEM bulk via magnetic processing. By measuring the density of GEM bulks and observing the pictures taken by SEM, we estimate the porosity of the bulks is lower than 20%.
The study can be divided two parts: First is to synthesize the high density graphite encapsulated nickel nanoparticles and to find out the possible affecting factors. Then we design a number of experiments based on the possible affecting factors as variable parameters. Second is to derive the possible mechanisms of the formation of the high density graphite encapsulated nickel nanoparticles.
Though it is impossible to directly observe the rearranging and densification processes of GEM particles in a magnetic field, the following four factors may all play an important role: First is acid bath and ultrasonic mixing, which break up the aggregation of GEM, nickel nanoparticles and amorphous carbon, and disperse the particles. Second is when the GEM immersed in methanol, the methanol molecules adsorb on the surface of nanoparticles and decrease the van der Waals forces between them. Third is when the GEM put into an external magnetic filed, the ferromagnetic nickel nanoparticles could slide, rotate, and move themselves into a more compact position. Finally is when the methanol evaporates, and GEM becomes even denser through capillarity forces.
Subjects
石墨包裹奈米鎳晶粒
graphite encapsulated nickel nanoparticles
high density
Type
thesis
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