Preliminary results of using synthetic diamond and a blown arc to produce graphite encapsulated iron nanoparticles
Date Issued
2006
Date
2006
Author(s)
Chen, Yung-Der
DOI
zh-TW
Abstract
Graphite Encapsulated Metal (GEM) nanoparticle is a new composite
material first found in 1993. GEM has a shell (graphite layers) and core
(metal nanocrystals) structure, and a 10~100 nm size range. Because the
graphite layers can protect the inner metal cores form oxidation and acid
erosion, the new material provides an excellent opportunity to study the
property and behaviors of nanoparticles.
We have been using the modified arc-discharge method to synthesize
GEM for some years, and have come up with some effective processes to
improve the efficiency of the method. For example, by adding methane into
the arc-discharge or by annealing the synthesized raw powder, both processes
can increase the yields of GEM. However, neither process can control the
size distribution of the GEM, i.e., the properties of the powders are not uniform.
To control the sizes of the powder, using a blown-arc may be the best method.
Unfortunately, the blown-arc method will also decrease the production rate
dramatically.
To control the sizes of GEM, a new arc-discharge system with a circular
blown jet was designed and built. The preliminary results show that the sizes
of the Fe-GEM produced in this new system are so small that once exposed to
the air the GEM spontaneously oxidize into iron oxides. Though the
oxidation can be prevented by collecting the GEM into water, the powder will
still oxidize during the acid-bath process.
To maintain an adequate production rate while controlling the sizes of the
GEM, a modified arc-discharge method using synthetic diamond powder as
carbon source (in stead of graphite) was developed. Using diamond carbon
3
source proved to be an effective modification that the amount of the as-made
powder has increased by 50%, and the after acid-bath powder has also
increased by 250%. Because diamond is a metastable phase under ordinary
temperature and pressure, it dissolved into the metal much easier than graphite.
As a result that the carbon distributes more evenly in the melting metal, and
thus the carbon vapor mixes more uniformly with the metal vapor during the
evaporation.
Subjects
石墨
包裹
鐵
graphite
encapsulate
iron
Type
thesis
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