Dispersion of the Graphite Encapsulated Nickel Nanocrystals with Different Particle Sizes in the NP-9 Colloidal System
Date Issued
2006
Date
2006
Author(s)
Li, Shang-Shih
DOI
zh-TW
Abstract
Graphite encapsulated metal (GEM) nanoparticles is a relatively new material. With an inner ferromagnetic metal core and several layers of outer graphitic shells, GEM (1-100 nm in diameter) can survive in severe environments and still preserve its nanocrystalline properties. GEM has many potential applications, and some of which require dispersive particles, e.g. as a dispersive catalyst on a substrate when making carbon nanotubes; yet before this type of applications could ever become reality one major problem must be solved. The problem is the severe agglomeration of the GEM nanoparticles, which is due to both the van der Waal’s forces among the particles and the strong magnetic forces of their ferromagnetic cores. Because the sizes of agglomerated particles are much larger than nanometer scale, the characteristic properties of nanoparticles, such as high surface to volume ratio and better absorption, will be lost.
To effectively disperse the GEM nanoparticles, many organic solvents such as methanol, oleic acid and acetone had been used but with little success. The best results came when a non-ionic surfactant – nonylphenol ethoxylate (NP-9) – was used, combined with an improved synthesis technique to control the average particle sizes by adjusting total pressure, that GEM nanoparticles uniformly suspended in NP9 solution and formed a colloid. Colloids are distinguished from true solutions by the presence of particles that are too small to be observed under a microscope yet are much larger than common molecules.
The viscosity of GEM colloids of various weight percentage of NP-9, with fixed temperature and pH, were analyzed by a rheometer. The viscosity apparently decreases with the particle size of GEM. In addition, the solution becomes saturated jelly-like substance as the weight percentage of NP-9 is equal to 40%-50%. Preliminary results show that the key of success is to reduce the average particle sizes of GEM, e.g. from 25 nm to 14 nm such as in this work, thus minimize the magnetic interaction between GEM and increase the effective reaction surface area with surfactant NP-9. Other factors such as temperature and pH value will be included in future experiments.
Subjects
分散
石墨包裹金屬晶粒
膠體系統
界面活性劑
dispersion
graphite encapsulated metal
colloidal system
surfactant
Type
thesis
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