科研之友
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摘要
Graphite encapsulated metal nickel (Ni-GEM) nanoparticles are a relatively new material. With an inner ferromagnetic metal core and several layers of outer graphitic shells, Ni-GEM (5-100 nm in diameter) can survive in severe environments and still preserve its nanocrystalline properties. The as-made Ni-GEM particles agglomerate due to both the van der Waals and strong magnetic forces between the nanoparticles. To reduce the negative influence of severe agglomeration, several dispersants were added and tested for effective dispersion; among these, one non-ionic surfactant, nonyl phenol ethoxylate (NP-9), showed the best results. In addition, two different sized Ni-GEM (23 nm and 14 nm in diameter) were synthesized by using a modified tungsten arc-discharge method in this research; the strength of the saturated magnetization was decreased from 30-40 emg/g to 11.6 emg/g for the smaller 14 nm Ni-GEM particles. Based on three separate test results of steady-stage, transient, and dynamic tests on a rheometer, the 14 nm Ni-GEM in a 40% NP-9 colloid showed the best dispersive property. Preliminary results showed that the key to the success of dispersion is the reduction of the average particle sizes of GEM, whereby the magnetic forces could be decreased and the effective surface areas for the surfactant NP-9 increased. Based on this research, it was found that the rheological measurements, which are closely related to the surfactant concentrations, particle sizes and internal structure development, can be efficiently and conveniently used to detect the various behaviors of a GEM-dispersed colloidal system.
- 出版日期2011-2
