© Korean Powder Metallurgy Institute 1189 -2006 POWDER METALLURGY World Congress PC09-W-13 PC09-W-14
The Preparation of Chemically Functionalized Magnetic
Jeong Ho Chang1, Young Keun Jeong1, Moo Eon Park1
1
Nanomaterials Application Division, Korea Institute of Ceramic Engineering and Technology, Korea
This work reported the how to be a chemically functionalized magnetic nanoparticles by the self-assembly technique and their characterization including a magnetic properties and electrochemical properties. Two kinds of magnetic nanoparticles such as maghemite and magnetite were synthesized, and then coated by silica comprising a controlled coated thickness as a function of silica precursor concentration from 10 to 200 nm. Several functional groups such as amine, halides, carboxyl, and aldehyde group were introduced on the silica coated magnetic nanoparticles. In case of amino-functionalization, the alkyl chain length was very imported because the amine group in the longer alkyl chain length could be easily interacted with hydroxyl group in the surface. This phenomenon was detected by the solid state 29Si and 13C NMR with silica nanoparticles. As increase a coating thickness, the particle size was increased, but the magnetic strength, pore volume, and surface areas were decreased regularly. The CV red-ox curve showed the reduction and oxidation status of the magnetic nanoparticle and silica coated magnetic nanoparticles.
Effects of Particle Size and Shape on Permeability and Coercivity
of Nanocrystalline Soft Magnetic Alloy Cores
Byoung-Gi Moon1, Keun Yong Sohn2, Won-Wook Park2 and Taek-Dong Lee3 1
Advanced Materials Research Division, Korea Institute of Machinery and Materials
2
School of Nano Engineering, Inje University
3
Dept. of Materials Science and Engineering, Korea Advanced Institute of Science and Technology
The soft magnetic properties of FeSiB-based nanocrystalline alloys are significantly changed during the fabrication process of induction cores, including the fragmentation of rapidly solidified ribbons by milling. Enhancing the permeability of the P/M processed cores and minimizing the loss have been an issue. The soft magnetic behavior is directly related to the size and shape of fragmented particles, and the size of grains within them. Residual stress generated during mechanical forming of cores is another factor to be considered. In this paper, the variations of initial permeability and coercivity of Fe73Si16B7Nb3Cu1 nanocrystalline alloy cores on milling time were investigated. Amorphous ribbons with a thickness of
~30 µm prepared by planar flow casting process were pulverized and ball-milled after crystallization heat treatment at 550℃ for 1 hour. The powder was classified and subsequently consolidated into a toroidal shape of cores at a pressure of 18 ton/cm2. Results showed that ball milling of the flake shape of pulverized powder for 2~4 hours improved the density and
initial permeability of consolidated cores. The intrinsic coercivity of the particles decreased as well. The coercivity of fine powders smaller than 45 m significantly increased with increasing milling time, although their grain sizes were almost same. It resulted from the demagnetization effect, which increases with increasing the fraction of finer particles close to spherical shape.
