• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.32-39
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• 2011

The present investigation was performed on the die compaction and sintering behavior of Fe micro-nano mixed powder with a mixed binder for powder injection molding. Warm die compaction of the feedstock for simulation of the static injection molding process was conducted using a cylindrical mold of 10 mm diameter at $100^{\circ}C$ under 4MPa. The die compaction of the micro-nanopowder feedstock underwent a uniform molding behavior showing a homogeneous distribution of nanopowders among the micropowders without porosity and distortion. After debinding, the powder compact maintained a uniform structure without crack and distortion, leading to a high green density of 64.2% corresponding to the initial powder loading of 65%. The sintering experiment showed that the micro-nanopowder compact underwent a near full and isotropic densification process during sintering. It was observed that the nanopowders effectively suppressed the growth of micropowder grains during densification process. Conclusively, the use of nanopowder for PIM feedstock might provide a new concept for processing a full density PIM parts with fine microstructure.

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.630-638
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• 2010

The present investigation has been performed on the mixing behavior and microstructural development during fabrication of Fe micro-nano powder feedstock for a micro-powder injection molding process. The mixing experiment using a screw type blender system was conducted to measure the variations of torque and temperature during mixing of Fe powder-binder feedstock with progressive powder loading for various nano-powder compositions up to 25%. It was found that the torque and the temperature required in the mixing of feedstock increased proportionally with increasing cumulative powder loading. Such an increment was larger in the feedstock containing higher content of nano-powder at the same powder loading condition. However, the maximum value was obtained at the nano-powder composition of not 25% but 10%. It was owing to the 'roller bearing effect' of agglomerate type nano-powder acting as lubricant during mixing, consequently leading to the rearrangement of micro-nano powder in the feedstock. It is concluded that the improvement of packing density by rearrangement of nano-powders into interstices of micro-powders is responsible for the maximum powder loading of about 71 vol.% in the nano-powder composition of 25%.

• Journal of the Korean Ceramic Society
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• v.39 no.12
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• pp.1119-1123
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• 2002

Nanostructured spinel NiZn ferrites were prepared by the sol-gel method from metal nitrate raw materials. Analyses by X-ray diffraction and scanning electron microscopy showed the average particle size of NiZn ferrite was under 50 nm. The single phase of NiZn ferrites was obtained by firing at 250${\circ}C$, resulting in nanoparticles exhibiting normal ferrimagnetic behavior. The nanostructured $Ni_{1-X}Zn_XFe_2O_4$ (x=0.0∼1.0) were found to have the cubic spinel structure of which the lattice constants ${\alpha}_2$ increases linearly from 8.339 to 8.427 ${\AA}$ with increasing Zn content x, following Vegard's law, approximately. The saturation magnetization $M_s$ was 48 emu/g for x=0.4 and decreased to 8.0 emu/g for higher Zn contents suggesting the typical ferrimagnetism in mixed spinel ferrites. Pure NiZn ferrite phase substituted by Cu was observed before using the additive but hematite phase was partially appeared at $Ni_{0.2}Zn_{0.2}Cu_{0.6}Fe_2O_4$. On the other hand, the hematite phase in this NiZn Cu ferrite was disappeared after using the additive of acethyl aceton with small amount. The saturation magnetization Ms of $Ni_{0.2}Zn_{0.8-y}Cu_yFe_2O_4$(y=0.2∼0.6) as measured was about 51 emu/g at 77K and 19 emu/g at room temperature, respectively.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2003.10a
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• pp.107-107
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• 2003

• Journal of the Korean Society for Heat Treatment
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• v.22 no.3
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• pp.149-154
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• 2009

Dense $5Cu_{0.6}Fe_{0.4}-Al_2O_3$ composite was consolidated from mechanically synthesized powders by pulsed current activated sintering method within 1 min. $5Cu_{0.6}Fe_{0.4}-Al_2O_3$ powder was synthesized from 3CuO and 2FeAI using the high energy ball milling. Dense $5Cu_{0.6}Fe_{0.4}-Al_2O_3$ with relative density of up to 95% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. Mechanical properties and grain size of the composite were investigated.

• Journal of Powder Materials
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• v.9 no.6
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• pp.381-393
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• 2002

Recent developments in nanocrystalline and nanocomposite rare earth-transition metal magnets are reviewed and emphasis is placed on research work at IFW Dresden. Principal synthesis methods include high energy ball milling, melt spinning, mold casting and hydrogen assisted methods such as reactive milling and hydrogenation-disproportionation-desorption-recombination. These techniques are applied to NdFeB-, PrFeB- and SmCo-type systems with the aim to produce high remanence magnets with high coercivity. Concepts of maximizing the energy density in nanostructured magnets by either inducing a texture via anisotropic HDDR or hot deformation or enhancing the remanence via magnetic exchange coupling are evaluated. With respect to high temperature applications melt spun $Sm(Co_{0.74}Fe_{0.1}Cu_{0.12}Zr_{0.04})_{7.5}$ ribbons were prepared, which showed coercivities of up to 0.53 T at 50$0^{\circ}C$. Partially amorphous $Nd_{60}Fe_xCo_{30-x}Al_{10}(0{\leq}x{\leq}30)$ alloys were prepared by copper mold casting. The effect of transition metal content on the glass-forming ability and the magnetic properties was investigated. The $Nd_{60}Co_{30}Al_{10}$ alloy exhibits an amorphous structure shown by the corresponding diffraction pattern. A small substitution of Co by 2.5 at.% Fe results In the formation of Fe-rich crystallites embedded in the Nd-rich amorphous matrix. The Fe-rich crystallites show hard magnetic behaviour at room temperature with a coercivity value of about 0.4 T, relatively low saturation magnetization and a Curie temperature of 500 K.

• Korean Journal of Materials Research
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• v.14 no.4
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• pp.293-299
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• 2004

Transition metal ions doped $TiO_2$ nanostructured powders were prepared with simply heating aqueous $TiOCl_2$ solutions, contained various metal ions (Ni, Al, Fe, Zr, and Nb) of 1.47 mol% added as metal-chlorides, at $100^{\circ}C$ for 4 hrs by homogeneous precipitation process under suppressing conditions of water vaporization. The characterizations for prepared $TiO_2$ powders were carried out to observe doping of metal ions, their concentrations and microstructures using XRD, UV-VIS (DRS), XPS, SEM, TEM and ICP. Also, photo-oxidative abilities were evaluated by decomposition of 4-chlorophenol (4CP) under ultraviolet light irradiations. No secondary oxide phases were formed in all the $VTiO_2$ powders, showing doping with various transition metal ions. When adding ions ($Ni^{2+}$ or$ Al^{3+ }$ and $Zr^{4+}$ ) having valance states or ionic radii greatly different from those of $Ti^{4+}$ , the $TiO_2$ powders of mixed anatase and rutile phases were formed, whereas in the case of additions of $^Fe{3+ }$ and $Nb^{ 5+}$ as well as no addition of metal ion the powders with pure rutile phase alone were formed. Among the prepared $TiO_2$ powders, Ni$^{2+}$ doped $TiO_2$ powders, containing a small amount of anatase phase, showed excellent photo-oxidative ability in 4CP decomposition because of relative decreases in electron-hole recombination and poisoning of $TiO_2$ surface during the photoreaction.n.