• Bulletin of the Korean Chemical Society
• /
• v.18 no.6
• /
• pp.612-618
• /
• 1997

$LiMn_2O_4$ powders were prepared by burning and subsequent calcination of PEG-metal nitrate precursor. After the burning stage of the precursor, some minor phases such as $Mn_2O_3$ (or $Mn_3O_4$), MnO, and carbonate were formed and single phases of $LiMn_2O_4$ were obtained by further calcinations above 400 ℃. From thermal analysis of the precursor, a violent thermal decomposition, which was indicated by a drastic weight loss accompanied by a sharp and strong exothermic peak, was observed and probably caused by an oxidation-reduction reaction between oxidizer and fuel. The formation of the minor phases could be explained in terms of the burning behavior of the precursor by employing valence concepts of propellant chemistry. The calcined powders were composed of submicron-sized but highly agglomerated particles and showed very broad particle size distribution.

• Journal of Magnetics
• /
• v.12 no.1
• /
• pp.49-52
• /
• 2007

We investigated annealing effect of microforged powders on magnetic properties and electromagnetic absorption behaviors for ferromagnetic Fe-Cr metal alloy powder-polymer composites. The coercive properties greatly decreased with annealing temperature and the magnetic permeability had significantly increased after microforging and subsequent annealing treatment, due to a reduction in lattice strain of the microforged powders. The power loss in the far field regime also had greatly increased after microforging and subsequent annealing treatment in frequency range from 50 MHz to 6 GHz. As a result, the electromagnetic absorption of ferromagnetic Fe-Cr alloy metal powder-polymer composites was highly improved because of the relaxation of the internal strain during annealing process.

• Korean Journal of Materials Research
• /
• v.22 no.2
• /
• pp.78-81
• /
• 2012

$Y_2O_3$ nanomaterials have been widely used in transparent ceramics and luminescent devices. Recently, many studies have focused on controlling the size and morphology of $Y_2O_3$ in order to obtain better material performance. $Y_2O_3$ powders were prepared under a modified solvothermal condition involving precipitation from metal nitrates with aqueous ammonium hydroxide. The powders were obtained at temperatures at $250^{\circ}C$ after a 6h process. The properties of the $Y_2O_3$ powders were studied as a function of the solvent ratio. The synthesis of $Y_2O_3$ crystalline particles is possible under a modified solvothermal condition in a water/ethylene glycol solution. Solvothermal processing condition parameters including the pH, reaction temperature and solvent ratio, have significant effects on the formation, phase component, morphology and particle size of yttria powders. Ethylene glycol is a versatile, widely used, inexpensive, and safe capping organic molecule for uniform nanoparticles besides as a solvent. The characterization of the synthesized Y2O3 powders were studied by XRD, SEM (FE-SEM) and TG/DSC. An X-ray diffraction analysis of the synthesized powders indicated the formation of the $Y_2O_3$ cubic structure upon calcination. The average crystalline sizes and distribution of the synthesized $Y_2O_3$ powders was less than 2 um and broad, respectively. The synthesized particles were spherical and hexagonal in shape. The morphology of the synthesized powders changed with the water and ethylene glycol ratio. The average size and shape of the synthesized particles could be controlled by adjusting the solvent ratio.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2001.11a
• /
• pp.58-59
• /
• 2001

• Journal of Powder Materials
• /
• v.22 no.2
• /
• pp.138-145
• /
• 2015

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2004.11a
• /
• pp.82-83
• /
• 2004

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2002.04b
• /
• pp.51-51
• /
• 2002

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2002.11a
• /
• pp.149-149
• /
• 2002

• Proceedings of the Korean Magnestics Society Conference
• /
• 2003.06a
• /
• pp.94-95
• /
• 2003

• Journal of Powder Materials
• /
• v.15 no.4
• /
• pp.285-291
• /
• 2008

Fe based ($Fe_{68.2}C_{5.9}Si_{3.5}B_{6.7}P_{9.6}Cr_{2.1}Mo_{2.0}Al_{2.0}$) amorphous powder were produced by a gas atomization process, and then ductile Cu powder fabricated by the electric explosion of wire(EEW) were mixed in the liquid (methanol) consecutively. The Fe-based amorphous - nanometallic Cu composite powders were compacted by a spark plasma sintering (SPS) processes. The nano-sized Cu powders of ${\sim}\;nm$200 produced by EEW in the methanol were mixed and well coated with the atomized Fe amorphous powders through the simple drying process on the hot plate. The relative density of the compacts obtained by the SPS showed over 98% and its hardness was also found to reach over 1100 Hv.