• Korean Journal of Materials Research
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• v.10 no.6
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• pp.403-408
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• 2000

The Al-Cr-Zr composite metal powders were prepared by mechanical alloying and consolidated by vacuum hot pressing. The microstructural characteristics and the thermal stability of the MA Al-Cr-Zr alloys were evaluated by means of microhardness measurement, XRD and TEM in order to develop high temperature, high strength aluminum alloys. The mechanical alloying was conducted in attritor with 300rpm for 20 hours. The density of the vacuum hot pressed Al-Cr-Zr alloy reached at 97% of theoretical one. After exposing at $300^{\circ}C$ for 100 hours, there is almost no variation in hardness change of the MA alloys. Even after exposing at $ 500^{\circ}C$ for 100 hours, the hardness of the alloy was decreased within 6% of the initial value. The fine stable $Al_3Zr\;and\; Al_{13}Cr_2$ intermetallics were formed at the stage of consolidation and heat treatment in aluminum matrix. The good thermal stability of the MA Al-Cr-Zr alloy can ab attributed to the role of the dispersoids, inhibiting grain growth of nanocrystalline, and the final grain size after heat treatment was less than 150nm.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.4
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• pp.202-207
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• 2009

Nanocomposite formation of metal-metal oxide systems by mechanical alloying (MA) has been investigated at room temperature. The systems we chose are the $Fe_3O_4$-M (M = AI, Ti), where pure metals are used as reducing agent. It is found that $Fe/Al_2O_3$ and $Fe/TiO_2$ nanocomposite powders in which $Al_2O_3$ and $TiO_2$ are dispersed in ${\alpha}$-Fe matrix with nano-sized grains are obtained by MA of $Fe_3O_4$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the shorter MA time for the nanocomposite formation in $Fe/Al_2O_3$ is due to a large negative heat associated with the chemical reduction of magnetite by aluminum. X-ray diffraction results show that the average grain size of ${\alpha}$-Fe in $Fe/TiO_2$ nanocomposite powders is in the range of 30 nm. The change in magnetic properties also reflects the details of the solid-state reduction of magnetite by pure metals during MA.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.26 no.2
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• pp.225-236
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• 2016

Objectives: Nanomaterials have been used in various fields. As use of nanoproducts is increasing, workers dealing with nanomaterials are also gradually increasing. Exposure assessments for nanomaterials have been carried out for protection of worker's health in workplace. Exposure studies were mainly focused on manufacturing processes, but these studies on after-treatment processes such as refinement, weighing, and packing were insufficient. So, we investigated exposure characteristics of particles during after-treatment processes of $Al_2O_3$ fibers and Ni powders. Methods: Mass-production of Ni powder process was carried out in enclosed capture-type canopy hood. In a developing stage, $Al_2O_3$ was handled with a local ventilation unit. Exposure characteristics of particles were investigated for $Al_2O_3$ fiber and Ni powder processes during the periods of 10:00 to 16:00, 20 May 2014 and 13:00 to 16:00, 21 May 2014, respectively. Three real-time aerosol instruments were utilized in exposure assessment. A scanning mobility particle sizer(SMPS, nanoscan, model 3910, TSI) and an optical particle counter(OPC, portable aerosol spectrometer, model 1.109, Grimm) were used to determine the particle size distribution in the size range of 10-420 nm and $0.25-32{\mu}m$, respectively. In addition, a nanoparticle aerosol monitor(NAM, model 9000, TSI) was used to measure lung-deposited nanoparticle surface area. Membrane filters(isopore membrane filter, pore size of 100 nm) were also used for air sampling for the FE-SEM(model S-5000H, Hitachi) analysis using a personal sampling pump(model GilAir Plus by 2.5 L/min, Gilian). Conclusions: For Ni powder after-treatment process, only 27% increase in particle concentration was found during the process. However, for $Al_2O_3$ fiber after-treatment process, significant exposure(1.56-3.34 times) was observed during the process.

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.64-69
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• 2006

Cathode materials of Al-doped $Li(Ni_{1/3}Co_{1/3}Mn_{1/3-x}Al_x)O_2$ (x=0.0, 0.005, 0.01 0.05) for lithium ion batteries were synthesized with ultra-sonic spray pyrolysis method and single-step heat treatment. No secondary phases were found in all synthesized powders. The intensity ratio of $I_{003}\;to\;I_{104}$, however, slightly decreased and the particle size increased with the Al contents. The cells with bare, 0.5 and 1.0 at% Al-doped powders showed the initial discharge capacities of 182, 180 and $184mAhg^{-1}$ in a voltage range of $3.0\sim4.5V$ at 1C rate, and the capacity retentions of 81, 77 and 78% at the end of 30 cycles, respectively. But in the voltage range of $3.0\sim4.6V$, the Al-doping significantly enhanced the cycle stability. For example, the discharge capacity after 50 cycles was maintained to 70% in the 0.5 at% Al-doped sample compared to only 30% in no doped sample. The improvement of the cycle stability was thought to be due to $Mn^{3+}$ ion decrease as the Al doping from the XPS analysis results.

• Resources Recycling
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• v.20 no.4
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• pp.36-45
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• 2011

The recovery of platinum group metals (PGMs) from the leach solution of spent auto-catalyst and the wash solution of the leach residue was investigated in the laboratory scale experiments by the cementation process using metal powders as the reductant. In this study, the effect of Al, Mg and Zn powders on the cementation process was particularly examined. Aluminum powder was selected as the most suitable reductant for the cementation of PGMs. At the cementation time of 10 minute under the aluminium stoichimetric amount of 19.3 and the reaction temperature of $50{\sim}60^{\circ}C$, the recovery of platinum group metals from the leach solution of the spent auto-catalyst was found to be 99.3%, 99.4%, 90.2% for Pt, Pd and Rh, respectively. Under the same conditions with the aluminium stoichimetric amount of 45, the recovery of platinum group metals from the wash solution of the leach residue of spent catalyst was observed to be 97%, 97% and 90% for Pt, Pd and Rh, respectively. In addition, it was possible to upgrade the platinum group metals in the precipitates obtained from the cementation process by about 10% through the removal of metal impurities by the nitric acid leaching at ambient temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.645-650
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• 1998

Alumina- and yttria-coated SiC powder was prepared by the surface-induced precipitation method, and sintered properties of silicon carbide prepared from this powder were investigated. After a well dispersion of SiC powders in the aqueous solution of $Al_2(SO_4)_3$ and $Y_2(SO_4)_3$, the mixed precursors of aluminum hydroxide, aluminum carbonate, yttrium hydroxide, and yttrium carbonate were precipitated on the surfaces of SiC particles through the hydrolysis reaction of urea. SiC specimens with alumina and yttria exhibit, 97.8% of theoretical density after the sintering at $1900^{\circ}C$ for 2 hrs. During annealing at $2000^{\circ}C$, $\beta$longrightarrow$\alpha$ phase transformation of SiC had taken place and resulted with a rodlike microstructure. Toughness of sintered SiC was enhanced by crack deflection around the rodlike grains. In case of annealing less than that of 3 hr, the fracture toughness of SiC was slightly improved with increasing the amount of sintering aid. However, annealed specimens for a long time showed constant fracture toughness even though the amount of sintering aid increased. It is resulted that the main factor for toughening in annealed SiC for a long time is the pullout effect of rodlike grains during the propagation of cracks, and the amount of sintering aids is less effective on the fracture toughness of SiC.

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.733-740
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• 2016

$Al_2O_3$ nanosol dispersed under ethanol or N-Methyl-2-pyrrolidone(NMP) was studied and optimized with various dispersion factors and by utilizing the silane modification method. The two kinds of $Al_2O_3$ powders used were prepared by thermal decomposition method from aluminum ammonium sulfate$(AlNH_4(SO_4)_2)$ while controlling the calcination temperature. $Al_2O_3$ sol was prepared under ethanol solvent by using a batch-type bead mill. The dispersion properties of the $Al_2O_3$ sol have a close relationship to the dispersion factors such as the pH, the amount of acid additive(nitric acid, acetic acid), the milling time, and the size and combination of zirconia beads. Especially, $Al_2O_3$ sol added 4 wt% acetic acid was found to maintain the dispersion stability while its solid concentration increased to 15 wt%, this stability maintenance was the result of the electrostatic and steric repulsion of acetic acid molecules adsorbed on the surface of the $Al_2O_3$ particles. In order to observe the dispersion property of $Al_2O_3$ sol under NMP solvent, $Al_2O_3$ sol dispersed under ethanol solvent was modified and solvent-exchanged with N-Phenyl-(3-aminopropyl)trimethoxy silane(APTMS) through a binary solvent system. Characterization of the $Al_2O_3$ powder and the nanosol was observed by XRD, SEM, ICP, FT-IR, TGA, Particles size analysis, etc.

• KIEE International Transactions on Electrophysics and Applications
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• v.2C no.6
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• pp.314-320
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• 2002

Three different ZnO nanomaterials (nanobelts, nanorods, and nanowires) were synthesized at 138$0^{\circ}C$ from ball-milled ZnO powders by a thermal evaporation procedure with an argon carrier gas without any catalysts. Transmission electron microscopy (TEM) revealed that the ZnO nanobelts are single crystalline with the growth direction perpendicular to the (010) lattice plane, and that the ZnO nanorods and nanowires are single crystalline with the growth directions perpendicular to the (001) and (110) lattice Planes, respectively. In cathodoluminescence (CL), the energy Position of the near band-edge (NBE) peak is 3.280 eV for the 100-, 250-, and 500-nm thick nanobelts, 3.262 eV for the 100- and 250-nm thick nanorods, and 3.237 eV for the 500-nm thick nanorods. The synthesized ZnO nanorods were coated conformally with aluminum oxide (Al$_2$O$_3$) material by atomic layer deposition (ALD). $Al_2$O$_3$films were then deposited on these ZnO nanorods by ALD at a substrate temperature of 300 $^{\circ}C$ using trimethylaluminum (TMA) and distilled water ($H_2O$). Transmission electron microscopy (TEM) images of the deposited ZnO nanorods revealed that 40nm-thick $Al_2$O$_3$ cylindrical shells surround the ZnO nanorods.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.1-11
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• 1996

Mechanical alloying is an effective process to finely distribute inert dispersoids in an Al-TM(TM is a transition metal) system. It has been considered that high melting point aluminides are formed by precipitation from supersaturated Al(Ti) powder. This analysis is based on the fact that much higher content of TM than the solubioity can be dissolved in alpha aluminum during the high energy ball milling. Thus, decomposition behavior of Ti in the Al(Ti) was considered very important. But it is confirmed that the higher portion of Ti than Al(Ti) solid solution is existed as nano-sized Ti particles in the MA powders by high energy ball nilling from the XRD spectrum and TEM analysis in this study. Therefore, the role of undissolved TM particles affect the formation of aluminides should be suitably considered. In this study, we present experimental observation on the formation of $Al_3Ti$ fron mechanical alloyed Al-Ti alloys in the hyperperitectic region. This study showed that, in the mechanically alloyed Al-20wt%Ti specimen, intermediate phase of cubic $Al_3Ti$ and tetragonal $Al_{24}Ti_8$ formed at $300{\sim}400^{\circ}C$ and $400{\sim}500^{\circ}C$, respectively, before the MA state reaches to equilibrium at higher temperatures. The formation behavior of $Ll_2-Al_3Ti$ is interpreted by interdiffusion of Al and Ti in solid state based on the fact that large amount of nano-sized Ti particles exist in the milled powder. Present analysis indicated undissolved Ti particles of nanosize should have played an important role initiation the formation of $Al_3Ti$ phase during annealing.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.441-442
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• 2008

For this study, Yttrium aluminum garnet (YAG) particles co-doped with $Ce^{3+}$ and $Eu^{3+}$ were prepared via the combustion process using the 1:1 ratio of metal ions to reagents. The characteristics of the synthesized nano powder were investigated by means of X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and photoluminescence (PL). The various YAG peaks, with the (420) main peak, appeared at all Eu concentrationin XRD patterns. The YAG phase crystallized with results that are in good agreement with the JCPDS diffraction file 33-0040. The SEM image showed that the resulting YAG:Ce,Eu powders had uniform sizes and good homogeneity. The grain size was about 50nm. The photoluminescence spectra of the YAG:Ce,Eu nanoparticles were investigated to determine the energy level of electron transition related to luminescence processes. It was composed a broad band of $Ce^{3+}$ activator into the weak line peak of $Eu^{3+}$ in YAG host. The PL intensity of $Ce^{3+}$ has the wavelengths of 480-650 nm and The PL intensity of $Eu^{3+}$ has main peak at 590nm.