• Korean Journal of Materials Research
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• v.21 no.3
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• pp.168-173
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• 2011

Precipitation of the ordered icosahedral quasicrystal in Mg-6wt%Zn-1wt%Y alloy has been characterized by transmission electron microscopy observations. The lamellar-type icosahedral qusicrystal phases (I-phase) with the face-centered icosahedral (FCI) structure are observed in alloy after solution treatment at $550^{\circ}C$. In the alloy annealed at $400^{\circ}C$, polygon-shaped I-phases are observed in the ${\alpha}$-Mg matrix. The interfaces of the I-phase with the matrix are facetted and the facets are on five-fold and two- fold plane of the I-phase. The orientation relationship of the I-phase with the matrix is determined to be $[I5]_I//[001]_{Mg}$, $(2f)_I//(2\overline{1}0)_{Mg}$ and $[I2]_I//[311]_{Mg}$, $(5f)_I//(0\overline{1}1)_{Mg}$. The icosahedral grains are occasionally found to be twinned with one of the five-fold axis as the twin axis. The twin boundaries appear to be fairly straight and perpendicular to the fivefold twin axis. The icosahedral twin can be expressed as a rotation of $63.4^{\circ}$ or $116.62^{\circ}$ around two fold zone axis.

• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2293-2298
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• 2010

Focused electrospray (FES) deposition method is presented for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. FES ion optics consists of two cylindrical focusing electrodes capped with a truncated conical electrode through which an electrospray emitter passes along the cylindrical axis. A spray of charged droplets is focused onto a sample well on a MALDI target plate under atmospheric pressure. The shape and size distributions of matrix crystals are visualized by scanning electron microscope and the mass spectra are obtained by time-of-flight mass spectrometry. Angiotensin II, bradykinin, and substance P are used as test samples, while $\alpha$-cyano-4-hydroxycinnamic acid and dihydroxybenzoic acid are employed as matrices. FES of a sample/matrix mixture produces fine crystal grains on a 1-3 mm spot and reproducibly yields the mass spectra with little shot-to-shot and spot-to-spot variations. Although FES greatly stabilizes the signals, the space charge due to matrix ions limits the detection sensitivity of peptides. To avoid the space charge problem, we adopted a dual FES/FES mode, which separately deposits matrix and sample by FES in sequence. The dual FES/FES mode reaches the detection sensitivity of 0.88 amol, enabling ultrasensitive of peptides by homogeneously depositing matrix and sample under atmospheric pressure.

• Resources Recycling
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• v.7 no.4
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• pp.50-54
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• 1998

In order to obtain desired electromagnetic propertieι high initial permeability and good frequency dependance of initial p permeability, the adding effects of sevral seeds were experimented in Mn-Zn ferrite system. As adding seed grams, calcined at sintering temperature, abnormal grains were disappeared clearly but the density and the initial permcability of sintered Mn-Zn ferrite body were decreased. On the contrary, in case of adding seed rains which were calcined below the calcination temperatnre of matrix particle, abnormal grains remained but the initial permeability was increas$\xi$d with proper s$\xi$ed content. W With proper seed content, the initial permeability was increased by 10-20% but tbe $\alpha$ltoff frequency was not changed.

• Journal of Powder Materials
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• v.8 no.3
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• pp.210-213
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• 2001

$Si_3N_4$/TiN nano/nano-type composites were successfully fabricated by the combination of a mechano-chemical grinding (MCG) method and a short time sintering process, and their wear resistance was evaluated. Powder mixtures of $\alpha-Si_3N_4$and Ti were prepared using mechano-chemical grinding process and the resulting nanocomposite powder mixtures were consolidated using pulsed electric current sintering (PECS). TEM observation showed that the nano/nano-type composites consisted of homogeneous and very fine matrix grains with the size less than 100 nm. The obtained $Si_3N_4$-based nano/nano-type showed high wear resistance and electric discharge machinability.

• Journal of Powder Materials
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• v.11 no.3
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• pp.247-252
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• 2004

Recently, it has been found that mechanical alloying (MA) facilitates the nanocomposites formation of metal-metal oxide systems through solid-state reduction during ball milling. In this work, we studied the MA effect of Fe$_{3}$O$_{4}$-M (M = Al, Ti) systems, where pure metals are used as reducing agents. It is found that composite powders in which $Al_{2}$O$_{3}$ and TiO$_{2}$ are dispersed in $\alpha$-Fe matrix with nano-sized grains are obtained by mechanical alloying of Fe$_{3}$O$_{4}$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the large negative heat associated with the chemical reduction of magnetite by aluminum is responsible for the shorter MA time for composite powder formation in Fe$_{3}$O$_{4}$-Al system. X-ray diffraction results show that the reduction of magnetite by Al and Ti if a relatively simple reaction, involving one intermediate phase of FeAl$_{2}$O$_{4}$ or Fe$_{3}$Ti$_{3}$O$_{10}$. The average grain size of $\alpha$-Fe in Fe-TiO$_{2}$ composite powders is in the range of 30 nm. From magnetic measurement, we can also obtain indirect information about the details of the solid-state reduction process during MA.

• Metals and materials international
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• v.24 no.6
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• pp.1359-1368
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• 2018

The mechanical properties and microstructure evolution of Mg-8Li-3Al-1Y alloy undergoing different rolling processes were systematically investigated. X-ray diffraction, optical microscope, scanning electron microscopy, transmission electron microscopy as well as electron backscattered diffraction were used for tracking the microstructure evolution. Tensile testing was employed to characterize the mechanical properties. After hot rolling, the $MgLi_2Al$ precipitated in ${\beta}-Li$ matrix due to the transformation reaction: ${\beta}-Li{\rightarrow}{\beta}-Li+MgLi_2Al+{\alpha}-Mg$. As for the alloy subjected to annealed hot rolling, ${\beta}-Li$ phase was clearly recrystallized while recrystallization rarely occurred in ${\alpha}-Mg$ phase. With regard to the microstructure undergoing cold rolling, plenty of dislocations and dislocation walls were easily observed. In addition, the microstructure of alloys subjected to annealed cold rolling revealed the formation of new fresh ${\alpha}-Mg$ grains in ${\beta}-Li$ phase due to the precipitation reaction. The mechanical properties and fracture modes of Mg-8Li-3Al-1Y alloys can be effectively tuned by different rolling processes.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.4
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• pp.552-557
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• 1996

Microstructural development of $Si_3N_4$/20 vol% SiC nanocomposites doped 2 wt% $Al_2O_3$ and 6 wt% $Y_2O_3$ as sintering additives were analyzed by sintering interruption. Density of samples was significantly increased between $1500^{\circ}C$ and $1700^{\circ}C$, and near full density was achieved at $1800^{\circ}C$. Transformation rate from $\alpha-Si_3N_4$ to $\betha-Si_3N_4$ was increased at $1700^{\circ}C$ and $1800^{\circ}C$, and then elongated matrix grains were appeared. Small size SiC particles had suppressive effect on densification rate and transformation of $Si_3N_4$ phase.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.405-411
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• 2001

Compacts of a mixture of fine $\alpha$-Si$_3$N$_4$powders, 6% $Y_2$O$_3$and 1% $Al_2$O$_3$were attrition milled time on phase and microstructural development in silicon nitride ceramics. The sintered surface and the interior showed different behaviors in phase and microstructral developments. Increased oxygen content with increased milling time of powder mixture leads to the formation of Si$_2$$N_2$O phase at temperatures as low as 155$0^{\circ}C$. Si$_2$$N_2$O is stable in the interior of the samples but unstable in the surface region of the specimen sintered at higher temperature. This results in a duplex structure where the interior consists of Si$_2$$N_2$O grains dispersed in $\beta$-Si$_3$N$_4$matrix and a surface which contains only $\beta$-Si$_3$N$_4$. The alpha to beta phase transformation and the microstructural development are shown to be influenced by the formation and decomposition of the Si$_2$$N_2$O.

• 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.

• Korean Journal of Metals and Materials
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• v.50 no.10
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• pp.711-720
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• 2012

In this study, the effect of aging treatment on the microstructure and tensile properties of AZ61-xPd (x = 0, 1 and 2 wt%) alloys were investigated. The microstructure of as-cast AZ61-xPd alloys mainly consisted of ${\alpha}-Mg$, $Mg_{17}Al_{12}$ and $Al_4Pd$ phases. After solution treatment, most of the $Mg_{17}Al_{12}$ phases were dissolved into the Mg matrix. Thereafter, $Mg_{17}Al_{12}$ phases were finely formed and distributed near thermally stable $Al_4Pd$ phases and inside the grains through aging treatment at $220^{\circ}C$ during 88 hours. With the aging at $220^{\circ}C$, the peak aged AZ61-xPd alloys showed higher hardness than as-cast and solution treated AZ61-xPd alloys. In particular, the AZ61-1Pd alloy was optimized due to refined $Mg_{17}Al_{12}$ and $Al_4Pd$ phases. Further, the peak aging time was reduced with increasing Pd addition (>1 wt%). Tensile strength was increased by Pd addition at $25^{\circ}C$, $150^{\circ}C$, both as-cast and peak aged AZ61-xPd alloys. After aging treatment, room and high temperature tensile strength were increased more than the as-cast specimens. The AZ61-1Pd alloy especially showed the largest strength increase range. Elongation was decreased with addition Pd at $25^{\circ}C$ and $150^{\circ}C$.