• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.857-858
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• 2006

In order to clarify the wear resistance as cutting tools, the effect of oxygen addition on oxidation behavior of the ${\beta}-Si_3N_4$ ceramics with 5 mass% $Y_2O_3$ and 2 or 4 mass% $Al_2O_3$ was investigated by performing oxidation tests in air at $1300^{\circ}$ to $1400^{\circ}C$ and cutting performance tests. From test results, we could conclude that the mechanical properties of ${\beta}-Si_3N_4$ ceramics depending on oxygen introduction are much effective on cutting performance improvements of ${\beta}-Si_3N_4$ ceramics.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.261-267
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• 1988

$\beta$-Sialon powder was prepared by the reduction-nitridation reaction from the mixture of Wando Pyrophyllite and carbon black at 135$0^{\circ}C$ in $N_2$ atmosphere. $\beta$-SiC powder was added to the prepared $\beta$-Sialon powder to make $\beta$-Sialon-SiC composite. The $\beta$-Sialon-SiC composites were sintered pressurelessly at 175$0^{\circ}C$ for 2h, using $Y_2O_3$ and $ZrO_2$(monoclinic) as sintering aids. Comparatively higher values of the fracture toughness (3.8 MN/㎥/2), M.O.R. (470 MN/$m^2$) and vickers microhardness (13.7 MN/$m^2$) were obtained when 10 wt% $Y_2O_3$ was added as a sintering aid. The improved fracture toughness and M.O.R. are assumed to be the results of crack deflection and crack branching by the second phase SiC particles.

• Journal of Magnetics
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• v.6 no.3
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• pp.90-93
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• 2001

Co/$Al_O_3$/NiFe and CO/$Al_O_3$/Co tunnel junctions were fabricated by a radio frequency magnetron sputtering at room temperature with hard mask on glass and $4^{\circ}$ tilt cut Si (111) substrates. The barrier layer was formed through two steps. After the Al layer was deposited, it was oxidized in the chamber of a reactive ion etching system (RIE) with $O_2$plasma at various conditions. The dependence of the TMR value and junction resistance on the thickness of Al layer (before oxidation) and oxidation parameters were investigated. Magnetoresistance value of 7% at room temperature was obtained by optimizing the Al layer thickness and oxidation conditions. Circular shape junctions on $4^{\circ}$tilt cut Si (111) substrate showed 4% magnetoresistance. Photovoltaic energy conversion effect was observed with the cross-strip geometry junctions on Si substrate.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1109-1113
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• 1999

sothemal reduction at $50^{\circ}C$ using $Pt/MoO_3$ or $Pt/MoO_3/SiO_2$ made by dry impregnation or physical mixture of $Pt^{\circ}$ and $MoO_3$ demonstrated that the $H_2$ uptake vis $H_2$ spillover from Pt into $MoO_3$ was enhanced as calcination temperature was increased. Surface area of exposed Pt crystallites measured by CO chemisorption was decreased with higher calcination temperature. In addition, TEM showed that $MoO_x$ overlayers were formed on Pt crystallites after calcination at $400^{\circ}C$. Consequentially, it was found that this increased active contact sites between Pt and $MoO_3$ due to surface morphological change was one of the dominant factors for this increased $H_2$uptake via $H_2$ spillover from Pt crystallites into $MoO_3$.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.115-120
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• 2015

$K_2CO_3$-based dry regenerable sorbents were prepared by spray-drying techniques to improve mass produced $K_2CO_3-Al_2O_3$ sorbents (KEP-CO2P, hereafter), and then tested for their $CO_2$ sorption capacity by a $2,000Nm^3/h$ (0.5 MWe) $CO_2$ capture pilot plant built for Unit 3 of the Hadong thermal power station in 2010. Each of the sample sorbents contained 35 wt.% $K_2CO_3$ as the active materials with various support materials such as $TiO_2$, MgO, Zeolite 13X, $Al_2O_3$, $SiO_2$ and hydrotalcite (HTC). Their physical properties and reactivity were tested to evaluate their applicability to a fluidized-bed or fast transport-bed $CO_2$ capture process. The $CO_2$ sorption capacity and percentage utilization of $K_2CO_3$-MgO based sorbent, Sorb-KM2, was $8.6g-CO_2/100g$-sorbents and 90%, respectively, along with good mechanical strength for fluidized-bed application. Sorbs-KM2 and KT were almost completely regenerated at $140^{\circ}C$. No degradation of Sorb-KM by $SO_2$ added as a pollutant in flue gas was observed during a cycle test.

• Korean Journal of Materials Research
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• v.3 no.1
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• pp.7-11
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• 1993

Abstract Oxidation kinetics of silicon oxide films formed by rapid thermal oxidizing Si substrate in $N_2$O ambient studied. The data on $N_2$0 oxidation shows that the interfacial nitrogen-rich layers results in oxide growth in the parabolic regime by impeding oxidant diffusion to the Si$O_2$-Si interface even for ultrathin oxides. The activation energy of parablic rate constant, B, is about 1.5 eV, and the energy increses with oxide thickness.

• Applied Chemistry for Engineering
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• v.21 no.1
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• pp.81-86
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• 2010

On adsorbing carbon monoxide (CO) on the silica supported ruthenium/iron alloy ($Ru/Fe-SiO_2$) samples above mole ratio 9/1 of Ru/Fe five bands ($2138.7{\sim}2142.5cm^{-1}$, $2067.3{\sim}2073.1cm^{-1}$, $1976.7{\sim}2017.2cm^{-1}$, $1737.9{\sim}1799.3cm^{-1}$, $1625.7cm^{-1}$) were observed, and in $Ru/Fe-SiO_2$ samples below mole ratio 8/2 of Ru/Fe two bands ($1934.0{\sim}1990.2cm^{-1}$, $1625.7cm^{-1}$) were observed. The $2138.7{\sim}2142.5cm^{-1}$ bands, the $2067.3{\sim}2073.1cm^{-1}$ bands, and the $1988.3{\sim}2030.7cm^{-1}$ bands may be ascribed to stretching vibrations of CO molecules lineally bonded to the Ru atoms on supported Ru/Fe cluster surface, the $1737.9{\sim}1799.3cm^{-1}$ bands to stretching vibrations of CO molecules bridge bonded to the Ru atoms on supported Ru/Fe cluster surface or to stretching vibrations of CO molecules bonded to the Ru atoms on high Miller index planes, and the $1934.0{\sim}1990.2cm^{-1}$ bands to stretching vibrations of CO molecules lineally bonded to the Fe atoms on supported Ru/Fe cluster surface. The absorbances of the $1934.0{\sim}1990.2cm^{-1}$ bands in $Ru/Fe-SiO_2$ samples gradually increased with the increases of Ru/Fe mole ratio below the ratio of 8/2. This phenomena may be ascribed to the increases of Fe concentration of surface compared with the one of the sample and to the increases of surface area of supported Ru/Fe cluster according as increase of Ru/Fe mole ratio below the ratio of 8/2 compared with the $Fe-SiO_2$ sample.

• Journal of the Korean Magnetics Society
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• v.16 no.6
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• pp.279-282
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• 2006

Magnetic tunnel junctions (MTJs), which consisted of amorphous ferromagnetic NiFeSiB free layers, were investigated. The NiFeSiB layers were used to substitute for the traditionally used CoFe and/or NiFe layers with the emphasis being given to obtaining an understanding of the effect of the amorphous free layer on the switching characteristics of the MTJs. $Ni_{16}Fe_{62}Si_{8}B_{14}$ has a lower saturation magnetization ($M_{s}:\;800\;emu/cm^{3}$) than $Co_{90}Fe_{10}$ and a higher anisotropy constant ($K_{u}:\;2700\;erg/cm^{3}$) than $Ni_{80}Fe_{20}$. The $Si/SiO_{2}/Ta$ 45/Ru 9.5/IrMn 10/CoFe $7/AlO_{x}/CoFeSiB\;(t)/Ru\;60\;(in\;nanometers)$structure was found to be beneficial for the switching characteristics of the MTJ, leading to a reduction in the coercivity ($H_{c}$) and an increase in the sensitivity resulted from its lower saturation magnetization and higher uniaxial anisotropy. Furthermore, by inserting a very thin CoFe layer at the tunnel barrier/NiFeSiB interface, the TMR ratio and switching squareness were improved more with the increase of NiFeSiB layer thickness up to 11 nm.

• Korean Journal of Crystallography
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• v.6 no.2
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• pp.125-133
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• 1995

The crystal structure of dehydrated, partially Co(II)-exchanged zeolite X, stoichiometry Co2+Na+-X (Co41+Na10Si100Al92O384) per unit cell, has been determined from three-dimensional X-ray diffraction data gathered by counter methods. The structure was solved and refined in the cubic space group Fd3:α=24.544(1)Å at 21(1)℃. The crystal was prepared by ion exchange in a flowing stream using a solution 0.025 M each in Co(NO3)2 and Co(O2CCH3)2. The crystal was then dehydrated at 380℃ and 2×10-6 Torr for two days. The structure was refined to the final error indices, R1=0.059 and R2=0.046 with 211 reflections for which I > 3σ(I). Co2+ ions and Na+ ions are located at the four different crystallographic sites. Co2+ ions are located at two different sites of high occupancies. Sixteen Co2+ ions are located at the center of the double six-ring (site I; Co-O = 2.21(1)Å, O-Co-O = 90.0(4)°) and twenty-five Co2+ ions are located at site II in the supercage. Twenty-five Co2+ ions are recessed 0.09Å into the supercage from its three oxygen plane (Co-O = 2.05(1)Å, O-Co-O = 119.8(7)°). Na+ ions are located at two different sites of occupandies. Seven Na+ ions are located at site II in the supercage (Na-O = 2.29(1)Å, O-Na-O = 102(1)°). Three Na+ ions are statistically distribyted over site III, a 48-fold equipoint in the supercages on twofold axes (Na-O = 2.59(10)Å, O-Na-O = 69.0(3)°). Seven Na+ ions are recessed 1.02Å into the supercage from the three oxygen plane. It appears that Co2+ ions prefer sites I and II in order, and that Na+ ions occupy the remaining sites, II and III.

• Journal of Korea Foundry Society
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• v.14 no.6
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• pp.499-507
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• 1994

The effect of sodium gluconic acid on the collapsability of the sodium silicate type $CO_2$ mold was studied. The bending strength was saturated with gassing $CO_2$ for 60 sec. under $1kg/cm^2$ and with the flow rate of $10\;{\ell}\;/min$. It was decreased with aging after having been fully hardened. The retained strength was reduced in the heating temperature range of $100{\sim}1,100^{\circ}C$ and the retained strength peak near the heating temperature of $100^{\circ}C$ was removed by the effect of the sodium gluconic acid. Silica gel, $Na_2CO_3$ and dehydrated sodium silicates were formed from the binder of sodium silicate with the addition of sodium gluconic acid at the heating temperature of $100^{\circ}C$. $Na_4SiO_4$ was formed by the reaction of $Na_2O$, from decomposed $Na_2CO_3$, with the dehydrated sodium silicate at $500^{\circ}C$. The crystobalite type of $SiO_2$ was formed at $900^{\circ}C$. The sodium gluconic acid had no effect on the bending strength at around $1,100^{\circ}C$ due to the combustion loss of it.