• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.311-314
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• 1998

The effects of the additions of transition metal oxides on ZrO$_2$ - Y$_2$O$_3$ (Y$_2$O$_3$ - containing tetragonal zirconia polycrystals : Y-TZP) system has been studied by investigating fracture toughness and phase stability of the sintered specimens. In the specimens sintered at 1450$^{\circ}C$ for 2hrs in air the phase transformation from tetragonal to monoclinic was observed. The ratios of monoclinic phase to tetragonal phase were changed with the additions of CoO, Fe$_2$O$_3$ and MnO$_2$, respectively, from 0.00 to 8.00wt%. The fracture toughness was increased with increasing the monoclinic to tetragonal phase ratio and was maximum at the ratio of about 18%. However, the hardness was decreased with increasing the ratio. The additions of CoO, Fe$_2$O$_3$ and MnO$_2$ together into Y-TZP resulted in more complex behaviors of fracture toughness and hardness. The specimen with the additions of 1.5wt% Fe$_2$O$_3$, 3.0wt% Al$_2$O$_3$ and 1.5wt% CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of 10.8 MPa.m$\^$$\frac{1}{2}$/ and Vickers hardness of 1201kgf/mm$^2$.

• Nuclear Engineering and Technology
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• v.42 no.2
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• pp.183-192
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• 2010

An electrochemical reduction of a mixture of metal oxides was conducted in a LiCl molten salt containing 3 wt% $Li_2O$ at $650^{\circ}C$. The oxide reduction was carried out by applying a current to an electrolysis cell, and the $Li_2O$ concentration was analyzed during each run. The concentration of $Li_2O$ in the electrolyte bulk phase gradually decreases according to Faraday's law due to a slow diffusion of the $O^{2-}$ ions. A hindrance effect of the unreduced metal oxides was observed for the reduction of the uranium oxide. Cs, Sr, and Ba of high heat-load fission products were diffused into and accumulated in the salt phase as predicted with thermodynamic consideration.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.1
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• pp.41-47
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• 1998

The (Sr$_1$-\ulcorner.Ca\ulcorner)TiO$_3$(0.05 x 0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[$^{\circ}C$] in a reducing atmosphere($N_2$gas). After being fired in a reducing atmosphere, metal oxides(CuO) was painted on the both surface of the specimens to diffuse to the grain boundary. The capacitance changes slowly and almost linearly in the temperature region of -40~+85[$^{\circ}C$]. The capacitance characteristics appears a stable value within $\pm$10[%]. According to increase of the frequency as a functional of temperature, all specimens used in this study showed the dielectric relaxation, and the relaxation frequency was above 10\ulcorner[Hz]. The capacitance is almost unchanged below about 20[V] but it decrease slowly over 20[V]. The voltage-current characteristics of specimens observed in the temperature range of 25~125[$^{\circ}C$] as the current increased appears that it is due to space charge condensed to interface between grain and grain boundary.

• Electrical & Electronic Materials
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• v.8 no.5
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• pp.611-618
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• 1995

The (Sr$_{1-x}$ .Ca$_{x}$)TiO$_{3}$+0.6[mol%]Nb$_{2}$O$_{5}$ (0.05.leq.x.leq.0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[.deg. C] in a reducing atmosphere(N$_{2}$ gas). Metal oxides, CuO, was painted on the both surface of the specimens to diffuse to the grain boundary. They were annealed at 1100 [.deg. C] for 2 hours. The 2nd phase formed by thermal diffusing from the surface lead to a very high apparent dielectric constant. According to increase of the frequency as a functional of temperature, all specimens used in this study showed the dielectric relaxation, and the relaxation frequency was above 106 [Hz], it move to low frequency with increasing resistivity of grain. The specimens showed three kinds of conduction mechanisms in the temperature range 25-125 [.deg. C] as the current increased: the region I below 200 [V/cm] shows the ohmic conduction. The region rt between 200 [V/cm] and 2000 [V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000 [V/cm] is dominated by the tunneling effect.fect.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.6
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• pp.412-417
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• 2000

High electric field stressed trap distributions were investigated in the thin silicon oxide of polycrystalline silicon gate metal oxide semiconductor capacitors. The transient currents associated with the off time of stressed voltage were used to measure the density and distribution of high voltage stress induced traps. The transient currents were due to the discharging of traps generated by high stress voltage in the silicon oxides. The trap distributions were relatively uniform near both cathode and anode interface in polycrystalline silicon gate metal oxide semiconductor devices. The stress generated trap distributions were relatively uniform the order of $10^{11}$~$10^{12}$ [states/eV/$\textrm{cm}^2$] after a stress. The trap densities at the oxide silicon interface after high stress voltages were in the $10^{10}$~$10^{13}$ [states/eV/$\textrm{cm}^2$]. It was appeared that the transient current that flowed when the stress voltages were applied to the oxide was caused by carriers tunneling through the silicon oxide by the high voltage stress generated traps.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.4
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• pp.347-357
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• 2024

Oxide semiconductor gas sensors are widely used for detecting toxic, explosive, and flammable gases due to their simple structure, cost-effectiveness, and potential integration into compact devices. However, their reliable gas detection is hindered by a longstanding issue known as humidity dependence, wherein the sensor resistance and gas response change significantly in the presence of moisture. This problem has persisted since the inception of oxide semiconductor gas sensors in the 1960s. This paper explores the root causes of humidity dependence in oxide semiconductor gas sensors and presents strategies to address this challenge. Mitigation strategies include functionalizing the gas-sensing material with noble metal/transition metal oxides and rare-earth/rare-earth oxides, as well as implementing a moisture barrier layer to prevent moisture diffusion into the gas-sensing film. Developing oxide semiconductor gas sensors immune to humidity dependence is expected to yield substantial socioeconomic benefits by enabling medical diagnosis, food quality assessment, environmental monitoring, and sensor network establishment.

• Journal of Hydrogen and New Energy
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• v.18 no.2
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• pp.124-131
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• 2007

Methane is partially oxidized to produce the syngas by the lattice oxygen of metal oxides in the absence of gaseous oxygen. The present work deals with ferrite including copper component, which does not chemisorb methane, to investigate the suppression of the carbon deposition during the reduction of metal oxides by methane. Iron-based oxides of $Cu_xFe_{3-x}O_4$(X=0.25, 0.5, 1.0) was synthesized by the co-precipitation method. Thermogravimetric Analysis(TGA) was used to observe the isothermal reduction behavior of $Cu_xFe_{3-x}O_4$ and $Fe_3O_4$ at $600-900^{\circ}C$ under methane atmosphere. The crystal structures of reduced specimens were characterized by X-rays powder diffraction(XRD) technique. From the analyses of TGA, it is concluded that the reduction kinetics of $CuFe_2O_4$ was the fastest among $Fe_3O_4$ and $Cu_xFe_{3-x}O_4$(X=0.25, 0.5, 1.0). The X-ray diffraction analyses indicated that $Cu_xFe_{3-x}O_4$ was decomposed to Cu and $Fe_3O_4$ phase at $600^{\circ}C$ and was reduced to Cu and Fe phase at $800^{\circ}C$. $Fe_3O_4$, which was reduced at $900^{\circ}C$, showed Fe, graphite and $Fe_3C$ phases. On the contrary, $Cu_xFe_{3-x}O_4$ does not show the graphite or $Fe_3C$ phases. This results infer that Cu component suppress the carbon deposition on Cu-ferrite.

• Korean Journal of Materials Research
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• v.26 no.3
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• pp.130-135
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• 2016

To alloy high melting point elements such as boron, ruthenium, and iridium with copper, heat treatment was performed using metal oxides of $B_2O_3$, $RuO_2$, and $IrO_2$ at the temperature of $1200^{\circ}C$ in vacuum for 30 minutes. The microstructure analysis of the alloyed sample was confirmed using an optical microscope and FE-SEM. Hardness and trace element analyses were performed using Vickers hardness and WD-XRF, respectively. Diffusion profile analysis was performed using D-SIMS. From the microstructure analysis results, crystal grains were found to have formed with sizes of 2.97 mm. For the copper alloys formed using metal oxides of $B_2O_3$, $RuO_2$, and $IrO_2$ the sizes of the crystal grains were 1.24, 1.77, and 2.23 mm, respectively, while these sizes were smaller than pure copper. From the Vickers hardness results, the hardness of the Ir-copper alloy was found to have increased by a maximum of 2.2 times compared to pure copper. From the trace element analysis, the copper alloy was fabricated with the expected composition. From the diffusion profile analysis results, it can be seen that 0.059 wt%, 0.030 wt%, and 0.114 wt% of B, Ru, and Ir, respectively, were alloyed in the copper, and it led to change the hardness. Therefore, we verified that alloying of high melting point elements is possible at the low temperature of $1200^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.130-131
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• 2013

Nanostructured oxides are widely used in heterogeneous catalysis where their catalytic properties are closely associated with the size and morphology at nanometer level. The effect of particle size has been well decumented in the past two decades, but the shape of the nanoparticles has rarely been concerned. Here we illustrate that the redox and acidic-basic properties of oxides are largely dependent on their shapes by taking $Co_3O_4$, $Fe_2O_3$, $CeO_2$ and $La_2O_3$ nanorods as typical examples. The catalytic activities of these rod-shaped oxides are mainly governed by the nature of the exposed crystal planes. For instance, the predominant presence of {110} planes which are rich in active $Co^{3+}$ on $Co_3O_4$ nanorods led to a much higher activity for CO oxidation than the nanoparticles that mainly exposed the {111} planes. The simultaneous exposure of iron and oxygen ions on the surface of $Fe_2O_3$ nanorods have significantly enhanced the adsorption and activation of NO and thereby promoted the efficiency of DeNOx process. Moreover, the exposed surface planes of these rod-shaped oxides mediated the reaction performance of the integrated metal-oxide catalysts. Au/$CeO_2$ catalysts exhibited outstanding stability under water-gas shift conditions owing to the strong bonding of gold particle on the $CeO_2$ nanorods where the formed gold-ceria interface was resistant towards sintering. Cu nanoparticles dispersed on $La_2O_3$ nanorods efficiently catalyzed transfer dehydrogenation of primary aliphatic alcohols based on the uniue role of the exposed {110} planes on the support. Morphology control at nanometer level allows preferential exposure of the catalytically active sites, providing a new stragegy for the design of highly efficient nanostructured catalysts.

• Journal of Welding and Joining
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• v.24 no.6
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• pp.33-38
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• 2006

Since the 1990's, European shipbuilding industries introduced hybrid welding process in order to decrease thermal distortion of welded joints in passenger shipbuilding. In this study, we investigated effects of hybrid welding parameters on the toughness of weld metal using DH36 steel in order to obtain more sound welds in passenger shipbuilding. Type of leading process, joint gap distance and chemical composition of consumables were considerably correlated with the toughness of weld metal. Especially, the toughness was considerably increased with high-Ti containing consumables. In addition, hybrid welding speed increased by using plasma cut edges, the oxides layer of which increased absorption efficiency of laser beam.