• Korean Journal of Metals and Materials
• /
• v.49 no.6
• /
• pp.474-487
• /
• 2011

Bars of OFHC Cu with the diameter of 45 mm were processed by equal channel angular pressing up to 16 passes via route $B_c$, and homogeneity of their microstructures and mechanical properties was examined at every four passes which develop the equiaxed ultrafine grains. In general, overall hardness, yield strength and tensile strength increased by 3, 7, and 2 times respectively compared with those of unECAPed sample. Cross-sectional hardness exhibited a concentric distribution. Hardness was the highest at the center of bar and it decreased gradually from center to surface. After 16 passes, overall hardness decreased due to recovery and partial recrystallization. Regardless of the number of passage, yield strength and tensile strength were quite uniform at all positions, but elongation showed some degree of scattering. At 4 passes, coarse and ultrafine grains coexisted at all positions. After 4 passes, uniform equiaxed ultrafine grains were obtained at the center, while uniform elongated ultrafine grains were manifested at the upper half position. At the lower half position, grains were equiaxed but its size were inhomogeneous. It was found that inhomogeneity of grain morphology and grain size distribution at different positions are to be attributed to scattering in elongation but they did not affect strength. The present results reveal the high potential of practical application of equal channel angular pressing on fabrication of large-sized ultrafine grained bars with quite homogeneous mechanical properties.

• Economic and Environmental Geology
• /
• v.22 no.3
• /
• pp.253-266
• /
• 1989

The Cu-Pb-Zn-Ag hydrothermal vein type deposits which comprise the Dongil and Dong-cheogogsan mines occur within the Cretaceous sedimentary rocks in the Euiseong Basin of the southern Korean peninsula. The ore mineralization is contained within three stage(I,II and III) quartz and calcite veins. Ore minerals occur as dominant chalcopyrite, galena, sphalerite, tetrahedrite and Pb, Ag, Sb and Bi-bearing sulfosalts. Stage I ore minerals were deposited between $400^{\circ}C$ and $200^{\circ}C$ from the fluid with moderate salinities(7.0 to 4.5 eq. wt. % NaCl). Evidence of boiling suggests pressure of less than 150 bars during stage I mineralization. This pressure corresponds to maximum depths of 650 m and 1700 m, respectively, assuming lithostatic and hydrostatic loads. The data on mineralogy, temperature and salinity, together with information on the solubility of Cu complex, suggest that Cu deposition is a result of boiling coupled with declining temperature from $350^{\circ}$ to $250^{\circ}C$ or declining log $a_{o_2}$(from -29.8 to -35.9 atm.)and increasing in pH. Pb, Ag, Sb and Bi-bearing sulfosalts were deposited by cooling and dilution at temperature of less than $250^{\circ}C$ from the ore fluid with less than -35.9 atm. of log $a_{o_2}$.

• Journal of Welding and Joining
• /
• v.31 no.6
• /
• pp.58-64
• /
• 2013

Several joining methods involving resistance welding, laser welding, ultrasonic welding and mechanical joining are currently applied in manufacturing lithium-ion batteries. Cu and Al alloys are used for tab and bus bar materials, and laser welding characteristics for these alloys were investigated with similar and dissimilar material combinations in this study. The base materials used were Al 1050 and oxygen-free Cu 1020P alloys, and a disk laser was used with a continuous wave mode. In bead-on-plate welding of both alloys, the joint strength was higher than the strength of O tempered base material. In overlap welding, the effect of welding parameters on the tensile shear strength and bead shape was evaluated. Tensile shear strength of overlap welded joint was affected by interfacial bead width and weld defect formation. The tensile-shear specimen was fractured at the heat affected zone by selecting proper laser welding parameters.

• Journal of Korea Foundry Society
• /
• v.3 no.1
• /
• pp.13-21
• /
• 1983

In order to determine the feeding distance of aluminiun alloys (Alsi7Mg and AlCu4Ti) bar castings in the sand mold, the distance of the sound castings has been observed by radiograph for various risers, melt treatment, and casting design. Variation of porosity and hardness with the distance from the riser were also measured in order to determine the casting soundness. The results obained were as follows; 1) The modulus of riser should be 1.4 times of the casting`s 2) The maximum distance which can be made sound is greatly dependent on chemical composition and ingate location, and follows the rules given by the formula; a) When the melt flows into the casting first, and the riser afterward, D = 37.7 ${\sqrt{T}}$ for AlSi7Mg D = 31.2 ${\sqrt{T}}$ for pure aluminium D ${\ge}$ 54.8 ${\sqrt{T}}$ for AlCu4Ti Where T = casting thickness in mm Of this maximum distance, $aa{\sqrt{T}}$ for AlSi7Mg and 7.5 ${\sqrt{T}}$ for pure aluminium is made sound by the chilling effect of the casting edge. b) When the melt flows into the casting passing through the riser, $30{\times}30{\times}600mm$ bars can be made sound in all cases 3) Percentage of porosity is higer in AlCu4Ti than AlSi7Mg. And it is increased gradually by moving closer to the riser in case of $30{\times}30{\times}600mm$ bars, but for the $30{\times}30{\times}600mm$ bars it is increased gradually by moving closer to the center of bars. 4) Hardness variation is similar to the tendency of porosity. And it decreased gradually with approaching to the center in case of $30{\times}30{\times}600mm$ bars.

• 한국초전도학회:학술대회논문집
• /
• v.9
• /
• pp.185-188
• /
• 1999

Biepitaxial Y$_1Ba_2Cu_3O_{7-x}$ (YBCO) and La$_{0.2}Sr_{0.8}MnO_3$ (LSMO) thin films have been prepared on SrTiO$_3$ buffer layer and MgO seed layer grown on Al$_2O_3$(11${\bar{2}}$0)substrates by dc-sputtering with hollow cylindrical targets, respectively. We charaterized Josephson properties and significantly large magnetoresistance in YBCO and LSMO films with 45$^{\circ}$ grain boundary junction, respectively. The observed working voltage (I$_cR_n$) at 77 K in grain boundary junction was below 10${\mu}$V, which is typical I$_cR_n$ value of single biepitaxial Josephson junction. The field magnetoresistance ratio (MR) of LSMO grain boundary juncoon at 77K was enhanced to 13%, which it was significant MR value with high magnetic field sensitivity at a low field of 250 Oe. These results indicate that inserting the insulating layer instead of the grain boundary layer with metallic phase can be possible to apply a new SIS Josephson junction and a novel magnetic device using spin-polarized tunneling junction.

• Journal of Hydrogen and New Energy
• /
• v.34 no.6
• /
• pp.581-586
• /
• 2023

As the development of alternative energy is required due to the depletion of fossil fuels, interest in the use of hydrogen energy is increasing. Hydrogen is a promising clean energy source with high energy density and can lead to the application of environmentally friendly technologies. However, due to difficulties in production, storage, and transportation that prevent the application of hydrogen-based eco-friendly technology, research on reforming reactions using dimethyl ether (DME) is being conducted. Unlike other hydrocarbons, DME is attracting attention as a hydrogen carrier because it has excellent storage stability and transportability, and there is no C-C bond in the molecule. The reaction between DME and steam is one of the reforming processes with the highest hydrogen yield in theory at a temperature lower than that of other hydrocarbons. In this study, a hydrogen reforming device using DME was developed and a catalyst prepared by supporting Cu in alumina was put into a reactor to find optimal hydrogen production conditions for supplying hydrogen to fuel cells while changing reaction temperature (300-500℃), pressure (5-10 bar), and steam/carbon ratio (3:1 to 5:1).

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1093-1094
• /
• 2006

Magnetic characteristics observed in BiSrCaCuO superconductor were studied. In the measurement of differential conductance, it was cleared that the mechanism of magnetic memory effect couldn't be explained by using conventional flux flow model. By changing the density of external magnetic flux, changes in inductance of a coil in which a superconducting bar inserted were also measured. The results showed that the filament model was valid to explain the mechanism of the occurrence of a voltage in superconducting sample. It was concluded that the electromagnetic characteristics arose from the interaction between the trapped magnetic flux and weak link of the filament formed in the superconducting bulk.

• Archives of Pharmacal Research
• /
• v.11 no.1
• /
• pp.74-79
• /
• 1988

Crystals of tolazamide, $C_{14}H_{21}N_3O_3S$, are triclinic space group $P{\bar{1}}$ with cell dimensions of a = 6.355 (2), b = 9.223 (2), c = 13.510 (3) A, ${\alpha}\;=\;101.04\;(8),\;{\beta}=92.80(5),\;{\gamma}\;=\;85.72\;(6)^{\circ}$ and Z = 2. Intensities were collected on an automated four-circle diffractometer using graphite-monochromated Cu K ${\alpha}$ radiations. The structure was solved by direct method and refined by full-matrix least-squares to an R factor of 0.058 for 1184 observed reflections. The molecules are dimerized by the $N-H{\cdots}O$ hydrogen bonds. There are only van der Waals interactions between these molecular dimers.

• Bulletin of the Korean Chemical Society
• /
• v.22 no.4
• /
• pp.379-382
• /
• 2001

A new ligand containing the long aliphatic hydrocarbon chain, dipyridylstearylamine (dps) and its copper(Ⅱ) complex, Cu(dps)(NO3)2 have been prepared. The copper complex was characterized structurally and spectroscopically. The XRD crystal structure of the copper complex reveals that copper is octahedrally coordinated by dps and two nitrato ligands. The nitrato groups ligate asymmetrically to the copper. Crystal data are P1bar, a=8.249(2), b=10.416(3), $c=20.915(4)\AA$, $\alpha=86.54(2)$, $\beta=84.026(2)$, $\gamma=72.32(2)^{\circ}$, V=1702.7(7) $\AA3$ , Z=2, ${\lambda}$(Mo $K\alpha)=0.71073\AA$, $\mu=0.689$ mm-1 , T=293(2) K, R=0.0560 for 3529 reflections. The dps and the copper complex are stable in the air and the copper complex exhibits features of typical of other copper(Ⅱ) complexes containing dipyridylamine-based ligand.

• Journal of Industrial and Engineering Chemistry
• /
• v.67
• /
• pp.448-460
• /
• 2018

Copper nanoparticle-doped and graphitic carbon nanofibers-covered porous carbon beads were used as an efficient catalyst for treating synthetic phenolic water by catalytic wet air oxidation (CWAO) in a packed bed reactor over 10-30 bar and $180-230^{\circ}C$, with air and water flowing co-currently. A mathematical model based on reaction kinetics assuming degradation in both heterogeneous and homogeneous phases was developed to predict reduction in chemical oxygen demand (COD) under a continuous operation with recycle. The catalyst and process also showed complete COD reduction (>99%) without leaching of Cu against a high COD (~120,000 mg/L) containing industrial wastewater.