• Journal of the Mineralogical Society of Korea
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• v.21 no.1
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• pp.45-56
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• 2008

This study was carried out to determine the effects of mineral composition and grain size of zeolite and bentonite from Po-hang and Kyung-ju, South Korea on the adsorption of heavy metals. Zeolite specimen consists mainly of mordenite, clinoptilolite, heulandite etc. And bentonite specimen is mainly composed of montmorillonite. Five heavy metals, Cd, Cr, Cu, Mn, and Pb were used to conduct the relevant adsorption experiments with the fixed concentrations of 10 ppm and 20 ppm, respectively. Host specimens excluding specimen for Cr resulted in the adsorption rate over average 80 percent, and over 95 percent for Pb. This study indicates that zeolite is more efficient in the adsorption of the heavy metals than bentonite, and its adsorption rate tends to decrease with increasing concentration of the heavy metals.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.10
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• pp.897-901
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• 2003

The microstructure and varistor characteristics of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Dy$_2$O$_3$(ZPCCD)-based ceramics were investigated with Dy$_2$O$_3$ content in the range of 0.0∼2.0 mol%. As Dy$_2$O$_3$ content is increased, the average grain size was decreased in the range of 18.6∼4.7 $\mu$m and the density was decreased in the range of 5.53∼4.34 g/cm$^3$. While, the varistor voltage was increased in the range of 39.4∼436.6 V/mm and the nonlinear exponent was in the range of 4.5-66.6 with increasing Dy$_2$O$_3$ content. The addition of Dy$_2$O$_3$ highly enhanced the nonlinear properties of varistors, compared with the ceramics without Dy$_2$O$_3$ Particularly, the ceramics with Dy$_2$O$_3$ content of 0.5 mol% exhibited the highest nonlinearity, in which the nonlinear exponent is 66.6 and the leakage current is 1.2 $\mu$A.A.A.

• Journal of the Korean Electrochemical Society
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• v.6 no.4
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• pp.236-241
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• 2003

Magnetic CoW thin film alloys were electrodeposited from citrate baths to investigate the resulting microstructure and magnetic properties. Deposit tungsten (W) content in the films electrodeposited at $70^{\circ}C$ were independent of current density, while coercivity decreased from hard $(H_{c,//}\~150\;Oe\;and\;H_{c.{\bot}}\;\~240\;Oe)$ to soft magnetic properties $(H_{c,//}\~20\;Oe\;and\;H_{c.{\bot}}\;\~30\;Oe)$ with increasing current densities from $10\;to\;100mA{\cdot}cm^2$, with deposit W content $(\~40\%)$ relatively unaffected by the applied current density. X-ray diffraction analysis indicated that hcp $Co_3W$ phases [(200), (201) and (220) planes] in the CoW films electrodeposited at $70^{\circ}C\;and\;10mA{\cdot}cm^{-2}$ were dominant, whereas amorphous CoW phases with small amount of hcp $Co_3W$ [(002) planes] were dominant with deposition at $70^{\circ}C\;and\;100mA{\cdot}cm^{-2}$. At intermediate current densities $(25\;and\;50mA{\cdot}cm^{-2}),\;hop\;Co_3W$ phases [(200), (002), (201) and (220)] were observed. The average grain size was measured to be 30 nm from Sheller formula. It is suggested that the change of the deposit coercivities in the CoW thin films electrodeposited at $70^{\circ}C$ is attributed to the change of microstructures with varying the current density. Nanostructured $Co_3W/amorphous-CoW$ multilayers were fabricated by alternating current density between 10 and $100 mA{\cdot}cm^{-2}$, varying the individual layer thickness. The magnetic properties of $Co_3W/amorphous-CoW$ multilayers were strongly dependent on the thickness of the alternating hard and soft magnetic thin films. The nanostructured $Co_3W/amorphous-CoW$ multilayers exhibited a shift from low to high coercivities suggesting a strong coupling effect.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.99.2-99.2
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• 2011

Transparent conducting oxides (TCOs) supported on glass are widely used as substrates in PEC studies for photovoltaic hydrogen generation applications However, high sheet resistane ($10{\sim}15{\Omega}/cm^2$) and fragileness of glass-supported TCO substrates are the obstacles to produce the large area PEC cells. Such internal sheet resistance is detrimental to efficient collection of photogenerated majority charge carriers at the photoactive material and electrolyte interface. Moreover, these TCO substrates are very expensive and consume about 40~60% cost of the devices. Hence, a low sheet resistance of the substrate is a key point in improving the performance of PEC devices. Metallic substrates coated with a photoactive material would be a good choice for efficient charge collection. Such metal substrates based photanodes are best candidate for large-scale phtoelectrochemical water splitting for hydrogen generation. In this study, we report the enhanced PEC performance of $WO_3$ film on metal(chemical etched, bare) substrate. It is proposed that interface between $WO_3$ and the metal substrate is responsible for efficient charge transfer and demonstrated significant improvement in the photoelectrochmical performance. X-ray diffration and FESEM suduies reveled that $WO_3$ films are monoclinic, porous, polycrystalline with average grain size of ~50nm. Photocurrent of $WO_3$ prepared on metal substrates was measured in 0.5M $H_2SO_4$ electroyte under simulated $100mW/cm^2$ illumination.

• Journal of the Korean institute of surface engineering
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• v.50 no.1
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• pp.29-34
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• 2017

Chloride plating solution was fabricated by dissolving metal Ni powders in a mixed solution with HCl and de-ionized water. Effects of $Ni^{2+}$ and saccharin concentrations in the plating baths on current efficiency, residual stress, surface morphology and microstructure of Ni films were studied. In the case of $0.2M\;Ni^{2+}$ concentration, current efficiency was decreased to about 65 % with increasing saccharin concentration, but, in the case of $0.7M\;Ni^{2+}$ concentration, it was shown more than 90 % with the increase of saccharin concentration. Residual stress of Ni thin film was appeared to be about 400 MPa up to 0.0244 M saccharin concentration at the $0.2M\;Ni^{2+}$ concentration and surface morphology with severe cracks was observed in the range of 0.0487~0.0975 M saccharin concentration. Residual stress of Ni thin films was measured to be about 750 MPa without saccharin addition and 114~148 MPa at the range of 0.0097~0.0975 M saccharin concentration for the $0.7M\;Ni^{2+}$ concentration. Relatively low residual stress values (114~148 MPa) of the Ni films at the range of 0.0097~0.0975 M saccharin concentration may be resulted from codeposition of S from saccharin. Ni films at $0.7M\;Ni^{2+}$ concentration showed smooth surface morphology and were independent of saccharin concentration. Ni films at $0.7M\;Ni^{2+}$ concentration consist of FCC(111), FCC(200), FCC(220) and FCC(311) peaks and the intensities of FCC(111) and FCC(200) peaks increased with increasing saccharin concentration. Also, the average grain size decreased with increasing saccharin concentration from about 30 nm to about 15 nm.

• Economic and Environmental Geology
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• v.12 no.3
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• pp.115-126
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• 1979

The Jecheon granite mass has turtle-shape exposure of about $190km^2$ at vicinity of Jecheon-eup, and is elongated in the direction of NEE-SWW. It discordantly intrudes the Bakdalryong metamorphic rocks and the great limestone series(Samtaesan and Hungwolri formation) which belong to the pre-Cambrian and Ordovician, respectively. The mass is composed of five facies of different grain size; texture and charecteristic minerals. The five facies are (1) coarse grained biotite granodiorite, (2) fine grained hornblende biotite granodiorite, (3) coarse grained pink feldspar granodiorite (4) leucogranite, and (5) porphyritic biotite granite. The mutual relationship between each facies is intrusion in (1)-(2) and (2)-(3), but unknown in (3)-(4) and (4)-(5). 22 modal analyses and and 10 chemical analyses on more than a hundred of representative samples taken from the mass are listed as tables. Triangular plot of modal and normative Q-Kf-Pl of this mass show a continuous differentiation products from certain common magma by change of chemical composition and anorthite contents in plagioclase. The metamorphic facies of contact aureole in surrounding rocks adjacent to the granite body are corresponded to hornblende hornfels facies with mineral assemblages of wollastonite-diopside-calcite in calcareous rocks, and of quartz-biotite-muscovite-cordierite in argillaceous rocks. Variation of silica versus oxides of major elements shows that the mass is similar to the trend of Daly's average basalt-andesite-dacite-rhyolite which shows the trend of the fractional crystallization of magma, and is equivalent to the calc-alkali rock series by Peacock. AMF diagram shows that Jecheon granite mass is equivalent to normal diffentiation products such as skaergaard intrusion. The above evidences suggest that the Jecohon granite mass is normal differentiation products formed by fractional crystallization under relatively slow cooling condition.

• The Journal of Advanced Prosthodontics
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• v.8 no.4
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• pp.259-266
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• 2016

PURPOSE. The purpose of this study was to assess the effect of surface treatments on shear bond strength of resin composite bonded to thermocycled and non-thermocycled CAD/CAM resin-ceramic hybrid materials. MATERIALS AND METHODS. 120 specimens ($10{\times}10{\times}2mm$) from each material were divided into 12 groups according to different surface treatments in combination with thermal aging procedures. Surface treatment methods were airborne-particle abrasion (abraded with 50 micron alumina particles), dry grinding (grinded with $125{\mu}m$ grain size bur), and hydrofluoric acid (9%) and silane application. According to the thermocycling procedure, the groups were assigned as non-thermocycled, thermocycled after packing composites, and thermocycled before packing composites. The average surface roughness of the non-thermocycled specimens were measured after surface treatments. After packing composites and thermocycling procedures, shear bond strength (SBS) of the specimens were tested. The results of surface roughness were statistically analyzed by 2-way Analysis of Variance (ANOVA), and SBS results were statistically analyzed by 3-way ANOVA. RESULTS. Surface roughness of GC were significantly lower than that of LU and VE (P<.05). The highest surface roughness was observed for dry grinding group, followed by airborne particle abraded group (P<.05). Comparing the materials within the same surface treatment method revealed that untreated surfaces generally showed lower SBS values. The values of untreated LU specimens showed significantly different SBS values compared to those of other surface treatment groups (P<.05). CONCLUSION. SBS was affected by surface treatments. Thermocycling did not have any effect on the SBS of the materials except acid and silane applied GC specimens, which were subjected to thermocycling before packing of the composite resin.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.8
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• pp.470-475
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• 2016

In this study, $Zn_xMn_{3-x}O_4$ (x=0.95~1.20) specimens were prepared by using a conventional mixed oxide method. All specimens were sintered in air at $1,200^{\circ}C$ for 12 h and cooled at a rate of $2^{\circ}C/min$ to $800^{\circ}C$, subsequently quenching to room temperature. We investigated the structural and electrical properties of $Zn_xMn_{3-x}O_4$ specimens with variation of ZnO amount for the application of NTC thermistors. As results of X-ray diffraction patterns, all specimens showed the formation of a complete solid solution with tetragonal spinel phase. And, the second phase was observed by the solubility limit of Zn ions in $x{\geq}1.10$ composition. The average grain size was increased from $2.72{\mu}m$ to $4.18{\mu}m$ with increasing the compositional ratio of Zn ion from x=0.95 to 1.20, respectively. $Zn_{1.10}Mn_{1.90}O_4$ specimen showed the minimum electrical resistance of $57.5k{\Omega}$ at room temperature and activation energy of 0.392 eV.

• Korean Journal of Materials Research
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• v.28 no.5
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• pp.295-300
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• 2018

Effects of annealing temperature on the microstructure and mechanical properties through thickness of a Cu-3.0Ni-0.7Si alloy processed by differential speed rolling are investigated in detail. The copper alloy with a thickness of 3 mm is rolled to a 50 % reduction at ambient temperature without lubricant and subsequently annealed for 0.5 h at $200-900^{\circ}C$. The microstructure of the copper alloy after annealing is different in the thickness direction depending on the amount of the shear and compressive strain introduced by the rolling; the recrystallization occurs first in the upper roll side and center regions which are largely shear-deformed. The complete recrystallization occurs at an annealing temperature of $800^{\circ}C$. The grain size after the complete recrystallization is finer than that of the conventional rolling. The hardness distribution of the specimens annealed at $500-700^{\circ}C$ is not uniform in the thickness direction due to partial recrystallization. This ununiformity of hardness corresponds well to the amount of shear strain in the thickness direction. The average hardness and ultimate tensile strength has the maximum values of 250 Hv and 450 Mpa, respectively, in the specimen annealed at $400^{\circ}C$. It is considered that the complex mode of strain introduced by rolling directly affects the microstructure and the mechanical properties of the annealed specimens.

• Journal of the Korean Magnetics Society
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• v.24 no.6
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• pp.186-190
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• 2014

To establish the coating conditions for $^{57}Co$, non-radioactive Co ions are dissolved in an acid solution and electroplated on to a copper plate. Then, the thermal diffusion of electroplated Co into a copper matrix was studied to apply a $^{57}Co$ $M{\ddot{o}}ssbauer$ source. Nanocrystalline Co particles were coated on a Cu substrate using DC electro-deposition at a pH of 1.89 to 5 and $20{\sim}30mA/cm^2$. The average grain size was up to 54 nm as the pH increased to 5. The second phase of Co-oxide was formatted as the pH was increased above 4. The diffusion degree was evaluated by mapping using scanning electron microscopy (SEM). The influence of different annealing conditions was investigated. The diffusion depth of Co depends on the annealing temperature and time. The results obtained confirm that the deposited Co diffused almost completely into a copper matrix without substantial loss at an annealing temperature of $900^{\circ}C$ for 2 hours.