• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.207-207
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• 2003

최근 광촉매 재료로 각광받고 있는 TiO$_2$는 band gap 에너지가 3.0-3.2eV로 자외선 영역과 일부 가시광선 영역에서 활성을 갖는 것으로 알려져 있다. 따라서 용액 중에 결정화 및 안정화 되어있는 TiO$_2$의 band gap 에너지를 낮춘다면 가시광 영역의 광반응을 얻을 수 있다. 이에 본 연구는 G. Sato등이 제안한 방법으로 TiO$_2$ sol을 제조할 때 band gap 에너지를 낮추고자 천이 금속원소를 첨가하여 복합 및 담지된 TiO$_2$계 복합 sol을 합성하고자 하였다 출발원료는 TiC1$_4$를 가수분해하여 제조한 TiOCl$_2$에 천이금속원소인 V, Cr, Fe, Ni, Nb 등의 chloride 화합물을 첨가하여 중화 및 세척과정을 거친 후, 과산화수소수에 용해하여 전구체 용액인 titania peroxo용액을 제조하였다 제조된 전구체 용액은 온도와 시간을 변수로 각각 열처리하여 TiO$_2$계 복합 sol을 합성하였다. 제조된 시편은 X-선 회절 분석, 투과전자현미경, particle size analyzer, ζ-potential analyzer 및 UV-VIS Spectrometer 통을 이용하여 천이금속 첨가에 따른 TiO$_2$계 복합 sol의 형성과정과 특성변화를 관찰하였다.

• Journal of the Korean Electrochemical Society
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• v.7 no.1
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• pp.1-8
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• 2004

This paper deals with the recent development of high-voltage cathode materials of mono- and di- metal ions substituted spinel $LiMn_2O_4$ for lithium batteries. $LiCu_xMn_{2-x}O_4(0{\leq}x{\leq}0.5)$ shows reversible intercalation/deintercalation in two potential regions, $3.9\~43\;and\;4.8-5.0V$ and stable electrochemical cycling behavior but with low capacity. $LiNi_{0.5}Mn_{1.5}O_4$ obtained by a sol-gel process delivers a capacity of 127mAh $g^{-1}$ on the first cycle and sustains a value of 124 mAh $g^{-1}$ even after the 60th cycle. The $Li_xCr_yMn_{2-y}O_4(0{\leq}x{\leq}0.5)$ solid-solutions exhibit enhanced specific capacity, larger average voltage, and improved cycling behaviors for low Cr content. $LiCr_yMn_{2-y}O_4$ presents a reversible Li deintercalation process at 4.9V, whose capacity is proportional to the Cr content in the range of $0.25{\leq}x{\leq}0.5$ and delivers higher capacities. $LiM_yCr_{0.5-y}Mn_{1.5}O_4(M=Fe\;or\;Al)$ shows that the capacity retention is lowered compared with lithium manganate. The cumulative capacities obtainable with Al-substitutted materials are less than those with Fe-substituted materials. $LiCr_xNi_{0.5-x}Mn_{1.5}O_4(x=0.1)$ delivers a high initial capacity of 1$152mAh\;g^{-1}$ with excellent cycleability.

• Bulletin of the Korean Chemical Society
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• v.23 no.8
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• pp.1062-1066
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• 2002

The complexes [Ni(L)(INT)2]${\cdot}$5H2O (1) and [Cu(L)(H2O)](Cl)(INT)${\cdot}$3H2O (2) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,01.18 ,07.12 ]docosane, INT = isonicotinate) have been prepared and characterized by X-ray crystallography, electronic absorption, and cyclic voltammetry. The crystal structure of 1 reveals an axially elongated octahedral geometry with two axial isonicotinate ligands. The electronic spectra, magnetic moment, and redox potentials of 1 also show a high-spin octahedral geometry. However, 2 shows that the coordination environment around the copper atom is a distorted square-pyramid with an axial water molecule. The spectra and electrochemical behaviors of 2 are also discussed.

• Journal of the Korean Electrochemical Society
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• v.17 no.3
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• pp.149-155
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• 2014

In this study, a positive-electrode material in a lithium secondary battery $Li[Ni_{0.575}Co_{0.1}Mn_{0.325}]O_2$ was synthesized as precursor by co-precipitation. Cathode material was synthesized by adding iron. The synthesized cathode material was analyzed by scanning electron microscope and x-ray diffraction. The analysis of x-ray diffraction showed that the a-axis and c-axis is increased by doping iron. And $I_{(003)}/I_{(104)}$ is increased and $I_{(006)}+I_{(102)}/I_{(101)}$ is decreased. Through this result, it was confirmed that the structural stability is improved. And impedance measurements show that the charge transfer resistance ($R_{ct}$) is lowered by doping iron. Consequently, electrochemical properties are improved by doping iron. In particular, the cycle characteristics are improved at a high temperature condition (328 K). Structural stabilities are contributing to the cycle properties.

• The Journal of the Petrological Society of Korea
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• v.11 no.1
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• pp.17-28
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• 2002

This study has been designed to elucidate the petrography and geochemical characteristics of the Taeheung-ri lava in southeastern Jeju Island. The lava is divided into the alkaline basalt and tholeiitic basalt. More than 4 layers of tholeiitic basalt are overlain by layers of alkaline basalt. Compared with alkaline basalt, tholeiitic basalt has lower contents of $K_2O$, $P_2O_5$, Ba and Ta, but slight higher contents of $SiO_2$ and CaO. The contents of Ba and Rb of all basalts are enriched, but those of Ni and Cr are depleted compared with primitive mantle compositions. All basalts show inclined chondrite-normalized REE patterns with LREE enriched more than HREE and alkaline basalt has relatively higher. The basalts of this study area are plotted in the field of within plate basalt on the tectonomagmatic discrimination diagram. Tholeiitic basalt has higher ratios of Zr/Nb, Y/Nb, and $Al_2O_3/P_2O_5$ than alkaline basalt. Both tholeiitic and alkaline basalt are similar in their K/Ba ratios. The geochemical data suggest that the parental magma of both basalts might be produced by different degrees of partial melting of similar source mantle. The tholeiitic basalt formed by higher degree of partial melting than the alkaline basalt.

• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.523-532
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• 2010

Co-application of organic coating and cathodic protection has not provided enough durability to low-alloyed steels inseawater ballast tank (SBT) environments. An attempt has made to study the effect of alloy elements (Al, Cr, Cu, Mo, Ni, Si, W) on general and localized corrosion resistance of steels as basic research to develop new low-allowed steels resistive to corrosion in SBT environments. For this study, we measured the corrosion rate by the weigh loss method after periodic immersion in synthetic seawater at $60^{\circ}C$, evaluated the localized corrosion resistance by an immersion test in concentrated chloride solution with the critical pH depending on the alloy element (Fe, Cr, Al, Ni), determined the permeability of chloride ion across the rust layer by measuring the membrane potential, and finally, we analyzed the rust layer by EPMA mapping and compared the result with the E-pH diagram calculated in the study. The immersion test of up to 55 days in the synthetic seawater showed that chromium, aluminium, and nickel are beneficial but the other elements are detrimental to corrosion resistance. Among the beneficial elements, chromium and aluminium effectively decreased the corrosion rate of the steels during the initial immersion, while nickel effectively decreased the corrosion rate in a longer than 30-day immersion. The low corrosion rate of Cr- or Al-alloyed steel in the initial period was due to the formation of $Cr_2FeO_4$ or $Al_2FeO_4$, respectively -the predicted oxide in the E-pH diagram- which is known as a more protective oxide than $Fe_3O_4$. The increased corrosion rate of Cr-alloyed steels with alonger than 30-day exposure was due to low localized corrosion resistance, which is explained bythe effect of the alloying element on a critical pH. In the meantime, the low corrosion rate of Ni-alloyed steel with a longer than 30-day exposure wasdue to an Ni enriched layer containing $Fe_2NiO_4$, the predicted oxide in the E-pH diagram. Finally, the measurement of the membrane potential depending on the alloying element showed that a lower permeability of chloride ion does not always result in higher corrosion resistance in seawater.

• Economic and Environmental Geology
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• v.42 no.6
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• pp.549-559
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• 2009

The objectives of this study are to investigate the biomineralization of goethite and lepidocrocite formed on the twisted-stalk and the sheathed-filament structure that is suggest microbe origin, and heavy metal in the yellow Fe-hydroxide. On the ratio of Cl and the Cl/Br ratios that are a pollution and non-pollution of groundwaters, it is indicated that the groundwater in this areas were relatively contaminated by human activity. The composition of the yellow Fe-hydroxide consisted mainly of $Fe_2O_3$ and $SiO_2$. The content of $Fe_2O_3$ ranges from 58.57 wt.% to 75.7 3wt.%, and $SiO_2$ content ranges from 5.8 wt.% to 16.17 wt.%. Heavy metal elements such as Zn(max. 6,160 mg/kg), Pb(max. 377 mg/kg), U(max. 503 mg/kg), Cr(max. 203 mg/kg), Cu(max. 77 mg/kg), V(max. 162 mg/kg), Ni(max. 105 mg/kg) were observed to be rich in those yellow Fe-hydroxide. The lath and platy crystals and needle-shaped crystals were clearly observed on the twisted-stalks and sheathed-filaments structure. The goethite, gypsum, and lepidocrocite were identified in the yellow Fe-hydroxide by x-ray powder diffraction.

• Journal of Welding and Joining
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• v.18 no.3
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• pp.51-59
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• 2000

Sink roll has been used in molten 55%Al-Zn alloy bath of continuous galvanizing line for sinking and stabilizing working steel strip in molten metal bath. In the process, the sink roll body inevitably build up dross compounds and pitting on the sink roll surface during 55%Al-Zn alloy coated strip production, and the life time of the sink roll is shorten by build up dross compounds and pitting. The present study examined the application of thermally sprayed ceramic coatings method on sink roll body for improving erosion resistance at molten 55% Al-Zn pool. In this experiment, the stainless steels such as STS 316L and STS 430F were used as the substrate materials. The CoNiCr and WE-Co powder were selected as bond coating materials. Moreover $Al_2O_3-ZrO_2-SiO_2 and ZrO_2-SiO_2$ powders selected as the top coating materials. Appearances of the specimens before and after dipping to molten 55%Al-Zn pool were compared and analyzed. As a result of this study, STS430F of substrate, WC-Co of bond spray coatings, $ZrO_2-SiO_2$ power of top spray coatings is the best quality in erosion resistance test at molten 55%Al-Zn pool

• Journal of Sensor Science and Technology
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• v.22 no.6
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• pp.379-386
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• 2013

The influences of the load resistance $R_L$ on the magnetoelectric (ME) characteristics of $NiZnFe_2O_4+PZT$ composite were investigated in the non-resonance frequency range. The ME coefficient peak increases with increasing $R_L$, but the frequency indicating the ME coefficient peak decreases with increasing $R_L$. The maximum output power peak is approximately $9.3{\times}10^{-10}mW/Oe$ near $R_L=3.3M{\Omega}$ at f=280 Hz, and the ME coefficient seems to be saturated at $R_L>20M{\Omega}$. This frequency shift effect of $R_L$ shows that the frequency range for an ME sensor application can be modulated with the appropriate value of $R_L$. The ME output voltage has a good linear response to the ac field Hac and shows fair stability over a range of temperatures. The measured non-linearity of this sample is approximately 0.8%. This sample will allow for a low-strength magnetic ac-field sensor. The result from this sample will serve as basic data for a signal-processing circuit system.

• Journal of the Korean Vacuum Society
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• v.8 no.2
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• pp.127-135
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• 1999

Nickel oxide films were prepard by using the electron beam evaporation technique. Coloring and bleaching experiments for cyclic durability were repeated in KOH electrolyte by cyclic voltammetry. Visible spectrophtometry was used to assess the stability of the transmittance in the degraded films. X-ray photoelectron spectroscopy results showed that the grain surface are oxygen-rich compared to the grain interiors in a NiO film. Open circuit memory of colored films is about 400hours in lN KOH. The rate of self discharge was evaluated by measuring the transmittance at 550nm of a fully oxidized NiO film. The rate of self discharge was increased polynomially with time and the film is nearly bleached after about 400hours. It was also found that the degraded film by repeated cycles in the KOH solution changed the grain shape of film surface The film prepared under a vacuum pressure of $3\times10^{-4}$ mbar was found to be rather stable when subjected to the repeated coloring and bleaching cycles in KOH electrolyte. Band theory applied to explain the electrochromic mechanism was discussed.