• Journal of the Korean Ceramic Society
• /
• v.38 no.10
• /
• pp.894-900
• /
• 2001

The spinel $Li{Mn_2}{O_4}$ catalysts for $CO_2$ decomposition were synthesized by a sol-gel method using manganese acetate and lithium hydroxide as starting materials through drying at $150^{\circ}C$ for 12 hrs under oxygen atmosphere followed by heat treatment at $480^{\circ}C$ for 12 hrs. The synthesized $Li{Mn_2}{O_4}$ were reduced by hydrogen for 3 hrs at various temperatures and the decomposition rate of carbon dioxide was investigated at 300, 325, 350, 375 and $400^{\circ}C$ using the $Li{Mn_2}{O_4}$ reduced by hydrogen gases. As a result of experiment, the optimum temperature of hydrogen reduction and $CO_2$ decomposition was shown $350^{\circ}C$. The physicochemical properties of the spinel $Li{Mn_2}{O_4}$ the reduced $Li{Mn_2}{O_4}$ and the $Li{Mn_2}{O_4}$ after $CO_2$ decomposition were examined with XRD, SEM and TGA.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.24 no.5
• /
• pp.553-568
• /
• 2018

Chromophoric Dissolved Organic Matter (CDOM) plays a dominant role in absorbing UV-VIS light and is also important in the biogeochemical carbon cycle due to the production of carbon dioxide from photo-oxidation at the sea surface in marine environments. Since absorption by CDOM was recently found to be responsible for increasing the energy absorbed in the mixed layer by 40 % over pure seawater, the importance of CDOM absorption in seawater for increasing sea surface temperature has come to be well recognized. We measured aCDOM and the absorption characteristics of CDOM during spring 2012 and 2014 in the southwestern East Sea. Distribution of CDOM in spring 2012 and 2014 was compared and S value was used to find the source of CDOM in the study area. As a result, the average $a_{CDOM}$ was $0.237m^{-1}$ ($0.009{\sim}0.988m^{-1}$) and the average S value was $16{\mu}m^{-1}$,which shows coastal properties. Also a positive correlation between Chl a and CDOM was observed ($r^2=0.34$), with an especially strong correlation near coastal stations. aCDOM in 2014 was about 40 % higher than aCDOM in 2012 during spring in the study area. This difference in aCDOM concentration resulted not only from annual variation but also from stratification and photobleaching in late spring 2012. This observation implies the possibility of flux of carbon dioxide into the atmosphere as a result of photo-oxidation in the East Sea.

• Korean Journal of Materials Research
• /
• v.18 no.6
• /
• pp.339-346
• /
• 2008

Single-crystal $ZnIn_2S_4$ layers were grown on a thoroughly etched semi-insulating GaAs (100) substrate at $450^{\circ}C$ with a hot wall epitaxy (HWE) system by evaporating a $ZnIn_2S_4$ source at $610^{\circ}C$. The crystalline structures of the single-crystal thin films were investigated via the photoluminescence (PL) and Double-crystal X-ray rocking curve (DCRC). The temperature dependence of the energy band gap of the $ZnIn_2S_4$ obtained from the absorption spectra was well described by Varshni's relationship, $E_g(T)=2.9514\;eV-(7.24{\times}10^{-4}\;eV/K)T2/(T＋489K)$. After the as-grown $ZnIn_2S_4$ single-crystal thin films was annealed in Zn-, S-, and In-atmospheres, the origin-of-point defects of the $ZnIn_2S_4$ single-crystal thin films were investigated via the photoluminescence (PL) at 10 K. The native defects of $V_{Zn}$, $V_S$, $Zn_{int}$, and $S_{int}$ obtained from the PL measurements were classified as donor or acceptor types. Additionally, it was concluded that a heat treatment in an S-atmosphere converted $ZnIn_2S_4$ single crystal thin films into optical p-type films. Moreover, it was confirmed that In in $ZnIn_2S_4$/GaAs did not form a native defects, as In in $ZnIn_2S_4$ single-crystal thin films existed in the form of stable bonds.

• Korean Journal of Crystallography
• /
• v.4 no.2
• /
• pp.74-85
• /
• 1993

Single crystals of LiNbO3 have found extensive application in electro-optic and nonlinear optic devices. However, laser-induced refartive index inhomogeneities, which have been labeled opical damage impose limits on device optical damage in LiNbO3 is imporved if more than 4.5 rml% MgO is added to the melt The laser damage thrueshold increased as much as 100 times better then that of undoped crystals. The MgO doped cystal has thus been urterlsiv81y studied since then. In the study, Mgo:LiNbOs(MLA) single crystals dopsd with 0, 2.5, 5.0, 7.5, 10.0 mol% MgO have been grown by the czocrualski technique. The metls were prepared in the platinum crluible and 15∼20mm diameter crystals were grown with a length of 20∼30mm in a resitance heater. The growth rate was 2.5mm/hr, the rotation speed 15rpn. Before sawing MLN single crystals were annealed for 24 hours under atmosphere at a temperature of 1080℃. After sawing, we have found an annual ring cross section of MNA crystals only in the direction of perpendicilar to the c-axis. Nonuniform dispusion of MgO was pointed out that the cuties of the state of oxide were strongly affected by oxygen partial pressure in.

• Korean Journal of Materials Research
• /
• v.9 no.10
• /
• pp.1025-1031
• /
• 1999

Alloys of TiAl with six different compositions. i. e., Ti-(42, 44)Al-2Nb-4V. Ti-(42, 44)Al-4Nb-2V and Ti -(42, 44)Al-4Nb-2Cr, were manufactured by arc-melting. and their oxidation behavior was studied. Both isothermal and cyclic oxidation tests were performed at 700, 800 and $900^{\circ}C$ in air for 50hr. The oxidation resistance increased in the order of Ti-(42, 44)Al-2Nb-4V, Ti-(42, 44)Al-4Nb-ZV and Ti-(42, 44)Al-4Nb-2Cr. It was found that V was a deleterious element, while Cr was a beneficial element in terms of oxidation resistance. During oxidation, a simultaneous interdiffusion was observed. All the constituent elements in the base alloys diffused outward. whereas oxygen from the atmosphere diffused inward, to form triple oxide layers composed of an outermost $\textrm{TiO}_2$ layer. upper ($\textrm{TiO}_2+\textrm{Al}_2\textrm{O}_3$) mixed layer, and lower $\textrm{TiO}_2$-rich layer.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.8 no.1
• /
• pp.33-39
• /
• 2010

The electrolytic reduction of a spent oxide fuel involves a liberation of the oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical structural materials. Accordingly, it is essential to choose the optimum material for the processing equipment that handles the high molten salt. In this study, hot corrosion studies were performed on bare as well as coated superalloy specimens after exposure to lithium molten salt at $675^{\circ}C$ for 216 h under an oxidizing atmosphere. The IN713LC superalloy specimens were sprayed with an aluminized NiCrAlY bond coat and then with an $Y_2O_3$ top coat. The bare superalloy reveals an obvious weight loss due to spalling of the scale by the rapid scale growth and thermal stress. The chemical and thermal stability of the top coat has been found to be beneficial for increasing to the corrosion resistance of the structural materials for handling high temperature lithium molten salts.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.23 no.4
• /
• pp.267-279
• /
• 1990

The temporal and spatial distribution of the coastal cold waters which was formed due to winter colling in the South Sea of Korea was analyzed by IR images from satellite and in situ data from shipboard observations. The coastal waters are known to be consisted of the Yellow Sea Coastal Waters(YSCW) and the South Korean Coastal Waters(SKCW). The former is driven around the Chuja-do and drifted into the Cheju Strait by residual currents, while the latter expands toward offsea by southward wind forcing. The expansion patterns of the SKCW were observed as sinking expansion or drifting expansion such that both were strongly dependent on the surface heat flux conditions. Under the condition of positive heat flux(warmer sea surface) or when the sea surface heat is lost to the atmosphere, the surface water started sinking and eventually expanded toward the open sea causing the cooling of the water column. For the negative heat flux the surface water was just drifted horizontally and expanded seaward and in this case only the surface layer of water was cooled.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.23 no.2
• /
• pp.108-113
• /
• 2013

Chalcopyrite material $CuInSe_2$ (CIS) is known to be a very prominent absorber layer for high efficiency thin film solar cells. Current interest in the photovoltaic industry is to identify and develop more suitable materials and processes for the fabrication of efficient and cost-effective solar cells. Various processes have been being tried for making a low cost CIS absorber layer, this study obtained the CIS nanoparticles using commercial powder of 6 mm pieces for low cost CIS absorber layer by high frequency ball milling and cryogenic milling. And the CIS absorber layer was prepared by paste coating using milled-CIS nanoparticles in glove box under inert atmosphere. The chalcopyrite $CuInSe_2$ thin films were successfully made after selenization at the substrate temperature of $550^{\circ}C$ in 30 min, CIS solar cell of Al/ZnO/CdS/CIS/Mo structure prepared under various deposition process such as evaporation, sputtering and chemical vapor deposition respectively. Finally, we achieved CIS nanoparticles solar cell of electric efficient 1.74 % of Voc 29 mV, Jsc 35 $mA/cm^2$ FF 17.2 %. The CIS nanoparticles-based absorber layers were characterized by using EDS, XRD and HRSEM.

• Journal of the Korean Chemical Society
• /
• v.18 no.5
• /
• pp.381-388
• /
• 1974

When mixture of p-phenylenediamine (PPD) and m-aminophenol (MAP) were reacted with formaldehyde (F) varying their amounts under $N_2$ stream at the temperature of -5∼0$^{\circ}$, addition condensation reaction occurred and brown colored resins(in some cases orange colored) were formed immediately. All resins thus formed were insoluble in most ordinary organic solvents and did not melt up to 300$^{\circ}$. When the resins were treated with dilute(7 %) aqueous sodium hydroxide solution, the adsorptivity of methylene blue on them showed marked improvement reaching as much as 80 mg of methylene blue on 1 g of the resin. On the other hand, in the case of bromophenol blue, its amount of adsorption appeared 250 mg per 1 g of the resin. The TGA under $N_2$ atmosphere indicated that the resin formed in molar ratio of 1 : 3 : 8 (PPD : MAP : F) showed the best heat-resistant property among others. About 40 % weight loss was observed for this resin at 900$^{\circ}$ with heating rate of 2$^{\circ}$ per minute.

• Journal of Ecology and Environment
• /
• v.41 no.12
• /
• pp.336-344
• /
• 2017

Background: Because of climate change, interest in the development of carbon pools has increased. In agricultural ecosystems, which can be more intensively managed than forests, measures to control carbon dioxide ($CO_2$) emission and absorption levels can be applied relatively easily. However, crop residues may be released into the atmosphere by decomposition or combustion. If we can develop scientific management techniques that enable these residues to be stocked on farmland, then it would be possible to convert farmlands from carbon emission sources to carbon pools. We analyzed and investigated soil respiration (Rs) rate characteristics according to input of carbonized residue of red peppers (Capsicum annuum L.), a widely grown crop in Korea, as a technique for increasing farmland carbon stock. Results: Rs rate in the carbonized biomass (CB) section was $226.7mg\;CO_2\;m^{-2}h^{-1}$, which was 18.1% lower than the $276.9mg\;CO_2\;m^{-2}h^{-1}$ from the red pepper residue biomass (RB) section. The Rs rate of the control was $184.1mg\;CO_2\;m^{-2}h^{-1}$. In the following year, Rs in the CB section was $204.0mg\;CO_2\;m{-2}h^{-1}$, which was 38.2% lower than the $330.1mg\;CO_2\;m^{-2}h^{-1}$ from the RB section; the control emitted $198.6mg\;CO_2\;m^{-2}h^{-1}$. Correlation between Rs and soil temperature ((Ts) at a depth of 5 cm) was $R^2=0.51$ in the RB section, which was higher than the other experimental sections. A comparison of annual decomposition rates between RB and CB showed a large difference, 41.4 and 9.7%, respectively. The results showed that carbonization of red pepper residues reduced the rates of decomposition and Rs. Conclusions: The present study confirmed that the Rs rate can be reduced by carbonization of residue biomass and putting it in the soil and that the Rs rate and Ts (5 cm) were positively correlated. Based on the results, it was determined that approximately $1.2t\;C\;ha^{-1}$ were sequestered in the soil in the first year and $3.0t\;C\;ha^{-1}$ were stored the following year. Therefore, approximately $1.5t\;C\;ha^{-1}year^{-1}$ are expected to be stocked in the soil, making it possible to develop farmlands into carbon pools.