• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.4
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• pp.600-608
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• 1996

Specific structural properties of Li intercalation reaction into the spinel relatedmanganese dioxide, $Li_{x}Mn_{2}O_{4}(0.2{\leq}x{\leq}2.0)$, are investigated by X-ray diffractional and electrochemical studies of Li/1M $LiClO_{4}$-propylene carbonate solution/$Li_{x}Mn_{2}O_{4}$ cell. The effect of the chemical composition and the reaction temperature on electrochemical parameter of $Li_{x}Mn_{2}O_{4}$ are studied by the phenomena of phase-transition, analysis of crystal lattice, fine structure, and thermal analysis. Treatment of the spinel $Li_{x}Mn_{2}O_{4}$ with aqueous acid was found to result in conversiton of $Li_{x}Mn_{2}O_{4}$ to nearly pure $MnO_{2}$, as evidenced by a reduction in the lattice constant $a_{c}$ from 8.255 to $8.031\;{\AA}$. At a composition range of $0.2{\leq}x{\leq}0.6$ in $Li_{x}Mn_{2}O_{4}$ the reduction proceeded in a homogeneous phase, which was characterized by a constant voltage of 3.9~3.7 V together with a lattice constant of $8.255\;{\AA}$.

• Journal of Korean Society on Water Environment
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• v.18 no.2
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• pp.201-212
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• 2002

The objective of this study was to investigate the treatment efficiency, kinetics, and morphological characteristics of biofilm in upflow $Biobead^{(R)}$ process, a kind of biological aerated filter(BAF). The $Biobead^{(R)}$ system showed high removal rates of $COD_{Mn}$(76~83%), $BOD_5$(67~88%) and SS(71~91%) for food wastewater with high salt concentration ($>4,000mg/{\ell}$) under short reaction times(2~3hrs). Even at aerobic condition, the system had high treatment efficiency for both T-N (51~63%) and T-P(62~81%). The removal kinetics of $COD_{Mn}$, $BOD_5$, T-N, T-P, and $Cl^-$ in the $Biobead^{(R)}$ system showed a plug-flow pattern with reaction rate constants($hr^{-1}$) of 0.58, 0.63, 0,30, 0.48, and 0.38 respectively. A backwashing process to remove excess biomass and filtered solids was needed at least once during 22-hour operation at $0.5kg\;BOD\;m^{-3}{\cdot}d^{-1}$ loading. At the higher loading($1.0kg\;BOD\;m^{-3}{\cdot}d^{-1}$) the backwashing interval was shorten by 8 hours. The COD, BOD, T-N, and T-P were removed from 43 to 66% only by aerobic biodegradation. The SS was removed over 70% by the filtering of $Biobead^{(R)}$ media in the treatment system. The first one of three serial Biobead reactors showed the highest removal values for $COD_{\alpha}$(52.3%), $COD_{Mn}$(38.8%), BOD(62.5%), and T-N(40.0%). The SS and T-P had the highest removal values(47.5% and 29.2%) at the second one of the serial reactors. The biofilm had non-homogeneous spatial distribution and the colonies were embedded in the sunk area of the Biobead. The thickness of the biofilm was very thin ($5.0{\sim}29.4{\mu}m$) compared to the biofilm thickness($200{\sim}300{\mu}m$) used in other BAF systems.

• Journal of the Mineralogical Society of Korea
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• v.18 no.1
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• pp.11-17
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• 2005

Na-A zeolite were synthesized from melting slag of the incinerated ash by the alkaline activation processes. The experiments were performed in stainless steel vessels, with continuous stirring during the reaction periods. The silica-rich solution, a starting material, which was the waste of crystal growth factory, contains 5.7 wt% SiO₂ and 3.2 wt% Na₂O. And NaAlO₂ was made by the reaction of aluminium dross and NaOH solution and its molar ratios were Na₂O/Al₂O₃= 1.2 and H₂O/Na₂O=9. During the residence time of 7∼8 h at 80℃, the mixing of the silica-rich solution, NaAlO₂ and melting slag yields the production of homogeneous Na-A zeolite. The optimal reactant composition in molar ratio of Na₂O:Al₂O₃:SiO₂ was 1.3∼l.4 : 0.8∼0.9 : 2 and mixing ratio of solution and slag was 1/7∼10 (g/cc). Synthesized Na-A zeolite has cubic form uniformly and its size ranges about 1 ㎛. Ca/sup 2+/ ion exchange capacity of the Na-A was about 180∼210 meq/100g, corresponding approximately 80% to the commercial detergent builder.

• Journal of the Mineralogical Society of Korea
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• v.19 no.1 s.47
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• pp.7-14
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• 2006

Melting slag generated from the lots of municipal incineration ash, which causes the one of big urban problems in modern industrial society, was used as starting material for the hydrothermal synthesis of zeolite. P-type zeolite has been successfully synthesized by the combined process of both 'hydrogelation' and 'clay conversion' method. Commercial sodium silicate was used as Si source, and $NaAlO_2$ was prepared by the reaction in a $Na_{2}O/Al_{2}O_{3}$ molar ratio of 1.2. The optimum conditions for zeolite synthesis was found to be the $SiO_{2}/Al_{2}O_{3}$ ratio in the 3.2 and 4.2 range, the $H_{2}O/Na_{2}O$ ratio in the 70.7 and 80.0 range, and more than 15-hour reaction time at $80^{\circ}C$, In the synthesized zeolite, inhomogeneous melting slag particles were disappeared and homogeneous P-type zeolite crystal was grown. The cation exchange capacity of the synthesized zeolite was determined to be approx. 240 cmol/kg.

• Economic and Environmental Geology
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• v.32 no.6
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• pp.611-631
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• 1999

Enviromental geochemisty and heary metal contamination at the Kongjueil mine creek were underaken on the basis of physicohemical properties and mineralogy for various kinds of water (surface, mine and ground water),soil, precipitate and sediment collected of April and December in 1998. Hydrgeochemical composition of the water samples are characterized by relatively significant enricant of Ca+Na, alkiali ions $NO_3$ and Cl inground and surfore water, wheras the mine waters are relatively eneripheral water of the mining creek have the characteristics of the (Ca+Mg)-$(HCO_3+SO_4)$type. The pH of the mine water is high acidity (3.24)and high EC (613$\mu$S/cm)compared with those of surface and ground water. The range of $\delta$D and $\delta^{18}O$ values (relative to SMOW) in the waters are shpwn in -50.2 to -61.6% and -7.0 to -8.6$\textperthousand$(d value=5.8 to 8.7). Using computer program, saturation index of albite, calcite, dolomite in mine water are nearly saturated. The gibbiste, kaolinite and smectite are superaturated in the surface and ground water, respectively. Calculated water-mineral reaction and stabilities suggest that weathing of silicate minerals may be stable kaolinite owing to the continuous water-rock reaction. Geochemical modeling showed that mostly toxic heavy metals may exist larfely in the from of metal-sulfate $(MSO_4\;^2)$and free metal $(M^{2+})$ in nmine water. These metals in the ground and surface water could be formed of $CO_3$ and OH complex ions. The average enrichment indices of water samples are 2.72 of the groundwater, 2.26 of the surface water and 14.15 of the acid mine water, normalizing by surface water composition at the non-mining creek, repectively. Characteristics of some major, minor and rate earth elements (Al/Na, K/Na, V/Ni, Cr/V, Ni/Co, La/Ce, Th/Yb, $La_N/Yb_N$, Co/Th, La/Sc and Sc/Th) in soil and sediment are revealed a narrow range and homogeneous compositions may be explained by acidic to intermediate igneous rocks. And these suggested that sediment source of host granitic gneiss colud be due to rocks of high grade metamorphism originated by sedimentary rocks. Maximum concentrations of environmentally toxic elements in sediment and soil are Fe=53.80 wt.% As=660, Cd=4, Cr=175, Cu=158, Mn=1010, Pb=2933, Sb=4 and Zn=3740 ppm, and extremely high concentrations are found are found in the subsurface soil near the ore dump and precipitates. Normalizing by composition of host granitic gneiss, the average enerichment indices are 3.72 of the sediments, 3.48 of the soils, 10.40 of the precipitates of acid mine drainage and 6.25 of the soils near the main adit. The level of enerichment was very severe in mining drainage sediments, while it was not so great in the soils. mineral composition of soil and sediment near the mining area were partly variable being composed of quartz, mica, feldspar, chlorite, vermiculite, bethierin and clay minerals. reddish variable being composed of quartz, mica, feldspar, chlorite, vermiculite, bethierin and clay minerals. Reddish brown precipitation mineral in the acid mine drainage identifies by schwertmanite. From the separated mineralgy, soil and sediment are composed of some pyrite, arsenopyite, chalcopyrite, sphalerite, galena, malachite, goethite and various kinds of hydroxied minerals.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.366-378
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• 1998

Thermocondensation root canal filling technique have been used to fill accessary canals or to obtain homogeneous root caral fillings. But these thermocondensation technique inevitably produce heat in the canal which can be transmitted through the dentin and cementum and consequently damage periodontal ligamental cells and osteoblasts. In this study, System $B^{TM}$(Analytic technology, WA.D.S.A.) was used to evaluate the reaction of periodontal ligament tissue to "Continous Wave condensation technique" introduced by Buchanan, and the transmitted root surface temperature was measured according to measured root thicknesses. 12 Mandibular incisors of two adult dogs were used for the experiment. 6 controls were filled by lateral condensation technique with sealer.3 specimens were apically filled by Continuous Wave technique at $200^{\circ}C$ for 5 seconds and remaining 3 specimens were additionally backfilled using System $B^{TM}$(Analytic technology, WA.D.S.A.) was used to evaluate the reaction of periodontal ligament tissue to "Continous Wave condensation technique" introduced by Buchanan, and the transmitted root surface temperature was measured according to measured root thicknesses. 12 Mandibular incisors of two adult dogs were used for the experiment. 6 controls were filled by lateral condensation technique with sealer.3 specimens were apically filled by Continuous Wave technique at $200^{\circ}C$ for 5 seconds and remaining 3 specimens were additionally backfilled using System $B^{TM}$ at $100^{\circ}C$ for 20 seconds. Six weeks later, the dogs were sacrificed and the teeth stained with Hematoxylin and Eosin for histologic examination. 6 extracted human teeth were used to measure the transmitted temperature. After cutting off the crown, the canals were prepared and divided into 3 groups with root thickness of 1.5mm, 1.0mm, 0.5mm, 2 teeth in each group. Inside each root canal, System $B^{TM}$ was heated as with the temperature for the apically condensed and the back filled group, and the transmitted heat was measured on the external surface of the root. The temperature of System $B^{TM}$ heat spreader at $200^{\circ}C$ and $100^{\circ}C$ was also measured at root temperature. It can be concluded as follows: 1. In the thin area (200-$250{\mu}m$) of the root, root resorption could be seen even with heating at $200^{\circ}C$ for 5 seconds. 2. When the spreader was heated at $200^{\circ}C$ for 5 seconds and additionally at $100^{\circ}C$ for 20 seconds for backfill, all teeth showed root resorption regardless of their root thickness. 3. The transmitted external root surface temperature was higher as the root thickness decreased and as the heating time increased. In the thermocompaction technique using System $B^{TM}$, the spreader should be heated for the minimal time and used only in the apical area. The heated spreader shouldn't inserted to the binding point of the canal and backfilling should be done with other means of minimally heated gutta percha technique.

• Journal of the Korean Chemical Society
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• v.36 no.6
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• pp.894-905
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• 1992

Dioxygen binding and homogeneous catalytic oxidation of hydrazobenzene were investigated by employing tetradentate Schiff base Cobalt(II) complexes such as Co(II)(SED)$(Py)_2$, Co(II)(SOPD)$(Py)_2$ and Co(II)(SND)$(Py)_2$ in saturated oxygen methanol solvent. The major product of hydrazobenzene ($H_2$AB) oxidation by catalysts of superoxo type [Co(III)(SED)(Py)$O_2$] and [Co(III)(SOPD)(Py)$O_2$] complexes are trans-azobenzene (t-AB) and rate constants k for oxidation reaction was 7.692 ${\times}$ $10^{-2}$ M/sec for [Co(III)(SED)(Py)$O_2$] and 5.076 ${\times}$ $10^{-2}$ M/sec for [Co(III)(SOPD)(Py)$O_2$]. But cis-azobenzene (c-AB) are obtained as a major product with ${\mu}$-peroxo type [Co(III)(SED)(Py)]$_2O_2$ catalyst, and rate constant k is 1.266 ${\times}$ $10^{-2}$ M/sec. The rate constants of oxidation reaction has been studied spectrophotometrically and the rate law established. A mechanism involving a intermediate activated complexes of catalyst, hydrazobenzene and oxygen has been proposed. $H_2$AB + Co(II)(Schiff base)$(Py)_2$ + $O_2$ ${\rightleftharpoons}_{MeOH}^K$ Co(III)(Schiff base)(Py)$O_2$${\cdot}$$H_2$AB + Py $\longrightarrow^k$ Co(II)(Schiff base)$(Py)_2$ + t-AB + $H_2O_2$(Scchiff base : SED and SOPD). $H_2$AB + 2Co(II)(SND)$(Py)_2$ + $O_2$ ${\rightleftharpoons}_{MeOH}^K$ [Co(III)(SND)(Py)]$_2O_2$${\cdot}$H_2$AB + 2Py ${\longrightarrow}^k$ (Co(II)(SND)$(Py)_2$ + c-AB + $H_2O_2$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.165-171
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• 2010

The Homogeneous Charge Compression Ignition (HCCI) engine concept allows for both NOx and particulate matter to be reduced simultaneously, and it is a promising way to meet the next environmental challenges. Unfortunately, HCCI combustion often increases CO and HC emissions. The development of oxidation catalyst (OC) requires high conversion efficiency for CO and HC at low temperature. Conventional oxidation catalyst technologies may not be able to convert these emissions because of the saturation of active catalytic sites. The OC used in this study was 600 cpsi cordierite. Three kinds of OC with different amounts of Pt and Pd were used. The influence of the space velocity (SV), $H_2O$ and $O_2$ concentration was also studied. All types of OCs were found to have over 90% CO conversion efficiencies at $170^{\circ}C$. When in the presence of water vapor, CO conversion was increased, but $C_3H_8$ conversion was decreased. The performance of the OC was not influenced by initial the HC concentration. The 2Pt/Pd catalyst was better in terms of thermal aging than the Pt-only catalyst. The $LOT_{50}$ of both fresh and aged OC was increased with increasing SV and with the presence of $H_2O$.

• Korean Journal of Materials Research
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• v.22 no.12
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• pp.675-681
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• 2012

We aimed to examine the co-doping effects of 1/6 mol% $Mn_3O_4$ and 1/4 mol% $Cr_2O_3$ (Mn:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Mn,Cr-doped ZBS, ZBS(MnCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ (also ${\beta}-Bi_2O_3$ at Sb/Bi ${\leq}$ 1.0) were detected for all of the systems. Mn and Cr are involved in the development of each phase. Pyrochlore was decomposed and promoted densification at lower temperature on heating in Sb/Bi = 1.0 system by Mn rather than Cr doping. A more homogeneous microstructure was obtained in all systems affected by ${\alpha}$-spinel. In ZBS(MnCr), the varistor characteristics were improved dramatically (non-linear coefficient, ${\alpha}$ = 40~78), and seemed to form ${V_o}^{\cdot}$(0.33 eV) as a dominant defect. From impedance and modulus spectroscopy, the grain boundaries can be seen to have divided into two types, i.e. one is tentatively assigned to ZnO/$Bi_2O_3$ (Mn,Cr)/ZnO (0.64~1.1 eV) and the other is assigned to the ZnO/ZnO (1.0~1.3 eV) homojunction.

• Korean Journal of Materials Research
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• v.22 no.12
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• pp.689-695
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• 2012

We have examined the co-doping effects of 1/2 mol% NiO and 1/4 mol% $Cr_2O_3$ (Ni:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and the grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Ni,Cr-doped ZBS, ZBS(NiCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ were detected for all of compositions. For the sample with Sb/Bi = 1.0, the Pyrochlore was decomposed and promoted densification at lower temperature by Ni rather than by Cr. A homogeneous microstructure was obtained for all of the samples affected by ${\alpha}$-spinel. The varistor characteristics were not dramatically improved (non-linear coefficient, ${\alpha}$ = 5~24), and seemed to form ${Zn_i}^{{\cdot}{\cdot}}$(0.17 eV) and ${V_o}^{\cdot}$(0.33 eV) as dominant defects. From impedance and modulus spectroscopy, the grain boundaries were found to have been divided into two types, i.e., one is tentatively assigned to ZnO/$Bi_2O_3$ (Ni,Cr)/ZnO (0.98 eV) and the other is assigned to a ZnO/ZnO (~1.5 eV) homojunction.