• Korean Journal of Dental Materials
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• v.44 no.3
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• pp.207-216
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• 2017

The effect of cooling rate on precipitation hardening of a Pd-Cu-Ga-Zn metal-ceramic alloy during porcelain firing simulation was investigated and the following results were obtained. When the cooling rate was fast (Stage 0), the hardness of the alloy increased at each firing step and the high hardness value was maintained. When the cooling rate was slow (Stage 3), the hardness was the highest at the first stage of the firing, but the final hardness of the alloy after complete firing was lower. The increase in hardness of the specimens cooled at the cooling rate of Stage 0 after each firing step was caused by precipitation hardening. The decrease in hardness of the specimens cooled at the cooling rate of Stage 3 after each firing step was attributed to the coarsening of the spot-like precipitates formed in the matrix and plate-like precipitates. The matrix and the plate-like precipitates were composed of the $Pd_2(Cu,Ga,Zn)$ phase of CsCl-type, and the particle-like structure was composed of the Pd-rich ${\alpha}$-phase of face-centered cubic structure. Through the porcelain firing process, Cu, Ga, and Zn, which were dissolved in Pd-rich ${\alpha}$ particles, precipitated with Pd, resulting in the phase separation of the Pd-rich ${\alpha}$ particles into the Pd-rich ${\alpha}^{\prime}$ particles and ${\beta}^{\prime}$ precipitates composed of $Pd_2(Cu,Ga,Zn)$. These results suggested that the durability of the final prosthesis made of the Pd-Cu-Ga-Zn alloy can be improved when the cooling rate is fast during porcelain firing simulation.

• Journal of Applied Biological Chemistry
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• v.58 no.1
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• pp.39-50
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• 2015

Stabilization of heavy metals such as Pb, Cd, Zn, and Cu was evaluated in contaminated soil treated with poultry manure (PM) as well as its biochars pyrolyzed at $300^{\circ}C$ (PBC300) and $700^{\circ}C$ (PBC700) at the application rates of 2.5, 5.0, and 10.0 wt% along with the control, prior to 21-days incubation. After incubation, soil pH was increased from 6.94 (control) to 7.51, 7.24, and 7.88 in soils treated with PM 10 wt%, PBC300 10 wt%, and PBC700 10 wt% treatments, respectively, mainly due to alkalinity of treatments. In the soil treated with PM, the concentrations of the toxicity characteristic leaching procedure (TCLP)-extractable Pb, Cd, Zn, and Cu were increased by up to 408, 77, 24, and 955%, respectively, compared to the control. These increases may possibly be associated with an increased dissolved organic carbon concentration by the PM addition. However, in the soil treated with PBC700, TCLP-extractable Pb, Cd, Zn, and Cu concentrations were reduced by up to 23, 38, 52, and 36%, respectively, compared to the control. Thermodynamic modelling using the visual MINTEQ was done to predict the precipitations of $Pb(OH)_2$, $Cu(OH)_2$ and P-containing minerals, such as chloropyromorphite [$Pb_5(PO_4)_3Cl$] and hydroxypyromorphite [$Pb_5(PO_4)_3OH$], in the PBC700 10 wt% treated soil. The SEM-elemental dot mapping analysis further confirmed the presence of Pb-phosphate species via dot mapping of PBC700 treated soil. These results indicate that the reduction of Pb concentration in the PBC700 treated soil is related to the formations of chloropyromorphite and hydroxypyromorphite which have very low solubility.

• Journal of Soil and Groundwater Environment
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• v.10 no.5
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• pp.25-36
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• 2005

Several metalliferous and coal mines, including Myungjin, Seojin and Okdong located at the upper watershed of Okdong stream, were abandoned or closed since 1988 due to the mining industry promotion policy. Thus these disposed an enormous amount of mining wastes without a proper treatment facilities, resulting in water pollution in the downstream areas. Acid mine drainage (AMD) and waste water effluents from the closed coal mines were very strongly acidic showing pH ranges of 2.7 to 4.5 and had a high level of Total Dissolved Solids (TDS) showing the ranges of 1,030 to 1,947 mg/L. Also heavy metal concentrations in these samples such as Fe, Cu, Cd and anion such as sulfate were very high. Concentrations of water soluble heavy metals in the Okdong streams were in the orders of Fe>Al>Mn>Zn>Cu>Pb>Cd, indicating Fe from the AMD and waste water effluents contributed greatly to the quality of water and soil in the lower watershed of Okdong stream. Copper concentrations in the effluents from the tile drainage of mine tailings dams were highest during the raining season. Water Pollution Index (WPI) of the surface water at the upper stream of Okdong river where AMD of the abandoned coal mines was flowed into main stream were in the ranges of 16.3 to 47.1. On the other hand, those at the mid stream where effluents from tailings dams and coal mines flowed into main stream were in the WPI ranges of 10.6 to 19.5. However, those at the lower stream were ranged from 10.6 to 14.9. These results indicated that mining wastes such as AMD and effluents from the closed mines were the major source to water pollution at the Okdong stream areas.

• Economic and Environmental Geology
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• v.45 no.1
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• pp.9-21
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• 2012

In this study, we investigated the chemical characteristics of soils collected from the several deserts and loess in China known as the typical source areas of Asian dust (the Taklamakan desert, the Alashan desert, the Ordos desert and the Loess Plateau). Based on our analysis, we examined the possibility of adverse effects on environments and human health. In each desert and loess, major elemental compositions of soils did not show large variations, implying that the long-periodic mixing of soils in each area made their chemical compositions homogeneous. Minor elements of soils in each desert and loess showed more complicated patterns with strong correlations each other (e.g., Cr, Cu, As, Co, Ni, V, Y, Sc, Sn, Pb, Zn, Cd, Cs, Li, Th, U). These results thus enable us to discriminate the soil of the Loess Plateau from those of the other deserts in China. The results of sequential extraction experiments for soils showed that the chemical speciation of Fe was dominant in residual fraction (>85%) in all deserts and loess, but the fractions of Mn and Ca chemical speciations were very different in each area. In the case of Mn, the fraction of amorphous Fe-Mn hydroxides (55.4%) in the Central Loess Plateau and the carbonate fraction (33.8%) in Taklamakan desert were higher as much as 2 to 5 times than other deserts. The chemical speciations of Ca are dominant in carbonate fraction in Taklamakan (75.9%) and Alashan (50.5%) deserts, but carbonate fractions of Ca in the Loess Plateau and Ordos deserts were low (6.6% and 2.1%, respectively). According to the mobility of trace elements inferred from the results of sequential extraction procedure, we could classify them into five groups, and the mobility of Cd, Pb and Cu are more than 87%, 33% and 30%, respectively. Therefore, Cd, Pb and Cu in soils of deserts and loess could be easily dissolved when interacted with surface water. As such, they could give adverse effects on surficial environments and human health.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.12
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• pp.1249-1256
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• 2005

This study was performed to investigate the efficiency of the corrosion prevention in the simulated distribution system using CCPP(Calcium Carbonate Precipitation Potential) as the anti-corrosive index by adjusting pH, total dissolved solids, alkalinity and calcium hardness in the water treatment pilot process. The materials of the simulated distribution system(SDS) were equiped with same materials of real field water distribution system. CCPP concentrations controlled by $Ca(OH)_2$, $CO_2$ gas and $Na_2CO_3$ in the simulated distribution system and uncontrolled by the chemicals in the general water distribution system were average 0.61 mg/L and -7.77 mg/L. The concentrations of heavy metals like Fe, Zn, Cu ions in effluent water of the simulated distribution system controlled with water quality were decreased rather than the general water distribution system uncontrolled with water quality. In simulated distribution system(SDS), corrosion prevention film formed by CCPP control was observed that scale was come into forming six months later and it was formed into density as time goes on. We were analyzed XRD(X-ray diffraction) for investigating component of crystal compounds and structure for galvanized steel pipe(15 mm). Finding on analysis, scale was compounded to $Zn_4CO_3(OH)_6{\cdot}H_2O$ (Zinc Carbonate Hydroxide Hydrate) after ten months late, and it was compounded on $CaCO_3$(Calcium Carbonate) and $ZnCO_3$(Smithsonite) after nineteen months later.

• Korean Journal of Environmental Agriculture
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• v.20 no.1
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• pp.20-27
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• 2001

Stream water chemistry in the abandoned Boeun Jeil coal mine area was studied for a period of 3 months, including rainy and dry season. The stream waters were a nearly neutral and slightly alkali condition, and $Mg-SO_4$ type with Mg>Ca>Na>K and $SO_4>HCO_3>Cl>NO_3$. Chemical composition of the stream water was quite irregular during the experimental period. Concentrations of Na, K, $HCO_3$, U, Sr, and Cr decreased by $10{\sim}30%$ during rainy season, caused by dilution effects with rain. The concentration of Ca, Mg, $NO_3$, Cd, and Co increased during the rainy season, caused by more easily dissolved from bedrocks or mine drainage with slightly acidic condition than dry season. The stream water was enriched in Mg, Ca, $HCO_3$, $SO_4$, Al, Fe, Zn, Ni, Co, Cr, Cd, Sr and U. Concentrations of Na, Mg, Ca, $SO_4$, $HCO_3$, Fe, Zn, Ni, Sr, and U decreased linearly with distance from the mine adit. These elements were strongly controlled by dilution of unpolluted water influx and/or adsorption on the clay minerals and iron oxyhydroxide precipitates. This mine area exhibited two main weathering processes ; 1) oxidation with acidification derived from Fe sulphides, and 2) pH buffering due to Ca and Mg carbonate dissolution. This weathering processes were followed by adsorption of metals on iron oxyhydroxides and precipitation.

• Korean Journal of Environmental Biology
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• v.27 no.2
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• pp.183-190
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• 2009

Characterization of the analysis of forest vegetation, soil environmental conditions and water quality were performed from March 2003 to March 2007. The two basins were characterized by cultivated area (Kaesim reservoir) and mountain area (Jangchan reservoir), and divided into eleven small basins, where dynamics of pollutants, forest vegetation and soil environmental conditions were surveyed. The vegetation can be divided into 10 types by $Z\ddot{u}rich$-Montpellier school's method. Pearson coefficients between vegetation type and water quality were correlated with dissolved oxygen (DO) in the Quercus variabilis community at the 5% level and total phosphorus (TP) in the Larix leptolepis plantation at the 1% level. Especially total phosphorous and total nitrogen increased in small basins where the proportion of cultivated and residential area increased. The analysis of influences of pollutant discharge on water quality showed that pollutant charge was very low in forest land area ($Y_{T-P}$=-0.0017X+0.2215, r=0.16, $Y_{COD}$=- 0.0395X+8.5051 r=0.47). The soil types of western area were comparatively simple, but those of eastern area were complicated with regosols, red-yellow soils, lithosoles, etc. The pH, total solid (TS) and volatile substance (VS) of the forest and agricultural land soils collected in each site were 5.4~6.9, 75.8~80.2%, and 3.80%~5.80%, respectively. According to the analytical result of soil environmental conditions, heavy metal contents fell short to the mean value of natural conditions. Runoff amount (Y) and depth of topsoil (X) were negatively correlated, $Y_{ron}=-1.0088X_{top}+35.378$ (r=0.68). The correlation was much lower in up-stream but much higher in down-stream, because permeation into soil particle was larger on down-stream due to its more or less gentle slope. Pearson coefficients between soil pH and water pH were statistically significant at 1% level.

• Restorative Dentistry and Endodontics
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• v.22 no.1
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• pp.1-33
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• 1997

The objective of this study was to analyze the in vitro and in vivo corrosion products of low and high copper amalgams. The four different types of amalgam alloy used in this study were Fine cut, Caulk spherical, Dispersalloy, and Tytin. After each amalgam alloy and Hg were triturated according to the directions of the manufacturer by means of the mechanical amalgamator(Amalgam mixer. Shinhung Co. Korea), the triturated mass was inserted into a cylindrical metal mold which was 12mm in diameter and 10mm in height. The mass was condensed by 150Kg/cm compressive force. The specimen was removed from the mold and aged at room temperature for about seven days. The standard surface preparation was routinely carried out by emery paper polishing under running water. In vitro amalgam specimens were potentiostatically polarized ten times in a normal saline solution at $37^{\circ}C$(potentiostat : HA-301. Hukuto Denko Corp. Japan). Each specimen was subjected to anodic polarization scan within the potential range -1700mV to+400mV(SCE). After corrosion tests, anodic polarization curves and corrosion potentials were obtained. The amount of component elements dissolved from amalgams into solution was measured three times by ICP AES(Inductive Coupled Plasma Atomic Emission Spectrometry: Plasma 40. Perkim Elmer Co. U.S.A.). The four different types of amalgam were filled in occlusal and buccal class I cavities of four human 3rd molars. After about five years the restorations were carefully removed after tooth extraction to preserve the structural details including the deteriorated margins. The occlusal surface, amalgam-tooth interface and the fractured surface of in vivo amalgam corrosion products were analyzed. In vivo and in vitro amalgam specimens were examined and analyzed metallographically by SEM(Scanning Electron Microscope: JSM 840. Jeol Co. Japan) and EDAX(Energy Dispersive Micro X-ray Analyser: JSM 840. Jeol Co. Japan). 1. The following results are obtained from in vitro corrosion tests. 1) Corrosion potentials of all amalgams became more noble after ten times passing through the in vitro corrosion test compared to first time. 2) After times through the test, released Cu concentration in saline solution was almost equal but highest in Fine cut. Ag and Hg ion concentration was highest in Caulk spherical and Sn was highest in Dispersalloy. 3) Analyses of surface corrosion products in vitro reveal the following results. a)The corroded surface of Caulk spherical has Na-Sn-Cl containing clusters of $5{\mu}m$ needle-like crystals and oval shapes of Sn-Cl phase, polyhedral Sn oxide phase. b)In Fine cut, there appeared to be a large Sn containing phase, surrounded by many Cu-Sn phases of $1{\mu}m$ granular shapes. c)Dispersalloy was covered by a thick reticular layer which contained Zn-Cl phase. d)In Tytin, a very thin, corroded layer had formed with irregularly growing Sn-Cl phases that looked like a stack of plates. 2. The following results are obtained by an analysis of in vivo amalgam corrosion products. 1) Occlusal surfaces of all amalgams were covered by thick amorphous layers containing Ca-P elements which were abraded by occlusal force. 2) In tooth-amalgam interface, Ca-P containing products were examined in all amalgams but were most clearly seen in low copper amalgams. 3) Sn oxide appeared as a polyhedral shape in internal space in Caulk spherical and Fine cut. 4) Apical pyramidal shaped Sn oxide and curved plate-like Sn-Cl phases resulted in Dispersalloy. 5) In Tytin, Sn oxide and Sn hydroxide were not seen but polyhedral Ag-Hg phase crystal appeared in internal space which assumed a ${\beta}_l$ phase.

• The Korean Journal of Malacology
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• v.29 no.1
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• pp.51-63
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• 2013

To assess the effect of environmental factors on the sustainability of cultured production shellfish, we investigated the habitat characteristics of tidal flat (Namhae-po in Taean). We measured the physiochemical parameters (temperature, salanity, pH, dissolved oxygen and nutrients) and the geochemical characteristics (chemical oxygen demand, ignition loss, C/N ratio and C/S ratio). Surface sediments were collected from several site of tidal flat to examine the geochemical characteristics of both the benthic environment and heavy metal pollution. The grain size for research area of tidal flat were similar at the ratio of silt and clay in comparison with the other site of it. The C/N ratio was more than 5.0, reflecting the range arising from the mix of marine organism and organic matter. The C/S ratio (about 2.8) showed that survey area had anoxic or sub-anoxic bottom conditions. The enrichment factor (Ef) and index of accumulation rate (Igeo) of the metals showed that those research areas can be classified as heavily polluted, heavily to moderately polluted, or more or less unpolluted, respectively. Adult surf clam (Mactra veneriformis) density was highest at St. 2 (middle part of the Namhae-po), on the other hand, surf clam spat density was highest at St. 3 (lower part of the Namhae-po). Heavy rain, terrigenous suspended clay with fresh water from neighboring agricultural land, and severe high air temperature during summer could be thought as detrimental causes of spat and adult mortality in Namhae-po tidal flat. We suggested that the growth of shellfish in the tidal flat was effected by the various environmental conditions, so an improvement in the cultured method was needed.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.26 no.2
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• pp.124-134
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• 2021

Water in the Mulgol pond on Dokdo (island), Korea, was historically used for drinking water, but now it has been no longer used for this purpose due to regionally low water quality. Since 2007, this pond has been covered with a metal lid to protect from pollutants of seabirds, indicating limited light penetration into the Mulgol pond. Here, we investigated water quality in the pond and potential relationships of nitrogen components and microbes in May, June, August, and November 2020. The source salinity ranged from 1.39 to 1.57 psu. Suspended solids (0.8~5.1 mg L^-1) and chlorophyll-a (<0.01~0.49 ㎍ L^-1) remained low. The concentration of dissolved inorganic nitrogen (DIN) was between 35.9 and 47.2 mg L^-1. Thus, water in the Mulgol pond proves to be brackish water with low chlorophyll-a and high nutrients. This unique environment may be established by limited light intensity, sea fog (or seawater), and fecal pellets from many seabirds. Although the light source (800~8000 lux) was exposed to the four subsamples, chlorophyll-a concentrations were below <0.5 ㎍ L^-1 during the incubation periods. This result suggests that the biomass of phytoplankton does not increase along with an increase in light intensity. Furthermore, the content of nitrate constituted more than 90% of DIN, and a significant negative correlation between nitrate concentration and bacterial abundance was shown in May and June 2020 during the light exposure experiments (R=-0.762, p<0.05). Thus, it is possible that bacteria may be a significant agent to reduce nitrate concentration in the Mulgol pond, the relationship between nitrate concentration and bacterial abundance may vary seasonally.