• Journal of the Korean Society for Heat Treatment
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• v.33 no.3
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• pp.129-134
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• 2020

Due to excellent properties such as high specific strength and low density, application of magnesium alloys have been rapidly increased. However, magnesium alloy has a serious problem that is easily oxidized when exposed to high-temperature. For this reason, magnesium alloys have been generally used for SF6 gas such as protective cover gas in casting and melting, but it has been reported that this gas has a serious influence on global warming. Therefore, many researchers have been studied to improve the oxidation resistance of magnesium alloy. It was reported that addition of Be, Ca and CaO in magnesium alloy can improve the oxidation properties. In this study, the possibility of improving the oxidation resistance by adding CaO extracted from oyster shells was investigated. Oyster shells were completely decomposed into CaO and CO₂ by annealing. With the addition of CaO, a coexistence region of MgO + CaO was formed in the oxide layer and its thickness was also reduced.

• Membrane Journal
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• v.18 no.4
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• pp.354-361
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• 2008

Effects of operational conditions and solution chemistry on permeate flux in a hybrid ozone-ceramic ultra-filtration (UF) membrane system treating natural organic matter (NOM) were investigated. Results showed that the extent of permeate flux decline was higher at higher cross-flow velocity and ozone dosage, but it was higher at lower transmembrane pressure (TMP). The mechanism of fouling mitigation was found to be more dependent upon reaction between ozone and natural organic matter at/near catalytic membrane surface than scouring effect due to ozone gas bubbles. Addition of calcium into model NOM solution at high pH led to significant decline in permeate flux while the calcium effect on permeate flux decline was less pronounced at lower pH. After permeate flux decline during the early stage of filtration, the flux started recovering and approached fully to the initial value of it due to degradation of NOM by catalytic ozonation at ceramic membrane surface in the hybrid ozone-ceramic membrane system.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.89-92
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• 2007

Partail oxidation(POX) of n-butane was investigated in this research by employing ceria-promoted Ni/calcium hydroxyapatite catalysts ($Ce_xNi_{2.5}Ca_{10}(OH)_2(PO_4)_6$ ; x = $0.1{\sim}0.3$) which had recently been reported to exhibit good catalytic performance in POX of methane and propane. The experiments were carried out with changing ceria content, $O_2/n-C_4H_{10}$ ratio and temperature. As the $O_2/n-C_4H_{10}$ feed ratio increased up to 2.75, n-$C_4H_{10}$ conversion and $H_2$ yield increased and the selectivity of methane and other hydrocarbons decreased. But with $O_2/n-C_4H_{10}$ = 3.0, $n-C_4H_{10}$ conversion and $H_2$ yield decreased. This is considered due to that too much oxygen may inhibit the reduction of Ni or induce the oxidation of Ni, which results in poor catalytic activity. The optimum $O_2/n-C_4H_{10}$ ratio lay between 2.50 and 2.75. $Ce_{0.1}Ni_{2.5}Ca_{10}(OH)_2(PO_4)_6$ showed the highest $n-C_4H_{10}$ conversion and $H-2$ yield on the whole. In durability tests, higher hydrogen yield and better catalyst stability were obtained with the $O_2/n-C_4H_{10}$ ratio of 2.75 than with the ratio of 2.5.

• Journal of the Korean Chemical Society
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• v.32 no.1
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• pp.22-29
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• 1988

The reaction of methanol-water mixture to $CO_2$ and $H_2$ on alkaline earth metal-copper-zinc oxide has been studied in the temperature range of 150 ${\sim}\;300^{\circ}C$. Generally the addition of the alkaline earth metal to Cu/ZnO resulted in an enhancement of selectivity for $CO_2$ formation and a reduction of catalytic activity. Measurable activities were found from 150$^{\circ}C$, 200$^{\circ}C$, and 250$^{\circ}C$ on Mg/Cu/ZnO, Ca/Cu/ZnO, and Ba/Cu/ZnO respectively. However, the highest selectivity for $CO_2$ formation was observed in Ba/Cu/ZnO catalyst at 250$^{\circ}C$. The effect of alkaline earth metal or ZnO on the reactivity was investigated using temperature programmed desorption of $CO_2$ or temperature programmed reduction with $H_2$ over catalysts respectively. It was found that $CO_2$ interacts more strongly in the sequence of MgO < CaO < BaO and ZnO decereases the reduction temperature of CuO. From the results, it was suggested that ZnO activates $H_2$ in the redox process of Cu component and alkaline earth metals adsorbs $CO_2$ in the catalytic process.

• The Korean Journal of Pharmacology
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• v.26 no.1
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• pp.55-66
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• 1990

In both resting and opsonized zymosan activated neutrophils, ATP stimulated superoxide generation, whereas adenosine inhibited it slightly. The superoxide generation in activated neutrophils to ATP was greater than that of resting neutrophils. In $Ca^{++}$ free medium, inhibitory effect of adenosine on superoxide generation was detectable, whereas ATP did not have any effect. The stimulatory effect of ATP on superoxide generation was inhibited by adenosine in a dose dependent manner. Neither ATP nor adenosine had any effect on NADPH oxidase acitivity. Effects of ATP or adenosine on superoxide generation were more prominent than that by other triphosphate nucleotides or nucleosides. ATP and ADP further stimulated $Ca^{++}$ uptake and increased cytosolic free $Ca^{++}$ level in neutrophils activated by opsonized zymosan, but adenosine inhibited a $Ca^{++}$ mobilization. Verapamil effectively and tetrodotoxin slightly inhibited an increase of cytosolic free $Ca^{++}$ level induced by ATP. Inhibitory effect of either verapamil or tetrodotoxin on superoxide generation in the ATP plus opsonized zymosan-activated neutrophils was greater than in the cells activated by opsonized zymosan alone. Tetraethylammonium chloride had no apparent effect on superoxide generation. CCCP, 2,4-dinitrophenol, diphenylhydantoin and procaine all inhibited superoxide generation in neutrophils activated by opsonized zymosan. Among these, CCCP only inhibited a stimulatory effect of ATP. ATP further stimulated a loss of sulfhydryl groups in activated neutrophils, whereas adenosine had no effect on it. These results suggest that functional responses of neutrophils may be regulated at least partly by purines. ATP and adenosine may further after functional responses of activated neutrophils through their effect on $Ca^{++}$ uptake, membrane phosphorylation and oxidation of soluble sulfhydryl groups.

• Journal of Applied Biological Chemistry
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• v.64 no.2
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• pp.165-170
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• 2021

In this study, the antioxidant effects of mineral-containing deep sea water (DSW) on kidney function was confirmed using a cell model. DSW samples were prepared with different mineral concentrations including calcium and magnesium-the main minerals found in DSW-to derive the following sample groups: trace minerals (TM), high magnesium (HM), high magnesium, low salt (HMLS) and high magnesium, high calcium (HMHC). The purpose of this preparation was to determine the optimal calcium/magnesium ratio in DSW. Human embryonic kidney (HEK293) cells were exposed to sodium chloride (NaCl) for 2 h to induce release of reactive oxygen species (ROS). Thereafter, the cells were treated with the respective DSW samples before ROS concentrations, as well as antioxidant enzyme activity and protein levels, were measured. Among the water samples, HMLS showed the most protective effect against ROS, whereas the intracellular glutathione content was highest in cells from the HMLS- and HMHC-treated groups. However, TM- and HMHC-treated cells showed similar tendencies to the control group, in terms of mRNA expression of antioxidant genes. These results suggested that DSW may aid in preventing renal oxidative stress caused by excessive sodium intake. Furthermore, it was determined that HMLS and HMHC water samples displayed good antioxidant effects in the kidney cell model, based on the combined results of ROS concentration and antioxidant marker measurements.

• Journal of the Korean Chemical Society
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• v.42 no.6
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• pp.618-628
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• 1998

Pure CaO, Mn-doped CaO, Mn/CaO, and K/CaO catalysts were prepared and tested as catalysts for the oxidative coupling of methane in the temperature range of 600 to 800$^{\circ}C$ to investigate the effects of Mn- and K-addition on the catalytic activity of calcium oxide. To characterize the catalysts, X-ray powder diffraction(XRD), XPS, SEM, DSC, and TG analyses were performed. The catalytic reaction was carried out in a single-pass flow reactor using on-line gas chromatography system. Normalized reaction conditions were generally $p(CH_4)/p(O_2)=250$ Torr/50 Torr, total feed flow rate=30 mL/min, and 1 atm of total pressure with He being used as diluent gas. Among the catalysts tested, 6.3 mol% Mn-doped CaO catalyst showed the best $C_2$ yield of 8.0% with a selectivity of 43.2% at 775$^{\circ}C$. The $C_2$ selectivity increased on lightly doped CaO catalysts, while decreased on heavily doped CaO([Mn] > 6.3 mol%) catalysts. 6 wt.% Mn/CaO and 6 wt.% K/CaO catalysts showed the $C_2$ selectivities of 13.2% and 30.9%, respectively, for the reaction. Electrical conductivities of CaO and Mn-doped CaO were measured in the temperature range of 500 to 1000$^{\circ}C$ at Po2's of $10^{-3}\; to\;10^{-1}\;atm.$ The electrical conductivity was decreased with Mn-doping and increased with increasing $P0_2$in the range of $10^{-3}\;to\;10^{-1}\;atm,$ indicating the specimens to be p-type semiconductors. It was suggested that the interstitial oxygen ions formed near the surface can activate methane and the formation of interstitial oxygen ions was discussed on the basis of solid-state chemistry.

• Korean Journal of Soil Science and Fertilizer
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• v.36 no.2
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• pp.80-85
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• 2003

This study was conducted to find out the effect of a lime stabilized slaughterhouse waste(LSW) on the growth of chinese cabbage and soil pH. Two levels of the lime stabilized slaughterhouse waste treatment, 169 and $338kg\;10a^{-1}$, with N-P-K fertilization were tested, and treatments of N-P-K and N-P-K with slaked lime were included in the experiment as a control. Fresh weight of chinese cabbage at harvest was not significantly different among the treatments. However, in the LSW treatment of $169kg\;10a^{-1}$, fresh weight of chinese cabbage was 5% higher comparing to the N-P-K treatment. Contents of N, P, and K in chinese cabbage were higher in the LSW treatments in comparison to the control treatments. Competitive inhibition of Mg uptake by Ca in the treatments of LSW and lime was apparent. Soil pH was increased by the application of LSW, and the increase in the LSW treatment of $169kg\;10a^{-1}$ was nearly the same as the soil pH increase in the slaked lime treatment. The lime stabilized slaughterhouse waste can be considered as a potential soil amendment for amelioration of soil acidity and supply of organic matter as well.

• Korean Journal of Agricultural Science
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• v.27 no.2
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• pp.95-100
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• 2000

This study was carried out to estimate the effect of forest fire on physical and chemical properties of soil. The forest fire was in April 1997 in pinus densiflora dominant forest at Chungju of Chungbuk. After forest fire, dead trees were not cut. Soil samples were collected at 0-5, 5-10, and 10-20cm soil depths in November 1998 from the burned and unburned sites. The analyzed factors were soil organic matter, total N, available P, exchangeable K, Ca, and Mg, and CEC, pH, bulk density, and moisture content. There was no forest floor in burned site, but unburned site has the forest floor of 4cm thick. There were no differences in soil organic matter, total N, available P, exchangeable K, Ca, and Mg, and CEC, pH, bulk density, moisture content in all soil depth, between burned and unburned sites, except in available P in 5-10cm soil depth. Forest fire had not changed the physical and chemical soil properties in this study. However, burning of vegetation and forest floor organic matter may have adverse influence on long-term site productivity.

• Resources Recycling
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• v.18 no.4
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• pp.24-30
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• 2009

Rare earth based calcium aluminate phosphor ($CaAl_2O_4:Eu^{2+}$, $Nd^{3+}$) supported $TiO_2$ nanoparticles are synthesized by using sol-gel method, which are further characterized using powder X-ray diffraction (XRD), fourier transform infrared (FT-IR), diffuse reflectance UV-Visible spectroscopy (DRS UV-Vis) and transmission electron microscopy (TEM). The XRD pattern of as-prepared and sintered phosphor supported $TiO_2$ does not show the tendency to change the crystal structure from anatase to rutile phase up to $600^{\circ}C$. This indicates that the phosphor support might inhibit the densification and crystallite growth by providing dissimilar boundaries. The diffuse reflectance spectral (DRS) measurements showed shift towards longer wavelength indicating reduction in the band-gap energy as compared to free $TiO_2$. The FT-IR spectra of phosphor supported $TiO_2$ nanoparticles show shift in the peak positions to lower wavelengths. This indicates that the $TiO_2$ nanoparticles are not free, but covalently bonded to the phosphor support. TEM micrographs show presence of crystalline and spherical $TiO_2$ nanoparticles (8 - 15 nm diameter) dispersed uniformly on the surface of phosphor.