• Journal of the Korean Ceramic Society
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• v.20 no.4
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• pp.305-314
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• 1983

In order to enhance the rate of th nitridation and to give the high density of reaction-bonded silicon nitride MgO powder as nitriding aid were added to silicon powders and the mixture was pressed isostatically into compacts which were nitrided in the furnace of 1, 35$0^{\circ}C$ where 95% $N_2$-5% $H_2$ gases were flowing. As the other nitriding aid $Mg(NO_3)_2 6H_2O$ was selected, A slip made of magnesium nitrate solution and fine silicon particles was spray-dried and then decomposed at 30$0^{\circ}C$. Magnesium oxide-coated silicon powders were formed into compacts prior to the nitridation on the same condition as the former. Magnesium nitrate (MgO, produced from the decomposition of magnesium nitrate) was more effective for the formation of the $\beta$-phase in the initial stage of the nitridation probably due to the easy formation of $MgO-SiO_2$-metal oxide eutectic melt. It has been confirmed that forsterite was formed as a result of the reaction between MgO and $SiO_2$ film of silicon surface. It was considered that MgO produced from magnesium nitrate may be finer more reactive and more uniformly distributed on the surface of silicon particles than original MgO. The higher the forming pressure was the more the $\beta$-phase was formed.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1147-1158
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• 1994

From Zr(O-nC3H7)4-H2O-C2H5OH-HNO3 starting solutions, MgO-doped stabilized zirconia fibers with varying content of MgO (10~18 mol%) from different MgO sources were fabricated by sol-gel method. The MgO sources used are magnesium nitrate hexahydrate, magnesium acetate tetrahydrate, and magnesium ethylate. The phase transformation studies of a drawn MgO-ZrO2 fiber were carried out using X-ray diffraction, IR spectroscopy, and Raman spectroscopy. The microstructure, tensile strength, and microporosity of fibers were investigated using SEM, tensile strength test, and microporosimeter. Although various MgO sources such as magnesium nitrate, acetate, and ethylate were used, the crystallization behavior of MgO-ZrO2 fibers at different temperatures could be summarized as follows: CubiclongrightarrowMetastable TetragonallongrightarrowMonocliniclongrightarrowCoexistence of Monoclinic and CubiclongrightarrowCubic(trace of monoclinic). At 150$0^{\circ}C$, the phase transformation of MgO-ZrO2 fibers shows the following change depending on the amount of MgO[Mg(NO3)2.6H2O]: At 10 mol%, both monoclinic and cubic phase coexist, at 12 mol%, monoclinic phase decreases rapidly, and then at 14 mol%, only cubic phase remains. When the MgO-ZrO2 fibers containing 12 mol% magnesium nitrate were heated at 80$0^{\circ}C$ for 1hr, average tensile strength of fibers is 4.0 GPa at diameters of 20 to 30 ${\mu}{\textrm}{m}$. As the heat-treatment temperatures increase to 100$0^{\circ}C$ for 1 hr, tensile strength of MgO-ZrO2 fibers decreases rapidly to 0.7 GPa.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.51-56
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• 2002

The effect of kind of starting materials used for a sintering additive. magnesium acetate and magnesium nitrate, on the mechanical properties of alumina sintered body made by adding 1000 ppm of the additives, respectively, was investigated. As for the alumina sintered bodies prepared from magnesium acetate and magnesium nitrate, we observed that their relative densities decreased rapidly with increasing sintering temperature 1$600^{\circ}C$. Outer layer of alumina bodies had a duplex microstructure consisting of pores and grain growth. Also the inner layer had a second phase between alumina grain boundaries. By EPMA analysis, we confirmed that the grain boundary phase was a compound containing Mg.

• Korean Journal of Environmental Agriculture
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• v.20 no.5
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• pp.340-345
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• 2001

High rates of nitrogen fertilization dangerously increase the nitrate content of vegetable crops, and the accumulation of nitrate in edible crops is undesirable because of potential risks to human health. Micronutrient solution containing Cu, Mn, Mo, Zn was tested for the suppression of nitrate accumulation in lettuce grown in pots treated with Mg fertilizer under a greenhouse condition. The micronutrient solution was sprayed on leaves at 3 and 4 weeks after transplanting of 20-day old seedlings. Plants were harvested after 5-week growth, and yield, contents of chlorophyll, sugar, micronutrient and nitrate, and also nitrate reductase activity were measured. Fresh weight of lettuce was significantly increased by the application of Mg and micronutrients, and the effect was the most significant in the Mg+micronutrient treatment. Also contents of chlorophyll and micronutrients were higher in the plants of micronutrient treatments. Contents of nitrate were reduced by about 14-18% in lettuce with Mg and/or micronutrient applications. Compared to the plants of control treatment, nitrate reductase activity was also higher in those plants treated with micronutrients, and in the treatment of Mg+micronutrients the enzyme activity was six times as high as that of control treatment. Although the effect of mineral nutrients on the suppression of nitrate accumulation in lettuce was relatively small in this study, an appropriate supply of mineral nutrients could be one of the solutions for the nitrate accumulation in vegetables.

• International Journal of Industrial Entomology and Biomaterials
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• v.3 no.1
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• pp.69-73
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• 2001

The effect of topical application 100,300 and 500 $\mu$g/ ml with Mineral Salts of magnesium sulphate and potassium nitrate on economic parameters was ana- lyzed following treatment of last larval stadium. The treated larvae showed significantly decreased larval weight and silk gland weight in all the treated groups along with other decreased Iarval, cocoon and adult parameters. The female cocoon weight was significantly decreased in all the treated groups with decreased female cocoon shell weight and male cocoon weight at 300 and 500$\mu$g/ml respectively. The length and weight of filament was significantly decreased at 300 and 500 $\mu$g/ml respectively and denier at 500 $\mu$g/ ml. The fecundity decreased significantly in 300 and 500 $\mu$g/ml treated groups when compared with the corresponding parameters of the carrier control.

• Journal of Soil and Groundwater Environment
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• v.19 no.1
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• pp.63-69
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• 2014

This paper presents the feasibility of using different iron oxides (microscale hematite (HT), microscale magnetite (MT), and nanoscale maghemite (NMH)) in enhancing nitrate reduction by zero-valent iron (Fe(0)) under two solution conditions (artificial acidic water and real groundwater). Addition of MT and NMH into Fe(0) system resulted in enhancement of nitrate reduction compared to Fe(0) along reaction, especially in groundwater condition, while HT had little effect on nitrate reduction in both solutions. Field emission scanning electron microscopy (FESEM) analysis showed association of MT and NMH with Fe(0) surface, presumably due to magnetic attraction. The rate enhancement effect of the minerals is presumed to arise from its role as an electron mediator that facilitated electron transport from Fe(0) to nitrate. The greater enhancement of MT and NMH in groundwater was attributed to surface charge neutralization by calcium and magnesium ions in groundwater, which in turn facilitated adsorption of nitrate on Fe(0) surface.

• Korean Journal of Environmental Agriculture
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• v.41 no.3
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• pp.158-166
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• 2022

BACKGROUND: Kiwifruit is a fruit tree with relatively small cultivation area in Korea and researches on its soil and physiology are very limited compared to those on cultivar development. Therefore, there are limited information for farmers to cope with the reduction in productivity due to various physiological disorders and premature aging. This study was conducted to investigate the soil and leaf chemical properties, and fruit characteristics, which will be used as basic data for stable kiwifruit orchard soil management. METHODS AND RESULTS: The soil and leaf chemical properties, and fruit characteristics were investigated for two years in 16 kiwifruit orchards growing 'Hayward' (Actinidia deliciosa) in Jeollanam-do and Gyeongsangnam-do. Soil and leaf samples were collected in July and fruit quality was investigated by harvesting fruits about 170 days after full bloom. The average soil chemical properties of kiwi orchards were generally higher than the recommended level, except for pH, and especially, the exchangeable potassium reached about 300% of the recommended level. The proportions of orchards that exceeded the recommended level of soil chemical properties were 63, 31, 100, 69, 94, 88 and 69% for pH, EC, organic content, available phosphate, and exchangeable potassium, calcium and magnesium, respectively. Thirty-three percent of orchards had more than 100 mg/kg of nitrate nitrogen in soil. Available phosphate in soil showed a significantly positive correlation with leaf nitrogen, phosphoric acid and calcium content, but showed a significantly negative correlation with leaf potassium content. The magnesium content in the leaves was significantly correlated with soil pH. The highest fruit weight was observed in about 25 g/kg of leaf nitrogen content which could be attained when plants were grown on the soil containing about 100 mg/kg of nitrate nitrogen content. The average soluble solids content among 16 orchards was 9.58 °Brix at harvest and 13.9 °Brix after ripening, which increased about 45%, and the average fruit weight was about 110 g. CONCLUSION(S): For fruit quality, fruit soluble solids (sugar compounds) content was significantly correlated with leaf potassium content, fruit hardiness with leaf total nitrate, calcium and magnesium, and fruit titratable acidity with leaf magnesium; however, leaf calcium and magnesium negatively affect the soluble solids contents in fruits.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.663-669
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• 2004

Mullite and cordierite, which were stable oxides having excellent thermal and chemical characteristics, were widely used as an engineering and electronic materials. However, thermal shock resistance of the mullite was detriorated, and strength of the cordierite was also reduced at high temperatures. The mullite-cordierite composite powders were synthesized for solving these problems in this study. The mullite-cordierite composite powders were manufactured by the solution-polymerization method using mixtures of fused silica, aluminium nitrate, magnesium nitrate, and PVA. Crystallinity, phase formation, density, and surface area of the synthesis powders were characteristics. Fine mullite-cordlerite composite powders were successfully synthesized at 1300$^{\circ}C$ and their surface areas were about 20㎡/g after planetary milling for 1h. With increasing the milling time, surface area increased to 23 ㎡/g for 4h ana 24㎡/g for 8h.

• The Korean Journal of Ceramics
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• v.5 no.3
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• pp.239-244
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• 1999

Ultrafine lead magnesium niobate $Pb(Mg_{1/3}Nb_{2/3}) O_3$ (PMN) powders have been successfully prepared via a micro-emulsion processing technique. By stepwise hydrolysis using aqueous as the precipitant, hydroxide precursor was obtained from nitrate solutions dispersed in the nanosized aqueous domains of a microemulsion consisting of cyclohexane, non-ionic surfactant (NP5+NP9) and an aueous phase. Upon calcination of the microemulsion-derived precursor at $800^{\circ}C$, PMN powders with 100% perovskite phase was obtained.

• Journal of Korean Society for Atmospheric Environment
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• v.16 no.6
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• pp.573-583
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• 2000

In order to investigate the characteristics of PM(sub)2.5 in the background area, the following pollutant were measured from February 1996 to June 1999 in Kanghwa: PM(sub)2.5 mass, sulfate, nitrate, chloride, ammonium, sodium, calcium, magnesium and potassium. The mean concentration of PM(sub)2.5 mass was 25.8$\pm$1.2$\mu\textrm{g}$/㎥(range 5.18~85.74). This value was higher than the annual PM(sub)2.5 US NAAQS(15$\mu\textrm{g}$/㎥) and the total number of samples higher than the 24-h PM(sub)2.5 US NAAQS(65$\mu\textrm{g}$/㎥) was seven. PM(sub)2.5 masses also showed temporal variations both yearly and seasonally. Total water soluble ions constituted about 45% of PM(sub)2.5 miss, and sulfate, nitrate and ammonium were main components in water soluble ions. Compared with the literature data from other areas, the measured PM(sub)2.5 concentrations were relatively high.