• Korean Journal of Soil Science and Fertilizer
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• v.48 no.5
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• pp.436-441
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• 2015

The chemical properties of paddy fields in Gyeonggi province were monitored every 4 years from 1999 to 2015 in order to provide basic information for soil fertility management of paddy fields. In 2015, the soil chemical properties of paddy fields were 5.9 in pH, $23g\;kg^{-1}$ in organic matter (OM), and $84mg\;kg^{-1}$ in available phosphate (Avail. $P_2O_5$). Exchangeable (Exch.) potassium (K), calcium (Ca) and magnesium (Mg) were 0.30, 5.1 and $1.3cmol_ckg^{-1}$, respectively, and available silicate (Avail. $SiO_2$) was $129mg\;kg^{-1}$. In the long-term analysis, the contents of Avail. $SiO_2$, Exch. Ca and pH of paddy soils showed increasing tendency. However, Avail. $P_2O_5$ and Exch. K tended to decrease, and there were no significant changes in the contents of OM and Exch. Mg. Paddy soil within appropriate pH range increased from 44% in 1999 to 76% in 2003, 84% in 2007, 63% in 2011, and 80% in 2015. But soil within appropriate range of Exch. Ca tended to decrease, showing 36% in 1999, 42% in 2003, 38% in 2007, 37% in 2011 and 32% in 2015. In case of Avail. $SiO_2$, soil within appropriate range increased from 14% in 1999 to 17% in 2003, 18% in 2007, 16% in 2011, and 31% in 2015. As a result, paddy fields with less in nutrient level need to be more fertilized based on soil analysis. And the application of silicate fertilizer is strongly recommended to those of paddy fields in need. Also soil management such as the cultivation of green manure crop or application of rice straw will be necessary to increase the organic matter content of paddy soil.

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.948-954
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• 2002

Porous reaction bonded SiC with high fracture strength was developed using Si melt infiltration method for use of the support layer in high temperature gas filter that is essential to develop the next generation power system such as integrated gasification combined cycle system. The porosity and pore size of porous RBSC developed in this study were in the range of 32∼36% and 37∼90 ${\mu}m$ respectively and the maximum fracture strength of porous RBSC fabricated was 120 MPa. The fracture strength and thermal shock resistance of porous RBSC fabricated by Si melt infiltration were much improved compared to those of commercially available porous clay bonded SiC due to the formation of the strong SiC/Si interface between SiC particles. The characteristics of pore structure of porous RBSC was varied depending on the amounts of residual Si as Well as the size of SiC particle used in green body.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.367-369
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• 1988

We suggest a new annealing method for stabilization of $Si-SiO_2$ interface state in MOS device using $NH_3$(10%) + $N_2$(90%) ambient gases. The annealing effect was examined through C-V characteristics, threshold voltage, effective mobility on channel, respectively. The experimental result show that the new method is available to improvement of MOS device characteristics.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.119-126
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$ balls were fabricated using different raw materials, sintering aids and sintering conditions, Commercially available Si3N4 ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 9.525mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) mjcrostructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$Phase.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.240-244
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• 1999

Monolithic SiC and SiC/C functionally gradient material (FGM) layers were deposited on graphite substrates by CVD method. Temperature a profiles and thermal stress distributions in the deposited layers under the thermal shock were calculated by a commercially available software package. The designed FGM specimens were found to show an efficient relaxation of thermal stresses at the interfaces, and the specimens were intact even under a thermal shock of $\Delta$T=1600 K.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.676-678
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• 2004

In order to develop new yellow phosphor that emit efficiently under the 450 - 470 nm excitation range, we have synthesized a $Eu^{2+}$-activated $Sr_3SiO_5$ yellow phosphor and investigated an attempt to develop white LEDs by combining it with a InGaN blue LED chip (460 nm). Two distinct emission bands from the InGaN-based LED and the $Sr_3SiO_5$:Eu phosphor are clearly observed at 460 nm and at 570 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that InGaN (460 nm chip)-based $Sr_3SiO_5$:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460 nm chip)-based YAG:Ce.

• Journal of the Korean Chemical Society
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• v.56 no.4
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• pp.478-483
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• 2012

We successfully synthesized $Fe_3O_4/SiO_2$ nanoparticles with ultrathin silica layer of $1.0{\pm}0.5$ nm that was fine controlled by changing concentration of $Fe_3O_4$. Among various reaction conditions for silica coating, increasing concentration of $Fe_3O_4$ was more effective approach to decrease silica thickness compared to water-to-surfactant ratio control. Moreover, we found that concentration of the 1-octanol is also important factor to produce the homogeneous $Fe_3O_4/SiO_2$ nanoparticles. The present approach could be available to apply on preparation of other core/shell nanoparticles with ultrathin silica layer.

• Tribology and Lubricants
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• v.15 no.2
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• pp.150-155
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$balls were fabricated using different raw materials, sintering aids and sintering conditions. Commercially available Si$_3$N$_4$ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls fer Ball Bearings) with a size of 9.525 mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) microstructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$phase.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.243-245
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• 2009

The single phase $Ba_2SiS_4$ doped with $Eu^{2+}$ was successfully synthesized by direct sulfurization of an oxide precursor prepared by a spray drying method using a novel water soluble silicon compound, which remains soluble in a given aqueous solution. The intensity of the emission peak of thus obtained $Ba_2SiS_4:Eu^{2+}$ was 1.75 times larger than that of a sample prepared by a solid state reaction method, and it approached 106% compared to one of the best commercially available YAG:$Ce^{3+}$ phosphor.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1274-1275
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• 2009

We report on preparation of $CaBaSiS_4:Eu^{2+}$ material by an advanced chemical solution method and fluorescent properties of the new material. The emission spectrum of $CaBaSiS_4:Eu^{2+}$ has the main peak centered at 598 nm, with the corresponding excitation maximum at around 420 nm. The strongest emission intensity of this material approached 96% compared to one of the best commercially available YAG:$Ce^{3+}$ phosphor.