• Applied Chemistry for Engineering
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• v.4 no.3
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• pp.569-575
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• 1993

The addition of Sn to Pt/${\gamma}$-$A1_2O_3$ catalyst greatly enhanced the activity and decreased the deactivation rate for the dehydrocyclization of paraffins. For the dehydrocyclization of n-octane, there appeared to be an optimal ratio of Pt:Sn=1:4 for 0.75 wt% Pt/${\gamma}$-$A1_2O_3$ catalyst. The addition of K to Pt/${\gamma}$-$A1_2O_3$ also produced a similar effect on the dehydrocyclization of n-hexane. In the case of n-octane, the addition of K led to a less selective catalyst.

• Journal of the Korean Society of Combustion
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• v.8 no.2
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• pp.1-6
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• 2003

Numerical simulations are conducted at atmospheric pressure in order to understand the effect of the oxygen enrichment level on structure of $CH_4/O_2/N_2$ premixed flames. Under several equivalence ratios the flame speeds are calculated and compared with those obtained from the experiments, the results of which are in good agreement. The effects of the oxygen enrichment are investigated on flames under fuel-rich conditions. As the oxygen enrichment level is increased from 0.21 to 1, the flame speed and the temperature are increased. The emission index of $CO_2$ is decreased in cases of flames for fuel rich mixtures, so the efficiency of combustion may be decreased. The maximum emission index of NO is obtained for 0.6 of the oxygen enrichment level.

• Journal of the Korean Ceramic Society
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• v.32 no.11
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• pp.1227-1232
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• 1995

Effect of heating rate on the microstructure of the silicon nitride ceramics has been investigated. The specimens with composition of 92Si3N4-6Y2O3-2Al2O3 (in wt%) were sintered at 176$0^{\circ}C$ under 127 kPa for 3h in N2 atmosphere at various heating rates from 1 to 10$0^{\circ}C$/min. The grain size of larger than 2${\mu}{\textrm}{m}$ and less than 1${\mu}{\textrm}{m}$ were measured and compared for the specimens. Regardless of heating rate, grain size of all the specimens showed bimodal distributions and the fracture toughness remained in the range of 5.53~5.72 MPa.m1/2. However, the aspect ratio of the grains of diameter above 2${\mu}{\textrm}{m}$ increased with the heating rate while their grain size and volume fraction decreased.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.6
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• pp.1010-1015
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• 2011

The objectives of this study were to investigate soil chemical characteristics for forest rehabilitation and suggest management in abandoned coal mine areas in Hwasun-gun, South Jeolla Province. Total study sites were 8 sites, and soil analysis particular were soil pH, TOC, total-N, C/N ratio, Avail. $P_2O_5$, and CEC. Average soil pH was 5.8 (4.7~6.4). Average contents of TOC, total-N and C/N ratio were 1.1% (0.2~2.0%), 0.08% (0.02~0.13%) and 15.0 (7.9~31.4), respectively. Average Avail. $P_2O_5$ was $8.3mg\;kg^{-1}$ (2.7~15.0) and Average CEC was $13.7cmol_c\;kg^{-1}$ ($9.9{\sim}18.5cmol_c\;kg^{-1}$). Soil pH was decreased according to elapsed time from forest rehabilitation, while TOC, total N and CEC were increased. Av. $P_2O_5$ did not show any relationship with elapsed time. Soil pH was stable comparing with general forest soil in South Jeolla Province (5.1), while contents of TOC and total N were lower than general forest soil in South Jeolla Province (4.9% and 0.18%, respectively). Therefore, sustainable managements such as fertilization for TOC and total N are necessary for good rooting and growth of vegetation.

• Journal of the Korean Ceramic Society
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• v.21 no.1
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• pp.11-18
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• 1984

$eta$-Sialon synthesis was investigated via the simultaneous reduction and nitridation of Hadong Pink Kaolin using the graphite as a reducing agent at 135$0^{\circ}C$ under 80% $N_2-20%H_2$ atmosphere. When Hadong Pink Kaolin-graphite-silicon nitride seed(molar ratio ; $SiO_2:C:Si_3N_4$=1;3.5:0.05) mixture was heated at 135$0^{\circ}C$ for as long as 20h in 80%$N_2-20%H_2$ atmosphere a homogeneous $eta$-Sialon$(Si_{3.5}Al_{2.5}O_{2.5}N_{2.5})$ was mainly formed together with a small amount of $\alpha$-$Si_3N_4$.

• Journal of the Korean Magnetic Resonance Society
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• v.18 no.2
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• pp.74-81
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• 2014

The $N_2O_2$ tetradentate Schiff base ligand, N,N'-bis(salicylidene)pentane-1,3-diamine (Salpn), coupled with 1:2 concentration ratio of 1,3-diaminopentane and salicylaldehyde was used to produce a series of macrocyclic Nikel(II) complexes. In the metal complexation, it was observed that Salpn macrocyclic ligand can adopt more than a metal ion giving an unique multinuclear metal complexes including Ni(II)Salpn and $Ni(II)_3(Salpn)_2$. Characteristic IR ${\upsilon}(M-O)$ peaks for Ni(II)Salpn and $Ni(II)_3(Salpn)_2$ were observed to be $1028cm^{-1}$ and $1024cm^{-1}$, respectively. Characteristic UV-Vis absorption ${\lambda}_{max}$ peaks for $Ni(II)_3(Salpn)_2$ were observed to be 241nm and 401 nm. Structural characterization of $Ni(II)_3(Salpn)_2$ by NMR exhibits that the salicylidene ring moiety has two different resonance signals originated from the magnetically asymmetric diligand and trinuclear bis complex. Complete NMR signal assignments and characterizations elucidating structural features of $Ni(II)_3(Salpn)_2$ were described in detail.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.13 no.3
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• pp.178-189
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• 2008

The distribution of inorganic nutrients and their remineralization ratio in the divergence zone ($7^{\circ}{\sim}10.5^{\circ}N$) of the northeastern Pacific were investigated from July 2003 to July 2007. A divergence zone along the boundary of the North Equatorial Counter Current (NECC) and North Equatorial Current (NEC) at $10^{\circ}N$ was observed in July 2007 when the La Nina event and divergence-related upwelling was strong. The mean depth of oligotrophic surface mixed layer in the divergence zone was 46, 61, and 30 m in July 2003, August 2005, and July 2007, respectively. Below the surface mixed layer, a nutricline was clearly observed. The depth integrated value of nitrate including nitrite (DIVn) in the upper layer($0{\sim}100$ m depth) ranged from 5.51 to 21.71 $gN/m^2$(mean 12.82 $gN/m^2$) in July 2003, from 5.62 to 8.46 $gN/m^2$ (mean 7.15 $gN/m^2$) in August 2005, and from 8.98 to 27.80 $gN/m^2$(mean 21.12 $gN/m^2$) in July 2007. The maximum DIVn was observed at the divergence zone. The distributions of phosphate(DIVp) and silicate(DIVsi) were similar to that of DIVn and the DIVn/DIVsi ratio was $0.87{\pm}0.11$ in the upper layer. The limiting nutrient for phytoplankton growth in the study area was identified as nitrogen(N/P ratio=14.6). The nitrate (including nitrite) concentrations were lower in the region mainly affected by NEC than in the region affected by NECC. The study area of low silicate concentrations was also considered to be Si-limiting environment. The remineralization ratios of nutrients were $P/N/-O_2=1/14.6{\pm}1.1/100.4{\pm}8.8(23.44{\leq}Sigma-{\theta}{\leq}26.38)$ in the study area. These ratios suggested remineralization process in the surface layer of divergence zone.

• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.82-87
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• 2008

$N_2O$ decomposition characteristics of dual bed mixed metal oxide catalytic system was investigated. The partial oxidation of methane at first reactor of dual bed catalytic system was performed over Co-Rh-Al (1/0.2/1) catalyst under the optimized condition of $8,000h^{-1}$ GHSV, gas ratio ($CH_4:O_2=5:1$) at $500^{\circ}C$. In the dual bed system investigated herein, the second catalyst bed was employed for the $N_2O$ decomposition using product of partial oxidation of methane at first bed. An excellent $N_2O$ conversion activity even at lower temperature ($<250^{\circ}C$) was obtained with Co-Rh-Al (1/0.2/1) or Co-Rh-Zr-Al (1/0.2/0.3/1) catalyst by combining Co-Rh-Al (1/0.2/1) hydrotalcite catalyst for the partial oxidation of methane in a dual-bed system. The $N_2O$ conversion activity is drastically reduced in the presence of oxygen in second bed of a dual-bed system over Co-Rh-Al (1/0.2/1) catalyst at $300^{\circ}C$.

• Journal of the Korean institute of surface engineering
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• v.48 no.5
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• pp.211-217
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• 2015

To fabricate white LED having a high color rendering index value, red color phosphor mixed with the green color phosphor together in the blue chip, namely the blue chips with RG phosphors packaging is most favorable for high power white LEDs. In our previous papers, we reported on successful syntheses of $Sr_{2-}$ $Si_5N_8:Eu^{2+}$ and $CaAlSiN_3$ phosphors for red phosphor. In this work, for high power green phosphor, greenemitting ternary nitride $Ba_3Si_6O_{12}N_2:Eu^{2+}$ phosphor was synthesized in a high frequency induction furnace under $N_2$ gas atmosphere at temperatures up to $1400^{\circ}C$ using $EuF_3$ as a raw material for $Eu^{2+}$ dopant. The effects of molar ratio of component and experimental conditions on luminescence property of prepared phosphors have been investigated. The structure and luminescence properties of prepared $Ba_3Si_6O_{12}N_2:Eu^{2+}$ phosphors were investigated by XRD and photoluminescence spectroscopy. The excitation spectra of $Ba_3Si_6O_{12}N_2:Eu^{2+}$ phosphors indicated broad excitation wavelength range of 250 - 500 nm, namely from UV to blue region with distinct enhanced emission spectrum peaking at ${\approx}530nm$.

• Membrane and Water Treatment
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• v.6 no.4
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• pp.263-276
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• 2015

This paper deals with the influence of chemical oxygen demand to nitrogen ratio ((COD/N) ratio) on the performance of an membrane bioreactor. We aim at establishing relations between COD/N ratio, organisms' distribution and sludge properties (specific resistance to filtration (SRF) and membrane fouling). It is also essential to define new criteria to characterize the autotrophic microorganisms, as the measurements of apparent removal rates of ammonium seem irrelevant to characterize their specific activity. Two experiments (A and B) have been carried on a 30 L lab scale membrane bioreactor with low COD/N ratio (2.3 and 1.5). The obtained results clearly indicate the role of the COD/N ratio on the biomass distribution and performance of the membrane bioreactor. New specific criteria for characterising the autotrophic microorganisms activity, is also defined as the ratio of maximum ammonium rate to the specific oxygen uptake rate in the endogenous state for autotrophic bacteria which seem to be constant whatever the operating conditions are. They are about 24.5 to 23.8 $gN-NH_4{^+}/gO_2$, for run A and B, respectively. Moreover, the filterability of the biological suspension appear significantly lower, specific resistance to filtration and membrane fouling rate are less than $10^{14}m^{-2}$ and $0.07\;10^{12}m^{-1}.d^{-1}$ respectively, than in conventional MBR confirming the adv < antage of the membrane bioreactor functioning under low COD/N ratio.