• Journal of the Korean Applied Science and Technology
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• v.31 no.3
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• pp.446-452
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• 2014

Methanol was directly produced by the partial oxidation of methane with four-component mixed oxide catalysts. Four-component(Mo-Bi-Cr-Si) mixed oxide catalysts were prepared by the co-precipitation and sol-gel methods. The catalyst prepared by the sol-gel method showed about eleven times higher surface area than that prepared by the co-precipitation method. From the $O_2$-TPD experiment of the prepared catalysts, it was proven that there exists two types of oxygen species, and the oxygen species that participates in the partial oxidation reaction is the lattice oxygen desorbing around $750^{\circ}C$. The optimum reaction condition for methanol production was $420^{\circ}C$, 50 bar, flow rate of 115 mL/min, and $CH_4/O_2$ ratio of 10/1.5, providing methane conversion and methanol selectivity of 3.2 and 26.7%, respectively.

• Journal of the Korean Applied Science and Technology
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• v.30 no.4
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• pp.649-655
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• 2013

Methanol was directly produced by the partial oxidation of methane with perovskite and mixed oxide catalysts. Perovskite ($ABO_3$) catalysts were prepared by the malic acid method with changing A and B site components. Three-component mixed oxide catalysts that have Mo and Bi as a main component were prepared by the co-precipitation method. Among the perovskite catalysts, $SrCrO_3$ showed the highest methanol selectivity of 11% at $400^{\circ}C$. For the three-component mixed oxide catalysts, there were no remarkable changes in methane conversion. Among the mixed oxide catalysts, Mo-Bi-Cr mixed oxide catalyst showed the highest methanol selectivity of 15.3% at $400^{\circ}C$. The catalytic activity and methanol selectivity of the three-component mixed oxide catalysts were directly proportional to the surface area of the catalysts.

• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.41-49
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• 2012

This study was aimed at the development of catalysts for the direct methanol synthesis by partial oxidation of methane. Mo-Bi-V-Al mixed oxide catalysts were prepared and characterized and used in the direct methanol synthesis reaction. The catalysts prepared by the sol-gel method had much larger surface areas than those prepared by the co-precipitation method. The larger the surface area was, the less the methanol selectivity was. The catalysts having larger surface area facilitate the complete oxidation of methane, decreasing the selectivity of methanol. The catalysts prepared by the sol-gel method showed higher methanol selectivity of 13% at $20^{\circ}C$ lower temperature than those prepared by the co-precipitation method. Through XRD analysis, it was revealed that the structures of the catalysts prepared by the two methods were different. In the reaction, methanol selectivity increased and carbon dioxide selectivity decreased with pressure due to the suppression of complete oxidation reaction at a high pressure.

• Atmosphere
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• v.27 no.2
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• pp.163-175
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• 2017

The global terrestrial ecosystems have shown a large spatial variability in recent decades and represented a carbon sink pattern at mid-to-high latitude in Northern Hemisphere. However, there are many uncertainties in magnitude and spatial distribution of terrestrial carbon fluxes due to the effect of climate factors. So, it needs to accurately understand the spatio-temporal variations on carbon exchange flux with climate. This study focused on the effects of climate factors, .i.e. temperature, precipitation, and solar radiation, to terrestrial biosphere carbon flux. We used the terrestrial carbon flux that is simulated by a CarbonTracker, which performs data assimilation of global atmospheric $CO_2$ mole fraction measurements. We demonstrated significant interactions between Net Ecosystem Production (NEP) and climate factors by using the partial correlation analysis. NEP showed positive correlation with temperature at mid-to-high latitude in Northern Hemisphere but showed negative correlation pattern at $0-30^{\circ}N$. Also, NEP represented mostly negative correlation with precipitation at $60^{\circ}S-30^{\circ}N$. Solar radiation affected NEP positively at all latitudes and percentage of positive correlation at tropical regions was relatively lower than other latitudes. Spring and summer warming had potentially positive effect on NEP in Northern Hemisphere. On the other hand as increasing the temperature in autumn, NEP was largely reduced in most northern terrestrial ecosystems. The NEP variability that depends on climate factors also differently represented with the type of vegetation. Especially in crop regions, land carbon sinks had positive correlation with temperature but showed negative correlation with precipitation.

• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.561-566
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• 2005

For the homogeneous dispersion of $ZrO_2$ particles in $Al_2O_3/ZrO_2$ceramics, Zr-precusors were mixed with oxide $Al_2O_3$powders by chemical routes such as partial precipitation or partial polymerization of Zr-nitrate solutions. In case of the mechanical mixing of ultrafine $Al_2O_3$ and $ZrO_2$ oxide powders, relatively homogeneous dispersion was difficult to achieve so that the particle size and distributions of $ZrO_2$ were relatively inhomogeneous after sintering at high temperature. But when the Zr-Y-hydroxide were co-precipitated to ultrafine $Al_2O_3$ oxide powders followed by calcinations, homogeneous dispersion of nano-sized $ZrO_2$ particles in $Al_2O_3/ZrO_2$ composite ceramics were obtained. But because of the coalescence of dispersed $ZrO_2$ particles, dispersed $ZrO_2$ was grown up to more than 0.2${mu}m$ (200 nm) when sintered at the temperature of higher than $1500^{\circ}C$ But when the sintering temperature was kept to lower than $1400^{\circ}C$ by using nano-sized $\alpha-alumina$, the particle size of dispersed $ZrO_2$ could be sustained below 0.1 ${\mu}m$. But the coalescence of dispersed $ZrO_2$ between $Al_2O_3$ particles could not be avoided so that the mechanical properties were not enhanced contrary to the expectations. So Zr-polyester precursors were precipitated and coated to the surface of ultrafine $\alpha-alumina$ powders by the polymerization of Ethylene Glycol with Citric Acid and Zirconium Nitrate. By this dispersion much more uniform dispersion of $ZrO_2$ was achieved at $1450\~1600^{\circ}C$ of sintering temperature ranges. And due to especially discrete dispersion of $ZrO_2$ between $Al_2O_3$ particles, their mechanical strength was more enhanced than mechanical mixing or hydroxide precipitation methods.

• Journal of the Korean Magnetics Society
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• v.2 no.3
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• pp.244-250
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• 1992

Iron nitride $Fe_4N$ by partial substitution of nitrogen by carbon was prepared by nitriding the iron oxalate whose thermal decomposition gives a carburating atmosphere. Iron oxalates, the precursors, were prepared by precipitation and co-precipitation. The size and shape of the carbonitride particles could be controlled by modifying the conditions of preparation of the oxalate precursor. From the results of electron micrographs, it is clear that the $Fe_4N$ pigment particle maintains the original shape(needle shape) of the starting materials and that it consists of fine unit particles which link together to form a stereo-network structure. An investigation of the $Fe^{II}_3\;Fe^I_{1-x}\;Sn_xN_{1-y}C_y$ solid solution has shown that Sn plays the role of a growth inhibitor of the elementary microcrystallites of the iron carbonitride. The coercive force and saturation magnetization of iron carbonitride obtained from co-precipitated iron oxalate were 500 Oe and 120 emu/g, respectively.

• Journal of the Korean Chemical Society
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• v.25 no.5
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• pp.318-324
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• 1981

The effects of$ Fe_2O_3$ aggregation on the sintering of Ba-ferrite (BaFe$_{12}O_{19}$) were studied. $BaCO_3-Fe_2O_3$ mixtures were prepared by partial precipitation mixing and ball-mill mixing method using two different $Fe_2O_3 $powders. Techniques employed were TG, XRD and SEM. X-ray diffraction analysis showed that the over all reaction basically consists of the two consecutive reaction; $BaCO_3 + 6Fe_2O_3\;{\longrightarrow}\;BaFe_2O_3 + 5Fe_2O_3 + CO_2{\uparrow}\;BaFe_2O_4 + 5Fe_2O_3 \;{\longrightarrow}\;BaFe_{12}O_{19}$ It is also shown that the aggregation state of $Fe_2O_3$ raw materials, as well as the mixing method, has a remarkable effect on solid state reaction between $BaCO_3\;and\;Fe_2O_3$.

• Clean Technology
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• v.20 no.1
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• pp.42-50
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• 2014

In this study, the $Mg(OH)_2$ slurry was made form ferro-nickel slag and then used for $CO_2$ sequestration. The experiments were in the order as leaching step, precipitation, carbonation experiments. According to the leaching results, the optimal leaching conditions were $H_2SO_4$ concentration of 1 M and the temperature of 333 K. In the $Mg(OH)_2$ manufacturing step, NaOH was added to increase the pH upto 8, the first precipitation was confirmed as $Fe_2O_3$. After removal the first precipitation, the pH was upto 11, the $Mg(OH)_2$ was generated by XRD analysis. The $Mg(OH)_2$ slurry was used for $CO_2$ sequestration. The pseudo-second-order carbonation model was used to apply for $CO_2$ sequestration. The $CO_2$ sequestration rate was increased by the $CO_2$ partial pressure and temperature. However, $CO_2$ sequestration rate was decreased when temperature upto 323 K. After $CO_2$ sequestrated by $Mg(OH)_2$, the $CO_2$ can be sequestrated stable as $MgCO_3$. This study also presented optimal sequestration condition was the pH upto 8.38, the maximum $MgCO_3$ can be generated. This study can be used as the basic material for $CO_2$ sequestration by ferro-nickel slag at pilot scale in the future.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.1
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• pp.55-62
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• 1997

The morphology of deformation induced dislocations in polycrystalline $Ni_3$(Al, Cr) containing $M_{23}C_6$ precipitates has been investigated in terms of transmission electron microscopy(TEM). Fine Polyhedral precipitates of $M_{23}C_6$ appeared in the matrix by aging at temperatures around 973 K after solution annealing at 1423 K. TEM examination revealed that the $M_{23}C_6$ phase and the matrix lattices have a cube-cube orientation relationship and keep partial atomic matching at the {111} interface. After deformation at temperature below 973 K, typical Orowan loops were observed surrounding the $M_{23}C_6$ particles. At higher deformation temperatures, the Orowan loops disappeared and the morphology of dislocations at the particle-matrix interfaces suggested the existence of attractive interaction between dislocations and particles. The change of the interaction modes between dislocation and particles with increasing deformation temperature can be considered as a result of strain relaxation at the interface bet ween matrix and particles.

• Korean Journal of Materials Research
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• v.31 no.9
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• pp.525-531
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• 2021

Carbon-encapsulated Ni catalysts are synthesized by an electrical explosion of wires (EEW) method and applied for CO₂ methanation. We find that the presence of carbon shell on Ni nanoparticles as catalyst can positively affect CO₂ methanation reaction. Ni@5C that is produced under 5 % CH₄ partial pressure in Ar gas has highest conversions of 68 % at 350 ℃ and 70 % at 400 ℃, which are 73 and 75 % of the thermodynamic equilibrium conversion, respectively. The catalyst of Ni@10C with thicker carbon layer shows much reduced activity. The EEW-produced Ni catalysts with low specific surface area outperform Ni catalysts with high surface area synthesized by solution-based precipitation methods. Our finding in this study shows the possibility of utilizing carbon-encapsulated metal catalysts for heterogeneous catalysis reaction including CO₂ methanation. Furthermore, EEW, which is a highly promising method for massive production of metal nanoparticles, can be applied for various catalysis system, requiring scaled-up synthesis of catalysts.