• Korean Chemical Engineering Research
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• v.43 no.6
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• pp.751-755
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• 2005

Carbon dioxide, included in the flue gas from the combustion of fossil fuel, was known as a representative green house gas and various removal and utilization technologies of it has been studied for the prevention of global warming. This study was performed as an effort to find out a method to reuse carbon dioxide separated from flue gas by magnetite powder. Magnetite powder was synthesized using various oxidizers and alkalinity controlled aqueous solutions of $FeSO_4{\cdot}7H_2O$ and NaOH at 50, 80, 90, $100^{\circ}C$ and analyzed by XRD and SEM. The analysis results showed that magnetite powder synthesized at higher alkalinity and temperature had crystalline spinel and cubic structure. The reduction by hydrogen and the oxidation by carbon dioxide of synthesized powder were studied by TGA. The results showed that magnetite powder synthesized at low alkalinity and temperature was non-cubical amorphous but crystalline and cubical at high alkalinity and temperature. Comparing magnetite powders synthesized using oxidants(air and oxygen) and nitrogen, magnetite powder using more oxygen containing oxidant synthesized more crystalline magnetite powder. The experimental results of redox reaction of the synthesized magnetite powder showed that the reduction by hydrogen and the oxidation by carbon dioxide were seldom observed below $400^{\circ}C$ and observed well at $500^{\circ}C$. Magnetite powder synthesized at $100^{\circ}C$ and alkalinity(molal concentration ratio of $FeSO_4{\cdot}7H_2O$ to NaOH) of 2.0 using $O_2$ showed the highest reduction of 27.15 wt％ and oxidation of 26.73 wt％, especially at reaction temperature of $500^{\circ}C$.

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.1-6
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• 2002

Al$\^$3+/ substituted garnet Y$_3$Fe$\_$5-x/Al$\_$x/O$\_$12/ (x=0.0, 0.25, 0.5, 0.75, 1.0) was fabricated by sol-gel method. The crystallographic and magnetic properties of Y$_3$Fe$\_$5-x/Al$\_$x/O$\_$12/ have been studied with Mossbauer spectroscopy, x-ray diffraction (XRD), thermogravimetry analysis (TGA), differential thermal analysis (DTA), and vibrating samples magnetometer (VSM). The crystal structure of Y$_3$Fe$\_$5/O$\_$12/ is found to be a cubic with the lattice constant a$\_$0/= 12.381$\pm$0.005 $\AA$. The lattice constants a$\_$0/ decreases linearly from 12.381 to 12.304 A as the Al concentration (x) increases from x=0.0 to 1.0. Mossbauer spectra of measured at Y$_3$Fe$\_$5-x/A1$\_$x/O$\_$12/ various absorber temperatures of 13 to 600 K. Mossbauer spectrum for x = 0.0 is consist of well resolved two sets of six line patterns. While with increasing Al concentration outer sextet patters, which is originating from octahedral sites, broadens widely. These phenomena are interpreted in terms of random probability distributions of Fe$\^$3+/ and Al$\^$3+/ in tetrahedral site.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.222-222
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• 2012

Metal oxide gas sensors based on semiconductor type have attracted a great deal of attention due to their low cost, flexible production and simple usability. However, most works have been focused on n-type oxides, while the characteristics of p-type oxide gas sensors have been barely studied. An investigation on p-type oxides is very important in that the use of them makes possible the novel sensors such as p-n diode and tandem devices. Monoclinic cupric oxide (CuO) is p-type semiconductor with narrow band gap (~1.2 eV). This is composed of abundant, nontoxic elements on earth, and thus low-cost, environment-friendly devices can be realized. However, gas sensing properties of neat CuO were rarely explored and the mechanism still remains unclear. In this work, the neat CuO layers with highly ordered mesoporous structures were prepared by a template-free, one-pot solution-based method using novel ink solutions, formulated with copper formate tetrahydrate, hexylamine and ethyl cellulose. The shear viscosity of the formulated solutions was 5.79 Pa s at a shear rate of 1 s-1. The solutions were coated on SiO2/Si substrates by spin-coating (ink) and calcined for 1 h at the temperature of $200{\sim}600^{\circ}C$ in air. The surface and cross-sectional morphologies of the formed CuO layers were observed by a focused ion beam scanning electron microscopy (FIB-SEM) and porosity was determined by image analysis using simple computer-programming. XRD analysis showed phase evolutions of the layers, depending on the calcination temperature, and thermal decompositions of the neat precursor and the formulated ink were investigated by TGA and DSC. As a result, the formation of the porous structures was attributed to the vaporization of ethyl cellulose contained in the solutions. Mesoporous CuO, formed with the ink solution, consisted of grains and pores with nano-meter size. All of them were strongly dependent on calcination temperature. Sensing properties toward H2 and C2H5OH gases were examined as a function of operating temperature. High and fast responses toward H2 and C2H5OH gases were discussed in terms of crystallinity, nonstoichiometry and morphological factors such as porosity, grain size and surface-to-volume ratio. To our knowledge, the responses toward H2 and C2H5OH gases of these CuO gas sensors are comparable to previously reported values.

• Journal of the Mineralogical Society of Korea
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• v.27 no.1
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• pp.41-51
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• 2014

The four natural zeolites collected in Pohang and Gyeongju area, Kyungsangbuk-do, Korea, were characterized by XRD, XRF, DTA, TGA, and CEC analysis. The primary species of these zeolite are heulandite, modenite, illite, and illite in Kuryongpo (Ku), Pohang (Po), Yangbuk-A (Ya-A), and Yangbuk-B (Ya-B) samples. The XRF analysis showed that the four zeolites contain Si, Al, Na, K, Mg, Ca, and Fe. Cation exchange capacity of Kuryongpo (Ku) zeolite was the highest compared to other zeolites. The adsorption capacities of Cs and Sr in the four natural zeolites were compared at $25^{\circ}C$. On the basis of adsorption data Langmuir and Freundlich adsorption isotherm model were confirmed. The equilibrium process was descried well by Langmuir isotherm model. This study shows that Ya-A zeolite is the most efficient for the $Cs^+$ and $Sr^{2+}$ ion adsorption compared to the other natural zeolites.

• Membrane Journal
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• v.28 no.2
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• pp.121-128
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• 2018

Terpolymers, which are chemical compounds composed of three different chemical compounds, have rarely been utilized for gas separation membranes. In this study, we demonstrate a simple process to fabricate a composite membrane for $CO_2/N_2$ separation based on a terpolymer synthesized from poly(2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl] ethylmethacrylate)(PBEM), poly(oxyethylene methacrylate)(POEM), and methyl methacrylate (MMA) via free radical polymerization. A solution of the as-synthesized PBEM-PMMA-POEM was coated onto a microporous polysulfone (PSf) support to form a composite membrane. The successful polymerization and the characteristics and morphology of the membrane were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FE-SEM). The gas permeance and $CO_2/N_2$ selectivity of the PBEM-PMMA-POEM terpolymer membrane were measured at $25^{\circ}C$. A maximum $CO_2/N_2$ selectivity of 30.2 was obtained at a $CO_2$ permeance of 57.4 GPU ($1GPU=10^{-6}cm^3$(STP)/($s\;cm^2\;cmHg$)).

• Asian-Australasian Journal of Animal Sciences
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• v.23 no.1
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• pp.116-121
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• 2010

Long-chain polyunsaturated fatty acids (LC-PUFA) promote the development of brain and vision of the fetus, relieve inflammation, inhibit oral dysplasia of rumor cell, decrease the incidence of cardiovascular disease and regulate arrhythmia. ${\Delta}-6$ desaturase is the rate-limited enzyme in the desaturation process. This study reports the cloning, characterization and tissue expression of a ${\Delta}-6$ desaturase gene in the chicken. PCR primers were designed based on the predicted sequence of chicken ${\Delta}-6$ desaturase (accession number: XM421053) and used to isolate a cDNA fragment of 1,323 bp from chicken liver. Based on the 1,323 bp fragment an EST (BI390105) was obtained by BLAST. The EST and 5'nd of the 1,323 bp fragment were partially overlapped. Gene specific primers derived from the EST were used for amplification of the 5'nd. Another gene-specific primer derived from the 1,323 bp fragment was used for amplification of the 3'nd by 3'ACE. Then the three overlapping cDNA sequences obtained were assembled with DNAMAN software and a full-length ${\Delta}-6$ desaturase of 2,153 bp was obtained. The full-length cDNA contained an ORF of 1,335 bp with a 5'ntranslated region of 147 nucleotides followed by an ATG initiation codon. Stop codon TGA was at position 1,481-1,483 bp. The deduced amino acids shared an homology above 77% with bovine, mice, orangutan, rat and human. The protein sequence had three histidine-rich regions HDFGH (HisI region), HFQHH (HisII region) and HH (HisIII region), a cytochrome $b_{5}$-like domain containing a heme-binding motif and two transmembrane domains. Sequence analysis of the chicken genomic DNA revealed that the coding sequence of chicken ${\Delta}-6$ desaturase included 12 exons and 11 introns. Semi-quantitative RT-PCR showed that the ${\Delta}-6$ desaturase expression levels were in turn liver, spleen, pancreas, lung, breast muscle, heart, and abdominal fat. The expression of ${\Delta}-6$ desaturase in liver was significantly higher than that in breast muscle (p<0.01). The expression of ${\Delta}-6$ desaturase in lung was significantly higher than that in abdominal fat (p<0.01). This is the first clone of chicken ${\Delta}-6$ desaturase.

• Applied Chemistry for Engineering
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• v.26 no.2
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• pp.145-153
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• 2015

$Cr_2O_3/AP$ (ammonium perchlorate) energetic composites were prepared by a method of solvent/anti-solvent. XRD analysis revealed that the crystalline structure of AP in $Cr_2O_3/AP$ composites is the same as that of pure AP. SEM photomicrograph shows that an average size of cuboid $Cr_2O_3/AP$ composites is approximately $2.5{\mu}m$. TGA analysis shows that the addition of submicron $Cr_2O_3$ particles into AP lowers the HTD (high-temperature decomposition) compared to that of neat AP and the activation energy of the $Cr_2O_3/AP$ composites was calculated by the isoconversional Starlink method. Considering changes in the activation energy, the decomposition reaction mechanism of AP was suggested as follows; the decomposition with the formation of nucleation sites renders formation of porous structure in the composites up to conversion of about 0.25 and after further conversion of over 0.3, it seems that decomposition reaction vigorously takes place rather than sublimation of AP.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.31-37
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• 2010

This study was carried out to investigate the thermal decomposition and execute EIDS slow cook-off test for the propellant ingredients and 2 kinds of HTPE propellants. The thermal analysis of the propellant ingredients used in this study showed that the thermal stability of these materials decreases in the following order : AP > HTPE > AN > BuNENA. In addition, propellant HTPE 002 containing AN showed that an endothermic process at around $125^{\circ}C$ corresponding to the solid phase change(II$\rightarrow$I) of AN was followed by the exothermic process of BuNENA/AN mixture up to $200^{\circ}C$. In EIDS slow cook-off tests, HTPE 001 and HTPE 002 reacted at around $250^{\circ}C$ and $152^{\circ}C$ respectively, and both of them showed sudden temperature increase curves at $115^{\circ}C$. The critical temperatures, $T_c$, of thermal explosion for the propellants HTPE 001 and HTPE 002, were obtained from both the non-isothermal curves at various heating rates and Semenov's thermal explosion theory. Kissinger's method that was used to calculate $T_c$ was also employed to obtain the activation energies for thermal decompositions.

• Journal of the Korean Wood Science and Technology
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• v.44 no.3
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• pp.406-414
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• 2016

The lignin-based carbon nanofiber reinforced epoxy composite has been prepared by immersing carbon nanofiber mat in epoxy resin solution in order to evaluate the physical and mechanical properties. The thermal and mechanical properties of the carbon nanofiber reinforced epoxy composite were analyzed using thermogravimetric analysis (TGA), differential scanning calorimeter (DSC) and tensile tester. It was found that the thermal properties of the carbon nanofiber reinforced epoxy composite improved, with its glass-transition temperature ($T_g$) increased from $90.7^{\circ}C$ ($T_g$ of epoxy resin itself) to $106.9^{\circ}C$. The tensile strengths of carbon nanofiber mats made from both lignin-g-PAN copolymer and PAN were 7.2 MPa and 9.4 MPa, respectively. The resulting tensile strength of lignin-based carbon nanofiber reinforced epoxy composite became 43.0 MPa, the six times higher than that of lignin-based carbon nanofiber mats. The carbon nanofibers were pulled out after the tensile test of the carbon nanofiber reinforced epoxy composite due to high tensile strength (478.8 MPa) of an individual carbon nanofiber itself as well as low interfacial adhesion between fibers and matrices, confirmed by the SEM analysis.

• Journal of Hydrogen and New Energy
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• v.22 no.2
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• pp.161-167
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• 2011

Proton conductors have attracted considerable attention for solid oxide fuel cell (SOFC), hydrogen pump, gas sensor, and membrane separators. Doped $SrCeO_3$ exhibits appreciable proton conductivity in hydrogen-containing atmosphere at high temperature. However commercial realization has been hampered due to the reactivity of $SrCeO_3$ with $CO_2$. The chemical stability and proton conductivity are dependent on dopant type. The purpose of this work is to investigate chemical stability of $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$ composites in $CO_2$ and $H_2$ gases. Thermogravimetric analysis (TGA) was performed in gaseous $CO_2$ and electrical conductivity of the composites were also measured between 500 and $900^{\circ}C$ in air and $H_2$ atmosphere. $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$ composite membranes showed good chemical stability of in $CO_2$ atmosphere and high conductivity at hydrogen condition. The hydrogen permeation of $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$ composite membranes was investigated as a function of volumetric content of $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}$. The $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$(6:4) membrane with a thickness of 1.0 mm showed the highest hydrogen permeability with the flux reaching of 0.12 $ml/min{\cdot}cm^2$ at $800^{\circ}C$ in 100%$H_2/N_2$ as feed gas.