• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.173-176
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• 1998

We experimentally investigated the dielectric relaxation phenomena of a liquid crystal monolayers by the Displacement current techique and displacement current flowing across monolayers is analyzed using rod-like molecular model. It is revealed that the dielectric reaxation time $\tau$ of monolaters in the isotropic polar orientational phase is determined using a linear relashionship between the monolayers compression speed $\alpha$ and the molecular area. The dielectric relaxation time of phospholipid monolayers was examined on the basis of the analysis developed here.

• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.703-709
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• 2006

We report on the synthesis of highly uniform, single phase zinc and cobalt thin films prepared by the Liquid Phase Deposition (LPD) method. X-Ray diffraction, TGA and EDX measurements support the assumption that the as deposited films are constituted by a mixture of crystallized FeOOH and amorphous M(OH)$_2$ (M=Co, Zn) which is converted upon heat treatment in air at 600?C into the corresponding zinc ferrites. The films with adjustable chemical compositions are identified with a crystal structure as spinel-type and present a spherical or rod-like microstructure, depending on the both the nature and concentration of the divalent transition metal ions. Zinc ferrite thin films present a superparamagnetic behavior above blocking temperatures which decrease with increasing the Zn content and are ferromagnetic at 5 K with coercivities ranging between 797.8 and 948.5 Oe, whereas the cobalt ferrite films are ferromagnetic at room temperature with magnetic characteristics strongly dependent on the chemical composition.

• Journal of the Korean Applied Science and Technology
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• v.35 no.2
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• pp.350-356
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• 2018

Hydroxyapatite has been used for biomaterials since it has high biocompatibility. In this study, c-plane oriented hydroxyapatite was synthesized by hydrolysis of dicalcium phosphate intermediate by controlling temperature, concentration and pH. In basic condition, rod-like hydroxyapatite crystals were aggregated to form irregular particles in low concentration and plate-like particles exposed c-plane of hydroxyapatite crystal were obtained in high concentration, causing difference of 3 mV in zeta potential. Physicochemical properties of product were characterized by XRD, SEM, FT-IR, zeta potential measurement.

• Journal of the Mineralogical Society of Korea
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• v.21 no.4
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• pp.383-395
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• 2008

To enhance the grade and recovery rate of the gold/silver ores which yield at Philippine Mankayan mine, we studied the characteristics which are the geologic and mineralogical features of gold and silver ore, the liberation by crushing and grinding, the separation by sieving and shaking table. Gold/silver ore is composed of the sulfide minerals like pyrite, sphalerite, galena; and the gangue minerals which is quartz, clay. Gold/silver element are mainly contained in a sulfide minerals like pyrite, sphalerite and galena. To increase the liberation rate of sulfide minerals containing gold/silver element, the gold/silver ore has to be grounded under $100{\mu}m$ very finely because the crystal size of sulfide minerals is distributed from $1{\mu}m$ to $100{\mu}m$. The liberation rate of gold/silver ore increases to 92% when the particle size ($d_{90}$) of ore is grounded below $100{\mu}m$ by jaw crusher $\to$ cone crusher $\to$ rod mill by steps. The grade and recovery of sulfide minerals could not be enhanced by sieving separation because those crystal size is distributed homogeneously below $100{\mu}m$. But, when we separated the sieved ore using shaking table, the gold and silver grade increased to 40 ppm and 140 ppm, respectively. Then the recovery rate of gold reach almost 100% but that of silver is no more that 50%.

• Bulletin of the Korean Chemical Society
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• v.28 no.10
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• pp.1651-1655
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• 2007

Rod-like polymerizable LC molecules having two different reactive groups, i.e. acryl and diacetylene groups were prepared. 4-Hydroxyphenyldiacetylenes were synthesized by the coupling reaction of 1-bromoalkynes with 4-ethynylphenol and then reacted with 4-(6-acryloyloxyalkyloxy)benzoic acid to give polymerizable LC molecules 4a-d. The mesomorphic properties of compounds 4a-d were investigated by differential scanning calorimetry, polarized optical microscopy and X-ray diffractometry. Compounds 4a-c exhibited smectic and nematic phases, but compound 4d having a longest alkyl tail among the series formed only a smectic phase. Photopolymerizability of acryl and diacetylene groups was investigated by IR spectroscopy. An anisotropic polymer film could be prepared by selective polymerization of acryl groups with 365 nm UV light in the presence of a photoinitiator (2,2-dimethoxy-2-phenylacetophenone). The subsequent reaction of diacetylene groups with 254 nm UV light disrupted the anisotropic structure, suggesting that these LC molecules could be used for imaging on the film.

• Journal of Korea Foundry Society
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• v.15 no.5
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• pp.459-468
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• 1995

For high performance aerospace structures, the properties of highest priority are low density, high strength, and high stiffness(modulus of elasticity). Addition of beryllium decrease the density of the aluminum alloy and increase the strength and the stiffness of the alloy. However it is very difficult to produce the Al-Be alloy having useful engineering properties by conventional ingot casting, because of the extremely limited solid solubility of beryllium in aluminum. So, rapid solidification processing is necessary to obtain extended solid solubility. In this study, rapidly solidified Al-6 at% Be alloy were prepared by twin roll melt spinning process and single roll melt spinning process. Twin roll melt spun ribbons were extruded at $450^{\circ}C$ with reduction in area of 25 : 1 after vacuum hot pressing at $550^{\circ}C and 375^{\circ}C$. The microstructure of melt spun ribbon exhibited a refined cellular microstructure with dispersed Be particles. As advance velocity of liquid/solid interface increase, the morphology of Be particle vary from rod-like type to spherical type and the crystal structure of Be particle from HCP to BCC. These microstructural characteristics of rapidly solidified Al-6at.%Be alloy were described on the basis of metastable phase diagram proposed by Perepezko and Boettinger. The extruded ribbon consisted of recrystallized grains dispersed with Be particles and exhibited improved tensile property compared with that of extruded ingot.

• Journal of Powder Materials
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• v.27 no.3
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• pp.198-202
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• 2020

The effect of sublimable vehicles on the pore structure of Cu fabricated by freeze drying is investigated. The 5 vol% CuO-dispersed slurries with camphene and various camphor-naphthalene compositions are frozen in a Teflon mold at -25℃, followed by sublimation at room temperature. After hydrogen reduction at 300℃ and sintering at 600 ℃, the green bodies of CuO are completely converted to Cu with various pore structures. The sintered samples prepared using CuO/camphene slurries show large pores that are aligned parallel to the sublimable vehicle growth direction. In addition, a dense microstructure is observed in the bottom section of the specimen where the solidification heat was released, owing to the difference in the solidification behavior of the camphene crystals. The porous Cu shows different pore structures, such as dendritic, rod-like, and plate shaped, depending on the composition of the camphornaphthalene system. The change in pore structure is explained by the crystal growth behavior of primary camphor and eutectic and primary naphthalene.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.116-117
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• 2006

I-D ZnO nanostructures were fabricated by thermal evaporation method on Si(100), GaN and $Al_2O_3$ substrates without a catalyst at the reaction temperature of $700^{\circ}C$. Only pure Zn powder was used as a source material and Ar was used as a carrier gas. The shape and growth direction of synthesized ZnO nanostructures is determined by the crystal structure and the lattice mismatch between ZnO and substrates. The ZnO nanostructure on Si substrate were inclined regardless of their substrate orientation. The origin of ZnO/Si interface is highly lattice-mismatched and the surface of the Si substrate inevitably has the $SiO_2$ layer. The ZnO nanostructure on the $Al_2O_3$ substrate was synthesized into the rod shape and grown into particular direction. For the GaN substrate, however, ZnO nanostructure with the honeycomb-like shape was vertically grown, owing to the similar lattice parameter with GaN substrate.

• Journal of the Korean Wood Science and Technology
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• v.47 no.5
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• pp.597-606
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• 2019

Cellulose nanocrystals (CNCs) were successfully isolated from oil palm fronds (OPFs) using different concentrations of ammonium persulfate (APS), and their characteristics were analyzed by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and thermogravimetric analysis (TGA). APS oxidation effectively isolated CNCs with rod-like morphology in nanometer scale. The dimensions of the CNCs decreased with increasing APS concentration. FTIR and XRD analyses revealed that all the CNCs showed crystals in the form of cellulose I without crystal transformation occurring during APS treatment. The relative crystallinity of the CNCs increased with increasing APS concentration, whereas their thermal stability decreased. An APS concentration of 2 M was found to be optimal for isolating the CNCs.

• Journal of the Korean Chemical Society
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• v.50 no.6
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• pp.440-446
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• 2006

ZnO nanoparticles were prepared by laser ablation of the ZnO powder dispersed in deionized water and surfactant solutions, and characterized using UV-VIS absorption spectroscopy, X-ray diffractometer and Transmission electron microscopy(TEM). ZnO nanoparticles produced show the pure ZnO crystal state without mixed state with Zn(OH)2 or Zn, and have the band gap energy of 3.35 eV, which is comparable to that of bulk ZnO. While ZnO nanoparticles prepared in SDS solution have the average diameter of 28nm with near spherical shape, those prepared in CTAB solution have the average size of 40 nm with mainly rod-like shape. ZnO colloidal solution of CTAB is more stable than that of SDS. These difference according to surfactants can be explained by difference of electrostatic interaction between surface charge of ZnO and surfactant molecules and by solvation effect in solution.