• Journal of the Korean Society for Heat Treatment
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• v.23 no.6
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• pp.315-322
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• 2010

Effect of hardenability, grain size and microstructural change according to the change of austenitizing temperature was analyzed in Jominy hardenability test of AISI 51B20 steel. Grain growth was small, 7 ${\mu}m$ and 12 ${\mu}m$ austenite grain sizes at austenitizing temperature of $900^{\circ}C$ and $1000^{\circ}C$, respectively, while rapid grain growth was observed up to 30 ${\mu}m$ austenite grain size at austenitizing temperature of $1100^{\circ}C$. As austenitizing temperature increased from $900^{\circ}C$ to $1100^{\circ}C$, hardenability in the region within 15 mm from end-quenched surface decreased due to the grains growth of bainite and martensite mixture, on the other hand the hardenability in the region exceeding 15 mm from end-quenched surface increased. Increased hardenability was attributed to different microstructures; pearlite, fine pearlite and bainite, and bainite and martensite structures at austenitizing temperature of $900^{\circ}C$, $1000^{\circ}C$ and $1100^{\circ}C$, respectively.

• Rapid Communication in Photoscience
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• v.2 no.3
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• pp.79-81
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• 2013

A novel method of fabricating polythiophene-gold nanoparticle composite film electrodes for photoelectric conversion is demonstrated. The method includes electrodeposition of gold and electropolymerization of 2,2'-bithiophene onto an indium-tin-oxide (ITO) electrode. First, electrodeposition of gold onto the ITO electrode was carried out with various repetition times of pulsed applied potential (0.25 s at -2.0 V vs. Ag/AgCl) in an aqueous solution of $HAuCl_4$. Significant progress of the number density of deposited gold nanoparticles was confirmed from scanning electron micrographs, from 4 (1 time) to 25% (15 times). Next, electropolymerization of 2,2'-bithiophene onto the above ITO electrode was performed under controlled charge condition (+1.4 V vs. Ag wire, 15 $mC/cm^2$). Structural characterization of as-fabricated films were carried out by spectroscopic and electron micrographic methods. Photocurrent responses from the sample film electrodes were investigated in the presence of electron acceptors (methyl viologen and oxygen). Photocurrent intensities increased with increasing the density of deposited gold nanoparticles up to ~10%, and tended to decrease above it. It suggests that the surplus gold nanoparticles exhibit quenching effects rather than enhancement effects based on localized electric fields induced by surface plasmon resonance of the deposited gold nanoparticles.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.10
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• pp.1365-1372
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• 2001

In the planar flow casting(PFC) process, the conditions of the melt puddle between nozzle and rotating wheel affect significantly the quality and dimensional uniformity of the downstream ribbon. For stable puddle formation, the nozzle is placed very close to the quenching wheel, so the surface-tension and wall-adhesion forces have an important effect upon the fluid flow.\`In this study the planar flow casting process has been mode]ed using the VOF method for free surface tracking. The transient puddle formation from the present analysis shows good agreements with the previous experimental results. Furthermore, the variation of melt temperature and the corresponding cooling rate of the melt have been examined. The present results also show how the melt puddle can be farmed on the rotating substrate, how the melt flows within the puddle, and how the changes of the process variables affect the puddle formation and its corresponding fluid flow and heat transfer behavior.

• Korean Journal of Food Science and Technology
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• v.13 no.2
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• pp.114-120
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• 1981

A rapid and simple method for detecting colors was attempted on the basis of absorption and emission spectra of reflected light at $45^{\circ}$ angle from color-adsorbed filter paper illuminated by ultraviolet light through interference filter. Absorption spectra of prepared samples revealed more characteristic patterns than emission spectra. Detection of colors was readily accomplished by the investigation of wave length range, distribution pattern, the number of absorption bands and the degree of quenching.

• Journal of Powder Materials
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• v.19 no.4
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• pp.317-321
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• 2012

In this study, Cu-5Ni-10Sn(wt%) spinodal alloy was manufactured by gas atomization spray forming, and the microstructural features and mechanical properties of Cu-5Ni-10Sn alloy have been investigated during homogenization, cold working and age-hardening. The spray formed Cu-5Ni-10Sn alloy consisted of an equiaxed microstructure with a mixture of solid solution ${\alpha}$-(CuNiSn) grains and lamellar-structure grains. Homogenization at $800^{\circ}C$ and subsequent rapid quenching formed a uniform solid solution ${\alpha}$-(CuNiSn) phase. Direct aging at $350^{\circ}C$ from the homogenized Cu-5Ni-10Sn alloy promoted the precipitation of finely distributed ${\gamma}$' or ${\gamma}-(Cu,Ni)_3Sn$ phase throughout the matrix, resulting in a significant increase in microhardness and tensile strength. Cold working prior to aging was effective in strengthening Cu-5Ni-10Sn alloy, which gave rise to a maximum tensile strength of 1165 MPa. Subsequent aging treatment slightly reduced the tensile strength to 1000-1100 MPa due to annealing effects.

• Journal of Magnetics
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• v.8 no.1
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• pp.18-23
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• 2003

In our previous work, microstructure and magnetic properties of two-phase exchange-coupled $Sm_2Fe_{15}Ga_2C_{x}$/$\alpha$-Fe nanocomposites have been investigated by means of x-ray diffraction, transmission electron microscopy and magnetization measurement. It was found the exchange coupling between the magnetically hard phase $Sm_2Fe_{15}Ga_2C_{x}$ and the magnetically soft one ${\alpha}$-Fe results in an enhancement of the remanence. The sizes of crystallites of both phases are, however much larger than the Block domain-wall width of the magnetically hard phase. This microstructure gives rise to a concave demagnetization curve and consequently reduces the maximum energy Product. In order to improve their magnetic properties, a few Percent of Zr, which may be effective to refine the microstructure through rapid quenching, was introduced into the nanocomposites. The addition of Zr was found to improve the magnetic properties significantly, Under optimum heat-treatment conditions, the remanence, coercivity and maximum energy Product increase from 0.65 T, 0.48 T and 50 kJ/$m^{3}$ for the Zr-free sample to 0.72 T, 0.77 T and 71.6 kJ/$m^{3}$ for the 1 at.% Zr-containing one, respectively, The improvements of magnetic properties are due to the refinement of microstructure by the addition of Zr.

• Journal of Korea Foundry Society
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• v.5 no.2
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• pp.118-124
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• 1985

The thickness ranges and conditions to form the supersaturated solid solution in Al-Cr alloys were investigated with various rapid solidification conditions. Al-Cr alloys, rapidly solidified by using the small droplet chill quenching method, were examined by means of micro-vickers hardness, lattice parameter, thermal analysis and microscopic observation. The results obtained were as follows; 1. With the increase of solidification rate, the solidified structures were changed to intermetallic compound + solid solution, incompletely supersaturated solid solution, completely supersaturated solid solution, in turn. 2. The minimum solidification rate required to form completely supersaturated solid solution was $2.5{\times}10^{-2}cm/sec$, $3.6{\times}10^{-2}cm/sec$ and $6.0{\times}10^{-2}cm/sec$ for Al-1.0wt%Cr, Al-1,2wt%Cr and Al-1.5wt%Cr, respectively. 3. The maximum distance from the chill surface required to form completely supersaturated solid solution was 5mm, 1.3mm and 0.3mm for Al-1.0wt%Cr, Al-1.2wt%Cr and Al-1.5wt% Cr, respectively.

• Bulletin of the Korean Chemical Society
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• v.30 no.6
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• pp.1252-1256
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• 2009

A simple, selective and sensitive fluorescence quenching method was developed to the determination Cr(VI). The method is based on the oxidation of $I^-\;to\;{{I_3}^-}$ by Cr(VI) in sulfuric acid solution followed by immediate formation of ion association compound between I3 − and rhodamine 6G in Tween-80 micellar media at room temperature. The influence of several surfactants on rhodamine 6G fluorescence signal was studied; particular attention was paid in the aggregation behavior of rhodamine 6G–Tween-80 system. The experimental parameters (e.g., type of surfactant, reagent concentration) were studied and the optimal conditions were established. The linear calibration graph was obtained in the range 2.0 - 100.0 ng m$L^{-1}$ Cr(VI). The detection limit of the method was 0.37 ng m$L^{-1}$. The relative standard deviation (R.S.D.) is less than 5% (n = 5). The efficiency of the method for the determination of Cr(VI) in the presence of Cr(III) in the sample was investigated. The method was applied successfully to the determination of Cr(VI) and total Cr in water, and liver tissue samples.

• Bulletin of the Korean Chemical Society
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• v.30 no.1
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• pp.129-132
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• 2009

Monodisperse ZnS colloidal particles with precisely specified diameters over a broad size range were synthesized by controlled aggregation. Sub-10nm ZnS seed crystals were first nucleated at ambient temperature and then grown at an elevated temperature, which produced large polydisperse colloidal particles. Subsequent rapid thermal quenching and heating processes induced a number of secondary nucleations in addition to growing the large polydisperse microparticles which were finally removed by centrifugation and discarded at the completion of the reaction. The secondary nuclei were then aggregated further at elevated temperatures, resulting in colloidal particles which exhibited a nearly monodisperse size distribution. Particle diameters were controlled over a wide size range from 50 nm to 1 μm. Mie simulations of the experiment extinction spectra determined that the volume fraction of the ZnS is 0.66 in an aggregated colloidal particle and the colloidal particle effective refractive index is approximately 2.0 at 590 nm in water. The surface of the colloidal particles was subsequently coated with silica to produce ZnS@silica core-shell particles.

• Korean Journal of Metals and Materials
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• v.50 no.4
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• pp.293-299
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• 2012

Ultrafine-grained or nanostructured alloys usually lack the strain hardening capability needed to sustain uniform tensile deformation under high stresses. To circumvent this problem, we fabricated the Cu-based composite reinforced with the 3-dimensionally interconnected $Cu_5Zr$ phase using the combined technique of rapid quenching and subsequent hot-rolling. The alloy exhibited a tensile ductility of ~2.5% together with a strength of 1.57 GPa, which exceeds the values of most commercially available Cu-Be alloys. In this study, we elucidated the structural origin of the high strength and tensile ductility of the developed alloy by examining the thermal stability of the $Cu_5Zr$ reinforcing phase and the energy (work) absorption capability of the Cu matrix.