• Journal of Powder Materials
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• v.8 no.2
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• pp.110-116
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• 2001

Abstract To investigate the effect of mechanical alloying process to thermoelectric properties of PbTe sintered body, Pb-Te mixed powder with Pb : Te : 1 : 1 composition was mechanically alloyed using tumbler-ball mill. Thermoelectric properties of the sintered body were evaluated by measuring of the Seebeck coefficient and specific electric resistivity from the room temperature to 50$0^{\circ}C$. Sintered body of only mechanically alloyed PbTe powder showed p-type behavior at the room temperature, and occurred type transition from p-type to n-type at about 30$0^{\circ}C$. PbTe sintered body which was fabricated using heat treated powder in $H_2$ atmosphere after mechanical alloying showed stable n-type behavior under 50$0^{\circ}C$. N-type PbTe sintered body fabricated by mechanical alloying process had 4 times higher power factor than that fabricated by the melt-crushing process. Application of a mechanical alloying process to fabricate of n-type PbTe thermoelectric material seemed to be useful to increase the power factor of PbTe sintered body.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.347-352
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• 2002

The Cut off-type progressive die for U-bending production part is a very specific division. This study reveals the sheet metal forming process with multi-forming die by Center Carrier type feeding system. Through the FEM simulation by DEFORM, it was accepted to u-bending process as the first performance to design of strip process layout. The next process of die development was studied according to sequence of die development, i.e. die structure, machining condition for die making, die materials, heat treatment of die components, know-how and so on. The feature of this study is the die development of scrapless progressive die of multi-stage through the Modeling on the I-DEAS program, components drawing on the Auto-Lisp, CAD/CAM application, ordinary machine tool operating and revision by tryout.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.4
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• pp.155-160
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• 2019

Diamond Like Carbon (DLC) is a metastable form of amorphous carbon that have superior material properties such as high mechanical hardness, chemical inertness, abrasion resistance, and biocompatibility. Furthermore, its material properties can be tuned by additional doping such as nitrogen or boron. However, either pure DLC or doped DLC show poor adhesion property that makes it difficult to apply contact processing technique. Therefore we propose ultrafast laser micromachining which is non-contact precision process without mechanical degradation. In this study, we developed precision machining process of DLC thin film using an ultrafast laser by investigating the process window in terms of laser fluence and laser wavelength. We have also demonstrated various patterns on the film without generating any microcracks and debris.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.198-204
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• 1993

The study is concerned with finite element analysis and design of axisymmetric deep drawing by local heating. When the bottom shape of a cup is not flat but in complex-shaped, i.e., hemispherical, the cup cannot be drawn in one or two processes in the conventional deep drawing process and the limit drawing ratio is limited as well. By introducing local heating selectively with regards to the heating position, the formability of the sheet metal can be greatly increased with the reduced number of processes. In the Process analysisthe rigid- viscoplastic finite element method is employed and the temperature effect is incorporated. Bishop's step-wise decoupled method is employed to analyze the thermomechanical interaction between deformation and heat transfer. Axisymmetric deep drawing of a hemisphere-bottomed cup has been analyzed for various combinations of heat application in the punch and the die. At the first stage of deep drawing stretch forming is practically carried out by firmly pressing the blankholder with the punch and the die heated at various levels of temperature. Then at the second stage the same cup is drawn for the saame or different combination of temperature. From the computation, it has thus been shown that the fromability of a cup is greatly increased in two-stage deep drawing with increased limet drawing ratio.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.1
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• pp.15-18
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• 2003

High purity single crystalline calcium fluoride ($CaF_2$) has excellent optical transmission characteristics down to deep UV and is therefore selected as the main optical material for the next generation of lithography apparatus operating at wavelength of 157 nm. The growth of large sized $CaF_2$ single crystals with the required properties for this optical application can be achieved only by optimizing the crystal growth process by the aid of numerical simulation. This needs especially a precise calculation of the heat transport and temperature distribution in the solid and liquid $CaF_2$ under crystal growth conditions. As $CaF_2$ is considered to be semitransparent, the internal radiative heat transfer in $CaF_2$ plays an decisive role in the simulation of the heat transport. On the other hand it is very difficult to obtain quantitative experimental data for evaluating numerical models as $CaF_2$ is extremely corrosive at high temperatures. In this work we present a newly developed experimental technique to perform temperature measurements in $CaF_2$-crystal as well as in the melt under conditions of crystal growth process. These experimental results are compared to calculated temperature data, which were obtained by using different numerical models concerning the internal heat transfer in semitransparent $CaF_2$. It will be shown, that an advanced model, which was developed by the authors, gives a much better agreement with experimental data as a standard model, which was taken from the literature.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.64-70
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• 2008

Temperatures of engine head and liner depend on many factors such as spray and combustion process, coolant passage flow and engine related structures. To estimate the temperature distribution of engine structure, multi-dimensional computational fluid dynamics (CFD) codes have been mainly adopted. In this case, it is of great importance to obtain the realistic wall temperature distribution of entire engine structure. In the present work, a CFD-FEM coupling methodology was presented to address this demand. This approach was applied to a real large-size marine diesel engine. CFD combustion and coolant flow simulations were coupled to FEM temperature analysis. Wall heat flux and wall temperature data were interfaced between combustion simulation and solid component temperature analysis via translator by a commercial CFD package named FIRE by AVL. Heat transfer coefficient and surface temperature data were exchanged and mapped between coolant flow simulation and FEM temperature analysis. Results indicate that there exists the optimum cell thickness near combustion chamber wall to reasonably predict the wall heat flux during combustion period. The present study also shows that the effect of cell refining on predicting in-cylinder pressure during combustion is negligible. Hence, the basic guidance on obtaining the wall heat flux needed for the reasonable CFD-FEM coupling analysis has been established. It is expected that this coupling methodology is a robust tool for practical engine design and can be applied to further assessment of the temperature distribution of other engine components.

• Membrane and Water Treatment
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• v.1 no.1
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• pp.1-12
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• 2010

Membrane distillation process was used for purification of pre-treated natural water (tap water). The rejection of inorganic and organic compounds in this process was investigated. The obtained rejection of inorganic solutes was closed to 100%, but the volatile organic compounds (VOCs) diffused through the membrane together with water vapour. The content of trihalomethanes (THMs) in the obtained distillate was two-three fold higher than that in the feed, therefore, the rejection of the total organic compounds present in the tap water was reduced to a level of 98%. The intensive membranes scaling was observed during the water separation. The morphology and composition of the fouling layer was studied using scanning electron microscopy coupled with energy dispersion spectrometry. The influence of thermal water pre-treatment performed in a heat exchanger followed by filtration on the MD process effectiveness was evaluated. This procedure caused that significantly smaller amounts of $CaCO_3$ crystallites were deposited on the membrane surface, and a high permeate flux was maintained over a period of 160 h.

• Proceedings of the IEEK Conference
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• 2001.06b
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• pp.273-276
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• 2001

The origin of image-slicking in metal-insulator-metal type thin-film-diode(TFD) LCDs is the asymmetric current-voltage(I-V) characteristic of TFD element. we developed that MIM-LCDs have reduced-image-sticking and perfect symmetry characteristic. One-Time Post-Annealing (OPTA) heat treatment process was introduced to reduce the asymmetry and shift of the I-V characteristics, respectively. OPTA means that the whole layers of lower metal, insulator, and uuper metal are annealed at one time. The treatment temperatures and fabricated process of TFD element were under foot. Also, this low temperature fabricated process allows the application of plastic substrates.

• Carbon letters
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• v.14 no.3
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• pp.193-195
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• 2013

Expanded graphite (EG) was prepared using a drying process for application as an oil-adsorbent: the morphology, expansion volume, and oil absorption capacity of the EG were investigated. The expanded volume of the EG increased with an increasing reaction time and heat treatment temperature. The oil adsorption capacity of the EG was 45 g of n-dodecane per 1 g of EG. It is noted that the drying process of EG is a useful technique for a new oil-adsorbent.

• Korean Journal of Materials Research
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• v.17 no.7
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• pp.352-357
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• 2007

Since a pattern defects "repair" system using a diode pumped solid state laser for Flat Panel Display (FPD) was suggested, a lot of laser systems have been explored and developed for mass-production microfabrication process. A maskless lithography system using 405 nm violet laser and Digital Micromirror Device (DMD) has been developed for PDP and Liquid Crystal Display (LCD) Thin Film Transistor (TFT) photolithography process. In addition, a "Laser Direct Patterning" system for Indium Tin Oxide (ITO) for Plasma Display Panel(PDP) has been evaluated one of the best successful examples for laser application system which is applied for mass-production lines. The "heat" and "solvent" free laser microfabrications process will be widely used because the next-generation flat panel displays, Flexible Display and Organic Light Emitting Diode (OLED) should use plastic substrates and organic materials which are very difficult to process using traditional fabrication methods.