• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.36-41
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• 2006

A simplified model of plastic layer and internal gas pressure In a coke oven is presented. We calculate internal gas pressure using presented model. And results are compared with calculated results using experimental data. Results show the difference of internal gas pressure by coal composition. The model is used to show that the permeability at the resolidification end of the plastic layer is a key determinant of the magnitude of the internal gas pressure.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1739-1743
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• 2006

Recent advances in the microstructural modification of metal films using excimer laser projection irradiation and lateral resolidification are discussed. Pure copper films have been directionally resolidified into large sheet-like grains when properly encapsulated for suppression of liquid-phase dewetting. A survey and quantitative assessment of the defects found in these icrostructures, typical for rapidly solidified metals, is presented.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1184-1189
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• 2004

Coking process is the thermal decomposition of bituminous coal with final temperature of about $900^{\circ}C$ Because coke plays important roles in ironmaking process in a blast furnace it's essential for developing modeling of coke oven. In this study, An unsteady 2-dimesional model is proposed to simulate coking process in a coke oven. In this model, gas and solid phase are assumed homogeneous continnum and solid bed is assumed as porous media . The model contains governing equations for the solid phase and the gas phase. Complicated phenomena such as swelling, softening, resolidification and shrinkage are neglected and mass loss by drying and devolatilization is reflected by generation of internal pores. Drying, devolatilization, heat transfer and generation of internal pores are also reflected in source terms. Calulated results are compared with experimental data

• Journal of the Korean Society for Precision Engineering
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• v.5 no.4
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• pp.59-65
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• 1988

This paper describes the transmutation layer of CNC Wire electrical discharte machined surface. In order to analayze and invesigate transmutation layer of the carbon tool steel, workpieces was heat-treated by quenching, tempering, normaling. The obtained results are summarized as follows. 1. The result showed that wire electrical discharge machined surface region was transmuted into the recdast layer in the range of about 10${\mu}$m deep by resolidification and next zone was transmuted into the heat affected zone in the range of about 15${\mu}$m deep by high temperature. 2. The hardness of the recast layer and heat affected zone was decreased on its machined surface. 3. The more wire feedrate was increased, the more electrical discharge machine gap was decreased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.14-16
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• 2002

Melting and re-solidification nature of $SmBa_2Cu_3O_{7-y}$ (Sm123) grains in Ba-Cu-O (Ba:Cu=3:5) liquid containing 0.7 at.% yttrium were investigated at the temperature lower than its melt point. When Sm123 grains/liquid powder compacts were heated to a temperature between two melting points of Ba-Cu-O liquid ($1000^{\circ}C$) and a Sm123 phase ($1060^{\circ}C$) and held at this temperature for appropriate time, Sm123 grains melted partly in the liquid that was formed by melting of the liquid-forming powder. During subsequent slow cooling, (Sm,Y)$Ba_2Cu_3O_{7-y}$ solidified at the outer parts of the unmelted Sm12 grains, which is distinguished from the core regions by lower $Sm_2BaCuO_5$ (211) density.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.4 no.3
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• pp.32-38
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• 2005

Electrical discharge machining is the method of using thermal energy by electrical discharge. Generally, if the material of workpiece has conductivity even though very hard materials and complicated shape which are difficult to cut such as quenching steel, cemented carbide, diamond and conductive ceramics, the EDM process is favorable one of possible machining processes. But, the process is necessarily required of finish cut and heat treatment because of slow cutting speed, no mirror surface, brittleness and crack due to the residual stress for manufactured goods. In this experimental thesis, the super EDM drilling was developed for high precision semiconductor die steel and for minimization of leadframe width. It was possible to development of EDM drilling machine for high precision semiconductor die with the electrode guide and its modelling and stress analysis. The development of electrode with the copper pipe type was conducted to drill the hole from the diameter of 0.1mm to 3.0mm with the error of from 0.02mm to 0.12mm. From the SEM and EDX analysis, the entrance of the EDM drill was found the resolidification of not only the component of tungsten but also the component of copper.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.1
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• pp.82-89
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• 2014

The damage in germanium (Ge) optical window irradiated by a near-infrared continuous wave (CW) laser was studied. Laser-induced heating and melting process were surveyed, and the specific laser power and the irradiance time to melt were estimated by numerical simulation. The experiments were also carried out to investigate the macro and micro structure change on Ge window. Results showed that the surface deformation was formed by melting and resolidification process, the damaged surface had a polycrystalline phase, and the transmittance as an optical performance factor in mid-infrared region was decreased. We confirmed that an abnormal polycrystalline phase and surface deformation effect such as hillock formation and roughness increase reduced the transmittance of Ge window and were the damage mechanism of CW laser induced damage on Ge window.

• Laser Solutions
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• v.18 no.1
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• pp.12-17
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• 2015

This work performed numerical analysis of electromagnetic field and thermal phenomena occurring in femtosecond laser irradiation of silver nanowires. The local electric field enhancement was computed to calculate the optical energy dissipation as a Joule heating source and the thermal transport was analysed based on the two-temperature model (TTM). Electron temperature increased up to 1000K after 50fs and its spatial distribution became homogeneous after 80fs at the fluence of 100mJ/cm2. The result of this work is expected to contribute to revealing the photothermal effects on silver nanowires induced by femtosecond laser irradiation. Although the highest increase of lattice temperature was substantially below the melting point of silver, the experimental results showed resolidification and fragmentation of the silver nanowire into nanoparticles, which cannot be explained by the photothermal mechanism. Further studies are thus needed to clarify the physical mechanisms.

• Journal of Welding and Joining
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• v.27 no.6
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• pp.68-73
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• 2009

Recently, as titanium and titanium alloys are being increasingly used in wide areas, there are on-going researches to obtain high quality weld zone. In particular, growing interest is being drawn to laser welding, which involves low heat input and large aspect ratio in various welding processes and can facilitate shield in atmospheric condition compared with electron beam welding. The first report covered the analysis of embrittlement by the bead color of weld zone through quantitative analysis of oxygen and nitrogen and measurement of hardness as basic experiment to apply laser welding to titanium. Results indicated that the element that affect embrittlement the most was nitrogen, and as embrittlement and oxygenation go on, bead color changed to silver, gold, brown, blue and gray. This study performed butt welding of pure titanium and STS304 by using 1kW CW Nd:YAG laser, and to find out basic physical properties, evaluated welding performance by laser output, welding speed, root gap and misalignment etc, and examined mechanical properties through tensile stress and Erichsen test. The reason particles of pure titanium welded metal and HAZ are greater than STS304 is because they are pure metal and do not include many impure elements that work as nuclei in case of resolidification, thus becoming coarse columnar crystals eventually. In addition, the reason STS304 requires more energy during welding than pure titanium is because the particle size of base metal is smaller.

• Journal of Periodontal and Implant Science
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• v.27 no.3
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• pp.495-514
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• 1997

The purpose of this study was to evaluate the in vitro effects of Nd:YAG laser irradiation on removal of a root surface smear layer after root planing in comparison with Tetracycline HCl. The 60 extracted human teeth due to severe periodontal disease were vigorously scaled and root planed with Gracey curet. Thirty specimen($5{\times}5{\times}2mm$) were obtained from root planed surface of 30 human teeth and assigned randomly to one of three groups : root planed group(5 specimen), Tetracycline HCI group(5 specimen, burnished for 5 minutes), and Nd:YAG laser group(25 specimen, German Dental Laser, Fotona Twinlight). Nd:YAG laser group was divided into 4 subgroups according to power of 1W, 1.5W, 2W, 3W at frequency to 10Hz. The specimen were then fixed, and examed by Scanning electron microscopic study. 30 of 60 human teeth used to measurement of the intrapulpal temperature rise during laser irradiation. Laser-irradiated surface exhibited various surface texture from relative flat surface to irregular surface with patent dentinal tubules of various shape and size. In some area, the root surface alteration which are carbonization, pit and crater formation and melting and resolidification were observed. The number of exposed dentinal tubules per unit($100_{\mu}m^2$) on tetracycline HCI group was more than that in the laser group below 1.5W of power(150mJ/pulse) and was significantly less than that in laser group above 2W of power(200mJ/pulse)(P<0.OOl). As power increased the intrapulpal temperature rise also increased. The result suggested that the parameter which effectively remove root surface smear layer than tetracycline HCI may cause thermal damage to pulp and root surface alteration result from laser exposure would indicate need for additional instrumentation. Thus, Nd:YAG laser irradiation in these parameter may not be appropriate for clinical use as adjunct to conventional periodontal therapy.