• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.97-103
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• 2014

Among various lead-free solders, the Sn-58Bi solders have been considered as a highly promising lead-free solders because of its low melting temperature and high tensile strength. However, Sn-58Bi solder has the poor ductility. To enhance the mechanical property of Sn-58Bi solder, epoxy-enhanced Sn-58Bi solders have been studied. This study compared the microstructures and the mechanical properties of Sn-58Bi solder and Sn-58Bi epoxy solder with aging treatment. The solders ball were formed on the printed circuit board (PCB) with organic solderability preservative (OSP) surface finish, and then the joints were aged at 85, 95, 105 and $115^{\circ}C$ for up to 100, 300, 500 and 1000 hours. The shear test was conducted to evaluate the mechanical property of the solder joints. $Cu_6Sn_5$ intermetallic compound (IMC) layer grew with increasing aging time and temperature. The IMC layer for the Sn-58Bi epoxy solder was thicker than that for the Sn-58Bi solder. According to result of shear test, the shear strength of Sn-58Bi epoxy solder was higher than that of Sn-58Bi solder and the shear strength decreased with increasing aging time.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1665-1673
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• 2013

Recently, the interest and demand on free formed structure providing aesthetic value as well as functionality has been increasing. Formwork has numerous advantages such as high strength, convenience, accuracy and good quality of surface roughness. Nevertheless, it increases construction cost and period to build complex shapes. For these purpose, deposition construction systems such as Contour Crafting and Concrete Printing have been developed with active collaboration between university and industry by applying the rapid prototyping technology to the construction industry in USA and England. Since there has been no related research in Korea, the possibility of spin-off technology and its fusion cannot be expected. In this paper, design elements including mechanical system and control system related to automatic deposition construction system prototype for constructing a free curved structure without mold are described. As for an appropriate material for the system, fiber reinforced mortar was selected by experiments on compressive strength, fluidity, viscosity and setting time. By performing transfer and extrusion experiments, the possibility of the development of deposition construction system was demonstrated. Based on this research results, it is required to keep the automatic deposition construction system improve and extend it into the new application area in construction industry.

• Resources Recycling
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• v.13 no.5
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• pp.45-50
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• 2004

To investigate the characteristics of phases formed in iron carbides, super iron carbide was synthesized from hematite fines with $CO-H_2$ gas mixture after reduction under $H_2$ gas at $600^{\circ}C$. Before carburization, the surface of iron powder reduced was pre-treated in the atmosphere of 0.05 vol% $NH_3$-Ar. The synthesized iron carbides were comprehensively explored by C/S analyzer(Low C/S determinator), M$\"{o}$ssbauer spectroscopy, X-ray diffraction patterns(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), and Raman spectroscopy at various reaction time of 5, 10, 15, 20, 25, 30, and 35 min, respectively. By adding a small amount of $NH_3$ gas, the super iron carbides containing 10 wt% carbon were synthesized, and its addition stabilized iron carbides. It was found that the $NH_3$ treatment played a major role in the formation of iron carbide without decomposition($Fe_3C{\to}$3Fe+C) of iron carbides and precipitation of free carbon. It also succeed to synthesize super iron carbide, $Fe_5C_2$, as a stable single phase without involving Fe and $Fe_3C$ phases.

• Journal of the Mineralogical Society of Korea
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• v.32 no.3
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• pp.213-222
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• 2019

Birnessite (birnessite, $7{\AA}$ manganate, ${\delta}-MnO_2$) is a major mineral comprising manganese nodule. Various synthetic methods have been studied and evaluated because it can be used as an ion exchange agent and a battery recharging material. However, it is difficult to obtain a single birnessite phase because it does not have a stoichiometric chemical composition. Feitknechtite (${\beta}-MnOOH$) is formed as an intermediate product during birnessite synthesis and in this study, the transition of this phase to birnessite was compared by using XRD and SEM. Two different methods, Feng et al. (2004) and Luo et al. (1998), based on redox reaction were used. It was possible to obtain the impurity-free birnessite for the sample aged 60 days at $27^{\circ}C$ by Feng et al. (2004) method and 3 days at $60^{\circ}C$ by Luo et al. (1998) method. The phase transition rate of the feitknechtite phase was slower in the case of $Mg^{2+}$ doped birnessite which was synthesized by Luo et al. (1998) method, and almost single phase almost single phase birnessite was identified at high temperature. Crystal surface and morphology also confirmed the difference between the samples synthesized by two methods.

• Journal of the Korean association of regional geographers
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• v.4 no.2
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• pp.49-64
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• 1998

Bing-gye valley(Kyongbuk Province, South Korea) is well known as a tourist attraction because of its meteorologic characteristics that show subzero temperature during midsummer. Also, there are some interesting geomorphic features in the valley area. Therefore, the valley is worth researching in geomorphology field. The aim of this paper is to achieve two purposes. These are to clarify geomorphic features on talus within Bing-gye valley area, and to infer the origin of Bing-gye valley. The main results are summarized as follows. 1) The formation of Bing-gye valley It would be possible to infer the following two ideas regarding the formation of Bing-gye valley. One is that the valley was formed by differential erosion of stream along fault line, and the other is that the rate of upheaval comparatively exceeded the rate of stream erosion. Especially, the latter may be associated with the fact that the width of the valley is much narrow. Judging that the fact the width of the valley is much narrow, compared with one of its upper or lower valley, it is inferred that Bing-gye valley is transverse valley. 2) The geomorphic features of talus (1) Pattern It seems to be true that the removal of matrix(finer materials) by the running water beneath the surface can result in partly collapse hollows. Taluses are tongue-shaped or cone-shaped in appearance. They are $120{\sim}200m$ in length, $30{\sim}40m$ in maximum width. and $32{\sim}33^{\circ}$ in mean slope gradient. The component blocks are mostly homogeneous in size and shape(angular), which reflect highly jointed free face produced by frost action under periglacial environment. (2) Origin On the basis of previous studies, the type of the talus is classified into rock fall talus. When considered in conjunction with the degrees of both weathering of blocks and hardness of blocks, it can be explained that the talus was formed under periglacial environment in pleistocene time. (3) The inner structure of block accumulation I recognize a three-layered structure in the talus as follows: (a) superficial layer; debris with openwork texture at the surface, 1.3m thick. (b) intermediate layer: small debris(about 5cm in diameter) with fine matrix(including humic soil), 70cm thick. (c) basal layer: over 2m beneath surface, almost pure soil horizon without debris (4) The stage of landform development Most of the blocks are now covered with lichen, and/or a mantle of weathering. It is believed that downslope movement by talus creep well explains the formation of concave slope of the talus. There is no evidence of present motion in the deposit. Judging from above-mentioned facts, the talus of this study area appears to be inactive and fossil landform.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.179-200
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• 1996

The intrinsic instabilities of fluid flow occurred in the melt of the Czochralski crystal growth system Czochralski method, asymmetric flow patterns and temperature profiles in the melt have been studied by many researchers. The idea that the non-symmetric structure of the growing equipment is responsible for the asymmetric profiles is usually accepted at the first time. However further researches revealed that some intrinsic instabilities not related to the non-symmetric equipment structure in the melt could also appear. Ristorcelli had pointed out that there are many possible causes of instabilities in the melt. The instabilities appears because of the coupling effects of fluid flow and temperature profiles in the melt. Among the instabilities, the B nard type instabilities with no or low crucible rotation rates are analyzed by the visualizing experiments using X-ray radiography and the 3-D numerical simulation in this study. The velocity profiles in the Silicon melt at different crucible rotation rates were measured using X-ray radiography method using tungsten tracers in the melt. The results showed that there exits two types of fluid flow mode. One is axisymmetric flow, the other is asymmetric flow. In the axisymmetric flow, the trajectory of the tracers show torus pattern. However, more exact measurement of the axisymmetrc case shows that this flow field has small non-axisymmetric components of the velocity. When fluid flow is asymmetric, the tracers show random motion from the fixed view point. On the other hand, when the observer rotates to the same velocity of the crucible, the trajectory of the tracer show a rotating motion, the center of the motion is not same the center of the melt. The temperature of a point in the melt were measured using thermocouples with different rotating rates. Measured temperatures oscillated. Such kind of oscillations are also measured by the other researchers. The behavior of temperature oscillations were quite different between at low rotations and at high rotations. Above experimental results means that the fluid flow and temperature profiles in the melt is not symmetric, and then the mode of the asymmetric is changed when rotation rates are changed. To compare with these experimental results, the fluid flow and temperature profiles at no rotation and 8 rpm of crucible rotation rates on the same size of crucible is calculated using a 3-dimensional numerical simulation. A finite different method is adopted for this simulation. 50×30×30 grids are used. The numerical simulation also showed that the velocity and flow profiles are changed when rotation rates change. Futhermore, the flow patterns and temperature profiles of both cases are not axisymmetric even though axisymmetric boundary conditions are used. Several cells appear at no rotation. The cells are formed by the unstable vertical temperature profiles (upper region is colder than lower part) beneath the free surface of the melt. When the temperature profile is combined with density difference (Rayleigh-B nard instability) or surface tension difference (Marangoni-B nard instability) on temperature, cell structures are naturally formed. Both sources of instabilities are coupled to the cell structures in the melt of the Czochralski process. With high rotation rates, the shape of the fluid field is changed to another type of asymmetric profile. Because of the velocity profile, isothermal lines on the plane vertical to the centerline change to elliptic. When the velocity profiles are plotted at the rotating view point, two vortices appear at the both sides of centerline. These vortices seem to be the main reason of the tracer behavior shown in the asymmetric velocity experiment. This profile is quite similar to the profiles created by the baroclinic instability on the rotating annulus. The temperature profiles obtained from the numerical calculations and Fourier transforms of it are quite similar to the results of the experiment. bove esults intend that at least two types of intrinsic instabilities can occur in the melt of Czochralski growing systems. Because the instabilities cause temperature fluctuations in the melt and near the crystal-melt interface, some defects may be generated by them. When the crucible size becomes large, the intensity of the instabilities should increase. Therefore, to produce large single crystals with good quality, the behavior of the intrinsic instabilities in the melt as well as the effects of the instabilities on the defects in the ingot should be studied. As one of the cause of the defects in the large diameter Silicon single crystal grown by the

• Korean Journal of Remote Sensing
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• v.37 no.5_1
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• pp.903-916
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• 2021

An area's topography refers to the shape of the earth's surface, described by its elevation, slope, and aspect, among other features. The topographical conditions determine energy flowsthat move water and energy from higher to lower elevations, such as how much solar energy will be received and how much wind or rain will affect it. Another common factor, the topographic wetness index (TWI), is a calculation in digital elevation models of the tendency to accumulate water per slope and unit area, and is one of the most widely referenced hydrologic topographic factors, which helps explain the location of forest vegetation. Analyses of topographical factors can be calculated using a geographic information system (GIS) program based on digital elevation model (DEM) data. Recently, a large number of free open source software (FOSS) GIS programs are available and developed for researchers, industries, and governments. FOSS GIS programs provide opportunitiesfor flexible algorithms customized forspecific user needs. The majority of biodiversity in island areas exists at about 20% higher elevations than in land ecosystems, playing an important role in ecological processes and therefore of high ecological value. However, island areas are vulnerable to disturbances and damage, such as through climate change, environmental pollution, development, and human intervention, and lacks systematic investigation due to geographical limitations (e.g. remoteness; difficulty to access). More than 4,000 of Korea's islands are within a few hours of its coast, and 88% are uninhabited, with 52% of them forested. The forest ecosystems of islands have fewer encounters with human interaction than on land, and therefore most of the topographical conditions are formed naturally and affected more directly by weather conditions or the environment. Therefore, the analysis of forest topography in island areas can be done more precisely than on its land counterparts, and therefore has become a major focus of attention in Korea. This study is focused on calculating the performance of different topographical factors using FOSS GIS programs. The test area is the island forests in Korea's south and the DEM of the target area was processed with GRASS GIS and SAGA GIS. The final slopes and TWI maps were produced as comparisons of the differences between topographic factor calculations of each respective FOSS GIS program. Finally, the merits of each FOSS GIS program used to calculate the topographic factors is discussed.

• Journal of the Korean Ceramic Society
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• v.43 no.2 s.285
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• pp.98-105
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• 2006

YBCO film was synthesized by using a new approach to the TFA-MOD method. In the fabrication process, $Y_2Ba_1Cu_1O_x\;and\;Ba_3Cu_5O_8$ powders were used as precursors (the so called '211 process'), instead of Y-, Ba-, and Cu-based acetates, and dissolved in trifluoroacetic acid followed by calcining and firing heat treatment. Consequently, we successfully fabricated YBCO film and evaluated the phase formation, texture evolution, and critical properties as a function of the calcining and firing temperature and humidity, in order to explore its possible application in coated conductor fabrication. The films were calcined at $430-460^{\circ}C$ and then fired at $750-800^{\circ}C\;in\;a\;0-20\%$ humidified $Ar-O_2$ atmosphere. We observed that $BaF_2$ phase was effectively reduced and that a sharp and strong biaxial texture formed under humidified atmosphere leading to increased critical properties. In addition, we found that the microstructure varied significantly with the firing temperature: the grain grew further, the film became denser, and the degree of texture and phase purity varied as the firing temperature increased. For the film fired at $775^{\circ}C$ after calcining at $460^{\circ}C$, the critical current was obtained to be 39 A/cm-width (corresponding critical current density is $2.0\;MA/cm^2$ which was probably attributed to such factors as the enhanced phase purity and out-of-plane texture, the moderate film density and grain size, and crack-free surface.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.71-76
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• 2017

The roll damping problem in the design of ships and offshore structures remains a challenge to many researchers due to the fluid viscosity and nonlinearity of the phenomenon itself. In this paper, the study on viscous roll damping of a circular cylinder was carried out using forced oscillations. The roll moment generated by forced oscillation using a torque sensor was measured for each forced oscillation period and compared with the empirical formula. Although the magnitude of the measured torque from the shear force was relatively small, the results were qualitatively similar to those obtained from the empirical formula, and showed good agreement with the quantitative results in some oscillation periods. In addition, the flow around the circular cylinder wall was observed closely through the PIV measurements. Owing to the fluid viscosity, a boundary layer was formed near the wall of the circular cylinder, and a minute wave was generated by periodical forced oscillations at the free surface through the PIV measurement. In this study, the suitability of the empirical formula for the roll moment caused by viscous roll damping was verified by model tests. The wave making phenomenon due to the fluid viscosity around the wall of a circular cylinder was testified by PIV measurements.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.795-801
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• 2019

The aim of this study was to investigate the possibility of the skin-friction reduction by vortex control. A vortical system such as a horseshoe vortex, a hairpin vortex, and a wake region was induced around a hemisphere attached on a Perspex flat plate in the circulating water channel. Hairpin vortices were developed from the wake region and horseshoe vortices were formed by an adverse pressure gradient in front of the hemisphere. The horseshoe vortices located on the flank of the hemisphere induced a high momentum flow in the wake region by the direction of their vorticity. This process increased the frequency of the hairpin vortices as well as the frictional drag on the surface of the wake region. To reduce the skin-friction drag, suction control in front of the hemisphere was applied through a hole. Flow visualization was performed to optimize the free-stream velocity, size of the hemisphere, and size of the suction hole. Once the wall suction control mitigated the strength of the horseshoe vortex, the energy supplied to the wake region was reduced, causing the frequency of the hairpin vortex generation to decrease by 36.4 %. In addition, the change in the skin-friction drag, which was measured with a dynamometer connected to a plate in the wake region, also decreased by 2.3 %.