• Economic and Environmental Geology
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• v.30 no.1
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• pp.35-49
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• 1997

The coal formation of the Deokpyeong area are interbedded along metapelites of the Ogcheon Supergroup, which are composed mainly of graphite, quartz, muscovite and associated with small amounts of biotite, chlorite, pyrite and barite. The ratios of $SiO_2/Al_2O_3$, $Al_2O_3/Na_2O$ and $K_2O/Na_2O$ of the coaly metapelite are variable and wide range from 1.80 to 10.21, from 27.8 to 388.8 and from 7.6 to 61.8, respectively. These coal formation were deposited in basin of marine environments, and the REE of these rocks are not influenced with metamorphism and hydrothermal alterations on the basis of $Al_2O_3$ versus La, La against Ce, the ratios of La/Ce (0.19 to 0.99) and Th/U (0.02 to 4.75). These rocks also show much variation in $La_N/Yb_N$ (1.19 to 22.89), Th/Yb (0.14 to 21.43) and La/Th (0.44 to 13.67), and their origin is explained by derivation from a mixture of sedimentary and igneous rocks. The wide range in trace and REE element characteristics as Co/Th (0.12 to 2.78), La/Sc (0.33 to 10.18), Sc/Th (0.57 to 5.73), V/Ni (8 to 2347), Cr/V (0.02 to 0.67) and Ni/Co (1.56 to 32.95) of these coaly metapelites argues for inefficient mixing of the various source lithologies during sedimentation. Deep to pale green barium-vanadium muscovites (vanadium-oellacherite) have been found in this coal formations. Modes of occurrence and grain size of muscovite are heterogeneous, but most of the barium and vanadium-bearing muscovites occur along the boundaries between graphite and quartz grains, ranging from 200 to $350{\mu}m$ in length and from 40 to $60{\mu}m$ in width. Results of X-ray diffraction data of the minerals characterized to be monoclinic system with $a=5.249{\AA}$, $b=8.939{\AA}$, $c=20.924{\AA}$ and ${\beta}=95.894^{\circ}$. Representative chemical formula of the muscovite was $(Na_{0.09}K_{1.44}Ba_{0.46})(Al_{2.75}Ti_{0.07}V_{0.56}Fe_{0.08}Mg_{0.50})(Si_{6.12}Al_{1.88})O_{22}$. The V possibly substitute octahedral Al, and the Ba is coupled substitution of $K^+Si^{4+}=Ba^{2+}Na^+Ca^{2+}$, which compositional ranges of V and Ba are from 0.42 to 0.69 and from 0.34 to 0.56 based on $O_{22}$, respectively. Formation mechanism of the barium-vanadium muscovites in the coaly metapelite is shown that the formed by high pressure and temperature from regional metamorphism origanated during diagenesis at the interface between a basinal brine and organic matter.

• Journal of Soil and Groundwater Environment
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• v.14 no.6
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• pp.87-94
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• 2009

Surfactant-enhanced air sparging (SEAS) was developed to suppress the surface tension of groundwater prior to air sparging resulting in higher air saturation and larger contact area between NAPL and gas during air sparging. Larger contacting interface between NAPL and gas means faster mass transfer of contaminants from NAPL to gas phase. This new technique, however, is limited to relatively volatile contaminants because vaporization is its basic mechanism of mass transfer. In this study, SEAS was tested at an elevated temperature for a semi-volatile n-decane, which is expected not to be a good candidate of SEAS application due to its low vapor pressure at ambient temperature. Three sparging experiments were conducted using 1-dimensional column (5 cm id, 80 cm length) packed with sand; (1) ambient temperature ($23^{\circ}C$), column saturated with distilled water, (2) SEAS at ambient temperature ($23^{\circ}C$), for n-decane contaminated sand, (3) SEAS at elevated temperature ($73^{\circ}C$), for n-decane contaminated sand. Higher air saturation was achieved by SEAS compared to that by air sparging without surfactant application. The n-decane removal efficiency of SEAS at elevated temperature was significantly higher(> 10 times) than that of ambient SEAS. The n-decane concentrations in the gas effluent from column during SEAS at $73^{\circ}C$ are found to be 10 times of those measured at ambient temperature. Thus, SEAS technique can be applied for removal of semi-volatile contaminants provided that an appropriate technique for elevating aquifer temperature is available.

• Investigative Magnetic Resonance Imaging
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• v.11 no.1
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• pp.10-19
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• 2007

Conventional MRI methods using T1-, T2-, diffusion-, perfusion-weighting, and functional imaging rely on characterizing the physical and functional properties of the tissue. In this review, we introduce an imaging modality based on measured the mechanical properties of soft tissue, namely magnetic resonance elastography (MRE). The use of palpation to identify the stiffness of tissue remains a fundamental diagnostic tool. MRE can quantify the stiffness of the tissue thereby providing a objective means to measure the mechanical properties. To accomplish a successful clinical setting using MRE, hardware and software techniques in the area of transducer, pulse sequence, and imaging processing algorithm need to be developed. Transducer, a mechanical vibrator, is the core of MRE application to make wave propagate invivo. For this reason, considerations of the frame of human body, pressure and friction of the interface, and high magnetic field of a MRI system needs to be taken into account when designing a transducer. Given that the wave propagates through human body effectively, developing an appropriate pulse sequence is another important issue in obtaining an optimal image. In this review paper, we introduce the technical aspects needed for MRE experiments and introduce several applications of this new field.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.10a
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• pp.15-15
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• 1999

In chip plating, several parameters must be taken into consideration. Current density, solution concentration, pH, solution temperature, components volume, chip and media ratio, barrel geometrical shape were most likely found to have an effect to the process yields. The 3 types of barrels utilized in chip plating industry are the conventional rotating barrel. vibrational barrel (vibarrel), and the centrifugal type. Conventional rotating barrel is a close type and is commonly used. The components inside the barrel are circulated by the barrel's rotation at a horizontal axis. Process yield has known to have higher thickness deviation. The vibrational barrel is an open type which offers a wide exposure to electrolyte resulting to a stable thickness deviation. It rotates in a vertical axis coupled with multi-vibration action to facilitate mixed up and easy transportation of components, The centrifugal barrel has its plated work centrifugally compacted against the cathode ring for superior electrical contact with simultaneous rotary motion. This experiment has determined the effect of barrel vibration intensity to the plating thickness distribution. The procedures carried out in the experiment involved the overall plating process., cleaning, rinse, Nickel plating, Tin-Lead plating. Plating time was adjusted to meet the required specification. All other parameters were maintained constant. Two trials were performed to confirm the consistency of the result. The thickness data of the experiment conducted showed that the average mean value obtained from higher vibrational intensity is nearer to the standard mean. The distribution curve shown has a narrower specification limits and it has a reduced variation around the target value, Generally, intensity control in vi-barrel facilitates mixed up and easy transportation of components, However, it is desirable to maintain an optimum vibration intensity to prevent solution intrusion into the chips' internal electrode. A cathodic reaction can occur in the interface of the external and internal electrode. $2HD{\;}+{\;}e{\;}{\rightarrow}20H{\;}+{\;}H_2$ Hydrogen can penetrate into the body and create pressure which can cause cracks. At high intensity, the chip's motion becomes stronger, its contact between each other is delayed and so plating action is being controlled. However, the strong impact created by its collision can damage the external electrode's structure thereby resulting to bad plating condition. 1 lot of chip was divided into two equal partion. Each portion was loaded to the same barrel one after the other. Nickel plating and tin-lead plating was performed in the same station. Portion A maintained the normal barrel vibration intensity and portion B vibration intensity was increased two steps higher. All other parameters, current, solution condition were maintained constant. Generally, plating method find procedures were carried out in a best way to maintained the best plating condition. After plating, samples were taken out from each portion. molded and polished. Plating thickness was investigated for both. To check consistency of results. 2nd trial was done now using different lot of another characteristics.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.102-102
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• 2018

Electronic industry had required the finer size and the higher performance of the device. Therefore, 3-D die stacking technology such as TSV (through silicon via) and micro-bump had been used. Moreover, by the development of the 3-D die stacking technology, 3-D structure such as chip to chip (c2c) and chip to wafer (c2w) had become practicable. These technologies led to the appearance of HBM (high bandwidth memory). HBM was type of the memory, which is composed of several stacked layers of the memory chips. Each memory chips were connected by TSV and micro-bump. Thus, HBM had lower RC delay and higher performance of data processing than the conventional memory. Moreover, due to the development of the IT industry such as, AI (artificial intelligence), IOT (internet of things), and VR (virtual reality), the lower pitch size and the higher density were required to micro-electronics. Particularly, to obtain the fine pitch, some of the method such as copper pillar, nickel diffusion barrier, and tin-silver or tin-silver-copper based bump had been utillized. TCB (thermal compression bonding) and reflow process (thermal aging) were conventional method to bond between tin-silver or tin-silver-copper caps in the temperature range of 200 to 300 degrees. However, because of tin overflow which caused by higher operating temperature than melting point of Tin ($232^{\circ}C$), there would be the danger of bump bridge failure in fine-pitch bonding. Furthermore, regulating the phase of IMC (intermetallic compound) which was located between nickel diffusion barrier and bump, had a lot of problems. For example, an excess of kirkendall void which provides site of brittle fracture occurs at IMC layer after reflow process. The essential solution to reduce the difficulty of bump bonding process is copper to copper direct bonding below $300^{\circ}C$. In this study, in order to improve the problem of bump bonding process, copper to copper direct bonding was performed below $300^{\circ}C$. The driving force of bonding was the self-annealing properties of electrodeposited Cu with high defect density. The self-annealing property originated in high defect density and non-equilibrium grain boundaries at the triple junction. The electrodeposited Cu at high current density and low bath temperature was fabricated by electroplating on copper deposited silicon wafer. The copper-copper bonding experiments was conducted using thermal pressing machine. The condition of investigation such as thermal parameter and pressure parameter were varied to acquire proper bonded specimens. The bonded interface was characterized by SEM (scanning electron microscope) and OM (optical microscope). The density of grain boundary and defects were examined by TEM (transmission electron microscopy).

• Journal of Korea Foundry Society
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• v.11 no.6
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• pp.475-481
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• 1991

In this study the fabrication technology and mechanical properties of AC8A/$Al_2O_3$ Composites by squeeze casting process were investigated to develope for application as the piston materials that require good friction, wear resistance, and thermal stability. AC8A/$Al_2O_3$ composistes without a porosity and the break of preform were fabricated at the melt temperature of $740^{\circ}C$, the preform temperature of $500^{\circ}C$, and mold temperature of $400^{\circ}C$ under the applied pressure of $1200kg/cm^2$ as the results of the observation of microstructures. As the results of this study, the tensile strength of AC8A/$Al_2O_3$ composites was not increased linearly with $Al_2O_3$ volume fraction and so it seemed not to agree with the rule of mixture, which had been used often in metal matrix composite. Also the tensile strength after thermal fatigue test was little different from that before the test. Consequently it was thought that AC8A/$Al_2O_3$ composites fabricated under our experimental conditions had a good thermal stability and subsequently a good interface bonding. Wear rate(i.e., volume loss per unit sliding distance) of AC8A/$Al_2O_3$ composites was decreased with $Al_2O_3$ volume fraction and the sliding speed at both room temperature and $250^{\circ}C$ and so there was a good correlation between wear rate and hardness. Also the wear rate of AC/8A20% $Al_2O_3$ composities was obtained the value of $1.65cm^3/cm$ at sliding speed of 1.14m/sec as compared with about $3.0\;{\times}10^{-8}cm^3/cm$ hyereutectie Al-Si alloy(Al-16%Si-2%Cu-1%Fe-1%Ni), which applied presently for piston materials. The wear behavior of $Al_2O_3$ composites was observed to a type of abrasive wear by the SEM view of wear surface.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.12
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• pp.11-17
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• 2000

We investigated the growth of InGaN/GaN multiple quantum wells (MQWs) structures which emit blue light. The samples were grown in a low pressure metalorganic chemical vapor deposition system. We examined InGaN/GaN MQWs by varying growth temperatures and thicknesses of InGaN well and GaN barrier layers in MQWs. Especially, the thickness of GaN barrier in InGaN/GaN MQWs was found to severely affect the interfacial abruptness between InGaN well and GaN barrier layers. The higher order satellite peaks in the high resolution x-ray diffraction spectra and the high resolution cross sectional transmission electron microscope image of MQW structrues revealed that the interface between InGaN and GaN layers was very abrupt. Room-temperature photoluminescence spectra also showed a blue emission from InGaN/GaN MQWs at the wavelength of 463.5nm with a narrow full width at half maximum of 72.6meV.

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.70-76
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• 2006

Micro-droplet cell with free droplet as a micro-electrochemical technique has been limited to apply to electrochemical systems with high wetting properties such as an acidic solution and low grade stainless steels(Type 316L). By loading negative pressure to a droplet, control of droplet size, and use of hydrophobic gasket, the cell is modified to be allowed to use for electrochemical systems with high wetting properties. For giving the reliability of new cell, studies on local corrosion were conducted for three different systems-an acidic chloride solution and high chromium ferritic stainless steel, the other acidic chloride solution and type 316, and a neutral chloride solution and type 316. stainless steel. Firstly, the modified micro-droplet cell allows the anodic polarization curves in an acidic chloride solution to show the fact that the local corrosion of high chromium stainless steel near the $\alpha/\sigma$ interface is due to the Cr depleted zone. Secondly, the local anodic polarization test of type 316 L in the other acidic chloride solution can be successfully conducted in the cell. Furthermore, the local polarization curves help elucidating the corrosion of type 316 with $\delta-ferrite$ phase. Finally, the polarization curves of type 316 L in a neutral chloride solution indicates that the factor affecting the pitting corrosion resistance was inclusions rather than $\delta-ferrite$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.7-17
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• 2019

With increasing demand for large offshore infrastructures, suction cofferdams have been large, and the lid stiffener arrangement for a suction cofferdam has become a key element in cofferdam design to constrain the flexural deformation effectively. This study analyzed the changes in the structural behavior of a lid for a suction cofferdam due to lid stiffeners to provide insights into effective stiffener arrangements. By investigating conventional suction anchors, several stiffener patterns of a lid for a polygonal suction cofferdam were determined and analyzed. The structural performance of the stiffened lids was estimated by comparing the stress and deformation, and the reaction distributions on the edge of lid were investigated to analyze the effects of the stiffener arrangement on the lid-wall interface. Finite element analysis showed that radial stiffeners contribute dominantly to decreasing the stress and vertical deflection of the lids, but the stiffeners cause an increase in shear forces between the lid and wall; the forces are concentrated on the lid near the areas reinforced with radial stiffeners, which is negative to lid-wall connection design. On the other hand, inner and outer circumferential stiffeners show little reinforcement effects in themselves, while they can help reduce the stress and deformation when arranged with partial radial stiffeners simultaneously.

• Applied Chemistry for Engineering
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• v.22 no.1
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• pp.37-44
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• 2011

The critical micelle concentration (CMC) of sorbitan laurate SP 20 surfactant in this paper was near $7.216{\times}10^{-4}mol/L$ and the surface tension at CMC was about 26.0 mN/m, which showed higher CMC and lower surface tension than those of octylphenol ethoxylate octylphenol ethoxylate (OPE) 10 surfactant. Dynamic surface tension measurement using a maximum bubble pressure tensiometer showed that the adsorption rate at the interface between air and surfactant solution was found to be slower with SP 20 surfactant, presumably due to a low mobility of SP 20 surfactant monomer. The contact angle of SP 20 surfactant solution was observed to decrease with an increase in surfactant concentration and showed a larger value than that of OPE 10 surfactant solution. Half-life time for foams generated with 1 wt% surfactant solution was also larger with SP 20 surfactant, which indicated higher foam stability with SP 20 surfactant. Dynamic behavior study reveals that the solubilization of n-decane oil was much lower with SP 20, which is in good agreement with experimental results of foam stability, contact angle and CMC. Dynamic interfacial tension measurement by a spinning drop tensiometer shows that interfacial tensions at equilibrium condition in both systems were almost the same but the time required to reach equilibrium was longer with SP 20.