• Journal of the Korean Ceramic Society
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• v.53 no.3
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• pp.349-353
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• 2016

We prepared a number of reaction-bonded silicon carbides (RBSCs) made from various mixing ratios of raw SiC particles, and investigated their microstructure and etch characteristics by Reactive Ion Etch (RIE). Increasing the amount of $9.5{\mu}m$-SiC particles results in a microstructure with relatively coarser Si regions. On the other hand, increasing that of $2.6{\mu}m$-SiC particles produces much finer Si regions. The addition of more than 50 wt% of $2.6{\mu}m$-SiC particles, however, causes the microstructure to become partially coarse. We also evaluated their etching behaviors in terms of surface roughness (Ra), density and weight changes, and microstructure development by employing Confocal Laser Scanning Microscope (CLSM) and Scanning Electron Microscope (SEM) techniques. During the etching process of the prepared samples, we confirmed that the residual Si region was rapidly removed and formed pits isolating SiC particles as islands. This leads to more intensified ion field on the SiC islands, and causes physical corrosion on them. Increased addition of $2.6{\mu}m$-SiC particles produces finer residual Si region, and thus decreases the surface roughness (Ra.) as well as causing weight loss after etching process by following the above etching mechanism.

• Journal of Korean Society of Forest Science
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• v.95 no.5
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• pp.556-561
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• 2006

This study was conducted to choose end-members and tracers for application of End Member Mixing Analysis (EMMA) model for the coniferous forest catchment, Gwangneung Gyeongi-do near Seoul metropolitan of South Korea (N $37^{\circ}$ 45', E $127^{\circ}$ 09'). This coniferous forest of Pinus Korainensis and Abies holophylla was planted at stocking rate of $3.0stems\;ha^{-1}$ in 1976. Thinning and pruning were carried out two times in the spring of 1996 and 2004 respectively. We monitored two successive rainfall events during ten days from June 26, 205 to July 5, 2005. Two storm events were selected to determine the end members and natural traces for hydrograph separation. The event 1 amounts to 161.9 m for two days from June 26 to 27, 2005. The event 2 precipitates to 139.2 mm for one day of July 1, 205. Throughfall, groundwater, soil water and stream water of the two events above were sampled through the bulk and automatic sampler. Their chemical properties were analyzed for prediction of the main tracer. The end members that contribute to the stream runoff were identified from the three components including groundwater, soil water and throughfall. Each component and stream water in the two events formed the suitable mixing diagram in case of chloride-nitrate ion and sulfate-potassium ion. Especially, chloride-nitrate ion was found to be the most suitable tracers for EMMA model in the two events.

• Journal of the Korea Institute of Building Construction
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• v.22 no.5
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• pp.425-430
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• 2022

Concrete used for the foundation of high-rise buildings is often placed through in an integrated pouring to ensure construction efficiency and quality. However, if concrete is placed integrally, there is a high risk of temperature cracking during the hydration reaction, and it is necessary to determine the optimal mixing design of high-performance, high-durable concrete through the replacement of the admixture. In this study, experiments on salt damage, carbonation, and sulfate were conducted on the specimen manufactured from the optimal high-performance low-heating concrete combination determined in the author's previous study. The resistance of the cement matrix to chlorine ion diffusion coefficient, carbonation coefficient, and sulfate was quantitatively evaluated. In the terms of compression strength, it was measured as 141% compared to the structural design standard of KCI at 91 days. Excellent durability was expressed in carbonation and chlorine ion diffusivity performance evaluation. In particular, the chlorine ion diffusion coefficient, which should be considered the most strictly in the marine environment, was measured at a value of 4.09×E-12m²/y(1.2898×E-10m²/s), and is expected to be used as a material property value in salt damage durability analysis. These results confirmed that the latent hydroponics were due to mixing of the admixture and high resistance was due to the pozzolane reaction.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.408-412
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• 2004

A total of 23 springs distributed in the southern and northern sides of Mt. Hala in Jeju Island were seasonally sampled and analyzed for their major ion chemistry and oxygen and hydrogen isotope compositions to investigate their hydrogeochemical and isotopic characteristics. Dissolved ion concentrations of the south-side springs slightly increase with decreasing altitude. This indicates that dissolved ion concentrations of groundwater recharged at higher altitudes increase by water-rock interaction during the downgradient migration of groundwater through highly permeable volcanic aquifer. Dissolved ion concentrations of the north-side springs also slightly increase with decreasing altitude, but dramatically increase at ～300 m.a.s.l. This may indicate a sudden input of contaminants to the north-side groundwater system around ～300 m.a.s.l. Springs located in areas above ～300 m.a.s.l. have very low concentrations of dissolved ions, showing little seasonal variations. Whereas springs located in areas below ～300 m.a.s.l. show a big seasonal variation in the concentration of dissolved ions. Seasonal variation of oxygen isotope compositions of springs is ～3$\textperthousand$ for high-altitude springs (～1700 m.a.s.l.) and is ～2$\textperthousand$ near shore, indicating an attenuation of the variation through mixing with other groundwater bodies during migration.

• Korean Journal of Materials Research
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• v.4 no.1
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• pp.9-23
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• 1994

Epitaxial $CoSi_2$ layer has been grown on NaCl(100) substrate at low deposition temperature($200^{\circ}C$) by multitarget bias cosputter deposition(MBCD). The phase sequence and crystallinity of deposited silicide as a function of deposition temperature and substrate bias voltage were studied by X-ray diffraction(XRD) and transmission electron microscopy(TEM) analysis. Crystalline Si was grown at $200^{\circ}C$ by metal induced crystallization(M1C) and self bias effect. In addition to, the MIC was analyzed both theoretically and experimentally. The observed phase sequence was $Co_2Si \to CoSi \to Cosi_2$ and was in good agreement with that predicted by effective heat of formation rule. The phase sequence, the CoSi(l11) preferred orientation, and the crystallinity had stronger dependence on the substrate bias voltage than the deposition temperature due to the collisional cascade mixing, the in-situ cleaning, and the increase in the number of nucleation sites by ion bombardment of growing surface. Grain growth induced by ion bombardment was observed with increasing substrate bias voltage at $200^{\circ}C$ and was interpreted with ion bombardment dissociation model. The parameters of $E_{Ar}\;and \alpha(V_s)$ were chosen to properly quantify the ion bombardment effect on the variation in crystallinty at $200^{\circ}C$ with increasing substrate bias voltage using Langmuir probe.

• Journal of the Korean Society of Visualization
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• v.6 no.1
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• pp.41-46
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• 2008

In this paper, the recirculation flow motion and mixing characteristics driven by air bubble stream in a rectangular water tank is studied. The time-resolved PIV technique is adopted for the quantitative visualization and analysis. 488 nm Ar-ion CW laser is used for illumination and orange fluorescent ($\lambda_{ex}=540nm,\;\lambda_{em}=560nm$) particle images are acquired by a PCO 10bit high-speed CCD camera (1280$\times$1024). To obtain clean particle images, 545 nm long pass optical filter and an image intensifier are employed and the flow rates of compressed air is 3 l/min at 0.5 MPa. The recirculation and mixing flow field is further investigated by time-resolved POD analysis technique. It is observed that the large scale recirculation resulting from the interaction between rising bubble stream and side wall is the most dominant flow structure and there are small scale vortex structures moving along with large scale recirculation flow. It is also verified that the sum of 20 modes of velocity field has about 67.4% of total turbulent energy.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.5
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• pp.265-269
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• 2000

$(Ba, Sr)TiO_3$thin films were etched with a magnetically enhanced inductively coupled plasma (MEICP) at different CF4/Ar gas mixing ratios. Experimental was done by varying the etching parameters such as rf power, dc bias and chamber pressure. The maximum etch rate of the BST films was $1800{AA}/min$ under $CF_4/(CF_4+Ar)$ of 0.1, 600 W/350 V and 5 mTorr. The selectivity of BST to Pt and PR was 0.6, 0.7, respectively. X-ray photoelectron spectroscopy (XPS) results show that surface reaction between Ba, Sr, Ti and C, F radicals occurs during the (Ba, Sr)TiO3 etching. To analyze the composition of surface residue after the etching, films etched with different CF_4/Ar$ gas mixing ratio were investigated using XPS and secondary ion mass spectroscopy (SIMS).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.866-869
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• 2001

In this study, (Ba,Sr)TiO$_3$(BST) thin films were etched with a magnetically enhanced inductively coupled plasma(MEICP). Etching characteristics of BST thin films including etch rate and selectivity were evaluated as a function of the etching parameters such as gas mixing ratio, rf power, dc bias voltage and chamber pressure. The maximum etch rate of the BST films was 1700 $\AA$/min at Ar(90)/CF$_4$(10), 600 W/350 V and 5 mTorr. The selectivity of BST to PR was 0.6, 0.7, respectively. To analyze the composition of surface residue remaining after the etching, samples etched with different CF$_4$/Ar gas mixing ratio were investigated with X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). From the results of XPS and SIMS, there are chemical reaction between Ba, Sr, Ti and C, F radicals during the etching and remained on the surface.

• Journal of the Korean Chemical Society
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• v.6 no.2
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• pp.122-124
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• 1962

The silver halide precipitate tends to separate in curdy form of flocculated colloid when it is precipitated by direct mixing of reactant solutions. This type of precipitate has a great tendency to adsorb or occlude foreign ions in the solution.When silver halide in precipitated from homogeneous solution using the slow hydrolysis of Alkyl halide or Ally halide, the precipitate becomes dense, filterable and uniform in particle size which is very advantageous in gravimetric analysis.We found that silver halide precipitates obtained from homogeneous solution with hydrogen halide formed by the hydrolysis of alkyl halide do not give the color change with fluorescein as adsorption indicater, while silver halide precipitates obtained by direct mixing method give sharply pink color which appear to be uniformly distributed through the solution in silver ion excess.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.290-295
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• 2000

An experimental study was carried out in a cavity with upper channel and square heat surface by visualization equipment with Mach-Zehnder interferometer and laser apparatus. The visualization system consists of 2-dimensional sheet light by Argon-Ion Laser with cylindrical lens and flow picture recording system. Instant simultaneous velocity vectors at whole field were measured by 2-D PIV system(CACTUS'2000). Obtained result showed various flow patterns. Severe unsteady flow fluctuation within the cavity are remarkable and sheared mixing layer phenomena are also found at the region where inlet flow is collided with the counter-clockwise rotating main primary vortex. Photographs of Mach-Zehnder are also compared in terms of constant heat flux.