• Journal of Powder Materials
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• v.24 no.6
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• pp.437-443
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• 2017

SiC-based composite materials with light weight, high durability, and high-temperature stability have been actively studied for use in aerospace and defense applications. Moreover, environmental barrier coating (EBC) technologies using oxide-based ceramic materials have been studied to prevent chemical deterioration at a high temperature of $1300^{\circ}C$ or higher. In this study, an ytterbium silicate material, which has recently been actively studied as an environmental barrier coating because of its high-temperature chemical stability, is fabricated on a sintered SiC substrate. $Yb_2O_3$ and $SiO_2$ are used as the raw starting materials to form ytterbium disilicate ($Yb_2Si_2O_7$). Suspension plasma spraying is applied as the coating method. The effect of the mixing method on the particle size and distribution, which affect the coating formation behavior, is investigated using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) analysis. It is found that the originally designed compounds are not effectively formed because of the refinement and vaporization of the raw material particles, i.e., $SiO_2$, and the formation of a porous coating structure. By changing the coating parameters such as the deposition distance, it is found that a denser coating structure can be formed at a closer deposition distance.

• Economic and Environmental Geology
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• v.33 no.5
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• pp.391-404
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• 2000

This study investigated the geochemical characteristics of mine drainage discharged from an abandoned coal mine in the Hwasoon area. Surface water samples were collected from 23 locations along the Hancheon creek. The concentration of Zn and Cu in stream waters was highest at low pH (3.53), whereas the content of TDS and TDI was highest at high pH (7.78) due to the concentration of Ca, $HCO_3$ and $SO_4$. At the upstream site, the Ba, Fe, Mn, Zn, and $SO_4$ contents were relatively high but decreased significantly with the distance from the coal mine. On the contrary, the Na and $NO_3$ contents were low at the upstream site but increased downstream. Yellow precipitate material collected in the Hancheon consisted mainly of iron and LOI. This yellow precipitate was heated from 100 to $900^{\circ}C$ for 1 hour. With increasing temperature, the intensity of hematite peaks were sharply produced in X-ray pattern and the absorption band Fe-O of hematite increased in IR due to dehydration and melting. The yellow to brown precipitate and evaporite materials were collected by a air-dry from the acid mine water at the laboratory. After drying, the concentration of ions in the acid water samples increased progressively in oversaturation with respect to either gypsum, ferrohexahydrite or quenstedetite. The X-ray powder diffraction studies identified that the precipitated and evaporated materials after drying were well crystallized gypsum, ferrohexahydrite and quenstedetite. Diagnostic peaks used for identification of gypsum were the 7.65, 4.28, 3.03, 2.87 and 2.48$\AA$ peaks and those for ferrohexahydrite were the 5.46, 5.12, 4.89, 4.44, 4.05, 3.62, 3.46, 3.40, 3.20, 3.03, 2.94, 2.53, 2.28, 2.07, 1.88 and 1.86${\AA} peaks. The IR spectra with OH-stretching, deformation of $H_2O$and ${SO_4}^{2-}$stretching vibration include the existence of gypsum, ferrohexahydrite and quenstedetite in the precipitated and evaporite materials. In the SEM and EDS analysis for the evaporite material, gypsum with well-crystallized, acicular, and columnar form was distinctly observed.

• Journal of Veterinary Clinics
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• v.27 no.1
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• pp.93-96
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• 2010

We describe a case of enterolithiasis in an eight-year-old male Grant's zebra (Equus burchelli boehmi) that died after a 10-day history of depression, anorexia, dehydration and colic. On necropsy, an enterolith was discovered at the conjunction of the descending colon and the rectum. The spherical enterolith weighed 1,660 g and was $13.5cm{\times}8cm$ in size. According to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), the nidus consisted primarily of $SiO_2$ with outer layers of magnesium and phosphate. The formation of enteroliths is closely related to diet. We suggest that this captive zebra's diet, which consisted primarily of alfalfa hay with mineral supplements, was the cause of enterolithiasis in this case. This is the first report of enterolithiasis in a captive equid in Korea. Our findings provide information valuable for the development of dietary guidelines to prevent enterolithiasis in captive wild equids.

• Journal of Welding and Joining
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• v.30 no.5
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• pp.64-69
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• 2012

Sn-Bi eutectic alloy has been widely used as one of the key solder materials for step soldering at low temperature. The Sn-58Bi solder paste containing chloride flux was adopted to compare with that using the chloride-free flux. The paste was applied on the electroless nickel-immersion gold (ENIG) surface finish by stencil printing, and the reflow process was then performed at $170^{\circ}C$ for 10 min. After reflow, the solder joints were aged at $125^{\circ}C$ for 100, 200, 300, 500 and 1000 h in an oven. The interfacial microstructures were obtained by using scanning electron microscopy (SEM), and the composition of intermetallic compounds (IMCs) was analyzed using energy dispersive spectrometer (EDS). Two different IMC layers, consisting of $Ni_3Sn_4$ and relatively very thin Sn-Bi-Ni-Au were formed at the solder/surface finish interface, and their thickness increased with increasing aging time. The wettability of solder joints was investigated by wetting balance test. The mechanical property of each aging solder joint was evaluated by the ball shear test in accordance with JEDEC standard (JESD22-B117A). The results show that the highest shear force was measured when the aging time was 100 h, and the fracture mode changed from ductile fracture to brittle fracture with increasing aging time. On the other hand, the chloride flux in the solder paste did not affect the shear force and fracture mode of the solder joints.

• Journal of the Korea Institute of Building Construction
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• v.11 no.4
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• pp.345-352
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• 2011

The purpose of this study was to investigate the expansion of alkali-activated mortar based on ground granulated blast furnace slag containing reactive aggregate due to alkali-silica reaction. In addition, this study was particularly concerned with the behavior of these alkaline materials in the presence of reactive aggregates. The experimental program included expansion measurement of the mortar bar specimens, as well as the determination of the morphology and composition of the alkali-silica reaction products by using scanning electron microscopy(SEM), and energy dispersive x-ray(EDX). The experiment showed that while alkali-activated ground granulated blast furnace slag mortars showed expansion due to the alkali-silica reaction, the expansion was 0.1% at Curing Day 14, showing that it is safe. After the accelerated test, SEM and BEM analysis showed the presence of alkali-silica gel and rim around the aggregate and cement paste. According to the EDX, the reaction products decreased markedly as alkali-activated ground granulated blast furnace slag was used. In addition, for the substitutive materials of mineral admixture, a further study on improving the quality of alkali-activated ground granulated blast furnace slag is needed to assure of the durability properties of concrete.

• Journal of the Korean Magnetics Society
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• v.19 no.4
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• pp.121-125
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• 2009

Amorphous $Ge_1$_$_xMn_x$ semiconductor thin films grown by low temperature vapor deposition were annealed at various temperatures from 400 to $700^{\circ}C$ for 3 minutes in high vaccum chamber. The electrical and magnetotransport properties of as-grown and annealed samples have been studied. X-ray diffraction patterns analysis revealed that the samples still maintain amorphous state after annealling at $500^{\circ}C$ for 3 minutes and they were crystallized when annealing temperature increase to $600^{\circ}C$. Temperature dependence of resistivity measurement implied that as-grown and annealed $Ge_1$_$_xMn_x$ films have semiconductor characteristics, the increase of resistivity with annealling temperature was obseved. The $700^{\circ}C$-annealed sample exhibited negative magnetoresistance (MR) at low temperatures and the MR ratio was ${\sim}$8.5% at 10 K. The asymmetry was present in all MR curves. The anomalous Hall Effect was also observed at 250 K.

• Journal of the Korean Wood Science and Technology
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• v.37 no.3
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• pp.245-254
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• 2009

As a substitute for CCA, which is inhibited due to its environmental pollution and human harmfulness, and CuAz and ACQ with a high cost, okara-based wood preservatives were formulated with okara hydrolyzates using copper sulfate and/or borax as a metal salt. The efficacy of the preservatives and X-ray microanalysis of wood specimens treated with the preservatives were examined to confirm the potential of the okara-based wood preservatives. Most of the preservatives showed excellent decay resistance against brown-rot fungi, Postia placenta and Gloeophyllum trabeum. The efficacy was improved when the acid concentration and temperature used for the hydrolysis of okara increased. In addition, when borax was added into copper sulfate/okara hydrolyzates preservative formulations, any decay was not found in the specimens. From the microscopic observation of the specimens treated with okara-based wood preservatives, it seems that okara is contributed to the fixing of metal salts in wood blocks. Therefore, it is speculated that okara-based wood preservatives can effectively protect wood against fungal attack as CuAz, and that the preservatives are sufficient to use as an alternative wood preservative of CCA, ACQ and CuAz.

• Polymer(Korea)
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• v.29 no.5
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• pp.501-507
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• 2005

Small intestinal submucosa (SIS) had been widely used as a biomaterial without immune rejection responses. SIS sponges prepared by crosslinking with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). SIS powders dissolved in $3\%(v/v)$ acetic acid aqueous solution for 48hrs and freeze-dried. EDC solution ($H_2O$ : ethanol = 5 : 95) as a crosslink agent was used in concentration of 100mM. In vitro, rat-BMSCs seeded in SIS sponges and induced the osteogenesis for 28 days. We have characterized the osteogenic potential of rat-BMSCs in SIS sponges by alkaline phosphatase activity(ALP), n assay, SEM and RT-PCR for osteogenic phenotype. In SEM, all morphology of SIS sponges was regular and showed interconnected pore structure. By RT-PCR analysis, we observed type I collagen expression. These results demonstrate osteogenic differentiation of rat-BMSCs. In conclusion, we confirmed that the morphology of surface, cross-section, and side of SIS sponges were highly porous with good interconnections between each pores, which can support the surface of cell growth, proliferation, and differentiation. This result indicates that SIS sponge is useful for osteogenesis of BMSCs.

• Journal of Korean Society of Transportation
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• v.19 no.6
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• pp.105-118
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• 2001

Incident detection rate and false alarm rate are the key measures tot estimating the performance of automatic incident detection algorithms. It is, however inherently very difficult to improve the two measures simultaneously. The main purpose of this study is to present some methods for solving the problem. For this, an incident detection algorithm has been designed in this study. The algorithm is consisted of two functions, one for detecting incident and another for detecting congestion. A logic for distinguishing non-recurrent congestion from recurrent congestion was employed in the algorithm. The new algorithm basically requires speed, flow, and occupancy data for defining incident situation, but the algorithm is able to perform this task without one of the three parameters. The performance of the algorithm has been evaluated by using the field data collected from Interstate Highway 880 in Bay Area, California. The empirical analysis results are very promising and thus, the algorithm proposed may be very useful for the analysts. This paper presents some empirical test results for the performance of California incident detection algorithm, only for the reference purpose.

• Korean Journal of Food Science and Technology
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• v.46 no.3
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• pp.347-351
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• 2014

We studied the green synthesis and antibacterial activity of chitosan-silver (Ag) nanocomposite films for application in food packaging. Green synthesis of Ag nanoparticles (AgNPs) was achieved by a chemical reaction involving a mixture of chitosan-silver nitrate ($AgNO_3$) in an autoclave at 0.1 MPa, $121^{\circ}C$, for 15-120 s. The formation of AgNPs in chitosan was confirmed by both UV-Visible spectrophotometry and transmission electron microscopy (TEM) and the effects of chitosan-$AgNO_3$ concentration and reaction time on the synthesis of AgNPs in chitosan were examined. The resulting chitosan-Ag composite films were characterized by various analytical techniques and their antibacterial activity was evaluated based on the formation of halo zones around films, indicating inhibition of the growth of Escherichia coli. A fourier-transform infrared (FTIR) spectroscopy analysis showed that free amino groups in chitosan acted as effective reductants and AgNP stabilizers. The composite films exhibited enhanced antibacterial activity with increasing Ag content on the surface of as-prepared composite films.