• Composites Research
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• v.30 no.2
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• pp.84-93
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• 2017

This study investigates thermal and mechanical characterization of environmental barrier coating on the $SiC_f-SiC$ composites. The spherical environmental barrier coating (EBC) powders are prepared using a spray drying process for flowing easily during coating process. The powders consisting of mullite and 12 wt% of Ytterbium silicate are air plasma sprayed on the Si bondcoat on the LSI SiC fiber reinforced SiC composite substrate for protecting the composites from oxidation and water vapor reaction. We vary the process parameter of spray distance during air plasma spray of powders, 100, 120 and 140 mm. After that, we performed the thermal durability tests by thermal annealing test at $1100^{\circ}C$ for 100hr and thermal shock test from $1200^{\circ}C$ for 3000 cycles. As a result, the interface delamination of EBC never occur during thermal durability tests while stable cracks are prominent on the coating layer. The crack density and crack length depend on the spray distance during coating. The post indentation test indicates thermal tests influence on the indentation load-displacement mechanical behavior.

• Economic and Environmental Geology
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• v.29 no.2
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• pp.129-138
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• 1996

The ores of the Bobae mine are mainly composed of sericite and quartz, and with appreciable amount of some other minerals such as andalusite. pyrophyllite, and albite, etc.. Sericite occurs in various a1teration zones having different crystal size and habit. Sericites can be c1assified into two types based on the crystal size; fine-grained and coarse-grained sericite. Fine-grained sericite occurs as an aggregate. Mineralogical characterizations of both types of sericites have been studied with various methods. Lattice parameters of two types of sericites occurred in various alteration zones are almost identical. but b parameter of coarse-grained sericite appears to be slight1y bigger than that of fine-grained aggregates. Average structural formula of fine- and coarse-grained sericite is $K_{1.44}Al_{3.86}(Si_{6.35}Al_{1.65})O_{20}(OH)_4$ and $K_{1.71}Al_{3.82}(Si_{6.20}Al_{1.80})O_{20}(OH)_4$, respectively. Structural formulae of coarse-grained sericites are close to that of muscovite. Infrared spectra show that there is slight distinction between sericites occurred in andalusite-pyrophyllite zone and other subzones. IR spectra of sericites due to Si-O vibration ($540{\sim}530cm^{-1}$) tend to shift to smaller wavenumber side from center to outer alteration zone. All samples have litt1e or no interstratified minerals. and this is demonstrated by Ir and DTA-TG results. It indicates that the Bobae mine is formed at relatively high temperature. That the ratio of quartz to sericite in ores varies greatly indicates that several discontinuous hydrothermal alteration processes have been involved.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.9
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• pp.659-666
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• 2014

The purpose of this study was to suggest a standard design procedure of landfarming for clean-up of oil-contaminated soils. The standard design procedure consisted of four main phases; soil characterization, determination of contaminated soil volume, determination of nutrient and microbial doses, and estimation of the total remedial period. This study selected standard design parameter values or ranges among various forms used in environmental engineer communities. Those were determination procedures for the contaminated soil volume, the initial contamination concentration and nutrient doses. The suggested standard design procedure were applied for a landfarm design for remediation of a real oil-contaminated site. Soil texture of the site was classified as sandy clay loam and sandy loam. Total nitrogen and total phosphorus were estimated to be 57.01 mg/kg and 83.40 mg/kg, respectively. Also the viable bacterial numbers was assessed to be $1.78{\times}10^4CFU/g$ dry soil. The amount of TPH contaminated soil was estimated to be $4,092m^3$. With the application of remedial factors, it was estimated that the contaminated soil could be treated through 9 batches with a duration of 315 days for a landfarming unit of $15m{\times}40m{\times}1m$. The amount of liquid microorganisms and fertilizers were recommended to be 4,025L and 4,641kg, respectively.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.241-248
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• 2004

The rheological properties of cement paste system mixed with mineral admixtures (MAs) used to increase the strength and improve durability and fluidity of concrete were investigated. And cement paste systems were designed as one-, two- and three-ingredients blended paste systems. The rheological properties of paste systems were assessed by Rotovisco RT 20 rheometer (Hakke inc.) having a cylindrical serrated spindle. The rheological properties of one-ingredient paste systems were improved with increasing the dosage of superplasticizer. For two-ingredients paste systems, as increasing the replacement ratio of blast furnace slag (BFS) and fly ash (FA), the yield stress and plastic viscosity were decreased compared with non-replacement. In the ordinary portland cement (OPC)-silica fume (SF) paste systems, in accordance with an increase in the replacement ratio of SF, the yield stress and plastic viscosity were increased steeply. For three-ingredients paste systems, both OPC-BFS-SF and OPC-FA-SF paste systems, the rheological properties were improved compared with the only replacement of SF. In the case of both two-and three-ingredients paste systems, the rheological properties using BFS were improved more than FA.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.458-463
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• 2010

Since the acoustic nonlinearity is sensitive to the minute variation of material properties, the nonlinear ultrasonic technique(NUT) has been considered as a promising method to evaluate the material degradation or fatigue. However, there are certain limitations to apply the conventional NUT using the bulk wave to thin plates. In case of plates, the use of Lamb wave can be considered, however, the propagation characteristics of Lamb wave are completely different with the bulk wave, and thus the separate study for the nonlinearity of Lamb wave is required. For this work, this paper analyzed first the conditions of mode pair suitable for the practical application as well as for the cumulative propagation of quadratic harmonic frequency and summarized the result in for conditions; (1) phase matching, (2) non-zero power flux, (3) group velocity matching, and (4) non-zero out-of-plane displacement. Experimental results in aluminum plates showed that the amplitude of the secondary Lamb wave and nonlinear parameter growed up with increasing propagation distance at the mode pair satisfying the above all conditions and that the ration of nonlinear parameters measured in Al6061-T6 and Al1100-H15 was closed to the ratio of the absolute nonlinear parameters.

• Environmental Analysis Health and Toxicology
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• v.10 no.1_2
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• pp.1-14
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• 1995

The purpose of this research is to assess the health risk of pollutants in drinking water and recommend the guidelines and management plans for maintaining good quality of drinking water. This study has been funded as a national project for three years from 1992 to 1995. This study(the second year, 1993-1994) was conducted to monitor 32 species of carcinogenic chemicals such as volatile organic compounds(VOCs), polynuclear aromatic hydrocarbons(PAHs), pesticides and heavy metals of drinking water at some area in six cities of Korea, and evaluate health risk due to these chemicals through four main steps of risk assessment in drinking water. In hazard identification, 32 species of carcinogenic chemicals were identified by the US EPA classification system. In the step of exposure assessment, sampling of raw, treated and tap water from the public water supply system had been conducted from 1993 to 1994, and 32 chemicals were analyzed. In dose-response assessment, cancer potencies, unit risk estimates and virtually safe doses of carcinogens were obtained by TOX-RISK (Version 3.1). In risk characterization of detected chemicals, health risk due to carcinogens such as vinyl chloride, carbon tetrachloride, dichloromethane, 1, 2-dichloromethane, chloroform, benzene and arsenic of tap water in several cities exceeded 10$^{-5}$ level. We suggest that non-regulated chemicals which exceed 10$^{-5}$ excess cancer risk level, such as vinyl chloride, carbon tetrachloride and 1, 2-dichloroethane, should be monitored periodically and be regulated by the Drinking Water Management Act, and database for exposure parameter of our own situation should be established.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.439-445
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• 2001

The destructive method is reliable and widely used lot the estimation of material degradation but, it have time-consuming and a great difficulty in preparing specimens from in-service industrial facilities. Therefore, the estimation of degraded structural materials used at high temperature by nondestructive evaluation such as electric resistance method, replica method, Barkhausen noise method, electro-chemical method and ultrasonic method are strongly desired. Ultrasonic nondestructive evaluation technique has been reported good to attain efficiency of measurement, high sensitivity of measurement, and rapidity and reliability of result interpretation. In this study, it was verified experimentally the feasibility of the evaluation of degraded 2.25Cr-1Mo steel specimens which were prepared by the isothermal aging heat treatment at $630^{\circ}C$ by high frequency longitudinal wave method investigating the change of attenuation coefficient by FFT analysis and wavelet transform. Because of carbide precipitation increase and spheroidization near grain boundary of microstructure to aging degradation, attenuation coefficient had a tendency to increase as degradation proceeded. It was identified possibly to evaluate degradation using the characteristics of high-frequency ultrasonics. Frequency dependence of ultrasonic attenuation coefficient to aging degradation appeared large, which made sure that attenuation coefficient is an important parameter for evaluation of aging degradation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.134-134
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• 2011

High-k dielectric materials such as $HfO_2$, $ZrO_2$ and $Al_2O_3$ increase gate capacitance and reduce gate leakage current in MOSFET structures. This behavior suggests that high-k materials will be promise candidates to substitute as a tunnel barrier. Furthermore, stack structure of low-k and high-k tunnel barrier named variable oxide thickness (VARIOT) is more efficient.[1] In this study, we fabricated the $WSi_2$ nanocrystals nonvolatile memory device with $SiO_2/HfO_2/Al_2O_3$ tunnel layer. The $WSi_2$ nano-floating gate capacitors were fabricated on p-type Si (100) wafers. After wafer cleaning, the phosphorus in-situ doped poly-Si layer with a thickness of 100 nm was deposited on isolated active region to confine source and drain. Then, on the gate region defined by using reactive ion etching, the barrier engineered multi-stack tunnel layers of $SiO_2/HfO_2/Al_2O_3$ (2 nm/1 nm/3 nm) were deposited the gate region on Si substrate by using atomic layer deposition. To fabricate $WSi_2$ nanocrystals, the ultrathin $WSi_2$ film with a thickness of 3-4 nm was deposited on the multi-stack tunnel layer by using direct current magnetron sputtering system [2]. Subsequently, the first post annealing process was carried out at $900^{\circ}C$ for 1 min by using rapid thermal annealing system in nitrogen gas ambient. The 15-nm-thick $SiO_2$ control layer was deposited by using ultra-high vacuum magnetron sputtering. For $SiO_2$ layer density, the second post annealing process was carried out at $900^{\circ}C$ for 30 seconds by using rapid thermal annealing system in nitrogen gas ambient. The aluminum gate electrodes of 200-nm thickness were formed by thermal evaporation. The electrical properties of devices were measured by using a HP 4156A precision semiconductor parameter analyzer with HP 41501A pulse generator, an Agillent 81104A 80MHz pulse/pattern generator and an Agillent E5250A low leakage switch mainframe. We will discuss the electrical properties for application next generation non-volatile memory device.

• Journal of Korea Water Resources Association
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• v.31 no.6
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• pp.795-806
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• 1998

Soil moisture is affected by regional climate, soil characteristics and land surface condition, etc,. Especially, the changes in land surface condition is more than other factors, which is mainly due to rapid urbanization and industrialization. This study is to evaluate how the change of land surface condition impacts on soil moisture field evolution using a simple model of soil moisture dynamics. For the quantification of soil moisture field, the first half of the paper is spared for the statistical characterization based on the first- and second-order statistics of Washita '92 and Monsoon '90 data. The second half is for evaluating the impact of land cover changes through simulation study using a model for soil moisture dynamics. The model parameters, the loss rate and the diffusion coefficient, have been estimated using the observed data statistics, where the changes of surface conditions are considered into the model by applying various parameter sets with different second-order statistics. This study is concentrated on evaluating the impact due to the changes of land surface condition variability. It is because we could easily quantify the impact of the changes of its areal mean based on the linear reservoir concept. As a result of the study, we found; (1)as the variability of land surface condition, increases, the soil moisture field dries up more easily, (2)as the variabilit y of the soil moisture field is the highest at the beginning of rainfall and decreases as time goes on to show the variability of land surface condition, (3)the diffusion effect due to surface runoff or water flow through the top soil layer is limited to a period of surface runoff and its overall impact is small compared to that of the loss rate field.

• Clean Technology
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• v.26 no.2
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• pp.131-136
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• 2020

Biomass bamboo charcoal is utilized as anode for lithium-ion battery in an effort to find an alternative to conventional resources such as cokes and petroleum pitches. The amorphous phase of the bamboo charcoal is partially converted to graphite through a low temperature graphitization process with iron oxide nanoparticle catalyst impregnated into the bamboo charcoal. An optimum catalysis amount for the graphitization is determined based on the characterization results of TEM, Raman spectroscopy, and XRD. It is found that the graphitization occurs surrounding the surface of the catalysis, and large pores are formed after the removal of the catalysis. The formation of the large pores increases the pore volume and, as a result, reduces the surface area of the graphitized bamboo charcoal. The partial graphitization of the pristine bamboo charcoal improves the discharge capacity and coulombic efficiency compared to the pristine counterpart. However, the discharge capacity of the graphitized charcoal at elevated current density is decreased due to the reduced surface area. These results indicate that the size of the catalysis formed in in-situ graphitization is a critical parameter to determine the battery performance and thus should be tuned as small as one of the pristine charcoal to retain the surface area and eventually improve the discharge capacity at high current density.