• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.362-363
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• 2006

Nano-structured tungsten carbide compacts with cobalt matrices (WC-Co) offer new opportunities for achieving superior hardness and toughness combinations. A unified modeling and simulation tool has been developed to produce maps of sintering pathways from nanocrystalline WC powder to sintered nano-structured WC-Co compacts. This tool includes (1) die compaction, (2) grain growth, (3) densification, (4) sensitivity analysis, and (5) optimization. All material parameters were obtained by curve fitting based on results with two WC-Co powders. Critical processing parameters are determined based on sensitivity analysis and are optimized to minimize grain size with high density.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.3
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• pp.464-471
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• 2003

Among various methods to acquire high strength in plain carbon steel, the mettled of grain refinement by controlling thermo-mechanical processing parameters has gained a great attention if steel rolling industries. In the present study, three different rolling pass schedules are proposed to obtain fine grains which are based on combined results of recrystallization modelling, finite element analysis and experiment. Since meta-dynamic or dynamic recrystallization has been found to be very effective in producing fine grains, reduction ratio and interpass time in the proposed rolling pass schedules were determined in order to invoke such recrystallization as often as possible.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.7
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• pp.670-674
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• 1991

This paper presents the material properties of LPCVD silicon films formed using Si2H6 gas at various deposition temperatures. To study the structural properties depending on the deposition temperature, XRD, EBD and TEM analyses were used. The maximum grain size in this experiment was obtained at the deposition temperature of 485ø C. It is discussed that LPCVD films formed below the deposition temperature of 485ø C are promising for low temperature TFT applications. The enhancement of the film characteristics results from the reduction of grain boundary density. We also observed that the film properties of Si2H6 at 600ø C was quite different from those of Si H4 at 600ø C. It has shown that the grain structure from a TEM analysis was elliptical and not dependent on the deposition temperature.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1849-1853
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• 2007

In this study, flow-sediment discharge characteristics and relationships are estimated for the Cheonggyecheon basin, newly restored in 2005. Flow and sediment discharge measurement is performed on Ogansugyo, Majanggyo 2 and Yongdugyo during the rainy seasons in 2005-2006. The parameters of Clark UH are estimated using measured data, and sediment rating curves are derived by using grading and concentration analysis. Concentration time and storage coefficient of Clark UH are estimated 0.5 hr and 0.63 hr for Majanggyo 2, and 0.4 hr and 0.45 hr for Yongdugyo, respectively. Grain size of sediments are composed of fine silt to fine sand (0.008-0.25mm) based on the sediment grain size classification (Lane, 1947). Flow-sediment relationships derived by using concentration analysis shows that sediment discharge has no obvious relationship with flow discharge.

• Journal of Conservation Science
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• v.31 no.4
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• pp.331-339
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• 2015

This study were conducted the particle-size analysis on 57 blue pigments to understand the step distribution characteristics of blue pigments made out of Azurite by using Malvern's Mastersizer 2000. As the result, most of the conventional blue pigments in Korea, Japan, and Chinese showed good granularity step separation except for few, and the smaller the particle, the more the Span value increased and the wider the granularity distribution range. On the basis of Friedman and Sanders's Grain size, most of the pigments were sand size to silt size. 72.2% of B-100 was clay size and 2.5% of A-14 was gravel size. Even the same components can differ by the grain size directly affecting the important property such as color formation, oil absorption, specific gravity, usability, etc. so the information about the granularity distribution would be used for basic data to deal with natural pigments.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.354-354
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• 2017

Rice grain yield is determined by crop dry matter production that is sensitive to temperature. Our objective was to determine whether the difference in temperature between years had an impact on the relationship between yield components and grain yield. Field experiments were conducted under machine transplanting cultivation by using yield data of two japonica rice varieties, Odaebyeo (early maturing) and Nampyeong (mid-late maturing), in 2013 to 2016 in Suwon, Korea. Plant height, dry weight, and yield components were examined by analysis of variance, correlation. The milled rice yield of the two varieties were the highest in 2016, however the lowest yields were observed in the different years. In 2016, Odaebyeo produced $0.96t\;ha^{-1}$ greater milled rice yield than in 2015, and Nampyeong produced $1.11t\;ha^{-1}$ greater yield than in 2013. The correlation analysis indicated that spikelet per panicle (R = 0.53) was associated with grain yield of Odaebyeo. In Nampyeong, biomass at heading date (R = 0.74), 1000-grain weight (R = 0.71), spikelet per panicle (R = 0.58), and panicle number per $m^2$ were associated with grain yield. Sink size (spikelet number per $m^2$) of the two varieties responded to accumulative temperature from transplanting to panicle initiation stage. In this experiment, optimal accumulative temperature before panicle initiation has effect on increased spikelet number and/or number of panicle that were mainly responsible for yield difference. Rice production research to increase grain yield should consider all yield components, but increased emphasis on biomass production before heading is also necessary as well as grain ripening conditions.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1218-1230
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• 1994

In manufacturing process of porous glass-ceramics by the filler method, the sintering behaviour of crystallizable glass powder mixed with various salts was studied and also the effects of precipitated crystal phases on the properties of porous glass-ceramics were investigated. Fine-grained crystallizable glass powder was homogeneously mixed with various slat having grain size 100~200 ${\mu}{\textrm}{m}$ and sintered for densification. After washing out the inorganic salt with distilled water, the porous sintered body was heat treated additionly for crystallization. The MgO-Al2O3-SiO2 base glass was used as crystallizable glass powder and the water soluble salts such as K2SO4 and MgSO4 were used as filler. When K2SO4 was used, leucite crystal phase was formed as a result of the ion exchange and porous glass-ceramics which exhibit high temperature resistance and high thermal expansion coefficient of 17$\times$10-6/$^{\circ}C$ could be obtained. On the contrary, when MgSO4 was used, only slight ion exchange is observed and $\mu$-cordierite and $\alpha$-cordierite crystal phases were formed and porous glass-ceramics which exhibit low thermal expansion coefficient schedule were determined with the results of DTA curves, thermal shrinkage curves and XRD patterns analysis. From DTA curves and thermal shrinkage curves, it was found that the sintering densification have been completed at the temperature range of exothermic peak for crystallization. The pore size distributions and pore diameters were measured by mercury porosimeter. The pore diameter of porous glass-ceramics was 10~15 ${\mu}{\textrm}{m}$ when 100~200${\mu}{\textrm}{m}$ grain size of K2SO4 was used and it was 25~30 ${\mu}{\textrm}{m}$ when the same grain size of MgSO4 was used. The porous glass-ceramics K2SO4 used shows bimodal pore size distribution and its porous skeleton structure was ascertained by SEM observation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.317-326
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• 2004

This study investigated tile local austenite grain size (AGS) distribution In rolling of SCM435 steel which is commonly used for high strength bolt. To investigate AGS distribution, round-oval (R-O) and square-diamond (S-D) rolling experiments were carried out with pilot mill. In round-oval rolling, local AGS has a tendency to increase when it goes to outward. In square-diamond rolling, local AGS has a tendency to increase when it goes to free surface. To investigate relation between AGS and process parameter, three dimensional FE analysis was carried out along with rolling experiment. To validate accuracy of FE analysis, we compared deformed geometry with FE result. The AGS prediction combined AGS model with numerical analysis was also carried out for center node of S-D rolling. Although this study brought experimental observation and its qualitative analysis into focus and quantitative AGS prediction will be done as a further work.

• Nuclear Engineering and Technology
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• v.49 no.7
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• pp.1524-1536
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• 2017

During the fabrication process of reactor vessel head penetration (RVHP), the grain size of the tube material can be changed by hot or cold work and the inner side of the tube can also be shrunk due to welding outside of the tube. Several nonregular time-of-flight diffraction (TOFD) signals were found because of deformed grains. In this paper, an investigation of nonregular TOFD indications acquired from RVHP tubes using experiments and computer simulation was performed in order to identify and distinguish TOFD signals by coarse grains from those by Primary Water Stress Corrosion Crack (PWSCC). For proper understanding of the nonregular TOFD indications, microstructural analysis of the RVHP tubes and prediction of signals scattered from the grains using Finite Element Method (FEM) simulation were performed. Prediction of ultrasonic signals from the various sizes of side drilled holes to find equivalent flaws, determination of the size of the nonregular TOFD indications from the coarse grains, and experimental investigation of TOFD signals from coarse grain and shrinkage geometry to identify PWSCC signals were performed. From the computer simulation and experimental investigation results, it was possible to obtain the nonregular TOFD indications from the coarse grains in the alloy 690 penetration tube of RVHP; these nonregular indications may be classified as PWSCC. By comparing the computer simulation and experimental results, we were able to confirm a clear difference between the coarse grain signal and the PWSCC signal.

• Korean Journal of Materials Research
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• v.29 no.4
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• pp.233-240
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• 2019

This study analyzes the mechanical properties, including the attrition rate, of $50{\mu}m$ size yttria-stabilized zirconia (YSZ) beads with different microstructures and high-energy milling conditions. The yttria distribution in the grain and grain-boundary of the fully sintered beads relates closely to Vickers hardness and the attrition rate of the YSZ beads. Grain size, fractured surfaces, and yttrium distribution are analyzed by electronic microscopes. For standardization and a reliable comparison of the attrition rate of zirconia beads with different conditions, Zr content in milled ceramic powder is analyzed and calculated by X-ray Fluorescence Spectrometer(XRF) instead of directly measuring the weight change of milled YSZ beads. The beads with small grain sizes sintered at lower temperature exhibit a higher Vickers hardness and lower attrition rate. The attrition rate of $50{\mu}m$ YSZ beads is measured and compared with the various materials properties of ceramic powders used for high-energy milling. The attrition rate of beads appears to be closely related to the Vickers hardness of ceramic materials used for milling, and demonstrates more than a 10 times higher attrition rate with Alumina(Hv ~1650) powder than $BaTiO_3$ powder (Hv ~315).