• Title/Summary/Keyword: Pore 형성

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Numerical Simulation of Bubble and Pore Generations by Molten Metal Flow in Laser-GMA Hybrid Welding (레이저-GMA 하이브리드 용접에서 유동에 의한 기포 및 기공 형성 해석)

  • Cho, Won-Ik;Cho, Jung-Ho;Cho, Min-Hyun;Lee, Jong-Bong;Na, Suck-Joo
    • Journal of Welding and Joining
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    • v.26 no.6
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    • pp.67-73
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    • 2008
  • Three-dimensional transient simulation of laser-GMA hybrid welding involving multiple physical phenomena is conducted neglecting the interaction effect of laser and arc heat sources. To reproduce the bubble and pore formations in welding process, a new bubble model is suggested and added to the established laser and arc welding models comprehending VOF, Gaussian laser and arc heat source, recoil pressure, arc pressure, electromagnetic force, surface tension, multiple reflection and Fresnel reflection models. Based on the models mentioned above, simulations of laser-GMA hybrid butt welding are carried out and besides the molten pool flow, top and back bead formations could be observed. In addition, the laser induced keyhole formation and bubble generation duo to keyhole collapse are investigated. The bubbles are ejected from the molten pool through its top and bottom regions. However, some of those are entrapped by solid-liquid interface and remained as pores. Those bubbles and pores are intensively generated when the absorption of laser power is largely reduced and consequently the full penetration changes to the partial penetration.

Development of Polymer-Concrete Composite(I) - Physical Properties of Polymer-Cement Concrete Composites - (폴리머-콘크리트 복합재료 개발(I) - 폴리머-시멘트 콘크리트의 물성 -)

  • Hwang, Eui-Hwan;Kil, Deog-Soo;Oh, In-Seok
    • Applied Chemistry for Engineering
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    • v.8 no.6
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    • pp.979-984
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    • 1997
  • Test specimens of polymer-cement concrete composites were prepared using styrene-butadiene rubber(SBR) latex, ethylenevinyl acetate(EVA) and polyacrylic ester(PAE) emulsions as polymer dispersions in cement modified system at constant slump($10{\pm}0.5cm$), then compressive and flexural strengths water absorption, pore size distribution, and microstructures were investigated. Compressive and flexural strengths of these composites were remarkably improved with an increase of polymer-cement ratio. These composites had a desirable pore size distribution against frost damage due to a small capillary pore volume. Continuous polymer film was able to form in higher than 15% of polymer cement ratio.

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Breeding and Reproductive Studies on Korean Native Loach (Misgurnus anguillicaudatus) IV. Electron Microscopic Observation on Vitellogenesis and Maturation in Oocytes (한국산 미꾸리에 관한 육종.번식학적 연구 IV. 난모세포의 난황 형성 및 성숙에 관한 전자현미경적 관찰)

  • 윤종만;이종영;이경호;박인홍
    • Korean Journal of Animal Reproduction
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    • v.16 no.3
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    • pp.247-260
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    • 1992
  • This study was carried out to investigate the histomorphological changes of ovaries obtained from 100 of 1-year-old female Korean loach(misgurnus anguillicaudatus). The light microscopic and ultrastructural changes ofooplasm and follicular membranes of oocytes, were observed by lightand transmission electron microscope during the reproductive cycle. All data were collected from November in 1991 to May in 1992. The results obtained in this study were as follows: The size of the nucleoli and number of the yolk granules increased as the oocytes grown. Yolk granules were loosely deposited in the oocytes as crystalline granules. Due to the presence of large early and late maturing oocytes, their ovaries were enlarged, transparent, granular and yellowish in color. The lattice was broken down at hydration, leaving the egg transparent. As the percentages of fish in LMO and RO stage increased from March to April, mean gonadosomatic index(GSI) values(18.49%) increased. Zona radiata change a squamous into cuboid shape in EMO stage. Processes from the granulosa cells and from the oocyte, microvilli grow and make contact with other in the pore canals of the zona radiata during vitellogenesis, but are withdrawn as the zona radiata becomes more compact and devoid of pore canals during oocyte maturation. Seasonal changes in the microscopic appearance of the ovaries were well correlated with those in both GSI and macroscopic appearance.

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Thermomechanical Behavior of Porous Carbon/Phenolic Composites in Pyrolysis Environments (고온 열분해 환경의 다공성 탄소/페놀릭 복합재의 열기계적 거동)

  • Kim, Sung-Jun;Han, Su-Yeon;Shin, Eui-Sup
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.8
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    • pp.711-718
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    • 2011
  • The thermoelastic behavior of the porous carbon/phenolic composites is studied using the thermomechanical response model of chemically decomposing composites. The model includes thermal dependence of the porous composites, porosity in the pyrolysis process, pore pressure due to decomposing gases, and shrinkage. The poroelastic coefficients are calculated based on representative volume element model and finite element analysis. The internal stress distribution caused by pores and pore pressure, and the overall deformation are verified. The effects of the poroelastic coefficients on the thermoelastic behavior are examined through numerical experiments.

The Effect of PVA-Al(III) Complex on the Pore Formation and Grain Growth of UO$_2$ Sintered Pellet (PVA-Al(III) 착물이 UO$_2$ 소결체의 기공형성과 결정립성장에 미치는 영향(I))

  • 이신영;김형수;노재성
    • Journal of the Korean Ceramic Society
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    • v.35 no.8
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    • pp.783-790
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    • 1998
  • The characterization of the complexation reaction of PVA and Al(III) ion at different pH and the sint-ering behaviour of UO2 containing the PVA-Al(III) complexes were investigated. Compared with pure PVA powder the complexed PVA-Al(III) powder had compacter shape and lower decomposition temperature The major phase of PVA-Al(III) complex decomposed at 90$0^{\circ}C$ was $\alpha$-Al2O3 The PVA-Al(III) complex formed at pH 9 had the lowest relative viscosity the highest Al content of 36% and the smallest particle size of 19${\mu}{\textrm}{m}$ While the pure UO2 pellet appeared with bimodal one. The grain size of the pure UO2 pellet was 7${\mu}{\textrm}{m}$ but that of the PVA-Al(III) complex added UO2 pellet was increased up to 36${\mu}{\textrm}{m}$ The largest grain size was ob-tained when the PVA-Al(III) complex formed at pH9 was added and the PVA-Al(III) complex formed at pH 11 had the greatest effect on increasing pore size.

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Effect of 2nd Anodization on the Pore Formation for Alumina Nano Templates (알루미나 나노템플레이트의 기공형성에 미치는 2차 양극산화의 영향)

  • Cho, S.H.;Oh, H.J.;Joo, E.K.;Yoo, C.W.;Chi, C.S.
    • Korean Journal of Materials Research
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    • v.12 no.7
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    • pp.533-539
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    • 2002
  • Porous anodic aluminum oxide layer for nano templates was prepared in acidic solutions. In order to investigate effects of 2nd anodization on ordered formation behaviors of the porous oxide layers, electrochemical and microstructural studies were performed, primarily using TEM, FE- SEM, AFM, and Ultramicrotomy. The pore diameter of the anodic oxide layer increased approximately linearly with increasing voltages, and to the contrary, the pore density decreased. It was shown that 2nd anodizing on the cell base after dissolving 1st anodic oxide layer was remarkably effective for forming ordered array of the pores, comparing with the case for 1st anodization only. And for controlling the diameter of pores, widening method by chemical dissolution seemed more practical than by electrochemical methods.

Enhanced Migration of Gasohol Fuels in Clay Soils and Sediments (Gasoline-ethanol(Gasohol)혼합액의 점토층 내 이동에 대한 연구)

  • Hee-Chul Choi;W.M. Stallard;Kwang-Soo Kim;In-Soo Kim
    • Journal of Korea Soil Environment Society
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    • v.1 no.1
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    • pp.67-79
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    • 1996
  • Clay soils typically have low hydraulic conductivities in the presence of high polarity pore fluid, such as water. Low polarity fluids, such as hydrocarbon fuels and halogenated organic solvents, typically cannot migrate into clay pores because they cannot displace the pore water. Oxygenated additives in gasoline, such as alcohols and methyl-tert-butyl ether, are increasingly used to control air pollution emissions. These relatively polar and highly water-soluble compounds may facilitate displacement of pore water and enhance migration of fuels and solvents through clay-rich soil strata. In the reported research, the migration of gasoline-alcohol fuel mixtures (gasohol) through consolidated clay was examined. Prepared kaolinite clay samples were consolidated from slurry, and various combinations of gasoline, alcohol, and water were applied to the clays under 152 Pa gauge pressure. Movement of the fluids into the clay samples was monitored by measur ing displaced pore fluid and by magnetic resonance imaging of the samples. The structures of selected samples were examined using environmental scanning electron microscopy. Results of the research suggest that alcohol added to hydrocarbon fuels can enhance migration through some clays significantly. Gasoline did not migrate appreciably into water saturated clay, even after 14 days under pressure. The gasohol mixture migrated readily into the clay in only 20 minutes. Increased hydraulic conductivity of the clay in the presence of gasohol is hypothesized to be due to the collapse of the clays pore structure when ethanol is present, creating larger pores. Increasing pore diameter decreases the capillary pressure needed for the gasohol to replace water and allows gasohol to migrate through the clay.

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A study of physical characteristics of foaming glass by recycling waste glass (폐유리 재활용을 위한 발포시 물리적 특성에 관한 연구)

  • Cho Hea-Yong;Choi Chang-Ha;Lee Soo-Wohn;Kim Hyung-Ju;Chang Pil-Kyu
    • Proceedings of the KAIS Fall Conference
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    • 2005.05a
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    • pp.309-311
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    • 2005
  • 본 연구에서는 폐유리를 별도의 전처리 과정 없이 최적조건에서 발포된 발포유리의 pH, 밀도, 열전도율, 압축강도 그리고 흡음율을 측정하였다. 최적조건에서의 온도변화에 따른 물성특성을 측정한 결과, 온도가 높아짐에 따라 밀도는 감소하였는데 이는 융용상 형성이 증가하고 표면에 형성된 응용상의 발포된 기체를 내부에 포집하여 큰 기공을 형성하여 밀도가 감소하는 것으로 사료된다. 또한 온도가 높아짐에 따라 pore size가 커지고, 압축강도가 감소하는 경향을 보인다.

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균일막 형성을 위한 항공기 부품용 타이타늄의 양극산화 최적 공정

  • Lee, Da-Yeong;Han, A-Yeong;Jeong, Na-Gyeom;Choe, Jin-Seop
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2018.06a
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    • pp.66.2-66.2
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    • 2018
  • 금속의 양극산화 공정(anodizing)은 전해질 내 금속에 인위적으로 전위를 가해 금속 표면에 얇은 산화막(oxide layer)을 형성하여 금속의 내식성, 내마모성을 증가시키는 공정이다. 타이타늄은 가볍고 단단하여 산업분야에 유용하게 사용되며 이와 같은 양극산화 공정을 통해 내식성, 내마모성을 크게 높일 수 있다. 본 연구에서는 항공기 부품용 타이타늄의 최적 양극산화 조건을 찾기 위해 전압의 파형, 전해액의 조성에 따라 양극산화 실험을 진행하였다. SEM, AFM, EDS, 분광측색계, 색채색차계 등을 이용하여 각 조건에 해당하는 타이타늄의 산화막($Tio_2$)의 두께, crack 형태, pore 형태, 균일도, 표면 조도, 내전압, 색 수치를 분석하였다. 그 결과 전압 DC 140 V, 주성분이 KOH $Na_3PO_4{\cdot}12H_2O$인 전해액으로 이루어진 양극산화 조건에서 가장 균일하고 색 재현성이 우수한 타이타늄의 산화막($Tio_2$)을 형성하였다.

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Characteristics of porous 3C-SiC thins formed by anodization (양극 산화법으로 형성된 다공질 3C-SiC 막의 특성)

  • Kim, Kang-San;Chung, Gwiy-Sang
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2009.11a
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    • pp.45-45
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    • 2009
  • This paper describes the formation of porous 3C-SiC by anodization. 3C-SiC thin films were deposited on p-type Si(100) substrates by APCVD using HMDS (Hexamethyildisilane: $Si_2(CH_3)_6$). UV-LED(380 nm) was used as a light source. The surface morphology was observed by SEM and the pore size was increased with increase of current density. Pore diameter of 70 ~ 90 nm was achieved at 7.1 $mA/cm^2$ current density and 90 sec anodization time. FT-IR was conducted for chemical bonding of thin film and porous 3C-SiC. The Si-H bonding was observed in porous 3C-SiC around wavenumber 2100 $cm^{-1}$. PL shows the band gap enegry of thin film (2.5 eV) and porous 3C-SiC (2.7 eV).

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