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Levitation 법에 의한 고순도 Fe-C-Si 합금중의 흑연결정의 핵생성 및 성장
김영직,서수정 ( Young Jig Kim,Su Jeong Shur ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.3
N/A This paper describes a study of the nucleation and growth of graphite crystal of levitation melted high purity Fe-C-Si alloys with emphasis on hypereutectic composition. Spherulitic graphite was observed to form at high purity alloy and converted to compacted by changing the starting iron from ultra-pure zone refined iron to 99.95 pct electrolitic iron. Residual C-C clusters might be acting as an effective nucleation site for graphite, and sulphur was the element to prevent graphite from nucleating. The graphite morphology changed from compacted to spherulitic as the sulphur content decreased.
김영직 ( Young Jig Kim ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.6
N/A This study describes the influence of the trace amount of sulphur on the nucleation behavior of graphite crystals in high purity Fe-C-Si alloys prepared by levitation melting method. Detailed microstructural analyses of high purity(HP) and sulphur added(HP+S) samples showed that the nucleation of graphite crystals was prevented by sulphur. With decreasing the sulphur content, the shape of graphite crystals tended to spherulitic, and below 2ppm S, that of graphite crystals was only nodular. The critical cooling rate for the nucleation of griphite crystals was calculated as 1.5×10³k/s . It is obvious from this work that residual C-C clusters act as an effective nucleation site for graphite crystals and one of the important role of nodularizing elements is to act as scavenger which removes harmful impurities from the solution.
금속기 복합재료의 틱소포밍 특성 ($SiC_p/AZ91HP$ Mg 복합재료의 상분석을 중심으로)
이정일,김영직,Lee, Jung-Il,Kim, Young-Jig 한국현미경학회 1999 Applied microscopy Vol.29 No.3
교반관법으로 제조한 $AZ91HP/SiC_p$ Mg 복합재료를 틱소포팅하여 미세조직과 존재상들을 조사하였다. $AZ91HP/SiC_p$ Mg 복합재료를 반응고 가공시 액상율 50% 이상에서 완전 충전이 이루어겼으며 전형적인 반응고 조직을 보였다. 복합재료내의 강화상이 초정 $\alpha$상의 합체, 조대화를 억제하여 보다 용이하게 thixotropic 조직을 가질 수 있었다. TEM 관찰결과, 복합재료내의 계면반응 생성물은 MgO, $Mg_2Si$ 및 $Al_{12}Mg_{17}$등이며, 직접 가압시 정출상으로 나타나는 비평형상인 decagonal T상이 관찰되었으며, 이 상은 간접가압시 안정상인 $Al_6Mn$의 형태로 관찰되었다. 이는 간접가압시 승온시간이 직접가압보다 상대적으로 길어, 비평형의 decagonal T상이 안정한 $Al_6Mn$상으로 생성된 것으로 판단된다. 아직까지 생성과정이 명확하진 않으나 교반관법으로 제조 후, 2차가압 성형시 비평형상의 존재는 재료의 강화에 기여할 것으로 판단된다. The stirred and thixoformed $SiC_p/AZ91HP$ Mg composites are studied on the basis of microstructural analysis using transmission electron microscopy (TEM). The products of interfacial reaction are identified as $Mg_2Si$, MgO and $Mg_{17}Al_{12}$ phases and the crystallized phases are found to be orthorhmbic $Al_6Mn$ and decagonal T phases. It is shown that $Mg_2Si$ and $Mg_{17}Al_{12}$ phases are found at the surface of $SiC_p$ and $Al_6Mn$ is found near interface and crystallized on the matrix. Phase identification is carried out by crystallographic work based on primitive cell volume, zero order Laue zone (ZOLZ) patterns and single convergent beam electron diffraction (CBED) patterns containing higher order Laue zone ring from a nanosized region.
TiO<sub>2</sub> 복합 광촉매의 표면 특성과 광촉매 효율
이종호,윤정일,김영직,오한준,Lee, Jong-Ho,Youn, Jeong-Il,Kim, Young-Jig,Oh, Han-Jun 한국재료학회 2014 한국재료학회지 Vol.24 No.10
To synthesize a high-performance photocatalyst, N doped $TiO_2$ nanotubes deposited with Ag nanoparticles were synthesized, and surface characteristics, electrochemical behaviors, and photocatalytic activity were investigated. The $TiO_2$ nanotubular photocatalyst was fabricated by anodization; the Ag nanoparticles on the $TiO_2$ nanotubes were synthesized by a reduction reaction in $AgNO_3$ solution under UV irradiation. The XPS results of the N doped $TiO_2$ nanotubes showed that the incorporated nitrogen ions were located in interstitial sites of the $TiO_2$ crystal structure. The N doped titania nanotubes exhibited a high dye degradation rate, which is effectively attributable to the increase of visible light absorption due to interstitial nitrogen ions in the crystalline $TiO_2$ structure. Moreover, the precipitated Ag particles on the titania nanotubes led to a decrease in the rate of electron-hole recombination; the photocurrent of this electrode was higher than that of the pure titania electrode. From electrochemical and dye degradation results, the photocurrent and photocatalytic efficiency were found to have been significantly affected by N doping and the deposition of Ag particles.
Ti기 (TiC+TiB) 하이브리드 복합재료 반응생성합성 및 정밀주조
성시영 ( Si Young Sung ),박근창 ( Keun Chang Park ),이상화 ( Sang Hwa Lee ),김영직 ( Young Jig Kim ) 한국주조공학회 2004 한국주조공학회지 Vol.24 No.3
N/A The aim of the present work is to investigate the possibility of in-situ synthesis and net-shape forming of the titanium matrix (TiC+TiB) hybrid composites using a casting route. From the scanning electron microscopy, electron probe micro-analyzer, X-ray diffraction and thermodynamic calculations, the spherical TiC and needle like TiB reinforced hybrid titanium matrix composites could be obtained in-situ by the conventional melting and casting route between titanium and B₄C. No melt-mold reaction occurred between the titanium matrix (TiC+TiB) hybrid composites and the SKK mold, since the mold is consisted with interstitial and substitutional metal-mold reaction products. Not only the sound in-situ synthesis but also the economic net-shape forming of the titanium matrix (TiC+TiB) hybrid composites could be possible by the conventional casting route.
Plasma Electrolytic Oxidation 방식으로 제조된 B Doped TiO<sub>2</sub>의 표면특성과 광촉매 특성
이종호,이영기,김영직,오한준,Lee, Jong-Ho,Lee, Young-Ki,Kim, Young-Jig,Oh, Han-Jun 한국재료학회 2021 한국재료학회지 Vol.31 No.10
For the purpose of manufacturing a high efficiency TiO<sub>2</sub> photocatalyst, B-doped TiO<sub>2</sub> photocatalysts are synthesized using a plasma electrolytic oxidation method in 0.5 M H<sub>2</sub>SO<sub>4</sub> electrolyte with different concentrations of H<sub>3</sub>BO<sub>3</sub> as additive. For the B doped TiO<sub>2</sub> layer fabricated from sulfuric electrolyte having a higher concentration of H<sub>3</sub>BO<sub>3</sub> additive, the main XRD peaks of (101) and (200) anatase phase shift gradually toward the lower angle direction, indicating volume expansion of the TiO<sub>2</sub> anatase lattice by incorporation of boron, when compared with TiO<sub>2</sub> layers formed in sulfuric acid with lower concentration of additive. Moreover, XPS results indicate that the center of the binding energy peak of B1s increases from 191.45 eV to 191.98 eV, which suggests that most of boron atoms are doped interstitially in the TiO<sub>2</sub> layer rather than substitutionally. The B doped TiO<sub>2</sub> catalyst fabricated in sulfuric electrolyte with 1.0 M H<sub>3</sub>BO<sub>3</sub> exhibits enhanced photocurrent response, and high efficiency and rate constant for dye degradation, which is ascribed to the synergistic effect of the new impurity energy band induced by introducing boron to the interstitial site and the improvement of charge transfer reaction.
김달식,김길수,김영직 ( Dal Sik Kim,Kil Soo Kim,Young Jig Kim ) 한국주조공학회 1996 한국주조공학회지 Vol.16 No.3
N/A The purpose of this study was to investigate semi-liquid forming process as it was applied to magnesium alloys and to characterize the effects of processing variables on forming process. Magnesium billet was produced by a grain refining method. The possibility of the semi-liquid method for producing the slurry with thixotropic property was considered. This was followed by heating process for the desired fine globular microstructure and the process for subsquently shaping the semi-liquid slurry. The mold filling behavior was investigated at various processing variables including injection velocity, injection pressure, and material temperature(liquid fraction of Mg alloy). The tensile property of the specimen was measured at the constant semi-liquid forming condition(injection velocity : 0.5m/s, injection pressure : 135㎏/㎠, liquid fraction : 0.6). Liquation initiated from the solute segregation parts and the shape of solid particles turned into spheres without stirring. It was observed that the mold filling behavior was improved as the injection velocity and the injection pressure increased. Unexpectedly, the tensile property of the specimen was measured a little lower than that of diecasting.