Crystal structure of UDP-N-acetylenolpyruvylglucosamine reductase (MurB) from Thermus caldophilus

Kim, Mun-Kyoung,Cho, Min Kwan,Song, Hye-Eun,Kim, Dooil,Park, Bo-Hyu,Lee, Jun Hyuck,Kang, Gil Bu,Kim, Sung Hyun,Im, Young Jun,Lee, Dae-Sil,Eom, Soo Hyun Wiley Subscription Services, Inc., A Wiley Company 2007 Proteins Vol.66 No.3

금속 소결 필터의 성능과 내식성에 관한 연구

김관휴(Kwan Hyu Kim),이도재(Doh Jae Lee) 대한금속재료학회(구 대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.2

Experiments on characteristics of sintered stainless steel and bronze filters have been performed. The variables in this experiment are powder shape, particle size distribution, sintering temperature and atmosphere. The experimental data are presented to show permeability, maximum pore size, shear strength and corrosion resistance on various sintering conditions. The permeability is influenced to a greater extent by varying porosity than by varying the particle size which is only significant when the particle shape is spherical. The sintered bronze f1lter made of nearly spherical particle leads to an increment in permeability with larger sieve fraction even though it has almost same sintered porosity. However, the sintered stainless steel filter made of irregular particle shows negligible difference in permeability by varying particle size. The maximum mean pore size and permeability are significantly affected by powder shape; the filter made of spherical particle shows larger pore size and better permeability than that of irregular particle shape. The stainless steel filter sintered in N2, atmosphere shows higher shear strength than the filter sintered in H2 or Ar atmosphere, while the filter tends to show lower corrosion resistance.

304 스테인리스강의 석출 탄화물 증가에 따른 공식거동

김관휴,최한철 대한금속재료학회(대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.10

Effect of carbide precipitation on pitting behavior of 304 stainless steel was studied by a potentiostatic technique. Different amounts of carbide precipitation were achieved by senstifation treatments at 800℃ for 1, 3 and 5 hours, respectively after solution treatment in vacuum atmosphere of 10^(-6) torr Corrosion behavior of these specimens were investigated by studying polarization curves in 1.0 N H₂SO₄solution. The specimens were pitted in 1.0N H₂SO₄+0.5N HCl solution by a potentiostatic method and the morphology of the pitts was observed by a scanning electron microscope. It was found that the as-solution treated specimen showed the widest passive region and the passive region became narrower as the amounts of carbide precipitation increased. As the potential increased and amounts of carbide increased, the induction time linearly decreased and pitting rate increased. Microstrucrures of the all specimens showed slow grain boundary corrosion during the induction time region. In the pit growth region, pits were observed in the grain interior in the case of the as-solution treated specimens whereas they appeared more in the grain boundary areas in the case of the carbides precipitated specimens. As corrosion time increased, the number and size of the piles also increased. Pits appeared remarkably around twin and grain boundary regions in the specimens sensitized for 3 hrs.

이온질화된 오스테나이트계 스테인리스강의 공식거동 (2)

김관휴,최한철 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.4

Electrochemical techniques have been applied to study on the pitting behavior of ion-nitrided 304L(304LSS) and 316L(316LSS) stainless steels at 25℃ in 0.5M H₂SO₄, 0.1M HCl, 0.5M H₂SO₄+ 0.1M HCl and 0.5M H₂SO₄+ 0.5M HCl solutions. Ion-nitriding was carried out at 550℃ for 10, 20, and 30hrs under pressure of 6 torr. The structure and thickness of nitrided layer and the corrosion morphology of nitrided surface were investigated using optical microscopy, SEM, TEM and EDX. Nitriding at 550℃ produced a regular surface morphology with the spherical nitrides. The ε-phase of compound layer thickened as nitriding time increased, resultting in the corrosion resistance. Electrochemical measurements showed that the corrosion potential, passive film breakdown potential and repassivation potential of ion-nitrided austenitic stainless steels decreased with increasing nitriding tune but the critical anodic current density at active region and the current density at passive region increased. The passive film stability of the 10hr nitrided 316LSS was higher than that of the nitrided 304LSS, whereas the rates of pit nucleation and growth were lower. When nitrided at 550℃ for 30hrs, larger pits were observed in the of 304LSS case rather than the 316LSS one.

Ti 함량에 따른 304 스테인리스강의 미세조직과 기계적 성질

김관휴,최한철,차승옥 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.2

In order to investigate the microstructure and mechanical properties of stainless steel(SS) with various Ti content. The SS specimens containing Ti up to 1.0wt% were fabricated at vacuum furnace and solutionized for 1hr at 1050℃ . and subsequently sensitized for 5hr at 650℃ under argon atmosphere. The microstructures were examined by using optical microscopy, TFM. XRD, SEM and EDX. The δ-ferrite phase in γ grain boundaries and TiC precipitates in grain increased with increasing Ti content. M_(23)C_6 precipitates were observed, especially, at γ/δ interfaces for the sensitized SS. The hardness of both the solutionized and the sensitized SS increased with Ti content. The tensile strength of the solutioniaed SS decreased with increasing Ti content and that of the sensitized SS containing 0.42wt% Ti appeared to be the best due to of TiC formation.

이온질화된 오스테나이트계 스테인리스강의 공식거동 (1)

김관휴,최한철 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.8

The pitting behavior of ion-nitrided austenitic stainless steels was investigated by electrochemical methods. Ion-nitriding was carried out at 380 and 550℃ for 10hrs. Passive film breakdown potential(E_b), corrosion potential(E_(corr)) and repassivation potential(E_r) of ion-nitrided AISI 316L stainless steel(SS) were higher than those of ion-nitrided AISI 304LSS, whereas critical anodic current density (I_c) and current density at passive region(I_p) were lower. The pitting resistance of ion-nitrided AISI 316LSS appeared to be better than that of AISI 304LSS and the corrosion morphology showed severe pitting in the case of ion-nitrided AISI 304LSS at 550℃ for 10hrs.

AISI 304 스테인리스강에 코팅된 Ti/TiN film 의 미세조직과 기계적 특성

김관휴,최한철,박지윤 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.9

The microstructure and mechanical properties of Ti/TiN film coated on AISI 304 stainless steels have been studied. AISI 304 stainless steels containing 0.1∼1.0 wt% Ti were fabricated by using vacuum furnace and followed by solutionization treatment at 1050℃ for 1hr. The specimens were coated by Ti and TiN with 1㎛ and 2㎛ thickness by electron-beam PVD method. The microstructure and phase analysis were carried out by using XRD, WDS and SEM. Mechanical properties such as hardness (Micro-Vickers) and wear resistance were examined. Coated films showed fine columnar structure and some defects. Surface roughness increased in all specimens after TiN coating. XRD patterns showed that the TiN(111) peak was major in TiN single-layer and the other peaks were very weak, but TiN(220) and TiN(200) peaks were developed in Ti/TiN double-layer. The hardness of the coating film was higher in Ti/TiN double-layer than in TiN single-layer and not affected by the Ti content of substrate. Ti/TiN double-layer showed better wear resistance than TiN single-layer. The observed wear traces were sheared type in all coated specimens.

Ti 함유 오스테나이트계 스테인리스강의 부식특성

김관휴,최한철,차승옥 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.1

Corrosion behavior of austenitic stainless steel containing Ti has been studied by using electrochemical techniques. The samples containing Ti from 0.1 to 1.0 wt% were solutionized at 1050℃ for lhr and then sensitized at 650℃ for 5hr under argon atmosphere. Microstructure and phase analysis of the samples after heat treatment and corrosion tests were carried out by using XRD, TEM, SEM and optical microscope. The amount of a-ferrite and TiC precipitates in matrix increased as the Ti content increased. In the sensitized samples, Cr_(23),C_6 precipitates were observed at γ/δ interface. Degree of sensitization(DOS) was lower than 1.0 in all of the solutionized samples and the sensitized samples of Ti content above 0.4 wt% whereas the sensitized samples of Ti content lower than 0.4 wt% showed DOS higher than 1.0. Intergranular attack appeared mainly at grain boundaries in the sensitized sample containing 0.1 wt% Ti and at the γ/δ interface of the higher Ti content. In the latter, however, the attack was not so severe. Pitting potential(E_(put)) and repassivation potential(E_(tep)) of the solutionized and sensitized samples were increased with increasing Ti content. The number and size of the pits decreased with increasing Ti content in the sensitized samples. The pits nucleated at Cr_(23)C_6 site and the γ/δ interface.

AISI 316 스테인리스강의 입계부식과 공식거동에 미치는 shot peening의 영향

김관휴,최한철 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.3

Effects of shot peening(SP) on the intergranular and pitting corrosion behavior of AISI 316 type stainless steels(SS) have been studied by using the electrochemical techniques. Samples were solutionized for an hour at 1050℃ and sensitized for five hours at 650℃ in Ar gas atmosphere. Subsequently shot-peening treatments were carried out on the heat-treated surface of AISI 316SS for 1, 2, 4, and 10 minutes using the steel balls of Φ 0.5 ㎜. The structure and corrosion morphology of samples were investigated using TEM, SEM and XRD. The Cr-carbide(Cr_(23)C_6) peaks were not observed from X-ray diffraction pattern studies as SP treatment time increased. Electrochemical measurements showed that, in the case of solution treated samples, the corrosion and pitting potential decreased for SP treated SS, whereas reactivation, passivation and active current density increased as the SP time increased. For the samples with sensitization treatment pitting potential increased as the SP time increased from 1 min to 4 min, but reactivation current density decreased with SP time due to the SP induced removal of Cr-carbide(Cr_(23)C_6) from the grain boundaries. The corrosion morphology of shot-peened SS after sensitization showed the appearance of reduced intergranular corrosion, due to the removal of chromium carbide(Cr_(23)C_6) as SP time increased.

Iron Aluminides 의 공식에 미치는 Cr, Mo 및 B 의 첨가영향

김관휴,최한철,최답천 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.12

Effects of Cr, Mo and Boron additions on the pitting corrosion of iron aluminides(Fe-28at%Al alloy) in the solution containing Cl were investigated using electrochemical tests. The corrosion morphologies were examined by utilizing the optical microscope and scanning electron microscope(SEM). It was observed that the addition of Cr and Mo to Fe-28at%Al increased corrosion potential, pitting potential and repassivation potential. The active current density and passive current density decreased as Cr and Mo were added. In the case of Mo addition, the passive current density was slightly higher in H₂SO, solution than in solutions containing Cl. When boron was added to Fe-28at%Al, corrosion potential and repassivation potential decreased, whereas the critical anodic current density, passive current density, and pitting potential increased, Fe-28at%Al containing Mo and Cr showed remarkably improved pitting resistance against Cl attact, due to the formation of chromium oxide(Cr₂O₃) and molybdenum oxide(MoO₃) and to the enrichment of molybdate(MoO₄^(2-)) on the surface. In the case of Fe-28at%Al containing boron, pits were found at grain boundaries which boride precipitates have aluady existed.