A combinatorial approach for the synthesis and analysis of Al_<i>x</i>Cr_<i>y</i>Mo_<i>z</i>NbTiZr high-entropy alloys: Oxidation behavior

Waseem, Owais Ahmed,Auyeskhan, Ulanbek,Lee, Hyuck Mo,Ryu, Ho Jin Published for the Materials Research Society by th 2018 Journal of materials research Vol.33 No.19

<▼1><B>Abstract</B><P/></▼1><▼2><P>To overcome the limited feasibility of various refractory high-entropy alloys (HEAs) due to the presence of (i) very dense elements (W and Ta), (ii) costly elements (Hf and Ta), and (iii) oxidation prone elements (V) in them, Al<I>x</I>Cr<I>y</I>Mo<I>z</I>NbTiZr HEAs were prepared via arc-melting. Considering the critical nature of oxidation resistance in high-temperature applications, HEAs were characterized to form a combinatorial library of microstructural and oxidation behavior. Al<I>x</I>Cr<I>y</I>Mo<I>z</I>NbTiZr HEAs revealed multiphase microstructures consisting of intermetallic phases along with BCC matrices. Mass loss and porous microstructures were obtained in Mo-rich HEAs after oxidation at 1000 °C for 1 h. The presence of Al enhanced the oxidation resistance and developed a protective oxide layer on the HEAs. Al30Cr10-NTZ exhibited promising potential for use in high temperature applications, as it showed an oxidation time exponent of ∼0.5 and a dense and continuous oxide layer.</P></▼2>

Uniform thin film electrode made of low-temperature-sinterable silver nanoparticles: optimized extent of ligand exchange from oleylamine to acrylic acid

Lee, Yung Jong,Kim, Na Rae,Lee, Changsoo,Lee, Hyuck Mo KLUWER 2017 JOURNAL OF NANOPARTICLE RESEARCH Vol.19 No.2

<P>Lowering the sintering temperature of nanoparticles in the electrode deposition process holds both academic and industrial interest because of the potential applications of such electrodes in polymer devices and flexible electronics. In addition, achieving uniform electrode formation after ligand exchange is equally important as lowering the sintering temperature. Here, we report a simple chemical treatment by the addition of ligand-exchanging interfaces to lower the sintering temperature; we also determine the optimum extent of ligand exchange for crack-free electrode formation. First, we investigated the structural change of Ag thin films with respect to the concentration of acrylic acid (AA) solutions. Second, we used thermal analysis to evaluate the effects of changes in the sintering temperature. We observed that the resulting conductivity of the Ag patterns was only one order of magnitude lower than that of bulk Ag when the patterns were sintered at 150 degrees C. The simple chemical treatment developed in this work for solution-processed Ag electrode formation can be adopted for flexible electronics, which would eliminate the need for vacuum and high-temperature processes.</P>

Synthesis of oxide-free aluminum nanoparticles for application to conductive film

Lee, Yung Jong,Lee, Changsoo,Lee, Hyuck Mo IOP 2018 Nanotechnology Vol.29 No.5

<P>Aluminum nanoparticles are considered promising as alternatives to conventional ink materials, replacing silver and copper nanoparticles, due to their extremely low cost and low melting temperature. However, a serious obstacle to realizing their use as conductive ink materials is the oxidation of aluminum. In this research, we synthesized the oxide-free aluminum nanoparticles using catalytic decomposition and an oleic acid coating method, and these materials were applied to conductive ink for the first time. The injection time of oleic acid determines the size of the aluminum nanoparticles by forming a self-assembled monolayer on the nanoparticles instead of allowing the formation of an oxide phase. Fabricated nanoparticles were analyzed by transmission electron microscopy and x-ray photoelectron spectroscopy to verify their structural and chemical composition. In addition, conductive inks made of these nanoparticles exhibit electrical properties when they are sintered at over 300 °C in a reducing atmosphere. This result shows that aluminum nanoparticles can be used as an alternative conductive material in printed electronics and can solve the cost issues associated with noble metals.</P>

Effects of shell thickness on Ag-Cu₂O core-shell nanoparticles with bumpy structures for enhancing photocatalytic activity and stability

Lee, Changsoo,Shin, Kihyun,Lee, Yung Jong,Jung, Chanwon,Lee, Hyuck Mo Elsevier 2018 CATALYSIS TODAY - Vol.303 No.-

<P><B>Abstract</B></P> <P>Here we examine Ag-Cu<SUB>2</SUB>O core-shell nanoparticles with bumpy structures for use in plasmonic photocatalysts. We synthesized the nanoparticles using a very simple co-reduction process. The shell thickness of the nanoparticles was controlled in order to investigate the effects of shell thickness on photocatalytic activity and stability. With increasing shell thickness, it was be observed that the activity and the stability were simultaneously improved. A thin shell lead to de-wetting of Cu<SUB>2</SUB>O from the Ag core and considerable oxidation of Cu<SUB>2</SUB>O to CuO. The high activity could be due to the unique structure of Ag-Cu<SUB>2</SUB>O, which has a high surface area and plasmonic charge transfer from the Ag core. In addition, we elucidated the stability tendency using conducted density functional theory (DFT) calculation. Strain induced between the Ag core and shell is critical to the stability, leading to de-wetting and oxidation of Cu<SUB>2</SUB>O.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We synthesized Ag-Cu<SUB>2</SUB>O core-shell NPs with bumpy structure. </LI> <LI> The Ag-Cu<SUB>2</SUB>O core-shell NPs have high surface area and broad range of UV–vis absorption. </LI> <LI> Shell thickness of Ag-Cu<SUB>2</SUB>O NPs play a key role for activity and stability of the photocatalysts. </LI> <LI> Combined experimental and theoretical study was conducted. </LI> <LI> High strain between core and shell of thin core-shell NPs induce de-wetting and oxidation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Tuning Molecular Interactions for Highly Reproducible and Efficient Formamidinium Perovskite Solar Cells via Adduct Approach

Lee, Jin-Wook,Dai, Zhenghong,Lee, Changsoo,Lee, Hyuck Mo,Han, Tae-Hee,De Marco, Nicholas,Lin, Oliver,Choi, Christopher S.,Dunn, Bruce,Koh, Jaekyung,Di Carlo, Dino,Ko, Jeong Hoon,Maynard, Heather D.,Ya American Chemical Society 2018 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.140 No.20

<P>The Lewis acid-base adduct approach has been widely used to form uniform perovskite films, which has provided a methodological base for the development of high-performance perovskite solar cells. However, its incompatibility with formamidinium (FA)-based perovskites has impeded further enhancement of photovoltaic performance and stability. Here, we report an efficient and reproducible method to fabricate highly uniform FAPbI<SUB>3</SUB> films via the adduct approach. Replacement of the typical Lewis base dimethyl sulfoxide (DMSO) with <I>N</I>-methyl-2-pyrrolidone (NMP) enabled the formation of a stable intermediate adduct phase, which can be converted into a uniform and pinhole-free FAPbI<SUB>3</SUB> film. Infrared and computational analyses revealed a stronger interaction between NMP with the FA cation than DMSO, which facilitates the formation of a stable FAI·PbI<SUB>2</SUB>·NMP adduct. On the basis of the molecular interactions with different Lewis bases, we proposed criteria for selecting the Lewis bases. Owed to the high film quality, perovskite solar cells with the highest PCE over 20% (stabilized PCE of 19.34%) and average PCE of 18.83 ± 0.73% were demonstrated.</P> [FIG OMISSION]</BR>

Ag₂S-CoS hetero-nanowires terminated with stepped surfaces for improved oxygen evolution reaction

Lee, Changsoo,Lee, Chulhee,Shin, Kihyun,Song, Taeyoung,Jeong, Hu Young,Jeon, Duk Young,Lee, Hyuck Mo Elsevier 2019 CATALYSIS COMMUNICATIONS - Vol.129 No.-

<P><B>Abstract</B></P> <P>Water electrolysis has received great attention for producing hydrogen, but sluggish kinetics of oxygen evolution reaction (OER) has remained a big challenge. Recently, cobalt sulfide materials have been widely explored as great choice in highly efficient electrocatalysts due to their good electrical conductivity and bi-functionality toward OER and hydrogen evolution reaction (HER). However, cobalt sulfide shows outstanding HER activity, but its OER activity should be improved. Herein, hexagonal-phase cobalt sulfide (CoS) nanowires with abundant stepped surfaces and defect sites were prepared via a seed-growth approach with silver sulfide (Ag<SUB>2</SUB>S) nanoparticles. The Ag<SUB>2</SUB>S-CoS hetero-nanowires (HNWs) exhibited excellent electrochemical performances for oxygen evolution reaction (overpotential = 275 mV, Tafel slope = 77.1 mVdec<SUP>−1</SUP>, charge transfer resistance = 1.3 Ω) in 1.0 M KOH solution. The origin of superior activity was investigated using a combined experimental and theoretical approach. This work highlights the importance of surface defects for improving oxygen evolution reaction performance of water electrolysis.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hexagonal-phase CoS hetero-nanowires were synthesized using seeded growth with Ag<SUB>2</SUB>S nanoparticles. </LI> <LI> Abundant stepped surface improved catalytic activity toward oxygen evolution reaction. </LI> <LI> Combined experimental and theoretical study for explaining the excellent catalytic performances </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

25Cr 계 초 내식성 이상 스테인레스 강에서 W 첨가가 열 재현된 용접 열영향부 충격인성에 미치는 영향

이호,이혁모,유충화 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.12

The effect of partial replacement of Mo with W on the simulated heat-affected zone (HAZ) toughness of 25Cr-base super duplex stainless steels has been investigated, All the simulated alloys exhibited a decrease in toughness at fast cooling due to high proportion of ferrite and intragranular precipitates. Impact toughness also decreased at slow cooling, Δt_(12/8)=270sec, because of large matrix ferrite grain size despite higher austenite content. Peak impact toughness level was observed at cooling time of 33sec for all the alloys. It was also found that the substitution of W for Mo produces high impact toughness at all cooling conditions resulting from the increased austenite content, decreased intragranular precipitates and smaller ferrite matrix grain size. In conclusion, the addition of W has favorable effects on HAZ toughness of 25Cr-base super duplex stainless steels.

Positional Intraocular Pressure of Vitrectomized and Normal Fellow Eyes

Jae Hyuck Lee,Jae Yeun Lee,Jeong Hun Bae,Joon Mo Kim 대한안과학회 2018 Korean Journal of Ophthalmology Vol.32 No.5

Purpose: To compare posture-induced intraocular pressure (IOP) changes in vitrectomized eyes and normal eyes of patients who had vitrectomy in one eye. Methods: A total of 31 patients older than 20 years of age who underwent vitrectomy were enrolled in the study. At least six months after vitrectomy, we measured IOP in both eyes using a rebound tonometer 10 minutes after the patient assumed sitting, supine, right lateral decubitus, and left lateral decubitus positions. Patients with a history of ocular surgery (not including vitrectomy) or recent medication use associated with IOP were excluded. IOP and ocular parameters of vitrectomized and normal fellow eyes were compared. For the decubitus position, IOP values of dependent and nondependent eyes were compared. Results: No significant difference was observed in IOP between vitrectomized and normal eyes in the sitting and supine positions. The IOP for dependent eyes (on the lower side in the lateral decubitus position) was significantly higher than the IOP for nondependent eyes in both right lateral decubitus (right vitrectomized eye 19.31 ± 4.20 vs. 16.71 ± 4.02 mmHg, p < 0.001; left vitrectomized eye 18.35 ± 1.75 vs. 16.04 ± 3.02 mmHg, p = 0.003) and left lateral decubitus (right vitrectomized eye 17.32 ± 4.63 vs. 19.15 ± 3.83 mmHg, p = 0.004; left vitrectomized eye 16.19 ± 1.81 vs. 18.12 ± 2.29 mmHg, p < 0.001) positions. Conclusions: IOP was higher in the dependent than the nondependent eye in the lateral decubitus position, for both vitrectomized and nonoperated eyes.

GPS L1 C/A 코드 신호의 신호추적 및 항법기만 가능성 분석

이병현(Byung Hyun Lee),임준혁(Jun-Hyuck Im),임성혁(Sung-Hyuck Im),지규인(Gyu-In Jee),양진모(Jin Mo Yang),이민준(Min Joon Lee) 한국통신학회 2011 한국통신학회 학술대회논문집 Vol.2011 No.6

기만(spoofing)신호는 원래 신호와 동일하거나 또는 유사한 신호를 만들어 원래 신호의 이용을 방해 또는 기만신호를 이용하여 잘못된 결과를 도출하게 만드는 목적을 갖는다. 따라서 유도무기에서 많이 사용되는 GPS 수신기가 이러한 기만신호에 의해서 잘못된 항법해를 도출하여 유도무기의 항법기능을 무력화 시킬 수 있는 가능성에 대해서 거론되고 있다. 본 논문에서는 GPS 수신기가 기만신호에 의해서 기만될 수 있는 가능성에 대해서 신호추적 및 항법기만 실험을 통하여 확인하였다. 실험을 위해서 GPS 신호와 기만신호를 생성하는 RF 레벨의 GPS/기만신호 발생장치를 개발하였다. 개발된 발생장치는 GPS+Spoofing 신호를 생성하여 National Instrument 사의 RF 신호 발생기를 통하여 L1 대역으로 생성하여 수신기의 안테나 입력에 신호를 인가할 수 있도록 제작되었다. 실험결과 상용 GPS 수신기(Novatel OEMV3/OEM-V1, Ublox 등)에 기만신호를 인가하여 완전히 기만될 수 있음을 확인하였다. 하지만 기만되는 상황을 만들기 위해서는 많은 제약조건이 존재하며, 제약조건의 변화에 따른 영향을 분석하여 제시하였다.

파쇄대에 접근하는 터널의 내공변위 변화 해석

이인모,이승주,이주공,이대혁,Lee, In-Mo,Lee, Seung-Ju,Lee, Joo-Gong,Lee, Dae-Hyuck 한국터널지하공간학회 2002 터널기술 Vol.4 No.3

The purpose of this study is to figure out the tendency of tunnel convergence during excavation and to present a methodology for the prediction of a fault zone ahead of a tunnel face by analyzing three dimensional displacements in various ways. 3-D numerical analysis was performed to investigate changes of tunnel convergence vectors near a fault zone and to propose a flow chart for predicting fault zones. Results of the site investigation and results of trend line analysis of in-situ data were compared to verify the usefulness of a trend line analysis. It is concluded that the orientation of faults can be predicted by using stereonets and the direction of initial stresses can be predicted from the arm length of a displacement vector as a tunnel approaches fault zones. The results of the trend line analysis coincided with those of the site investigation, and a methodology for the prediction of a fault zone was proposed. 본 연구는 터널 굴착시 막장 전방의 지반변화를 사전에 예측할 수 있는 방법을 제시하고자 하였다. 이를 위하여 막장 전방에 파쇄대가 방향성을 가지고 존재 할 때 터널의 3차원 해석을 통하여 터널의 내공변위의 변화 경향을 살펴보았으며, 이를 통하여 막장전방의 지반 변화를 파악하고자 하였다. 이러한 터널의 내공변위의 변화는 경향선과 영향선을 이용하여 표현할 수 있으며 이를 이용하여 막장 전방에 존재하는 파쇄대를 예측하고자 하였다. 수치해석 결과에 의하면 막장전방에 파쇄대가 존재 할 경우 막장이 파쇄대에 접근할 수록 급격한 경향선의 변화가 나타난다. 또한 파쇄대가 방향성을 가지고 있는 경우에는 경향선의 급격한 변화 외에 측벽부의 변위 경향이 비대칭을 이루므로 인하여 평사투영도 상에 나타난 변위가 비대칭을 형성하는 것으로 파악되었다. 이러한 수치해석결과에 의한 내공변위 해석결과를 현장 계측 자료와 비교하였으며, 현장에서 계측한 오차를 줄일 수 있도록 계측데이터가 정규분포 한다고 가정하여 현장데이터를 분석한 결과 막장전방의 파쇄대의 존재 유무를 파악할 수 있는 것으로 나타났다.