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Ilho Kim,Soon-Bok Lee IEEE 2009 IEEE transactions on components and packaging tech Vol.32 No.3
<P>Drop-impact forces cause portable electronic devices to fail. Assessment of resistance against drop-impact force is required to predict life of an electronic package. Several methods have been used to evaluate impact-fatigue life and other advanced methods have been proposed. However, such conventional impact tests require excessive time and cost. In this paper, a novel micro-impact-fatigue tester is developed to overcome such drawbacks of conventional methods. A newly developed impact-fatigue apparatus directly applies impact force to solder joints and measures deformation of the solder joints. The impact-fatigue test apparatus consists of an electromagnetic actuator, an impact-pin, a load-cell, a displacement sensor, and a main frame. Electromagnetic actuator produces a repeatable impact force with a changeable amplitude and pulse duration. Impact-fatigue apparatus was used to test reliability of a lead-free solder (96.5Sn4.0Ag0.5Cu). An evaluation of impact-fatigue life was performed over a wide range of 1-10<SUP>4</SUP> cycles with various applied forces ranging from 40 N to 110 N. Two failure modes were observed in a section inspection. First type of failure was a mixed mode failure, where a bulk solder failure and interface failure coincide and the relation between the impact load and fatigue life is almost linear. Stress-based life-prediction model is proposed for the mixed mode failure. The second type of failure, interface failure between the Ni(P) layer and the solder, occurs under a high-load condition. Fatigue life is shorter in the second type of failure than in the mixed mode failure. Brittleness of the interface reduces the impact-fatigue life.</P>
Bio Toxicity Assessment and Kinetic Model of 6 Heavy Metals Using Luminous Bacteria
Ilho Kim,Jaiyeop Lee 한국도시환경학회 2018 한국도시환경학회지 Vol.18 No.4
In addition to North America and Europe, Korea is also responding to the toxic damage caused by the production and distribution of chemicals. Methods for assessing bio-toxicity of harmful substances have been widely introduced, but it is required of quantitative and speedy information for modeling. For 6 heavy metals, as zinc, copper, chrome, cadmium, mercury and lead, bio-toxicity assessment and kinetics model were constructed using Vibrio fischeri which is widely used luminous bacteria. The degree of luminescence activity and the toxicity of heavy metals were relative limunescence unit, RLU measured as by using a photomultiplier embedded device. The toxicity was assessed by the concentration levels giving under 20% lethality and lethal concentration, EC50. In the results, the toxicity order were followed from mercury, lead, copper, chrome, zinc and cadmium. EC50, ∞ obtained by trends of EC50 by time follows had highly linear agreement with main parameters of bio-toxicity modelling. The average error rates of the reproduced lethality obtained from DAM and TDM model on the basis of body residue, were 10.2% for mercury, lead, copper, chrome and 20.0 for the all 6 methals.
Ilho Kim,Soon-Bok Lee IEEE 2008 IEEE transactions on components and packaging tech Vol.31 No.2
<P>Nowadays, interest in the bending reliability of ball grid array packages has increased with the increase in mobile devices. Initially, bending tests were conducted to certify the safety of an electronic package during the manufacturing and shipping processes. But recently, the purpose of the bending test has changed: cyclic bending tests are being used to evaluate the electronic package's endurance against handling damage such as bending, twisting and key pressure. Furthermore, the bending test is being adopted as an alternative to a drop test. In this study, a four-point cyclic bending test was performed under various loading levels to investigate the fatigue behavior of solder joints with chemical compositions of 95.5Sn4.0Ag0.5Cu and 63Sn37Pb. It was found that the lead-free solder has a longer fatigue life than the lead-contained solder when the applied load is low. A finite element analysis (FEA) with plasticity and creep constitutive equations was conducted because there are no suitable sensors to measure stress and strain of solder ball joints directly. From the analysis results, it was found that the inelastic energy dissipation could be used as a good damage parameter. Also, from the inspection of the failure site and the FEA, it was found that the fatigue crack initiated at the exterior solder joints and propagated into the inner solder joints.</P>
Kim, Ilho,Lee, Gihoon,Jeong, Heondo,Park, Jong Ho,Jung, Ji Chul Elsevier 2017 Journal of energy chemistry Vol.26 No.3
<P>Alcohol-assisted low-temperature methanol synthesis was conducted over Cu/ZnO_X catalysts while varying the copper content (X). Unlike conventional methanol synthesis, ethanol acted as both solvent and reaction intermediate in this reaction, creating a different reaction pathway. The formation of crystalline phases and characteristic morphology of the co-precipitated precursors during the co-precipitation step were important factors in obtaining an efficient Cu/ZnO catalyst with a high dispersion of metallic copper, which is one of the main active sites for methanol synthesis. The acidic properties of the Cu/ZnO catalyst were also revealed as important factors, since alcohol esterification is considered the rate-limiting step in alcohol-assisted low-temperature methanol synthesis. As a consequence, bifunctionality of the Cu/ZnO catalyst such as metallic copper and acidic properties was required for this reaction. In this respect, the copper content (X) strongly affected the catalytic activity of the Cu/ZnO_ X catalysts, and accordingly, the Cu/ZnO_0.5 catalyst with a high copper dispersion and sufficient acid sites exhibited the best catalytic performance in this reaction. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.</P>
Ilho Kim,Jaiyeop Lee 대한환경공학회 2022 Environmental Engineering Research Vol.27 No.2
This study analyzed residues of PPCPs in secondary treated sewage water, and their amount eliminated by ozonation processes. A microbubble nozzle and ejector were used to dissolve ozone. To consider a low concentration of PPCPs, a SPE method was performed on samples prior to the analysis. The concentration of dissolved ozone was 4.00 mg/L in the microbubble and 2.49 mg/L in the ejector. To examine elimination trends, the experiment was also performed at a low concentration of ozone, 1/10 of its original concentration. The maximum elimination rate on average was 93.0% in the ejector, higher than that in the microbubble (90.1%), but 16 PPCPs were found to show a relatively high elimination rate in the microbubble, higher than the ejector. Elimination trends with respect to time were distinguished based on inflection point, and 11 PPCPs were concentrated on the latter half of the microbubble after the inflection point at the low concentration of ozone, which was compared to other cases. In the source water, concentrations of 2 PPCPs were higher than the reference toxic concentration based on the QSAR model, but after treatment, only bezafibrate was over the value when the ejector with low ozone injection concentration was applied.
Selective oxygen species for the oxidative coupling of methane
Kim, Ilho,Lee, Gihoon,Na, Hyon Bin,Ha, Jeong-Myeong,Jung, Ji Chul Elsevier 2017 Molecular catalysis Vol.435 No.-
<P>Herein, we attempt to identify selective oxygen species for the oxidative coupling of methane using lanthanum-based perovskite catalysts (LaXO3, X = Al, Fe, or Ni), which are well-known not only as stoichiometric materials with simple and definite structures but also as materials with outstanding catalytic activities in various methane conversion reactions. The catalytic activities of LaXO3 in the presence or absence of oxygen clearly demonstrated that surface lattice oxygen species are responsible for the selective conversion of methane. More importantly, electrophilic (LaAlO3), moderate (LaFeO3), and nucle-ophilic (LaNiO3) lattice oxygen species selectively catalyze the oxidative coupling of methane to C-2 hydrocarbons, the direct partial oxidation of methane to carbon monoxide, and the methane combustion to carbon dioxide, respectively. In addition, adsorbed oxygen species originating from gas-phase oxygen play roles both in converting methane to CO. and in filling surface lattice oxygen vacancies, which are caused by the reaction of lattice oxygen and methane. Finally, we concluded that electrophilic lattice oxygen species and the facile filling of surface lattice oxygen vacancies by gas-phase oxygen are key factors for the systematic design of efficient catalysts for the oxidative coupling of methane. (C) 2017 Elsevier B.V. All rights reserved.</P>