• Journal of Advanced Marine Engineering and Technology
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• v.24 no.3
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• pp.43-51
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• 2000

The effect of time, temperature and gas composition on the case hardened thickness, hardness and nitride formation in the surface of ductile cast iron(GCD400) have been studied by micro-pulse plasma technique. Typically, external compound layer and internal diffusion layer which is much thicker than compound layer was observed in the nitride hardening of ductile cast iron. The relative amount kind of phases formed in the nitrided hardening changed with the change of nitriding conditions. Generally, only nitride phases such as $\gamma^'$($Fe_4N$), or $\varepsilon$($Fe_{2-3}N$) phases were detected in compound layer by XRD analysis. The thickness of compound layer increased with the increase of nitrogen content in the gas composition. The optimum nitriding temperature was obtained at $520^{\circ}C$. The nitrided hardening thickness parabolically with nitriding time(t) and thus, the case hardened layer(d) fits well with the typical parabolic equation ; d=kt. The material constant k for GCD400 nitrided at $520^{\circ}C$ was $0.04919\times10^3{\mu}m.hr^{-1/2}$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.369.2-369.2
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• 2014

Diamond-like Carbon(DLC) films doping Si were deposited by linear ion source(LIS)-physical vapor deposition method on Si wafer. We have studied the effects of Si content on friction and wear properties of DLC films and the characteristics of the films were investigated using Nano-indentation, Micro raman spectroscopy, Field Emission-Scanning Electron Microscope (FM-SEM) and X-ray Photoelectron Spectroscopy (XPS). The films has been various low-friction and low-stress by varying the flow rates of silane gas. Under the about 2% of Si doping is very suitable for improving the adhesion of films and reducing internal stress while maintaining the surfaces hardness of DLC films. Linear ion source (LIS)를 사용하여 Si wafer위에 Si 이온이 첨가된 DLC 박막을 증착하였다. 참가된Si 이온의 양에 따라 DLC 박막에 미치는 영향을 분석하기 위하여 마찰 계수 및 경도를 비교하였고, Micro raman spectroscopy, Field Emission-Scanning Electron Microscope (FM-SEM) and X-ray Photoelectron Spectroscopy (XPS)를 통하여 표면 상태를 분석하였다. 천체 주입된 가스량의 약 2%까지 Si 이온 주입이 늘어날수록 DLC 박막의 마찰계수는 낮아졌고, 경도는 Si 이온이 주입되지 않았을 경우와 비슷한 값(약 20~23 GPa)을 가졌다. 2% 이상의 주입량에서는 마찰계수는 주입량이 늘어날수록 높아졌으며 경도는 떨어지는 경향을 보였다. 이는 Si이온이 2%이하로 첨가되었을 경우, DLC 박막의 생성시 탄소 이온들의 결합 Stress를 줄여 마찰계수가 줄어든다고 볼 수 있으며, 그 양이 2%이상이 되면 오히려 불순물로 작용하여 DLC 박막의 Stress는 급격히 증가하고 마찰계수도 높아짐을 알 수 있다.

• Korean Journal of Microbiology
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• v.5 no.1
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• pp.15-19
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• 1967

Chlorella ellipsoidea cells were cultured in an iron, copper, zinc, manganese, molybdenum or boron-free medium. Physiological activities such as growth rate, reproduction, endogenous and glucose respiration, photosynthetic activity and biosythesis of chlorophyll of the micro-element definition cells were measured. It generally, growth rate, respiratory and photosynthetic activities, and biosynthesis of chlorophyll of the micro-element deficient cells decreased more or less, compared with those of the normal cells. The growth of the algal cells in an iron-free medium were retarded severely with the chlorosis, and the photosynthetic activity of the cells decreased remarkably even though the low content of chlorophyll in the cells owing to the iron-deficiency is considered. Therefore, it is deduced that iron takes part in the photosynthetic process itself, possibly by its participation in the photo phosphorylation coupled with electron transport. Respiratory activity of boron-deficient cells showed the most severe decrease whereas those of the molybdenum-deficient cells showed very slight decrease in spite of severe growth retardation.

• Tribology and Lubricants
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• v.18 no.5
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• pp.324-332
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• 2002

In order to enhance the thermal stability of binder materials of bonded type solid lubricants, several metal-alkoxide based sol-gel materials such as methyltrimethoxysilane(MTMOS), titaniumisopropoxide$(Ti(Opr^i)_4),$ zirconiumisopropoxide $(Zr(Opr^i)_4)$ and aluminumbutoxide$(Al(Obu^t)_4)$ were chemically modified by epoxy-, acrylic- and fluoro-silane compounds, respectively. Friction and wear characteristics of these hybrid ceramic materials were tested with a micro tribo-tester, and evaluated with respect to both heat-curing temperature and the time. Test results generally showed that hybrid ceramic materials modified by epoxy-silane compounds had a low friction compared to others. And the higher het-curing temperature and the longer heat treatment time resulted in the higher friction and the lower wear. IR spectroscopic analyses revealed that these results were caused mainly by the increased metal oxide content in hybrid ceramics when the heat-curing temperature was over $320^{\circ}C.$

• Journal of Powder Materials
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• v.20 no.6
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• pp.439-444
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• 2013

Fe foam with above 90% porosity and 2 millimeter pore size was successfully fabricated by a slurry coating process. In this study, the binder contents were controlled to produce the Fe foam with different pore size, strut thickness and porosity. Firstly, the slurry was prepared by uniform mixing with Fe powders, distilled water and polyvinyl alcohol(PVA) as initial materials. After slurry coating on the polyurethane(PU) foam the sample was dried at $80^{\circ}C$. The PVA and PU foams were then removed by heating at $700^{\circ}C$ for 3 hours. The debinded samples were subsequently sintered at $1250^{\circ}C$ with holding time of 3 hours under hydrogen atmosphere. The three dimensional geometries of the obtained Fe foams with open cell structure were investigated using X-ray micro CT(computed tomography) as well as the pore morphology, size and phase.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.809-816
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• 1995

Ti1-xAlxN films were successfully deposited on high speed steel and silicon wafer by plasma-assisted chemical vapor deposition using a TiCl4/AlCl3/N2/Ar/H2 gas mixture. Plasma process enabled N2 gas to nitride AlCl3, which is not possible in sense of thermodynamics. XPS analyses revealed that the deposited layer contained Al-N bond as well as Ti-N bond. Ti1-xAlxN films were polycrystalline and had single phase, B1-NaCl structure of TiN. Interplanar distance, d200, of (200) crystal plane of Ti1-xAlxN was, however, decreased with Al content, x. Al incorporation into TiN caused the grain size to be finer and changed strong (200) preferred orientation of TiN to random oriented microstructure. Those microstructural changes with Al addition resulted in the increase of micro-hardness of Ti1-xAlxN film up to 2800Kg/$\textrm{mm}^2$ compared with 1400Kg/$\textrm{mm}^2$ of TiN.

• Clinical and Experimental Reproductive Medicine
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• v.43 no.2
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• pp.59-81
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• 2016

It is well established that there is a heritable element of susceptibility to chronic human ailments, yet there is compelling evidence that some components of such heritability are transmitted through non-genetic factors. Due to the complexity of reproductive processes, identifying the inheritance patterns of these factors is not easy. But little doubt exists that besides the genomic backbone, a range of epigenetic cues affect our genetic programme. The inter-generational transmission of epigenetic marks is believed to operate via four principal means that dramatically differ in their information content: DNA methylation, histone modifications, microRNAs and nucleosome positioning. These epigenetic signatures influence the cellular machinery through positive and negative feedback mechanisms either alone or interactively. Understanding how these mechanisms work to activate or deactivate parts of our genetic programme not only on a day-to-day basis but also over generations is an important area of reproductive health research.

• Macromolecular Research
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• v.11 no.2
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• pp.122-127
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• 2003

A glass-like carbon was fabricated using furan resin. The influence of heat treatment temperature during fabrication process on the chemical and micro-structural changes was studied by various analytical and spectroscopic methods including TGA, FT-IR, CHN, TEM and XRD. The chemical resistance properties of the fabricated glass-like carbon were also investigated. It has been found that the heat-treated samples at higher temperature up to 2600 $^{\circ}C$ in $N_2$ atmosphere had little weight loss, small amounts of functional groups, and high carbon content. The fabricated glass-like carbons upon heat treatment at 2600 $^{\circ}C$ showed an amorphous stage without any grain growth and/or reconstruction of structure. The glass-like carbon had much better chemical resistance than the artificial graphite, and exhibited a high chemical resistance due to its low surface areas, minimum impurities, and low graphite crystallites.

• Macromolecular Research
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• v.15 no.7
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• pp.633-639
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• 2007

A variety of NMR techniques were applied to the micro-chemical structural characterization of polyanilines prepared via an efficient synthetic method in a self-stabilized dispersion medium in which the polymerization was conducted in a heterogeneous organic/aqueous biphasic system without any stabilizers. Here, the monomer and growing polymer chain were shown to function simultaneously as a stabilizer, imparting compatibility for the dispersion of the organic phase, and as a form of flexible template in an aqueous reaction medium. Polymerizations predicated on this concept generated polyanilines with a low defect content: solution state $^{13}C-NMR$ and solid $^{13}CDD/CP/MAS$ spectroscopy indicated that the synthesized HCPANi and its soluble derivative, HCPANi-t-BOC, evidenced distinctly different NMR spectra with fewer side peaks, as compared to conventionally prepared PANis, and the complete structural assignments of the observed NMR peaks could be determined via the combination of both 1D and 2D techniques. Ortho-linked defects in HCPANi were estimated to be as low as 7%, as shown by a comparison of the integration of the carbonyl carbon resonance peaks.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.7
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• pp.621-628
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• 2009

Nickel-phosphorus alloys are attractive materials for diamond turning applications such as fabrication of large optics and other high precision parts. It is also well-known that the higher phosphorus content of the alloys minimizes the diamond tool wear. Due to the weakness of electoless nickel plating that the phosphorus contents is limited to 13-14% (wgt), increased attention has been paid at electro-nickel plating which enables the alloys with 15-16% phosphorus. In this study, experiments were carried out to observe the wear characteristic of single crystal diamond tools in micro-grooving of electro-nickel plated drums. The experiments shows that long distance (50km) machining of micro-grooving on electro-nickel plated drum is possible with a single crystal diamond tool without any significant tool wear and defective machined surface.