• Polymer(Korea)
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• v.29 no.5
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• pp.423-432
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• 2005

Over last three decades, various biomaterials has been developed and applied in the biomedical market. The practical utilization of biomaterials depends on the study about an appropriate physical and biological response of biomaterials. The modification of biomaterials using various surface treatment methods has recently become an interesting topic in the field of surface engineering. A padient surface is the surface on which a gradually varying chemical composition exists along its length. A large number of research groups have been focused on the preparation of gradient surfaces. Such gradient surface is of particular interest for basic and applied studies of the interactions between biological species and surfaces since the effect of a selected property like wettability or chemical composition can be examined in a single experiment on one surface. The present review focuses on the preparation and characterization of various gradient surfaces, and their interactions with biological species.

• Korean Journal of Materials Research
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• v.30 no.5
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• pp.231-238
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• 2020

The composition of martensite transformation in NiAl alloy is determined using pure nickel and aluminum powder by vacuum hot press powder metallurgy, which is a composition of martensitic transformation, and the characteristics of martensitic transformation and microstructure of sintered NiAl alloys are investigated. The produced sintered alloys are presintered and hot pressed in vacuum; after homogenizing heat treatment at 1,273 K for 86.4 ks, they are water-cooled to produce NiAl sintered alloys having relative density of 99 % or more. As a result of observations of the microstructure of the sintered NiAl alloy specimens quenched in ice water after homogenization treatment at 1,273 K, it is found that specimens of all compositions consisted of two phases and voids. In addition, it is found that martensite transformation did not occur because surface fluctuation shapes did not appear inside the crystal grains with quenching at 1,273 K. As a result of examining the relationship between the density and composition after martensitic transformation of the sintered alloys, the density after transformation is found to have increased by about 1 % compared to before the transformation. As a result of examining the relationship between the hardness (Hv) at room temperature and the composition of the matrix phase and the martensite phase, the hardness of the martensite phase is found to be smaller than that of the matrix phase. As a result of examining the relationship between the temperature at which the shape recovery is completed by heating and the composition, the shape recovery temperature is found to decrease almost linearly as the Al concentration increases, and the gradient is about -160 K/at% Al. After quenching the sintered NiAl alloys of the 37 at%Al into martensite, specimens fractured by three-point bending at room temperature are observed by SEM and, as a result, some grain boundary fractures are observed on the fracture surface, and mainly intergranular cleavage fractures.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.157-160
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• 2007

The catalyst layer of a proton exchange membrane (PEM) fuel cell is a mixture of polymer, carbon, and platinum. The characteristics of the catalyst layer play critical role in determining the performance of the PEM fuel cell. This research investigates the role of catalyst layer composition using a Central Composite Design (CCD) experiment with two factors which are Nafion content and carbon loading while the platinum catalyst surface area is held constant. For each catalyst layer composition， polarization curves are measured to evaluate cell performance at common operating conditions, Electrochemical Impedance Spectroscopy (EIS), and Cyclic Voltammetry (CV) are then applied to investigate the cause of the observed variations in performance. The results show that both Nafion and carbon content significantly affect MEA performance. The ohmic resistance and active catalyst area of the cell do not correlate with catalyst layer composition, and observed variations in the cell resistance and active catalyst area produced changes in performance that were not significant relative to compositions of catalyst layers.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.29 no.1
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• pp.26-35
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• 1997

A study was carried out to investigate such optical properties of coated papers as brightness, opacity and gloss affected by the coating pigment composition and coat weight using clay, ground calcium carbonate, precipitated calcium carbonate, and plastic pigment as pigments. The effects of drying methods and supercalendering on optical properties were also evaluated. Gloss increased abruptly while brightness and opacity decreased slightly by supercalendering due to surface smoothing and consolidating effects of the coating layers. Optical properties changed little by drying methods. Pigment composition showed significant influences on optical properties. Brightness of coated papers decreased or increased linearly as the coat weight was increased depending on the pigment composition, while opacity increased linearly for all formulations. Gloss increased abruptly at low coat weights for all formulations and approached a plateau value at coat weight of 15-20g/$m^2$. Third order polynomial regression equations relating the coat weight with gloss have been derived and tabulated.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.124-130
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• 2005

The research on surface modification technology has been advanced to improve the properties of engineering materials. ion implantation is a novel surface modification technology to enhance the mechanical, chemical and electrical properties of substrate's surface using accelerated ions. In this research, nitrogen ions were implanted into aluminum substrates which would be used for mold of rubber materials. The composition of nitrogen ion implanted aluminum alloy and nitrogen ion distribution profile were analyzed by Auger Electron Spectroscopy (AES). To analyze the modified surface, properties such as hardness, friction coefficient, wear resistance, contact angle, and surface roughness were measured. Hardness of ion implanted specimens was higher than that of untreated specimens. Friction coefficient was reduced, and wear resistance was improved. From the experimental results, it can be expected that ion implantation of nitrogen enhances the surface properties of aluminum mold.

• Transactions of Materials Processing
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• v.15 no.8 s.89
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• pp.539-543
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• 2006

Experimental studies are carried out in order to investigate the effects of heat treatment on the surface machined by W-EDM. In this work, two ways of heat treatment after W-EDM are considered. As a comparison, the machined surface by a traditional method such as milling/grinding is also considered. Thereby, specimens are prepared by four different machining methods. Those are (1) milling and then grinding, (2) wire-cut electric discharge machining (W-EDM), and (3) low temperature heat treatment or (4) high temperature heat treatment after W-EDM. The resulting surface roughness are measured and the changes of surface microstructures are investigated using the scanning electron microscope (SEM) with energy dispersive X-ray spectrometer (EDS). In general, heat treatment after W-EDM result in smoother surface and better chemical composition at the machined surface. Especially, high temperature tempering could remove defects in the thermally affected zone, which cause an overall deterioration of the surface machined by W-EDM.

• Polymer(Korea)
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• v.37 no.2
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• pp.196-203
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• 2013

Surface modification of meta-aramid fibers was performed by phosphoric acid treatment. Surface morphology and element composition of untreated and treated fibers were analyzed by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Effects of surface modification on the mechanical strength of aramid papers made from meta-aramid fibers and fibrid were investigated. Surface modification conditions were optimized by response surface analysis (RSA). Results show that phosphoric acid treatment increases the surface roughness and oxygen content of aramid fibers. They improve the interface bonding strength between aramid fibers and fibrid, which improves the tensile strength of aramid papers. The results of response surface analysis indicate that the tensile strength of aramid papers increases by 47.5% and reaches the maximum when meta-aramid fibers are treated with 21.1wt% phosphoric acid solution at $39.3^{\circ}C$ for 36.7 min.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.11a
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• pp.159-160
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• 2007

저온 플라즈마 침탄 처리 후 연속적인 공정으로 저온 플라즈마 질화를 실시하여 내식성과 표면경도를 향상시키는 처리에서 질화처리 시 Ar 가스가 표면특성에 미치는 영향을 조사 하였다. 모든 시편의 경도가 미처리재 보다 약4배 증가하였으며, Ar가스의 양이 증가할수록 N의 침투깊이가 깊어졌다. 전체 경화증의 두께는 거의 일정하였고, 경화층은 모재보다 내식성이 증가되어 단면조직사진에서 밝게 나타났다.

• Journal of the Korean institute of surface engineering
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• v.33 no.4
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• pp.261-265
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• 2000

Geometrically and chemically well defined Pt/alumina model catalysts have been prepared. To this end, we fabricated electrochemically alumina supports in which pores of constant size, length and shape were regularly distributed over a wide area of the surface. Platinum particles were dispersed on the pore surfaces via organometallic chemical vapor deposition technique using (trimethyl) methylcyclopentadienylplatinum (IV) as a precursor. The chemical composition of the alumina plane surfaces was examined by Auger electron spectroscopy and the adsorption characteristics of the platinum particles were studied by thermal desorption spectroscopy. A variety of industrial catalytic problems are now open for further investigation utilizing the Pt/alumina model catalysts.

• Journal of the Mineralogical Society of Korea
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• v.18 no.2
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• pp.127-134
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• 2005

Although the bulk composition of materials is one of the major considerations in extractive metallurgy and environmental science, surface composition and topography control surface reactivity, and consequently play a major role in determining metallurgical phenomena and pollution by heavy metals and organics. An understanding of interaction mechanisms of different chemical species at the mineral surface in an aqueous media is very important in natural environment and metallurgical processing. X-ray photoelectron spectroscopy (XPS) has been used as an ex-situ analytical technique, but the material to be analyzed can be any size from $100\;{\mu}m$ up to about 1 cm. It can also measure mixed solids powders, but it is impossible to ascertain the original source of resulting x-ray signals where they were emitted from, since it radiates and scans the macro sample surface area. The study demonstrated the ability of TOF-SIMS to detect individual organic species on the surfaces of mineral particles from plant samples and showed that the TOF-SIMS techniques provides an excellent tool for establishing the surface compositions of mineral grains and relative concentrations of chemicals on mineral species.