• Tribology and Lubricants
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• 제31권2호
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• pp.62-68
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• 2015

A magnetorheological (MR) fluid is a smart material whose rheological behavior can be controlled by varying the parameters of the applied magnetic field. Because the damping force and shear force of an MR fluid can be controlled using a magnetic field, it is widely employed in many industrial applications, such as in vehicle vibration control, powertrains, high-precision grinding processes, valves, and seals. However, the characteristics of friction caused by iron particles inside the MR fluid need to be understood and improved so that it can be used in practical applications. Surface process technologies such as polytetrafluoroethylene (PTFE) coatings and diamond-like carbon (DLC) coatings are widely used to improve the surface friction properties. This study examines the friction characteristics of an MR fluid with different surface process technologies such as PTFE coatings and DLC coatings, by using a reciprocating friction tester. The coefficients of friction are in the following descending order: MR fluid without any coating, MR fluid with a DLC coating, and MR fluid with a PTFE coating. Scanning electron microscopy is used to observe the worn surfaces before and after the experiment. In addition, energy dispersive X-ray spectroscopy is used to analyze the chemical composition of the worn surface. Through a comparison of the results, the friction characteristics of the MR fluid based on the different coating technologies are analyzed.

• Tribology and Lubricants
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• 제31권2호
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• pp.56-61
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• 2015

In this study, we investigated the effectiveness of an ultrasonic nanocrystal surface modification (UNSM) technique on the mechanical and wear properties of tungsten carbide (WC). The UNSM technique is a newly developed surface modification technique that increases the mechanical properties of materials by severe plastic deformation. The objective of this study was to improve the wear resistance of press die made of WC by applying the UNSM technique. We observed the microstructures of the untreated and UNSM-treated specimens using a scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX) was used to investigate the chemical composition. The SEM observations showed the pore size and the number of pores decreased after the UNSM treatment. We assessed the wear behavior of both the untreated and UNSM-treated specimens using a scratch test. The test results showed that the wear resistance of the UNSM-treated specimens increased by about 46% compared with the untreated specimens. This may be attributed to increased hardness, reduced surface roughness, induced compressive residual stress, and refined grain size following the application of the UNSM technique. In addition, we found that the UNSM treatment increased the carbon concentration to 63% from 33%. We expect that implementing the findings of this study will lead to an increase in the life of press dies.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.397-397
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• 2010

Bone is considered as hierarchically organized biocomposites of organic (collagen) and inorganic (hydroxyapatite) materials. The precise structural dependence between hydroxyapatite (HAp, $Ca_{10}(PO_4)_6(OH)_2)$ crystals and collagen fibril is critical to unique characteristics of bone. To meet those conditions and obtain optimal properties, it is essential to understand and control the initial growth mechanisms of hydroxyapatite at the molecular level, such as other nano-structured materials. In this study, collagen fibrils were prepared by adsorbing native type I collagen molecules onto hydrophobic surface. Hydrophobicity was introduced on the Si wafer surface by using PECVD (plasma enhanced chemical vapor deposition) method and cyclohexane as a precursor. Biomimetic nucleation and growth of HAp on the self-assembled collagen nanofibrils were occurred through incubation of the sample in SBF (simulated body fluid). Chemical and morphological evolution of HAp nanocrystals was investigated by surface-sensitive analytical techniques such as ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) and AFM (Atomic Force Microscopy) in the early growth stages (< 24 hrs). The very initial stages (< 12 hrs) of mineralization could be clearly demonstrated by ToF-SIMS chemical mapping of surface. In addition to ToF-SIMS and AFM measurement, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis were conducted to characterize the HAp layer in the late stages. This study is of great importance in the growth of real bone-like materials with a structure analogous to that of natural bones and the development of biomimetic nanomaterials.

• 한국표면공학회지
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• 제37권5호
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• pp.253-262
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• 2004

Calcareous deposits are the consequence of pH increase of the electrolyte adjacent to metal surface affected by cathodic current in seawater. It obviously has several advantages over conventional coatings, since the calcareous deposit coating is formed from coating (Mg$^{2+}$, $Ca^{2+}$) naturally existing in seawater. In consideration of this respect, environment friendly calcareous deposit films were formed by an electro deposition technique on steel substrates submerged in 48$^{\circ}C$ natural seawater. And the influence of current density, coating time and attachment of steel mesh on composition ratio, structure and morphology of the electrodeposited films were investigated by Scanning Electron Microscopy(SEM), Energy Dispersive Spectroscopy(EDS) and X-Ray Diffractor(XRD), respectively. Accordingly, this study provides a better understanding of the composition between the growth of $Mg(OH)_2$ and $CaCO_3$ during the formation of electro deposit films on steel substrate under cathodically electrodeposition in $48^{\circ}C$ natural seawater. The Mg compositions, in general, are getting decreased regardless of current density but Ca compositions are getting increased as electrodeposition time runs. That is, $Mg(OH)_2$ compounds of brucite structure shaped as flat type is formed at the initial stage of electrodeposition, but CaCO$_3$ compounds of aragonite structure shaped as flower type is formed in large scale. Besides, $Mg(OH)_2$ compounds were much formed at 5 A/$\m^2$ environment condition compared to the 3 A/$\m^2$ and 4 A/$\m^2$ environment conditions. This is because that OH- which was comparatively largely generated at the metal surface is preferably combined with $Mg^{2+}$TEX>.

• 한국분말재료학회지
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• 제26권5호
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• pp.405-409
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• 2019

Piezoelectric ceramic specimens with the $Pb(Mg_{1/3}Nb_{2/3})_{0.65}Ti_{0.35}O_3$ (PMN-PT) composition are prepared by the solid state reaction method known as the "columbite precursor" method. Moreover, the effects of the $Li_2O-Bi_2O_3$ additive on the microstructure, crystal structure, and piezoelectric properties of sintered PMN-PT ceramic samples are investigated. The addition of $Li_2O-Bi_2O_3$ lowers the sintering temperature from $1,200^{\circ}C$ to $950^{\circ}C$. Moreover, with the addition of >5 wt.% additive, the crystal structure changes from tetragonal to rhombohedral. Notably, the sample with 3 wt.% additive exhibits excellent piezoelectric properties ($d_{33}=596pC/N$ and Kp = 57%) and a sintered density of $7.92g/cm^3$ after sintering at $950^{\circ}C$. In addition, the sample exhibits a curie temperature of $138.6^{\circ}C$ at 1 kHz. Finally, the compatibility of the sample with a Cu electrode is examined, because the energy-dispersive X-ray spectroscopy data indicate the absence of interdiffusion between Cu and the ceramic material.

• 한국안전학회지
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• 제34권4호
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• pp.1-5
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• 2019

In the field of combined cycle power generation, thermal barrier coating(TBC) protects the super-heat-resistant alloy, which forms the core component of the gas turbine, from high temperature exposure. As the turbine inlet temperature(TIT) increases, TBC is more important and durability performance is also important when considering maintenance cost and safety. Therefore, studies have been made on the fabrication method of TBC and super-heat-resistant alloy in order to improve the performance of the TBC. In recent years, due to excellent properties such as high temperature creep resistance and high temperature strength, turbine blade material have been replaced by a single crystal superalloy, however there is a lack of research on TBC applied to single crystal superalloy. In this study, to understand the isothermal degradation performance of the TBC applied to the single crystal superalloy, isothermal exposure test was conducted at various temperature to derive the delamination life. The growth curve of thermally grown oxide(TGO) layer was predicted to evaluate the isothermal degradation performance. Also, microstructural analysis was performed by scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy (EDS) to determine the effect of mixed oxide formation on the delamination life.

• 한국건설순환자원학회논문집
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• 제9권4호
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• pp.499-505
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• 2021

이 연구의 목적은 거푸집 종류별로 콘크리트 표면의 물리/화학적 특성을 실험적으로 조사하는 것이다. 이를 위하여 건설공사에 일반적으로 사용되는 합판 거푸집과 코팅된 합판 거푸집을 준비하였고, 추가로 콘크리트 표면 열화나 거친 표면을 모사하기 위해 사포를 부착한 합판 거푸집을 준비하였다. 콘크리트는 일반 콘크리트를 사용하였다. 콘크리트 표면 특성은 육안관찰, 주사전자현미경 관찰, 성분 이미지 맵핑, 화학성분 분석, 2차원과 3차원 표면 형상 분석, 그리고 제타 전위 측정을 통해 조사하였다. 실험결과 코팅된 거푸집과 접한 콘크리트 표면이 가장 매끄럽고, 사포를 부착한 거푸집과 접한 콘크리트 표면이 가장 거친 것으로 나타났다. 이외에도 거푸집 종류별로 표면 특성에 뚜렷한 차이가 나타났다. 다만 표면 거칠기가 화학 성분이나 제타 전위에 비하여 차이가 크게 나타났다.

• 대한치과교정학회지
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• 제49권1호
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• pp.12-20
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• 2019

Objective: The aim of this study was to analyze the surface composition, roughness, and relative friction of metal clips from various ceramic self-ligating brackets. Methods: Six kinds of brackets were examined. The control group (mC) consisted of interactive metal self-ligating brackets while the experimental group (CC, EC, MA, QK, and WA) consisted of interactive ceramic self-ligating brackets. Atomic force microscopy-lateral force microscopy and scanning electron microscopy-energy-dispersive X-ray spectroscopy were used to analyze the surface of each bracket clip. Results: All the clips in the experimental groups were coated with rhodium except for the QK clip. The results showed that the QK clip had the lowest average roughness on the outer surface, followed by the MA, EC, WA, and CC clips. However, the CC clip had the lowest average roughness on the inner surface, followed by the QK, WA, MA, and EC clips. The QK clip also had the lowest relative friction on the outer surface, followed by the MA, EC, CC, and WA clips. Likewise, the CC clip had the lowest relative friction on the inner surface, followed by the QK, WA, MA, and EC clips. Conclusions: The surface roughness and relative friction of the rhodium-coated clips were generally higher than those of the uncoated clips.

• 한국지하수토양환경학회지:지하수토양환경
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• 제23권6호
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• pp.104-113
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• 2018

A three-dimensional electrochemical process using nanosized zero-valent iron (NZVI)/activated carbon (AC) particle electrode and persulfate (PS) was developed for oxidizing pollutants. X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and Brunauer-Emmett-Teller (BET) surface area analysis were performed to characterize particle electrode. XRD and SEM-EDS analysis confirmed that NZVI was impregnated on the surface of AC. Compared with the conventional two-dimensional electrochemical process, the three-dimensional particle electrode process achieved three times higher efficiency in phenol removal. The system with current density of $5mA/cm^2$ exhibited the highest phenol removal efficiency among the systems employing 1, 5, and $10mA/cm^2$. The removal efficiency of phenol increased as the Fe contents in the particle electrode increased. The particle electrode achieved more than 70% of phenol removal until it was reused for three times. The sulfate radical played a predominant role in phenol removal according to the radical scavenging test.

• 한국결정성장학회지
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• 제29권4호
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• pp.143-148
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• 2019

우리는 분자선 에피택시(Molecular Beam Epitaxy) 법을 사용하여 광전기화학적 물분해 수소생산용 고종횡비 GaN 기반 나노와이어를 Si 기판 위에 성공적으로 제작하였다. 주사전자현미경(SEM)과 에너지분산형 분광법(EDX)은 p-GaN:Mg 및 p-InGaN 나노와이어가 고밀도와 함께 수직으로 성장 되었음을 증명하였다. 또한, p-InGaN 나노와이어의 발광 파장을 552 nm에서 590 nm까지의 조절이 가능하다는 것을 확인하였다. 이렇게 제작된 p-InGaN 나노와이어는 태양광을 통해 외부 전위 없이 물분해가 가능한 수소생산용 광촉매로써 매우 유용하게 사용될 수 있다.