• 한국표면공학회지
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• 제48권6호
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• pp.253-259
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• 2015

The test equipment becomes more important with the development of semiconductor industry. MEMS probe is an important testing component to detect the defects from the generated electric signal when it contacts the metal pad of semiconductor devices. Ni-Pd alloy has been paid attention to as a candidate of MEMS probe material because of its high surface hardness and relatively low resistivity. In this study, electroplated Ni-Pd alloy has been prepared by using ethylene diamine as a complexing agent. Solid solution alloy coating could be formed when concentration of palladium chloride and current density were in the ranges of 1~5 mM and $0.2{\sim}1.5A/dm^2$, respectively. The increase of current density brought about an decrease in palladium content, which made both of lattice parameter and grain size smaller. As a result of grain refinement, high hardness could be obtained. However, surface cracking was observed due to residual stress when the current density was above $1.3A/dm^2$. When effects of heat treatment temperature on hardness and sheet resistance were investigated, the accompanied grain growth decreased both of them. The decrease of hardness remained stable at a temperature of $200^{\circ}C$. The sheet resistance was drastically reduced at $100^{\circ}C$. After that, it was found to become constant.

• 한국표면공학회지
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• 제46권1호
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• pp.1-8
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• 2013

Cathodic current on a metal tends to increase the $OH^-$ neighboring to the metal surface, especially during electro-deposition in seawater. The increased pH at metal/seawater interface results in precipitation of brucite crystal structure-$Mg(OH)_2$ as following formula; $Mg^{2+}+2OH^-{\rightarrow}Mg(OH)_2$, that is typical mechanism of the main calcareous deposits-compound in electro deposited coating films. In this study, the effects of anode and current density on deposition rate, composition structure and morphology of the deposited films were systematically investigated by scanning electron microscopy(SEM) and x-ray diffraction(XRD), respectively in order to overcome the problems such as deposition rate and a weak adhesion between deposit film and metal surface. The adhesion and corrosion resistance of the coating films were also evaluated by anodic polarization test. The electro-deposited film formed by using AZ31-Mg anode had the most appropriate physical properties. Weight gain of electro-deposit films increased with increasing cathodic current. Electro-deposit prepared at $5A/cm^2$ current density shows better adhesion than that formed at $8{\sim}10A/cm^2$.

• 한국결정성장학회지
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• 제22권2호
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• pp.99-104
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• 2012

BCP(biphasic calcium phosphate) 분말을 제조하기 위하여 $Ca(NO_3)_2{\cdot}4H_2O$, $(NH_4)_2HPO_4$를 출발 물질로 공침법(co-precipitation process)을 이용하여 합성하였다. 합성된 분말의 열처리 전 후의 HAp(Hydroxyapatite)/${\beta}$-TCP(${\beta}$-Tricalcium phosphate) 결정상 비율 및 분광학적 특성을 XRD 및 FT-IR를 이용하여 분석하였다. BCP 분말의 생체활성 거동을 평가하기 위하여 Hanks' Balanced Salt Solution(HBSS)에 침적시켜 시간에 따라 형상, 이온농도의 변화 및 결정상을 분석한 결과 낮은 결정화도의 HAp가 생성됨을 확인하였다. BCP분말의 세포독성 평가에서도 대조군에 비하여 세포성장률이 우수함을 관찰하였다.

• Bulletin of the Korean Chemical Society
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• 제24권1호
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• pp.49-54
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• 2003

TiO₂nanoparticles were synthesized using the metallorganic chemical vapor deposition process. Particles with and without metal ion dopants were obtained. X-ray photoelectron and energy dispersive X-ray spectroscopic measurements confirmed the stoichiometry of the TiO₂nanoparticles. X-ray diffraction patterns showed a polycrystalline anatase structure of TiO₂. Transmission electron microscopy revealed that these particles are of nanoscale dimensions. Exact particle size and size distribution analyses were carried out by dynamic light scattering. The average particle size was determined to be 22 nm. The nanosize particles provided large surface area for photocatalysis and a large number of free surface-charge carriers, which are crucial for the enhancement of photocatalytic activity. To improve the photocatalytic activity, metal ions, including transition metal ions $(Pd^{2+},\;Pt^{4+},\;Fe^{3+})$ and lanthanide ion $(Nd^{3+})$ were added to pure TiO₂nanoparticles. The effects of dopants on photocatalytic kinetics were investigated by the degradation of 2-chlorophenol under an ultraviolet light source. The results showed that the TiO₂nanoparticles with the metal ion dopants have higher photocatalytic activity than undoped TiO₂. The $Nd^{3+}$ ion of these dopant metal ions showed the highest catalytic activity. The difference in the photocatalytic activity with different dopants is related to the different ionic radii of the dopants.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3761-3766
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• 2012

$Ag_2Se$-Graphene/$TiO_2$ composite was synthesized by a facile sonochemical method. The as-prepared products were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectrophotometer. During the reaction, both of the reduction of graphene oxide and loading of $Ag_2Se$ and $TiO_2$ particles were achieved. The as-prepared $Ag_2Se$-Graphene/$TiO_2$ composites possessed great adsorptivity of dyes, extended light absorption range, and efficient charge separation properties simultaneously. Hence, in the photodegradation of rhodamine B (Rh.B), a significant enhancement in the reaction rate was observed with $Ag_2Se$-Graphene/$TiO_2$ composites, compared to the pure $TiO_2$. The high activity can be attributed to the synergetic effects of high charge mobility, and red shift in absorption edge of $Ag_2Se$-Graphene/$TiO_2$ composites.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제5권1호
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• pp.22-28
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• 2002

A New concept for the LNG-FPSO ship, with moonpool and bilge step in bottom, is proposed. This concept is investigated with regard to motion reduction and sloshing phenomena of the cargo and operation tanks. The principal dimensions of the ship are $L\timesb B\times D\times t(design)=270.0\times51.0\times32.32\times13.7(m)$, with a total cargo capacity of 161KT; a 98% loading condition is considered for this study. The moonpools and rectangular step at the bilge have been designed for the purpose of decreasing the motion within the tank. For the motion analysis, linearized three-dimensional diffraction theory, with the simplified boundary condition was used. The six-degree of freedom coupled motion responses were calculated for the LNG-FPSO ship. Viscous effects on the roll motion responses of a vessel were taken into account in this calculation program, using an empirical formula suggested by Himeno(1981). The case study for the moonpool size has been conducted using theoretical estimation and the experimental method. For the optimization of the moonpool size and effect of the bilge step, 9 cases of its size, both with and without bilge step, were involved in the study. no motion responses, especially roll motion, for the designed LNG-FPSO ships are much lower than those of other drill ships and shuttle tankers. The limit criterions are satisfied. To check the cargo tank and operation tank sizes, we performed a sloshing analysis in the irregular waves which focuses on the pressure distribution on the tank wall and the time history of pressure and free surface for No.2 and 5 tanks of LNG-FPSO with chamfers. Finally, optimum tank sire was estimated.

• 한국세라믹학회지
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• 제36권1호
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• pp.21-29
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• 1999

흑연 기판에 탄화규소 전환층을 형성하는데 있어서 기판의 밀도와 기공 크기 분포의 영향이 조사되었다. 전환층형성을 위한 화학 반응은 기판의 표면 또는 표면 하부에서 SiO 기체의 침투를 통해 이루어졌다. 전환 공정 동안 기판 표면에서의 충분한 양의 SiO 기체 침투 및 연속적인 화학반응에 요구되는 기공크기 분포는 1.0~10.0$\mu\textrm{m}$ 범위인 것으로 추정되엇다. 유한요소법에 의한 탄화규소 층의 응력 해석에서는 열적 불일치에 기인하는 잔류응력 분포를 나타냈다. 그러나. X-선 회절에 의해 탄화규소 층에서는 압축응력이 측정되었으며, 탄화규소 층에서의 잔류응력 분포에 대해 SiC 층과 흑연 기판간의 interlayer의 constraining 효과, 전환층의 치밀화 거동 및 입자성장에 의해 주로 영향받는 것으로 추정되었다.

• 한국항만학회지
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• 제13권2호
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• pp.399-408
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• 1999

Copeland’s(1985) hyperbolic mild-slope equation including diffraction refraction and reflection in the wave field is used as a governing equation in this study. The result of Maruyama & Kajima(1985) is used to calculate wave direction and that of Watanabe & Maruyama(1986) is used as a energy dissipation formula. Numerical solutions are obtained by the Leap-Frog scheme and compared with Watanabe & Maruyama’s (1984) hydraulic experimental results and numerical simulation results for the detached breakwater. This wave model is applied to a detached breakwater and compared with Watanabe and Maruyama’s (1984) hydraulic model results to check the characteristics of reflected wave field around a detached breakwater. The distribution of wave height and we phase in front of a detached breakwater is more accurate than the Watanabe and Maruyama’s numerical results. The results from our wave model show good agreements with the others and also show nonlinear effects around the detached breakwater. This model is applied to the Gamcheon harbor of pusan. the field observations were carried out at Pusan harbor wave station in 1986-1995 and the results were accepted as a design wave condition in this study. The wave height and wave period was measured by Dong-A university at one station in the Gamcheon harbor in 1996-1997 and used as a calibration criterion. The measured data were used as input data for the numerical simulation and also compared with simulated results. The numerical simulation shows a fairly good results which considering the effect of topographic characteristics and effect of narrow entrance due to two separated breakwaters in Gamcheon harbor. The wave distribution characteristics inside Gamcheon harbor is quite different with the offshore wave direction and wave period.

• 한국전기전자재료학회논문지
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• 제29권12호
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• pp.764-768
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• 2016

To investigate excess $Na^+$ effect, $Bi_{0.5}(Na_{0.78+x}K_{0.22})_{0.5}TiO_3$ ($0{\leq}x{\leq}0.05$) (BNKT) ceramics were prepared by using a conventional solid-state reaction method. The structure and ferroelectric properties of BNKT ceramics were characterized by XRD (X-ray diffraction) and polarization dependence by external electric field. Also, the temperature dependence of dielectric constant and loss were studied. From these results, it was found that appropriate excess $Na^+$ into BNKT ceramics compensate the volatility and induce dense ceramics. The enhanced piezoelectric coefficient (158 pC/N) and depolarization temperature ($202^{\circ}C$) were obtained for the x=0.01 composition.

• 한국전기전자재료학회논문지
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• 제31권7호
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• pp.502-509
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• 2018

Epitaxial ZnO nanowires (NWs) were synthesized on sapphire (001) substrates using a hydrothermal process. The effects of the pH value of the precursor solution on the structural and optical properties of the resulting NWs was studied. The epitaxial relationship and the domain matching configuration between the sapphire (001) substrate and the as-grown ZnO NWs were determined using synchrotron X-ray diffraction measurements. The (002) plane of $w{\ddot{u}}rtzite$ ZnO NW grows in the surface normal direction parallel to the sapphire (001) direction. However, three types of in-plane domain matching configurations were observed, such as the on-position, $30^{\circ}$-rotated position, and ${\pm}8.5^{\circ}$-rotated position relative to the on-position, which might be attributed to inheriting the in-plane domain configuration of the ZnO seed layer.