• 한국레이저가공학회지
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• 제4권3호
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• pp.30-39
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• 2001

This work was tamed out to apply a laser welding technique in joining between a Zn coated low carbon steel plate(SECC) and a free cutting carbon steel shaft(SUM24L) with or without W coating. Experiments were carried out and analysed by applying the FD(factorial design)method to obtain the optimum Laser welding condition. Optical microscopy, SEM, TEM and XRD analyses were performed in order to observe the microstructures in the fusion zone and the HAZ. Mechanical properties of the welded specimens were examined by microhardness test, tensile test and twist test. There was no flawed Zn in the fusion zone by EDS analysis. This means that during the welding process, Zn gas could be eliminated by appropriate shielding gas flow rate and butt welding gap. Ni coating itself did not influence on the tensile strength and hardness. However, twist bending strength and the weld depth of the Ni-coated free cutting carbon steel were lower as compared with those of the uncoated free cutting carbon steel. It was attributed to a lower absorbance of laser beam to the shin Ni surface. According to the results of the factorial design tests, the twist bending strength of welded specimens was primarily affected by pulse width, laser power, frequency and speed.

• Bulletin of the Korean Chemical Society
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• 제34권4호
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• pp.1188-1194
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• 2013

Transparent $TiO_2$ thin films have been prepared by sol-gel spin coating method. The sols used for deposition of thin films were prepared with different ethanol content. The effect of ethanol (solvent) concentration and annealing temperature on the performance of $TiO_2$ thin film solar cells has been studied. The results indicate that the as deposited films are amorphous in nature. $TiO_2$ thin films annealed at temperatures above $350^{\circ}C$ exhibited crystalline nature with anatase phase. The results also indicated that the crystallinity of the films improved with increase of annealing temperature. The high resolution transmission electron microscope images showed lattice fringes corresponding to the anatase phase of $TiO_2$. The band gap of the deposited films has been found to decrease with increase in annealing temperature and increase with increase in ethanol concentration. The dependents of photovoltaic efficiency of the dye-sensitized $TiO_2$ thin film solar cells (DSSCs) with the amount of ethanol used to prepare thin films was determined from photocurrent-voltage curves.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 C
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• pp.1454-1456
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• 1994

$Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramic thin films were fabricated from an alkoxide-based solution by Sol-Gel method. $Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramic thin films were formed by spin coating method on $Pt/SiO_2/Si$ substrate at 3000rpm for 30 seconds. The coating process was repeated 6 times and then heat-treated at temperature between 500 - $800[^{\circ}C]$ for 1 hour. The final thickness of the thin films were about 4800[A]. The 100% ferroelectric perovskite phases precipitated under the heat treated at $700[^{\circ}C]$ for 1 hour. $Pb(Zr_{0.52}Ti_{0.48})O_3$ thin films heat-treated at $700[^{\circ}C]$ for 1 hour showed good dielectric constant (812) property.

• 한국분말재료학회지
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• 제19권3호
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• pp.177-181
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• 2012

Copper composite materials have attracted wide attention for energy applications. Especially $CuInS_2$ has a desirable direct band gap of 1.5 eV, which is well matched with the solar spectrum. $CuInS_2$ nanoparticles could make it possible to develop color-tunable $CuInS_2$ nanoparticle emitter in the near-infrared region (NIR) for energy application and bio imaging sensors. In this paper, $CuInS_2$ nanoparticles were successfully synthesized by thermo-decomposition methods. Surface modification of $CuInS_2$ nanoparticles were carried out with various semiconductor materials (CdS, ZnS) for enhanced optical properties. Surface modification and silica coating of hydrophobic nanoparticles could be dispersed in polar solvent for potential applications. Their optical properties were characterized by UV-vis spectroscopy and photoluminescence spectroscopy (PL). The structures of silica coated $CuInS_2$ were observed by transmission electron microscopy (TEM).

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기물성,응용부문
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• pp.123-124
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• 2006

The sandwiched PZT/$BaTiO_3$/PZT thick films were fabricated by two different methods thick films of the PZT by screen printing method on alumina substrateselectrodes with Pt, thin films of $BaTiO_3$ by the spin-coating method on the PZT thick films and once more thick films of the PZT by the screen printing method on the $BaTiO_3$ layer. The structural and the dielectric properties were investigated for effect of various stacking sequence of sol-gel prepared $BaTiO_3$ coating solution at interface of the PZT thick films, The insertion of BaTi03 interlayer yielded the PZT thick films with homogeneous and dense grain structure with the number of $BaTiO_3$ layers. The leakage current density of the $PZT/BaTiO_3-1$ film is less that $4.41{\times}10^{-9}A/cm^2$ at 5 V.

• Journal of Welding and Joining
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• 제34권4호
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• pp.55-61
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• 2016

During laser overlap welding of galvanized steel sheets, explosion of weld pool by the high pressure zinc vapor induces weld defects like porosity and blowhole. In this study, laser 2-pass welding was implemented to prevent the weld defects. Through the 1st pass welding, zinc layers on the faying surfaces were removed when proper heat input was applied. Excessive heat input could result in explosion even during the 1st pass welding and insufficient heat input could not remove enough region of zinc layer for the 2nd pass welding. Coating weights of $45g/m^2$ and $60g/m^2$ were considered and for both cases sound welds without weld defects could be achieved. In spite of 2-pass welding, softening of weld and heat affected zone was not observed and Zn coating was not diluted into the weld metal.

• Journal of Welding and Joining
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• 제34권4호
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• pp.40-47
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• 2016

The Zn coating on automotive galvanized steel sheets can improve corrosion resistance. However, the boiling temperature of Zn is lower than the melting temperature of steel and it causes well-known spatter and porosity problem. One of most prominent solutions is a pretreatment of Zn coating by an additional welding arc prior to the main welding process. In this research, GTA and GMA are selected as heat sources for pretreatment and main welding processes, respectively. The authors suggested three possible mechanisms to reduce weld defects by the GTA pretreatment: (1) Formation of gap between the sheets; (2) Evaporation of Zn layer; (3) Oxidation of Zn layer. Among them, Zn Oxidation is the most important mechanism to reduce weld defects in the GTA-GMA hybrid process.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1351-1355
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• 2018

The photocurrent characteristics of zinc-oxide (ZnO) thin-film transistors (TFTs) prepared using radio-frequency sputtering and spin-coating methods were investigated. Various characterization methods were used to compare the physical and the chemical properties of the sputtered and the spin-coated ZnO films. X-ray photoelectron spectroscopy was used to investigate the chemical composition and state of the ZnO films. The transmittance and the optical band gap were measured by using UV-vis spectrometry. The crystal structures of the prepared ZnO films were examined by using an X-ray diffractometer, and the surfaces of the films were investigated by using scanning electron microscopy. ZnO TFTs were prepared using both sputter and solution processes, both of which showed photocurrent characteristics when illuminated by light. The sputtered ZnO TFTs had a photoresponsivity of 3.08 mA/W under illumination with 405-nm light while the solution-processed ZnO TFTs had a photoresponsivity of 5.56 mA/W. This study provides useful information for the development of optoelectronics based on ZnO.

• Journal of Ceramic Processing Research
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• 제20권6호
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• pp.603-608
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• 2019

In this study, the multilayered thin films of (Ba,Sr)TiO3/K(Ta,Nb)O3 were fabricated by the sol-gel and spin coating methods, and their structural and electrical properties were investigated. The specimen showed polycrystalline X-ray diffraction (XRD) characteristics with a tetragonal structure. The average grain size and film thickness for one coating were about 30~40nm and 60nm, respectively. The phase transition temperature of specimen was lower than 10 ℃. The dielectric constant and loss at 20 ℃ of the specimen coated six times were 1,231 and 0.69, respectively. The rate of change in dielectric constant at an applied direct current (DC) voltage of the six times coated thin films was 17.3%/V. The electrocaloric effect was the highest around the temperature at which the remanent polarization rapidly changed. When an electric field of 660kV/cm was applied to the triply coated thin films, the highest electrocaloric property of 4.41 ℃ was observed.

• 멤브레인
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• 제26권3호
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• pp.205-211
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• 2016

새롭게 제조된 납석기반 세라믹 멤브레인의 기본성능을 관찰하였다. 실규모 하수처리 membrane bioreactor (MBR) 미생물 고농도 현탁액을(MLSS : 약 6 g/L) 처리하는 납석기반 멤브레인 파울링 현상을 서로 다른 공기 폭기량과 막 간격에 대해 관찰하였다. 공극크기가 약 $1.0{\mu}m$인 비코팅 납석기반 세라믹 멤브레인 지지체의 순수투과도의 경우 약 $1100L/m^2{\cdot}hr{\cdot}bar$로 측정되었으나 알루미나로 코팅된 납석기반 세라믹 멤브레인은 공극크기의 감소로($0.3{\mu}m$) 순수 투과도는 두 배가량 감소하였다. 실규모 MBR 미생물 현탁액을 적용한 침지식 여과실험에서 납석 기반 세라믹 멤브레인 지지체의 경우 투과플럭스 20 LMH에서 공기폭기량을 증가시켰을 때 파울링은 감소하였다. 그러나 공기폭기가 파울링에 미치는 영향은 막간 간격에 상당히 의존하였다. 일정한 공기폭기 유량에서 막간간격의 증가는 파울링을 감소시켰으나 막간 간격을 3.5에서 5.4 cm로 증가시켰을 때 파울링 속도는 오히려 증가하였다. 알루미나 용액으로 표면코팅된 납석기반 지지체의 경우 유사한 결과가 관찰되었으나 파울링 속도는 코팅층이 없는 지지체에 비해 상대적으로 낮았다. 표면코팅에 상관없이 납석기반 지지체와 멤브레인의 경우 거의 완벽한 SS 제거효율을 나타내었다. 또한 납석 지지체 알루미나 표면코팅은 PEG (분자량 8,000 kDa)을 적용하였을 시 멤브레인의 유기물 배제율을 향상시켰다.