• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2005년도 추계학술대회 논문집
• /
• pp.247-250
• /
• 2005

The need for improved fuel efficiency, weight reduction has motivated the automotive industry to focus on aluminum alloys as a replacement for steel-based alloy. To cope with the needs for high structural rigidity with low weight, it is forecasted that substantial amount of cast components will be replaced by tubular parts which are mainly manufactured by the extruded aluminum tubes. The extrusion process is utilized to produce tubes and hollow sections. Because there is no weld seam, the circumferential mechanical properties may be uniform and advantageous for hydroforming. However the possibility of the occurrence of a surface defect is very high, especially due to the temperature increase from forming at high pressure when it comes out of the bearing and the roughness of the bearing, which cause the surface defects such as the dies line and pick-up. And when forming a extruded aluminum tube, the free surface of the tube becomes rough with increasing plastic strain. This is well known as orange peel phenomena and has a great effect not only on the surface quality of a product but also on the forming limit. In an attempt to increase the forming limit of the tubular specimen, in the present paper, surface asperities generated during the hydroforming process are polished to eliminate the weak positions of the tube which lead to a localized necking. It is shown that the forming limit of the tube can be considerably improved by simple method of polishing the surface roughness during hydroforming. And also the extent of the crack propagation caused by dies lines generated during the extrusion process is evaluated according to the deformed shape of the tube.

• Journal of Welding and Joining
• /
• 제2권1호
• /
• pp.4-17
• /
• 1984

Overlaid weld metals of austenitic stainless steel in a pressure vessel of power reactor are usually post-weld heated for a long period of time after welding. The PWHT is considered as a kind of sensitizing and it is important to check the soundness of the weld metal after PWHT, especially about the precipitation of carbides. The purpose of this report is to obtain information on the relation between the change of microstructure and Post-Weld Heat Treatment in the overlaid weld metals. Metallurgical aspects of the problem on austenitic stainless steel heated at $625^{\circ}C$, $670^{\circ}C$, $720^{\circ}C$ and $760^{\circ}C$ for 3, 10, 30, 100 and 300 hours have been investigated by means of optical-micrography, micro-hardness measurement, scanning electron microscope and electron-probe micro analysis. From the results obtained, the following conclusions are drawn; 1) The PWHT above $625^{\circ}C$ for a long time causes a diffusion of carbon atoms from low alloy steel into stainless steel, and consequently carbon is highly concentrated at the boundary layer of stainless steel. 2) C in ferritic steel migrated to austenitic steel and carbides precipitated in austenitic steel along fusion line. At higher temperatures, the ferrite grains coarsened in the decarburized zone. 3) In the change of microstructure of stainless steel overlaid weld metal, the width of carbides precipitated zone and decarburized zone increased with increase of PWHT temperature and time. 4) At about $625^{\circ}C$ to $760^{\circ}C$, chromium carbides, mainly $M_{23} C_6$, precipitate very closely in the carburized layer with remarkable hardening. 5) Precipitation of delta ferrite from molten weld metal depends on solidification phenomenon. There was a small of ferrite near the bond in which the local solidification time was short, comparing with after parts of weld metal. Shape and amount of ferrite were not changed by Post-Weld Heat Treatment after solidification.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
• /
• pp.254-254
• /
• 2011

The memories with nano-particles are very attractive because they are promising candidates for low operating voltage, long retention time and fast program/erase speed. In recent, various nano-floating gate memories with metal-oxide nanocrystals embedded in organic and inorganic layers have been reported. Because of the carrier generation in semiconductor, induced photon pulse enhanced the program/erase speed of memory device. We studied photo-induced electrical properties of these metal-oxide nanocrystal memory devices. At first, 2~10-nm-thick Sn and In metals were deposited by using thermal evaporation onto Si wafer including a channel with $n^+$ poly-Si source/drain in which the length and width are 10 ${\mu}m$ each. Then, a poly-amic-acid (PAA) was spin coated on the deposited Sn film. The PAA precursor used in this study was prepared by dissolving biphenyl-tetracarboxylic dianhydride-phenylene diamine (BPDA-PDA) commercial polyamic acid in N-methyl-2-pyrrolidon (NMP). Then the samples were cured at 400$^{\circ}C$ for 1 hour in N atmosphere after drying at 135$^{\circ}C$ for 30 min through rapid thermal annealing. The deposition of aluminum layer with thickness of 200 nm was followed by using a thermal evaporator, and then the gate electrode was defined by photolithography and etching. The electrical properties were measured at room temperature using an HP4156a precision semiconductor parameter analyzer and an Agilent 81101A pulse generator. Also, the optical pulse for the study on photo-induced electrical properties was applied by Xeon lamp light source and a monochromator system.

• 한국버섯학회지
• /
• 제12권1호
• /
• pp.24-28
• /
• 2014

표고버섯균의 균사생육에 적합한 배지로는 PDA 배지, MYA 배지로 조사되었으며 배양환경 조사로 균사생육에 적합한 온도는 $25^{\circ}C$를 나타났다. 영양원 선발 결과 탄소원은 2%의 농도에서 Malt extract를 사용하였을 때 균사생장 및 밀도가 높게 나타났다. 질소원은 0.2%의 농도에서 Yeast extract를 사용하였을 때 균사생장 및 밀도가 높게 나타났다. 표고버섯(산조701호)의 수종별 추출액 배지를 이용한 결과, 신갈나무, 굴참나무, 상수리나무, 밤나무에서는 PDA(대조구)와 같이 생장이 우수하였다. 배양기간에 따른 버섯 생산성을 조사 해본 결과, 배양 110일에서 120일에서 우수한 수확량을 보였다. 재배수종에 따른 생산성은 굴참나무에서 가장 좋은 결과를 보였다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
• /
• pp.211-211
• /
• 2012

The electrical loss of the photo-generated carriers is dominated by the recombination at the metal- semiconductor interface. In order to enhance the performance of the solar cells, many studies have been performed on the surface treatment with passivation layer like SiN, SiO2, Al2O3, and a-Si:H. In this work, Al2O3 thin films were investigated to reduce recombination at surface. The Al2O3 thin films have two advantages, such as good passivation properties and back surface field (BSF) effect at rear surface. It is usually deposited by atomic layer deposition (ALD) technique. However, ALD process is a very expensive process and it has rather low deposition rate. In this study, the ICP-assisted reactive magnetron sputtering method was used to deposit Al2O3 thin films. For optimization of the properties of the Al2O3 thin film, various fabrication conditions were controlled, such as ICP RF power, substrate bias voltage and deposition temperature, and argon to oxygen ratio. Chemical states and atomic concentration ratio were analyzed by x-ray photoelectron spectroscopy (XPS). In order to investigate the electrical properties, Al/(Al2O3 or SiO2,/Al2O3)/Si (MIS) devices were fabricated and characterized using the C-V measurement technique (HP 4284A). The detailed characteristics of the Al2O3 passivation thin films manufactured by ICP-assisted reactive magnetron sputtering technique will be shown and discussed.

• 한국재료학회지
• /
• 제22권5호
• /
• pp.237-242
• /
• 2012

We report on the NO gas sensing properties of Al-doped zinc oxide-carbon nanotube (ZnO-CNT) wire-like layered composites fabricated by coaxially coating Al-doped ZnO thin films on randomly oriented single-walled carbon nanotubes. We were able to wrap thin ZnO layers around the CNTs using the pulsed laser deposition method, forming wire-like nanostructures of ZnO-CNT. Microstructural observations revealed an ultrathin wire-like structure with a diameter of several tens of nm. Gas sensors based on ZnO-CNT wire-like layered composites were found to exhibit a novel sensing capability that originated from the genuine characteristics of the composites. Specifically, it was observed by measured gas sensing characteristics that the gas sensors based on ZnO-CNT layered composites showed a very high sensitivity of above 1,500% for NO gas in dry air at an optimal operating temperature of $200^{\circ}C$; the sensors also showed a low NO gas detection limit at a sub-ppm level in dry air. The enhanced gas sensing properties of the ZnO-CNT wire-like layered composites are ascribed to a catalytic effect of Al elements on the surface reaction and an increase in the effective surface reaction area of the active ZnO layer due to the coating of CNT templates with a higher surface-to-volume ratio structure. These results suggest that ZnO-CNT composites made of ultrathin Al-doped ZnO layers uniformly coated around carbon nanotubes can be promising materials for use in practical high-performance NO gas sensors.

• 한국의류학회지
• /
• 제35권2호
• /
• pp.218-229
• /
• 2011

Dyeing properties of cotton and ramie fabrics with pine needles colorants were studied by investigating the analysis of pine needles colorants, the effect of dyeing conditions (such as dye concentration, dyeing temperatures and times on dye uptakes), effect of mordants, and color change. The various colorfastness of dyed fabrics were evaluated for practical use; in addition, the antimicrobial ability, ultraviolet-cut ability, and deodorant ability were estimated. In the UV-Visible spectrum, the wavelength of the maximum absorption for pine needles extract was 285nm, and pine needles colorants produced a yellow color. From FT-IR and GC-MS results, it was assumed that chromophoric substance from pine needles extracts were mixed with flavonol tannin and flavanol tannin. An increased dyeing concentration resulted in a larger dye uptake and a Freundlich absorption isotherm was obtained. A larger dye uptake occurred as the dyeing time and temperature increased. Post-mordanting was more effective than pre-mordanting and the dye uptake of fabrics improved by mordanting. The colorfastness of dyed fabrics showed a low rating; however, colorfastness to washing and dry cleaning of cotton fabrics mordanted with N.Cu, and friction fastness of ramie fabric mordanted with Cu improved. The dyed fabrics showed very good antimicrobial abilities of 99.9%. In addition, the ultraviolet-cut ability and deodorant ability improved in fabrics dyed with pine needles extracts.

• 한국의류학회지
• /
• 제35권2호
• /
• pp.206-217
• /
• 2011

The dyeing properties of cotton fabrics with bamboo colorants were studied by investigating the analysis of bamboo colorants, the effect of dyeing conditions (dye concentrations, dyeing temperatures and times on dye uptakes), effect of mordants, and color change. The various colorfastness of dyed fabrics were evaluated for practical use; in addition, the antimicrobial ability, ultraviolet-cut ability, and deodorant ability were also estimated. In the UV-Visible spectrum, the wavelength of the maximum absorption for bamboo stems and leaves extracts was found to be 280nm and 295nm, respectively; in addition, bamboo colorants produced a yellow color. From the FT-IR and GC-MS results, it was assumed that the chromophoric substance from bamboo extracts was composed of flavones substances with tricin. An increased dyeing concentration resulted in a larger dye uptake and a Freundlich absorption isotherm was obtained. A larger dye uptake occurred as the dyeing time and temperature increased. The post-mordanting was more effective than pre-mordanting. Mordants, Fe and N.Fe, were effective for an increased dye uptake. The color of fabrics mordanted with Cu and N.Cu changed to GY. Regardless of mordanting, the colorfastness on the washing of dyed fabrics showed a low rating compared to other fastness. Mordanting adversely affected the lightfastness of dyed fabric. The dyed fabric showed very good antimicrobial abilities of 99.9%. In addition, the ultraviolet-cut ability and deodorant ability improved in cotton fabric dyed with bamboo extracts.

• Korean Chemical Engineering Research
• /
• 제50권1호
• /
• pp.83-87
• /
• 2012

활성탄소섬유를 사용하여 염소소독 후 수돗물 내에 부산물로 존재하는 4종 트리할로메탄을 제거하였다. THMs의 종류별 농도 및 용액의 온도를 달리하면서 흡착실험을 수행하고 활성탄소섬유의 표면특성에 따른 흡착능력과 흡착메카니즘을 살펴본 결과, 4종의 THMs은 모두 Langmuir 타입의 흡착등온곡선을 보이면서 매우 신속하게 활성탄소섬유에 흡착되었다. THMs의 흡착은 활성탄소섬유의 표면에 균일하게 발달된 미세공의 입구에 물리적 및 화학적 수소결합으로 이루어졌다고 판단된다. Langmuir 타입은 특히 저농도 오염원 일때 제거효율이 높기 때문에 수돗물 내에 약 $30{\mu}g/L$ 수준으로 존재하는 THMs의 제거에는 활성탄소섬유가 매우 효과적임을 알 수 있다. 4종 THMs 종류별 흡착량은 큰 차이는 없으나 chloroform, bromodichloromethane, dibromochloromethane, 및 bromoform 의 순서로 증가하였다. 이는 brom 원자수의 증가와 일치하며 극성의 감소로 용해도가 낮아짐에 따라 흡착량이 증가한 것이다.

• 한국전기전자재료학회논문지
• /
• 제18권11호
• /
• pp.1043-1047
• /
• 2005

To investigate the electrical properties of the ZnO films which are interested in the next generation of short wavelength LEDs and Lasers, our ZnO thin films were deposited by RF sputtering system. At sputtering process of ZnO thin films, substrate temperature, work pressure respectively is $300^{\circ}C$ and 5.2 mTorr, and the purity of target is ZnO 5N. The thickness of ZnO thin films was about $2.1\;{\mu}m$ at SEM analysis after sputtering process. Phosphorus (P) and arsenic (As) were diffused into the undoped ZnO thin films sputtered by RF magnetron sputtering system in ampoule tube which was below $5\times10^{-7}$ Torr. The dopant sources of phosphorus and arsenic were $Zn_3P_2$ and $ZnAs_2$. Those diffusion was perform at 500, 600, and $700^{\circ}C$ during 3 hr. We found the diffusion condition of the conductive ZnO films which had n- and p-type properties. Our ZnO thin film has not only very high carrier concentration of above $10^{17}/cm^3$ but also low resistivity of below $2.0\times10^{-2}\;{\Omega}cm$.