• Composites Research
• /
• v.28 no.3
• /
• pp.81-88
• /
• 2015

In this paper, we evaluate structural integrity of the wearable robot by using finite element analysis, which is made of CFRP(Carbon Fiber Reinforced Plastic) composite materials to be lightened. On the basis of the ASTM(American Standard Test Method), mechanical tests of the material are carried out in tensile, compressive and shear test for analytical evaluation. With the tested composite material, the main frame and two femoral frames of the robot is redesigned to satisfy the lightening design requirements. It is verified with the structural analysis that the redesigned frames are good for the part of the wearable robot.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.37 no.4
• /
• pp.25-30
• /
• 2000

Ion mass doping method has been implemented for the fabrication of large area electronic devices such as TFT-LCD. In this work, the effect of ion mass doping on the velocity and the behavior of MILC was investigated. When amorphous silicon was either doped or bombarded by accelerated ions, MILC velocity was reduced by over 50% and the front edge of MILC became coarse. In order to analyze the dependence of silicon film's properties on ion mass doping, ultraviolet reflectance and sulfate roughness were investigated. Both the velocity and the behavior of MILC were found to be related with the increase of surface roughness by ion bombardment.

• Journal of the Korean Chemical Society
• /
• v.15 no.4
• /
• pp.191-197
• /
• 1971

Ruthenium content in highly purified palladium metal (99.9%) was determined by counting $^{105}Rh$ nuclide which was produced by $^{104}Ru(n,{\gamma};{\beta}^-)^{105}Rh$ nuclear reaction. Palladium sample and ruthenium standard were irradiated by neutron with the Pneumatic Transfer System of TRIGA MARK II reactor. Palladium and ruthenium were dissolved by treating with aqua-regia and by fusing with sodium peroxide flux respectively. $^{105}Rh$ was separated through anion and cation exchange resin columns. The ruthenium content was determined by comparing the $^{105}Rh$ activities, obtained from the palladium sample, with that from pure ruthenium standard. The detection limit of ruthenium by the present method is about 1 ppm of ruthenium in 10 mg of palladium, which is approximately 40 times more sensitive than that of the conventional radioactivation method which employs $^{102}Ru(n,{\gamma})^{103}Ru$ nuclear reaction.

• Membrane Journal
• /
• v.29 no.6
• /
• pp.299-307
• /
• 2019

Photocatalysis is an environment friendly technique for degrading organic dyes in water. Tungsten oxide is becoming an active area of research in photocatalysis nanomaterials for having a smaller bandgap than the previously favored titanium dioxide. Synthesis of hierarchical structures, doping platinum (Pt), coupling with nanocomposites or other semiconductors are investigated as valid methods of improving the photocatalytic degradation efficiency. These impact the reaction by creating a redshift in the wavelength of light used, effecting charge transfer, and the formation/recombination of electron-hole pairs. Each of the methods mentioned above are investigated in terms of synthesis and photocatalytic efficiency, with the simplest being modification on the morphology of tungsten oxide, since it does not need synthesis of other materials, and the most efficient in photocatalytic degradation being complex coupling of metal oxides and carbon composites. The photocatalysis technology can be incorporated with water purification membrane by modularization process and applied to advanced water treatment system.

• Composites Research
• /
• v.33 no.1
• /
• pp.19-24
• /
• 2020

In this paper, the microwave irradiation process was conducted during the Poly(vinylidene fluoride) (PVDF) nano-composite film fabrication process to analyze how the β-crystalline is increased. TiO₂ was added as a nanoparticle reinforcement to further improve the β-crystalline conformation of the PVDF films by van der Waals force due to the difference of electronegativity between PVDF and the metal oxide nanoparticle. The crystalline conformation of the fabricated films was analyzed by X-ray diffraction and Fourier transform infrared spectroscopy. According to these analysis results, it was confirmed that the microwave irradiation process during the solvent evaporation process increases the crystallinity of the PVDF films, and more β-crystalline can be obtained after additional film stretching process. It was also found that the PVDF nano-composite films with the metal oxide have relatively higher β-crystalline conformation rather than the neat PVDF films.

• Journal of Korea Technology Innovation Society
• /
• v.16 no.2
• /
• pp.391-407
• /
• 2013

The paper tests the embodiment hypothesis by measuring the technological obsolescence of a specific year (1990)'s technology and investigating the relationship between labor productivity and technological obsolescence. This approach is based on Salter (1969) that emphasizes the economic aspect of technology. We use the rate of economic surplus as the proxy of technological obsolescence for 10 main industries, including food processing, textiles, chemicals, non-steel metals, steels, metal products, machinery, electronics, precision machinery, and transportation equipments. The result shows that the embodiment hypothesis is not accepted for the overall manufacturing sector. However, we found the vintage effect - a positive relationship between technological obsolescence and labor productivity over time - in textiles, chemicals, non-steel metals, metal products, electronics, and transportation equipments. Therefore, the government should support R&D investment as well as capital equipments investment for the industries with large vintage effect.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.116-116
• /
• 2009

마그네슘 합금은 구조용으로 사용 가능한 금속 재료 중 가장 가벼운 소재이며, 동시에 비강도 및 비강성과 같은 기계적 특성이 우수하여 알루미늄 합금의 뒤를 이을 차세대 경량 재료로써 주목을 받고 있다. 더욱이 석유자원의 대부분을 소비하고 있는 운송기기 분야에서는 경량화를 통한 연비향상과 배출가스 저감이 가장 큰 과제이며, 이 문제를 해결하기 위한 노력의 일환으로 최경량 소재인 마그네슘 합금의 사용량은 더욱 증가할 것으로 기대된다. 한편 기존의 마그네슘 합금 관련 연구는 새로운 합금의 개발에 치우쳐 있었으며, 상대적으로 이들 합금을 활용하기 위한 가공기술, 특히 용접에 대한 연구는 아직까지 많이 부족한 실정이다. 이는 철강재와 비교하여 마그네슘 합금의 고유물성이 용접의 관점에서는 상당히 열악하기 때문으로, 마그네슘은 융점 및 비점은 낮은 반면, 증기압과 열전도율은 높고 표면장력 및 점성은 낮은 특성을 가지고 있다. 그러므로 타 공법에 비해 상대적으로 입열이 적고 고속용접이 가능한 레이저의 적용이 최적으로 판단된다. 따라서 본 연구에서는 Nd:YAG 레이저를 사용하여 압연판재로 상용화되어 있는 AZ31B 마그네슘 합금의 맞대기 용접성을 조사하였으며, 용접부의 미세조직과 용접조건에 따른 용접부의 기계적 특성을 비교 및 검토하였다. 용접부의 기계적 특성은 인장 및 경도시험을 통해 평가하였다. 그 결과 레이저 출력 1.2kW를 적용한 경우에 안정적인 강도를 얻을 수 있었으며 레이저 출력 1.5kW, 용접속도 80mm/sec의 조건에서 모재 인장강도 대비 103% 그리고 연신율 대비 47.1%의 최적의 결과가 얻어졌다. 또한 용접부의 경도는 모재와 동등하거나 다소 높은 수준이었다. 이는 용접시 용접부내 잔류하는 알루미늄에 의한 고용 강화 효과와 금속간화합물의 석출 빈도 증가, 그리고 레이저 용접의 특징인 급열급랭 공정에 기인한 결정립 미세화의 영향 때문으로 사료된다. 한편 용접부 미세조직을 관찰한 결과, 열영향부의 존재는 두드러지지 않았으며 용융경계부에서는 주상정이, 그리고 용접부 가운데에서는 등축정이 관찰되었다.

• Journal of Hydrogen and New Energy
• /
• v.20 no.6
• /
• pp.505-511
• /
• 2009

The hydriding and electrochemical characteristics of Zr-based $AB_2$ alloy produced by gas atomization have been extensively examined. For the particle morphology of the as-cast and gas-atomized powders, it can be seen that the mechanically crushed powders are irregular, while the atomized powder particles are spherical. The increase of jet pressure of gas atomization process results in the decrease of hydrogen storage capacity and the slope of plateau pressure significantly increases. TEM and EDS studies showed the increase of jet pressure in the atomization process accelerated the phase separation within grain of the gas-atomized alloy, which brought about a poor hydrogenation property. However, the gas-atomized $AB_2$ alloy powders produced by jet pressure of 50 bar kept up the reversible $H_2$ storage capacity and discharge capacity similar to the mechanically crushed particles. In addition, the electrode of gas-atomized Zr-based $AB_2$ alloy of 50 bar showed improved cyclic stability over that of the cast and crushed particulate, which is attributed to the restriction of crack propagation by grain boundary and dislocation with ch/discharging cycling.

• Journal of Radiation Protection and Research
• /
• v.17 no.1
• /
• pp.1-10
• /
• 1992

A number of investigators have reported the formation of the radiolytic ultrafine particles produced by the interaction of ionizing radiation with water vapor. Previous studies have suggested that a very high localized concentration of the OH radical produced by the radiolysis of water can react with trace gas like organic vapors and produce lower vapor pressure compounds that can then nucleate. In order to determine water vapor dependence of the active, positively charged, first radon daughter(Po-218), an experiment was conducted using a well-controlled radon chamber. The activity size distribution of the radon daughter in the range of 0.5-100nm was measured using the parallel graded wire screens system. Measurements were taken for different relative humidity. The resultant activity size distributions were analyzed. The addition of water vapor to the radon carrier gases resulted in the formation of ultrafine particles by OH radicals formed by radon radiolysis. It may be due to the neutralization of charged Po-218 ion with water vapor through the radio lysis.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2009.05a
• /
• pp.49.1-49.1
• /
• 2009

최근 손상된 생체조직의 재생 또는 대체를 위하여 다공성의 지지체(scaffold)를 이용하는 연구가 활발히 이루어져 왔다. 지지체 재료는 조직 재생을 목적으로 하는 경우에는 생분해성 고분자, 생흡수성 세라믹스 또는 이들의 복합재료가 사용되고, 조직 대체를 목적으로 하는 경우에는 금속 또는 세라믹스 재료가 단독으로 사용된다. 현재 경조직 대체를 위한 임플란트 재료로 사용되고 있는 금속재료 중 대부분이 타이타늄 또는 타이타늄 합금이다. 타이타늄은 비강도, 내식성이 우수하며, 생체 내 환경에서 부동태피막 재생 속도가 빠르고, 섬유상 결체조직 형성 두께가 얇아 생체의료용 소재로서 각광을 받고 있다. 다공성 타이타늄은 기존 타이타늄 소재의 장점에 다공체의 구조적인 특성을 부가하여 하중을 받는 골 결손부에 사용될 경우 뼈와의 탄성계수 차이에서 기인하는 응력차폐(stress shielding) 효과를 최소화할 수 있고, 다공체 내부로 골조직 성장을 유도할 수 있어 지지체와 골조직이 일체화되는 골융합 효과의 극대화를 기대할 수 있다. 본 연구에서는 기공 구조를 다양하게 제어할 수 있고, 3차원적 연결 기공구조를 만들 수 있는 적층조형(layer manufacturing) 기술을 이용하여 3차원 다공성 타이타늄 지지체를 제조하였으며, 이에 대한 세포독성, 조골세포 증식능 등 in vitro 생체적합성을 평가하고, Rat model 을 이용한 in vivo 생체적합성을 평가하였다. 또한 지지체의 골조직 재생 유도성의 증대를 위한 생체활성처리 영향도 분석 평가하였다.