• 한국분말재료학회지
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• 제26권1호
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• pp.11-15
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• 2019

In this study, a method to remove residual powder on a multi-layered graphene and a new approach to transfer multi-layered graphene at once are studied. A graphene one-step transfer (GOST) method is conducted to minimize the residual powder comparison with a layer-by-layer transfer. Furthermore, a residual powder removing process is investigated to remove residual powder at the top of a multi-layered graphene. After residual powder is removed, the sheet resistance of graphene is decreased from 393 to 340 Ohm/sq in a four-layered graphene. In addition, transmittance slightly increases after residual powder is removed from the top of the multi-layered graphene. Optical and atomic-force microscopy images are used to analyze the graphene surface, and the Ra value is reduced from 5.2 to 3.7 nm following residual powder removal. Therefore, GOST and residual powder removal resolve the limited application of graphene electrodes due to residual powder.

• 한국분말재료학회지
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• 제9권4호
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• pp.235-244
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• 2002

The effects of residual impurities on solid state sintering of the powder injection molded (PIMed) W-15wt%Cu nanocomposite powder were investigated. The W-Cu nanocomposite powder was produced by the mech-ano-chemical process consisting of high energy ball-milling and hydrogen reduction of W blue powder-cuO mixture. Solid state sintering of the powder compacts was conducted at $1050^{\circ}C$ for 2~10 h in hydrogen atmosphere. The den-sification of PIM specimen was slightly larger than that of PM(conventional PM specimen), being due to fast coalescence of aggregate in the PIM. The only difference between PIM and PM specimens was the amount of residual impurities. The carbon as a strong reduction agent effectively reduced residual W oxide in the PIM specimen. The $H_2O$ formed by $H_2$ reduction of oxide disintegrated W-Cu aggregates during removal process, on the contrary to this, micropore volume rapidly decreased due to coalescence of the disintegrated W-Cu aggregates during evolution of CO.It can be concluded that the higher densification was due to the earlier occurred Cu phase spreading that was induced by effective removal of residual oxides by carbon.

• 한국자기학회지
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• 제10권6호
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• pp.291-296
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• 2000

분말사출성형법에 의한 니켈 함량이 46.6, 47.2 wt%인 퍼말로이 소결체의 제조 방법을 조사하였다. 퍼말로이의 자기특성은 소결체의 잔류탄소 및 산소의 함량에 영향을 받는 것으로 알려져 있다. 본 연구에서는소결체내의 탄소의 함량을 최소화할 수 있는 용매추출과 열분해 방법을 개발하였는데 , 잔류탄소는 분말사출을 위한 결합제의 열분해 조건에 영향을 받으며, 잔류산소는 제조 공정중 소결 분위기에 좌우되는 것으로 밝혀졌다. 분말사출성형으로 제조된 퍼말로이 소결체의 잔류탄소의 함량은 50 ppm. 잔류찬소의 함량은 150 ppm.이었으며 그 자기특성은 보자력 0.46 Oe, 최대투자율14,600의 값을 가졌다.

• 대한기계학회논문집A
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• 제24권1호
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• pp.29-37
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• 2000

The effect of a ceramic ball inclusion on densification behavior of a metal powder compact was investigated under cold isostatic pressing, pressureless sintering and hot isostatic pressing. To simulate those processes, proper constitutive models were implemented into a finite element program (ABAQUS). Measured density distributions of metal powder compacts were also compared with finite element results and showed the same trend with simulated results. Residual stress distributions were calculated by finite element analysis to study the effect of ceramic ball inclusions with different thermal expansion coefficients. The higher residual stress was observed in a metal powder compact when the difference between thermal expansion coefficients for a ceramic ball and metal powder became larger. Samples produced by Wing showed more uniform density distributions and lower residual stresses compared to those by sintering after cold isostatic pressing. For various sizes of ceramic ball inclusions, densification and deformation of powder compacts were also studied during hot isostatic pressing.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.566-567
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• 2006

The characteristics of residual stresses occurring in PM steel based nickel (FLN2-4405) was investigated. The measurements of residual stresses were carried out by electrochemical layer removal technique. The values and distributions of residual stresses occurring in PM steel processed under various densities and heat treatment conditions were determined. In most of the experiments, tensile residual stresses were recorded in surface of samples. The residual stress distribution on the surface of the PM steels is affected by the heat treatment conditions and density. Maximum values of residual stresses on the surface were observed sinter hardened condition and $7.4\;g/cm^3$ density. Minimum level of recorded tensile residual stresses are150 MPa and its maximum level is 370 MPa.

• 한국식품위생안전성학회지
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• 제20권2호
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• pp.114-117
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• 2005

대표적 8개 유기인계 농약에 대한 tap water 세척의 제거효과인 $-1.25\~13.27\%$에 비해 powder CaO와 liquid CaO 세척은 각각 $5.16\~17.61,\;8.7\~41.59\%$로 매우 높은 농약제거 효과를 보였다. 조개껍질을 연소시켜 얻은 천연 CaO는 잔류농약 세척제로 사용하기에 적합하다고 사료되며,특히 액체가 가루에 비해 농약제거제로 더욱 효과적인 것으로 나타났다. 그러나 가루제품 역시 tap water로 세척 한 것에 비해서는 다소 높은 제거율을 보여 세척제로서의 사용이 가능한 것으로 판단된다. 이에 CaO등을 활용한 천연물 세척제가 조속히 실용화되어 국민의 안전한 식탁을 지키는데 활용되어야 할 것이다.

• 한국전기전자재료학회논문지
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• 제19권9호
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• pp.862-867
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• 2006

Bi-based nano-varistors and micro-varistors fabricated with each ZnO nano-powder and micro-powder were studied about characteristics on the surge capability in this study. ZnO nano-varistors were sintered in air at $1050^{\circ}C$ for 2 hr. The voltage-current and residual voltage properties of ZnO nano-varistor were compared with their of ZnO micrio-varistor. As a result of these properties, our ZnO nano-varistor has about 3 times at operating voltage as compared with conventional ZnO varistor fabricated with micro-powder and the residual voltage was 8.06 kV at nominal discharge current 101kA in the lighting impulse current test. And then the residual voltage rate 1.72 of our nano-varistor has had better performance than the 1.79 of micro-varistor because ZnO nano-varistor has shown much quick response property because of increasing effective cross-section area. Also, to analysis surge capability took thermal images for pyrexia temperature distribution with each of the varistors after operating varistors. Nano-varistor doesn't have shown local overheating and can confirm accurate temperature grade on the surface of its.

• 한국분말재료학회지
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• 제1권1호
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• pp.52-59
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• 1994

Since the coefficient of thermal expansion (CTE) of matrix phase is larger about 4 times than that of W particle in tungsten heavy alloy, the thermal stresses due to the CTE difference between the two phases are induced in the alloy during heating and cooling processes. In the present study, a series of W heavy alloy containing various W particle volumes of 0 to 90% is made to investigate the residual stress taking place during cooling process. The CTE and residual stress of the series of alloy are measured by dilatometer and X-ray diffractometer. The residual stress of W particle is in compressive stress irrespective of W particle vol% and tends to increase with decreasing W particle vol% while that of the matrix phase is in tensile stress. The measured residual stress of W particle is about a third of calculated thermal stress. The influence of W particle vol% on the residual stress of W heavy alloy is discussed in terms of the deformation behaviors of W particle and matrix phase.

• 소성∙가공
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• 제31권3호
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• pp.136-142
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• 2022

The purpose of this study was to investigate the effects of sample thickness and support structure on the residual stress of Hastelloy X superalloy samples fabricated by laser powder bed fusion (LPBF), which is an additive manufacturing process. The residual stresses of LPBF samples with different thicknesses and support structures were measured using X-ray diffraction. The results revealed that as the thickness of sample increased from 2.5 mm to 20 mm, its tensile residual stress gradually decreased from 443.5 MPa to 182.2 MPa. Additionally, the residual stress in the bottom region of sample was higher than that in the top region, and the residual stress difference in the bottom and top regions became more pronounced as the sample thickness decreased. The residual stress of LPBF sample also varied depending on the structure of support. The residual stress of sample decreased with increasing contract area between the sample and the support, because the larger contract area led to smaller temperature gradient throughout the sample.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1997년도 추계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.32-33
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• 1997