• Journal of Powder Materials
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• v.26 no.1
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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.

• Journal of Powder Materials
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• v.9 no.4
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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.

• Journal of the Korean Magnetics Society
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• v.10 no.6
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• pp.291-296
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• 2000

The manufacturing method of permalloy soft magnet with the Ni contents of 46.6 and 47.2 wt% was investigated by powder injection molding technology. The magnetic properties of permalloy were greatly affected on the residual carbon and oxygen content of the sintered magnet. Solvent extraction and thermal debinding process to minimize the residual carbon content in sintered magnet were developed by controlling the debinding atmosphere. The residual carbon content depends on the debinding condition of the binder system for powder injection molding and the residual oxygen content on the sintering atmosphere. The sintered magnet produced by powder injection molding process had a 50 ppm. residual carbon, 150 ppm. residual oxygen. The coercivity and maximum relative permeability of permalloy soft magnet were 0.46 Oe and 14,600 respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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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.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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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.

• Journal of Food Hygiene and Safety
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• v.20 no.2
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• pp.114-117
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• 2005

Although the removal efficiency of residual pesticides using tap water were ranged from -1.25 to $13.27\%$, the removal efficiencies of residual pesticides using both powder CaO and liquid CaO were $5.16\~l7.61,\;8.7\~41.59\%$, respectively. And those results showed much higher residual effect of the CaO washing than tap water washing. Natural CaO made by burning of scallop-shell considered to be a good reducing agent for pesticides. Furthermore, liquid CaO showed much higher removal efficiency than powder CaO. However, powder CaO also can be used as a good natural eliminator of pesticides in Mini-Tomato.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.9
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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.

• Journal of Powder Materials
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• v.1 no.1
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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.

• Transactions of Materials Processing
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• v.31 no.3
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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.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1997.10a
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• pp.32-33
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• 1997