• Journal of Powder Materials
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• v.28 no.1
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• pp.25-30
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• 2021

The surface of silicon dummy wafers is contaminated with metallic impurities owing to the reaction with and adhesion of chemicals during the oxidation process. These metallic impurities negatively affect the device performance, reliability, and yield. To solve this problem, a wafer-cleaning process that removes metallic impurities is essential. RCA (Radio Corporation of America) cleaning is commonly used, but there are problems such as increased surface roughness and formation of metal hydroxides. Herein, we attempt to use a chelating agent (EDTA) to reduce the surface roughness, improve the stability of cleaning solutions, and prevent the re-adsorption of impurities. The bonding between the cleaning solution and metal powder is analyzed by referring to the Pourbaix diagram. The changes in the ionic conductivity, H2O2 decomposition behavior, and degree of dissolution are checked with a conductivity meter, and the changes in the absorbance and particle size before and after the reaction are confirmed by ultraviolet-visible spectroscopy (UV-vis) and dynamic light scattering (DLS) analyses. Thus, the addition of a chelating agent prevents the decomposition of H2O2 and improves the life of the silicon wafer cleaning solution, allowing it to react smoothly with metallic impurities.

• Journal of Powder Materials
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• v.10 no.5
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• pp.344-347
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• 2003

Pure tantalum powder has been produced by combining Na as a reducing agent, $K_2$TaF$_{7}$ as feed material, KCl and KF as a diluent in a stainless steel (SUS) bomb, using the method of metallothermic reduction. And we examined various types of after-treatment that affect the high purification of powder. A significant amount of impurities contained in recovered powder was removed in various conditions of acid washing. In particular, 20% (HCl + HNO$_3$) was effective in removing heavy metal impurities such as Fe, Cr and Ni, 8% H$_2$SO$_4$ + 8% $Al_2$(SO$_4$)$_3$ in removing fluorides such as K and F from non-reactive feed material, and 2% $H_2O$$_2$ + 1 % HF in removing oxides that formed during reaction. Significant amounts of oxygen and part of light metal impurities could be removed through deoxidation and heat treatment process. On the other hand, because it is difficult to remove completely heavy metal impurities such as Fe, Cr, and Ni through acid washing or heat treatment process if their contents are too high, it is considered desirable to inhibit these impurities from being mixed during the reduction process as much as possible.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.1
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• pp.49-58
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• 2013

A selected halogenated organic contaminant, monochlorophenol was successfully degraded by photocatalytic reaction in a circulating batch system. The photocatalytic degradation in most cases follows first-order kinetics. The photocatalytic reaction rate increased in the $TiO_2$ dosage range of 0.1 g/L to 0.4 g/L, then decreased with further increase of the dosage. Also the degradation rate increased over the range of the retention time from 0.49 min. to 0.94 min., then decreased with further increase of the retention time in the circulating batch reactor. The photocatalytic activity was enhanced by addition of metal impurities, platinum(Pt) and palladium(Pd) onto the photocatalysts. The photocatalytic degradation rate increased with the increase of Pt and Pd in the content range of 0 to 2wt %, then decreased with further increase of the metal contents. Therefore the metal loading to $TiO_2$ influence the degradation rate of a halogenated organic compound by acting as electron traps, consequently reducing the electron/positive hole pair recombination rate.

• Electrical & Electronic Materials
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• v.10 no.5
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• pp.447-452
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• 1997

Effects of metal impurities in insulation of distribution cables on electrical conduction of distribution cables was investigated. Samples of Al, Cu, Fe are fabricated as metallic impurities, and measured electrical conductivity in the voltage range of 0~10 KV. Temperature dependent effect of hysteresis curves and the relationship between forward and reverse current due to impurity content are discussed.

• Journal of Industrial Technology
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• v.41 no.1
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• pp.25-30
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• 2021

Hydride-dehydride process for efficient recycling of tantalum (Ta) is used for manufacturer of Ta powder. In case of metal powder, Impurities as like nitride, oxygen, hydrogen is decreased of physical properties. For manufacture of Ta powder, control of theses impurities is important. In this study, to decreased of impurities on Ta powder using HDH process optimize dehydride condition. Dehydration behavior of Ta is depended on temperature, time, and atmosphere. Phase transition of Ta hydride is analyzed by X-ray diffraction (XRD). Concentration of hydrogen is decreased with temperature increased. At high temperature, concentration of hydrogen in Ta is similar according to time increased. Size and morphology of powder is not observed after dehydride. Ta powder, which is less than 20 um, concentration of hydrogen under 800 ppm is obtain.

• Journal of Ceramic Processing Research
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• v.20 no.4
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• pp.388-394
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• 2019

In this study, high-purity single-walled carbon nanotubes (SWCNTs) were prepared by removing the unreacted metal constituents and amorphous carbon impurities using a post-annealing process. Unlike conventional thermal processing techniques, this technique involved different gas atmospheres for efficient removal of impurities. A heat treatment was conducted in the presence of chlorine, oxygen, and chlorine + oxygen gases. The nanotubes demonstrated the best characteristics, when the heat treatment was conducted in the presence of a mixture of chlorine and oxygen gases. The scanning electron microscopy, transmission electron microscopy, ultraviolet absorbance, and sheet resistance measurements showed that the heat treatment process efficiently removed the unreacted metal and amorphous carbon impurities from the as-synthesized SWCNTs. The high-purity SWCNTs exhibited improved electrical conductivities. Such high-purity SWCNTs can be used in various carbon composites for improving the sensitivity of gas sensors.

• Journal of the Korean Chemical Society
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• v.12 no.2
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• pp.47-50
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• 1968

Two methods for separation of the impurities from bismuth metal have been found by the use of Dowex $1{\times}4,$ anion exchange resins. The first method is that Dowex $1{\times}4$ resins are packed into the two stage columns (height of under stage is 22cm and upper stage is 3cm, and diameter of columns are 1.5cm), and the impurities of Pb(II), Ag(I) and Cu(II) are separated by the eluent of 7.5M HCl soln, Zn(II), Fe(III) by 0.5M HCl solns, and Te(IV) in the upper stage by 2M NaOH soln. Remained Au(III) in the upper stage is determined by the ignition with resins. The 2nd method is that for the separation of all the impurities simultaneously the same resins are packed into single stage column(height is 10cm and diameter is 1.5cm), and all the impurities of Pb(II), Zn(II), Cu(II), Fe(III) and Ag(I) are eluted by the eluent of 0.5M HCl soln. Separated impurities are determined by the colorimetry.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1199-1202
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• 2005

Inside of working PDP, there exist highly reactive conditions in the gap between two glass panels. MgO film and phosphor have been investigated as a function of discharge, also phosphor and sealing frits have been investigated as a function of temperature. Changes of impurity generation of MgO, phosphor and sealing fits were measured by using x-ray photoelectron spectroscopy (XPS) and quadropole mass spectroscopy (XPS) and quadropole mass spectrometer (QMS). Impurities such as CO, $CO_2$, OH and $H_2O$ were increased during discharge and heating treatment. Gaseous impurities such as carbon compounds and water deteriorated the characteristics of PDP operation during of lifetime. So metal is used to remove the impurities of phosphor and sealing frits during hearting, the result that the quantity of the impurities such as carbon monoxide and water was reduced.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.198.1-198.1
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• 2010

고분자전해질 연료전지(PEMFC)의 핵심부품인 스택의 MEA는 전극과 멤브레인 전해질, GDL(Gas Diffusion Layer)로 구성되며, 전극은 Anoth극과 Cathod극으로 나뉘어 각각의 전극 특성에 적합한 전극촉매를 적용하게 된다. Anoth극과 Cathod극은 탄소 지지체 위에 원하는 사양의 희유금속이 도포되어 존재하는데 이들 희유금속은 그 희귀성으로 인해 사용 후 반드시 재사용되어야 한다. 사용된 전극에서의 희유금속 회수는 산침출, 불순물제거, 추출, 탈거 공정으로 이루어지며, 산침출 시 산화제로 사용된 NaOCl로 인한 침출용액 내의 Na+ 이온의 증가는 불순물제거 공정에 의해 반드시 제거되어야 한다. 따라서 본 연구에서는 CCG 방식으로 전극촉매를 GDL에 코팅한 MEA로부터 백금족 희유금속을 회수 시 MEA에 포함되어 있는 소량의 불순물을 제거하고자 한다.

• Journal of the Microelectronics and Packaging Society
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• v.10 no.3
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• pp.67-71
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• 2003

Sawing silicon ingot with abrasive slurry generates sludge that includes abrasive powders, cutting oil, and silicon powders. The abrasive powders and cutting oil are being separated and reused. Mixing the remained stodged silicon powders with carbon powders and subsequent heat-treatment are conducted to produce silicon carbide. The size of SiC whiskers and powders was smaller than the conventionally grown silicon carbide whiskers that were synthesized by adding micron-size metal impurities. Impurity related mechanism is attributed to the formation of the silicon carbide whiskers, as metal impurities are contained in the stodged silicon powders.