• Korean Journal of Materials Research
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• v.14 no.3
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• pp.218-223
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• 2004

P-type $\beta$-FeSi$_2$ with a nominal composition of $Fe_{0.92}Mn_{0.08}Si_2$ powders has been produced by mechanical alloying process. As-milled powders were spray dried and consolidated by atmospheric plasma thermal spraying as a rapid sintering process. As-milled powders were of metastable state and fully transformed to $\beta$-$FeSi_2$ phase by subsequent isothermal annealing. However, as-thermal sprayed $Fe_{0.92}Mn_{0.08}Si_2$ consisted of untransformed mixture of $\alpha$-$Fe_2Si_{5}$ and $\varepsilon$-FeSi phases. Isothermal annealing has been carried out to induce transformation to the thermoelectric semiconducting $\beta$-$FeSi_2$ phase. Isothermal annealing at $845^{\circ}C$ in vacuum gradually led to the thermoelectric semiconducting $\beta$-$FeSi_2$ phase transformation, but some residual metallic $\alpha$ and $\varepsilon$ phases were unavoidable even after prolonged annealing. Thermoelectric properties of $\beta$-$FeSi_2$ materials before and after isothermal annealing were evaluated. Seebeck coefficient increased and electric conductivity decreased with increasing annealing time due to the phase transition from metallic phases to semiconducting phases. Thermoelectric properties showed gradual increment, but overall properties appeared to be inferior to those of vacuum hot pressed specimens.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.683-688
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• 2013

Candidate coating materials for re-usable metallic nuclear fuel crucibles, TaC, TiC, ZrC, $ZrO_2$, and $Y_2O_3$, were plasmasprayed onto a niobium substrate. The microstructure of the plasma-sprayed coatings and thermal cycling behavior were characterized, and U-Zr melt interaction studies were carried out. The TaC and $Y_2O_3$ coating layers had a uniform thickness, and high density with only a few small closed pores showing good consolidation, while the ZrC, TiC, and $ZrO_2$ coatings were not well consolidated with a considerable amount of porosity. Thermal cycling tests showed that the adhesion of the TiC, ZrC, and $ZrO_2$ coating layers with niobium was relatively weak compared to the TaC and $Y_2O_3$ coatings. The TaC and $Y_2O_3$ coatings had better cycling characteristics with no interconnected cracks. In the interaction studies, ZrC and $ZrO_2$ coated rods showed significant degradations after exposure to U-10 wt.% Zr melt at $1600^{\circ}C$ for 15 min., but TaC, TiC, and $Y_2O_3$ coatings showed good compatibility with U-Zr melt.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.04b
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• pp.1-5
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• 2000

As the semiconductor devices are miniaturized, the number of the unit cleaning processes increases. In order to processes by conventional RCA cleaning process, the consumption of volume of liquid chemical and DI water became huge. Therefore, the problem of environmental issues are evolved by the increased consumption of chemicals. To resolve this matter, an advanced cleaning process by Electrolyzed Water was studied in this work. The electrolyzed water was made by an electrolysis equipment which was composed of three chambers of anode, cathode, and middle chambers. In the case of electrolyzed water with electrolytes in the middle chamber, oxidatively acidic water of anode and reductively alkaline water of cathode were obtained. The oxidation/reduction potentials and pH of anode water and cathode water were measured to be +l000mV and 4.8, and -530mV and 6.3, respectively. The Si-wafers contaminated with metallic impurities were cleaning with the electrolyzed water. To analysis the amounts of metallic impurities on Si-water surfaces, ICP-MS(Inductively Coupled Plasma-Mass spectrometer) was introduced. From results of ICP-MS measurements, it was concluded that the ability of electrolyzed water was equivalent to that of the conventional RCA cleaning.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11a
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• pp.61-64
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• 2003

This study was conducted to investigate the chemical characteristics of $PM^{10}$ at Anmyeon-do during the periods from January 1998 to December 2001. The $PM^{10}$ samples ($PM^{10}$) were collected by High Volume Air sampler (HVAS). The measured items were mass concentration of $PM^{10}$ with the major ions ($Cl^{-}$, ${SO_{4}}^{2-}$, ${NO_3}^{-}$, ${Mg}^{2+}$, ${Ca}^{2+}$, ${K}^{+}$etc.) and metallic elements (AI, Fe, Mn, Cr, Zn, Pb etc.). The chemical analysis of major ion components were made by Ion Chromatography (DX-500) and that of metallic elements were made by Inductively Coupled Plasma Spectrometer (ICP-AES, ICP-Mass). The average mass concentration of $PM^{10}$ increased substantially during the heavy dust periods (Asian Dust cases). For water-soluble ions, concentrations of ${Ca}^{2+}$, ${SO_{4}}^{2-}$ and ${NO_3}^{-}$ were remarkably enhanced. Concentrations and mass fraction of crustal elements such as Na, Mg, Ca, Fe, Mn were highly elevated, but those of pollution-derived heavy metals were appreciably decreased. The factor analysis was conducted in order to make the large and diverse data set as manageable levels and to qualitatively examine the relationship between the variables.

• Korean Journal of Materials Research
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• v.16 no.2
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• pp.80-84
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• 2006

The removal efficiency of Cu and Fe contaminants on the silicon wafer surface was examined to investigate the effect of cleaning solutions on the behavior of metallic impurities. Silicon wafers were intentionally contaminated with Cu and Fe solutions by spin coating and cleaned in different types of cleaning solutions based on $NH_4OH/H_2O_2/H_2O\;(SC1),\;H_2O_2/HCl/H_2O$ (SC2), and/or HCl/$H_2O$ (m-SC2) mixtures. The concentration of metallic contaminants on the silicon wafer surface before and after cleaning was analyzed by vapor phase decomposition/inductively coupled plasma-mass spectrometry (VPD/ICP-MS). Cu ions were effectively removed both in alkali (SC1) and in acid (SC2) based solutions. When $H_2O_2$ was not added to SC2 solution like m-SC2, the removal efficiency of Cu impurities was decreased drastically. The efficiency of Cu ions in SC1 was not changed by increasing cleaning temperature. Fe ions were soluble only in acid solution like SC2 or m-SC2 solution. The removal efficiencies of Fe ions in acid solutions were enhanced by increasing cleaning temperature. It is found that the behavior of metallic contaminants as Cu and Fe from silicon surfaces in cleaning solutions could be explained in terms of Pourbaix diagram.

• Journal of the Korean Vacuum Society
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• v.10 no.2
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• pp.267-274
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• 2001

Removal of Cr, Ni and Cu impurities on Si surfaces using remote plasma-excited hydrogen was investigated. Si surfaces were contaminated intentionally by acetone with low purity. To determine the optimum process condition, remote plasma-excited hydrogen cleaning was conducted for various rf-powers and plasma exposure times. After remote plasma-excited hydrogen cleaning, Si surfaces were analyzed by Total X-ray Reflection Fluorescence(TXRF), Surface Photovoltage(SPV) and Atomic Forece Microscope(AFM). The concentrations of Cr, Ni and Cu impurities were reduced and the minority carrier lifetime increased after remote plasma-excited hydrogen. Also RMS roughness decreased by more than 30% after remote plasma-excited hydrogen cleaning. AFM analysis results also show that remote plasma-excited hydrogen cleaning causes no damage to the Si surface. TXRF analysis results show that remote plasma-excited hydrogen cleaning is effective in eliminating metallic impurities from Si surface only if it is performed under an optimum process conditions. The removal mechanism of the Cr, Ni and Cu impurities using remote plasma-excited hydrogen treatments is proposed to be the lift-off during removal of underlying chemical oxides.

• Journal of Hydrogen and New Energy
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• v.7 no.1
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• pp.81-92
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• 1996

The Ar/Ar-$H_2$ plasma method was applied to reduce oxides and refine metals of V, Ta and B. In addition, the high temperature chemical reaction in Ar plasma and of the refining reaction in the Ar-(20%)$H_2$ plasma were analyzed. The crude V of 96wt% purity was obtained at the ratio of $C/V_{2}O_{5}=4.50$ by the Ar plasma reduction grade and the maximum reduction was obtained at $C/V_{2}O_{5}=4.50$ due to the $O_{2}$ loss from the thermal decomposition of vanadium oxide. In the Ar-(20%)$H_2$ plasma refining, the metallic V of 99.2wt% was produced at the ratio of $C/V_{2}O_{5}=4.40$. It was considered that a main refining reaction resulted from the chemical reaction between the residual carbon and residual oxygen. The metallic Ta of 99.8wt% was obtained at the ratio of $C/Ta_{2}O_{5}=5.10$ in a Ar plasma reduction and the Oz loss from the thermal decomposition of tantalum pentoxide did not take place. The deoxidation reaction was more significant than the decarburization reaction in the Ar-(20%)$H_2$ plasma refining and the metallic Ta of 99.9wt% was produced within the range of $C/Ta_{2}O_{5}$ ratio of 4.50 to 5.10. The Vickers hardness of Ta in the above mentioned range was about 220Hv due to the decrease in a residual oxygen by the deoxidation reaction. On the other hand, C is no suitable agent for the reduction of $B_{2}O_{3}$ by the Ar and Ar-$H_2$ plasma. But Fe-B-Si alloy was produced with the reduction of $B_{2}O_{3}$ in the melt when Fe, C, $B_{2}O_{3}$, and ferroboron mixtures were melted by the high frequency induction melting.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.3
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• pp.360-368
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• 1999

The paper describes spectroscopic characteristics of plasma induced in the pulsed YAG laser welding of alloys containing a large amount of volatile elements. The authors have conducted the spectroscopic analyses of laser induced Al-Mg alloys plasma in the air and argon atmosphere. In the air environment the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn and singly ionized Mg lines as well as the intense molecular spectra of ALO and MgO formed by chemi-cal reactions of evaporated Al and Mg atoms from the pool surface with oxygen in the air. In argon atmosphere MgO and AlO spectra vanished but AlH spectrum was detected. the hydrogen source was presumable hydrogen dissolved in the base metals water absorbed on the surface oxide layer or $H_2$ and $H_2O$ in the shielding gas. The resonant lines of Al and Mg were strongly self-absorbed in particular self-absorption of the Mg line was predominant. These results show that the laser induced plasma was made of metallic vapor with relatively low temperature and high density.

• Journal of Powder Materials
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• v.20 no.6
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• pp.411-424
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• 2013

In this study, the synthesis of nickel nanoparticles and copper nanospheres for the potential applications of MLCC electrode materials has been studied by plasma arc evaporation method. The change in the broad distribution of the size of nickel and copper nanopowders is successfully controlled by manifesting proper mixture of gas ambiance for plasma generation in the size range of 20 to 200 nm in diameter. The factors affecting the mean diameter of the nanopowder was studied by changing the composition of reactive gases, indicating that nitrogen enhances the formation of larger particles compared to hydrogen gas. The morphologies and particle sizes of the metal nanoparticles were observed by SEM, and ultrathin oxide layers on the powder surface generated during passivation step have been confirmed using TEM. The metallic FCC structure of the nanoparticles was confirmed using powder X-ray diffraction method.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.47-47
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• 2010

Discharge under the water is very hard and demand considerable high voltage. But specially improved electrode can generate plasma discharge to salty water with relatively low voltage. A round shape ceramic electrode having many pinholes combined with metallic one can generate plasma. 400 volt, 10 kHz and 3 micro second pulse width were applied to repeatedly running synthetic seawater with 10 L/m velocity, containing cultivated E. coli and Bacillus. As a result, 18, 94, 99.97, 100, 100 % disinfection rates to E. coli and 17.1, 17.1, 82.9, 99.4, 99.9 % disinfection rates to Bacillus subtilis were achieved to 1, 2, 3, 4, 5 times repetitive treatment respectively. In the plasma condition, the ions and electrons are separated and new kinds of components are re-synthesized by the intensive movement of the components. Especially chlorine ions are separated and recombined to residual free chlorine like HOCl, $OCl^-$. The residual free chlorine concentrations of discharged water were 0.25, 0.88, 1.39, 1.59, 1.66 mg $Cl_2$/L after 5 times treatment respectively. Another unconfirmed radical and oxidants for example, OH, $H_2O_2$, and $O_3$ can have an effect on microorganism of course.