• 한국세라믹학회지
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• 제46권5호
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• pp.456-461
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• 2009

Chemical composition and status of chemical bonding of the YAG($Y_3Al_5O_{12}$) ceramics after the exposure to fluorine plasma have been investigated using X-ray photoelectron spectroscopy, with the analysis on its erosion behavior. On the surface, F showed the maximum content, decreasing with depth, meanwhile the cation composition remained almost constant, irrespective of the position. The peaks due to Y in the reaction layer consisted of two kinds, showing the Y-O and Y-F bonds. These surface modifications under fluorine plasma seem to promote the erosion of the YAG ceramics. Excess addition of $Al_2O_3$ or $Y_2O_3$ into stoichiometric YAG produced 2nd phases of $Al_2O_3$ and $YAlO_3$, respectively, resulting in the slight difference in the local erosion rates. But, the overall average erosion rate was not sensitive to such excess additions of $Al_2O_3$ or $Y_2O_3$.

• 한국세라믹학회지
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• 제53권6호
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• pp.597-603
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• 2016

Tantalum carbide, which is one of the ultra-high temperature ceramics, was deposited on graphite by low pressure chemical vapor deposition from a $TaCl_5-C_3H_6-Ar-H_2$ mixture. To maintain a constant $TaCl_5/C_3H_6$ ratio during the deposition process, $TaCl_5$ powders were continuously fed into the sublimation chamber using a screw-driven feeder. Sublimation behavior of $TaCl_5$ powder was measured by thermogravimetric analysis. TaC coatings have various phases such as $Ta+{\alpha}-Ta_2C$, ${\alpha}-Ta_2C+TaC_{1-x}$, and $TaC_{1-x}$ depending on the powder feeding methods, the $C_3H_6/TaCl_5$ ratio, and the deposition temperatures. Near-stoichiometric TaC was obtained by optimizing the deposition parameters. Phase compositions were analyzed by XRD, XPS, and Raman analysis.

• 한국재료학회지
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• 제15권4호
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• pp.275-280
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• 2005

The growth of hafnium oxide thin films by atomic layer deposition was investigated in the temperature range of $175-350^{\circ}C$ using $Hf[N(CH_3)_2]_4\;and\;O_2$ as precursors. A self-limiting growth of $0.6\AA/cycle$ was achieved at the substrate temperature of $240-280^{\circ}C$. The films were amorphous and very smooth (0.76-0.80 nm) as examined by X-ray diffractometer and atomic force microscopy, respectively. X-ray photoelectron spectroscopy analysis showed that the films grown at $300^{\circ}C$ was almost stoichiometric. Electrical measurements performed on $MoW/HfO_2$(20 nm)/Si MOS structures exhibited high dielectric constant$(\~17)$ and a remarkably low leakage current density of at an applied field of $1.5-6.2\times10^{-7}A/cm^2$ MV/cm, probably due to the stoichiometry of the films.

• 대한기계학회논문집B
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• 제37권8호
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• pp.743-752
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• 2013

본 논문은 대형 상용기관을 모사한 정적연소실에서 매립지 가스의 연소 특성에 대한 복수의 논문 중 두 번째로, 연소압력 측정을 기반으로 연소과정을 해석하였다. 해석 결과 연소에 유리한 조건일수록 두 개의 압력 정점이 존재하며, 이는 연소에 의한 열발생과 열전달에 의한 냉각효과의 상호 작용이며 두 정점의 크기는 미연가스 분율에 따라 달라진다. 또한 연소과정 중 열발생에는 4개의 주요 변곡점이 발생하고, 이는 점화위치로부터 화염전파에 따른 전열 면적 변화과정이 주원인이며 연소에 불리한 조건일수록 변곡점은 증가하고 열발생은 복잡한 형태를 지니는데, 이는 연소기간 연장이 주원인이다. 결론적으로 점화위치와 관련된 화염전파 과정 및 전열 면적의 변화과정 그리고 대형 연소실에 의한 연소기간 연장의 효과가 상호 복잡하게 작용하면서 매우 특이한 형태의 열발생 곡선이 생성된다.

• Bulletin of the Korean Chemical Society
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• 제23권1호
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• pp.123-131
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• 2002

Solvolyses rate constant of 1- and 2- naphthoyl chlorides (1 and 2) are reported for aqueous binary mixtures with methanol, ethanol, fluorinated alcohol, acetonitrile and dioxane. Kinetic solvent isotope effects (KISE) in methanol and product selectivities (S) of 2-naphthoyl chloride (2) in alcohol-water are also reported. Dispersions in Grunwald-Winstein correlations $(r{\leq}0.901)$ are discussed by multiple regression analysis incorporating ionizing power $(Y_{Cl})$ scale and rate-rate profiles. Major causes for these phenomena are investigated as an aromatic ring solvation effects, in conjunction with weakly nucleophilic solvation effects ($S_N2$ character), for solvolyses of 1 and for solvolyses of 2, as dual reaction channels, described as $S_N1$-$S_N2$ and $S_AN$-$S_N2$ processes. Distinct border lines between the two pathways are derived from solvolyses rates of 2 in 18 solvent using the results of $log(k/k_o)=mY_{Cl}+lN_T+hI$ plot with values of 1.13 for m, 0.37 for l and 0.15 for h value in 5 aqueous fluorinated alcohol mixtures. Using rate-product correlation, the validity of a third order model based on a general base catalyzed by solvent and contribution from these rate constants, $k_{aa},\;k_{aw}$ and $k_{aw}$, are investigated for $S_AN$-$S_N2$ solvolyses of 2 favored in more rich alcohol media and gradual addition of water to alcohol solvent shows a great shift away from stoichiometric solvation to predominantly medium effects. Rate-rate correlation between solvolyses of 2 and trimethyl acetylchloride (5) with alkyl group in the 29 aqueous solvent mixtures shows appreciable linearity (slope = 0.84, r = 0.987), caused by the same pathway ($S_N1$-$S_N2$ process), even if this correlation coincides with appreciable dispersion (different solvation effect).

• Corrosion Science and Technology
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• 제17권2호
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• pp.60-67
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• 2018

The compounds associated with corrosion, in metallic archaeological samples of carbon steel of insular origin were evaluated to establish their degree of deterioration and structural damage against air pollution. The iron phases present in samples of archaeological artifacts were detected by Raman spectroscopy and confocal Raman microcopy. These samples mainly exhibited ing mainly ${\beta}$-FeO(OH) type goethite oxyhydroxides and small amounts of akaganeite ${\alpha}$-FeO(OH) lepidocrocite ${\gamma}$-FeO(OH) due to dominant chloride in a marine environment and non-stoichiometric oxyhydroxides Fe (II + / III +) as indicators of early corrosion. Some parts showed the presence of magnetic maghemite indicating high corrosion. ${\gamma}$-FeO(OH) is a precursor of phases associated with advanced marine corrosion. By studying its decomposition by Raman spectroscopy, it was synthesized with the following sequence: ${\gamma}-FeO(OH){\rightarrow}{\alpha}-FeO(OH)+{\gamma}-FeO(OH)$, ${\rightarrow}{\gamma}-Fe_2O_3+Fe_3O_4$. Ferric compounds provided evidence for the effect of intensity of laser on them, constituting a very useful input for the characterization of oxidation of iron in this type of artifacts. Thus, destructive analysis techniques should be avoided in addition to the use of small amounts of specimen.

• Carbon letters
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• 제26권
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• pp.31-42
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• 2018

Adsorption is one of the best methods for wastewater purification. The fact that water quality is continuously decreasing requires the development of novel, effective and cost available adsorbents. Herein, a simple procedure for the preparation of a magnetic adsorbent from agricultural waste biomass and ferrofluid has been introduced. Specifically, ferrofluid mixed with wheat straw was directly pyrolyzed either by microwave irradiation (900 W, 30 min) or by conventional heating ($550^{\circ}C$, 90 min). Magnetic biochars were characterized by X-ray powder diffraction, $M{\ddot{o}}ssbauer$ spectroscopy, textural analysis and tested as adsorbents of As(V) oxyanion and cationic methylene blue, respectively. Results showed that microwave pyrolysis produced char with high adsorption capacity of As(V) ($Q_m=25.6mg\;g^{-1}$ at pH 4), whereas conventional pyrolysis was not so effective. In comparison to conventional pyrolysis, one-step microwave pyrolysis produced a material with expressive microporosity, having a nine times higher value of specific surface area as well as total pore volume. We assumed that sorption properties are also caused by several iron-bearing composites identified by $M{\ddot{o}}ssbauer$ spectroscopy ([super] paramagnetic $Fe_2O_3$, ${\alpha}-Fe$, non-stoichiometric $Fe_3C$, ${\gamma}-Fe_2O_3$, ${\gamma}-Fe$) transformed from nano-maghemite presented in the ferrofluid. Methylene blue was also more easily removed by magnetic biochar prepared by microwaves ($Q_m=144.9mg\;g^{-1}$ at pH 10.9) compared to using conventional techniques.

• 한국의학물리학회지:의학물리
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• 제8권1호
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• pp.69-79
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• 1997

뫼스바우어 분광법을 사용해서 다목적용으로 제조된 의학용 치료 연고제내에 포함된 자성물질 입자들의 성질들이 연고제내에서 안정되게 존재하고 있는 지를 연구하였다. 자성물질 내에 들어있는 $^{57}$ Fe 동위철 핵자들에 의해 나타나는 뫼스바우어 스펙트럼에 대해 분석한 결과들과 Fe$_3$O$_4$-${\gamma}$-Fe$_2$O$_3$ 체계에 대해 잘 알려진 분석결과들을 비교 연구하여 자성입자들의 구성상태를 규명할 수 있었다. 결과적으로 나타난 연고제내에 자성물질의 합성상태는 합성되지 않은 순수한 자성물 질만의 성분 분석과는 다른 결과를 나타내었다. 한편, 자성물질 입자의 크기 (~100$\AA$)가 매우 작음에도 불구하고 이들 입자들은 95K~300K 범위에서 초 상자성 형태의 뫼스바우어 스펙트럼 특성을 나타내지 않았다. 또한, 연고제를 방사성 살균한 후에도 자성물질 성분 구성에는 변화가 없었다.

• 한국미생물·생명공학회지
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• 제2권1호
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• pp.45-50
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• 1974

1. L-cysteine을 pyruvate, sulfide 및 ammonia로 분해하는 반응을 촉매하는 효소인 cysteinedesulfhydrase의 촉매기능에 대해 연구해온 바 Aerobacter aerogenes로부터 유도생산한 cysteinedesulfhydrase를 사용하여 분해반응의 역반응에 의해 pyruvate, ammonia 및 sulfide로부터 cysteine의 유도체인 S-methyl-L-cysteine 및 S-ethyl-L-cysteine을 합성하였다. 2. 합성반응에 있어서 S-methyl-L-cysteine 및 S-ethyl-L-cysteine의 생성량은 반응시간과 효소량에 비예적인 관계를 나타내었고 반응의 최적 pH는 10.0이었다. 3. 효소적 합성법에 의해 생산된 S-methyl-L-cysteine 및 S-ethyl-L-cysteine을 반응액으로 부터 단리, 결정화해서 이들 합성산물에 대한 Ion exchange chromatogram, NMR spectrum, element analysis, molecular weight 및 melting point 측정 등의 분석시험을 행한 바 이들 화합물에 대한 이론치와 잘 일치되는 결과를 얻었다.

• 한국결정학회지
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• 제4권1호
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• pp.18-24
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• 1993

백금-안티모니갔의 상평형 및 안정 화합물에 대한 연구를 위해 합성실험을 실시하였다. 반응생성물은 반 사현미경, X-선 회절분석, 전자현미분석 등으로 규명하 였다. 백금-안티모니계에는 Pt5Sb, Pt3Sb, Pt3Sb2, PtSb, PtSb5등 5종류의 화합물이 존재하며 Pt5Sb2는 존재하지 않는 것으로 밝혀졌다. Pt5Sb는 처음 발견된 화합물로서 83at.%Pt의 화학성분을 가지며, 정방정계와 격자상수 a=3.948(3), c=16.85(1)차를 가진다. Ptssb 의 X-선회절 분말자료는 a=3.9455(7), c=16.959(5) A 인 정방정계의 구조로 격자지수화가 가능하다. PtSb의 화학성분은 800연까지 50at.% Pt이나 10반종에서는 49at.%정 회이다. 백금속의 안티모니 고용한계는 1000°, 800°, 600°에서 각각 7.5, 10.0, 6.1at.%이다. Ptsb2와 Sb를 잇는 액상곡선의 형태도 수정되었다.