• 제목/요약/키워드: electron transition

검색결과 679건 처리시간 0.023초

기계적합금화법을 이용하여 제조된 $NO_{x}$ 제거용 천이금속/ZSM-5촉매의 미세구조 및 반복사용특성 (Microstructures and Repeated Usage-Properties of de-$NO_{x}$ Transition Metals/ZSM-5 Catalyst Made by Mechanical Alloying Method)

  • 조규봉;안인섭;남태현
    • 한국분말재료학회지
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    • 제5권4호
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    • pp.273-278
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    • 1998
  • $De-NO_x$ transition metals(Cu, Co)/ZSM-5 catalyst was made by mechanical alloying method, and their microstructures and repeated usage-properties were investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The conversions ability of NO in the catalyst was measured. A part of ZSM-5 in CO/ZSM-5 composite powders was amorphous and the amorphous phase became less stable with increasing Co content. Conversion ability of NO in 10Cu/ZSM-5 powders decreased from 89% to 12% and that in 10Co/ZSM-5 decreased from 22% to 17% by 7 times conversion tests.

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Electron Spin Transition Line-width of Mn-doped Wurtzite GaN Film for the Quantum Limit

  • Park, Jung-Il;Lee, Hyeong-Rag;Lee, Su-Ho;Hyun, Dong-Geul
    • Journal of Magnetics
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    • 제17권1호
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    • pp.13-18
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    • 2012
  • Starting with Kubo's formula and using the projection operator technique introduced by Kawabata, EPR lineprofile function for a $Mn^{2+}$-doped wurtzite structure GaN semiconductor was derived as a function of temperature at a frequency of 9.49 GHz (X-band) in the presence of external electromagnetic field. The line-width is barely affected in the low-temperature region because there is no correlation between the resonance fields and the distribution function. At higher temperature the line-width increases with increasing temperature due to the interaction of electrons with acoustic phonons. Thus, the present technique is considered to be more convenient to explain the resonant system as in the case of other optical transition systems.

Shikonin의 지표약적 성질에 관한 연구 (Studies on Color Transition Mechanism of Shikonin)

  • 이왕규;유경수
    • 약학회지
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    • 제24권3_4호
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    • pp.151-157
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    • 1980
  • Color transition mechanism of shikonin as an acid-alkali indicator was studied. It was confirmed that the presence of phenolic hydroxy radical was essential for the color change of shikonin. But in accordance with shikonin sodium salt (blue color), which was presumed to make chelation as six membered rings. Shikonin in alkaline solution, by dissociated phenolic protons of naphthoquinone nucleous, converted to the corresponding anion and instead of disappearance tautomerization, electron delocalization occurred and an additional pair of nonbonding electrons in the anion was available for interaction with .phi. electron system of the ring with further extension of the conjugation. It was responsible for its blue color(corresponding color: orange) with needs less energy difference (${\phi}{\rarw}{\phi}^{*}$) because of conjugation extension. Shikonin sodium salt seems to have similar nuclear structure as shikonin anion.

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Novel Properties of Boron Added Amorphous Rare Earth-transition Metal Alloys for Giant Magnetostrictive and Magneto-optical Recording Materials

  • Jai-Young Kim
    • Journal of Magnetics
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    • 제3권3호
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    • pp.78-81
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    • 1998
  • Large magneto crystalline anisotropy energy and demagnetization energy of rare earth-transition metal (RF-TM) alloys play roles of bottlenecks towards their commercial applications for giant magnetostrictive and blue wavelength magneto optical recording materials, respectively. To solve the above problems, boron is added into amorphous RE-TM alloys to produce its electron transferring. The boron added amorphous RE-TM alloys show novel magnetic and magneto-optical properties as follows; 1) an amorphous $(Sm_{33}Fe_{76})$97B3 alloy obtains the magnetostriction of$ -550{times}10^{-6}$ at 400 Oe compared with saturation magnetostriction of$ -60{\times}10^{-6}$ in conventional Ni based alloys, 2) an amorphous$ (Nd_{33}Fe_{67})_{95}B_5$ alloy increases effective magnetic anisotropy to$ -0.5{\times}10^{-6} ergs/cm^3 from -3.5{\times}10^6 ergs/cm^3$ without boron, which correspond to the polar Kerr rotation angles of 0.52$^{\circ}$and 0.33$^{\circ}$, respectively. These results attribute to selective 2p-3d electron orbits exchange coupling (SEC).

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실리콘과 코발트 박막의 계면구조에서 발생하는 1/f 잡음현상 연구 (Generation of 1/f Noise in Interfacial Structures between Silicon Substrate and Cobalt Thin Film)

  • 조남인;남형진;박종윤
    • 한국진공학회지
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    • 제5권1호
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    • pp.48-53
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    • 1996
  • We present a microscopic description for generation of 1/f noise in interfaces between cobalt thin film and silicon substrate. Along with surface resistance measurements and transmission electron diffraction observations. 1/f noise power spectral density has been measured for the interfacial structures at the liquid nitrogen temperature . The cobalt films have been deposited by the electron-beam evaporation technique onto p-type (100) silicon in the high vacuum condition. The measured noise power spectral density shows highest magnitude near the structural transition and metallization transition region. The noise magnitude rapidly decreased after the cobalt silicide nucleation. The noise parameter is concluded to be originated form the structural fluctuations.

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CRYSTAL TRANSITION PROCESS DURING POST-BREAKDOWN IN THE MOLTEN SALT

  • Han, S.H.;Thompson, G.E.
    • 한국표면공학회지
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    • 제32권3호
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    • pp.440-443
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    • 1999
  • The morphology and composition of anodic films, formed on aluminium at various current densities, in the range 1-$100{\;}Am^{-2}$, in the molten bisulphate melt at different temperatures (418-498K), have been studied using transmission electron microscopy of ultramicrotomed film sections, and ion beam thinned films. From the structural analysis of the electron diffraction patterns taken from the ultramicrotomed sections and ion beam thinned films, it can be concluded that the crystal modification process from ${\gamma}-Al_2O_3{\;}to{\;}{\alpha}-Al_2O_3$ proceeds in the following steps : (equation omitted)

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Theoretical Studies on the Gas-Phase Wolff Rearrangement of Ketocarbenes

  • 김찬경;이익준
    • Bulletin of the Korean Chemical Society
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    • 제18권4호
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    • pp.395-401
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    • 1997
  • The substituent effects in the gas-phase rearrangement of carbenes to ketenes involved in the Wolff reaction have been investigated theoretically using the AM1 method. In the initial state, carbene, there is a relatively strong vicinal n-σ* interaction between the lone pair (n) and carbonyl group (σ*). In the bridged transition state (TS), electronic charge is transferred from the migrating ring (Z-ring) toward the nonmigrating ring (Y-ring). The carbenes are stabilized by an electron donor Y (δσY < 0) whereas the TS is stabilized by an electron acceptor Y (δσY > 0). Multiple regression analysis of log (kYZ/kHH)(=-δΔG≠/2.3RT) leads to a relatively large negative cross-interaction constant, ρYZ=-0.53, log (kYZ/kHH)=2.96 σY--1.40 σZ-0.53 σY-σZ reflecting an extensive structural change in the transition state due to the stabilization of the initial state by the vicinal n-σ* overlap. When the solvent (water) effects are accounted for by the SM2.1 model of the Cramer and Truhlar method, the magnitude of all the selectivity parameters, ρY-, ρZ and ρYZ (=-0.66) are increased.

Comparison of the Ligating Ability of Anonic Transition Metal Complex $(Mn(CO)_{5}{^-})$, Transition Metal Hydrides $(HCr(CO)_{5}{^-},\;HW(CO)_{5}{^-},\;cis-HW(CO)_{4}P(OMe)_{3}{^-},\;HFe(CO)_{4}{^-},\;trans-\;HFe(CO)_{3}P(OMe)_{3}{^-})$, and Traditional Ligands $(Br^-,\;P(C_{6}H_{5})_{3})\;to\;M(CO)_{5}{^0}$ (M = Cr, W)

  • Park, Yong K;Han, In S;Marcetta Y. Darensbourg
    • Bulletin of the Korean Chemical Society
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    • 제15권6호
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    • pp.436-442
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    • 1994
  • Heterobimetallic complexes have a donor-accepter metal-metal bond in which two electrons from the electron-rich metal moiety are donated to the other electron-deficient one. Based on the competition reactions, Cotton-Kraihanzel force constants, ν(CO)IR band resolution and the relative nucleophilicity comparison of the donor ligands, the following relative ligating ability of the donor ligands toward $M(CO)_5$ (M=Cr, W) is assessed: cis-HW$(CO)_4P(OMe)_3^-$, $HW(CO)_5^-$ > $HCr(CO)_5^-$-$Br^-$ > trans-HFe$(CO)_3P(OMe)_3^-$ > $Mn(CO)_5^-$ > $HFe(CO)_4^-$ > PP$h_3$

Kinetics and Mechanism of the Pyridinolysis of Benzyl Bromides in Dimethyl Sulfoxide

  • 홍성완;고한중;이혜황;이익춘
    • Bulletin of the Korean Chemical Society
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    • 제20권10호
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    • pp.1172-1176
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    • 1999
  • Nucleophilic substitution reaction of Y-benzyl bromide with X-pyridines are investigated in DMSO at 45.0℃. Biphasic rate dependence is observed on varying the substituents in the substrate (Y) as well as in the nucleophile (X). The two well-defined straight lines in the Hammett (ρy) and Bronsted ( βx) plots are interpreted to indicate the changes in transition-state structure, a decrease in bond cleavage as the substituent on the substrate is changed from electron-donors ( ρy < 0) to electron-acceptors ( ρy > 0), and an increase in the extent of bond formation with the corresponding changes of the substituent on the pyridine. A Jencks' type analysis of separate polar (ρ) and resonance (ρr) effects can also be accounted for by the change of the transition-state structure, not by the variable combination of polar and resonance effects.

Dynamic heat capacity of perovskite manganites: calorimetric evidence for a first order transition and its implication to the magnetocaloric effect

  • Kim, Y. B.;Y. H. Jeong
    • 한국자기학회:학술대회 개요집
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    • 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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    • pp.40-40
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    • 2003
  • Finding a solid material with a large value of the magnetocaloric effect near room temperature is of exceeding importance, since this would lead to the development of more compact and environmentally safer cooling systems. Recently, manganites become the focus of attention due to its large magnetocaloric effect. We demonstrate, via dynamic calorimetric measurements, that the large magnetocaloric effect in perovskite manganites stems from the first-order nature of the magnetic transition. Our results offer a clue in search for ideal magnetocaloric materials working in the vicinity of room temperature.

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