• Bulletin of the Korean Chemical Society
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• 제15권8호
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• pp.658-662
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• 1994

Ab initio and extended Huckel calculations have been applied to discuss the electronic structure, ring inversion barrier, and geometry of the $Cp_2TiS_3$ compound. The deformation of four membered ring in the planar geometry is originated from a second-order Jahn-Teller distortion due to the small energy gap between HOMO and LUMO on the basis of extended Huckel calculations. The puckered $C_s$ geometry is stabilized by the interaction of the $x^2-y^2$ metal orbital with the hybrid orbital in sulfur. Ab initio calculations have been carried out to explore the ring inversion process for the model $Cl_2TiS_3$ compound. We have optimized $C_s$ and $C_{2v}$ structures of the model compound at the RHF level. The energy barriers for the ring inversion are sensitive to the used basis set. With 4-31$G^*$ for the Cl and S ligands, the barriers are computed to be 8.41 kcal/mol at MP2 and 8.02 kcal/mol at MP4 level.

• 한국결정성장학회지
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• 제14권6호
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• pp.262-266
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• 2004

초기 RF유도가열을 위해 Ti 금속링을 사용하여 스컬법에 의해 루릴 단결정을 성장시켰다. 성장시킨 단결정은 ${\varnothing}55.5{\times}1.0mm$의 wafer로 가공하였으며,$1300^{\circ}C$에서 15시간까지 대기중에서 열처리 하여 $\lambda=200~25000nm$의 범위에서 투광도를 비교하였다.

• Bulletin of the Korean Chemical Society
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• 제20권11호
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• pp.1269-1276
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• 1999

Metallocenes, whether using a cocatalyst or not, act as catalysts in ethylene polymerization. The positive charge on the transition metal of a metallocene might have an important role in polymerization as an active site in our model approach. Using semiempirical calculations in the absence of cocatalyst, we show one of the possibilities that the positive charge on a metallocene might be more easily transferred through the Cp ring of a ligand to the ethylene than to transfer directly from the transition metal to the ethylene. In these calculations, the charge on titanium in an eight C2H4 system is transferred and a polymer chain is produced. This reaction takes place only when ethylenes are arranged in a particular direction with respect to the ring, but does not take place for ethylenes near Ti or Cl atoms. The same mechanism is shown for a metallocene ligand which is sterically hindered or where the Cp ring is replaced by fluorenyl. These results suggest an entirely new polymerization mechanism in the absence of a cocatalyst in which the Cp ring is the active site.

• Bulletin of the Korean Chemical Society
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• 제31권1호
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• pp.116-119
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• 2010

Adsorption structures of the self-assembled thin films of $\alpha$-cyano-4-hydroxycinnamic acid (CHCA) anchoring on $TiO_2$ surfaces have been studied by using temperature-dependent diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy. From the presence of the strong $\nu(COO^-)$ band at ~1390 $cm^{-1}$ along with the disappearance of the OH bands in the carboxylic acid group in the DRIFT spectra at room temperature, CHCA appeared to adsorb onto $TiO_2$ surfaces as a carboxylate form. The absence of the out-of-plane benzene ring modes of CHCA in the DRIFT spectra suggests a rather vertical orientation of CHCA on $TiO_2$. Above ~220$ ^{\circ}C$, CHCA seemed to start to thermally degrade on $TiO_2$ surfaces referring from the disappearance of most vibrational modes in the DRIFT spectra, whereas the $\nu$(C ≡ N) bands were found to remain relatively conspicuous as the temperature increased even up to ~460$^{\circ}C$.

• 대한치과보철학회지
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• 제38권2호
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• pp.214-225
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• 2000

The purpose of this study was to investigate the effects of investing conditions on the marginal discrepancy of conical telescope outer crown with Co-Cr-Ti alloy(Dentitan) and to compare the marginal discrepancy and the retention force of outer crowns using different pattern materials(plastic foil, casting wax, pattern resin). To evaluate the effects of investing conditions on the marginal discrepancy, patterns with plastic foil were invested under three different liquid/powder ratio conditions using phosphate bonded investment(Univest-nonprecious): standard, 10% decreased and 10% increased. At each liquid/powder ratio condition, metal ring was lined with single or double layers of ceramic ring liner. The marginal discrepancy of outer crown at different investing conditions was measured by ${\times}100$ compact measuring microscope(STM5, Olympus, Japan). For measurement of the marginal discrepancy and the retention force of outer crown using different pattern materials, the investing condition of 10% decreased liquid/powder ratio and double layers of ring liner was selected because this investing condition resulted in the best fit of outer crown. Marginal discrepancy was measured in the same way above and retention force on universal testing machine. Under the conditions of this study, the following conclusions were drawn: 1. The thickness of ring liner had more influence on the marginal discrepancy of outer crown than the liquid/powder ratio, and the acceptable marginal fitness could not be expected at the investing condition directed by investment manufacturer 2. There were no differences in the marginal discrepancy of outer crown among three different pattern materials(P>0.05). 3. Casting wax showed the greatest retention force(1640g) of outer crown, followed by pattern resin(1110g), plastic foil(820g). However, there was no significant difference between plastic foil and pattern resin(P>0.05). 4. Plastic foil showed the least variation in marginal discrepancy and retention force.

• 한국결정성장학회지
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• 제15권5호
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• pp.175-181
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• 2005

스컬용융법에 의해 루틸 단결정들을 성장시켰으며, 서로 다른 융액의 유지시간에 따른 ingot의 특성을 비교하였다. 스컬용융법은 교류전자기장(RF)에 의해 전기가 흐르는 융액의 직접유도가열에 근거하며, 가열은 RF 에너지의 흡수로 실행된다. $TiO_2$는 상온에서는 부도체이지만 온도가 올라갈수록 전기 전도성이 증가한다. 따라서, 초기 RF 유도가열을 위해 티타늄 금속 링(외경 : 6cm, 내경 : 4cm, 두께 : 0.2cm)을 $TiO_2$ 분말(아나타제상, CERAC, 3N)내부에 묻었다. 스컬용융법에 의한 산화물 용융에서 매우 중요한 것은 융점에서의 전기 저항 값, RF generator의 주파수 그리고 냉각도가니 크기이다. 본 연구에서는, $TiO_2$의 융점에서의 전기저항$(10^{-2}\~10^{-1}\;{\Omega}{\cdot}m)$은 알루미나$(10^{-1}\;{\Omega}{\cdot}m)$의 지르코니아$(10^{-3}\;{\Omega}{\cdot}m)$의 전기저항 데이터를 바탕으로 추정하였다. 냉각도가니의 내부직경은 11cm, 높이는 14cm였으며, 이것은 침투깊이$(0.36\~1.13cm)$와 RF generator 주파수를 고려하여 결정하였다

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 D
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• pp.1546-1548
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• 1998

Dual mode ring resonators(DMRR) have been fabricated using laser ablated $YBa_2Cu_3O_{7-x}$ superconducting thin films. The transition temperature of YBCO thin films were 85 - 88 K and the film thicknesses were about 5,000 $\AA$. Dual mode ring resonators were patterned by standard photolithography process and wet-etching. Then two-layer metal thin films (Ti/Ag) have been deposited for the ground plane on the back side of substrate by e-beam and thermal evaporation. The input/output feedline angles of each resonator were $60^{\circ}$, $100^{\circ}$, $180^{\circ}$. A network analyzer was used for testing the performance of the resonators in the frequency range of 6-13 GHz at 77 K.

• Journal of Advanced Marine Engineering and Technology
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• 제32권8호
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• pp.1178-1184
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• 2008

In this study, techniques of ion implantation were used in order to improve the characteristics of metal materials such as the oxidation and wear resistant. In particular it is necessary to develope their oxidation and wear resistant that could be used in severe environmental conditions. There are mainly two elementary technologies including ion implantation and/or thin film coating. Ion implantation method was performed for surface modification. As a result, it was found that some ion implantations methods such as Nb, high-temperature Nb ion implantation and Nb+C combined implantation are somewhat effective for improving the oxidation resistance of TiAl alloy. Furthermore, the fluorine PBII treatment is more effective for improving the oxidation resistance of the TiAl alloy with three-dimensional shapes. The implantation of boron ion into thin film of TiN was also effective for improving the properties of materials like high temperature wear resistance. TiCrN film was applied to the actual seal ring for steam turbines, and it was observed that its sliding property showed a successfully good performance.

• 한국전기전자재료학회논문지
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• 제25권5호
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• pp.361-365
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• 2012

A bolt-clamped ultrasonic viscometer was designed and fabricated using a pair of ring-shaped piezoelectric ceramic resonators. For its compactness and low operation frequencies, simulation of piezoelectric resonators was carried out using an ATILA program. Ring-shaped resonators using $0.05Pb(Mn_{1/3}Sb_{2/3})O_3-0.95Pb(Zr_{0.475}Ti_{0.525})O_3$ ceramics were prepared by a conventional ceramic processing, which were then clamped with a pair of metal caps. The fabricated sensor module with a small volume of less than 1 $cm^3$ and an operation frequency as low as 26.5 kHz showed a good relationship between its quality factor and the viscosity of oil.

• 대한화학회지
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• 제19권2호
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• pp.92-97
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• 1975

$TiCl(OC_6H_5)_3{\cdot}C_6H_5OH\;및\;Ti(OC_6H_5)_4{\cdot}C_6H_5OH$의 분자량 측정과 전자 흡수스펙트럼을 고찰함으로써 이들 두 유기-리탄 화합물들의 용액 상태에서의 분자 및 전자구조에 대하여 연구하였다. $Ti(OC_6H_5)_4{\cdot}C_6H_5OH$는 고체상태에서는 이합체로 존재하지만 분자량 측정 결과 묽은 용액에서는 단위체로 완전해리되며 $TiCl(OC_6H_5)_3{\cdot}C_6H_5OH$도 8mM농도에서 해리를 시작함을 알수 있었다. 따라서 이들 두 착화합물은 묽은 용액에서 5배위 착화합물로 존재하며 분자구조는 trigonalbipyramid으로 생각된다. 두 화합물의 전자 흡수스펙트럼은 자외부쪽에 똑같은 진동구조를 갖는 벤젠고리 특유의 흡수밴드를 나타내며 가시부에서는 $TiCl(OC_6H_5)_3{\cdot}C_6H_5OH$의 경우 26.8kK에 $Ti(OC_6H_5)_4{\cdot}C_6H_5OH$는 29.6kK에 각각 흡수 밴드를 나타낸다. 이가시부 흡수밴드는 리간드에서 금속쪽으로 전하이전에 의한 $^1A_1''{\to}^1E'\;or\;^1E''$ 전이로 생각된다.