• Bulletin of the Korean Chemical Society
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• 제33권12호
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• pp.4028-4034
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• 2012

Tris(2-phenylphenoxo)aluminum ($(2-PhC_6H_4O)_3Al$) exists as a dimeric form in toluene. When toluene-insoluble anhydrous cobalt acetate is treated with tris(2-phenylphenoxo)aluminum in toluene, the toluene-soluble adduct $(2-PhC_6H_4O)_3Al{\cdot}Co(OAc)_2$ is formed. The 2-phenylphenoxo ligand in the adduct can be replaced with another aryloxo ligand to give (aryloxo)$(2-PhC_6H_4O)_2Al{\cdot}Co(OAc)_2$ (aryloxo = 2-methylphenoxo, 2-isopropylphenoxo, 4-methylphenoxo, 4-isopropylphenoxo, or 4-tert-butylphenoxo). These complexes are active for butadiene polymerization without gel formation when activated with an equivalent amount of $(2-PhC_6H_4O)AlEt_2$ for 2 h. The highest activity, 175 kg/mol-Co (turnover number, 3200) was achieved with $(2-PhC_6H_4O)_3Al{\cdot}Co(OAc)_2$ at $65^{\circ}C$ for 2 h. The microstructure of the polymer chains is mostly trans-1,4-configuration (70-75%) with the remaining being 1,2-vinyl. The cis-1,4-configuration observed by IR is minimal (1-5%). By replacing the 2-phenylpheoxo with a 4-alkylphenoxo ligand, the amount of 1,4-configuration slightly increases, resulting in increase in the endothermic melting signal at $-30{\sim}50^{\circ}C$ in the DSC curve. The molecular weights of the polymers are high ($M_n$: 300000~800000) with a fairly narrow molecular weight distribution ($M_w/M_n$, 2.0-2.7).

• 한국응용과학기술학회지
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• 제34권4호
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• pp.883-891
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• 2017

고분자 전해질 연료전지의 연료에 포함된 일산화탄소의 선택적 산화를 위하여, 귀금속 촉매를 대체하기 위한 CuO-$CeO_2$ 복합 산화물 촉매를 졸-겔법과 공침법으로 제조하였다. 졸-겔법으로 촉매 제조 시 Cu/Ce의 비와 가수분해 비를 변화시켰다. 제조한 촉매의 활성은 귀금속 촉매($Pt/{\gamma}-Al_2O_3$)와 비교하였다. Cu/Ce의 비를 변화시키면서 제조한 촉매 중 Cu/Ce의 비가 4:16인 촉매가 가장 높은 CO 전환율(90%)과 선택도(60%)를 나타내었다. 촉매의 제조에서 가수분해 비가 증가할수록 촉매 표면적이 증가하였고, 아울러 촉매 활성 또한 증가하였다. 공침법으로 제조한 촉매와 1wt% $Pt/{\gamma}-Al_2O_3$ 촉매의 가장 높은 CO 전환율은 각각 82% 및 81%인 반면, 졸-겔법으로 제조한 촉매의 경우는 90%가 얻어졌다. 이는 졸-겔법으로 제조한 촉매가 공침법으로 제조한 촉매나 귀금속 촉매보다 더 높은 촉매활성을 보임을 의미한다. CO-TPD 실험을 통하여, 낮은 온도($140^{\circ}C$)에서 CO를 탈착하는 촉매가 본 반응에서 더 높은 촉매활성을 보임을 알 수 있었다.

• 한국표면공학회지
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• 제42권3호
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• pp.122-127
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• 2009

Ga/Al doped ZnO (GAZO) thin films were prepared on non-alkali glass substrate by co-sputtering system using two DC cathodes equipped with AZO ($Al_2O_3$:2.0 wt%) target and GZO ($Ga_2O_3$:6.65 wt%) target. This study examined the influence of Al/Ga concentration and substrate temperature on the electrical, structural and optical properties of GAZO films. The lowest resistivity $1.95{\times}10^{-3}{\Omega}cm$ was obtained at room temperature. With increasing substrate temperature, resistivity of GAZO film decreased to a minimum value of $7.47{\times}10^{-4}{\Omega}cm$ at below $300^{\circ}C$. Furthermore, when 0.05% $H_2$ gas was introduced, resistivity of GAZO film decreased to $6.69{\times}10^{-4}{\Omega}cm$. All the films had a preferred orientation along the (002) direction, indicating that the deposited films have hexagonal wurtzite structure formed by the textured growth along the c-axis. The average transmittance of the films was more than 85% in the visible light range.

• 한국재료학회지
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• 제25권8호
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• pp.423-428
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• 2015

Impedancemetric $NO_x$ (NO and $NO_2$) gas sensors were designed with a stacked-layer structure and fabricated using $LaCr_xCo_{1-x}O_3$ (x = 0, 0.2, 0.5, 0.8 and 1) as the receptor material and $Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ plates as the solid-electrolyte transducer material. The $LaCr_xCo_{1-x}O_3$ layers were prepared with a polymeric precursor method that used ethylene glycol as the solvent, acetyl acetone as the chelating agent, and polyvinylpyrrolidone as the polymer additive. The effects of the Co concentration on the structural, morphological, and $NO_x$ sensing properties of the $LaCr_xCo_{1-x}O_3$ powders were investigated with powder X-ray diffraction, field emission scanning electron microscopy, and its response to 20~250 ppm of $NO_x$ at $400^{\circ}C$ (for 1 kHz and 0.5 V), respectively. When the as-prepared precursors were calcined at $700^{\circ}C$, only a single phase was detected, which corresponded to a perovskite-type structure. The XRD results showed that as the Co concentration of the $LaCr_xCo_{1-x}O_3$powders increased, the crystal structure was transformed from an orthorhombic phase to a rhombohedral phase. Moreover, the $LaCr_xCo_{1-x}O_3$ powders with $0{\leq}x<0.8$ had a rhombohedral symmetry. The size of the particles in the $LaCr_xCo_{1-x}O_3$powders increased from 0.1 to $0.5{\mu}m$ as the Co concentration increased. The sensing performance of the stack-structured $LaCr_xCo_{1-x}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensors was found to divide the impedance component between the resistance and capacitance. The response of these sensors to NO gas was more sensitive than that to $NO_2$ gas. Compared to other impedancemetric sensors, the $LaCr_{0.8}Co_{0.2}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensor exhibited good reversibility and reliable sensingresponse properties for $NO_x$ gases.

• 한국재료학회지
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• 제9권1호
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• pp.3-7
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• 1999

The change of phosphorescent property with chemical modification and co-doping of Nd as an auxiliary activator in CaAl$_2$$O_4$: Eu\ulcorner, Nd\ulcorner phosphor, employing Nd\ulcornerion(0.6%) and an co-activator maintained its afterglow for 4.5 hours. And also the initial persistent brightness and phosphorescent property were further improved both by substituting Al by B atoms and incorporation of Nd\ulcorner ion. It was found that the persistent time was 30 hours for&Ca(Al_{0.97}\;B_{0.03}) $_2$$O_4$:EU\ulcorner(0.3%), Nd\ulcorner(0.6%) phosphor.

• Journal of Electrochemical Science and Technology
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• 제7권4호
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• pp.263-268
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• 2016

This study describes the effect of coating the $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$ cathode surface with a homogeneous carbon layer produced by carbonization of polyvinylidene fluoride (PVDF) as a novel organic source. The phase integrity of the above cathode was not affected by the carbon coating, whereas its rate capability and cycling performance were enhanced. Similarly, the cathode thermal stability was also improved after coating, which additionally protected the cathode surface against the reactive electrolyte containing hydrofluoric acid (HF). The results show that coating the $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$ cathode with carbon using the PVDF precursor is an effective approach to enhance its electrochemical properties.

• 한국자기학회지
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• 제6권4호
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• pp.204-210
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• 1996

제철소의 부산물인 mill scale과 $Fe_{2}O_{3}$, 그리고 이들의 혼합물을 사용하여 M형 ferrite를 제조하였다. $Fe_{2}O_{3}$와 $BaCO_{3}$의 몰비를 5.2~6.0으로 변화시킨 혼합물의 하소 및 소결은 각각 $1150^{\circ}C,\;1250^{\circ}C$에서 2시간 행하였으며, 하소시에 mill scale 중의 불순물 성분인 $SiO_{2},\;Al_{2}O_{3},\;MgO,\;CaO\;및\;Na_{2}O$를 적당량 첨가한 시편으로 자기적 특성과 형상을 조사하였다. $Na_{2}O$를 첨가한 시편은 미반응의 $Fe_{2}O_{3}$와 중간 화합물인 $BaFe_{2}O_{4}$의 영향으로 자기적 특성이 감소하였으나, $BaO.5.6Fe_{2}O_{3}$ 조성에 $SiO_{2}$와 $Al_{2}O_{3}$의 첨가는 특성의 증진을 보였으며, 특히 $Al_{2}O_{3}$는 $M_{s}$ 값은 감소시켰으나 $_{B}H_{c}$ 값을 증가시켰다. BM($BaCo_{3}$와 mill scale의 혼합물)과 BFM($BaCO_{3},\;Fe_{2}O_{3}$, mill scale의 혼합물) 소결 시편의 ${(BH)}_{max}$는 각각 0.86, 1.04 MGOe였으며, $440^{\circ}C$ 부근에서 자기 특성의 변화를 보였다.

• 한국세라믹학회지
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• 제19권4호
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• pp.287-292
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• 1982

Nonohmic properties of ZnO ceramics with various small amounts of additives were studied in relation to experimental methods, additive contant and sintaring temperature. The kinds of additives used to following chemicals were basic additives ($0.5Bi_2O_3$, $0.3BaCO_3$, $0.5MnCO_3$, $0.5Cr_2O_3$, $0.1KNO_3$), $TiO_2$ and $Al(OH)_3$. Expecially, this study has focused on the effectsof $TiO_2$ and $Al(OH)_3$ in ZnO ceramics with the basic additives. SEM studies indicated that the addition of TiO2 promoted grain growth but retarded grain growth with the addition of $Al(OH)_3$. Also, in the case of calcination of ZnO with $TiO_2$ and ZnO with $Al(OH)_3$ previously, grain size of ZnO with $TiO_2$ was larger and that of ZnO with Al(OH)3 was smaller in comparison to the case with out calcination. From the viewpoint of nonohmic exponent and nonohimic resistance, electrical characteristics of ZnO, $TiO_2$ and the basic additives was more effective than that of ZnO, $Al(OH)_3$ and the basic additives. Nonohmic exponent and nonohmic resistance of ZnO, $TiO_2$ and the basic additives was 11-13 and 40-65 respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.54-54
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• 2008

$Eu^{2+}$, $Nd^{3+}$ co-doped $BaAl_2O_4$ are known as a long afterglow phosphor. We found that $Eu^{2+}$-doped $BaAl_2O_4$ showed ptotoconductivity in the range of UV and visual light. In this study, $BaAl_2O_4$:Eu thin film has been prepared by RF sputtering method and a sensing characteristics to UV and visual light was performed. Only $Eu^{2+}$ and $Nd^{3+}$ co-doped $BaAl_2O_4$ powders and targets for deposition were prepared by a convention solid state method, and the deposition was performed in a reducing $H_2$-Ar mixture gas on Si substrates. The observation of crystalline phase and morphology of the sputtered film were performed using XRD, EDX. The photoluminescence and photocurrent to UV and visual light were measured simultaneously using 300W-Xe solar simulator as a light source. It was confirmed that the photocurrent induced by irradiation of light showed a linear relationship to the light intensity.

• 한국결정학회지
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• 제9권1호
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• pp.48-52
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• 1998

Nd2O3, BaCo3, Co3O4를 출발물질로 하여 새로운 Nd3Ba5Co4O15상을 고상반응법에 의하여 합성하였다. 반응 온도는 1200℃ 로 하였고 열처리 중 반복적인 혼합을 실시하였다. Nd3Ba5Co4O15상의 결정구조는 분말 X-선회절법에 의한 데이터를 Rietveld법을 이용하여 정밀화하였다. 출발 모델은 Nd3.43Ba4.42Co2.23Al1.77O15의 결정구조를 따랐고 공간군 P63mc(186), 격자상수 a=11.636(5) Å, c=6.846(3) Å. 최종 신뢰도 R값은 Rwp=0.097, Rp=0.068로 나타났다. 이 상의 결정구조는 CoVICoIV3O15 클러스터로 구성되어 있고 이 클러스터는 CoVI 육면체가 3개의 CoIV 사면체와 corner sharing하는 형태를 보인다.