• 한국세라믹학회지
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• 제27권7호
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• pp.899-906
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• 1990

The cordierite powders were prepared from Mg(NO3)2.6H2O, Al(NO3)3.9H2O and colloidal silica by the coprecippitation method, and the sintering behavior of the powders were investigated. Two different methods were applied for producing the precursor powders. The one was to added the aqueous solution of Mg(NO3)2.6H2O and Al(NO3)3.9H2O to NH4OH to adjust pH at 10 where the colloidal silica of pH 10 was added. The other wa to add the aqueous solution of Mg(NO3)2.6H2O and Al(NO3)3.9H2O to the colloidal silica with NH4OH to control the final mixture to be at pH 10. It was confirmed that more homogeneous powders were obtained from the latter method. The firing linear shrinkage of the powder compacts fabricated from the calcined powder between 90$0^{\circ}C$ and 110$0^{\circ}C$ was found to be larger as the calcination temperature was low. But all of them stopped shrinking around 120$0^{\circ}C$. The powder compacts, fabricated using the calcined powders at 90$0^{\circ}C$ and 95$0^{\circ}C$ for 2hours and sintered at 142$0^{\circ}C$ for 2hours, showed relative density of 93-96%, 3-point bending strength of 81-83MPa, KIC of 1.9-2.4 MPam1/2 and thermal expansion coefficient of 0.213-0.732$\times$10-6$^{\circ}C$.

• 한국자기공명학회논문지
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• 제23권2호
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• pp.40-45
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• 2019

The phase transition temperatures and thermodynamic properties of $(NH_4)_2MnCl_4{\cdot}2H_2O$ grown by the slow evaporation method were studied using differential scanning calorimetry and thermogravimetric analysis. A structural phase transition occurred at temperature $T_{C1}$ (=264 K), whereas the changes at $T_{C2}$ (=460 K) and $T_{C3}$ (=475 K) seemed to be chemical changes caused by thermal decomposition. In addition, the chemical shift and the spin-lattice relaxation time $T_{1{\rho}}$ were investigated using $^1H$ magic-angle spinning nuclear magnetic resonance (MAS NMR), in order to understand the role of $NH_4{^+}$ and $H_2O$. The rise in $T_{1{\rho}}$ with temperature was related to variations in the symmetry of the surrounding $H_2O$ and $NH_4{^+}$.

• Bulletin of the Korean Chemical Society
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• 제23권1호
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• pp.35-40
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• 2002

Photoreaction of guest organic anions in layered organic-inorganic hybrid materials was investigated. The layered hybrids were synthesized by an anion-exchange reaction of $[LiAl_2(OH)_6]Cl{\cdot}yH_2O$ layered double hydroxide with aqueous (Z,Z)- and (E,E)-muconates under inert atmospheric condition, to give new organicinorganic hybrids of $[LiAl_2(OH)_6]_2[(Z,Z)-C_6H_4O_4]{\cdot}zH_2O$ and $[LiAl_2(OH)_6]_2[(E,E)-C_6H_4O_4]{\cdot}H_2O$, respectively. The basal spacings calculated by XRPD of intercalates indicate that muconate anions have almost vertical arrangements against the host $[LiAl_2(OH)_6]^+$ lattices in the interlayer of organic-inorganic hybrid materials. When UV light was irradiated on the suspension of $[LiAl_2(OH)_6]_2[(Z,Z)-C_6H_4O_4]{\cdot}zH_2O$, the (Z,Z)-muconate anions of the gallery space of hybrids were polymerized in the aqueous media while it was isomerized into more stable (E,E)-muconate in the methanollic suspension in the presence of catalytic amount of molecular iodine. All the products were characterized using elemental analysis, TGA, XRPD, FT-IR, $^1H$ NMR and $^{13}C$ CP-MAS NMR.

• Bulletin of the Korean Chemical Society
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• 제7권6호
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• pp.466-468
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• 1986

Reaction of $Ir(ClO_4)(CO)(PPh_3)_2$ with trans-$C_6H_5CH$ = $CHCO_2C_2H_5$ produces a new cationic iridium(I) complex, [Ir (trans-$C_6H_5CH$ = $CHCO_2C_2H_5)(CO)(PPh_3)_2]ClO_4$ where trans-$C_6H_5CH$ = $CHCO_2C_2H_5$ seems to be coordinated through the carbonyl oxygen rather than through the $\pi$-system of the olefinic group according to the spectral data. It has been found that Ir$(ClO_4)(CO)(PPh_3)_2$ catalyzes the hydrogenation of $CH_2$ = $CHCO_2C_2H_5$, trans-$CH_3CH$ = $CHCO_2C_2H_5$ and trans-$C_6H_5CH$ = $CHCO_2C_2H_5$ to $CH_3CH_2CO_2C_2H_5$, $CH_3CH_2CH_2CO_2C_2H_5$ and $C_6H_5CH_2CH_2CO_2C_2H_5$, respectively at room temperature under the atmospheric pressure of hydrogen. The relative rates of the hydrogenation of the unsaturated esters are mostly understood in terms of steric reasons.

• 태양에너지
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• 제11권2호
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• pp.41-50
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• 1991

본 연구는 상변화물질로써 용융점온도가 $62^{\circ}C$인 파라핀($C_{28}H_{58}$)과 용융점온도가 $79^{\circ}C$인 피로인산나트륨($Na_4P_2O_7{\cdot}10H_2O$)을 사용하여 축열 및 방열과정 시 잠열축열조내에서 각 상변화물질의 시간경과에 따른 온도특성 및 열전달현상을 실험적으로 규명한 것으로 각 상변화물질의 온도분포와 축열량 및 방열량을 계산하고 이를 비교, 검토한 것이다. 파라핀의 경우 축열과정초기에 자연대류 열전달현상으로 인하여 온도가 서서히 증가하는 반면 피로인산나트륨의 경우는 전도 열전달 현상의 지배적인 영향으로 인하여 축열과정 초기에 온도가 급격히 증가하는 형태로 나타났다. 또한 축열 및 방열과정 시 파라핀의 경우 tube의 상하부벽면에서의 온도변화와 중심부의 온도변화가 큰 차이를 보였으나 피로인산나트륨의 경우 tube의 상하부 벽면에서의 온도와 중심부에서의 온도는 큰 차이를 나타내지 않았다. 그리고 축열과정 시 동일질량에 대한 각 상변화물질의 축열량은 파라핀보다 피로인산나트륨이 약 16%정도 많은 것으로 나타났다.

• 전기전자학회논문지
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• 제26권1호
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• pp.111-118
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• 2022

본 논문에서는 고전압 SiC Power 소자와 집적이 가능한 4H-SiC CMOS에 대해 연구하였다. SiC CMOS 소자 연구를 통해 고출력 SiC Power 소자와 함께 제작을 가능하게 함으로써 SiC 전력소자를 이용하는 고출력 시스템의 효율 및 비용면에서 우수한 성능을 기대할 수 있다. 따라서 4H-SiC 기판에서 CMOS를 설계한 후 TCAD 시뮬레이션을 통해 전기적 특성 및 고온 동작 신뢰성을 비교하였다. 특히 높은 온도에서 신뢰성 있는 동작을 위해 gate dielectric으로 HfO₂를 변경함으로써 SiO₂보다 열적 특성이 개선됨을 확인하였다.

• 대한화학회지
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• 제39권6호
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• pp.434-439
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• 1995

산소, 질소, 그리고 황 주개 원자의 이염기성 세자리 리간드로서 S-methyl-3(-2-hydroxy-x-phenyl)methylenedithiocarbazate($L^1:x=5-H$)와 그 유도체($L^2:x=5-CH_3,\;L^3:x=3CH_3O,\;L_4:x=5,6-C_4H_4\; 그리고\;x^5:ㅌ=5-NO_2$)의 6-배위 몰리브덴(V)-산소 착물, ($R_4N$)[MoO(NCS)_2L](R=CH_3,\;C_3H_5,\;n-C_4H_9)$들을 합성하고 원소분석, 몰 전도도, UV-Vis, IR, $1^H$ NMR 그리고 CV 등을 이용하여 착물의 구조와 분광학적 및 전기화학적 성질 등을 조사하였다.

• 전기전자학회논문지
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• 제18권4호
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• pp.447-455
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• 2014

본 연구에서는 4H-SiC MOSFET의 주요 문제점인 $SiC/SiO_2$ 계면의 특성을 향상시키기 위해 PECVD (plasma enhanced chemical vapor deposition) 공정을 이용하여 n-based 4H-SiC MOS Capacitor를 제작하였다. 건식 산화 공정의 낮은 성장속도, 높은 계면포획 밀도와 $SiO_2$의 낮은 항복전계 등의 문제를 극복하기 위하여 PECVD와 NO어닐링 공정을 사용하여 MOS Capacitor를 제작하였다. 제작이 끝난 후, MOS Capacitor의 계면특성을 hi-lo C-V 측정, I-V 측정 및 SIMS를 이용해 측정하고 평가하였다. 계면의 특성을 건식 산화의 경우와 비교한 결과 20% 감소한 평탄대 전압 변화, 25% 감소한 $SiO_2$ 유효 전하 밀도, 8MV/cm의 증가한 $SiO_2$ 항복전계 및 1.57eV의 유효 에너지 장벽 높이, 전도대 아래로 0.375~0.495eV만큼 떨어져 있는 에너지 영역에서 69.05% 감소한 계면 포획 농도를 확인함으로써 향상된 계면 및 산화막 특성을 얻을 수 있었다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.89-92
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• 2007

Partail oxidation(POX) of n-butane was investigated in this research by employing ceria-promoted Ni/calcium hydroxyapatite catalysts ($Ce_xNi_{2.5}Ca_{10}(OH)_2(PO_4)_6$ ; x = $0.1{\sim}0.3$) which had recently been reported to exhibit good catalytic performance in POX of methane and propane. The experiments were carried out with changing ceria content, $O_2/n-C_4H_{10}$ ratio and temperature. As the $O_2/n-C_4H_{10}$ feed ratio increased up to 2.75, n-$C_4H_{10}$ conversion and $H_2$ yield increased and the selectivity of methane and other hydrocarbons decreased. But with $O_2/n-C_4H_{10}$ = 3.0, $n-C_4H_{10}$ conversion and $H_2$ yield decreased. This is considered due to that too much oxygen may inhibit the reduction of Ni or induce the oxidation of Ni, which results in poor catalytic activity. The optimum $O_2/n-C_4H_{10}$ ratio lay between 2.50 and 2.75. $Ce_{0.1}Ni_{2.5}Ca_{10}(OH)_2(PO_4)_6$ showed the highest $n-C_4H_{10}$ conversion and $H-2$ yield on the whole. In durability tests, higher hydrogen yield and better catalyst stability were obtained with the $O_2/n-C_4H_{10}$ ratio of 2.75 than with the ratio of 2.5.

• 분석과학
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• 제20권4호
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• pp.355-360
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• 2007

The title complex, $(C_3H_{12}N_2)[\{Cd(H_2O)(C_6H_5O_7)\}_2]{\cdot}6H_2O$, I, has been prepared and its structure characterized by FT-IR, EDS, elemental analysis, ICP-AES, and X-ray single crystallography. It is triclinic system, $P{\bar{1}}$ space group with a = 10.236(2), b = 11.318(2), c = $13.198(2){\AA}$, ${\alpha}=77.95(1)^{\circ}$, ${\beta}=68.10(1)^{\circ}$, ${\gamma}=78.12(1)^{\circ}$, V = $1373.5(3){\AA}^3$, Z = 2. Complex I has constituted by protonated 1,3-diaminopropane cations, citrate coordinated cadmium(II) anions, and free water molecules. The central cadmium atoms have a capped trigonal prism geometry by seven coordination with six oxygen atoms of three different citrate ligands and one water molecule. Citrate ligands are bridged to three different cadmium atoms. Each cadmium atom is linked by carboxylate and hydroxyl groups of citrate ligand to construct an one-dimensional ladder-type assembly structure. The polymeric crystal structure is stabilized by three-dimensional networks of the intermolecular O-H${\cdots}$O and N-H${\cdots}$O hydrogen-bonding interaction.