• 전기화학회지
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• 제15권2호
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• pp.67-73
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• 2012

본 연구에서는 습식분쇄, 구형화 분무건조 및 열처리 공정을 통해 구형의 $LiMn_{2-x}M_xO_4$(M = Al, Mg, B) 스피넬계 양극소재를 합성하고, 이의 전기화학적 성능을 평가하였다. $MnO_2$ (Tosoh, 91.94%), $Li_2CO_3$ (SQM, 97%), $MgCO_3$ (Aldrich, 99%), $Al(OH)_3$ (Aldrich, 99%) 및 $B_2O_3$ (Aldrich, 99%)를 원료로 사용하였으며, 분무건조공정에서 전구체의 구형화도 증가를 위해 PAAH 바인더를 첨가하였다. 200~500 nm 크기로 분쇄된 혼합 슬러리 용액으로부터 분무건조법을 통해 구형의 전구체를 제조하고, 이를 다양한 조건에서 열처리하여 최종 스피넬계 $LiMn_{2-x}M_xO_4$ (M = Al, Mg, B) 양극소재를 제조하였다. 제조된 구형의 $LiMn_{2-x}M_xO_4$ (M = Al, Mg, B) 양극재료는 이종원소 치환량, 특히 Boron 치환량에 따라 입자 표면 및 내부의 치밀도가 변화하는 것을 확인할 수 있었으며, 치밀도가 증가함에 따라 소재의 출력특성이 향상되었으며, 최적 조성의 양극소재는 상온 5 C 용량이 0.2 C 용량 대비 90% 이상이 됨을 확인하였다. 또한 표면의 치밀도도 증가함에 따라 $60^{\circ}C$ 고온 충방전 조건에서 수명특성이 향상되어 500회 사이클 이후에도 초기용량의 80% 이상을 유지하였다.

• 한국분말재료학회지
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• 제25권3호
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• pp.203-207
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• 2018

Plastic pollution is threatening human health and ecosystems, resulting in one of the biggest challenges that humanity has ever faced. Therefore, this study focuses on the preparation of macroporous carbon from biowaste (MC)-supported manganese oxide ($MnO_2$) as an efficient, reusable, and robust catalyst for the recycling of poly(ethylene terephthalate) (PET) waste. As-prepared $MnO_2/MC$ composites have a hierarchical pore network and a large surface area ($376.16m^2/g$) with a narrow size distribution. $MnO_2/MC$ shows a maximum yield (98%) of bis(2-hydroxyethyl)terephthalate (BHET) after glycolysis reaction for 120 min. Furthermore, $MnO_2/MC$ can be reused at least nine times with a negligible decrease in BHET yield. Based on this remarkable catalytic performance, we expect that $MnO_2$-based heterogeneous catalysts have the potential to be introduced into the PET recycling industry.

• KEPCO Journal on Electric Power and Energy
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• 제2권2호
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• pp.285-291
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• 2016

In chemical-looping combustion, pure oxygen is transferred to fuel by solid particles called as oxygen carrier. Chemical-looping combustion process usually utilizes a circulating fluidized-bed process for fuel combustion and regeneration of the reduced oxygen carrier. The performance of an oxygen carrier varies with the active metal oxide and the raw support materials used. In this work, spraydried Mn-based oxygen carriers were prepared with different raw support materials and their physical properties and oxygen transfer performance were investigated to determine that the raw support materials used are suitable for spray-dried manganese oxide oxygen carrier. Oxygen carriers composed of 70 wt% $Mn_3O_4$ and 30 wt% support were produced using spray dryer. Two different types of $Al_2O_3$, ${\gamma}-Al_2O_3$ and ${\alpha}-Al_2O_3$, and $MgAl_2O_4$ were applied as starting raw support materials. The oxygen carrier prepared from ${\gamma}-Al_2O_3$ showed high mechanical strength stronger than commercial fluidization catalytic cracking catalyst at calcination temperatures below $1100^{\circ}C$, while the ones prepared from ${\alpha}-Al_2O_3$ and $MgAl_2O_4$ required higher calcination temperatures. Oxygen transfer capacity of the oxygen carrier prepared from ${\gamma}-Al_2O_3$ was less than 3 wt%. In comparison, oxygen carriers prepared from ${\alpha}-Al_2O_3$ and $MgAl_2O_4$ showed higher oxygen transfer capacity, around 3.4 and 4.4 wt%, respectively. Among the prepared Mn-based oxygen carriers, the one made from $MgAl_2O_4$ showed superior oxygen transfer performance in the chemical-looping combustion of $CH_4$, $H_2$, and CO. However, it required a high calcination temperature of $1400^{\circ}C$ to obtain strong mechnical strength. Therefore, further study to develop new support compositions is required to lower the calcination temperature without decline in the oxygen transfer performance.

• 한국세라믹학회지
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• 제52권4호
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• pp.237-242
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• 2015

$Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3$ (BNKT) lead-free piezoelectric ceramics modified by $LaMnO_3$ (LM) were fabricated by conventional solid-state method. The crystal structure and the morphology of the lead free ceramics were analyzed by XRD (X-ray diffraction) and FE-SEM (Field Emission Scanning Electron Microscopy). The LM modified BNKT ceramics have a phase transition from ferroelectric tetragonal to non-polar pseudo-cubic. Despite decreases in the remnant polarization ($P_r$) and coercive field ($E_c$) in the P-E hysteresis loops, the electric-field induced strain properties were significantly enhanced by the LM modification. The highest value of $S_{max}/E_{max}=412pm/V$ at an applied electric field of 5 kV/mm was found in BNKT-0.01LM ceramic.

• 한국전기전자재료학회논문지
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• 제27권12호
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• pp.825-830
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• 2014

$[(Co_{1-x}Cu_x)_{0.2}(Ni_{0.3}Mn_{0.7})_{0.8}]_3O_4$ ($0{\leq}x{\leq}1$) thin films prepared by metal organic decomposition process were fabricated on SiN/Si substrate for infrared sensor application. Their structural and electrical properties were investigated with variation of Cu dopant. The $[(Co_{1-x}Cu_x)_{0.2}(Ni_{0.3}Mn_{0.7})_{0.8}]_3O_4$ (CCNMO) film annealed at $500^{\circ}C$ exhibited a dense microstructure and a homogeneous crystal structure with a cubic spinel phase. Their crystallinity was further enhanced with increasing doped Cu amount. The 120 nm-thick CCNMO (x=0.6) thin film had a low resistivity of $53{\Omega}{\cdot}cm$ at room temperature while the Co-free film (x=1) showed a significantly decreased resistivity of $5.9{\Omega}{\cdot}cm$. Furthermore, the negative temperature coefficient of resistance (NTCR) characteristics were lower than $-2%/^{\circ}C$ for all the specimens with $x{\geq}0.6$. These results imply that the CCNMO ($x{\geq}0.6$) thin films are a good candidate material for infrared sensor application.

• 한국재료학회지
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• 제21권5호
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• pp.277-282
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• 2011

Negative temperature coefficient (NTC) materials have been widely studied for industrial applications, such as sensors and temperature compensation devices. NTC thermistor thick films of $Ni_{1+x}Mn_{2-x}O_{4+{\delta}}$ (x = 0.05, 0, -0.05) were fabricated on a glass substrate using the aerosol deposition method at room temperature. Resistance verse temperature (R-T) characteristics of the as-deposited films showed that the B constant ranged from 3900 to 4200 K between $25^{\circ}C$ and $85^{\circ}C$ without heat treatment. When the film was annealed at $600^{\circ}C$ 1h, the resistivity of the film gradually decreased due to crystallization and grain growth. The resistivity and the activation energy of films annealed at $600^{\circ}C$ for 1 h were 5.203, 5.95, and 4.772 $K{\Omega}{\cdot}cm$ and 351, 326, and 299 meV for $Ni_{0.95}Mn_{2.05}O_{4+{\delta}}$, $NiMn_2O_4$, and $Ni_{1.05}Mn_{1.95}O_{4+{\delta}}$, respectively. The annealing process induced insulating $Mn_2O_3$ in the Ni deficient $Ni_{0.95}Mn_{2.05}O_{4+{\delta}}$ composition resulting in large resistivity and activation energy. Meanwhile, excess Ni in $Ni_{1.05}Mn_{1.95}O_{4+{\delta}}$ suppressed the abnormal grain growth and changed $Mn^{3+}$ to $Mn^{4+}$, giving lower resistivity and activation energy.

• 대한토목학회논문집
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• 제26권3B호
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• pp.321-327
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• 2006

본 연구는 축산폐수처리를 위해 광촉매의 적용가능성과 처리효율 및 범위를 실험하여 축산폐수처리에 대한 기초 자료로 제시하고자 한다. 축산폐수처리에 대한 광촉매양의 증가는 높은 처리효율을 나타냈으며 알카리 영역에서 보다 산성영역 특히 pH3에서 축산폐수처리 효과는 우수하게 나타났다. 또한 광촉매양의 증가에 따라 색도 보다는 $TCOD_{Mn}$의 제거가 빠르게 이루어 졌다. UV 또는 $TiO_2$를 단독으로 사용하여 폐수처리를 하였을 때 보다 $UV/TiO_2$를 함께 적용하였을 때가 처리효율은 우수하게 나타났으며 산화제로 과산화수소를 주입하였을 때 처리효율은 $UV/TiO_2$만을 적용하였을 때 보다 처리효율이 우수하게 나타났다. 본 실험에서의 과산화수소 적정 주입량은 200 mg/L이며 과산화수소 적정주입량이 보다 많이 주입되었을 때는 처리효율이 떨어지는 것으로 나타났다. 또한 과산화수소의 주입량은 실험 시 계속적으로 주입이 되어야 높은 처리효율을 얻을 수 있었다.

• 한국세라믹학회지
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• 제39권9호
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• pp.829-834
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• 2002

$Er(NO_3)_3{\codt}5H_2O,\;Mn(CH_3CO_2)_2{\cdot}4H_2O$를 출발원료로 사용하여 졸-겔 법으로 Si(100) 기판 위에 코팅된 $ErMnO_3$ 박막의 강유전 특성에 관하여 연구하였다. $ErMnO_3$ 박막은 800$^{\circ}C$에서 결정화가 시작되었으며, (001)로 우선 배향된 $ErMnO_3$ 박막을 얻을 수 있었다. 본 실험에서 800$^{\circ}C$에서 1 h 열처리하여 얻은 $ErMnO_3$ 박막은 1∼100 KHz의 주파수 범위에서 유전 상수(k)는 26, 유전 손실(tan ${\delta}$)은 0.032의 값을 나타내었으며, 이때 $ErMnO_3$ 박막의 입자 크기는 10∼30 nm이었다. 강유전 특성은 (001) 배향성이 증가할수록 잔류 분극 값이 증가하였으며, 800$^{\circ}C$에서 1시간 열처리하여 $ErMnO_3$ 박막의 잔류 분극 값($P_r$)은 400 nC/$cm^2$를 나타내었다. 또한 열처리 시간이 증가할수록 치밀하고 균일한 박막을 얻어 낮은 항전계 ($E_c$) 값을 가졌다.

• 한국전기전자재료학회논문지
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• 제20권9호
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• pp.771-775
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• 2007

In this study, in order to develop low temperature sintering ceramics for thickness vibration mode multilayer piezoelectric transformer, $PbTiO_3$ system ceramics were fabricated using $Na_2CO_3,\;Li_2CO_3,\;MnO_2\;and\;Bi_2O_3$ as sintering aids and their dielectric and piezoeletric properties were investigated according to the amount of $Bi_2O_3$ addition. At the sintering temperature of $900^{\circ}C\;and\;Bi_2O_3$ addition of 0.1 wt%, density, grain size, thickness vibration mode eletromechanical coupling factor($k_t$), thickness vibration mode mechanical quality factor($Q_{mt}$) and dielecteic constant(${\varepsilon}_r$) showed the optimum value of $6.94g/cm^3,\;2.413{\mu}m$, 0.497, 3,162 and 209, respectively, for thickness vibration mode multilayer piezoelectric transformer application.

• Bulletin of the Korean Chemical Society
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• 제34권1호
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• pp.89-94
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• 2013

Layered $Li_{1+x}(Mn_{0.4}Ni_{0.4}Fe_{0.2})_{1-x}O_2$ (0 < x < 0.3) solid solutions were synthesized using solgel method with adipic acid as chelating agent. Structural and electrochemical properties of the prepared powders were examined by means of X-ray diffraction, Scanning electron microscopy and galvanostatic charge/discharge cycling. All powders had a phase-pure layered structure with $R\bar{3}m$ space group. The morphological studies confirmed that the size of the particles increased at higher x content. The charge-discharge profiles of the solid solution against lithium using 1 M $LiPF_6$ in EC/DMC as electrolyte revealed that the discharge capacity increases with increasing lithium content at the 3a sites. Among the cells, $Li_{1.2}(Mn_{0.32}Ni_{0.32}Fe_{0.16})O_2$ (x = 0.2)/$Li^+$ exhibits a good electrochemical property with maximum initial capacity of 160 $mAhg^{-1}$ between 2-4.5 V at 0.1 $mAcm^{-2}$ current density and the capacity retention after 25 cycles was 92%. Whereas, the cell fabricated with x = 0.3 sample showed continuous capacity fading due to the formation of spinel like structure during the subsequent cycling. The preparation of solid solutions based on $LiNiO_2-LiFeO_2-Li_2MnO_3$ has improved the properties of its end members.