• Advances in Energy Research
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• 제5권1호
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• pp.13-29
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• 2017

The roles of Na, Mn, W and silica, and the synergistic effects between each metal in the $MnNa_2WO_4/SiO_2$ catalyst have been investigated for oxidative coupling of methane (OCM). The crystallisation of amorphous silica during calcination at $900^{\circ}C$ was promoted primarily by Na, but Mn and W also facilitated this process. The interaction between Na and Mn tended to increase the extent of conversion of $Mn_3O_4$ to $Mn_2O_3$. The formation of $Na_2WO_4$ was dependent on the order in which Na and W were introduced to the catalyst. The impregnation of W before Na resulted in the formation of $Na_2WO_4$, but this did not occur when the impregnation order was reversed. $MnWO_4$ formed in all cases where Mn and W were introduced into the silica support, regardless of the impregnation order; however, the formation of $MnWO_4$ was inhibited in the presence of Na. Of the prepared samples in which a single metal oxide was introduced to silica, only $Mn/SiO_2$ showed OCM activity with significant oxygen conversion, thus demonstrating the important role that Mn plays in promoting oxygen transfer in the reaction. The impregnation order of W and Na is critical for catalyst performance. The active site, which involves a combination of Na-Si-W-O, can be formed in situ when distorted $WO_4^{2-}$ interacts with silica during the crystallisation process facilitated by Na. This can only occur if the impregnation of W occurs before Na addition, or if the two components are introduced simultaneously.

• 한국세라믹학회지
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• 제42권7호
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• pp.503-508
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• 2005

A simple and effective method for the synthesis of LiMn$_{2}$O$_{4}$ powder as a cathode material for lithium secondary battery is reported. Micrometer size LiMn$_{2}$O$_{4}$ was prepared by combustion synthesis technique employing initial mixture of l.l LiNO$_{3}$ -1.3Mn-0.7MnO$_{2}$-1NaCl composition. Parametric study of the combustion process including molar ratio of Mn/MnO$_{2}$ and NaCl concentration were carried out under air atmosphere. The combustion products obtained were additionally heat treated at the temperature 900$^{\circ}C$ and the washed by distilled water. The results of charging-discharging characteristics revealed that LiMn$_{2}$O$_{4}$ cell synthesized in the presence of NaCl had a high capacity and much better reversibility than one formed without NaCl An approximate chemical mechanism for LiMn$_{2}$O$_{4}$ formation is proposed.

• Bulletin of the Korean Chemical Society
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• 제23권5호
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• pp.679-682
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• 2002

Layered Na0.7[Ni0.05Mn0.95]O2 compounds have been synthesized by a sol-gel method, using glycolic acid as a chelating agent. Na0.7[Ni0.05Mn0.95]O2 precursors w ere used to prepare layered lithium manganese oxides by ion exchange for Na by Li, using LiBr in hexanol. Powder X-ray diffraction shows the layered Na0.7[Ni0.05Mn0.95]O2 has an O3 type structure, which exhibits a large reversible capacity of approximately 190 mA h g-1 in the 2.4-4.5 V range. Na0.7[Ni0.05Mn0.95]O2 powders undergo transformation to spinel during cycling.

• 상하수도학회지
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• 제36권5호
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• pp.249-260
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• 2022

The effect of permanganate oxidation was investigated as water treatment strategy with a focus on comparing the reaction characteristics of NaOCl and sodium permanganate (NaMnO₄) in algae (Monoraphidium sp., Micractinium inermum, Microcystis aeruginosa)-contained water. Flow cytometry explained that chlorine exposure easily damaged algae cells. Damaged algae cells release intracellular organic matter, which increases the concentration of organic matter in the water, which is higher than by NaMnO₄. The oxidation reaction resulted in the release of toxin (microcystin-LR, MC-LR) in water, and the reaction of algal organic matter with NaOCl resulted in trihalomethanes (THMs) concentration increase. The oxidation results by NaMnO₄ significantly improved the concentration reduction of THMs and MC-LR. Therefore, this study suggests that NaMnO₄ is effective as a pre-oxidant for reducing algae damage and byproducts in water treatment process.

• 한국수소및신에너지학회논문집
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• 제17권4호
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• pp.353-361
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• 2006

As one of the thermochemical water splitting hydrogen production cycles, which could be operated at the lower temperature below 1200 K, we investigated the feasibility of the cyclic operation of Ispra Mark 2 cycle with the addition of $ZrO_2$. The cycle is theoretically composed of three reaction steps; (1) 1st step($2MnO_2{\rightarrow}Mn_2O_3+0.5O_2$), (2) 2nd step($Mn_2O_3+4NaOH{\rightarrow}2Na_2O{\cdot}MnO_2+H_2+H_2O$) and (3) 3rd step($2Na_2O{\cdot}MnO_2H_2O{\rightarrow}4NaOH+2MnO_2$). From the TPR tests, the temperature ranges for $O_2$ production in 1st step and $H_2$ production in 2nd step were $550{\sim}750^{\circ}C$ and $650{\sim}750^{\circ}C$, respectively. In $MnO_2/Mn_2O_3/NaOH$ system, the formation of molten products due to the reaction between manganese oxides and NaOH were greatly decreased with the addition of $ZrO_2$. In addition, the results of a cyclic test were discussed with the viewpoint of $H_2$ production amounts and the feasibility of the process improvement.

• 한국세라믹학회지
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• 제46권6호
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• pp.689-694
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• 2009

Layer-structured $Na_xCo_2O_4$ was synthesized from $Na_2CO_3\;and\;Co_3O_4$ powders. The chemical concentrations of Na and additive were controlled to enhance the thermoelectric properties over the temperature range from 400 K to 1,150 K. As a result, we obtained the maximum thermoelectric properties at a single phase region with Na content of x=1.5. When Na content was smaller than x=1.5, the thermoelectric properties was low due to formation of second phases of CoO and other oxides. Additionally, Mn was doped to improve thermoelectric properties by means of decreasing thermal conductivity. The results showed that the concentrations of both Na and Mn are all governing factors to determine the thermoelectric properties of $Na_xCo_2O_4$ system.

• 대한환경공학회지
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• 제29권5호
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• pp.571-576
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• 2007

본 연구에서는 세 가지 다른 방법으로 제조된 망간사에 의한 용존 $Mn^{2+}$의 제거특성을 회분식 및 칼럼실험을 통하여 조사하였다. 실험실 규모에서 망간의 주입농도를 달리하여 망간사 제조시, 모래에 코팅된 망간 코팅량은 주입된 망간 농도에 비례하여 나타났다. 망간사에 의한 용존 망간의 제거는 용액의 pH 증가에 따라 증가하는 양이온형 흡착경향을 따랐다. 흡착을 통한 용존 망간의 제거는 망간사 코팅방법 및 코팅량에 거의 영향을 받지 않고 모든 pH 영역에서 유사하게 나타났다. NaClO를 산화제로써 주입하였을 때 망간사에 의한 용존 망간의 제거는 NaClO 농도에 비례하였다. 이러한 결과는 NaClO 주입농도 증가에 따라 용존 망간이 망간산화물로 산화되고 이때 생성되는 산화망간이 망간사 표면으로의 코팅이 증가되어 나타난 현상으로 여겨진다. 칼럼반응기를 이용한 용존 망간제거 실험에서, NaClO를 주입하지 않은 경우에는 4,100 bed volume 이 후 땅간의 파과가 이루어졌지만, NaClO를 주입하였을 경우에는 파과가 1.6배 지연되어 나타나서 산화제를 사용하는 것이 용존 망간의 제거율을 높이는 것임을 또한 확인할 수 있었다.

• 전기학회논문지
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• 제60권4호
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• pp.801-804
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• 2011

Electrical properties and microstructure were investigated on the effects of $MnO_2$ and the lead-free $(Na_{0.44}K_{0.52}Li_{0.04})(Nb_{0.83}Sb_{0.07}Ta_{0.1})O_3$ ceramics with the addition of $MnO_2$ were fabricated by a conventional mixed oxide method. A gradual change in the crystal and microstructure was observed with the increase of $MnO_2$ addition. For the NKN-LST-xmol%$MnO_2$ sintered at $1100^{\circ}C$, bulk density increased with the addition of $MnO_2$ and showed maximum value at addition 1.0mol% of $MnO_2$. Curie temperature of the NKN-LST ceramics slightly decreased with adding $MnO_2$. The dielectric constant, piezoelectric constant ($d_{33}$) and electromechanical coupling factor ($k_p$) increased below 0.25mol% of $MnO_2$ addition, which might be due to the increase in density. The high piezoelectric properties = 145 pC/N, electromechanical coupling factor = 0.421 and dielectric constant = 2883 were obtained for the NKN-LST-0.25mol%$MnO_2$ sintered at $1100^{\circ}C$ for 4h.

• 대한환경공학회지
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• 제32권2호
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• pp.193-200
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• 2010

복합 오염물질 처리를 위해 제조한 다기능성 흡착제인 철과 망간이 동시에 코팅된 모래(Iron and Manganese Coated Sand, IMCS)를 이용하여 용존 Mn(II) 처리 특성을 평가하였다. 실험에 사용된 IMCS는 0.05 M의 Mn(II)과 Fe(III) 용액을 pH 7에서 혼합하여 담체로 쓰인 모래에 코팅하여 제조하였다. IMCS는 ${\gamma}-MnO_2$ 형태의 Mn 산화물과 goethite 및 magnetite($F_{e3}O_4$) 형태의 철산화물이 동시에 존재하는 것으로 나타났다. Mn과 Fe의 함유량은 각각 826 및 1676 mg/kg으로 분석되었으며 $pH_{pzc}$는 6.40으로 측정되었다. IMCS와 산화제로서 NaOCl과 $KMnO_4$를 이용하여 Mn(II)의 제거에 관한 회분식 실험을 pH, 시간, 주입 농도를 변수로 하여 수행하였다. IMCS를 이용하여 Mn(II)을 처리하였을 때, pH 7.4에서 약 34%의 제거율을 나타내었고, 산화제인 NaOCl(13.6 mg/L)을 주입 후 IMCS와 반응시킨 결과 pH 7.0에서 96%의 제거율을 나타냈고, $KMnO_4$(4.8 mg/L)을 이용한 경우 pH 7.6에서 89%의 제거율을 나타내었다. IMCS와 산화제를 이용하여 Mn(II)을 제거할 경우, 용액의 pH가 증가함에 따라 제거율이 증가하는 양이온 형태의 제거 경향을 따랐으며, 반응 시간 6시간이 경과 후 거의 일정한 상태에 도달하는 것으로 나타났다. IMCS만을 이용하여 Mn(II)을 제거한 경우 833.3 mg/kg의 최대제거량을 나타냈고, 산화제로 NaOCl(13.6 mg/L), $KMnO_4$(4.8 mg/L)를 주입 후 IMCS와 반응시킨 경우 최대제거량은 각각 1428.6 및 1666.7 mg/kg으로 나타났다. IMCS에 의한 Mn(II)의 제거는 2차 반응속도식 및 Langmuir 식으로 잘 표현되었다.

• Journal of the Korean Physical Society
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• 제73권12호
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• pp.1863-1866
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• 2018

The sodium-iron phosphate maricite-$NaFe_{0.9}Mn_{0.1}PO_4$ was synthesized using the ball mill method. The crystal structure and magnetic properties of the prepared materials were studied using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and $M{\ddot{o}}ssbauer$ spectroscopy. Structural refinement of maricite-$NaFe_{0.9}Mn_{0.1}PO_4$ was analyzed using the FullProf program. From the XRD patterns, the crystal structure of maricite-$NaFe_{0.9}Mn_{0.1}PO_4$ was found to be orthorhombic with the space group Pmnb. The lattice parameters of maricite-$NaFe_{0.9}Mn_{0.1}PO_4$ are as follows: $a_0=6.866{\AA}$, $b_0=8.988{\AA}$, $c_0=5.047{\AA}$, and $V=311.544{\AA}^3$. Maricite-$NaFePO_4$ has an edge-sharing structure that consists of $FeO_6$ octahedral. Under an applied field of 100 Oe, the temperature dependences of zero-field-cooled (ZFC) and field-cooled (FC) curves were measured from 4.2 to 295 K. $M{\ddot{o}}ssbauer$ spectra were also recorded at various temperatures ranging from 4.2 to 295 K. We thus confirmed that the $N{\acute{e}}el$ temperature of $NaFe_{0.9}Mn_{0.1}PO_4$ ($T_N=14K$) was lower than that of maricite-$NaFePO_4$ ($T_N=15K$).