• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.2299-2300
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• 2008

The Velocity Autocorrelation Function (VAF) of the sodium ions is calculated for a range of temperature from 250K to 1000K and converted into the linear ac-conductivity and ac-susceptibility response via Fourier transformation. A peak is found in the conductivity around $6{\times}10^{12}$ Hz that has some of the character of a Poley absorption. Here it is shown to be due to an harmonically coupled site vibrations of the sodium atoms, which extend only over a limited range. At frequencies below the peak the conductivity tends towards a constant i.e. dc value corresponding to a constant flow of ions through the simulation cell. At high temperatures the conductivity due to this ion transport process behaves like a metal with an insulator to metal transition occurring around a specific temperature.

• 한국염색가공학회지
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• 제19권4호
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• pp.10-17
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• 2007

Chitosan(CS) and cellulose acetate(CA) composite films were prepared using formic acid as a cosolvent by casting, solvent evaporating and neutralization method. This study examines if the blending method, which uses formic acid as a cosolvent is efficient in improving the mechanical properties of CS film, especially wet strength and elongation. Formic acid is an effective cosolvent for the blend of CS and CA. Under wet condition, tensile strength and elongation of the composite films were obviously higher than those of the films made from pure CS. FTIR, DSC, and X-ray diffraction showed that the composite films exhibit a high level of compatibility and that strong interaction between the CS and CA was caused by intermolecular hydrogen bonding. The affinity series of composite film to transition metal ions are Cu(II) > Cd(II) > Cr(III). The adsorption of Cu((II) ion was shown to be highly pH sensitive.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.379-380
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• 2008

Molecular Dynamics (MD) simulations have been used to model the dynamics of the charge-compensating sodium ions in the non-stoichiometric hollandite Nax$(Ti_{8-x}Cr_x)O_{16}$. These interstitial ions reside in 'tunnels' in the crystal structure and move under the forces of both the ions making up the cage structure and the many body interactions of the other sodium ions in the tunnel. The Velocity Autocorrelation Function (VAF) of the sodium ions is calculated for a range of temperature from 250K to 1000K and converted into the linear ac-conductivity and ac-susceptibility response via Fourier transformation. A peak is found in the conductivity around $6\times10^{12}$ Hz that has some of the character of a Poley absorption. Here it is shown to be due to an harmonically coupled site vibrations of the sodium atoms, which extend only over a limited range. At frequencies below the peak the conductivity tends towards a constant i.e. dc value corresponding to a constant flow of ions through the simulation cell. At high temperatures the conductivity due to this ion transport process behaves like a metal with an insulator to metal transition occurring around a specific temperature.

• 한국표면공학회지
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• 제57권2호
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• pp.57-70
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• 2024

Nickel-cobalt-manganese (NCM) lithium-ion batteries(LIBs) are increasingly prominent in the energy storage system due to their high energy density and cost-effectiveness. However, they face significant challenges, such as rapid capacity fading and structural instability during high-voltage operation cycles. Addressing these issues, numerous researchers have studied the enhancement of electrochemical performance through the coating of NCM cathode materials with substances like metal oxides, lithium composites, and polymers. Coating these cathode materials serves several critical functions: it acts as a protection barrier against electrolyte decomposition, mitigates the dissolution of transition metals, enhances the structural integrity of the electrode, and can even improve the ionic conductivity of the cathode. Ultimately, these improvements lead to better cycle stability, increased efficiency, and enhanced overall battery life, which are crucial for the advancement of NCM-based lithium-ion batteries in high-demand applications. So, this paper will review various cathode coating materials and examine the roles each plays in improving battery performance.

• Bulletin of the Korean Chemical Society
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• 제33권8호
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• pp.2711-2718
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• 2012

The alkylation of the ambident enolates of a methyl glycinate Schiff base with ethyl chloride was studied at B3LYP and MP2 levels with $6-31+G^*$ basis set. The free (E)-enolates and (Z)-enolate are similar in energy and geometry. The transition states for the alkylation of the free (E)/(Z)-enolate with ethyl chloride have similar energy barriers of ~13 kcal/mol. However, with a lithium ion, the (E)-enolate behaves as an ambident enolate and makes a cyclic lithium-complex in bidentate pattern which is more stable by 11-23 kcal/mol than the (Z)-enolate-lithium complexes. And the TS for the alkylation of (E)-enolate-lithium complex coordinated with one methyl ether is lower in energy than those from (Z)-enolate-lithium complexes by 4.3-7.3 kcal/mol. Further solvation model (SCRF-CPCM) and reaction coordinate (IRC) were studied. This theoretical study suggests that the alkylation of ambident enolates proceeds with stable cyclic bidentate complexes in the presence of metal ion and solvent.

• 대한화학회지
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• 제28권2호
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• pp.135-142
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• 1984

초과산화이온$(O_2^-)$의 발생원으로서 $KNO_2$를 사용하여 새로운 형태의 산착화합물가교팔라듐착화합물을 합성했다. 이 방법은 구핵치환과 전자 이동에 의한 반응으로서, 저원자가전이금속착화합물에 산소분자를 산화적으로 부가시켜 합성한 종전의 방법과는 완전히 다르다. $O_2^-$에 의하여 {\pi}$-알릴리간드를 갖는 새로운 형태의 5가지 산소가교팔라듐착화합물을 합성했다

• 공업화학전망
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• 제23권5호
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• pp.12-20
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• 2020

최근 층상구조를 가진 전이금속 칼코겐 화합물이 새로운 고성능 리튬이온전지 음극소재로서 주목받고 있다. 층상구조 물질들의 고성능 전극 소재 활용에 있어 박리를 이용한 정확한 층의 개수 조절은 전기화학 반응성을 증가시키고, 전극 필름 내에서의 균일한 거동을 위해서 매우 중요하다. 볼 밀링 공정은 이차전지 전극 소재 제조에 있어서 주로 물질의 분쇄나 고상 화학반응을 유도하여 합금 형태의 전극 소재 개발에 보편적으로 사용되는 공정이나, 층상구조를 가진 전이금속 칼코겐 화합물에 적용하면 층상구조 물질에 고체윤활작용을 일으켜 박리가 촉진된다. 이러한 성질을 이용하여 다양한 종류의 전이금속 칼코겐 화합물(예: MoS₂, MoSe₂, NbSe₂)에 적절한 카본 매트릭스 물질과 복합화를 통해 새로운 전극 소재를 합성하고, 이를 통해 고성능 리튬이온전지 음극 소재를 제조하는 연구 동향에 대해 보고하고자 한다.

• 대한화학회지
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• 제35권2호
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• pp.119-127
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• 1991

고리를 구성하는 원자의 수가 15개에서 18개인 디아자 크라운계의 고대고리 화합물인 1,12-diaza-3, 4 : 9, 10-dibenzo-5, 8-dioxacyclopentadecane(NtnOenH$_4$), 1,13-diaza-3,4 : 10,11-dibenzo-hydroxy-5,9-dioxacyclohexadecane(NtnOtnH$_4$), 1,13-diaza-3,4 : 10,11-dibenzo-15-hydroxy-5,9-dioxacyclohexadecane(Ntn(OH)OtnH$_4$), 1,15-diaza-3,4 : 12,13-dibenzo-5,8,11-trioxacycloheptadecane (NenOdienH$_4$) and 1,15-diaza-3,4 : 12,13-dibenzo-5,8,11-trioxacyclooctadecane(NtnOdienH$_4$)의 양성자화와 금속이온과의 착물 형성을 전위차적정법과 핵자기 공명법으로 연구하였다. 양성자화상수는 크라운 에테르의 염기도를 예측하는데 상용하였다. 본 연구에서 사용한 거대고리 화합물의 염기도 순서는 NenOdienH$_4$ < Ntn(OH)OtnH$_4$ < NtnOenH$_4$ < NtnOtnH$_4$ < NtnOdienH$_4$였다. 염기도의 이와 같은 변화를 거대고리에 대한 치환기와 양성자화가 일어날 때의 고리의 비틀림 정도로 설명하였다. 금속이온과의 착물 형성에 대한 안전도상수는 전이금속이온에 대해서는 Co(II) < Ni(II) < Cu(II) < Zn(II)순이었으며, 중금속이온에 대해서는 Cd(II) < pb(II) < Hg(II)의 순이었다. 금속 착물 형성에 대한 이와 같은 안정도상수의 변화에는 Co(II), Ni(II) 및 Cu(II) 착물의 경우 리간드 고리의 크기가 영향을 미치고 있었으며, Zn(II), Cd(II), pb(II) 및 Hg(II) 착물의 경우에는 리간드의 염기도가 주로 영향을 미치고 있었다. 후전이금속 착물에 대한 $^1$H와 $^{13}$C 핵자기공명 분광법에서는 고리의 질소원자가 산소원자보다 금속이온에 더 큰 친화력을 가짐을 알 수 있었고, 금속이온과 착물을 형성할 때에 고리의 평면성이 상실되고 있음도 밝혀졌다.

• Bulletin of the Korean Chemical Society
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• 제32권5호
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• pp.1599-1603
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• 2011

Novel chemosensors based on 2-(2'-hydroxyphenyl)quinoline were prepared and evaluated for sensing metal cations. The photophysical properties of chemosensors 1-3 were examined and their ion-selectivity was evaluated by measuring their fluorescent emission responses to alkali, alkaline earth, and transition metal ions. Chemosensors 1, 2 and 3 show ratiometric and enhanced fluorescence changes with transitional metals that are efficient fluorescence quenchers, especially 3 has a high binding constant with $Hg^{+2}$ in $CH_3CN$.

• 환경위생공학
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• 제14권3호
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• pp.80-89
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• 1999

The ion exchange resins have been synthesized from chlormethyl styrene-1,4-divinyl benzene(DVB) with 1%, 5%, and 10%-crosslinking and macrocyclic ligand of cryptand type by copolymerization method and the adsorption characteristics of uranium(VI), lead(II) and holmium(III) ions have been investigated in various experimental conditions. The correlation between the adsorption characteristics of rare earths and transition metal on the resins and stability constants of complexes with macrocyclic ligand have been examined. The $UO_2^{2+}$ aqueous solutions are not adsorbed on the resins below pH 3.0, but the power of adsorption of $UO_2^{2+}$ increased rapidly above pH 4.0. The adsorption power was in the order of 1%, 10%, and 5%-crosslinked resin, but adsorptive characteristics of resins decreased in proportion to the order of dielectric constants of solvents.