• Journal of the Korean Chemical Society
• /
• v.42 no.1
• /
• pp.122-134
• /
• 1998

In this review, we describe the electrochemical properties of spinel-type lithium manganese oxides $(Li_xMn_2O_4)$ and their failure modes encountered in 4 V lithium rechargable cells. The long-term cyclability (reversibility) of spinel electrodes is determined partly by the purity, size and distribution of spinel particles, and also by the microstructure of electrode plates. A proper selection of electrolytes is another important task in cyclability enhancements. In the spinel preparation, impurity formation and cation mixing should be minimized. The carbon content in composite cathodes should also be minimized to the extent where the cell polarization does not bring about adverse effects on cell performances. The binder content should be optimized on the basis of dispersion of component materials and mechanical strength of the plates. Cathodic capacity losses arising from solvent oxidation and spinel dissolution can be mitigated by using electrolytes composed of carbonates and/or fluorine-containing lithium salts. The carbon additives may be selected after a trade-off between the cell polarization in composite cathodes and the solvent oxidation on carbon surface.

• 연구논문집
• /
• s.29
• /
• pp.141-149
• /
• 1999

Brazing of Fe-Cr-Al alloy was carried out at $1200^{\circ}C$ in vacuum furnace using nickel-based filler metals : BNi-5 powder(Ni-Cr-Si-Fe base alloy} and MBF-50 foil (Ni-Cr-Si-B). The effect of boron content on the stability of oxide scale on the brazed joint was investigated by means of cyclic oxidation test performed at $1050^{\circ}C$ and $1200^{\circ}C$. Apparently, the joints brazed with MBF-50 containing boron showed relatively stable oxidation rates compared to boron-free BNi-5 at both temperatures. However, it was considered that the slower weight loss of MBF-50 brazed specimen wasn’t resulted from the low oxidation rate but from the spallation of oxide layer. The oxide layer consisted of thick spinel oxide on the surface and $Al_2 O_3$ internal oxide layer along the interface between mother alloy and braze, the mother alloy was also eroded seriously by the formation of spinel oxides such as $FeCr_2 O_4$ and $NiCr_2 O_4$ on the surface, likely to be induced by the change of oxide forming mechanism due to diffusion of boron from the braze. On the contrary, the joint brazed with BNi-5 showed the good oxidation resistance during the cyclic oxidation test. It seems that the oxidation can be retarded by the formation of stable $Al_2 O_3$ layer at the surface.

• Korean Journal of Materials Research
• /
• v.12 no.4
• /
• pp.274-278
• /
• 2002

Discrete-variational(DV)-$X{\alpha}$ method was applied to investigate the electronic structures of spinel- type manganese oxide which is well known to the high performance adsorbent or cathode material for lithium ion. The results of DOS(density of states) and Mulliken population analysis showed that Li was nearly fully ionized and interactions between Mn and O were strong covalent bond. The effective charge of Li and Mn was +0.77 and +1.44 respectively and the overlap population between Mn and O was 0.252 in $LiMn_2O_4$. These results from DV-X$\alpha$ method were well coincided with the experimental result by XPS analysis and supported the feasibility of theoretical interpretation for the $LiMn_2O_4$ compound.

• Journal of the Korean Ceramic Society
• /
• v.56 no.5
• /
• pp.474-482
• /
• 2019

Chromium-doped zinc ferrite nanoparticles with the general formula Cr_yZnFe_2-yO₄ (y = 0, 0.025, 0.05, 0.075, and 0.1) were synthesized by a surfactant-assisted chemical co-precipitation route using metal nitrate salt precursors. The phase purity and structural parameters were determined by powder X-ray diffraction. The concentration of Cr³⁺ doped into ZnFe₂O₄ (ZF) noticeably affected the crystallite size, which was in the range of 22 nm to 36 nm, and all samples showed a single cubic spinel structure without any secondary phase or impurities. The lattice parameter, X-ray density, and skeletal density increased with an increase in the Cr-doping concentration; on the other hand, a decreasing trend was observed for the particle size and porosity. The influence of Cr³⁺ substitution on ZF magnetic properties were studied under an applied field of 15 kOe. The overall results revealed that the incorporation of a small amount of Cr dopant changed the structural, electrical, and magnetic properties of ZF.

• Corrosion Science and Technology
• /
• v.21 no.6
• /
• pp.466-475
• /
• 2022

Surface oxides and intergranular (IG) oxidation phenomena in Alloy 600 depending on hydrogen concentration were characterized to obtain clear insight into the primary water stress corrosion cracking (PWSCC) behavior upon exposure to pressurized water reactor primary water. When hydrogen concentration was between 5 and 30 cm³ H₂/kg H₂O, NiFe₂O₄ and NiO type oxides were found on the surface. NiO type oxides were found inside the oxidized grain boundary when hydrogen concentration was 5 cm³ H₂/kg H₂O. However, only NiFe₂O₄ spinel on the surface and Ni enrichment were observed when hydrogen concentration was 30 cm³ H₂/kg H₂O. These results indicate that the oxidation/reduction reaction of Ni in Alloy 600 depending on hydrogen concentration can considerably affect surface oxidation behavior. It appears that the formation of NiO type oxides in a Ni oxidation state and Ni enrichment in a Ni reduction (or metallic) state are common in primary water. It is believed that the above different oxidation/reduction reactions of Ni in Alloy 600 depending on hydrogen concentration can also significantly affect the resistance to PWSCC of Alloy 600.

• Korean Journal of Materials Research
• /
• v.13 no.8
• /
• pp.519-523
• /
• 2003

We report the synthesis of cubic spinel $ZnCo_2$$O_4$thin films and the tunability of the conduction type by control of the oxygen partial pressure ratio. Zinc cobalt oxide films were grown on$ SiO_2$(200 nm)/Si substrates by reactive magnetron sputtering method using Zn and Co metal targets in a mixed Ar/$O_2$atmosphere. We found from X-ray diffraction measurements that the crystal structure of the zinc cobalt oxide films grown under an oxygen-rich condition (the $O_2$/Ar partial pressure ratio of 9/1) changes from wurtzite-type $Zn_{1-x}$ $Co_{X}$O to spinel-type $ZnCo_2$$O_4$with the increase of the Co/Zn sputtering ratio,$ D_{co}$ $D_{zn}$ . We noted that the above structural change accompanied by the variation of the majority electrical conduction type from n-type (electrons) to p-type (holes). For a fixed $D_{co}$ $D_{zn}$ / of 2.0 yielding homogeneous spinel-type $_2$O$ZnCo_4$films, the type of the majority carriers also varied, depending on the$ O_2$/Ar partial pressure ratio: p-type for an $O_2$-rich and n-type for an Ar-rich atmosphere. The maximum electron and hole concentrations for the Zn $Co_2$ $O_4$films were found to be 1.37${\times}$10$^{20}$ c $m^{-3}$ and 2.41${\times}$10$^{20}$ c $m^{-3}$ , respectively, with a mobility of about 0.2 $\textrm{cm}^2$/Vs and a high conductivity of about 1.8 Ω/$cm^{-1}$ /.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 2002.11a
• /
• pp.191-194
• /
• 2002

매체 순환식 연소(Chemical-Looping Combustion, CLC)는 금속 산화물(산소공여매체, oxygen carrier)의 산소를 이용하여 화석연료를 산화(연료 연소 공정)시키고, 환원된 금속을 다시 산화(매체 산화 공정)시키는 간접적인 연소 공정의 하나이다. 이 방식은 온실효과의 주발생원인 $CO_2$를 원천적으로 회수할 수 있고, 또한 화염이 없는 상태에서 연소반응이 진행됨으로 thermal NOx의 발생을 미연에 방지할 수 있어 고효율의 환경친화적인 연소공정이다.(중략)

• Bulletin of the Korean Chemical Society
• /
• v.23 no.5
• /
• pp.679-682
• /
• 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.

• Journal of Magnetics
• /
• v.1 no.1
• /
• pp.51-54
• /
• 1996

The effects of additional P-doping on the magnetic properties, thermal stability and cation distribution of Co-doped ${\gamma}-{Fe_2} {O_3}$have been investigated by means of magnetic annealing and measurements with vibration sample magnetometer and torque magnetometer. It is found that the P-doping promotes the coercivity and its magnetic-thermal stability, which may be attributed to increase of the cubic magneto-crystalline anisotropy constant, $K_1$ and the activation energy, E, for cation rearrangement, respectively. The cation distribution of P and Co-substituted iron oxide was calculated from the variation of the saturation magnetization with P-doping on the basis of the Neel model. It was found that the most of P ions in the iron oxides occupied the B-site of spinel lattice.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.27 no.4
• /
• pp.226-231
• /
• 2014

Thin thermistor films of solutions with nickel and manganese oxides were prepared by metal-organic decomposition (MOD). The structural properties of the thin films were investigated as a function of annealing temperature. Field emission scanning electron microscope (FE-SEM) results indicated that the thin films had a thin thickness, smooth and dense surface. The crystallization temperature of $414.9^{\circ}C$ was confirmed from thermogavimetric-differential thermal analysis (TG-DTA) curve. A single phase of cubic spinel structure was obtained for the thin film annealed from $700^{\circ}C$ to $800^{\circ}C$, which was confirmed from the X-ray diffraction (XRD). From the selected area electron diffraction (SAED) in high resolution transmission electron microscope (HRTEM), the nano grains (2~3 nm) of spinel phase with (311) and (222) planes were detected for the thin film annealed at $500^{\circ}C$, which could be applicable to read-out integrated circuit (ROIC) substrate of the uncooled microbolometer with low processing temperature.