• Korean Journal of Materials Research
• /
• v.5 no.5
• /
• pp.560-567
• /
• 1995

Interfacial reactions, phase equilibria and elecrrical properties of Co films on (001) oreinted GaAs substrate, in the temperature range 300-$700^{\circ}C$ for 30min. have been investigated using x-ray diffraction and Augger electron spectropcopy. Cobalt started to react with GaAs at 38$0^{\circ}C$ by formation of Co$_{2}$GaAs phase. At 42$0^{\circ}C$, CoGa and CpAs nucleated at the Co and Co$_{2}$GaAs interface and grew with Co$_{2}$GaAs upto 46$0^{\circ}C$. contacts produced in this annealing regime were rectifying and Schottky varrier heights increased from 0.688eV(as-deposite state) up to 0.72eV(42$0^{\circ}C$). In the subsequent reation, the ternary phase started to decompose and lost stoichiometry at 50$0^{\circ}C$. At higher temperature, Co$_{2}$GaAs disappered and CoGa/CoAs/GaAs layer structures were formed. Contacts produced at higher temperature regime(>50$0^{\circ}C$) showed very low effective barriers. The results of interfacial reactions can be understood from the Co-Ga-As ternary phase diagram.

• Journal of the Korean Ceramic Society
• /
• v.47 no.2
• /
• pp.199-204
• /
• 2010

A dual-phase ceramic membrane consisting of gadolinium-doped ceria (GDC) as an oxygen ion conducting phase and $MnCo_2O_4$ as an electron conducting phase was fabricated by sintering a GDC and $MnCo_2O_4$ powder mixture. The $MnCo_2O_4$ was found to maintain its spinel structure at temperatures lower than $1200^{\circ}C$. (Mn,Co)(Mn,Co)$O_4$ spinel, manganese and cobalt oxides formed in the sample sintered at $1300^{\circ}C$ in an air atmosphere. XRD analysis revealed that no reaction phases occurred between GDC and $MnCo_2O_4$ at $1200^{\circ}C$. The electrical conductivity did not exhibit a linear relationship with the $MnCo_2O_4$ content in the composite membranes, in accordance with percolation theory. It increased when more than 15 vol% of $MnCo_2O_4$ was added. The oxygen permeation fluxes of the composite membranes increased with increasing $MnCo_2O_4$ content and this can be explained by the increase in electrical conductivity. However, the oxygen permeation flux of the composite membranes appeared to be governed not only by electrical conductivity, but also by the microstructure, such as the grain size of the GDC matrix.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.14 no.6
• /
• pp.267-271
• /
• 2004

Lithium cobalt oxide $(LiCoO_2)$ cathode powders for rechargeable battery have been successfully prepared using urea hydrolysis method. The obtained hydrolysis-derived precursors with different Li/Co molar ratio were calcined at various temperatures. Low temperature phase $(LT-LiCoO_2)$ and high temperature phase $(HT-LiCoO_2)$ were obtained after calcination at $500^{\circ}C$ for 2 hr, and phase transformation from $LT-LiCoO_2{\;}to{\;}HT-LiCoO_2$ was completely occurred over $700^{\circ}C$. The layered structure of $LiCoO_2$ was well developed with a rise in the calcination temperature. Charge-discharge test show that the lithium cobalt oxide with 1.2 molar ratio prepared at $800^{\circ}C$ has an initial discharge capacity as high as 152 mAh/g, and the relatively stable cycling characteristic with 9.2 % of capacity fading was obtained after 40th charge-discharge test.

• Journal of Powder Materials
• /
• v.25 no.4
• /
• pp.296-301
• /
• 2018

In this study, an experiment is performed to recover the Li in $Li_2CO_3$ phase from the cathode active material NMC ($LiNiCoMnO_2$) in waste lithium ion batteries. Firstly, carbonation is performed to convert the LiNiO, LiCoO, and $Li_2MnO_3$ phases within the powder to $Li_2CO_3$ and NiO, CoO, and MnO. The carbonation for phase separation proceeds at a temperature range of $600^{\circ}C{\sim}800^{\circ}C$ in a $CO_2$ gas (300 cc/min) atmosphere. At $600{\sim}700^{\circ}C$, $Li_2CO_3$ and NiO, CoO, and MnO are not completely separated, while Li and other metallic compounds remain. At $800^{\circ}C$, we can confirm that LiNiO, LiCoO, and $Li_2MnO_3$ phases are separated into $Li_2CO_3$ and NiO, CoO, and MnO phases. After completing the phase separation, by using the solubility difference of $Li_2CO_3$ and NiO, CoO, and MnO, we set the ratio of solution (distilled water) to powder after carbonation as 30:1. Subsequently, water leaching is carried out. Then, the $Li_2CO_3$ within the solution melts and concentrates, while NiO, MnO, and CoO phases remain after filtering. Thus, $Li_2CO_3$ can be recovered.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1998.11a
• /
• pp.311-314
• /
• 1998

The effects of the additions of transition metal oxides on ZrO$_2$ - Y$_2$O$_3$ (Y$_2$O$_3$ - containing tetragonal zirconia polycrystals : Y-TZP) system has been studied by investigating fracture toughness and phase stability of the sintered specimens. In the specimens sintered at 1450$^{\circ}C$ for 2hrs in air the phase transformation from tetragonal to monoclinic was observed. The ratios of monoclinic phase to tetragonal phase were changed with the additions of CoO, Fe$_2$O$_3$ and MnO$_2$, respectively, from 0.00 to 8.00wt%. The fracture toughness was increased with increasing the monoclinic to tetragonal phase ratio and was maximum at the ratio of about 18%. However, the hardness was decreased with increasing the ratio. The additions of CoO, Fe$_2$O$_3$ and MnO$_2$ together into Y-TZP resulted in more complex behaviors of fracture toughness and hardness. The specimen with the additions of 1.5wt% Fe$_2$O$_3$, 3.0wt% Al$_2$O$_3$ and 1.5wt% CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of 10.8 MPa.m$\^$$\frac{1}{2}$/ and Vickers hardness of 1201kgf/mm$^2$.

• Journal of Convergence for Information Technology
• /
• v.7 no.2
• /
• pp.91-99
• /
• 2017

The purpose of this study was to clarify the differences between the K-pop and B-boy dancers'characteristics based on the biomechanical variables through the isolation movement by independent variable t-test using spss 18.0. As a result, first, the CoM composite displacement of the K-pop dancer was larger than that of the B-boy(p<.05) in phase1 and phase2. Second, in phase2 and phase3, the movement speed of CoM was faster in K-pop dancer than in B-boy(p<.05). Third, in phase1, the planar angle between the body and pelvis was greater in the right planar angle of the K-pop dancer, while in the phase2 and phase3, the left planar angle of the B-boy was larger(p<.05). Fourth, the composite hip joint moments of B-boy were larger than those of K-pop in phase1, However, K-pop dancers showed greater moments in phase2, phase3 and phase4, and ankle joint moments in phase3(p<.05). Thus, even with the same isolation, we found that K-pop and B-boy dancers performed differently.

• Journal of the Korean Ceramic Society
• /
• v.44 no.8
• /
• pp.424-429
• /
• 2007

Novel conductive $CO_2$ membranes composed of dual phases, molten carbonates and electronic conducting ceramics, were investigated. As the microstructure control of electronic conducting ceramic supports is extremely important to keep the molten carbonates stable in the membranes by a capillary force applied by the pore structure of the supports, we have scrutinized the microstructure of the electronic conducting supports utilizing microscopic images and gas permeability measurement. From the evaluation of the electrical conductivities of the molten carbonates and the electronic conducting ceramic supports, we found that the ionic conductivity of the molten carbonates could determine $CO_2$ flux through the dual phase membranes if the surface exchange rate were relatively high enough.

• Proceedings of the KSME Conference
• /
• 2000.11b
• /
• pp.180-185
• /
• 2000

Nano crystalline or non-crystalline particles have been widely used in various industrial area, such as ceramics, catalysis, electronics, metallurgy and optic device. In all applications, synthesizing the particles as small as possible and controlling the crystalline phase according to its purpose are necessary for the enhancement of processing performance. In some cases, non-agglomerated particles may be necessary for solving the packing problems. This motivates our attempt of controlling size, morphology, phase of nano titania and silica particles. If one can enhance sintering rate of small aggregates independently of collision rate, one may expect that original aggregates can be changed into volume equivalent spheres and thereby the decrease of collision frequency due to the change leads to much smaller rate of growth of the particles. This is the basic idea of our control strategy.

• Journal of the Korean Ceramic Society
• /
• v.20 no.1
• /
• pp.43-48
• /
• 1983

The formation of strontium titanate from several molar $SrCO_3$ and $TiO_2$ mixtures was studied in air and $CO_2$ gas Mixtures of $SrCO_3$ and $TiO_2$ were heated in air at 400-$600^{\circ}C$ DTA-TG was used to obtain thermal histories of simples heated in air and $CO_2$ gas. X-ray diffraction analysis was used to determine both the phase composition and the amounts of each phase present. The phase relationship of various compounds $SrTiO_3$, $Sr_2TiO_4$, $Sr_2Ti_3O_7$ and $Sr_4Ti_3O_{10}$ formed by the sintering in each composition was shown by the calibration curves. High temperature X-ray analysis was used to determine both the formation process and deformation process of each products. Small amount of SrTiO3 is formed first at the surface af contact SrTiO3 reacts with $SrCO_3$ to form Sr2TiO4 this is affected on the $CO_2$ pressure.

• Journal of Magnetics
• /
• v.7 no.4
• /
• pp.143-146
• /
• 2002

Mechanical milling technique is considered to be a useful way of processing the fine Nd-Fe-B-type powder with high coercivity. In the present study, phase evolution of the $Nd_{15}(Fe_{1-x}Co_{x})_{77}B_{8}$ (x=0-0.6) alloys during the high energy mechanical milling and annealing was investigated. The effect of Co-substitution on the crystallization of the mechanically milled $Nd_{15}(Fe_{1-x}Co_{x})_{77}B_{8}$ amorphous material was examined. The Nd-Fe-B-type alloys can be amorphized completely by a high-energy mechanical milling. On annealing of the amorphous material, fine $\alpha$-Fe crystallites form first from the amorphous. These fine $\alpha$-Fe crystallites reacts with the remaining amorphous afterwards, leading to crystallization to $Nd_2Fe_{14}$B phase. The Co-substitution for Fe in $Nd_{15}(Fe_{1-x}Co_{x})_{77}B_{8}$ ($\mu$x=0∼0.6) alloys lower significantly the crystallization temperature of the amorphous phase to the $Nd_2Fe_{14}$B phase. The mechanically milled and annealed $Nd_{15}Fe_{77}B_8$ alloy without Co-substitution exhibits consistently better magnetic properties with respect to the alloys with Co-substitution.