• Journal of the Mineralogical Society of Korea
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• v.23 no.4
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• pp.305-313
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• 2010

Mineralogical characteristics of Cu-Co ores from the Central African Copperbelt in the Democratic Repblic of Congo are studied using powder X-ray diffractometer, general area detector X-ray diffractometer, and electron proble microanalyzer. Black ores are mainly composed of heterogenite (cobalt oxide/hydroxide mineral) and malachite (copper carbonate mineral), whereas green ores are only composed of malachite. Heterogenite shows very bright white color under the reflected microscope, and belongs to 3R polytype, because it has d-spacings at $4.39{\AA}$ and $2.316{\AA}$. Since NiO and $Fe_20_3$ content of heterogenite are lower than those of 3R polytype from other localities, it cannot completely exclude the presence of 2H polytype in heterogenite from this study. Malachite is light grey color under the reflected microscope with approximate chemical formula of $Cu_{1.97}Co_{0.02}Fe^{2+}{_{0.01}}CO_3(OH)_2$. Heterogenite and malachite were probably formed at the supergene emichment stage, the last mineralization stage in the Central African Copperbelt. Cobalt seems to be much more emiched in the black supergene (oxy)hydroxide ore than those in the primary sulfide ore.

• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.164-167
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• 2000

Flue gases in the iron foundry consist of 15~20% CO2 as an air pollution gas whose emission should be mitigated in order to protect the environment. In the present study, ultrafine powders of NixZn1-xFe2O4 as a potential catalyst for the CO2 decomposition were prepared by the coprecipitation methods. Oxygen deficient ferrites (MeFe2O4-$\delta$) can decompose CO2 as C and O2 at a low temperature of about 30$0^{\circ}C$. The XRD result of synthesized ferrites showed the spinel structure of ferrites and ICP-AES and EDS quantitative analyses showed the composition similar with initial molar ratios of the mixed solution prior to reaction. The BET surface area of the (Ni, Zn)-ferrites was about 77~89.5$m^2$/g and their particle size was observed about 10~20 nm. The CO2 decomposition efficiency of the oxygen deficient (Nix, Zn1-x)-ferrites was the highest at x=0.3, and the ternary (Ni, Zn)-ferrites was better than that of binary Ni-ferrites.

• Journal of the Korean Magnetics Society
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• v.17 no.3
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• pp.124-127
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• 2007

Magnetic tunnel junctions (MTJs), which consisted of amorphous CoFeSiB layers, were investigated. The CoFeSiB layers were used to substitute for the traditionally used CoFe and/or NiFe layers with an emphasis given on understanding the effect of the amorphous free layer on the switching characteristics of the MTJs. CoFeSiB has a lower saturation magnetization ($M_s\;:\;560\;emu/cm^3$) and a higher anisotropy constant ($K_u\;:\;2800\;erg/cm^3$) than CoFe and NiFe, respectively. An exchange coupling energy ($J_{ex}$) of $-0.003\;erg/cm^2$ was observed by inserting a 1.0 nm Ru layer in between CoFeSiB layers. In the Si/$SiO_2$/Ta 45/Ru 9.5/IrMn 10/CoFe 7/$AlO_x$/CoFeSiB 7 or CoFeSiB (t)/Ru 1.0/CoFeSiB (7-t)/Ru 60 (in nm) MTJs structure, it was found that the size dependence of the switching field originated in the lower $J_{ex}$ using the experimental and simulation results. The CoFeSiB synthetic antiferromagnet structures were proved to be beneficial for the switching characteristics such as reducing the coercivity ($H_c$) and increasing the sensitivity in micrometer size, even in submicrometer sized elements.

• Journal of Magnetics
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• v.9 no.1
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• pp.5-8
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• 2004

For the ferromagnetic combined samples, results of x-ray diffraction patterns showed no evidence of reaction between the $La_{0.67}Ca_{0.33}MnO_3, La_{0.67}Sr_{0.33}MnO_3$ and $CoFe_2O_4$. For the amount of $CoFe_2O_4$ increased, the Curie temperature of combined samples showed no appreciable change, whereas a metal-semiconductor transition temperature rapidly decreased. For the $La_{0.67}Sr_{0.33}MnO_3$ and 20 wt % $CoFe_2O_4$ combined sample, the metal-semiconductor transition temperature was decreased to 160 K compared with the $La_{0.67}Sr_{0.33}MnO_3$ with 192 K.

• Journal of Magnetics
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• v.19 no.3
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• pp.227-231
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• 2014

We fabricated textured polycrystalline $CoFe_2O_4$ thin films on $Pt(111)/TiO_2/SiO_2/Si$ substrate through a sol-gel method. We varied the thickness of the films, by using precursor solutions with different concentrations of 0.1, 0.2, and 0.3 M, and by depositing 5, 8, or 10 layers on the substrate by spin-coating. X-ray diffraction spectra indicated that when the precursor concentration of the solution was higher than 0.1 M, the spin-coated films were preferentially oriented in the <111> direction. Inspection of the surface morphology by scanning electron microscopy revealed that $CoFe_2O_4$ thin films prepared with 0.2 M solution and 5-time spin-coatings had smoother surface, as compared to the other conditions. Each coating had an average thickness of about 50 nm. The magnetic properties measured by vibrating sample magnetometer showed magnetic anisotropy, as evidenced from the difference in the in-plane and out-of-plane hysteresis loops, which we attributed to the textured orientation of the $CoFe_2O_4$ thin films.

• Journal of the Korean Magnetics Society
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• v.22 no.1
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• pp.19-22
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• 2012

$Ba_2Mg_{0.5}Co_{1.5}(Fe_{0.99}In_{0.01})_{12}O_{22}$ was prepared by the conventional solid-state reaction method, and studied by x-ray diffractometer, vibrating sample magnetometer, and Mossbauer spectrometer. The crystal structure was determined to be a single-phased rhombohedral with space group R-3m. Magnetization value were $M_s$ = 28.6 emu/g at 295 K. The hysteresis loops indicate that all the samples are ferrimagnetic behaviors. Mossbauer spectra of $Ba_2Mg_{0.5}Co_{1.5}(Fe_{0.99}In_{0.01})_{12}O_{22}$ have been 6-sextet taken at various temperatures ranging from 4.2 to 620 K. Based on the isomer shift (${\delta}$) values of all samples, the charge states were found to be $Fe^{3+}$ state at all temperatures, the Curie temperature was determined to be 630 K by the ZVC curve.

• Journal of the Mineralogical Society of Korea
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• v.28 no.4
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• pp.333-341
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• 2015

As results of X-ray diffraction analysis, samples of asbestos and soil were composed maily of dolomite ($CaMg(Co_3)_2$, tremolite ($Ca_2Mg_5Si_{18}O_{22}(OH)_2$), actinolite ($Ca(Mg,\;Fe)_6Si_8O_{22}(OH)_2$), talc ($Mg_3Si_4O_{10}(OH)_2$), calcite ($CaCO_3$) and small amounts of quartz ($SiO_2$) and clay minerals. The average size of asbestos fibers was about $100{\mu}m$ and maximum of some asbestos was $250.0{\mu}m$ in length. The aspect ratio of asbestos fiber were over 3 : 1 and inclined extinction in the range of $8.0-19.5^{\circ}$. Single isolated fragments of asbestos are probably fiber and acicula form in crystal edge along the cleavage plane. Tremolite that composed main asbestos mineral in rock and soil around Dong-a mine is higher content of Fe than actinolite asbestos.

• Journal of the Korean Chemical Society
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• v.38 no.4
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• pp.276-282
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• 1994

Perovskite-type mixed oxides LaBO$_3$(B = Mn, Fe, Co) were prepared by citrate sol-gel method in $air(850^{\circ}C$, 24h). The oxygen stoichiometries and structures of these oxides were determined by XRD and TPR results as followings; LaMnO$_{3.16}$(a = 5.507, c = 13.329 $\AA$, hexagonal), LaFeO$_{3.17}$(a = 5.554, b = 5.555, c = 7.863 $\AA$, orthorhomibic), LaCoO$_{3.0}$(a = 5.436, c = 13.095 $\AA$, hexagonal). The temperature programmed reduction(TPR) experiments in static 300 torr H$_2$ atmosphere shows that the reduction reaction of LaBO$_3$(B = Mn, Fe, Co) proceeds into two stages, and thermal stabilities of these oxides decreased in the order of LaMnO$_3$ > LaFeO$_3$ > LaCoO$_3$. According to the kinetic analysis the lowest activation energy was obtained for LaCoO$_3$.

• Journal of the Korean Electrochemical Society
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• v.13 no.4
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• pp.264-269
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• 2010

$LiNi_{0.5}Mn_{0.3}Co_{0.2}O_2$ active material was prepared by simple-combustion method and investigated as the cathode material for li-ion battery. The structural characterization was analyzed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The XRD patterns of $LiNi_{0.5}Mn_{0.3}Co_{0.2}O_2$ sample was indicated a phase of layered hexagonal structure. The size of particles has not uniform diameters ranging from 100 to 300 nm. The electrochemical performance of the $LiNi_{0.5}Mn_{0.3}Co_{0.2}O_2$ was measured by Cyclic Voltammetry and galvanostatics. The $LiNi_{0.5}Mn_{0.3}Co_{0.2}O_2$ shows the discharge capacity of ~162 mAh/g in the range of 2.8 to 4.3 V at the first cycle.

• Journal of Magnetics
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• v.3 no.1
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• pp.31-35
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• 1998

Metal/cobalt ferrite composite thin films with the saturation magnetization (M_s$)of~580 emu/cm3 and the coercivity(Hc) of 1700 Oe were prepared by the reactive sputtering. With increasing substrate temperature, Ms of the thin films increased, while Hc of the thin films decrease. This sttributed to the precipitation of $Co_xFe_{1-x}(x {\appro}x0.62)$ metal phase in the thin films. The metal phase showed the BCC structure ($a_0$=2.89 $\AA$) and Im3m space group. Also, the cobalt ferrite phase was identified as$ CoFe_2O_4$ with a cubic structure ($a_0=8.39 $\AA$$) and a space group of Fd3m. For the higher cobalt content than the stoichiometric composition,$ Co_{37.8}Fe_{62.2}$, the thin films with high Ms and Hc could be obtained in the wide substrate temperature range (200-40$0^{\circ}C$).