• Journal of the Korean Ceramic Society
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• v.37 no.6
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• pp.559-563
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• 2000

To decompose carbon dioxide, magnetite was synthesized with 0.2M-FeSO4$.$7H2O and 0.5 M-NaOH by coprecipitation. The deoxidized magnetite was prepared from the magnetite by hydrogen reduction for 1, 1.5, 2 hr. The degree of hydrogen reduction and the decomposition rate of carbon dioxide were investigated with hydrogen reduction time. The crystal structure of the magnetite was identified spinel structute by the X-ray powder diffractions. After magnetite was reduced by hydrogen, magnetite reduced by hydrogen become new phae(${\alpha}$-Fe2O3, ${\alpha}$-Fe) and spinel type simultaneously. After decomposing of carbon dioxide at 350$^{\circ}C$, new phse(${\alpha}$-Fe2O3, ${\alpha}$-Fe) were removed and the spinel type only existed. The specific surface area of the synthesized magnetite was 46.69㎡/g. With the increase of the hydrogen reduction time, the grain size, the hydrogen reduction degree and the decomposition rate of carbon dioxide was increased.

• Journal of the Korean Ceramic Society
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• v.23 no.6
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• pp.71-75
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• 1986

The forming reaction processes of magnesium aluminate spinel by a thermal decomposition of sulfate hydrate were studied with DTA, TG. SEM and X-ray powder diffraction methods. The hydrous salt composed of the mixture of the two compounds of $MgSO_4$ $6H_2O$ and ${AL_2}({SO_4})_17H_2O_3$ in which both sulfates were crystalline. On heating the hydrous slat the crystalline magnesium and aluminum sulfate anhydride to amorphous alumina magnesium sulfate anhydride decomposed to amorphous magnesia and these amorphous oxides reacted completely each other to form a spinel at $1000^{\circ}C$ The apparent activation energy of forming reaction of spinel was 36.5 kcal/mole($900^{\circ}C$~$1000^{\circ}C$) The crystallite size of spinel obtained at $1000^{\circ}C$ after 1 h was 380$\AA$.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.633-637
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• 2010

In this study, lithium manganese oxide spinel ($LiMn_{1.9}Fe_{0.1}Nb_{0.0005}O_4$) as a cathode material of lithium ion secondary batteries is synthesized with spray drying, and in order to increase its crystallinity and electrochemical properties, the granulated $LiMn_{1.9}Fe_{0.1}Nb_{0.0005}O_4$ particle surface is coated with lithium titanium oxide spinel ($Li_4Ti_5O_{12}$) through a sol-gel method. The granulated particles present a higher tap density and lower specific surface area. The crystallinity and discharge capacity of the $Li_4Ti_5O_{12}$ coated material is relatively higher than uncoated material. With the coating layer, the discharge capacity and cycling stability are increased and the capacity fading is suppressed successfully.

• Journal of the Mineralogical Society of Korea
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• v.11 no.1
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• pp.32-44
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• 1998

The transformation sequence of kaolinite to mullite is examined with new electron diffraction data obtained mainly by an energy filtering transmission electron microscope. Kaolinite is transformed finally into mullite and cristobalite through several steps of continuous reactions by heating, which result in metakaolinite, microcrystalline spinel-type phase and amorphous silica. Metakaolinite maintains a short-range order in its structure ven at $920^{\circ}C$. Spinel phase results from a topotactictransformation of metakaolinite apart from the breakdown of metakaolinite structure. the first strong exothermic peak on DTA curve is mainly due to the extraction of amorphous silica from metakaolinite and the gradual nucleation of mullite. Metakaolinite decomposes around$ 940^{\circ}C$ to mullite that doesn't show a clear crystallographic relationship to the parent metakaolinite structure. However, spinel phase produced previously is maintained. The initially formed spinel and mullite phases are suggested to be Al-rich, but progressively gain Si in their structures at higher temperatures. Spinel phase decomposes completely through a second weak exothermic reaction promoting the growth of mullite, and crystallization of amorphous silica to cristobalite.

• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.843-849
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• 1998

Fine powders of Mn-Zn ferrite were prepared by the alcoholic dehydration method and densification beha-vior of synthesized powder was investigated. The concentration and pH of solution for optimal precipitation was 0.4M and 2.5 respectively. The spinel single phase metastable state was formed by thermal decom-position of precipitate and then spinel phase was disintegrated into hematite and spinel {{{{ { { ZnFe}_{2 }O }_{4 } }} at 600$^{\circ}C$ With increase of temperature reaction of solid solution between hematite and spinel was proceeded and resulted in the spinel single phase (Mn, Zn Fe){{{{ { {Fe }_{2 }O }_{4 } }} On account of high reactivity of uncalcined powders densification started at 200$^{\circ}C$ lower and completed at 50$^{\circ}C$ lower in comparison with calcined powders.

• Journal of the Korean Ceramic Society
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• v.33 no.7
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• pp.779-784
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• 1996

The spinel/cubic stabilized zirconia composites were fabricated via, The reaction sintering of monoclinic zirco-nia(baddeleyite) added with MgAl powder. During heating Mg and Al were oxidizedfirst and subsequently the oxides formed spinel (MgAl2O4) and finally remained MgO stabilized the zirconia, Because the oxides formed during the oxidation process would have very fine grain size (order of submicron) mainly due to the effects of attrition milling the reaction sintering was more effective in densification and improvement of strength and fracture toughness than conventional sintering with direct addition of MgO. The sintering behavior phase transformation during firing and mechanical properties of sintered body were investigated with emphasis on the relations between spinel formation due to MgAl addition and sintering and mechanical properties.

• Journal of the Korean Ceramic Society
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• v.27 no.5
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• pp.661-667
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• 1990

Spinel powders were synthesized at the comparatively low-temperature range(800~90$0^{\circ}C$) by the emulsion-hot kerosene drying method and the effects of kerosene-evaporative conditions on powder characteristics were investigated. In emulsion drying, more unagglomerated and sinterable powders could be synthesized through rapid evaporation of emulsion at the higher kerosene temperature. The completion of formation reaction of spinel observed at the low-temperature range confirmed the high reactivity of powders. The relative theoretical density and the fracture toughness of spinel pellets sintered at 1$650^{\circ}C$ for 4hrs. were 98% and 2.1MN/m3/2, respectively.

• Bulletin of the Korean Chemical Society
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• v.20 no.8
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• pp.939-942
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• 1999

The tie lines delineating ion-exchange equilibria between NiFe2O4-NiCr2O4 spinel solid solution and Fe2O3-Cr2O3 corundum solid solution were determined at 900, 1000, and 1200 ℃ by electron microprobe and energy dispersive X-ray analysis of oxide phases, using the flux growth technique. Activities of the spinel components were calculated from the tie lines, assuming Temkin's ideal mixing in the corundum solid solution. The spinel phase could be expressed by a regular solution with negative deviations from ideality. The Gibbs free energies of mixing for spinel solid solution were discussed in terms of the cation distribution model, based on site preference energies and assuming random mixing on both tetrahedral and octahedral sites.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.3
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• pp.239-244
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• 2000

Synthesis and high temperature phase stability of $_{1+x}$ Co$_{y}$ Mn$_{2-y}$ $O_4$(0$\leq$x$\leq$0.2,y=0,1/9,1/6) spinel, both the excess lithium and cobalt added, have been studied. The spinel was prepared by oxalate precipitation method as the wet chemical process. Oxalate derived spinel was synthesized by heating of precipitates at temperature lower than $600^{\circ}C$. As a result of the TG-DTA and XRD analysis of prepared and quenched powders, it was found that reversible phase transitions started at temperatures $T_1$, $T_2$및 $T_{2'}$. The transitions involved weight (oxygen) loss and gain during heating and cooling. The effects of Li excess and Co doping on the spinel lattice constant, phase stability and transition temperatures of the prepared powders are investigated. This study would provide important data for determining the spinel preparation process such as synthesis temperature and cooling speed.

• Journal of the Mineralogical Society of Korea
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• v.18 no.4 s.46
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• pp.237-248
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• 2005

Results from in-situ high temperature X-ray diffraction measurements show that $Mg_{2}SiO_{4}{-}$spinel converts back to olivine phase only when heated in vacuum, and that at some high temperature, the olivine phase grows with time at the expense of the spinel phase strongly suggesting a 'nucleation and growth' type transition. In order to obtain the activation energy of spinel-olivine back transformation, kinetics measurements were performed on $Mg_{2}SiO_{4}{-}$spinel in vacuum at high temperatures between 1023 and 1116 K. Activation energy was determined using 'time to a given fraction method'. By employing the Avrami equation, it was found that n values generally increase with increasing temperature in a wide range implying that the nucleation and growth mechanism is probably temperature-dependent. It is likely that in spinel, at a relatively lower transformation temperature, after nucleation sites saturated, the growth of the new phase starts on the surface and gradually moves inwards. At high temperatures, however, after nucleation sites saturated, the growth starts both on the surface as well as at the interior.