• Journal of the Korean Ceramic Society
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• v.21 no.3
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• pp.221-230
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• 1984

In this study an investigation was made to determine optimum ratio between $SO_3$, MgO and $K_2O$ that maximizes $C_2S$ formation in Clinkering reaction Using response surface analysis method. It was proved that 1) Residual $K_2O$ int he clinker should be converted to $K_2SO_4$ because $K_2SO_4$ has less effect on the burnability than $K_2O$, 2) Optimum ratio if $SO_3$/K2O is 1.5, 3) Optimun balance between $CaSO_4$ and MgO is to be adjusted to such a level that w/o SO3=0.7(w/o MgO-2).4) In case of lack of $K_2O$ free CaO was minimized when $K_2SO_4$=2.3w/o and MgO=1.5w/o but if remaining $K_2O$ was 2w/o free CaI was minimized in the level that $K_2SO_4$=2.3w/o and MgO =1.5 w/o but if remaining $K_2O$ was 2 w/o free CaO was minimized in the level that $K_2SO_4$=4.5w/o and MgO =3.0 w/o.

• Journal of the Korean Ceramic Society
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• v.32 no.2
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• pp.234-238
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• 1995

MgFe2O4 formation, grain growth in Fe2O3, Fe solid-solution limit in MgO for MgO-Fe2O3 mixture were studied by means of investigating the distribution of phases and compositions in reaction area between MgO and Fe2O3. The reaction area at equlibrium was composed with MgO-FexO matrix and MgFe2O4 precipitation, MgFe2O4 was formed by precipitating from MgO-FexO matrix dependent on oxygen partial pressure. Fe contents was exponentially decreased with diffusion distance in MgO single crystal, and thus Fe solid-solution limitation in MgO was about 4mol%. The grain growth rate in Fe2O3 base was increased with Mg contents diffused from MgO single crystal.

• Journal of the Mineralogical Society of Korea
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• v.23 no.2
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• pp.117-124
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• 2010

The sorption of $AsO_4,\;SeO_3,\;CrO_4$ on schwertmannite and thermal analysis of sorbed samples were carried out. The results of sorption experiments showed that sorption characteristics of those three oxyanions on schwertmannite can be divided into two groups. The extent of sorption of $AsO_4$ and $SeO_3$ were 100% at up to 1 mM solution concentration, and they increased no more significantly. This can be interpreted as $AsO_4$ and $SeO_3$ substituting $SO_4$ in schwertmannite strucure by the ratio of 1 : 1. The extent of the sorption of $CrO_4$ was much lower than those of other two oxyanions. Thermal analysis was performed using two kinds of sorbed samples at 0.1 and 1.25 mM concentrations. The results of the thermal analysis showed that the samples sorbed by three different oxyanions have different thermal characteristics. The samples sorbed by $AsO_4$ showed smaller weight loss around $600^{\circ}C$ than the original loss of pure schwertmannite, and it is attributed to the substitution of $AsO_4$ for $SO_4$, which was caused by the loss of $SO_4$, than pure schwertmannite due to the substitution of $SO_4$ by $AsO_4$. It also showed additional weight loss around $600^{\circ}C$ due to the decomposition of $AsO_4$ at that temperature. The weight loss of samples sorbed by $SeO_3$ started at slightly lower temperature than that sorbed by $SO_4$ and kept that loss at wider temperature range, probably indicating that the decomposition of $SeO_3$ occurs at slightly lower temperature. However, for the samples sorbed by $CrO_4$, the weight loss caused by the decomposition of $SO_4$ was also smaller and there was no additional weight loss at higher temperature due to the thermal stability of $CrO_4$, indicating that $SO_4$ was also substituted by $CrO_4$ in schwertmannite. Sorption experiment and thermal analysis indicate that $CrO_4$ sorbs on schwertmannite by substiuting $SO_4$, but the affinity to $SO_4$ or instability of $CrO_4$ in scwertmannite structure probably prohibit perfect 1 : 1 substitution.

• Proceedings of the KIEE Conference
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• 2000.11c
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• pp.506-508
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• 2000

Oxide of the form $Mn_{3}O_{4}-NiO-Fe_{2}O_{3}$ present properties that make them useful as multilayer chip NTC thermistor for mobile phone NTC thermistor electric properties of $Mn_{3}O_{4}-NiO-Fe_{2}O_{3}$ system has been measured as a function of temperature and composition. In $Mn_{3}O_{4}-NiO-Fe_{2}O_{3}$ composition, it can be seen that resistivity and B-constant were increased as the ratio of $Mn_{3}O_{4}/F_{2}O_{3}$ and $Mn_{3}O_{4}$/NiO was increased. In particular, resistance change ratio (${\Delta}R$), the important factor for reliability varied within ${\pm}1%$, indicating the compositions of these products could be available for mobile phone.

• Korean Journal of Materials Research
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• v.22 no.5
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• pp.253-258
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• 2012

Activated magnetite ($Fe_3O_{4-{\delta}}$) was applied to reducing $CO_2$ gas emissions to avoid greenhouse effects. Wet and dry methods were developed as a $CO_2$ removal process. One of the typical dry methods is $CO_2$ decomposition using activated magnetite ($Fe_3O_{4-{\delta}}$). Generally, $Fe_3O_{4-{\delta}}$ is manufactured by reduction of $Fe_3O_4$ by $H_2$ gas. This process has an explosion risk. Therefore, a non-explosive process to make $Fe_3O_{4-{\delta}}$ was studied using $FeC_2O_4{\cdot}2H_2O$ and $N_2$. $FeSO_4{\cdot}7H_2O$ and $(NH_4)_2C_2O_4{\cdot}H_2O$ were used as starting materials. So, ${\alpha}-FeC_2O_4{\cdot}2H_2O$ was synthesized by precipitation method. During the calcination process, $FeC_2O_4{\cdot}2H_2O$ was decomposed to $Fe_3O_4$, CO, and $CO_2$. The specific surface area of the activated magnetite varied with the calcination temperature from 15.43 $m^2/g$ to 9.32 $m^2/g$. The densities of $FeC_2O_4{\cdot}2H_2O$ and $Fe_3O_4$ were 2.28 g/$cm^3$ and 5.2 g/$cm^3$, respectively. Also, the $Fe_3O_4$ was reduced to $Fe_3O_{4-{\delta}}$ by CO. From the TGA results in air of the specimen that was calcined at $450^{\circ}C$ for three hours in $N_2$ atmosphere, the ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was estimated. The ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was 0.3170 when the sample was heat treated at $400^{\circ}C$ for 3 hours and 0.6583 when the sample was heat treated at $450^{\circ}C$ for 3 hours. $Fe_3O_{4-{\delta}}$ was oxidized to $Fe_3O_4$ when $Fe_3O_{4-{\delta}}$ was reacted with $CO_2$ because $CO_2$ is decomposed to C and $O_2$.

• Journal of the Korean Chemical Society
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• v.26 no.6
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• pp.383-388
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• 1982

$Mo_2O_4Cl_2$$(X-py)_4{\cdot}2H_2$O and $(X-pyH)_4$[$Mo_2O_4(NCS)_6)$]${\cdot}H_2$O have been prepared. The infrared, electronic and reflectance spectra, molar conductances and magnetic susceptibility data of complexes are reported. $Mo_2O_4Cl_2$$(X-py)_4{\cdot}2H_2$O (X-py were 3-and 4-cyanopyridine, nicotinamide, 3,5-lutidine and 2-amino-4-picoline) were obtained by hydrolysis of the corresponding substituted pyridinium oxopentachloromolybdates(Ⅴ). Addition of water and substituted pyridines to molybdenum(Ⅴ)-thiocyanate ethylacetate extract yielded brown compounds, $(X-pyH)_4$[$Mo_2O_4(NCS)_6)$]${\cdot}H_2$O where X-py were pyridine, ${\alpha}$, 3-bromopyridine 3,5-lutidine, 3-benzoylpyridine and 4-acetylpyridine. Binuclear, $Mo_2O_4Cl_2(X-py)_4{\cdot}2H_2$ prepared from hydrolysis of $(X-pyH)_2[MoOCl_5]{\cdot}H_2O$ were diamagnetic and nonelectrolytes. The anion of $(X-pyH)_4$[$Mo_2O_4(NCS)_6)$]${\cdot}H_2$O was formulated as dimer and electrolyte.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.265-265
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• 2007

In the present work, we have studied low temperature sintering and microwave dielectric properties of $ZnAl_2O_4$-zinc borosilicate (ZBS, 65ZnO-$25B_2O_3-10SiO_2$) glass composites. The focus of this paper was on the improvement of sinterability, low dielectric constant, and on the theoretical proof regarding of microwave dielectric properties in $ZnAl_2O_4$-ZBS glass composites, respectively. The $ZnAl_2O_4$ with 60 vo1% ZBS glass ensured successful sintering below $900^{\circ}C$. It is considered that the non-reactive liquid phase sintering (NPLS) occurred. In addition, $ZnAl_2O_4$ was observed in the $ZnAl_2O_4$-(x)ZBS composites, indicating that there were no reactions between $ZnAl_2O_4$ and ZBS glass. $ZnB_2O_4\;and\;Zn_2SiO_4$ with the willemite structure as the secondary phase was observed in the all $ZnAl_2O_4$-(x)ZBScomposites. In terms of dielectric properties, the application of the $ZnAl_2O_4$-(x)ZBS composites sintered at $900^{\circ}C$ to LTCC substrate were shown to be appropriate; $ZnAl_2O_4$-60ZBS (${\varepsilon}_r$= 6.7, $Q{\times}f$ value= 13,000 GHz, ${\tau}_f$= -30 ppm/$^{\circ}C$). Also, in this work was possible theoretical proof regarding of microwave dielectric properties in $ZnAl_2O_4$-(x)ZBS composites.

• Journal of the Korean Ceramic Society
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• v.31 no.2
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• pp.213-219
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• 1994

The formations of spinel and colors of ZnO-Fe2O3-TiO2-SnO2 system have been researched on the basis of ZnO-Fe2O3 system. Specimens were prepared by substituting Fe3+, with Ti4+ or Sn4+ when mole ratios between Fe3+ and Ti4+ or between Fe3+ and Sn4+ were 0.2 mole. The reflectance measurement and X-ray diffraction analysis of the formation of spinel and the colors of there specimens were carried out. ZnO-Fe2O3 system in which Fe2O3 was substituted with SnO2 and TiO2 was formed the spinel structure of 2ZnO.TiO2, 2ZnO.SnO2, ZnO.Fe2O3. The stable stains which were colored with yellow and brown could be manufactured.

• Bulletin of the Korean Chemical Society
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• v.28 no.8
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• pp.1265-1272
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• 2007

A solid acid catalyst, NiSO4/CeO2-ZrO2 was prepared simply by promoting ZrO2 with CeO2 and supporting nickel sulfate on CeO2-ZrO2. The support of NiSO4 on ZrO2 shifted the phase transition of ZrO2 from amorphous to tetragonal to higher temperatures because of the interaction between NiSO4 and ZrO2. The surface area of 10-NiSO4/1-CeO2-ZrO2 promoted with CeO2 and calcined at 600 oC was very high (83 m2/g) compared to that of unpromoted 10-NiSO4/ZrO2 (45 m2/g). This high surface area of 10-NiSO4/1-CeO2-ZrO2 was due to the promoting effect of CeO2 which makes zirconia a stable tetragonal phase as confirmed by XRD. The role of CeO2 was to form a thermally stable solid solution with zirconia and consequently to give high surface area and acidity of the sample, and high thermal stability of the surface sulfate species. 10-NiSO4/1- CeO2-ZrO2 containing 1 mol% CeO2 and 10 wt% NiSO4, and calcined at 600 oC exhibited maximum catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation.

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.57-62
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• 1986

Oxidation of $[Mo_3O_4(C_2O_4)_3(H_2O)_3]^{2-}$ with HCr$O_4^-$ yields the molybdenum(Ⅳ) complex, $[Mo_2O_5(C_2O_4)_2(H_2O)_2]^{2-}$. Stoichiometry for the reaction of $[Mo_3O_4(C_2O_4)_3(H_2O)_3]^{2-}$ with HCr$O_4^-$ are expressed as $2Mo_3^{IV} + 4Cr^{VI} {\to} 3Mo_2^{VI} + 4Cr^{III}$. Observed rate constants are dependent on hydrogen ion concentration. The kinetic data are consistent with a mechanism in which three successive single-electron steps convert $Cr^{VI}$to $Cr^{III}$ by way of intermediate $Cr^V$ and $Cr^{IV}$. Detailed mechanisms are presented and discussed.