• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.357-361
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• 2001

The possibility of producing Cr$_2$O$_3$powder from waste magnesia-chromium refractory was investigated by sulfuric acid reaction, alkali fusion, water leaching & purification and heat treatment. The effects of temperature, the amount of NaOH added and the flow rate of air on chromium extraction efficiency in an alkali fusion step were investigated. The fusion product was leached with methanol to solve free-NaOH, and then leached with water to produce a Na$_2$CrO$_4$solution. The purity of chrome(Ⅵ) oxides, prepared both from monochromate with an impurity content and monochromate purified with $CO_2$were also examined. The purified monochromate solution was reduced from Cr(Ⅵ) to Cr(III) with NaHSO$_3$solution. The reduced solution was neutralized with NaOH to produce Cr(OH)$_3$. Water washing was treated to eliminate Na$_2$SO$_4$from neutralized Cr(OH)$_3$slurry. The washed Cr(OH)$_3$was dried and thermally treated to produce Cr$_2$O$_3$powder. The properties like lightness and hue of Cr$_2$O$_3$fabricated in this study were L=47.47, a=-14.40 and b=17.21.

• Transactions of Materials Processing
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• v.8 no.3
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• pp.327-327
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• 1999

The oxidation behavior of 60%Cu-40%Zn brass haying small amounts of Zr, Cr, Mg, Al, and Si was studied between 873 and 1043 K in air. The alloying element of Mg was harmful, while other alloying elements were beneficial to oxidation resistance. Particularly, the simultaneous addition of Al and Si decreased the oxidation rate drastically. During oxidation, Zr formed ZrO₂, Cr formed CuCr₂O₄, Mg formed MgO, Al formed A1₂CuO₄, and Si formed amorphous SiO₂. These oxides were incorporated in the oxide scale composed predominantly of ZnO. The oxide scales formed on all the tested alloyswere prone to cracking, wrinkling, and spallation.

• Corrosion Science and Technology
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• v.3 no.4
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• pp.172-177
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• 2004

Biaxially oriented polyethylene terephthalate copolymer(BO - PET)film laminated aluminiums have been applied for chip condenser case. The BO PET film is characterized by high molecular which gives high corrosion resistance, good adhesion and high heat resistance. The higher orientation lowers formability of the film. So, optimum orientation has to be controlled during the laminating process. And to confirm the adhesion between BO PET and aluminium and to guarantee the formability of PET laminated aluminums, we have controlled the chromium oxides weight on the aluminium and laminating condition ( laminating temperature, soaking temperature and lag time after nip roll and quenching conditions) This paper discusses the effect of the laminating conditions on the formability of laminated aluminums. As results, it is clear that the orientation of the BO PET film decreased with an increase in the strip temperature. When the film temperature is over the melting point of the film, its orientation drastically decreased.

• Korean Journal of Soil Science and Fertilizer
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• v.32 no.4
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• pp.327-332
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• 1999

Manganese (Mn) oxides in soils have been a research subject since they react with nutrients and contaminants and Mn itself is an essential element for plant growth. Birnessite was synthesized in the presence of iron (Fe) in the precipitating solution. Influence of Fe, one of common elements in soils, on crytallinity, morphology, and chemical reactivity of birnessite was examined using X-ray diffraction (XRD), electron microscope, canon exchange capacity (CEC), and chromium (Cr) oxidation capacity. With increasing Fe concentration in the precipitating solution, crystallinity and crystal size decreased. Hexagonal plates of the birnessites formed at low Fe concentration were dominant and replaced more and more by aggregate of small particles with increasing the Fe concentration. There is no significant change in CEC with changing the Fe concentration. Chromium oxidation capacity of the birnessite increased with increasing the Fe concentration. Iron in the precipitating solution poisoned crystal growth by adsorption on the surface and increased nucleation. Since Fe is a common constituent under pedogenic environment and Fe and Mn oxides often coexist in Mn oxide nodules, the birnessite with small particle, low crystallinity, and high chemical reactivity is the form which is more likely to be formed in soils. The high CEC ($140cmol_ckg^{-1}$) and oxidation capacity of birnessite indicate that birnessite can be used in environment and agriculture.

• Journal of the Korean Ceramic Society
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• v.48 no.3
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• pp.222-227
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• 2011

The hexavalent chromium ions in wastewater are highly toxic chemicals even at low concentrations. It causes serious diseases, such as cancer, skin disease, digestive trouble et. al. In this study, $Cr^{6+}$ ions were removed by using borosilicate glasses. Various glasses system with different compositions were prepared and then reacted in a solution contaning $Cr^{6+}$ ions. After the reaction, the concentration of the $Cr^{6+}$ ions remained in the solution was measured by ICP-OES. The reacted surface of the glasses was also analyzed by using a XRD, SEM, and EDS. When $Na_2O-RO-SiO_2-B_2O_3$ (RO=MgO, CaO, SrO, BaO) glasses were reacted with a solution containing $Cr^{6+}$ ions, the optimum removal efficiency of $Cr^{6+}$ ions was observed in the BaO glass. $Ba^{2+}$ ions leached out of these glasses combine with $Cr^{6+}$ ions in a solution to form $BaCrO_4$ crystals on the glass surface. In this manner, the $Cr^{6+}$ ions can be removed from the solution. It is conceivable that $Ba^{2+}$ ions are reacted with $Cr^{6+}$ ions in a solution immedeately after leaching out of the glasses. The pH of the solution for optimum removal of $Cr^{6+}$ ions were 3.0~5.0.

• Applied Chemistry for Engineering
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• v.2 no.3
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• pp.279-288
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• 1991

Mg- and Zn-ferrites having spinel structure, a kind of complex oxides showing the advantageous properties of constituent single metal oxides, were selected to find a relationship between their catalytic activities in the dehydrogenation of ethylbenzene to styrene and the catalytic properties. For the structural and physical analyses of ferrites, XRD, BET, TG/DTA, ESCA, TEM, and TPD methods were employed. The effects of Cr-substitution were intensively studied by the experimental methods mentioned above. Chromium which showed a preferential tendency to diffuse to the surface acted as a structural promoter by increasing surface area and stability of catalyst structure. In the dehydrogenation of ethylbenzene, catalytic activity, and the effects of Cr-substitution were investigated. Oxygen mobility was decreased with the amount of Cr-substitution in $MgCr_xFe_{2-x}O_4$, which resulted in the increase of selectivity to styrene and the suppression of total oxidation.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.6
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• pp.657-662
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• 2005

Iron sulfide(FeS) is significantly produced through both abiotic and biotic processes in natural sediments and pore waters. In this study, chromium(VI) reaction with iron sulfide at various initial concentrations and at pH values of 4 and 8 was conducted to better understand the interactions between Cr(VI) and Fe(II) species dissolved from iron sulfide in both the aqueous and solid phases. Also, the removal efficiency of iron sulfide was compared with zero valent iron and other iron bearing oxides such as ${\alpha}-Fe_2O_3$, ${\alpha}-FeOOH$ and $Fe_3O_4$. The Cr(VI) removal rate by iron sulfide was higher at pH 4 than at pH 8 because more dissolved Fe(II) existed at pH 4 than at pH 8. Chromium and iron(oxyhydroxide) could be identified on the iron sulfide surface with transmission microscopy imaging and energy dispersive spectroscopy. The removal capacity of iron sulfide was much higher than zero valent iron and other iron oxide minerals due to the synergic effect of hydrogen sulfide and ferrous iron.

• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.714-718
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• 2015

Both lead molybdate ($PbMoO_4$) and chromium substituted lead molybdate ($PbMo_{1-x}Cr_xO_4$) were successfully synthesized using a conventional hydrothermal method and characterized by XRD, DRS, Raman, SEM and PL. We also investigated the photocatalytic activity of these materials for the decomposition of rhodamine B under UV-visible irradiation. The XRD and Raman results revealed the successful synthesis of well-crystallized $PbMoO_4$ crystals with the diameter of 51-59 nm, regardless of the addition of chromium ion. The DRS spectra of $PbMo_{1-x}Cr_xO_4$ catalysts showed new intensive absorption bands in the visible region. The $PbMoO_4$ catalysts showed the lowest photocatalytic activity and the activity increased with an increase of chromium substitution amounts under visible irradiation. PL peaks appeared at about 540-580 nm for all catalysts and excitonic PL signals were proportional to the photocatalytic activity for the decomposition of rhodamine B.

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

• Nuclear Engineering and Technology
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• v.32 no.5
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• pp.514-520
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• 2000

The mechanism of corrosion behavior has to be understood clearly to select an optimum material for handling molten salts to be used in the oxide reduction process of PWR spent fuel. In this study, the oxidation states of corrosion products on the surface of Inconel 600 and 800H as well as their chemical compositions and structural informations were determined by using XPS, ICP-AES, AAS, EPMA and XRD after the corrosion experiment with lithium molten salts at 75$0^{\circ}C$ for 25 hours. Nickel and oxygen were detected from the corrosion products on the surface of Inconel plates and chromium was found to be dissolved out into lithium molten salts leaving cracks on the surface. The corrosion products were identified as metal oxides such as Fe$_2$O$_3$, Cr$_2$O$_3$, NiO, NiFe$_2$O$_4$and MnO by using XPS and XRD.