• Journal of Korean Society of Environmental Engineers
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• v.28 no.4
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• pp.368-375
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• 2006

Single and complex metal oxide catalysts supported onto a commercial DT51D $TiO_2$ have been investigated for gas-phase TCE oxidation in a continuous flow type fixed-bed reaction system to develop a better design approach to catalysts for this reaction. Among the $TiO_2$-supported single metal oxides used, i.e., $CrO_x,\;FeO_x,\;MnO_x,\;LaO_x,\;CoO_x,\;NiO_x,\;CeO_x\;and\;CuO_x$, with the respective metal contents of 5 wt.%, the $CrO_x/TiO_2$ catalyst was shown to be most active for the oxidative TCE decomposition, depending significantly on amounts of $CrO_x\;on\;TiO_2$. The use of high $CrO_x$ loadings greater than 10 wt.% caused lower activity in the catalytic TCE oxidation, which is probably due to production of $Cr_2O_3$ crystallites on the surface of $TiO_2$. $CrO_x/TiO_2$-supported $CrO_x$-based bimetallic oxide catalysts were of particular interest in removal efficiency for this TCE oxidation reaction at reaction temperatures above $200^{\circ}C$, compared to that obtained with $CrO_x$-free complex metal oxides and a 10 wt.% $CrO_x/TiO_2$ catalyst. Catalytic activity of 5 wt.% $CrO_x-5$ wt.% $LaO_x$ in the removal reaction was similar to or slightly higher than that acquired for the $CrO_x$-only catalyst. Similar observation was revealed for 5 wt.% $CrO_x$-based bimetallic oxides consisting of either 5 wt.% $MnO_x,\;CoO_x,\;NiO_x\;or\;FeO_x$. These results represent that such $CrO_x$-based bimetallic systems for the catalytic TCE oxidation on significantly minimize the usage of $CrO_x$ that is well known to be one of very toxic heavy metals, and offer a very useful technique to design new type catalysts for reducing chlorinated volatile organic substances.

• Journal of the Mineralogical Society of Korea
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• v.21 no.2
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• pp.161-175
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• 2008

The soil developed from volcanic ash in Jeju Island, Korea, were classified as typical Andisols. The soils had acidic pH, high water contents, high organic matters and clay-silty textures. The crystalline minerals of the samples were mainly composed of ferromagnesian minerals such as olivine and pyroxene, and iron oxides such as magnetite and hematite derived from basaltic materials. A large amount of gibbsite was found at the subsurface horizon as a secondary product from the migration of excessive aluminum. In addition, our study has shown that considerable amounts of poorly ordered minerals like allophane and ferrihydrite were present in Jeju soils. The contents of $SiO_2$ were lower than those of other soil orders, but $A1_2O_3$ and $Fe_2O_3$ contents were higher. These results are some of the important chemical properties of Andisols. The contents of heavy metals were in the range of $84{\sim}198$ for Zn, $56{\sim}414$ for Ni, $38{\sim}150$ for Co, $132{\sim}1164\;mg\;kg^{-1}$ for Cr, which are higher than the worldwide values in most of the soils. Some soil samples contained relatively high levels of Cr exceeding 1000 mg/kg. Mean reduction capacity of the Jeju soils was $6.53\;mg\;L^{-1}$ reduced Cr(VI), 5.1 times higher than that of the non-volcanic ash soils from inland of Korea. The soil reduction capacity of the inland soils had a good correlation with total carbon content (R = 0.90). However, in spite of 20 times higher total carbon contents in the Jeju soils, there was a week negative correlation between the reduction capacity and the carbon content (R = -0.469), suggesting that the reduction capacity of Jeju soils is not mainly controlled by the carbon content and affected by other soil properties. Correlations of the reduction capacity with major elements showed that Al and Fe were closely connected with the reduction capacity in Jeju soil (R = 0.793; R = 0.626 respectively). Moreover, the amounts of Ni, Co and Cr had considerable correlations with the reduction capacity (R = 0.538; R = 0.647; R = 0.468 respectively). In particular, in relation to the behavior of redox-sensitive Cr, the oxidation of the trivalent chromium to mobile and toxic hexavalent chromium can be restricted by the high reduction capacity in Jeju soil. The factors controlling the reduction capacity in Jeju soils may have a close relation with the andic soil properties explained by the presence of considerable allophane and ferrihydrite in the soils.

• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.58-66
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• 1999

The catalytic oxidation of vinyl chloride was investigated over $CrO_x$ impregnated on $Al_2O_3$ at temperature between 200 and $400^{\circ}C$. The major carbonaceous products were CO and $CO_2$, and the selectivity of $CO_2$ was gradually increased with increasing reaction temperature, while that of CO was dropped consequently. This suggests that CO is the first product which is further oxidized to $CO_2$ in the oxidation of vinyl chloride over $CrO_x/Al_2O_3$. The addition of HCl in the feed didn't affect the conversion of vinyl chloride, but the selectivity of $CO_2$ decreased by adding HCl. It implies that HCl inhibits, the complete oxidation of vinyl chloride to $CO_2$. When oxidizing vinyl chloride in dry air, significant amounts of $Cl_2$ were observed, while no $Cl_2$ was detected in the humid condition. The activities of several catalysts including various precious metals and other transition metal oxides were measured, it was found that the catalytic activity of 12% $CrO_x/Al_2O_3$ was higher than other catalysts except 1% $Pt/Al_2O_3$. The reaction rate of 12% $CrO_x/Al_2O_3$ was 1.2 times lower than that of 1% Pt/alumina, but it was 3 to 8 times more active than other catalysts for vinyl chloride oxidation at $275^{\circ}C$.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.5
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• pp.727-733
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• 2011

A new Korean standard for the determination of Cr(VI) in soils has been officially published as ES 07408.1 in 2009. This analytical method is based on the hot alkaline digestion and colorimetric detection prescribed by U.S. EPA method 3060A and 7196A. The hot alkaline digestion accomplished using 0.28 M $Na_2CO_3$ and 0.5 M NaOH solution (pH 13.4) at $90{\sim}95^{\circ}C$ determines total Cr(VI) in soils extracting all forms of Cr(VI), including water-soluble, adsorbed, precipitated, and mineral-bound chromates. This aggressive alkaline digestion, however, proved to be problematic for certain soils which contain large amounts of soluble humic substances or active manganese oxides. Cr(III) could be oxidized to Cr(VI) by manganese oxides during the strong alkaline extraction, resulting in overestimation (positive error) of Cr(VI). In contrast, Cr(VI) reduction by dissolved humic matter or Fe(II) could occur during the neutralization and acidic colorimetric detection procedure, resulting in underestimation (negative error) of Cr(VI). Futhermore, dissolved humic matter hampered the colorimetric detection of Cr(VI) using UV/Vis spectrophotometer due to the strong coloration of the filtrate, resulting in overestimation (positive error) of Cr(VI). Without understanding the mechanisms of Cr(VI) and Cr(III) transformation during the analysis it could be difficult to operate the experiment in laboratory and to evaluate the Cr(VI) results. For this reason, in this paper we described the theoretical principles and limitations of Cr(VI) analysis and provided useful guidelines for laboratory work and Cr(VI) data analysis.

• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.506-513
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• 2010

The composite coatings of $(ZrO_2-8Y_2O_3)$/(Ni-22Cr-10Al-1Y) were prepared by the air plasma spraying method. They consisted of (Ni,Cr)-rich regions,$(ZrO_2-Y_2O_3)$-rich regions, and $Al_2O_3$-rich regions that were formed by oxidation of Al from (Ni-22Cr-10Al-1Y) during spraying. The coatings corroded at 800 and $900^{\circ}C$ in NaCl-$Na_2SO_4$ molten salts up to 50 hr. Ni, Cr and Al oxidized to NiO, $Cr_2O_3$ and ${\alpha}-Al_2O_3$, respectively. These oxides and $(ZrO_2-Y_2O_3)$ were dissolved off into the molten salts during hot corrosion, which resulted in the ever-lasting corrosion of the composite coatings. Chromium diffused out from the (Ni,Cr)-rich regions and oxidized to $Cr_2O_3$, which was most frequently found as surface scales. Aluminum retained in the (Ni,Cr)-rich regions were similarly diffused out.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.554-560
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• 2021

CRUD (chalk river unidentified deposits) is a porous material deposited on the surface of nuclear fuel during nuclear power plant operation. The CRUD is composed of metal oxides, such as iron, nickel, and chromium. It is essential to investigate the effects of the CRUD layer on the wall heat transfer between the nuclear fuel surface and the coolant in the event of a nuclear accident. CRUD only negatively affects the temperature of the nuclear fuel due to heat resistance because the effects of the CRUD layer on two-phase boiling heat transfer are not considered. In this study, the physical property models for the porous CRUD layer were developed and implemented into the SPACE code. The effects of boiling heat transfer models on the peak cladding temperature and quenching were investigated by simulating a reflood experiment. The calculation results showed some positive effects of the CRUD layer.

• Bulletin of the Korean Chemical Society
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• v.27 no.9
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• pp.1310-1314
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• 2006

Sulfur-substituted $LiMn_{0.9}Cr_{0.1}O_{2-x}S_x$ $(0\;\leq\;x\;\leq\;0.1)$ layered oxides have been prepared by solid state reaction under inert atmosphere. From powder X-ray diffraction analyses, all the present lithium manganates were found to be crystallized with monoclinic-layered structure. Electrochemical measurements clearly demonstrated that, in comparison with the pristine $LiMn_{0.9}Cr_{0.1}O_2$, the sulfur-substituted derivatives exhibit smaller discharge capacities for the entire cycle range but the recovery of discharge capacity after the initial several cycles becomes faster upon sulfur substitution. The effect of the sulfur substitution on the chemical bonding nature of $LiMn_{0.9}Cr_{0.1}O_{2-x}S_x$has been investigated using X-ray absorption spectroscopic (XAS) analyses at Mn and Cr K-edges. According to Mn K-edge XAS results, the trivalent oxidation state of manganese ion remains unchanged before and after the substitution whereas the local structure around manganese ions becomes more distorted with increasing the substitution rate of sulfur. On the other hand, the replacement of oxygen with sulfur has negligible influence on the local atomic arrangement around chromium ions, which is surely due to the high octahedral stabilization energy of $Cr^{+III} $ ions. Based on the present experimental findings, we have suggested that the decrease of discharge capacity upon sulfur substitution is ascribable to the enhanced structural distortion of $MnO_6$ octahedra and/or to the formation of covalent Li-S bonds, and the accompanying improvement of cyclability would be related to the depression of Mn migration and/or to the pillaring effect of larger sulfur anion.