• Korean Journal of Materials Research
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• v.12 no.11
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• pp.845-849
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• 2002

Alloys of $Fe_3$Al, $Fe_3$Al-6Cr, $Fe_3$Al-4Cr-1Mo, $Ni_3$Al, and $Ni_3$Al-2.8Cr were oxidized at $1000^{\circ}C$ in air, and the oxide scales formed were studied using XRD. SEM, EPMA, and TEM. The oxide scales that formed on $Fe_3$Al-based alloys consisted primarily of $\alpha$-$Al_2$$O_3$ containing a small amount of dissolved Fe and Cr ions, whereas those that formed on $Ni_3$Al-based alloys consisted primarily of $\alpha$-$Al_2$$O_3$, together with a small amount of $NiAl_2$$O_4$, NiO and dissolved Cr ions. For the entire alloys tested, nonadherent oxide scales formed, and voids were inevitably existed at the scale-matrix interface.

• Journal of environmental and Sanitary engineering
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• v.8 no.1
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• pp.107-116
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• 1993

This study is conducted to investigate treatability by activated sludge process for wastewater from acetaldehyde manufacturing plant. The optimum hydraulic retention time in aeration tank for removal of high strength substrate were measured. The removal efficiency were checked out by hydraulic retention time : 35hr., 40hr. and 45hr., respectively. $COD_{Cr}$, like substances were removed in all hydraulic retention time zone directed for efficiency, but non-biodegradable substances were remained. $COD_{Cr}$ biomass loading was 0.81kg $COD_{Cr}/kgMLVSS$ . day at 35hr. of retention time, 0.34 kg$COD_{Cr}$/kg MLVSS . day at 40hr., and O.l9kg$COD_Cr$/kgMLVSS . day at 45hr. And the mean $COD_{Cr}$, removal efficiency was 65.5%, 81.6% and 83.0%, respectively. And also $COD_{Cr}$, volume loading was 1.01kg$COD_{Cr}/m^3$ day, 0.87kg$COD_{Cr}/m^3$ - day, and 0.79kg$COD_{Cr}/m^3{\cdot }$day, respectively. The basic design parameter obtained is as fallows. The value of Specific substrate removal rate coefficient (k), Yield coefficient(Y) and Decay coefficient($k_d$) was $0.0013day^{-1}$, $0.505kgMLVSS/kgCOD_{Cr}$ and $0.040day^{-1}$, respectively.

• Journal of the Korean Ceramic Society
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• v.33 no.11
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• pp.1285-1291
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• 1996

Using Cr2O3 Al and graphite powders as starting materials Cr3C2 was synthesized by combustion synthesis process according to the following reaction : 3Cr3C2 +4C+6Allongrightarrow2Cr3C2 +3Al2O3. The synthesis was conducted at 2 atm in an argon atmosphere. in this study main-product was monolithic phase of Cr3C2 /Cr7C3 mixture and sub-product was slag state of $\alpha$-Al2O3. Single phase of Cr3C2 was obtained when crushed main-product was heat-treated at 120$0^{\circ}C$ for 3h in vacuum state with addition of 2.5wt% C. The obtained Cr3C2 powder can be used as plasma-arc deposit material because the flowability index of powder with the size of 9-50${\mu}{\textrm}{m}$ was 66.

• Elastomers and Composites
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• v.50 no.1
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• pp.7-12
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• 2015

The $BaCrO_4$ nanoparticles were synthesized from a 0.1 M $K_2CrO_4$ and 0.1 M $BaCO_3$ solution with stirring for 10 h. The product was washed several times with acetone and heated to $700^{\circ}C$ for 6 h. At that time, the color of mixture was a greenish yellow. The graphene/$BaCrO_4$ nanocomposites were prepared with graphene and $BaCrO_4$ nanoparticles by stirring in tetrahydrofuran and heated in an electric furnace at $700^{\circ}C$ for 2 h. The $BaCrO_4$ nanoparticles, graphene/$BaCrO_4$ and heated graphene/$BaCrO_4$ nanocomposites were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The graphene/$BaCrO_4$ nanocomposites and heated graphene/$BaCrO_4$ nanocomposites were evaluated as a photocatalyst and discussed about kinetics study for the degradation of organic dyes, such as methylene blue and rhodamine B under ultraviolet light irradiation at 254 nm.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.3
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• pp.153-157
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• 2005

The biosorption of Pb and Cr by Sargassum thunbergii was investigated in a batch conditions. The Pb and Cr uptake capacity of Sargassum thunbergii was 232.5 mg Pb/g biomass and 91.6 mg Cr/g biomass, respectively. An adsorption equilibria was reached within about 0.5 hr for both the Pb and the Cr. The adsorption parameters for both the Pb and the Cr were determined according to the Langmuir and Freundlich model. With increasing pH values, more negative sites are becoming available for the adsorption of Pb and Cr. The selectivity of mixture solution showed an uptake order of Pb>Cu>Cr>Cd. Pb and Cr adsorbed by S. thunbergii could be recovered ken 0.1 M HCl, 0.1 M $HNO_3$ and 0.1M EDTA by a desorption process, and the efficiency of Pb desorption was above $95.8\%$, whereas the efficiency of the Cr desorption was below $50.7\%$.

• Journal of the Korean Chemical Society
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• v.34 no.6
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• pp.534-538
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• 1990

Chromium(Ⅵ) compound, [$C_9H_7$NH]$_2Cr_2O_7$ has been prepared by the reaction of isoquinoline with chromium trioxide under the presence of water. [$C_9H_7$NH]$_2Cr_2O_7$ is nonhydroscopic and dissolved in water very well. Structure of [$C_9H_7$NH]$_2Cr_2O_7$ is identified by FTIR spectra and elemental analysis data. The ability of [$C_9H_7$NH]$_2Cr_2O_7$ for the oxidation of alcohols were examined in methylene chloride. [$C_9H_7$NH]$_2Cr_2O_7$ was found as efficient oxidizing agent for the conversion of allyl, primary and secondary alcohols to the corresponding aldehydes or ketones.

• Bulletin of the Korean Chemical Society
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• v.25 no.2
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• pp.226-232
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• 2004

Ground and low-lying electronic states of Cr atoms in the gas phase were generated from photolysis of $Cr(CO)_6$ vapor in He or Ar using an unfocussed weak UV laser pulse and their reactions with $O_2$ and $N_2O$ were studied. When 0.5-1.0 Torr of $Cr(CO)_6$ /$O_2$ /He or Ar mixtures were photolyzed using 295-300 nm laser pulses, broadband chemiluminescence peaked at ~420 and ~500 nm, respectively, was observed in addition to the atomic emissions from $z^7P^{\circ}$, $z^5P^{\circ}$, and $y^7P^{\circ}$ states of Cr atoms. When $N_2O$ was used instead of $O_2$, no chemiluminescence was observed. The chemiluminescence intensities as well as the LIF intensities for those three low-lying electronic states ($a^7S_3,\;a^5S_2\;and\;a^5D_J$) showed second-order dependence on the photolysis laser power. Also, the chemiluminescence intensities were first-order in $O_2$ pressure, but the presence of excess Ar showed a strong inhibition effect on them. Based on the experimental results, the chemiluminecent species in this work is attributed to $CrO_2^*$ generated from hot ground state Cr atoms with $O_2$. The apparent radiative lifetimes of the chemiluminescent species and collisional quenching rate constants by $O_2$ and Ar also were investigated.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.298-302
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• 2011

This study developed a pigment by doping Cr to Pyrochlore-type stannate crystals and investigated the chromogenic relationship in a glaze. Crystal phases of the pigment according to firing temperatures were analyzed by XRD, and the doping relationship was analyzed by Raman Spectroscopy. Color and reflection rate of the pigment were measured by UV-vis Spectrophotometer. Consequently, stannate characteristic band appeared at 307, 408, 505 and $755cm^{-1}$ until 0.1 mole substitution of $Cr_2O_3$. However, as amount of $Cr_2O_3$ increased, the stannate characteristic peak was decreased and shift happened at the left hand side due to Cr-dope. In composition of 0.12~0.14 mole substituted, the unreacted $Cr_2O_3$ stannate characteristic peak, which was not engaged, was shown. This result shows the maximum limit of solid solution was 0.1 mole $Cr_2O_3$. The color of the glaze, which was produced by adding 6 wt% of $Y_2Sn_{1.94}Cr_{0.06}O_7$ pigment in a lime or a lime-magnesia glaze and fired the mixture at $1260^{\circ}C$, was grayish pink with $L^*$ 70.29, $a^*$ 5.68 and $b^*$ 6.27. It showed gray with $L^*$ 68.82, $a^*$ 3.07and $b^*$ 8.13 for $Y_2Sn_{1.9}Cr_{0.1}O_7$.

• Journal of Korean Society for Atmospheric Environment
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• v.18 no.1
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• pp.39-49
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• 2002

In this study, limits of detection (LOD), accuracy and precision of four sampling/ analytical methods were evaluated and compared for the determination of airborne hexavalent chromium, Cr (VI). The methods include : (1) a combination of the National Institute for Occupational Safety and Health (NIOSH) Method 7600/U. S. Environmental Protection Agency (EPA) Method 218.6 (NIOSH/EPA Method) proposed by Shin and Paik, 2) two impinger methods using 2% NaOH/3% Na$_2$CO$_3$. (3) same as (2) but with 0.02 N NaHCO$_3$absorbing solution, and (4) the Occupational Safety and Health (OSHA) Method ID-215. An ion chromatograph/visible absorbance detector was used for the analysis of Cr (VI) in sample solution. Limit of detection (LOD) , analytical accuracy, and precision were also tested using Cr (VI) spike samples. Recoveries (as index of accuracy) and coefficient of variation (CV) (as a index of precision) were determined. Two-way ANOVA and Turkey's test were performed to test the significance in differences among recoveries and CVs of the methods. In all the methods, the peaks of Cr (VI) were separated sharply on chromatograms and exhibited a strong linearity with Cr (VI) concentrations in solution. The correlation coefficients of calibration curves typically ranged from 0.9997 to 0.9999, and the analytical LODs from 0.025 to 0.1$\mu\textrm{g}$/sample. All the method had good sensitivities and linearities between Cr (VI) levels and peak areas. The accuracies (% mean recoveries) of the methods ranged from 80.1 to 104.2%, while the precisions (pooled coefficient of variation) ranged from 3.16 to 4.43%. The impinger methods showed higher recoveries ( > 95%) than those of the PVC filter methods (the OSHA Method and the NIOSH/EPA Method). It was assumed that Cr (VI) on PVC filter was exposed to air and reduced to trivalent chromium, Cr (III), whereas it was stabilized in alkali solution contained in impinger. Thus, a special treatment of Cr (VI) samples collected on PVC filters may be required.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.583-588
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• 2003

Cation exchange capacity of clay, white clay and zeolite was measured by the adsorption test for 3 different heavy metal (Cd, Cr, Zn) standard solutions whose concentrations were varied by 10, 20, 30 ppm and pH were varied by 3, 5, 7, 9, respectively. The adsorption rate of Cd and Zn increased with increasing pH and slowly increased with increasing pH above pH 5. However, adsorption rate of Cr did not increase with increasing pH. Especially, Cr adsorption rate of the mixture of clay and white clay at pH 5 showed an half decrease compared to that at pH 3. The adsorption rate of mixed heavy metal solutions was in the order of Cd, Zn > Cr; however, the order was changed by Fe>Pb, Cu>Cr>Zn>Cd in case of Cu, Fe and Pb addition.