• Journal of the Korean institute of surface engineering
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• v.44 no.6
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• pp.233-238
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• 2011

The friction and wear characteristics of CrN and TiN coatings on SKD61 which is mold material using for extrusion of AZ80 magnesium alloy were investigated. The coatings were deposited by the arc ion-plating method, and the thickness were about $3.59{\mu}m$ and $3.28{\mu}m$, respectively. Reciprocating friction wear tests were conducted by varying pin load and temperature of counter substrate at un-lubricated condition. The pin loads were 11, 15 and 19 kgf, and the substrate temperatures were room temperature and $120^{\circ}C$. CrN coating which has a lower friction coefficient and a smaller adhesive wear with AZ80 magnesium alloy showed better wear resistance than TiN coating.

• Journal of the Korean Chemical Society
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• v.46 no.2
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• pp.145-150
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• 2002

A Method to determine Cr(III)ion in aqueous solution by chemiluminescence method using a stopped flow system has been studied. The method is based on the increased chemiluminescence intensity with the addition of Cr(III) to a solution of lucigenin a nd hyrogen peroxide. The effects of pH, injection volumes of reagent and sample, and concentration of lucigenin and hyrogen peroxide on the chemiluminescence intensity have been investigated. The calibration curve for Cr(III) ion was linear over the range from 1.0${\times}$$10^{-6}$ to 1.0${\times}$$10^{-3}$M and the detection limit was 5.2${\times}$$10^{-8}$M under the optimal experimental condition of 437nm, 12.8,and 1.0${\times}$$10^{-6}$ and 2.0M for emission wavelength, pH, and concentration of lucigenin and hyrogen peroxide, respectively.

• Journal of Magnetics
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• v.11 no.1
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• pp.51-54
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• 2006

Variation of magnetic properties through Cr substitution for Co in inverse-spinel $CoFe_2O_4$ has been investigated by vibrating-sample magnetometry (VSM) and conversion electron $M\ddot{o}ssbauer$ spectroscopy (CEMS). $Cr_{x}Co_{1-x}Fe_2O_4$ samples were prepared as thin films by a sol-gel method. The lattice constant of the $Cr_{x}Co_{1-x}Fe_2O_4$ samples was found to remain unchanged, explainable in terms of a reduction of tetrahedral $Fe^{3+}$ ion to $Fe^{2+}$ due to substitution of $Cr^{3+}$ ion into octahedral $Co^{2+}$ site. The existence of the tetrahedral $Fe^{2+}$ ions in $Cr_{x}Co_{1-x}Fe_2O_4$ was confirmed by CEMS analysis. Room-temperature magnetic hysteresis curves for the $Cr_{x}Co_{1-x}Fe_2O_4$ films measured by VSM revealed that the saturation magnetization $M_s$ increases by Cr doping. The $M_s$ is maximized when x = 0.1 and decreases for higher x but is still bigger than that of $CoFe_2O_4$. The increase of $M_s$ can be explained partly by the reduction of the tetrahedral $Fe^{3+}$ ion to $Fe^{2+}$.

• Bulletin of the Korean Chemical Society
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• v.26 no.7
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• pp.1044-1050
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• 2005

The reaction of cis-[Cr([14]-decane)($OH_2)_2]^+$ ([14]-decane = rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-teraazacyclotetradecane) with auxiliary ligands {$L_a$ = isothiocyanate ($NCS^-$), azide ($N3^-$) or chloroacetate(caa)} leads to a new cis-[Cr([14]-decane)($NCS)_2]ClO_4{\cdot}H_2O$ (1), cis-[Cr([14]-decane)($N_3)_2]ClO_4$ (2) or cis-[Cr([14]-decane)($caa)_2]ClO_4$ (3). These complexes have been characterized by a combination of elemental analysis, conductivity, IR and Vis spectroscopy, mass spectrometry, and X-ray crystallography. Analysis of the crystal structure of cis-[Cr([14]-decane)($NCS)_2]ClO_4{\cdot}H_2O$ reveals that central chromium(III) has a distorted octahedral coordination environment and two $NCS^-$anions are bonded to the chromium(III) ion via the Ndonor atom in the cis positions. The angle $N_{axial}-Cr-N_{axial}$ deviates by 13$^{\circ}$ from the ideal value of 180$^{\circ}$ for a perfect octahedron. The bond angle N-Cr-N between the Cr(III) ion and the two nitrogen atoms of the isothiocyanate ligands is close to 90$^{\circ}$. The bond lengths of Cr-N between the chromium and $NCS^-$groups are 1.964(5) and 2.000(5) $\AA$. They are shorter than those between chromium and nitrogen atoms of the macrocycle. The IR spectra of 1, 2 and 3 display bands at 2073, 1344 and 1684 $cm^{-1}$ attributed to the $NCS^-$, ${N_3}^-$ and caa groups stretching vibrations, respectively.

• Journal of Environmental Health Sciences
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• v.9 no.2
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• pp.75-81
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• 1983

The Biochemical Oxygen Demand(BOD) indicates that microbes are proliferating or that oxygen is being spent by breathing action when examining water under the same aerobic condition. In this research of the mesurement of BOD are the poisonous elements of heavy metal ions such as Cu-ion, Cr-ion, Pb-ion and Zn-ion. They exert an unfavorable influence in the analysis of BOD and research was performed to provide certain data of minimum negative influence by the poisonous matters. The results of the research confirm that heavy metal ion(Cu, Cr, Pb, Zn) do direct an influence upon the normal growth of aerobic microbes in actual tests of chemical analysis of portable water or sewage. The most critical concentration for a negative effect on lowering oxygen quantity and disturbing the aerobic mocrobes normal growth was found to be 0.01 mg/l. Therefore, test results are not valid if the heavy metal concentration is to or greater than 0.0mg/l, To improve comprehension through out the research the author uses the following abbreviations: 1. The Cu-ion is to be excluded before experimental analysis if it is over 0.01mg/l inorder to obtain a real value for the BOD. 2. The Cr-ion is to be excluded before experimental analysis if it is over 0.01mg/l in order to obtain a real value for the BOD. 3. The Pb-ion is to be excluded before experimental analysis if it is over 0.01mg/l in order to obtain a real value for the BOD. 4. The Zn-ion is to be excluded before experimental analysis if it is over 0.01mg/l in order to obtain a real value for the BOD.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.10a
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• pp.33-33
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• 1999

• Journal of the Korean Ceramic Society
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• v.46 no.6
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• pp.615-620
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• 2009

The present research was performed to determine the optimal firing condition and holding time for malayaite crystal, which is responsible for the stable pink-red coloration in glaze at high temperatures, using Cr$Cl_3$ as chromophore for the synthesis of $Cr_2O_3-SnO_2-CaO-SiO_2$ system pigments. The malayaite crystal was influenced by the raw materials used for synthesis, firing temperature, and holding time. Thus there are differences in the crystal phase and in the coloration according to the condition of synthesis. When Cr$Cl_3$ was used as chromophore, the pigment could be synthesized at lower temperatures, because Cr$Cl_3$ melts at $1500{^{\circ}C}$, which is much lower than the temperature at which $Cr_2O_3$ melts (higher than $2435{^{\circ}C}$). And the employed Cr ion showed a change in oxidation state. When a mineralizer was used to improve the employment of malayaite and the Cr ion, and the low temperature was maintained at which the malayaite crystal is produced, the production of malayaite crystal was promoted and the employment of chromophore was also promoted in the oxidation state of Cr (IV). The results of the experiment showed that the optimal firing condition was 18 h of holding time at $800{^{\circ}C}$, using Cr$Cl_3$ as chromophore, followed by 2 h at the raised temperature of $1150{^{\circ}C}$. The change in coloration of the Cr (IV) employed by malayaite showed a very rich color of red. Thus it was possible to effectively synthesize sphene-pink pigments with more red tint at a low temperature.

• Journal of the Korean Chemical Society
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• v.44 no.3
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• pp.212-219
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• 2000

An absorption spectrometry coupled with flow injection analysis has been developed and tested for the analysis of the Cr$_2O_7^{2-}$/Nn$O_4^-$ mixtures. Even though one has to inject the sample twice into the FIA system and the process of the sample treatment is required to completely destroy the Mn$O_4^-$ ion for the analysis of the Cr$_2O_7^{2-}$ ion, the new method has definite advantages over the current method. It utilizes only a single analytical wavelength (570 nm) and enables one to construct calibration curves which accurately follow the Beer's law over wide ranges of analytical concentrations of both ions ($2.0{\times}10^{-6}$M∼$8.0{\times}10^{-3}$M for Cr$_2O_7^{2-}$ ion, $2.0{\times}10^{-6}$M∼$4.0{\times}10^{-3}$M for MnO4- ion).

• Applied Chemistry for Engineering
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• v.26 no.1
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• pp.92-98
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• 2015

In this study, phenol-based activated carbons (ACs) were fluorinated at various fluorine partial pressures (0.01~0.03 MPa) and the $Cr^{6+}$ ion adsorption of fluorinated ACs was investigated. According to BET and XPS results, the specific surface area and total pore volume of fluorinated ACs increased by 24.7 and 55.8%, respectively, and fluorine functional groups were introduced to AC surface. The most optimized condition of $Cr^{6+}$ ion adsorption was confirmed at the fluorine partial pressure of 0.02 MPa. And also the removal efficiency of $Cr^{6+}$ ion was up to 98% at 300 mg/L of the initial concentration, and these results showed an approximately three-fold increase compared to that of using untreated ACs. Furthermore, the $Cr^{6+}$ ion adsorption of fluorinated ACs was completed in less than 30 min in contrast with untreated ACs, which was expected to be an increase of the affinity between $Cr^{6+}$ ions and ACs surfaces by fluorination.

• Journal of Radiation Industry
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• v.2 no.1
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• pp.9-14
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• 2008

Livestock wastewater containing high concentrations of organic matters and ammonia-nitrogen has been known as one of the recalcitrant wastewater. It is difficult to treat by conventional wastewater treatment techniques. This study was carried out to evaluate the feasibility of zeolite ion exchange and gamma-ray irradiation treatment of livestock wastewater. The removal efficiencies of $SCOD_{Cr}$ and $NH_3-N$ were significantly enhanced by gamma-ray irradiation after zeolite ion exchange as a pre-treatment. However, the effects of zeolite particle size on the $SCOD_{Cr}$ and $NH_3-N$ removal efficiencies were insignificant. These results indicate that the combined process of zeolite ion exchange and gamma-ray irradiation has potential for the treatment of livestock wastewater.