• Journal of the Korean Chemical Society
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• v.39 no.2
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• pp.87-93
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• 1995

The amount of Cr(Ⅲ) and Cr(Ⅵ) in a chromium plating solution could be determined simultaneously within five minutes using UV/VIS spectrophotometer coupled with a flow-through analysis(FTA) setup. The λmax's at 580 nm and 440 nm which correspond to Cr(Ⅲ) and Cr(Ⅵ), respectively, well obey the Beer-Lambert law in the range over 0.05 g/L for Cr(Ⅲ) and 0.005 g/L for Cr(Ⅵ). when the pH of the sample is less than 4.0, the absorption extinction coefficients of those peaks are not much dependent on the proton concentration. The amount of Cr(Ⅲ) and Cr(Ⅵ), and the total chromium in post treatment chromium plating solution, which normally has few g/L of Cr concentration, could be easily measured using UV/VIS spectrophotometry after the sample had been diluted with sulfuric acid of pH=1.0 in the flow-through analysis setup; this method is far more convenient and faster than the common redox titration (which requires at least 40 min/sample) method, while the accuracy of the method is highly comparable to conventional titrimetric method. Since the implementation of an PTA-UV/VIS setup in any plating industry is cost effective and easy to operate, the analytic method described in this paper may be applied directly for in situ analysis of plating solutions.

• Bulletin of the Korean Chemical Society
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• v.26 no.4
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• pp.634-640
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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 {$L_a$ = citrate(cit)} leads to a new dimeric complex cis-[{Cr([14]-decane)($\mu$-cit)}$_2](ClO_4)_2$. This binuclear complex has been structurally 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)($\mu$-cit)})($_2]^+$ reveals that each chromium has a distorted octahedral coordination environment and citrato ligands are monodentate to the two chromium atoms via the carboxyl groups. For dimeric complex the bridging geometry is as follows: Cr$\ldots$Cr = 7.361 $\AA$; Cr-O(average) = 1.958 (8) $\AA$; Cr-N range = 2.108 (9)-2.147(9) $\AA$; N(1)-Cr-N(3) (equatorial position) = 98.0(4)$^{\circ}$; N(2)-Cr-N(4) (axial position) = 166.4(4)$^{\circ}$; O(1)-Cr-N(2) = 98.1(4)$^{\circ}$; O(3)-Cr-N(4) = 96.6(3)$^{\circ}$; O(1)-Cr-O(3) = 90.4$^{\circ}$. The FAB mass spectrum of the dimeric complex displays peak due to the molecular ions cis-[{Cr([14]-decane)($\mu$-cit)})($_2]^+$ at m/z 1053.

• Journal of Soil and Groundwater Environment
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• v.22 no.4
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• pp.27-32
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• 2017

In this study, a remedial investigation using reductive stabilization was conducted to treat Cr(VI)-contaminated soil. The influences of various operational parameters, including reaction time and the mass of ferrous iron, were also evaluated. The study site was contaminated with a large amount of Cr(III) and Cr(VI), and the selected treatment method was to stabilize Cr(VI) with ferrous iron, which reduced Cr(VI) to Cr(III) and stabilized the chromium, although a greater mass of ferrous iron than the stoichiometric amount was required to stabilize the Cr(VI). However, some Cr(III) re-oxidized to Cr(VI) during the drying process, and addition of a strong reducing agent was required to maintain reducing conditions. With this reducing agent, the treated soil met the required regulatory standard, and the mass of Cr(III) re-oxidized to Cr(VI) was significantly reduced, compared to the use of only Fe(II) as a reducing agent.

• Journal of Korea Soil Environment Society
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• v.4 no.2
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• pp.11-31
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• 1999

Removal of hexavalent chromium from artificial groundwater (AGW) by granular activated carbon (GAC) was investigated in batch and continuous-flow column studies. Experimental parameters that were examined included solution pH, presence of dissolved oxygen (DO), and GAC pretreatment with Fe(II). As the solution pH increased from 4 to 7.5, the amount of Cr(VI) removed by both GACs decreased significantly. Exclusion of DO from the experimental systems resulted in greater removal of Cr(VI) from solution, possibly as a result of reduction to Cr(III). However, pretreatment of the GAC with a reductant (Fe(II)) did not improve Cr(VI) removal. Equilibration With 0.01 M $K_2$$HPO_4$[to extract adsorbed Cr(VI)] followed by a wash with 0.02 N $K_2$$HPO_4$[to remove precipitated/sorbed Cr(III)] proved to be a viable approach for the regeneration of carbons whose Cr(VI) removal capacities had been exhausted. The performance of the regenerated carbons exceeded that of the virgin carbons, primarily because of the favorable adsorption of Cr(VI) at lower pH values and the reduction of Cr(VI) to Cr(III), The presence of Cr(III) in acid wash solutions provides direct evidence that Cr(VI) is reduced to Cr(III) in GAC systems under relatively acidic conditions. GAC performance over five complete cycles was consistently high, which suggests that such a system will be able to function over many operation cycles without deleterious effects.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1625-1631
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• 2013

We report a facile synthetic approach of high-quality chromium(III) terephthalate [MIL-101(Cr)] by acetate-assisted method in the absence of toxic HF. Results indicate that the morphology and surface area of the MIL-101(Cr) can be tuned by modifying the molar ratio of acetate/$Cr(NO_3)_3$. The Brunauer-Emmett-Teller (BET) surface area of MIL-101(Cr) synthesized at the optimized condition can exceed 3300 $m^2/g$. It is confirmed that acetate could promote the dissolution of di-carboxylic linker and accelerate the nucleation ratio. So the pure and small size of MIL-101(Cr) with clean pores can be obtained. $CO_2$, $CH_4$ and $N_2$ adsorption isotherms of the samples are studied at 298 K and 313 K. Compared with the traditional method, MIL-101(Cr) synthesized by acetate-assisted method possess enhanced $CO_2$ selective adsorption capacity. At 1.0 bar 298 K, it exhibits 47% enhanced $CO_2$ adsorption capacity. This may be attributed to the high surface area together with clean pores of MIL-101(Cr).

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.1
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• pp.125-142
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• 1996

Bond strength of four different cements to dental casting alloys which were treated with #600 emery, tin-plating, and $50{\mu}m$ sandblasting were evaluated. The alloy specimens were Type III Gold alloy(Degulor C), Palladium-Silver alloy(Pors on 4), Nickel-Chromium(Rexillium III) alloy, which were embedded in acrylic resin disc. The specimens were treated with #600 emery and tin plating, #600 emery and sandblasting, then bonded using Fuji I, Ketac Cem(Glass ionomer cements), Poly F, Livcarbo(Polycarboxylate cements). The specimens were immersed in water for 24 hours and shear bond strengths were evaluated by Instron Machine. Tin plated, sandblasted, and debonded alloy surfaces were observed using scanning electron microscope. On the basis of this study, the following conclusions could be drawn. 1. In the tin plated alloy group, increase in bond strength of glass ionomer cements was statistically insignificant. 2. In the tin plated alloy group, increase in bond strength of polycarboxylate cements was statistically significant, except nickel-chromium alloy. 3. Sandblasted alloy group showed higher bond strength than that of tin-plated alloy group.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.4
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• pp.79-85
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• 2016

It is imperative to find environment-friendly coatings as an alternative to the currently used hexavalent chromate conversion coatings for the purpose of improving the anti-corrosion properties of aluminum alloys. Hence, in this study, the corrosion properties of a trivalent chromate conversion coating solution are analyzed and measured. Because of the presence of multiple components in trivalent chromate conversion coating solutions, it is difficult to control plating, attributed to their mutual organic relationship. It is of significance to determine the concentrations of the components present in these coatings; hence, qualitative and quantitative analysis is required. The coating solution contained not only an environment-friendly component chromium(III), but also zirconium, fluorine, sulfur, and potassium, in the coating film. These metals are confirmed to produce a film with improved corrosion resistance to form a thin layer. The excellent corrosion resistance for the trivalent chromate solution is attributed to various inorganic and organic additives.

• Environmental Analysis Health and Toxicology
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• v.13 no.1_2
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• pp.1-9
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• 1998

The ROS-producing potency of chromium compounds of several oxidation states were determined in the H4 cells. $K_2Cr_2O_7$ as Cr (VI), synthetic Cr (V) compounds and Cr (III) as TPP produced high level of ROS. However, ROS values of Cr-picolinate as Cr (III), CrCl$_2$, CrCI$_2$, were almost equal to the control. The effects of physiological antioxidants compounds which react with free radicals were examined for their effects on chromate-induced production of reactive oxygen species (ROS) in A549 cells after the addition of $K_2Cr_2O_7$. The compounds used were vitamin C (ascorbate), vitamin E ($\alpha$-tocopherol), superoxide dismutase (SOD) and catalase. The preincubation of ascorbate (200uM) with A549 cells for 20hr resulted in a significant reduction of hexavalent chromate(100uM) induced ROS. However, there is no effects of preincubation of the cells with vitamin E succinate (10 and 20uM, 20hr) on the ROS production. Also, the effects of Cr (VI) on the cell cycle of A549 cells was measured by adding the DNA intercalating agent, propidium iodide. S phase of the cell cycle was increased by the chromium (VI) compounds up to 20uM indicating toxicity or possible mitogenic action of the cell. The shoulder in Go/G1 phase at 20uM Cr (VI) with 24 hr treatment indicates apoptosis.

• Clean Technology
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• v.7 no.1
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• pp.75-80
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• 2001

In this study, hexavalent chromium (Cr(VI)) plating wastewater in strong acidic condition was treated by reduction and alkalization. Ferrous sulfate ($FeSO_4$), known to reduce Cr(VI) to Cr(III) rapidly at acidic pH, was used as a reductant of Cr(VI). The optimum reduction condition of Cr(VI) was observed at iron to chromium dose ratio of 3:1 by mole concentration. The precipitation of Cr(III) as $Cr(OH)_3$, was achieved by the pH adjustment in the limestone aeration bed. The precipitates were removed less than the upper limit of chromium for effluent at pH over 5.0. The continuous removal of Cr(VI) was performed using the process consisting of reduction vessel, limestone aeration bed, and sedimentation tank coupled with metal screen membrane. As pH was maintained around 5.0 in the limestone aeration bed, insoluble chromic hydroxide flocs was formed continuously. Most chromic hydroxide flocs were filtered by the metal screen membrane with 1450 mesh size, and the treated water to meet the upper limits of chromium for effluent (Cr Conc. 0.25~0.90 mg/l) was obtained in 30 minutes. Periodic backwashing decreased the fouling on the membrane rapidly.

• Carbon letters
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• v.9 no.4
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• pp.275-282
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• 2008

Chemically activated carbons were prepared from maize cobs, using phosphoric acid of variable concentration. The textural parameters of the activated carbons were determined from the nitrogen adsorption isotherms measured at 77 K. The chemistry of the carbon surface was determined by measuring the surface pH, the pHPZC and the concentration of the carbon - oxygen groups of the acid type on the carbon surface. Kinetics of Cr(VI) sorption/reduction was investigated at 303 K. Two processes were investigated in terms of kinetics and equilibrium namely; Cr(VI) removal and chromium sorption were studied at various initial pH (1-7). Removal of Cr(VI) shows a maximum at pH 2.5. At pH<2.5, sorption decreases because of the proton competition with evolved Cr(III) for ion exchange sites. The decrease of sorption at pH>2.5 is due to proton insufficiency and to the decrease of the extent of Cr(VI) reduction. The chemistry of the surface of activated carbon is an important factor in determining its adsorption capacity from aqueous solutions particularly when the sorption process involves ion exchange.