• 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 the Korea Contents Association
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• v.6 no.4
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• pp.136-145
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• 2006

The main purpose of the present study was to find the effect of short term creatine loading on repeated bouts of kicking, plasma creatine phosphokinase and anaerobic power in male taekwondo player from high school. Eighteen male were randomly assigned to two groups. They were tested before and after 6 days of placebo($4{\times}5$ glucose d-1, N=9) or Creatine monohydrate loading(consume 0.3g kg-1, N=9). Only creatine loading group were significantly increased of repeated bouts of kicking, plasma creatine phosphokinase and anaerobic power These results suggest that short creatine loading was effective diet protocol in taekwondo player from male high school.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.9
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• pp.924-929
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• 2004

The microstructure, electrical and dielectric characteristics of $ZnO-{Pr}_6{O}_11-{CoO}-{Dy}_2{O}_3$-based varistors were investigated without and with various metal oxide additives(NiO, MgO, Cr$_2$O$_3$). The average grain size decreased in the range of 18.4 $\backsim$ 11.5 $\mu$m, in order of NiO\longrightarrowMgO\longrightarrow{Cr}_2{O}_3$ and the density decreased in the range of 5.62 \backsim 5.33 $g/{cm}^3$ in order of NiO\longrightarrowCr$_2$O$_3$\longrightarrowMgO. While, the nonlinear exponent increased In the range of 19.8$\backsim$67.4 in order of NiO\longrightarrowMgO\longrightarrow${Cr}_2{O}_3$ and the leakage current decreased in the range of 25.6 $\backsim$ 1.2 $\mu$A in order of NiO\longrightarrow${Cr}_2{O}_3$\longrightarrowMgO. Among all varistors, the Cr$_2$O$_3$-added varistor exhibited the highest nonlinearity, with a nonlinear exponent of 67.4 and a leakage current of 1.2 $\mu$A. Furthermore, this varistor exhibited the lowest dielectric dissipation factor of 0.0407.

• Bulletin of the Korean Chemical Society
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• v.33 no.6
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• pp.1867-1872
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• 2012

The 5-parameter Morse potential (5-MP) method for the interaction between O atom and Cr surfaces is constructed in the present work. The adsorption of O on Cr (100), (110), (111), and (211) surfaces are studied with 5-MP in detail. The fourfold hollow site of the Cr (100) surface is favored for O atom. On Cr (110), quasithreefold site is favored with the parallel frequencies (the frequencies of O atom paralleling the metal surface) of 342 and 538 $cm^{-1}$, and perpendicular frequency (the frequency of O atom perpendicular to the metal surface) at 526 $cm^{-1}$. On Cr (111), the most favored mode for O atom is found to be the quasi-threefold site with the perpendicular frequency at 553 $cm^{-1}$ and the parallel frequencies at 253 and 399 $cm^{-1}$. According to our calculation results, we speculate the most preferred mode for O adsorption on Cr (211) surface is the quasithreefold site with the perpendicular frequency at 583 $cm^{-1}$ and the parallel frequencies at 449 and 185 $cm^{-1}$.

• Environmental Engineering Research
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• v.10 no.6
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• pp.294-305
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• 2005

The effectiveness of fly ash-, quicklime-, and quicklime-fly ash-based stabilization/solidification(S/S) in chromium(Cr) contaminated soils was investigated using modified semi-dynamic leaching tests. Artificial soil samples composed of kaolinite or montmorillonite contaminated with chromium nitrate(4000 mg $Cr^{3+}\;kg^{-1}$ of solid) were prepared and then subjected to S/S treatment using quicklime, fly ash, or quick lime-fly ash. The effectiveness of the treatment was evaluated by assessing the cumulative fraction of leached $Cr^{3+}$ as well as, by computing the effective diffusivity ($D_e$) and the leachability index (LX) of the treated samples. The reduction in $Cr^{3+}$ release for the untreated samples was more pronounced in the presence of montmorillonite, which was attributed to sorption. Treatment with quicklime, fly ash, or quick lime-fly ash was significantly effective in reducing $Cr^{3+}$ release most probably due to the formation of pozzolanic reaction products and $Cr(OH)_3$ precipitation. The most effective treatment was observed in montmorillonite-sand soil samples treated with quicklime-fly ash (99.8% removal). The mean $D_e$ decreased significantly and the mean LX was greater than 9 for all treated samples, indicating that the treated soils were acceptable for "controlled utilization". The mechanism controlling $Cr^{3+}$ leaching from all treated samples during the first 5 days appeared to be diffusion.

• Journal of the Korean institute of surface engineering
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• v.47 no.6
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• pp.323-329
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• 2014

Effects of sealant and sealing procedure on corrosion resistance of high velocity oxy-fuel (HVOF) sprayed coatings were studied. HVOF-sprayed CrC-20NiCr coatings were sealed using three commercial sealants based on phenolics and epoxy. Penetration depth of sealants, measured by fluorescent microscope technique, was between $19{\mu}m$ and $340{\mu}m$ depending on sealant, sealing condition or sealing procedure. It was found that sealing on rotation status was more effective than that on stationary specimen due to the Coriolis effect of fluid in pores of the coating. From the CASS results, corrosion resistance of properly sealed CrC-20NiCr coatings was equal to that of hexa-valent chromium plating.

• Elastomers and Composites
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• v.56 no.1
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• pp.6-11
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• 2021

In order to develop an ultra-high-density elastomeric material for substitution of steel dynamic dampers, a new curing system and technique for high-loading of the filler were examined in this study. Mechanochemical modification of chloroprene rubber (MAH-g-CR) using an internal mixer was carried out with maleic anhydride (MAH) as a reactive monomer. The optimum amount of MAH was 10 phr and the efficient grafting of MAH on CR could be achieved at a mixing temperature of 100℃. After preparing MAH-g-CR, 50 mol% epoxidized natural rubber (ENR 50) was blended with MAH-g-CR to develop a "self-curable rubber blend system" via reaction between the functional groups of the elastomeric matrices without the curing agent and additives. The content of ENR 50 was fixed at 30 wt.% throughout evaluation of the curing behavior of the MAH-g-CR/ENR blend. Tungsten powder was added to the MAH-g-CR/ENR matrix up to 60 vol.% to obtain ultra-high-density, and the maximum density obtained was 7.57 g/㎤. Stable ts2 (scorch time) and t90 (90% cure time) could be obtained even when tungsten powder was incorporated up to 60 vol.%. In addition, the tensile strength and damping properties of MAH-g-CR/ENR containing 60 vol.% of tungsten were better than those of CR containing 60 vol.% of tungsten.

• Journal of the Korean institute of surface engineering
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• v.38 no.6
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• pp.207-211
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• 2005

In this work a multi-layered nanostructured TiAIN/CrN superlattice coatings was synthesized using closed-field unbalanced magnetron sputtering method and the relationships between their superlattice period (1), micro-structure, hardness and elastic modulus were investigated. In addition, wear test at $500^{\circ}C$ and oxidation resistance test at $900^{\circ}C$ were performed to investigate high temperature properties of these thin films. The coatings were characterized in terms of microstructure and mechanical properties by transmission electron microscopy (TEM) and nano-indentation test. Results from TEM analysis showed that superlattice periods was inversely proportional to the jig rotation speed. The maximum hardness and elastic modulus of 37 GPa and 375 GPa were observed at superalttice period of 6.1 nm and 4.4 nm, respectively. An higher value of microhardness from TiAIN/CrN thin films than either TiAIN (30 GPa) or CrN (26 GPa) was noted while the elastic modulus was approximately an average of TiAIN and CrN films. These enhancement effects in superlattice films could be attributed to the resistance to dislocation glide across interface between the CrN and TiAIN layers. Much improved plastic deformation resistance ($H^3/E^2$) of 0.36 from TiAIN/CrN coatings was observed, compared with 0.15 and 0.16 from TiAIN and CrN, respectively. Also the wear resistance at $500^{\circ}C$ was largely increased than those of single TiAIN and CrN coatings and TiAIN/CrN coatings showed much reduced weight gain after exposure at $900^{\circ}C$ for 20 hours.

• Applied Chemistry for Engineering
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• v.8 no.4
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• pp.631-636
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• 1997

This study was conducted to increase the adorption capacity of microporous carbon which is widely used as an adsorbent. After increasing the adsorption capacity of microporous carbon by heat-treatment, chromium($Cr^{+6}$) solution, which is the one of hazardous heavy metals, was selectively adsorbed on microporous carbon. Optimum temperature range for the heat-treatment of microporous carbon was $340{\sim}350^{\circ}C$, and the average specific surface area was measured as $1380m^2/g$ by BET (Brunauer-Emmett-Teller) method. The weight loss was about 10 percents during the heating to optimum temperature. However, It became a qualitative adsorbent due to a larger specific surface area. Removal of chromium($Cr^{+6}$) in solution by heat-treated microporous carbon was successfully carried out.

• Korean Chemical Engineering Research
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• v.44 no.2
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• pp.107-113
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• 2006

Not only Cr(VI) is very toxic, but also it is a major pollutant in soil and groundwater. Thus Cr(VI)-containing wastewater must be treated before being discharged into the environments. Recently, biosorption technology using abundant biomass has been considered as an innovative one for removing Cr(VI) from aqueous solution. In this review article, current research and future works on Cr(VI) biosorption were widely described. Particularly, the removal mechanism of Cr(VI) by biomass was described in detail, which has been misunderstood by many researchers until now.