• Journal of the Korean institute of surface engineering
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• v.36 no.3
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• pp.251-255
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• 2003

With increasing environmental demands in surface treatment of steel sheets, the passivation layers containing hexavalent chromium $(Cr^{+6})$ are being replaced by non-chromium or trivalent chromium compounds. After review on the various types of inorganic compounds, the zirconates was chosen as the candidate for alternative to sodium dichromate in the aspect of its barrier properties with excellent adhesion to organics. The ammonium zirconium carbonate (AZC) and sodium hexafluorozirconate (SFZ) could be reach $70-80\%$ level of CDC (cathodic dichromate) treatment by their single applications. But high porosity in the AZC layer and poor electrical conductivity of SFZ solution limit the single application of zirconate. Mixed composition of zirconates to compensate their inferiorities or incorporation of organic compounds to seal the porosity seems to be inevitable to match up the target level of Cr-free passivation of tinplate.

• Journal of Microbiology
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• v.35 no.1
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• pp.25-29
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• 1997

Microbial reduction of hexavalent (VI) to trivalent (III) chromium decreases its toxicity by two orders of magnitude. In order to investigate the nature of Cr-reduction, Cr-resistant Pseudomonas aeruginosa HP014 was isolated and tested for its reduction capability. At the concentration of 0.5 mM Cr(VI), cell growth was not inhibited by the presence of Cr(VI) in a liquid medium, and Cr(VI) reduction was accompanied by ell growth. When cell-free extract was tested, the reduction of Cr(VI) showed a saturation kinetics with the maximum specific activity of 0.33 .mu.mol min$\^$-1/ mg$\^$-1/ cell protein, and an apparent K. of 1.73 mM Cr(VI). The activity required either NADH or NADPH as an electron donor. However, NADPH gave 50% as mush activity as sequently the supernatant and pelleted membrane fractions were tested for Cr(VI) reduction activity. The supernatant of the centrifugation showed almost the same Cr(VI) reduction activity as compared with that of the cell-free extract, indicating that the Cr(VI)-reducing activity of P. aeruginosa HP-14 is due to soluble enzyme. Moreover, the activity appeared to be the highest among the known activities, suggesting that the strain might be useful for remediation of Cr(VI)-contaminated sites.

• Analytical Science and Technology
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• v.12 no.5
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• pp.447-459
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• 1999

A study was conducted to compare three analytical methods for determination of hexavalent chromium in the welding fume. Precision and accuracy arc documented for colorimetric, ion chromatographic, and inductively coupled plasma-optical emission spectroscopic method. Evidence is presented that welding fume can affect the oxidation of trivalent chromium. A simple sonication extraction method, proposed in this study, instead of hot alkaline extraction has the advantage of minimizing the potential for chromium oxidation.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.6 no.2
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• pp.292-300
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• 1996

Hexavalent chromium($Cr^{+6}$) compounds are considered to be particularly hazardous, primarily because of the associated risk of allergic reaction and cancer. The analytic method of hexavalent chromium such as the s-diphenylcarba-zide(DPC) method and all ether previously used methods are often made uncertain due to significant interferences from organic components. This report can provide a technique for the more rapid and simple determination of total hexavalent chromium. than other currently using methods. The s-diphenylcarbazide method proposed by the U.S. National Institute for Occupational Safety and Health has low recovery rate(15.67 - 48.20%) due to interference, iron chloride and nickel chloride. A microwave oven technique has high recovery rate(about 70%) of insoluble hexavalent chromium. For the difference of ionic charges of $Cr^{+3}$-ethylenediamine tetraacetic acid(EDTA) chelate and $CrO_4{^{-2}}$, we could detect them simultaneously by ion exchanged high performance liquid chromatography. The confirmation of $Cr^{+3}$ and $Cr^{+6}$ were checked by fraction collector and flameless atomic absorption spectrometer. We observed that the small amount of hexavalent chromium is converted to trivalent chromium due to enhancement of chromium reduction by $Fe^{+3}$ or $Ni^{+2}$. As a result of this study, on the analysis of insoluble hexavalent chromium with microwave oven was used for, it may be better and more precise analysis after pretreatment by 2% NaOH-3% $Na_2CO_3$ and then analysis UV-spectrophotometer. It should be done for various studies on insoluble hexavalent chromium on the basis work environmental monitoring so called welding, painting etc.

• 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 Korean Society of Water and Wastewater
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• v.29 no.1
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• pp.33-38
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• 2015

In this study, flat-type photocatalytic reaction system is applied to reduce toxic hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) in aqueous solution under UV irradiation. To overcome the limitation of conventional photocatalysis, a novel approach toward photocatalytic system for reduction of hexavalent chromium including nanotubular $TiO_2$ (NTT) on two kinds of titanium substrates (foil and mesh) were established. In addition, modified Ti substrates were prepared by bending treatment to increase reaction efficiency of Cr(VI) in the flat-type photocatalytic reactor. For the fabrication of NTT on Ti substrates, Ti foil and mesh was anodized with mixed electrolytes ($NH_4F-H_2O-C_2H_6O_2$) and then annealed in ambient oxygen. The prepared NTT arrays were uniformly grown on two Ti substrates and surface property measurements were performed through SEM and XRD. Hydraulic retention time(HRT) and substrate type were significantly affected the Cr(VI) reduction. Hence, the photocatalytic Cr(VI) reduction was observed to be highest up to 95% at bended(modified) Ti mesh and lowest HRT. Especially, Ti mesh was more effective as NTT substrate in this research.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.209-209
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• 2015

EPA, OSHA의 크롬 mist 배출강화기준, ROHS 등에 의한 6가 크롬사용이 억제되어 그 대안으로 친환경 프로세스인 3가 크롬도금이 핸드폰 부품을 중심으로 적용이 되어 대량 생산 기술이 확립이 되고, 최근 자동차 장식도금 분야에 까지 적용이 확대되어 가고 있다. 그러나 아직도 3가 크롬도금을 적용하는데는 많은 혼선과 문제점이 보고되고 있다. 이에 본 발표에서는 3가 크롬도금의 최신 기술 동향을 소개하고, 3가 크롬도금에 대한 정확한 정보를 제공, 현장 적용사례를 보고하여 3가 크롬도금 적용 활성화에 도움을 주고자 한다. 본 발표에서는, - 3가 크롬도금에 대한 소개 - 아토텍 프로세스의 소개 - 염산욕과 황산욕의 비교 - 내식성 관련 자료 - 현장관리 및 적용사례 등을 포함하여 간략하게 소개하고자 한다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.210-210
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• 2015

3가 크롬도금으로부터 크롬도금을 얻는 방법은 1854년 R. D. Buseen의 보고가 최최이고 2년 후 6가 크롬이온으로 부터 최초의 크롬독므이 Geuther에 의해 보고되었다. 초기 3가 크롬도금 프로세스는 도금용액의 안정성이 떨어져서 선택성 이온교환막을 이용한 격막으로 양극을 분리하는 방법이 채용되었다. 그 후 1970년대에 Albright & Wilson사와 IBM-Canning사에 의해 개발된 3가 크롬 프로세스가 기초기술이 되어 개량된 현재의 3가 크롬도금용액이 탄생하였다. 이후 여러 도금약품 회사에서 여러 종류의 3가 크롬도금 용액과 프로세스가 개발이 되어 핸드폰, 자동차 등에 사용이 되고 있으나, 아직도 개선의 여지가 많이 남아 있다고 할 수 있다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.04a
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• pp.169-171
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• 2007

에어컨 콤프레셔 실린더에 도금되는 3가 크롬의 도금 두께 균일화를 위하여 컴퓨터 시뮬레이션 작업을 수행하였다. 컴퓨터 시뮬레이션의 정확도를 위하여 현장에서 사용되는 경질 3가 크롬의 전기화학적 특성을 측정하였다. 그리고, 이를 입력 값으로 하여 헐셀에 대하여 실험과 컴퓨터시뮬레이션을 수행하였다. 이 시뮬레이션 결과를 실제의 헐셀 실험 결과와 비교 검토함으로써 컴퓨터 시뮬레이션의 타당성정도를 점검하였고, 3가 크롬의 특성을 비교분석하였다. 이러한 자료를 근거로 3가 크롬 도금두께 균일화를 위한 시뮬레이션 작업을 에어컨 콤프레셔 실린더에 적용시켜 최적의 도금조건을 도출하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.04a
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• pp.124-125
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• 2007

3가크롬도금 공정 최적화를 위하여 다양한 전기화학적인 기법-즉, Hull cell test, 동전위 분극 실험, 정전류 분극 실험-과 표면 형상 분석이 수행되었다. 3가크롬도금은 용액 pH가 증가함에 따라 조악한 표면 형상을 가졌고, 도금액 온도 증가 시 표면 상 nodule 밀도가 낮아졌다. 본 실험 환경에서 3가크롬도금 공정 최적 조건은 pH2.5-3.0, 온도 $30-40^{\circ}C$, 인가전류밀도 $10-20A/dm^2$이었다.