• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.169-169
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• 2016

크롬산 용액에 황산을 촉매로 하여 Sargent에 의해 개발된 크롬도금은 경도, 내식성, 내마모성 등의 특성이 우수하다. 이로 인해 장식용 박막 도금뿐만 아니라 경질의 후막 도금층을 형성이 가능함으로써 기계 부품류를 비롯한 산업 전반에 걸쳐 폭넓게 적용되고 있다. 이러한 크롬도금이 적용된 소재부품에 대해 장수명화와 더불어 가혹한 환경에서의 사용요구가 점차 증가하고 있으며, 이를 위해서는 보다 더 우수한 내식성과 기계적 물성을 확보해야할 필요성이 높다. 한편 경질 크롬 도금의 내식성과 관련해 도금 과정에서 발생하는 마이크로 크랙에 의해 제품의 내식성의 한계를 나타내게 된다. 본 연구에서는 내식성이 우수할 뿐만 아니라 표면 경도가 우수한 도금층을 얻기 위해 도금 전류 조건으로 펄스 전류를 적용하는 방안을 시도한 것으로 펄스전류를 적용하여 경질크롬도금 시 크랙 발생에 미치는 영향을 조사하였다. 도금욕은 일반적인 경질크롬도금에 사용되는 Sargent 욕을 이용하였고, duty ratio를 조절하여 전류 조건 변화에 따른 단면 내 크랙의 수 변화를 관찰하여 최적의 전류 조건을 도출하였다. 그리고 도출된 전류 조건을 이용해 도금 두께에 따른 크랙 수 변화를 관찰하였고, 이때의 경도를 측정하였다. 또한 XRD 분석을 통해 도금 전류 조건 및 시간 변화에 따른 결정구조 변화를 확인하였다. 실험결과 펄스 전류를 적용하는 경우, 기존 직류 적용 시에 비해 크랙 발생을 현저하게 감소시킬 수 있었으며, 사실상 크랙프리(Crack free) 도금이 가능하였다. 또한 크랙의 감소와 함께 경도 저하가 나타나게 되나 펄스 전류 인자의 최적화에 따라 이러한 경도 저하 현상의 최소화가 가능하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.11a
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• pp.56-56
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• 2001

Ni-W alloy deposit is one of the best alternatives to hard chromium plating because of its good mechanical properties (high hardness, high strength, and good wear resistance). Ni-W alloy is deposited from weakly acidic or alkaline electrolytic bath with nickel sulfate, sodium tungstate or APT, and some kinds of organic hydroxy-acid complex and ammonia salts. W content of the deposit can be changed from 0 to 5Owt% and the coating with high W content is more attracted. But, meanwhile, the deposited layers are always found high internal stress, which cause them to become brittle and to bond insufficiently with the substrate. On the second hand, as the W content is incresed, the current efficiency reduced, which results in large quantities of hydrogen evolution and then produces bubbles on surface and pitting appearance In this paper, the influence of some additives on Ni-W alloy electroplating was investigated by means of compositional analysis and SEM. The initial results showed that 2-butyne-1,4-diol was the best brightener for Ni-W plating process. It could brighten and level deposit, but decreased the cathodic current efficiency. Its optimum concentration range is from O.lgjL to 0.5gjL. Besides, three kinds of additives including 2-butyne-1,4-diol were examined with Dagguchi method.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.4
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• pp.401-407
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• 2021

To confirm the change of muzzle velocity and the most suitable probability distribution model of the 155 mm K9 howitzer barrel with chrome plating and changed rifling. Using a statistical program, the muzzle velocity were plotted on a normal distribution, a 2-parameter and 3-parameter Weibull distribution on a probability paper. Also, statistical parameters were estimated and muzzle velocity fitness test and probability of K676 charge were plotted. In both the chrome-plated with standard rifling and changed rifling for K9 barrel, the 2-parameter and 3-parameter Weibull distribution were skewed to the left compared to the normal distribution. It was confirmed that the muzzle velocity of the K9 barrel with chromium-plated is suitable for the normal distribution and 3-parameter Weibull distribution model.

• Corrosion Science and Technology
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• v.22 no.4
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• pp.232-241
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• 2023

The mechanical properties of the hydrogen valve responsible for supplying and blocking hydrogen gas in a hydrogen fuel cell electric vehicle (FCEV) were researched. Mechanical properties by hydrogen embrittlement were investigated by coating chromium nitride (CrN) and titanium nitride (TiN) on aluminum alloy by arc ion plating method. The coating layer was deposited to a thickness of about 2 ㎛, and a slow strain rate test (SSRT) was conducted after hydrogen embrittlement to determine the hydrogen embrittlement resistance of the CrN and TiN coating layers. The CrN-coated specimen presented little decrease in mechanical properties until 12 hours of hydrogen charging due to its excellent resistance to hydrogen permeation. However, both the CrN and TiN-coated specimens exhibited deterioration in mechanical properties due to the peeling of the coating layer after 24 hours of hydrogen charging. The specimens coated at 350 ℃ presented a significant decrease in ultimate tensile strength due to abnormal grain growth.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.5
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• pp.17-23
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• 2013

Six-valent chromium ($Cr^{6+}$) is a highly toxic pollutant, supplied in a variety of industrial activities such as leather tanning, cooling tower blowdown, and plating. Herein, we investigated the removal of $Cr^{6+}$ from aqueous phase using low-cost adsorbents. Steel slag, montmorillonite, illite, kaolinite, red mud, and acid treated red mud with 0.5, 1.0, and 2.0 M HCl were used as adsorbent for the removal of $Cr^{6+}$ and the results showed that acid treated red mud with 2.0 M HCl (ATRM-2.0 M) had higher adsorption capacity of $Cr^{6+}$ than other adsorbents used. Accordingly, $Cr^{6+}$ removal by ATRM-2.0 M were studied in a batch system with respect to changes in initial concentration of $Cr^{6+}$, initial solution pH, adsorbent dose, adsorbent mixture, and seawater. Equilibrium sorption data were described well by Freundlich isotherm model. The influence of initial solution pH on $Cr^{6+}$ adsorption was insignificant. The use of the ATRM-2.0 M alone was more effective than mixing it with other adsorbents including red mud, zeolite, oyster shell, lime stone, and montmorillonite for the removal of $Cr^{6+}$. The $Cr^{6+}$ removal of the ATRM-2.0 M was slightly less in seawater than deionized water, resulting from the presence of anions in seawater competing for the favorable adsorption site on the surface of ATRM-2.0 M. It was concluded that the ATRM-2.0 M can be used as a potential adsorbent for the removal of $Cr^{6+}$ from the aqueous solutions.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.7 no.2
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• pp.223-232
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• 1997

The accuracy and precision of a modified method of NIOSH Method 7600 and EPA method 218.6 was determined for analyzing hexavalent chromium, Cr(VI), collected on PVC filter from workplace air. The method was designed to extract from Cr(VI) on PVC filter with a alkali solution, 2% NaOH/3% $Na_2CO_3$, and to analyze it using ion chromatography/visible absorbance detection(IC/VAD). The results and conclusion are as the following. 1. The peak of Cr(VI) was separated sharply on chromatogram and was linearly related with Cr(VI) concentration in sloution. The correlation coefficient was 0.9999 in a calibration curve. The limit of detection was 0.25 $0.25{\mu}g/sample$. 2. The accuracy(% recovery) was 93.3% in a set of sample($9-50{\mu}g$) stored for a day, and 100.1%($10-60{\mu}g$) in another set of samples stored for 2 hours. It is assumed that the difference in recovery by storage time was due to reduction of Cr(VI) to Cr(III). 3. The precision(coefficient of variation, CV) of the method was 0.015 in spiked samples with Cr(VI) standard solution, and 0.010 in spiked samples with plating solution from a chrome electroplating factory. The overall CV in all types of samples was 0.0013. 4. The Cr(VI) was stable in 2% NaOH/3% $Na_2CO_3$ at least for 10 hours. In conclusion, the IC/VAD method is appropriate for determining low-level Cr(VI) in workplace air containing various interferences.

• Korean Journal of Metals and Materials
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• v.49 no.12
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• pp.937-944
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• 2011

Studies have been carried out in order to reduce fuel-cladding chemical interaction (FCCI) behavior of metallic fuel in sodium-cooled fast reactors (SFR) using an electroplating technique. A $20{\mu}m$ thick Cr layer has been plated by the electrochemical method in the Sargent bath over the HT9 (12Cr-1Mo) clad material and diffusion couple tests of the U-10Zr metallic fuel as well as the rare earth alloy (70Ce-29La) have been conducted. The results show that the Cr plating can prevent FCCI behavior along the fuel-clad interface. However, cracks developed through the thickness during plating, which resulted in the migration of some fuel constituents. Variation of bath temperature, application of pulse current, and post heat treatment have been conducted to control such cracks. We found out that some conditions like the pulse current and the post heat treatment enhanced the layer property by reducing the internal cracks and improving the diffusion couple test.

• Journal of Preventive Medicine and Public Health
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• v.23 no.3 s.31
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• pp.358-368
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• 1990

To investigate the possibility of utilizing of sister chromatid exchange(SCE) analysis in lymphocytes as an indicator which could evaluate the effects of mutagenicity after in vivo exposure to hexavalent chromium, this study was conducted using some of chromium plating workers occupationally exposed to hexavalent chromium, chromium trioxide ($CrO_3$) in Taegu city. The study population was 12 Cr platers with perforation of nasal septum, 12 Cr platers without perforation of nasal septum and 20 controls. The SCE in peripheral blood lymphocytes of the subjects was analyzed and blood chromium concentration was estimated using the atomic absorption spectrophotometer (IL551) equipped with furnace atomizer (IL755). The mean SCE frequencies for Cr platers with and without perforation of nasal septum were statistically higher than those for control. The difference in SCE frequencies by age, smoking habits were not statistically significant both in Cr platers and controls. There was no difference in SCE frequencies by career of Cr platers workers. In Cr platers, the correlation between the mean SCE frequencies and chromium concentration in blood was not statistically significant. Using the transformation $y=(sum\;SCE)^{\frac{1}{2}}+(sum\;SCE+1)^{\frac{1}{2}}$, when the data was studied by multiple regression, it appeared that the influence of the occupation was the most important. Age, smoking, occupation and CrB(blood chromium concentration) together explain only 32.3% of interpersonal variation on SCE. The results in this study suggest tt a genetic risk due to occupationally exposure to hexavalent chromium is clearly inferable and thus, SCE analysis in human lymphocytes may be used indicator of biological toxic effects of chromium. Further, populatio analysis stuies are required before SCE frequency can be used as a mutagenic indicator in human population.

• Korean Journal of Materials Research
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• v.17 no.5
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• pp.256-262
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• 2007

Effects of interlayer and the combination of different coating methods on the mechanical and corrosion behaviors of TiN and CrN coated on 420 stainless steel have been studied. STS 420 specimen were tempered at $300^{\circ}C$ for 1 hr in vacuum furnace. The TiN and CrN thin film with 2 ${\mu}m$ thickness were coated by arc ion plating and DC magnetron sputtering following the formation of interlayer for pure titanium and chromium with 0.2 ${\mu}m$ thickness. The microstructure and surface analysis of the specimen were conducted by using SEM, XRD and roughness tester. Mechanical properties such as hardness and adhesion also were examined. XRD patterns of TiN thin films showed that preferred TiN (111) orientation was observed. The peaks of CrN (111) and $Cr_2N$ (300) were only observed in CrN thin films deposited by arc ion plating. Both TiN and CrN deposited by arc ion plating had the higher adhesion and hardness compared to those formed by magnetron sputtering. The specimen of TiN and CrN on which interlayer deposited by magnetron sputtering and thin film deposited by arc ion plating had the highest adhesion with 22.2 N and 19.2 N. respectively. TiN and CrN samples shown the most noble corrosion potentials when the interlayers were deposited by using magnetron sputtering and the metal nitrides were deposited by using arc ion plating. The most noble corrosion potentials of TiN and CrN were found to be approximately -170 and -70 mV， respectively.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.600-602
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• 1995

Using the $O_2$ RIE process, 20{\mu}m$-height polyimide microstructures are fabricated. In LIGA-like process, metal microstructure can be formed by the electroplating using these polyimide microstructures as a plating mould. Reactive ion Etching technique using oxygen gas is used for the patterning of polyimide. The etching rate of the polyimide is increased with increased pressure and RF power. The anisotropic vertical sidewall can be obtained at low pressure, but the etched surface state is not so good yet. "Micrograss", which is formed during the RIE and disturbs uniform electroplating, can be removed effectively by the wet itching of the chromium sacrificial layer. More studies about the improvement of an etched surface state and the removal of microsgrass are needed.