• 한국재료학회지
• /
• 제14권8호
• /
• pp.558-564
• /
• 2004

In order to improve the low hardness and low wear resistance of Ti-6Al-4V alloy, plasma carburization treatment and CrN film coating were carried out. Effects of the plasma carburization and CrN coating were analyzed and compared with the non-treated alloy by mechanical and creep tests. After plasma carburization and CrN coating treatments, the carburized layer was about 150 ${\mu}m$ in depth and CrN coated layer was about 7.5 ${\mu}m$ in thickness. Hardness value of about $H_{v}$ 402 of the non-treated alloy was improved to $H_{v}$ 1600 and 1390 by plasma carburization and CrN thin film coating, respectively. Stress exponent(n) was decreased from 9.10 in CrN coating specimen to 8.95 in carburized specimen. However, the activation energy(Q) was increased from 242 to 250 kJ/mol. It can be concluded that the static creep deformation for Ti-6Al-4V alloy is controlled by the dislocation climb over the ranges of the experimental conditions.

• 마이크로전자및패키징학회지
• /
• 제26권4호
• /
• pp.133-140
• /
• 2019

열 사이클 조건이 전해 Cr/Ni-P 이중도금 시편의 접합강도 및 균열성장거동에 미치는 영향을 분석하였다. 전해 Ni-P 도금층을 열처리를 통해 결정화 시킨 후 전해 Cr 도금 후 한번 더 열처리한 결과, Cr/Ni-P 계면에서 상호확산으로 인해 Cr-Ni 고용체 band layer가 관찰되었다. 열 사이클 전 접합강도는 25.6 MPa이였으나, 1,000사이클 후 Cr 도금층의 균열 밀도 및 표면 거칠기 증가로 인해 도금층과 접착제 사이의 기계적 고착효과가 향상되어 접착제와 Cr 도금층 사이에서 박리되었고, 접합강도는 47.6 MPa로 점차적으로 증가하였다.

• Bulletin of the Korean Chemical Society
• /
• 제23권2호
• /
• pp.184-188
• /
• 2002

Unsaturated $Cr(CO)_x(1{\leq}x{\leq}5)$molecules were generated in the gas phase from photolysis of $Cr(CO)_6$vapor in He using an unfocussed weak UV laser pulse and their reactions with $O_2$ and $N_2O$ have been studied. The formation and disappearance of the ground state CrO molecules were identified by monitoring laser-induced fluorescence(LIF) intensities vs delay time between the photolysis and probe pulses. The photolysis laser power dependence as well as the delay time dependence of LIF intensities from the CrO orange system showed different behavior as those from ground state Cr atoms, suggesting that the ground state CrO molecules were generated from the reaction between $O_2/N_2O$ and photo-fragments of $Cr(CO)_6$ by one photon absorption. The depletion rate constants for the ground state CrO by $O_2$ and $N_2O$ are $5.4{\pm}0.2{\times}10^{-11}$ and $6.5{\pm}0.4{\times}10^{-12}cm^3molecule^{-1}s^{-1}$, respectively.

• 한국주조공학회지
• /
• 제27권3호
• /
• pp.120-125
• /
• 2007

The microstructure, mechanical properties and melting range of Ni-Cr-Mo based alloys were investigated to develop Be-free Ni-Cr-Mo base dental alloys for Porcelain-Fused-to-Metal Firing(PFM). All as-cast alloys showed dendritic structure. Rockwell hardness of 20Cr7Mo was increased with addition of Si and Ti. On the contrary, it was decreased with addition of Co. The duplex alloying elemental addition such as 3Co + xTi, 2Si + xCo and 2Si + xTi to 20Cr7Mo resulted in much increase of hardness. Rockwell hardness and compressive strength for 20Cr3CoSiTi or 17Cr6CoSiTi alloy that add Si-Ti had similar values compared to the commercial alloys. Melting range for 20Cr3CoSiTi and 17Cr6CoSiTi alloy that add Si-Ti showed similar or lower than commercial alloys. In conclusion, 20Cr3CoSiTi and 17Cr6CoSiTi alloys can be applied for commercial use.

• 대한의생명과학회지
• /
• 제12권3호
• /
• pp.261-265
• /
• 2006

Toxic effect of Hexavalent chromium $(CrO_3)$ on various cells and organs has been well recognized. However, the mechanism and degree of cytotoxicity of $CrO_3$ remain unclear. This study was performed to examine the cytotoxicity of $CrO_3$ on $C_6$ glioma cells by measuring cell viability. The XTT assay, one of the sensitive methods to determine the cell viability, was taken to examine the viability of glioma cells treated with $CrO_3$. In this study, not only decreased the number of glioma cells but morphologic changes of them were noted and cell viability decreased in a time and dose-dependent manner after treated with various concentrations of $CrO_3$ for 48hours. $IC_{90}\;and\;IC_{50}$ values in XTT assay were determined at $25{\mu}M\;and\;55{\mu}M$ $CrO_3$, respectively. These results suggest that Hexavalent chromium has a highly cytotoxic effect and has a time and dose-dependent cytotoxicity on $C_6$ glioma cells.

• Journal of Microbiology and Biotechnology
• /
• 제16권6호
• /
• pp.855-862
• /
• 2006

Hexavalent chromium ($Cr^{6+}$) is a highly harmful pollutant, which can be detoxified and precipitated through reduction to $Cr^{3+}$. Bacillus megaterium TKW3 previously isolated from chromium-contaminated marine sediments was capable of reducing $Cr^{6+}$ in concomitance with metalloids ($Se^{4+}$, $Se^{6+}$, and $As^{5+}$). Notwithstanding approximately 50% inhibition, it was the first report of simultaneous bacterial reduction of $Cr^{6+}$ and $Se^{4+}$ (to elemental Se). No significant difference was observed among electron donors (glucose, maltose, and mannitol) on $Cr^{6+}$ reduction by B. megaterium TKW3. The reduction was constitutive and determined to be non-plasmid mediated. Peptide mass fingerprints (PMF) revealed a novel aerobic membrane-associated reductase with $Cr^{6+}$-induced expression and specific reductive activity (in nmol $Cr^{6+}$/mg protein/min) of 0.220 as compared with 0.087 of the soluble protein fraction. Respiratory inhibitor $NaN_3$ did not interfere with the reductase activity. Transmission electron microscopy with energy dispersive X-ray (TEM-EDX) analysis confirmed the aggregation of reduced chromium along the intracellular membrane region. Future identification of the N-terminal amino acid sequence of this reductase will facilitate purification and understanding of its enzymatic action.

• Asian-Australasian Journal of Animal Sciences
• /
• 제16권2호
• /
• pp.227-233
• /
• 2003

Two experiments were conducted to evaluate the effects of chromium (Cr) on the growth performance, bone trait, serum traits, and immune responses in broilers. The broilers were fed corn-soybean meal basal diet supplemented with Cr at level of 0(control), 200, 400, or 800 ppb in the form of chromium picolinate (CrPic). The broilers were fed treated diets for 6 weeks in Exp. 1, but the Cr supplement was removed for the last 3 weeks in Exp. 2. Exp. 1 showed that dietary supplement of Cr did not affect growth performance of the broiler, though improved feed efficiency (p<0.05) was observed during 0 to 3 weeks. Moreover, serum total (p<0.05) and HDL cholesterols (p<0.06) were significantly higher in pooled Cr added group at 6 weeks of age, however, the difference was not significant in Exp. 2. The pooled Cr added group in Exp.1 had significantly lower (p<0.05) alkaline phosphatase activity and higher (p<0.09) calcium at 3 weeks. Significantly lower phosphorus was also observed in Exp. 2. With continued supplement of Cr as in Exp. 1, the alkaline phosphatase activity maintained higher at 6 weeks, as opposed to significantly lower in Exp. 2, which had no further Cr supplement. Higher bone breaking strength was observed in 400 ppb Cr supplemented in Exp. 1, though not significantly different. Serum glucose and triglyceride were not affected by Cr supplement. Antibody against Infectious Bronchitis (IB) was significantly (p<0.05) higher with 400 ppb Cr supplemented, and anti-Newcastle disease (ND) antibody also tended to be higher (p<0.06) in pooled Cr added group at 6 weeks of age in Exp. 1. Peripheral blood blastogenesis activity was not different among the treatments. The results suggest that diet supplemented with 400 ppb CrPic may be beneficial to the broiler.

• 한국구조물진단유지관리공학회 논문집
• /
• 제17권6호
• /
• pp.88-94
• /
• 2013

시멘트 내 6가 크롬은 피부질환이나 암을 유발할 수 있는 유해한 인체에 유해한 이온으로 잘 알려져 있다. 본 연구에서는 사람에게 영향을 주는 시멘트 내 6가 크롬의 정량적 분석을 하고자 시멘트 및 시멘트 경화체 내 6가 크롬의 고정화에 대해 평가하였다. 국내에서 생산되는 일반 포틀랜드 시멘트 3종과 플라이애쉬, 고로슬래그 미분말, 실리카퓸을 사용하여 수용성 및 산가용성 6가 크롬을 분광광도법으로 측정하였다. 측정결과, 시멘트 내 수용성 6가 크롬의 농도는 10.5-18.9 mg/kg-cement 범위였으며 혼화재료 내 수용성 6가 크롬의 양은 매우 적게 측정되었다. 시멘트 내 산가용성 6가 크롬의 농도는 172.4-318.2 mg/kg-cement 범위로 측정되었으며 수용성 6가 크롬에 비해 증가하였다. 그러나 크롬의 pH에 의존적인 용해 특성에 따라 용매의 pH가 저감된다고 하여 산가용성 6가 크롬의 농도가 항상 크게 측정되지는 않았다. 시멘트 수화 후 수용성 6가 크롬은 2.0 mg/kg-cement 정도로 감소하였으며 이는 크롬산-에트링게이트 생성에 의한 결과임을 확인할 수 있었다.

• 자원환경지질
• /
• 제40권4호
• /
• pp.403-418
• /
• 2007

본 연구의 목적은 대전 산업단지 폐수종말처리장 내 국가지하수관측망(대전, 문평)의 6가 크롬 오염지하수의 오염 현황을 파악하고 그 확산 여부를 평가하는 것이다. 대전(문평) 관측소에서 나타나는 6가 크롬($Cr^{+6}$) 수질장해의 원인을 규명하고 6가 크롬의 오염 범위를 파악하기 위해 금번 연구에서는 보조 관측정을 설치 활용하였다. 수질분석 결과, 6가 크롬이 $3.2{\sim}4.5mg/L$ 정도 검출됨으로써 6가 크롬에 의한 관측소 충적공의 수질오염은 지속되고 있음이 파악되었다. 그러나 관측소의 암반관정 및 0.05mg/L 수질기준 이하의 농도를 보이는 MPH-1과 3번 관측공을 제외한 주변 관측공에서는 검출되지 않았다. 따라서 6가 크롬 및 총 크롬 함량의 오염 범위는 관측소 충적층 관정 인근에 한정되어 나타나고 있는 것으로 파악되었다. 또한 신규 5개 보조 관측정에서 채취한 77개의 시추 코어 및 슬라임 시료 모두에서 수용성/교환성 6가 크롬이 검출 한계(0.01mg/L) 이하로 나타나, 오염이 관측된 관측소 관정 주변의 토양 및 풍화토에서는 직접적으로 6가 크롬의 오염원이 확인되지 않았다. 지하수 수질분석 및 코어시료 분석 결과, 그 오염원의 중심 및 오염 확산 범위는 관측소 주위 반경 100m 이내로 매우 한정되는 것으로 판단되며 그 확산의 범위가 매우 좁을 것으로 예상된다. 시추조사 결과, 폐수종말처리장 부지조성 당시의 불량 매립층이 확인되었으며, 이러한 불량 매립산업폐기물이 관측소 인근의 6가 크롬 수질장해 원인으로 추론된다. 지표매질의 6가 크롬 자연저감능 평가를 위해 초기 농도 5mg/L Cr(VI)을 이용한 6가 크롬 유효 환원능을 분석하였다. 그 결과, 암회색 점토층에서 각각 58%, 66%, 64% 정도의 높은 6가 크롬 저감율을 보였으며, 이는 유기물 함량과 상호 관련이 있을 것으로 판단되었다. 비포화대/충적층 매질에 대한 6가 크롬 함량 및 자연저감 능력의 정량적 평가 결과, 매질에 의한 6가 크롬의 자연 저감능이 확인되었으며 관정 주변으로의 오염 확산은 충분히 제어되고 있는 것으로 판단된다. 그러나 시추 관측정 및 기설 관정의 수가 부족했기 때문에 매우 제한적인 선택적 유동(preferential flow) 경로에 의한 확산 가능성을 완전히 배제할 수 없다. 정기적인 양수작업을 통하여 지하수에 부화된 6가 크롬의 농도를 지속적으로 제거하고 관측소 주변에 설치된 보조 관측정들을 지속적으로 활용하여 6가 크롬의 농도 변화 추이 및 시간의 흐름에 따른 오염 확산 여부를 지속적으로 관측하고 감시하는 방안이 필요할 것으로 판단된다.

• 한국세라믹학회지
• /
• 제56권3호
• /
• pp.317-324
• /
• 2019

Cr-diamond-like carbon (Cr-DLC) films were deposited using a hybrid method involving both physical vapor deposition and plasma-enhanced chemical vapor deposition. DLC sputtering was carried out using argon and acetylene gases. With an increase in the DC power, the Cr content increased from 14.7 to 29.7 at%. The Cr-C bond appeared when the Cr content was 17.6 at% or more. At a Cr content of 17.6 at%, the films showed an electrical conductivity of > 363 S/cm. The current density was 9.12 × 10^-2 ㎂/㎠, and the corrosion potential was 0.240 V. Therefore, a Cr content of 17.6 at% was found to be optimum for the deposition of the Cr-DLC thin films. The Cr-DLC thin films developed in this study showed high conductivity and corrosion resistance, and hence, are suitable for applications in separators.