• 분석과학
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• 제11권4호
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• pp.254-259
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• 1998

참나무톱밥에 의한 6가크롬의 흡착과 환원특성이 연구되었다. 용액의 pH를 변화하면서 톱밥의 Cr(VI)에 대한 분포계수($K_d$)와 흡착용량을 측정하여 최적조건을 발견하였다. 결과, pH 2.0이 최적조건이었다. 왜냐하면 이 pH에서 Cr(VI)의 $K_d$는 최대이고 Cr(III)로의 환원량은 최소이었기 때문이다. 이러한 참나무 톱밥의 특성을 이용하여 공장폐수중 Cr(VI)의 제거방법도 연구하였다.

• 상하수도학회지
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• 제23권6호
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• pp.843-853
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• 2009

The sediment samples were collected from Seonakdong River and were analyzed for sulfide species such Acid Volatile Sulfide(AVS) and Elemental Sulfur(ES) and Chromium Reducible Sulfide(CRS). Then characteristics of the formation of sulfide species were investigated for six selected samples. Finally the relationship between environmental factors and sulfate reducing rate(SRR) was investigated using two selected samples. Concentrations of AVS and CRS were relatively high, which suggests that organics input to the sediments has been continued until recently and that potential of heavy metals leaching from the sediments is low. SRR in the sediments was closely related to fraction of fine particles(silt+clay) and also to dissolved organic carbon content of the sediment(DOCsed). The dependences of environmental factors such as organic content, temperature, sulfate concentration on the SRR was relatively strong in the selected experiments conducted with the samples from Noksan gate and Daejeo gate samples. The environmental factor dependencies were stronger in the Noksan gate samples than in the Daejeo gate samples, which is probably due to higher surface area of the Noksan gate sediments.

• Applied Microscopy
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• 제7권1호
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• pp.45-49
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• 1977

용탕의 온도는 탄소의 비율을 높이기 위하여 $1500^{\circ}C$ 이하로 해야 하며, 주입온도는 $1460^{\circ}C$ 내외가 적당하다. 주조상태에서 소지의 침상석출물은 orthorhombic $(Fe,\;Mn)_3C$로 판명되었다. 냉간압연비는 클수록 결정이 미세화되고 또한 경도도 증가하였다. 표면탈탄이 얼어 나면 표면층에 martensite가 형성되어 성형하기가 어려우므로 argon 분위기를 쓰는 것이 좋았다. 두께 1 mm 판재의 경우 수인처리 온도가 $950^{\circ}C$ 이하일 때 탄화물 stringer 가 나타났고, $1020^{\circ}C$ 에서 30 분간 가열했을 때 탄화물이 의 소지에 고용되었다. C 함량이 클수록 인장강도와 연신률이 증가하였다. Ni, Cr 및 V 을 미량 첨가했을 때 인장강도 및 연신률이 커졌으며 또한 굽힘성도 좋았다.

• 한국생산제조학회지
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• 제26권4호
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• pp.365-370
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• 2017

In this article, a 20 kHz Titanium (Ti) ultrasonic waveguide system for a nano-surface reformation process was designed and fabricated. First, finite element analysis using ANSYS software was performed to find the optimal dimensions. The obtained anti-resonance frequency for the Ti transducer with the piezoelectric device was 20.0 kHz, which value agreed well with the experiment result of 20.1 kHz (0.5% error). To test the system, chromium molybdenum steel (SCM) 435 was chosen as a test-piece. The result proved that the reformed depth was $36{\mu}m$. In addition, hardness was measured before and after the process. The value was changed from 14 HRC to 21 HRC, which is 50% increasing rate. Finally, the friction coefficient test result showed that the surface coefficient was reduced from 0.14 to 0.10 (28.6% reduction). Based on the results, the Ti ultrasonic equipment is regarded as a useful device for nano-scale surface reformation.

• Nuclear Engineering and Technology
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• 제32권5호
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• pp.514-520
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• 2000

The mechanism of corrosion behavior has to be understood clearly to select an optimum material for handling molten salts to be used in the oxide reduction process of PWR spent fuel. In this study, the oxidation states of corrosion products on the surface of Inconel 600 and 800H as well as their chemical compositions and structural informations were determined by using XPS, ICP-AES, AAS, EPMA and XRD after the corrosion experiment with lithium molten salts at 75$0^{\circ}C$ for 25 hours. Nickel and oxygen were detected from the corrosion products on the surface of Inconel plates and chromium was found to be dissolved out into lithium molten salts leaving cracks on the surface. The corrosion products were identified as metal oxides such as Fe$_2$O$_3$, Cr$_2$O$_3$, NiO, NiFe$_2$O$_4$and MnO by using XPS and XRD.

• Imaging Science in Dentistry
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• 제54권2호
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• pp.139-145
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• 2024

Purpose: This study examined the influence of a metal artifact reduction (MAR) tool, sharpening filters, and their combination on the diagnosis of vertical root fracture (VRF) in teeth with metallic posts using cone-beam computed tomography (CBCT). Materials and Methods: Twenty single-rooted human premolars - 9 with VRF and 11 without - were individually placed in a human mandible. A metallic post composed of a cobalt-chromium alloy was inserted into the root canal of each tooth. CBCT scans were then acquired under the following parameters: 8 mA, a 5×5 cm field of view, a voxel size of 0.085 mm, 90 kVp, and with MAR either enabled or disabled. Five oral and maxillofacial radiologists independently evaluated the CBCT exams under each MAR mode and across 3 sharpening filter conditions: no filter, Sharpen 1×, and Sharpen 2×. The diagnostic performance was quantified by the area under the receiver operating characteristic curve (AUC), sensitivity, and specificity. These metrics were compared using 2-way analysis of variance with a significance level of α=5%. Intra- and inter-examiner agreement were assessed using the weighted kappa test. Results: Neither MAR nor the application of sharpening filters significantly impacted AUC or specificity (P>0.05). However, sensitivity increased when MAR was combined with Sharpen 1× and Sharpen 2× (P=0.015). The intra-examiner agreement ranged from fair to substantial (0.34-0.66), while the inter-examiner agreement ranged from fair to moderate (0.27-0.41). Conclusion: MAR in conjunction with sharpening filters improved VRF detection; therefore, their combined use is recommended in cases of suspected VRF.

• 전기화학회지
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• 제8권2호
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• pp.82-87
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• 2005

고전압 용 양극산화물 $LiNi_{0.5}Mn_{1.5}O_4$는 고온에서 합성 시, 입자 내에 산소결함에 의한 불순물상을 만들게 된다. 불순물상은 불완전한 스피넬 구조를 형성하며 리튬이온의 삽입$\cdot$탈리를 방해하여 전극의 성능을 감소시킨다. 본 연구에서는 고온 열처리 시 생성되는 이러한 불순물상의 거동을 파악하기 위해 크롬을 치환한 $LiNi_{0.5-x}Mn_{1.5}Cr_xO_4(0{\leq}x{\leq}0.05)$를 졸$\cdot$겔법을 이용하여 합성하여 고온 열분석을 실시하였다. 열분석 결과 크롬이 치환되지 않은 양극활물질은 산소결함에 의한 $2\%$의 무게 감소를 보였으나, 크롬이 치환된 경우 무게 감소분이 줄어들어 불순물 생성이 억제됨을 알 수 있었다. XRD 분석에서도 크롬이 치환된 경우 불순물 상이 억제됨을 나타내었으며 불순물상의 감소로 인해 크롬을 첨가한 양극활물질 $LiNi_{0.5-x}Mn_{1.5}Cr_xO_4$를 사용한 경우 충·방전 실험 시 가역 용량과 싸이클 안정성이 향상됨을 볼 수 있었다.

• 대한방사선기술학회지:방사선기술과학
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• 제39권4호
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• pp.595-600
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• 2016

진단방사선 검사 시 환자선량을 감소하기 위한 목적으로 진단용 다엽콜리메이터를 제작하고자 하며, 제작 전 사전연구로서 진단용 다엽콜리메이터에 사용되는 차폐물질 및 차폐효율에 대한 몬테칼로 시뮬레이션을 수행하였다. 몬테칼로 시뮬레이션 코드(MCNPX, LANL, USA)를 이용하여 진단방사선 기기(ReX-650R, Listem, Korea)을 모델링하기 위하여, SRS-78 프로그램을 이용하여 관전압(80, 100, 120 kVp)에 따라 에너지 스펙트럼을 획득하였다. 진단용 다엽콜리메이터의 제작을 위하여 사용된 재료는 SKD-11(탄소 : 1.6%, 규소 : 0.4%, 망간 : 0.6%, 크롬 : 5%, 몰리브덴 : 1%, 바나듐 : 0.3%, 밀도: $7.87g/cm^3$)이며 이를 진단방사선 기기에 진단용 다엽콜리메이터($10{\times}0.5{\times}0.5cm^3$, 좌우 20개씩) 형태로 전산 모사하였다. 진단용 다엽콜리메이터의 차폐효율을 확인하기 위하여 MCNPX 코드의 tally6을 이용하여 에너지별로 차폐효율을 계산하였다. 에너지에 따른 차폐효율은 80 kVp 일 때, 98.3% 차폐되었으며, 100 kVp는 95.7%, 마지막으로 120 kVp는 93.6%가 차폐되는 것을 확인할 수 있었다. 본 연구결과를 기반으로 MLC형태 및, 누설선량에 대한 연구를 진행하여 진단방사선 기기에서 사용 가능한 진단용 다엽콜리메이터 개발에 필요한 정보를 제공할 수 있을 것이라 사료된다.

• Corrosion Science and Technology
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• 제11권6호
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• pp.275-279
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• 2012

Ni-W alloy deposits have lately attracted the interest as an alternative surface treatment method for hard chromium electrodeposits because of higher wear resistance, hardness at high temperature, and corrosion resistance. This study deals with influences of process variables, such as electodeposition current density, plating temperature and pH, on the internal stress of Ni-W nanocrystalline deposits. The internal stress was increased with increasing the applied current density. With increasing applied current density, the grain size of the deposit decreases and concentration of hydrogen in the deposit increases. The subsequent release of the hydrogen results in shrinkage of the deposit and the introduction of tensile stress in the deposit. Consequently, for layers deposited at high current density, cracking occurs readily owing to high tensile stress value. By increasing the temperature of the electrodeposition from $60^{\circ}C$ to $80^{\circ}C$, the internal stress was decreased. It seems that an increase in the number of active ions overcoming the activation energy at elevated temperature caused a decline in the concentration polarization and surface diffusion. It decreased the level of hydrogen absorption due to the lessened hydrogen evolution reaction. Therefore, the lower level of hydrogen absorption degenerated the hydride on the surface of the electrode, resulting in the reduction of the internal stress of the deposits. By increasing the pH of the electrodeposition from 5.6 to 6.8, the internal stress in the deposits were slightly decreased. It is considered that the decrease in internal stess of deposits was due to supply of W complex compound in cathode surface, and hydrogen ion resulted from decrease of activity.

• 대한치과보철학회지
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• 제40권6호
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• pp.590-596
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• 2002

The resin : metal interface is at the basis of most bonding failures in resin-bonded prosthesis. Although debonding has been a problem with adhesive fixed partial dentures, various dentists classify them as long-term restorations. The advantages of resin-bonded fixed partial dentures include minimal tooth reduction and the possibility of rebonding. if resin-bonded protheses can be easily rebounded, it is of clinical importance to know if the lutingagents rebond as well the second time as they did originally. Several retentive systems for resin-to-metal bonding have recommended. Treatments such as electrolytic etching and silicone coating, despite the good result of bond strength, have proved to be time-consuming and technique-sensitive. Therefore a simple and more reliable method is desirable. This study evaluated the effect of metal surface treatments on the rebond strength of panavia 21 cement to a nickel-chromium(Ni-Cr) alloy. The samples were received the following surface treatments : Group No.1 (control or served as the control) treatment with sandblasting with 50um aluminum oxide and ultrasonically cleaned for 10minutes in double-deionized water, Group No.2 were no surface treatments. Group No.3 were treated with metal primer. Group No.4 were treated with sandblasting as previously described, and then metal priming. From the analysis of the results, the following conclusions were drawn. 1. Sandblasting and metal priming appears to be an effective method for treatment of metal after accidental debonding. 2. Group without surface treatment had significantly lower bond strengths compared with other groups. 3. The combination of sandblasting and metal priming may not develop superior bonding strengths compared with other techniques that used the Ni-Cr alloys. 4. Combination of cohesive and adhesive failures were the most common type observed. The results support the use of sandblasting as a viable procedure when rebonding accidentally lost adhesive partial denture. We concluded that sandblasting and metal priming of metal surface before bonding could provide the adequate bond strength during rebonding of resin-bonded fixed partial denture.