• Corrosion Science and Technology
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• 제22권5호
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• pp.359-367
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• 2023

The localized corrosion resistance of the Ni-based Inconel 718 alloy after solution heat treatment was evaluated using electrochemical techniques in a solution of 25 wt% NaCl and 0.5 wt% acetic acid. Solution heat treatment at 1050 ℃ for 2.5 hours resulted in an increased average grain diameter. Both Ti carbides (10 ㎛ diameter) and Nb-Mo carbides (1 - 9 ㎛ diameter) were distributed throughout the material. Despite heat treatment, the shape and composition of these carbides remained consistent. An increase in solution temperature led to a decrease in pitting potential value. However, the pitting potential value of solution heat-treated Inconel 718 was consistently higher than that of as-received Inconel 718 at all tested temperatures. Localized corrosion initiation occurred at 0.4 V_SSE in a temperature environment of 80 ℃ for both as-received and solution heat-treated Inconel 718 alloys. X-ray photoelectron spectroscopic analysis indicated that the composition of the passive film formed on specimen surfaces remained largely unchanged after solution heat treatment, with O1s, Cr2p_3/2, Fe2p_3/2, and Ni2p_3/2 present. The difference in localized corrosion resistance between as-received and solution heat-treated Inconel 718 alloys was attributable to microstructural changes induced by the heat treatment process.

• 전자공학회논문지C
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• 제36C권5호
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• pp.13-26
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• 1999

본 논문은 다양한 회로 연결선 모형 중에서 연결선 변수 및 동작 환경에 다라 최적 모형을 쉽게 선택할 수 있는 기준을 제시하고자 한다. 이를 위하여 먼저 연결선의 총 저항, 인덕턴스, 커패시턴스 값 및 신호의 동작주파수를 기반으로 정량적 모형화 오차 분석에 근거하여 인덕턴스의 영향을 고려하여 모형화해야 하는 RLC-class 모형 영역과 그럴 필요가 없는 RC-class모형 영역으로 분할하는 방법을 제시한다. 칩 내부 연결선의 대부분을 차지하는 RC-class 회로 모형은 모형 차수 축소 기법을 통하여 효율적으로 해석될 수 있다. RLC-class 회로 모형은 주어진 허용 모형화 오차 및 전기 변수에 따라 ILC(Iterative Ladder Circuit) 거시 모형, MC(Method of Characteristics)거시 모형 및 상태 기반 컨벌루션(comvolution) 방법 중에서 최적인 모형을 선정하게 된다. 본 논문은 SPICE류의 범용 회로 시뮬레이션 앨고리즘을 가정할 때, 세부 모형들의 시뮬레이션 비용을 감안하고서 최적 모형을 찾는 영역 구성도를 제시한다. 본 논문에서 제시하는 거시모형화 방법은 회로의 수동성을 유지하며, 따라서 무조건적 안정도를 보장할 수 있다.

• 대한화학회지
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• 제56권4호
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• pp.448-458
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• 2012

In order to develop alloy resistance in aggressive sulphat ion, the corrosion behavior of metallic glasses $Ni_{92{\cdot}3}Si_{4.5}B_{32}$, $Ni_{82,3}Cr_7Fe_3Si_{4.5}B_{3.2}$ and $Ni_{75.5}Cr_{13}Fe_{4.2}Si_{4.5}B_{2.8}$ (at %) at different concentrations of $H_2SO_4$ solutions was examined by electrochemical methods and Scanning Electron Microscope (SEM) and X-ray Photoelectron Microscopy (XPS) analyses. The corrosion kinetics and passivation behavior was studied. A direct proportion was observed between the corrosion rate and acid concentration in the case of $Ni_{92{\cdot}3}Si_{4.5}B_{32}$ and $Ni_{75.5}Cr_{13}Fe_{4.2}Si_{4.5}B_{2.8}$ alloys. Critical concentration was observed in the case of $Ni_{82,3}Cr_7Fe_3Si_{4.5}B_{3.2}$ alloy. The influence of the alloying element is reflected in the increasing resistance of the protective film. XPS analysis confirms that the protection film on the $Ni_{92{\cdot}3}Si_{4.5}B_{32}$ alloy was NiS which is less protective than that formed on Cr containing alloys. The corrosion rate of $Ni_{82,3}Cr_7Fe_3Si_{4.5}B_{3.2}$ and $Ni_{75.5}Cr_{13}Fe_{4.2}Si_{4.5}B_{2.8}$. alloys containing 7% and 13% Cr are $7.90-26.1{\times}10^{-3}$ mm/y which is lower about 43-54 times of the alloy $Ni_{92{\cdot}3}Si_{4.5}B_{32}$ (free of Cr). The high resistance of $Ni_{75.5}Cr_{13}Fe_{4.2}Si_{4.5}B_{2.8}$ alloy at the very aggressive media may due to thicker passive film of $Cr_2O_3$ which hydrated to hydrated chromium oxyhydroxide.

• Corrosion Science and Technology
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• 제14권5호
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• pp.239-246
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• 2015

Stainless steel is generally known to have characteristics of excellent corrosion resistance and durability, but in a marine environment it can suffer from localized corrosion due to the breakdown of passivity film due to chloride ion in seawater. Furthermore, the damage behaviors are sped up under a cavitation environment because of complex damage from electrochemical corrosion and cavitation-erosion. In this study the characteristics of electrochemical corrosion and cavitation erosion behavior were evaluated on 16.7Cr-10Ni-2Mo stainless steel under a cavitation environment in natural seawater. The electrochemical experiments have been conducted at both static conditions and dynamic conditions inducing cavitation with different current density parameters. The surface morphology and damage behaviors were compared after the experiment. After the cavitation test with time variables morphological examinations on damaged specimens were analyzed by using a scanning electron microscope and a 3D microscope. the galvanostatic experiment gave a cleaner surface morphology presented with less damage depth at high current density regions. It is due to the effect of water cavitation peening under the cavitation condition. In the cavitation experiment, with amplitude of $30{\mu}m$ and seawater temperature of $25^{\circ}C$, weight loss and cavitation-erosion damage depth were dramatically increased after 5 hours inducing cavitation.

• Corrosion Science and Technology
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• 제2권2호
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• pp.68-74
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• 2003

The effects of Niobium on the structure and properties(especially electric properties) of passive film of Zirconium alloys in pH 8.5 buffer solution are examined by the photo-electrochemical analysis. For Zr-xNb alloys (x = 0, 0.45, 1.5, 2.5 wt%), photocurrent began to increase at the incident energy of 3.5 ~ 3.7 eV and exhibited the $1^{st}$ peak at 4.3 eV and the $2^{nd}$ peak at 5.7 eV. From $(i_{ph}hv)^{1/2}$ vs. hv plot, indirect band gap energies $E_g{^1}$= 3.01~3.47 eV, $E_g{^2}$= 4.44~4.91 eV were obtained. With increasing Nb content, the relative photocurrent intensity of $1^{st}$ peak significantly increased. Compared with photocurrent spectrum of thermal oxide of Zr-2.5Nb, It was revealed that $1^{st}$ peak in photocurrent spectrum for the passive film formed on Zr-Nb alloy was generated by two types of electron transitions; the one caused by hydrous $ZrO_2$ and the other created by Nb. Two electron transition sources were overlapped over the same range of incident photon energy. In the photocurrent spectrum for passive film formed on Zr-2.5Nb alloy in which Nb is dissolved into matrix by quenching, the relative photocurrent intensity of $1^{st}$ peak increased, which implies that dissolved Nb act as another electron transition source.

• 공학교육연구
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• 제8권3호
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• pp.26-35
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• 2005

정보통신의 발달과 기술의 개발은 세계를 국제화 및 지식정보화 사회로의 급격히 변화시키고 있다. 이에 따라 공과대학에서의 공학교육도 급변하는 추세에 발맞추어 국제적 인재 양성이라는 교육목표로의 수정을 요구받고 있다. 국제적으로 인정받는 인재라는 것은 팀에서의 팀원 및 리더로서의 역할을 수행할 수 있는 인재, 사회에서의 다양한 학제간의 융합에 부응할 수 있는 인재, 사회적 및 국제적 의사소통기술을 겸비한 인재, 전공에 있어서 기초 및 응용을 충분히 습득한 인재 등으로 요약된다. 따라서 본 연구는 이러한 인재양성을 위하여 공과대학의 저학년들을 위한 공학설계입문이라는 교과목을 개발하고자 한다. 공과대학 학생들을 위한 공학설계입문의 교과목 개발 목표는 창의적 설계 주제 연구를 통하여 팀웍기술 배양, 문제해결 능력 향상, 의사소통 기술 증진 및 공학에 대한 창의적 사고방식을 갖춘 국제적 인재양성을 목표로 하고 있다.

• 대한치과보철학회지
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• 제42권4호
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• pp.412-424
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• 2004

Statement of problem: Several prosthetic options are available for the restoration of multiple adjacent implants. A passively fitting prosthesis has been considered a prerequisite for the success and maintenance of osseointegration. Passivity is a particular concern with multiple implants because of documented inaccuracies in the casting and soldering process. One way to avoid this problem is to restore the implants individually, however, the restorations of individual adjacent impants requires careful adjustment of interproximal contacts. Purpose: The purpose of this study was to compare the stress distribution pattern and amount surrounding Bicon implants with individual crowns and splinted restorations. Material and method: A photoelastic model of a human partially edentulous left mandible with 3 Bicon implants($4{\times}11mm$) was fabricated. For non-splinted restorations, individual crowns were fabricated on 3 abutments ($4{\times}0.65mm,\;0^{\circ}$, 2.0 mm post, Bicon Inc., Boston, USA) After the units were cemented, 4 levels of interproximal contact tightness were evaluated: open, ideal ($8{\mu}m$ shim stock drags without tearing), medium($40{\mu}m)$), and heavy($80{\mu}m$). Splinted 3-unit fixed partial dentures were fabricated and cemented to the model. Changes in stress distribution under simulated non-loaded and loaded conditions(7.5, 15, 30 lb) were analyzed with a circular polaricope. Results: 1. Stresses were distributed around the entire body of fin in Bicon implants. 2. Splinted restorations were useful for distribution of stress around implants especially with higher loads. 3. By increasing the contact tightness between the individually restored three implants, the stress increased in the coronal portion of implants. Conclusions: Ideal adjustment of the contact tightness was important to reduce the stresses around individually restored Bicon implants.

• 대한화학회지
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• 제28권5호
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• pp.271-278
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• 1984

염기성 용액에서 기계적으로 연마한 고순도 철의 전위를 환원 전위로부터 부동화 전위로 급격히 변화시켜서 부동화 막이 전극표면에 형성되게 하면서 철의 반사율 변화와 타원편광반사법(Ellipsometry) 측정을 하였다. 철 표면이 부동화 될때 일어나는 반사광의 편광 파라메터(${\Delta},\;{\psi}$)와 반사율(R) 변화를 자동화된 타원편광반사계로 기록하였고, 이로부터 철을 부동화 상태에 들어가게 하는 표면막의 두께(${\tau}$)와 광학상수(n, k)들의 변화하는 값을 계산할 수 있었다. 광학상수 값들로 나타나는 막의 성질이 시간에 따라 급격한 전이를 하는 것은 관찰되지 않았으며, 비교적 짧은 시간(수초)내에 정상 상태 값에 접근하였다. 효과적으로 부동화를 일으키는 막의 두께는 $14\;{\sim}\;23{\AA}$의 범위에 있었다. 형성된 부동화 막은 용액의 pH가 큰 경우에는 얇고 치밀한 구조를 가진 것으로 보이며, pH가 작은 경우에는 두께는 두껍지만 pH가 큰 경우보다 덜 치밀한 부동화 막이 형성되는 것으로 보였다. 이들 부동화 막은 약간의 흡광성을 가지는 것으로 나타났다.

• The Journal of Advanced Prosthodontics
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• 제5권3호
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• pp.312-318
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• 2013

PURPOSE. The aim of this study was to compare the passivity of implant superstructures by assessing the strain development around the internal tapered connection implants with strain gauges. MATERIALS AND METHODS. A polyurethane resin block in which two implants were embedded served as a measurement model. Two groups of implant restorations utilized cement-retained design and internal surface of the first group was adjusted until premature contact between the restoration and the abutment completely disappeared. In the second group, only nodules detectable to the naked eye were removed. The third group employed screw-retained design and specimens were generated by computer-aided design/computer-aided manufacturing system (n=10). Four strain gauges were fixed on the measurement model mesially and distally to the implants. The strains developed in each strain gauge were recorded during fixation of specimens. To compare the difference among groups, repeated measures 2-factor analysis was performed at a level of significance of ${\alpha}$=.05. RESULTS. The absolute strain values were measured to analyze the magnitude of strain. The mean absolute strain value ranged from 29.53 to 412.94 ${\mu}m/m$ at the different strain gauge locations. According to the result of overall comparison, the cement-retained prosthesis groups exhibited significant difference. No significant difference was detected between milled screw-retained prostheses group and cement-retained prosthesis groups. CONCLUSION. Within the limitations of the study, it was concluded that the cement-retained designs do not always exhibit lower levels of stress than screw-retained designs. The internal adjustment of a cement-retained implant restoration is essential to achieve passive fit.

• Corrosion Science and Technology
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• 제20권6호
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• pp.426-434
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• 2021

The effect of two different annealing temperatures on the level of the second phase precipitated in the microstructure and the corrosion behaviors of super austenitic stainless steel were examined. The sample annealed at a higher temperature had a significantly lower fraction of the sigma phase enriched with Cr and Mo elements, showing more stable passivity behavior during the potentiodynamic polarization measurement. However, after the welding process with Inconel-type welding material, severe corrosion damage along the interface between the base metal and the weld metal was observed regardless of the annealing temperature. This was closely associated with the precipitation of the fine sigma phase with a high Mo concentration in the unmixed zone (UMZ) during the welding process, leading to the local depletion of Mo concentrations around the sigma phase. On the other hand, the fraction of the newly precipitated fine sigma phase in the UMZ was greatly reduced by post-weld heat treatment (PWHT), and the corrosion resistance was greatly improved. Based on the results, it is proposed that the alloy composition of welding materials and PWHT conditions should be further optimized to ensure the superior corrosion resistance of welded super austenitic stainless steel.