• 대한치과기공학회지
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• 제34권3호
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• pp.237-245
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• 2012

Purpose: This study was conducted to evaluate the corrosion resistance of metal ions of alloys and use the results as the dental health data. These were performed by examining the corrosion levels of Co-Cr alloys for the full and removable partial denture metal frameworks and porcelain-fused-to-metal crown, among the dental casting nonprecious alloys. Methods: The alloy specimens (N = 10) were manufactured in $15mm{\times}10mm{\times}1.2mm$ and stored in two types of corrosive solutions at $37^{\circ}C$ for seven days. The metal ions were quantitatively analyzed using the Inductively Coupled Plasma-Atomic Emission Spectrometer. Results: Of the three Co-Cr alloys, the Co ion concentration of the porcelain-fused-to-metal alloy was 1.512 ${\mu}g/cm^2$, which indicated the highest metal ion dissolution. The metal corrosion was higher in the more acidic pH 2.2 solution compared with the pH 4.4 solution. In all three Co-Cr alloys, Co ion dissolution was predominant in the two corrosive solutions. Conclusion: The corrosion resistance of the three Co-Cr alloys was high, indicating a good biocompatibility.

• 한국표면공학회지
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• 제41권3호
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• pp.121-128
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• 2008

High strength 7xxx aluminum alloys have been applied to automotive bump back beam of the some limited model for light weight vehicle. The aluminum bump back beam is manufactured through extrusion, bending and welding. The residual stress given on these processes combines with the corrosive atmosphere on the road spreaded with corrosive chemicals to melt snow to occur the stress corrosion cracking. The composition of commercial 7xxx aluminum has Zn/Mg ratio about 3 and Cu over 2 wt% for better strength and stress corrosion cracking resistivity. But this composition isn't adequate for appling to the automotive bump back beam with high resistance to extrusion and bad weldability. In this study the composition of 7xxx aluminum alloy was modified to high Zn/Mg ratio and low Cu content for better extrusion and weldability. To estimate the resistivity against stress corrosion cracking of this aluminum alloy by slow strain rate test, the corrosion atmosphere and strain rate separate the stress corrosion cracking from conventional corrosion must be investigated. Using 0.6 Mol NaCl solution on slow strain rate test the stress corrosion cracking induced fracture was not observed. By adding 0.3% $H_2O_2$ and 0.6M $Na_2SO_4$ to 1M NaCl solution, the corrosion potential and current density of polarization curve moved to active potential and larger current density, and on the slow strain rate test the fracture energy in solution was lower than that in pre-exposure. These mean the stress corrosion cracking induced fracture can be estimated in this 1M NaCl + 0.3% $H_2O_2$ + 0.6M $Na_2SO_4$ solution. When the strain rate was below $2{\times}10^{-6}$, the stress corrosion cracking induced fracture start to be observed.

• 한국구조물진단유지관리공학회 논문집
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• 제16권1호
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• pp.110-119
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• 2012

최근 고부식 환경에 놓여 있는 철근 콘크리트 구조물의 철근 부식 문제를 해결할 수 있는 방안 중 하나로 뛰어난 내부식성을 가진 섬유복합체(Fiber Reinforced Polymer, FRP)로 제작된 보강근이 주목받고 있다. 유리섬유복합체로 제작된 보강근이 상용화된 상태이나 가격, 철근보다 낮은 탄성계수, 취성파괴 특성 등의 이유로 사용 실적은 많지 않은 것이 현실이다. 이러한 문제점을 해결하기 위한 방편 중 하나는 유리섬유복합체 보강근의 성능을 고도화하는 것이다. 성능 고도화를 통해 강도 대비 가격을 낮출 수 있으며, 인장성능을 향상시킬 수 있다. 본 연구는 주어진 재료와 조건 하에서 보강근 성능에 영향을 미치는 인자들의 효율성 향상을 통한 고인장 성능 유리섬유복합체 보강근의 개발에 관한 것이다. 이를 위해 구성재료와 제작방법 등 유리섬유복합체 보강근의 인장성능에 영향을 미치는 인자들에 대해 분석을 수행하여 개선 방안을 제안하였으며, 이를 통해 보강근의 주재료인 유리섬유의 성능을 기존 제품보다 더욱 효율적으로 활용하는 보강근을 제작하였으며, 다양한 변수에 대한 인장시험을 통하여 그 성능을 비교 분석함으로써 개선 방안의 적절성을 검증하였다.

• Structural Engineering and Mechanics
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• 제81권5호
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• pp.565-574
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• 2022

The infrastructures such as offshore, bridges, power plant, oil and gas piping and aircraft operate in a harsh environment during their service life. Structural integrity of engineering components used in these industries is paramount for the reliability and economics of operation. Two regression models based on the concept of Gaussian process regression (GPR) and Minimax probability machine regression (MPMR) were developed to predict stress intensity factor range (𝚫K). Both GPR and MPMR are in the frame work of probability distribution. Models were developed by using the fatigue crack growth data in MATLAB by appropriately modifying the tools. Fatigue crack growth experiments were carried out on Eccentrically-loaded Single Edge notch Tension (ESE(T)) specimens made of API 5L X65 Grade steel in inert and corrosive environments (2.0% and 3.5% NaCl). The experiments were carried out under constant amplitude cyclic loading with a stress ratio of 0.1 and 5.0 Hz frequency (inert environment), 0.5 Hz frequency (corrosive environment). Crack growth rate (da/dN) and stress intensity factor range (𝚫K) values were evaluated at incremental values of loading cycle and crack length. About 70 to 75% of the data has been used for training and the remaining for validation of the models. It is observed that the predicted SIF range is in good agreement with the corresponding experimental observations. Further, the performance of the models was assessed with several statistical parameters, namely, Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Efficiency (E), Root Mean Square Error to Observation's Standard Deviation Ratio (RSR), Normalized Mean Bias Error (NMBE), Performance Index (ρ) and Variance Account Factor (VAF).

• Corrosion Science and Technology
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• 제22권1호
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• pp.21-29
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• 2023

In this paper, a SiC nano electroless nickel plating layer with excellent corrosion resistance was fabricated using the Taguchi method. The electroless plated low carbon steel was subjected to tests to examine the influence of corrosive media, microhardness, and corrosion rate on the corrosion resistance of this alloy. Three different corrosive media (HCl, Na₂SO₄, and NaCl) at various temperatures (80, 90, and 100 ℃) were used, and at three different times (40, 80, and 120 min.) with a speed of stirring equal to 500 rpm. The results of microhardness were found from 134.276 HV to 278.578 HV at various conditions, while the corrosion rate results were obtained from 0.89643 mpy to 7.12571 mpy at different circumstances. Corrosion, and mechanical characteristics were explained using Taguchi design. Taguchi technique was used to account for all possible combinations of elements in order to conduct a complete study. Models that link the response and procedure parameters were developed using the results of these tests, and the analysis of variance was utilized to validate these models (ANOVA). For maximum efficiency, a function called "desirability" was applied to all responses at once.

• Clinical and Experimental Pediatrics
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• 제52권4호
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• pp.446-452
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• 2009

목 적 : 소아 부식식도염 환자에서 후기 합병증 예측을 위한 조기내시경 검사의 유용성에 대해서 분석하고자 하였다. 방 법 : 1989년 1월부터 2007년 12월까지 빙초산과 가성소오다 등의 부식성물질 섭취 후 급성기에 서울대학교 어린이병원과 분당서울대학교병원에 내원하여 내시경을 시행한 34명의 환자를 대상으로 내시경 검사와 의무기록 조사 및 보호자 전화면담을 통하여 정보를 수집하였다. 결 과 : 식도의 내시경 소견을 보면 grade 0, grade 1, grade 2a, grade 2b, grade 3인 경우가 각각 8명, 2명, 7명, 13명, 4명이었다. 구토, 침흘림, 삼킴곤란 등의 증상의 유무는 내시경상 식도 점막 손상의 유무와 유의한 상관관계를 보이지 않았다. 구강 손상의 유무는 내시경상 식도 점막 손상의 유무와 유의한 상관관계를 보였다(P=0.014). 내시경 시행 후 점막째짐, 출혈, 천공 등의 합병증은 발생하지 않았다. 협착은 12명(36.3%)의 환아에서 발생하였고, 식도의 협착은 11명, 유문부의 협착은 1명이었다. 식도 점막 손상의 정도가 심해질수록 식도협착이 많이 발생하는 경향을 보였다(P=0.002). 식도협착이 있었던 11명 중 2명(18.1%)은 반복적인 식도확장술만으로 증상이 호전되었고, 나머지 7명(63.6 %)은 수술이 필요하였다. 결 론 : 부식성 물질을 실수로 섭취한 소아에서 내시경 검사는 안전하고 유용한 검사이며, 점막 손상의 정도와 부위를 확인함으로써 후기 합병증 발생 예측에 도움이 되기 때문에 조기에 식도내시경을 시행하는 것이 필요하다.

• Corrosion Science and Technology
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• 제8권2호
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• pp.45-52
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• 2009

The corrosive behavior of mild steel in 0.05 M to 10 M $H_2SO_4$ solutions containing different concentrations of tetrahydropyrimidine derivatives (THPM) was investigated using weight loss method, gasometric technique, electrochemical studies which include AC - impedance and potentiodynamic polarization method, atomic absorption studies and synergistic effect. The results obtained reveal that THPM derivatives is an efficient mixed type inhibitor but slightly anodic and it is more effective in reducing corrosion of mild steel in $H_2SO_4$ media. The adsorption of the inhibitor on the mild steel surface obeys the Langmuir adsorption isotherm. The thermodynamic parameters of adsorption reveal a strong interaction and spontaneous adsorption of THPM on the mild steel surface. The influence of temperature and inhibitor concentration on the corrosion of mild steel has also been investigated.

• 한국주조공학회지
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• 제24권4호
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• pp.202-208
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• 2004

Effects of Co addition on sliding wear properties of multi-component white cast iron were investigated. The microstructures of multi-component white cast iron containing from 0%Co to 10%Co exhibited little difference. However, the hardness increased with an increase of the Co content. Increasing the Co content, wear properties were improved and the iron oxide on worn surface was increased in the low sliding speed range of the steady-state wear region. Hence, Co addition was effective to improve the wear properties of multi-component white cast iron by accelerating the corrosive wear as well as the enhancement effect of hardness.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.3-5
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• 1997

Synthesis of ammonium aluminum hydrogen carbonate(AAHC) via reaction of aluminum bicarbonate and aluminum salt and thermal decomposition is oner of the important processes for preparation of high pure and ultra fine alumina. Kato and coworkers[1] developed this process, at same time Von Erdos and Altorfe[2] found AAHC in the corrosive products of aluminum in the atmosphere of carbon dioxide and ammonia. Murase and Iga[3] synthesized acicular AAHC in a autoclave under 60 to 12$0^{\circ}C$ Hayashi[4] optimized the conditions for preparation of AAHC and alumina. Attemp has been made in this paper to reveal the conditions affect the morphology of the synthesized AAHC and the consequently produced alumina.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.189-194
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• 1999

The antiwear performance of several organic phosphates ,such as tricrecylphosphate(TCP), tributylphosphate(TBP), diphenylhydrogenphosphate(DPHP) ,dissolved in polyol ester based oils is studied. These organic phosphates are well known for antiwear additive for lubricating oil that produce reacted surface protective film. These antiwear additives can drastically reduce wear with their concentration increasing, because the amount of additive adsorbed on metal sur(ace increases. But in the higher concentration region, the wear is increased by excessive and corrosive reaction of the metal surface with these additives. That is to say, there is an optimum concentration for minimum wear. The optimum concentration was different with the kinds of base oils and additives. Different polyolesters showed different optimum concentrations of the additive. The order of optimum concentration among the polyolesters was different with different phosphates. The order of the optimum concentration is shown that the effect of the concentration of additives on the antiwear performance. It can be explained by the interaction between additives and base oils using the solubility parameter.