• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.2047-2052
• /
• 2004

Inconel-600 alloy has been used as steam generator tube material for current pressurized water reactors (PWRs). The long-term operation of steam generators showed that the use of this material induced localized corrosion damages and increased tube wear of steam generator. To protect these problems, steam generator tube material is being changed to Inconel-690 alloy. Based on the current trend, we have chosen Inconel 690 as the Advanced Power Reactor 1400 (APR1400) steam generator(SG) tube material and performed the design optimization of preventive measure against tube fretting wear for the APR1400 steam generator. In this paper, we examined the technical consideration in this modification : the selection of material, wear characteristics, effect of the Egg-crate Flow Distribution Plate installation, and effect analysis of vertical strip installation.

• Applied Chemistry for Engineering
• /
• v.10 no.4
• /
• pp.620-627
• /
• 1999

Electrochemical properties of the Al current collector being used in lithium ion batteries have been studied in the 4 different aprotic electrolytes(1 M $LiBF_4$ EC : DMC, 1 M $LiBF_4$ EC : EMC. 1 M $LiPF_6$ EC : DMC. 1 M $LiPF_6$ EC : EMC) employing cyclic voltammetry and impedance measurement. Al electrode showed a wide range of the electrochemical window(0.5~4.1 V vs. $Li/Li^{+}$). However, solid interfacial materials has been formed on the Al surface due to reduction of impurities($H_2O$, $O_2$, etc), lithium salts, and electrolytes at low applied potentials, and aluminum oxides in the highly oxidizing potential as well. Especially, Al current collector was susceptible to localized in consequence of impurities in electrolytes.

• Korean Journal of Materials Research
• /
• v.10 no.6
• /
• pp.398-402
• /
• 2000

Three kinds of $Al_3Ti-Cr$ alloys, namely, $Al_{67}Ti_{25}Cr_8,\;Al_{66}Ti_{24}Cr_{10}\;and\;Al_{59}Ti_{26}Cr_{15}$, were prepared by induction melting followed by the thermomechanical treatment. The corrosion behavior in 3.5% NaCl solution and the high-temperature oxidation behavior at 1000, 1100 and $1200^{\circ}C$ for the prepared alloys were investigated. Electrochemical results indicated increased resistance to localized corrosion with increasing Cr content. Cr additions were found to prevent passive film from undergoing brittle fracture. XPS results revealed the passive films of $Al_3Ti-Cr$ alloys were composed mainly of $Al_2O_3$ that coexisted with $TiO_2$ and $Cr_2O_3$. The overall oxidation resistance of the prepared alloys were excellent. Specifically, the oxidation resistance increased in the order of $Al_{59}Ti_{26}Cr_{15},\;Al_{66}Ti_{24}Cr_{10}\;and\;Al_{67}Ti_{25}Cr_8$. As the Al content in the base alloys increased, the $Al_2O_3$ formation was facilitated leading to the increased oxidation resistance.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.393-396
• /
• 2008

The purpose of this paper is to find out quantitatively the relationship between the surface shape and the mechanical properties of corroded reinforcement. Three-dimensional measurements were carried out on the surface shape of variously corroded reinforcements and parameters expressing the characteristics of the shape, which included the maximum decrement of sectional area of reinforcement, its distribution along the axis. It was investigated that which parameters could correspond to the mechanical properties of corroded reinforcement and it was confirmed that the maximum decrement of sectional area of reinforcement could express the mechanical properties most appropriately. Finally, this paper proposes a constitutive model of corroded reinforcement for analyzing the structural behavior of reinforced concrete structures considering the localized corrosion of by finite element method.

• Journal of the Korean institute of surface engineering
• /
• v.56 no.2
• /
• pp.115-124
• /
• 2023

Anodization is an electrochemical process that electrochemically converts a metal surface into an oxide layer, resulting in enhanced corrosion resistance, wear resistance, and improved aesthetic appearance. Local anodization, also known as selective anodization, is a modified process that enables specific regions or patterns on the metal surface to undergo anodization instead of the entire surface. Several methods have been attempted to produce oxide layers via localized anodic oxidation, such as using a mask or pre-patterned substrate. However, these methods are often intricate, time-consuming, and costly. Conversely, the direct writing or patterning approach is a more straightforward and efficient way to fabricate the oxide layers. This review paper intends to enhance our comprehension of local anodization and its potential applications in various fields, including the development of nanotechnologies. The application of anodization is promising in surface engineering, where the anodic oxide layer serves as a protective coating for metals or modifies the surface properties of materials. Furthermore, anodic oxidation can create micro- and nano-scale patterns on metal surfaces. Overall, the development of efficient and cost-effective anodic oxidation methods is essential for the advancement of various industries and technologies.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.20 no.4
• /
• pp.276-284
• /
• 2000

The acoustic emission (AE) behavior of reinforced concrete beams tested under flexural loading was investigated to characterize and identify the source of damage. This research was aimed at identifying the characteristic AE response associated with micro-crack development, localized crack propagation, corrosion, and debonding of the reinforcing steel. Concrete beams were prepared to isolate the damage mechanisms by using plain, notched-plain, reinforced, and corroded-reinforced specimens. The beams were tested using four-point cyclic step-loading. The AE response was analyzed to obtain key parameters such as the time history of AE events, the total number and rate of AE events, and the characteristic features of the waveform. Initial analysis of the AE signal has shown that a clear difference in the AE response is observed depending on the source of the damage. The Felicity ratio exhibited a correlation with the overall damage level, while the number of AE events during unloading can be an effective criterion to estimate the level of corrosion distress in reinforced concrete structures. Consequently, AE measurement characterization appears to provide a promising approach for estimating the level of deterioration in reinforced concrete structure.

• Journal of the Korea Concrete Institute
• /
• v.20 no.6
• /
• pp.713-719
• /
• 2008

Various types of coatings have been developed for use as reinforcement in concrete and to resist chloride environment. The most commonly used coatings are inhibited and sealed cement slurry coating, cement polymer compositing coating and epoxy coating. Cement slurry offers passive protection, epoxy coating offers barrier protection whereas polymer coating offers both passive protection and barrier protection. Moreover, damage during handling of the steel may result in disbondment of the epoxy coating, which would increase the risk of localized corrosion. In the present study, inhibiting technique was used to increase the calcium hydroxide content at the interface up to 20%. Calcium hydroxide provides a high buffering capacity that resists a local fall in pH and thus maintains the alkaline environment necessary to prevent chloride corrosion. This study examines the use of a calcium hydroxide coating on the steel surface to enhance the pH buffering capacity of steel-concrete interface. Finally, the chloride threshold level (CTL) of polymer inhibitive coating calcium hydroxide is evaluated.

• Journal of Chest Surgery
• /
• v.5 no.1
• /
• pp.45-56
• /
• 1972

Esophageal perforation is one of the most grave prognostic problems among thoracic and general surgical emergencies which necessitate urgent operative measures. In Korea,there are still many persons ingesting lye for suicidal attempt and thoracic surgeons in Korea have more chances to deal with lye burned esophagus with or without instrumental perforation than those in Western countries. Main cause of esophageal perforation in Korea is instrumental perforation in patients with lye stricture of the esophagus during diagnostic endoscopy or therapeutic bouginage. Other causes are corrosion of the esophagus due to ingestion of caustic agents, pathologic perforation, surgical trauma, stab wound and spontaneous rupture of the esophagus in our series. Therapeutic measures are various,and depend on duration of perforation, severity of its complications, pathology of perforated portion of the esophagus and degrees of inflammation at the point of perforation. The most important therapeutic measures are prevention of this grave condition during esophagoscopy, bouginage and surgical procedures on lungs and mediastinal structures and to make early diagnosis with prompt therapeutic measures. During the period of January, 1959, to December, 1971, the authors experienced 65 cases ofesophageal perforation including acquired esophagorespiratory fistula at Dept. of Chest Surgery, the National Medical Center in Seoul, and obtained following results in the series. 1. Female were 35 cases, and peak age incidence was 2nd and 3rd decades of life. 2. Among 65 cases, 43 were corrosive esophagitis or benign stricture of the esophagus due to caustic agents, 7 were patients with esophageal cancer. and there were 5 cases of esophageal perforation developed after pneumonectomy or pleuropneumonectomy. 3. Causes of perforation are instrumental perforation in 45, acute corrosion in 7, pathologic perforation in 7, surgical trauma in 3, stab wound in 2 cases, and one spontaneous rupture of the esophagus. 4. Most frequent sites of esophageal perforation were upper and mid thoracic esophagus, and 8 were cases with cervical esophageal perforation. 5. Complications of esophageal perforation were mediastinitis in 42, empyema or pneumothorax in 35, esophagorespiratory fistula in 12, retroperitoneal fistula or abscess in 5,pneumoperitoneum in 3, and localized peritonitis in 1 case. 6. Cases with malignant esophagorespiratory fistula were only 3 in the series which is predominant cause of acquired esophagorespiratory fistula in Western countries. 7. Various therapeutic measures were applied with mortality rate of 27.7% in the series. 8. In usual cases early treatment gave better prognosis, and least mortality rate in cases with perforation in mid thoracic esophagus. 9. Main causes of death were respiratory complications,acute hemorrhage with asphyxia, and septic complications. 10. Esophageal perforation developed after pneumonectomy gave more difficult therapeutic problems which were solved in only 1 among 5 cases.

• Smart Structures and Systems
• /
• v.8 no.1
• /
• pp.139-155
• /
• 2011

Polymeric thin-film assemblies whose bulk electrical conductivity and mechanical performance have been enhanced by single-walled carbon nanotubes are proposed for measuring strain and corrosion activity in metallic structural systems. Similar to the dermatological system found in animals, the proposed self-sensing thin-film assembly supports spatial strain and pH sensing via localized changes in electrical conductivity. Specifically, electrical impedance tomography (EIT) is used to create detailed mappings of film conductivity over its complete surface area using electrical measurements taken at the film boundary. While EIT is a powerful means of mapping the sensing skin's spatial response, it requires a data acquisition system capable of taking electrical impedance measurements on a large number of electrodes. A low-cost wireless impedance analyzer is proposed to fully automate EIT data acquisition. The key attribute of the device is a flexible sinusoidal waveform generator capable of generating regulated current signals with frequencies from near-DC to 20 MHz. Furthermore, a multiplexed sensing interface offers 32 addressable channels from which voltage measurements can be made. A wireless interface is included to eliminate the cumbersome wiring often required for data acquisition in a structure. The functionality of the wireless impedance analyzer is illustrated on an experimental setup with the system used for automated acquisition of electrical impedance measurements taken on the boundary of a bio-inspired sensing skin recently proposed for structural health monitoring.

• Journal of the Korean Society for Precision Engineering
• /
• v.26 no.1
• /
• pp.71-81
• /
• 2009

Die steel for plastic molding were used as mold material of automobile parts and electronic component industry. The material of this paper has superior to mechanical properties, such as repair weldability, corrosion resistance and high temperature strength, required mold parts for semitransparent. Laser-induced surface hardening technology is widely adopted to improver fatigue life and wear resistance via localized hardening at the surface of mold parts. The objective of this research work is to investigate on the characteristics of surface hardening of the laser process parameters, such as beam travel speed, laser power and defocsued spot position, for the case of die steel for plastic molding. Lens for surface hardening of large area is plano-convex type with elliptical profile to maintain uniform laser irradiation. According to the experimental results, large size of hardened layer at the surface of die steel for plastic molding was achieved, and microstructure of this layer was lath martensite. Optimal surface status and mechanical property of hardened layer could be obtained at 1095Watt, $0.25{\sim}0.3m/min$, 0mm (focal length: 232mm) for laser power, beam travel speed, and focal position. Where, heat input was $0.793{\times}10^{3}J/cm^2$, and width of hardened layer was 27.58mm.