Myung-Hoon Lee

Formation mechanism of new corrosion resistance magnesium thin films by PVD method

Abstract Magnesium thin films were deposited on cold-rolled steel by physical vapor deposition sputtering technique. The crystal orientation and morphology of the deposited films were investigated by using XRD and scanning electron microscopy, respectively. The effect of crystal orientation and morphology of magnesium films on corrosion behaviors was estimated by measuring anodic polarization curves in deaerated 3% NaCl solution. With the increase of argon gas pressure, the morphology of the deposited magnesium films changed from columnar to granular structure and the diffraction peaks of the film became little sharp and broad. And all the sputtered magnesium films obviously showed good corrosion resistance compared with 99.99% magnesium target metal. Formation mechanism on the crystal orientation and morphology of magnesium films can be explained by applying the effects of adsorption and occlusion of argon gas.

Study on the effect of ultrasonic waves on the characteristics of electroless nickel deposits from an acid bath

Abstract The effect of ultrasonic waves on the properties of electroless nickel deposits was studied using an acidic bath of different pH values ranging from 4.3 to 5.7. Three frequencies, 28, 40 and 68 kHz, were applied to the bath containing different amounts of Pb(NO3)2 as a stabilizer up to 2.8 ppm. The deposition parameters were optimized in view of the hardness, surface morphology and the deposition amount by employing a statistical technique of central composite design (CCD). Thus, the deposition amount was improved by 15% and the hardness increased by 11%. The maximum deposit amount and Knoop hardness were obtainable in this study as a result of the application of an ultrasonic wave frequency at 40 kHz to the bath with a Pb(NO3)2 content of 0.4 ppm at pH 5.5. Although the ultrasonic frequency increased, pitting and erosion phenomena did not appear on the plated surface.

The effect of post-weld heat treatment affecting corrosion resistance and hydrogen embrittlement of HAZ part in FCAW

Evaluation of corrosion resistance of material surface was investigated with electrochemical factors, such as corrosion potential, corrosion current density with parameters of as-welded, post-weld heat treatment (PWHT) of 550, 600, 650 °C for a RE36 steel and mechanical properties such as elongation, hydrogen embrittlement and analysis of SEM fractography were also investigated with slow strain rate test (SSRT) method with applied constant cathodic potential in case of as-welded and PWHT of 550 °C. An optimum temperature for corrosion resistance improvement was apparently observed at 550 °C of PWHT and elongation was also increased with PWHT of 550 °C than that of as-welded condition. Therefore, the susceptibility of hydrogen embrittlement was considered to be decreased with PWHT of 550 °C compared to that of as-welded condition and to be increased according to potential shifting in the low direction.

Effect of W/C ratio and cover thickness on polarization characteristics of embedded steel in mortar

Abstract The effects of cover thickness and W/C (water-to-cement) ratio on polarization properties of embedded steel bar were investigated with electrochemical methods. Corrosion potentials shift to the noble direction with increasing the cover thickness. In addition, when the cover thickness increasingly becomes thinner and thinner, effect of the W/C ratio on variation of corrosion potential increases as well. Impedance value at 100 kHz indicating the resistance of cover thickness increases with the decrement of W/C ratio as well as the increment of cover thickness. However, in the case of W/C ratio at 0.6, impedance at 10 mHz shows the relatively larger value than that at W/C ratio of 0.4 or 0.5 in the range of cover thickness from 4 to 8 cm, which is probably expected that oxide film built up on the surface of steel bar due to strong alkali environment by hydration reaction with increasing W/C ratio is performed as the resistance polarization. It is also observed that liquid junction potential tends to increase with decreasing W/C ratio.

The effect of additives on the corrosion resistance of Zn electrode in alkaline battery system

Zn electrodes are widely used as an anode material in alkaline battery systems in highly concentrated KOH electrolyte. However, it is well known that their life cycle is significantly shortened due to dendrite growth caused by high dissolution and rapid electrochemical reaction. In this study, additives such as Ca(OH)£σ, citrate, tartrate, and gluconate were added to 40% KOH electrolyte solution at 25 and 5 wt.% Pb3O4 was mixed with the Zn electrode. The effects of both Pb3O4 and the additives on the electrochemical behavior of the Zn electrode were investigated through corrosion potential measurements, potentiodynamic polarization curves, cyclic voltammetry, and SEM photographs. The addition of Pb3O4 had a considerable effect on decreasing the corrosion rate of the Zn electrode, and the corrosion potential of the Zn electrode with Pb3O4 addition shifted to a more positive potential than that of a pure Zn electrode. However, upon addition of other additives, the corrosion potential was slightly shifted to the negative direction again. The addition of 4 kinds of additives appeared to play an important role in improving the corrosion resistance. Moreover, among the four additives, tartrate displayed a relatively good effect in terms of increasing the corrosion resistance as well as improving the discharging characteristics among.

Evaluation of Corrosion Property of Welding Zone of Stainless Steel by Laser Welding

*Department of Marine Equipment Engineering, Korea Maritime Uni versity, Pusan, Korea**Department of Marine System Engineering, Korea Maritime Unive rsity, Pusan, Korea***Education and Research Division, Korea Institute of Maritime and Fisheries Technology. Pusan, KoreaKEY WORDS: Laser welding 레이저용접, Intergranular corrosion 입계부식, Weld metal 용접금속, Heat affected zone 열영향부, Corrosion current density 부식전류밀도, Chromium depletion 크롬결핍ABSTRACT: Laser welding was carried out on austenitic 304 (STS 304) and 2 2 APU stainless steels. In this case, the differences between t he corrosion characteristics of the welding zones of the two stain less steels were investigated using electrochemical methods. Th e Vickers hardness values of the weld metal (WM) zones in both cases, the STS 304 and 22 APU stainless steels, showed relatively higher values th an those of other welding zones. The corrosion current densities of the heat affe cted zone (HAZ) of the 22 APU and the base metal (BM) zone of t he STS 304 exhibited the highest values compared to the other welding zone s. It is generally accepted that when STS 304 stainless steel i s welded using a general welding method, intergranular corrosion is often observ ed at the grain boundary because of its chromium depletion area . However, when laser welding was performed on both the STS 304 and 22 APU stai nless steels, no intergranular corrosion was observed at any of the welding zones. Consequently, it is considered that the intergranular co rrosion of stainless steel can be controlled with the application of laser welding.교신저자 김진경: 부산광역시 영도구 동삼동 1125번지, 051-620-5791, jg21kim@naver.com

Evaluation of Corrosion Characteristics of Underwater Hardening Paint

*Dept. of Marine Equipment Engineering, Korea Maritime Univ., Busan, Korea**Dept. of Marine System Engineering, Korea Maritime Univ., Bus an, KoreaKEY WORDS: Corrosion resistance 내식성, Underwater hardening paints 수중경화형도료, Electrochemical methods 전기화학적방법, Resin series 수지계열, Diffusion limiting current density 확산한계전류밀도ABSTRACT: Many protection methods such as surface coating, electric protection, or other methods have been applied to the numerous steel structures widely used in continental and marine areas to control their corrosion, which is done from an economic point of vie w. Most of these steel structures are primarily protected by coating methods. However, some steel piles under seawater are protected by the ele ctric protection method, that is, either using an impressed current or a sacrifi cial anode method. Furthermore, environmental contamination may cause a severely corrosive environment, which, in turn, causes the accelerated corrosion of steel structures. Subsequently, coated steel structures could deteriorate more rapidly than the designed lifetime because of the acid rain caused by air pollution, etc. Therefore, a coatin g of marine paint exposed to seawater, that is, underwater hardening painting, is increasingly required to be fast drying as well as highly corr osion resistant. In this study, five types of underwater hardening paints were prepared with different resin series and additives. Their corrosion and water resistances were investigated using electrochemical methods such as corrosion potential, polarization curves, impedance and cyclic voltammogram measurements, etc. Even though it is generally acc epted that the corrosion resistance of bare steel tends to incr ease with a shift of the corrosion potential in the noble direction, the corrosio n resistance of a sample with a coating exhibited a relatively better tendency when it had a lower corrosion potential in this study. The corrosion current density was also decreased with a decrease in the diffusion limiting current density, which may mean that there is some relationship between corrosion and water resistance. The S sample of the ceramic resin series showed the relatively best corrosion and water resistance among those of samples, while the worst corrosion and water r esistance were observed for the R sample of the epoxy resin series. The corrosion and water resistance of those samples tended to deteriorate with an increase in the immersion days, and their corrosion and water resistance s were considered to be apparently improved by the types of resin and additives.교신저자 김윤해: 부산광역시 영도구 동삼2동, 051-410-4355, yunheak@hhu.ac.kr