• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.896-903
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• 2002

The susceptibility of SCC for the weldment and PWHT specimens of HT-60 steel was evaluated using a slow strain rate method under applied potential by means of the potentiostat in synthetic seawater. In case of the parent, anodic polarization voltage was inappropriate in elongating the time to failure(TTF). -0.8V corresponding to cathodic protection range is most effective in improving the SCC resistance against corrosive environment. In case of the weldment, the values of reduction of area(ROA) and TTF at -0.68V corresponding to cathodic polarization value were 45.2% and 715,809sec which were the largest and longest life among other applied potentials. Those were vise versa at -1.1V. In case of the PWHT specimens, TTF and ROA at -0.68V was longest and largest like the weldment. Besides, PWHT is effective in prolonging the time to failure of the welded off-shore structure due to softening of effect. Regardless of the weldment and PWHT specimen, as corrosion rate gets higher, TTF becomes shorter and deformation behaviour for the weldment and PWHT specimen at -1.1V was shown to be irregular. Finally, it was found that specimens showed brittle fracture at -1.1V, but more ductile fracture accompanying the micro-cracks at applied potential of -0.68V.

• Journal of the Korean institute of surface engineering
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• v.43 no.1
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• pp.17-24
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• 2010

In this study, surface characteristics of dental implant fixture with various manufacturing process have been researched using electrochemical methods. The dental implant fixture was selected with 5 steps by cleaning, surface treatment and sterilization with same size and screw structure; the 1st step-machined surface, 2nd step-cleaned by thinner and prosol solution, 3th step-surface treated by RBM (resorbable blasting media) method, 4th step-cleaned and dried, 5th step-sterilized by gamma-ray. The electrochemical behavior of dental implant fixture has been evaluated by using potentiostat (EG&G Co, 2273A) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The corrosion surface was observed using field-emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDS). The step 5 sample showed the cleaner and rougher surface than step 3 sample. The step 5 sample of implant fixture treated by RBM and gamma sterilization showed the low corrosion current density compared to others. Especially, the step 3 sample of implant fixture treated by RBM was presented the lowest value of corrosion resistance and the highest value of corrosion current density. The step 3 sample showed the low value of polarization resistance compared to other samples. In conclusion, the implant fixture treated with RBM and gamma sterilization has the higher corrosion resistance, and corrosion resistance depends on the step of manufacturing process.

• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.202-210
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• 2016

This study was intended to investigate the effect of the amount of magnesium addition and heat treatment in the Al-Mg coating film in order to improve corrosion resistance of aluminum coating. Al-Mg alloy films were deposited on cold rolled steel by physical vapor deposition sputtering method. Heat treatment was fulfilled in an nitrogen atmosphere at the temperature of $400^{\circ}C$ for 10 min. The morphology was observed by SEM, component and phase of the deposited films were investigated by using GDLS and XRD, respectively. The corrosion behaviors of Al-Mg films were estimated by exposing salt spray test at 5 wt.% NaCl solution and measuring polarization curves in deaerated 3 wt.% NaCl solution. With the increase of magnesium content, the morphology of the deposited Al-Mg films changed from columnar to featureless structure and particle size was became fine. The x-ray diffraction data for deposited Al-Mg films showed only pure Al peaks. However, Al-Mg alloy peaks such as $Al_3Mg_2$ and $Al_{12}Mg_{17}$ were formed after heat treatment. All the sputtered Al-Mg films obviously showed good corrosion resistance compared with aluminum and zinc films. And corrosion resistance of Al-Mg film was increased after heat treatment.

• Corrosion Science and Technology
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• v.8 no.4
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• pp.162-169
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• 2009

Pure titanium and its alloys are drastically used in implant materials due to their excellent mechanical properties, high corrosion resistance and good biocompatibility. However, the widely used Ti-6Al-4V is found to release toxic ions (Al and V) into the body, leading to undesirable long-term effects. Ti-6Al-4V has much higher elastic modulus than cortical bone. Therefore, titanium alloys with low elastic modulus have been developed as biomaterials to minimize stress shielding. For this reason, Ti-30Ta-xZr alloy systems have been studied in this study. The Ti-30Ta containing Zr(5, 10 and 15 wt%) were 10 times melted to improve chemical homogeneity by using a vacuum furnace and then homogenized for 24 hrs at $1000^{\circ}C$. The specimens were cut and polished for corrosion test and Ti coating and then coated with TiN, respectively, by using DC magnetron sputtering method. The analyses of coated surface were carried out by field emission scanning electron microscope(FE-SEM). The electrochemical characteristics were examined using potentiodynamic (- 1500 mV~+ 2000 mV) and AC impedance spectroscopy(100 kHz~10 mHz) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The equiaxed structure was changed to needle-like structure with increasing Zr content. The surface defects and structures were covered with TiN/Ti coated layer. From the polarization behavior in 0.9% NaCl solution, The corrosion current density of Ti-30Ta-xZr alloys decreased as Zr content increased, whereas, the corrosion potential of Ti-30Ta-xZr alloys increased as Zr content increased. The corrosion resistance of TiN/Ti-coated Ti-30Ta-xZr alloys were higher than that of the TiN-coated Ti-30Ta-xZr alloys. From the AC impedance in 0.9% NaCl solution, polarization resistance($R_p$) value of TiN/Ti coated Ti-30Ta-xZr alloys showed higher than that of TiN-coated Ti-30Ta-xZr alloys.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.245-253
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• 2009

The importance of chloride ions in the corrosion of steel in concrete has led to the concept for chloride threshold level (CTL). The CTL can be defined as the content of chlorides at the steel depth that is necessary to sustain local passive film breakdown and hence initiate the corrosion process. Despite the importance of the CTL, due to the uncertainty determining the actual limits in various environments for chloride-induced corrosion, conservative values such as 0.4% by weight of cement or 1.2 kg in 1 $m^3$ concrete have been used in predicting the corrosion-free service life of reinforced concrete structures. The paper studies the CTL for blended cement concrete by comparing the resistance of cementitious binder to the onset of chloride-induced corrosion of steel. Mortar specimens were cast with centrally located steel rebar of 10 mm in diameter using cementitious mortars with ordinary Portland cement (OPC) and mixed mortars replaced with 30% pulverized fuel ash (PFA), 60% ground granulated blast furnace slag (GGBS) and 10% silica fume (SF), respectively, at 0.4 of a free W/B ratio. Chlorides were admixed in mixing water ranging 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binder(Based on $C1^-$). Specimens were curd 28 days at the room temperature, wrapped in polyethylene film to avoid leaching out of chloride and hydroxyl ions. Then the corrosion rate was measured using the polarization resistance method and the order of CTL for binder was determined. Thus, CTL of OPC, 60%GGBS, 30%PFA and 10%SF were determined by 1.6%, 0.45%, 0.8% and 2.15%, respectively.

• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.269-275
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• 2005

We analyzed the unit cell performance against the cathode porosity, which is supposed to be closely related with active sites for the cathode reaction. In order to fabricate the unit cells with different porosity in the cathode layer we changed the mixing ratio of fine and coarse LSCF cathode powders. The final porosity of each cathode layer was 14, 23, 27, $39\%$ respectively. According to the electrochemical analysis of unit cell performance via DC current interruption and AC impedance method, the electrodic polarization resistance was diminished as the cathode porosity increased. The decrease of polarization resistance was attributed due to the increase of active reaction sites and the enhancement of overall unit cell performance could be explained in the same line.

• Carbon letters
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• v.23
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• pp.22-29
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• 2017

The compressive strength and electrical resistance of pitch-based carbon fiber (CF) in cementitious materials are explored to determine the feasibility of its use as a functional material in construction. The most widely used CFs are manufactured from polyacrylonitrile (PAN-based CF). Alternatively, short CFs are obtained in an economical way using pitch as a precursor in a melt-blown process (pitch-based CF), which is cheaper and more eco-friendly method because this pitch-based CF is basically recycled from petroleum residue. In the construction field, PAN-based CFs in the form of fabric are used for rehabilitation purposes to reinforce concrete slabs and piers because of their high mechanical properties. However, studies have revealed that construction materials with pitch-based CF are not popular. This study explores the compressive strength and electrical resistances of a cement paste prism using pitch-based CF.

• Corrosion Science and Technology
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• v.6 no.5
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• pp.251-256
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• 2007

Plasma nitriding is a surface treatment process which is increasingly used to improve wear, fatigue and corrosion resistance of industrial parts. Active screen plasma nitriding (ASPN) has both the advantages of the classic cold wall and the hot wall conventional dc plasma nitriding (DCPN) method and the parts to be nitrided are no longer directly exposed to the plasma. In this study, AS plasma nitriding has been used to nitride the UNS S31803 duplex stainless steel, AISI 304 and AISI 316 austenitic stainless steel, and AISI 420 martensitic stainless steel. Treated specimenswere characterized by means of microstructural analysis, microhardness measurements and electrochemical tests in NaCl aerated solutions. Hardness of the nitride cases of AISI 420 stainless steel by Knoop test can get up to 1300 HK0.1. From polarization tests, the corrosion current densities of AISI 420 and UNS S31803specimens ASPN at $420^{\circ}C$ were generally lower than those of their untreated substrates. The corrosion resistance of UNS S31803 duplex stainless steel can be enhanced by plasma nitriding at $420^{\circ}C$ Cowing to the formation of the S-phase.

• Korean Membrane Journal
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• v.3 no.1
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• pp.17-23
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• 2001

Polyethersulfone (PES) and cellulose acetate (CA) ultrafiltration (UF) membranes having different molecular weight cut-off values were prepared by immersion precipitation method by changing the compositions of easting solution. Egg white solution was concentrated to volume concentration ratio 4 in tubular UF with membranes made of moderately hydrophobic PES and hydrophilic CA. The process Parameters such as pressure and fluid velocity were controlled in order to apply successfully for egg white solution and to investigate the pressure dependency. The resistance values were measured to investigate the fouling and concentration polarization effect on membrane performance. During concen- tration of egg white solution by UF, the fouling layer appeared to contribute little resistance to flux compared to that of polarized layer.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.22-25
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• 2008

In this study, calcium titanate $(CaTiO_3)$ gel was prepared by mixing calcium nitrate and titanium isopropoxide in 2-methoxy-ethanol. $CaTiO_3$ gel was single-layer coated on Ti-6Al-4V using a sol-gel dip-coating technique. The coating was calcined at $750^{\circ}C$ in air by utilizing a very slow heating rate of $2^{\circ}C/min$. The crystalline phases of the coating were characterized by x-ray diffraction using a slow scan rate of $1^{\circ}/min$. The morphology of the coating was analyzed by scanning electron microscopy. The corrosion behavior of Ti-6Al-4V samples coated with $CaTiO_3$ films were tested in an artificial saliva solution by potentiodynamic polarization and were quantified by the Tafel extrapolation method. The electrochemical parameters showed a considerable increase in the corrosion resistance for the $CaTiO_3$-coated Ti-6Al-4V samples compared to bare substrates.