한국부식방식학회

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Composite PEO-Coatings as Defence Against Corrosion and Wear: A Review
This paper reviews recent approaches to develop composite polymer-containing coatings by plasma electrolytic oxidation (PEO) using various low-molecular fractions of superdispersed polytetrafluoroethylene (SPTFE). The features of the unique approaches to form the composite polymer-containing coating on the surface of MA8 magnesium alloy were summarized. Improvement in the corrosion and tribological behavior of the polymer-containing coating can be attributed to the morphology and insulating properties of the surface layers and solid lubrication effect of the SPTFE particles. Such multifunctional coatings have high corrosion resistance (Rp = 3.0×107 Ω cm2) and low friction coefficient (0.13) under dry wear conditions. The effect of dispersity and x-potential of the nanoscale materials (ZrO2 and SiO2) used as electrolyte components for the plasma electrolytic oxidation on the composition and properties of the coatings was investigated. Improvement in the protective properties of the coatings with the incorporated nanoparticles was explained by the greater thickness of the protective layer, relatively low porosity, and the presence of narrow non-through pores. The impedance modulus measured at low frequency for the zirconia-containing layer (|Z|f=0.01 Hz = 1.8×106 Ω·cm2) was more than one order of magnitude higher than that of the PEO-coating formed in
the nanoparticles-free electrolyte (|Z|f=0.01 Hz = 5.4×104 Ω·cm2).
KEYWORDs : Protective coating, Plasma electrolytic oxidation, Nanoparticles
AUTHORs : S. V. Gnedenkov†, S. L. Sinebryukhov, V. I. Sergienko, and A. S. Gnedenkov

Page : 206 - 211 DOWNLOAD
Superhard SiC Thin Films with a Microstructure of Nanocolumnar Crystalline Grains and an Amorphous Intergranular Phase
Silicon carbide (SiC) thin films become superhard when they have microstructures of nanocolumnar crystalline grains (NCCG) with an intergranular amorphous SiC matrix. We investigated the role of ion bombardment and deposition temperature in forming the NCCG in SiC thin films. A direct-current (DC) unbalanced magnetron sputtering method was used with pure Ar as sputtering gas to deposit the SiC thin films at fixed target power of 200 W and chamber pressure of 0.4 Pa. The Ar ion bombardment of the deposited films was conducted by applying a negative DC bias voltage 0-100 V to the substrate during deposition. The deposition temperature was varied between room temperature and 450°C. Above a critical bias voltage of -80 V, the NCCG formed, whereas, below it, the SiC films were amorphous. Additionally, a minimum thermal energy (corresponding to a deposition temperature of 450°C in this study) was required for the NCCG formation. Transmission electron microscopy, Raman spectroscopy, and glancing angle X-ray diffraction analysis (GAXRD) were conducted to probe the samples’ structural characteristics. Of those methods, Raman spectroscopy was a particularly efficient non-destructive tool to analyze the formation of the SiC NCCG in the film, whereas GAXRD was insufficiently sensitive.
KEYWORDs : Silicon carbide, Nanocomposite structure, Hardness, Nanocolumnar crystalline grain, Amorphous matrix phase
AUTHORs : Kwan-Won Lim, Yong-Sub Sim, Joo-Youl Huh, Jong-Keuk Park, Wook-Seong Lee, and Young-Joon Baik†

Page : 196 - 205 DOWNLOAD
Effect of the Amplitude in Ultrasonic Nano-crystalline Surface Modification on the Corrosion Properties of Alloy 600
Surface modification techniques are known to improve SCC by adding large compressive residual stresses to metal surfaces. This surface modification technology is attracting attention because it is an economical and practical technology compared to the maintenance method of existing nuclear power plants. Surface modification techniques include laser, water jet and ultrasonic peening, pinning and ultrasonic Nano-crystal surface modification (UNSM). The focus of this study was on the effect of ultrasonic amplitude in UNSM treatment on the corrosion properties of Alloy 600. A microstructure analysis was conducted using an optical microscope (OM), scanning electron microscope (SEM) and electron backscattering diffraction (EBSD). A cyclic polarization test and AC-impedance measurement were both used to analyze the corrosion properties. UNSM treatment influences the corrosion resistance of Alloy 600 depending on its amplitude. Below the critical amplitude value, the pitting corrosion properties are improved by grain refinement and compressive residual stress, but above the critical amplitude value, crevices are formed by the formation of overlapped waves. These crevices act as corrosion initiators, reducing pitting corrosion resistance.
KEYWORDs : Alloy 600, UNSM, Amplitude, Corrosion, Electrochemical properties
AUTHORs : Ki Tae Kim and Young Sik Kim†

Page : 190 - 195 DOWNLOAD
Ni Plating Technology for PWR Reactor Vessel Cladding Repair
SA508 low-alloy steel for a reactor vessel was exposed to primary water in a pressurized water reactor (PWR) plant because the cladding layer of type 309 stainless steel for the RPV was removed, due to an accident in which the detachment of the thermal sleeve occurred. The major advantage of the electrochemical deposition (ECD) Ni plating technique is that the reactor pressure vessel can be repaired without significant thermal effects, and Ni has solid corrosion resistance that can withstand boric acid. The corrosion rate assessment of the damaged part was performed, and its trend was analyzed. Essential variables of the Ni plating for repair of the damaged part were derived. These conditions are applicable variables for the repair plating device, and have been carefully adjusted using the repair plating device. The process for establishing ASME technical standards called Code Case N-840 is described. The process of developing Ni-plating devices, and the electroplating procedure specification (EPS) are described.
KEYWORDs : ASME code, PWR, Low-alloy steel, Stainless steel cladding, Ni plating
AUTHORs : Seong Sik Hwang† and Dong Jin Kim

Page : 182 - 189 DOWNLOAD
Corrosion Resistance and Thermo-optical Properties of Lithium Polysilicate Spray Coated Anodized AZ31B Magnesium Alloy for Space Applications
A thin spray coating of inorganic black lithium polysilicate (IBLP) on black anodized AZ31B magnesium alloy was fabricated for better corrosion resistance and thermo-optical properties for thermal control of spacecraft components. The morphology of the specimens with and without IBLP-based spray coating was characterized by SEM-EDS techniques. Impedance and potentiodynamic measurements on the specimens revealed better corrosion resistance for the specimen with a thin coating of lithium polysilicate. This was primarily due to the presence of lithium polysilicate inside the micro-cracks of the black anodized specimen, restricting the diffusion paths for corrosive media. Environmental tests, namely, humidity, thermal cycling, thermo vacuum performance, were used to evaluate the space-worthiness of the coating. The thermo-optical properties of the coating were measured before and after each environmental test to ascertain its stability. The specimen with an IBLP-based spray coating showed enhanced thermo-optical properties, greater than ~0.90. Hence, the proposed coating demonstrated better handling, better corrosion resistance, and space-worthiness during the pre-launch phase owing to its improved thermo-optical properties.
KEYWORDs : Potentiodyamic polarization, Impedance spectroscopy, Magnesium alloy, Coatings, Lithium polysilicate
AUTHORs : Rahul Ghosh†, Hari K. Thota, and R. Uma Rani

Page : 175 - 181 DOWNLOAD
Investigation of Pellet-Clad Mechanical Interaction in Failed Spent PWR Fuel
A failed spent fuel rod with 53,000 MWd/tU from a nuclear power plant was characterized, and the fission products and oxygen layer in the pellet-clad mechanical interaction region were observed using an EPMA (Electron Probe Micro-Analyzer). A sound fuel rod burned under similar conditions was used to compare and analyze, the results of the failed fuel rod. In the failed fuel rod, the oxide layer represented 10 μm of the boundary of the cladding, and 35 μm of the region outside the cladding. By comparison, in the sound fuel rod, the oxide layer was 8 μm, observed in the cladding boundary region. The cladding inner surface corrosion and the resulting fuel-cladding bonding were investigated using an EPMA. Zirconium existed in the bonding layer of the (U, Zr)O compound beyond the pellet cladding interaction gap of 20 μm, and composition of UZr2O3 was observed in the failed fuel rod. This paper presents the results of the EPMA examination of a spent fuel specimen, and a technique to analyze fission products in the pellet-clad mechanical interaction region.
KEYWORDs : Pellet-clad mechanical interaction, A fission product, Hot-cell, Bonding layer
AUTHORs : Yang Hong Jung†and Seung Je Baik

Page : 168 - 174 DOWNLOAD
Enhanced Corrosion Protection Performance by Novel Inhibitor-Loaded Hybrid Sol-Gel Coatings on Mild Steel in 3.5% NaCl Medium
The sol-gel methodology has been applied successfully in the synthesis of a novel hybrid coating based on dimethoxymethyl-n-octadecylsilane precursor. The newly synthesized parent coating was functionalized further with two commercially-available corrosion-inhibitive pigments Moly-white® 101-ED and Hfucophos Zapp®, applied to mild steel panels, and immersed continuously in 3.5% NaCl electrolytic solution for 288 h. The corrosion protection performance of the prepared functional coatings was evaluated using electrochemical impedance spectroscopy (EIS) and DC polarization techniques. An enhancement in the barrier properties has been revealed from the electrochemical characterization data of the hybrid films, in comparison with untreated mild steel substrates following long-term immersion in 3.5% NaCl. The corrosion resistance properties of the newly developed coatings over mild steel substrates found to be largely dependent on the type of the loaded inhibitive pigment in which the Moly-white inhibitor has a positive impact on the corrosion protection performance of the parent coating, while an opposite behavior was observed upon mixing the base polymeric matrix with the commercially-available Zapp corrosion inhibitor.
KEYWORDs : Sol-gel, Coatings, Mild steel, Inhibitor, Impedance spectroscopy
AUTHORs : Rami K. Suleiman†

Page : 155 - 167 DOWNLOAD
Experimental Investigation and Quantum Chemical Calculations of Some (Chlorophenyl Isoxazol-5-yl) Methanol Derivatives as Inhibitors for Corrosion of Mild Steel in 1 M HCl Solution
In this study, two novel Schiff base compounds including (3-(4-Chlorophenyl isoxazole-5-yl) methanol and (3-(2,4 dichlorophenol isoxazole-5-yl) methanol as corrosion inhibitors for mild steel in 1 M hydrochloric acid solution were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and density functional theory (DFT) computations. The results showed that the corrosion inhibition efficiency (IE) is remarkably enhanced with the growing concentration of the Schiff base inhibitors. The results from Tafel polarization and EIS methods showed that IE decreases with gradual increments of temperature. This process can be attributed to the displacement of the adsorption/desorption balance and hence to the diminution of the level of a surface coating. Also, the adsorption of two inhibitors over mild steel followed the Langmuir adsorption isotherm. Too, the results of the scanning electron microscope (SEM) images showed that the Schiff base inhibitors form an excellent protective film over mild steel and verified the results by electrochemical techniques. Additionally, the results from the experimental and those from DFT computations are in excellent accordance.
KEYWORDs : Corrosion inhibitor, Mild steel surface, Hydrochloric acid solution, Electrochemical techniques, Density functional theory
AUTHORs : Rogayeh Sadeghzadeh, Ladan Ejlali, Moosa Es’haghi†, Hadi Basharnavaz, and Kambiz Seyyedi

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