• Journal of Advanced Marine Engineering and Technology
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• v.38 no.4
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• pp.409-417
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• 2014

Since the oil price has been significantly jumped for recent some years, the diesel engine of the merchant ship has been mainly used the heavy oil of low quality. Thus, it has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas in a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of most parts surrounded with combustion chamber is more serious compared to the other parts of the engine. Therefore, an optimum weldment for these parts is very important to prolong their lifetime in a economical point of view. In this study, four types of filler metals such as Inconel 625, 718, 1.25Cr-0.5Mo and 0.5Mo were welded with SMAW and GTAW methods in the forged steel which would be generally used with piston crown material. And the corrosion properties of weld metal, heat affected zone and base metal were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H2SO4 solution. The weld metal and base metal exhibited the best and worst corrosion resistance in all cases of filler metals. In particular, the weld metal welded with filler metals of Inconel 718 revealed the best corrosion resistance among the filler metals, and Inconel 625 followed the Inconel 718. Hardness relatively indicated higher value in the weld metal compared to the base metal. Furthermore, Inconel 625 and 718 indicated higher values of hardness compared to 1.25cr-0.5Mo and 0,5Mo filler metals in the weld metal.

• Korean Journal of Metals and Materials
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• v.47 no.2
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• pp.129-137
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• 2009

Corrosion behaviors of TiN coated dental casting alloys have been researched by using various electrochemical methods. Three casting alloys (Alloy 1: 63Co-27Cr-5.5Mo, Alloy 2: 63Ni-16Cr-5Mo, Alloy 3: 63Co-30Cr-5Mo) were prepared for fabricating partial denture frameworks with various casting methods; centrifugal casting(CF), high frequency induction casting(HFI) and vacuum pressure casting(VP). The specimens were coated with TiN film by RF-magnetron sputtering method. The corrosion behaviors were investigated using potentiostat (EG&G Co, 263A. USA) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The corrosion morphologies were analyzed using FE-SEM and EDX. Alloy 1 and Alloy 2 showed the ${\alpha}-Co$ and ${\varepsilon}-Co$ phase on the matrix, and it was disappeared in case of TiN coated Alloy 1 and 2. In the Alloy 3, $Ni_2Cr$ second phases were appeared at matrix. Corrosion potentials of TiN coated alloy were higher than that of non-coated alloy, but current density at passive region of TiN coated alloy was lower than that of non-coated alloy. Pitting corrosion resistances were increased in the order of centrifugal casting, high frequency induction casting and vacuum pressure casting method from cyclic potentiodynamic polarization test.

• Bulletin of the Korean Chemical Society
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• v.27 no.3
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• pp.403-406
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• 2006

The surface structure and electrochemical behavior of self-assembled monolayers (SAMs) formed by aromatic thiols on Au(111) were investigated by scanning tunneling microscopy (STM) and cyclic voltammetry. Benzenethiol (BT) forms disordered phases on Au(111) which are composed of many bright domains, while benzyl mercaptan (BM), with a methylene unit between the aromatic group and sulfur atom, forms twodimensional ordered SAMs on Au(111). In addition, two phase-separated domains consisting of disordered and ordered phases were observed in binary SAMs formed from a 1 : 1 mixed ethanol solution of BT and BM. From STM and CV measurements, we found that the blocking efficiency of aromatic thiol SAMs coated on an Au(111) electrode for an electron transfer reaction decreases as the structural order of the SAMs increases. Molecular-scale STM and CV results obtained here will be very useful in designing functional SAMs for further applications, such as the improvement of corrosion passivation of Au(111) on an aromatic thiolmodified Au(111) surface.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.193-196
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• 2006

This paper presents the results of catalytic endo- to exo- isomerization of saturated poly cyclic compound. Several zeolites were tested and influences of, Si/Al ratio and Structures of the zeolites on the reaction were investigated. The results showed that Y zeolites were more active than other zeolites, because of its large pore size and relative strong acidity. In all Y zeolites with different Si/Al, Y-5.4 is best. In all the zeolites tested, Y calcined at $450^{\circ}C$ was favorable. Still now the aluminium chloride catalyst is more active than zeolites. However, considering of environmental problems, corrosion, and treatment can make the zeolite catalyst substitute the aluminium chloride catalyst.

• Journal of the Korean institute of surface engineering
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• v.28 no.6
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• pp.333-342
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• 1995

Stainless steels are widely selected as commercial engineering materials mainly because of their excellent corrosion resistance, oxidation resistance and strength. Because the manufacturing temperature of stainless steels is relatively high, the chemical and physical properties of the oxide film which was formed on the stainless steels are of importance in determining the rate of oxidation and the life of equipment exposed to high temperature oxidizing environments. In this study, the oxidation behavior of S. S. 304 and S. S. 430 added by a small amount of oxygen active elements(each +0.5wt% Hf and Y) was studied to improve oxidation resistance. The results of cyclic and isothermal oxidation on S. S. 304 added by OAE showed relatively poor oxidation resistance due to spallations and cracks of $Cr_2O_3$ layer. But all S. S. 430+0.5wt% OAE maintained constant oxidation rates and stable oxide layers at high temperature environment. Especially S. S. 430+0.5wt% Y formed a $Cr_2O_3$ oxide layer and improved cyclic oxidation resistance preventing loss of protective layers about 1000 hours at $1000^{\circ}C$

• Corrosion Science and Technology
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• v.6 no.4
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• pp.198-205
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• 2007

The initial stages of electrochemical oxidative CuI film formation on Cu(111), as studied by means of Cyclic Voltammetry (CV), in-situ Scanning Tunneling Microscopy (STM) and ex-situ Synchrotron X-ray Photoemission Spectroscopy (SXPS), indicate a significant acceleration of copper oxidation in the presence of iodide anions in the electrolyte. A surface confined supersaturation with mobile CuI monomers first leads to the formation of a 2D-CuI film via nucleation and growth of a Cu/I-bilayer on-top of a pre-adsorbed iodide monolayer. Structurally, this 2D-CuI film is closely related to the (111) plane of crystalline CuI (zinc blende type). Interestingly, this film causes no significant passivation of the copper surface. In an advanced stage of copper dissolution a transition from the 2D- to a 3D-CuI growth mode can be observed.

• Corrosion Science and Technology
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• v.6 no.4
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• pp.177-185
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• 2007

The purpose of this study is to evaluate freezing-thawing and surface scaling resistance in order to examine the frost durability of concrete in a chloride-inherent environment. The mixing design for this study is as follows: 3 water binder ratios of 0.37, 0.42, and 0.47; 2-ingredient type concrete (50% OPC concrete and 50% ground granulated blast-furnace slag), and 3-ingredient type concrete (50% OPC concrete, 15% fly ash, and 35% ground granulated blast-furnace slag). As found in this study, the decrease of durability was much more noticeable in combined deterioration through both salt damage and frost damage than in a single deterioration through either ofthese; when using blast-furnace slag in freezing-thawing seawater, the frost durability and surface deterioration resistance was evaluated as higher than when using OPC concrete. BF 50% concrete, especially, rather than BFS35%+FA15%, had a notable effect on resistance to chloride penetration and freezing/expansion. It has been confirmed that surface deterioration can be evaluated through a quantitative analysis of scaling, calculated from concrete's underwater weight and surface-dry weight as affected by the freezing-thawing of seawater.

• Corrosion Science and Technology
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• v.15 no.3
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• pp.129-134
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• 2016

The effects of Ti on the high temperature oxidation of Ni-based superalloys were investigated by cyclic oxidation at $850^{\circ}C$ and $1000^{\circ}C$. The oxide scale formed at $850^{\circ}C$ consists of $Cr_2O_3$, $Al_2O_3$, and $NiCr_2O_4$ layers, while a continuous $Al_2O_3$ layer was formed at $1000^{\circ}C$. The oxidation rate of the alloy with higher Ti content was higher than the alloy with less Ti content at $850^{\circ}C$, possibly due to the increase in the metal vacancy concentration in the $Cr_2O_3$ layer involved by incorporation of $Ti^{4+}$. However, Ti improved the oxidation resistance of the superalloy at $1000^{\circ}C$ by reducing oxygen vacancy concentration in $Al_2O_3$ layer.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.157-166
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• 2005

This article involves architecting prototype-fuzzy expert system for designing the nominal cover thickness by means of fuzzy inference for quantitatively representing the environment affecting factor to reinforced concrete in chloride-induced corrosion environment. In this work, nominal cover thickness to reinforcement in concrete was determined by the sum of minimum cover thickness and tolerance to that defined from skill level, constructability and the significance of member. Several variables defining the quality of concrete and environment affecting factor (EAF) including relative humidity, temperature, cyclic wet and dry, and the distance from coast were treated as fuzzy variables. To qualify EAF the environment conditions of cycle degree of wet-dry, relative humidity, distance from coast and temperature were used as input variables. To determine the nominal cover thickness a qualified EAF, concrete grade, and water-cement ratio were used. The membership functions of each fuzzy variable were generated from the engineering knowledge and intuition based on some references as well as some international codes of practice.

• Journal of the Korean Chemical Society
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• v.18 no.6
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• pp.391-399
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• 1974

Corrosion and passivation of metallic cobalt was studied by means of electrochemical experiments including potentiostatic and galvanostatic measurements and cyclic voltammograms. The mechanisms of active dissolution and passivation of cobalt at the metal/borate buffer solution interface are deduced from the Tafel slope, pH dependence of the Flade potential, and dissolution kinetic data. Hydroxyl group adsorbed on cobalt surface seems to participate in surface oxidation and formation of the passive layer. The growth kinetic data as measured by the current density suggests a mechanism in which the growth of the passive layer is determined by field-assisted transport of ions through the layer. Thickness of the passive layer was estimated by coulometry to be about 10${\AA}$ at the lowest passive potential and to grow gradually with anodic potential to about 20${\AA}$.