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In order to investigate the corrosion resistance at the anode side separator for molten carbonate fuel cell, STS310S and SC-STS310S (chromium and aluminum were simultaneously deposited by diffusion into STS310S austenitic stainless steel substrate by pack-cementation process) were used as the separator material. In case of STS310S, corrosion proceeded via three steps; a formation step of corrosion product, a protection step against corrosion, an advance step of corrosion after breakaway. From the standpoint of the behavior of the elements in the specimen, Fe, Cr and Ni were formed richly in the region of corrosion product, in the region of corrosion protection, and at the Cr-deplete zone respectively. Especially, STS310S would be impossible to be used as a separator without suitable surface modification because of rapid corrosion rate after formation of corrosion product, making the severe problem on stability of cell during long-time operation. Whereas, SC-STS310S showed higher corrosion resistance than the present separator, STS310S. And SC-STS 310S can be expected to use for an alternative separator at the anode side by developing coating and pre-treatment process which can lead to dense coating layer and very high corrosion resistance respectively.

keyword : Separator, Molten carbonate fuel cell, Pack-cementation process, Corrosion resistance

In order to improve the low hardness and low wear resistance of Ti-6Al-4V alloy, plasma carburization treatment and CrN film coating was carried out. Effects of the plasma carburization and CrN coating were analyzed and compared with the non-treated alloy by microstructural observation, structural characterization and mechanical property test. The plasma carburization treated alloy formed a carburized layer of about 150 mm in depth from the surface, where a fine and hard particles of TiC and V₄C₃ were evenly homogeneously dispersed through the layer. CrN thin film thickness was about 7.5 mm and grew with (111) orientation. Hardness value of about Hv 402 in the matrix was improved as Hv 1,600, 1,390 by plasma carburization, CrN thin film, respectively. Roughness test is an important method to evaluate the surface treatment effect on the wear resistance. The optimum surface roughness of about 0.063 mm could be obtained by CrN film coated, while, about 0.321 mm and 0.211 ㎛ in the matrix and plasma carburization specimens, respectively.

keyword : Ti-6A1-4V alloy, Plasma-carburizing, CrN thin film, Hardness, Wear

The corrosion behavior of copper in neutral aerated synthetic tap water was investigated using electrochemical methods, SEM and XPS. All potentiodynamic polarization curves showed active corrosion behavior, and the corrosion rate was more sensitive to flow velocity than Cl^(-) ion concentration and temperature. The result of potentiostatic test indicated that the current density decreased with increasing time regardless of Cl^(-) ion concentration and temperature in stagnant condition because copper compounds were formed uniformly on the surface. The EIS plot was changed from two time constants to three time constants with the formation of Cu₂O, and the charge transfer resistance (R_(ct)) was very large and increased with increasing immersion time. From all results, copper had good corrosion resistance in this potable water system.

keyword : Copper, Tap water, Electrochemical methods, SEM, XPS, Copper oxide, Corrosion behavior

The aqueous corrosion characteristics of 1% Cr-steel alloyed with small amounts of Co and W, in synthetic seawater was studied by using immersion weight-loss tests, electrochemical corrosion tests (potentiodynamic test and electrochemical impedance spectroscopy (EIS) measurements) and analytical techniques. 1% Cr steels containing Co or W from 0.2 to 0.4 wt.% showed higher corrosion resistance than the 1% Cr steel in the immersion and potentiodynamic tests. EIS measurements showed that the Nyquist plot presented one time constant. Furthermore, the Co- and W-bearing steels present higher Rp values than the 1% Cr steel through all the test period. The better corrosion resistance of the Co-and W-bearing steels is attributed to protectiveness of the surface layer. The corrosion products were examined using electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). The results of EPMA indicated that Cr was concentrated in the inner region of the rust layer, while Co and W were distributed all over the rust layer. XPS results showed that Co existed as a trivalent oxide in the rust layer and W in the rust appeared in the form of a WO₄ compound.

keyword : Alloying element, Carbon steel, Seawater, EIS, Aqueous environments, Rust layer, Corrosion behavior

The effect of the accumulated annealing parameters on corrosion was investigated for the Zr-based alloy, whose Nb content was more than its solubility limit. From the corrosion tests, the corrosion resistance of the alloy decreased with the increase of the accumulated annealing parameter in all corrosion conditions. And it was observed that the size of the precipitates and the hydrogen pick-up fraction increased with increasing the accumulated parameter. The large precipitates induced the high corrosion rate because the large precipitates resulted in the early transformation of the oxide structure from t-ZrO₂ to m-ZrO₂ and oxide micro structure from columnar to equiaxed structure.

keyword : Zr, Accumulated annealing parameters, Corrosion resistance