In order to investigate the effect of pH on the dissolution behavior of iron from stainless steel bipolar plates for PEFC, type 304 stainless steel was polarized in the sulfuric acid solutions of pHs 3.0 and 3.2 for 100 h at 0.6 V （vs. Ag/AgCl）, and the amount of dissolved metallic ions was determined by ICP-MS. In the solution of pH 3.2, more than 90％ of the anodized iron was deposited on the stainless steel surface as corrosion products, whereas about 75％ of the anodized iron was dissolved in the solution of pH 3.0. These results suggest that the contamination of MEA by the dissolved iron is more concerned when the pH of the environment becomes lower than 3.0, while the increase in interfacial contact resistance is rather concerned when the pH is higher than 3.2.
The corrosion behavior of pure aluminum in the dilute sodium fluoride and sodium sulfate solutions as simulating the PEMFC environment was studied through immersion process at different time. The corrosion was accelerated in the presence of fluoride ions whereas sulfate ions caused very less amount of corrosion. The electrochemical measurement, SEM and EDX analyses were carried out to examine the corrosion resistance, surface morphology and elemental compositions, respectively.
Corrosion resistance of stainless steels and Ni-based alloys were evaluated in a sulfuric acid decomposition gas at high temperature. The evaluation were carried out in an environment simulated in the sulfuric acid decomposition reaction vessel for thermochemical hydrogen production process （IS process）. Their corrosion films were also analyzed for better understanding of the corrosion behavior. As a result, after 100 hour corrosion test, Ni-based alloy containing 2.4％ Si showed good corrosion resistance. Ferritic stainless steel containing 3％ Al （3Al-Ferrite） showed better corrosion resistance. Its corrosion rate was lower than that of SiC （0.1 mm/year）, which is a candidate material for the sulfuric acid decomposition reaction vessel. On the other hand, Ni-based alloy pre-filmed with Al2O3 is prepared as the relative corrosion film of 3Al-Ferrite. Its corrosion rate was significantly higher than that of 3Al-Ferrite. As the result of EPMA analysis of these oxide films, Ni-based alloy containing 2.4％ Si formed Si oxide film which had some cracks after the long term corrosion test. Therefore S penetrated into grain boundaries of the matrix through the oxide film. 3Al-Ferrite formed a thin and uniform Al2O3 film, and the penetration of S into the grain boundaries was not observed. Al2O3 pre-film of Ni-based alloy also showed S penetration in the matrix because the Al2O3 pre-film had many small defects originally. The corrosion oxide film of 3Al-Ferrite was compared to the pre-film of Ni-based alloy using XRD. The corrosion oxide film of 3Al-Ferrite consisted of only α-Al2O3, while the Al2O3 pre-film consist of α-Al2O3 and γ-Al2O3. Those results suggest that the better corrosion resistance of 3Al-Ferrite is due to the uniform formation of dense α-Al2O3 film at the early stage of the corrosion.
This paper is the comprehensive paper on the crevice corrosion mechanism for stainless steels by using the newest in-situ instruments. The in-situ observation apparatus, the in-situ semiconductor pH sensor and the in-situ raman spectroscopy were applied to the study of the crevice corrosion behavior of stainless steels in Cl－ solution. The propagation of crevice corrosion was divided to 4 stages of Stage I～Stage IV. The propagation behavior in these Stages was closely related to the hydration and the formation of metal coordination compounds （hydrolysis and chlorido complex ions）. The reppassivation of crevice corrosion was achieved by the pH raise resulting from hydrogen generation in the crevice as cathodic reaction. Furthermore, it was cleared that the initiation of crevice corrosion was caused by the metastable pitting in the crevice.
The new evalutation methods on the initiation and propagation of crevice corrosion were proposed.