2013 Volume 62 Issue 3 Pages 122-128
The iodine-sulfur thermochemical cycle for hydrogen production takes place in very harsh environments. Structural metallic materials for the hydrogen-iodide decomposition are exposed in the high-temperature halogen corrosion and the hydrogen embrittlement environment. To evaluate adaptability of the materials, corrosion rates and mechanical properties (the yield strength, the tensile strength, and the elongation) were measured. Prepared test specimens were exposed to ambient gas consisting of HI, I2, H2O and H2 (molar fraction, 1：1：6：0.16) at 450℃ for 1000 hours at the atmospheric pressure. After the exposure, the corrosion rates were obtained by the weight loss of each specimen. Nickel-based alloys (Hastelly C-276, MAT21, Inconel 625) exhibited appropriate corrosion resistance (＜0.03 g m−2h−1). In addition, no degradations of the mechanical properties for the MAT21 and the Inconel 625 were observed. The specimens of tantalum and titanium showed the hydrogen embrittlement ; the specimens of zirconium and niobium exhibited poor corrosion resistance. The specimens of molybdenum (Mo) exhibited good corrosion resistance, however strength degradation of Mo is causing concern. As the results, the nickelbased alloys are well suited for the structural materials within this environment from the viewpoint of the corrosion resistance. MAT21 among them is the outstanding material with an eye to its corrosion resistance and mechanical properties.
