Abstract
The corrosion resistances of Fe-Cr-Ni alloys in high temperature gases composed of iodine and oxygen have been investigated in order to develop the construction materials for the second stage reaction of the magnesium-iodine thermochemical cycle. The results obtained are summarised as follows; (1) The corrosion of Fe-Cr-Ni alloys is appreciably accerelated by coexistence of I2 and O2 gases. (2) Cr is the most predominant alloying element that improves the corrosion resistance of Fe-Cr-Ni alloys, and this beneficial effect of Cr is considered to be related to the formation of the protective layer of chromium oxide. (3) The corrosion resistance of 25Cr-20Ni steel, which has been selected as the most practical material, can be improved by the alloying of small amounts of Si+Al, Y or Ca. For example, the tendency toward uneven attack of 25Cr-20Ni steel was appreciably reduced. The effect of such alloying elements may be attributed to the characteristics of protective layer improved. (4) The addition of H2O vapor (up to 10vol. %) to the gas mixture of I2 and O2 and the deposit of Mg(IO3)2 on the metal surface have little influence on the depression of the corrosion resistances of 25Cr-20Ni steels.
