Long-term corrosion resistance of Al-Ni-plated material and Al-plated material in molten carbonate environment

Al-Ni-plated material, which was produced by Ni and Al electroplating on a Type 310S stainless steel substrate followed by heat-treating at 1023 K, ha s been developed for the wee-seal material of MCFC. In order to compare the corrosion resistance of Al-Ni-plated material with that of Al-plated mater ial, which simulated the Al-sprayed material presently used as wet-seal mat erial, an immersion test was carried out in molten carbonate in 70% air-30% CO2 gas at 923 K for 14,500 h. Both Al-Ni-plated material and Al-plated ma terial showed good corrosion resistance during this test period. From the a nalyses of the surface, in cross-section, of these materials after the test , however, it was confirmed. that a large amount of Al in Al-Ni-plated mate rial was retained as an Al-Ni intermetallic compound under the LiAlO2 layer , while the Al in Al-plated material tended to diffuse from the surface int o the substrate during the test. It is suggested that the lifetime of the A l-Ni-plated material is longer than that of the Al-plated material, since A l-Ni intermetallic compounds in the Al-Ni-plated material provide a supply of Al to the LiAlO2 layer, the stability of which leads to prolonged corros ion resistance of the wet-seal material to molten the carbonate. Therefore, it is expected that the Al-Ni-plated material maintains a higher corrosion resistance, compared with the present material used for the wet-seal area of MCFC. (C) 2000 Elsevier Science S.A. All rights reserved.