Sulfuric acid corrosion behaviour of the materials for the NHDD project

Nuclear hydrogen development and demonstration (NHDD) has been an on-going project in Korea since 2004. Iodine sulfur (IS) process is one of the promising processes for a hydrogen production by using a high temperature heat generated by a very high temperature gas cooled reactor (VHTR) in the nuclear power industries. Even though the IS process is very efficient for a hydrogen production and it is not accompanied by a carbon dioxide evolution, the highly corrosive environment of the process limits an application of this process in the industry. Therefore corrosion tests of various materials were performed in sulfuric acid to select appropriate materials compatible with the IS process. The materials used in this work were Fe-Ni- Cr alloys, Fe-Si alloys, Ni base alloys, Ta, Au, Zr, SiC and so on. The test environments were boiling 50 wt% and 98 wt% sulfuric acids. Corrosion rates were measured by using the weight change after an immersion. The surface morphologies of the corroded materials were examined by using SEM equipped with EDS. Corrosion rates for various materials were supported by a potentiodynamic experiment. From the results of the weight loss and potentiodynamic experiments, it was found that a Si enriched oxide is attributable to the corrosion resistance concerning Fe-Si in boiling 98 wt% sulfuric acid. Au and SiC showed an excellent corrosion resistance in 98 wt% sulfuric acid while Ta showed a poor corrosion resistance. For the other materials, their corrosion behaviours are discussed in terms of weight loss, corrosion morphology and surface layer's composition. (authors)