Improvement of hydrogen permeation barrier performance by iron sulphide surface films

Fe-S compounds with hexagonal crystal structure are potential hydrogen permeation barrier during H2S corrosion. Hexagonal system Fe-S films were prepared on carbon steel through corrosion and CVD deposition, and the barrier effect of different Fe-S films on hydrogen permeation was tested using electrochemical hydrogen permeation method. After that, the electrical properties of Fe-S compound during phase transformation were measured using thermoelectric measurement system. Results show that the mackinawite has no obvious barrier effect on hydrogen penetration, as a p-type semiconductor, and pyrrhotite (including troilite) has obvious barrier effect on hydrogen penetration, as an n-type semiconductor. Hydrogen permeation tests showed peak permeation performance when the surface was deposited with a continuous film of pyrrhotite (Fe1-xS) and troilite. The FeS compounds suppressed hydrogen permeation by the promotion of the hydrogen evolution reaction, semiconducting inversion from p- to n-type, and the migration of ions at the interface.