Molecular mechanism of the sulfide corrosion of α-iron

The reaction between aqueous sulfide and α-iron at ambient temperatures produces a ferrous monosulfide with a tetragonal mackinawite structure, FeS _m. The reaction is epitactic with the Fe structure in FeS _m being similar, but not identical, to the Fe structure in α-iron. The strain induced by these small structural differences results in spallation of the FeS _m product. This causes the exposure of new α-iron sites and determines the rate of sulfide corrosion of α-iron. The results provide a fundamental explanation for the real-world observation that pitting of steel pipes in sulfide environments is a major source of corrosion and pipe failure.