The Growth of Ferrous Sulfide on Iron

The rate of growth of ferrous sulfide on iron in sulfur vapor was studied between 650 and 900 C with sulfur vapor pressures between 10 and 500 mm of mercury. When differences in conditions are taken into account, the rates seem to be substantially higher than those found by Hiauffe and Rahmel. The behavior of inert markers and the sulfidation of eutectic mixtures of iron and ferrous sulfide indicate that the iron ion is much more mobile in ferrous sulfide than is the sulfide ion. Self-diffusion coefficients for the iron ions were calculated approximately, assuming that Wagner’s theory of scale growth is applicable. The markers were often found a considerable distance from their expected location at the metal- sulfide interface. This has been attributed to cracking at the interface in some cases and to interference with growth by the markers in other cases. It has been shown that nonreactive inclusions slow down the rate of sulfidation. 3.2.3