Growth of the Iron Sulfide  ( Fe1 − δ  S  )  Scale on Iron at Temperatures 600°–1000°C

Abstract

Measurements of the parabolic sulfidation kinetics were carried out at sulfur pressures ranging from i0 -Iz to 10 -2 arm and at temperatures in the range 600~176The effect of sulfur activity on these kinetics is most pronounced at low sulfur pressures. Temperature exhibits the largest influence on these kinetics at high sulfur pressures. An expression is derived for the parabolic rational rate constant in terms of the chemical diffusivity and nonstoichiometry of iron sulfide using the Wagner equation for scaling by iron diffusion and the Libowitz point defect model involving a strong repulsive interaction between iron vacancies to relate nonstoichiometry to sulfur pressure. The predicted values for these rate constants were in good agreement with those found experimentally. A comparison of available results on the parabolic scaling rates at sulfur pressures ranging up to 1 atm suggests that a transition in scale texture with sulfur pressure influences the sulfidation rates since iron diffusion is more rapid in the "c" than in the "a" crystallographic direction of iron sulfide.

Magnetic diffusion anomaly at the Néel temperature of pyrrhotite, Fe1−xS

“…The best-fit error function solutions are overlaid on top of experimental data with a range of uncertainty in Fig.4. †Increased diffusion activation energy from spontaneous magnetizationValues of *D Fe obtained from error function fitting are shown in Arrhenius form in Fig.5, alongside representative literature results from Fryt et al10 and Condit et al,14 whose data are also displayed in Fig.1. † We include for comparison only those data corresponding to the stoichiometry range 0.03 r x r 0.1 in Fe 1Àx S, which is close to the composition of our samples analyzed via SIMS.…”

“…Fig.5Values for iron self-diffusion coefficient *D Fe results obtained in this work are compared to data from Fryt et al10 and Condit et al14 The known magnetostructural ordering (Ne ´el) temperature T N of 316 1C is indicated with a dashed line. Above T N the activation energy slope in the paramagnetic state is Q P = 0.83 AE 0.03 eV.…”

“…Vacancy-vacancy interactions further lead to the formation of composition-dependent, ordered superstructures at low temperatures that govern overall, macroscopic magnetic properties. 9 Previous measurements of Fe self-diffusion *D Fe in paramagnetic Fe 1Àx S have been carried out by several authors using thermogravimetric [10][11][12] and radiotracer 13,14 methods, as compiled in Fig. 1a.…”

Evolution of Scale Microstructure and the Pressure Dependence of the Sulfidation Rate of Iron

“…The Fe/S ratio is known as a function of Sulfur pressure for this material, see Fryt et aZ. (1). When iron specimens were sulfidized to completion in our apparatus at the pressures used in our study, the Fe/S ratios compiled and reported by Fryt et aI.…”

Metallic, oxygen-containing reaction products after polarisation of iron in H2S saturated saline solutions

“…This result is in agreement with results of the electrochemical experiments: the anodic branch of the linear polarisation experiments does not show formation of a protective layer (though layer formation clearly takes place), and the charge transfer resistance determined by EIS is low. Indeed, several studies have shown that FeS films behave as metallic conductors [62,5]. Computational studies of mackinawite also indicate a metallic behaviour for at least one spin channel [63][64][65][66].…”