Mechanism of high‐temperature sulphide corrosion of metals and alloys

Abstract

Sulfidation appears to be considerably more suitable than oxidation for studying the high-temperature behaviour of metals. Sulfide scales are formed at considerably higher rates and at lower temperatures, in addition it is much easier to work with the radioactive sulfide isotope. The experiments can be conducted in sulfur vapour or in hydrogen fhydrogen sulfide mixtures; differences are due only to different sulfur partial pressures. Sulfide scale is formed on pure metals (e. g. Cu, Ag, N i ) as well as in binary or ternary alloys. (e. g. FeNi, NiCr, CuZn, CoCr, FeCrAl) with consistantly reproducible results. Irrespective o f scale thickness and structure the reaction rates are always controlled by outward diffusion with the high defect concentration favouring high reaction rates. Since various metals tend to form low melting metalfmetal sulfide eutectics, it is necessary to keep temperatures below the particular melting point. Contrary to inner oxidation there is no inner sulfidation. The protective action o f sulfide scale is considerably inferior to that o f oxide scale. According to the results of the present compilation no material has become available which combines sufficient scaling resistance with good high-temperature mechanical properties. Solution of this problem may perhaps be found by adding rare earth metals.

Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

“…The absence of any increased sample weight gain between 1000 h and 5000 h for the Fe-12.5Al alloy was a surprising result. This alloy exhibited the greatest degree of iron sulfide formation of all three alloys at both 500 and 5000 h. The high deviation from stoichiometry of iron sulfide allows for rapid diffusion of sulfur or base metal ions through it at high temperatures [27] and the formation of this phase usually corresponds to rapid corrosion kinetics for iron aluminum alloys [28][29][30][31][32]. The fact that the weight gain for this alloy was essentially the same at both 1000 and 5000 h suggests that the scale that formed at 1000 h was in fact protective enough to prevent further significant corrosion with prolonged exposure time.…”

Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

“…The development of the different sulfides on the two 12.5 wt% aluminum has an important consequence on the corrosion resistance, since iron sulfide typically has a more defective structure than chromium sulfide. In a review of sulfidation of metals and alloys, Mrowec [10] reported that the maximum deviation from stoichiometry for FeS at 800°C is 0.2, while for Cr 2 S 3 at 700°C, it is 0.08. While there is a difference in temperature in the present work, and the stoichiometry of the sulfides formed here could not be determined, Mrowec's data indicates that iron sulfide will have a higher lattice defect concentration than chromium sulfide.…”

Sulphidation of Low-Alloyed Steels Used in Power Industry

“…Burning of coal containing sulphur often leads to the formation of sulphide scales on the high-temperature components. Such scales are much less protective than oxide scales, and metal sulphidation rates are much higher than oxidation rates [5][6][7][8]. Particular attention needs to be paid to the section where highly reducing atmospheres are formed.…”