The High Temperature Corrosion of Iron in SO<sub>2</sub> Atmospheres

Kurokawa Kazuya, Narita Toshio, Nishida Keizo

doi:10.3323/jcorr1974.30.7_396

The scaling kinetics of iron in the argon-diluted sulfur dioxide gas atmospheres were investigated by thermogravimetry at 1073K in SO₂ partial pressures from 20 to 10⁵Pa; the reacted specimens were characteried by means of metallography, X-ray diffractometry, and electron microprobe analysis. The scaling kinetics varied with corrosion time, that is, (1) from linear to primary parabolic (below 10³Pa), (2) from primary parabolic to secondary parabolic (between 10³ and 10⁴Pa), and (3) only secondary parabolic (above 10⁴Pa) rate laws. The morphology of scales formed in the SO₂ partial pressures lower than 10⁴Pa showed the lamellar structure consisting of oxide and sulfide, which was produced in linear and primary parabolic periods, and in the secondary parabolic period the oxide was mainly produced. In high SO₂ partial pressures (above 10⁴Pa), the scales were composed of the oxides of wüstite and magnetite phases, though the mixture of wüstite and ferrous sulfide was observed in the vicinity of the metal/scale interface. The platinum marker located on the metal surface was found always just on the metal surface during corrosion over the whole range of SO₂ partial pressures. The linear rate constant was proportional to about 0.63 power of SO₂ partial pressure. The kinetics in the linear period was discussed from the observed linear rate constant and calculated mass fluxes of SO₂, O₂, and S₂ molecules in the gas atmosphere. Thus, the dissociation process of the adsorbed O₂ and S₂ molecules produced on the scale surface was concluded to be the rate determining step in the linear period.

The High Temperature Corrosion of Iron in SO<sub>2</sub> Atmospheres

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