Corrosion of manganese in sulfur dioxide at high temperatures

The reaction of manganese with sulfur dioxide at 0.1 MPa at 973–1173 K was studied. The composition and morphology of the scales were investigated by scanning electron microscopy (SEM) and various of X-ray analysis techniques. Transport phenomena occurring in the growing scales were studied by means of radiotracer techniques using sulfur dioxide labeled with the radioactive isotope of sulfur, ³⁵S. The kinetics of the process was measured by means of the gravimetric method. After an initial stage (not examined), the reaction exhibits two subsequent parabolic stages. The scales were mainly composed of oxides with some sulfide, even though the sulfide is unstable in the reaction conditions. The dominant transport process is the outward diffusion of manganese. Some inward transport of SO₂/S₂ was also observed. The sulfide present next to the metallic core is formed during the very initial stage of the reaction in mixture with the oxide. The process initially occurs mainly by means of reaction of manganese with sulfur dioxide. Further growth of this mixed layer proceeds by means of an inward transport of SO₂/S₂ molecules.