Corrosion in the Presence of Sulfur Compounds

The presence of sulfur compounds (H2S, SO2, SO3) in a hot gas generally promotes high temperature corrosion. To understand the phenomena in question we first study the chemical equilibria in the metal-sulfur-oxygen system. 

Sulfur is a member of group VI of the periodic table, just below oxygen. In analogy to high temperature oxidation, metals react with gaseous sulfur to form sulfides. 

Under oxidizing conditions, sulfur is normally present in the form of SO2 or SO3. Depending on the partial pressure of oxygen, reaction with a metal leads to either oxides, sulfides or sulfates. In the following, different possible reactions of a metal leading to the bivalent compounds MO, MS or MSO4 are listed  

F ure 932 Equilibrium diagram of the system M-SO2-O2 showing the stability regions for different species in the presence of SO2 and O2 (schematic). 

According to these reaction equilibria every point in the logPso2 log o2 plane corresponds to a certain partial pressure of SO3 and 82- We can therefore also draw the phase stability diagram in the planes logF so3-log 02 or log/ s2 log 02- 

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