Mechanisms of hot corrosion of pure nickel at 700°C: Influence of testing conditions

Highlights: • Mechanisms of hot corrosion governed by both $p_{O_2}$ and $p_{{SO}_3}$. • Inward transport of SO₂/SO₃ demonstrated to rule the oxidation-sulphidation of pure nickel. • The Na₂SO₄ deposit decreases the $p_{O_2}$ and the $p_{{SO}_3}$ at the scale surface. • A sufficient $p_{{SO}_3}$ is required to stabilize Na₂SO4-NiSO₄ liquid solutions and simulate Type-II hot corrosion conditions. • The role of capillarity effects is elucidated. - Abstract: The hot corrosion behaviour of pure nickel was investigated at 700 °C to highlight the influence of testing conditions (composition of the atmosphere and presence or not of a Na₂SO₄ deposit) on the mechanisms of hot corrosion. The influence of SO₂/SO₃ inward transport through the porous NiO growing scales was studied by exposing nickel in synthetic air and in synthetic air + 0.5% SO₂/SO₃ without Na₂SO₄. The addition of Na₂SO₄ decreased the $p_{O_2}$ and the $p_{{SO}_3}$ at the sample surface, which promoted the formation of Ni-S liquid solution at the metal/scale interface. A sufficient $p_{{SO}_3}$ was required to stabilize liquid Na₂SO₄-NiSO₄ solutions and simulate Type-II hot corrosion conditions.