Effects of different inorganic anions on equipment material corrosion behaviour in subcritical water oxidation

ABSTRACT

In this work, possible corrosion mechanisms of Fe- and Ni-based alloys are discussed which are protected by Cr₂O₃, NiO and MoO₂ surface layers. But chloride ions can dissolve these oxide films and there is a strong synergistic effect between hydronium ions and oxygen, leading to severe local alloy corrosion. On the other hand, titanium and Zr-3 alloys show good corrosion resistance in acidic oxidising subcritical water containing different inorganic salts. A double-layer oxide film (TiO and TiO₂) is formed on the surface of TA2 and TA9 alloys, while a triple oxide layer (TiO, Ti₂O₃ and TiO₂) is formed on TA10 surfaces in such aqueous solutions containing chloride and sulphate ions. In addition to the two oxide layers, Ti₃(PO₄)₄ deposits are also formed on the surface of TA2 and TA9 alloys when the subcritical water contains phosphates. Moreover, (TiO)₂P₂O₇ deposits form besides Ti₃(PO₄)₄ layers on the surface when the TA10 alloy is oxidised under the latter conditions.

KEYWORDS:

• Acidic oxidising subcritical water
• corrosion
• inorganic salt
• titanium alloy
• Zr-3 alloy

Acknowledgement

The authors thank Professor Andreas Goldbatch for his help in editing.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Major Science and Technology Projects of Shandong Province [grant number 2015ZDXX0402B01] and the Key Programs of the Chinese Academy of Sciences [grant number ZDRW-ZS-2016-5].