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The corrosion behaviour of nickel‐base alloy 625 (NiCr22Mo9Nb; 2.4856) and ceria stabilized tetragonal zirconia polycrystal (Ce‐TZP) against oxidizing aqueous solutions of hydrofluoric acid (HF), hydrobromic acid (HBr), and hydriodic acid (HI) at sub‐ and supercritical temperatures
Author(s) -
Kritzer P.,
Schacht M.,
Dinjus E.
Publication year - 1999
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/(sici)1521-4176(199909)50:9<505::aid-maco505>3.0.co;2-x
Subject(s) - hydrobromic acid , hydrofluoric acid , corrosion , oxidizing agent , aqueous solution , alloy , chemistry , intergranular corrosion , inorganic chemistry , sulfuric acid , metallurgy , materials science , organic chemistry
In the present article, the corrosion of the nickel‐base alloy 625 (NiCr22Mo9Nb; 2.4856) in strongly oxidizing hydrothermal aqueous solutions of hydrofluoric acid (HF), hydrobromic acid (HBr), or hydriodic acid (HI), respectively, is investigated. The reaction conditions were temperatures between 25 and 500°C, pressure of 24 MPa, acid concentrations of 0.05 mol/kg, oxygen concentrations of 0.5 mol/kg, and reaction times of 50 h (for HF and HBr), or 3.5 h (for HI), respectively. The investigated alloy 625 tubular samples were corroded by a continously flowing solution. The corrosion of alloy 625 caused by HF is only weak corrosion over the entire temperature range. HBr causes pitting at T > 170°C. At temperatures between 320 and 380°C, general corrosion due to transpassive dissolution leads to severe material loss. In supercritical solutions of low densities, corrosion is negligible. HI was oxidized almost completely to iodine leading to a plugging of the reactors after short times. Samples of ceria stabilized tetragonal zirconia polycrystal (Ce‐TZP) were corroded inside the tubes in a section where T = 500°C. The only corrosion phenomenon which was observed in all acids was intergranular corrosion, with HF being less corrosive than HBr. Neither a weight loss nor a tetragonal to monoclinic phase transformation could be measured. Furthermore, the corrosion behaviour of both materials was compared to that caused by other acids.