The importance of pH-dependent breakthrough reactions of NiCrMo materials in media of chemical and environmental engineering with a high redox potential

• Published in: Materials and corrosion 1995-01, Vol.46 (1), p.27-32
• Main Authors: Voigt, C, Werner, H, Kirchheiner, R, Schambach, L
• Format: Article
• Language: eng ; ger
• ISSN: 0043-2822
• DOI: 10.1002/maco.19950460106

Compared to CrNiMo steels, NiCrMo alloys show a specific property at relatively positive potentials. As a result of breakthrough reaction which is not connected to the presence of Cl exp - ions, Ni alloys show a stable and uniform dissolution in media with pH values between 4-9, whereas steels are not attacked. This phenomenon was studied for steels 1.4563 (Nicrofer 3127 LC), 1.4562 (Nicrofer 3127hMo) and Ni alloys 2.4856 (Nicrofer 6020hMo) and 2.4605 (Nicrofer 5923hMo) in Cl exp - and SO sub 4 exp 2- solutions in the pH range 3-10. In the breakthrough reaction chromium and molybdenum dissolve 6-valently and nickel 2-valently. The breakthrough potential is the same in Cl exp - and SO sub 4 exp 2- solutions and is hardly influenced by the Mo content. The reaction rate increases with increasing Mo content of the alloy. This material property of Ni alloys has to be considered if they should be used in slightly acid to slightly alkaline media having a high redox potential.