| Abstract: | The importance of pH-dependent break-through reactions of NiCrMo-materials in media of chemical and environmental engineering with a high redox potential 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?-ions Ni-alloys show a stable and uniform dissolution in media with pH-values between 4 and 9, whereas steels were not attacked. This phenomenon was studied for steels 1.4563 (Nicrofer 3127 LC), 1.4562 (Nicrofer 3127 hMo) and Ni-alloys 2.4856 (Nicrofer 6020 hMo) and 2.4605 (Nicrofer 5923 hMo) in Cl? -and SO -solutions in the pH-range of pH = 3–10. In the break-through reaction Cr and Mo dissolve 6-valently and Ni 2-valently. The break-through potential is the same in Cl?- and SO -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. |
