Anodic behavior modeling of the C-276 alloy in chlorinated media simulating the hydrothermal conditions of organic waste treatment

Experimental current–potential curves corrected from the contribution due to the medium oxidation are used to propose a dissolution–passivation model of the nickel base alloy C-276. This model is controlled by the major presence of nickel and shows a reaction chain mechanism with a bifurcation and two competitive determinant branches for the setup of the protection of the alloy. Considering a Langmuir-type adsorption, we formulate a current–potential law which leads, via a mathematical optimization calculation using Nelder's simplex, to the eight kinetics parameters involved in the five considered elementary steps. The respective influence of the different branches can be determined. It is used in association with the scanning electron microscopy profiles obtained at fixed potentials, to evaluate the limited reliability of the C-276 alloy as a plant reactor material for waste treatment under hydrothermal conditions, either sub- or supercritical oxidation. This evaluation relies on the comparison with the titanium T60 whose anodic behavior and performances have already been published. The determination of the kinetic parameters also underlines the role played by the oxygen source (H2O2) on the mechanism, a role partly hidden by strict observation of the current–potential experimental curves