Jean-Pierre Caire

Modelling coupled transfers in an industrial fluorine electrolyser

The construction of efficient electrolysers requires a detailed knowledge of the mass flows, currents and temperatures in the cell. The paper describes three successive models designed for modelling transfers in an industrial electrolysis cell for fluorine production. The conservation laws for charge, mass and energy are approximated by use of a Galerkin finite element code. The solution of coupled transfers is necessary to describe the thermal behaviour of the cell. The method used here may be extended to the modelling of other electrochemical cells.

Origin of the anodic overvoltage observed during fluorine evolution in KF-2HF

The kinetics of the fluorine evolution reaction was studied in molten KF-2HF with a horizontal disk electrode in a large potential window. A new model was proposed recently for representing the electrode/electrolyte interface; it includes the presence of a fluidized layer between the surface carbon-fluorine film (C-F) generated on the carbon anode during electrolysis and the fluorine gas film. This model was confirmed here to he consistent. The fluidized layer is composed of liquid KF-2HF melt and dissolved fluorine gas. With our electrode geometry, it was shown that the main electroactive surface area is located at the lateral side of the disk electrode. Finally, the contributions of the C-F film, η C+F . and of the fluidized layer. η fluid . to the total anodic overvoltage, η T , were studied using a numerical calculation method. It was shown that both contributions must he taken into account for a global understanding of the fluorine evolution process.

AISI 304 L stainless steel decontamination by a corrosion process using cerium IV regenerated by ozone. Part I: Study of the accelerated corrosion process

This paper describes the study of a new decontamination process of AISI 304L stainless steel from dismantled nuclear power plants. A very thin active contaminated surface layer was stripped from the underlying metal by corrosion in a solution of nitric acid with the addition of cerium nitrate. The Ce4+/Ce3+ concentration ratio was initially equal to unity and ozone/oxygen bubbles were used to regenerate Ce3+ ions into Ce4+ ions. The study was performed in a laboratory cell prior to preliminary optimization in a three-litre reactor. The objective was to obtain a corrosion rate of about 10 micrometers per day. This target was reached in 10−2 mol l−1 of cerium nitrate with bubbling of a 1.56 g h−1 ozone flow in a 60 l h−1 total gas flow. The corrosion rate depended essentially on the Ce4+ concentration. The stainless steel exhibited intergranular corrosion. The corrosion rate was monitored by measuring the solution oxidizing potential using a precious metal electrode.

AISI 304 L stainless steel decontamination by a corrosion process using cerium IV regenerated by ozone Part II: Process optimization

Empirical and analytical approaches were used to model a pre-industrial pilot reactor to optimise a new decontamination process for AISI 304 L stainless steel. The alloy corrosion rate was modelled as an analytical function of the total cerium content and the ozone flow injected in the reactor. The empirical model of the corrosion rate, obtained by gravimetry, takes into account all the parameters, including the kinetics of alloy grains detached from the metal by intergranular corrosion. The discrepancy observed between the analytical and empirical models was explained by a two-step corrosion process. The dimensions and quantity of grains falling in the liquid were at first both underestimated. The study showed that the grains had to be extracted continuously from recirculating liquid in the future industrial reactor.