Skip to Main content Skip to Navigation
Theses

Cinétique et mécanismes de corrosion sèche d'un cermet à base Cu-Ni

Abstract : In the course of the development of new materials for inert anodes in the aluminum electrolysis process, cermets have been shown to be good candidates due to combined properties of conduction and resistance to corrosion. At temperatures as high as 900-1000°C, these materials must be particularly resistant, not only to the corrosion by the electrolytic bath, but also to the corrosion by the gaseous atmosphere, which contains oxygen and fluorides. This study was devoted to the kinetics of oxidation in air of a cermet composed with ferrite nickel (NixFe3-xO4), nickel oxide (NiyFe1-yO) and nickel-copper alloy (CuzNi1-z) and corrosion by hydrogen fluoride.

First, we present thermogravimetric measurements at 960°C in the range 1-1000 hPa and SEM observations of the oxidized samples. The influence of oxygen pressure on the rate of oxidation was determined by means of sudden changes in PO2 in the course of oxidation experiments. The data indicate that over a partial pressure of 51 hPa (PCu), the oxygen pressure did not influence the rate of oxidation. The presence of the two copper oxides CuO and Cu2O explains the independence. Thermodynamically, the coexistence of those two oxides determines the partial oxygen pressure under this interface. Below PCu, only Cu2O was detected in the outermost layer of the oxidized samples, and the oxidation rate was found to depend on the oxygen pressure. Complementary analysis by EPMA showed the formation of a sub layer containing a monoxide phase (NiCuFe)O, the consumption of the metallic phases initially present in the bulk of the cermet, with nickel oxide localized around the metal phases. In addition to these modifications, it was observed the dissolution of small amounts of copper inside the grains of nickel ferrite and monoxide.

These results can be explained on the basis of an oxidation mechanism involving both external oxidation (copper oxides formation) and bulk oxidation (grain boundary oxygen diffusion). Diffusion of copper towards the surface and diffusion of oxygen inwards the material must account for the rate of weight gain measured in the isothermal experiments, as well as the influence of oxygen pressure in the range 1-51 hPa.
Complete list of metadata

https://tel.archives-ouvertes.fr/tel-00012081
Contributor : Andrée-Aimée Toucas <>
Submitted on : Tuesday, April 4, 2006 - 5:59:34 PM
Last modification on : Wednesday, June 24, 2020 - 4:18:32 PM
Long-term archiving on: : Saturday, April 3, 2010 - 11:07:03 PM

Identifiers

  • HAL Id : tel-00012081, version 1

Citation

Fabien Rioult. Cinétique et mécanismes de corrosion sèche d'un cermet à base Cu-Ni. Génie des procédés. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2005. Français. ⟨tel-00012081⟩

Share

Metrics

Record views

1241

Files downloads

6364