| Numéro |
Journal européen d’hydrologie
Volume 25, Numéro 1, 1994
|
|
|---|---|---|
| Page(s) | 13 - 24 | |
| DOI | https://doi.org/10.1051/water/19942501013 | |
| Publié en ligne | 27 octobre 2010 | |
Etude des domaines de corrosion et de passivation du zinc dans les eaux de consommation
Study of zinc corrosion and passivation in drinkable water
1
L.C.I.E., 33, avenue du Général-Leclerc, 92260 Fontenay-aux-Roses
2
Laboratoire de Chimie Analytique, Université de Montpellier, 34095 Montpellier cedex 5
L'étude thermodynamique de la corrosion du zinc a permis de définir les domaines de précipitation du carbonate, de l'hydroxycarbonate et de l'hydroxyde de zinc en fonction de la pression partielle en dioxyde de carbone. Les mesures d'impédance électrochimique mettent en évidence les propriétés protectrices du carbonate de zinc. Le calcul des diagrammes potentiel-pH montre que la composition ionique de la solution influe sur les domaines de précipitation des sels de zinc et sur le potentiel du couple ZnII/Zn.
Abstract
Thermodynamical calculations were made to study the three phase system gas atmosphere/liquid film/metal surface. They use conventional laws of chemistry and they permit to determine the stability conditions for corrosion layers on the surface of metal.
The precipitation areas for zinc salts were calculated for different partial pressures of carbon dioxide. In the case of high partial pressures, zinc carbonate precipitates. When the values decrease, zinc hydroxicarbonate and zinc hydroxide precipitate successively.
Impedance measurements were made on zinc electrodes immersed in aqueous solutions containing CO2 at concentrations corresponding firstly to the theoritical formation of carbonate, secondly to the formation of hydroxide.
These measurements have clearly demonstrated the protective effect of zinc carbonate which forms a barrier layer at the surface of metal.
The conditions for stability of zinc carbonate layers have been estimated too in the case of three aqueous solutions of different compositions, clearly defined by their value. Ionic composition has no influence on the precipitation areas of zinc salts for different CO2 partial pressures. On the other hand, the equilibrium pH and the potential of Zn II/Zn redox system are modified, especially for the lowest values of CO2 pressure.
The potentiel-pH diagram shows an extension of the area for the precipitation of zinc carbonate and zinc hydroxicarbonate when value is negative; in this case, the ZnII/Zn potential is lower.
© ASEES 1994