Multiscale study of interactions between the corrosion product layer formed on heritage copper objects and organic protection treatments

Maëva L'Héronde (1, 2) , Muriel Bouttemy (2) , Delphine D. Neff (1, 3) , Florence F. Mercier-Bion (1, 3) , Emilande Apchain (1, 3) , Arnaud Etcheberry (2) , Philippe Dillmann (1, 3)

1 LAPA - UMR 3685 - Laboratoire Archéomatériaux et Prévision de l'Altération
2 ILV - Institut Lavoisier de Versailles
3 IRAMAT - LMC - IRAMAT - Laboratoire Métallurgies et Cultures

In the outdoor environment, bronze and copper statues undergo alterations caused by water and atmospheric pollution. This leads to physical and aesthetic modifications of the copper objects by the formation of a corrosion product layer (CPL) composed of a thin inner layer of cuprite Cu 2 O (5 to 10 μm) at the metal/CPC interface and an outer and thicker layer (20 to 50 μm) consisting mainly of brochantite Cu 4 SO 4 (OH) 6. To limit these effects, the restorers mainly use treatments with microcrystalline waxes but requiring frequent applications. The search for new corrosion inhibiting treatments, non-toxic, is a major issue in the field of heritage. The new treatments based on carboxylate, saturated carbonaceous long chain, in solutions (HC 10) have been developed, in particular on ferrous alloys, and seem promising for copper alloys. However, little information exists on the CPC/carboxylate layer interaction mechanisms. Our work focuses on the study of the efficiency of the HC 10 treatment by visualizing its penetration deep inside the CPL to enhance the protection effect as well as the interactions at the CPL/metal interface from micrometric to nanometric scale via a set of complementary analytical techniques mainly implemented on cross sections: μ-Raman spectroscopy for structural analyzes, EDS and electron spectroscopies, and particularly nano-Auger, for chemical investigations. This methodology will be detailed and illustrated on samples issued from the roof of the cathedral of Metz with and without HC 10 treatment. Main result shows that CuC10 can precipitate at the cuprite/brochantite interface.

Domaines: Matériaux

Maëva L'Héronde, Muriel Bouttemy, Delphine D. Neff, Florence F. Mercier-Bion, Emilande Apchain, et al.. Multiscale study of interactions between the corrosion product layer formed on heritage copper objects and organic protection treatments. E-MRS Spring Meeting 2019, May 2019, Nice, France. ⟨cea-02327920⟩