Chemical corrosion by chlorides on ancient-like bronzes and treatment by hydrogen glow discharge plasma
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Chemical corrosion by chlorides on ancient-like bronzes and treatment by hydrogen glow discharge plasma O. Papadopoulou · J. Novakovic · P. Vassiliou · E. Filippaki · Y. Bassiakos
Received: 14 April 2013 / Accepted: 19 April 2013 © Springer-Verlag Berlin Heidelberg 2013
Abstract Three representative ancient-like bronzes are employed for the chemical synthesis of Cu2 (OH)3 Cl rich patinas in order to study the influence of the alloying elements in the evolution of the chloride attack and to further conduct stabilization treatment via Hydrogen Glow Discharge Plasma (HGDP) at low temperature and pressure. The corrosion behavior of specimens having Sn and Pb as main alloying elements is governed by a decuprification mechanism and by the formation of Sn–Pb–O enriched barrier layers. In the case of the Zn containing alloy, dezincification is more pronounced at the corrosion initial stages, and copper species predominate the corrosion products evolution. A three-hour HGDP treatment leads to Cu+ production and metallic Cu, Sn, Zn, and Pb redeposition, as a result of metal cation reduction. This process is accompanied by partial removal of Cl species, O diminution, and change in coloration. The further increase of the Cl/O atomic ratio measured on the post-treated surfaces leads to the formation of nantokite and thus to the conclusion that the stabilization of objects with extensive Cl attack is not feasible by HGDP without preliminary chemical treatment.
1 Introduction Copper alloys, depending on the corrosive environment, may exhibit a variety of corrosion products. The most agO. Papadopoulou () · J. Novakovic · P. Vassiliou School of Chemical Engineering, National Technical University of Athens, 9 Iroon Polytechniou Str., 15780 Athens, Greece e-mail: [email protected] E. Filippaki · Y. Bassiakos Laboratory of Plasma Physics, Institute of Materials Science, NCSR ‘Demokritos’, Athens, Greece
gressive environments are those rich in chlorine species due to the instability that their presence imparts to the metallic surface. Thus, the removal of these species from the surface of bronze artefacts is very important in order to inhibit a self-accelerated corrosion process known as “bronze disease” [1, 2]. It is not only the chemical composition of an alloy that affects both the corrosion profile and the cleaning treatment efficiency; different metallurgical characteristics such as the composition and size of dendritic formations can create microgalvanic phenomena during the corrosion process [3–6]. Thus surfaces of extensive heterogeneity are produced, which greatly complicate every effort to understand how these “subsystems” contribute to the overall corrosion mechanism and to apply a suitable stabilization treatment. Although there is a considerable number of chemical treatments for the conservation of copper, bronze, and brass, most are not satisfactory for cupreous metals recovered from marine sites [7]. Taking into account effectiveness and what patination changes are acceptable, traditional methods exhibit many di
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