Oxidation phenomena at the surface of molten Ag-Cu alloys described by different theoretical approaches

In the framework of OXYTHERM ESA-MAP Project, a systematic study of oxygen influence on molten Ag-Cu alloys, taken as binary model system, was performed. The project is aimed to the development of improved physico-chemical models providing a deeper understanding of the basic interaction mechanisms of oxygen on liquid alloys and on the influence on their thermophysical properties such as surface tension, viscosity, and density. It exploits measurements performed on board of the ISS by using MSL-EML facility equipped with the Oxygen Sensing and Control device (OSC), in order to obtain information will serve as a benchmark for the quality of ground based experiments. In this work, the interactions between Ag-Cu molten alloys and an oxidising atmosphere are theoretically approached by applying different models: a thermodynamic Belton's like model [1], which allows the adsorption isotherms to be evaluated and a fluid dynamic model [2], which allows to determine the boundary separating oxidation and de-oxidation regimes, for the liquid alloys surface. The models have been validated by surface tension data measured as a function of oxygen partial pressure in two different apparatuses by using a containerless- and a container- based technique, respectively. The former is very similar to the device, named TEMPUS, designed by DLR, that is used on the ISS for the microgravity measurements. In this apparatus the surface tension was measured by oscillating drop method using electromagnetic levitation (EML) over a wide range of temperatures above the melting point and under oxygen control (OSC)[3]. In the other one, dynamic surface tension measurements [4] have been performed by the large drop method in order to study the evolution of the molten alloy surface in the presence of traces amount of oxygen. Such measurements are out of equilibrium and they can provide information about the kinetics and the mechanisms of mass transfer to and through the surface. [1] R. Novakovic R., D. Giuranno, E. Ricci, Molten 2009 Proceeding article n. cap. 02 ( 2009) 70. [2] E. Arato, M. Bernardi, D. Giuranno, E. Ricci, Applied Surface Sci. 258 (2012) 2686. [3]M. Schulz, J. Brillo, C.Stenzel, H. Fritze , Solid State Ionics 225 (2012) 332. [4] E. Ricci, E. Arato, A. Passerone, P. Costa, Advance of Colloid and Interface Science 117 (2005) Acknowledgements: This work was performed in the framework of the European Space Agency (ESA) Microgravity Applications Support Programme (MAP) and supported by the Italian Space Agency (ASI) under contract DC-MIC-2011-036 "OXYTHERM".