Electrochemically controlled high-temperature oxidation of copper within a large oxygen partial pressure window

Abstract

Understanding the oxidation process of copper is of great interest since its occurrence poses a major risk in various industrial processes and technological applications. In the past, numerous studies on the thermal oxidation of copper have investigated the formation of oxides, oxidation rates, chemical composition and morphology as a function of temperature and oxygen partial pressure [1][2]. In this work a powerful method for electrochemically controlled oxidation is presented, whereby the oxygen partial pressure on the metal surface can be varied over the entire range of 100 to 10 25¬ bar in a single measurement. A controllable oxidation rate is achieved in a solid-state electrochemical cell by polarizing a copper sample in contact with an yttria-stabilized zirconia crystal, which is a sufficiently good oxygen ion conductor at elevated temperatures (300-600°C). An applied potential sweep pumps the oxygen through this crystal whereby the amount of oxygen can be quantified by the flowing current. The obtained voltammograms contain thermodynamic and kinetic information about the oxidation processes. Thereby the potential corresponding to the oxygen partial pressure determines the different oxidation reactions, whereas the rate of the layer growth as well as the thickness of the initial oxide layer are quantified by the current. Surface analytical investigations of the oxide layer provide additional information about the chemical composition and structure of the oxide films. The combined data are used to build a model for oxide layer growth, with particular attention to the defect chemistry of the copper oxide.

[1] Grzesik, Z., & Migdalska, M. (2011). Oxidation mechanism of Cu2O and defect structure of CuO at high temperatures. High Temperature Materials and Processes, 30(4), 277-287. [2] Zhu, Y., Mimura, K., & Isshiki, M. (2005). Influence of oxide grain morphology on formation of the CuO scale during oxidation of copper at 600–1000° C. Corrosion science, 47(2), 537-544.