Corrosion behavior of aluminum in molten hydrated salt phase change materials for thermal energy storage

Abstract

The corrosion behavior of aluminum 1060 in hydrated salt phase change materials (PCM) melts comprised of Na2HPO4•12H2O - Na2SO4•10H2O was investigated through electrochemical tests as a function of pH. The pH of PCM medium was adjusted by adding H2SO4 or NaOH. Electrochemical impedance spectroscopy reveals the existence of concentration difference layer at aluminum/PCM interface ascribed to the adsorption of PCM species and the formation of aluminum oxides. The observed anodic branch of DC polarization exhibits potential independence which is ascribed to the formation of surface oxide film and the accumulation of hydrogen molecules inside surface pores. The oxide film formed at neutral condition is characterized as the most compact and corrosion resistant while as the environmental pH shifts away from 7 the oxides/aluminum dissolution is accelerated and more aluminum 1060 substrate is exposed.