Electrochemistry and photoelectrochemistry of ferrosilicide (Fe//xSi) alloys in neutral solutions

The corrosion and passivation behaviour of ferrosilicide (Fe//xSi) alloys in neutral solutions has been studied as a function of alloy composition (0 - 30 wt % Si) in deoxygenated borate and phthalate buffers using cyclic voltammetry, a scraped rotating ring-disc electrode (SRRDE), photocurrent spectroscopy, a. c. impedance and X-ray photoelectron spectroscopy (XPS). The thermodynamics of the system have been summarised in the form of activity-pH and E//h-pH diagrams, the latter showing that preferential oxidation of the silicon component of the alloy could occur, producing an (amorphous) SiO//2 surface phase at potentials more negative than required for oxidation of iron. At higher potentials, passivation was shown to be due to a silica-rich Fe (III) oxide film, exhibiting n-type semiconducting properties with a bandgap of 1. 9 - 2. 02 eV, for 0 - 15. 8 wt % Si ferrosilicon alloy compositions.