Corrosion of Chromium in Glass Melts

Abstract

The corrosion of pure chromium was studied in four molten glasses, using both scanning electron microscopy and electrochemical methods to characterize the metal/glass interactions. It is shown that direct immersion of chromium into glass does not allow obtaining a protective oxide scale, even if the glass contains oxidizing species such as FeIII, ZnII, etc. In these conditions, the corrosion mechanisms vary with temperature and glass composition. When the metal is oxidized in hot air preliminary to glass diving, the passive state is reached and related to the presence of a Cr2 O3 continuous layer at the metal/glass interface. It is maintained up to a temperature called "depassivation temperature." This temperature is close to 1160°C in a borosilicate glass and is shifted to the higher values when the glass is enriched into oxidizing species (FeIII). Coupling both SEM and electrochemical data shows that the Cr2 O3 layer continuity is ensured by microgalvanic couples occurring between parts where the oxide scale is in contact with the metal substrate and other parts where the oxide scale is peeled off. When the glass temperature is higher than the depassivation temperature, a chromium boride CrB layer develops at the metal/glass interface. © 2006 The Electrochemical Society. All rights reserved.