Passivity Breakdown on Solid Versus Liquid Gallium

Abstract

Pits are found to nucleate on solid gallium in buffered chloride solutions, and we propose that the pits nucleate from blisters that form beneath the passive film on the metal substrate. The proposed association of pitting with blister formation is accounted for by the point defect model for the growth and breakdown of passive films, and has been tested by comparing the behaviors of solid and liquid gallium upon anodic polarization in chloride‐containing environments. This study shows that liquid gallium resists passivity breakdown much more readily than does the solid, which we attribute to the inhibition of cation vacancy condensation, in liquid substrate, and hence to the formation of blister precursors at the metal/film interface. Thus, solid gallium is added to the growing list of metals and alloys that apparently suffer passivity breakdown via a vacancy condensate precursor.