In situ study of gas transport through Al(OH)3 gels during AC processing

In this work the nature of gas transport through different Al(OH)3 gels (smut) formed during the AC electrograining process is characterized. A new in situ approach that combines small angle X-ray scattering (SAXS) with the electrochemical response is used to show that gas transport through the smut is different with and without additives. We conclude that gas transport occurs, predominantly, through temporary passageways when no additives are used and through permanent pores with additives, indicating a difference in the gel (smut) rheological properties in each case. Gas transport, through the smut, is therefore considered to be a phenomenon that depends on the electrolyte composition, which is expected to alter the gel properties. These changes in the gas transport away from the metal surface correlate with changes in the potential response of the system. The uniquely lower overpotential, associated with temporary passageways results in an etched-like morphology, suggesting that the gas permeability of the surface gel is a factor that affects the final pit morphology.