Alkaline dissolution of aluminum: surface chemistry and subsurface interfacial phenomena
In this dissertation, direct imaging of interfacial voids formed in aluminum during alkaline dissolution was attempted, using TEM and STEM. Additional microscopic observations by FE-SEM are reported, following removal of controlled depths of metal to expose subsurface voids. Information obtained from the microscopy about depths, geometry and number densities of voids in the metal is analyzed with respect to logistics of a void formation mechanism involving vacancy diffusion at room temperature. The second part of the work deals with studies on hydrogen interactions with aluminum during alkaline dissolution processes using the DS cell and Al/Pd bilayer films. The change in the electrochemical potential on hydrogen entry and exit side was monitored and used to calculate the chemical potential of hydrogen in equilibrium with the aluminum. The calculated H-chemical potential is used to quantitatively characterize the thermodynamic conditions of H in aluminum and its implications for H-absorption and H-vacancy defect formation is discussed. Additionally, surface chemical processes accompanying anodic and open circuit alkaline dissolution were studies using SIMS, AFM, cyclic voltammetry and potential-step experiments. These surface analytical and electrochemical techniques identified the presence of surface hydride on aluminum during dissolution. The potential at the metal-film interface was found to correspond with the Nernst potential for aluminum hydride dissolution.