Electrochemical and in situ atomic force microscopy and scanning tunneling microscopy investigations of titanium in oxalic acid solution

The growth of an oxide film and the dissolution of the metal were studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) for titanium electrodes which had been pretreated by a chemical polishing procedure. Images were obtained with a gas-solid interface and under an aqueous solution containing 0.1 M oxalic acid. The electrochemical polarization of titanium in 0.1 M oxalic acid is qualitatively the same as observed in chloride or sulfate medium, and the dissolution reaction in oxalic acid appears to follow the same monolayer coverage mechanism as in the other media. The titanium specimen is poly crystalline and the presence of grain boundaries between individual crystallites is observed by AFM. In situ microscopy indicates that both the rate of growth of oxide and the dissolution of the metal are dependent on the crystallographic face of the titanium. AFM and STM show that the growth of titanium (IV) oxide or hydrous oxide has the appearance of hemispherical domes which grow together to form peaks on the surface. Dissolution of the metal in the active region occurs first in areas between the peaks where the oxide is thin, and later the oxide coverage of the small peaks appears to coalesce to a smaller number of large peaks.