The dissolution kinetics of iron filamentary single crystals were found to obey a mechanistic analysis based on the terrace-ledge-kink surface model. At low undersaturations, dissolution-ledge propagation from edge sites of finite crystals controlled the process and the dissolution rate was found to be a linear function of the ferrous ion concentration in solution. Generation of ledges from spiral or screw dislocation sources was rate-controlling at moderate undersaturations, the rate being dependent upon the logarithm of the under saturation ratio. A linear relationship was again followed at high undersaturations because the spacing of ledges emitted from spiral sources was small, which dictated evolution to a limiting linear case.
An anodic polarization curve for the dissolution of iron whiskers in 1 N sulfuric acid, obtained by varying potassium persulfate depolarizer additions in solution, agreed favorably with the literature. The Tafel curve in the active range bifurcated with increasing current density and showed a greater rate of dissolution perpendicular to {110} surfaces. As the dissolution rate was shown to depend on the logarithm of the interfacial free energy, the orientation-dependent dissolution phenomena were in accord with the mechanistic model for surface anisotropy, especially with respect to ledge-kink configurations.
