Stress generation during anodic oxidation of titanium and aluminum

One-Dimensional Titanium Dioxide Nanomaterials: Nanotubes

“…As in case of other growing metal oxide films, also for anodic TiO 2 formation on a titanium substrate, Stoney curves (stress × thickness vs. thickness curves) as presented in Figure 12.b, 317 show during anodization and thus with growing film thickness a transition from compressive stress to tensile stress. One explanation given, in agreement with Nelson et al 318 , is that after the expected initial compressive stress the observed steady tensile stress is caused by free space generated at the metal/oxide interface by a metal to ion transition. This argument may 36 be put forward to explain the need to form an initiation layer prior to steady-state pore or tube growth.…”

A Model for Coupled Electrical Migration and Stress-Driven Transport in Anodic Oxide Films

“…Other studies of porous anodic alumina growth found the same trend. 19,20 Two papers cited similar current densities of about 0.6-1 mA/cm 2 at the transition. 9,19 However, Wüthrich, using a different experimental technique, found only compressive growth stresses, which increased in magnitude with current density.…”

“…19,20 Two papers cited similar current densities of about 0.6-1 mA/cm 2 at the transition. 9,19 However, Wüthrich, using a different experimental technique, found only compressive growth stresses, which increased in magnitude with current density. 11 Several studies agree that the stress shifts in the tensile direction upon turning off the anodizing current, but while Bradhurst and Nelson found shifts corresponding to the expected electrostatic stress, those observed by Vermilyea and Wüthrich were appreciably larger.…”

“…1 exhibit the experimentally documented transition from compressive to tensile stress with increasing current density. 9,19 This transition is due to the greater sensitivity to electric field of the migration flux of cations relative to anions because of the greater charge of Al +3 . At a low current density, the electrical migration of O −2 ions dominates because of their high pre-exponential migration velocity.…”

“…[14][15][16][17] Like the materials in these experiments, anodic alumina films are amorphous, and stresses large enough to drive significant creep ͑10-100 MPa͒ are found during the growth of both porous and planar anodic alumina. 9,11,[18][19][20][21] Stresses during anodizing may arise from volume constraints at the metaloxide interface, and from electrostatic forces in the oxide dielectric. [22][23][24] In this paper, we present a model for transport in planar anodic films by coupled electrical migration, plastic flow, and migration in the stress field.…”