An Investigation of Composite Aluminum Oxide Films by Radiotracer and Gravimetric Methods

Abstract

Composite oxide films on aluminum were produced by reaction with boiling water followed by anodic oxidation in a phosphate electrolyte tagged with p32 tracer. The amount of phosphorus remaining in the film was followed during stepwise dissolution. It was found that the phosphorus concentration in the barrier portion of this film was two orders of magnitude lower than in a conventional anodie oxide. The amounts of hydrous oxide and barrier oxide in the composite film were determined using a combination of film stripping and metal dissolution procedures. The weight of barrier oxide was only 75% of the weight of a conventional anodic oxide, while the dielectric constants of the two films were about the same. Some important properties of the hydrous oxide were inferred from the behavior observed in these experiments.

Hydrogen Profiles of Anodic Aluminum Oxide Films

“…For these films the pseudoboehmite tail extends into the barrier oxide and from the beam energy at half-height an apparent thickness of 167 nm was calculated for the hydrous oxide. This is about 60 nm less than the initial thickness because some of the hydrous oxide loses water and is converted to barrier A1203 (23,24). From data reported for a 5 min boil -}-175V composite oxide (24), it was calculated that 70 nm of pseudoboehmite was transformed, in reasonable agreement with these results.…”

“…This is about 60 nm less than the initial thickness because some of the hydrous oxide loses water and is converted to barrier A1203 (23,24). From data reported for a 5 min boil -}-175V composite oxide (24), it was calculated that 70 nm of pseudoboehmite was transformed, in reasonable agreement with these results.…”

Interface Stability in the Electrolytic Decomposition of Silicon Dioxide Films at Elevated Temperatures

“…After a time, the voltage reached a steady-state value indicating that a balance had been achieved between the rate of decomposition and the rate of formation of SiO2. The observed steady-state voltage was approximately 1.75V at 850~ which corresponds closely to the reversible cell emf one would calculate from free energy data for the formation of amorphous SiO2 (10), assuming four equivalents are transferred in the cell reaction.…”

Incorporation and migration of phosphorus species within anodic films on an Al‐W alloy

“…The formation of amorphous barrier‐type anodic films on valve metals commonly results in the incorporation of species derived from the anions of the electrolyte into an outer region of the film 1–3. The ratio of the depth of the outer region to the total thickness of the film is usually determined by the transport numbers of the metal and oxygen species of the anodic oxide and the migration rate of the incorporated species relative to that of either the metal species or the oxygen species 4.…”