TEM investigation of barrier‐like anodic oxide films on aluminum

Abstract

The present study focuses mainly on non-electrochem. investigation of thin barrier-like oxide films formed under different pulse frequencies. The TEM investigation principally shows amorphous oxide films, which are dense and free of pores. The various pulse expts. have no influence on these film properties. The oxide growth factor was calcd. to 1.06 nmV-1 in all cases. The microstructure (crystallog. orientation, grain boundaries) of the underlying substrate does not affect the oxide films. Independent of the pulse frequency, electrolyte species are not incorporated into the oxide films. The evidenced differences in the film thickness are caused by intrinsic peculiarities of the high-field mechanism of growing oxide

Anodizing—Interplay between bath aging and oxide formation and properties

“…Consequently, the barrier layer thickness should be slightly increased and this layer can be assumed as more or less free of OHgroups. 31 Considering the results presented in Figure 7, this assumption is not in contradiction to the aforementioned discussion, but the calculated results concerning Figure 7 are unfortunately not sufficiently significant. The ratio between OH deformation and stretching band #4 and #2 is constant.…”

“…The identification of the bands is based on comparison with the literature . Four bands are identified and discussed as follows: Band #1 with a maximum of between 940 and 960 cm −1 because of the Al‐O vibration mode and is commonly interpreted as typical for Al 2 O 3 fits well with earlier results of the authors Band #2 with a maximum between 1130 and 1150 cm −1 and a shoulder to higher wave numbers is the most interesting signal.…”

“…Otherwise, the ratio #4:#1 shifts to #1, which can be explained by the lower dissolution force of the bath with ongoing aging. Consequently, the barrier layer thickness should be slightly increased and this layer can be assumed as more or less free of OH‐groups . Considering the results presented in Figure , this assumption is not in contradiction to the aforementioned discussion, but the calculated results concerning Figure are unfortunately not sufficiently significant.…”

Development of the local proton concentration during pulse anodizing

“…For example, it was shown that high local heat impact and thus structural destruction of the oxide can be avoided by targeted pulse anodizing . Additionally, it was found that an adjustment of the pulse parameters leads to a notable reduction of energy consumption during anodizing …”

“…9,10 Additionally, it was found that an adjustment of the pulse parameters leads to a notable reduction of energy consumption during anodizing. 11,12 Herein, the influence of pulse parameters on the local concentration of the electrolyte in the porous oxide is examined. During anodizing, the reactants, e.g., H 2 O, will be depleted in front of the electrode and the concentration of reaction products, eg, protons H + , will increase.…”