Chapter 6
Stresses of Anodic Oxide Films Grown
on Metal Electrode
Abstract Stresses are generated in anodic oxide films grown on valve metals during
anodic oxidation. The stress generated in anodic oxide film, i.e. the film stress is
influenced by many electrochemical and physical factors associated with the formation and growth mechanism of anodic oxide film such as volume change, transport
number of mobile species in the films, electrostriction, crystallization, and oxygen
evolution. The main factors influencing the film stress during anodic oxidation are
separately explained, and the contributions of the respective factors to the film stress
are discussed on the basis of the typical experimental results for anodic oxidation
of Al and Ti. Furthermore, the stress variation toward compressive direction during
cathodic polarization of the anodic oxide film on Ti is explained in terms of the
volume expansion due to hydrogen uptake of the film, and the plastic flow driven
by the compressive stress in the barrier layer on Al is discussed with relation to the
formation of the porous layer.
Keywords Film stress · Pilling–Bedworth ratio · Film growth · Transport
number · Electrostriction
6.1 Introduction
A cantilever bending method has been employed for the measurement of film stress
as well as surface stress. The measured quantity is the product of film stress σ f and
thickness d f with a unit of N m
−1 or J m
−2 which is equivalent to that of surface stress g,
i.e. g = (σ f · d f ). The unit of film stress, therefore, is Pa or J m
−3 . If the change in
film thickness is known, an average value σ f of film stress can be obtained by dividing
g by d f . Stresses are generated in anodic oxide films grown on valve metals such
as Al and Ti during anodic oxidation. The anodic oxide films on valve metals have
been used as electrolytic capacitors in the electronic industry. The stress generated
in anodic oxide film, i.e. the film stress is influenced by the electrochemical and
physical factors associated with the film formation and growth mechanism, such as
volume change, transport number of mobile species, electrostriction, crystallization,
and oxygen evolution. The performance of the anodic oxide films as electrolytic
© Springer Nature Singapore Pte Ltd. 2020
M. Seo, Electro-Chemo-Mechanical Properties of Solid Electrode Surfaces,
https://doi.org/10.1007/978-981-15-7277-7_6
149
Stresses of Anodic Oxide Films Grown
on Metal Electrode
Abstract Stresses are generated in anodic oxide films grown on valve metals during
anodic oxidation. The stress generated in anodic oxide film, i.e. the film stress is
influenced by many electrochemical and physical factors associated with the formation and growth mechanism of anodic oxide film such as volume change, transport
number of mobile species in the films, electrostriction, crystallization, and oxygen
evolution. The main factors influencing the film stress during anodic oxidation are
separately explained, and the contributions of the respective factors to the film stress
are discussed on the basis of the typical experimental results for anodic oxidation
of Al and Ti. Furthermore, the stress variation toward compressive direction during
cathodic polarization of the anodic oxide film on Ti is explained in terms of the
volume expansion due to hydrogen uptake of the film, and the plastic flow driven
by the compressive stress in the barrier layer on Al is discussed with relation to the
formation of the porous layer.
Keywords Film stress · Pilling–Bedworth ratio · Film growth · Transport
number · Electrostriction
6.1 Introduction
A cantilever bending method has been employed for the measurement of film stress
as well as surface stress. The measured quantity is the product of film stress σ f and
thickness d f with a unit of N m
−1 or J m
−2 which is equivalent to that of surface stress g,
i.e. g = (σ f · d f ). The unit of film stress, therefore, is Pa or J m
−3 . If the change in
film thickness is known, an average value σ f of film stress can be obtained by dividing
g by d f . Stresses are generated in anodic oxide films grown on valve metals such
as Al and Ti during anodic oxidation. The anodic oxide films on valve metals have
been used as electrolytic capacitors in the electronic industry. The stress generated
in anodic oxide film, i.e. the film stress is influenced by the electrochemical and
physical factors associated with the film formation and growth mechanism, such as
volume change, transport number of mobile species, electrostriction, crystallization,
and oxygen evolution. The performance of the anodic oxide films as electrolytic
© Springer Nature Singapore Pte Ltd. 2020
M. Seo, Electro-Chemo-Mechanical Properties of Solid Electrode Surfaces,
https://doi.org/10.1007/978-981-15-7277-7_6
149