310
Fundamentals of Corrosion
Interface inhibition
•
Electrolyte layer inhibition
•
Membrane inhibition
•
Passivation
•
Subsequently, Lorenz and Mansfield 8 proposed a clear distinction between
interface and interphase inhibition, representing two different types of retardation mechanisms of electrode reactions, including corrosion. Interface
inhibition presumes a strong interaction between the inhibitor and the
corroding surface of the metal. 1, 7, 9 In this case, the inhibitor adsorbs as a
potential-dependent, two-dimensional layer. This layer can affect the basic
reactions in different ways:
By a geometric blocking effect of the electrode surface because of the
•
adsorption of a stable inhibitor at a relatively high degree of coverage of the metal surface.
By blocking the effect of the surface sites because of the adsorption
•
of a stable inhibitor at a relatively low degree of coverage.
By reactive coverage of the metal surface. In this case, the adsorption
•
process is followed by electrochemical or chemical reactions of the
inhibitor at the interface.
According to Lorenz and Mansfield, 8 interface inhibition occurs in corroding systems exhibiting a bare metal surface in contact with the corrosive medium. This condition is often realized for active metal dissolution
in acid solutions.
Interphase inhibition presumes a three-dimensional layer between the
corroding surface and the electrolyte. 7, 10, 11 Such layers generally consist of
weakly soluble corrosion products and/or inhibitors. Interphase inhibition
is mainly observed in neutral media with the formation of porous or nonporous layers. Clearly, the inhibition efficiency strongly depends on the properties of the formed three-dimensional layer.
10.1 Inhibitor Evaluation
Because there may be more than one inhibitor suitable for a specific application, it is necessary to have a means of comparing the performance of each.
This can be done by determining the inhibitor efficiency according to the
following correlation:
Fundamentals of Corrosion
Interface inhibition
•
Electrolyte layer inhibition
•
Membrane inhibition
•
Passivation
•
Subsequently, Lorenz and Mansfield 8 proposed a clear distinction between
interface and interphase inhibition, representing two different types of retardation mechanisms of electrode reactions, including corrosion. Interface
inhibition presumes a strong interaction between the inhibitor and the
corroding surface of the metal. 1, 7, 9 In this case, the inhibitor adsorbs as a
potential-dependent, two-dimensional layer. This layer can affect the basic
reactions in different ways:
By a geometric blocking effect of the electrode surface because of the
•
adsorption of a stable inhibitor at a relatively high degree of coverage of the metal surface.
By blocking the effect of the surface sites because of the adsorption
•
of a stable inhibitor at a relatively low degree of coverage.
By reactive coverage of the metal surface. In this case, the adsorption
•
process is followed by electrochemical or chemical reactions of the
inhibitor at the interface.
According to Lorenz and Mansfield, 8 interface inhibition occurs in corroding systems exhibiting a bare metal surface in contact with the corrosive medium. This condition is often realized for active metal dissolution
in acid solutions.
Interphase inhibition presumes a three-dimensional layer between the
corroding surface and the electrolyte. 7, 10, 11 Such layers generally consist of
weakly soluble corrosion products and/or inhibitors. Interphase inhibition
is mainly observed in neutral media with the formation of porous or nonporous layers. Clearly, the inhibition efficiency strongly depends on the properties of the formed three-dimensional layer.
10.1 Inhibitor Evaluation
Because there may be more than one inhibitor suitable for a specific application, it is necessary to have a means of comparing the performance of each.
This can be done by determining the inhibitor efficiency according to the
following correlation: