316
Fundamentals of Corrosion
organic compound acts as a good inhibitor for some metals but not others is
explained from this specific electronic interaction of the polar groups with
the metal surface.
The molecular structure and size of the organic compound influence their
inhibitive action. The structures with benzene rings are particularly effective inhibitors. Primary amines become more effective as the chain length
increases. This is presumably because of the steric effect (i.e., diffusion barrier) provided by long chains. However, for mercaptans and aldehydes, the
efficiency decreases with the increasing chain length. The sharp decrease in
corrosion rate with organic inhibitors is shown in Figure 10.2.
Sodium benzoate, sodium cinnamate, and sodium pyrophosphate are
examples of nonoxidizing compounds that effectively passivate iron in the
near-neutral range, apparently by facilitating the adsorption of dissolved
oxygen. As little as 10 −4 M sodium benzoate (0.0014%) effectively inhibits in
aerated distilled water, but inhibition is not observed in deaerated water.
Organic inhibitors find application as pickling inhibitors. Acid pickling of
hot-rolled steel is necessary to remove mill scale. Pickling inhibitors resist
corrosion of the substrate metal. These inhibitors are used for acid cleaning
0.20
0.15
0.10
Inhibitor Concentration, Wt. %
0.5
0.0
20
40
% Decrease in Corrosion Rate
60
80
Ethyl octynol
Propargyl alcohol
100
FigurE 10.2
Effect of concentration of organic inhibitors on corrosion rate.
Fundamentals of Corrosion
organic compound acts as a good inhibitor for some metals but not others is
explained from this specific electronic interaction of the polar groups with
the metal surface.
The molecular structure and size of the organic compound influence their
inhibitive action. The structures with benzene rings are particularly effective inhibitors. Primary amines become more effective as the chain length
increases. This is presumably because of the steric effect (i.e., diffusion barrier) provided by long chains. However, for mercaptans and aldehydes, the
efficiency decreases with the increasing chain length. The sharp decrease in
corrosion rate with organic inhibitors is shown in Figure 10.2.
Sodium benzoate, sodium cinnamate, and sodium pyrophosphate are
examples of nonoxidizing compounds that effectively passivate iron in the
near-neutral range, apparently by facilitating the adsorption of dissolved
oxygen. As little as 10 −4 M sodium benzoate (0.0014%) effectively inhibits in
aerated distilled water, but inhibition is not observed in deaerated water.
Organic inhibitors find application as pickling inhibitors. Acid pickling of
hot-rolled steel is necessary to remove mill scale. Pickling inhibitors resist
corrosion of the substrate metal. These inhibitors are used for acid cleaning
0.20
0.15
0.10
Inhibitor Concentration, Wt. %
0.5
0.0
20
40
% Decrease in Corrosion Rate
60
80
Ethyl octynol
Propargyl alcohol
100
FigurE 10.2
Effect of concentration of organic inhibitors on corrosion rate.