Abstract
The effect of some phosphonic acid derivatives on the corrosion behaviour of carbon steel has been investigated in hydrochloric acid solutions by gravimetric and electrochemical methods. Some phosphonic acids were found to have inhibitive effects. These effects depend on the molecular structure: on the number of nitrogen atoms and of phosphono groups, but mainly on their position in the molecules, as shown by the differences in corrosion rate in the presence of various phosphonic acids. The variation of polarisation resistance with time suggests that the inhibitive action of diethylenetriaminepentamethylenephosphonic acid depends mainly on the protective inhibitor film formed on the surface of the steel and is independent of changes in solution composition with time.
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