Applicability of multistep potentiostatic pulse measurements in inhibitor research

Abstract

The kinetics of the formation and desorption of inhibitor layers are complicated and not well understood owing to the participation of the dominating fast corrosion reaction. Simultaneous computer supported potentiostatic pulse measurements can be used to measure the current density j ( t ) as well as the double-layer capacity C ( t ) over a large time scale. It is shown that processes such as film formation, ageing, and desorption can be investigated with sufficient accuracy. Transients can be analysed using modified concepts of electrocrystallization or oxide formation. Measurements with the copper—aminoheptyltriazole (AHT) system are shown as an example. The film is formed independently of the potential in the range of some seconds and changes its properties by ageing and growth during a period of some 1000 s. The film desorption obeys a potential dependent localized process in the time range of milliseconds which can be analysed in terms of the formation of pits. While single-pulse measurements give information on the desorption only, double-pulse transients can be used to investigate the layer formation and to realize various states. Details of film ageing and corrosion can be obtained from triple-pulse measurements.