The Open-Circuit Steady State

According to ASTM G15-71, the corrosion potential is the potential of a corroding surface in an electrolyte relative to a reference electrode meas- 

The stationary corrosion potential has been measured directly, under open-circuit conditions, or determined from the intersection of the initial or steady-state Tafel lines. Despite the fact that hundreds of articles concerning iron corrosion in acid media have been published, only a small number include the open-circuit characteristics, probably due to the dynamic nature of the interface and to the difficulties in reproducing the results. 

In addition to the rather systematic study of the pH dependence of corrosion potential and corrosion rate, some other influences have also been investigated. Thus, Drazic et observed that after a strong 

Despite the fact that the small amount of experimental data available does not afford a firm basis for correlations, it appears that the purity of 

It can be seen from this relation that if the difference pH2 - pHi is greater near the surface than in the bulk of electrolyte and if this difference increases with time (because the higher the pH, the slower the H diffusion), the slope A °7ApH must increase with an increase in the waiting time. 

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Generally, it is considered that an asymptotic trend with a slope IA °VArl < 5 mV h" characterizes the open-circuit steady state. This condition is usually reached after 15 min from the moment of electrode immersion. 

Summary of the Open Circuit Steady-State Characteristics for the Limiting Cases... 

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