Can anyone give me the explication why the efficiency decrease when i increase the concentration of my inhibitor?
dear Said; it depends on the type of corrosive environment whether it is acidic, basic or neutral. In some cases, increasing the concentration of the inhibitor don't effect. but in another case like anodic inhibitor, there is a limit for the concentration of inhibitor that it shouldn't exceed it otherwise, the corrosion rate increases.
I think it's directly attributed to active sites. When the steel sites became cover fully increment of inhibitor concentration did not change the efficiency.
Dear Ali Dehghani and Mahmood H. M. thanks for your responses. I need to know the reason why the efficiency decrease when I increase the concentration of inhibitor for example the efficiency reached a 92% a 10-3 M than decease to 85%05.10-3M.
Said Abbout as i said previously after an specific inhibitor quantities increment in solution no active site existed for adsorption. so the inhibitors molecules couldn't adsorb on steel substrate. However, corrosion is still occurred (which means the inhibitive layer didn't change but corrosion activity increased against immersion time). So for this reason the efficiency decreased to lower values.
Dear Said; The inhibition efficiency reached a maximum value at 10-3M. The latter can be considered as the optimal threshold of the inhibitor.
You can verify this by the value of the anodic constant of Tafel. The minimum value of βa is obtained at the optimum.
Dear mohamed, yes I'm again with you. But why efficiency decrease when I increase the concentration it must be the same.
Dear Said;
Simply it depends on the system, type of inhibitors and their structure.
don't worry you can see this paper for more clarity the above explanation.
Isoxazolidine derivatives as corrosion inhibitors for low carbon steel in HCl solution: experimental, theoretical and effect of KI studies, RSC Adv, DOI: 10.1039/c7ra11549k
Dear Said Abbout
Most of the time corrosion inhibitor provides a protective layer that helps to prevent or slow down the corrosion process. While the increase in inhibitor concentration or temperature of the solution causes a weakness in the corrosion prevention layer of corrosion inhibitor protection further more allowing and accelerating the process of corrosion in the corrosive media. Sometimes increasing in inhibitor concentration can damage protective layers, inhibitor film , FeS or FeCO3 layer. for effectiveness of a corrosion inhibitor, the structure of the inhibitor's compound and the mechanism of the protection is crucial.
Dear Said Abbout,
In my case, I suppose there might be reversed progressions that happened in the same moments. One supports the inhibition process and another goes against. So it is better figure out what is the dominated progress, support or against the corrosion. That should be awared of the synergistic effect more than single impact.
Recently i was studying a paper in the case of synergism of organic and inorganic inhibitors, the authors stated that " It seems that at higher concentrations of Zn2+, the greater volume of the solution is made up of Zn-inhibitor complex such that there is difficulty in diffusion of this complex from the solution to the metal surface and as a consequence, the metal-inhibitor complex which should protect the metal surface is not sufficiently form." i think it does make sense. In the high load of inhibitors there is a traffic of constructed structures and therefore the protective complexes cannot reach the metal surface from the bulk solution.
I think this the best interpretation in this field.
S. Rajendran, B.V. Apparao, N. Palaniswamy, Corrosion inhibition by phenyl phosphonate and Zn2+, Anti-Corros. Meth. Mater. 45 (1998) 158–161.
Inhibition efficiency What is the weight loss value in absence and presence of inhibitors ?
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