‘Green’ corrosion inhibitors derived from plant materials provide environmentally friendly alternatives to conventional corrosion inhibitors. They are also much cheaper if using a biomass waste stream or abundant plant material as the source material. There are many examples in literature of different trials, from henna leaves to celery seeds to banana peel. Although it is known that extracts contain electron-rich polar atoms such as N, O, S and P which make them potentially effective inhibitors, it is difficult to predict on a molecular basis what will work well and what will not, since many interacting factors may be at play in complementary interactions. To assist in predicting the inhibition efficiency of inhibitors under varying conditions and choosing the most effective, what is needed is a short-term test which will obviate the need for tedious weight loss experiments. The Electrochemical Noise Method (ENM) uses the natural fluctuations which arise during electrochemical activity to gain information about the corrosion process. Using ENM is quick and non-intrusive method which makes it ideal for screening. Hence a rig has been designed and manufactured which allows for measurement to be made in stirred as well as static conditions and minimises the occurrence of crevice corrosion at the electrodes. Crevice corrosion is a hazard for ENM electrodes when trying to make a comparison with corrosion inhibition calculated using the standard weight loss measurement after immersion (WLM) method. For these preliminary trials we are exploring corrosion of mild steel in HCl in both stirred and unstirred conditions at room temperature. Results are presented comparing ENM measurements with conventional WLM for both Propargyl Alcohol (a conventional industrial corrosion inhibitor) and broccoli extract. Our results suggest that stirring does not make any difference to the noise measured in ENM. The amount of material lost calculated by ENM and WLM (Rn and weight loss values) can be directly compared and show close comparison.
It seems likely that as a way of assessing inhibitors quickly (which is particularly important in the testing of "green" inhibitors) that this ENM approach has a lot to offer.