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Assessing the efficiency of a corrosion inhibitor
The figure shows (first left on both traces) the effect of a 20 µl Loop Injection of acetic acid, 0·5% (w/v), on an iron sample milled in pentane, followed by saturation and desorption of 0·25% (w/v) SWI corrosion inhibitor. To the far right on both traces, the thermal (top) and matter transfer (lower) show the effect of the final 20 µl acetic acid injection.
The acid interacts very strongly with the iron before the inhibitor is introduced, as can be seen from the large heat of interaction and the small quantity of acid appearing in the lower trace. Following the adsorption and desorption of the inhibitor, a repeat injection of the acid produced much less heat of interaction with a lot more of the acid arriving at the down stream detector, indicating how well the SWI is protecting the iron surface.
When the SWI was introduced, the down stream detector shows a large negative peak which is caused by the SWI preferentially displacing the reaction products between the iron and the acetic acid, followed by the continued adsorption of the SWI onto the surface of the iron. The desorption of the excess SWI from the surface of the iron follows as the carrier fluid percolates through the instrument.
A few years ago we were asked if we could develop a technique to assess the efficiency of a corrosion inhibitor. The flow--through design of the flow adsorption microcalorimeter allows us to examine how a surface is attacked, how it can be protected, and how efficient that protection is. We can see a similar approach in the data shown above. With these data we can deduce how materials interact at the fluid–molecular–solid surface. Since we can also watch the treatment, and measure the heat and matter transfer values in the same experiment, we can gain a more complete picture of the surface, its treatment and its vulnerability to attack from the probe in this automated test.
The thermal trace (top) indicates that less than half the heat was evolved from the second acid pulse compared to the first, whilst the refractive index analyser indicates that more than three times the acid is passing straight over the iron and therefore not interacting with it.
The model of Flow Microcalorimeter used for these studies was an FMC–4014, plus a refractive–index analyser. |
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