ROLE OF SOLUTION RESISTANCE IN MEASUREMENTS FROM ATMOSPHERIC CORROSIVITY SENSORS

摘要

The measurement of corrosion rates by various electrochemical methods in conductive solutions has a sound theoretical basis. In many practical cases, the influence of solution resistance is negligible compared to the polarization resistance of the electrodes. However, where these techniques are applied to measuring atmospheric corrosivity, the role of ionic resistance between electrodes seems to be under estimated. The influence of solution resistance for four types of atmospheric corrosivity sensors was analyzed on the basis of their equivalent electrical circuits. These included time-of-wetness, galvanic, linear polarization resistance, and electrochemical noise sensors. Analysis of the equivalent circuits indicated that solution resistance plays a confounding role in interpreting apparent corrosivity measurements. Therefore the effects of changes in solution resistance must be accounted for in order to properly interpret apparent corrosivity measurements. One proposed solution is to manufacture corrosivity sensors that have a constant ionic resistance between the electrodes. This may be possible with a material that functions as a solid-state ionic conductor. Another proposed solution is to measure solution resistance in parallel with the apparent corrosivity. Depending on the type of sensor, the true corrosivity can then be calculated from the apparent corrosivity and solution resistance according to an appropriate model.