Two Kinds Of Corrosion Monitoring Sensor Based On Electrochemical Noise Technique

As a key issue of engineering and production safety, corrosion monitoring is worth researching. As the basis of the corrosion monitoring of metal structures or equipment,Corrosion monitoring sensor provides conditions for the implementation of various corrosion monitoring technology. Currently, there are still many problems in corrosion monitoring, such as using invasive installation to realize connection and there is few research on the galvanic corrosion monitoring of complex structure composed with different materials in atomospheric environment. Considering that the electrochemical noise technique has become the forefront of electrochemical monitoring techniques because of its advantages of in-situ and non-destructive, and to solve the two problems above, two kinds of corrosion monitoring sensors based on electrochemical noise technique has been designed in this paper, one of which is suitable for monitoring the metal structures or equipments in the aqueous environment which can avoid the damage caused by electro connection while monitoring;another is suitable for monitoring the galvanic corrosion of complex structure in atomospheric environment.The applicability of three cells and two cells "NOCS"(No Connection to Substrate)sensor in the corrosion monitoring of coating system, corrosion inhibitor system and bare metal system was studied by electrochemical noise, electrochemical impedance spectroscopy and linear polarization techniques. And the electrode which is suitable for the sensor has been selected from SCE electrode, Pt and home-made Ag/AgCl electrode. The results show that different electrodes are not always suitable to be the connection electrode of NOCS sensor.Only when the potential noise of the electrode is less then which is generated in the corrosion process and the resistance of the process that the ion transfers to electron is small enough and does not affect the collection of current noise, the electrode is suitable for three cells NOCS sensor. Influenced by the self-noise of the connecting electrode, the three cells NOCS sensor connected with different electrodes has different monitoring range. The sensor connected with SCE electrode is only suitable for the coating system, and is suitable for coating and corrosion inhibitor system while conncted with home-made Ag/AgCl electrode, the electrode which is suitable for the bare metal system still needs further research and selection.The two cells NOCS sensor can realize the corrosion monitoring only when the resistance of the process that the ion transfers to electron is small enough and the potential noise of the connecting electrodes is similar to which produces during the process of corrosion which is caused by its structural characteristics,so the design of the two cells NOCS sensor is failed as the two preconditions are mutual contradiction.The three-electrode and two-electrode sensor have been designed based on the traditional atmospheric corrosion monitor which are applicable to monitoring the corrosion of complex galvanic strutures in atmospheric environment. In order to investigate the reliability of the two-electrode and three-electrode sensor, electrochemical noise measurement, galvanic potential and current measurement and macroscopic morphology observe has been done. The results show that the three-electrode sensor based on electrochemical noise technique can monitor the rate change trend of the galvanic corrosion, and make predictions to the time that the dangerous caused by corrosion may occur and give the corrosion rate at this very moment based on macroscopic morphology observation. The two-electrode sensor which has been simplified is not suitable for monitoring the corrosion of complex galvanic structures, because it cannot provide the electrochemical signal separately which is reflect the corrosion status of the galvanic structures.