Electrical Impedance for Coating Residual Lifetime

Thread by Charles Fisher on 12 Jul 2010 at 16:19:50 
Dear All:

Thanks for the CheFEM part on this website. The prediction of fluid-coating interactions is still of major importance in many industrial applications. So, for selection of the proper materials, a software tool like CheFEM is very helpful. But can the software also be used to predict the residual lifetime of an industrial coating applied in real life circumstances (assuming that the processing environment was not ideally)?

Reason for asking is that recently I read an article in which they state that Electrical Impedance Spectroscopy (EIS) can be used for measuring the residual corrosion lifetime of industrial coatings. By measuring the deviation in the conductivity (caused by diffused water) from stationary conditions, they say that the lifetime of the coating can be determined.

My experience with EIS in diffusion & blister measurements is that the method is miles away from robustness. For example, in accelerated testing we got blister formation on the substrate without a noticeable change in conductivity. So is the EIS story for residual coating corrosion life time prediction another flavor of the month?

Regards,
Charles

    Comment by Sylvia on 13 Jul 2010 at 13:47:27  | |responses: 3|
    Electrical Impedance for Coating residual lifetime is a project in which the wish has been the father to the thought. The data generated by the method is not robust and hardly reproducable. It gives many headaches to derive a single water diffusion coefficient from the method, and the Fickian equilibrium is not attained explicitely. Hence, it can not deal with cyclic environmental moisture variations, and the programmed baseline will be dependent on the material (of which the diffusion coefficient could have been measured using the mass uptake method, or the software on this site anyway), it can not deal significantly with corrosion and degradation of the polymer chains, and the promised inclusion of UV degradation is close to crap.

    Regards,
    Sylvia

      Comment by Composite Agency on 13 Jul 2010 at 15:00:27  | |responses: 2|
      Dear All,

      In 2007 we have done some pilot Electrochemical Impedance Spectroscopic (EIS) measurements and Electrochemical Noise Measurements (ENM) for determining the diffusion coefficient of water in several thin films. The results were indeed not so good, and DVS weight measurements appeared to be necessary. We do not believe that any substantial or fundamental has happened since then, apart from a database that has been developed to cover all the materials (read: variations). Moreover, for some reason, a standard has been developed (NEN-EN-ISO 16773-1:2007 en. Verven en vernissen - Elektrochemische impedantiespectroscopie (EIS) op hoge-impedantie beklede monsters).

      Regards,
      Composite Agency

      p.s. As a result of the EIS experiments in 2007, we have nevertheless included the EIS interpretation coding in the CheFEM, Module 100. So if someone would like to give it a second try, the EIS and ENM interpretation (eventually coupled to the database) can be carried out...

        Comment by Charles on 25 Aug 2010 at 19:56:46  | |responses: 1|
        Composite Agency & Sylvia,

        Thanks for your help.

        Charles

          Comment by Sylvia on 26 Aug 2010 at 16:01:37  | |responses: 0|
          Charles and Composite Agency,

          You are welcome!