I elaborated an Ni-W coating under pulsed currents. For corrosion tests, I studied the evolution of the phase angle diagram by EIS (Electrochemical Impedance Spectroscopy). The porosity of films was calculated using image analysis. I'd like to know if there is a mathematical relationship between porosity of the coating and the phase angle vs. frequency diagram.
There is a relationship between the polarization resistance and porosity
see the following paragraph:
The porosity of the coating can be estimated from following equation:
P = (Rps / Rp) × 10 – (ΔEcorr / bA)
Where P is the total coating porosity , Rps is the polarization resistance of the substrate, Rp is the polarization resistance of the coated substrate, ΔEcorr is the difference potential between the free corrosion potentials of the coated metal and the bare substrate, and bA is the anodic Tafel slope for the substrate. For measuring the porosity of a coating, according to Notter and Gabe and Weng et al. the linear polarization method is valid only if the polarization current of the coating is negligible compared to the substrate and in test solution no passivation phenomena take place on the substrate.
i worked on porous electrodes - you attempt using phase angle - for perfectly porous electrode phase angle is 22.5 degree
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