Investigating an effective model to estimate the water diffusion coefficient of a hybrid polymer-oxide coating

An effective model was developed to predict the water diffusion coefficient in a hybrid polymer-oxide coating. The composite coating consists of microarc oxidation (MAO) coating and silicone-epoxy (SE) coating. The performance of the SE/MAO coating and MAO-coated samples were studied by adhesion tests, X-ray photoemission spectroscopy (XPS), Fourier transform infrared spectrometer (FTIR) and scanning electron microscopy (SEM). The electrochemical impedance spectroscopy (EIS) was used to study the water transport behavior of the coatings. The diffusion coefficient (D^exp) obtained from the EIS experimental measurement was compared with the effective diffusivity (D^eff) predicted by the mathematical model based upon the Ohm's law and the model based on the effective validation model (EVM) which considers the water concentration jump at the SE and MAO coating interface The results demonstrated that the noncontinuity of the water concentration at the SE/MAO interface resulted in a difference between the diffusion coefficient obtained by the EIS results and mathematical model. The effective diffusion (D^eff) coefficient derived from the EVM (6.47 × 10⁻¹² cm²·s⁻¹) was similar to the D^exp obtained by the EIS experimental method (7.22 × 10⁻¹² cm²·s⁻¹).