Abstract: The diffusing behavior of water through alkyd coatings with different pigment volume concentration (PVC) has been studied by EIS and SEM techniques. T he corresponding diffusion coefficients were also calculated. The experimental r esults showed that, in 0.5 mol•L－1 NaCl solution, the diffusion process of wat er through alkyd coatings with different PVC followed the idealFick′s law in the initial period.Within the PVC value concerned, the diffusion coefficients in itially decreased with the increase of PVC parameter, reaching a minimum value a t 60 ％, which is the CPVC of micaceous iron oxide, and then increased with the PVC increase. When the PVC was less than CPVC, the barrier property produced by the pigment was the main factor that affected the water diffusion behavior. Howe ver, the microstructure of the alkyd coatings played an important role when the PVC was greater than CPVC.

Key words: Electrochemical impedance spectroscopy(EIS), SEM, Pigment volume co ncentration (PVC), Alkyd coatings, Diffusion behavior, Diffusion coefficient