Electrochemical Impedance Spectroscopy (EIS) of parylene coated magnesium stents in organic solvent to study early corrosion control

Layers on stents of Mg-Nd-Zn-Zr alloy, after different treatments were studied by electrochemical techniques in an organic electrolyte. Electrochemical impedance results show a constant-phase-element (CPE) behavior, which was attributed to the layers on stent surface, as well as diffusion impedance associated with Mg2+ ions diffusion. Power law model was suggested to characterize electrical properties of the layers. Additionally, samples with oxide layers presented a high-frequency distribution which was well described by complex ohmic impedance. Compared with bare and plasma pre-treated stents, the parylene coatings showed lower capacitances values, associated with a thicker layer which is maintained after crimping and expansion.