Magnetic iron nanoparticles have been studied for the last years due to their properties and it potential application in biomedical topics; as hyperthermia, magnetic resonance imaging (MRI) agents, biosensors, magnetic carriers and targeted drug delivery. In this context, the aim of this study was to study the electrochemical behavior of a nanostructured magnetic polycaprolactone/hematite-alumina composite in order to identify the corrosion mechanisms of coating immersed in an artificial body solution at 37 °C. The composite material was developed during the synthesis of the polycaprolactone (PCL) matrix with simultaneous additions of alumina (Al₂O₃) and hematite (Fe₂O₃) nanoparticles in a 1.5 % of weight ratio. Hematite fraction was the magnetic factor of composite coating. The particles were synthesized by sol-gel technique, using stoichiometric aluminum isopropoxide Al(OC₃H₇)₃ and ferric chloride (FeCl₃) as precursors maintained at 85 °C during 72 hours of reaction in propanol as solvent and 6 M nitric acid as catalyst under continuous stirring. The synthesis was realized at vacuum of -300 mercury millimeters (Hg mm) condition with an injection of 1.39 g of helium flux as inert gas. The resulting sols were dried to 60 °C during 48 hours. Obtained powders were characterized by DSC/TGA, Fourier transform infrared spectroscopy (FTIR) and X-Ray Diffraction analysis (XRD), Morphological characterization of powders and composite coatings were done by scanning electron microscopy (SEM), and hysteresis parameters showed the formation of magnetic hematite and alumina nanoparticles. In accord with DSC/TGA analysis, each sample were heat treated at 1100 °C. Coatings were obtained by immersion technique using foils of 316L stainless steel as substrate and composite mixture in liquid condition, and then were dried in oven at 60 °C. Corrosion behavior were evaluated by the three electrochemical techniques. Potentiodinamic test applying a -500 to 1500 mV vs open corrosion potential (OCP) with a 1 mV/s scan rate. Linear polarization resistance (LPR) realized within a ± 15 mV vs OCP at 1 mV/s scan rate each 15 minutes during 48 h. Impedance spectroscopy (EIS) was realized in the frequency of 30 kHz to 0.01 Hz with a potential signal amplitude of 30 mV vs OCP. Hank's saline solution at 37 °C was the used electrolyte. Three electrodes cell arrangement was used with an Ag/AgCl saturated reference electrode, platinum wire as auxiliary electrode and the coating samples. Results showed an average thickness of the coating of 1.43 μm. Electrochemical results showed the coating sample behavior with two potential range windows associated to the effect of PCL/Al₂O₃-Fe₂O₃ nanoparticles composite and the substrate reaction interface respectively, since PCL and 316L substrate showed wide resistive potential window and moderated window respectively with a difference of 3 order of magnitude between both. The EIS results presented a high resistive mechanism by the PCL coating, but decreased by the oxides particles additions, showing a mechanism governed by diffusion of species through polymeric matrix paths promoted by the oxide nanoparticles. The SEM characterization of samples after immersion was realized in order to complement the discussions of results.

Keywords: polycaprolactone/hematite-alumina composite; Electrochemical techniques; Hank’s solution.

Acknowledgements

The present research was supported by CONACYT for the project financing number: CB-2014-01-243236, I0017 Fund.