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Investigating the Effect of the Size of Zirconia Nanoparticles on the Corrosion Resistance of AZ31 Magnesium Alloy Coronary Stents Using the Plasma Electrolytic Oxidation Method

Adib Anbardan, Faezeh | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58664 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Afshar, Abdullah; Dolati, Abolghasem
  7. Abstract:
  8. The magnesium alloy AZ31 has emerged as a suitable alternative to stainless steels and titanium for the production of medical stents due to its superior biocompatibility and biodegradability compared to other biodegradable metals such as zinc and iron. However, magnesium and its alloys exhibit high reactivity, with a standard potential of -2.36 V relative to the standard hydrogen electrode, making them the most active metals in human blood plasma. As a result, the high corrosion rate of magnesium and its alloys presents one of the greatest challenges in the production of medical materials from this metal. One approach to reducing the corrosion rate of AZ31 magnesium alloy is surface modification via plasma electrolytic oxidation (PEO). The PEO coatings usually possess a porous structure with microcracks, allowing corrosive electrolytes to penetrate through the pores and reach the substrate, which results in increased corrosion beneath the coating. To improve the surface morphology of the coatings and reduce the size and density of the pores, zirconia nanoparticles have been utilized. The purpose of this study is to investigate the effect of zirconia nanoparticle sizes (50 nm and 100 nm) on the corrosion resistance and surface morphology of the coatings. The morphology of the coatings was examined using Field Emission Scanning Electron Microscopy (FESEM). The chemical composition and phase structure of the coatings were determined through Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) analysis. Corrosion resistance of the coatings was assessed using Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS) techniques. The study results show that zirconia nanoparticles with a grain size of 100 nm significantly improve the corrosion resistance and surface morphology of AZ31 magnesium coatings. Specifically, the corrosion current density of uncoated magnesium, which was initially 1.6×10−5 A/cm², was reduced to 6.1×10−8 A/cm² for the sample coated with 100 nm zirconia nanoparticles. Additionally, the average pore diameter on the surface improved from 0.63μm for the PEO coating without additives to 0.14μm for the coating incorporating 100 nm zirconia nanoparticles.
  9. Keywords:
  10. Plasma Electrolytic Oxidation ; Stent ; Zirconia Nanoparticles ; Particle Size Detection ; AZ31 Magnesium Alloy ; Biodegradable Implants

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