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Electrophoretic Deposition of Graphene Oxide Nanocomposite on Magnesium substrate Modified by PEO

Abrar, Bahareh | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56808 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. Plasma electrolyte oxidation process is one of the surface coating methods which is recommended to use as a surface preparation before applying the final coating on magnesium alloys due to its unique properties such as excellent adhesion.The aim of this study was to create an oxide layer on the AZ91 substrate and after optimizing the PEO coating conditions and choosing the best coating in order to increase adhesion and corrosion resistance, the composite coating of graphene oxide, hydroxyapatite and chitosan was applied by electrophoretic method. After studying the morphology of PEO oxide coating at current densities of 0.25, 0.35, 0.4, 0.5 and 0.6 amp/cm2 during times of 5 and 8 minutes, it was found that applying coatings at a current density of 0.35 amp/cm2 for 5 minutes in silicate electrolyte resulted the formation of the best coating. In the next step، synthesis and characterization of graphene oxide was done using XRD and UV-vis and then composite coating at 20 V voltage was applied on PEO oxide layer by electrophoretic. In order to investigate the coatings، field emission scanning electron microscopy and X-ray energy diffraction spectroscopy were used and it was observed that adding graphene oxide even in small amounts (0.5%) can reduce cracks in hydroxyapatite and chitosan coatings and by adding it up to 1.5%, it can achieve uniform morphology، while in 2% of graphene oxide the presence of cracks is observed. In order to investigate the antibacterial properties and bioactivity of the coatings, disk diffusion test was performed in order to determine the diameter of the inhibition zone and to investigate the formation of new hydroxyapatites after immersion in SBF solution in incubator for 7 days, morphology of the surfaces were studied. The results showed that with 2% increase of graphene oxide, the diameter of the inhibition zone increased to 27±1 mm, while the PEO oxide coating has shown no activity against Gram-positive bacteria, and new hydroxyapatites are uniformly formed on composite coatings of 1.5% and 2% graphene oxide. It should be noted that XRD analysis is done to study the formed phases in different coatings and the phases of MgO and Mg2SiO4 are formed after PEO process and by applying the second layer of coating, Ca2SiO4 phase is formed due to presence of hydroxyapatite in coating. In order to investigate the corrosion behavior, linear polarization test was performed in SBF solution at 37°C. It was observed that increasing graphene oxide up to 1.5% reduced corrosion current from 54.95 μA/cm2 to 0.35 μA/cm2 compared to uncoated magnesium substrate. Finally, it can be concluded that the coating containing 1.5% and 2% graphene oxide on the AZ91 substrate which has been PEO is a suitable surface for cell migration, proliferation and growth
  9. Keywords:
  10. Plasma Electrolytic Oxidation ; Electrophoretic ; Graphene Oxide ; AZ91 Magnesium Alloy ; Hydroxyapatite ; Chitosan

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