Browsing by Subject "electrochemical behaviors"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Electrochemical Behavior of Micro-arc Oxidation Coated Magnesium Alloy in Cell Culture Medium
    (Office of the Vice Chancellor for Research, 2015-04-17) Liu, Jiayang; Zhang, Jing
    The electrochemical behaviors of MAO (micro-arc oxidation) coated AZ31 magnesium alloys immersed in cell culture medium are reported. Four different MAO processing times (1 minute, 5 minutes, 15 minutes and 20 minutes) were used to produce the MAO coatings on AZ31 magnesium alloy sample surface. After cell culture medium immersion tests, all samples demonstrate similar electrochemical behaviors regardless of MAO processing time, which is in contrast with immersion in simulated body fluids. The corrosion rates in cell culture medium are much lower than in simulated body fluid. This can be explained by the organic molecules in the cell culture medium and a dense passive layer formed on the samples surface, which prevent aggressive ions, such as chloride ions, from corroding the alloy substrate.
  • Thumbnail Image
    Item
    Electrochemical behaviors of micro-arc oxidation coated magnesium alloy
    (2014) Liu, Jiayang; Zhang, Jing; Chen, Jie; Li, Jiliang; Na, Sungsoo
    In recent years, magnesium alloys, due to their high strength and biocompatibility, have attracted significant interest in medical applications, such as cardiovascular stents, orthopedic implants, and devices. To overcome the high corrosion rate of magnesium alloys, coatings have been developed on the alloy surface. Most coating methods, such as anodic oxidation, polymer coating and chemical conversion coating, cannot produce satisfactory coating to be used in human body environment. Recent studies demonstrate that micro-arc oxidation (MAO) technique can produce hard, dense, wear-resistant and well-adherent oxide coatings for light metals such as aluminum, magnesium, and titanium. Though there are many previous studies, the understanding of processing conditions on coating performance remains elusive. Moreover, previous tests were done in simulated body fluid. No test has been done in a cell culture medium, which is much closer to human body environment than simulated body fluid. In this study, the effect of MAO processing time (1 minute, 5 minutes, 15 minutes, and 20 minutes) on the electrochemical behaviors of the coating in both conventional simulated body fluid and a cell culture medium has been investigated. Additionally a new electrolyte (12 g/L Na2SiO3, 4 g/L NaF and 4 ml/L C3H8O3) has been used in the MAO coating process. Electrochemical behaviors were measured by performing potentiodynamic polarization and electrochemical impedance spectroscopy tests. In addition to the tests in simulated body fluid, the MAO-coated and uncoated samples were immersed in a cell culture medium to investigate the corrosion behaviors and compare the difference in these two kinds of media. The results show that in the immersion tests in conventional simulated body fluid, the 20-minute MAO coated sample has the best resistance to corrosion due to the largest coating thickness. In contrast, in the cell culture medium, all MAO coated samples demonstrate a similar high corrosion resistance behavior, independent of MAO processing time. This is probably due to the organic passive layers formed on the coating surfaces. Additionally, a preliminary finite element model has been developed to simulate the immersion test of magnesium alloy in simulated body fluid. Comparison between the predicted corrosion current density and experimental data is discussed.