Title : Accurate calculation of nano scale oxide layer thickness of titanium alloys by electrochemical impedance equivalent circuit modeling
Metallic materials such as stainless steel, Co-Cr alloys as well as more advanced alloys such as titanium-based Ti-Al-V or Ni-Ti alloys are widely used for biomedical applications such as orthopedic implants, cardiovascular devices, and dental implants.
Despite the mechanical advantages biomedical alloys provide, their potential risk of corrosion and ion release, while in contact with surrounding tissues and body fluids, limit their use as biomaterials, therefore, improving corrosion resistance of metallic materials has been an ongoing area of research. One of the very common methods for improving the corrosion resistance of biomedical alloys is forming a protective barrier on the alloy surface where the implant-tissue interactions is expected to take place. While this barrier may be inserted in the form of a coating, a more effective method is using the thin passive-oxide layer that naturally forms on some alloys when subjected to body fluids. However, during extended exposure to body fluids, the natural passive oxide layer is also subjected to a continuous cycle of dissolution and reformation, through which its thickness varies, and its protectiveness is affected. Consequently, it becomes crucial to estimate the oxide layer thickness and be able to observe its dissolution and reformation behavior during prolonged exposures to body fluids for a proper corrosion analysis of metallic biomaterials. Specifically, estimation of the oxide layer thickness at various durations of exposure to body fluids along with ion release data at each specific time span can provide valuable information on the durability and the protectiveness of an oxide layer for actual use. The ongoing interest on metals as biomedical materials despite the development of novel and advanced non-metallic biomaterials is mainly due to the mechanical advantage they provide, especially for implant materials.
Experimental characterization of passive oxide layer thickness is a challenging process, since the naturally formed layer thickness is around nano scale and can be easily destroyed. Some commonly used experimental methods for oxide layer thickness estimation in previous studies include imaging techniques such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Transmission Electron Microscopy (STEM) as well as quantitative methods like X-ray Photoelectron Spectroscopy (XPS) however each method has their limitations and to the best of the author’s knowledge, an experimental method, which provides accurate information about passive oxide layer thickness together with corresponding ion release data from an ongoing experiment without disrupting the experimental set-up, has not been developed yet.
With this motivation, the current study aims to develop a method for the accurate measurement of passive oxide layer thickness on metallic biomaterials in simulated body fluid media, during an ongoing experiment at various time periods of exposure, without disrupting the experimental set-up. For this purpose, Electrochemical Impedance Spectroscopy (EIS), non-invasive and straightforward technique, combined with equivalent circuit modeling was used to calculate the nano scale level oxide film thickness of Ti-based alloys.
- The audience will learn and be able to apply the approach to measure nano scale oxide layer thickness of metals accurately in a practical way.
- The audience will understand the importance of the oxide layer on metals used in biomaterial applications.
- The audience will see a connection between electrochemical engineering and nanotechnology by this study.