Effects of Open Circuit Immersion Time and Vertex Potential on Cyclic Potentiodynamic Polarization Scans of Two Metallic Biomaterials

Abstract

Electrodes made of commercially pure titanium (CP-Ti) and a CoCrMo alloy were immersed at open circuit in a phosphate buffer saline electrolyte at room temperature for different durations prior to electrochemical analyses. Open circuit potential measurements, electrochemical impedance spectroscopy measurements and cyclic potentiodynamic polarization (CPP) scans were used to assess the impact of the immersion time on derived property values. Stable passivation layers formed on both materials during immersion. The corrosion potentials determined from anodic legs of CPP scans became more cathodic and the corrosion currents decreased to lower values after longer immersion times. Layers formed on CP-Ti stabilized during forward anodic scans and persisted to the vertex potential, whereas passivation breakdown occurred during anodic scans with CoCrMo with active corrosion at voltages up to the vertex potential. The characteristics of the return cathodic legs of CPP scans represented the surface conditions present at the vertex potential: characteristic corrosion property values derived from the test responses represented passivated surfaces on CP-Ti and leached surfaces on CoCrMo rather than intrinsic properties of those materials.