The influence of cathodic polarization and simulated inflammation on titanium electrochemistry.

This study evaluated the influence of simulated inflammation and cathodic polarization on the electrochemical properties of commercially pure titanium (CpTi) and titanium-6%aluminum-4%vanadium (Ti6Al4V). Normal conditions immersed the metals in phosphate buffered saline at open circuit potential (OCP). Inflammatory conditions immersed the metals in a 150 mM hydrogen peroxide titrated to pH = 5.0 at OCP. Cathodic inflammatory conditions immersed the metals in the inflammatory electrolyte at -1 V versus Ag/AgCl. Cathodic polarization scans revealed a more electropositive corrosion potential (Ecorr ) and an increased corrosion current density (Icorr ) for both metals after incubation at inflammatory conditions (CpTi: Ecorr  = 171 mV, Icorr  = 147 nA/cm(2) and Ti6Al4V: Ecorr  = 241 mV and Icorr  = 413 nA/cm(2) ) as compared to normal conditions (CpTi: Ecorr  = -249 mV, Icorr  = 19 nA/cm(2) and Ti6Al4V: Ecorr  = -263 mV and Icorr  = 11 nA/cm(2) ). Electrochemical impedance spectroscopy showed the polarization resistance (Rp ) decreases and constant phase element (CPE) magnitude increases for both metals when comparing normal (CpTi: Rp  = 3.5 MΩ cm(2) , CPE = 35 µS s(α) /cm(2) and Ti6Al4V: Rp  = 6.5 MΩ cm(2) and CPE = 30 µS s(α) /cm(2) ) to inflammatory (CpTi: Rp  = 79 kΩ cm(2) , CPE = 55 µS s(α) /cm(2) and Ti6Al4V: Rp  = 230 kΩ cm(2) and CPE = 56 µS s(α) /cm(2) ) to cathodic inflammatory (CpTi: Rp =24 kΩ cm(2) , CPE = 290 µS s(α) /cm(2) and Ti6Al4V: Rp  = 12 kΩ cm(2) and CPE = 250 µS s(α) /cm(2) ) conditions. These observed changes are consistent with the formation of a thin and defective oxide film. Inductively coupled plasma mass spectroscopy revealed that inflammatory conditions increased dissolution of both metals and that the addition of cathodic potential significantly increased the dissolution of the beta phase elements of Ti6Al4V.