Effect of Temperature, Electrolyte Composition and Immersion Time on the Electrochemical Corrosion Behavior of CoCrMo Implant Alloy Exposed to Physiological Serum and Hank's Solution

A new study about corrosion behavior of CoCrMo alloy used as implant material exposed to the physiological serum and Hank's solution in different temperatures, electrolyte compositions and immersion time were simulated, using open circuit potential (OCP), potentiodynamic polarization curves (PPC) and electrochemical impedance spectroscopy (EIS.) From the results, it can be concluded that CoCrMo biomaterial is influenced by electrolyte composition and temperature, and the passive films were more protective when formed in presence of physiological serum. Comparing the Ecorr for both solutions, it is possible to verify that the Hank's solution presented values more negative for the two studied temperatures (25 and 37 °C), indicating a greater susceptibility to the corrosion process. Regarding the results of potentiodynamic polarization, the ipass, decreased as function of time, indicating a more protective passive film at 25 °C. In regards to the physiological serum, the highest ipass values at 37 ºC evidenced the formation of a less stable passive film. The different behavior of ipass in Hank's solution may be related to the competitiveness between a possible film of D-glucose and oxides of the alloy metals. EIS studies suggest that the film formed in presence of physiological serum is nobler than that with Hank's solution.

本研究针对作为植入材料的钴铬钼（CoCrMo）合金展开，模拟其在不同温度、电解质组分及浸泡时长下，于生理盐水（physiological serum）与汉克液（Hank's solution）中的腐蚀行为；测试采用开路电位（open circuit potential, OCP）、动电位极化曲线（potentiodynamic polarization curves, PPC）以及电化学阻抗谱（electrochemical impedance spectroscopy, EIS）三种表征手段。基于实验结果可得出如下结论：该生物医用CoCrMo合金的腐蚀行为受电解质组分与温度的显著影响，且在生理盐水中形成的钝化膜（passive film）具备更优异的防护性能。对比两种溶液中的腐蚀电位（corrosion potential, Ecorr）可发现，在本次研究的两个测试温度（25℃与37℃）下，汉克液中的腐蚀电位数值更负，表明合金在汉克液中更易发生腐蚀。针对动电位极化曲线的测试结果，钝化电流密度（passive current density, ipass）随浸泡时长的增加呈下降趋势，这说明25℃下形成的钝化膜防护性能更佳。而就生理盐水体系而言，37℃下测得的最高钝化电流密度值则印证了此时形成的钝化膜稳定性相对更差。汉克液中钝化电流密度的变化规律与生理盐水体系存在差异，这可能与D-葡萄糖可能形成的薄膜与合金金属氧化物之间的竞争作用相关。电化学阻抗谱测试结果表明，生理盐水中形成的钝化膜比汉克液中形成的钝化膜具备更高的钝性，即更耐腐蚀。