Evaluación electroquímica de la degradación de la aleación de Mg-Zn-Ca en la solución fisiológica de Hanks

Abstract

The effect of Zn (0.95% wt.) and Ca (0.15% wt.) alloying elements on the general degradation mechanism of Mg was investigated in this work. Pure Mg and Mg-Zn-Ca alloy surfaces were characterized during their exposure to Hanks’ physiological solution (at 37 °C) for up to 7 days by SEM-EDS and XPS techniques. The layers formed on the alloy surface contained Ca10(PO4)6(OH)2, which may improve the bone compatibility. The intermetallic particles composed of Mg2Ca-phase, as well as the presence of Zn, promoted the formation of a more uniform protective layer. The EIS and electrochemical noise (EN) tests indicated that the polarization resistance (Rp) of pure Mg is one order of magnitude lower and the current noise resistance (Rn) ≈ 5 times, than those of Mg-Zn-Ca alloy. The pitting index (PI) values of each material were below 0.6, suggesting that the corrosion attack is not highly localized. At the end of the immersion tests, the concentration of Mg-ion released during degradation was ≈ 4.5 times higher for pure Mg (1.63 ± 0.02 mg·cm−2) than that of Mg-Zn-Ca (0.35 ± 0.03 mg·cm−2). Consequently, the calculated corrosion current density (jcorr) for pure Mg was two times higher (1.33 μA·cm−2) than that of ZX10 Mg-alloy (0.59 μA·cm−2).