Corrosion Resistance of Mg₇₂Zn₂₄Ca₄ and Zn₈₇Mg₉Ca₄ Alloys for Application in Medicine

The aim of this work was to monitor the corrosion rate of the Mg₇₂Zn₂₄Ca₄ and Zn₈₇Mg₉Ca₄ alloys. The purity of the alloying elements was 99.9%. The melt process was carried out in an induction furnace. The melting process took place under the cover of an inert gas (argon). The copper form was flooded by liquid alloy. Then, in order to obtain ribbons, the cast alloy, in rod shape, was re-melted on the melt spinning machine. The corrosion resistance of both alloys has been determined on the basis of the following experiments: measurements of the evolution of OCP (open circuit potential), LSV (linear sweep voltamperometry) and EIS (electrochemical impedance spectroscopy). All corrosion tests were carried out in Ringer's solution at 37 °C and pH 7.2. The corrosion tests have revealed that the zinc alloy, Zn₈₇Mg₉Ca_4, exhibits significantly higher corrosion resistance in the Ringer solution compared to the magnesium alloy, Mg₇₂Zn₂₄Ca₄. Moreover, it has been shown that the cathodic reaction proceeds faster on the surface of ribbons. EIS measurements show that the dissolution of Mg alloy proceeds with two steps: transfer of Mg²⁺ ions to the Ringer solution and then the formation of the corrosion products, which are deposited on the surface of magnesium alloy. It has been revealed, too, that for both bulk materials, diffusion of chloride ions through the corrosion product's layer takes place.