Degradation rates of pure zinc, magnesium, and magnesium alloys measured by volume loss, mass loss, and hydrogen evolution

Degradation rate is an important property to evaluate bioabsorbable metallic material; however, values vary depending on the method of measurement. In this study, three different methods of measuring corrosion rate are compared. The degradable samples to analyze corrosion rates include pure magnesium (Mg), lab produced Mg-Zn-Ca alloy (47-7-2), Mg-Zn-Zr-RE (rare earth) alloys (60-13, 60-14), Mg-Zn-Ca-RE alloy (59B), and pure zinc (Zn). A eudiometer was used to measure hydrogen evolution from the reaction of degradable alloys in Hank's Balanced Salt Solution (HBSS). Corrosion rates based on volume loss of tested alloys in 30 days were calculated using Micro-computed tomography (micro-CT). Final mass change due to corrosion and corrosion removal was measured with a scale. We observed that the corrosion rates indicated by hydrogen evolution were high initially, and slowed down sharply in the following measurements. The corrosion rates of tested alloys calculated by volume loss and mass loss from high to low are: 60-13 ≈ 60-14 ≈ 47-7-2 > 59B > Mg > Zn (p < 0.05). The results provide instruction to experimental methodology to measure corrosion rates of degradable alloys.