2.4.6. Corrosion Tests

Corrosion tests were performed in testing tubes filled with 250 mL simulated body fluid (SBF) with a composition according to SBF27 from [43], a pH value of 7.35. The tests were conducted at a temperature of 37 ◦C and the SBF was changed every seven days. Two disc-shaped samples with the same diameter of 10 mm and a height between 0.4 mm and 0.7 mm were immersed together in order to have a larger total surface area. The samples were polished with SiC-paper (1200 grid) and cleaned with ethanol directly before the start of the test.

The corrosion of Mg alloys leads to the formation of hydrogen gas, which accumulates at the top of the testing tubes [44,45], according to the reaction

$$\text{Mg} + 2\text{H}\_2\text{O} \rightarrow \text{Mg(OH)}\_2 + \text{H}\_2$$

The amount of H2 gas was recorded every 4 h and normalized by the initial sample's surface area. A numerical derivation was conducted to obtain the corrosion rate followed by a moving average algorithm to smoothen the curves. Two tests were performed for each material in each condition. The corrosion test set-up has already been described previously [46,47].
