Evaluation on corrosion behavior of Mg immersed in a simulated body fluid environment

We first investigated the effects of three different corrosion solutions on the corrosion behavior of Mg by measuring the time course of potential and pH and surface observations. In a 120-minute immersion test using distilled water and NaCl solution as the corrosion solution, the potential and pH changed monotonically, and surface changes were minimal. Surface observations revealed the formation of bubbles on the Mg surface and the peeling of corrosion products toward the end of the immersion test. In contrast, in SBF, the potential increased and then decreased over time, but the pH remained almost unchanged. We next conducted a 360-minute immersion test using SBF as the corrosion solution. The corrosion behavior was divided into four stages and surface observations revealed that the surface was divided into two regions: one in which white corrosion products formed and another in which black discoloration occurred. The results of elemental analysis suggested that the white corrosion products were calcium phosphate compounds, and the black areas were deposits of magnesium oxide and magnesium hydroxide. These results suggest that the corrosion behavior of Mg in the human body may change in a complex manner over time.