Question

1. Titanium does not generally undergo crevice corrosion at temperatures below 70°C. However, when surgeons have carried out operations to remove titanium hip implants that were causing pain, they have noticed corrosion on the stem of the implants, and measured a decrease in pH at the location of the corrosion. They have also noted that the bone cement used to attach the implant to the bone has become detached from the implant. Explain the process that causes the corrosion.

Answer 1

Titanium metal is highly non-corrosive metal in normal condition because when it exposes to the atmosphere, it forms a highly dense and nonporous TiO2 layer, which acts as a protecting layer. As long as the oxide layer is stable the bulk metal is protected. But when the pH around the implant decreases (body fluid is acidic) to the acidic range, the oxide layer would dissolve and the passive protective layer breaks down, which makes the implant to undergo corrosion specifically at that reason of acidic environment. This type of corrosion ia called as crevice corrosion.