Titanium

If we are ever to use the motion of the seas as a source of sustainable energy then titanium will make it possible. The thin oxide layer on the surface of this metal resists the corroding action of sea water which is why it is used in off-shore rigs, submarines, ships' propellers, and desalination plants. Nor does the human body attack or reject the metal, so titanium is used for pinning together broken bones, for hip and knee replacements, pacemakers, and cranial plates for skull fractures.