Titanium
Titanium can combine with other chemicals to make different materials. When titanium mixes with oxygen from the air, it forms titanium dioxide (TiO2) or titania, which forms a hard passivation layer around the metal that prevents corrosion. Titanium dioxide is a white pigment that is often used to make things less transparent, brighter, or rougher - because it does not react with chemicals inside the human body, it is safe to use in foods and other applications, like toothpaste.