Passivation is the process of making a material "passive".  The material is made inert or with reduced ability to react with the surroundings.  This is necessary to prevent rust formation and corrosion.

Passivation involves the creation of a protective layer on the surface of the material.  This is usually an oxide.  Iron can be passivated by heating it in an atmosphere of oxygen.  A layer of oxide is formed.  This layer prevents further attack by oxygen.

Nickel pipes can be used to handle fluorine by passivation.  A layer of fluoride is allowed to form on the surface.  This prevents further reaction.