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Chemical characteristics

Hafnium reacts in air to form a protective film that inhibits further corrosion. Despite this, the metal is attacked by hydrofluoric acid and concentrated sulfuric acid, and can be oxidized with halogens or burnt in air. Like its sister metal zirconium, finely divided hafnium can ignite spontaneously in air. The metal is resistant to concentrated alkalis.

As a consequence of lanthanide contraction, the chemistry of hafnium and zirconium is so similar that the two cannot be separated based on differing chemical reactions. The melting and boiling points of the compounds and the solubility in solvents are the major differences in the chemistry of these twin elements.