Hafnium: reactions of elements
Reaction of hafnium with air
Hafnium metal is coated with an oxide layer that usually renders it inactive. However hafnium will burn in air if provoked to form hafnium dioxide, HfO2. Finely divided hafnium is pyrophoric making it a fire hazard.
Hf(s) + O2(g) → HfO2(s)
Reaction of hafnium with water
Hafnium does not react with water under normal conditions.
Reaction of hafnium with the halogens
Hafnium does react with the halogens upon warming to form hafnium(IV) halides. So, hafnium reacts with fluorine, F2, chlorine, Cl2, bromine, Br2, and iodine, I2, to form respectively hafnium(IV) fluoride, HfF4, hafnium(IV) chloride, HfCl4, hafnium(IV) bromide, HfBr4, and hafnium(IV) iodide, HfI4.
Hf(s) + 2F2(g) → HfF4(s) [white]
Hf(s) + 2Cl2(g) → HfCl4(l) [white]
Hf(s) + 2Br2(g) → HfBr4(s) [white]
Hf(s) + 2I2(g) → HfI4(s) [white]
Reaction of hafnium with acids
Hafnium metal is coated with an oxide layer that usually renders it inactive. Most cold mineral acids have little effect. Hafnium does dissolve in hydrofluoric acid, HF, presumably to form fluoro complexes.
Reaction of hafnium with bases
Hafnium does not appear to react wih alkalis under normal conditions, even when hot.