Hafnium - Hf General Information Discovery Hafnium was discovered by D. Coster and G.C. von Hevesey in 1923 in Copenhagen, Denmark. Appearance Hafnium is a lustrous, silvery, ductile metal. Source Most zirconium minerals contain 1-5% hafnium, and the metal is prepared by reducing the tetrachloride with sodium or magnesium. Uses Hafnium has a good thermal absorption cross-section for neutrons, so is used in control rods in nuclear reactors. It has been successfully alloyed with several metals including iron, titanium and niobium. It is also used in gas-filled and incandescent lights. Biological Role Hafnium has no known biological role, and is non-toxic. General Information Hafnium resists corrosion due to an oxide film, but powdered hafnium will burn in air. It is unaffected by all acids except hydrogen fluoride, and also all alkalis. At high temperatures it reacts with oxygen, nitrogen, carbon, boron, sulfur and silicon.

	Physical Information
	Atomic Number		72
	Relative Atomic Mass (12C=12.000)		178.49
	Melting Point/K		2503
	Boiling Point/K		5470
	Density/kg m-3		13310 (293K)
	Ground State Electron Configuration		[Xe]4f145d26s2
	Electron Affinity(M-M-)/kJ mol-1		+61

	Key Isotopes
	nuclide	172Hf	174Hf	175Hf	176Hf	177Hf
	atomic mass		173.9		175.9	176.9
	natural abundance	0%	0.2%	0%	5.2%	18.6%
	half-life	5 yrs	2x1015 yrs	70 days	stable	stable
	nuclide	178Hf	179Hf	180Hf	181Hf	182Hf
	atomic mass	177.9	178.9	179.9
	natural abundance	27.1%	13.7%	35.2%	0%	0%
	half-life	stable	stable	stable	42.5 days	9x106 yrs

Other Information
Enthalpy of Fusion/kJ mol-1		25.5
Enthalpy of Vaporisation/kJ mol-1		570.7
Oxidation States
main	Hf+4
others	Hf+1, Hf+2, Hf+3

	Ionisation Energies/kJ mol-1
	M - M+	642
	M+ - M2+	1440
	M2+ - M3+	2250
	M3+ - M4+	3216
	M4+ - M5+
	M5+ - M6+
	M6+ - M7+
	M7+ - M8+
	M8+ - M9+
	M9+ - M10+