Britannica Nobel Prize: Hafnium
Detailed overview and data.
ChemicalElements.com: Hafnium
Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Hafnium
Atomic structure, chemical and physical properties, and table of nuclides.
It's Elemental: Hafnium
Basic physical and historical information.
Lenntech: Hafnium
Physical data, chemical properties, health and environmental effects.
Visual Elements: Hafnium
General and physical information, source, uses, key isotopes, and ionisation energies.
WebElements: Hafnium
Extensive information on history, uses, occurrence, compounds, and properties.
Wikipedia: Hafnium
Properties of the element, including its history, applications, and characteristics.