Symbol: Hf
Atomic Number: 72
Atomic Weight: 178.49
Element Classification: Transition Metal
Discovered By: Dirk Coster, Georg von Hevesy
Discovery Date: 1923 (Denmark)
Name Origin: Hafnia, the Latin name of Copenhagen.

Density (g/cc): 13.31
Melting Point (K): 2503
Boiling Point (K): 5470
Appearance: Silvery, ductile metal
Atomic Radius (pm): 167
Atomic Volume (cc/mol): 13.6
Covalent Radius (pm): 144
Ionic Radius: 78 (+4e)
Specific Heat (@20C J/g mol): 0.146
Fusion Heat (kJ/mol): (25.1)
Evaporation Heat (kJ/mol): 575
Thermal Conductivity (@25C W/m K):
Debye Temperature (K): n/a
Pauling Negativity Number: 1.3
First Ionizing Energy (kJ/mol): 575.2
Oxidation States: 4
Electronic Configuration: [Xe] 4f14 5d2 6s2
Lattice Structure: Hexagonal (HEX)
Lattice Constant (): 3.200
Lattice C/A Ratio: 1.582

Mineral Hardness [no units]: 5.5
Brinell Hardness [/MN m-2]: 1700
Vickers Hardness [/MN m-2]: 1760

Note: Pure hafnium is a soft, ductile hexagonal close-packed metal that can deform by mechanical twinning if handled aggressively in sectioning and grinding. As with most refractory metals, grinding and polishing removal rates are low and eliminating all polishing scratches and deformation can be difficult. It may even be possible to form mechanical twins in compression mounting. Hafnium alloys can contain very hard phases that make relief control more difficult. To improve polarized light response, it is common practice to chemically polish specimens after mechanical polishing. Alternatively, attack polishing additions can be made to the final polishing abrasive slurry, or vibratory polishing may be employed.

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