Aluminium

Symbol: Al
Atomic Number: 13
Atomic Weight: 26.981539
Element Classification: Other Metal
Discovered By: Hans Christian Oersted
Discovery Date: 1825 (Denmark)
Name Origin: Latin: alumen, aluminis, (alum).

Density (g/cc): 2.6989
Melting Point (K): 933.5
Boiling Point (K): 2740
Appearance: Soft, lightweight, silvery-white metal
Atomic Radius (pm): 143
Atomic Volume (cc/mol): 10.0
Covalent Radius (pm): 118
Ionic Radius: 51 (+3e)
Specific Heat (@20C J/g mol): 0.900
Fusion Heat (kJ/mol): 10.75
Evaporation Heat (kJ/mol): 284.1
Thermal Conductivity (@25C W/m K):
Debye Temperature (K): 394.00
Pauling Negativity Number: 1.61
First Ionizing Energy (kJ/mol): 577.2
Oxidation States: 3
Electronic Configuration: [Ne] 3s2 3p1
Lattice Structure: Face-Centered Cubic (FCC)
Lattice Constant (): 4.050
Lattice C/A Ratio: n/a

Mineral Hardness [no units]: 2.75
Brinell Hardness [/MN m-2]: 245
Vickers Hardness [/MN m-2]: 167

Note: Aluminum is a soft, ductile metal. Deformation induced damage is a common preparation problem in the purer compositions. After preparation, the surface will form a tight protective oxide layer that makes etching difficult. Commercial grades contain many discrete intermetallic particles with a variety of compositions. These intermetallic particles are usually attacked by etchants before the matrix. Although the response to specific etchants has been used for many years to identify these phases, this procedure requires careful control. Today, energy-dispersive analysis is commonly performed for phase identification due to its greater reliability.

For many aluminum alloys, excellent results can be obtained using a four step procedure. This procedure retains all of the intermetallic precipitates observed in aluminum and its alloys and minimizes relief. Synthetic napless cloths may also be used for the final step with colloidal silica and they will introduce less relief than a low or medium nap cloth, but may not remove fine polishing scratches as well. For very pure aluminum alloys, this procedure could be followed by vibratory polishing to improve the surface finish, as these are quite difficult to prepare totally free of fine polishing scratches.

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