In our next series of blogs we will review some of the most important chemical elements in heat treatment and metallurgy. We will start with aluminum, or as the rest of the world says, aluminium.
Aluminum (chemical symbol: Al) – lucky number 13
The discovery of aluminum is quite a tale. The ancient Greeks and Romans used alum (aluminum sulfate with potassium) in medicine and dyes. The name originates from the Latin word alumen (alun). de Morveau recognized the base in alum in 1761 and proposed that it be called alumine. Lavoisier thought that alum was an oxide of some undiscovered metal. In 1807, Davy proposed the name alumium for this undiscovered metal, but it wasn't until 1827 that Wohler actually isolated aluminum (an impure form was isolated by Oersted two years earlier). The new metal was called aluminum. Two years later it was changed to “aluminium” (pronounced al-u-min'-i-um) to conform with the "ium" in most other elements. The American Chemical Society changed the spelling back to aluminum in 1925, which we still use. England and elsewhere in the world still spell and pronounce it aluminium.
Aluminum is the most abundant element in the Earth’s crust but is always found in compounds; that is, in combination with other elements. Pure aluminum is a silvery-white metal with many desirable characteristics. It is light, nontoxic (as the metal), non-magnetic and non-sparking. It is somewhat decorative. It is easily formed, machined and cast. It is a good electrical and thermal conductor and has high reflectivity and resistance to oxidation. Pure aluminum is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese and other elements have very useful properties. The Bayer process is used to refine aluminum from bauxite, an aluminum ore, so it can be accommodated in the Hall-Heroult refining process, which is used to make most aluminum.
Aluminum forms numerous compounds including: fluorides (AlF3); chlorides (AlCl3, AlCl3.6H2O); bromides (AlBr3.6H2O, [AlBr3]2); iodides ([AlI3]2); hydrides (AlH3); oxides (Al2O3); sulfides (Al2S3); selenides (Al2Se3); tellurides (Al2Te3); and nitrides (AlN).
Here are a few important facts about aluminum:
Atomic number = 13
Atomic weight (u) = 26.981
Atomic radius (A) = 1.82
Density @ 300K (g/cm3) = 2.70
Melting point (K) = 933.25
Boiling point (K) = 2793
Thermal conductivity (W/cm-K) = 2.37
Electrical conductivity (106/ohm-cm) = 0.377
Heat of vaporization (kJ/mole) = 293.4
(First) Ionization potential (V) = 5.986
Heat of fusion (kJ/mole) = 10.79
Electro-negativity = 1.61
Specific heat (J/g-K) = 0.90
Oxidation state = +3
Electron configuration = [Ne] 3s2 p1
Other noteworthy facts: The crystal structure is face-centered cubic, and it is element 13 in the periodic table of elements.
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