Rhenium

Rhenium,  ₇₅Re

General properties
Name, symbol	Rhenium, Re
Appearance	Silvery-gray metal
Rhenium in the periodic table
Tc ↑ Re ↓ Bh Tungsten ← Rhenium → Osmium
Atomic number	75
Standard atomic weight (Ar)	186.207(1)
Group, block	VII; d-block
Period	period 6
Electron configuration	[Xe] 4f14 5d5 6s2
per shell	2, 8, 18, 32, 13, 2
Physical properties
Silvery-gray
Phase	Solid
Melting point	3459 K ​(3186 °C, ​​5767 °F)
Boiling point	5869 K ​(5596 °C, ​10,105 °F)
Density near r.t.	21.02 g/cm3
when liquid, at	18.9 g/cm3
Heat of fusion	60.43 kJ/mol
Heat of	704 kJ/mol
Molar heat capacity	25.48 J/(mol·K)
pressure
Atomic properties
Oxidation states	7, 6, 5, 4, 3, 2, 1, 0, −1, −3 ​​(a mildly acidic oxide)
Electronegativity	Pauling scale: 1.9
energies	1st: 760 kJ/mol 2nd: 1260 kJ/mol 3rd: 2510 kJ/mol (more)
Atomic radius	empirical: 137 pm
Covalent radius	151±7 pm
Miscellanea
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound thin rod	4700 m/s (at 20 °C)
Thermal expansion	6.2 µm/(m·K)
Thermal conductivity	48.0 W/(m·K)
Electrical resistivity	193 Ω·m (at 20 °C)
Magnetic ordering	Paramagnetic
Young's modulus	463 GPa
Shear modulus	178 GPa
Bulk modulus	370 GPa
Poisson ratio	0.30
Mohs hardness	7.0
Vickers hardness	1350–7850 MPa
Brinell hardness	1320–2500 MPa
CAS Registry Number	7440-15-5
History
Naming	after the river Rhine (German: Rhein)
Discovery and first isolation	Masataka Ogawa (1908)
Named by	Walter Noddack, Ida Noddack, Otto Berg (1922)

Rhenium is a chemical element with symbol Re and atomic number 75. It is a silvery-gray or silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust.

Properties

Chemical

Rhenium resembles manganese and technetium chemically. Rhenium has good chemical resistance to acids, such as sulfuric acid, hydrochloric acid, aqua regia, as well as alkalis, but it dissolves in concentrated nitric acid. It also reacts with halogens at high temperatures, such as fluorine at 400 °C.

Physical

Rhenium is a silvery-white (or gray) hard metal. Rhenium has one of the highest melting points of all elements (3186 °C), third after tungsten and carbon (though carbon is not a metal and does not melt under standard pressure). It also has the highest boiling point of all elements (5596 °C). Rhenium's density (21.02 g/cm³) is only exceeded by platinum, iridium and osmium. These properties make rhenium a valuable metal in the manufacturing of superalloys.

Availability

Rhenium is sold by various chemical suppliers and other metal companies, though it's not cheap.

Isolation

Rhenium can be obtained by reducing ammonium perrhenate (APR) at high temperatures with a reducing agent, such as hydrogen.

2 NH₄ReO₄ + 7 H₂ → 2 Re + 8 H₂O + 2 NH₃

The rhenium obtained this way is in powdered form.

Heating must be done slowly because ammonium perrhenate decomposes to volatile Re₂O₇ starting at 250 °C. When heated in a sealed tube at 500 °C, APR decomposes to rhenium dioxide:

2 NH₄ReO₄ → 2 ReO₂ + N₂ + 4 H₂O

Melting the powder to bulk metal can only be done using an electric arc furnace, in an inert atmosphere.

Projects

• Make ammonium perrhenate
• Metal coatings
• Catalysts
• Make rhenium(VII) oxide

Handling

Safety

Little is known about rhenium's biological effects. Medical studies performed on animals indicate that both the metal and its salts show little toxicity, though only potassium perrhenate and rhenium trichloride have been tested.

Storage

Rhenium can be stored in any container, though it should be kept away from nitric acid.

Disposal

Due to its rarity, it's best to recycle rhenium and its compounds as much as possible, instead of throwing it away.

References

Relevant Sciencemadness threads

• ammonium perrhenate reduction