Rhenium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements

75 tungsten ← rhenium → osmium Tc ↑ Re ↓ Bh Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	rhenium, Re, 75
Chemical series	transition metals
Group, Period, Block	7, 6, d
Appearance	grayish white
Atomic mass	186.207 (1) g/mol
Electron configuration	[Xe] 4f14 5d5 6s2
Electrons per shell	2, 8, 18, 32, 13, 2
Physical properties
Phase	solid
Density (near r.t.)	21.02 g·cm−3
Liquid density at m.p.	18.9 g·cm−3
Melting point	3459  K (3186 ° C, 5767 ° F)
Boiling point	5869 K (5596 ° C, 10105 ° F)
Heat of fusion	60.43 kJ·mol−1
Heat of vaporization	704 kJ·mol−1
Heat capacity	(25 °C) 25.48 J·mol−1·K−1
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 3303 3614 4009 4500 5127 5954
Atomic properties
Crystal structure	hexagonal
Oxidation states	7, 6, 4, 2, −2 (mildly acidic oxide)
Electronegativity	1.9 (Pauling scale)
Ionization energies ( more)	1st: 760 kJ·mol−1
	2nd: 1260 kJ·mol−1
	3rd: 2510 kJ·mol−1
Atomic radius	135 pm
Atomic radius (calc.)	188 pm
Covalent radius	159 pm
Miscellaneous
Magnetic ordering	?
Electrical resistivity	(20 °C) 193 nΩ·m
Thermal conductivity	(300 K) 48.0 W·m−1·K−1
Thermal expansion	(25 °C) 6.2 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 4700 m/s
Young's modulus	463 GPa
Shear modulus	178 GPa
Bulk modulus	370 GPa
Poisson ratio	0.30
Mohs hardness	7.0
Vickers hardness	2450 MPa
Brinell hardness	1320 MPa
CAS registry number	7440-15-5
Selected isotopes
Main article: Isotopes of rhenium iso NA half-life DM DE ( MeV) DP 185Re 37.4% Re is stable with 110 neutrons 187Re 62.6% 4.35×1010 y α 1.653 183Ta β- 0.003 187Os
References

Rhenium ( IPA: /ˈɹiːniəm/) is a chemical element in the periodic table that has the symbol Re and atomic number 75. A silvery-white, rare, heavy, polyvalent transition metal, rhenium resembles manganese chemically and is used in some alloys. Rhenium is obtained as a by-product of molybdenum refinement and rhenium-molybdenum alloys are superconducting. This was the last naturally-occurring element to be discovered and belongs to the ten most expensive metals on Earth (over US$ 4000.-/kg).

Notable characteristics

Rhenium is a silvery white metal, lustrous, and has one of the highest melting points of all elements, exceeded by only tungsten and carbon. It is also one of the most dense, exceeded only by platinum, iridium, and osmium. The oxidation states of rhenium include -3,-1,+1,+2,+3,+4,+5,+6 and +7 oxidation states. The oxidation states +7,+6,+4,+2 and -1 are the most common.

Its usual commercial form is a powder, but this element can be consolidated by pressing and resistance-sintering in a vacuum or hydrogen atmosphere. This procedure yields a compact shape that is in excess of 90 percent of the density of the metal. When annealed this metal is very ductile and can be bent, coiled, or rolled. Rhenium-molybdenum alloys are superconductive at 10 K; tungsten-rhenium alloys are also superconductive, around 4-8 K depending on the alloy .

Applications

This element is used in platinum-rhenium catalysts which in turn are primarily used in making lead-free, high-octane gasoline and in high-temperature superalloys that are used to make jet engine parts. Other uses:

• Widely used as filaments in mass spectrographs and in ion gauges.
• An additive to tungsten and molybdenum-based alloys to increase ductility in these alloys.
• Rhenium catalysts are very resistant to chemical poisoning, and so are used in certain kinds of hydrogenation reactions.
• Electrical contact material due to its good wear resistance and ability to withstand arc corrosion.
• Thermocouples containing alloys of rhenium and tungsten are used to measure temperatures up to 2200 ° C.
• Rhenium wire is used in photoflash lamps in photography.

History

Rhenium (Latin Rhenus meaning "Rhine") was the last naturally-occurring element to be discovered. The existence of an as-yet undiscovered element at this position in the periodic table had been predicted by Henry Moseley in 1914. It is generally considered to have been discovered by Walter Noddack, Ida Tacke, and Otto Berg in Germany. In 1925 they reported that they detected the element in platinum ore and in the mineral columbite. They also found rhenium in gadolinite and molybdenite. In 1928 they were able to extract 1 g of element by processing 660 kg of molybdenite.

The process was so complicated and the cost so high that production was discontinued until early 1950 when tungsten-rhenium and molybdenum-rhenium alloys were prepared. These alloys found important applications in industry that resulted in a great demand for the rhenium produced from the molybdenite fraction of porphyry copper ores.

Occurrence

Rhenium is not found free in nature, and it was only recently that the first rhenium mineral was found. In 1994, Nature published a letter describing a rhenium sulfide mineral found condensing from a fumarole on Russia's Kudriavy volcano. This is not an economically viable source of the element. Rhenium is widely spread through the Earth's crust at approximately 0.001 ppm.

Commercial rhenium is extracted from molybdenum roaster-flue dusts obtained from copper-sulfide ores. Some molybdenum ores contain 0.002% to 0.2% rhenium. Total world production is between 40 and 50 tons/year; the main producers are in Chile, USA and Kazakhstan. Recycling of used Pt-Re catalyst and special alloys allow the recovery of another 10 tons/year.

The metal form is prepared by reducing ammonium perrhenate with hydrogen at high temperatures.

Isotopes

Naturally occurring rhenium is a mix of ¹⁸⁵Re, which is stable, and ¹⁸⁷Re, which is unstable but has a very long half-life. There are twenty-six other unstable isotopes recognized.

Precautions

Little is known about rhenium toxicity so it should be handled with care.