75
  Re  
186.207000
Rhenium

Name: Rhenium
Symbol: Re
Atomic Number: 75
AtomicWeight: 186.207000
Family: Transition Metals
CAS RN: 7440-15-5
Description: A greyish white metal, very dense with a high melting point.
State (25 ° C): Solid
Oxidation states: ±1, +2, ±3, +4, +5, +6, +7
Molar Volume: 9.07 cm3/mole
Valence Electrons: 5d56s2

 Boiling Point:  5900°K, 5627°C, 10161°F
Melting Point: 3453°K, 3180°C, 5756°F
Electrons Energy Level: 2, 8, 18, 32, 13, 2
Isotopes: 34 + 1 Stable
Heat of Vaporization: 715 kJ/mol
Heat of Fusion: 33.2 kJ/mol
Density: 21.04 g/cm3 @ 300°K
Specific Heat: 0.13 J/g°K
Atomic Radius: 1.97Å
Ionic Radius: 0.56Å
Electronegativity: 1.9 (Pauling); 1.46 (Allrod Rochow)
Vapor Pressure: 3.24 Pa @ 3180°C

1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d5 6s2

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.

In 1908, Japanese chemist Masataka Ogawa announced that he discovered the 43rd element, and named it nipponium (Np) after Japan (which is Nippon in Japanese).   However, later analysis indicated the presence of rhenium (element 75), not element 43.  The symbol Np was later used for the element neptunium.

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.   Rhenium has the widest range of oxidation states of any known element: -3,-1,+1,+2,+3,+4,+5,+6 and +7.  The oxidation states +7,+6,+4,+2 and -1 are the most common.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d5
6s2

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 10oK; tungsten-rhenium alloys are also superconductive, around 4-8oK depending on the alloy.

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 1 ppb.

Commercial rhenium is extracted from molybdenum roaster-flue gas 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.

This was the last naturally-occurring element to be discovered and belongs to the ten most expensive metals on Earth (over $4000/kg).

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

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:

Isotope

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

atom.gif (700 bytes)

Isotope  
Atomic Mass
 		 Half-Life
160Re 159.98212 0.82 ms
161Re 160.97759 0.37 ms
162Re 161.97600 107 ms
163Re 162.972081 390 ms
164Re 163.97032 0.53 seconds
165Re 164.967089 ~1 seconds
166Re 165.96581 ~2 seconds
167Re 166.96260 3.4 seconds
168Re 167.96157 4.4 seconds
169Re 168.95879 8.1 seconds
170Re 169.958220 9.2 seconds
171Re 170.95572 15.2 seconds
172Re 171.95542 15 seconds
173Re 172.95324 1.98 minutes
174Re 173.95312 2.40 minutes
175Re 174.95138 5.89 minutes
176Re 175.95162 5.3 minutes
177Re 176.95033 14 minutes
178Re 177.95099 13.2 minutes
179Re 178.949988 19.5 minutes
180Re 179.950789 2.44 minutes
181Re 180.950068 19.9 hours
182Re 181.95121 64.0 hours
183Re 182.950820 70.0 days
184Re 183.952521 38.0 days
185Re 184.9529550 Stable
186Re 185.9549861 3.7186 days
187Re 186.9557531 41.2 x 109 years
188Re 187.9581144 17.0040 hours
189Re 188.959229 24.3 hours
190Re 189.96182 3.1 minutes
191Re 190.963125 9.8 minutes
192Re 191.96596 16 seconds
193Re 192.96747 ~30 seconds
194Re 193.97042 ~2 seconds

Precautions

40px-Skull_and_crossbones.svg.jpg (1420 bytes) Little is known about rhenium toxicity so it should be handled with care.

atom.gif (700 bytes)

Rhenium Data
 

Atomic Structure

  • Atomic Radius: 1.97Å
  • Atomic Volume: 8.85cm3/mol
  • Covalent Radius: 1.28Å
  • Cross Section (Thermal Neutron Capture) Barns: 89.7
  • Crystal Structure: Hexagonal
  • Electron Configuration:
    1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d5 6s2
  • Electrons per Energy Level: 2, 8, 18, 32, 13, 2
  • Ionic Radius: 0.56Å
  • Filling Orbital: 5d5
  • Number of Electrons (with no charge): 75
  • Number of Neutrons (most common/stable nuclide): 111
  • Number of Protons: 75
  • Oxidation States: 6, 4, ± 2
  • Valence Electrons: 5d5 6s2

Chemical Properties

  • Electrochemical Equivalent: 0.9924 g/amp-hr
  • Electron Work Function: 4.96eV
  • Electronegativity: 1.9 (Pauling); 1.46 (Allrod Rochow)
  • Heat of Fusion: 33.2 kJ/mol
  • Incompatibilities:
  • Ionization Potential
    • First: 7.88
  • Valence Electron Potential (-eV): 180

Physical Properties

  • Atomic Mass Average: 186.207
  • Boiling Point: 5900°K, 5627°C, 10161°F
  • Coefficient of Lineal Thermal Expansion/K-1: 6.63E-6
  • Conductivity
    Electrical: 0.0542 106/cm
    Thermal: 0.479 W/cm°K
  • Density: 21.04 g/cm3 @ 300°K
  • Description:
    Rare and expensive silver white metal, which is usually obtained as a grey powder.
  • Elastic Modulus:
    • Bulk: 334/GPa
    • Rigidity: 181/GPa
    • Youngs: 466/GPa
  • Enthalpy of Atomization: 791 kJ/mole @ 25°C
  • Enthalpy of Fusion: 33.05 kJ/mole
  • Enthalpy of Vaporization: 707.1 kJ/mole
  • Flammablity Class:
  • Freezing Point: see melting point
  • Hardness Scale
    • Brinell: 1320 MN m-2
    • Mohs: 7
    • Vickers: 2450 MN m-2
  • Heat of Vaporization: 715 kJ/mol
  • Melting Point: 3453°K, 3180°C, 5756°F
  • Molar Volume: 9.07 cm3/mole
  • Physical State (at 20°C & 1atm): Solid
  • Specific Heat: 0.13 J/g°K
  • Vapor Pressure: 3.24 Pa @ 3180°C

Regulatory / Health

  • CAS Number
    • 7440-15-5
  • OSHA Permissible Exposure Limit (PEL)
    • No limits set by OSHA
  • OSHA PEL Vacated 1989
    • No limits set by OSHA
  • NIOSH Recommended Exposure Limit (REL)
    • No limits set by NIOSH
  • Levels In Humans:
    Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
    • Blood/mg dm-3: n/a
    • Bone/p.p.m: n/a
    • Liver/p.p.m: n/a
    • Muscle/p.p.m: n/a
    • Daily Dietary Intake: n/a
    • Total Mass In Avg. 70kg human: n/a
  • Discovery Year: 1925
  • Name Origin:
    Greek, Rhenus for the Rhine River.
  • Abundance:
    • Earth's Crust/p.p.m.: 0.0004
    • Seawater/p.p.m.: 0.000004
    • Atmosphere/p.p.m.: N/A
    • Sun (Relative to H=1E12): 2
  • Sources:
    Found in small amounts in gadolinite and molybdenite. It is usually extracted from the flue dusts of molybdenum smelters. Annual world production is around 4.5 tons.
  • Uses:
    It is added to tungsten and molybdenum alloys and is used in refractory metal components of missiles, electronic filaments, electrical contacts, high-temperature thermocouplers, oven filaments, electrodes, igniters for flash bulbs, jewelry, plating of metals by electrolysis and vapor-phase deposition.
  • Additional Notes:
    Rhenium is a metallic element that has a very high tensile strength (80,000psi), high modulus of elasticity, is virtually insoluble in hydrochloric acid and does not oxidize or corrode in saltwater. In addition it has the widest range of valences of any element and it retains its crystalline structure all the way to its melting point. Alloys of rhenium-molybdenum are superconductive at 10K.
Ionization Energy: 7.88 eV
Estimated Crustal Abundance: 7×10-4 milligrams per kilogram
Estimated Oceanic Abundance: 4×10-6 milligrams per liter
Transition Metals
Group 3
(IIIB)		 4
(IVB)		 5
(VB)		 6
(VIB)		 7
(VIIB)		 8
(VIIIB)		 9
(VIIIB)		 10 (VIIIB) 11
(IB)		 12
(IIB)
Period 4 21
Sc
44.95		 22
Ti
47.86		 23
V
50.94		 24
Cr
51.99		 25
Mn
54.93		 26
Fe
55.84		 27
Co
58.93		 28
Ni
58.69		 29
Cu
63.54		 30
Zn
65.39
Period 5 39
Y
88.90		 40
Zr
91.22		 41
Nb
92.90		 42
Mo
95.94		 43
Tc
98.00		 44
Ru
101.0		 45
Rh
102.9		 46
Pd
106.4		 47
Ag
107.8		 48
Cd
112.4
Period 6 57
La
138.9		 72
Hf
178.4		 73
Ta
180.9		 74
W
183.8		 75
Re
186.2		 76
Os
190.2		 77
Ir
192.2		 78
Pt
195.0		 79
Au
196.9		 80
Hg
200.5
Period 7 89
Ac
227.0		 104
Rf
261.0		 105
Db
262.0		 106
Sg
266.0		 107
Bh
264.0		 108
Hs
269.0		 109
Mt
268.0		 110
Ds
269.0		 111
Rg
272.0		 112
Uub
277.0