For jewelry plating.
| Atomic Number: | 75 | Atomic Symbol: | Re |
| Atomic Weight: | 186.207 | Electron Configuration: | 2-8-18-32-13-2 |
| Shells: | 2,8,18,32,13,2 | Filling Orbital: | 5d5 |
| Melting Point: | 3180oC | Boiling Point: | 5627oC |
| Description: | Rare and costly silver white metal. |
| Uses: | Mixed with tungston or platinum to make filaments for mass
spectrographs. |
History
(L. Rhenus, Rhine) Discovery of rhenium is generally attributed
to Noddack, Tacke, and Berg, who announced in 1925 they had detected the element
in platinum ore and columbite. They also found the element in gadolinite and
molybdenite. By working up 660 kg of molybdenite in 1928 they were able to
extract 1 g of rhenium.
Sources
Rhenium does not occur free in nature or as a compound in a
distinct mineral species. It is, however, widely spread throughout the earth's
crust to the extent of about 0.001 ppm. Commercial rhenium in the U.S. today is
obtained from molybdenum roaster-flue dusts obtained from copper-sulfide ores
mined in the vicinity of Miami, Arizona, and elsewhere in Arizona and Utah.
Some molybdenum contain from 0.002% to 0.2% rhenium. More than 150,000 troy
ounces of rhenium are now being produced yearly in the United States. The total
estimated Free World reserve of rhenium metal is 3500 tons. Rhenium metal is
prepared by reducing ammonium perrhentate with hydrogen at elevated
temperatures.
Isotopes
Natural rhenium is a mixture of two stable isotopes. Twenty six
other unstable isotopes are recognized.
Properties
The element is silvery white with a metallic luster; its
density is exceeded only by that of platinum, iridium, and osmium, and its melting
point is exceeded only by that of tungsten and carbon .
The usual commercial form of the element is powder, but it can be
consolidated by pressing and resistance-sintering in a vacuum or hydrogen
atmosphere. This process produces a compact shape in excess of 90 percent of the
density of the metal.
Annealed rhenium is very ductile, and can be bent, coiled, or rolled. Rhenium
is used as an additive to tungsten and molybdenum -based alloys to impart useful properties.
Uses
It is widely used as filaments for mass spectrographs and ion
gages. Rhenium-molybdenum alloys are superconductive at 10 K.
Rhenium is also used as an electrical contact material because it has good
wear resistance and withstands arc corrosion. Thermocouples made of Re-W are
used for measuring temperatures up to 2200C, and rhenium wire is used in
photoflash lamps for photography.
Rhenium catalysts are exceptionally resistant to poisoning from nitrogen, sulfur, and phosphorus, and are used for hydrogenation of fine chemicals.
Costs
In 1928 rhenium cost $10,000/g. The price today is about $250/troy
oz.
Hazards
Because little is known about its toxicity, it should be handled
with care until more data becomes available.