Rhenium (pronounced /ˈriːniəm/, REE-nee-əm)
is a chemical element with the symbol Re and atomic
number 75. It is a silvery-white, heavy, third-row transition
metal in group 7 of the periodic
table. With an average concentration of 1 part per billion (ppb), rhenium is one of the
rarest elements in the Earth's
crust. The free element has the third-highest melting
point of any element, exceeded only by tungsten
and carbon.
Rhenium resembles manganese chemically and is obtained as a by-product
of molybdenum
and copper
refinement. Rhenium shows in its compounds a wide variety of oxidation
states ranging from −1 to +7.
Detailed description
Discovered in
1925, rhenium was the last naturally occurring stable element to be discovered
(francium was the last identified naturally
occurring element, but it is unstable). Rhenium was named after the river Rhine.
Nickel-based superalloys for use in jet engines contain up to 6% of rhenium, making
jet engine construction the largest use for the element, with chemical industry
catalytic uses being next-most important. Because of the low availability
relative to demand, rhenium is among the most expensive industrial metals, with
an average price exceeding US$6,000 per kilogram, as of 2009.
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History
Rhenium (Latin Rhenus meaning Rhine)[2] was the next-to-last naturally
occurring element to be discovered and the last element to be discovered having
a stable isotope.[3] The existence of a yet undiscovered
element at this position in the periodic table had been predicted by Henry Moseley in 1914.[4] 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.[5] In 1928 they were able to extract 1 g
of the element by processing 660 kg of molybdenite.[6] The process was so complicated and
expensive 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.[7] The symbol Np was later used for the
element neptunium.
Characteristics
Rhenium is a
silvery-white metal with one of the highest melting points of all elements, exceeded by only tungsten and carbon. It is also one of the densest, exceeded only
by platinum, iridium and osmium.
Its usual
commercial form is a powder, but this element can be consolidated by pressing
and sintering in a vacuum or hydrogen atmosphere. This procedure yields a
compact solid having a density above 90% of the density of the metal. When annealed this metal is very ductile and can be
bent, coiled, or rolled.[8] Rhenium-molybdenum alloys are superconductive at 10 K; tungsten-rhenium alloys are also
superconductive[9] around 4-8 K, depending on the alloy.
Rhenium metal superconducts at 2.4 K.[10][11]
Rhenium was
originally thought to form the rhenide anion, Re−, in which
it has the −1 oxidation state. This was based on the product of the reduction
of perrhenate salts, such as the reduction of
potassium perrhenate (KReO4) by potassium metal.[25] "Potassium rhenide" was
shown to exist as a tetrahydrated complex, with the postulated chemical formula
KRe·4H2O.[26] This compound exhibits strongly
reducing properties, and slowly yields hydrogen gas when dissolved in water.
The lithium and thallous salts were also reported. Later
research, however, indicates that the "rhenide" ion is actually a
hydridorhenate complex. "Potassium rhenide" was shown to be in fact
the nonahydridorhenate, K2ReH9,
containing the ReH92− anion in which the oxidation state
of rhenium is actually +7.[27][28] Other methods of reduction of
perrhenate salts yield compounds containing other hydrido- complexes, including
ReH3(OH)3(H2O)−.[29]
Occurrence
Rhenium is one of
the rarest elements in Earth's crust with an average concentration of
1 ppb;[16] other sources quote the number of
0.5 ppb making it the 77th most abundant element in Earth's crust.[30] Rhenium is probably not found free in
nature (its possible natural occurrence is uncertain), but occurs in amounts up
to 0.2%[16] in the mineral molybdenite (which is primarily molybdenum
disulfide), the major commercial source, although single molybdenite samples
with up to 1.88% have been found.[31] Chile has the world's largest rhenium reserves,
part of the copper ore deposits, and was the leading producer as of 2005.[32] It was only recently that the first
rhenium mineral was found and described (in 1994), a
rhenium sulfide
mineral (ReS2)
condensing from a fumarole on Russia's Kudriavy volcano, Iturup island, in the Kurile Islands.[33] Named rheniite, this rare mineral commands high
prices among collectors,[34]
but is not an economically viable source of the element.
Production
Commercial
rhenium is extracted from molybdenum roaster-flue gas obtained from
copper-sulfide ores. Some molybdenum ores contain 0.001% to 0.2% rhenium.[16][31] Rhenium(VII)
oxide and perrhenic acid readily dissolve in water; they are
leached from flue dusts and gasses and extracted by precipitating with potassium or ammonium chloride as the perrhenate salts, and purified by recrystallization.[35] Total world production is between 40
and 50 tons/year; the main producers are in Chile, the United States, and
Kazakhstan.[36] Recycling of used Pt-Re catalyst and
special alloys allow the recovery of another 10 tons per year. Prices for the
metal rose rapidly in early 2008, from $1000–$2000 per kg in 2003-2006 to over $10,000 in February
2008.[37][38] The metal form is prepared by
reducing ammonium
perrhenate
with hydrogen at high temperatures:[35]
2 NH4ReO4 + 7 H2
→ 2 Re + 8 H2O + 2 NH3
Applications
Rhenium is added
to high-temperature superalloys that are used to make jet engine parts, making 70% of the worldwide
rhenium production.[39] Another major application is in
platinum-rhenium catalysts, which are primarily used in making lead-free, high-octane gasoline.[36][40]
Alloys
The nickel-based superalloys have improved creep
strength with the
addition of rhenium. The alloys normally contain 3% or 6% of rhenium.[41] Second generation alloys contain 3%;
these alloys were used in the engines of the F-16 and F-15, while the newer single-crystal third
generation alloys contain 6% of rhenium; they are used in the F-22 and F-35 engines.[40][42] Rhenium is also used in the
superalloys, such as CMSX-4 (2nd gen) and CMSX-10 (3rd gen) that are used in
industrial gas turbine engines like the GE's 7FA. Rhenium
can cause superalloys to become microstructurally unstable,
forming undesirable TCP (topologically close packed) phases. In 4th and 5th generation superalloys, ruthenium is used to avoid this effect. Among
others the new superalloys are EPM-102 (with 3 % Ru) and
TMS-162 (with 6 % Ru), both contain 6 % rhenium,[43] as well as TMS-138[44] and TMS-174.[45][46]
For 2006, the
consumption is given as 28% for General Electric, 28% Rolls-Royce plc and 12% Pratt & Whitney, all for superalloys, while the use
for catalysts only accounts for 14% and the remaining applications use 18%.[39] In 2006, 77% of the rhenium
consumption in the United States was in alloys.[40]
Rhenium improves
the properties of tungsten and is therefore the most important
alloying material for tungsten. Tungsten-rhenium alloys are more ductile at low
temperature making them easier to machine, while the high-temperature stability
is also improved. The effect increases with the rhenium concentration, and
therefore tungsten alloys are produced with up to 27% of Re, which is the
solubility limit.[47] One application for the
tungsten-rhenium alloys is X-ray sources. The high melting point of
both compounds, together with the high atomic mass, makes them stable against
the prolonged electron impact.[48] Rhenium tungsten alloys are also
applied as thermocouples to measure temperatures up to 2200 °C.[49]
The high
temperature stability, low vapor pressure, good wear resistance and ability to withstand arc
corrosion of rhenium are useful in self-cleaning electrical contacts. In particular, the discharge
occurring during the switching oxidizes the contacts. However, rhenium oxide Re2O7
has poor stability (sublimates at ~360 °C) and therefore is removed during the
discharge.[39]
Rhenium has a
high melting point and a low vapor pressure similar to tantalum and tungsten,
however, rhenium forms no volatile oxides. Therefore, rhenium filaments exhibit
a higher stability if the filament is operated not in vacuum, but in
oxygen-containing atmosphere.[50] Those filaments are widely used in mass spectrographs, in ion gauges.[51] and in photoflash lamps in photography.[52]
Catalysts
Rhenium in the
form of rhenium-platinum alloy is used as catalyst for catalytic
reforming, which is a
chemical process to convert petroleum refinery naphthas with low octane ratings into high-octane liquid products.
Worldwide, 30% of catalysts used for this process contain rhenium.[53] The olefin metathesis is the other reaction for which
rhenium is used as catalyst. Normally Re2O7 on alumina is used for this process.[54] Rhenium catalysts are very resistant
to chemical
poisoning from nitrogen,
sulfur and phosphorus, and so are used in certain kinds of hydrogenation
reactions.[8][55][56]
Other uses
188Re and 186Re isotopes are
radioactive and are used for treatment of liver cancer. They both have similar penetration
depth in tissue (5 mm for 186Re and 11 mm for 188Re),
but 186Re has advantage of longer lifetime (90 hours vs. 17 hours).[57][58]
Related by periodic trends, rhenium has a similar chemistry with
technetium; work done to label rhenium onto
target compounds can often be translated to technetium. This is useful for
radiopharmacy, where it is difficult to work with technetium – especially the
99m isotope used in medicine – due to its expense and short half-life.[57][59]
Packaging details
We usually bag ores in
50kg,100kg,150kg and 200kgs depending on specifications. Now for a 50kg bagged
ore it will contain 480 bags for 20ft
container,610 bags for 40ft container, 642 and 674 bags for 48ft and 53ft containers respectively. For a
100kg bagged ore we shall have 240 bags for
20ft container, 305 bags for 40ft
container,329 bags for a 48ft and 344 bags for a 53ft container. However, the
best method to transport ores such as iron is through ship loads such as 25000
,50000, tonnes and so on, because through this way the transporting is less
cumbersome and one can transport more materials at a given time.
PRICE
$2850/KG OR $1295/IB
For more information:
mobile: +2348039721941
contact person: emeaba uche
e-mail: emeabau@yahoo.com
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