EDITOR’S CHOICE
THE FUTURE OF RHENIUM
MATMATCH
WHY IT IS INDISPENSABLE FOR THE HIGH-TECH WORLD
Here, Dr Heiko Wildner, chief operating
officer of materials comparison database,
Matmatch, explains the applications for
rhenium and why it is indispensable for the
high-tech world.
Saffron is said to be the most expensive and
rarest spice of all. Its annual production is
around 200 tonnes. The metallic equivalent
of saffron is rhenium with indispensable
production of 60 tonnes. At a density of 21g/
cm3, this translates into a volume of less
than 3 m3 or a sphere of a diameter of less
than two meter.
The metal is contained in the Earth’s crust
in extremely sparse amounts and has been
found to occur naturally only in a volcano
on the Kuril Islands in Southeast Asia. It
took until 1925 for rhenium to be isolated
for the first time. In the periodic table of
the elements, rhenium takes on a position
between the refractory and noble metals.
What’s so special about rhenium?
No primary sources of rhenium are at hand,
but rhenium is extracted as a by-product
from molybdenum concentrates, which
themselves are a by-product of mining
copper ores. Rhenium has a melting point
of 3186 degrees Celsius, which is the third
highest melting point among all elements
after carbon and tungsten. In terms of the
boiling point, it ranks at top positions with
5627 degrees Celsius.
RHENIUM
Rhenium can show its superiority in
applications that are subject to very hot
temperatures and require stable structures.
Unfortunately, rhenium oxidises rapidly
in air at moderate temperatures, forming
volatile oxides. It has very high strength at
high temperatures and offers good cold
working properties.
In the early 1950s, molybdenum-rhenium
and tungsten-rhenium alloys were
developed. The first industrial applications
of tungsten-rhenium alloys included high-
temperature thermocouples and vacuum
tubes used in electronic devices.
For a while, rhenium was also used to
produce darts (‘rhenium darts’) to positively
influence flight characteristics, although
this application arguably uses more of a
tungsten alloy and just a small amount of
rhenium.
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PECM Issue 36
A SPICE FOR HIGH-TECH
ALLOYS Tungsten-rhenium alloys are also used
in X-ray anodes in high-resolution X-ray
equipment – for example in mammography,
angiography and computed tomography.
Luminescent rhenium complexes have
been used in intracellular bio-applications
because of their efficient cellular
internalisation and attractive photophysical
properties.
Rhenium improves the alloys’ creep
resistance, resulting in more durable
components that ensure greater fuel
efficiency at elevated temperatures – an
important contribution toward lowering fuel
consumption in the aerospace industry.
The second most frequent use of rhenium is
that of a catalyst. Platinum rhenium catalysts
are used to produce high-octane lead-free
gasoline. Being a relatively ‘young’ element,
researchers and developers still see great
potential for rhenium in future applications.
One of the most promising properties
of rhenium alloys is their favourable
biocompatibility, making them very
attractive for the production of medical
products. Specifically, molybdenum-
rhenium alloys have performed better in
implants than conventional titanium alloys.
Additionally, rhenium is needed in the
form of molybdenum-rhenium alloys in
the aviation and electronics industry for
reactors, semiconductors, electrical contacts,
filaments and ignition wires. Molybdenum-
tungsten-rhenium alloys are particularly well
suited for use at very high temperatures or
applications subject to high wear. Additionally, researchers have examined
the properties of rhenium diboride as a
material for hard coatings and found that
its hardness is almost equivalent to that of
cubic boron nitride.
Today, the production of superalloys for
jet engines represents the largest single
use for the element rhenium. These nickel
superalloys contain three to six per cent
rhenium and are used in combustion
chambers, turbine blades and propelling
nozzles of jet plane engines.
THE FUTURE
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