History
Niobium, discovered in 1801 by C. Hatchett, an English Chemist in an ore
called columbite, is a metal that is closely related to tantalum. It was
originally thought that the material was chromium but upon analysis it was
determined it was not chromium but an oxide of an unknown element. The
element was named columbium but many scientists believed that it was
actually tantalum and the element was not universally accepted. Fifty
years later European scientists determined the element niobium came from
tantalum and that columbium was the same element. The effort to change the
name back failed however so we are left with the niobium designation used
today. It offers similar corrosion resistance to tantalum but is formable,
weldable, and easier to machine. However, neither niobium nor tantalum are
considered to be easy to machine.
Niobium's combination of strength, melting point, resistance to chemical
attack, and low neutron absorption cross-section promotes its use in the
nuclear industry. It has been identified as the preferred construction
material for the first reactors in the space power systems programs. As
C-103 alloy, it has been used for rocket nozzles and exhaust nozzles for
jet engines and rockets because of its high strength and oxidation
resistance at a low weight. Recently, it has been gaining favor in its
pure form for semiconductor equipment components and corrosion resistant
parts. Niobium mill products are used in the fabrication of corrosion
resistant process equipment including reaction vessels, columns, bayonet
heaters, shell and tube heat exchangers, U-tubes, thermowells, spargers,
rupture diaphragms, and orifices. It is also frequently used in
pacemakers, artificial joints, dental implants and jewelry. The latest
explored use of Niobium is as a replacement to tantalum in capacitor
production since niobium is much more abundant and costs substantially
less than tantalum. This has been an ongoing study for several years but
has become more important since there is a fear that world supplies of
tantalum ore will be insufficient to meet future demand.
Niobium is very similar to tantalum and several alloys are available in
the arc-cast and wrought condition. It has the lowest melting point of all
the refractory metals covered, the lowest modulus of elasticity and
thermal conductivity, and the highest thermal expansion. It also has the
lowest strength and lowest density of the refractory metals. This metal
also has the low thermal neutron capture cross-section required for
nuclear applications. Its high melting point warrants its use at
temperatures above the maximum service temperatures of the iron, nickel
and cobalt base metals. It has excellent ductility and fabricatibility. Pure
niobium has a re-crystallization temperature range of 1800 to 2000°F (982°
to 1093°C). Niobium offers nearly the corrosion resistance of tantalum and
nearly the melting temperature of molybdenum. Yet its cost is about 1/6th
that of tantalum and 25% more than molybdenum. Niobium was used as an
alloy for many years. Nb/1% Zr was and still is used in nuclear reactors as
the tubing for the fuel pellets because of its resistance to neutron
bombardment. Niobium can be rolled, drawn, deep-drawn and formed at room
temperature up to its maximum work hardening.
This metal is an ideal candidate as a lower cost alternative where
tantalum is being considered. H Cross Company supplies niobium in strip,
ribbon, foil, sheet, rod, and wire forms.
|
