Geology Reference
In-Depth Information
Ta removing
w/vacuum
remelting
Ultrapurification:
Zone refining and Solid-State
Electrotransport in Ultra High Vacuum
Fluoride
reduction
Vacuum
melting
RE metal
(ultrapure)
Ce, La, Pr, Nd
Ta removing
w/vacuum
distillation
Ultrapurification:
Electron Beam Zone Melting
and SSE in Ultra High Vacuum
Fluoride
reduction
Vacuum
melting
RE metal
(ultrapure)
Gd, Tb, Y, Lu
Ta removing
w/vacuum
sublimation
Ultrapurification:
Radio-Frequency Float Melting
and SSE in inert gas atm
Fluoride
reduction
Vacuum
melting
RE metal
(ultrapure)
Sc, Er, Ho, Dy
Direct REO
reduction-
distillation
Vacuum
Sublimation
RE metal
(ultrapure)
Eu, Sm, Yb, Tm
Fig.8.15Purificationof
REE metals
8.13.9REEalloys
Many applications of rare earths require their alloys rather than their pure metals.
Among the different alloys the authors describe here the production of mischmetal
and permanent magnets.
A mischmetal (MM) can be obtained if the rare earth ore is processed as a single
metal instead of a light REE mixture. Its composition runs parallel to the ratio
found in the mineral resource. It is commercially produced by the electrolysis of
anhydrous MM-trichloride operating in a molten alkali bath, in a manner as des-
cribed above for the single RE-trichlorides electrolysis (Gupta and Krishnamurthy,
2005).
Some rare earth metals alloyed with transition metals (REE TM) form per-
manent magnets with high resistance to de-magnetisation (coercivity) and high
(maximum static) energy product
30
, as is the case of derivatives of SmCo and
NiFeB alloys. They store 4 to 5 times greater energy per unit of volume than
conventional magnets such as PtCo or AlNiCo and importantly hold high coerciv-
ity even at the typical temperature range of working machinery. Their preparation
essentially consists of two stages: synthesis of the alloy and magnetisation.
Techniques such as high frequency vacuum induction for co-melting the REE
with a transition metal or fused salt electrolysis with cobalt cathodes have been
used to prepare RECo permanent magnets, notably SmCo
5
material. However,
direct reduction of RE
2
O
3
, achieved by a calciothermic reduction of the REO in the
presence of cobalt powder, is preferred since it saves on energy and materials. Indeed
it has been used to produce high e
cient permanent magnets such as derivatives
of Sm Co, Sm Pr Co, Sm-Mischmetal-Co, and Sm TM, with TM =
Co;Cu;Fe;Zr (Gupta and Krishnamurthy, 2005).
The production of NdFeB alloys follows other routes which predominately
consist of calciothermic reduction of either neodymium oxide or fluoride followed
30
Energy product is referred to the maximum magnetic induction B multiplied by the field strength
H.
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