U.S. patent application number 10/204465 was filed with the patent office on 2003-03-13 for method of manufacture for ferro-titanium and other metal alloys electrolytic reduction.
Invention is credited to Godfrey, Alastair B, Ward-Close, Charles M.
Application Number | 20030047462 10/204465 |
Document ID | / |
Family ID | 26243686 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030047462 |
Kind Code |
A1 |
Ward-Close, Charles M ; et
al. |
March 13, 2003 |
Method of manufacture for ferro-titanium and other metal alloys
electrolytic reduction
Abstract
A method for the production of a master alloy including the
steps of; introducing mixed ores comprising the metals of the
alloy; introducing the mixed ores into an electrochemical cell, the
cell containing a liquid electrolyte comprising a fused salt or
mixture of salts generally designated as M.sub.2Y in which
contaminants X contained in the mixed ores are soluble, and a
relatively inert anode; conducting electrolysis under conditions
favourable to the selective dissolution of contaminants contained
in the mixed ores in preference to the deposition of the M.sub.2
cation; and following electrolysis, reclaiming the purified mixed
ore form the cathode.
Inventors: |
Ward-Close, Charles M;
(Farnborough Hants, GB) ; Godfrey, Alastair B;
(Farnborough Hants, GB) |
Correspondence
Address: |
Nixon & Vanderhye
8th Floor
1100 North Glebe Road
Arlington
VA
22201-4714
US
|
Family ID: |
26243686 |
Appl. No.: |
10/204465 |
Filed: |
September 10, 2002 |
PCT Filed: |
February 19, 2001 |
PCT NO: |
PCT/GB01/00653 |
Current U.S.
Class: |
205/366 ;
205/365 |
Current CPC
Class: |
C22C 47/14 20130101;
C25C 3/28 20130101; C25C 5/04 20130101; C22B 4/06 20130101; C22B
5/02 20130101; C22B 34/1263 20130101; B22F 9/20 20130101; C25C 3/00
20130101; C22B 34/129 20130101; C22C 47/04 20130101; B22F 2999/00
20130101; C22B 5/00 20130101; B22F 2999/00 20130101; B22F 9/20
20130101; C25C 3/28 20130101 |
Class at
Publication: |
205/366 ;
205/365 |
International
Class: |
C25C 003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 22, 2000 |
GB |
0003971.9 |
May 8, 2000 |
GB |
0010873.8 |
Claims
1. A method for the production of an alloy from a mixed metal oxide
feedstock, by electrolysis in a fused salt of M.sub.2Y or a mixture
of such salts under conditions such that ionisation of oxygen
rather than M.sub.2 deposition occurs and that oxygen dissolves in
the electrolyte M.sub.2Y, characterised in that the feedstock
comprises a combination of naturally occurring ores wherein the
ores are mixed in proportions suitable for forming an alloy of the
required stoichiometry.
2. A method as claimed in claim 1 wherein the alloy is
Ferro-titanium.
3. A method as claimed in any preceding claim wherein the selected
ores include ilmenite.
4. A method as claimed in any preceding claim wherein the selected
ores include rutile.
5. A method as claimed in any preceding claim wherein the ores
comprise iron and titanium and are mixed in proportions suitable to
provide a eutectic Ferro-titanium alloy comprising about 70% Ti to
about 30% Fe by weight.
6. A method as claimed in any preceding claim wherein the ores are
crushed, ground or powdered prior to mixing.
7. A method as claimed in claim 6 wherein the particle size of the
crushed, ground or powdered ores are in the range 100-600
microns.
8. A method as claimed in claim 6 wherein the particle size of the
crushed, ground or powdered ores is a few millimeters.
9. A method as claimed in any of claims 6 to 8 wherein the crushed,
ground or powdered particles are preformed to a near net shape of
the end product prior to electrolysis.
10. A method as claimed in any preceding claim, wherein the
electrochemical reduction is halted when the quantity of oxygen in
the feedstock has been reduced to a predetermined acceptable
maximum level which is greater than the minimum level achievable if
reduction is completed.
11. A method for the production of a master alloy substantially as
described herein.
Description
[0001] This invention relates to a method for the manufacture of
alloys from metal ores. More particularly, the invention is
directed to the reduction of metal ores to form alloys. Such alloys
include but are not limited to Ferro-titanium alloys.
[0002] WO99/64638 and the Applicants co-pending applications
British Patent applications nos. GB 0003971.9 and GB 0010873.8 the
disclosures of which are incorporated herein by reference) describe
methods for the electrolytic reduction of metal compounds.
[0003] Certain embodiments of these methods involve the
electrolysis of metal oxides or other compounds (M.sub.1X) in a
cell containing a liquid (fused salt M.sub.2Y) electrolyte and an
anode, the metal oxide or other compound forming the cathode.
Conditions are controlled so as to bring about the selective
dissolution of the oxygen or other contaminant of the cathode in
preference to deposition of the metal cation. Improved efficiency
of this process can be achieved by various methods as described in
GB 0003971.9 and GB 0010873.8 some of which are summarised
below.
[0004] Production of powder by reduction of sintered metal oxide
granules
[0005] Sintered granules or powders of metal oxide can be used as
the feedstock for the electrolysis described in the above
referenced method, as long as appropriate conditions are present.
In one example, powdered titanium dioxide in the form of granules
or a powder is used, the powdered particles preferably have a size
in the region of 200 .mu.m.
[0006] Production of powder by deposition of M.sub.1 onto the
cathode
[0007] If a metal is deposited onto a cathode (based on the
electrolytic process previously described) from a second source of
the metal M.sub.1 which is maintained at a more positive potential,
the resulting metal deposited thereon is dendritic in
structure.
[0008] This is particularly so where the metal is titanium. This
form of titanium is easy to break up in to a powder as the
individual particles are connected together only by a small surface
area. This method can be used to produce titanium powder from
titania. In this method, a second cathode is provided which is
maintained at a potential which is more negative than the first
cathode. When the deposition of titanium on the first cathode has
progressed sufficiently, the second electrode is switched on,
leading to the dissolution of titanium from the first cathode and
deposition onto the second cathode in dendritic form.
[0009] Feedstock production by addition of binder to rutile and
amorphous titania
[0010] The manufacture of titanium dioxide from the raw ore (sand
mined illemite) comprises a large number of steps in the production
of titanium.
[0011] During one of these stages titanium dioxide in the form of
an amorphous slurry undergoes calcining. The titanium dioxide
slurry can be used as the principle feedstock in the above
described electrolytic method. A small percentage of calcined
material is mixed with amorphous material and a binder to obtain
the most satisfactory results after sintering. The calcined
material should constitute at least about 5% by weight of the
mixture.
[0012] Production of alloy metal matrix composites (MMC's)
[0013] Individual SiC fibres are coated with an oxide/binder slurry
(or mixed oxide slurry for an alloy) of the appropriate thickness.
Alternatively, the fibres may be combined with an oxide paste or
slurry to produce a preformed sheet consisting of parallel fibres
in a matrix of oxide powder and binder, or, a complex three
dimensional shape containing the fibres in the correct positions
could be cast or pressed from oxide slurry or paste. The coated
fibres, preform sheet or three dimensional shape can then be made
the anode of an electrochemical cell (with or without a pre-sinter
step) and the oxide powder may be reduced by the previously
described electrolytic process to a metal or alloy. The product may
then be washed or vacuum annealed to remove salt and then hot
isostatically pressed to give a 100% dense fibre reinforced
composite.
[0014] In the proposed method, fine ceramic particles such as
titanium diboride are blended with titania powder to give a uniform
mixture prior to sintering and electrolytic reduction. After
reduction the product is washed or vacuum annealed to remove salt,
and then hot pressed to give a 100% dense composite material.
Depending on the reaction chemistries, the ceramic particles may
either remain unchanged by the electrolysis and hot pressing or may
be converted to another ceramic material which would then be the
reinforcing element of the MMC. For example, in the case of
titanium diboride, the ceramic reacts with the titanium to form
titanium monoboride. In a variation of this process, fine metal
powder is mixed with the titania powder in place of a ceramic
powder, with the intention of forming a fine distribution of a hard
ceramic or intermetallic phase by reaction with titanium or another
alloying element or elements. For example, boron powder can be
added, and this reacts to form titanium monoboride particles in the
alloy.
[0015] Use of continuous powder feed
[0016] Continuously feeding a fine powder of metal oxide into the
electrochemical cell, allows for a constant current and a higher
reaction rate. A carbon electrode is preferred for this method.
This method permits the use of cheaper feedstock as a sintering
and/or forming stage is no longer needed.
[0017] Production of metal foams
[0018] Metal foams, more typically titanium foams, are attractive
for a number of applications such as filters, medical implants and
structural fillers. The fabrication of a sponge-like sintered oxide
pre-form from the starting material M.sub.1X can be converted into
a solid metal/alloy foam via the electrolytic method previously
described. Various established methods may be used to make the foam
like material from the mixture of oxide powders. The foam preform
desirably has open porosity that is, porosity which is
interconnected and open to the exterior.
[0019] In a preferred embodiment of this method, a natural or
synthetic polymeric foam is infiltrated with a metal (eg titanium)
oxide slip, then dried and fired to remove the polymeric foam,
leaving an open "foam" which is an inversion of the original
polymeric foam. The sintered preform is then electrolytically
reduced in accordance with the previously described method to
convert it into a titanium/titanium alloy foam. The foam is then
washed or vacuum distilled to remove the salt.
[0020] Alternatively, the metal oxide powder may be mixed with
organic foaming agents. These materials are typically two liquids
which when mixed, react to evolve a foaming gas, and then cure to
give a solidified foam with either an open or closed structure. The
metal powder is mixed with one or both of the precursor liquids
prior to production of the foam. The foam is then fired to remove
the organic material, leaving the ceramic foam which is then
electrolytically reduced in accordance with the previously
described method.
[0021] Production of metal or metal alloy components
[0022] A near net shape component may be made using the previously
described electrolytic method by reducing a ceramic facsimile of
the component made from a mixture of a metal oxide or mixture of
metal oxide and the oxides of other alloying elements. Again this
method is particularly suited to the manufacture of titanium metal
and alloy components. The ceramic facsimile may be produced using
any of a variety of well known production methods for ceramic
articles which include; pressing, injection moulding, extrusion and
slip casting, followed by firing (sintering). Full density of the
metallic component can be achieved by sintering with or without the
application of pressure, either in the electrochemical cell, or in
a subsequent operation. Shrinkage of the component during the
conversion to metal or alloy should be allowed for by making the
ceramic facsimile proportionally larger than the desired
component.
[0023] Electrolysis of a preformed sintered mass
[0024] The electrolysis is performed on a preformed sintered mass
comprising a mixture of metal oxide made up of a proportion of
particles of size generally greater than 20 microns and a
proportion of finer particles of less than 7 microns. Preferably
the finer particles make up between 10 and 55% by weight of the
sintered block.
[0025] High density granules of approximately the size required for
the powder are manufactured and then are mixed with very fine
unsintered metal oxide (e.g., titanium dioxide), binder and water
in the appropriate ratios and formed into the required shape of
feedstock. This feedstock is then sintered to achieve the required
strength for the reduction process. The resulting feedstock, after
sintering but before reduction, consists of high density granules
in a lower density (porous) matrix.
[0026] The feedstock can be reduced in block form using the
previously described electrolytic method and the result is a
friable block which can easily be broken up into powder.
[0027] The calcine discharge used can be replaced by cheaper
amorphous TiO.sub.2. The key requirement for this "matrix" material
is that it sinters easily with significant shrinkage during the
sintering process. Any oxide or mixture of oxides which fulfil
these criteria would be usable. In the case of TiO.sub.2 this means
the particle size must be less than about 1 .mu.m. It is estimated
that at least 5% of the matrix material should be present in order
to give any significant strength to the sintered product.
[0028] The starting granules for this method need not be rutile
sand but could be manufactured by a sintering and crushing process,
and in principle there is no reason to suppose that alloy powders
could not be made by this route.
[0029] Electrolytic reduction using swarf or chips as starting
materials
[0030] Manufacturing operations generate large quantities of swarf
and chips, some of which can be processed and recycled. However,
certain operations such as cutting create high temperatures in the
swarf and chips and cause absorption of high quantities of oxygen
into these pieces. The high surface area to volume ratio of such
pieces may result in penetration of oxygen through almost the
entire body of the piece. Beyond an optimum, increasing quantities
of oxygen in the metal have an increasingly detrimental effect on
its mechanical properties.
[0031] Where the quantities of oxygen absorbed are low to moderate,
it is known to mix these waste products with quantities of scrap
having lower levels of oxygenation and/or with quantities of virgin
metals to ensure that the end product of the mixture has below a
certain desired maximum oxygen content. At higher levels of
contamination, it becomes increasingly uneconomical to dilute the
highly contaminated metal in this manner and consequently, much of
this potentially useful material is abandoned as redundant.
[0032] A co-pending application made this same date by the
Applicants proposes novel methods for the reclamation of metals
from highly contaminated metal waste utilising some of the
principles of the methods previously described, these methods
prescribe reclaiming a metal M.sub.1 from a source of highly
contaminated scrap material M.sub.1X, including the steps of:
[0033] introducing the highly contaminated scrap metal into an
electrochemical cell, the cell containing a liquid electrolyte
comprising a fused salt or mixture of salts generally designated as
M.sub.2Y in which contaminant X is soluble, and a relatively inert
anode;
[0034] conducting electrolysis under conditions favourable to the
selective dissolution of the contaminant X in preference to the
deposition of the M.sub.2 cation; and
[0035] following electrolysis, reclaiming the decontaminated metal
M.sub.1 from the cathode.
[0036] In any of the aforementioned methods X may be a metalloid
such as oxygen, sulphur, carbon or nitrogen, preferably, X is
oxygen. M.sub.1 may be a Group IVA element such as Ti, SI, Ge, Zr,
Hf, Sm, Nd, Mo, Cr, Nb or an alloy of any of the preceding metals,
preferably, M.sub.1 comprises titanium. A preferred electrolyte,
M.sub.2Y, is calcium chloride (CaCl.sub.2). Other suitable
electrolytes include but are not limited to the molten chlorides of
all common alkali and alkaline earth metals. Other preferred metals
for M.sub.2 are barium, caesium, lithium, strontium and yttrium.
The anode of the cell is preferably of a relatively inert material.
One suitable anode material is graphite.
[0037] Processing conditions suitable for the favourable
dissolution of the contaminant X require that the potential of the
cell preferably be maintained at a potential which is less than the
decomposition potential of the molten electrolyte M.sub.2Y during
the process. Allowing for polarisation and resistive losses in the
cell, it will be understood that the cell potential may be
maintained at a level equal to, or marginally higher than, the
decomposition potential of M.sub.2Y and still achieve the desired
result. Potentiostatic methods may be used to control the
potential.
[0038] It is also preferred that the temperature of the cell is
maintained at an elevated temperature which is significantly above
the melting point of M.sub.2Y but below the boiling point of
M.sub.2Y. Where M.sub.2Y is CaCl.sub.2. suitable processing
parameters include a potential of up to about 3.3 V and a
processing temperature of between about 825 and 975.degree. C.
[0039] Optionally, this more recent method may include an
additional step wherein the scrap metal may be processed before
being introduced into the electrochemical cell, for example to form
small granules, or a powder, or an amorphous slurry of the
contaminated material. Alternatively or in addition to this
additional processing step, the scrap metal may be fabricated into
a sponge-like sintered oxide preform prior to electrolysis.
Alternatively or in addition to the additional processing step, the
scrap material may be sintered in a mixture containing particles of
M.sub.1X greater than 20 microns in size and finer particles of
M.sub.1X less than about 7 microns in size, binder and water to
form a friable block. Preferably in this method, the finer
particles are in a proportion of about 10 to about 55% by weight of
the sintered block. Alternatively or in addition to the additional
processing step, the scrap metal may be fabricated into a ceramic
facsimile of a desired metal or metal alloy component before
introduction into the electrochemical cell. This fabrication may be
achieved by various known methods including pressing, injection
moulding, extrusion and slip casting followed by sintering.
[0040] The present application proposes a further novel application
for these technologies.
[0041] The present invention provides a method for the production
of a Ferro-titanium master alloy including the steps of:
[0042] introducing mixed ores comprising the metals of the alloy in
suitable proportions to meet the desired proportions of the master
alloy;
[0043] introducing the mixed ores into an electrochemical cell, the
cell containing a liquid electrolyte comprising a fused salt or
mixture of salts generally designated as M.sub.2Y in which
contaminants contained in the mixed ores are soluble, and a
relatively inert anode;
[0044] conducting electrolysis under conditions favourable to the
selective dissolution of contaminants contained in the mixed ores
in preference to the deposition of the M.sub.2 cation; and
[0045] following electrolysis, reclaiming the purified alloy from
the cathode.
[0046] The invention is particularly suited to the manufacture of
Ferro-titanium alloys. Preferred ores include ilmenite and rutile,
other suitable ores will no doubt occur to the skilled addressee.
Preferably, the ores are mixed in proportions suitable to provide a
eutectic Ferro-titanium alloy comprising about 70% Ti to about 30%
Fe by weight.
[0047] The ores can be obtained already crushed into small pieces
or powders or may be ground or crushed as a first step of the
method. For good homogeneity in the end alloy, preferred sizes of
the crushed pieces are in the order of 100 to 600 microns. The ores
are mixed in proportions suitable to provide the constituent alloy
metals in correct stoichiometric quantities to form the chosen
alloy. The mixed particles of ore are sintered and may be used as a
starting material in any of the variations of the electrochemical
reduction processes previously described. In the particular case of
Ferro-titanium for use in the steel making process, it is not
necessary to reduce the contaminant level to the low levels
actually obtainable by the reduction process. The process may
therefore be applied for a shortened period to reduce the
contamination to below a maximum acceptable level. Also, since
homogeneity is not important for this application, crushed pieces
of the order of a few millimeters in size are acceptable.
[0048] At present, around 50,000 tons/year of Ferro-titanium is
used in the steel making industry as a deoxidant. Prior to the
present invention, this Ferro-titanium has been manufactured by
melting together iron and scrap titanium based materials. It is
recognised by the inventors that naturally occurring ores may
contain a range of metallic impurities which might not normally be
found in Ferro-titanium alloys produced by the prior art methods,
equally, it is appreciated that these impurities are unimportant
where the Ferro-titanium is to be used as a deoxidant in steel
making in accordance with usual practices. It is further
appreciated by the inventors that the purification of the mixed
ores provided by the electrolytic reduction method described
herein, may not need to be completed, since the total elimination
of contaminants such as oxygen is not essential for these purposes.
For example, in Ferro-titanium, oxygen levels of up to 2% by weight
are considered acceptable. Accordingly, the present invention maybe
used to partially purify the mixed ores to a state where the
contaminant levels are acceptable but not negligible. The time
taken to reduce the level of contaminant oxygen to about 2% in
Ferro-titanium made according to this method has been found to be
only about 70% of the time taken to reduce the levels to about 0.1%
by weight, the preferred level for other commercial applications of
the alloy. Trials carried out by the inventors have also shown the
process to have a current efficiency of around 70% in reducing the
oxygen to about 2% as opposed to about 40% efficiency in reducing
the oxygen levels to about 0.1%. Thus, the partial purification
reduces the overall processing cost in manufacturing the
Ferro-titanium alloy.
[0049] A preferred electrolyte, M.sub.2Y, is calcium chloride
(CaCl.sub.2). Other suitable electrolytes include but are not
limited to the molten chlorides of all common alkali and alkaline
earth metals. Other preferred metals for M.sub.2 are barium,
caesium, lithium, strontium and yttrium. The anode of the cell is
preferably of a relatively inert material. One suitable anode
material is graphite.
[0050] Processing conditions suitable for the favourable
dissolution of the contaminants require that the potential of the
cell preferably be maintained at a potential which is less than the
decomposition potential of the molten electrolyte M.sub.2Y during
the process. Allowing for polarisation and resistive losses in the
cell, it will be understood that the cell potential may be
maintained at a level equal to, or marginally higher than, the
decomposition potential of M.sub.2Y and still achieve the desired
result. Potentiostatic methods may be used to control the
potential.
[0051] It is also preferred that the temperature of the cell is
maintained at an elevated temperature which is significantly above
the melting point of M.sub.2Y but below the boiling point of
M.sub.2Y. Where M.sub.2Y is CaCl.sub.2. suitable processing
parameters include a potential of up to about 3.3 V and a
processing temperature of between about 825 and 1050.degree. C.
[0052] By adapting the method in accordance with various
embodiments previously described herein and in GB 00039719 and GB
0010873.8 from which this application claims priority, the
Ferro-titanium alloy can be provided in various physical forms, eg,
powdered, foamed, sintered plate or 3-dimensional shape as may be
required in different applications.
* * * * *