U.S. patent application number 11/196069 was filed with the patent office on 2005-12-01 for cast cermet anode for metal oxide electrolytic reduction.
This patent application is currently assigned to Pel Technologies, LLC. Invention is credited to Bengali, Abid, Cheetham, Jeffrey K., Meissner, David C., Musat, Jeffrey B., Srivastava, Ashvin.
Application Number | 20050262964 11/196069 |
Document ID | / |
Family ID | 31946802 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050262964 |
Kind Code |
A1 |
Meissner, David C. ; et
al. |
December 1, 2005 |
Cast cermet anode for metal oxide electrolytic reduction
Abstract
The invention is a method for producing a cast cermet anode for
metal oxide electrolytic reduction by feeding metallic iron and
metallic nickel in solid form to an oxidizing reactor; melting and
oxidizing the iron and nickel and forming molten nickel ferrite;
mixing the molten nickel ferrite with a base metal of high
electrical conductivity such as nickel, copper, silver, or alloys
thereof in a holding vessel such as ladle or tundish, and casting
the mixture into a mold to form a near net shape of the desired
anode. Apparatus for carrying out the method, and the resulting
product are also disclosed.
Inventors: |
Meissner, David C.;
(Charlotte, NC) ; Srivastava, Ashvin; (Sarasota,
FL) ; Musat, Jeffrey B.; (Canton, OH) ;
Cheetham, Jeffrey K.; (N. Canton, OH) ; Bengali,
Abid; (Naperville, IL) |
Correspondence
Address: |
DOUGHERTY, CLEMENTS, HOFER, BERNARD & WALKER
1901 ROXBOROUGH ROAD
SUITE 300
CHARLOTTE
NC
28211
US
|
Assignee: |
Pel Technologies, LLC
|
Family ID: |
31946802 |
Appl. No.: |
11/196069 |
Filed: |
August 3, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11196069 |
Aug 3, 2005 |
|
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|
10641634 |
Aug 15, 2003 |
|
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60405021 |
Aug 21, 2002 |
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Current U.S.
Class: |
75/232 ; 266/186;
75/10.63 |
Current CPC
Class: |
C25C 3/12 20130101; B22D
1/002 20130101; C22C 1/056 20130101; C22C 29/12 20130101 |
Class at
Publication: |
075/232 ;
075/010.63; 266/186 |
International
Class: |
C22C 029/12 |
Claims
What is claimed is:
1. A method for producing a cast cermet anode for metal oxide
electrolytic reduction, comprising the steps of: feeding metallic
iron and metallic nickel in solid form to an oxidizing reactor;
melting and oxidizing the iron and nickel and forming molten nickel
ferrite; discharging molten nickel ferrite from the oxidizing
reactor at a temperature sufficient to maintain the molten nickel
ferrite in the molten state; adding a base metal of high electrical
conductivity to the nickel ferrite to form a mixture; and casting
the mixture into a mold to form a near net shape of the anode.
2. A method according to claim 1 further comprising attaching an
electrical connector to said anode.
3. A method according to claim 1 wherein the metallic iron and
metallic nickel are fed in briquet form to the oxidizing
reactor.
4. A method according to claim 1 wherein the base metal is selected
from the group consisting of nickel, copper, silver, copper-silver
alloy, nickel-copper alloy, and nickel-copper-silver alloy.
5. A method according to claim 1, further comprising feeding iron
oxide and nickel oxide to the oxidizing reactor.
6. A method according to claim 1 wherein the molten nickel ferrite
is discharged into a holding vessel and base metal is kept in
suspension in the holding vessel by gas stirring.
7. A method according to claim 6 wherein gas stirring is carried
out with an inert gas or an oxygen-containing gas.
8. A method according to claim 7, wherein said oxygen-containing
gas is air or oxygen.
9. A method according to claim 1 wherein the base metal is
maintained in a molten state.
10. A method according to claim 1 wherein the metal oxide for
electrolytic reduction is selected from the group consisting of
aluminum, magnesium, lithium, and calcium oxides.
11. A method according to claim 1 wherein the base metal forms 5 to
25% of said mixture.
12. A cast cermet anode product for metal oxide electrolytic
reduction made by the method of claim 1.
13. A method for producing a cast cermet anode for metal oxide
electrolytic reduction, comprising the steps of: feeding at least
one compound selected from the group consisting of nickel oxides,
iron oxides, nickel ferrite, iron sulfides, nickel sulfides, iron
carbonates, nickel carbonates, and mixtures thereof to the melting
vessel; melting the compounds and forming molten nickel ferrite;
discharging molten nickel ferrite from the melting vessel at a
temperature sufficient to maintain the molten nickel ferrite in the
molten state; adding a base metal of high electrical conductivity
to the nickel ferrite to form a mixture; and casting the mixture
into a mold to form a near net shape of the anode.
14. Apparatus for producing a cast cermet anode for metal oxide
electrolytic reduction, comprising: an oxidizing reactor; means for
feeding metallic iron and metallic nickel to said oxidizing
reactor; means for discharging molten material from said oxidizing
reactor; a ladle or tundish positioned for receiving molten
material from said oxidizing reactor; means for adding high
electrical conductivity metal to said ladle or tundish; a mold
positioned to receive molten material from said ladle or tundish;
and means for discharging molten material from said ladle or
tundish into said mold to form said anode.
15. Apparatus according to claim 14, further comprising means for
providing stirring action in said ladle or tundish.
16. Apparatus according to claim 15, wherein said means for
providing stirring action is a gas injection system.
17. Apparatus according to claim 15, wherein said means for
providing stirring action is a lance communicating with a source of
gas, said gas being an inert gas or an oxygen-containing gas.
18. Apparatus according to claim 14, further comprising means for
adding heat to molten material within said ladle or tundish.
19. Apparatus according to claim 14, further comprising means for
heating said ladle or tundish to prevent molten material therein
from solidifying.
20. Apparatus for producing a cast cermet anode for metal oxide
electrolytic reduction, comprising: a melting vessel; means for
feeding iron and nickel compounds to said melting vessel; means for
discharging molten material from said vessel; a ladle or tundish
positioned for receiving molten material from said vessel; means
for adding high electrical conductivity metal to said ladle or
tundish; a mold positioned to receive molten material from said
ladle or tundish; and means for discharging molten material from
said ladle or tundish into said mold to form said anode.
21. Apparatus according to claim 20, further comprising means for
providing stirring action in said ladle or tundish.
22. Apparatus according to claim 21, wherein said means for
providing stirring action is a gas injection system.
23. Apparatus according to claim 21, wherein said means for
providing stirring action is a lance communicating with a source of
gas, said gas being an inert gas or an oxygen-containing gas.
24. Apparatus according to claim 20, further comprising means for
heating said ladle or tundish to prevent molten material therein
from solidifying.
25. Apparatus according to claim 20, wherein said melting vessel is
selected from the group consisting of a gas fired furnace, an
induction furnace, or an electric arc furnace.
26. A cast cermet anode for metal oxide electrolytic reduction
comprising: from about 75 to about 95% ceramic, selected from the
group consisting of nickel ferrite, iron ferrite, nickel oxide, and
mixtures thereof; and from about 5 to about 25% base metal or base
metal alloy.
27. A cast cermet anode according to claim 26, wherein said base
metal or base metal alloy is selected from the group consisting of
nickel, silver, copper, copper-silver alloy, copper-nickel alloy,
and copper-nickel-silver alloy.
28. A cast cermet anode according to claim 26, comprising: from
about 75 to about 95% nickel ferrite; and from about 5 to about 25%
copper or copper-silver alloy.
29. A cast cermet anode according to claim 26, comprising: about
85% nickel ferrite; and about 15% copper or copper-silver
alloy.
30. A cast cermet anode useful in the chlor-alkali industry for the
electrolysis of brine to produce sodium hydroxide and chlorine,
said anode comprising: from about 75 to about 95% ceramic, selected
from the group consisting of nickel ferrite, iron ferrite, nickel
oxide, and mixtures thereof; and from about 5 to about 25% base
metal or base metal alloy.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/405,021, filed Aug. 21, 2002.
FIELD OF THE INVENTION
[0002] The present invention relates to a method and apparatus for
producing a cast cermet anode for metal oxide electrolytic
reduction, and a cast cermet anode product.
BACKGROUND OF THE INVENTION
[0003] Since the advent of the electrolytic reduction process for
producing aluminum, the anodes used have been made of carbon which
is consumed during the electrolytic reduction process. In the more
recent past (20 years), there has been an effort to produce an
inert anode or electrode that is not consumed during reduction.
Metal anodes, ceramic anodes, and cermet anodes have been proposed
for development. Of these, the cermet anode has been at the
forefront of the development race. According to published patents,
the best available practice to produce a cermet anode heretofore
has been to mix ceramic and metal powders with a binder, press at
very high pressures, then sinter at high temperature. Specifically,
nickel ferrite (NiFe.sub.2O.sub.4) powder has been mixed with
metallic copper powder and copper/silver alloy powder, a binder
added, and the mixture pressed and sintered to make the cermet
anode. The manufacture of a nickel ferrite powder is a complex and
expensive process. The subsequent processing of the nickel ferrite
by blending and mixing with copper powder and organic binder,
followed by pressing at high pressure, then followed by sintering
at high temperatures (greater than 1300 C) for long times, is also
quite complex and expensive.
DESCRIPTION OF THE PRIOR ART
[0004] Applicant is aware of the following U.S. patents concerning
cermet electrodes for electrolytic reduction of aluminum:
1 U.S. Pat. No. Inventor Title 5,865,980 Ray et al. ELECTROLYSIS
WITH A INERT ELECTRODE CONTAINING A FERRITE, COPPER AND SILVER
6,126,799 Ray et al. INERT ELECTRODE CONTAINING METAL OXIDES,
COPPER AND NOBLE METAL 6,030,518 Dawless et al. REDUCED TEMPERATURE
ALUMINUM PRODUCTION IN AN ELECTROLYTIC CELL HAVING AN INERT ANODE
6,217,739 Ray et al. ELECTROLYTIC PRODUCTION OF HIGH PURITY
ALUMINUM USING INERT ANODES 6,332,969 Ray et al. INERT ELECTRODE
CONTAINING METAL OXIDES, COPPER AND NOBLE METAL 6,372,119 Ray et
al. INERT ANODE CONTAINING OXIDES OF NICKEL IRON AND COBALT USEFUL
FOR THE ELECTROLYTIC PRODUCTION OF METALS
SUMMARY OF THE INVENTION
[0005] The invention provides a method for producing a cast cermet
anode for metal oxide electrolytic reduction by feeding metallic
iron and metallic nickel in solid form to an oxidizing reactor;
melting and oxidizing the iron and nickel and forming molten nickel
ferrite; mixing the molten nickel ferrite with a base metal of high
electrical conductivity, such as nickel, copper, silver, or
copper/silver alloy, in a holding vessel such as a ladle or
tundish, and casting the mixture into a mold to form a near net
shape of the desired anode.
[0006] The invention also comprises apparatus for producing a cast
cermet anode for metal oxide electrolytic reduction, comprising an
oxidizing reactor; means for feeding metallic iron and metallic
nickel to the oxidizing reactor; a ladle or tundish positioned for
receiving molten material from the reactor; means for adding high
electrical conductivity metal to the ladle or tundish; a mold
positioned to receive molten material from the ladle or tundish;
and means for discharging molten material from the ladle or tundish
into the mold to form the anode.
[0007] The invention also comprises the product of the method, a
cast cermet anode for metal oxide electrolytic reduction comprising
from about 75 to about 95% ceramic material, consisting of one or
more of nickel ferrite, iron ferrite and nickel oxide, and from
about 5 to about 25% of a base metal or base metal alloy,
preferably copper, copper-silver alloy, nickel, nickel-copper
alloy, silver, or nickel-copper-silver alloy.
OBJECTS OF THE INVENTION
[0008] The principal object of the present invention is to provide
a process for the manufacture of cast cermet type inert anodes for
the electrolytic reduction of metal oxides.
[0009] Another object of the invention is to provide a process for
the manufacture of cermet type inert anodes that is simpler and
more cost efficient than the current state of the art of cermet
anode manufacture.
[0010] Another object of the invention is to produce a cermet anode
that has as good or better properties of conductivity, strength,
and resistance to attack by the electrolyte than sintered cermet
anodes.
[0011] Another object of the invention is to provide a process that
allows near net shape casting of an inert cermet anode.
[0012] A further object of this invention is to provide apparatus
for the manufacture of cermet type cast inert anodes.
[0013] Another object of the invention is to provide an anode
useful in the chlor-alkali industry for the electrolysis of brine
to produce sodium hydroxide and chlorine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The foregoing and other objects will become more readily
apparent by referring to the following detailed description and the
appended drawings in which:
[0015] FIG. 1 is a schematic diagram of the method and apparatus of
the preferred embodiment of the invention.
[0016] FIG. 2 is a schematic diagram of the method and apparatus of
an alternative embodiment of the invention.
[0017] FIG. 3 is a schematic diagram of the method and apparatus of
another alternative embodiment of the invention.
[0018] FIG. 4 is a schematic diagram of the method and apparatus of
another alternative embodiment of the invention.
[0019] FIG. 5 is a schematic diagram of the method and apparatus of
another alternative embodiment of the invention.
[0020] FIG. 6 is a schematic diagram of the method and apparatus of
a further alternative embodiment of the invention which utilizes a
melting furnace rather than an oxidizing furnace.
[0021] FIG. 7 is a schematic diagram of alternative embodiment of
the invented method utilizing a variation of feed materials to the
oxidizing furnace.
DETAILED DESCRIPTION
[0022] Referring now to the drawings, and particularly to FIG. 1,
molten metal oxide is formed by oxidizing iron and other metal(s)
to form a molten ferrite of the general formula
A.sub.(x)B.sub.(1-x)Fe.sub.2O.sub.4
[0023] where A&B are divalent metal ions such as Mg, Ni, Mn,
Co, Fe and Zn; and x can vary from 0 to 1.0. The molten ferrite is
then mixed with a base metal of high electrical conductivity in
percentages of base metal from about 5% up to about 25%. The molten
mixture of the ferrite and the base metal such as nickel, copper,
silver, copper-silver alloy, nickel-copper alloy, or
nickel-silver-copper alloy, is then cast, solidified and cooled.
The mixture may be cast into a near net shape of the desired cermet
anode. An electrical connector may be attached to the cermet anode
by cementing after cooling, or by insertion during the time the
anode is molten in the mold.
[0024] In a preferred embodiment, metallic iron and metallic nickel
in briquet form from source 10 are fed to an oxidizing reactor 12
wherein the iron and nickel are melted and oxidized by oxygen from
a source 14. The iron and nickel are fed into the reactor in a
molar ratio of:
Fe/Ni=2/1.
[0025] A molten nickel ferrite of formula Ni Fe.sub.2O.sub.4 is
formed.
[0026] It is possible to utilize a molar ratio of Fe/Ni of greater
than 2/1 to produce a mixture of nickel ferrite (NiFe.sub.2O.sub.4)
and iron ferrite (Fe.sub.3O.sub.4). It is also possible to operate
with a molar ratio or Fe/Ni less than 2 in order to produce a
nickel ferrite plus excess nickel oxide (NiO).
[0027] The molten nickel ferrite is discharged from the oxidizing
reactor at a temperature sufficient to maintain it in the molten
state plus sufficient superheat to melt the base metal being added
thereto. The molten nickel ferrite is discharged through outlet 16
into a receiving and holding vessel 18 such as a tundish or ladle.
Copper or copper/silver alloy 20 is added and mixed into the molten
nickel ferrite in the holding vessel in which the base metal melts.
The base metal is kept in suspension by gas stirring and not
allowed to separate from the nickel ferrite and settle to the
bottom of the ladle. The gas 22 used for stirring can be an inert
gas or it can be an oxygen-containing gas, including oxygen and
air. The gas can be injected through a gas injection port or inlet
24 or through a lance 26. The copper that is added can be in the
form of powder or larger particles that are readily melted. The
ladle can be heated to prevent the molten mixture from
solidifying.
[0028] The injection of oxygen containing gas, in addition to
stirring the molten material, can be used to oxidize all or part of
any nickel metal carried over from the oxidizing reactor 12 or
melter 13 (FIG. 6). Nickel metal from the oxidizing reactor or
melter that is not oxidized in the ladle will become part of the
base metal system of nickel, copper, silver and combinations or
alloys thereof. It is preferable that oxidation be incomplete,
leaving some free metal in the product to be cast. Injection of an
inert gas for stirring may be used to insure that nickel metal is
not oxidized when it is desired to have metallic nickel in the base
metal system. Inert gas will generally be used when adding copper
and/or silver.
[0029] Vacuum degassing of the ladle may be employed to remove
entrapped gases and minimize porosity of the resulting final cast
anode product.
[0030] The mixture of nickel ferrite and copper is then removed
from the holding vessel and cast into a mold to form a near net
shape inert anode 32, after which it is allowed to cool. Controlled
cooling rates, post-heat treatment, and bubbling of argon gas for
coalescing and removal of entrapped gases may be employed as
methods for reducing stresses and porosity in the cast anode.
During the solidification process an electrical connector rod 34
made of nickel may be inserted into the still-molten nickel
ferrite/copper casting. The finished product is a cast inert anode
32 of correct shape with the electrical connector 34 attached.
[0031] A suitable post-heat treatment can be annealing in the
presence of an oxygen-containing gas. This controls the cooling
rate, and assures that the metal on the outer surface of the anode
is oxidized, which makes it resistant to attack by electrolyte
solutions.
[0032] Molten and cast material inherently has better resistance to
attack by molten salt bath solution than a sintered material
because the true density of the cast material is greater than that
of sintered material because of the lack of voids.
Alternative Embodiments
[0033] Iron and nickel feed material may be provided in metallic
form other than briquets, such as from punchings, turnings, or
other high purity solid form.
[0034] In an alternative embodiment of the method, as shown in FIG.
2, copper or base metal alloy may be added between the melting
vessel and the tundish or ladle by introducing it into the
discharge runner 16 between the melting vessel 12 and the tundish
18. The base metal or base metal alloy is advantageously added in
the form of wire or wire rod for accurate control of the molten
cermet composition, or the base metal may be added in powder
form.
[0035] In another alternative embodiment of the method, as shown by
dotted lines in FIG. 2, copper or base metal alloy 20 may be added
directly to the casting mold 30 before or during filling of the
mold with the molten nickel ferrite. The base metal or alloy may be
added in the form of wire, wire rod, or powder.
[0036] In another alternative embodiment, shown in FIG. 3, copper
oxide is fed into the reactor in which it is reduced to copper by
reaction with metallic iron and metallic nickel, and it oxidizes
the metallic iron and metallic nickel. Alternatively, copper oxide,
along with metallic iron and metallic nickel (in the same ratio as
it is or would be fed into the reactor) may be fed from source 40
to the tundish by feed 42, or to the mold 30 by feed 44, as shown
in FIG. 4.
[0037] As shown in FIG. 5, copper oxide, iron oxide and nickel
oxide from source 48 can be fed into the reactor 12, with metallic
nickel and iron, to form molten nickel ferrite. Additional base
metal or base metal alloy can be introduced to the tundish 18 or
the mold 30, as desired. An electrical connector rod 34 (as in FIG.
2), preferably made of nickel, may be inserted into the still
molten anode casting 32. The resulting product is as described
earlier, a cast inert anode of correct shape with the electrical
connector attached.
[0038] In the alternative embodiment shown in FIG. 6, solid nickel
ferrite 50, or a mixture 52 of nickel ferrite, nickel oxide and
iron oxides, such as hematite or iron ferrite, is melted in a
melting furnace or vessel 13, which in this case is not an
oxidizing vessel, to form molten nickel ferrite. The melting vessel
13 is a gas fired furnace, induction furnace, or electric arc
furnace. Other iron-containing or nickel-containing compounds, such
as metal sulfides or carbonates, can be used as feed material in
place of the metal oxides 50, 52.
[0039] In the alternative embodiment shown in FIG. 7, mostly
metallic iron and nickel 10 are fed to the reactor 12 along with
some iron oxide and/or nickel oxide, which are melted and oxidized
to form molten nickel ferrite. There is sufficient exothermic heat
available from the oxidation of nickel and iron to allow the use of
nickel oxide and iron oxide as feed materials to the reactor. The
molten nickel ferrite is then discharged into a ladle or tundish 18
and further treated according to the remaining steps of the method
to form a cast cermet anode 32. In this embodiment, solid nickel
oxide 54, or iron oxide 58, or a mixture of nickel oxide and iron
oxide 60 is introduced to and melted in an oxidizing reactor or
vessel 12, to form molten nickel ferrite.
[0040] It is also to be understood that a cermet type inert anode
made from a ferrite may be used in electrolytic reduction processes
besides aluminum reduction, such as electrolytic reduction of
magnesium, lithium, or calcium. A cast cermet anode useful in the
chlor-alkali industry for the electrolysis of brine to produce
sodium hydroxide and chlorine, comprises about 75 to about 95%
ceramic, selected from the group consisting of nickel ferrite, iron
ferrite, nickel oxide, and mixtures thereof, and from about 5 to
about 25% base metal or base metal alloy.
Summary of the Achievement of the Objects of the Invention
[0041] From the foregoing, it is readily apparent that we have
invented an improved process for the manufacture of cast cermet
type inert anodes that is simpler and more cost efficient than the
current state of the art of cermet anode manufacture, and that
allows near net shape casting of an inert cermet anode; a cast
cermet anode product that has as good or better properties of
conductivity, strength, resistance to attack by the electrolyte
than sintered cermet anodes, and apparatus for the manufacture of
cermet type cast inert anodes.
[0042] It is to be understood that the foregoing description and
specific embodiments are merely illustrative of the best mode of
the invention and the principles thereof, and that various
modifications and additions may be made to the apparatus by those
skilled in the art, without departing from the spirit and scope of
this invention, which is therefore understood to be limited only by
the scope of the appended claims.
* * * * *