CA1037420A - Electrodes for aluminum reduction cells - Google Patents
Electrodes for aluminum reduction cellsInfo
- Publication number
- CA1037420A CA1037420A CA210,695A CA210695A CA1037420A CA 1037420 A CA1037420 A CA 1037420A CA 210695 A CA210695 A CA 210695A CA 1037420 A CA1037420 A CA 1037420A
- Authority
- CA
- Canada
- Prior art keywords
- metals
- metal
- oxide
- trivalent
- divalent
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
- C25C3/12—Anodes
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B42/00—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means
- G03B42/02—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means using X-rays
- G03B42/04—Holders for X-ray films
- G03B42/045—Holders for X-ray films apparatus for loading or unloading the holders
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Electrolytic Production Of Metals (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method for producing aluminum by molten salt elec-trolysis of aluminum oxide which comprises electrolyzing aluminum oxide dissolved in a molten salt containing aluminum sodium fluoride as the main component by passing a direct current through an anode to a cathode disposed in said molten salt, wherein at least a portion of at least one of said anode and said cathode that is brought into contact with said molten salt is made of or covered with a composition containing at least about 50%
by weight of electronic conductive oxide ceramics having chemical resistance to the molten salt, said oxide ceramics being selected from spinal structure oxides having the general formula XYY'04 wherein X is a divalent or tetravalent metal, Y
and Y' may be either the same or different and are trivalent or divalent metals, O is oxygen atom, provided that when X is a divalent metal, Y and Y' are selected from trivalent metals but the spinel structure oxides are excluded in which both Y
and Y' are trivalent iron, Fe (III), and when X is tetravalent metal, Y and Y' are selected from divalent metals, provskite structure oxides having the general formula RMO3 wherein R is a monovalent divalent or trivalent metal, M is a pentavalent, tetravalent or trivalent metal, O is oxygen atom, provided that when R is a monovalent metal, M is selected from pentavalent metals, when R is divalent metal, M is selected from tetravalent metals, and when R is a trivalent metal, M is selected from trivalent metals or a mixture thereof, the remainder of the composition being comprised of an oxide, carbide, nitride, boride or silicide of an element selected from transition metals, platinum group metals and rare earth elements.
A method for producing aluminum by molten salt elec-trolysis of aluminum oxide which comprises electrolyzing aluminum oxide dissolved in a molten salt containing aluminum sodium fluoride as the main component by passing a direct current through an anode to a cathode disposed in said molten salt, wherein at least a portion of at least one of said anode and said cathode that is brought into contact with said molten salt is made of or covered with a composition containing at least about 50%
by weight of electronic conductive oxide ceramics having chemical resistance to the molten salt, said oxide ceramics being selected from spinal structure oxides having the general formula XYY'04 wherein X is a divalent or tetravalent metal, Y
and Y' may be either the same or different and are trivalent or divalent metals, O is oxygen atom, provided that when X is a divalent metal, Y and Y' are selected from trivalent metals but the spinel structure oxides are excluded in which both Y
and Y' are trivalent iron, Fe (III), and when X is tetravalent metal, Y and Y' are selected from divalent metals, provskite structure oxides having the general formula RMO3 wherein R is a monovalent divalent or trivalent metal, M is a pentavalent, tetravalent or trivalent metal, O is oxygen atom, provided that when R is a monovalent metal, M is selected from pentavalent metals, when R is divalent metal, M is selected from tetravalent metals, and when R is a trivalent metal, M is selected from trivalent metals or a mixture thereof, the remainder of the composition being comprised of an oxide, carbide, nitride, boride or silicide of an element selected from transition metals, platinum group metals and rare earth elements.
Description
:; ~0374Z0 - :
~ The present invention relates to a method for produc-ing aluminum hy molten salt electrolysis of aluminum oxide.
More particularly, it relates to an electrode, and particularly ; -an anode, used in the method, which is made of or covered with electronic conductive oxide ceramics. ` `
It is known to produce aluminum by molten salt ~; ~
' ~ ! . I
electrolysis of alurninum oxide dissolved in a bath of aluminum sodium fluoride ~AlF3.3NaF) or so-called cryolite, by using . . . .
~; a carbon anode. This electrolisis is usually conducted at ` -about 900 - 1000C. ~ ;~
When aluminum is produced by using a carbon anode, the carbon anode iB oxidized and consumed hy about 330 kg : . ~
~ theoretically and about 400 - 450 kg actually per ton oE
,~. .
aluminum due to oxygen produced throuyh the decomposition of ; aluminum oxide. For this reason, it is necessary to continuous-ly adjust the position of the electrode -to maintain it at a ,~"" ,, ~; constant level~ and it is also required to replace the anode ... .
'~ by a new one before it is completely consumed. These are ~;~ economical and operational defects.
~ 20 As an approach to obviate the above-mentioned defects ;_ ~ in t~he carbon electrode, various non-consumable anodes have been recently developed. For example, a method using an oxygen i ion-conductive ànode consisting mainly of zirconium oxide has been proposed (British Patent Specification 1,152,124). This method, howeverj is disadvantageous in that it required an apparatus for removing oxygen produced and the operation is complex. A method using an anode consisting of electronic conductive metal oxide containing at least 80~ hy weight ;;`
~
: . :
~037421D
:~ of tin oxide has also heen proposed (British Patent Specifie-ation 1,295,117). This method is also disadvantageous in that -: the anode has poor chemical resistance to the molten salt.
~ The present invention provides a so-called non-consumable electrode which does not react with oxyqen produced . in molten salt electrolysis of aluminum oxide and which has ehemieal resistanee to the molten salt.
. ~ In the aeeompanying drawings;
Figs. 1 and 2 show embodiments of the electrodes ~` 10 used in the method aecordincJ to the present invention, and ,. . . :~
Fig. 3 shows an example o aluminum reduetion eells using the electrode accordi.ng to the method o~ the present ;' invention, ... .
:, The inventors of the present lnvention have made ;.
extensive investigation to Eind non-consurnable eleetrodes for molten salt electrolysis of aluminum oxide and have found that ~:
:;, ,;; , .
_ spinel strueture oxides or perovskite strueture oxides have ~ exeellent eleetronie conductivity at a temperature of about .~ 900 - 1000C, exhibit~catalytie action for the generation of : .:
.: 20 oxygen, and exhihit chemical resistance to the molten salt. .~
, ;"~
Based on this finding, they have developed non-consu~.able .
electrodes for aluminum electrolyti.c cells. ..
_: Accordlng to the present invention there is provided `
~:~ a method for producing aluminum by molten salt electrolysis of .
;~,: aluminum oxide which eomprises electrolyzing aluminum oxide ,'_ dissolved in a molten salt containing.aluminum sodium fluoride .
as the main eomponent by passincJ a direct eurrent through an ~'..
. anode to a cathode disposed in said molten salt, wherein at ;
/e~ o ~e 0?~l , ; ~ . least a portion of~said anode and said ca-thode that is brought .. 30 into contact with said molten salt is made of or covered with .
"i, .. . .
, , a eomposit.ion eontaininc~ at least about 50~ by weight of ,~ ~
., ~, . . . .
',; eleetronie eonduetive oxide eeramics havincJ chemical resistance ~ ~ ~
. ~ ,.. ..
.; .. . .
.~ ~ 2 - . .
., ''~' ', ~, . , ~", i~ , . ; ..
~: .
~037~0 ` `
. to the molten salt, said oxide ceramics being selected from ` ;~
.:: . .
spinel structure oxides having the ~eneral formula XYYl04 ~: wherein X is a divalent or tetravalent metal, Y and Y' may be .. .
... ... .. .
either the same or different and are trivalent or divalent metals, 0 is oxygen atom, provided that when X is a divalent i'.. `~
. metal, Y and yl are selected from trivalent metals but the ~:
spinel structure oxides are excluded in which both Y and Y' are . trivalent iron, Fe (III), and when X is tetravalent metal, Y ..
~ . . .:
.. and Y' are selected from divalent metals, provskite structure ;:.:
. lO oxides having the general formula RM03 wherein R is a mono~
valent clivalent or trivalent metal, M is a pentavalent, tetra-;: valent or trivalent metal, 0 is oxygen atom, provided that when :;
; . . .
R is a monovalent metal, M is selected from pentavalent metals, ~.
when R is c1ivalent metal, M is selectecl Erom tetraval~nt metals, :
and when R is a trïvalent metal, M is selected from trivalent .`~
metals or a mixture thereof, the remainder of the composition `''i being comprised of an oxide, carbide, nitride, boride or .;
.,:.~ ... .
;~ silicide of an element selected from transition metals, ;.
platinum group metals and rare earth elements. `....... :
: 20 Accord:ing to the present invention, the electrode ~ :
base is covered, at~ least in its portion that is brought into ~ :
contact with a molten salt, w1th a composit1on containing at least about 509 by weight of electronic conductive oxide :' ceramics selected from spinel structure oxides having the general formula XYY'04 twherein X, Y, Y' and 0 are as defined above~, perovskite structure oxides having the general formula .7 ~103 twherein R, M and 0 are as defined above), and a mixture .
j: thereof. Alternatively, the above-mentioned part of the ~ electrode may be made of the above-mentioned oxide ceramics. .
~ 30 Usually, in the spinel structure oxitles having .
,: ., :
.: ., ., ~, `:
~ 3 - ~:
. . .
; ~03742~ :~
''' ;.
1 the general formula XYY'04, X is a divalent metal such as barium, magnesium, calcium, strontium, zinc, lead copper, molybdenum? manganese, iron, cobalt, nickel or the like, and preferably copper, molybdenum, manganese, 5 iron, cobalt or nickel, or a tetravalent metal such as .
titanium, vanadium, tin, germanium or the like, and pre-ferably titanium or vanadium, Y and Y' are trivalent :~`
. metals such as aluminum, gallium, indium, manganese, iron,cobalt, nickel, chromium, vanadium, rhodium, lanthanum, 10 yttrium or the like, and preferably indium, manganese, -.
iron, cobalt, nickel, chromium, rhodium or lanthanum, or dlvalent metals such as magnesium, zino, man~ane~e, iron, cobalt, nickel or the like, and pre~erably iron, cobalt or nickel (provided that when X is a divalent ~ 15 metal, Y and Y' are selected ~rom trivalent metals, and `.
when X is a tetravalent metal, Y and Y' are selected .: from divalent metals). In the perovskite structure .~ oxides having the general formula RM03, R is a mono-valent metal such as lithium, sodium, potassium or the like, or a divalent metal such as calcium, magnesium, barium, lead or the like, or a trivalent metal such as : : .
i: ~ ~; -, : . lanthanum, yttrium, chromium, aluminum, manganese, cobalt, i~
; : nickel or the like, M is a pentavalent metal such as niobium, tantalum or the like, or a tetravalent metal .. : ~ ,. . .
.;.; 25 such as zirconium, titanium, tin or the like, or a tri- ;~
. ~ valent metal such as lanthanum, yttrium, chromium, aluminum, : manganese, cobalt, nickel or the like (provided that when ; R is a monovalent metal, M is selected ~rom pentavalent . :
;~i metals, when R is a divalent metal, M is selected ~rom .:~:.
` ~ 30 te-travalent metals, and when R is a trivalent metal, . ~:
. , '. ::'.:
` , r,~
!. ~ . . ' i,: '~, :
1037420 :
1 M is selected from trivalent metals). The perovskite structure oxides in which R and M are trivalent metals are preferable.
More particularly, spinel structure oxides such ,-~
as MgV24~ FeV24~ ZnV204~ MgCr204, MnCr204, FeCr204, CCr24~ Niar24~ CUCr24~ ZnCr204, ZnMn204,~MnMn204, FeAlFeO4, MgCo204, CUCO2O4~ ZnC24~ ~eNi24~ MgRh24 . ~ . ...
CoRh204, CURh2o4~ MnRh2o4~ NiRh2o4~ ZnRh24~ MgA124~ ~... .
SrA1204, MoA1204, FeA1204, CoA1204, NiA1204, CuA1204, ZnAl2o4~ MgGa24~ ZnGa204, CaGa204, MgIn204, MnIn204, FeIn24~ CIn24~ NiIn24, MgFeA104, NiFeA104, Cu~a204, ~a24~ Ni~a24~ TiMg24~ '~iMn204, '~iCo204, '~iFe204, ~I!iNi204~ 'riZn24, SnMg204, SnZn204, SnCo204, VMg204 , (Note: Although pure spinel such as MgA1204, SrA120 or TiMg204 has, in general, very small electronic con-ductivity and it is dif~icult to use as an electronic ~i ~ conductlve materlal,~lt may be rendered highly conductive q;~ by addlng another component thereto. The~spinel which has~thus been~provided uith conductlvity lS oonventional~
20 ~ }y expressed~as~MgA1204,~ etc. Therefore, such an~ex- J',~A,;
- presslon~ls also employed ln the present invention~, ~
or perovsklte~structure oxides such as ~iNbO3, K~bO3, ~ ;
NaNbO3, ~iTaO3, BaTiO3, PbTi03, PbZrO3, LaCrO3, ~aA103, aNiO3, ~aY03, YCrO3 or IaCoO3 may be used.
.. i ~ ~ ~ . , .
The above-mentioned spinel andjor perovskite structure oxides~are of electronic conductor and are dif~erent in~eleotro-oonductive mode than known ion-con-,., ~ ~ : , . . .
~o ductive electrodes and are also dif~erent in crystal structure than;the tin oxide electrode, and hence they provide electrodes cons-tructed of completely novel . ~ . . , .:. ,".
~` ` ' 1, '', `;
- ~0374ZO `:
....
1 componentsO The electrodes constructed of such electronic conductive oxide ceramics exhibit excellent conductlvity ... , : .
under the electrolysis condition and also have excellent resistance to the molten bath.
The electrodes according -to the present inven-tion are made of or covered with a composition containing -at least 50% by weight, and preferably at least 70% by : weight and most preferably at least 80~o by weight, of .~ the said spinel structure oxide, perovskite structure oxide or a mixture thereof at least in their portion that is brought into contact With the molten salt.
In the production of the electrode o~ the present invention, in order to improve the electrode i~
density, heat resistance, thermal shock resistance, ; -~
~-i 15 resistance to molten bath and electric conductivity, ;~
ii~ oxides, carbides, nitrides, borides or sillcides of :~ alkali metals, alkallne earth metals, transition metals, platinum group~metals~, rare earth elements or the like ~ ~
may~be added, if necessary, to tke electronic conductive -; -20 oxlde~ceramics~. When~the amount of the additive exceeds i~;
50~o by welght,~however, the electric~oonductivity, re-:sistance to bath and oxidation resistance of the electrode are deteriorated. Therefore, the amount of the additive should be kept at 50% by weight or less. Par-ticularly preferable additives are tranSition metal oxides such ~ as manganese oxide, nickel oxide, cobalt oxide a~d iron ; ~ ~- oxide, and platinum group metal oxidesi such as ruthenium oxide, palladium oxide and rhodium oxide, and rare earth element oxides such as yttrium oxide, ytterbium oxide and neodium oxide, and titanium nitride, titanium boride ~',' , ' ,, '. ~
. . ~ ... - . . .
- 6 - ~
~ , .
~. ' `,, ~`
~: :
; . , ..:
:: :
~:
l and tungsten silicide.
The optlmum electric resistance of the electronic conductive oxide ceramics used in the production of the electrode varies depending on the shape of the electrode ,, .. :
' 5 such as t,he thickness o~ the coating or the like, but ~
. .
usually the material having a conductivity of at least -~
~ about 0.1 Q -1 cm~l (at 1000C) lS most preferably ^
: used.
. . . .
: The electronic conductive oxide ceramic for ` 10 coating or forming the electrode o~ the present inven- ;
tion may have a meltlng point higher than the operating temperature of the electrolytic cell, and usually higher than about 1000C and pre~erably higher than 1200C.
;~ The electrode of the present invention may be formed from an electrode base made o~ a conductive materi-. . .
... .
i al such as a metal or alloy e.g. titanium, nickel or copper, or~carbonj graphite, or a carbide, nitride, borlde, siliclde, tltanium, molybdenum or tungsten, on the surface~of~which~a composition contalning said oxide 20~ ~ceramics is~coated, or the~entire electrode may be formed "
~,?~ of`said oxide ceramics In~the coating of the oxide ceramics on the electrode base~surfaoe, a composition containing the spinel and/or perovskite struoture oxide are ~lame sprayed ~;
or plasma sprayed and, i~ necessary, subjected to heat treatment or~electroplating process. Alternatively, ~; an inorganic or organic metal compound, which can pro-duce a spinel and/or perovskite structure oxide upon sintering, is~ coated, dipped, sprayed or thermal de-0 composition-evaporated and then thus treated electrode , , ~; , ., .
.: -,. , ...
.~ ,.. .
... .
`
10374;:0 -~
- 1 base is slntered. As a further alternative, an electrode base made of an alloy which can produce a spinel and/or~
perovskite structure oxide upon oxidization or a base , .
coated with such alloy is oxidized. It should be under-stood that in the coating of the electrode base with the oxide ceramics, an intermediate layer of a platinum group metal oxide or the like may be interposed to en~
; hance the adhasiveness between the oxide ceramics and the base.
: 10 The spinel and/or perovskite structure oxldes may be oonveniently prepared by the firing o~ a mixture ;'~ having an appropriate composition o~ oxides, hydroxides, ~' ;
,,,~ ~,., .:
chlorides, sul~ates, ni-trates, carbonates, oxalates o~
said metals usually at a temperature o~ 500C or more j- ;
and pre~erably at 800 - 2500C. Sintering is conducted " by hot pressing in a high frequency induction furnace ; or a resistive heating furnace at about 500C or more and preferably;~at~800 - 2500C, and under reduced pressure, `r "" ,~
atmospher1c~pressure or elevated pressure, and preferably ;~ -under a pressure of~50 - lOOO kg/cm2 by hot pressing.
In~the applieation of the electrode of the prebent`inventlon to the aluminum electrolysis, a con-necting means between the electrode and a conductor is not limited but any conventional means may be used.
25 r~hus, the connection may be e~ected by threading, `~
j welding or casting, or it may be e~fected through a low melting point metal such as aluminum, tin or copper, i '! or an alloy or a compound thereof.
i r~he application o~ the electrode o~ the present inventlon to an anode for the production o~ aluminum ,, ::
, i~ . .
; ~ . :, .: 1037~0 ~`
1 will now be described with reference to the accompanying . drawings.
Fig. 1 shows an embodiment of the anode ac-cording to the present invention. In Fig. I, a con-ductive bar 1 is embedded in an anode base formed of a conductive material such as a metal, an alloy, carbon ;-~ ;
or graphite having a melting point higher than the ~ electrolysis temperature. Applied onto the surface `~
: of the anode base 2 by an appropriate method is a coat-ing 3 of the electronic conduc-tive oxide ceramics accordin~
to the present inVention.
Fig. 2 shows another embodiment o~ the present invention, in which an anode 4 is entirely ~ormed of the ; electronic conductive oxide ceramics according to the present invention, in which the conductive bar 1 is em-bedded.
~; ~ Fig.~ shows the running state of an electrolysis of aluminum~oxide by the application of the anode of the present inventlon placed ln a~reduction cell. The reduc-tion cell comprises a steel outer shell, a thermal in-~ sula;tion 5 of~an~appropriate lnsulating material and a -"`~ lin mg~6 of a carbonacious material, carbide, boride or the ceramics according to the present invention. A
conductive bar 7 is embedded in the lining 6. Molten aluminum ~ precipitates at the bottom of molten electrolyte 9, the top surface c~f which is covered with a crust 10. ~ ;
he anodes 4 of the present invention suspending from the conductive bar 1 are arranged in the molten electrolyte ~ ~;
9 and appropriately spaced from the surface of -the pre-cipitated aluminum. The conductive bar 1 is movably .! ::`-: :
.:............................................ . . .
``
1037420 `
1 connected with a bus bar 11. In the reduction cell ~-having the above-mentioned structure, aluminum is pre-cipitated when current is introduced.
Although the use o~ the electrode as an anode -5 is illustrated in Fig. 3, it should be understood that `';
the electrode of the present invention can also be used ~;
as a cathode for the aluminum electrolyzer.
'rhe electrode of the present invention has the ~;
' following advantages over the prior art carbon anode:
, 10 (1) Since the electrode of the present invention is not ` ;
,;,. ... ..
consumed unlike the prior art consumable carbon anode, ~ the electrode oan be u~ed without replacement ~or several ; months or more and usually 0.5 to 1 year. '~herefore, `~
the number of times for the electrode replacement can be considerably reduced. (2) Since the electrode o~
the present invention is not consumed unlike the con- ;;
',! ... ...
sumable carbon anode, the ~requency of adjusting the ~ -distance between the~anode and the precipitated aluminum is~considerably lower~ed, thereby the electrolysis opera-20~ tion lS ~slmpllfled, the production cost is reduced and `~
erroneous~operation of operators is avoided. ~;
The present invention is illustrated by re-; ferring to the ~ollowing examples, in which parts are ~;~ by weight unless otherwise indicated. ; `
;~`
,'..: .
j Example 1 Mixed oxide powder consisting o~ 62.3 parts of chromic oxide, 35.7 parts o~ cobaltous oxide, and 2 parts Qf nickel monoxide was dry-mixed in a ball mill for 15 hours and formed under pressure (1000 kg/cm2) "~
, .
~ i'.'.. .'' `, ,~,::, ' : :`
1~374~
1 by a rubber press, and then sintered in a high frequency ;~ induction furnance at 1800C for two hours to produce .. , :, an electrode consisting mainly of the spinel structure oxide of CoCr204. The sintered anode was rigid and ;
compact and exhibited a conductivity of 1.0 Q~l cm~
at 1000C. The anode was then drilled and copper was casted in the drilled hole. The copper was connected -with a platinum lead wire to complete the anode for use 1 , , in the electrolysis. ~
;~ .: .
By the use of the anode formed in this manner, a cryolite bath containing saturated aluminum oxide ~;
maintained at 950C was continuously electrolyeed ~or ' 5 3 months while sequentially adding aluminum oxide at a current density of 1 A/cm2 and at 5.7 volts. ~he decomposition voltage was 2.2 V, which was close to the theoretical value of 2.1 V (at 950C), and the over-~;~ voltage was small. ~The current efficiency was 95%, ~;
and the corrosion of the anode after the electrolysis was not observed. ~ -;~
Example~2~
Mlxed oxlde powder consisting of 60.2 parts of lanthanum oxide, 33.9 parts of chromic oxide, and ., ~. .... .
5.9 parts of strontium carbonate was dry-mixed in a ball mill for 15 hours and formed under pressure (1000 kg/cm2)~by a rubber press and -then sintered in a high frèquenoy induction furnace at 1900C ~or one :j ,.;
hour to produce an electrode consistin~ mainly o~ the perovskite structure oxide of ~aCr03. '~he sintered .. "f, 30 anode was rigid and compact and exhibited a conductivity . ~:
,., :. .:
! `
~ :`
:~ 1037420 , j; . ., .`.
1 of 10 Q-l cm~l at 1000C. The anode was then drilled ~ii - and copper was cast in the drilled hole. The copper was connected with a platinum lead wire to complete the anode for the electrolysis.
' :,' , ~ . . i, ; .
By using o~ the anode thus constructed, aluminum .':!'"`''' ,~, !," .
oxide was electrolyzed continuously for three months ;; `
under the same conditions as in Example 1. The decom~
position voltage was 2.2 V, the current efficiency was r . ,,~, `
95%. No corrosion of the anode after the electrolysis ~: . , ~ 10 was observed.
., ,, , ,: ,, ~xample 3 `
. .
Mixed oxide powder consisting of 32.2 parts ~;
of titanium oxide, 64.5 parts o~ ferrous oxide, ~.3 15 parts of manganese oxide was dry-mixed in a ball mill -for 24 hours and ~ormed under pressure (1000 kg/cm2) ;~
- by oil hydraulic press, and sintered in a silicon carbide reslstor;el~eotric~furnace at I400C ~or 10 hours to ~;produce an eleotrode cons~isting malnly of spinel struc~
20~ ture oxide~of ~lFe204, The slntered anode was rigid and compact~and exhiblted a conductivity o~ 1 Q -1 cm~
at 1000O. ~The anode~was connected to a platinum lead wire through tin metal to complete the anode for the ~ ;
electrolysis. ~
~By the use of the anode thuæ ~ormed, cryolite `;
bath containing saturated aluminum oxide maintained at 950C was oontlnuously electrolyzed for 3 months while sequentially adding aluminum oxide at a current density of 0.9 A/cm2 and at 5.7 V. The decomposition voltage was 2.1 V, whioh substantially corresponded to the . ., . ' .
~2 - , _ ~.;
: . , ' .
~337420 ~ ~
'- 1 theoretical decomposition voltage, and the overvoltage was very small. The current efficiency was about 95%.
~o corrosion of the anode after the electrolysis was :. :,; . .
observed.
;-. . . :
Example 4 A mixture consisting of 65,8 parts of lanthanum oxide, 3~.7 parts of nickel sesquioxide and 0.5 part of indium oxide and a small amount of water were wet-mixed in a ball mill for 24 hours and then heated in a silicon carbide resistor electrio furnace at 1600C ~or lO hours.
'~he sintered product was crushed into particle~ of `;
. ~ ; .
200 mesh or les~ in ~ize. '~he partioles were then , ; applied onto a titanium substrate by a plasma spray . .
;~ 15 unit, In this manner, an anode for the electrolysis ¢l having a coating consisting mainly of the perovskite structure oxide of ~a~iO~ on the titanium substrate was prepared.
3y the~ use~of the anode thus formed, cryolite bath containlng saturated~alumlnum~oxide was continuously electrolyz~ed~or;3 months, while sequentially adding alumlnum oxlde,~at;a;current density of 0.9 A/cm2~and at 5.7 V.~The decomposition voltage measured substantial-ly oorrespcnded to th~e theoretical decomposition voltage.
~he current efficiency was 95~o. ~either corrosion nor ~; .
strip-off of the anode coating was observed.
`~ ! Example 5 ~
Mixed oxide powder consisting of 20 parts of yttrium oxide, 48 parts of ohromic oxide, 22 parts of i ~Y
`~ 3 ~:
... .
e~ 1 cobaltous oxide and 10 parts of nickelous oxide was dry-mixed in a ball mill for 15 hours and formed under , .,. , ~
pressure (1000 kg/cm2) by a rubber press, and then ~ ~
sintered in a high frequency induction furnace at ~ i 5 1800C for 2 hours. The sintered product was crushed `;
into particles of 200 mesh or less in size in a ball i .: ..
mill. A titanium substrate was plated with palladium in an alkaline aqueous solution containing palladium chloride by passing a current of 0.2 A/cm2 for ten `
minutes. The plated surface was subjected to oxidation treatment at 600C for 30 minutes. On the titanium substrate having the surface coating of palladi.um j ~ oxide thereon, the spinel and perovsklt~ struoture oxidos `;~
i~ powder of aoY20~, Coar20~, NiCr20~ and YCrO3 as prepared above were applied by a plasma spray unit to complete the anode for the electrolysis.
Using the anode thus formed, the aluminum ~i oxide`~uas contlnuously electrolyzed for 3 months under the same condltions~as in Example 4. The decomposition j -voltage was 2.~2 V, ~nd~the current efficiency 95%.
elther~oorroslon~nor strip-off;of the anode after the electrolysis was observed. ~-Fxample 6 Mixed oxide powder consisting of 1~.0 parts .. ~ ~ ~ ,. . .
i.j of titanium nitride, 55.5 parts of chromic oxide, 20.5 parts of ~iobaltous oxide and 10.0 parts of nickelous ; oxide was~dry-mixed in a ball mill for 24 hours and formed under pressure (1000 kg/cm2) into a shape as i shown by 6 in Fig. 3 by a rubber press. I-t was then ' `". ` ' ' ,", ' .,:"~ . . ..
`~:
i ~ 1037430 ;;
l sintered in a high frequency induction furnace at 1800G -; .
- for 2 hours to prepare a cathode consisting mainly of ! ,'' the spinel structure oxides of CoCr204 and NiCo204.
; ~he sintered cathode was then drilled and copper was casted and connected with a titanium bar to complete the cathode for the elec-trolysis.
y the use of the cathode thus formed and ~:t ~: a carbon anode, a cryolite bath containing saturated .. ..
;~ aluminum oxide maintained at 950C was electrolyzed , .:
i~; 10 continuously for 3 months while sequentially adding aluminum oxide and periodically replacing the anode , graphite, at a ¢urrent density of l A/cm2 and at 4.7 V.
i, No corrosion o~ the cathode by electrolyte bath and ,i ., .:: , .
"~ molten aluminum was observed.
'''.'' li ' ' '' .
i j ~ , : t:: ~
!:
. ! ~
... ` 15 ~:
: .:
.. .,` '' .. .
1.` . . :...... . .
~ The present invention relates to a method for produc-ing aluminum hy molten salt electrolysis of aluminum oxide.
More particularly, it relates to an electrode, and particularly ; -an anode, used in the method, which is made of or covered with electronic conductive oxide ceramics. ` `
It is known to produce aluminum by molten salt ~; ~
' ~ ! . I
electrolysis of alurninum oxide dissolved in a bath of aluminum sodium fluoride ~AlF3.3NaF) or so-called cryolite, by using . . . .
~; a carbon anode. This electrolisis is usually conducted at ` -about 900 - 1000C. ~ ;~
When aluminum is produced by using a carbon anode, the carbon anode iB oxidized and consumed hy about 330 kg : . ~
~ theoretically and about 400 - 450 kg actually per ton oE
,~. .
aluminum due to oxygen produced throuyh the decomposition of ; aluminum oxide. For this reason, it is necessary to continuous-ly adjust the position of the electrode -to maintain it at a ,~"" ,, ~; constant level~ and it is also required to replace the anode ... .
'~ by a new one before it is completely consumed. These are ~;~ economical and operational defects.
~ 20 As an approach to obviate the above-mentioned defects ;_ ~ in t~he carbon electrode, various non-consumable anodes have been recently developed. For example, a method using an oxygen i ion-conductive ànode consisting mainly of zirconium oxide has been proposed (British Patent Specification 1,152,124). This method, howeverj is disadvantageous in that it required an apparatus for removing oxygen produced and the operation is complex. A method using an anode consisting of electronic conductive metal oxide containing at least 80~ hy weight ;;`
~
: . :
~037421D
:~ of tin oxide has also heen proposed (British Patent Specifie-ation 1,295,117). This method is also disadvantageous in that -: the anode has poor chemical resistance to the molten salt.
~ The present invention provides a so-called non-consumable electrode which does not react with oxyqen produced . in molten salt electrolysis of aluminum oxide and which has ehemieal resistanee to the molten salt.
. ~ In the aeeompanying drawings;
Figs. 1 and 2 show embodiments of the electrodes ~` 10 used in the method aecordincJ to the present invention, and ,. . . :~
Fig. 3 shows an example o aluminum reduetion eells using the electrode accordi.ng to the method o~ the present ;' invention, ... .
:, The inventors of the present lnvention have made ;.
extensive investigation to Eind non-consurnable eleetrodes for molten salt electrolysis of aluminum oxide and have found that ~:
:;, ,;; , .
_ spinel strueture oxides or perovskite strueture oxides have ~ exeellent eleetronie conductivity at a temperature of about .~ 900 - 1000C, exhibit~catalytie action for the generation of : .:
.: 20 oxygen, and exhihit chemical resistance to the molten salt. .~
, ;"~
Based on this finding, they have developed non-consu~.able .
electrodes for aluminum electrolyti.c cells. ..
_: Accordlng to the present invention there is provided `
~:~ a method for producing aluminum by molten salt electrolysis of .
;~,: aluminum oxide which eomprises electrolyzing aluminum oxide ,'_ dissolved in a molten salt containing.aluminum sodium fluoride .
as the main eomponent by passincJ a direct eurrent through an ~'..
. anode to a cathode disposed in said molten salt, wherein at ;
/e~ o ~e 0?~l , ; ~ . least a portion of~said anode and said ca-thode that is brought .. 30 into contact with said molten salt is made of or covered with .
"i, .. . .
, , a eomposit.ion eontaininc~ at least about 50~ by weight of ,~ ~
., ~, . . . .
',; eleetronie eonduetive oxide eeramics havincJ chemical resistance ~ ~ ~
. ~ ,.. ..
.; .. . .
.~ ~ 2 - . .
., ''~' ', ~, . , ~", i~ , . ; ..
~: .
~037~0 ` `
. to the molten salt, said oxide ceramics being selected from ` ;~
.:: . .
spinel structure oxides having the ~eneral formula XYYl04 ~: wherein X is a divalent or tetravalent metal, Y and Y' may be .. .
... ... .. .
either the same or different and are trivalent or divalent metals, 0 is oxygen atom, provided that when X is a divalent i'.. `~
. metal, Y and yl are selected from trivalent metals but the ~:
spinel structure oxides are excluded in which both Y and Y' are . trivalent iron, Fe (III), and when X is tetravalent metal, Y ..
~ . . .:
.. and Y' are selected from divalent metals, provskite structure ;:.:
. lO oxides having the general formula RM03 wherein R is a mono~
valent clivalent or trivalent metal, M is a pentavalent, tetra-;: valent or trivalent metal, 0 is oxygen atom, provided that when :;
; . . .
R is a monovalent metal, M is selected from pentavalent metals, ~.
when R is c1ivalent metal, M is selectecl Erom tetraval~nt metals, :
and when R is a trïvalent metal, M is selected from trivalent .`~
metals or a mixture thereof, the remainder of the composition `''i being comprised of an oxide, carbide, nitride, boride or .;
.,:.~ ... .
;~ silicide of an element selected from transition metals, ;.
platinum group metals and rare earth elements. `....... :
: 20 Accord:ing to the present invention, the electrode ~ :
base is covered, at~ least in its portion that is brought into ~ :
contact with a molten salt, w1th a composit1on containing at least about 509 by weight of electronic conductive oxide :' ceramics selected from spinel structure oxides having the general formula XYY'04 twherein X, Y, Y' and 0 are as defined above~, perovskite structure oxides having the general formula .7 ~103 twherein R, M and 0 are as defined above), and a mixture .
j: thereof. Alternatively, the above-mentioned part of the ~ electrode may be made of the above-mentioned oxide ceramics. .
~ 30 Usually, in the spinel structure oxitles having .
,: ., :
.: ., ., ~, `:
~ 3 - ~:
. . .
; ~03742~ :~
''' ;.
1 the general formula XYY'04, X is a divalent metal such as barium, magnesium, calcium, strontium, zinc, lead copper, molybdenum? manganese, iron, cobalt, nickel or the like, and preferably copper, molybdenum, manganese, 5 iron, cobalt or nickel, or a tetravalent metal such as .
titanium, vanadium, tin, germanium or the like, and pre-ferably titanium or vanadium, Y and Y' are trivalent :~`
. metals such as aluminum, gallium, indium, manganese, iron,cobalt, nickel, chromium, vanadium, rhodium, lanthanum, 10 yttrium or the like, and preferably indium, manganese, -.
iron, cobalt, nickel, chromium, rhodium or lanthanum, or dlvalent metals such as magnesium, zino, man~ane~e, iron, cobalt, nickel or the like, and pre~erably iron, cobalt or nickel (provided that when X is a divalent ~ 15 metal, Y and Y' are selected ~rom trivalent metals, and `.
when X is a tetravalent metal, Y and Y' are selected .: from divalent metals). In the perovskite structure .~ oxides having the general formula RM03, R is a mono-valent metal such as lithium, sodium, potassium or the like, or a divalent metal such as calcium, magnesium, barium, lead or the like, or a trivalent metal such as : : .
i: ~ ~; -, : . lanthanum, yttrium, chromium, aluminum, manganese, cobalt, i~
; : nickel or the like, M is a pentavalent metal such as niobium, tantalum or the like, or a tetravalent metal .. : ~ ,. . .
.;.; 25 such as zirconium, titanium, tin or the like, or a tri- ;~
. ~ valent metal such as lanthanum, yttrium, chromium, aluminum, : manganese, cobalt, nickel or the like (provided that when ; R is a monovalent metal, M is selected ~rom pentavalent . :
;~i metals, when R is a divalent metal, M is selected ~rom .:~:.
` ~ 30 te-travalent metals, and when R is a trivalent metal, . ~:
. , '. ::'.:
` , r,~
!. ~ . . ' i,: '~, :
1037420 :
1 M is selected from trivalent metals). The perovskite structure oxides in which R and M are trivalent metals are preferable.
More particularly, spinel structure oxides such ,-~
as MgV24~ FeV24~ ZnV204~ MgCr204, MnCr204, FeCr204, CCr24~ Niar24~ CUCr24~ ZnCr204, ZnMn204,~MnMn204, FeAlFeO4, MgCo204, CUCO2O4~ ZnC24~ ~eNi24~ MgRh24 . ~ . ...
CoRh204, CURh2o4~ MnRh2o4~ NiRh2o4~ ZnRh24~ MgA124~ ~... .
SrA1204, MoA1204, FeA1204, CoA1204, NiA1204, CuA1204, ZnAl2o4~ MgGa24~ ZnGa204, CaGa204, MgIn204, MnIn204, FeIn24~ CIn24~ NiIn24, MgFeA104, NiFeA104, Cu~a204, ~a24~ Ni~a24~ TiMg24~ '~iMn204, '~iCo204, '~iFe204, ~I!iNi204~ 'riZn24, SnMg204, SnZn204, SnCo204, VMg204 , (Note: Although pure spinel such as MgA1204, SrA120 or TiMg204 has, in general, very small electronic con-ductivity and it is dif~icult to use as an electronic ~i ~ conductlve materlal,~lt may be rendered highly conductive q;~ by addlng another component thereto. The~spinel which has~thus been~provided uith conductlvity lS oonventional~
20 ~ }y expressed~as~MgA1204,~ etc. Therefore, such an~ex- J',~A,;
- presslon~ls also employed ln the present invention~, ~
or perovsklte~structure oxides such as ~iNbO3, K~bO3, ~ ;
NaNbO3, ~iTaO3, BaTiO3, PbTi03, PbZrO3, LaCrO3, ~aA103, aNiO3, ~aY03, YCrO3 or IaCoO3 may be used.
.. i ~ ~ ~ . , .
The above-mentioned spinel andjor perovskite structure oxides~are of electronic conductor and are dif~erent in~eleotro-oonductive mode than known ion-con-,., ~ ~ : , . . .
~o ductive electrodes and are also dif~erent in crystal structure than;the tin oxide electrode, and hence they provide electrodes cons-tructed of completely novel . ~ . . , .:. ,".
~` ` ' 1, '', `;
- ~0374ZO `:
....
1 componentsO The electrodes constructed of such electronic conductive oxide ceramics exhibit excellent conductlvity ... , : .
under the electrolysis condition and also have excellent resistance to the molten bath.
The electrodes according -to the present inven-tion are made of or covered with a composition containing -at least 50% by weight, and preferably at least 70% by : weight and most preferably at least 80~o by weight, of .~ the said spinel structure oxide, perovskite structure oxide or a mixture thereof at least in their portion that is brought into contact With the molten salt.
In the production of the electrode o~ the present invention, in order to improve the electrode i~
density, heat resistance, thermal shock resistance, ; -~
~-i 15 resistance to molten bath and electric conductivity, ;~
ii~ oxides, carbides, nitrides, borides or sillcides of :~ alkali metals, alkallne earth metals, transition metals, platinum group~metals~, rare earth elements or the like ~ ~
may~be added, if necessary, to tke electronic conductive -; -20 oxlde~ceramics~. When~the amount of the additive exceeds i~;
50~o by welght,~however, the electric~oonductivity, re-:sistance to bath and oxidation resistance of the electrode are deteriorated. Therefore, the amount of the additive should be kept at 50% by weight or less. Par-ticularly preferable additives are tranSition metal oxides such ~ as manganese oxide, nickel oxide, cobalt oxide a~d iron ; ~ ~- oxide, and platinum group metal oxidesi such as ruthenium oxide, palladium oxide and rhodium oxide, and rare earth element oxides such as yttrium oxide, ytterbium oxide and neodium oxide, and titanium nitride, titanium boride ~',' , ' ,, '. ~
. . ~ ... - . . .
- 6 - ~
~ , .
~. ' `,, ~`
~: :
; . , ..:
:: :
~:
l and tungsten silicide.
The optlmum electric resistance of the electronic conductive oxide ceramics used in the production of the electrode varies depending on the shape of the electrode ,, .. :
' 5 such as t,he thickness o~ the coating or the like, but ~
. .
usually the material having a conductivity of at least -~
~ about 0.1 Q -1 cm~l (at 1000C) lS most preferably ^
: used.
. . . .
: The electronic conductive oxide ceramic for ` 10 coating or forming the electrode o~ the present inven- ;
tion may have a meltlng point higher than the operating temperature of the electrolytic cell, and usually higher than about 1000C and pre~erably higher than 1200C.
;~ The electrode of the present invention may be formed from an electrode base made o~ a conductive materi-. . .
... .
i al such as a metal or alloy e.g. titanium, nickel or copper, or~carbonj graphite, or a carbide, nitride, borlde, siliclde, tltanium, molybdenum or tungsten, on the surface~of~which~a composition contalning said oxide 20~ ~ceramics is~coated, or the~entire electrode may be formed "
~,?~ of`said oxide ceramics In~the coating of the oxide ceramics on the electrode base~surfaoe, a composition containing the spinel and/or perovskite struoture oxide are ~lame sprayed ~;
or plasma sprayed and, i~ necessary, subjected to heat treatment or~electroplating process. Alternatively, ~; an inorganic or organic metal compound, which can pro-duce a spinel and/or perovskite structure oxide upon sintering, is~ coated, dipped, sprayed or thermal de-0 composition-evaporated and then thus treated electrode , , ~; , ., .
.: -,. , ...
.~ ,.. .
... .
`
10374;:0 -~
- 1 base is slntered. As a further alternative, an electrode base made of an alloy which can produce a spinel and/or~
perovskite structure oxide upon oxidization or a base , .
coated with such alloy is oxidized. It should be under-stood that in the coating of the electrode base with the oxide ceramics, an intermediate layer of a platinum group metal oxide or the like may be interposed to en~
; hance the adhasiveness between the oxide ceramics and the base.
: 10 The spinel and/or perovskite structure oxldes may be oonveniently prepared by the firing o~ a mixture ;'~ having an appropriate composition o~ oxides, hydroxides, ~' ;
,,,~ ~,., .:
chlorides, sul~ates, ni-trates, carbonates, oxalates o~
said metals usually at a temperature o~ 500C or more j- ;
and pre~erably at 800 - 2500C. Sintering is conducted " by hot pressing in a high frequency induction furnace ; or a resistive heating furnace at about 500C or more and preferably;~at~800 - 2500C, and under reduced pressure, `r "" ,~
atmospher1c~pressure or elevated pressure, and preferably ;~ -under a pressure of~50 - lOOO kg/cm2 by hot pressing.
In~the applieation of the electrode of the prebent`inventlon to the aluminum electrolysis, a con-necting means between the electrode and a conductor is not limited but any conventional means may be used.
25 r~hus, the connection may be e~ected by threading, `~
j welding or casting, or it may be e~fected through a low melting point metal such as aluminum, tin or copper, i '! or an alloy or a compound thereof.
i r~he application o~ the electrode o~ the present inventlon to an anode for the production o~ aluminum ,, ::
, i~ . .
; ~ . :, .: 1037~0 ~`
1 will now be described with reference to the accompanying . drawings.
Fig. 1 shows an embodiment of the anode ac-cording to the present invention. In Fig. I, a con-ductive bar 1 is embedded in an anode base formed of a conductive material such as a metal, an alloy, carbon ;-~ ;
or graphite having a melting point higher than the ~ electrolysis temperature. Applied onto the surface `~
: of the anode base 2 by an appropriate method is a coat-ing 3 of the electronic conduc-tive oxide ceramics accordin~
to the present inVention.
Fig. 2 shows another embodiment o~ the present invention, in which an anode 4 is entirely ~ormed of the ; electronic conductive oxide ceramics according to the present invention, in which the conductive bar 1 is em-bedded.
~; ~ Fig.~ shows the running state of an electrolysis of aluminum~oxide by the application of the anode of the present inventlon placed ln a~reduction cell. The reduc-tion cell comprises a steel outer shell, a thermal in-~ sula;tion 5 of~an~appropriate lnsulating material and a -"`~ lin mg~6 of a carbonacious material, carbide, boride or the ceramics according to the present invention. A
conductive bar 7 is embedded in the lining 6. Molten aluminum ~ precipitates at the bottom of molten electrolyte 9, the top surface c~f which is covered with a crust 10. ~ ;
he anodes 4 of the present invention suspending from the conductive bar 1 are arranged in the molten electrolyte ~ ~;
9 and appropriately spaced from the surface of -the pre-cipitated aluminum. The conductive bar 1 is movably .! ::`-: :
.:............................................ . . .
``
1037420 `
1 connected with a bus bar 11. In the reduction cell ~-having the above-mentioned structure, aluminum is pre-cipitated when current is introduced.
Although the use o~ the electrode as an anode -5 is illustrated in Fig. 3, it should be understood that `';
the electrode of the present invention can also be used ~;
as a cathode for the aluminum electrolyzer.
'rhe electrode of the present invention has the ~;
' following advantages over the prior art carbon anode:
, 10 (1) Since the electrode of the present invention is not ` ;
,;,. ... ..
consumed unlike the prior art consumable carbon anode, ~ the electrode oan be u~ed without replacement ~or several ; months or more and usually 0.5 to 1 year. '~herefore, `~
the number of times for the electrode replacement can be considerably reduced. (2) Since the electrode o~
the present invention is not consumed unlike the con- ;;
',! ... ...
sumable carbon anode, the ~requency of adjusting the ~ -distance between the~anode and the precipitated aluminum is~considerably lower~ed, thereby the electrolysis opera-20~ tion lS ~slmpllfled, the production cost is reduced and `~
erroneous~operation of operators is avoided. ~;
The present invention is illustrated by re-; ferring to the ~ollowing examples, in which parts are ~;~ by weight unless otherwise indicated. ; `
;~`
,'..: .
j Example 1 Mixed oxide powder consisting o~ 62.3 parts of chromic oxide, 35.7 parts o~ cobaltous oxide, and 2 parts Qf nickel monoxide was dry-mixed in a ball mill for 15 hours and formed under pressure (1000 kg/cm2) "~
, .
~ i'.'.. .'' `, ,~,::, ' : :`
1~374~
1 by a rubber press, and then sintered in a high frequency ;~ induction furnance at 1800C for two hours to produce .. , :, an electrode consisting mainly of the spinel structure oxide of CoCr204. The sintered anode was rigid and ;
compact and exhibited a conductivity of 1.0 Q~l cm~
at 1000C. The anode was then drilled and copper was casted in the drilled hole. The copper was connected -with a platinum lead wire to complete the anode for use 1 , , in the electrolysis. ~
;~ .: .
By the use of the anode formed in this manner, a cryolite bath containing saturated aluminum oxide ~;
maintained at 950C was continuously electrolyeed ~or ' 5 3 months while sequentially adding aluminum oxide at a current density of 1 A/cm2 and at 5.7 volts. ~he decomposition voltage was 2.2 V, which was close to the theoretical value of 2.1 V (at 950C), and the over-~;~ voltage was small. ~The current efficiency was 95%, ~;
and the corrosion of the anode after the electrolysis was not observed. ~ -;~
Example~2~
Mlxed oxlde powder consisting of 60.2 parts of lanthanum oxide, 33.9 parts of chromic oxide, and ., ~. .... .
5.9 parts of strontium carbonate was dry-mixed in a ball mill for 15 hours and formed under pressure (1000 kg/cm2)~by a rubber press and -then sintered in a high frèquenoy induction furnace at 1900C ~or one :j ,.;
hour to produce an electrode consistin~ mainly o~ the perovskite structure oxide of ~aCr03. '~he sintered .. "f, 30 anode was rigid and compact and exhibited a conductivity . ~:
,., :. .:
! `
~ :`
:~ 1037420 , j; . ., .`.
1 of 10 Q-l cm~l at 1000C. The anode was then drilled ~ii - and copper was cast in the drilled hole. The copper was connected with a platinum lead wire to complete the anode for the electrolysis.
' :,' , ~ . . i, ; .
By using o~ the anode thus constructed, aluminum .':!'"`''' ,~, !," .
oxide was electrolyzed continuously for three months ;; `
under the same conditions as in Example 1. The decom~
position voltage was 2.2 V, the current efficiency was r . ,,~, `
95%. No corrosion of the anode after the electrolysis ~: . , ~ 10 was observed.
., ,, , ,: ,, ~xample 3 `
. .
Mixed oxide powder consisting of 32.2 parts ~;
of titanium oxide, 64.5 parts o~ ferrous oxide, ~.3 15 parts of manganese oxide was dry-mixed in a ball mill -for 24 hours and ~ormed under pressure (1000 kg/cm2) ;~
- by oil hydraulic press, and sintered in a silicon carbide reslstor;el~eotric~furnace at I400C ~or 10 hours to ~;produce an eleotrode cons~isting malnly of spinel struc~
20~ ture oxide~of ~lFe204, The slntered anode was rigid and compact~and exhiblted a conductivity o~ 1 Q -1 cm~
at 1000O. ~The anode~was connected to a platinum lead wire through tin metal to complete the anode for the ~ ;
electrolysis. ~
~By the use of the anode thuæ ~ormed, cryolite `;
bath containing saturated aluminum oxide maintained at 950C was oontlnuously electrolyzed for 3 months while sequentially adding aluminum oxide at a current density of 0.9 A/cm2 and at 5.7 V. The decomposition voltage was 2.1 V, whioh substantially corresponded to the . ., . ' .
~2 - , _ ~.;
: . , ' .
~337420 ~ ~
'- 1 theoretical decomposition voltage, and the overvoltage was very small. The current efficiency was about 95%.
~o corrosion of the anode after the electrolysis was :. :,; . .
observed.
;-. . . :
Example 4 A mixture consisting of 65,8 parts of lanthanum oxide, 3~.7 parts of nickel sesquioxide and 0.5 part of indium oxide and a small amount of water were wet-mixed in a ball mill for 24 hours and then heated in a silicon carbide resistor electrio furnace at 1600C ~or lO hours.
'~he sintered product was crushed into particle~ of `;
. ~ ; .
200 mesh or les~ in ~ize. '~he partioles were then , ; applied onto a titanium substrate by a plasma spray . .
;~ 15 unit, In this manner, an anode for the electrolysis ¢l having a coating consisting mainly of the perovskite structure oxide of ~a~iO~ on the titanium substrate was prepared.
3y the~ use~of the anode thus formed, cryolite bath containlng saturated~alumlnum~oxide was continuously electrolyz~ed~or;3 months, while sequentially adding alumlnum oxlde,~at;a;current density of 0.9 A/cm2~and at 5.7 V.~The decomposition voltage measured substantial-ly oorrespcnded to th~e theoretical decomposition voltage.
~he current efficiency was 95~o. ~either corrosion nor ~; .
strip-off of the anode coating was observed.
`~ ! Example 5 ~
Mixed oxide powder consisting of 20 parts of yttrium oxide, 48 parts of ohromic oxide, 22 parts of i ~Y
`~ 3 ~:
... .
e~ 1 cobaltous oxide and 10 parts of nickelous oxide was dry-mixed in a ball mill for 15 hours and formed under , .,. , ~
pressure (1000 kg/cm2) by a rubber press, and then ~ ~
sintered in a high frequency induction furnace at ~ i 5 1800C for 2 hours. The sintered product was crushed `;
into particles of 200 mesh or less in size in a ball i .: ..
mill. A titanium substrate was plated with palladium in an alkaline aqueous solution containing palladium chloride by passing a current of 0.2 A/cm2 for ten `
minutes. The plated surface was subjected to oxidation treatment at 600C for 30 minutes. On the titanium substrate having the surface coating of palladi.um j ~ oxide thereon, the spinel and perovsklt~ struoture oxidos `;~
i~ powder of aoY20~, Coar20~, NiCr20~ and YCrO3 as prepared above were applied by a plasma spray unit to complete the anode for the electrolysis.
Using the anode thus formed, the aluminum ~i oxide`~uas contlnuously electrolyzed for 3 months under the same condltions~as in Example 4. The decomposition j -voltage was 2.~2 V, ~nd~the current efficiency 95%.
elther~oorroslon~nor strip-off;of the anode after the electrolysis was observed. ~-Fxample 6 Mixed oxide powder consisting of 1~.0 parts .. ~ ~ ~ ,. . .
i.j of titanium nitride, 55.5 parts of chromic oxide, 20.5 parts of ~iobaltous oxide and 10.0 parts of nickelous ; oxide was~dry-mixed in a ball mill for 24 hours and formed under pressure (1000 kg/cm2) into a shape as i shown by 6 in Fig. 3 by a rubber press. I-t was then ' `". ` ' ' ,", ' .,:"~ . . ..
`~:
i ~ 1037430 ;;
l sintered in a high frequency induction furnace at 1800G -; .
- for 2 hours to prepare a cathode consisting mainly of ! ,'' the spinel structure oxides of CoCr204 and NiCo204.
; ~he sintered cathode was then drilled and copper was casted and connected with a titanium bar to complete the cathode for the elec-trolysis.
y the use of the cathode thus formed and ~:t ~: a carbon anode, a cryolite bath containing saturated .. ..
;~ aluminum oxide maintained at 950C was electrolyzed , .:
i~; 10 continuously for 3 months while sequentially adding aluminum oxide and periodically replacing the anode , graphite, at a ¢urrent density of l A/cm2 and at 4.7 V.
i, No corrosion o~ the cathode by electrolyte bath and ,i ., .:: , .
"~ molten aluminum was observed.
'''.'' li ' ' '' .
i j ~ , : t:: ~
!:
. ! ~
... ` 15 ~:
: .:
.. .,` '' .. .
1.` . . :...... . .
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for producing aluminum by molten salt electrolysis of aluminum oxide which comprises electrolyzing aluminum oxide dissolved in a molten salt containing aluminum sodium fluoride as the main component by passing a direct current through an anode to a cathode disposed in said molten salt, wherein at least a portion of at least one of said anode and said cathode that is brought into contact with said molten salt is made of or covered with a composition containing at least about 50%
by weight of electronic conductive oxide ceramics having chemical resistance to the molten salt, said oxide ceramics being selected from spinel structure oxides having the general formula XYY'04 wherein X is a divalent or tetravalent metal, Y
and Y' may be either the same or different and are trivalent or divalent metals, O is oxygen atom, provided that when X is a divalent metal, Y and Y' are selected from trivalent metals but the spinel structure oxides are excluded in which both Y
and Y' are trivalent iron, Fe (III), and when X is tetravalent metal, Y and Y' are selected from divalent metals, provskite structure oxides having the general formula RMO3 wherein R is a monovalent divalent or trivalent metal, M is a pentavalent, tetravalent or trivalent metal, O is oxygen atom, provided that when R is a monovalent metal, M is selected from a pentavalent metals, when R is divalent metal, M is selected from tetravalent metals, and when R is a trivalent metal, M is selected from trivalent metals or a mixture thereof, the remainder of the composition being comprised of an oxide, carbide, nitride, boride or silicide of an element selected from transition metals, platinum group metals and rare earth elements.
by weight of electronic conductive oxide ceramics having chemical resistance to the molten salt, said oxide ceramics being selected from spinel structure oxides having the general formula XYY'04 wherein X is a divalent or tetravalent metal, Y
and Y' may be either the same or different and are trivalent or divalent metals, O is oxygen atom, provided that when X is a divalent metal, Y and Y' are selected from trivalent metals but the spinel structure oxides are excluded in which both Y
and Y' are trivalent iron, Fe (III), and when X is tetravalent metal, Y and Y' are selected from divalent metals, provskite structure oxides having the general formula RMO3 wherein R is a monovalent divalent or trivalent metal, M is a pentavalent, tetravalent or trivalent metal, O is oxygen atom, provided that when R is a monovalent metal, M is selected from a pentavalent metals, when R is divalent metal, M is selected from tetravalent metals, and when R is a trivalent metal, M is selected from trivalent metals or a mixture thereof, the remainder of the composition being comprised of an oxide, carbide, nitride, boride or silicide of an element selected from transition metals, platinum group metals and rare earth elements.
2. A method according to Claim 1 wherein said electrode is formed of a composition containing at least 70%
by weight of said electronic conductive oxide ceramics,
by weight of said electronic conductive oxide ceramics,
3. A method according to Claim l wherein the electrical conductivity of said electronic conductive oxide ceramics is at least 0.1 .OMEGA. -1 cm -1 (at 1000°C).
4. A method according to Claim l, 2 or 3 wherein the melting point of said electronic conductive oxide ceramics is at least 1200°C.
5, A method according to Claim l wherein said electronic conductive oxide ceramics is selected from spinel structure oxides including CoCr2O4, TiFe2O4, CoY2O4, NiCr2O4 and NiCo2O4, perovskite structure oxides including LaCrO3 and LaNiO3 and a mixture thereof.
6. A method according to Claim 5 wherein nickel oxide, strontium oxide, manganese oxide, indium oxide or titanium nitride is added to said electronic conductive oxide ceramics.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11258973A JPS5536074B2 (en) | 1973-10-05 | 1973-10-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1037420A true CA1037420A (en) | 1978-08-29 |
Family
ID=14590509
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA210,695A Expired CA1037420A (en) | 1973-10-05 | 1974-10-03 | Electrodes for aluminum reduction cells |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5536074B2 (en) |
| BR (1) | BR7408156D0 (en) |
| CA (1) | CA1037420A (en) |
| CH (2) | CH613231A5 (en) |
| DE (1) | DE2446314B2 (en) |
| FR (1) | FR2246657B1 (en) |
| GB (1) | GB1461155A (en) |
| NO (1) | NO743603L (en) |
Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DD137365A5 (en) * | 1976-03-31 | 1979-08-29 | Diamond Shamrock Techn | ELECTRODE |
| JPS52140411A (en) * | 1976-05-19 | 1977-11-24 | Sumitomo Chem Co Ltd | Electrode to be used for production of aluminium by electrolysis |
| JPS5555079A (en) * | 1978-10-17 | 1980-04-22 | Honda Motor Co Ltd | Engine support structure of autobicycle |
| NO801818L (en) * | 1979-07-20 | 1981-01-21 | Conradty Nuernberg | RECOVERABLE, FORM-STABLE ELECTRODE FOR HIGH TEMPERATURE USE |
| JPS57972A (en) * | 1980-06-02 | 1982-01-06 | Honda Motor Co Ltd | Power unit suspension system for autobicycle |
| CA1181616A (en) * | 1980-11-10 | 1985-01-29 | Aluminum Company Of America | Inert electrode compositions |
| JPS62160977A (en) * | 1986-08-21 | 1987-07-16 | 本田技研工業株式会社 | Engine support structure of motorcycle |
| US5279715A (en) * | 1991-09-17 | 1994-01-18 | Aluminum Company Of America | Process and apparatus for low temperature electrolysis of oxides |
| US6030518A (en) * | 1997-06-26 | 2000-02-29 | Aluminum Company Of America | Reduced temperature aluminum production in an electrolytic cell having an inert anode |
| FR2830857B1 (en) | 2001-10-15 | 2004-07-30 | Pechiney Aluminium | COATING PRECURSOR AND METHOD FOR COATING A SUBSTRATE WITH A REFRACTORY LAYER |
| EP1438271A2 (en) * | 2001-10-15 | 2004-07-21 | Aluminum Pechiney | Coating precursor and method for coating a substrate with a refractory layer |
| FR2830856B1 (en) * | 2001-10-15 | 2004-07-30 | Pechiney Aluminium | COATING PRECURSOR AND METHOD FOR COATING A SUBSTRATE WITH A REFRACTORY LAYER |
| US7235161B2 (en) * | 2003-11-19 | 2007-06-26 | Alcoa Inc. | Stable anodes including iron oxide and use of such anodes in metal production cells |
| US10927465B2 (en) | 2016-11-21 | 2021-02-23 | Toyota Motor Engineering & Manufacturing North America, Inc. | Brownmillerite oxides for oxygen evolution catalyst |
| DE102020005130B3 (en) * | 2020-08-21 | 2022-02-10 | Technische Universität Bergakademie Freiberg, Körperschaft des öffentlichen Rechts | Process for the production of low-carbon and carbon-free electrode-honeycomb material composites for use in metallurgy |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE316875B (en) * | 1966-05-06 | 1969-11-03 | Lumalampan Ab | |
| BE759874A (en) * | 1969-12-05 | 1971-05-17 | Alusuisse | ANODE FOR ELECTROLYSIS IGNEATED WITH METAL OXIDES |
| US3711382A (en) * | 1970-06-04 | 1973-01-16 | Ppg Industries Inc | Bimetal spinel surfaced electrodes |
-
1973
- 1973-10-05 JP JP11258973A patent/JPS5536074B2/ja not_active Expired
-
1974
- 1974-09-27 DE DE2446314A patent/DE2446314B2/en not_active Withdrawn
- 1974-10-01 BR BR8156/74A patent/BR7408156D0/en unknown
- 1974-10-03 GB GB4295974A patent/GB1461155A/en not_active Expired
- 1974-10-03 CA CA210,695A patent/CA1037420A/en not_active Expired
- 1974-10-04 FR FR7433566A patent/FR2246657B1/fr not_active Expired
- 1974-10-04 CH CH1246078A patent/CH613231A5/en not_active IP Right Cessation
- 1974-10-04 CH CH1339974A patent/CH608036A5/en not_active IP Right Cessation
- 1974-10-04 NO NO743603A patent/NO743603L/no unknown
Also Published As
| Publication number | Publication date |
|---|---|
| NO743603L (en) | 1975-05-05 |
| JPS5536074B2 (en) | 1980-09-18 |
| FR2246657B1 (en) | 1977-07-08 |
| CH613231A5 (en) | 1979-09-14 |
| CH608036A5 (en) | 1978-12-15 |
| DE2446314B2 (en) | 1981-04-16 |
| BR7408156D0 (en) | 1975-07-22 |
| FR2246657A1 (en) | 1975-05-02 |
| DE2446314A1 (en) | 1975-04-17 |
| GB1461155A (en) | 1977-01-13 |
| AU7388674A (en) | 1976-04-08 |
| JPS5062114A (en) | 1975-05-28 |
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