Note: Descriptions are shown in the official language in which they were submitted.
:; ~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
5 -
. ~ . . , .:. ,".
~` ` ' 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
, , ~; ,
., .
- 7 -
.: -
,. ,
...
.~ ,.. .
... .
`
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.` . . :...... . .
